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In the pathophysiology of osteoarthritis and osteoporosis, articular cartilage and bone represent the target tissues, respectively, but muscle is also involved. Since many changes in energy metabolism occur in muscle with aging, the aim of the present work was to investigate the involvement of carnitine palmitoyl transferase 1b (Cpt1b) in the muscle pathophysiology of the two diseases. Healthy subjects (CTR, n = 5), osteoarthritic (OA, n = 10), and osteoporotic (OP, n = 10) patients were enrolled. Gene expression analysis conducted on muscle and myoblasts showed up-regulation of CPT1B in OA patients; this result was confirmed by immunohistochemical and immunofluorescence analyses and enzyme activity assay, which showed increased Cpt1b activity in OA muscle. In addition, CPT1B expression resulted down-regulated in cultured OP myoblasts. Given the potential involvement of Cpt1b in the modulation of oxidative stress, we investigated ROS levels, which were found to be lower in OA myoblasts, and gene expression of nicotinamide adenine dinucleotide phosphate hydrogen oxidase 4 (Nox4), which resulted up-regulated in OA cells. Finally, the immunofluorescence of BCL2/adenovirus E1B 19 kDa protein-interacting protein 3 (Bnip3) showed a decreased expression in OP myoblasts, with respect to CTR and OA. Contextually, through an ultrastructural analysis conducted by Transmission Electron Microscopy (TEM), the presence of aberrant mitochondria was observed in OP muscle. This study highlights the potential role of Cpt1b in the regulation of muscle homeostasis in both osteoarthritis and osteoporosis, allowing for the expansion of the current knowledge of what are the molecular biological pathways involved in the regulation of muscle physiology in both diseases.

Biological drugs, including monoclonal antibodies, represent a revolutionary strategy in all fields of medicine, offering promising results even in the treatment of osteoarthritis (OA). However, their safety and efficacy have not been fully validated, highlighting the need for in-depth studies. Therefore, we provided a comprehensive systematic review of the intra-articular use of monoclonal antibodies for the treatment of OA in animal models, reflecting ongoing efforts to advance therapeutic strategies and improve patient outcomes. A systematic literature search was conducted in December 2023 following the PRISMA guidelines, using the Web of Science, Google Scholar, and PUBMED databases. Out of a total of 456, 10 articles were included in the study analyzing intra-articular antibodies and focusing on various targets, including vascular endothelial growth factor (VEGF), nerve growth factor (NGF), interleukin 4-10 (IL4-10), tumor necrosis factor α (TNF-α), a disintegrin and metalloproteinase with thrombospondin motifs 5 (ADAMTS5), and matrix metalloproteinase 13 (MMP-13). Most studies administered the antibodies weekly, ranging from 1 to 10 injections. Animal models varied, with mean follow-up periods of 8.9 ± 4.1 weeks. The methods of assessing outcomes, including pain and morpho-functional changes, varied. Some studies reported only morphological and immunohistochemical data, while others included a quantitative analysis of protein expression. In conclusion, monoclonal antibodies represent a promising avenue in the treatment of OA, offering targeted approaches to modulate disease pathways. Further research and clinical trials are needed to validate their safety and efficacy, with the potential to revolutionize the management of OA and reduce reliance on prosthetic interventions.

Background: Musculoskeletal disorders (MSDs) involve muscles, nerves, tendons, joints, cartilage, and spinal discs. These conditions can be triggered by both the work environment and the type of work performed, factors that, in some cases, can also exacerbate pre-existing conditions. This systematic review aims to provide an overview of the impact that different work-related activities have on the musculoskeletal system. Methods: A global search of publications was conducted using the following international bibliographic web databases: PubMed and Web of Science. The search strategies combined terms for musculoskeletal disorders and workers. In addition, a meta-analysis was conducted to estimate the prevalence of MSDs within the healthcare sector. Results: A total of 10,805 non-duplicated articles were identified, and finally, 32 studies were reviewed in this article. Once the literature search was completed, occupational figures were categorized into healthcare, farming, industrial, and computer sectors. In the healthcare sector, the prevalence estimate for degenerative diseases of the lumbar spine was 21% (497 out of 2547 physicians and dentists) (95% CI, 17-26%), while for osteoarthritis of the hand, it was 37% (382 out of 1013 dentists) (95% CI, 23-51%). Conclusions: Musculoskeletal disorders significantly impair workers' quality of life, especially in healthcare sector. These conditions are also associated with high costs for employers, such as absenteeism, lost productivity, and increased costs for healthcare, disability, and workers' compensation.

Background: Osteoporosis is a worldwide health issue. Loss of bone mass is a potential risk factor for fragility fractures, and osteoporotic fractures place a considerable burden on society. Bone and muscle represent a functional unit in which the two tissues are intimately interconnected. Ropivacaine is a potent local anesthetic used in clinical practice for intraoperative anesthesia and postoperative pain management, in particular for hip surgery. When injected, Ropivacaine can diffuse locally through, in particular in surrounding skeletal muscle tissue, causing dose-dependent cytotoxicity, oxidative stress and myogenesis impairment. Based on those evidences, we focused our attention on Ropivacaine-induced cytotoxicity on cultured human myoblasts., Methods: Primary human myoblasts and myotubes from healthy subjects, osteoarthritic and osteoporotic patients (OP) were cultured in the presence of Ropivacaine. In some experiments, ascorbic acid (AsA) was added as a potent antioxidant agent. Cell viability and ROS levels were evaluated to investigate the myotoxic activity and Real-Time PCR and Western blot analysis carried out to investigate the expression of proliferation and myogenic markers., Results: A dose-dependent decrease of cell viability was observed after Ropivacaine exposure in both OP myoblasts and myotubes cultures, whereas those effects were not observed in the presence of Propofol, a general anesthetic. The adding of AsA reduced Ropivacaine negative effects in OP myoblast cultures. In addition, Ropivacaine exposure also increased ROS levels and upregulated Nox4 expression, an enzyme primarily implicated in skeletal muscle ROS generation. AsA treatment counteracted the oxidant activity of Ropivacaine and partially restored the basal condition in cultures. Positive myogenic markers, such as MyoD and Myf5, were downregulated by Ropivacaine exposure, whereas myostatin, a negative regulator of muscle growth and differentiation, was upregulated. The phenotypic deregulation of myogenic controllers in the presence of Ropivacaine was counteracted by AsA treatment., Conclusions: Our findings highlight the oxidative stress-mediated myotoxic effect of Ropivacaine on human skeletal muscle tissue cell cultures, and suggest treatment with AsA as valid strategy to mitigate its negative effects and allowing an ameliorated functional skeletal muscle recovery in patients undergoing hip replacement surgery for osteoporotic bone fracture., (© 2023. The Author(s).)

Osteosarcopenia (OSP) is a geriatric syndrome characterized by the coexistence of osteoporosis and sarcopenia and associated with an increased risk of fragility fractures, disability, and mortality. For patients with this syndrome, musculoskeletal pain represents the most significant challenge since, in addition to limiting the individual's functionality and promoting disability, it has a huge psychological burden involving anxiety, depression, and social withdrawal. Unfortunately, the molecular mechanisms involved in the development and persistence of pain in OSP have not yet been fully elucidated, although immune cells are known to play a key role in these processes. Indeed, they release several molecules that promote persistent inflammation and nociceptive stimulation, resulting in the gating of ion channels responsible for the generation and propagation of the noxious stimulus. The adoption of countermeasures to counteract the OSP progression and reduce the algic component appears to be necessary, providing patients with a better quality of life and greater adherence to treatment. In addition, the development of multimodal therapies, based on an interdisciplinary approach, appears to be crucial, combining the use of anti-osteoporotic drugs with an educational programme, regular physical activity, and proper nutrition to eliminate risk factors. Based on this evidence, we conducted a narrative review using the PubMed and Google Scholar search engines to summarize the current knowledge on the molecular mechanisms involved in the pain development in OSP and the potential countermeasures to be taken. The lack of studies addressing this topic highlights the need to conduct new research into the resolution of an ever-expanding social problem.

Spaceflight exposure, like prolonged skeletal unloading, is known to result in significant bone loss, but the molecular mechanisms responsible are still partly unknown. This impairment, characterizing both conditions, suggests the possibility of identifying common signalling pathways and developing innovative treatment strategies to counteract the bone loss typical of astronauts and osteoporotic patients. In this context, primary cell cultures of human osteoblasts derived from healthy subjects and osteoporotic patients were exposed to random positioning machine (RPM) to reproduce the absence of gravity and to exacerbate the pathological condition, respectively. The duration of exposure to RPM was 3 or 6 days, with the aim of determining whether a single administration of recombinant irisin (r-irisin) could prevent cell death and mineralizing capacity loss. In detail, cellular responses were assessed both in terms of death/survival, by MTS assay, analysis of oxidative stress and caspase activity, as well as the expression of survival and cell death proteins, and in terms of mineralizing capacity, by investigating the pentraxin 3 (PTX3) expression. Our results suggest that the effects of a single dose of r-irisin are maintained for a limited time, as demonstrated by complete protection after 3 days of RPM exposure and only partial protection when RPM exposure was for a longer time. Therefore, the use of r-irisin could be a valid strategy to counteract the bone mass loss induced by weightlessness and osteoporosis. Further studies are needed to determine an optimal treatment strategy based on the use of r-irisin that is fully protective even over very long periods of exposure and/or to identify further approaches to be used in a complementary manner., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Cariati, Bonanni, Rinaldi, Marini, Iundusi, Gasbarra, Tancredi and Tarantino.)

The vitamin D receptor (VDR) regulates bone development and calcium homeostasis, suggesting a central role in musculoskeletal diseases such as osteoporosis (OP). Several studies have examined the contribution of VDR polymorphisms and epigenetic signatures in bone metabolism and OP risk, with sometimes inconclusive results. Our study aimed to explore the association between genetic variability, expression and the methylation pattern of VDR with the risk of OP in a cohort of Caucasian patients. Genomic DNA from 139 OP, 54 osteopenic (Ope) and 73 healthy (CTR) subjects were used for genotyping the rs731236 ( TaqI ), rs2228570 ( FokI ) and rs11568820 ( Cdx2 ) polymorphisms of the VDR gene by an allelic discrimination assay. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis of VDR expression levels and pyrosequencing analysis of a VDR promoter CpG island were carried out in a subcohort (25 OP and 25 CTR) of subjects. Data obtained showed a significantly higher OP risk for rs11568820 G/A and A/A genotypes ( p = 0.05). qRT-PCR revealed lower VDR gene expression levels in the OP group compared to CTR subjects ( p = 0.0009), also associated with both the rs11568820 A/A genotype ( p = 0.03) and femoral fragility fractures ( p = 0.05). No association was found between the methylation pattern of the region analyzed of the VDR promoter and its expression levels. Our results identify a significative association between Cdx2 rs11568820 polymorphism and OP risk. In addition, the VDR transcriptomic profile suggests a putative interconnection with OP progression, providing a useful tool to stratify OP phenotype and fragility fracture risk.

Hip fractures in elderly patients are an arising problem due to aging of population and still represent a controversial challenge for orthopedic surgeon who should help achieve the best functional recovery in the shortest time. Cementation in hip replacement plays an important role, but it should be carefully planned considering the possible risks. According to the literature, there are still no certainties regarding the superiority of an uncemented implant compared to a cemented one. The purpose of this work is to conduct an overview of the scientific literature that can clarify the advantages and disadvantages of cemented and non-cemented implants from a biological and biomechanical point of view., Competing Interests: The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article., (© The Author(s), 2022.)

Osteoporotic fractures are one of the major problems facing healthcare systems worldwide. Undoubtedly, fragility fractures of the hip represent a far greater burden in terms of morbidity, mortality, and healthcare costs than other fracture sites. However, despite the significant impact on the health and quality of life of older adults, there is a general lack of awareness of osteoporosis, which results in suboptimal care. In fact, most high-risk individuals are never identified and do not receive adequate treatment, leading to further fragility fractures and worsening health status. Furthermore, considering the substantial treatment gap and the proven cost-effectiveness of fracture prevention programs such as Fracture Liaison Services, urgent action is needed to ensure that all individuals at high risk of fragility fracture are adequately assessed and treated. Based on this evidence, the aim of our review was to (i) provide an overview and comparison of the burden and management of fragility fractures, highlighting the main gaps, and (ii) highlight the importance of using alternative approaches, both surgical and non-surgical, with the aim of implementing early prevention of osteoporotic fractures and improving the management of osteoporotic patients at imminent and/or very high risk of fracture., (© 2022. International Osteoporosis Foundation and Bone Health and Osteoporosis Foundation.)

Osteosarcopenia (OS) is a newly defined condition represented by the simultaneous presence of osteopenia/osteoporosis and sarcopenia, the main age-related diseases. The simultaneous coexistence of the two phenotypes derives from the close connection of the main target tissues involved in their pathogenesis: bone and muscle. These two actors constitute the bone-muscle unit, which communicates through a biochemical and mechanical crosstalk which involves multiple factors. Altered pattern of molecular pathways leads to an impairment of both the functionality of the tissue itself and the communication with the complementary tissue, composing the OS pathogenesis. Recent advances in the genetics field have provided the opportunity to delve deeper into the complex biological and molecular mechanisms underlying OS. Unfortunately, there are still many gaps in our understanding of these pathways, but it has proven essential to apply strategies such as exercise and nutritional intervention to counteract OS. New therapeutic strategies that simultaneously target bone and muscle tissue are limited, but recently new targets for the development of dual-action drug therapies have been identified. This narrative review aims to provide an overview of the latest scientific evidence associated with OS, a complex disorder that will pave the way for future research aimed at understanding the bone-muscle-associated pathogenetic mechanisms., Competing Interests: The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article., (© The Author(s), 2022.)

Musculoskeletal pain is a condition that characterises several diseases and represents a constantly growing issue with enormous socio-economic burdens, highlighting the importance of developing treatment algorithms appropriate to the patient's needs and effective management strategies. Indeed, the algic condition must be assessed and treated independently of the underlying pathological process since it has an extremely negative impact on the emotional and psychic aspects of the individual, leading to isolation and depression. A full understanding of the pathophysiological mechanisms involved in nociceptive stimulation and central sensitization is an important step in improving approaches to musculoskeletal pain. In this context, the bidirectional relationship between immune cells and neurons involved in nociception could represent a key point in the understanding of these mechanisms. Therefore, we provide an updated overview of the magnitude of the musculoskeletal pain problem, in terms of prevalence and costs, and summarise the role of the most important molecular players involved in the development and maintenance of pain. Finally, based on the pathophysiological mechanisms, we propose a model, called the "musculoskeletal pain cycle", which could be a useful tool to counteract resignation to the algic condition and provide a starting point for developing a treatment algorithm for the patient with musculoskeletal pain.

Several scientific evidence have shown that exposure to microgravity has a significant impact on the health of the musculoskeletal system by altering the expression of proteins and molecules involved in bone-muscle crosstalk, which is also observed in the research of microgravity effect simulation. Among these, the expression pattern of myostatin appears to play a key role in both load-free muscle damage and the progression of age-related musculoskeletal disorders, such as osteoporosis and sarcopenia. Based on this evidence, we here investigated the efficacy of treatment with anti-myostatin (anti-MSTN) antibodies on primary cultures of human satellite cells exposed to 72 h of random positioning machine (RPM). Cell cultures were obtained from muscle biopsies taken from a total of 30 patients (controls, osteoarthritic, and osteoporotic) during hip arthroplasty. The Pax7 expression by immunofluorescence was carried out for the characterization of satellite cells. We then performed morphological evaluation by light microscopy and immunocytochemical analysis to assess myostatin expression. Our results showed that prolonged RPM exposure not only caused satellite cell death, but also induced changes in myostatin expression levels with group-dependent variations. Surprisingly, we observed that the use of anti-MSTN antibodies induced a significant increase in cell survival after RPM exposure under all experimental conditions. Noteworthy, we found that the negative effect of RPM exposure was counteracted by treatment with anti-MSTN antibodies, which allowed the formation of numerous myotubes. Our results highlight the role of myostatin as a major effector of the cellular degeneration observed with RPM exposure, suggesting it as a potential therapeutic target to slow the muscle mass loss that occurs in the absence of loading., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Cariati, Scimeca, Bonanni, Triolo, Naldi, Toro, Marini, Tancredi, Iundusi, Gasbarra and Tarantino.)

Bone marrow edema (BME) is defined as an area of low signal intensity on T1-weighted (T1W) MRI images and associated with intermediate or high signal intensity findings on T2-weighted (T2W) MRI images. BME represents a typical imaging finding that characterizes common stress-related bone injuries of professional and amateur athletes. The etiology of stress-related injuries is influenced by numerous factors, including the initiation of a new sports activity or changes in an existing training protocol. The clinical significance of BME remains unclear. However, a correlation between the imaging pattern of BME, the clinical history of the patient and the type of sports activity practiced is essential for correct diagnosis and adequate therapeutic treatment. It is also important to clarify whether there is a specific threshold beyond which exercise can adversely affect the bone remodeling process, as the clinical picture may degenerate into the presence of BME, pain and, in the most severe cases, bone loss. In our review, we summarize the current knowledge on the etiopathogenesis and treatment options for BME and highlight the main aspects that make it difficult to formulate a correct diagnosis and establish an adequate therapeutic treatment.

Bone and muscle tissues influence each other through the integration of mechanical and biochemical signals, giving rise to bone-muscle crosstalk. They are also known to secrete osteokines, myokines, and cytokines into the circulation, influencing the biological and pathological activities in local and distant organs and cells. In this regard, even osteoporosis and sarcopenia, which were initially thought to be two independent diseases, have recently been defined under the term "osteosarcopenia", to indicate a synergistic condition of low bone mass with muscle atrophy and hypofunction. Undoubtedly, osteosarcopenia is a major public health concern, being associated with high rates of morbidity and mortality. The best current defence against osteosarcopenia is prevention based on a healthy lifestyle and regular exercise. The most appropriate type, intensity, duration, and frequency of exercise to positively influence osteosarcopenia are not yet known. However, combined programmes of progressive resistance exercises, weight-bearing impact exercises, and challenging balance/mobility activities currently appear to be the most effective in optimising musculoskeletal health and function. Based on this evidence, the aim of our review was to summarize the current knowledge about the role of exercise in bone-muscle crosstalk, highlighting how it may represent an effective alternative strategy to prevent and/or counteract the onset of osteosarcopenia.

Background: Osteosarcopenia is a recently identified condition caused by the coexistence of osteoporosis and sarcopenia that affects the frail elderly population, leading to an increased risk of falls and fractures. Given the recent socio-economic interest associated with osteosarcopenia, the aim of this meta-analysis is to provide an overview of the factors potentially involved in its pathogenesis, assessing its population type, prevalence, and associated variables., Methods: A comprehensive systematic search for relevant studies, published from 2015 to 2020, was performed by using PubMed, EMBASE, and Cochrane databases. We analysed the variables of age, vitamin D, handgrip, and T-score in four different groups: healthy, osteopenic-osteoporotic, sarcopenic, and osteosarcopenic., Results: A total of 6504 patients from 16 studies were included in the final meta-analysis. The analysis of the individual variables reveals a statistically significant correlation between the handgrip test data and T-score ( p < 0.001)., Conclusions: The correlation between T-score values and handgrip strength suggests a new potential parameter in the development of predictive models that could be used in clinical practice, highlighting its importance for the diagnosis of osteosarcopenia.

Pentraxin 3 (PTX3) is a glycoprotein belonging to the humoral arm of innate immunity that participates in the body's defence mechanisms against infectious diseases. It has recently been defined as a multifunctional protein, given its involvement in numerous physiological and pathological processes, as well as in the pathogenesis of age-related diseases such as osteoporosis. Based on this evidence, the aim of our study was to investigate the possible role of PTX3 in both the osteoblastic differentiation and calcification process: to this end, primary osteoblast cultures from control and osteoporotic patients were incubated with human recombinant PTX3 (hrPTX3) for 72 h. Standard osteinduction treatment, consisting of β-glycerophosphate, dexamethasone and ascorbic acid, was used as control. Our results showed that treatment with hrPTX3, as well as with the osteogenic cocktail, induced cell differentiation towards the osteoblastic lineage. We also observed that the treatment not only promoted an increase in cell proliferation, but also the formation of calcification-like structures, especially in primary cultures from osteoporotic patients. In conclusion, the results reported here suggest the involvement of PTX3 in osteogenic differentiation, highlighting its osteoinductive capacity, like the standard osteoinduction treatment. Therefore, this study opens new and exciting perspectives about the possible role of PTX3 as biomarker and therapeutic agent for osteoporosis., Competing Interests: The authors declare no conflict of interest.

DNA methylation is one of the most studied epigenetic mechanisms that play a pivotal role in regulating gene expression. The epigenetic component is strongly involved in aging-bone diseases, such as osteoporosis and osteoarthritis. Both are complex multi-factorial late-onset disorders that represent a globally widespread health problem, highlighting a crucial point of investigations in many scientific studies. In recent years, new findings on the role of DNA methylation in the pathogenesis of aging-bone diseases have emerged. The aim of this systematic review is to update knowledge in the field of DNA methylation associated with osteoporosis and osteoarthritis, focusing on the specific tissues involved in both pathological conditions.

Bacillus circulans is mainly considered an opportunistic pathogen in immunocompromised patients. However, many different infections have been described in the literature: bacteremia, abscesses, meningitis, endophthalmitis, and wound infections. We observed a spondylodiscitis caused by Bacillus circulans in an immunocompetent patient. To date, this is the first case reported in literature. Vertebral osteomyelitis represents for clinicians a challenging infection to manage and treat, because of its insidious and indolent course. The diagnosis is frequently difficult and can often be delayed for several months and initially be misdiagnosed and mismanaged. For this reason, the clinical case was described and all published cases of infection caused by Bacillus circulans were reviewed., Competing Interests: The authors report no declarations of interest., (© 2021 The Author(s).)

Background: Osteoarthritis and osteoporosis are strongly coupled with alterations of muscles quality and fats metabolism. However, there are no studies for investigating possible differences between osteoporotic and osteoarthritic muscles. Understanding muscle-bone and muscle-cartilage interactions would be of high clinical value., Aim: Investigate potential microstructural and physiological differences between osteoporotic and osteoarthritic muscles by diffusion Nuclear Magnetic Resonance (NMR) imaging (diffusion MRI) and histological findings., Methods: Vastus-lateralis muscles excised from osteoporotic (n = 26, T Score <  - 2.5, Kellgren-Lawrence ≤ 2) and osteoarthritic (n = 26, T Score >  - 2.5, Kellgren--Lawrence 3 and 4) age-matched women were investigated by NMR relaxometry, diffusion-tensor imaging (DTI) at 9.4 T, and histological techniques. Intramyocellular (IMCL) and extramyocellular (EMCL) lipid were quantified. The percentage and mean diameters of fibers I and II were evaluated. Relationship between mean diffusivity (MD), fractional anisotropy (FA), the DTI eigenvalues (λ 1 , λ 2 , λ 3 ), histological findings in muscles and clinical data (Kellgren-Lawrence and T score, age, menopausal age, body mass index) were studied. Pairwise comparisons between groups were made using one-way analysis of variance and correlation between variables was assessed with linear correlation analysis (Pearson's r coefficient)., Results: Osteoporotic muscles showed higher MD, λ 1, λ 2 , λ 3 compared to osteoarthritis ones. This is explainable with a significant higher density of IMCL droplets found inside the osteoarthritic muscles and a large amount of fibrotic tissue and IMCL infiltration between fibers, i.e. in endomysium and perimysium that lead to a more hindered diffusion. Furthermore, histological analysis suggests mitochondrial degeneration as the origin of the greatest amount of IMCL droplets in osteoarthritic muscles., Conclusion: This work highlights differences between muscles of osteoporotic and osteoarthritic subjects that can be quantified by NMR DTI investigations.

Osteoporosis is a public health concern all over the world. As a chronic condition, it generally requires prolonged medical interventions to limit the risks of further bone loss, impaired skeletal integrity and the onset of fractures. This problem is further complicated by the fact that the abrupt cessation of some therapies may be associated with an increased risk of harm. It is in this context that the COVID-19 pandemic has caused an unprecedented disruption to the provision of healthcare worldwide, exceeding our worst expectations in terms of the number of lives lost and the rapidity at which consolidated economies and healthcare systems are being significantly damaged. In this review, we assessed the challenges and strategies used in the management of osteoporosis and fragility fracture care during the COVID-19 pandemic. We also examined the available evidence and provided clinical recommendations that will require reassessment as the worldwide response to COVID-19 evolves.

Background/aims: The study of the effects of simulated microgravity on primary cultures of human satellite cells represents a reliable model for identifying the biomolecular processes involved in mechanic load-related muscle mass loss. Therefore, this study aims to investigate the role of myostatin and Bone Morphogenetic Protein-2 in human satellite cells response to simulated microgravity condition., Methods: In order to identify the main molecules involved in the phenomena of degeneration/regeneration of muscle tissue related to the alteration of mechanic load, we performed a morphological and immunohistochemical study on 27 muscle biopsies taken from control, osteoporotic and osteoarthritic patients, underwent hip arthroplasty. For each patient, we set up primary satellite cell cultures subjected to normogravity and simulated microgravity (110h) regimens. Cellular functionality has been studied through a morphological evaluation performed by optical microscopy, and an ultrastructural evaluation carried out by transmission electron microscopy. Furthermore, we evaluated the expression of Bone Morphogenetic Protein-2 and myostatin through immunocytochemical reactions., Results: Our results showed that in the very early phases of simulated microgravity condition the satellite cells are more active than those subjected to the normogravity regime, as demonstrated by both the increase in the number of myotubes and the significant increase in the expression of Bone Morphogenetic Protein-2 in all experimental groups. However, with prolongated exposure to simulated microgravity regime (>72h), satellite cells and new formed myotubes underwent to cell death. It is important to note that, in early phases, simulated microgravity can stimulate the formation of new myotubes from satellite cells derived by osteoporotic patients. Furthermore, we observed that simulated microgravity can induce changes in myostatin expression levels by group-dependent variations., Conclusion: The results obtained allowed us to hypothesize a possible molecular mechanism of response to simulated microgravity, confirming the importance of Bone Morphogenetic Protein-2 and myostatin in the physio-pathogenesis of muscle tissue. In addition, these data can lay the foundation for new therapeutic approached in the prevention/cure of osteoporosis and sarcopenia., Competing Interests: The authors declare that they have no competing interests., (© Copyright by the Author(s). Published by Cell Physiol Biochem Press.)