CCL2 and musculoskeletal system disorder: Nevertheless, although VDD on the one hand, and IL-9, MCP-1/CCL2, and IL-34 on the other hand, have been implicated in the pathogenesis of OP and OA, and despite clinical and experimental evidence showing a correlation between VDD and elevated circulating cytokine levels, the potential link between VDD and these inflammatory factors in the etiology of musculoskeletal diseases remains largely unexplored.