Adropin regulates macrophage phenotype via PPARγ signalling: A preliminary study of adropin and Crohn's disease

Macrophage polarization is increasingly recognized as a vital pathogenetic factor in Crohn's disease (CD). Adropin is a secreted protein implicated in energy homeostasis, chiefly linked to glucose and lipid metabolism. However, the significance of adropin in CD is not clear. The objective of this study was to detect the expression of adropin in CD patients and investigate the effect of adropin on macrophage polarization induced by lipopolysaccharide (LPS) and its potential mechanism. Our study showed that serum adropin levels were markedly lower in patients with CD in active (CDA) than patients with CD in remission (CDR) and control groups (p < 0.01), however, there was no significant difference between in remission CD and healthy controls (p > 0.05). The colon mucous adropin levels in CDA were distinctly higher than CDR and controls (p < 0.01), while a significant difference between in remission CD and in healthy controls was not observed (p > 0.05). Exploration of the specific mechanism of action indicated that adropin promoted LPS-induced RAW264.7 macrophage polarization to M2 phenotype by modulating the expression and nuclear translocation of peroxisome proliferator receptor gamma (PPARγ), which may help weaken the intestinal inflammatory response. PPARγ inhibitor GW9662 reversed adropin-induced M2 macrophage polarization. Knockdown of GPR19, an adropin receptor, abrogated the M2 macrophage polarization caused by PPARγ. These findings suggest that adropin in colonic mucosa is a protective response in patients with active Crohn's disease.