Surfactant protein D alleviates chondrocytes senescence by upregulating SIRT3/SOD2 pathway in osteoarthritis

BACKGROUND: Osteoarthritis (OA) is an age-related degenerative disease that affects bones and joints. The hallmark pathogenesis of OA is associated with chondrocyte senescence. Surfactant protein D (SP-D) is a member of the innate immune proteins family, which can inhibit the immune inflammatory response of chondrocytes. However, the effect of SP-D on chondrocyte senescence phenotype is poorly studied. The present study investigated the phenotypic regulation of OA chondrocyte senescence mediated by SP-D and explored the underlying molecular mechanism. METHODS: In this study, an in vitro senescence chondrocyte model was generated by subjecting chondrocytes to IL-1β treatment. Furthermore, the expression of aging-related biomarkers and mitochondrial functions in SP-D overexpressing chondrocytes was observed. Co-immunoprecipitation was conducted to verify the association between SP-D and the identifed proteins within chondrocytes. Moreover, a rat OA model was established by destabilization of the medial meniscus surgery, and the effect of SP-D on reversing the aging phenotype of OA cartilage was investigated. RESULTS: The results indicated that SP-D significantly decreased senescence and enhanced mitochondrial functions in senescent chondrocytes. The RNA-sequencing analysis revealed that the SIRT3/SOD2 pathway predominantly modulated the effect of SP-D on alleviating senescence. In addition, SP-D overexpression mitigated chondrocyte senescence, suppressed senescence-associated secretory phenotype (SASP) secretion and ameliorated mitochondrial damage. In the rat OA model, SP-D inhibited aging-related pathological changes by upregulating SIRT3/SOD2 pathway, thereby protecting the cartilage tissue integrity. CONCLUSION: These findings indicate that SP-D modulates the inhibition of chondrocyte senescence by upregulating SIRT3/SOD2 pathway. These data indicate that targeting SP-D and the SIRT3/SOD2 pathway might be a promising therapeutic strategy for OA.