Submitted on November 20, 2007
Accepted on May 15, 2008
Protein kinase B/Akt activity is involved in renal TGF
-1 driven epithelial-mesenchymal transition in vitro and in vivo
Jayesh J Kattla1, Rosemarie M Carew2, Mediha Heljic3, Catherine Godson1, and Derek P Brazil1*
1 UCD Conway Institute, University College Dublin, Dublin, D4, Ireland
2 UCD Conway Institute, University College Dublin, Ireland
3 UCD Conway Institute, University College Dublin, Dublin, Dublin, Ireland
* To whom correspondence should be addressed. E-mail: derek.brazil{at}ucd.ie.
The molecular pathogenesis of diabetic nephropathy (DN), the leading cause of end-stage renal disease worldwide, is complex and not fully understood. Transforming growth factor-beta (TGF
1) plays a critical role in many fibrotic disorders, including DN. Here, we report protein kinase B (PKB/Akt) activation as a downstream event contributing to the pathophysiology of DN. We investigated the potential of PKB/Akt to mediate the profibrotic bioactions of TGF1 in kidney. Treatment of NRK52E renal epithelial cells with TGF1 resulted in activation of PI3K and PKB/Akt as evidenced by increased Ser473 phosphorylation and GSK3 phosphorylation. TGF1 also stimulated increased Smad3 phosphorylation in these cells, a response that was insensitive to inhibition of PI3kinase or PKB/Akt. NRK52E cells displayed a loss of ZO-1 and E-cadherin and gain in vimentin and alpha-smooth muscle actin (
-SMA) expression, consistent with the fibrotic actions of TGF1. These effects were blocked with inhibitors of phosphotidylinositol-3-kinase (PI3K) and PKB/Akt. Furthermore, over-expression of PTEN, the lipid phosphatase regulator of PKB/Akt activation inhibited TGF1-induced PKB/Akt activation. Interestingly, in the Goto Kakizaki rat model of type 2 diabetes, we also detected increased phosphorylation of PKB/Akt and its downstream target GSK3 in the tubules, relative to control Wistar rats. Elevated Smad3 phosphorylation was also detected in kidney extracts from Goto Kakizaki rats with chronic diabetes. Together, these data suggest that TGF1-mediated PKB/Akt activation may be important in renal fibrosis during diabetic nephropathy.
