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Background Methods Results Conclusions Traditionally, the intervertebral disks' (IVD) nucleus pulposus (NP) and annulus fibrosus (AF) are considered to have few cellular components and cell junctions. Patients affected by a new variant of endemic pemphigus foliaceus in El Bagre, Colombia, experience back pain in the spinal areas of the lower and upper back. Here, we investigate the reactivity of the patient's autoantibodies to structures in and around the IVDs at the cellular level.We first administered a questionnaire and performed a medical examination. We then tested for autoreactivity against IVDs by indirect immunofluorescence, confocal microscopy, and reflectance confocal microscopy using bovine and human tissues as antigen sources. We tested 45 sera from patients affected by the disease and 45 control sera from the endemic area matched by age, gender, demographics, and work activity.Most of the patient sera revealed polyclonal antibodies against newly discovered cell junctions in the NP and AF, including their translamellar cross‐bridges. Additional reactivities were detected against cell junctions in the spinal cord neurons, paraspinal nerves, blood vessels, anterior and posterior longitudinal ligaments, and paraspinal skeletal muscles. The reactivities of the patient's autoantibodies co‐localized with those of commercially available antibodies to desmoplakins I–II, armadillo repeat gene deleted in velo‐cardio‐facial syndrome, plakophilin‐4, and myocardium‐enriched zonula occludens‐1‐associated protein (p < 0.001).We discovered novel complex cell junctions in the IVDs using patients' autoantibodies. These discoveries open a new chapter in the knowledge of IVD, representing a breakthrough pertinent to many diseases. [ABSTRACT FROM AUTHOR]

Microvascular changes are considered key factors in the process of intervertebral disk degeneration (IDD). Microvascular invasion and growth into the nucleus pulposus (NP) and cartilaginous endplates are unfavorable factors that trigger IDD. In contrast, the rich distribution of microvessels in the bony endplates and outer layers of the annulus fibrosus is an important safeguard for the nutrient supply and metabolism of the intervertebral disk (IVD). In particular, the adequate supply of microvessels in the bony endplates is the main source of the nutritional supply for the entire IVD. Microvessels can affect the progression of IDD through a variety of pathways. Many studies have explored the effects of microvessel alterations in the NP, annulus fibrosus, cartilaginous endplates, and bony endplates on the local microenvironment through inflammation, apoptosis, and senescence. Studies also elucidated the important roles of microvessel alterations in the process of IDD, as well as conducted in‐depth explorations of cytokines and biologics that can inhibit or promote the ingrowth of microvessels. Therefore, the present manuscript reviews the published literature on the effects of microvascular changes on IVD to summarize the roles of microvessels in IVD and elaborate on the mechanisms of action that promote or inhibit de novo microvessel formation in IVD. [ABSTRACT FROM AUTHOR]

Study Design. Cross-sectional. Objective. The aim of this study was to describe morphologic changes of the annulus fibrosus (AF) and nucleus pulposus (NP) in children during growth using magnetic resonance imaging. Summary of Background Data. Little is known of intervertebral disk (IVD) maturation as opposed to degeneration, such as changes in relative AF/NP proportions and orientation during growth. Studies suggest that IVD plays a role in the etiology of pediatric spinal deformities. Therefore, understanding the morphologic development of the AF and NP during growth is key. Materials and Methods. An existing database of children aged 0 to 18 that had magnetic resonance imaging for indications unrelated to the spine were analyzed. The AF/NP were segmented semiautomatically from T1 to L5. The parameters: mean IVD height, cross-sectional area, slenderness (height/width ratio), volume (ratio), and relative position of the centroid of the NP within the IVD in three directions (x, y, z) were extracted, and compared between age, sex, and spinal level. Results. IVD height increased modestly and predominantly in the low-thoracic and lumbar spine during the first 5 to 10 years of life. Cross-sectional area and thus volume increased steadily at all levels throughout growth. IVD slenderness decreased sharply in the first years of life and remains relatively stable throughout the remainder of growth. IVDs were smaller and more slender in females, especially in the mid-thoracic spine at early adolescence. In the upper-thoracic and mid-thoracic spine the NP comprises 10% to 12% of total IVD volume during growth, this percentage increases in the low-thoracic and lumbar spine towards 20% to 25%. In the anterior-posterior direction, the position of the nucleus increasingly shifts with age, possibly in line with the developing sagittal profile of the spine. Conclusion. This study describes the development of thoracic and lumbar IVDs during growth and may be used as a reference for future studies on the role of IVD in the etiology of disk-related disorders. [ABSTRACT FROM AUTHOR]

Low back pain is among the most grave public health concerns worldwide and the major clinical manifestation of intervertebral disc degeneration (IVDD). The destruction of annulus fibrosus (AF) is the primary cause of IVDD. A sustainable and stable treatment system for IVDD is lacking because of the special organizational structure and low nutrient supply of AF. We here found that IVDD results in the impaired mitochondrial function of AF tissue, and mitochondrial autophagy (mitophagy) plays a protective role in this process. We therefore reported a thread-structural microneedle (T-MN) matching the ring structure of AF. Based on the adsorption effect of laminin, our T-MN could load with bone marrow mesenchymal stem cell-derived exosomes to envelope the regulating mitophagy microRNA (miRNA 378), named as T-MN@EXO@miR−378. In general, we offered in situ locking in the defect site of AF to prevent nucleus pulposus leakage and promoted AF repair. The design of the thread structure was aimed at bionically matching the layered AF structure, thereby providing stronger adhesion. The T-MN@EXO@miR−378 effectively attached to AF and slowly released therapeutic engineered exosomes, and prevented IVDD progression by restoring mitophagy, promoting AF cell proliferation and migration, and inhibiting the pathological remodeling of the extracellular matrix. This functional system can be used as an excellent tool for sustained drug release and has a certain prospect in substituting the conventional treatment of IVDD.

Growing clinical evidence suggests a correlation between diabetes and more frequent and severe intervertebral disc failure, partially attributed to accelerated advanced glycation end-products (AGE) accumulation in the annulus fibrosus (AF) through non-enzymatic glycation. However, in vitro glycation (i.e., crosslinking) reportedly improved AF uniaxial tensile mechanical properties, contradicting clinical observations. Thus, this study used a combined experimental-computational approach to evaluate the effect of AGEs on anisotropic AF tensile mechanics, applying finite element models (FEMs) to complement experimental testing and examine difficult-to-measure subtissue-level mechanics. Methylglyoxal-based treatments were applied to induce three physiologically relevant AGE levels in vitro. Models incorporated crosslinks by adapting our previously validated structure-based FEM framework. Experimental results showed that a threefold increase in AGE content resulted in a ∼55% increase in AF circumferential-radial tensile modulus and failure stress and a 40% increase in radial failure stress. Failure strain was unaffected by non-enzymatic glycation. Adapted FEMs accurately predicted experimental AF mechanics with glycation. Model predictions showed that glycation increased stresses in the extrafibrillar matrix under physiologic deformations, which may increase tissue mechanical failure or trigger catabolic remodeling, providing insight into the relationship between AGE accumulation and increased tissue failure. Our findings also added to the existing literature regarding crosslinking structures, indicating that AGEs had a greater effect along the fiber direction, while interlamellar radial crosslinks were improbable in the AF. In summary, the combined approach presented a powerful tool for examining multiscale structure-function relationships with disease progression in fiber-reinforced soft tissues, which is essential for developing effective therapeutic measures. STATEMENT OF SIGNIFICANCE: Increasing clinical evidence correlates diabetes with premature intervertebral disc failure, likely due to advanced glycation end-products (AGE) accumulation in the annulus fibrosus (AF). However, in vitro glycation reportedly increases AF tensile stiffness and toughness, contradicting clinical observations. Using a combined experimental-computational approach, our work shows that increases in AF bulk tensile mechanical properties with glycation are achieved at the risk of exposing the extrafibrillar matrix to increased stresses under physiologic deformations, which may increase tissue mechanical failure or trigger catabolic remodeling. Computational results indicate that crosslinks along the fiber direction account for 90% of the increased tissue stiffness with glycation, adding to the existing literature. These findings provide insight into the multiscale structure-function relationship between AGE accumulation and tissue failure.

Due to the limited self-repair ability of the annulus fibrosus (AF), current tissue engineering strategies tend to use structurally biomimetic scaffolds for AF defect repair. However, the poor integration between implanted scaffolds and tissue severely affects their therapeutic effects. To solve this issue, we prepared a multifunctional scaffold containing loaded lysyl oxidase (LOX) plasmid DNA exosomes and manganese dioxide nanoparticles (MnO2 NPs). LOX facilitates extracellular matrix (ECM) cross-linking, while MnO2 NPs inhibit excessive reactive oxygen species (ROS)-induced ECM degradation at the injury site, enhancing the crosslinking effect of LOX. Our results revealed that this multifunctional scaffold significantly facilitated the integration between the scaffold and AF tissue. Cells were able to migrate into the scaffold, indicating that the scaffold was not encapsulated as a foreign body by fibrous tissue. The functional scaffold was closely integrated with the tissue, effectively enhancing the mechanical properties, and preventing vascular invasion, which emphasized the importance of scaffold-tissue integration in AF repair.

Objective(s): Investigating the impact of cadmium (Cd) on annulus fibrosus (AF) cells and its potential mechanism was the purpose of the current study.Materials and Methods: Cd was cultivated in different concentrations (0, 1, 5, 10, and 20 μM) on AF cells and the potential effects of the metal were assessed. Using the CCK-8 method, cell viability and proliferation were identified. Using transcriptome analysis, the annulus fibrosus cells were sequenced both with and without cadmium chloride. The EdU method was used to determine the rate of cell proliferation; senescence-associated β-galactosidase (SA-β-Gal) staining was used to determine the number of positive cells; and western blot, RT-PCR, and immunofluorescence were used to determine the protein and mRNA expression of senescence-associated proteins (p16, p21, and p53) and c-Jun N-terminal kinase (JNK).Results: According to the findings, Cd has the ability to increase the production of senescence-associated genes (p16 and p21) and senescence-associated secreted phenotype (SASP), which includes IL-1β and IL-6. Through the JNK/p53 signal pathway, Cd exposure simultaneously accelerated AF cell senescence and promoted SASP. Following JNK inhibitor (SP600125) treatment, the expression of p53, JNK, and senescence-associated indices were all down-regulated.Conclusion: By activating the JNK/p53 signaling pathway, Cd can induce oxidative stress damage and AF cell senescence. These findings could provide a new approach for treating and preventing intervertebral disc degeneration (IVDD) caused by Cd exposure.

The investigation examines the transference of stiffness from intervertebral discs (IVDs) to the lumbar body of the L1 vertebra and the interactions among adjacent tissues. A computational model of the vertebra was developed, considering parameters such as cortical bone thickness, trabecular bone elasticity, and the nonlinear response of the nucleus pulposus to external loading. A nonlinear dynamic analysis was performed, revealing certain trends: a heightened stiffness of the annulus fibrosus correlates with a significant reduction in the vertebral body's ability to withstand external loading. At a supplied displacement of 6 mm, the vertebra with a degenerative disc reached its yielding point, whereas the vertebrae with a healthy annulus fibrosus exhibited a strength capacity exceeding 20%. The obtained findings and proposed methodology are potentially useful for biomedical engineers and clinical specialists in evaluating the condition of the annulus fibrosus and predicting its influence on the bone components of the spinal system. [ABSTRACT FROM AUTHOR]

Annulus fibrosus (AF) defect is an important cause of disc re-herniation after discectomy. The self-regeneration ability of the AF is limited, and AF repair is always hindered by the inflammatory microenvironment after injury. Hydrogels represent one of the most promising materials for AF tissue engineering strategies. However, currently available commercial hydrogels cannot withstand the harsh mechanical load within intervertebral disc. In the present study, an innovative triple cross-linked oxidized hyaluronic acid (OHA)-dopamine (DA)- polyacrylamide (PAM) composite hydrogel, modified with collagen mimetic peptide (CMP) and supplied with transforming growth factor beta 1 (TGF-β1) (OHA-DA-PAM/CMP/TGF-β1 hydrogel) was developed for AF regeneration. The hydrogel exhibited robust mechanical strength, strong bioadhesion, and significant self-healing capabilities. Modified with collagen mimetic peptide, the hydrogel exhibited extracellular-matrix-mimicking properties and sustained the AF cell phenotype. The sustained release of TGF-β1 from the hydrogel was pivotal in recruiting AF cells and promoting extracellular matrix production. Furthermore, the composite hydrogel attenuated LPS-induced inflammatory response and promote ECM synthesis in AF cells via suppressing NFκB/NLRP3 pathway. In vivo , the composite hydrogel successfully sealed AF defects and alleviated intervertebral disk degeneration in a rat tail AF defect model. Histological evaluation showed that the hydrogel integrated well with host tissue and facilitated AF repair. The strategy of recruiting endogenous cells and providing an extracellular-matrix-mimicking and anti-inflammatory microenvironment using the mechanically tough composite OHA-DA-PAM/CMP/TGF-β1 hydrogel may be applicable for AF defect repair in the clinic. Annulus fibrosus (AF) repair is challenging due to its limited self-regenerative capacity and post-injury inflammation. In this study, a mechanically tough and highly bioadhesive triple cross-linked composite hydrogel, modified with collagen mimetic peptide (CMP) and supplemented with transforming growth factor beta 1 (TGF-β1), was developed to facilitate AF regeneration. The sustained release of TGF-β1 enhanced AF cell recruitment, while both TGF-β1 and CMP could modulate the microenvironment to promote AF cell proliferation and ECM synthesis. In vivo , this composite hydrogel effectively promoted the AF repair and mitigated the intervertebral disc degeneration. This research indicates the clinical potential of the OHA-DA-PAM/CMP/TGF-β1 composite hydrogel for repairing AF defects. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Low back pain (LBP) mainly emerges from intervertebral disc (IVD) degeneration. However, the failing mechanism of IVD ́s components, like the annulus fibrosus (AF) and nucleus pulposus (NP), leading to IVD degeneration/herniation is still poorly understood. Moreover, the specific role of cellular populations and molecular pathways involved in the inflammatory process associated with IVD herniation remains to be highlighted. The limited knowledge of inflammation associated with the initial steps of herniation and the lack of suitable models to mimic human IVD ́s complexity are some of the reasons for that. It has become essential to enhance the knowledge of cellular and molecular key players for AF and NP cells during inflammatory-driven degeneration. Due to unique properties of immunomodulation and pluripotency, mesenchymal stem cells (MSCs) have attained diverse recognition in this field of bone and cartilage regeneration. MSCs therapy has been particularly valuable in facilitating repair of damaged tissues and may benefit in mitigating inflammation’ degenerative events. Therefore, this review article conducts comprehensive research to further understand the intertwine between the mechanisms of action of IVD components and therapeutic potential of MSCs, exploring their characteristics, how to optimize their use and establish them safely in distinct settings for LPB treatment.

Abstract Background Degenerative spine disease is one of the largest causes of disability worldwide and has a multifactorial aetiology. Determining the leading causes of this multifactorial disease could help create new treatment approaches. Purpose Study the impact of degenerative changes in the paraspinal muscles caused by local (prolonged compression) or systemic (high-fat diet) factors on the structure of the intervertebral discs (IVDs) and facet joints of the lumbar spine in rats. Methods The study was conducted using two animal models to create degenerative changes in the paraspinal muscles of 10 white laboratory rats for 90 days and five control rats: 1) high-fat diet model (model 1) involved keeping the rats on a high calorie diet; 2) compression model (model 2) involved binding the paraspinal muscles from L2 to S1 using non-absorbable sutures. Histological analysis for the facet joints and IVDs of rats (at the L1–L4 level) with semi-quantitative analysis of the structure conducted used by degeneration grading system for IVDs and cartilage degeneration score (OARSI) for facet joint. Results In both models, 90 days after the experiment, the degenerative changes observed in the rats’ IVDs were more severe in the annulus fibrosus than in the nucleus pulposus. The height of the IVD in model 1 did not differ from the control group, but in the model 2 was 1.3 times greater (p

Annulus fibrosus (AF) plays a crucial role in the biomechanical loading of intervertebral disc (IVD). AF is difficult to self-heal when the annulus tears develop, because AF has a unique intricate structure and biologic milieu in vivo. Tissue engineering is promising for repairing AF rupture, but construction of suitable mechanical matching devices or scaffolds is still a grand challenge. To deeply know the varied forces involved in the movement of the native annulus is highly beneficial for designing biomimetic scaffolds to recreate the AF function. In this review, we overview six freedom degrees of forces and adhesion strength on AF tissue. Then, we summarize the mechanical modalities to simulate related forces on AF and to assess the characteristics of biomaterials. We finally outline some current advanced techniques to develop mechanically adaptable biomaterials for AF rupture repair.

BACKGROUND: Traction is clinically used for the early treatment of intervertebral disc degeneration, but its effect on the normal intervertebral disc remains unknown. Whether it directly causes intervertebral disc degeneration or has a positive effect is the key point of this study. OBJECTIVE: To design a static traction model and observe the effect of static traction on the nucleus pulposus and annulus fibrosus of the intervertebral disc METHODS: Twenty Sprague-Dawley rats, 3 months of age, were included in the study. The intervertebral disc spaces between 7/8, 8/9 and 9/10 were stretched by 1 mm, and the intervertebral disc spaces between 6/7 and 10/11 were used as control. Five rats were randomly selected at 2, 4, 6, and 8 weeks of traction to perform MRI T2-weighted scans of the caudal vertebra, tissue section staining, and RT-PCR gene assays for anabolic metabolism to observe the effects of static traction on the nucleus pulposus and annulus fibrosus of the intervertebral disc. RESULTS AND CONCLUSION: After short-term static traction of the rat caudal vertebra, the T2-weighted image signal in the nucleus pulposus region was enhanced. During the traction period, nucleus pulposus cells grew well, the intercellular matrix was abundant, and the annulus fibrosus arranged regularly. The RT-PCR results showed that after traction, the mRNA expression of proteoglycan increased, the expression of matrix metalloproteinase-3 decreased, the expression of type I and II collagen decreased, and the expression of matrix metalloproteinase-13 increased and tissue inhibitor of matrix metalloproteinase 1 increased. These gene results also indicated that traction made proteoglycan more inclined to an anabolic state, and type I and II collagen more inclined to a catabolic state. To conclude, static traction promotes proteoglycan anabolism making the nucleus pulposus moist. [ABSTRACT FROM AUTHOR]

The incidence of lumbar disc herniation has gradually increased in recent years, and most patients have symptoms of low back pain and nerve compression, which brings a heavy burden to patients and society alike. Although the causes of disc herniation are complex, intervertebral disc degeneration (IDD) is considered to be the most common factor. The intervertebral disc (IVD) is composed of the upper and lower cartilage endplates, nucleus pulposus, and annulus fibrosus. Aging, abnormal mechanical stress load, and metabolic disorders can exacerbate the progression of IDD. Among them, high glucose and high-fat diets (HFD) can lead to fat accumulation, abnormal glucose metabolism, and inflammation, which are considered important factors affecting the homeostasis of IDD. Diabetes and advanced glycation end products (AGEs) accumulation- can lead to various adverse effects on the IVD, including cell senescence, apoptosis, pyroptosis, proliferation, and Extracellular matrix (ECM) degradation. While current research provides a fundamental basis for the treatment of high glucose-induced IDD patients. further exploration into the mechanisms of abnormal glucose metabolism affecting IDD and in the development of targeted drugs will provide the foundation for the effective treatment of these patients. We aimed to systematically review studies regarding the effects of hyperglycemia on the progress of IDD. [ABSTRACT FROM AUTHOR]

BACKGROUND: Ankylosing spondylitis is a chronic inflammatory disease with chronic rheumatic immunity.Soft tissue ossification and fusion and spinal stiffness can cause biomechanical changes. OBJECTIVE: To reconstruct the lumbar-sacral intervertebral disc in ankylosing spondylitis patients with lumbar kyphosis by finite element analysis,and to study the range of motion of each segment of T11-S1 and the biomechanical characteristics of annulus fibrosus and nucleus pulposus. METHODS: The imaging data were obtained from an ankylosing spondylitis patient with lumbar kyphosis.The original CT image data of continuously scanned spine were imported into Mimics 21.0 in DICOM format,and T11-S1 was reconstructed respectively. The established model was imported into 3-Matic software in the format of "Stl" to reconstruct the intervertebral disc,and the fibrous interve rtebral disc model was obtained. The improved model was further imported into Hypermesh software,and the ve rtebra,nucleus pulposus,annulus fibrosus and ligament were mesh-divided.After the material properties were given,the model was imported into ABAQUS software to observe the range of motion of each ve rtebral body in seven different working conditions of T11-S1, and analyze the biomechanical characteristics of each segment of annulus fibrosus and nucleus pulposus. RESULTS AND CONCLUSION: (1) The range of motion of L1 vertebrae was higher than that of other vertebrae under six different working conditions:extension,forward flexion,rotation (left and right),and lateral flexion (left and right). The maximum range of motion was 2.18° during L1 vertebral flexion,and the minimum range of motion was 0.12° during L5 vertebral extension. (2) The annular fiber flexion at L2-L3 segments was greater than the extension (P ＜0.05),and the annular fiber flexion at L3-L4 and L4-L5 segments was less than the extension (P ＜0.05). The left rotation of L1-L2 annular fibers was greater than the right rotation (P ＜0.05). The left flexion of the annulus was greater than the right flexion in L1-L2,L2-L3,L3-L4,L4-L5 and L5-S1 segments (P ＜0.05). (3) The nucleus pulposus stresses of T11-L12,L1-L2,L2-L3,L3-L4 and L4-L5 segments in forward flexion were greater than in extension (P ＜0.05). The left rotation of T12-L1and L3-L4 segments was smaller than the right rotation (P ＜0.05),and that of T11-T12、L1-L2,and L2-L3 segments was larger than the right rotation (P ＜0.05). The left flexion was larger than the right flexion in the T11-S1 segment. (4) It is concluded that in ankylosing spondylitis patients with lumbar kyphosis, the minimum range of motion of the vertebral body is located at the L5 vertebral body in extension.To prevent fractures, it is recommended to avoid exercise in the extension position. During the onset of lumbar kyphosis in patients with ankylosing spondylitis, the maximum stress of the annulus fibrosus and nucleus pulposus is located in the L1-L2 segment, which is fixed and will not alter with the change of body position. The late surgical treatment and correction of deformity should focus on releasing the pressure of the annulus fibrosus and nucleus pulposus in this segment to avoid the rupture of the annulus fibrosus and the injury of the nucleus pulposus. [ABSTRACT FROM AUTHOR]

The objective of this study is to compare the clinical effectiveness of visualization of percutaneous endoscopic lumbar discectomy (VPELD) combined with annulus fibrosus suture technique and simple percutaneous endoscopic lumbar discectomy (PELD) technique in the treatment of lumbar disc herniation. A retrospective analysis was conducted on 106 cases of lumbar disc herniation treated with foraminoscopic technique at our hospital from January 2020 to February 2022. Among them, 33 cases were treated with VPELD combined with annulus fibrosus suture in group A, and 73 cases were treated with PELD in group B. The preoperative and postoperative visual analogue scale (VAS), functional index (Oswestry Disability Index, ODI), healing of the annulus fibrosus, intervertebral space height, and postoperative recurrence were recorded and compared between the two groups. All patients underwent preoperative and postoperative MRI examinations, and the average follow-up period was 12 ± 2 months. Both groups showed significant improvements in postoperative VAS and ODI scores compared to the preoperative scores (P < 0.05), with no statistically significant difference between the groups during the same period (P > 0.05). There was no significant decrease in intervertebral space between the two groups after surgery (P > 0.05). Group A showed significantly lower postoperative recurrence rate and better annulus fibrosus healing compared to group B (P < 0.05). The VPELD combined with annulus fibrosus suture technique is a safe, feasible, and effective procedure for the treatment of lumbar disc herniation. When the indications are strictly adhered to, this technique can effectively reduce the postoperative recurrence rate and reoperation rate. It offers satisfactory clinical efficacy and can be considered as an alternative treatment option for eligible patients. [ABSTRACT FROM AUTHOR]

[Display omitted] The annulus fibrosus (AF), a permeable, hydrated, and fiber-reinforced soft tissue, exhibits complex responses influenced by fluid pressure, osmotic pressure, and structural mechanics. Existing models struggle to comprehensively represent these intricate interactions and the heterogeneous solid responses within the AF. Additionally, the mechanisms driving differential damage accumulation between non-degenerative and degenerative intervertebral discs remain poorly understood. In this study, we introduce a biphasic-swelling damage model for the AF. We conceptually develop and rigorously validate this model through tissue-level tests employing various loading modes, consistently aligning model predictions with experimental data. Leveraging parametric geometric algorithms and custom Python scripts, we construct models simulating both non-degenerative and degenerative discs. Following calibration, we subject these models to viscous loading protocols. Our findings reveal the posterior AF's susceptibility to damage, contingent upon loading rate and water content. We elucidate the underlying mechanisms by examining the temporal evolution of fluid pressure, osmotic pressure, and the regionally dependent fiber network. This research presents a highly accurate model of the AF, providing valuable insights into disc damage. Future research endeavors should expand this model to incorporate ionic transport and diffusion, enabling a more profound exploration of intervertebral disc mechanobiology. This comprehensive model contributes to a better understanding of AF behavior and may inform therapeutic strategies for disc-related pathologies. This research presents a comprehensive model of the annulus fibrosus (AF), a crucial component of the intervertebral disc that provides structural support and resists deformation. The study introduces a biphasic-swelling damage model for the AF and validates it through tissue-level tests. The model accounts for fluid pressure, osmotic pressure, and matrix mechanics, providing a more accurate representation of the AF's behavior. The study also investigates the differential damage accumulation between non-degenerative and degenerative discs, shedding light on the mechanisms driving disc degeneration. The findings have significant implications for medical treatments and interventions, as they highlight the posterior AF's susceptibility to damage. This research is of great interest to readers interested in biomechanics, tissue engineering, and medical treatments for disc degeneration. [ABSTRACT FROM AUTHOR]

Low back pain (LBP) mainly emerges from intervertebral disc (IVD) degeneration. However, the failing mechanism of IVD ́s components, like the annulus fibrosus (AF) and nucleus pulposus (NP), leading to IVD degeneration/herniation is still poorly understood. Moreover, the specific role of cellular populations and molecular pathways involved in the inflammatory process associated with IVD herniation remains to be highlighted. The limited knowledge of inflammation associated with the initial steps of herniation and the lack of suitable models to mimic human IVD ́s complexity are some of the reasons for that. It has become essential to enhance the knowledge of cellular and molecular key players for AF and NP cells during inflammatory-driven degeneration. Due to unique properties of immunomodulation and pluripotency, mesenchymal stem cells (MSCs) have attained diverse recognition in this field of bone and cartilage regeneration. MSCs therapy has been particularly valuable in facilitating repair of damaged tissues and may benefit in mitigating inflammation' degenerative events. Therefore, this review article conducts comprehensive research to further understand the intertwine between the mechanisms of action of IVD components and therapeutic potential of MSCs, exploring their characteristics, how to optimize their use and establish them safely in distinct settings for LPB treatment. Keypoints: • LBP Burden: Poorly understood factors contribute to significant low back pain impact on health and well-being. • IVD and LBP: Disc degeneration links to low back pain, disrupting the intervertebral matrix and causing pain. • Regenerative Focus: Improving IVD components crucial for targeted regenerative therapies addressing inflammation. • Research Advances: IVD complexity, inflammatory markers, and MSC potential guide research despite replication challenges. • MSC Therapies: MSCs offer the potential for anti-inflammation, regeneration, and reduced costs, with ongoing research needed. This review article focuses on low back pain (LBP) caused by intervertebral disc (IVD) degeneration and the need to better understand the mechanisms involved. The specific roles of cellular populations and molecular pathways in the inflammatory process associated with IVD herniation are not well understood, and suitable models to mimic human IVD complexity are insufficient. However, due to their unique immunomodulatory and pluripotency abilities, mesenchymal stem cells (MSCs) have gained recognition in cellular therapy for bone and cartilage regeneration. MSCs have shown the potential in facilitating tissue repair and mitigating inflammation-related degenerative events. Therefore, this review article explores the intertwine between the mechanisms of action of IVD components and therapeutic potential of MSCs, exploring their characteristics, how to optimize their use and establish them safely in distinct settings for LPB treatment. [ABSTRACT FROM AUTHOR]

Background: Degenerative spine disease is one of the largest causes of disability worldwide and has a multifactorial aetiology. Determining the leading causes of this multifactorial disease could help create new treatment approaches. Purpose: Study the impact of degenerative changes in the paraspinal muscles caused by local (prolonged compression) or systemic (high-fat diet) factors on the structure of the intervertebral discs (IVDs) and facet joints of the lumbar spine in rats. Methods: The study was conducted using two animal models to create degenerative changes in the paraspinal muscles of 10 white laboratory rats for 90 days and five control rats: 1) high-fat diet model (model 1) involved keeping the rats on a high calorie diet; 2) compression model (model 2) involved binding the paraspinal muscles from L2 to S1 using non-absorbable sutures. Histological analysis for the facet joints and IVDs of rats (at the L1–L4 level) with semi-quantitative analysis of the structure conducted used by degeneration grading system for IVDs and cartilage degeneration score (OARSI) for facet joint. Results: In both models, 90 days after the experiment, the degenerative changes observed in the rats' IVDs were more severe in the annulus fibrosus than in the nucleus pulposus. The height of the IVD in model 1 did not differ from the control group, but in the model 2 was 1.3 times greater (p < 0.001) compared with control. Degenerative changes in the IVD were scored out 5.3 ± 1.7 in model 1 and 5.32 ± 2.1 in model 2 of a possible 16. The height of the articular cartilage of the facet joints was smaller by 1.5 times (p < 0.001) and 1.4 times (p < 0.001) in model 1 and model 2, respectively, compared to the control. Degenerative changes of facet joint were scored out 3.7 ± 0.6 in model 1 and 3.8 ± 0.6 in model 2 of five points according to the cartilage degeneration score. Conclusions: It was determined that rats who had structural changes in the lumbar paraspinal muscles as a result of being kept on a high-fat diet or subjected to prolonged compression for 90 days, showed degenerative changes in intervertebral discs and osteoarthritis in facet joints of lumbar spine. [ABSTRACT FROM AUTHOR]

Abstract Background Through bioinformatics analysis to identify the hub genes of Intervertebral disc degeneration (IVDD) associated with basement membranes (BMs) and find out the potential molecular targets and drugs for BMs-related annulus fibrosus (AF) degeneration based on bioinformatic analysis and molecular approach. Methods Intervertebral disc degeneration (IVDD) related targets were obtained from GeneCards, DisGenet and OMIM databases. BMs related genes were obtained from Basement membraneBASE database. The intersection targets were identified and subjected to protein-to-protein interaction (PPI) construction via STRING. Hub genes were identified and conducted Gene ontology (GO) and pathway enrichment analysis through MCODE and Clue GO in Cytospace respectively. DSigDB database was retrieved to predict therapeutic drugs and molecular docking was performed through PyMOL, AutoDock 1.5.6 to verify the binding energy between the drug and the different expressed hub genes. Finally, GSE70362 from GEO database was obtained to verify the different expression and correlation of each hub gene for AF degeneration. Results We identified 41 intersection genes between 3 disease targets databases and Basement membraneBASE database. PPI network revealed 25 hub genes and they were mainly enriched in GO terms relating to glycosaminoglycan catabolic process, the TGF-β signaling pathway. 4 core targets were found to be significant via comparison of microarray samples and they showed strong correlation. The molecular docking results showed that the core targets have strong binding energy with predicting drugs including chitosamine and retinoic acid. Conclusions In this study, we identified hub genes, pathways, potential targets, and drugs for treatment in BMs-related AF degeneration and IVDD.

Intervertebral disc degeneration (IDD) is a leading cause of low back pain. The inflammatory responses caused by aberrant mechanical loading are one of the major factors leading to annulus fibrosus (AF) degeneration and IDD. Previous studies have suggested that moderate cyclic tensile strain (CTS) can regulate anti‐inflammatory activities of AF cells (AFCs), and Yes‐associated protein (YAP) as a mechanosensitive coactivator senses diverse types of biomechanical stimuli and translates them into biochemical signals controlling cell behaviors. However, it remains poorly understood whether and how YAP mediates the effect of mechanical stimuli on AFCs. In this study, we aimed to investigate the exact effects of different CTS on AFCs as well as the role of YAP signaling involving in it. Our results found that 5% CTS inhibited the inflammatory response and promoted cell growth through inhibiting the phosphorylation of YAP and nuclear localization of NF‐κB, while 12% CTS had a significant proinflammatory effect with the inactivation of YAP activity and the activation of NF‐κB signaling in AFCs. Furthermore, moderate mechanical stimulation may alleviate the inflammatory reaction of intervertebral discs through YAP‐mediated suppression of NF‐κB signaling in vivo. Therefore, moderate mechanical stimulation may serve as a promising therapeutic approach for the prevention and treatment of IDD. [ABSTRACT FROM AUTHOR]

A herniated intervertebral disc (IVD) is a common injury in the human population. Despite the injury being isolated to a singular IVD in the spine, it is important to look at the biomechanical effects that a damaged IVD has on the entire spine, specifically the IVD adjacent to the injury. This study examined the effects of a damaged IVD on the mechanical properties of the annulus fibrosus (AF) in the adjacent cranial IVD. Basic science study using an in-vitro porcine model. Sixteen porcine cervical spines were used; specifically spinal levels C3/4/5 were assigned to one of two experimental groups: 1) a control group that was not subjected any injuries (n=8); 2) an experimental group that experienced an injury to the anterolateral part of the disc, reaching the nucleus pulposus but without affecting the posterior portion of the AF in the C4/5 functional spine unit (FSU) (n=8). Each specimen underwent a previously published precondition compression protocol of 300 N of compression for 15 minutes followed by a cyclical compression protocol of compression protocol of 0.5 Hz sinusoidal waveform at 300 to 1200 N for 2 hours (3600 cycles). Post compression, the C3/4 AF was dissected to obtain two multilayer samples (one anterior and one posterior) as well as a peel sample (from the posterolateral region). A tensile strength test was conducted to examine the strength of the interlamellar matrix (peel sample) and the overall strength of the AF (multilayer samples). Significant results were found in the peel test samples. Specifically, experimental specimens were less stiff compared than control specimens (p<.01). In addition, experimental specimens also had a lower average strength then control specimens (p <.01). This reduction in both interlamellar strength and stiffness increases the risk of delamination in the experimental samples. In contrast, there were no differences found between the two groups when examining the AF as a whole through the multilayer tests (p>.05). It appears that a damaged IVD impacts the biomechanics of the spine and specifically the mechanical properties of the adjacent IVD. Specifically, the observed weakening of the interlamellar matrix in these adjacent IVDs may predispose it to delamination and subsequently degeneration or herniation. These findings may help clinicians when treating patients who have experienced a disc herniation or severe degeneration, as they may potentially experience accelerated adjacent disc degeneration. [ABSTRACT FROM AUTHOR]

BACKGROUND: Lumbar intervertebral disc herniation is a common clinical disease. Its incidence is increasing year by year, which seriously affects the quality of life of patients and brings huge economic losses to the families of patients and society. At present, it is considered that the destruction of the integrity of intervertebral disc fibrous annulus is an important factor affecting the occurrence and development of lumbar disc herniation. Therefore, it is of great significance to restore the integrity of the annulus fibrosus for the treatment and prevention of lumbar disc herniation. OBJECTIVE: To review the research advance in intervertebral disc annulus repair in recent years. METHODS: PubMed, Web of Science, China National Knowledge Infrastructure (CNKI), and WanFang databases were searched systematically, with the key words “intervertebral disc, annulus fibrosus, repair, regeneration” in Chinese and English. Relevant articles published in each database in the last five years were collected. RESULTS AND CONCLUSION: In recent years, some progress has been made in the repair and regeneration of annulus fibrosus in and outside China. Although traditional physical repair has some shortcomings, it is still the main way of clinical treatment, while the application of tissue engineering in annulus fibrosus repair is only in the experimental stage and has not been widely used in clinical practice. There are many ways to repair intervertebral disc annulus fibrous, but the best way needs extensive animal and clinical trials to verify its safety and efficacy. The study on tissue engineering of annulus fibrosus repair has broad clinical application prospects. [ABSTRACT FROM AUTHOR]

Background: Through bioinformatics analysis to identify the hub genes of Intervertebral disc degeneration (IVDD) associated with basement membranes (BMs) and find out the potential molecular targets and drugs for BMs-related annulus fibrosus (AF) degeneration based on bioinformatic analysis and molecular approach. Methods: Intervertebral disc degeneration (IVDD) related targets were obtained from GeneCards, DisGenet and OMIM databases. BMs related genes were obtained from Basement membraneBASE database. The intersection targets were identified and subjected to protein-to-protein interaction (PPI) construction via STRING. Hub genes were identified and conducted Gene ontology (GO) and pathway enrichment analysis through MCODE and Clue GO in Cytospace respectively. DSigDB database was retrieved to predict therapeutic drugs and molecular docking was performed through PyMOL, AutoDock 1.5.6 to verify the binding energy between the drug and the different expressed hub genes. Finally, GSE70362 from GEO database was obtained to verify the different expression and correlation of each hub gene for AF degeneration. Results: We identified 41 intersection genes between 3 disease targets databases and Basement membraneBASE database. PPI network revealed 25 hub genes and they were mainly enriched in GO terms relating to glycosaminoglycan catabolic process, the TGF-β signaling pathway. 4 core targets were found to be significant via comparison of microarray samples and they showed strong correlation. The molecular docking results showed that the core targets have strong binding energy with predicting drugs including chitosamine and retinoic acid. Conclusions: In this study, we identified hub genes, pathways, potential targets, and drugs for treatment in BMs-related AF degeneration and IVDD. [ABSTRACT FROM AUTHOR]

Objective Mechanical stress is an important risk factor for intervertebral disc degeneration (IVDD). Angiopoietin‐2 (ANG‐2) is regulated by mechanical stress and is widely involved in the regulation of extracellular matrix metabolism. In addition, the signaling cascade between HIF‐1α and NF‐κB is critical in matrix degradation. This study aims to investigate the role and molecular mechanism of ANG‐2 in regulating the degeneration of annulus fibrosus (AF) through the HIF‐1α/NF‐κB signaling pathway. Methods The bipedal standing mice IVDD model was constructed, and histological experiments were used to evaluate the degree of IVDD and the expression of ANG‐2 in the AF. Mouse primary AF cells were extracted in vitro and subjected to mechanical stretching experiments. Western blot assay was used to detect the effect of mechanical stress on ANG‐2, and the role of the ANG‐2‐mediated HIF‐1α/NF‐κB pathway in matrix degradation. In addition, the effect of inhibiting ANG‐2 expression by siRNA or monoclonal antibody on delaying IVDD was investigated at in vitro and in vivo levels. One‐way ANOVA with the least significant difference method was used for pairwise comparison of the groups with homogeneous variance, and Dunnett's method was used to compare the groups with heterogeneous variance. Results In IVDD, the expressions of catabolic biomarkers (mmp‐13, ADAMTS‐4) and ANG‐2 were significantly increased in AF. In addition, p65 expression was increased while HIF‐1α expression was significantly decreased. The results of western blot assay showed mechanical stress significantly up‐regulated the expression of ANG‐2 in AF cells, and promoted matrix degradation by regulating the activity of HIF‐1α/NF‐κB pathway. Exogenous addition of Bay117082 and CoCl2 inhibited matrix degradation caused by mechanical stress. Moreover, injection of neutralizing antibody or treatment with siRNA to inhibit the expression of ANG‐2 improved the matrix metabolism of AF and inhibited IVDD progression by regulating the HIF‐1α/NF‐κB signaling pathway. Conclusion In IVDD, mechanical stress could regulate the HIF‐1α/NF‐κB signaling pathway and matrix degradation by mediating ANG‐2 expression in AF degeneration.

Background: The objective of this research was to identify differentially expressed genes (DEGs) related to ferroptosis in the annulus fibrosus (AF) during intervertebral disc degeneration (IDD). Methods: We analyzed gene data from degenerated and normal AF obtained from the GSE70362 and GSE147383 datasets. An analysis to determine the functional significance of the DEGs was conducted, followed by the creation of a network illustrating the interactions between proteins. We further analyzed the immune infiltration of the DEGs and determined the hub DEGs using LASSO regression analysis. Finally, we identified the hub ferroptosis-related DEGs (FRDEGs) and verified their expression levels using Real-time quantitative polymerase chain reaction (RT-qPCR), Western blot, Immunohistochemical Staining (IHC), and Immunofluorescence (IF). Results: By analyzing the GSE70362 and GSE147383 datasets, we identified 118 DEGs. In degenerative AF groups, we observed a significant increase in immune infiltration of resting memory CD4+ T cells. LASSO regression analysis revealed 9 hub DEGs. The construction of a Receiver Operating Characteristic (ROC) curve yielded an Area Under the Curve (AUC) value of 0.762. Furthermore, we found that MGST1 is a hub gene related to ferroptosis. Our examination of immune infiltration indicated that MGST1 primarily influences macrophage M0 in different immune cell expression groups. Finally, our observations revealed a marked upregulation of MGST1 expression in the degenerated annulus fibrosus tissue. Conclusion: Our findings indicate an upsurge in MGST1 levels within degenerative AF, potentially playing a crucial role in the exacerbation of IDD. These findings provide a foundation for further exploration of the pathological mechanisms underlying IDD and offer potential drug targets for intervention.

Objective: To explore the repair effect of tissue engineering for annulus fibrosus (AF) injury in stress-stimulation environment. Methods: Non-adhesive fibrinogen (Fib) representing the repair with non-stress stimulation and adhesive hydrogel of fibrinogen, thrombin and genipin mixture (Fib-T-G) representing the repair with stress stimulation were prepared to repair the AF lesion. The relationship between adhesion and stress stimulation was studied in rheological measurements, tension tests and atomic force microscopy (AFM) experiments. The repair effect of stress stimulation was studied in designed acellular AF scaffold models with fissures and defects. The models were repaired by the two different hydrogels, then implanted subcutaneously and cultured for 21 ​d in rats. Histology and qPCR of COL1A1, COL2A1, aggrecan, RhoA, and ROCK of the tissue engineering of the interface were evaluated afterward. Moreover, the repair effect was also studied in an AF fissure model in caudal disc of rats by the two different hydrogels. Discs were harvested after 21 ​d, and the disc degeneration score and AF healing quality were evaluated by histology. Result: In interfacial stress experiment, Fib-T-G hydrogel showed greater viscosity than Fib hydrogel (24.67 ​± ​1.007 vs 459333 ​± ​169205 ​mPa ​s). Representative force-displacement and sample modulus for each group demonstrate that Fib-T-G group significantly increased the interfacial stress level and enhanced the modulus of samples, compared with Fib group (P ​

Intervertebral disc (IVD) herniation is a major cause of chronic low back pain and disability. The current nucleus pulposus (NP) discectomy effectively relieves pain symptoms, but the annulus fibrosus (AF) defects are left unrepaired. Tissue engineering approaches show promise in treating AF injury and IVD degeneration; however, the presence of an inflammatory milieu at the injury site hinders the mitochondrial energy metabolism of AF cells, resulting in a lack of AF regeneration. In this study, we fabricated a dynamic self-healing hydrogel loaded with melatonin (an endocrine hormone well-known for its antioxidant and anti-inflammatory properties) and investigate whether melatonin-loaded hydrogel could promote AF defect repair by rescuing the matrix synthesis and energy metabolism of AF cells. The protective effects of melatonin on matrix components (e.g. type I and II collagen and aggrecan) in AF cells were observed in the presence of interleukin (IL)-1β. Additionally, melatonin was found to activate the nuclear factor erythroid 2-related factor signaling pathway, thereby safeguarding the mitochondrial function of AF cells from IL-1β, as evidenced by the increased level of adenosine triphosphate, mitochondrial membrane potential, and respiratory chain factor expression. The incorporation of melatonin into a self-healing hydrogel based on thiolated gelatin and β-cyclodextrin was proposed as a means of promoting AF regeneration. The successful implantation of melatonin-loaded hydrogel has been shown to facilitate in situ regeneration of AF tissue, thereby impeding IVD degeneration by preserving the hydration of nucleus pulposus in a rat box-cut IVD defect model. These findings offer compelling evidence that the development of a melatonin-loaded dynamic self-healing hydrogel can promote the mitochondrial functions of AF cells and represents a promising strategy for IVD regeneration.

Objective: Mechanical stress is an important risk factor for intervertebral disc degeneration (IVDD). Angiopoietin‐2 (ANG‐2) is regulated by mechanical stress and is widely involved in the regulation of extracellular matrix metabolism. In addition, the signaling cascade between HIF‐1α and NF‐κB is critical in matrix degradation. This study aims to investigate the role and molecular mechanism of ANG‐2 in regulating the degeneration of annulus fibrosus (AF) through the HIF‐1α/NF‐κB signaling pathway. Methods: The bipedal standing mice IVDD model was constructed, and histological experiments were used to evaluate the degree of IVDD and the expression of ANG‐2 in the AF. Mouse primary AF cells were extracted in vitro and subjected to mechanical stretching experiments. Western blot assay was used to detect the effect of mechanical stress on ANG‐2, and the role of the ANG‐2‐mediated HIF‐1α/NF‐κB pathway in matrix degradation. In addition, the effect of inhibiting ANG‐2 expression by siRNA or monoclonal antibody on delaying IVDD was investigated at in vitro and in vivo levels. One‐way ANOVA with the least significant difference method was used for pairwise comparison of the groups with homogeneous variance, and Dunnett's method was used to compare the groups with heterogeneous variance. Results: In IVDD, the expressions of catabolic biomarkers (mmp‐13, ADAMTS‐4) and ANG‐2 were significantly increased in AF. In addition, p65 expression was increased while HIF‐1α expression was significantly decreased. The results of western blot assay showed mechanical stress significantly up‐regulated the expression of ANG‐2 in AF cells, and promoted matrix degradation by regulating the activity of HIF‐1α/NF‐κB pathway. Exogenous addition of Bay117082 and CoCl2 inhibited matrix degradation caused by mechanical stress. Moreover, injection of neutralizing antibody or treatment with siRNA to inhibit the expression of ANG‐2 improved the matrix metabolism of AF and inhibited IVDD progression by regulating the HIF‐1α/NF‐κB signaling pathway. Conclusion: In IVDD, mechanical stress could regulate the HIF‐1α/NF‐κB signaling pathway and matrix degradation by mediating ANG‐2 expression in AF degeneration. [ABSTRACT FROM AUTHOR]

Low back pain is a major public health concern experienced by 80% of the world's population during their lifetime, which is closely associated with intervertebral disc (IVD) herniation. IVD herniation manifests as the nucleus pulposus (NP) protruding beyond the boundaries of the intervertebral disc due to disruption of the annulus fibrosus (AF). With a deepening understanding of the importance of the AF structure in the pathogenesis of intervertebral disc degeneration, numerous advanced therapeutic strategies for AF based on tissue engineering, cellular regeneration, and gene therapy have emerged. However, there is still no consensus concerning the optimal approach for AF regeneration. In this review, we summarized strategies in the field of AF repair and highlighted ideal cell types and pro-differentiation targeting approaches for AF repair, and discussed the prospects and difficulties of implant systems combining cells and biomaterials to guide future research directions. Low back pain is a major public health concern experienced by 80% of the world's population during their lifetime, which is closely associated with intervertebral disc (IVD) herniation. However, there is still no consensus concerning the optimal approach for annulus fibrosus (AF) regeneration. In this review, we summarized strategies in the field of AF repair and highlighted ideal cell types and pro-differentiation targeting approaches for AF repair, and discussed the prospects and difficulties of implant systems combining cells and biomaterials to guide future research directions. [Display omitted] [ABSTRACT FROM AUTHOR]

Simple Summary: The intervertebral disc is an important organ providing structure, support and flexibility to the spine, yet it can degrade over an individual's lifetime resulting in a painful condition known as intervertebral disc degeneration. Historically, the degeneration or breakdown of the organ has been catalogued and studied in humans, mice and to some extent dogs, however research has expanded to rats, cows, horses, rabbits, cats, and monkeys in recent decades allowing for the application of new research methods. Expanded research has further clarified the mechanisms contributing to degeneration at a molecular and cellular level. This review examines stressors promoting degeneration, how the intervertebral disc responds to them, the variation in symptomatic presentation of intervertebral disc degeneration between species, physical differences in the disc at different levels in the spine and between animals, as well as how the cellular population of the disc changes over time. Examining these aspects both within and between species helps to characterize degenerative changes in the intervertebral disc necessary for development of treatment and therapy. Back pain caused by intervertebral disc (IVD) degeneration has a major socio-economic impact in humans, yet historically has received minimal attention in species other than humans, mice and dogs. However, a general growing interest in this unique organ prompted the expansion of IVD research in rats, rabbits, cats, horses, monkeys, and cows, further illuminating the complex nature of the organ in both healthy and degenerative states. Application of recent biotechnological advancements, including single cell RNA sequencing and complex data analysis methods has begun to explain the shifting inflammatory signaling, variation in cellular subpopulations, differential gene expression, mechanical loading, and metabolic stresses which contribute to age and stress related degeneration of the IVD. This increase in IVD research across species introduces a need for chronicling IVD advancements and tissue biomarkers both within and between species. Here we provide a comprehensive review of recent single cell RNA sequencing data alongside existing case reports and histo/morphological data to highlight the cellular complexity and metabolic challenges of this unique organ that is of structural importance for all vertebrates. [ABSTRACT FROM AUTHOR]

Background: Intervertebral disc (IVD) degeneration is a major contributor to low back pain (LBP), yet there are no clinical therapies targeting the underlying pathology. The annulus fibrosus (AF) plays a critical role in maintaining IVD structure/function and undergoes degenerative changes such as matrix catabolism and inflammation. Thus, therapies targeting the AF are crucial to fully restore IVD function. Previously, we have shown nonviral delivery of transcription factors to push diseased nucleus pulposus cells to a healthy phenotype. As a next step in a proof‐of‐concept study, we report the use of Scleraxis (SCX) and Mohawk (MKX), which are critical for the development, maintenance, and regeneration of the AF and may have therapeutic potential to induce a healthy, pro‐anabolic phenotype in diseased AF cells. Methods: MKX and SCX plasmids were delivered via electroporation into diseased human AF cells from autopsy specimens and patients undergoing surgery for LBP. Transfected cells were cultured over 14 days and assessed for cell morphology, viability, density, gene expression of key phenotypic, inflammatory, matrix, pain markers, and collagen accumulation. Results: AF cells demonstrated a fibroblastic phenotype posttreatment. Moreover, transfection of SCX and MKX resulted in significant upregulation of the respective genes, as well as SOX9. Transfected autopsy cells demonstrated upregulation of core extracellular matrix markers; however, this was observed to a lesser effect in surgical cells. Matrix‐degrading enzymes and inflammatory cytokines were downregulated, suggesting a push toward a pro‐anabolic, anti‐inflammatory phenotype. Similarly, pain markers were downregulated over time in autopsy cells. At the protein level, collagen content was increased in both MKX and SCX transfected cells compared to controls. Conclusions: This exploratory study demonstrates the potential of MKX or SCX to drive reprogramming in mild to moderately degenerate AF cells from autopsy and severely degenerate AF cells from surgical patients toward a healthy phenotype and may be a potential nonviral gene therapy for LBP. [ABSTRACT FROM AUTHOR]

Tissue engineering has promising applications in the treatment of intervertebral disc degeneration (IDD). The annulus fibrosus (AF) is critical for maintaining the physiological function of the intervertebral disc (IVD), but the lack of vessels and nutrition in AF makes it difficult to repair. In this study, we used hyaluronan (HA) micro-sol electrospinning and collagen type I (Col-I) self-assembly techniques to fabricate layered biomimetic micro/nanofibrous scaffolds, which released basic fibroblast growth factor (bFGF) to promote AF repair and regeneration after discectomy and endoscopic transforaminal discectomy. The bFGF enveloped in the core of the poly-L-lactic-acid (PLLA) core-shell structure was released in a sustained manner and promoted the adhesion and proliferation of AF cells (AFCs). Col-I could self-assemble on the shell of the PLLA core-shell scaffold to mimic the extracellular matrix (ECM) microenvironment, providing structural and biochemical cues for the regeneration of AF tissue. The in vivo studies showed that the micro/nanofibrous scaffolds promoted the repair of AF defects by simulating the microstructure of native AF tissue and inducing endogenous regeneration mechanism. Taken together, the biomimetic micro/nanofibrous scaffolds have clinical potential for the treatment of AF defects caused by IDD. The annulus fibrosus (AF) is essential for the intervertebral disc (IVD) physiological function, yet it lacks vascularity and nutrition, making repair difficult. Micro-sol electrospinning technology and collagen type I (Col-I) self-assembly technique were combined in this study to create a layered biomimetic micro/nanofibrous scaffold that releases basic fibroblast growth factor (bFGF) to promote AF repair and regeneration. Col-I could mimic the extracellular matrix (ECM) microenvironment, in vivo , offering structural and biochemical cues for AF tissue regeneration. This research indicates that micro/nanofibrous scaffolds have clinical potential for treating AF deficits induced by IDD. [Display omitted] [ABSTRACT FROM AUTHOR]

Multi‐faceted deformation capabilities of Annulus Fibrosus (AF) results from an intricate mechanical design by nature. Wherein, organization and interactions between the constituents, collagen type I (CI), collagen type II (C2), hyaluronan, aggrecan, and water are instrumental. However, mechanisms by which such interactions influence AF mechanics at tissue‐scale is not well understood. This work investigates nanoscale interfacial interactions between CI and hyaluronan (CI‐H) and presents insights into their influence on tissue‐scale mechanics of AF. For this, three‐dimensional molecular dynamics (MD) simulations of tensile and compressive deformation are conducted on atomistic model of CI‐H interface at 0%, 65%, and 75% water concentrations (WC). Results show hyaluronan lowers local hydration around CI component of interface, owing to its hydrophilic nature. Analyses show that increase in WC from 65% to 75% leads to increased interchain sliding in hyaluronan, which further lowers tensile modulus of the interface from 2.1 GPa to 660 MPa, contributing to softening observed from outer to inner AF. Furthermore, increase in WC from 65% to 75%, shifts compressive deformation from buckling‐dominant to non‐buckling‐dominant which contributes towards lower radial bulge at inner AF. Findings provide deeper insights into mechanistic interactions and mechanisms at fundamental length‐scale which influence the AF structure‐mechanics at tissue‐scale. [ABSTRACT FROM AUTHOR]

Aims: CRP is an acute-phase protein that is used as a biomarker to follow severity and progression in infectious and inflammatory diseases. Its pathophysiological mechanisms of action are still poorly defined. CRP in its pentameric form exhibits weak anti-inflammatory activity. The monomeric isoform (mCRP) exerts potent proinflammatory properties in chondrocytes, endothelial cells, and leucocytes. No data exist regarding mCRP effects in human intervertebral disc (IVD) cells. This work aimed to verify the pathophysiological relevance of mCRP in the aetiology and/or progression of IVD degeneration. Methods: We investigated the effects of mCRP and the signalling pathways that are involved in cultured human primary annulus fibrosus (AF) cells and in the human nucleus pulposus (NP) immortalized cell line HNPSV-1. We determined messenger RNA (mRNA) and protein levels of relevant factors involved in inflammatory responses, by quantitative real-time polymerase chain reaction (RT-qPCR) and western blot. We also studied the presence of mCRP in human AF and NP tissues by immunohistochemistry. Results: We demonstrated that mCRP increases nitric oxide synthase 2 (NOS2), cyclooxygenase 2 (COX2), matrix metalloproteinase 13 (MMP13), vascular cell adhesion molecule 1 (VCAM1), interleukin (IL)-6, IL-8, and Lipocalin 2 (LCN2) expression in human AF and NP cells. We also showed that nuclear factor-κβ (NF-κβ), extracellular signal-regulated kinase 1/2 (ERK1/2), and phosphoinositide 3-kinase (PI3K) are at play in the intracellular signalling of mCRP. Finally, we demonstrated the presence of mCRP in human AF and NP tissues. Conclusion: Our results indicate, for the first time, that mCRP can be localized in IVD tissues, where it triggers a proinflammatory and catabolic state in degenerative and healthy IVD cells, and that NF-κβ signalling may be implicated in the mediation of this mCRP-induced state. Cite this article: Bone Joint Res 2023;12(3):189–198.

Background: One of the main causes of low back pain is intervertebral disc degeneration (IDD). Annulus fibrosus (AF) is important for the integrity and functions of the intervertebral disc (IVD). However, the resident functional cell components such as progenitors and vascularization-associated cells in AF are yet to be fully identified. Purpose: Identification of functional AF cell subpopulations including resident progenitors and vascularization-associated cells. Methods: In this study, the single-cell RNA sequencing data of rat IVDs from a public database were analyzed using Seurat for cell clustering, gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) for functional analysis, StemID for stem cell identification, Monocle and RNA velocity for pseudotime differentiation trajectory validation, single-cell regulatory network inference and clustering (SCENIC) for gene regulatory network (GRN) analysis, and CellChat for cell–cell interaction analysis. Immunostaining on normal and degenerated rat IVDs, as well as human AF, was used for validations. Results: From the data analysis, seven AF cell clusters were identified, including two newly discovered functional clusters, the Grem1+ subpopulation and the Lum+ ​subpopulation. The Grem1+ subpopulation had progenitor characteristics, while the Lum+ ​subpopulation was associated with vascularization during IDD. The GRN analysis showed that Sox9 and Id1 were among the key regulators in the Grem1+ subpopulation, and Nr2f2 and Creb5 could be responsible for the vascularization function in the Lum+ ​subpopulation. Cell–cell interaction analysis revealed highly regulated cellular communications between these cells, and multiple signaling networks including PDGF and MIF signaling pathways were involved in the interactions. Conclusions: Our results revealed two new functional AF cell subpopulations, with stemness and vascularization induction potential, respectively. The Translational potential of this article: These findings complement our knowledge about IVDs, especially the AF, and in return provide potential cell source and regulation targets for IDD treatment and tissue repair. The existence of the cell subpopulations was also validated in human AF, which strengthen the clinical relevance of the findings.

Annulus fibrosus (AF) repair remains a challenge because of its limited self-healing ability. Endogenous repair strategies combining scaffolds and growth factors show great promise in AF repair. Although the unique and beneficial characteristics of decellularized extracellular matrix (ECM) in tissue repair have been demonstrated, the poor mechanical property of ECM hydrogels largely hinders their applications in tissue regeneration. In the present study, we combined polyethylene glycol diacrylate (PEGDA) and decellularized annulus fibrosus matrix (DAFM) to develop an injectable, photocurable hydrogel for AF repair. We found that the addition of PEGDA markedly improved the mechanical strength of DAFM hydrogels while maintaining their porous structure. Transforming growth factor-β1 (TGF-β1) was further incorporated into PEGDA/DAFM hydrogels, and it could be continuously released from the hydrogel. The in vitro experiments showed that TGF-β1 facilitated the migration of AF cells. Furthermore, PEGDA/DAFM/TGF-β1 hydrogels supported the adhesion, proliferation, and increased ECM production of AF cells. In vivo repair performance of the hydrogels was assessed using a rat AF defect model. The results showed that the implantation of PEGDA/DAFM/TGF-β1 hydrogels effectively sealed the AF defect, prevented nucleus pulposus atrophy, retained disc height, and partially restored the biomechanical properties of disc. In addition, the implanted hydrogel was infiltrated by cells resembling AF cells and well integrated with adjacent AF tissue. In summary, findings from this study indicate that TGF-β1-supplemented DAFM hydrogels hold promise for AF repair.

BackgroundWater content is a key parameter for simulating tissue swelling and nutrient diffusion. Accurately measuring water content throughout the intervertebral disc (NP = nucleus pulposus; AF = annulus fibrosus) is important for developing patient-specific models. Water content is measured using destructive techniques, Quantitative MRI has been used to estimate water content and detect early degeneration, but it is dependent on scan parameters, concentration of free water molecules, and fiber architecture.PurposeTo directly measure disc-tissue water content using quantitative MRI and compare MRI-based measurements with biochemical assays, and to quantify changes in disc geometry due to compression.Study typeBasic science, controlled.SpecimenTwenty bone-disc-bone motion segments from skeletally mature bovines.Field strength/sequence7T/3D fast low angle shot (FLASH) pulse sequence and a T2 rapid imaging with refocused echoes (RARE) sequence.AssessmentDisc volumes, NP and AF volumetric water content, and T2 relaxation times were measured through MRI; NP and AF tissue gravimetric water content, mass density, and glycosaminoglycan content were measured through a biochemical assay.Statistical testsCorrelations between MRI-based measurement and biochemical composition were evaluated using Pearson's linear regression.ResultsMechanical dehydration resulted in a decrease in disc volume by up to 20% and a decrease in disc height by up to 35%. Direct water content measurements for the NP was achieved by normalizing MRI-based spin density by NP mass density (1.10 ± 0.03 g/cm3 ). However, the same approach underestimated water content in the AF by ~10%, which may be due to a higher concentration of collagen fibers and bound water molecules.Data conclusionSpin density or spin density normalized by mass density to estimate NP and AF water content was more accurate than correlations between water content and relaxation times. Mechanical dehydration decreased disc volume and disc height, and increased maximum cross-sectional area.Level of evidenceTECHNICAL EFFICACY STAGE:   J. Magn. Reson. Imaging 2020;52:1152-1162.

The investigation examines the transference of stiffness from intervertebral discs (IVDs) to the lumbar body of the L1 vertebra and the interactions among adjacent tissues. A computational model of the vertebra was developed, considering parameters such as cortical bone thickness, trabecular bone elasticity, and the nonlinear response of the nucleus pulposus to external loading. A nonlinear dynamic analysis was performed, revealing certain trends: a heightened stiffness of the annulus fibrosus correlates with a significant reduction in the vertebral body’s ability to withstand external loading. At a supplied displacement of 6 mm, the vertebra with a degenerative disc reached its yielding point, whereas the vertebrae with a healthy annulus fibrosus exhibited a strength capacity exceeding 20%. The obtained findings and proposed methodology are potentially useful for biomedical engineers and clinical specialists in evaluating the condition of the annulus fibrosus and predicting its influence on the bone components of the spinal system.

Abstract Background Intervertebral disc (IVD) degeneration is a major contributor to low back pain (LBP), yet there are no clinical therapies targeting the underlying pathology. The annulus fibrosus (AF) plays a critical role in maintaining IVD structure/function and undergoes degenerative changes such as matrix catabolism and inflammation. Thus, therapies targeting the AF are crucial to fully restore IVD function. Previously, we have shown nonviral delivery of transcription factors to push diseased nucleus pulposus cells to a healthy phenotype. As a next step in a proof‐of‐concept study, we report the use of Scleraxis (SCX) and Mohawk (MKX), which are critical for the development, maintenance, and regeneration of the AF and may have therapeutic potential to induce a healthy, pro‐anabolic phenotype in diseased AF cells. Methods MKX and SCX plasmids were delivered via electroporation into diseased human AF cells from autopsy specimens and patients undergoing surgery for LBP. Transfected cells were cultured over 14 days and assessed for cell morphology, viability, density, gene expression of key phenotypic, inflammatory, matrix, pain markers, and collagen accumulation. Results AF cells demonstrated a fibroblastic phenotype posttreatment. Moreover, transfection of SCX and MKX resulted in significant upregulation of the respective genes, as well as SOX9. Transfected autopsy cells demonstrated upregulation of core extracellular matrix markers; however, this was observed to a lesser effect in surgical cells. Matrix‐degrading enzymes and inflammatory cytokines were downregulated, suggesting a push toward a pro‐anabolic, anti‐inflammatory phenotype. Similarly, pain markers were downregulated over time in autopsy cells. At the protein level, collagen content was increased in both MKX and SCX transfected cells compared to controls. Conclusions This exploratory study demonstrates the potential of MKX or SCX to drive reprogramming in mild to moderately degenerate AF cells from autopsy and severely degenerate AF cells from surgical patients toward a healthy phenotype and may be a potential nonviral gene therapy for LBP.

Over the past decade, single-cell RNA sequencing (scRNA-seq) has revolutionized research on biological mechanisms of diseases. Moreover, this technique has been utilized to identify and characterize unique cell types and subpopulations, thereby illuminating cellular heterogeneity. The true value of scRNA-seq lies in its ability to detect transcriptional alterations or perturbed pathways within specific cell types under pathological conditions. In the context of intervertebral disc degeneration (IVDD), the pathophysiological foundation is largely rooted in inflammation. The primary target cells of IVDD are nucleus pulposus cells, annulus fibrosus cells, cartilage endplate cells, and macrophages. The advancements in scRNA-seq technology have triggered remarkable progress in IVDD treatment, leading to breakthroughs in the identification of cell subsets, functional analysis, novel therapeutic targets, and the differentiation and development of various cell types. This review is the first of its kind to introduce the application of scRNA-seq techniques in IVDD, with a focus on the most recent scRNA-seq studies that have defined the populations of various cell types and specific cell-cell interactions in IVDD. Furthermore, we highlight several promising future research directions for scRNA-seq in IVDD.

Low back pain is often due to degeneration of the intervertebral discs (IVD). It is one of the most common age- and work-related problems in today's society. Current treatments are not able to efficiently restore the full function of the IVD. Therefore, the aim of the present work was to reconstruct the two parts of the intervertebral disc—the annulus fibrosus (AF) and the nucleus pulposus (NP)—in such a way that the natural structural features were mimicked by a textile design. Silk was selected as the biomaterial for realization of a textile IVD because of its cytocompatibility, biodegradability, high strength, stiffness, and toughness, both in tension and compression. Therefore, an embroidered structure made of silk yarn was developed that reproduces the alternating fiber structure of +30° and −30° fiber orientation found in the AF and mimics its lamellar structure. The developed embroidered ribbons showed a tensile strength that corresponded to that of the natural AF. Fiber additive manufacturing with 1 mm silk staple fibers was used to replicate the fiber network of the NP and generate an open porous textile 3D structure that may serve as a reinforcement structure for the gel-like NP. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to analyze the effect of pro-inflammatory cytokine-stimulated human annulus fibrosus cells (hAFCs) on the sensitization of dorsal root ganglion (DRG) cells. We further hypothesized that celecoxib (cxb) could inhibit hAFCs-induced DRG sensitization. Methods: hAFCs from spinal trauma patients were stimulated with TNF-α or IL-1β. Cxb was added on day 2. On day 4, the expression of pro-inflammatory and neurotrophic genes was evaluated using RT-qPCR. Levels of prostaglandin E2 (PGE-2), IL-8, and IL-6 were measured in the conditioned medium (CM) using ELISA. hAFCs CM was then applied to stimulate the DRG cell line (ND7/23) for 6 days. Then, calcium imaging (Fluo4) was performed to evaluate DRG cell sensitization. Both spontaneous and bradykinin-stimulated (0.5 μM) calcium responses were analyzed. The effects on primary bovine DRG cell culture were performed in parallel to the DRG cell line model. Results: IL-1ß stimulation significantly enhanced the release of PGE-2 in hAFCs CM, while this increase was completely suppressed by 10 µM cxb. hAFCs revealed elevated IL-6 and IL-8 release following TNF-α and IL-1β treatment, though cxb did not alter this. The effect of hAFCs CM on DRG cell sensitization was influenced by adding cxb to hAFCs; both the DRG cell line and primary bovine DRG nociceptors showed a lower sensitivity to bradykinin stimulation. Conclusion: Cxb can inhibit PGE-2 production in hAFCs in an IL-1β-induced pro-inflammatory in vitro environment. The cxb applied to the hAFCs also reduces the sensitization of DRG nociceptors that are stimulated by the hAFCs CM. [ABSTRACT FROM AUTHOR]

The intervertebral disc (IVD) acts as a fibrocartilaginous joint to anchor adjacent vertebrae. Although several studies have demonstrated the cellular heterogeneity of adult mature IVDs, a single‐cell transcriptomic atlas mapping early IVD formation is still lacking. Here, the authors generate a spatiotemporal and single cell‐based transcriptomic atlas of human IVD formation at the embryonic stage and a comparative mouse transcript landscape. They identify two novel human notochord (NC)/nucleus pulposus (NP) clusters, SRY‐box transcription factor 10 (SOX10)+ and cathepsin K (CTSK)+, that are distributed in the early and late stages of IVD formation and they are validated by lineage tracing experiments in mice. Matrisome NC/NP clusters, T‐box transcription factor T (TBXT)+ and CTSK+, are responsible for the extracellular matrix homeostasis. The IVD atlas suggests that a subcluster of the vertebral chondrocyte subcluster might give rise to an inner annulus fibrosus of chondrogenic origin, while the fibroblastic outer annulus fibrosus preferentially expresseds transgelin and fibromodulin. Through analyzing intercellular crosstalk, the authors further find that notochordal secreted phosphoprotein 1 (SPP1) is a novel cue in the IVD microenvironment, and it is associated with IVD development and degeneration. In conclusion, the single‐cell transcriptomic atlas will be leveraged to develop preventative and regenerative strategies for IVD degeneration. [ABSTRACT FROM AUTHOR]

Intervertebral disc (IVD) degeneration and accompanying lower back pain impose global medical and societal challenges, affecting over 600 million people worldwide. The IVD complex fibrocartilaginous structure is responsible for the spine biomechanical function. The nucleus pulposus (NP), composed of swellable glycosaminoglycan (GAG), transfers compressive loads to the surrounding fiber‐reinforced annulus fibrosus (AF) lamellae, which stretches under tension. Together, these substructures allow the IVD to withstand extremely high and complex loads. Key to mimic the complete disc must consider the properties of its substructures. This study presents three novel substructures–a biomimetic silk‐reinforced composite lamella for the AF, a GAG analog for the NP, and a novel biomimetic combined AF‐NP construct. The biomimetic AF demonstrates nonlinear, hyperelastic, and anisotropic behavior similar to the native human AF, while the NP analog demonstrates mechanical behavior similar to the human NP. The synergized biomimetic AF‐NP demonstrates similar behavior to the unconfined NP, with significantly increased deformations indicating improved performance. Validation of the AF‐NP construct mechanics using a finite element model yields results compatible with native human IVD under various physiological loadings. The ability of our AF‐NP construct to mimic the native IVD offers a revolutionary concept for the potential development of a fully functional IVD. [ABSTRACT FROM AUTHOR]

Study Design: A biomechanical study. Objectives: The purpose of this study was to investigate the effects of cruciform and square incisions of annulus fibrosus (AF) on the mechanical stability of bovine intervertebral disc (IVD) in multiple degrees of freedom. Methods: Eight bovine caudal IVD motion segments (bone-disc-bone) were obtained from the local abattoir. Cruciform and square incisions were made at the right side of the specimen's annulus using a surgical scalpel. Biomechanical testing of three-dimensional 6 degrees of freedom was then performed on the bovine caudal motion segments using the mechanical testing and simulation (MTS) machine. Force, displacement, torque and angle were recorded synchronously by the MTS system. P value <.05 was considered statistically significant. Results: Cruciform and square incisions of the AF reduced both axial compressive and torsional stiffness of the IVD and were significantly lower than those of the intact specimens (P <.01). Left-side axial torsional stiffness of the cruciform incision was significantly higher than a square incision (P <.01). Neither incision methods impacted flexional-extensional stiffness or lateral-bending stiffness. Conclusions: The cruciform and square incisions of the AF obviously reduced axial compression and axial rotation, but they did not change the flexion-extension and lateral-bending stiffness of the bovine caudal IVD. This mechanical study will be meaningful for the development of new approaches to AF repair and the rehabilitation of the patients after receiving discectomy. [ABSTRACT FROM AUTHOR]