Aims. This study aimed, through bioinformatics analysis, to identify the potential diagnostic markers of osteoarthritis, and analyze the role of immune infiltration in synovial tissue. Methods. The gene expression profiles were downloaded from the Gene Expression Omnibus (GEO) database. The differentially expressed genes (DEGs) were identified by R software. Functional enrichment analyses were performed and protein-protein interaction networks (PPI) were constructed. Then the hub genes were screened. Biomarkers with high value for the diagnosis of early osteoarthritis (OA) were validated by GEO datasets. Finally, the CIBERSORT algorithm was used to evaluate the immune infiltration between early-stage OA and end-stage OA, and the correlation between the diagnostic marker and infiltrating immune cells was analyzed. Results. A total of 88 DEGs were identified. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses indicated that DEGs were significantly enriched in leucocyte migration and interleukin (IL)-17 signalling pathways. Disease ontology (DO) indicated that DEGs were mostly enriched in rheumatoid arthritis. Six hub genes including FosB proto-oncogene, AP-1 transcription factor subunit (FOSB); C-X-C motif chemokine ligand 2 (CXCL2); CXCL8; IL-6; Jun proto-oncogene, AP-1 transcription factor subunit (JUN); and Activating transcription factor 3 (ATF3) were identified and verified by GEO datasets. ATF3 (area under the curve = 0.975) turned out to be a potential biomarker for the diagnosis of early OA. Several infiltrating immune cells varied significantly between early-stage OA and end-stage OA, such as resting NK cells (p = 0.016), resting dendritic cells (p = 0.043), and plasma cells (p = 0.043). Additionally, ATF3 was significantly correlated with resting NK cells (p = 0.034), resting dendritic cells (p = 0.026), and regulatory T cells (Tregs, p = 0.018). Conclusion. ATF3 may be a potential diagnostic marker for early diagnosis and treatment of OA, and immune cell infiltration provides new perspectives for understanding the mechanism during OA progression. Cite this article: Bone Joint Res 2022;11(9):679–689

The effects of dexamethasone (dex), during in vitro human osteogenesis, are contrasting. Indeed, dex downregulates SOX9 during osteogenic differentiation of human bone marrow mesenchymal stromal cells (HBMSCs). However, dex also promotes PPARG expression, resulting in the formation of adipocyte-like cells within the osteogenic monolayers. The regulation of both SOX9 and PPARG seems to be downstream the transactivation activity of the glucocorticoid receptor (GR), thus the effect of dex on SOX9 downregulation is indirect. This study aims at determining whether PPAR-γ regulates SOX9 expression levels, as suggested by several studies. HBMSCs were isolated from bone marrow of patients with written informed consent. HBMSCs were cultured in different osteogenic induction media containing 10 or 100 nM dex. Undifferentiated cells were used as controls. Cells were treated either with a pharmacological PPAR-γ inhibitor T0070907 (donors n=4) or with a PPARG-targeting siRNA (donors n=2). Differentiation markers or PPAR-γ target genes were analysed by RT-qPCR. Mineral deposition was assessed by ARS staining. Two-way ANOVA followed by a Tukey's multiple comparison test compared the effects of treatments. At day 7, T0070907 downregulated ADIPOQ and upregulated CXCL8, respectively targets of PPAR-γ-mediated transactivation and transrepression. RUNX2 and SOX9 were also significantly downregulated in absence of dex. PPARG was successfully downregulated by siRNA. ADIPOQ expression was also inhibited, while CXCL8 did not show any significant difference between siRNA treatment groups. RUNX2 was downregulated by the PPARG-siRNA treatment in presence of 100 nM dexamethasone, while SOX9 levels were not affected. ARS showed no change in the mineralization levels when PPARG expression or activity was inhibited. Understanding how dex regulates HBMSC differentiation is of pivotal importance to refine current in vitro models. These results suggest that PPARG does not mediate SOX9 downregulation. Unexpectedly, RUNX2 expression was also unaltered or even downregulated after PPAR-γ inhibition. Acknowledgements: AO Foundation, AO Research Institute (CH) and PRIN 2017 MUR (IT) for financial support

Mesenchymal stromal cells (MSCs) are promising candidate for cell therapy in osteoarthritis (OA) patients since that they exert anti-inflammatory, immunomodulatory, anti-fibrotic and anti-hypertrophic effects in the joint tissues. However, little is known about the OA milieu factors that could enhance the migration and tissue specific engraftment of exogenously injected MSC for successful regenerative cell therapy. GMP-clinical grade adipose stromal cells (ASC) were evaluated both in normoxic and hypoxic (2%O. 2. ) conditions, with or without OA synovium milieu. We found that both OA synovial fluids and OA synoviocytes derived conditioned medium (CM) contain approximately the same amounts of different cytokines/chemokines (i.e. IL6, CXCL8, CXCL10, CXCL12, CCL2, CCL3, CCL4, CCL5, CCL11). ASC migration was significantly increased by both OA synovium milieu and not affected by normoxic or hypoxic condition. We identify that ASC migration was mainly influenced by different macrophage chemokines (i.e. CCL2, CCL3, CCL4). In hypoxic condition basal GMP-ASC showed an increase of CXCR3 and CCR3, a decrease of CCR1 and CCR5 receptors, while CXCR1, CXCR4, CXCR7, CCR2 and IL6R were not modulated. The addition of OA synovium milieu induced CCR3, CXCR3 and IL6R and decreased CCR1 and not affected CCR2, CCR5, CXCR1, CXCR4, CXCR7 in hypoxic condition. Our data demonstrated that GMP-ASC chemotaxis was mainly induced by macrophage chemokines. Moreover, we evidenced that hypoxia, as better condition to mimic the OA milieu, affected some GMP-ASC cytokine/chemokine receptors, suggesting the involvement of specific chemokine-receptor axis

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This study aimed to explore the role of small colony variants (SCVs) of Staphylococcus aureus in intraosseous invasion and colonization in patients with periprosthetic joint infection (PJI).

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Developmental dysplasia of the hip (DDH) is a complex musculoskeletal disease that occurs mostly in children. This study aimed to investigate the molecular changes in the hip joint capsule of patients with DDH.