Role of DNA Damage Response Signalling in Autosomal Dominant Polycystic Kidney Disease

Abstract

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a systemic, hereditary condition characterised by expansile kidney cysts, and there are no effective treatments to prevent kidney failure. The DNA Damage Response (DDR) signalling pathway consists of over 450 proteins that serve to maintain genomic fidelity. Recent evidence suggests that the DDR may be dysregulated in cystic kidney diseases but its role in ADPKD has not been previously investigated. The aim of this thesis was to test the hypothesis that the DDR pathway is upregulated in ADPKD and to evaluate whether it is a potential therapeutic target. Chapter One of this thesis provides an overview of the evidence linking DDR signalling to cystic kidney diseases. The results of Chapter Two demonstrated that multiple DDR-related genes were dysregulated in ADPKD, and that DDR proteins [gamma (γ)-H2AX, phosphorylated Ataxia Telangiectasia and Rad3-related (ATR) and AT Mutated (ATM)] were increased and localised to cystic kidney epithelial cells. Furthermore, exogenous oxidative DNA damage augmented DDR signalling and cell survival in human ADPKD cells, and exacerbated in vitro cyst growth, suggesting that dysregulated DDR signalling may promote the survival of PKD-mutated cells. The results of Chapter Three showed that pharmacological inhibition of ATM reduced cyst growth in vitro, but unexpectedly, the long-term progression of cystic kidney disease was not altered in Pkd1RC/RC/ATM+/- mice, suggesting that ATM has a redundant role in ADPKD. Chapter Four tested the hypothesis that Cdk2-mediated inhibition reduces DDR signalling and improves cystic phenotype. However, contrary to the hypothesis, genetic ablation of Cdk2 did not alter renal disease progression or γ-H2AX expression, likely due to compensation by Cdk1. Finally, Chapter Five investigated whether improving cystic kidney disease using sodium nitrate supplementation attenuates DDR signalling. Despite supportive data in vitro, long-term sodium nitrate treatment in vivo did not reduce DNA damage or cystic kidney disease in Pkd1RC/RC mice. In conclusion, the main novel findings of this thesis were that DDR signalling was dysregulated in ADPKD and reducing ATM did not alter long-term cystic kidney disease progression in vivo. Furthermore, targeting dysregulated cell cycle and restoring NO bioavailability were ineffective at modifying DDR signalling or kidney disease outcomes. These data suggest that the DDR signalling pathway exhibits redundancy, and further studies are needed to investigate the role of other DDR components and pathways in ADPKD.