NOX4 and Hepatic fibrosis: Furthermore, hepatic stellate cells (HSCs), which have a key role during liver fibrosis, induce NOX4-dependent ROS formation upon stimulation with TGF-β1 (Proell et al. 2007) and the down-regulation of NOX4 by siRNA or the absence of NOX4 in mice inhibits the TGF-β-induced fibrotic process (Sancho et al. 2012).