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-Cul39) and the other specifically in vascular smooth muscle cells (SM22-Cul39). We conducted pharmacologic investigations on isolated aortas and generated stable and inducible HEK293 cell lines that overexpress the wild-type Cul3 or mutant Cul3 (Cul39) protein.

Results

As expected, pgk-Cul39 mice showed marked hypertension with significant hyperkalemia, hyperchloremia and low renin. BP increased significantly in SM22-Cul39 mice, independent of any measurable effect on renal transport. Only pgk-Cul39 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-Cul39 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 Cul39-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.