Direct Mineralocorticoid Receptor (MR) Activation, Independent of Increases in Blood Pressure, Drive Sex Differences in Tregs in DOCA‐salt rats

Abstract

Our lab has previously shown that greater T regulatory cells (Tregs) in females attenuate deoxycorticosterone acetate salt (DOCA)-induced increases in blood pressure (BP). Tregs do not contribute to BP control in male rats with DOCA hypertension. DOCA is a mineralocorticoid model of hypertension, and mineralocorticoid receptor activation alone can significantly increase fibrosis, oxidative stress, and inflammation, independent of an effect on BP. The goal of the current study was to test the hypothesis that direct mineralocorticoid effects, independent of increases in BP, drives sex differences in Tregs in DOCA-salt rats. At 10 wks of age, male and female Sprague-Dawley rats were anesthetized, a right uni-nephrectomy was performed, and a telemeter was implanted for continuous BP measurement. After one week of recovery, all rats received a subcutaneous 21-day slow-release DOCA pellet (200 mg) with 0.9% saline water to drink. To separate the effects of MR activation and increases in BP on DOCA-salt-induced alterations in renal Tregs, rats were randomized to the following groups: 1) BP lowering drugs hydrochlorothiazide (HCTZ; 55 mg/kg/day) and reserpine (RES; 4.5 mg/kg/day; N=9-12/group) or vehicle control (DOCA-salt only) or 2) MR blocker spironolactone (15 mg/kg/day; N=6/group) or vehicle control (DOCA-salt only). After 21 days, the remaining kidney was isolated for flow cytometric analysis of Tregs (CD3+CD4+FoxP3+). Treatment with HCTZ/RES prevented DOCA-induced increases in BP in both males (179 ± 3 mmHg vs 110 ± 5 mmHg; Ptreatment<0.0001) and females (157 ± 4 mmHg vs 101 ± 5 mmHg; Ptreatment<0.0001). Preventing DOCA-induced increases in BP did not alter sex differences in renal Tregs (Table) as females maintained more Tregs than males (Psex<0.0001; Ptreatment=0.11; Pinteraction=0.38). In contrast, treatment with spironolactone did not significantly alter BP in either male (180 ± 2 vs 178 ± 2 mmHg; Ptreatment=0.73) or female DOCA rats (170 ± 6 vs 162 ± 4 mmHg; Ptreatment=0.10). However, blocking the direct effects of MR activation with spironolactone abolished sex differences in renal Tregs by increasing Tregs (Table) in males (Psex=0.07; Ptreatment<0.0001; Pinteraction=0.04). Our data suggests that direct mineralocorticoid effects, independent of BP, drives sex differences in Tregs in DOCA-salt rats. Future studies will be designed to determine the specific mechanisms by which MR activation regulates Tregs in a sex-specific manner.