Skeletal Muscle PI3K p110β Regulates Expression of AMP-Activated Protein Kinase

Presentation Number: SUN 253
Date of Presentation: April 2nd, 2017

Ronald Wayne Matheny Jr.*, Mary N Abdalla, Alyssa V Geddis, Luis Angel Leandry and Christine Marie Lynch
US Army Research Institute of Environmental Medicine, Natick, MA

Abstract

Metabolic homeostasis in skeletal muscle is maintained through the balanced integration of numerous biochemical, genetic, and cell-signaling processes. Two principal molecular regulators of skeletal muscle metabolism include AMP-activated protein kinase (AMPK) and phosphatidylinositol 3-kinase (PI3K); however, PI3K exists as multiple isoforms, and specific metabolic actions of each isoform have not yet been fully elucidated in skeletal muscle. For example, while PI3K p110α has been shown to regulate phosphorylation of AMPK in myoblasts, little is known regarding the role of PI3K p110β in regulating AMPK in skeletal muscle. Given this lack of knowledge, we performed a series of experiments to define the extent to which PI3K p110β mediated expression and (or) activation of AMPK in skeletal muscle. To determine the effect of p110β inhibition on AMPK expression and phosphorylation in cultured cells, C2C12 myoblasts were treated with a pharmacological inhibitor of p110β (TGX-221), siRNA against p110β, or overexpression of kinase-dead p110β. Compared to control myoblasts, expression and phosphorylation of AMPK were not affected in myoblasts treated with TGX-221 or expressing kinase-inactive p110β; however, in myoblasts treated with siRNA against p110β, expressions of total and phosphorylated AMPK at T172 were significantly reduced (52% less total AMPK (P<0.05) and 43% less phosphorylated AMPK, (P<0.001)). When normalized to expression of total AMPK, phosphorylation of AMPK at S485/491 was increased by 2.5-fold in p110β-deficient myoblasts (P<0.05). Similar results were observed in tibialis anterior muscle of mice with conditional deletion of p110β in skeletal muscle (p110β-mKO mice). Analysis of AMPK transcript expression revealed decreased expression of Prkaa2in p110β-deficient myoblasts (19% decrease; P<0.05) and in p110β-mKO mouse tibialis anterior muscle (9% decrease, P<0.001). In C2C12 myoblasts, loss of p110β had no effect on the absolute abundance of phosphorylated AMPK or phosphorylated acetyl-CoA carboxylase (ACC) in response to oligomycin, although oligomycin-induced AMPK and ACC phosphorylation were significantly higher in p110β-deficient myoblasts than in control myoblasts when normalized to levels of total AMPK or total ACC (~3-fold increase for AMPK T172; P<0.001; ~4-fold increase for AMPK S485/491; P<0.001; and ~2-fold for ACC S79; P<0.05). All together, these findings suggest that p110β positively regulates expression of AMPK in cultured myoblasts and in skeletal muscle in vivo through a mechanism independent of its catalytic activity. Moreover, despite the reduced abundance of AMPK in p110β-deficient myoblasts, loss of p110β does not appear to impair AMPK activation following stimulus.

 

Nothing to Disclose: RWM Jr., MNA, AVG, LAL, CML