Regulation of Renin-Angiotensin System Activity and Blood Pressure by Vascular Smooth Muscle Cullin-3

Abstract

Mutations in the ubiquitin ligase scaffold protein Cullin 3 (CUL3) in smooth muscle cells (SMCs) cause vascular dysfunction, arterial stiffness, and severe hypertension. We hypothesized that conditional deletion of CUL3 in SMCs causes severe hypertension through a renin-angiotensin system (RAS)-dependent mechanism. Mice carrying a conditional allele of CUL3 were bred to mice expressing a tamoxifen-inducible CRE-recombinase driven by a smooth muscle promoter (ISM-CRE, control). Tamoxifen was administered to generate smooth muscle CUL3 knockout (S-CUL3KO). Primary aortic SMCs were used to elucidate the contribution of CUL3 to intracellular angiotensin II-mediated calcium flux. Calcium response in SMCs was analyzed via ratiometric confocal fluorescent microscopyS-CUL3KO mice demonstrated hypertension following three weeks of tamoxifen, mean arterial pressure (MAP) was 108±1 vs. 140±1 mmHg (ISM-CRE vs. S-CUL3KO). Aorta from S-CUL3KO mice exhibited impaired vasorelaxation to acetylcholine (ACh, max relaxation: 84±4% vs. 16±9%, p<0.05) and sodium nitroprusside (SNP, max relaxation: 95±3% vs. 56±9%, p<0.05). Captopril administration (7 days) markedly reduced MAP to 84±0.3 mmHg and improved vasorelaxation in response to both ACh (72±6%) and SNP (91±4%) in S-CUL3KO mice, suggesting RAS-dependency of the hypertension. Additionally, candesartan treatment (7 days) substantially decreased MAP from 138±1 to 96±3 mmHg suggesting that hypertension in S-CUL3KO group is angiotensin type-1 receptor mediated. Q-PCR and RNAScope analyses demonstrated no difference in renin expression in the kidney between the S-CUL3KO and control mice suggesting a blunting of the baroreceptor mechanism regulating renin mRNA expression. Equilibrium angiotensin II plasma levels in both groups were not different (2517±352 and 2379±549 pmol/L, p>0.05). Preliminary data demonstrated that acute application of 10 μM of angiotensin II to S-CUL3KO SMCs resulted in a sustained increase in intracellular calcium which was abolished by a preincubation with 2 μM of candesartan.Our data suggest that CUL3 may play a vital role in baroreceptor mechanism in the kidney and regulate angiotensin II response in SMCs which are essential for responding to changes in perfusion pressure. Ultimately, understanding CUL3 target proteins may benefit the development of novel treatments for hypertension. R35 HL144807 (to CDS). 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.