Activation of the Mineralocorticoid Receptor Leads to Increases in Protein Disulfide Isomerase Activity

Abstract

Activation of the mineralocorticoid receptor (MR), a critical component of the Renin‐Angiotensin‐Aldosterone (ALDO) System (RAAS), plays an important role in inflammatory and vascular endothelial responses in addition to its well‐described effects on sodium and water homeostasis. Activation of endothelial cells and leukocytes leads to, among other factors, increased protein disulfide isomerase (PDI) release. PDI is a multifunctional oxidoreductase that catalyzes thiol/disulfide interchange reactions within the endoplasmic reticulum, is also present in circulation and at the cell surface of platelets, lymphocytes, erythrocytes and endothelial cells and plays a critical role in initiating thrombus formation. However, the interaction of ALDO, MR activation and PDI remain unclear. We hypothesized that MR activation would lead to increased PDI levels thus contributing to inflammation and oxidative stress. We first studied EA.hy926 (EA) cells, a human endothelial cell line that expresses MR. We incubated EA cells with ALDO (10 −8 M), an MR agonist, for 24 hr and observed a rise in PDI mRNA levels by qRT‐PCR (p<0.01, n=5), an event that was blocked by pre‐incubation of EA cells with 1 μM canrenoic acid (CA), an MR antagonist (p<0.05, n=5). Consistent with these results, measurements of PDI levels by ELISA confirmed a rise in PDI that was likewise blocked by CA (p<0.01, n=4). Also, we measured PDI activity in the supernatant of ALDO‐stimulated EA cells using a Di‐E‐GSSH fluorescent marker and observed a rise in PDI activity following ALDO (10^−8 M) incubation when compared to vehicle treatment (p<0.05, n=5). We then studied the effects of ALDO on HL‐60 cells, a human promyelocytic cell line that was induced to differentiate into neutrophil‐like leukocytes by incubation for 5 days with 1.3% DMSO. In these cells, we detected the presence of MR by western blot analyses and observed that ALDO (10^−8 M) stimulated a rise in PDI activity that was blocked by CA (p<0.05, n=6). To test the in vivo effects of MR activation on PDI activity, we characterized a well‐described rodent model of RAAS‐mediated increased BP, inflammation and target organ damage using exogenous angiotensin II (AngII) infusion in Sprague–Dawley rats. Rats were randomized to three conditions: (1) control; (2) AngII infused (80 ng/min × 28 days); (3) AngII + eplerenone (100 mg eplerenone/kg/day × 21 days), an MR antagonist. Consistent with our in vitro data, AngII infusion led to significant increases in plasma PDI activity that was significantly reduced by approximately 65% following eplerenone treatment (p<0.05, n=5/group). Thus, MR activation represents a novel mechanism for PDI regulation that may contribute to the deleterious effects of disordered RAAS activity in cardiovascular disease.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.