Mouse Models of Insulin Resistance

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ABSTRACT Insulin resistance stands as a significant threat to public health worldwide, and a largely unmet medical need. To unravel the complex biology of this protean syndrome, we endeavored to apply genetic techniques to probe gene function and tissue interactions related to metabolism, and identify tractable targets for pharmacological intervention in type 2 diabetes. Over the ten years of the MERIT award, notable contributions of this grant to our knowledge of the insulin resistance syndrome have included: (i) mapping the tissue-specific contributions of insulin resistance to the onset and progression of diabetes; (ii) identification and molecular characterization of distinct cell types in the central nervous system that mediate different effects of insulin and counterregulatory hormones on plasma glucose levels, satiety, and energy balance; (iii) discovery and molecular characterization of Gpr17, an orphan receptor that mediates the anorexigenic effects of insulin in the hypothalamus; (iv) demonstration of the remarkable property of enteroendocrine cells to undergo conversion into glucose-responsive insulin-producing cells in experimental animals as well as human organoid cultures. Building on this foundation, the focus of this renewal application is to understand the divergence of insulin signaling pathways regulating hepatic glucose and lipid production, while bringing to the fore FoxO-independent mechanisms of transcriptional regulation by insulin. To that end, the PI presents preliminary data identifying a broad set of hormone- responsive hepatic transcription factors, and outlines two aims to characterize their contribution to insulin resistance. Aim 1 will delve into the role of transcription factors FoxK1 and FoxK2 in mediating the paradoxical admixture of increased glucose production and triglyceride synthesis that characterizes the diabetic liver. Specifically, experiments will test whether differential phosphorylation at Akt and mTOR sites on these proteins affects their transcriptional output. Aim 2 will analyze the contribution of the high mobility group transcription factor TOX4 to gluconeogenesis and de novo triglyceride synthesis. In both aims, extensive epistasis with existing models of insulin resistance will be employed to answer the question of whether the newly identified factors are independent of or overlapping with known insulin signaling modalities. The proposed body of work will advance our understanding of the insulin-resistant syndrome at the biochemical, genetic, and integrated physiological levels, with the ultimate goal of translating newly acquired information into innovative approaches to treatment.