S SARAVANABAVAN 1,2, J ZHANG 1,2, A MUNT 1,2, A WONG 1,2, G RANGAN 1,2
1Centre for Transplant and Renal Research, Westmead Institute for Medical Research, The University of Sydney , Westmead , Australia, 2Department of Renal Medicine, Westmead Hospital, Westmead. , Australia
Aim: To determine the combined effect of reducing ataxia telangiectasia mutated (ATM) protein and cisplatin on apoptosis in cystic epithelial cells in vivo.
Background: In some cancerous cells, inhibition of ATM, a proximal kinase in the DNA damage response (DDR) pathway together with cisplatin causes mitotic catastrophe and synthetic lethality. As multiple DDR signalling pathways are also dysregulated in ADPKD, we hypothesised that cisplatin combined with ATM loss induces the selective apoptosis of cystic epithelial cells.
Methods:Pkd1RC/RC/Atm+/- mice received a single sublethal dose of cisplatin (0.1, 0.5, 1.0, 3.5 or 7.0 mg/kg) or vehicle (n=1/group) and sacrificed 72-hours later. Renal histology and DNA double-strand breaks were assessed by quantitative image analysis of nuclear phosphorylated histone H2AX (γH2AX).
Results: In the vehicle group, baseline double-stranded breaks, as determined by γH2AX intensity, was 1.41±0.71-fold higher in cystic epithelial cells compared to normal tubular cells (p<0.05). As expected, cisplatin increased γH2AX in a dose-dependent manner in both cystic and normal tubular epithelial cells (r=0.58; 95% CI [0.50, 0.65] and r=0.81; 95% CI [0.72, 0.87] respectively). However, compared to normal tubular epithelial cells, the relative increase in γH2AX expression was lower in cystic epithelial cells (0.5 mg/kg: 2.36±0.55 vs. 1.54±0.73-fold; 7.0 mg/kg: 5.43±0.94-fold vs. 3.14±1.18-fold respectively; p<0.05). By light microscopy, cisplatin caused a dose-dependent increase in sublethal cortical tubular damage (dilatation, loss of brush border and cast formation) but did not lead to the selective apoptosis of cystic epithelial cells.
Conclusion: Contrary to our hypothesis, cystic epithelial cells exhibit cisplatin-resistance compared to normal tubular epithelial cells possibly due to higher baseline upregulation of DDR signalling and/or compensation by other DDR pathways.
Sayanthooran Saravanabavan is a Postdoctoral Fellow in Polycystic Kidney Disease at the Centre for Transplant and Renal Research, Westmead Institute for Medical Research, The University of Sydney. His work currently focuses on understanding the role of the DNA damage response in acute kidney injury repair and ADPKD progression. In addition, he is testing the potential use of peripheral blood mitochondrial DNA as a prognostic biomarker in ADPKD.