Abstract P504: Transient Angiotensin Converting Enzyme Inhibition Protects Against Future Fibrogenic Responses Via Sex-specific Mechanisms

Following washout of angiotensin converting enzyme inhibitor (ACEi) treatment in hypertensive rats (SHR), there is an increase in the proportion of homeostatic cardiac fibroblasts (CFs) characterized by a less fibrogenic gene profile. The present study investigated the impact of this shift in CFs on subsequent Ang II-induced oxidative stress and fibrogenic responses in the left ventricle (LV). Male and female SHRs (11 wk old) underwent a 6-week treatment scheme: 2-week ACEi (enalapril, 30mg/kg/day) or vehicle treatment, followed by a 2-week washout period, and then a 2-week Ang II (400ng/kg/min, s.c.) or vehicle infusion (n=5-11/group/sex). RT-qPCR for collagens and immunoblotting for LOX, Postn, OPN, NOX2, SOD2, and catalase was performed. In males, Ang II-induced increases in ColI, III, and IV expression were significantly attenuated by prior ACEi. While in females, Ang II significantly increased the expression of ColI and III similarly, regardless of prior ACEi treatment; highlighting a sex-specific impact of ACEi. After Ang II infusion, both Postn and LOX are reduced in LV of male and female SHR previously treated with an ACEi - suggesting reduced collagen cross-linking. Oxidative stress induced by NOX2 has been linked to OPN in fibrotic tissue. Ang II-induced increases in NOX2 are attenuated in LV of both sexes, while OPN is only reduced in females previously treated with an ACEi. NOX2 is significantly positively correlated with OPN in males only suggesting a sex-specific link between OPN and oxidative stress. Antioxidant (SOD2, catalase) levels were positively correlated to NOX2 in females, but not males. This suggests that females more efficiently neutralize oxidative stress than males - regardless of prior ACEi. Taken together, the persistent genomic and phenotypic changes in CFs following transient ACEi render the heart resistant to future fibrotic and oxidative effects of Ang II, but the mechanisms of protection may differ by sex. Collectively, these data reveal that there are sex-specific processes that govern collagen production vs. cross-linking and oxidative stress. Future studies will elucidate the mechanistic underpinnings of sex-specific cellular memory following transient ACEi with a goal of identifying novel therapeutic targets.