Vascular expression of polycystin-2

The expression of polycystin-1 in the vascular smooth muscle cells (VSMC) o f elastic and large distributive arteries suggests that some vascular manif estations of autosomal-dominant polycystic kidney disease (ADPKD) result di rectly from the genetic defect. Intracranial aneurysms have been reported i n PKD2, as well as in PKD1 families. To determine whether the vascular expr ession of polycystin-2 is similar to that of polycystin-1, the expression o f PKD2 mRNA and protein in cultured pig aortic VSMC was studied and immunof luorescence and immunohistochemistry were used to study the localization of polycystin-2 in cultured pig aortic VSMC, pig ascending thoracic aorta, an d normal elastic and intracranial arteries and intracranial aneurysms obtai ned at autopsy from patients without or with ADPKD. Tissues derived from Pk d2 wild-type and Pkd2 null mice were used to confirm the specificity of the immunostaining for polycystin-2. Northern blots of VSMC revealed the expec ted 5.3-kb band. Western blotting detected a 110-kb band in a 100,000 x g f raction of VSMC homogenates, Cultured VSMC as well as VSMC between the elas tic lamellae of pig thoracic aorta were positive for polycystin-2 by immuno fluorescence. The staining pattern was cytoplasmic. Treatment of the cells before fixation with Taxol, colchicine, or cytochalasin-D altered the patte rn of staining in a way suggesting alignment with the cytoskeleton. The imm unohistochemical staining for polycystin-2 was abolished by extraction with 0.5% Triton X-100, indicating that polycystin-2 is not associated with the cytoskeleton. Weak immunoreactivity for polycystin-2, which was markedly e nhanced by protease digestion, was detected in formaldehyde-fixed normal hu man elastic and intracranial arteries. Immunostaining of variable intensity for polycystin-2, which was not consistently enhanced by protease digestio n, was seen in the spindle-shaped cells of the wall of the intracranial ane urysms. The similar expression of polycystin-1 and polycystin-2 in the vasc ular smooth muscle is consistent with the proposed interaction of these pro teins in a single pathway. These observations suggest a direct pathogenic r ole for PKD1 and PKD2 mutations in the vascular complications of ADPKD.