Metabolic modeling of muscle metabolism identifies key reactions linked to insulin resistance phenotypes

ObjectiveDysregulated muscle metabolism is a cardinal feature of human insulin resistance (IR) and associated diseases, including type 2 diabetes (T2D). However, specific reactions contributing to abnormal energetics and metabolic inflexibility in IR are unknown.MethodsWe utilize flux balance computational modeling to develop the first systems-level analysis of IR metabolism in fasted and fed states, and varying nutrient conditions. We systematically perturb the metabolic network to identify reactions that reproduce key features of IR-linked metabolism.ResultsWhile reduced glucose uptake is a major hallmark of IR, model-based reductions in either extracellular glucose availability or uptake do not alter metabolic flexibility, and thus are not sufficient to fully recapitulate IR-linked metabolism. Moreover, experimentally-reduced flux through single reactions does not reproduce key features of IR-linked metabolism. However, dual knockdowns of pyruvate dehydrogenase (PDH), in combination with reduced lipid uptake or lipid/amino acid oxidation (ETFDH), does reduce ATP synthesis, TCA cycle flux, and metabolic flexibility. Experimental validation demonstrates robust impact of dual knockdowns in PDH/ETFDH on cellular energetics and TCA cycle flux in cultured myocytes. Parallel analysis of transcriptomic and metabolomics data in humans with IR and T2D demonstrates downregulation of PDH subunits and upregulation of its inhibitory kinase PDK4, both of which would be predicted to decrease PDH flux, concordant with the model.ConclusionsOur results indicate that complex interactions between multiple biochemical reactions contribute to metabolic perturbations observed in human IR, and that the PDH complex plays a key role in these metabolic phenotypes.

Schematic of targeted knockdowns that model phenotypes of insulin resistance. Knockdowns (KD; green) of fatty acid transporter (FAT), pyruvate dehydrogenase (PDH), and electron transfer flavoprotein (ETFDH) recapitulated the metabolic phenotypes of insulin resistance (red), defined as reduced ATP + P-Cr synthesis, TCA flux, and metabolic flexibility (RQ). Additional metabolic alterations identified are depicted by orange arrows.Figure optionsDownload as PowerPoint slide