Sex‐Selective Effects of Transient ACE Inhibition on Angiotensin II‐Stimulated Fibrogenic Responses

Abstract

Hypertensive heart disease is characterized by cardiac fibrosis in the left ventricle (LV). Angiotensin II (Ang II) promotes cardiac fibrosis through direct actions on cardiac fibroblasts. Inhibition of endogenous Ang II production with angiotensin converting enzyme (ACE) inhibitors has been shown to reduce interstitial collagen deposition in the LV. We have previously shown that transient treatment of male spontaneously hypertensive rats (SHRs) with an ACE inhibitor suppresses the fibrogenic capacity of cardiac fibroblasts and this persists even after stopping treatment. In this study, the goal was to investigate the impact of transient ACE inhibition on subsequent Ang II‐stimulated fibrogenic responses in the LV of male and female SHR. Male and female SHR (11‐week‐old) were treated with an ACE inhibitor (enalapril, 30mg/kg/day) or vehicle for 2 weeks followed by a 2‐week washout period. At the end of the washout, rats were given Ang II (400ng/kg/min, s.c.) or vehicle (saline) for 2 weeks (n=8‐11 per group per sex). Collagen I, III, and IV gene expression was assessed via RT‐qPCR, total collagen was quantified using a hydroxyproline assay, and immunoblotting for lysyl oxidase (LOX) and periostin (Postn) was performed. In males, the Ang II‐stimulated increase in collagen gene expression (i.e. Col1a1, Col3a1, and Col4a1) was significantly attenuated in SHR previously treated with enalapril. In female rats, Ang II significantly increased the expression of Col1a1 and Col3a1 similarly, regardless of prior enalapril treatment. We found a positive correlation between the degree of increase in Col1a1 and Col3a1 as well as with Col1a1 and Col4a1 in male controls with Ang II stimulation. However, in Ang II‐stimulated male rats transiently treated with enalapril, there was a negative correlation between Col1a1 and Col3a1 and no correlation between changes in Col1a1 and Col4a1. In female rats, there were significant positive correlations in all cases regardless of prior transient ACE inhibition. Total collagen content in both male and female rats was significantly increased by Ang II in control animals, but not in those previously treated with enalapril. Additionally, in both male and female rats stimulated with Ang II, cross‐linking proteins Postn and LOX showed lower expression in SHR that were transiently treated with enalapril. These data reveal that even after stopping treatment, ACE inhibition produces persistent changes in the myocardium that render it resistant to the effects of Ang II. The effects seen in females suggests a possible dysregulation between collagen production and extracellular matrix cross‐linking events following transient ACE inhibition. Future studies will elucidate the mechanisms underlying the sex‐specific response to ACE inhibition and the long‐term protective effect in male LV, with a goal of identifying novel therapeutic targets.