Abstract P243: Smooth Muscle Cullin-3 Deficiency Causes Severe Early Onset Hypertension and Nitric Oxide Resistance

Abstract

Mutations in Cullin-3 ( Cul3 ) resulting in exon 9 skipping (CUL3α9) cause human hypertension. We demonstrated that selective expression of CUL3α9 in smooth muscle causes arterial stiffness and hypertension. We hypothesized that deletion of CUL3 in smooth muscle causes severe hypertension. Mice carrying a conditional allele of CUL3 were bred with mice expressing a tamoxifen-inducible CRE-recombinase driven by a smooth muscle promoter. Mice were administered tamoxifen i.p. (75 mg/kg) for 5 consecutive days to generate smooth muscle CUL3 knockout (S-CUL3KO). CUL3 protein was undetectable whereas Cullin-1 protein was preserved in aorta from S-CUL3KO mice. We assessed vascular function in the cerebral basilar artery and aorta using pressurized and wire myograph, respectively. Blood pressure (BP) was measured by radiotelemetry. S-CUL3KO mice exhibited significantly increased systolic BP (SBP) at 2 weeks and 4 weeks post tamoxifen compared to corn oil controls (2 wks SBP mmHg: 145±1 vs 115±2, p<0.001; 4 weeks SBP: 169±1 vs 115±3, p<0.001). Pulse wave velocity was also increased in S-CUL3KO mice (3.7±0.1 m/s vs 2.2±0.1, P<0.001), suggesting increased arterial stiffness. Aorta from S-CUL3KO mice exhibited severely impaired vasorelaxation to acetylcholine (ACh) compared to controls (at 100 μM: 1.0±3% vs 77±5%, p<0.0001), and to the nitric oxide donor sodium nitroprusside (SNP) (at 100 μM: 15±4% vs 96±1%, p<0.001). In agreement with data from aorta, cerebral basilar artery from S-CUL3KO mice also exhibited significant impairment to ACh- and SNP-mediated vasorelaxation. Conversely, S-CUL3KO aorta retained an ability to relax in response to a cGMP analogue (8-pCPT-cGMP, at 100 μμ: 8-pCPT-cGMP 70±3%) and to the heme-independent soluble guanylate cyclase activator (BAY 58-2667, at 10 μμ: BAY 58-2667 94±2%), indicating that downstream mechanisms controlled by cGMP remain intact in the absence of CUL3. Captopril (120 mg/kg/day) was sufficient to normalized BP in S-CUL3KO mice to pre-tamoxifen levels (change in SBP mmHg: -50.2±1.9 S-CUL3KO vs -25.0±2 control, P<0.0001). We conclude that smooth muscle CUL3 is a major BP determinant, and identifying novel CUL3 substrates in smooth muscle would be beneficial as therapeutic targets in the treatment of hypertension.