Abstract. The expression of polycystin-1 in the vascular smooth muscle cells (VSMC) of elastic and large distributive arteries suggests that some vascular manifestations of autosomal-dominant polycystic kidney disease (ADPKD) result directly from the genetic defect. Intracranial aneurysms have been reported in PKD2, as well as in PKD1 families. To determine whether the vascular expression of polycystin-2 is similar to that of polycystin-1, the expression of PKD2 mRNA and protein in cultured pig aortic VSMC was studied and immunofluorescence and immunohistochemistry were used to study the localization of polycystin-2 in cultured pig aortic VSMC, pig ascending thoracic aorta, and normal elastic and intracranial arteries and intracranial aneurysms obtained at autopsy from patients without or with ADPKD. Tissues derived from Pkd2 wild-type and Pkd2 null mice were used to confirm the specificity of the immunostaining for polycystin-2. Northern blots of VSMC revealed the expected 5.3-kb band. Western blotting detected a 110-kb band in a 100,000 × g fraction of VSMC homogenates. Cultured VSMC as well as VSMC between the elastic lamellae of pig thoracic aorta were positive for polycystin-2 by immunofluorescence. The staining pattern was cytoplasmic. Treatment of the cells before fixation with Taxol, colchicine, or cytochalasin-D altered the pattern of staining in a way suggesting alignment with the cytoskeleton. The immunohistochemical 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 enhanced by protease digestion, was detected in formaldehydefixed normal human elastic and intracranial arteries. Immunostaining of variable intensity for polycystin-2, which was not consistently enhanced by protease digestion, was seen in the spindle-shaped cells of the wall of the intracranial aneurysms. The similar expression of polycystin-1 and polycystin-2 in the vascular smooth muscle is consistent with the proposed interaction of these proteins in a single pathway. These observations suggest a direct pathogenic role for PKD1 and PKD2 mutations in the vascular complications of ADPKD.

Autosomal dominant polycystic kidney disease (AD-PKD) is predominantly caused by mutations of the gene PKD1, which encodes a large protein, polycystin, of unknown function. A variety of arterial abnormalities occur with increased prevalence in ADPKD patients. Using an antiserum against the nonduplicated region of the polycystin protein, immunostaining of vascular smooth muscle cells was detected in normal adult elastic arteries. Partial digestion of tissue slices with nonspecific proteases greatly enhanced this staining. Similar enhancement was seen with specific elastase digestion. Immunostaining for smooth muscle actin was not affected by elastase. Antiserum preadsorbed with peptide antigen gave no staining. In specimens of intracranial aneurysms, aortic dissections, and dolichoectatic arteries from thirteen patients with ADPKD, immunostaining of variable intensity for polycystin was demonstrated in arterial smooth muscle cells and myofibroblasts, along with disruption of elastic laminae. Further elastase digestion did not significantly alter staining patterns. Intracranial aneurysms from patients without ADPKD also showed a variable degree of immunostaining with polycystin antisera in the same distribution. The expression of polycystin in arterial smooth muscle suggests a direct pathogenic role for ADPKD-related mutations in the arterial complications of this disease.