Cullin-3 (CUL3) mutations (CUL3Δ9) were previously identified in hypertensive patients with pseudohypoaldosteronism type-II (PHAII), but the mechanism causing hypertension and whether this is driven by renal tubular or extratubular mechanisms remains unknown. We report that selective expression of CUL3Δ9 in smooth muscle acts by interfering with expression and function of endogenous CUL3, resulting in impaired turnover of the CUL3 substrate RhoA, increased RhoA activity, and augmented RhoA/Rho kinase signaling. This caused vascular dysfunction and increased arterial pressure under baseline conditions and a marked increase in arterial pressure, collagen deposition, and vascular stiffness in response to a subpressor dose of angiotensin II, which did not cause hypertension in control mice. Inhibition of total cullin activity increased the level of CUL3 substrates cyclin E and RhoA, and expression of CUL3Δ9 decreased the level of the active form of endogenous CUL3 in human aortic smooth muscle cells. These data indicate that selective expression of the Cul3Δ9 mutation in vascular smooth muscle phenocopies the hypertension observed in Cul3Δ9 human subjects and suggest that mutations in CUL3 cause human hypertension in part through a mechanism involving smooth muscle dysfunction initiated by a loss of CUL3-mediated degradation of RhoA.
Larry N. Agbor, Stella-Rita C. Ibeawuchi, Chunyan Hu, Jing Wu, Deborah R. Davis, Henry L. Keen, Frederick W. Quelle, Curt D. Sigmund
(A) Pulse wave velocity measurements in nontransgenic (NT) and S-CUL3Δ9 mice, as determined by Doppler ultrasound. n = 7/genotype. *P < 0.05 S-CUL3Δ9 vs. NT by 1-way ANOVA. (B and C) Pressure-diameter curves (B) and stress-strain relationships (C) of NT and S-CUL3Δ9 aortas. n = 4–6/genotype/treatment. *P < 0.05 angiotensin II (Ang II) S-CUL3Δ9 vs. all other curves by 1-way repeated-measure ANOVA. (D) Aortic collagen, as measured by hydroxyproline assay. n = 4–6/genotype/treatment. *P < 0.05 Ang II S-CUL3Δ9 vs. all other samples by 1-way ANOVA. (E) Adventitial collagen was determined by Masson trichrome staining. Original magnification, ×40; scale bar: 100 μm. n = 4–6/genotype/treatment. *P < 0.05 Ang II S-CUL3Δ9 vs. all other samples analyzed by 1-way ANOVA.