Pkd2 haploinsufficiency alters intracellular calcium regulation in vascular smooth muscle cells

Abstract

Autosomal-dominant polycystic kidney disease is a multiorgan disease and its vascular manifestations are common and life-threatening. Despite this, little is known about their pathogenesis. Somatic mutations to the normal PKD allele in cystic epithelia and cyst development associated with the unstable Pkd2(WS25) allele suggest a two-hit model of cystogenesis. However, it is unclear if this model can account for the cardiovascular pathology or if haploinsufficiency alone is disease-associated. In the present study, we found a decreased polycystin-2 (PC2, protein encoded by Pkd2 gene) expression in Pkd2( +/-) vessels, roughly half the wild-type level, and an enhanced level of intracranial vascular abnormalities in Pkd2 (+/-) mice when induced to develop hypertension. Consistent with these observations, freshly dissociated Pkd2 (+/-) vascular smooth muscle cells have significantly altered intracellular Ca(2+) homeostasis. The resting [Ca(2+)](i) is 17.1% lower in Pkd2 (+/-) compared with wild-type cells (P=0.0003) and the total sarcoplasmic reticulum Ca(2+) store (emptied by caffeine plus thapsigargin) is decreased (P<0.0001). The store operated Ca(2+) (SOC) channel activity is also decreased in Pkd2 (+/-) cells (P=0.008). These results indicate that inactivation of just one Pkd2 allele is sufficient to significantly alter intracellular Ca(2+) homeostasis, and that PC2 is necessary to maintain normal SOC activity and the SR Ca(2+) store in VSMCs. Based on these findings, and the fact that [Ca(2+)](i) signaling is essential to the regulation of contraction, production and secretion of extracellular matrix, cellular proliferation and apoptosis, we propose that the abnormal intracellular Ca(2+) regulation associated with Pkd2 haploinsufficiency is directly related to the vascular phenotype.

Drosophila Pkd2 Is Haploid-insufficient for Mediating Optimal Smooth Muscle Contractility

“…Our study demonstrated that Drosophila PKD2 was required for optimal SMC contractility, and mutating just one of the two Pkd2 gene copies was sufficient to reduce the contractility by ϳ53%. This is consistent with a recent report that intracellular Ca 2ϩ is reduced in Pkd2ϩ/Ϫ heterozygous mouse vascular SMCs, and these mice show higher rates of vascular complications and lethality than Pkd2ϩ/ϩ control mice under an experimentally induced hypertension condition (26). Based on these data, we propose that haploinsufficiency of human PKD2 function leads to decreased vascular SMC contractility and function, and this may play a primary role in the development of a variety of vascular complications such as hypertension and aneurysms in ADPKD patients.…”

“…Vascular fragility and leakage have been reported in Pkd1Ϫ/Ϫ and Pkd2Ϫ/Ϫ mouse models (20,24,25). In Pkd2ϩ/Ϫ mouse vascular SMCs, there is a small (17%) but statistically significant reduction of intracellular calcium (26). While these phenotypes implicate the vascular smooth muscle cells, it is not known whether Pkd2 has specific functional roles in these cells.…”

Human ADPKD primary cyst epithelial cells with a novel, single codon deletion in the PKD1 gene exhibit defective ciliary polycystin localization and loss of flow-induced Ca2+ signaling

“…8). These diminished signals resemble those observed in aortic vascular smooth muscle cells of pkd2(ϩ/Ϫ) mice (48). Unlike the reduced thapsigargin and CCE responses, PKD cyst cell Ca i 2ϩ elevations in response to angiotensin II and to AVP are of normal magnitude, although slightly delayed in onset.…”

Cell biology of polycystin-2

“…Moreover, overexpression of the naturally occurring mutant PKD2-D511V had a dominant negative effect on Ca 2+ release transients [46] lending support to the idea that endogenous PKD2 was likely to function as an intracellular Ca 2+ -induced Ca 2+ release channel. Experiments in vascular smooth muscle cells [47] and immortalized lymphoblasts [48] from PKD2 knock out mice and ADPKD patients, respectively, showed that PKD2 played a role in G protein coupled receptor-induced Ca 2+ signaling, but the possibility that PKD2 could have also contributed to Ca 2+ signaling through Ca 2+ influx was not clearly addressed in these studies. Overall, despite the differences, there is significant gain-and loss-of-function evidence to suggest that in addition to residing in the ER, PKD2 also has a functional role in regulating intracellular Ca 2+ release in response to localized changes in intracellular Ca 2+ .…”