Herpud1 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 Ca²⁺ homeostasis under stress conditions. It has recently been reported that Herpud1-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 Herpud1 silencing decreased insulin-dependent glucose uptake, GLUT4 translocation to the plasma membrane, and Akt Ser⁴⁷³ phosphorylation in cultured L6 myotubes. A decrease in insulin-induced Akt Ser⁴⁷³ phosphorylation was observed in soleus but not in extensor digitorum longus muscle samples from Herpud1-knockout mice. Herpud1 knockdown increased the IP₃R-dependent cytosolic Ca²⁺ 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 Herpud1-depleted L6 cells. Based on these findings, we conclude that Herpud1 is necessary for adequate insulin-induced glucose uptake due to its role in Ca²⁺/calcineurin regulation in L6 myotubes.

Keywords: Akt; Calcineurin; Calcium; Herpud1; Insulin; Skeletal muscle.