Protein kinase B/Akt activity is involved in renal TGF-beta1-driven epithelial-mesenchymal transition in vitro and in vivo.
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-beta1) plays a critical role in many fibrotic disorders, including DN. In this study, 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 TGF-beta1 in kidney. Treatment of normal rat kidney epithelial cells (NRK52E) with TGF-beta1 resulted in activation of phosphatidylinositol 3-kinase (PI3K) and PKB/Akt as evidenced by increased Ser473 phosphorylation and GSK-3beta phosphorylation. TGF-beta1 also stimulated increased Smad3 phosphorylation in these cells, a response that was insensitive to inhibition of PI3K or PKB/Akt. NRK52E cells displayed a loss of zona occludins 1 and E-cadherin and a gain in vimentin and alpha-smooth muscle actin expression, consistent with the fibrotic actions of TGF-beta1. These effects were blocked with inhibitors of PI3K and PKB/Akt. Furthermore, overexpression of PTEN, the lipid phosphatase regulator of PKB/Akt activation, inhibited TGF-beta1-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, GSK-3beta, in the tubules, relative to that in control Wistar rats. Elevated Smad3 phosphorylation was also detected in kidney extracts from Goto-Kakizaki rats with chronic diabetes. Together, these data suggest that TGF-beta1-mediated PKB/Akt activation may be important in renal fibrosis during diabetic nephropathy.
Kattla
Jayesh J
JJ
UCD Diabetic Research Centre, School of Biomolecular and Biomedical Science, University College Dublin, Dublin, Ireland.
Carew
Rosemarie M
RM
Heljic
Mediha
M
Godson
Catherine
C
Brazil
Derek P
DP
D000818:Animals; D054338:Cell Transdifferentiation / Q000502:physiology*; D002867:Chromones / Q000494:pharmacology; D003921:Diabetes Mellitus, Experimental / Q000503:physiopathology; D003924:Diabetes Mellitus, Type 2 / Q000503:physiopathology; D003928:Diabetic Nephropathies / Q000473:pathology / Q000503:physiopathology*; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000502:physiology*; D007668:Kidney / Q000166:cytology / Q000187:drug effects; D059630:Mesenchymal Stem Cells / Q000187:drug effects / Q000502:physiology*; D009025:Morpholines / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000502:physiology*; D051381:Rats; D053773:Transforming Growth Factor beta1 / Q000502:physiology*
D002867:Chromones; D009025:Morpholines; D053773:Transforming Growth Factor beta1; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D051057:Proto-Oncogene Proteins c-akt; D004121:Dimethyl Sulfoxide