Rescuing Cystic Phenotypes In Pkd2-mutated Mouse Model By Ectopic Restoration Of Human PKD2

Autosomal dominant polycystic kidney disease (ADPKD) is a group of monogenic disorders that result in hepatorenal cyst development. Two causal genes (PKD1and PKD2) have been identified for this disease. Approximately85%of ADPKD patients have mutations in the PKD1gene, which encodes Polycystin-1(PC1). While～15%of ADPKD cases results from mutations in the PKD2gene, which encodes Polycystin-2(PC2).To understand the molecular mechanism of ADPKD, many animal models for the disease have been generated by genetic manipulations. Knockout mice for Pkdl and Pkd2exhibit embryonic lethality and marked cystogenesis in the kidney. There are also other cystic phenotypes and abnormalities in the heart, brain, pancreas, and liver. Pkd2knockout mice die in utero and display total body edema, abnormal left-right axis, focal areas of haemorrhage, structural defects in cardiac septation, cyst formation in maturing nephrons and pancreatic ducts.In order to better understand PC2functions in vivo, we have recently generated a transgenic mouse for PKD2(PKD2tg), in which human PKD2ORF cDNA is cloned into pCAGGS mammalian expression vector and controlled under a CMV enhancer and chicken β-actin promoter. Ectopic overexpression of human PC2can be found in heart, liver, kidney and many other tissues. However, hemizygous and homozygous PKD2transgene do not result in any abnormal phenotypes during mouse embryogenesis and orgenogenesis, indicating the ectopic overexpression of PC2is not deleterious function in vivo. By crossmating with Pkd2knockout mice, we obtained Pkd2-/-:PKD2+/tg7and Pkd2-/-:PKD2tg7/tg7mice. Pkd2-/-mice with human PKD2transgene can be survival into adulthood and escape embryonic lethality caused by losing of PC2. Most of Pkd2-/-:PKD2+/tg7and Pkd2-/-:PKD2tg7/tg7can be born and survive normally. Kaplan-Meier analysis illustrated that approximately50%of Pkd2-/-:PKD2+/tg7mice survive until6months, while over12months in that of Pkd2-/-:PKD2tg7/tg7mice, suggesting that human PKD2transgene can greatly replace PC2functions in mice lacking endogenous PC2. The fact shows that disease phenotypes of Pkd2-/-:PKD2tg7/tg7mice can survive much longer than the Pkd2-/-mice with a single Tg7allele. By pathological analysis, we also found that the Pkd2-/-:PKD2tg7/tg7mice exhibited significantly decreased cystic number and volume in pancreas, liver and kidneys compared to Pkd2-/-:PKD2+/tg7mice. In addition, renal function analyses also showed that the hepatorenal function in Pkd2-/-:PKD2tg7/tg7mice can be much better improved than in Pkd2-/-:PKD2+/tg7mice. These results strongly support that amelioration of ADPKD phenotypes by restoration of PC2is dose-dependent. Our finding elucidates functional role of PC2during mammalian embryogenesis and organogenesis, and also provide a molecular basis for gene therapy of ADPKD.