CCR2 and obesity due to melanocortin 4 receptor deficiency: Several recent studies have shown that high-fat diet-induced obesity and the related metabolic diseases in the visceral adipose tissue of mice express a large amount of Angptl2, which significantly promotes macrophage aggregation and proinflammatory cytokine expression [23], leading to chronic inflammation and systemic insulin resistance of adipose tissue [24].AP2-Angpt12 mice (adipose tissue- specific promoter Angptl2, AP2-Angpt12) showed a marked increase in inflammatory cytokines (CCL2, and TNF-α) and inflammatory cell surface markers (CCR2) in adipose tissue [17].