CCL2 and obesity due to melanocortin 4 receptor deficiency: Importantly, it has been confirmed in an obesity-induced OA animal model that this proinflammatory microbial shift coincided with an increase in key proinflammatory cytokines in the circulation, increased macrophage presence in the knee capsule, and upregulation of the monocyte chemokine MCP-1 in synovial tissue [42].