Abstract 110: Vascular Smooth Muscle RhoBTB1 Protects From Hypertension and Arterial Stiffness by Cullin-3 Dependent Ubiquitination of Phosphodiesterase 5

Abstract

We previously reported that vascular smooth muscle cell (VSMC) selective expression of hypertension (HT)-causing mutations in either PPARγ or the E3 Ring Ubiquitin Ligase Cullin-3 causes nitric oxide resistance and HT. Here we sought to assess the physiological role of RhoBTB1, a VSMC PPARγ target gene and Cullin-3 substrate adaptor. S-P467L mice which selectively express dominant negative PPARγ-P467L in VSMC exhibit RhoBTB1-deficiency. We bred S-P467L mice with mice inducibly expressing RhoBTB1 in response to Cre-recombinase. Inducible VSMC-specific restoration of RhoBTB1 in S-P467L mice fully corrected the HT (SBP, 141±6 vs 124±3 mmHg, p<0.01, n=8-10), arterial stiffness (Aortic Pulse Wave Velocity, 3.8±0.2 vs 2.5±0.1 mm/ms, p<0.01, n=11-13), and vasodilator function (Aorta, 46±5 vs 80±2% ACh-induced relaxation, p<0.01, n=6-9). Notably, the cardiovascular protection occurred despite preservation of increased agonist-mediated contraction and RhoA/Rho kinase activity, suggesting RhoBTB1 selectively controls vasodilation. Sodium nitroprusside-induced production of cGMP in aorta was severely impaired in S-P467L but restored by RhoBTB1. Consistent with this, phosphodiesterase 5 (PDE5) activity in aorta was augmented 2.5±0.3 fold in S-P467L but was returned to normal by RhoBTB1. PDE5 and RhoBTB1 reciprocally co-immunoprecipitated in HEK293 cells. Ubiquitination of PDE5 by Cullin-3 in HEK293 cells was RhoBTB1-dependent. Consistent with a role for Cullin-3 in mediating turnover of PDE5, PDE5 activity was augmented in MLN4924-treated aorta, a Cullin inhibitor, and abrogated by PDE5 inhibitor. The beneficial cardiovascular effect of RhoBTB1 in S-P467L mice was phenocopied by PDE5 inhibition. Angiotensin-II infusion also causes RhoBTB1-deficiency and HT which was reversed by smooth muscle specific RhoBTB1 restoration. We conclude that RhoBTB1 augments the cGMP response to nitric oxide by restraining the activity of PDE5 by acting as a substrate adaptor delivering PDE5 to the Cullin-3 E3 Ring ubiquitin ligase complex for ubiquitination and proteasomal degradation. RhoBTB1 provides protection from HT, vascular smooth muscle dysfunction, and arterial stiffness in at least two models of HT.