Renal Effects of Aldosterone

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The goal of this work is to determine how aldosterone causes cardiovascular disease, including hypertension and heart failure. Mice in which the mineralocorticoid receptor can be deleted in the kidney only will be used to examine aldosterone's role in signaling. These mice exhibit diminished sodium flux through both the thiazide-sensitive NaCl cotransporter and the epithelial sodium channel. Yet transport via the former is fully normalized when the mice are placed on low potassium diet, indicating that sodium channel stimulation is the major direct effect of aldosterone. The proposed experiments will test whether mineralocorticoid receptors along the second part of the distal convoluted tubule, known as the DCT2, modulate sodium chloride transport, but do so by occupancy with glucocorticoids, rather than by aldosterone. This will be done by comparing effects of deleting the aldosterone synthase gene, which leads to deficient aldosterone production, with the effects of deleting the mineralocorticoid receptor. The activity of the sodium channel will be measured using patch clamp and whole cell recording and the activity of the thiazide-sensitive NaCl cotransporter will be assessed using thiazide testing and phosphor-protein analysis. If channel transport activity is low in the receptor knockout, but not the synthase knockout, this will support the hypothesis. In a second aim, novel mediators of aldosterone signaling will be sought. We will dissect collecting ducts from mice with and without mineralocorticoid receptors, and consuming diets of varied electrolyte content. These collecting ducts will be subjected to RNAseq, to determine transcriptional differences that may underlie aldosterone effects. We will compare the transcripts differentially expressed in high aldosterone states versus those absent in mice with low aldosterone or lacking mineralocorticoid receptors. We will then select candidate genes to be tested using cultured epithelial cells, and ultimately in vivo. We will seek proteins that are essential for stimulating sodium channels under high aldosterone conditions.