The metabolic ER stress sensor IRE1α suppresses alternative activation of macrophages and impairs energy expenditure in obesity

Obesity is associated with metabolic inflammation and endoplasmic reticulum (ER) stress, both of which promote metabolic disease progression. Adipose tissue macrophages (ATMs) are key players orchestrating metabolic inflammation, and ER stress enhances macrophage activation. However, whether ER stress pathways underlie ATM regulation of energy homeostasis remains unclear. Here, we identified inositol-requiring enzyme 1 alpha (IRE1 alpha) as a critical switch governing M1-M2 macrophage polarization and energy balance. Myeloid-specific IRE1 alpha abrogation in Ern1(f/f); Lyz2-Cre mice largely reversed high-fat diet (HFD)-induced M1-M2 imbalance in white adipose tissue (WAT) and blocked HFD-induced obesity, insulin resistance, hyperlipidemia and hepatic steatosis. Brown adipose tissue (BAT) activity, WAT browning and energy expenditure were significantly higher in Ern1(f/f); Lyz2-Cre mice. Furthermore, IRE1 alpha ablation augmented M2 polarization of macrophages in a cell-autonomous manner. Thus, IRE1 alpha senses protein unfolding and metabolic and immunological states, and consequently guides ATM polarization. The macrophage IRE1 alpha pathway drives obesity and metabolic syndrome through impairing BAT activity and WAT browning.