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

• Applicants: Professor Dr. Carsten Bergmann; Professor Dr. Michael Krahn, Ph.D.
• Subject Area: Nephrology ; Nuclear Medicine, Radiotherapy, Radiobiology
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 418060010

Polycystic kidney disease (PKD) and associated ciliopathies are common life-threatening genetic disorders. While a subset of disease-causing genes has been identified in the past, no mutation in any of the known genes could be identified in a substantial number of PKD-patients. 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 mutations in the gene PATJ in three unrelated families with PKD. PATJ encodes for a PDZ-domain containing adaptor protein, which supports the assembly of the Crumbs complex at the TJ. We have shown that in addition to its known localization at the TJ, PATJ localizes to primary cilia. Knockout of PATJ in epithelial cells results in TJ defects as well as disturbed apical-basal polarity. Moreover, PATJ-knockout cells display a reduced number of primary cilia. Mechanistically, we demonstrated that PATJ directly binds the Histone Deacetylase 7 (HDAC7) and that inhibition or downregulation of HDAC7 can restore TJ assembly as well as apical-basal polarity and primary cilia in PATJ-deficient cells. In Zebrafish, knockdown or knockout of PATJ and its paralogue MUPP1 results in a reduction of primary cilia length and phenotypes typical for ciliopathies such as hydrocephalus and altered heart looping. Reintroduction of PATJ alleles identified in PKD patients in these fish resulted in cilia defects and corresponding phenotypes, demonstrating the importance of the mutations for the pathogenesis of the disease in these individuals. Thus, we identified a new function of PATJ regulating primary cilia formation and further explored the regulation of TJ and apical-basal polarity by PATJ. In this project we will address, which target genes are regulated by HDAC7 in PATJ-deficient cells and whether and which substrates are deacetylated by HDAC7. Subsequently, these candidates will be characterized regarding their function in TJ formation, apical-basal polarity and regulation of primary cilia in cell culture and in zebrafish. In a parallel approach, we will screen larger PKD patient cohorts for new PATJ mutations, which then will be characterized. In addition, the molecular pathomechanism and affected signalling pathways in PATJ alleles will be further explored. Finally, we will establish a PATJ/MUPP1 double knockout mouse in order to investigate the (redundant) physiological function of these proteins in mammals, in particular in the context of PKD. 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 and molecular mechanisms of cyst formation and ciliopathies, which might lead to the development of distinct therapeutic approaches.

• DFG Programme: Research Grants