Herpudl impacts insulin-dependent glucose uptake in skeletal muscle cells by controlling the Ca2+-calcineurin-Akt axis

Abstract

Skeletal muscle plays a central role in insulin-controlled glucose homeostasis. The molecular mechanisms related to insulin resistance in this tissue are incompletely understood. Herpud1 is an endoplasmic reticulum membrane protein that maintains intracellular Cat homeostasis under stress conditions. It has recently been reported that Herpudl-knockout mice display intolerance to a glucose load without showing altered insulin secretion. The functions of Herpud1 in skeletal muscle also remain unknown. Based on these findings, we propose that Herpud1 is necessary for insulin-dependent glucose disposal in skeletal muscle. Here we show that Herpudl silencing decreased insulin-dependent glucose uptake, GLUT4 translocation to the plasma membrane, and Akt Ser(473) phosphorylation in cultured L6 myotubes. A decrease in insulin-induced Akt Ser(473) phosphorylation was observed in soleus but not in extensor digitorum longus muscle samples from Herpudl-knockout mice. Herpudl knockdown increased the IP3R-dependent cytosolic Cat response and the activity of Ca2+-dependent serine/threonine phosphatase calcineurin in L6 cells. Calcineurin decreased insulin-dependent Akt phosphorylation and glucose uptake. Moreover, calcineurin inhibition restored the insulin response in Herpudl-depleted L6 cells. Based on these findings, we conclude that Herpudl is necessary for adequate insulin-induced glucose uptake due to its role in Ca2+/calcineurin regulation in L6 myotubes.