Arachidonic acid-dependent activation of a p22^phox-based NAD(P)H oxidase mediates angiotensin II-induced mesangial cell protein synthesis and fibronectin expression via Akt/PKB

Angiotensin II (Ang II) 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)II oxidase component p22^phox was explored in this signaling pathway and in Ang II-induced expression of the extracellular matrix protein fibronectin. Ang II causes activation of Akt/PKB and induces fibronectin protein expression, effects abrogated by phospholipase A₂ inhibition and mimicked by AA. Ang II 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 oligonacleotides for p22^phox prevented ROS generation in response to Ang II 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 II on Akt/PKB-induced protein synthesis and fibronectin expression.