Improvement of Adipose Macrophage Polarization in High Fat Diet-Induced Obese GHSR Knockout Mice

PURPOSE: Adipose tissue inflammation is the key linking obesity to insulin resistance. Over 50% of the interstitial cells in adipose tissue are macrophages, which produce inflammatory cytokines and therefore play an important role in the progression of insulin resistance. Within this classification view, macrophage biology is driven by two polarization phenotypes, M(1) (proinflammatory) and M(2) (anti-inflammatory). The unique functional receptor of ghrelin, growth hormone secretagogue receptor (GHSR), is a classic seven-transmembrane G protein-coupled receptor that is linked to multiple intracellular signaling pathways. Knockout of GHSR improves the obesity and glucose metabolic disorders, suggesting a crucial role of ghrelin activity in insulin resistance. Here, we discussed whether macrophage polarization phenotypes in adipose tissue were changed in GHSR knockout (GHSR-/-) mice. METHODS: GHSR-/- mice were fed with normal chow diet (NCD) or high fat diet (HFD). Markers of different macrophage polarization phenotypes were detected by real-time RT-PCR. RESULTS: The size of adipocytes decreased and interstitial cells, especially infiltrated macrophages, reduced in epididymal adipose tissue of GHSR-/- mice fed with HFD. Compared with wild type mice, the mRNA levels of inflammatory adipokines such as resistin, IL-6, and PAI-1 were significantly lower in epididymal adipose tissue of GHSR-/- mice, whereas anti-inflammatory adipokine, adiponectin, was significantly higher. M(1) markers, MCP-1, TNF-α, and iNOS, were significantly lower in epididymal adipose tissue of GHSR-/- mice, whereas M(2) markers, Arg-1, Mgl-1, were Mrc1, were significantly higher. CONCLUSION: The GHSR-/- mice fed with HFD showed suppressed adipose inflammation, reduced macrophage infiltration, and enhanced M(2) polarization of macrophages in adipose tissue, which improved insulin sensitivity.