Alpha4 is Critical for Adipocyte Maintenance and Mitochondrial Homeostasis through Regulation of Insulin Signaling. Alpha4 is Critical for Adipocyte Maintenance and Mitochondrial Homeostasis through Regulation of Insulin Signaling

Insulin signaling is mediated via a network of protein phosphorylation. Dysregulation of this network is central to obesity, type 2 diabetes and metabolic syndrome. Here we have investigated the role of phosphatase binding protein Alpha4 (α4) that is essential for the Ser/Thr protein phosphatase PP2A in insulin action/resistance in adipocytes. Unexpectedly, adipocyte-specific inactivation of α4 impairs insulin-induced Akt-mediated Ser/Thr phosphorylation despite a decrease in the PP2A levels. Interestingly, loss of α4 also reduces insulin-induced insulin receptor Tyr phosphorylation. This occurs through decreased association of α4 with Y-box protein 1 (YBX1), resulting in the enhancement of the Tyr phosphatase PTP1B expression. Moreover, adipocyte-specific knockout of α4 results in impaired adipogenesis and altered mitochondrial oxidation leading to increased inflammation, systemic insulin resistance, hepatosteatosis, islet hyperplasia, and impaired thermogenesis. Thus, the α4 /YBX1-mediated pathway of insulin receptor signaling is essential for maintaining insulin sensitivity, normal adipose tissue homeostasis and systemic metabolism. Overall design: iWAT and BAT mRNA profiles of Control and Ai-α4KO mice.