A regulatory role of polycystin-1 on cystic fibrosis transmembrane conductance regulator plasma membrane expression.

Autosomal dominant polycystic kidney disease (ADPKD) is caused by genetic mutations in either PKD1 or PKD2, the genes that encode polycystin-1 (PC-1) and polycystin-2 (PC-2), respectively. ADPKD is characterized by the formation of multiple, progressive, fluid-filled renal cysts. To elucidate the mechanism of fluid secretion by ADPKD cysts, we examined the effect of PC-1 on the plasma membrane expression of cystic fibrosis transmembrane conductance regulator (CFTR), a key Cl(-) secretory protein. Five stably transfected MDCK lines were used in this study: two transfected with empty vector (control cells) and three expressing human PC-1 (PC-1 cells). The cAMP-induced endogenous short circuit currents (I(sc)) were smaller in PC-1 cells than in control cells. Compared to control cells, PC-1 cells transiently expressing pEGFP-CFTR showed significant reduction of whole cell cAMP-activated Cl(-) currents. Cell surface biotinylation experiments also indicated a reduction in surface expression of CFTR in PC-1 cells compared to control. Furthermore, studies using CHO cells transiently expressing PC-1 and CFTR suggest the importance of the PC-1 COOH-terminus in the observed reduction of CFTR plasma membrane expression. No differences in either endogeneous K(+) currents or P2Y receptor responses were observed between PC-1 and control cells, indicating the specificity of PC-1's action. These results indicate that PC-1 selectively maintains low cell surface expression of CFTR. Moreover, these findings suggest that the malfunction of PC-1 enhances plasma membrane expression of CFTR, thus causing abnormal Cl(-)secretion into the cyst lumen

TRPP2 and TRPV4 form a polymodal sensory channel complex

The primary cilium has evolved as a multifunctional cellular compartment that decorates most vertebrate cells. Cilia sense mechanical stimuli in various organs, but the molecular mechanisms that convert the deflection of cilia into intracellular calcium transients have remained elusive. Polycystin-2 (TRPP2), an ion channel mutated in polycystic kidney disease, is required for cilia-mediated calcium transients but lacks mechanosensitive properties. We find here that TRPP2 utilizes TRPV4 to form a mechano- and thermosensitive molecular sensor in the cilium. Depletion of TRPV4 in renal epithelial cells abolishes flow-induced calcium transients, demonstrating that TRPV4, like TRPP2, is an essential component of the ciliary mechanosensor. Because TRPV4-deficient zebrafish and mice lack renal cysts, our findings challenge the concept that defective ciliary flow sensing constitutes the fundamental mechanism of cystogenesis

Fatty Acid Oxidation is Impaired in An Orthologous Mouse Model of Autosomal Dominant Polycystic Kidney Disease: Polycystic kidney disease Autosomal Dominant Polycystic Kidney Disease Pkd1 ADPKD Mouse model Systems biology Metabolism Fatty acid oxidation F

Background: The major gene mutated in autosomal dominant polycystic kidney disease was first identified over 20 years ago, yet its function remains poorly understood. We have used a systems-based approach to examine the effects of acquired loss of Pkd1 in adult mouse kidney as it transitions from normal to cystic state. Methods: We performed transcriptional profiling of a large set of male and female kidneys, along with metabolomics and lipidomics analyses of a subset of male kidneys. We also assessed the effects of a modest diet change on cyst progression in young cystic mice. Fatty acid oxidation and glycolytic rates were measured in five control and mutant pairs of epithelial cells. Results: We find that females have a significantly less severe kidney phenotype and correlate this protection with differences in lipid metabolism. We show that sex is a major determinant of the transcriptional profile of mouse kidneys and that some of this difference is due to genes involved in lipid metabolism. Pkd1 mutant mice have transcriptional profiles consistent with changes in lipid metabolism and distinct metabolite and complex lipid profiles in kidneys. We also show that cells lacking Pkd1 have an intrinsic fatty acid oxidation defect and that manipulation of lipid content of mouse chow modifies cystic disease. Interpretation: Our results suggest PKD could be a disease of altered cellular metabolism. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

The Molecular Basis of Focal Cyst Formation in Human Autosomal Dominant Polycystic Kidney Disease Type I

AbstractAutosomal dominant polycystic kidney disease (ADPKD) is a common disease and an important cause of renal failure. It is characterized by considerable intrafamilial phenotypic variation and focal cyst formation. To elucidate the molecular basis for these observations, we have developed a novel method for isolating renal cystic epithelia from single cysts and have used it to show that individual renal cysts in ADPKD are monoclonal. Loss of heterozygosity was discovered within a subset of cysts for two closely linked polymorphic markers located within the PKD1gene. Genetic analysis revealed that it was the normal haplotype that was lost. This study provides a molecular explanation for the focal nature of cyst formation and a probable mechanism whereby mutations cause disease. The high rate at which “second hits” must occur to account for the large number of cysts observed suggests that unique structural features of the PKD1gene may be responsible for its mutability

Fatty Acid Oxidation is Impaired in An Orthologous Mouse Model of Autosomal Dominant Polycystic Kidney Disease

Background: The major gene mutated in autosomal dominant polycystic kidney disease was first identified over 20 years ago, yet its function remains poorly understood. We have used a systems-based approach to examine the effects of acquired loss of Pkd1 in adult mouse kidney as it transitions from normal to cystic state. Methods: We performed transcriptional profiling of a large set of male and female kidneys, along with metabolomics and lipidomics analyses of a subset of male kidneys. We also assessed the effects of a modest diet change on cyst progression in young cystic mice. Fatty acid oxidation and glycolytic rates were measured in five control and mutant pairs of epithelial cells. Results: We find that females have a significantly less severe kidney phenotype and correlate this protection with differences in lipid metabolism. We show that sex is a major determinant of the transcriptional profile of mouse kidneys and that some of this difference is due to genes involved in lipid metabolism. Pkd1 mutant mice have transcriptional profiles consistent with changes in lipid metabolism and distinct metabolite and complex lipid profiles in kidneys. We also show that cells lacking Pkd1 have an intrinsic fatty acid oxidation defect and that manipulation of lipid content of mouse chow modifies cystic disease. Interpretation: Our results suggest PKD could be a disease of altered cellular metabolism

Rapamycin Ameliorates PKD Resulting from Conditional Inactivation of Pkd1

Aberrant activation of the mammalian target of rapamycin (mTOR) pathway occurs in polycystic kidney disease (PKD). mTOR inhibitors, such as rapamycin, are highly effective in several rodent models of PKD, but these models result from mutations in genes other than Pkd1 and Pkd2, which are the primary genes responsible for human autosomal dominant PKD. To address this limitation, we tested the efficacy of rapamycin in a mouse model that results from conditional inactivation of Pkd1. Mosaic deletion of Pkd1 resulted in PKD and replicated characteristic features of human PKD including aberrant mTOR activation, epithelial proliferation and apoptosis, and progressive fibrosis. Treatment with rapamycin was highly effective: It reduced cyst growth, preserved renal function, inhibited epithelial cell proliferation, increased apoptosis of cyst-lining cells, and inhibited fibrosis. These data provide in vivo evidence that rapamycin is effective in a human-orthologous mouse model of PKD