Caspases, Bcl-2 proteins and apoptosis in autosomal-dominant polycystic kidney disease

Background. Apoptosis is a characteristic feature of human autosomal-dominant polycystic kidney disease (ADPKD). The Han:Sprague-Dawley (SPRD) rat model closely resembles human ADPKD and presents an opportunity to investigate the apoptotic pathway in the pathogenesis of this disease. Methods. Han:SPRD rats were studied during the early stages of ADPKD (newborn, 2 and 6 weeks old). Apoptotic cells were detected by the TUNEL (Tdt-mediated dUTP nick end-labeling) assay. Caspase-3 activity was measured using the fluorescent substrate DEVD-AMC and cleavage of poly (ADP-ribose) polymerase [PAR-P]. Expression of pro- and anti-apoptotic B-cell lymphoma (Bcl-2) proteins was detected on Western blot analysis. Results. TUNEL (+) cells, caspase-3 activity and caspase-mediated PARP breakdown were significantly increased in 2-week-old heterozygous (Cy/+) and homozygous (Cy/Cy) rat kidneys compared to normal littermate controls. In Cy/+ rat kidneys, decreased expression of anti-apoptotic Bcl-X-L coincided with increased caspase-3 activity at 2 weeks of age while expression of Bcl-2, another anti-apoptotic protein, increased at 6 weeks of age. In Cy/Cy rat kidneys, decreased expression of Bcl-X-L and increased expression of Bcl-2 was present at 2 weeks of age. Pro-apoptotic Bax and Bad expression was unchanged at 2 weeks of age in both Cy/+ and Cy/Cy rat kidneys. Conclusions. Activation of caspase-3 and dysregulation of the balance between pro- and anti-apoptotic Bcl-2 family members, specifically a down-regulation of anti-apoptotic Bcl-X-L, correlates with increased apoptosis in polycystic Han:SPRD rat kidneys.