Peroxisome Proliferator-activated Receptor γ Regulates Expression of the Anti-lipolytic G-protein-coupled Receptor 81 (GPR81/Gpr81)

Abstract

The ligand-inducible nuclear receptor peroxisome proliferator-activated receptor ␥ (PPAR␥) plays a key role in the differentiation, maintenance, and function of adipocytes and is the molecular target for the insulin-sensitizing thiazoledinediones (TZDs). Although a number of PPAR␥ target genes that may contribute to the reduction of circulating free fatty acids after TZD treatment have been identified, the relevant PPAR␥ target genes that may exert the anti-lipolytic effect of TZDs are unknown. Here we identified the anti-lipolytic human G-protein-coupled receptor 81 (GPR81), GPR109A, and the (humanspecific) GPR109B genes as well as the mouse Gpr81 and Gpr109A genes as novel TZD-induced genes in mature adipocytes. GPR81/Gpr81 is a direct PPAR␥ target gene, because mRNA expression of GPR81/Gpr81 (and GPR109A/Gpr109A) increased in mature human and murine adipocytes as well as in vivo in epididymal fat pads of mice upon rosiglitazone stimulation, whereas small interfering RNA-mediated knockdown of PPAR␥ in differentiated 3T3-L1 adipocytes showed a significant decrease in Gpr81 protein expression. In addition, chromatin immunoprecipitation sequencing analysis in differentiated 3T3-L1 cells revealed a conserved PPAR:retinoid X receptorbinding site in the proximal promoter of the Gpr81 gene, which was proven to be functional by electromobility shift assay and reporter assays. Importantly, small interfering RNA-mediated knockdown of Gpr81 partly reversed the inhibitory effect of TZDs on lipolysis in 3T3-L1 adipocytes. The coordinated PPAR␥-mediated regulation of the GPR81/Gpr81 and GPR109A/Gpr109A genes (and GPR109B in humans) presents a novel mechanism by which TZDs may reduce circulating free fatty acid levels and perhaps ameliorate insulin resistance in obese patients.Because of a high calorie diet and a sedentary lifestyle, obesity and its associated co-morbidities like hypertension, type II diabetes, and atherosclerosis rapidly increase worldwide (1). Adipose tissue is the major site of lipid storage in the body and plays a pivotal role in the regulation of whole body metabolic homeostasis and therefore in the pathophysiology of obesity (2). After a meal, excess fuel substrates are partitioned to adipose tissue where they are processed and stored as triglycerides (TAG).2 Conversely, during fasting TAGs are hydrolyzed to free fatty acids (FFA) and glycerol, and the FFA released into the bloodstream can subsequently be used by other organs as energy substrates. The latter process, termed lipolysis, is tightly regulated by hormones and cytokines (3). The three main hormones that regulate lipolysis in humans are insulin, which inhibits lipolysis, and catecholamines (adrenaline and noradrenaline) and glucagon, which stimulate lipolysis. In rodents, inhibition of lipolysis by adenosine presents an additional regulatory pathway. Lipolysis is deregulated in obesity; basal lipolysis rates are increased (4), whereas the stimulation of lipolysis by catecholamines (5) as well as the anti-lipolytic action of insulin (6) are in...

International Union of Basic and Clinical Pharmacology. LXXXII: Nomenclature and Classification of Hydroxy-carboxylic Acid Receptors (GPR81, GPR109A, and GPR109B)

“…However, this has never been confirmed. Meanwhile, evidence has been provided that the receptor is primarily expressed in adipocytes (Wise et al, 2003;Ge et al, 2008;Jeninga et al, 2009;Liu et al, 2009;Ahmed et al, 2010). In humans, the HCA 1 receptor was found to be most abundantly expressed in brown adipose tissue with also rather high expression in white adipose tissue .…”

A Multiplex Immunoassay for Human Adipokine Profiling

“…Culturing and differentiation of the human SimpsonGolabi Behmel syndrome (SGBS) preadipocyte cell line was performed as described (16,17 ). On day 8 of differentiation, medium was conditioned for 24 h, aliquoted, and stored at Ϫ80°C.…”

Natural killer T cells in adipose tissue prevent insulin resistance

“…The human preadipocyte SGBS cell line was cultured and differentiated into adipocytes as described previously (46,71). Full-length cDNA encoding human CD1d was cloned into a pLenti CMV vector (Addgene).…”