197-LB: The Regulation of HSL by Macrophage Migration Inhibitory Factor (MIF) Contributes to Adipocyte Hypertrophy and Development of Obesity

Abstract

Inflammation is associated with lipolysis in adipose tissue. HSL is a key enzyme in mediating lipolysis through augmenting hydrolysis of triglycerides and diacylglycerides. Our study found that the procytokine MIF has both transcriptional and non-transcriptional effects on mediating HSL through activating AMPK signaling pathway. The activated AMPK downregulates HSL gene expression in adipocytes. It also upregulates a phosphorylation of HSL Ser565, an inhibitory phosphorylation site, leading to the reduction of HSL active site, Ser563 phosphorylation. These mechanisms are operative in either transgenic overexpressed MIF mouse models or WT mice with high circulating MIF levels following a high caloric diet feeding (HFD). The MIF/AMPK/HSL axis regulates the development of adipocyte hypertrophy and obesity. We also confirm that high plasma MIF levels are associated with decreased adipose HSL gene expression in human obesity. Interestingly, in Mif-/-mice, HSL gene expression is also inhibited, suggesting that MIF genotype is important to maintain adipose HSL expression. Following HFD feeding, Mif-/-mice demonstrates higher Akt and lower PKA phosphorylation, which further decrease HSL activation and exacerbate obesity compared to WT. Thus, HSL regulation by MIF may be an important molecular mechanism in the development of obesity. Disclosure L. Chen: None. Y. Huang: None. L. Li: None. H. Zabihi: None. Y. Qi: None. L. Leng: None. G. Sun: None. R. Bucala: None. D. Qi: None. Funding National Sciences and Engineering Research Council of Canada (RGPIN-2017-04542); Canadian Institutes of Health Research (PJT-156116)