The role of PATJ in ciliopathies and for the pathogenesis of kidney cysts

Basic data for this project

Description

Polycystic kidney disease (PKD) and associated ciliopathies are common life-threatening genetic disorders. In the recent years, a subset of disease causing genes have been identified and partially characterized. However, in a substantial number of patients with typical PKD or related ciliopathies no mutation in any of the known disease causing genes could be identified. Therefore, the identification and characterization of novel causative genes has become increasingly important to obtain a clearer picture of these diseases and their underlying pathomechanisms.We have identified different biallelic, truncating and non-truncating mutations in the gene PATJ in three unrelated families with PKD. So far, no mutations in PATJ have been described. PATJ encodes for a PDZ-domain containing adaptor protein, which supports the assembly of the Crumbs complex at the tight junctions (TJ) and primary cilia. Within this conserved complex, the adaptor protein Pals1 links the transmembrane protein Crumbs and PATJ. Together with the PAR/aPKC complex, the Crumbs complex determines the apical plasma membrane domain and regulates apical-basal polarity and cilia formation in epithelia. Notably, inactivation of one allele of Pals1 results in kidney cysts in mice. These mice show a disturbed regulation of the Hippo- and TGFbeta-signaling pathway, which are both involved in the pathogenesis of kidney cysts. PATJ supports adherens junctions (AJ)/TJ stability and myosin-dependent cell contractility in Drosophila and cultured kidney tubular cells. Furthermore, knock-down or knock-out of Patj results in impaired lumen formation and enhanced cyst growth in three-dimensional cyst assays. However, the cellular and molecular mechanisms of PATJ during TJ- and cilia formation and in particular tubulogenesis are still not fully understood.Therefore, the aim of this project is to investigate the role of PATJ during the pathogenesis of kidney cyst development/ciliopathies. First, we will use cultured epithelial cells from kidney tubules with a knock-out of PATJ to characterize the function of this protein during TJ assembly, signal transduction (in particular Hippo- and TGF-signaling), primary cilium function/signaling and tubulogenesis. Furthermore, we will reintroduce exogenous PATJ proteins bearing the mutations identified in PKD patients in these knockout cells and analyze the cellular phenotype and misregulation of the molecular signaling pathways. Finally, we will establish Patj knock-out mouse- and zebrafish models to evaluate our findings in vivo.From these experiments, we hope to get valuable insights into the physiological function of PATJ during lumen formation of kidney tubules and its misregulation in a group of patients with PKD. The results will further contribute to our understanding of the cellular mechanisms of cyst formation and ciliopathies, which might lead to the development of distinct therapeutic approaches.