Severe Arterial Hypertension from Cullin 3 Mutations Is Caused by Both Renal and Vascular Effects

Background Mutations in four genes, WNK lysine deficient protein kinase 1 and 4 ( WNK1 and WNK4 ), kelch like family member 3 ( KLHL3 ), or Cullin 3 ( CUL3 ), can result in familial hyperkalemic hypertension (FHHt), a rare Mendelian form of human arterial hypertension. Although all mutations result in an increased abundance of WNK1 or WNK4, all FHHt-causing CUL3 mutations, resulting in the skipping of exon 9, lead to a more severe phenotype. Methods We created and compared two mouse models, one expressing the mutant Cul3 protein ubiquitously ( pgk-Cul3∆9 ) and the other specifically in vascular smooth muscle cells ( SM22-Cul3∆9 ). We conducted pharmacologic investigations on isolated aortas and generated stable and inducible HEK293 cell lines that overexpress the wild-type Cul3 or mutant Cul3 (Cul3 ∆ 9) protein. Results As expected, pgk-Cul3∆9 mice showed marked hypertension with significant hyperkalemia, hyperchloremia and low renin. BP increased significantly in SM22-Cul3∆9 mice, independent of any measurable effect on renal transport. Only pgk-Cul3∆9 mice displayed increased expression of the sodium chloride cotransporter and phosphorylation by the WNK-SPAK kinases. Both models showed altered reactivity of isolated aortas to phenylephrine and acetylcholine, as well as marked acute BP sensitivity to the calcium channel blocker amlodipine. Aortas from SM22-Cul3∆9 mice showed increased expression of RhoA, a key molecule involved in regulation of vascular tone, compared with aortas from control mice. We also observed increased RhoA abundance and t 1/2 in Cul3 ∆ 9-expressing cells, caused by decreased ubiquitination. Conclusions Mutations in Cul3 cause severe hypertension by affecting both renal and vascular function, the latter being associated with activation of RhoA.