Abstract 64: Smooth Muscle Cullin-3 Regulates the Renal Baroreceptor Mechanism: a Link Between CUL3 and Integrin β1

Abstract

Cullin-3 (CUL3) is a critical component of the CUL3-Ring-Ligase (CRL) ubiquitin ligase complex. CUL3 mutants in smooth muscle cells (SMCs) cause vascular dysfunction, arterial stiffness, and severe hypertension (HTN). We hypothesized that conditional deletion of CUL3 in SMCs (S-CUL3KO) led to HTN via 1) a renin-angiotensin system (RAS)-dependent mechanism, and 2) impaired renal baroreceptor mechanism regulating renin expression. CUL3 Flox mice were bred to mice carrying tamoxifen-inducible CRE-recombinase under a smooth muscle promoter (ISM-CRE, control). S-CUL3KO mice exhibited augmented systolic blood pressure (SBP) (ISM-CRE: 124±1 vs. S-CUL3KO: 167±3 mmHg, p<0.05) 3-weeks post tamoxifen. Once HTN was established we used an angiotensin-converting enzyme inhibitor (captopril, 10 mg/kg/day in drinking water) for 1 week to reverse HTN. We observed a greater depressor effect in S-CUL3KO (ΔSBP -49±3 mmHg) compared to ISM-CRE (ΔSBP -33±1 mmHg, p<0.05). A similar effect was identified following angiotensin II type I receptor blocker (ARB, candesartan, 100 mg/kg/day in drinking water) treatment (ΔSBP, ISM-CRE: -27±2 vs. S-CUL3KO: -37±2, p<0.05). We prevented HTN in S-CUL3KO by administering ARB before tamoxifen injection (SBP 120±5 mmHg). Mesenteric arteries exhibited augmented Ang-II induced vasoconstriction, which was prevented with ARB, suggesting that HTN in S-CUL3KO is RAS-dependent and AT 1 R-mediated. Despite severe HTN, S-CUL3KO did not suppress renin mRNA expression in kidneys. We hypothesize that S-CUL3KO exhibits a defective renal baroreceptor mechanism causing impaired suppression of renin expression. We propose that CUL3 participates in the degradation of integrin β1, the key mechanosensory of the renal baroreceptor, via Rab-mediated trafficking and lysosomal fusion. Supporting this, HEK293 cells lacking CUL3 exhibited lower integrin β1 protein expression (0.51±0.08 vs. 0.09±0.01 normalized RFU, p<0.05) concomitant with increased Rab5 and Rab7 expression (3.6±0.3 vs. 1.9±0.1 and 0.95±0.12 vs. 0.37±0.04 normalized RFU). S-CUL3KO demonstrated severely impaired morphological distribution of integrin β1 protein in the juxtaglomerular apparatus. In conclusion, our findings support the hypothesis that 1) CUL3 regulates RAS via the renal baroreceptor, and 2) Rab proteins regulating integrin β1 expression are potential targets for the CRL3 pathway. Understanding CUL3 target proteins might contribute to the development of new strategies to treat HTN.