Abstract 091: Does Smooth Muscle Cullin-3 Regulate The Renin-angiotensin System?

Cullin-3 (CUL3) is a scaffold protein involved in the formation and function of the CUL3-RING E3 ubiquitin ligase complex. Loss of smooth muscle CUL3 promotes vascular dysfunction, arterial stiffness, and severe hypertension (HTN). We hypothesized that conditional deletion of CUL3 in smooth muscle cells causes severe HTN 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). Three weeks after tamoxifen, mean arterial pressure (MAP) was 140±1 vs. 108±1 mmHg (S-CUL3KO vs. ISM-CRE). Aorta from S-CUL3KO mice exhibited impaired acetylcholine-induced vasorelaxation (ACh, max relaxation: 19±11% vs. 84±5%, p<0.05). S-CUL3KO mice also manifested impaired vasorelaxation to sodium nitroprusside (SNP, max relaxation: 15±12% vs. 96±2%, 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 (87±4%) in S-CUL3KO mice, suggesting RAS-dependency of the HTN. Q-PCR analyses and RNAScope showed no difference in renin expression in the kidney between the S-CUL3KO and control mice suggesting a blunting of the baroreceptor mechanism regulating renin. In preliminary studies, lamin A/C, a crucial component of the nuclear mechanotransducer controlling expression of renin, displayed a trend to increased protein expression in S-CUL3KO animals (6±2 vs. 2±1 normalized RFU, p=0.12). Similarly, expression of connexin 40, a component responsible renin signal transduction in the renin cells, was significantly higher in S-CUL3KO mice (8±1 vs. 3±1 normalized RFU, p<0.05). Our data suggest that CUL3 may play a vital role in baroreceptor mechanism in the renin cells via regulation of components of the baroreflex sensor (connexin 40) and transducer (lamin A/C) which are essential for responding to changes in perfusion pressure. Hence, understanding CUL3 target proteins and the mechanism of the impaired baroreceptor mechanism is beneficial in developing new treatments of hypertension.