Modulation of the mechanical responses of synovial fibroblasts by osteoarthritis-associated inflammatory stressors

The role of mechanosensitive ion channel Piezo1 in knee osteoarthritis inflammation

Mechanosensitive ion channel Piezo1 is known to mediate a variety of inflammatory pathways and is also involved in the occurrence and development of many orthopedic diseases. Although its role in the inflammatory mechanism of knee osteoarthritis (KOA) has been reported, a systematic explanation is yet to be seen. This article aims to summarize the role of inflammatory responses in the pathogenesis of KOA and elucidate the mechanism by which the Piezo1-mediated inflammatory response contributes to the pathogenesis of KOA, providing a theoretical basis for the prevention and treatment of knee osteoarthritis. The results indicate that in the mechanism leading to knee osteoarthritis, Piezo1 can mediate the inflammatory response through chondrocytes and synovial cells, participating in the pathological progression of KOA. Piezo1 has the potential to become a new target for the prevention and treatment of this disease. Additionally, as pain is one of the most severe manifestations in KOA patients, the inflammatory response mediated by Piezo1, which causes the release of inflammatory mediators and pro-inflammatory factors leading to pain, can be further explored.

Unravelling the interplay between ER stress, UPR and the cGAS-STING pathway: Implications for osteoarthritis pathogenesis and treatment strategy

Osteoarthritis (OA) is a debilitating chronic degenerative disease affecting the whole joint organ leading to pain and disability. Cellular stress and injuries trigger inflammation and the onset of pathophysiological changes ensue after irreparable damage and inability to resolve inflammation, impeding the completion of the healing process. Extracellular matrix (ECM) degradation leads to dysregulated joint tissue metabolism. The reparative effort induces the proliferation of hypertrophic chondrocytes and matrix protein synthesis. Aberrant protein synthesis leads to endoplasmic reticulum (ER) stress and chondrocyte apoptosis with consequent cartilage matrix loss. These events in a vicious cycle perpetuate inflammation, hindering the restoration of normal tissue homeostasis. Recent evidence suggests that inflammatory responses and chondrocyte apoptosis could be caused by the activation of the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signalling axis in response to DNA damage. It has been reported that there is a crosstalk between ER stress and cGAS-STING signalling in cellular senescence and other diseases. Based on recent evidence, this review discusses the role of ER stress, Unfolded Protein Response (UPR) and cGAS-STING pathway in mediating inflammatory responses in OA.

Fibrotic pathways and fibroblast-like synoviocyte phenotypes in osteoarthritis

Osteoarthritis (OA) is the most common form of arthritis, characterized by osteophyte formation, cartilage degradation, and structural and cellular alterations of the synovial membrane. Activated fibroblast-like synoviocytes (FLS) of the synovial membrane have been identified as key drivers, secreting humoral mediators that maintain inflammatory processes, proteases that cause cartilage and bone destruction, and factors that drive fibrotic processes. In normal tissue repair, fibrotic processes are terminated after the damage has been repaired. In fibrosis, tissue remodeling and wound healing are exaggerated and prolonged. Various stressors, including aging, joint instability, and inflammation, lead to structural damage of the joint and micro lesions within the synovial tissue. One result is the reduced production of synovial fluid (lubricants), which reduces the lubricity of the cartilage areas, leading to cartilage damage. In the synovial tissue, a wound-healing cascade is initiated by activating macrophages, Th2 cells, and FLS. The latter can be divided into two major populations. The destructive thymocyte differentiation antigen (THY)1─ phenotype is restricted to the synovial lining layer. In contrast, the THY1+ phenotype of the sublining layer is classified as an invasive one with immune effector function driving synovitis. The exact mechanisms involved in the transition of fibroblasts into a myofibroblast-like phenotype that drives fibrosis remain unclear. The review provides an overview of the phenotypes and spatial distribution of FLS in the synovial membrane of OA, describes the mechanisms of fibroblast into myofibroblast activation, and the metabolic alterations of myofibroblast-like cells.

Prevalence and distribution of ultrasound-detected hand synovial abnormalities in a middle-aged and older population

OBJECTIVE

Synovial abnormalities are modifiable targets for hand pain and osteoarthritis. We examined the prevalence and distribution of ultrasound-detected hand synovial abnormalities in a community-derived sample of older people in China.

METHODS

Within the Xiangya Osteoarthritis Study, a community-based study, we assessed synovial hypertrophy (SH), joint effusion, and Power Doppler signal (PDS) on all fingers and thumbs of both hands using standardized ultrasound examinations (score: 0-3). We assessed distribution patterns of SH and effusion using χ2-test and interrelationships of SH and effusion in different joints and hands by generalized estimating equations.

RESULTS

Among 3,623 participants (mean age: 64.4 years; women: 58.1%), prevalence of SH, effusion and PDS were 85.5%, 87.3% and 1.5%, respectively. Prevalence of SH, effusion and PDS increased with age, was higher in the right hand than in the left hand and was more common in proximal than in distal hand joints. SH and effusion often occurred in multiple joints (P < 0.001). SH in one joint was strongly associated with presence of SH in the same joint of the opposite hand (odds ratio [OR]= 6.60, 95% confidence interval [CI]: 6.19-7.03) followed by SH in other joints in the same row, (OR=5.70, 95%CI: 5.32-6.11), and then other joints in the same ray of the same hand (OR=1.49, 95%CI: 1.39-1.60). Similar patterns were observed for effusion.

CONCLUSION

Hand synovial abnormalities are common among older people, often affect multiple hand joints and present a unique pattern. These findings suggest both systemic and mechanical factors play roles in their occurrence.

PSD95 as a New Potential Therapeutic Target of Osteoarthritis: A Study of the Identification of Hub Genes through Self-Contrast Model

Osteoarthritis (OA) is a worldwide joint disease. However, the precise mechanism causing OA remains unclear. Our primary aim was to identify vital biomarkers associated with the mechano-inflammatory aspect of OA, providing potential diagnostic and therapeutic targets for OA. Thirty OA patients who underwent total knee arthroplasty were recruited, and cartilage samples were obtained from both the lateral tibial plateau (LTP) and medial tibial plateau (MTP). GO and KEGG enrichment analyses were performed, and the protein-protein interaction (PPI) assessment was conducted for hub genes. The effect of PSD95 inhibition on cartilage degeneration was also conducted and analyzed. A total of 1247 upregulated and 244 downregulated DEGs were identified. Significant differences were observed between MTP and LTP in mechanical stress-related genes and activated sensory neurons based on a self-contrast model of human knee OA. Cluster analysis identified DLG4 as the hub gene. Cyclic loading stress increased PSD95 (encoded by DLG4) expression in LTP cartilage, and PSD95 inhibitors could alleviate OA progression. This study suggests that inhibiting PSD95 could be a potential therapeutic strategy for preventing articular cartilage degradation.

Healthy and Osteoarthritis-Affected Joints Facing the Cellular Crosstalk

Osteoarthritis (OA) is a chronic, progressive, severely debilitating, and multifactorial joint disease that is recognized as the most common type of arthritis. During the last decade, it shows an incremental global rise in prevalence and incidence. The interaction between etiologic factors that mediate joint degradation has been explored in numerous studies. However, the underlying processes that induce OA remain obscure, largely due to the variety and complexity of these mechanisms. During synovial joint dysfunction, the osteochondral unit undergoes cellular phenotypic and functional alterations. At the cellular level, the synovial membrane is influenced by cartilage and subchondral bone cleavage fragments and extracellular matrix (ECM) degradation products from apoptotic and necrotic cells. These "foreign bodies" serve as danger-associated molecular patterns (DAMPs) that trigger innate immunity, eliciting and sustaining low-grade inflammation in the synovium. In this review, we explore the cellular and molecular communication networks established between the major joint compartments-the synovial membrane, cartilage, and subchondral bone of normal and OA-affected joints.

Acute loading has minor influence on human articular cartilage gene expression and glycosaminoglycan composition in late-stage knee osteoarthritis: a randomised controlled trial

OBJECTIVE

Osteoarthritis (OA) remains clinically challenging. Regular physical exercise improves symptoms though it is unclear whether exercise influences cartilage at the molecular level. Thus, we aimed to determine the effect of acute loading on gene expression and glycosaminoglycan (GAG) content in human OA cartilage.

DESIGN

Patients with primary knee OA participated in this single-blind randomised controlled trial initiated 3.5 h prior to scheduled joint replacement surgery with or without loading by performing one bout of resistance exercise (one-legged leg press). Cartilage from the medial tibia condyle was sampled centrally, under the meniscus, and from peripheral osteophytes. Samples were analysed for gene expression by real-time reverse transcriptase polymerase chain reaction, and hyaluronidase-extracted matrix was analysed for GAG composition by immuno- and dimethyl-methylene blue assays.

RESULTS

Of 32 patients randomised, 31 completed the intervention: mean age 69 ± 7.5 years (SD), 58% female, BMI 29.4 ± 4.4 kg/m². Exercise increased chondroitin sulphate extractability [95% CI: 1.01 to 2.46; P = 0.0486] but cartilage relevant gene expression was unchanged. Regionally, the submeniscal area showed higher MMP-3, MMP-13, IGF-1Ea, and CTGF, together with lower lubricin and COMP expression compared to the central condylar region. Further, osteophyte expression of MMP-1, MMP-13, IGF-1Ea, and TGF-β3 was higher than articular cartilage and lower for aggrecan, COMP, and FGF-2. Hyaluronidase-extracted matrix from central condylar cartilage contained more GAGs but less chondroitin sulphate compared to submeniscal cartilage.

CONCLUSION

Acute exercise had minor influence on cartilage GAG dynamics, indicating that osteoarthritic cartilage is not significantly affected by acute exercise. However, the regional differences suggest a chronic mechanical influence on human cartilage.

CLINICALTRIALS

GOV REGISTRATION NUMBER

NCT03410745.

Elevation of MMP1 and ADAMTS5 mRNA expression in glenohumeral synovia of patients with hypercholesterolemia

Background

Epidemiological studies have reported a positive association between hypercholesterolemia and shoulder disease. Previous studies have focused on the effect of hypercholesterolemia on tendinopathy. Moreover, hypercholesterolemia has also been linked to joint pathology in the knee and hand. However, the effect of hyperlipidemia on glenohumeral joint remain unclear. A hypercholesterolemic condition has been reported to alter levels of A Disintegrin and Metalloprotease with Thrombospondin Motifs (ADAMTSs) and matrix metalloproteases (MMPs) in synovium of the knee joint. Here, we evaluated the mRNA expression of ADAMTSs and MMPs in the glenohumeral synovium of patients with and without hypercholesterolemia.

Methods

Study participants were 73 patients who underwent arthroscopic rotator cuff repair for degenerative rotator cuff tears. They were divided into two groups according to total cholesterol (TC) and triglyceride levels. Synovial membrane samples were harvested at the rotator interval during surgery, and mRNA expression levels of the aggrecanases ADAM-TS4 and ADAM-TS5 and MMPs (MMP-1, 3, 9, and 13) were analyzed quantitatively.

Results

ADAM-TS5 and MMP1 mRNA levels were significantly higher in the high TC group than in the low TC group (P = 0.023 and P = 0.025, respectively). In contrast, no significant differences were observed in ADAMTS4 or MMPs 3, 9, and 13 (ADAMTS4, P = 0.547; MMP3, P = 0.55; MMP9, P = 0.521; and MMP13, P = 0.785).

Conclusion

Hypercholesterolemia may alter MMP1 and ADAMTS5 expression in the synovium of the glenohumeral joint.

A Novel Mechanical-Based Injective Hydrogel for Treatment with Aromatase Inhibitors Caused Joint Inflammation via the NF-κB Pathway

Synovium has widely participated in induced inflammation, suggesting that it is a potential target to reduce aromatase inhibitors (AIs) causing joint inflammation or pain. Exercise and mechanical stimulation are important strategies for precaution and treatment of bone inflammation. In this work, we developed a novel thermo-sensitive hydrogel, which could be injected intra-articularly. The aim of this research was to investigate the role of various mechanical strength hydrogels in reducing synovium inflammation. The effect of different mechanical strength hydrogels on regulating synovium inflammation was used to stimulate human fibroblast-like synoviocytes (FLS) under a cyclic mechanical compression environment in vitro. Cytokine and metalloprotease expression in FLS was analyzed by the western blot and q-PCR method, in which FLS were cultured with the different mechanical strength hydrogels. The results showed that a moderate-intensity hydrogel mechanical stimulation might be suitable in reducing AI-induced FLS inflammation via the NK-κB pathway. In addition, we built an AI-treated rat model and injected the different mechanical strength hydrogels. Similarly, the moderate-strength mechanical hydrogel could reduce the inflammatory factor and metalloproteinase expression in synovial tissues and intra-articular synovia.