Fig. 1C-C motif chemokine receptor 5 (CCR5) promotes obesity-induced inflammation and insulin resistance. Kitade et al. [33] recently identified and characterized a role for CCR5, a CC chemokine receptor, and made several important observations. First, expression of CCR5 and its ligands is significantly increased and is equal to that of CCR2 and its ligands in white adipose tissue (WAT) of obese mice. Second, CCR5+ adipose tissue macrophages (ATMs) accumulate in WAT of obese mice. Third, Ccr5-/- mice are protected from insulin resistance and diabetes through both reduction in ATM accumulation and induction of an alternatively activated, M2 dominant shift in ATM. Taken together, these data indicate that CCR5 provides a novel link between obesity, adipose tissue inflammation, and insulin resistance. TNF, tumor necrosis factor; IL, interleukin; MCP, monocyte chemoattractant protein.
Fig. 2Hypothetical role of C-C motif chemokine receptor 5 (CCR5) and monocyte chemoattractant protein (MCP)-1-CCR2 in the development of adipose tissue inflammation and insulin resistance in obesity. Obesity causes both the recruitment and proiflammatory activation of adipose tissue macrophages (ATMs). Adipocytes or preadipocytes begin to secrete MCP-1 as well as other chemokines, such as MIP1α, MIP1β, and RANSTES (ligands for CCR5) in obesity. Thereafter, CCR2+ and/or CCR5+ macrophages accumulate and presumably maintain the inflammation as M1 or classically activated macrophages in obese adipose tissue. Ly6Chi monocytes exit the bone marrow in a CCR2-dependent manner and are recruited to inflamed tissues. CCR5 may also regulate recruitment of Ly6Chi and Ly6C- monocytes and their fate as M1/M2 ATMs. Once these ATMs are present and active, cytokines (tumor necrosis factor [TNF]-α, interleukin [IL]-6, and IL-1β) are produced. Therefore, CCR5, independently from and/or cooperatively with CCR2, could play an important role in the induction and maintenance of obesity-induced inflammation and insulin resistance.
Table 1Chemokines and chemokine receptors