Expression and functional relevance of NADPH oxidase 5 in human hepatic stellate cells
NADPH oxidase (Nox) variants Nox1, Nox2 and Nox4 have been implicated in the progression of liver fibrosis. However, the role of Nox5 is unknown, mainly due to the lack of this enzyme in rat and mouse genomes. Here we describe the expression and functional relevance of Nox5 in the human cell line of hepatic stellate cells (HSC), LX-2. Under basal conditions, these cells expressed a long (Nox5L) and a short (Nox5S) variant which were silenced with specific siRNAs for Nox5. Overexpression of Nox5L generated ROS in the presence of calcium, as judged by the production of extracellular hydrogen peroxide, L-012 luminescence and cytochrome c reduction, while Nox5S did not generated ROS under these conditions. In contrast, dihydroethidium oxidation was increased when either Nox5L or Nox5S were overexpressed. Functional studies revealed that both Nox5L and Nox5S stimulated the proliferation of LX-2 cells and the synthesis of type I collagen, while Nox5 siRNAs inhibited these effects. Interestingly, TGF-beta and angiotensin II induced Nox5, and silencing Nox5 reduced collagen production stimulated by TGF-beta. Collectively, these results suggest for the first time that Nox5 can play a relevant role in HSC proliferation and fibrogenesis.