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Osteoarthritis (OA) is a common and heterogeneous arthritic disorder. Patients suffer pain and their joints are characterized by articular cartilage loss and osteophyte formation. Risk factors for OA include age and obesity with inflammation identified as a key mediator of disease pathogenesis. Interleukin-17A (IL-17) is a pro-inflammatory cytokine that has been implicated in inflammatory diseases such as rheumatoid arthritis. IL-17 can upregulate expression of inflammatory cytokines and adipocytokines. The aim of this study was to evaluate IL-17 levels in the synovial fluid of patients with end-stage knee and hip OA in relation to inflammation- and pain-related cytokines and adipocytokines in synovial fluid and serum, and clinical and radiographic disease parameters. This is a cross-sectional study of 152 patients undergoing total hip and knee arthroplasty for OA. IL-17, IL-6, leptin, adiponectin, visfatin, resistin, C-C Motif Chemokine Ligand 2 (CCL2), C-C Motif Chemokine Ligand 7 (CCL7) and nerve growth factor (NGF) protein levels were measured in synovial fluid and serum using enzyme-linked immunosorbent assay (ELISA). Baseline characteristics included age, sex, body mass index, co-morbidities, pain and function, and radiographic analyses (OA features, K&L grade, minimal joint space width). 14 patients (9.2%) had detectable IL-17 in synovial fluid. These patients had significantly higher median concentrations of IL-6, leptin, resistin, CCL7 and NGF. Osteophytes, sclerosis and minimum joint space width were significantly reduced in patients with detectable IL-17 in synovial fluid. No differences were found in pain, function and comorbidities. IL-17 concentrations in synovial fluid and serum were moderately correlated (r = 0.482). The presence of IL-17 in the synovial fluid therefore identifies a substantial subset of primary end-stage OA patients with distinct biological and clinical features. Stratification of patients on the basis of IL-17 may identify those responsive to therapeutic targeting.

The advent of single-cell resolution sequencing and spatial transcriptomics has enabled the delivery of cellular and molecular atlases of tissues and organs, providing new insights into tissue health and disease. However, if the full potential of these technologies is to be equitably realised, ancestrally inclusivity is paramount. Such a goal requires greater inclusion of both researchers and donors in low- and middle-income countries (LMICs). In this perspective, we describe the current landscape of ancestral inclusivity in genomic and single-cell transcriptomic studies. We discuss the collaborative efforts needed to scale the barriers to establishing, expanding, and adopting single-cell sequencing research in LMICs and to enable globally impactful outcomes of these technologies.

The Human Cell Atlas (HCA) project aims to map tissues and organs during development, maturation and pathology at single cell resolution. The musculoskeletal HCA network is a community for fostering collaboration and shared expertise to help develop the therapeutic approaches needed to address the high global burden of musculoskeletal disorders.

Objectives Osteoarthritis (OA) is increasingly recognised as a whole joint disease, with an important role for synovium. However, the repertoire of immune cells and fibroblasts that constitute OA synovium remains understudied. This study aims to characterise the cellular composition of advanced OA synovium and to explore potential correlations between different cell types and patient demographics or clinical scores. Methods Synovium, collected from 10 patients with advanced OA during total knee replacement surgery, was collagenase-digested, and cells were stained for flow cytometry analysis. Formalin-fixed paraffin-embedded synovium was sectioned, stained with immunofluorescence, and imaged using the multiplex Cell DIVE platform. Patient demographics and clinical scores were also collected. Results The proportion of immune cells in OA synovium varied between patients (8–38% of all cells). Macrophages and T cells were the dominant immune cell populations, together representing 76% of immune cells. Age positively correlated with the proportion of macrophages, and negatively correlated with T cells. CCR6+ T cells were found in 6/10 patients; these patients had a higher mean Kellgren-Lawrence grade across the three knee compartments. Immunofluorescence staining showed that macrophages were present in the lining as well as distributed throughout the sublining, while T and B cells were mainly localised near vessels in the sublining. Fibroblast subsets (CD45−PDPN+) based on the expression of CD34/CD90 or FAP/CD90 were identified in all patient samples, and some populations correlate with the percentage of immune cells or clinical scores. Immunofluorescence staining showed that FAP expression was particularly strong in the lining layer, but also present throughout the sublining layer. CD90 expression was exclusively found around vessels in the sublining, while CD34 was mostly found in the sublining but also occasionally in the lining layer. Conclusions There are significant differences in the relative proportions and subsets of immune cells in OA synovium; exploratory correlative analyses suggest that these differences might be correlated with age, clinical scores, or fibroblast subsets. Additional studies are required to understand how different cell types affect OA pathobiology, and if the presence or proportion of cell subsets relates to disease phenotypes.

Polypropylene (PPL) mesh is widely used in pelvic floor reconstructive surgery for prolapse and stress urinary incontinence. However, some women, particularly those treated using transvaginal PPL mesh placement for prolapse, experience intractable pain and mesh exposure or extrusion. Explanted tissue from patients with complications following transvaginal implantation of mesh is typified by a dense fibrous capsule with an immune cell-rich infiltrate, suggesting that the host immune response has a role in transvaginal PPL mesh complications through the separate contributions of the host (patient), the biological niche within which the material is implanted and biomaterial properties of the mesh. This immune response might be strongly influenced by both the baseline inflammatory status of the patient, surgical technique and experience, and the unique hormonal, immune and microbial tissue niche of the vagina. Mesh porosity, surface area and stiffness also might have an effect on the immune and tissue response to transvaginal mesh placement. Thus, a regulatory pathway is needed for mesh development that recognizes the roles of host and biological factors in driving the immune response to mesh, as well as mandatory mesh registries and the longitudinal surveillance of patients.Complications related to the use of mesh in pelvic floor reconstructive surgery are related to a number of factors. This Review discusses the foreign body response, the biomaterial properties of mesh, the patient-specific and surgical risk factors and the failings in mesh development, all of which have contributed to these complications.

Background Epigenetic changes (i.e., chromatin modifications) occur during chondrogenesis and in osteoarthritis (OA). We investigated the effect of H3K27me3 demethylase inhibition on chondrogenesis and assessed its utility in cartilage tissue engineering and in understanding cartilage destruction in OA. Methods We used a high-content screen to assess the effect of epigenetic modifying compounds on collagen output during chondrogenesis of monolayer human mesenchymal stem cells (MSCs). The impact of GSK-J4 on gene expression, glycosaminoglycan output and collagen formation during differentiation of MSCs into cartilage discs was investigated. Expression of lysine (K)-specific demethylase 6A ( UTX ) and Jumonji domain-containing 3 ( JMJD3 ), the HEK27Me3 demethylases targeted by GSK-J4, was measured in damaged and undamaged cartilage from patients with OA. The impact of GSK-J4 on ex vivo cartilage destruction and expression of OA-related genes in human articular chondrocytes (HACs) was assessed. H3K27Me3 demethylase regulation of transforming growth factor (TGF)-β-induced gene expression was measured in MSCs and HACs. Results Treatment of chondrogenic MSCs with the H3K27me3 demethylase inhibitor GSK-J4, which targets JMJD3 and UTX, inhibited collagen output; expression of chondrogenic genes, including SOX9 and COL2A1 ; and disrupted glycosaminoglycan and collagen synthesis. JMJD3 but not UTX expression was increased during chondrogenesis and in damaged OA cartilage, suggesting a predominant role of JMJD3 in chondrogenesis and OA. GSK-J4 prevented ex vivo cartilage destruction and expression of the OA-related genes MMP13 and PTGS2. TGF-β is a key regulator of chondrogenesis and articular cartilage homeostasis, and TGF-β-induced gene expression was inhibited by GSK-J4 treatment of both chondrogenic MSCs and HACs. Conclusions Overall, we show that H3K27me3 demethylases modulate chondrogenesis and that enhancing this activity may improve production of tissue-engineered cartilage. In contrast, targeted inhibition of H3K27me3 demethylases could provide a novel approach in OA therapeutics.

Cellular senescence is an irreversible side effect of some pharmaceuticals which can contribute to tissue degeneration. Objective To determine whether pharmaceutical glucocorticoids induce senescence in tenocytes. Methods Features of senescence (β-galactosidase activity at pH 6 (SA-β-gal) and active mammalian/mechanistic target of rapamycin (mTOR) in cell cycle arrest) as well as the activity of the two main pathways leading to cell senescence were examined in glucocorticoid-treated primary human tenocytes. Evidence of senescence-inducing pathway induction in vivo was obtained using immunohistochemistry on tendon biopsy specimens taken before and 7 weeks after subacromial Depo-Medrone injection. Results Dexamethasone treatment of tenocytes resulted in an increased percentage of SA-βgal-positive cells. Levels of phosphorylated p70S6K did not decrease with glucocorticoid treatment indicating mTOR remained active. Increased levels of acetylated p53 as well as increased RNA levels of its pro-senescence effector p21 were evident in dexamethasone-treated tenocytes. Levels of the p53 deacetylase sirtuin 1 were lower in dexamethasone-treated cells compared with controls. Knockdown of p53 or inhibition of p53 activity prevented dexamethasone-induced senescence. Activation of sirtuin 1 either by exogenous overexpression or by treatment with resveratrol or low glucose prevented dexamethasone-induced senescence. Immunohistochemical analysis of tendon biopsies taken before and after glucocorticoid injection revealed a significant increase in the percentage of p53-positive cells (p=0.03). The percentage of p21-positive cells also tended to be higher post-injection (p=0.06) suggesting glucocorticoids activate the p53/p21 senescence-inducing pathway in vivo as well as in vitro. Conclusion As cell senescence is irreversible in vivo, glucocorticoid-induced senescence may result in long-term degenerative changes in tendon tissue.

We investigated endogenous tissue response to a woven and electrospun polydioxanone (PDO) and polycaprolactone (PCL) patch intended for tendon repair. A sheep tendon injury model characterised by a natural history of consistent failure of healing was chosen to assess the biological potential of woven and aligned electrospun fibres to induce a reparative response. Patches were implanted into 8 female adult English Mule sheep. Significant infiltration of tendon fibroblasts was observed within the electrospun component of the patch but not within the woven component. The cellular infiltrate into the electrospun fibres was accompanied by an extensive network of new blood vessel formation. Tendon fibroblasts were the most abundant scaffold-populating cell type. CD45 + , CD4 + and CD14 + cells were also present, with few foreign body giant cells. There were no local or systemic signs of excessive inflammation with normal hematology and serology for inflammatory markers three months after scaffold implantation. In conclusion, we demonstrate that an endogenous healing response can be safely induced in tendon by means of biophysical cues using a woven and electrospun patch.

Osteoclasts are multinucleated, bone-resorbing cells. However, they also digest cartilage during skeletal maintenance, development and in degradative conditions including osteoarthritis, rheumatoid arthritis and primary bone sarcoma. This study explores the mechanisms behind the osteoclast–cartilage interaction. Human osteoclasts differentiated on acellular human cartilage expressed osteoclast marker genes (e.g. CTSK , MMP9 ) and proteins (TRAP, VNR), visibly damaged the cartilage surface and released glycosaminoglycan in a contact-dependent manner. Direct co-culture with chondrocytes during differentiation increased large osteoclast formation ( p  < 0.0001) except when co-cultured on dentine, when osteoclast formation was inhibited ( p  = 0.0002). Osteoclasts cultured on dentine inhibited basal cartilage degradation ( p  = 0.012). RNA-seq identified MMP8 overexpression in osteoclasts differentiated on cartilage versus dentine (8.89-fold, p  = 0.0133), while MMP9 was the most highly expressed MMP. Both MMP8 and MMP9 were produced by osteoclasts in osteosarcoma tissue. This study suggests that bone-resident osteoclasts and chondrocytes exert mutually protective effects on their ‘native’ tissue. However, when osteoclasts contact non-native cartilage they cause degradation via MMPs. Understanding the role of osteoclasts in cartilage maintenance and degradation might identify new therapeutic approaches for pathologies characterized by cartilage degeneration.

Background Diseased tendons are characterised by fibrotic scar tissue, which adversely affects tendon structure and function and increases the likelihood of re-injury. The mechanisms and expression profiles of fibrosis in diseased tendon is understudied compared to pulmonary and renal tissues, where transforming growth factor (TGF)β and its associated superfamily are known to be key drivers of fibrosis and modulate extracellular matrix homeostasis. We hypothesised that differential expression of TGFβ superfamily members would exist between samples of human rotator cuff tendons with established disease compared to healthy control tendons. Methods Healthy and diseased rotator cuff tendons were collected from patients presenting to an orthopaedic referral centre. Diseased tendinopathic (intact) and healthy rotator cuff tendons were collected via ultrasound-guided biopsy and torn tendons were collected during routine surgical debridement. Immunohistochemistry and quantitative real-time polymerase chain reaction were used to investigate the protein and gene expression profiles of TGFβ superfamily members in these healthy and diseased tendons. Results TGFβ superfamily members were dysregulated in diseased compared to healthy tendons. Specifically, TGFβ-1, TGFβ receptor (R)1 and TGFβ R2 proteins were reduced ( p < 0.01) in diseased compared to healthy tendons. At the mRNA level, TGFβ R1 was significantly reduced in samples of diseased tendons, whereas TGFβ R2 was increased ( p < 0.01). BMP-2, BMP-7 and CTGF mRNA remained unchanged with tendon disease. Conclusions We propose that downregulation of TGFβ pathways in established tendon disease may be a protective response to limit disease-associated fibrosis. The disruption of the TGFβ axis with disease suggests associated downstream pathways may be important for maintaining healthy tendon homeostasis. The findings from our study suggest that patients with established tendon disease would be unlikely to benefit from therapeutic TGFβ blockade, which has been investigated as a treatment strategy in several animal models. Future studies should investigate the expression profile of fibrotic mediators in earlier stages of tendon disease to improve understanding of the targetable mechanisms underpinning tendon fibrosis.