Astaxanthin prevents osteoarthritis by blocking Rspo2-mediated Wnt/β-catenin signaling in chondrocytes and abolishing Rspo2-related inflammatory factors in macrophages

Chondrocyte degeneration and classically activated macrophage (AM)-related inflammation play critical roles in osteoarthritis (OA). Here, we explored the effects of astaxanthin and Rspo2 on OA in vitro and in vivo. We observed that the Rspo2 gene was markedly elevated in synovial tissues of OA patients compared with healthy controls. In 2D cultures, Rspo2 and inflammatory factors were enhanced in AMs compared with nonactivated macrophages (NMs), and the protein expression levels of Rspo2, β-catenin, and inflammatory factors were increased, and anabolic markers were reduced in osteoarthritic chondrocytes (OACs) compared to normal chondrocytes (NCs). Astaxanthin reversed these changes in AMs and OACs. Furthermore, Rspo2 shRNA significantly abolished inflammatory factors and elevated anabolic markers in OACs. In NCs cocultured with AM, and in OACs cocultured with AMs or NMs, astaxanthin reversed these changes in these coculture systems and promoted secretion of Rspo2, β-catenin and inflammatory factors and suppressed anabolic markers compared to NCs or OACs cultured alone. In AMs, coculture with NCs resulted in a slight elevation of Rspo2 and AM-related genes, but not protein expression, compared to culture alone, but when cocultured with OACs, these inflammatory mediators were significantly enhanced at both the gene and protein levels. Astaxanthin reversed these changes in all the groups. In vivo, we observed a deterioration in cartilage quality after intra-articular injection of Rspo2 associated with medial meniscus (DMM)-induced instability in the OA group, and astaxanthin was protective in these groups. Our results collectively revealed that astaxanthin attenuated the process of OA by abolishing Rspo2 both in vitro and in vivo.