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Summary Purpose The purpose of our study was to introduce and validate a metal-free, reproducible and reliable mouse model of anterior cruciate ligament (ACL) reconstruction (ACLR) surgery as an effective tool for a better understanding of molecular mechanisms of graft-tunnel healing after ACLR. Methods A total of 150 C57BL/6 mice were randomly allocated into five Groups: Group 1 (mice with intact ACL), Group 2–4 (mice underwent modified ACLR surgery and sacrificed 1-, 2-, and 4-weeks after surgery), and Group 5 (mice underwent unmodified ACLR surgery and sacrificed 4 weeks after surgery). Micro-computed tomography (CT), biomechanical histological as well as immunohistochemical (IHC) analyses were performed to characterize the modified ACLR. Results Micro-CT analysis demonstrated there is a non-significant increase in BV/TV and BMD of the bone tunnel during the tendon-to-bone healing following ACLR. Biomechanical tests showed that the mean load-to-failure forces of Group 3 and 4 are equal to 31.7% and 46.0% of that in Group 1, while the stiffness was 33.1% and 57.2% of that of Group 1, respectively. And no obvious difference in biomechanical parameters was found between Group 4 and 5. Histological analysis demonstrated that formation of fibrovascular tissue in the tibial tunnel and aperture in Groups 4 and 5 and direct junction appeared between tendon graft and tunnel both in Groups 4 and 5. IHC results showed that there are gradually enhanced expression of Patched1, Smoothened and Gli2 concomitant with decreased Gli3 protein in the tendon-bone interface during the tendon-bone healing process. Conclusion We introduced a metal-free, reproducible and reliable mouse model of ACLR compared to the unmodified ACLR procedure, and characterized the expression pattern of key molecules in Ihh signaling during the graft healing process. The translational potential of this article In the present study we introduced and validated, for the first time, a metal-free, reproducible and reliable ACLR mouse model, which could be used to investigate the detailed molecular mechanisms of graft-tunnel healing after ACLR. We also explored new strategies to promote the healing of tendon-to-bone integration.

Pullulanase is a starch-debranching enzyme that is generally employed to efficiently break down starch for the production of high-glucose syrup. Acidic adaptation of pullulanases is of special interest. In this study, we conducted protein engineering to improve the acidic adaptation of Bacillus acidopullulyticus pullulanase (BaPul) and used a hydrogen-bond-based approach to identify promising residues that may change the deprotonation constants (pKa) of the catalytic residues. A total of 19 amino acids were selected for mutation according to the crystal structure of BaPul. The pH optimum of the L627R mutant shifted from 5.0 to 4.0, and its relative activity at pH 4.0 was 117% that of the wide-type enzyme. The improved efficacy of the L627R mutant at pH 4.0 was confirmed by kinetic parameters and pKa prediction. Moreover, the L627R mutant exhibited increased tolerance against acid-mediated denaturation, and its maximum d -glucose content (97.4%) was obtained after 40 h incubation, which is shorter by 10 h compared with the time required by the wide-type enzyme to produce a comparable amount of the monosaccharide. The L627R mutant may be suitable for industrial application because its shortened reaction time translates to reduced energy consumption.

The repair of large maxillofacial bony defects using regular scaffolds is restricted by the osteogenic effect. It was postulated that a novel porous hydroxyapatite (HA) scaffolds with a 25–30 µm groove structure (HAG) may counter this limitation. In this study we evaluated the biocompatibility of HAG scaffolds both in vitro and in vivo in beagle dogs by investigating the enhancement of scaffolds bioactivity and osteogenesis. Compared with a regular HA scaffolds, the HAG scaffolds significantly promoted human placenta-derived mesenchymal stem cell (hPMSC) osteogenic differentiation and the maturation of osteoblasts. This is achieved by increasing protein adsorption, as well as promoting directed growth and expression of osteogenic genes in vitro. The compressive strength of HAG scaffolds was significantly greater than HA in both dorsal muscle and the mandibular distraction area after in vivo implantation, with hematoxylin and eosin staining demonstrating new bone formation and vasculogenesis. Immunochemical staining and micro-CT scanning demonstrated increased expression of osteogenic factors (BMP2, OCN and COL-1) and bone density in the HAG scaffolds compared with HA. Based on the above results, we conclude that HAG scaffolds that have a groove structure induce greater osteogenesis and possess improved ostoegenesis which could be utilized in the clinical treatment.

DNA methylation is a major mode of epigenetic regulation in the mammalian genome and is essential for embryonic development. The three catalytic DNA methyltransferases (Dnmts), Dnmt1, Dnmt3a, and Dnmt3b, catalyze the methylation of cytosine. Dnmt3b is highly expressed in chondrocytes and global knockout of Dnmt3b led to skeletal deformations and embryonic lethality, suggesting an essential role of Dnmt3b in endochondral bone formation. To further define the role of Dnmt3b in skeletal development, Dnmt3b was deleted in Col2 positive chondrocyte lineage cells. Both axial and appendicular skeletal size were reduced and bone mineralization delayed in Col2Cre(+);Dnmt3b(f/f) (Dnmt3b(Col2)) mice at E14.5 and E18.5. While Alcian Blue Hematoxylin/Orange G (ABH/OG) staining showed normal chondrocyte columns in control growth plates, the length of hypertrophic chondrocyte zone and type X collagen expression were decreased in E18.5 growth plates from Dnmt3b(Col2) mice. TUNEL and PCNA staining demonstrated that the delay in chondrocyte maturation observed in the Dnmt3b(Col2) growth plates was not secondary to altered chondrocyte apoptosis or proliferation. Complementary in vitro experiments were performed on primary sternal chondrocytes isolated from control and Dnmt3b(Col2) mice. Gene expression studies confirmed delayed terminal maturation as Mmp13 and Col10a1 expression was down-regulated in Dnmt3b(Col2) chondrocytes. In addition, alkaline phosphatase (ALP) and Alizarin Red staining confirmed that Dnmt3b deletion in chondrocytes delays in vitro chondrocyte hypertrophic differentiation and matrix mineralization. Mechanistically, Dnmt3b gene deletion resulted in decreased BMP signaling through reduction of Smad1 phosphorylation. These findings show that epigenetic factor, Dnmt3b is necessary for normal chondrocyte hypertrophic maturation and limb development.

We investigated enhancement of articular cartilage regeneration using a combination of human adipose derived stem cells (hADSCs) and TGF-β3 microspheres (MS) in vivo. Poly-lactic-co-glycolic acid (PLGA)MS were prepared using a solid/oil/water emulsion solvent evaporation-extraction method. The morphology of the MS was evaluated by scanning electron microscopy (SEM). The release characteristic of the TGF-β3 MS was evaluated. A New Zealand rabbit model for experimental osteoarthritis (OA) was established using the anterior medial meniscus excision method. Thirty OA rabbits were divided randomly into three groups according to different treatments of the right knee joints on day 7 after surgery: hADSCs/MS group received injection of both hADSCs and TGF-β3 MS; hADSCs group was injected with hADSCs; control group was injected with normal saline. Gross observation, histological staining and RT-PCR for collagen II and aggrecan) were used to assess the severity of OA and for evaluating the effect of combined use of hADSCs and TGF-β3 MS on articular cartilage regeneration in vivo. The MS were spherical with a smooth surface and the average diameter was 28 ± 2.3 µm. The encapsulation efficiency test showed that 73.8 ± 2.9% of TGF-β3 were encapsulated in the MS. The release of TGF- β3 lasted for at least 30 days. At both 6 and 12 weeks after injection, three groups exhibited different degrees of OA. Histological analysis showed that the hADSCs/MS group exhibited less OA than the hADSCs group, and the control group exhibited the most severe OA. Real-time RT-PCR showed that the gene expression of both collagen II and aggrecan were significantly up-regulated in the hADSCs/MS group. At 12 weeks after injection, the hADSCs/MS group also exhibited less OA than the other two groups. Combined use of hADSCs and TGF-β3 MS promoted articular cartilage regeneration in rabbit OA models.

Aims Transforming growth factor-β1 (TGF-β1) is a chondrogenic factor and has been reported to be able to enhance chondrocyte differentiation from bone marrow mesenchymal stem cells (BMSCs). Here we investigate the molecular mechanism through which TGF-β1 chronically promotes the repair of cartilage defect and inhibit chondrocyte hypertrophy. Main methods Animal models of full thickness cartilage defects were divided into three groups: model group, BMSCs group (treated with BMSCs/calcium alginate gel) and BMSCs + TGF-β1 group (treated with Lentivirus-TGF-β1-EGFP transduced BMSCs/calcium alginate gel). 4 and 8 weeks after treatment, macroscopic observation, histopathological study and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) were done to analyze phenotypes of the animals. BMSCs were transduced with Lentivirus-TGF-β1-EGFP in vitro and Western blot analysis was performed. Key findings We found that TGF-β1-expressiing BMSCs improved the repair of the cartilage defect. The impaired cartilage contained higher amount of GAG and type II collagen and was integrated to the surrounding normal cartilage and higher content of GAG and type II collagen. The major events include increased expression of type II collagen following Smad2/3 phosphorylation, and inhibition of cartilage hypertrophy by increasing Yes-associated protein-1 (YAP-1) and inhibiting Runx2 and Col10 after the completion of chondrogenic differentiation. Significance We conclude that TGF-β1 is beneficial to chondrogenic differentiation of BMSCs via canonical Smad pathway to promote early-repairing of cartilage defect. Furthermore, TGF-β1 inhibits chondrocyte hypertrophy by decreasing hypertrophy marker gene expression via Hippo signaling. Long-term rational use of TGF-β1 may be an alternative approach in clinic for cartilage repair and regeneration.

Long-term administration of glucocorticoid hormones is considered one of predominant pathological factors inducing osteonecrosis of the femoral head (ONFH) development and progression, in which reduction of blood supply leads to a progressive bone loss and impairment of bone structure in the majority of cases. In a non-hematopoietic system, erythropoietin (EPO) can stimulate angiogenesis and bone regeneration. However, the specific mechanism underlying the role of EPO in ONFH remains to be elucidated. Therefore, the purpose of this study was to determine the effect of EPO on the prevention of bone loss in ONFH. Male C57BL/6J mice 3 months old were divided into two groups: EPO group and control groups. ONFH was established by the administration prednisolone (PDS, 100 mg/kg) with co-treatment of lipopolysaccharide (LPS, 1 mg/kg). ONFH mice received recombinant mouse EPO (500 U/kg/day) or saline intramuscularly. The mice were sacrificed at 2, 4, 6 and 8 weeks following the initiation of treatment. Alterations in the general architecture and histomorphology of the right femoral head were determined by hematoxylin and eosin staining and micro computed tomography (micro-CT). The expression of runt-related transcription factor 2 (Runx2), osteocalcin, vascular endothelial growth factor (VEGF) and platelet endothelial cell adhesion molecule (CD31) in the femoral head was tested by immunohistochemistry. Terminal deoxynucleotidyl-transferase-mediated dUTP nick end labeling (TUNEL) assay was performed to detect apoptosis in femoral heads. Micro-CT data revealed that EPO significantly improved bone volume/total volume and bone mineral density following 6 and 8 weeks of treatment. Histological analysis further demonstrated that EPO treatment improved the arrangement of trabeculae, thinning of trabeculae and other fractures in femoral heads, especially following 6 and 8 weeks of treatment. Immunohistochemical analysis suggested that EPO treatment up-regulated the expressions of Runx2, osteocalcin, VEGF and CD31 at 4 and 8 weeks. The TUNEL apoptosis assay suggested that EPO intervention reduced apoptosis in avascular ONFH. Therefore, EPO prevents bone loss in ONFH in mice through enhancing Runx2-mediated osteogenesis, VEGF-mediated angiogenesis and inhibition of cell apoptosis.

As a traditional concept of Chinese medicine (CM), the theory of "Shen (Kidney) controlling bones" has been gradually proven. And in modern allopathic medicine, the multiple mechanisms of bone growth, development and regeneration align with the theory. Shen deficiency as a pathological condition has a negative effect on the skeleton of body, specifically the disorder of bone homeostasis. Present studies indicate that Shen deficiency shares a common disorder characterized by dysfunction of hypothalamic-pituitary-adrenal (HPA) axis. HPA axis may be an important regulator of bone diseases with abnormal homeostasis. Therefore, we posit the existence of hypothalamic-pituitary-adrenal-osteo-related cells axis: cells that comprise bone tissue (osteo-related cells) are targets under the regulation of HPA axis in disorder of bone homeostasis. Chinese herbs for nourishing Shen have potential in the development of treatments for disorder of bone homeostasis.

Recently we demonstrated that ablation of the DNA methyltransferase enzyme, Dnmt3b, resulted in catabolism and progression of osteoarthritis (OA) in murine articular cartilage through a mechanism involving increased mitochondrial respiration. In this study, we identify 4-aminobutyrate aminotransferase (Abat) as a downstream target of Dnmt3b. Abat is an enzyme that metabolizes γ-aminobutyric acid to succinate, a key intermediate in the tricarboxylic acid cycle. We show that Dnmt3b binds to the Abat promoter, increases methylation of a conserved CpG sequence just upstream of the transcriptional start site, and inhibits Abat expression. Dnmt3b deletion in articular chondrocytes results in reduced methylation of the CpG sequence in the Abat promoter, which subsequently increases expression of Abat. Increased Abat expression in chondrocytes leads to enhanced mitochondrial respiration and elevated expression of catabolic genes. Overexpression of Abat in murine knee joints via lentiviral injection results in accelerated cartilage degradation following surgical induction of OA. In contrast, lentiviral-based knockdown of Abat attenuates the expression of IL-1β-induced catabolic genes in primary murine articular chondrocytes in vitro and also protects against murine articular cartilage degradation in vivo. Strikingly, treatment with the FDA-approved small-molecule Abat inhibitor, vigabatrin, significantly prevents the development of injury-induced OA in mice. In summary, these studies establish Abat as an important new target for therapies to prevent OA.

We previously established that DNA methyltransferase 3b (Dnmt3b) is the sole Dnmt responsive to fracture repair and that Dnmt3b expression is induced in progenitor cells during fracture repair. In the current study, we confirmed that Dnmt3b ablation in mesenchymal progenitor cells (MPCs) resulted in impaired endochondral ossification, delayed fracture repair, and reduced mechanical strength of the newly formed bone in Prx1-Cre;Dnmt3b(f/f) (Dnmt3b(Prx1)) mice. Mechanistically, deletion of Dnmt3b in MPCs led to reduced chondrogenic and osteogenic differentiation in vitro. We further identified Rbpjκ as a downstream target of Dnmt3b in MPCs. In fact, we located 2 Dnmt3b binding sites in the murine proximal Rbpjκ promoter and gene body and confirmed Dnmt3b interaction with the 2 binding sites by ChIP assays. Luciferase assays showed functional utilization of the Dnmt3b binding sites in murine C3H10T1/2 cells. Importantly, we showed that the MPC differentiation defect observed in Dnmt3b deficiency cells was due to the upregulation of Rbpjκ, evident by restored MPC differentiation upon Rbpjκ inhibition. Consistent with in vitro findings, Rbpjκ blockage via dual antiplatelet therapy reversed the differentiation defect and accelerated fracture repair in Dnmt3b(Prx1) mice. Collectively, our data suggest that Dnmt3b suppresses Notch signaling during MPC differentiation and is necessary for normal fracture repair.

Osthole is a bioactive coumarin derivative and has been reported to be able to enhance bone formation and improve fracture healing. However, the molecular mechanism of Osthole in bone fracture healing has not been fully defined. In this study we determined if Osthole enhances bone fracture healing through activation of BMP2 signaling in mice. We performed unilateral open transverse tibial fracture procedure in 10-week-old C57BL/6 mice which were treated with or without Osthole. Our previous studies demonstrated that chondrocyte BMP signaling is required for bone fracture healing, in this study we also performed tibial fracture procedure in Cre-negative and Col2-Cre;Bmp2flox/flox conditional knockout (KO) mice (Bmp2Col2Cre ) to determine if Osthole enhances fracture healing in a BMP2-dependent manner. Fracture callus tissues were collected and analyzed by X-ray, micro-CT (μCT), histology, histomorphometry, immunohistochemistry (IHC), biomechanical testing and quantitative gene expression analysis. In addition, mouse chondrogenic ATDC5 cells were cultured with or without Osthole and the expression levels of chondrogenic marker genes were examined. The results demonstrated that Osthole promotes bone fracture healing in wild-type (WT) or Cre- control mice. In contrast, Osthole failed to promote bone fracture healing in Bmp2Col2Cre conditional KO mice. In the mice receiving Osthole treatment, expression of cartilage marker genes was significantly increased. We conclude that Osthole could promote bone strength and enhance fracture healing by activation of BMP2 signaling. Osthole may be used as an alternative approach in the orthopaedic clinic for the treatment of fracture healing.

Notoginsenoside R1 (NGR1), one of the main effective components of Panax notoginseng, appears to be effective in promoting osteogenesis and treating osteoporosis. However, hitherto, whether NGR1 can directly promote osteoblastogenesis remains to be elucidated. In the present study, we hereby examined the effects of NGR1 on the osteoblastogenesis of a pre-osteoblast cell line (MC3T3-E1) in in vitro time-course and dose-dependent experiments. Its efficacy was evaluated by assessing cell viability (indicator of proliferation), alkaline phosphatase (ALP) activity (a marker of early osteoblastic differentiation), levels of osteocalcin (OCN; a marker of late osteoblastic differentiation), calcium deposition (a marker of final mineralization) and the expression of a series of osteoblastogenic marker genes (such as collagen Iα, Runx2, ALP and OCN) at different time points. When examining the proliferation of and ALP activity in the pre-osteoblasts, a bell-shaped dose-response pattern was observed when the cells were treated with various concentrations of NGR1, with a peak being observed at the concentration of 50 µg/ml. NGR1 markedly increased the expression of OCN at the concentration of 1,000 µg/ml in a dose‑dependent manner. Furthermore, treatment with 1,000 µg/ml NGR1 resulted in the highest mineralization by 4.3- and 5.9-fold on the 21st and 28th day, respectively compared with the control group (no treatment). On the whole, our findings indicate that NGR1 significantly promotes the osteoblastogenesis of pre-osteoblasts, which suggests that NGR1 has potential for use as a bone regeneration agent.

Background Radix Rehmanniae Praeparata (RR), the steamed roots of Rehmannia glutinosa, is a traditional Chinese medicine with the function of kidney-nourishing, and it has been safety used for centuries to treat bone-related disorders. The aim of this study is to investigate the positive effect and underlying mechanism of RR enhancing bone fracture healing in mouse model. Methods Ten-week-old C57BL/6J mice were subjected to a unilateral open transverse tibial fracture and provided a daily treatment of RR. Bone samples were harvested for tissue analyses including x-ray, μCT, histology, histomorphometry, biomechanical testing, immunohistochemical (IHC) and quantitative gene expression analysis. To determine the role of TGF-β in accelerating fracture healing effect of RR, aforementioned experiments were performed on Gli1-CreER; Tgfbr2 flox/flox (Tgfbr2Gli1ER) conditional knockout mice. Results RR promoted bone fracture healing and strengthened bone intensity in wild-type and Cre− mice with the activation of TGF-β/Smad2 signaling, on the contrary, RR failed to accelerating fracture healing in Tgfbr2Gli1ER mice. Conclusion RR promotes bone fracture healing by intensify the contribution of Gli1+ cells on bone and cartilage formation mainly in TGF-β-dependent manner. RR is an alternative option for clinical treatment of fracture.

Objective. To investigate the effect and underlying mechanism of Bushenhuoxue (BSHX) formula on articular cartilage repair. Methods. Twenty-four full-thickness cartilage defect rats were divided into two groups: model group and BSHX group (treated with BSHX formula). Macroscopic observation and histopathological study were conducted after 4- and 8-week treatment. Additionally, we also evaluated chondrocyte proliferation, extracellular matrix (ECM) deposition, cartilage degradation, and chondrocyte hypertrophy-related genes expression in chondrogenic ATDC5 cells cultured in BSHX formula-mediated serum. Moreover, we assessed aforementioned genes expression and pSMAD2/3 protein level in Tgfβr2 siRNA transfected chondrogenic ATDC5 cells in order to address whether BSHX formula exerts cartilage repairing effect through TGF-β signaling. Results. Neocartilage regeneration promotion effect was observed in cartilage defect rats after BSHX formula treatment, with increases in Col2 and pSMAD2 and decreases in Mmp13 and Runx2. Moreover, cell proliferation, the elevated Col2a1, Aggrecan and pSMAD2/3, reduced Mmp13, Adamts5, Col10a1, and Runx2 expression were also observed in chondrogenic ATDC5 cells cultured in BSHX formula-mediated serum. Besides, the expression alteration of ECM deposition, cartilage degradation, chondrocyte hypertrophy-related genes, and pSMAD2/3 protein levels presented in Tgfβr2 downregulated chondrogenic ATDC5 cells couldn’t be adjusted by BSHX formula treatment. Conclusion. By activation of TGF-β signaling, BSHX formula can promote articular cartilage repair by accelerating chondrocyte proliferation and maintaining chondrocyte phenotype, upregulate ECM accumulation, and inhibit matrix degradation.

Yougui pills (YGPs) have been used for centuries in the treatment of Chinese patients with Kidney-Yang Deficiency Syndrome. Despite the fact that the efficiency of YGPs on treating osteoarthritis has been verified in clinic, the underlying mechanisms are not totally understood. The present study observes the therapeutic role of YGPs and mechanisms underlying its chondroprotective action in osteoarthritic cartilage. To evaluate the chondroprotective effects of YGPs, we examined the impact of orally administered YGPs in a model of destabilization of the medial meniscus (DMM). Male C57BL/6J mice were provided a daily treatment of YGPs and a DMM surgery was performed on the right knee. At 12 weeks post-surgery, the joints were harvested for tissue analyses, including histomorphometry, OARSI scoring, micro-CT and immunohistochemistry for COL-2, MMP-13 and pSMAD-2. We also performed the relative experiments mentioned above in mice with Tgfbr2 conditional knockout (TGF-βRIICol2ER mice) in articular cartilage. To evaluate the safety of YGPs, hematology was determined in each group. Amelioration of cartilage degradation was observed in the YGPs group, with increases in cartilage area and thickness, proteoglycan matrix, and decreases in OARSI score at 12 weeks post surgery. In addition, reduced BV/TV and Tb. Th, and elevated Tb. Sp were observed in DMM-induced mice followed by YGPs treatment. Moreover, the preservation of cartilage correlated with reduced MMP-13, and elevated COL-2 and pSMAD-2 protein expressional levels were also revealed in DMM-induced mice treated with YGPs. Similarly, TGF-βRIICol2ER mice exhibited significant OA-like phenotype. However, no significant difference in cartilage structure was observed in TGF-βRIICol2ER mice after YGPs treatment. Interestingly, no obvious adverse effects were observed in mice from each group based on the hematologic analyses. These findings suggested that YGPs could inhibit cartilage degradation through enhancing TGF-β/Smad signaling activation, and be considered a good option for the treatment of osteoarthritis.

Osteoarthritis (OA) is the most common form of arthritis worldwide. It is a complex disease affecting the whole joint but is generally characterized by progressive degradation of articular cartilage. Recent genome-wide association screens have implicated distinct DNA methylation signatures in OA patients. We show that the de novo DNA methyltransferase (Dnmt) 3b, but not Dnmt3a, is present in healthy murine and human articular chondrocytes and its expression decreases in OA mouse models and in chondrocytes from human OA patients. Targeted deletion of Dnmt3b in murine articular chondrocytes results in an early-onset and progressive postnatal OA-like pathology. RNA-Seq and methylC-Seq analyses of Dnmt3b loss-of-function chondrocytes show that cellular metabolic processes are affected. Specifically, TCA metabolites and mitochondrial respiration are elevated. Importantly, a chondroprotective effect was found following Dnmt3b gain of function in murine articular chondrocytes in vitro and in vivo. This study shows that Dnmt3b plays a significant role in regulating postnatal articular cartilage homeostasis. Cellular pathways regulated by Dnmt3b in chondrocytes may provide novel targets for therapeutic approaches to treat OA.

This study aimed to investigate if autologous bone marrow mesenchymal stem cells (MSCs) could treat osteonecrosis of the femoral head (ONFH) and what the fate and distribution of the cells are in dogs. Twelve Beagle dogs were randomly divided into two groups: MSCs group and SHAM operated group. After three weeks, dogs in MSCs group and SHAM operated group were intra-arterially injected with autologous MSCs and 0.9% normal saline, respectively. Eight weeks after treatment, the necrotic volume of the femoral heads was significantly reduced in MSCs group. Moreover, the trabecular bone volume was increased and the empty lacunae rate was decreased in MSCs group. In addition, the BrdU-positive MSCs were unevenly distributed in femoral heads and various vital organs. But no obvious abnormalities were observed. Furthermore, most of BrdU-positive MSCs in necrotic region expressed osteocalcin in MSCs group and a few expressed peroxisome proliferator-activated receptor-γ (PPAR-γ). Taken together, these data indicated that intra-arterially infused MSCs could migrate into the necrotic field of femoral heads and differentiate into osteoblasts, thus improving the necrosis of femoral heads. It suggests that intra-arterial infusion of autologous MSCs might be a feasible and relatively safe method for the treatment of femoral head necrosis.

Reduced mechanical stimuli in many pathological cases, such as hemimastication and limited masticatory movements, can significantly affect the metabolic activity of mandibular condylar chondrocytes and the growth of mandibles. However, the molecular mechanisms for these phenomena remain unclear. In this study, we hypothesized that integrin-focal adhesion kinase (FAK)-ERK (extracellular signal-regulated kinase)/PI3K (phosphatidylinositol-3-kinase) signaling pathway mediated the cellular response of condylar chondrocytes to mechanical loading. Primary condylar chondrocytes were exposed to hydrostatic compressive forces (HCFs) of different magnitudes (0, 50, 100, 150, 200, and 250 kPa) for 2 h. We measured the viability, morphology, and apoptosis of the chondrocytes with different treatments as well as the gene, protein expression, and phosphorylation of mechanosensitivity-related molecules, such as integrin α2, integrin α5, integrin β1, FAK, ERK, and PI3K. HCFs could significantly increase the viability and surface area of condylar chondrocytes and decrease their apoptosis in a dose-dependent manner. HCF of 250 kPa resulted in a 1.51 ± 0.02-fold increase of cell viability and reduced the ratio of apoptotic cells from 18.10% ± 0.56% to 7.30% ± 1.43%. HCFs could significantly enhance the mRNA and protein expression of integrin α2, integrin α5, and integrin β1 in a dose-dependent manner, but not ERK1, ERK2, or PI3K. Instead, HCF could significantly increase phosphorylation levels of FAK, ERK1/2, and PI3K in a dose-dependent manner. Cilengitide, the potent integrin inhibitor, could dose-dependently block such effects of HCFs. HCFs enhances the viability and decreases the apoptosis of condylar chondrocytes through the integrin-FAK-ERK/PI3K pathway.