(863.3) Eplerenone-induced natriuresis and hyperkalemia in mice lacking aldosterone results from aldosterone-independent mineralocorticoid receptor occupancy

Poster Board Number: E181

James McCormick (Oregon Health amp; Science University), Yujiro Maeoka (Oregon Health amp; Science University), Avika Sharma (Oregon Health amp; Science University), Xiao-Tong Su (Oregon Health amp; Science University), Wen-Hui Wang (New York Medical College), David Ellison (Oregon Health amp; Science University)

Background: Mineralocorticoid receptor (MR) antagonists are recommended for patients with resistant hypertension independent of circulating aldosterone levels. Aldosterone, secreted in response to salt depletion or hyperkalemia, activates MR to increase epithelial sodium channel (ENaC) activity. While glucocorticoids can also activate MR, they are metabolized by 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2), protecting MR from illicit glucocorticoid occupation. 11β-HSD2 is expressed at increasing levels from the DCT through the collecting duct. Here, we hypothesized that glucocorticoid occupies MR to stimulate ENaC in the DCT2 and early connecting tubule.

Methods: We studied aldosterone synthase knockout (AS−/−) mice provided by Dr. JM Luther. Kidney–specific MR knockout (MR−/−) mice were used for validation of Western blot for ENaC and immunofluorescence for MR. We measured plasma and urinary electrolytes at baseline, and following dietary salt restriction with or without administration of the MR antagonist eplerenone.

Results: AS−/− mice displayed higher plasma K+ levels than AS+/+ mice but not salt wasting under baseline. Under low salt (LS) diet, AS−/− mice exhibited higher urine Na+ excretion, but preserved body weight. Cleaved αENaC and γENaC abundances were lower in AS−/− than AS+/+ mice, and were not increased in AS−/− mice after LS diet. Notably, we found nuclear localization of MR was preserved in DCT2 of AS−/− mice. Administration of the MR blocker eplerenone to AS−/− mice fed LS diet led to hyperkalemia and decreased body weight with higher Na+ excretion, mimicking the phenotype of MR−/− mice.

Conclusions: Our results provide evidence that MR is occupied in the absence of aldosterone, suggesting glucocorticoid-binding to MR preserves sodium homeostasis in the DCT2 of AS−/− mice. This likely explains the milder phenotype of AS−/− mice compared with MR−/− mice.

J.A.M. National Institute of Diabetes and Digestive and Kidney Diseases Grant DK098141. Y.M. Postdoctoral award from the Uehara Foundation. X-T.S KidneyCure Ben J. Lipps postdoctoral fellowship. W-H.W National Institute of Diabetes and Digestive and Kidney Diseases Grant DK054983. D.H.E. National Institute of Diabetes and Digestive and Kidney Diseases Grants DK051496 and DK054983, Veterans Affairs Grant 1I01BX002228, and a Fondation LeDucq Transatlantic Network of Excellence.