Project Summary/Abstract Project background: This is a competing renewal R01 applicaton that proposes to study the cellular and genetic origins of the most common adrenal disease, primary aldosteronism (PA). The prevalence of PA is 6- 8% amongst all hypertensive patients suggesting that 1 in 40 American adults has PA. PA is hallmarked by renin-independent adrenal aldosterone production that results in excessive mineralocorticoid receptor (MR) activation. The two major subtypes of PA are unilateral aldosterone-producing adenoma (APA) and bilateral idiopathic hyperaldosteronism (IHA). While PA resulting from APA has a surgical cure, IHA requires life-long medical therapy using MR antagonists. There are no current therapeutic approaches that inhibit the disease- causing inappropriate aldosterone production in IHA patients. During the initial funding period of this grant, we made significant progress in defining genetic causes of PA. This includes the first in field use of a small cohort of IHA formalin-fixed paraffin-embedded (FFPE) adrenal tissues that showed a buildup of activating somatic mutations in CACNA1D (L-type calcium voltage-gated channel alpha 1D subunit). IHA CACNA1D mutations were found in aldosterone-producing cell clusters (APCC), a clonal adrenal dysplastic cellular entity that we initially described in the zona glomerulosa (ZG) of normal adrenals. These findings form the foundation for this competitive renewal application. Specific Aims. Aim 1 will define the aldosterone-driving somatic mutations that initiate dysregulation of aldosterone production in a large cohort of normal adrenals (˃ 400). Aim 2 will define the role of APCC and somatic gene mutations in bilateral adrenal IHA autonomous aldosterone production. Aim 3 will evaluate the potential for calcium channel blockers (CCBs) to specifically target and reduce autonomous aldosterone secretion in patients with IHA. Overall significance and clinical impact. Despite the high prevalence of PA, its clear impact on cardiovascular disease, and intriguing new genetic findings related to its cause, we know very little about the origin and progression of PA and particularly IHA. Because IHA results from bilateral adrenal disease, there is no surgical cure. Current strategies, although effective, do not target dysregulation of aldosterone release but instead target the MR, which can cause unfavorable off target side effects. The proposed research would significantly improve our understanding of the molecular mechanisms causing bilateral adrenal IHA and has the added potential of providing foundational research for the development of novel therapeutics that could directly inhibit IHA adrenal renin-independent aldosterone production.