RESUMEN
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.
Asunto(s)
Calcineurina/metabolismo , Señalización del Calcio/fisiología , Calcio/metabolismo , Glucosa/metabolismo , Insulina/metabolismo , Proteínas de la Membrana/metabolismo , Músculo Esquelético/metabolismo , Proteínas Proto-Oncogénicas c-akt/metabolismo , Animales , Calcineurina/genética , Glucosa/genética , Transportador de Glucosa de Tipo 4/genética , Transportador de Glucosa de Tipo 4/metabolismo , Insulina/genética , Proteínas de la Membrana/genética , Ratones , Ratones Noqueados , Proteínas Proto-Oncogénicas c-akt/genéticaRESUMEN
Cardiac hypertrophy is an adaptive response triggered by pathological stimuli. Regulation of the synthesis and the degradation of the Ca2+ channel inositol 1,4,5-trisphosphate receptor (IP3R) affects progression to cardiac hypertrophy. Herpud1, a component of the endoplasmic reticulum-associated degradation (ERAD) complex, participates in IP3R1 degradation and Ca2+ signaling, but the cardiac function of Herpud1 remains unknown. We hypothesize that Herpud1 acts as a negative regulator of cardiac hypertrophy by regulating IP3R protein levels. Our results show that Herpud1-knockout mice exhibit cardiac hypertrophy and dysfunction and that decreased Herpud1 protein levels lead to elevated levels of hypertrophic markers in cultured rat cardiomyocytes. In addition, IP3R levels were elevated both in Herpud1-knockout mice and Herpud1 siRNA-treated rat cardiomyocytes. The latter treatment also led to elevated cytosolic and nuclear Ca2+ levels. In summary, the absence of Herpud1 generates a pathological hypertrophic phenotype by regulating IP3R protein levels. Herpud1 is a novel negative regulator of pathological cardiac hypertrophy.