Impact of Mechanical Load on the Expression Profile of Synovial Fibroblasts from Patients with and without Osteoarthritis

Abstract

Osteoarthritis (OA) affects the integrity of the entire joint including the synovium. The most abundant cells in the synovium are fibroblasts (SF). Excessive mechanical loading might contribute to OA pathogenesis. Here, we investigate the effects of mechanical loading on SF derived from non-OA (N-SF) and OA patients (OA-SF). We treated N-SF and OA-SF with or without mechanical loading for 48h after 24h of preincubation. Then we assessed gene and protein expression of proinflammatory factors (TNFα, COX-2, PG-E2, IL-6), extracellular matrix (ECM) components (COL1, FN1) and glycosaminoglycans (GAGs) via RT-qPCR, ELISA, DMMB assay and HPLC. Mechanical loading significantly increased TNFα and PG-E2 secretion by N-SF and OA-SF, whereas in OA-SF IL-6 secretion was reduced. COL1 and FN1 secretion were downregulated in N-SF during loading. OA-SF secreted less COL1 compared to N-SF under control conditions. In contrast, OA-SF in general expressed more FN1. GAG synthesis was upregulated in N-SF, but not in OA-SF during loading with OA-SF displaying a higher charge density than N-SF. Mechanical loading enhanced proinflammatory factor expression and GAG synthesis and decreased secretion of ECM components in N-SFs, indicating a contributing role of SF to OA development.

Early OA Stage Like Response Occurs after Dynamic Stretching of Human Synovial Fibroblasts

“…Our results indicate that short-term high-frequency cyclic tensile strain induced a mechanical stress response, as a significant increase in the inflammatory and innate immune response activating marker IL-6 could be detected. This concurs with previous findings applying pressure on fibroblasts [24,48]. Interestingly, the application of the dynamic stretching protocol had beneficial effects on IL-6 expression in synovial fibroblasts, contrary to chondrocytes [23].…”

“…A deficiency of HAS-1 is associated with chronic joint inflammation and intra-articular fibrosis [60]. When static isotropic tension was applied to the synovial fibroblasts, increased levels of HA GAGs and HAS-1 were present, similar to observations done in a compressive setup [48]. In contrast, dynamic tensile strain reduced HA GAGs in the cell supernatant and HAS-1 expression, favouring inflammatory processes.…”

“…Increased IL-6 levels can be found in osteoarthritic groups [46], while synovial fluid levels of IL-6 seem not to correlate with OA severity [47]. The application of pressure as mechanical strain has a major impact on gene expression in synovial fibroblasts [48]. Mechanical strain can induce inflammation and can alter extracellular matrix composition.…”

Osteoarthritis and Cartilage Regeneration: Focus on Pathophysiology and Molecular Mechanisms

“…Accompanying OA progression, synovial fibroblasts (SF) elicit an immunological response and produce proinflammatory cytokines. Schröder et al, studied the impact of mechanical load on the expression profile of SFs derived from normal or OA patients [22]. Static compressive loading applied on cultured SFs of non-OA donors for 2 days enhanced the expression of proinflammatory factors such as TNFα, IL-6, and COX-2, reduced the expression of collagen I and fibronectin, and induced glycosaminoglycan (GAG) production.…”

Exposure to hypergravity during zebrafish development alters cartilage material properties and strain distribution

“…As increased mechanical loading is associated with higher glycosaminoglycan (GAG) synthesis and decreased extracellular matrix (ECM) secretion (Schröder et al , 2019), we performed wholemount Alcian blue and Alizarin red double staining (Figure 1H, H’) and Alcian blue, H & E on sections to visualize GAGs throughout the lower jaw (Figure 2D). From brightfield images, we observed no changes to mineralisation or GAGs at 5dpf (Figure 1H, H’, 2D), suggesting secretion of this ECM component is unaffected by altered loading.…”