One of the hallmarks of autosomal dominant polycystic kidney disease (ADPKD) is hypertension. True, most patients with advanced kidney disease get hypertension anyways--but often the degree of hypertension in ADPKD patients seems to be especially high. Is there something about the function of the polycystin proteins which explains the high blood pressure?
A recent article by Sharif-Naeini et al in this month's issue of Cell claims a pressure-sensing role for the polycystins. ADPKD is caused by mutations in two genes, PKD1 and PKD2, which encode for membrane proteins termed TRPP1 and TRPP2, respectively. It appears these genes function via regulating local calcium fluxes in and out of the cell. Although most efforts to understand TRPP1 and TRPP2 function have focused on renal tubular epithelial cells (since that's where cysts come from), a variety of extra-renal phenotypes are also observed. In this paper, the authors generated mice deficient in TRPP1 or TRPP2 ONLY in smooth muscle cells. Importantly, they found that the balance of TRPP1 and TRPP2 levels was critical for the ability of arterial smooth muscle to maintain appropriate blood pressure. These results imply that function of the polycystins may be different depending on cell type, and suggest a possible mechanism by which ADPKD patients may be especially prone to the development of abnormalities in blood pressure regulation.