Inflammatory milieu cultivated Sema3A signaling promotes chondrocyte apoptosis in knee osteoarthritis

Osteoarthritis (OA) is the leading degenerative joint disease and featured by articular cartilage destruction, where chondrocyte apoptosis plays a critical role. Semaphorin-3A (Sema3A) has been implicated in OA chondrocyte physiology. In this study we aimed to uncover how Sema3A signaling is regulated in chondrocytes and investigate its role in OA chondrocyte survival. Here, we report that Sema3A and its receptor neuropilin-1 (Nrp1) are synchronously upregulated in cartilage chondrocytes of knee OA patients. Their expressions in chondrocytes could be induced by the stimulation of proinflammatory cytokines IL-1 beta and TNF-alpha and subsequent transcriptional activation orchestrated by C/EBP beta. The resulting excessive Sema3A signaling promotes chondrocyte apoptosis through impairing PI3K/Akt prosurvival signaling. These findings indicate a regulatory mechanism and a proapoptotic function of aberrant Sema3A signaling in OA chondrocytes, and suggest that targeting Sema3A signaling might interfere OA pathogenesis.