Abnormal activation of the mineralocorticoid receptor in the aldosterone-sensitive distal nephron contributes to fructose-induced salt-sensitive hypertension

Abstract

Fructose high-salt (FHS) diets increase blood pressure (BP) in an angiotensin II (Ang II)-dependent manner. Ang II stimulates aldosterone release, which, by acting on the mineralocorticoid receptor (MR), regulates Na+ reabsorption by the aldosterone-sensitive distal nephron (ASDN). The MR can be transactivated by glucocorticoids, including those locally produced by 11{beta}-HSD1. The epithelial sodium channel (ENaC) is a key transporter regulated by MRs. We hypothesized that fructose-induced salt-sensitive hypertension depends in part on abnormal activation of MRs in the ASDN with consequent increases in ENaC expression. We found that aldosterone-upregulated genes in mice ASDN, significantly overlapped with 74 genes upregulated by FHS in the rat kidney cortex (13/74; p[≤]1x10-8), and that these 74 genes are prominently expressed in rat ASDN cells. Additionally, the average z-score expression of mice-aldosterone-upregulated genes is highly correlated with FHS compared to glucose high-salt (GHS) in the rat kidney cortex (Pearson correlation; r=0.66; p[≤]0.005). There were no significant differences in plasma aldosterone concentrations between the FHS and GHS. However, 11{beta}-HSD1 transcripts were upregulated by FHS (log2FC=0.26, p[≤]0.02). FHS increased BP by 23{+/-}6 mmHg compared to GHS, and blocking MRs with eplerenone prevented this increase. Additionally, inhibiting ENaC with amiloride significantly reduced BP in FHS from 148{+/-}6 to 134{+/-}5 mmHg (p[≤]0.019). Compared to GHS, FHS increased total and cleaved ENaC protein by 89{+/-}14 % (p[≤]0.03) and 47{+/-}16 % (p[≤]0.01) respectively. FHS did not change {beta}- or {gamma}-subunit expression. These results suggest that fructose-induced salt-sensitive hypertension depends, in part, on abnormal Na+ retention by ENaC, resulting from the activation of MRs by glucocorticoids.