Elucidating the role of aldosterone production on cell proliferation and apoptosis

Abstract

Many modifiable factors contribute to hypertension or high blood pressure, among them is the consumption of salt (sodium). Aldosterone, synthesized in the zona glomerulosa (ZG) by the enzyme aldosterone synthase (CYP11B2), plays a key role in sodium retention, blood volume regulation, and thus blood pressure homeostasis. In human adult adrenals, CYP11B2 expressing ZG cells are limited to pockets of cell clusters, likely due to chronic suppression of the renin-angiotensin system in response to modern high-sodium diets. In animal models, downregulation of aldosterone synthesis appears to influence ZG cell fate (apoptosis). Whether this occurs in humans and its relation to sodium diet remains unclear. This study investigated the effects of aldosterone suppression on human adrenocortical cell fate by inhibiting CYP11B2 in HAC15 cells using siRNA or the aldosterone synthase inhibitor Baxdrostat. Forty-eight hours post- transfection/treatment, aldosterone production was quantified, and RNA sequencing, transcriptomic analysis, and functional assays (EZMTT, xCELLigence, Annexin V/SYTOX) were performed. RNA-seq results suggest that aldosterone production capability modulates adrenocortical cell fate through autophagy/mitophagy pathways, with pharmacological inhibition of CYP11B2 leading to cell death (FC=1.42±0.05, n=144, P=1.3 x 10-10). However, both silencing of CYP11B2, or transfection with aldosterone-driving mutations (CTNNB1, GNA11, ATPIAI), had minimal effect on apoptosis. To investigate the relationship with sodium intake, 24-hour urinary sodium and aldosterone excretion were assessed in a multi-ethnic Malaysian cohort (n=759). Among individuals with high sodium intake (>200 mmol/day; n=60), 10.0% (95% CI [2.4, 17.6]) had autonomous aldosterone production (aldosterone excretion >10 ug/day). Whereas using the serum sodium to urinary sodium to (serum potassium)2 to urinary potassium (SUSPPUP) ratio as an autonomous aldosterone screening tool, the estimated prevalence in a subset with random sodium intake (110.18±3.615 mmol/day; n=174) was 4.6% (95% CI [1.5, 7.7]). Given that primary aldosteronism (PA) characterized by autonomous aldosterone production is one of the most common secondary cause of hypertension, these findings support inhibition of aldosterone synthesis as a therapeutic strategy for PA especially in populations with a high sodium intake. Further studies are warranted to verify that pharmacological inhibition of aldosterone synthesis could lead to regression of pathological ZG cell populations and thus a curative treatment to PA.