Inducible heterozygous knockout of Pik3r1 in adipocytes reverses glucose intolerance and enhances adipocyte insulin signaling in obese mice

Abstract

Insulin resistance is a central and defining feature of the metabolic diseases associated with obesity. 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 conical insulin signaling cascade in adipose tissue. PI3K activity is decreased in obese adipose tissue (AT); however, a global heterozygous (HZ) deletion of Pik3r1 (encodes p85/p55/050α) prevents the decrease in insulin‐stimulated PI3K activity, and reduces AT inflammation and systemic insulin resistance relative to obese control mice. Therefore, we hypothesized that adipocyte‐specific deletion of Pik3r1 in already obese mice would reverse obesity‐induced systemic insulin resistance by increasing insulin signaling downstream of PI3K in adipocytes. Inducible adipocyte‐specific Pik3r1 heterozygous (HZ) or homozygous (KO) knockout mice were generated by crossing Pik3r1 flox mice (LoxP sites flanking exon7 of the Pik3r1 gene) with Adipoq‐CreERT2 mice, which utilize tamoxifen‐dependent recombination. Pik3r1 flox/flox (FL/FL) mice were used as controls. At 8 weeks of age, mice were fed a high‐fat diet (HFD; 45% fat) or sucrose‐matched control diet (10% fat) for 10 weeks. At week 11, tamoxifen was delivered by oral gavage (100μL of 10 mg/mL) for 5 days and allowed to recover for 1 week) glucose tolerance was measured before and 1–2 weeks post tamoxifen. Total activity, energy expenditure and respiratory exchange ratio (RER) were collected for 3 days following one‐week acclimation and recovery. Isolated adipocytes from lean and obese mice were stimulated +/− 1.2nM insulin and signaling proteins were measured by immunoassay. There were differences in body weight, body composition before or after gene knockout with tamoxifen in HFD vs. CON, for WT, HZ and KO. Total activity (WT: 90±6; HZ: 115±12; KO: 106±10), energy expenditure (WT: 143±11; HZ: 122±12; KO: 134±12), and RER (WT: 0.73±0.001; HZ: 0.775±0.03; KO: 0.81±0.024) were not different for WT, HZ, and KO during HFD. Glucose AUC calculated from oral glucose tolerance test was significantly higher in all groups with HFD vs. CON. We find that after tamoxifen dosing, glucose (g) AUC was reduced by 59% in obese HZ mice as compared to pre‐tamoxifen levels. No changes in gAUC were found in obese WT or KO. Insulin‐stimulated AKT(S473) phosphorylation was decreased by 41% and 63% in adipocytes from obese WT and KO, respectively, compared to lean; however, only 17% in obese HZ. Taken together, these data show that adipocyte Pik3r1 plays a critical role in mediating systemic glucose metabolism and that novel treatments that target Pik3r1expression may be successful in improving insulin sensitivity in individuals with obesity.Support or Funding InformationSupported by Eugene & Clarissa Evonuk Memorial Fellowship, University of Oregon Graduate Student Food Studies Grant (Z.S.C) and National Institute of Diabetes Digestive and Kidney Diseases under Award Number RO1DK095926 (C.E.M)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.