Submitted on October 9, 2008
Revised on January 7, 2009
Accepted on January 21, 2009
The Cardiotonic Steroid Hormone Marinobufagenin Induces Renal Fibrosis. Implication of Epitheilal to Mesenchymal Transition
Larisa V. Fedorova1, Vanamala Raju, Nasser El-Okdi, Amjad Shidyak, David Joseph Kennedy, Sandeep Vetteth2, David R Giovannucci3, Alexei Y Bagrov, Olga V. Fedorova4, Joseph Isaac Shapiro5, and Deepak Malhotra6*
1 University of Toledo, Health Science Campus
2 University of Toledo Health Science Campus
3 University of Toledo College of Medicine
4 National Institute on Aging/NIH
5 University of Toledo- Health Science Campus
6 Univrsity of Toledo, Health Science Campus
* To whom correspondence should be addressed. E-mail: deepak.malhotra{at}utoledo.edu.
We recently demonstrated that the cardiotonic steroid, marinobufagenin (MBG), induced fibrosis in rat hearts through direct stimulation of collagen I secretion by cardiac fibroblasts. This stimulation was also responsible for the cardiac fibrosis seen in experimental renal failure. In this study the effect of MBG on the development of renal fibrosis in rats was investigated. Four weeks of MBG infusion stimulated up regulation of procollagen I, an increase in collagen I content in the interstitium, and appearance of fibrotic lesions. MBG also significantly induced the protein levels and nuclear localization of transcription factor Snail. It is known that activation of Snail is associated with epithelial-mesenchymal transition (EMT) during renal fibrosis. To examine whether MBG alone can trigger EMT we used porcine proximal tubular cell line, LLC-PK1. MBG (100 nM) caused LLC-PK1 cells grown to confluence to acquire a fibroblast like shape and have an invasive motility. The expressions of mesenchymal proteins collagen I, fibronectin and vimentin were increased two fold. But the total level of e-cadherin remained unchanged. These alterations in LLC-PK1 cells in the presence of MBG were accompanied by elevated expression and nuclear translocation of Snail. During the time course of EMT, MBG did not have measurable inhibitory effects on the ion pumping activity of its natural ligand, Na+, K+-ATPase. Our data suggest that the MBG may be an important factor in inducing EMT and, through this mechanism, elevated levels of MBG in chronic renal failure may play a role in the progressive fibrosis.
