1510-P: Lipid-Induced Renal Cortical Insulin Resistance Perturbs Gluconeogenic and Oxidative Metabolism via an sn-1,2-diacylglycerol-PKCe-Insulin Receptor Kinase Axis In Vivo

Recently, our group demonstrated that 3-week high fat diet feeding (HFD) impairs insulin signaling in the renal cortex at the level of the insulin receptor kinase (IRK). Specifically, IRK^Y1162 and AKT^S473 phosphorylation were reduced by ~50% during hyperinsulinemic-euglycemic clamp (HEC); however, it is unknown how renal cortical insulin resistance (IR) may affect gluconeogenic (GNG) and oxidative metabolism. To address this, here we measure renal cortical GNG fluxes in vivo using Q-Flux. In regular chow (RC) fed mice, hyperinsulinemia significantly suppressed mitochondrial pyruvate carboxylase (PC), as PC flux relative to α-ketoglutarate dehydrogenase flux (V_PC/V_OGDH) was 1.25 under basal conditions, but decreased by ~50%, to 0.57 during HEC. Similarly, PEPCK flux relative OGDH flux (V_PEPCK/V_OGDH) was reduced by ~60% during HEC. In contrast, insulin failed to suppress both PC and PEPCK fluxes with HFD. Using a [¹³C₆]glucose tracer, we also find insulin-stimulated mitochondrial pyruvate oxidation to be impaired by ~30% with HFD. Mechanistically, we previously found HFD led to a 2-fold increase in plasma membrane (PM) sn-1,2-diacylglycerol (DAG) and a 4-fold increase in Protein Kinase Cε (PKCε) translocation, suggesting renal cortical IR may be mediated by an sn-1,2-DAG-PKCε-IRK axis. We further interrogated this possibility here by assessing inhibitory phosphorylation at IRK^T1150, the key target of PKCε, finding a 42% increase with HFD. In addition, IRK^T1150A knockin mice, whose IRK cannot be phosphorylated by PKCε, were protected from HFD-induced signaling and pyruvate oxidation defects.

Conclusion: HFD inhibits renal cortical insulin signaling at the level of the IRK, which is associated with perturbed mitochondrial GNG and oxidative metabolism. IRK^T1150A mice are protected from HFD-induced defects, indicating a PM sn-1,2-DAG-PKCε-pIRK^T1150 mechanism for lipid-induced renal cortical IR.