VDR regulates energy metabolism by modulating remodeling in adipose tissue

Vitamin D receptor (VDR) plays an important role in regulating energy metabolism. Adipose tissue is a vital metabolic organ in energy balance and glucose homeostasis. In this study, we investigated the role of VDR expressed on adipose tissue in the balance of energy metabolism. This study was conducted in VDR-KO mice, VDR-Tg mice and wild-type mice. Energy metabolism was determined based on the energy expenditure, oxygen consumption, respiratory exchange rate, food and water intake, and a cool room test. VDR expression in the tissues of VDR-Tg mice was assessed by western blotting. The levels of total cholesterol, triglycerides, free fatty acids, leptin, and glucose were assessed using the respective kits. Insulin resistance in the whole body was evaluated by an intraperitoneal glucose tolerance test and insulin tolerance test. mRNA associated with energy metabolism expression in adipose and skeletal muscle tissue was examined by RT-PCR. Our results show that overexpression of VDR in adipose tissue induced an increase in body weight, fat mass, and serum lipid levels, and a decline in energy metabolism; these changes were ameliorated by VDR-KO mice. Overexpression of VDR in the adipose tissue of VDR-Tg mice induced a state of insulin resistance, which corresponded with decreased expression of UCP1, UCP2, UCP3, CPT2 and HK in both white adipose tissue and brown adipose tissue; these changes were also reversed by VDR-KO mice. Our study confirms that expression levels of VDR in adipose tissue play pivotal roles in energy balance and glycolipid metabolism by regulating adipose tissue remodeling.