Adipocyte Overexpression of p55alpha Subunit of Pi3k Improves Systemic Glucose Metabolism in Lean Mice

Phosphatidylinositol 3-kinase (PI3K), a heterodimeric enzyme composed of a regulatory subunit (p85α/β, p55α/γ, p50α) and a catalytic subunit (p110α/β), is an essential component of the canonical insulin signaling cascade in adipose tissue. Insulin-stimulated PI3K activity is decreased in obese adipose tissue in parallel with a 4-fold increase in p55α abundance; heterozygous deletion of Pik3r1 limits regulatory subunit expression and enhances adipocyte insulin signaling. Additionally, genetic deletion of p55α/p50α in mice has been shown to increase adipocyte glucose uptake and systemic insulin sensitivity. Therefore, we hypothesized that adipocyte-specific p55α overexpression (OX) would reduce adipocyte insulin signaling and decrease systemic glucose tolerance. To test this hypothesis, we generated mice with p55α knock-in at the endogenous ROSA26 locus. The recombination cassette was made by flanking the p55α cDNA and a floxed 4x SV40 polyA STOP signal with FRT and F3. The insertion of Pik3r1 at the ROSA26 locus mediated by Flp-recombinase in ES cells targeted with FRT-PGK-neo-F3 at the ROSA26 locus. The polyA STOP signal was removed by crossing the p55α flox (Fl/Fl) mice with mice carrying Adipoq-cre recombinase (OX). At 12 weeks of age, the metabolic phenotype, glucose tolerance and adipocyte insulin signaling were measured in Fl/FL and OX mice. In adipose tissue, p55α abundance was 7-fold higher in OX compared to FL/FL controls with no difference detected in p85α abundance. Body weight and adiposity was not different between FL/FL and OX mice. Food intake, energy expenditure and the respiratory quotient were not different in OX vs. FL/FL, despite a decrease in total activity in OX mice. Contrary to our hypothesis, glucose AUC calculated from oral glucose tolerance tests was 40% lower (P=0.005) in OX vs. FL/FL. Overall these data suggest that increased expression of the p55α regulatorysubunit, in contrast to p85α, enhances PI3K activity and insulin signaling in adipocytes.