Early development of polycystic kidney disease in transgenic mice expressing an activated mutant of the beta-catenin gene.

Autosomal dominant polycystic kidney disease (ADPKD) is common and is a major cause of renal failure. Although the genetics of ADPKD are well known and have led to the discovery of polycystins, a new protein family, the pathogenesis of the disease remains largely unknown. Recent studies have indicated that the beta-catenin signaling pathway is one of the targets of the transduction pathway controlled by the polycystins. We have generated transgenic mice that overproduce an oncogenic form of beta-catenin in the epithelial cells of the kidney. These mice developed severe polycystic lesions soon after birth that affected the glomeruli, proximal, distal tubules and collecting ducts. The phenotype of these mice mimicked the human ADPKD phenotype. Cyst formation was associated with an increase in cell proliferation and apoptosis. The cell proliferation and apoptotic indexes was increased 4-5-fold and 3-4-fold, respectively, in cystic tubules of the transgenic mice compared to that of littermate controls. Our findings provide experimental genetic evidence that activation of the Wnt/beta-catenin signaling pathway causes polycystic kidney disease and support the view that dysregulation of the Wnt/beta-catenin signaling is involved in its pathogenesis.

Hepatomegaly in transgenic mice expressing an oncogenic form of beta-catenin.

Inappropriate activation of the Wnt/beta-catenin signaling, resulting mainly from activating mutations of the beta-catenin gene, has been implicated recently in the development of hepatocellular carcinoma (HCC). We have generated transgenic mice expressing an oncogenic form of beta-catenin in their hepatocytes to analyze the effect of deregulated beta-catenin signaling on liver homeostasis. These mice rapidly developed hepatomegaly soon after birth, with livers three to four times heavier than those of nontransgenic littermates. The liver cell hyperplasia resulted from increased cell proliferation without any compensatory apoptosis. Although the genes encoding c-myc and cyclin D1 are potential targets of the beta-catenin signaling pathway, neither of them was overexpressed in the hyperplastic livers of beta-catenin transgenic mice. Thus, the key target genes of the beta-catenin signaling pathway in the liver remain to be identified.