Molecular Mechanisms of Distal Sodium Transport in Insulin Resistance

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DESCRIPTION (provided by applicant): Insulin resistance affects more than 50% of all hypertensive subjects and worsens their risk for cardiovascular disease. This syndrome is characterized by salt-sensitive hypertension due to increased sodium reabsorption in the distal nephron of the kidney. Currently there is no targeted therapy for this group of patients. Diuretics would counteract the natriferric effects of insulin resistance, but these agents adversely affect carbohydrate and lipid metabolism which may mitigate their benefit for hypertension. Discerning the molecular mechanisms which cause hypertension would highlight novel therapeutic targets for this syndrome. Several causes of this elevated blood pressure include compensatory hyperinsulinemia which may increase sodium transport despite peripheral insulin resistance, insulin-like growth factor-1 (IGF-1), which has also been demonstrated to increase sodium reabsorption in vivo, or perhaps altered intracellular signaling intermediates independent of insulin or IGF-1. Recent evidence suggests that the epithelial sodium channel (ENaC) which resides in the collecting duct may be responsible for enhanced distal sodium transport in insulin resistance. The Small Grant Award (NIH R03) will provide to the principal investigator (PI) the necessary resources to directly test the hypotheses that insulin resistance-associated hypertension is due to increased ENaC activity due to: (1) hyperinsulinemia, (2) IGF-1, or (3) altered post-insulin or post-IGF-1 receptor signaling within the distal nephron. The PI will isolate collecting duct (CD) cells from insulin-resistant vs. control mice and investigate the dose and time-dependent effects of insulin, IGF-1, or vehicle on receptor activation. Additionally, the PI will apply standard biochemistry and RNA interference techniques to elucidate the molecular pathways which regulate sodium transport in insulin, IGF-1, or vehicle-treated primary culture cells. Using two dietary and one genetic model of insulin resistance, will allow for broader, more clinically applicable conclusions to the data. The PI previously spent three years on the K08 studying the regulation of ENaC trafficking and for the final two years of the award will pursue related questions on sodium transport in pathophysiology. The proposed experiments are feasible and will lay the groundwork for generation of an independent R01-funded research program distinct from the primary mentor. PROJECT NARRATIVE As the incidence of insulin resistance increases in the general population, so will the incidence of hypertension and cardiovascular disease. By comparing sodium transport in kidney cells from mice with and without insulin resistance, we can learn more about how insulin resistance causes salt-sensitive hypertension and how to design specific therapies for this subset of individuals.