Role of Adipocyte P2Y2 Receptor in Adipogenesis and Insulin Resistance
Type of DegreePhD Dissertation
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Objective -- It has been known that obesity and type 2 diabetes are associated with inflammation and insulin resistance and that adipose tissue contributes to insulin sensitivity and glucose homeostasis. Also, it was reported that the P2Y2 receptor (P2Y2R) plays a significant role in diet-induced obesity and facilitates high fat diet-induced insulin resistance in the global P2Y2R knockout mouse model. however, the exact mechanism(s) of insulin resistance in adipose tissue remains incompletely understood. We hypothesize that inflammation promotes adipocyte P2Y2R upregulation which leads to insulin resistance by inhibiting the insulin-AKT signaling pathway. This study aimed to identify candidate treatment targets in obesity and diabetes associated with chronic inflammation and insulin resistance to control disease progression and reduce the risk of severe complications. Method and Results -- Real-time RT-PCR revealed that the P2Y2R mRNA was significantly upregulated during human visceral pre-adipocytes differentiation into mature adipocytes in vitro. Stimulation of the mature adipocytes by tumor necrosis factor α (TNFα) further increased P2Y2R mRNA expression. Functional P2Y2R upregulation was confirmed by intracellular Ca2+ mobilization assay in response to adenosine triphosphate (ATP) or uridine triphosphate (UTP) stimulation in mature human visceral adipocytes. In addition, stimulation of the P2Y2R by ATP or UTP suppressed basal and insulin-induced phosphorylation of AKT in a dose-dependent manner in mature adipocytes. These effects were significantly diminished by AR-C118925, a selective P2Y2R antagonist, suggesting a role of P2Y2R in insulin receptor signaling. Furthermore, we found that activation of the P2Y2R inhibited insulin-induced PIP3 production, glucose uptake, and glucose transporter 4 (GLUT4) membrane localization in mature adipocytes through functional assays. Conclusion -- The P2Y2R is upregulated during adipocyte differentiation and inflammation, and P2Y2R activation leads to insulin resistance by suppressing the AKT signaling pathway, reducing insulin-induced glucose uptake, downregulating PIP3 and GLUT4 translocation, highlighting P2Y2R being a potential new drug target to combat obesity and type 2 diabetes.