Senescent bone marrow mesenchymal stem cells exacerbate subchondral bone sclerosis and osteoarthritis via the senescence-associated secretory phenotype.

BACKGROUND: Osteoarthritis (OA) is a common joint disease characterized by articular cartilage degeneration, with subchondral bone sclerosis being a key pathological change. However, the mechanism underlying subchondral bone sclerosis remains unclear. Senescent stem cells have been found in OA cartilage, synovium, and subchondral bone. This study aimed to explore the role of senescent bone marrow mesenchymal stem cells (BMSCs) in subchondral bone sclerosis and OA progression. METHODS: This study utilized two mouse OA models: closed anterior cruciate ligament transection and spontaneous OA. Immunostaining was performed to assess the proportion of senescent cells especially BMSCs in subchondral bone during OA progression. A senescence model of BMSCs was constructed using H₂O₂, and transcriptomic sequencing was conducted to analyze secretory phenotypic changes in senescent BMSCs. In vitro experiments were performed to evaluate the effects of senescent BMSC-derived senescence-associated secretory phenotype (SASP) on osteogenic differentiation and osteogenic marker expression in normal BMSCs. We examined the mRNA expression of core molecules in osteogenesis-related pathways, which were activated by SASP. Additionally, OA mice were administered the senolytic combination of dasatinib and quercetin (D + Q), and its effects on senescent BMSCs, osteocalcin expression, subchondral bone sclerosis, and OA progression were assessed. RESULTS: Immunostaining results showed a significant increase in the proportion of senescent BMSCs in subchondral bone during OA progression. Transcriptomic sequencing revealed that senescent BMSCs acquired the SASP. In vitro experiments demonstrated that conditioned medium from senescent BMSCs (containing SASP) significantly promoted osteogenic differentiation and upregulated the expression of osteogenic markers in normal BMSCs. The SASP significantly upregulated Mapk8 and Mapk14 mRNAs in osteogenesis-related pathways. Administration of D + Q to OA mice effectively cleared senescent BMSCs, reduced osteocalcin expression in subchondral bone, inhibited subchondral bone sclerosis, and alleviated OA progression. CONCLUSIONS: This study indicates that senescent BMSCs promote subchondral bone sclerosis and OA progression through activating Mapk8 and Mapk14 via SASP in subchondral bone. The senolytic combination D + Q holds potential for OA treatment by eliminating senescent BMSCs in subchondral bone.