Adipose tissue plays a central role in regulating whole-body energy and glucose homeostasis through its subtle functions at both organ and systemic levels. On one hand, adipose tissue stores energy in the form of lipid and controls the lipid mobilization and distribution in the body. On the other hand, adipose tissue acts as an endocrine organ and produces numerous bioactive factors such as adipokines that communicate with other organs and modulate a range of metabolic pathways. Moreover, brown and beige adipose tissue burn lipid by dissipating energy in the form of heat to maintain euthermia, and have been considered as a new way to counteract obesity. Therefore, adipose tissue dysfunction plays a prominent role in the development of obesity and its related disorders such as insulin resistance, cardiovascular disease, diabetes, depression and cancer. In this review, we will summarize the recent findings of adipose tissue in the control of metabolism, focusing on its endocrine and thermogenic function.
Liping Luo and Meilian Liu
Xiaofeng Ding, Yan Luo, Xing Zhang, Handong Zheng, Xin Yang, Xuexian Yang and Meilian Liu
Group 2 innate lymphoid cells (ILC2s) in white adipose tissue (WAT) promote WAT browning and assist in preventing the development of obesity. However, how ILC2 in adipose tissue is regulated remains largely unknown. Here, our study shows that ILC2s are present in brown adipose tissue (BAT) as well as subcutaneous and epididymal WAT (sWAT and eWAT). The fractions of ILC2s, natural killer T (NKT) cells and eosinophils in sWAT, eWAT and BAT are significantly decreased by high-fat-diet (HFD) feeding and leptin deficiency-induced obesity. Consistent with this, the adipose expression and circulating levels of IL-33, a key inducing cytokine of ILC2, are significantly downregulated by obesity. Furthermore, administration of IL-33 markedly increases the fraction of ILC2 and eosinophil as well as the expression of UCP1 and tyrosine hydroxylase (TH), a rate-limiting enzyme in catecholamine biosynthesis, in adipose tissue of HFD-fed mice. On the other hand, cold exposure induces the expression levels of IL-33 and UCP1 and the population of ILC2 and eosinophil in sWAT, and these promoting effects of cold stress are reversed by neutralization of IL-33 signaling in vivo. Moreover, the basal and cold-induced IL-33 and ILC2/eosinophil pathways are significantly suppressed by sympathetic denervation via local injection of 6-hydroxydopamine (6-OHDA) in sWAT. Taken together, our data suggest that the ILC2/eosinophil axis in adipose tissue is regulated by sympathetic nervous system and obesity in IL-33-dependent manner, and IL-33-driven ILC2/eosinophil axis is implicated in the development of obesity.