Asporin regulated by miR-26b-5p mediates chondrocyte senescence and exacerbates osteoarthritis progression via TGF-ß1/Smad2 pathway.

OBJECTIVES: This study aimed to investigate the role and mechanism of asporin in modulating chondrocyte senescence in OA pathology. METHODS: Asporin and senescence-related hallmark expression were examined in human and experimental OA mouse cartilage samples. Twelve-week-old male C57 mice were administered with recombinant protein (rm-asporin)- or asporin-siRNA-expressing lentiviruses via intra-articular injection once a week after destabilization of the medial meniscus (DMM) surgery to induce OA. Cartilage damage was measured using the Osteoarthritis Research Society International score. Senescence-associated ß-galactosidase (SA-ß-Gal) staining, γH2AX, p21 and p16INK4a were analysed by immunofluorescence staining and western blot to assess the specific role of asporin in chondrocyte senescence. The TGF-ß1-Smad2 signalling pathway and miR-26b-5p were further evaluated to explore the mechanism of asporin in OA. RESULTS: Asporin was upregulated in articular chondrocytes of OA patients and DMM mice and accompanied by accumulation of senescent cells. Asporin overexpression exaggerated OA progression, whereas silencing asporin restored chondrocyte homeostasis and deferred chondrocyte senescence, leading to markedly attenuated DMM-induced OA. Cellular and molecular analyses showed that asporin can be inhibited by miR-26b-5p, which was significantly downregulated in OA cartilage, leading to exacerbation of experimental OA partially through inhibition of TGF-ß1-Smad2 signalling in chondrocytes. CONCLUSIONS: Our findings indicate that asporin plays an essential role in chondrocyte senescence and OA pathogenesis. Upregulated by miR-26b-5p, asporin inhibits the TGF-ß1-Smad2 pathway to accelerate chondrocyte senescence and exacerbate cartilage degeneration. Targeting the miR-26b-5p-asporin-Smad2 axis may serve as a practical therapeutic strategy to delay chondrocyte senescence and OA development.

Pentraxin 3 regulated by miR-224-5p modulates macrophage reprogramming and exacerbates osteoarthritis associated synovitis by targeting CD32.

Emerging evidence has shown an imbalance in M1/M2 macrophage polarization to play an essential role in osteoarthritis (OA) progression. However, the underlying mechanistic basis for this polarization is unknown. RNA sequencing of OA M1-polarized macrophages found highly expressed levels of pentraxin 3 (PTX3), suggesting a role for PTX3 in OA occurrence and development. Herein, PTX3 was found to be increased in the synovium and articular cartilage of OA patients and OA mice. Intra-articular injection of PTX3 aggravated, while PTX3 neutralization reversed synovitis and cartilage degeneration. No metabolic disorder or proteoglycan loss were observed in cartilage explants when treated with PTX3 alone. However, cartilage explants exhibited an OA phenotype when treated with culture supernatants of macrophages stimulated with PTX3, suggesting that PTX3 did not have a direct effect on chondrocytes. Therefore, the OA anti-chondrogenic effects of PTX3 are primarily mediated through macrophages. Mechanistically, PTX3 was upregulated by miR-224-5p deficiency, which activated the p65/NF-κB pathway to promote M1 macrophage polarization by targeting CD32. CD32 was expressed by macrophages, that when stimulated with PTX3, secreted abundant pro-inflammation cytokines that induced severe articular cartilage damage. The paracrine interaction between macrophages and chondrocytes produced a feedback loop that enhanced synovitis and cartilage damage. The findings of this study identified a functional pathway important to OA development. Blockade of this pathway and PTX3 may prevent and treat OA.

BMP5 silencing inhibits chondrocyte senescence and apoptosis as well as osteoarthritis progression in mice.

In this study, we using the in vivo destabilization of the medial meniscus (DMM) mouse model to investigate the role of bone morphogenetic protein 5 (BMP5) in osteoarthritis (OA) progression mediated via chondrocyte senescence and apoptosis. BMP5 expression was significantly higher in knee articular cartilage tissues of OA patients and DMM model mice than the corresponding controls. The Osteoarthritis Research Society International scores based on histological staining of knee articular cartilage sections were lower in DMM mice where BMP5 was knocked down in chondrocytes than the corresponding controls 4 weeks after DMM surgery. DMM mice with BMP5-deficient chondrocytes showed reduced levels of matrix-degrading enzymes such as MMP13 and ADAMTS5 as well as reduced cartilage destruction. BMP5 knockdown also decreased chondrocyte apoptosis and senescence by suppressing the activation of p38 and ERK MAP kinases. These findings demonstrate that BMP5 silencing inhibits chondrocyte senescence and apoptosis as well as OA progression by downregulating activity in the p38/ERK signaling pathway.

MFG-E8 regulated by miR-99b-5p protects against osteoarthritis by targeting chondrocyte senescence and macrophage reprogramming via the NF-κB pathway.

Milk fat globule-epidermal growth factor (EGF) factor 8 (MFG-E8), as a necessary bridging molecule between apoptotic cells and phagocytic cells, has been widely studied in various organs and diseases, while the effect of MFG-E8 in osteoarthritis (OA) remains unclear. Here, we identified MFG-E8 as a key factor mediating chondrocyte senescence and macrophage polarization and revealed its role in the pathology of OA. We found that MFG-E8 expression was downregulated both locally and systemically as OA advanced in patients with OA and in mice after destabilization of the medial meniscus surgery (DMM) to induce OA. MFG-E8 loss caused striking progressive articular cartilage damage, synovial hyperplasia, and massive osteophyte formation in OA mice, which was relieved by intra-articular administration of recombinant mouse MFG-E8 (rmMFG-E8). Moreover, MFG-E8 restored chondrocyte homeostasis, deferred chondrocyte senescence and reprogrammed macrophages to the M2 subtype to alleviate OA. Further studies showed that MFG-E8 was inhibited by miR-99b-5p, expression of which was significantly upregulated in OA cartilage, leading to exacerbation of experimental OA partially through activation of NF-κB signaling in chondrocytes. Our findings established an essential role of MFG-E8 in chondrocyte senescence and macrophage reprogramming during OA, and identified intra-articular injection of MFG-E8 as a potential therapeutic target for OA prevention and treatment.