OUABAIN ENHANCES PROGRAMMED CELL DEATH IN ADPKD CELLS
Lavakumar Reddy Aramadhaka1, 2, Gail A Reif 2, 3, Darren P. Wallace 1,2,3, and Gustavo Blanco1, 2.
Departments of Molecular and Integrative Physiology1, The Kidney Institute2 and Department of Medicine3, University of Kansas Medical Center, Kansas City, Kansas.
While the autosomal dominant polycystic kidney disease (ADPKD) is characterized by an increase in cell proliferation, apoptosis is also enhanced in the disease. Previous work in our laboratory has shown that the hormone ouabain, in concentrations similar to those circulating in plasma (3nM) stimulate the growth of cyst-lining renal epithelial cells obtained from patients with ADPKD. This effect involves the Na,K-ATPase signaling system and the activation of the epidermal growth factor receptor (EGFR), the kinase Src and the MAPK pathway. In this work, we investigated the effect of ouabain in ADPKD programmed cell death. Treatment of primary cultures of ADPKD cells with 3 nM ouabain for 24 h increased cell apoptosis as determined by TUNEL assay staining, a biochemical marker of DNA fragmentation and annexin V labeling. Ouabain stimulated the release of cytochrome c from mitochondria, a mediator of programmed cell death. Also, ouabain enhanced the cleavage and activity of caspase-3, a key executioner of the cell apoptotic pathway. These results suggest that ouabain has a dual effect in ADPKD cells, and while the hormone favors cell growth, it also causes cell apoptosis. The involvement of cytochrome c and caspase-3 in ouabain-induced ADPKD apoptosis indicates that the effect involves both the intrinsic and extrinsic pathway that mediate programmed cell death. Understanding the effects and mechanisms of action of ouabain in ADPKD cell growth and apoptosis is important, since it will help to understand the role that the hormone plays in ADPKD cystogenesis.