Introduction: Excess intake of high-fat (HFD) and high-fructose (HFrD) diets is strongly associated with impaired hepatic insulin signaling and disrupted glucose homeostasis. Activation of PKCε by diet-induced diacylglycerol (DAG) accumulation has been proposed to mediate inhibitory phosphorylation of the insulin receptor, promoting hepatic insulin resistance. Because this DAG–PKCε mechanism is also implicated in human metabolic disorders such as type 2 diabetes and fatty liver disease, understanding how PKCε shapes early hepatic responses to nutrient overload has important translational significance. Early diet-induced impairments in insulin signaling may represent a reversible phase of metabolic dysfunction, making this pathway a potential therapeutic target. However, the early molecular consequences of liver-specific PKCε reduction remain unclear. We previously reported that heterozygous liver PKCε deletion (LivPKCεfl/Δ) improves glucose tolerance in a sex-dependent manner after one month of HFD or HFrD feeding. Here, we sought to determine whether these whole-body improvements correspond to preserved hepatic insulin signaling at the molecular level. Methods: LivPKCεfl/Δ mice and littermate controls were placed on three diets: Control (Cntrl, Research Diets Inc., RDI D12450J), High Fructose (HFrD, RDI D02022704), and High Fat (HFD, RDI D12492). After 4 weeks, mice were sacrificed under basal conditions or 10 minutes after intraperitoneal insulin administration (0.25 IU). Liver lysates were analyzed by Western blot to assess insulin-signaling intermediates, including p-AKT, total AKT, p-FoxO1, FoxO1, and Actin as a loading control. Results: Insulin signaling responses displayed macronutrient-specific patterns. In Cntrl and HFrD groups, insulin robustly increased p-AKT, indicating preserved proximal hepatic insulin signaling in LivPKCεfl/Δ mice. In contrast, HFD-fed LivPKCεfl/Δ mice showed elevated basal p-AKT with only a minimal insulin-stimulated increase, consistent with early hepatic insulin resistance despite improved systemic glucose tolerance. p-FoxO1 increased after insulin across all diets, though the response was attenuated in HFD-fed mice, suggesting partial downstream impairment of AKT–FoxO1 signaling. Conclusion: Collectively, these findings indicate that liver-specific PKCε reduction preserves molecular insulin signaling under short-term HFrD exposure but is insufficient to fully prevent early HFD-induced hepatic insulin resistance. These results support a model in which PKCε is necessary for initiating lipid-driven insulin resistance, while prolonged nutrient excess activates additional pathways that impair hepatic insulin signaling independently of PKCε. By identifying nutrient-specific vulnerabilities in hepatic insulin signaling, this work provides mechanistic insight that may guide early intervention strategies for obesity-associated metabolic disease. Ongoing studies using homozygous knockouts (LivPKCεΔ/Δ) and phosphoproteomic profiling will further define how PKCε integrates diet-specific signals to regulate hepatic metabolic adaptation. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
Rahman et al. (Fri,) studied this question.