The complement system drives local inflammatory tissue priming by metabolic reprogramming of synovial fibroblasts.

Arthritis typically involves recurrence and progressive worsening at specific predilection sites, but the checkpoints between remission and persistence remain unknown. Here, we defined the molecular and cellular mechanisms of this inflammation-mediated tissue priming. Re-exposure to inflammatory stimuli caused aggravated arthritis in rodent models. Tissue priming developed locally and independently of adaptive immunity. Repeatedly stimulated primed synovial fibroblasts (SFs) exhibited enhanced metabolic activity inducing functional changes with intensified migration, invasiveness and osteoclastogenesis. Meanwhile, human SF from patients with established arthritis displayed a similar primed phenotype. Transcriptomic and epigenomic analyses as well as genetic and pharmacological targeting demonstrated that inflammatory tissue priming relies on intracellular complement C3- and C3a receptor-activation and downstream mammalian target of rapamycin- and hypoxia-inducible factor 1α-mediated metabolic SF invigoration that prevents activation-induced senescence, enhances NLRP3 inflammasome activity, and in consequence sensitizes tissue for inflammation. Our study suggests possibilities for therapeutic intervention abrogating tissue priming without immunosuppression.

Self-organized BMP signaling dynamics underlie the development and evolution of digit segmentation patterns in birds and mammals.

Repeating patterns of synovial joints are a highly conserved feature of articulated digits, with variations in joint number and location resulting in diverse digit morphologies and limb functions across the tetrapod clade. During the development of the amniote limb, joints form iteratively within the growing digit ray, as a population of distal progenitors alternately specifies joint and phalanx cell fates to segment the digit into distinct elements. While numerous molecular pathways have been implicated in this fate choice, it remains unclear how they give rise to a repeating pattern. Here, using single-cell RNA sequencing and spatial gene expression profiling, we investigate the transcriptional dynamics of interphalangeal joint specification in vivo. Combined with mathematical modeling, we predict that interactions within the BMP signaling pathway-between the ligand GDF5, the inhibitor NOGGIN, and the intracellular effector pSMAD-result in a self-organizing Turing system that forms periodic joint patterns. Our model is able to recapitulate the spatiotemporal gene expression dynamics observed in vivo, as well as phenocopy digit malformations caused by BMP pathway perturbations. By contrasting in silico simulations with in vivo morphometrics of two morphologically distinct digits, we show how changes in signaling parameters and growth dynamics can result in variations in the size and number of phalanges. Together, our results reveal a self-organizing mechanism that underpins amniote digit segmentation and its evolvability and, more broadly, illustrate how Turing systems based on a single molecular pathway may generate complex repetitive patterns in a wide variety of organisms.

Enhancer variants on chromosome 2p14 regulating SPRED2 and ACTR2 act as a signal amplifier to protect against rheumatoid arthritis.

Genome-wide association studies (GWASs) have repeatedly reported multiple non-coding single-nucleotide polymorphisms (SNPs) at 2p14 associated with rheumatoid arthritis (RA), but their functional roles in the pathological mechanisms of RA remain to be explored. In this study, we integrated a series of bioinformatics and functional experiments and identified three intronic RA SNPs (rs1876518, rs268131, and rs2576923) within active enhancers that can regulate the expression of SPRED2 directly. At the same time, SPRED2 and ACTR2 influence each other as a positive feedback signal amplifier to strengthen the protective role in RA by inhibiting the migration and invasion of rheumatoid fibroblast-like synoviocytes (FLSs). In particular, the transcription factor CEBPB preferentially binds to the rs1876518-T allele to increase the expression of SPRED2 in FLSs. Our findings decipher the molecular mechanisms behind the GWAS signals at 2p14 for RA and emphasize SPRED2 as a potential candidate gene for RA, providing a potential target and direction for precise treatment of RA.

Molecular mechanism of synovial joint site specification and induction in developing vertebrate limbs.

The vertebrate appendage comprises three primary segments, the stylopod, zeugopod and autopod, each separated by joints. The molecular mechanisms governing the specification of joint sites, which define segment lengths and thereby limb architecture, remain largely unknown. Existing literature suggests that reciprocal gradients of retinoic acid (RA) and fibroblast growth factor (FGF) signaling define the expression domains of the putative segment markers Meis1, Hoxa11 and Hoxa13. Barx1 is expressed in the presumptive joint sites. Our data demonstrate that RA-FGF signaling gradients define the expression domain of Barx1 in the first presumptive joint site. When misexpressed, Barx1 induces ectopic interzone-like structures, and its loss of function partially blocks interzone development. Simultaneous perturbations of RA-FGF signaling gradients result in predictable shifts of Barx1 expression domains along the proximo-distal axis and, consequently, in the formation of repositioned joints. Our data suggest that during early limb bud development in chick, Meis1 and Hoxa11 expression domains are overlapping, whereas the Barx1 expression domain resides within the Hoxa11 expression domain. However, once the interzone is formed, the expression domains are refined and the Barx1 expression domain becomes congruent with the border of these two putative segment markers.

Exploring the Early Molecular Pathogenesis of Osteoarthritis Using Differential Network Analysis of Human Synovial Fluid.

The molecular mechanisms that drive the onset and development of osteoarthritis (OA) remain largely unknown. In this exploratory study, we used a proteomic platform (SOMAscan assay) to measure the relative abundance of more than 6000 proteins in synovial fluid (SF) from knees of human donors with healthy or mildly degenerated tissues, and knees with late-stage OA from patients undergoing knee replacement surgery. Using a linear mixed effects model, we estimated the differential abundance of 6251 proteins between the three groups. We found 583 proteins upregulated in the late-stage OA, including MMP1, collagenase 3 and interleukin-6. Further, we selected 760 proteins (800 aptamers) based on absolute fold changes between the healthy and mild degeneration groups. To those, we applied Gaussian Graphical Models (GGMs) to analyze the conditional dependence of proteins and to identify key proteins and subnetworks involved in early OA pathogenesis. After regularization and stability selection, we identified 102 proteins involved in GGM networks. Notably, network complexity was lost in the protein graph for mild degeneration when compared to controls, suggesting a disruption in the regular protein interplay. Furthermore, among our main findings were several downregulated (in mild degeneration versus healthy) proteins with unique interactions in the healthy group, one of which, SLCO5A1, has not previously been associated with OA. Our results suggest that this protein is important for healthy joint function. Further, our data suggests that SF proteomics, combined with GGMs, can reveal novel insights into the molecular pathogenesis and identification of biomarker candidates for early-stage OA.

An Atlas of the Knee Joint Proteins and Their Role in Osteoarthritis Defined by Literature Mining.

Osteoarthritis (OA) is the most prevalent rheumatic pathology. However, OA is not simply a process of wear and tear affecting articular cartilage but rather a disease of the entire joint. One of the most common locations of OA is the knee. Knee tissues have been studied using molecular strategies, generating a large amount of complex data. As one of the goals of the Rheumatic and Autoimmune Diseases initiative of the Human Proteome Project, we applied a text-mining strategy to publicly available literature to collect relevant information and generate a systematically organized overview of the proteins most closely related to the different knee components. To this end, the PubPular literature-mining software was employed to identify protein-topic relationships and extract the most frequently cited proteins associated with the different knee joint components and OA. The text-mining approach searched over eight million articles in PubMed up to November 2022. Proteins associated with the six most representative knee components (articular cartilage, subchondral bone, synovial membrane, synovial fluid, meniscus, and cruciate ligament) were retrieved and ranked by their relevance to the tissue and OA. Gene ontology analyses showed the biological functions of these proteins. This study provided a systematic and prioritized description of knee-component proteins most frequently cited as associated with OA. The study also explored the relationship of these proteins to OA and identified the processes most relevant to proper knee function and OA pathophysiology.

Cellular and molecular diversity in Rheumatoid Arthritis.

Rheumatoid Arthritis (RA) is a chronic systemic autoimmune disease. RA mainly affects synovial joints, with inflammation of the synovial membrane (synovitis), characterised by neo-angiogenesis, hyperplasia of lining layer, and immune cell infiltration that drive local inflammation and, if untreated, can lead to joint destruction and disability. In parallel to the well-known clinical heterogeneity, the underlying synovitis can also be significantly heterogeneous, both at cellular and molecular level, which can at least in part explain why despite the availability of highly effective treatment options, a large proportion of patients are resistant to some individual treatments. The assimilation of recent high-throughput data from analysis at the single-cell level with rigorous and high-quality clinical outcomes obtained from large randomised clinical trials support the definition of disease and treatment response endotypes. Looking ahead, the integration of histological and molecular signatures from the diseased tissue into clinical algorithms may help decision making in the management of patients with Rheumatoid Arthritis in clinical practice.

Novel candidate metastasis-associated genes for synovial sarcoma.

Synovial sarcoma (SS) is an aggressive soft tissue sarcoma with poor prognosis due to late recurrence and metastasis. Metastasis is an important prognostic factor of SS. This study aimed to identify the core genes and mechanisms associated with SS metastasis. Microarray data for GSE40021 and GSE40018 were obtained from the Gene Expression Omnibus database. 186 differentially expressed genes (DEGs) were identified. The biological functions and signalling pathways closely associated with SS metastasis included extracellular matrix (ECM) organization and ECM-receptor interaction. Gene set enrichment analysis showed that the terms cell cycle, DNA replication, homologous recombination and mismatch repair were significantly enriched in the metastasis group. Weighted gene co-expression network analysis identified the most relevant module and 133 hub genes, and 31 crossover genes were identified by combining DEGs. Subsequently, four characteristic genes, EXO1, NCAPG, POLQ and UHRF1, were identified as potential biomarkers associated with SS metastasis using the least absolute shrinkage and selection operator algorithm and validation dataset verification analysis. Immunohistochemistry results from our cohort of 49 patients revealed visible differences in the expression of characteristic genes between the non-metastatic and metastatic groups. Survival analysis indicated that high expression of characteristic genes predicted poor prognosis. Our data revealed that primary SS samples from patients who developed metastasis showed activated homologous recombination and mismatch repair compared to samples from patients without metastasis. Furthermore, EXO1, NCAPG, POLQ and UHRF1 were identified as potential candidate metastasis-associated genes. This study provides further research insights and helps explore the mechanisms of SS metastasis.

Effect of Preoperative Antibiotic Therapy on Operative Culture Yield for Diagnosis of Native Joint Septic Arthritis.

BACKGROUND: Native joint septic arthritis (NJSA) is definitively diagnosed by a positive Gram stain or culture, along with supportive clinical findings. Preoperative antibiotics are known to alter synovial fluid cell count, Gram stain and culture results and are typically postponed until after arthrocentesis to optimize diagnostic accuracy. However, data on the impact of preoperative antibiotics on operative culture yield for NJSA diagnosis are limited. METHODS: We retrospectively reviewed adult cases of NJSA who underwent surgery at Mayo Clinic facilities from 2012-2021 to analyze the effect of preoperative antibiotics on operative culture yield through a paired analysis of preoperative culture (POC) and operative culture (OC) results using logistic regression and generalized estimating equations. RESULTS: Two hundred ninety-nine patients with NJSA affecting 321 joints were included. Among those receiving preoperative antibiotics, yield significantly decreased from 68.0% at POC to 57.1% at OC (p < .001). In contrast, for patients without preoperative antibiotics there was a non-significant increase in yield from 60.9% at POC to 67.4% at OC (p = 0.244). In a logistic regression model for paired data, preoperative antibiotic exposure was more likely to decrease OC yield compared to non-exposure (OR = 2.12; 95% CI = 1.24-3.64; p = .006). Within the preoperative antibiotic group, additional antibiotic doses and earlier antibiotic initiation were associated with lower OC yield. CONCLUSION: In patients with NJSA, preoperative antibiotic exposure resulted in a significant decrease in microbiologic yield of operative cultures as compared to patients in whom antibiotic therapy was held prior to obtaining operative cultures.

ELIXCYTE®, an Allogenic Adipose-Derived Stem Cell Product, Mitigates Osteoarthritis by Reducing Inflammation and Preventing Cartilage Degradation In Vitro.

Adipose-derived stem cells (ADSCs) comprise a promising therapy for osteoarthritis (OA). The therapeutic potential of ELIXCYTE®, an allogeneic human ADSC (hADSC) product, was demonstrated in a phase I/II OA clinical trial. However, the exact mechanism underlying such effects is not clear. Moreover, studies suggest that interleukin-11 (IL-11) has anti-inflammatory, tissue-regenerative, and immune-regulatory functions. Our aim was to unravel the mechanism associated with the therapeutic effects of ELIXCYTE® on OA and its relationship with IL-11. We cocultured ELIXCYTE® with normal human articular chondrocytes (NHACs) in synovial fluid obtained from individuals with OA (OA-SF) to investigate its effect on chondrocyte matrix synthesis and degradation and inflammation by assessing gene expression and cytokine levels. NHACs exposed to OA-SF exhibited increased MMP13 expression. However, coculturing ELIXCYTE® with chondrocytes in OA-SF reduced MMP13 expression in chondrocytes and downregulated PTGS2 and FGF2 expression in ELIXCYTE®. ELIXCYTE® treatment elevated anti-inflammatory cytokine (IL-1RA, IL-10, and IL-13) levels, and the reduction in MMP13 was positively correlated with IL-11 concentrations in OA-SF. These findings indicate that IL-11 in OA-SF might serve as a predictive biomarker for the ELIXCYTE® treatment response in OA, emphasizing the therapeutic potential of ELIXCYTE® to mitigate OA progression and provide insights into its immunomodulatory effects.

Synovial Sarcoma of the Gastrointestinal Tract.

We report the clinicopathologic and immunohistochemical features of 18 cases of confirmed primary synovial sarcoma of the gastrointestinal tract. The neoplasms arose in 10 women and 8 men ranging in age from 23 to 81 years (mean: 50; median: 57.5 years). The tumors for which size was known ranged from 1.8 to 15.0 cm (mean: 5.2; median: 5.1 cm). Microscopically, 14 synovial sarcomas were of the monophasic type, 2 were biphasic, and 2 were poorly differentiated. Immunohistochemical analysis of 4 cases showed strong, diffuse staining for SS18::SSX (4/4 cases). Pancytokeratin and EMA immunohistochemistry were performed on 13 and 9 tumors, respectively, and each showed patchy-to-diffuse staining. By reverse-transcription PCR, 3 cases were positive for the SS18::SSX1, and 2 cases were positive for the SS18::SSX2 gene fusion. Six cases contained an SS18 gene rearrangement by fluorescence in situ hybridization, and next-generation sequencing identified an SS18::SSX2 gene fusion in one case. Clinical follow-up information was available for 9 patients (4 months to 4.6 years; mean, 2.8 y; median: 29 months), and one patient had a recent diagnosis. Three patients died of disease within 41 to 72 months (mean, 56 months) of their diagnosis. Five patients were alive without evidence of disease 4 to 52 months (mean, 17.6 months) after surgery; of whom 1 of the patients received additional chemotherapy treatment after surgery because of recurrence of the disease. A single patient was alive with intraabdominal recurrence 13 months after surgery. We conclude that synovial sarcoma of the gastrointestinal tract is an aggressive tumor, similar to its soft tissue counterpart, with adverse patient outcomes. It is important to distinguish it from morphologically similar gastrointestinal tract lesions that may have different treatment regimens and prognoses.

EPO promotes the progression of rheumatoid arthritis by inducing desialylation via increasing the expression of neuraminidase 3.

OBJECTIVE: Erythropoietin (EPO) known as an erythrocyte-stimulating factor is increased in patients with rheumatoid arthritis (RA). Nevertheless, the function of EPO in the process of RA and relative mechanism needs to be further clarified. METHODS: The level of EPO in serum and synovial fluid from patients with RA and healthy controls was determined by . Collagen-induced arthritis (CIA) mice were constructed to confirm the role of EPO on RA pathogenesis. Differentially expressed genes (DEGs) of EPO-treated fibroblast-like synoviocyte (FLS) were screened by transcriptome sequencing. The transcription factor of neuraminidase 3 (NEU3) of DEGs was verified by double luciferase reporting experiment, DNA pulldown, electrophoretic mobility shift assay and chromatin immunoprecipitation-quantitative PCR (qPCR) assay. RESULTS: The overexpression of EPO was confirmed in patients with RA, which was positively associated with Disease Activity Score 28-joint count. Additionally, EPO intervention could significantly aggravate the joint destruction in CIA models. The upregulation of NEU3 was screened and verified by transcriptome sequencing and qPCR in EPO-treated FLS, and signal transducer and activator of transcription 5 was screened and verified to be the specific transcription factor of NEU3. EPO upregulates NEU3 expression via activating the Janus kinase 2 (JAK2)-STAT5 signalling pathway through its receptor EPOR, thereby to promote the desialylation through enhancing the migration and invasion ability of FLS, which is verified by JAK2 inhibitor and NEU3 inhibitor. CONCLUSION: EPO, as a proinflammatory factor, accelerates the process of RA through transcriptional upregulation of the expression of NEU3 by JAK2/STAT5 pathway.

Suppression of NUPR1 in fibroblast-like synoviocytes reduces synovial fibrosis via the Smad3 pathway.

BACKGROUND: Synovial fibrosis is a common complication of knee osteoarthritis (KOA), a pathological process characterized by myofibroblast activation and excessive extracellular matrix (ECM) deposition. Fibroblast-like synoviocytes (FLSs) are implicated in KOA pathogenesis, contributing to synovial fibrosis through diverse mechanisms. Nuclear protein 1 (NUPR1) is a recently identified transcription factor with crucial roles in various fibrotic diseases. However, its molecular determinants in KOA synovial fibrosis remain unknown. This study aims to investigate the role of NUPR1 in KOA synovial fibrosis through in vivo and in vitro experiments. METHODS: We examined NUPR1 expression in the murine synovium and determined the impact of NUPR1 on synovial fibrosis by knockdown models in the destabilization of the medial meniscus (DMM)-induced KOA mouse model. TGF-ß was employed to induce fibrotic response and myofibroblast activation in mouse FLSs, and the role and molecular mechanisms in synovial fibrosis were evaluated under conditions of NUPR1 downexpression. Additionally, the pharmacological effect of NUPR1 inhibitor in synovial fibrosis was assessed using a surgically induced mouse KOA model. RESULTS: We found that NUPR1 expression increased in the murine synovium after DMM surgical operation. The adeno-associated virus (AAV)-NUPR1 shRNA promoted NUPR1 deficiency, attenuating synovial fibrosis, inhibiting synovial hyperplasia, and significantly reducing the expression of pro-fibrotic molecules. Moreover, the lentivirus-mediated NUPR1 deficiency alleviated synoviocyte proliferation and inhibited fibroblast to myofibroblast transition. It also decreased the expression of fibrosis markers α-SMA, COL1A1, CTGF, Vimentin and promoted the activation of the SMAD family member 3 (SMAD3) pathway. Importantly, trifluoperazine (TFP), a NUPR1 inhibitor, attenuated synovial fibrosis in DMM mice. CONCLUSIONS: These findings indicate that NUPR1 is an antifibrotic modulator in KOA, and its effect on anti-synovial fibrosis is partially mediated by SMAD3 signaling. This study reveals a promising target for developing novel antifibrotic treatment.

CD34+ synovial fibroblasts exhibit high osteogenic potential in synovial chondromatosis.

Synovial chondromatosis (SC) is a disorder of the synovium characterized by the formation of osteochondral nodules within the synovium. This study aimed to identify the abnormally differentiated progenitor cells and possible pathogenic signaling pathways. Loose bodies and synovium were obtained from patients with SC during knee arthroplasty. Single-cell RNA sequencing was used to identify cell subsets and their gene signatures in SC synovium. Cells derived from osteoarthritis (OA) synovium were used as controls. Multi-differentiation and colony-forming assays were used to identify progenitor cells. The roles of transcription factors and signaling pathways were investigated through computational analysis and experimental verification. We identified an increased proportion of CD34+ sublining fibroblasts in SC synovium. CD34+CD31- cells and CD34-CD31- cells were sorted from SC synovium. Compared with CD34- cells, CD34+ cells had larger alkaline phosphatase (ALP)-stained area and calcified area after osteogenic induction. In addition, CD34+ cells exhibited a stronger tube formation ability than CD34- cells. Our bioinformatic analysis suggested the expression of TWIST1, a negative regulator of osteogenesis, in CD34- sublining fibroblasts and was regulated by the TGF-ß signaling pathway. The experiment showed that CD34+ cells acquired the TWIST1 expression during culture and the combination of TGF-ß1 and harmine, an inhibitor of Twist1, could further stimulate the osteogenesis of CD34+ cells. Overall, CD34+ synovial fibroblasts in SC synovium have multiple differentiation potentials, especially osteogenic differentiation potential, and might be responsible for the pathogenesis of SC.

Comparative analysis of late-stage rheumatoid arthritis and osteoarthritis reveals shared histopathological features.

OBJECTIVES: Osteoarthritis (OA) is a debilitating and heterogeneous condition, characterized by various levels of articular cartilage degradation, osteophytes formation, and synovial inflammation. Multiple evidences suggest that synovitis may appear early in the disease development and correlates with disease severity and pain, therefore representing a relevant therapeutic target. In a typical synovitis-driven joint disease, namely rheumatoid arthritis (RA), several pathotypes have been described by our group and associated with clinical phenotypes, disease progression, and response to therapy. However, whether these pathotypes can be also observed in the OA synovium is currently unknown. METHODS: Here, using histological approaches combined with semi-quantitative scoring and quantitative digital image analyses, we comparatively characterize the immune cell infiltration in a large cohort of OA and RA synovial tissue samples collected at the time of total joint replacement. RESULTS: We demonstrate that OA synovium can be categorized also into three pathotypes and characterized by disease- and stage-specific features. Moreover, we revealed that pathotypes specifically reflect distinct levels of peripheral inflammation. CONCLUSIONS: In this study, we provide a novel and relevant pathological classification of OA synovial inflammation. Further studies investigating synovial molecular pathology in OA may contribute to the development of disease-modifying therapies.

Association between synovial tissue damage and pain in late-stage knee osteoarthritis: A cross-sectional study.

OBJECTIVE: To identify the presence and distribution of histopathological features of synovial inflammation and tissue damage, and to test their associations with ultrasound (US) imaging measures of synovitis and patient-reported measures of pain in knee osteoarthritis (OA). DESIGN: In the cross-sectional study of 122 patients undergoing surgery for painful late-stage (Kellgren-Lawrence Grade 3 or 4) knee OA, we compared US measures of synovitis (n = 118) and pain (Knee Injury and Osteoarthritis Outcome Score) to histopathological measures of inflammation vs. synovial tissue damage in synovial tissue biopsies. Associations of histopathological features with US measures of inflammation or pain were assessed using linear or logistic regression while controlling for covariates. RESULTS: Histopathological features of inflammation were associated with higher odds of moderate/severe US synovitis (odds ratio [OR] = 1.34 [95%CI 1.04, 1.74), whereas features of synovial tissue damage were associated with lower odds of moderate/severe US synovitis (OR = 0.77 [95%CI 0.57, 1.03]). Worse histopathological scores for synovial tissue damage were associated with more pain (-1.47 [95%CI -2.88, -0.05]), even while adjusting for synovial inflammation (-1.61 [95%CI -3.12, -0.10]). CONCLUSIONS: Synovial tissue damage is associated with pain in late-stage knee OA, independent from inflammation and radiographic damage. These novel findings suggest that preventing synovial tissue damage may be an important goal of disease-modifying OA therapy.

Sex-specific effects of injury and beta-adrenergic activation on metabolic and inflammatory mediators in a murine model of post-traumatic osteoarthritis.

OBJECTIVE: Metabolic processes are intricately linked to the resolution of innate inflammation and tissue repair, two critical steps for treating post-traumatic osteoarthritis (PTOA). Based on lipolytic and immunoregulatory actions of norepinephrine, we hypothesized that intra-articular ß-adrenergic receptor (ßAR) stimulation would suppress PTOA-associated inflammation in the infrapatellar fat pad (IFP) and synovium. DESIGN: We used the ßAR agonist isoproterenol to perturb intra-articular metabolism 3.5 weeks after applying a non-invasive single-load compression injury to knees of 12-week-old male and female mice. We examined the acute effects of intra-articular isoproterenol treatment relative to saline on IFP histology, multiplex gene expression of synovium-IFP tissue, synovial fluid metabolomics, and mechanical allodynia. RESULTS: Injured knees developed PTOA pathology characterized by heterotopic ossification, articular cartilage loss, and IFP atrophy and fibrosis. Isoproterenol suppressed the upregulation of pro-fibrotic genes and downregulated the expression of adipose genes and pro-inflammatory genes (Adam17, Cd14, Icam1, Csf1r, and Casp1) in injured joints of female (but not male) mice. Analysis of published single-cell RNA-seq data identified elevated catecholamine-associated gene expression in resident-like synovial-IFP macrophages after injury. Injury substantially altered synovial fluid metabolites by increasing amino acids, peptides, sphingolipids, phospholipids, bile acids, and dicarboxylic acids, but these changes were not appreciably altered by isoproterenol. Intra-articular injection of either isoproterenol or saline increased mechanical allodynia in female mice, whereas neither substance affected male mice. CONCLUSIONS: Acute ßAR activation altered synovial-IFP transcription in a sex and injury-dependent manner, suggesting that women with PTOA may be more sensitive than men to treatments targeting sympathetic neural signaling pathways.

Interleukin receptor therapeutics attenuate inflammation in canine synovium following cruciate ligament injury.

OBJECTIVE: In the knee, synovial fibrosis after ligamentous injury is linked to progressive joint pain and stiffness. The objective of this study was to evaluate changes in synovial architecture, mechanical properties, and transcriptional profiles following naturally occurring cruciate ligament injury in canines and to test potential therapeutics that target drivers of synovial inflammation and fibrosis. DESIGN: Synovia from canines with spontaneous cruciate ligament tears and from healthy knees were assessed via histology (n = 10/group) and micromechanical testing (n = 5/group) to identify changes in tissue architecture and stiffness. Additional samples (n = 5/group) were subjected to RNA-sequencing to define the transcriptional response to injury. Finally, synovial tissue samples from injured animals (n = 6 (IL1) or n = 8 (IL6)/group) were assessed in vitro for response to therapeutic molecules directed against interleukin (IL) signaling (IL1 or IL6). RESULTS: Cruciate injury resulted in increased synovial fibrosis, vascularity, inflammatory cell infiltration, and intimal hyperplasia. Additionally, the stiffness of both the intima and subintima regions were higher in diseased compared to healthy tissue. Differential gene expression analysis showed that diseased synovium had an upregulation of immune response and cell adhesion pathways and a downregulation of Rho protein transduction pathways. In vitro application of small molecule therapeutics targeting IL1 (anakinra) or IL6 (tocilizumab) dampened expression of inflammatory and matrix deposition mediators. CONCLUSION: Spontaneous cruciate ligament injury in canines is associated with synovial inflammation and fibrosis in a relevant model for testing emerging intra-articular treatments. Small molecule therapeutics targeting IL pathways may be ideal interventions for delivery to the joint space after injury.

A major functional role of synovial fluid is to reduce the rate of cartilage fatigue failure under cyclical compressive loading.

OBJECTIVE: Based on our recent study, which showed that cartilage fatigue failure in reciprocating sliding contact results from cyclical compressive forces, not from cyclical frictional forces, we hypothesize that a major functional role for synovial fluid (SF) is to reduce the rate of articular cartilage fatigue failure from cyclical compressive loading. DESIGN: The rate of cartilage fatigue failure due to repetitive compressive loading was measured by sliding a glass lens against an immature bovine cartilage tibial plateau strip immersed in mature bovine SF, phosphate-buffered saline (PBS), or SF/PBS dilutions (50% SF and 25% SF; n=8 for all four bath conditions). After 24 hours of reciprocating sliding (5,400 cycles), samples were visually assessed and if damage was observed, the test was terminated; otherwise, testing was continued for 72 hours (16,200 cycles), with solution refreshed daily. RESULTS: All eight samples in the PBS group exhibited physical damage after 24 hours, with an average final surface roughness of Rq=0.210±0.067 mm. The SF group showed no damage after 24 hours; however, two of eight samples became damaged after 72 hours, producing a significantly lower average surface roughness than the PBS group (Rq=0.059±0.030 mm; p<10-4). For the remaining groups, at 72 hours one of eight samples damaged in the 50% SF group, and five of eight samples damaged in the 25% SF group. CONCLUSIONS: The results strongly support our hypothesis, showing that decreased amounts of SF in the testing bath produces increased rates of fatigue failure in cartilage that was subjected to reciprocating sliding contact.

Immunomodulation and fibroblast dynamics driving nociceptive joint pain within inflammatory synovium: Unravelling mechanisms for therapeutic advancements in osteoarthritis.

OBJECTIVE: Synovitis is a widely accepted sign of osteoarthritis (OA), characterised by tissue hyperplasia, where increased infiltration of immune cells and proliferation of resident fibroblasts adopt a pro-inflammatory phenotype, and increased the production of pro-inflammatory mediators that are capable of sensitising and activating sensory nociceptors, which innervate the joint tissues. As such, it is important to understand the cellular composition of synovium and their involvement in pain sensitisation to better inform the development of effective analgesics. METHODS: Studies investigating pain sensitisation in OA with a focus on immune cells and fibroblasts were identified using PubMed, Web of Science and SCOPUS. RESULTS: In this review, we comprehensively assess the evidence that cellular crosstalk between resident immune cells or synovial fibroblasts with joint nociceptors in inflamed OA synovium contributes to peripheral pain sensitisation. Moreover, we explore whether the elucidation of common mechanisms identified in similar joint conditions may inform the development of more effective analgesics specifically targeting OA joint pain. CONCLUSION: The concept of local environment and cellular crosstalk within the inflammatory synovium as a driver of nociceptive joint pain presents a compelling opportunity for future research and therapeutic advancements.