Transforming growth factor-β1 and phosphatases modulate COX-2 protein expression and TAU phosphorylation in cultured immortalized podocytes.

The aim of this study is to elucidate TGF-β1 signaling pathways involved in COX-2 protein induction and modulation of TAU protein phosphorylation in cultured podocytes. In vitro cultured immortalized podocytes were stimulated with TGF-β1 in presence and absence of pharmacologic inhibitors for various signaling pathways and phosphatases. Then, COX-2 protein expression, as well as P38MAPK, AKT and TAU phosphorylation levels were evaluated by western blot analysis. TGF-β1 induction of COX-2 protein levels was completely blocked by pharmacologic inhibitors of phosphatases, P38 MAPK, or NF-қB pathways. Time course experiments showed that TGF-β1 activated p38 MAPK after 5 min of stimulation. Interestingly, podocyte co-incubated with TGF-β1, high glucose and/or PGE2 showed strong increase in p38 MAPK and AKT phosphorylation as well as COX- 2 protein expression levels. Levels of phosphorylated AKT were further reduced and levels of phosphorylated p38 were increased when PGE2 was added to the culture media. Interestingly, selective phosphatases inhibitors completely abrogated PGE2-induced P38 MAPK and TAU phosphorylation. Also, inhibition of phosphatases reversed TGF-β1-induced COX-2 protein expression either alone or when incubated with high glucose or PGE2. These data suggest TGF-β1 mediates its effect in podocyte through novel signaling mechanisms including phosphatases and TAU protein phosphorylation.