Sex-specific splenic inflammation underlies sexual dimorphic effects of ACE2 in hypertension

Introduction: Sex differences in salt-sensitive hypertension and pharmacotherapy are commonly recognized. However, the mechanisms are largely unknown. ACE inhibitor is less effective in females than males, suggesting a better protective mechanism of the renin angiotensin system (RAS) in female hypertension. Angiotensin converting enzyme (ACE) 2, located on the X chromosome, is thereby a central candidate of sex differences in hypertension and pharmacotherapy. Thus, our objective is to test the sex specific protective role of ACE2 in salt hypertension. Since the females have a more regulatory RAS than males, we hypothesized that absence of ACE2 resulted in a higher blood pressure and more inflammation in females than males. Methods: ACE2 exon 2 was globally deleted using CRISPR/Cas9, resulting in a novel rat model in the Dahl salt-sensitive (S) background: male Ace2-/y and female Ace2-/+, Ace2-/-. Blood pressure was measured by telemetry in male (S n=7; S Ace2-/y n=6) and female (S n=7; Ace2-/+ n=7; Ace2-/- n=5) rats on 3 weeks high salt diets. Serum ACE2 activity was measured using ELISA. Spleen as the harbor of systemic immunity was studied for Inflammatory markers by gene expression analysis and flow cytometry. Results: Compared to sex-matched S rats, (1) serum ACE2 activity was decreased in female Ace2-/- (0.28 fold, p<0.0001) and male Ace2-/y (0.3 fold, p<0.0001); (2) systolic blood pressure was increased in female Ace2-/- (+67.89 mmHg, p<0.0001) and male Ace2-/y (+48.64 mmHg, p<0.0001) rats. Importantly, a sex-specific upregulation of the pro-inflammatory cytokines were found exclusively in the female Ace2-/- rat spleens: Il6 (1.8 fold, p<0.05), Il1b (2.1 fold, p<0.05) and Il17rc (2.3 fold, p<0.01). In contrast, male Ace2-/y rats showed no difference in Il6 and Il1b, but downregulation of the splenic Il17rc (0.78 fold, p<0.05), Th17 cells (IL17a on CD4+ cells, 0.76 fold, p<0.01), regulatory T cells (FOXP3 on CD4+ cells, 0.49 fold, p<0.01), CD68+ macrophage (0.76 fold, p<0.01) and CD11bc+ dendritic cells (0.89 fold, p<0.001).Furthermore, compared with female S rats, heterozygous female Ace2-/+ rats had decreased serum ACE2 activity (0.6 fold, p<0.001), rescued blood pressure increase (+7.5 mmHg, p<0.0001) and no increases in splenic inflammatory cytokines Il6, Il1b and Il17rc. Conclusions: Despite significantly lower serum ACE2 activity in heterozygous female Ace2-/+ rats, the protection in blood pressure and splenic inflammation was mainly preserved. This suggests a protective role of ACE2, beyond RAS, in inflammation-associated high blood pressure. Moreover, this novel protective role of ACE2 is exclusively in female salt hypertension, evidenced by greater increases in systolic blood pressure and splenic inflammation in female only. NIH R21AI164449 and R21AG079357. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.