Arachidonic acid-dependent activation of a p22phox-based NAD(P)H oxidase mediates angiotensin II-induced mesangial cell protein synthesis and fibronectin expression via Akt/PKB

Angiotensin 11 (Ang 11) induces protein synthesis and hypertrophy through arachidonic acid (AA)- and redox-dependent activation of the serine-threonine kinase Akt/PKB in mesangial cells (MCs). The role of NAD(P)H oxidase component p22(phox) was explored in this signaling pathway and in Ang II-induced expression of the extracellular matrix protein fibronectin. Ang 11 causes activation of Akt/PKB and induces fibronectin protein expression, effects abrogated by phospholipase A 2 inhibition and mimicked by AA. Ang 11 and AA also elicited an increase in fibronectin expression that was reduced with a dominant negative mutant of Akt/PKB. Exposure of the cells to hydrogen peroxide stimulates Akt/PKB activity and fibronectin synthesis. The antioxidant N-acetylcysteine abolished Ang II- and AA-induced Akt/PKB activation and fibronectin expression. Western blot analysis revealed high levels of p22(phox) in MCs. Antisense (AS) but not sense oligonucleotides for p22(phox) prevented ROS generation in response to Ang 11 and AA. AS p22(phox) inhibited Ang II- or AA-induced Akt/PKB as well as protein synthesis and fibronectin expression. These data provide the first evidence, in MCs, of activation by AA of a p22(phox)-based NAD(P)H oxidase and subsequent generation of ROS. Moreover, this pathway mediates the effect of Ang 11 on Akt/PKB-induced protein synthesis and fibronectin expression.