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310 DELETERIOUS ROLE OF CASPASE 3 AND APOPTOSIS IN POLYCYSTIC KIDNEY DISEASE.
  1. Y. Tao1,
  2. I. Zafar1,
  3. L. Lu1,
  4. Z. He1,
  5. R. W. Schrier1,
  6. C. L. Edelstein1
  1. 1Division of Renal Diseases, University of Colorado Health Sciences Center, Denver, CO.

Abstract

Increased apoptosis is a feature of polycystic kidney disease (PKD). Caspases 3 and 7 are the major mediators of apoptosis, and caspase 1 is a proinflammatory caspase. We have previously demonstrated that the pancaspase inhibitor IDN-8050 reduces tubular apoptosis and proliferation and slows disease progression in the Han:SPRD rat model of PKD (Tao, Edelstein, PNAS 2005). However, the exact caspases involved in PKD progression and the effect of specific caspase-3 inhibition on apoptosis in PKD is not known. cpk/cpk mice die of PKD and renal failure between 3 and 4 weeks of age. We backcrossed cpk/+ with caspase 3+/− mice to develop heterozygous (cpk/cpk casp-3+/−) and homozygous (cpk/cpk casp-3−/−) double knockout mice. On immunoblot analysis the active form of caspase 3 in the kidney is increased significantly (2.5-fold, p < .05) in cpk/cpk mice compared with +/+ mice, and there was reduced expression of caspase 3 in cpk/cpk casp-3+/− and no detectable expression in cpk/cpk casp-3−/− mice. The cpk/cpk casp-3+/− mice live three times longer (82 vs 24 days, p < .05) and the cpk/cpk casp-3−/− mice live at least four times longer (117 vs 24 days, p < .001) than cpk/cpk mice. Both cpk/cpk casp-3+/− and cpk/cpk casp-3−/− mice have a significantly lower cyst volume density and two kidney/total body weight ratio than cpk/cpk mice. In view of the deficiency of caspase 3, we determined the number of TUNEL-positive apoptotic cells. The number of TUNEL-positive tubular cells/HPF was 0.1 in cpk/cpk, 0.6 in cpk/cpk casp3+/− mice, and 0.4 in cpk/cpk casp3−/− mice (p = NS). Thus, despite the lack of caspase 3, the double-knockout mice still had significant apoptosis. Therefore, we investigated alternative pathways of apoptosis. On immunoblot analysis, caspase 7 was increased 2.6-fold (p = .03) in cpk/cpk, cpk/cpk casp-3+/− and cpk/cpk casp-3−/− versus +/+ littermates. The antiapoptotic protein Bcl-2 decreased significantly (twofold, p = .05) in cpk/cpk, cpk/cpk casp3+/−, and cpk/cpk casp3−/− mice compared with wild-type littermates. In summary, our data demonstrate that both heterozygous and homozygous caspase-3 deletion markedly prolongs life in cpk/cpk mice with PKD and that an alternative caspase 7-mediated pathway of apoptosis eventually dominates in the polycystic kidney.

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