Insulin receptor turnover in fasting is dependent on NAGLU-mediated beta-dystroglycan deglycosylation
Fasting exerts various physiological effects, most notably, reduced signaling through the insulin receptor. We showed that insulin receptor activity requires association with Dystrophin Glycoprotein Complex (DGC). Here, we demonstrate that insulin receptor turnover by lysosomes during fasting is dependent on deglycosylation of the principal DGC component, {beta}-dystroglycan. We show that the lysosomal enzymes HexA and Man2b1, which specifically remove N-linked glycans, mediate {beta}-dystroglycan deglycosylation and consequently insulin receptor-DGC loss. Surprisingly, the lysosomal enzyme NAGLU, which cannot process N-linked glycosylation, also facilitated {beta}-dystroglycan deglycosylation and insulin receptor loss. NAGLU enhances the activity of the transcriptional complex PPAR-{gamma}/RXR-, which in turn promotes Man2b1 and HexA induction and the resulting {beta}-dystroglycan deglycosylation. Accordingly, downregulation of HexA, Man2b1, NAGLU or RXR- during fasting blocked {beta}-dystroglycan deglycosylation, and caused accumulation of insulin receptor-DGC assemblies on the membrane. Thus, NAGLU mediates physiological adaptation to fasting by promoting indirectly {beta}-dystroglycan deglycosylation.