Wu, D.; Eeda, V.; Maria, Z.; Rawal, K.; Herlea-Pana, O.; Babu Undi, R.; Lim, H.-Y.; Wang, W.

Overnutrition engenders the expansion of adipose tissue and the accumulation of immune cells, in particular, macrophages, in the adipose tissue, leading to chronic low-grade inflammation and insulin resistance. In obesity, several proinflammatory subpopulations of adipose tissue macrophages (ATMs) identified hitherto include the conventional \"M1-like\" CD11C-expressing ATM and the newly discovered metabolically activated CD9-expressing ATM; however, the relationship among ATM subpopulations is unclear. The ER stress sensor inositol-requiring enzyme 1 (IRE1) is activated in the adipocytes and immune cells under obesity. It is unknown whether targeting IRE1 is capable of reversing insulin resistance and obesity and modulating the metabolically activated ATMs. We report that pharmacological inhibition of IRE1 RNase significantly ameliorates insulin resistance and glucose intolerance in diet-induced obesity mice. IRE1 inhibition also increases thermogenesis and energy expenditure, and hence protects against high fat diet-induced obesity. Our study shows that the \"M1-like\" CD11c+ ATMs are largely overlapping with but yet non-identical to CD9+ ATMs in obese white adipose tissue. Notably, IRE1 inhibition diminishes the accumulation of obesity-induced metabolically activated ATMs and \"M1-like\" ATMs, resulting in the curtailment of adipose inflammation and ensuing reactivation of thermogenesis, without augmentation of the alternatively activated M2 macrophage population. Our findings suggest the potential of targeting IRE1 for the therapeutic treatment of insulin resistance and obesity.