RT Journal Article
SR Electronic
T1 Modulation of muscle cell <em>Insr</em> and insulin receptor signaling by hyperinsulinemia <em>in vitro</em> and <em>in vivo</em>
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 556571
DO 10.1101/556571
A1 Haoning Howard Cen
A1 José Diego Botezelli
A1 Su Wang
A1 James D. Johnson
YR 2019
UL http://biorxiv.org/content/early/2019/08/26/556571.abstract
AB Hyperinsulinemia is often viewed as a compensatory mechanism for insulin resistance, but studies have shown that high levels of insulin may also contribute to insulin resistance. The precise mechanisms by which hyperinsulinemia contributes to insulin resistance remain poorly defined. To understand the direct effects of prolonged exposure to excess insulin in muscle cells, we incubated differentiated C2C12 mouse myotubes with elevated insulin for 16 hours, followed by a 6-hour period of serum starvation, before examining key insulin signaling nodes. Using our model, we found that prolonged high insulin treatment significantly increased the phosphorylation of insulin receptor (INSR) and AKT, but not ERK. After serum starvation, acute AKT and ERK signaling stimulated by 0.2 - 20 nM insulin were attenuated. INSR protein levels were significantly downregulated by hyperinsulinemia in an insulin-dose-dependent manner, which resulted in the comparative reduction of acute insulin signaling. Surface INSR was also reduced proportionally to total INSR levels. Mechanistically, we found that both isoforms of Insr mRNA were reduced by hyperinsulinemia and implicated the transcription factor FOXO1. Interestingly, 6h serum starvation reversed the effects of high insulin on basal phosphorylation of INSR, AKT and FOXO1, and Insr transcription. Finally, we validated our results in vivo by determining that INSR levels in mouse skeletal muscle were negatively correlated with circulating insulin. Together, our findings shed light on the mechanisms underlying hyperinsulinemia-induced insulin resistance in muscle cells, which are likely to be relevant in the pathogenesis of type 2 diabetes.