Genetic Targets of Hypertension End Organ Damage

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Project Summary Chronic kidney disease (CKD) is seen in all age groups, impacts more than 30 million people, and is associated with significant medical care costs in the United States. A critical barrier exists in understanding genetic factors that predispose people to hypertensive CKD as well as a lack of therapeutics that act to delay onset and/or progression of kidney dysfunction. The Dahl salt-sensitive (SS) rat is a widely studied model of hypertension that develops kidney injury and progressive decline in kidney function. Through positional cloning, Arhgef11, a Rho guanine nucleotide exchange factor, was implicated in kidney injury exhibited by the SS rat. ARHGEF11 catalyzes the exchange of GDP for GTP, thereby activating RhoA. RhoA-GTP then plays a pivotal role in several pathways that regulate a number of cell functions, including actin cytoskeletal organization, cell adhesion, cell motility, and gene expression. The study of an SS-Arhgef11-congenic model, which substitutes the S allele with that of the SHR (reduced expression/activity), demonstrated significantly decreased proteinuria, tubulointerstitial injury/fibrosis, and improved renal hemodynamics compared to the SS rat. The study of SS rat primary proximal tubules cells demonstrated increased expression of Arhgef11, activation of Rho-ROCK, and decreased uptake of FITC-albumin compared to the SS-Arhgef11-congenic. Conversely, knockdown of Arhgef11 in cell-lines resulted in reduced RhoA activity, decreased activation of Rho-ROCK pathway and less stress fiber formation versus control upon stimulation with TGFβ1 (profibrotic cytokine). In total, the animal and in vitro studies suggest that chronic activation of RhoA pathways by ARHGEF11 could have a significant impact on kidney injury. Thus, our central hypothesis is that allelic variants in Arhgef11 exhibited by the SS rat results in chronic dysregulation of Rho pathways, changes in proximal tubule cell morphology and function, and culminates in kidney injury and decline in kidney function. The specific aims of the proposal are to: (1) investigate the role of Arhgef11 in renal injury, renal hemodynamics, and blood pressure using animal models that augment the expression or knockout Arhgef11 (SS- Arhgef11-/-); (2) study the involvement of Arhgef11 in proximal tubule cells using primary cells and genetically modified cell- lines; and (3) investigate the role of specific Arhgef11 genetic variants/haplotypes (in rat and humans) responsible for altered expression/protein function and subsequent activation of Rho-ROCK. In summary, the successful completion of the proposed project will lead to a better understanding of the role of genetics in hypertensive CKD, the influence of factors that complicate kidney disease, and potential new therapeutic targets.