Abstract 084: Smooth Muscle Cullin-3 Regulates The Renal Baroreceptor Mechanism Via Lamin AC

Abstract

Cullin-3 (CUL3) is a critical component of the CUL3-Ring-Ligase (CRL) ubiquitin ligase complex. Patients carrying mutations in CUL3 exhibit early onset of hypertension (HTN). We demonstrated that conditional ablation of CUL3 in vascular smooth muscle cells (VSMCs) results in vascular dysfunction, arterial stiffness, and severe HTN in mice. We hypothesized that 1) conditional deletion of CUL3 in VSMCs (S-CUL3KO) results in severe HTN via the renin-angiotensin system (RAS)-dependent mechanism, and 2) S-CUL3KO mice exhibit an impaired baroreceptor mechanism regulating renin. Mice carrying a conditional allele of CUL3 were bred with mice expressing a tamoxifen-inducible CRE-recombinase driven by a smooth muscle promoter (ISM-CRE, control). S-CUL3KO mice exhibited elevated systolic blood pressure (SBP) 3 weeks after tamoxifen administration (S-CUL3KO: 164±1 vs. ISM-CRE: 124±4 mmHg, p<0.05). To test the first hypothesis captopril or candesartan (10 mg/kg/day and 100 mg/kg/day in drinking water, respectively) were administered to S-CUL3KO once severe HTN was already established. Captopril or candesartan treatment for 1 week reversed elevated SBP to 117±4 mmHg (p<0.05) and 127±2 mmHg (p<0.05), respectively, in S-CUL3KO. Despite the severity of HTN in S-CUL3KO, the level of renin mRNA in the kidney was surprisingly unaltered (p>0.05) when compared to the normotensive control mice. The protein expression of lamin AC, a crucial component of the nuclear mechanotransducer controlling renin expression, was significantly increased in S-CUL3KO kidneys (0.11±0.02 vs. 0.05±0.01 normalized RFU, p<0.05). This suggests lamin AC may be a target protein of CUL3-ubiquitin ligase complex. Supporting this concept, treatment of A10 smooth muscle cells with MLN4914, an inhibitor of the Cullin pathway, results in a 2-fold increase in lamin AC expression (0.007±0.001 vs. 0.0154±0.0004, normalized RFU, p<0.05). Furthermore, co-immunoprecipitation of CUL3 in HEK293 cells immunoprecipitated lamin AC. Our findings support the hypothesis that 1) CUL3 regulates RAS via the renal baroreceptor mechanism and 2) lamin AC is a potential target of the CRL3-mediated regulation. Understanding CUL3 target proteins might help the development of new strategies to mitigate HTN.