Ouabain acts through the Na,K-ATPase to stimulate proliferation in ADPKD

Abstract

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by multiple fluid-filled cysts resulting from increased proliferation and alterations in the fluid transport properties of the renal epithelium. The renal Na,K-ATPase is critical for the vectorial movement of salt and water, but its role in the pathophysiology of ADPKD is not understood. The cardiotonic steroid ouabain blocks the activity and transport properties of the Na,K-ATPase. In addition, ouabain stimulates proliferation in some cell types. We found that nanomolar concentrations of ouabain induced proliferation of kidney cells from patients with ADPKD, but had no effect on normal human kidney cells (NHK). The effect of ouabain was dependent on activation of Src and the EGFR. Inhibition of MEK blocked ouabain-induced cell proliferation, suggesting that the mitogenic effect of ouabain was mediated through the MEK-ERK pathway. In addition, ouabain increased apoptosis in ADPKD cells. However, proliferation is favored over apoptosis. Dose response curves for the interaction of ouabain with Na,K-ATPase activity showed that unlike NHK cells, the enzyme in ADPKD cells exhibits a higher affinity for ouabain. The aberrant ouabain affinity of ADPKD cells was not due to altered expression of Na,K-ATPase isoforms, because like NHK cells, ADPKD cells only possess the α1β1 isozyme. These results show that ouabain causes changes in the number of cells in the ADPKD epithelium, stimulating its growth. Because ouabain is an endogenous hormone present in blood, it may play a role in formation and progression of cysts in ADPKD. Supported by NIH grant HD043044 and the PKD Foundation.