The answer: angiotensin II. The question: what do inflammation, oxidant stress and fibrogenesis have in common?

Angiotensin II (Ang II) is a pro-oxidant and fibrogenic cytokine. We investigated the role of NADPH oxidase in Ang II-induced effects in hepatic stellate cells (HSCs), a fibrogenic cell type. Human HSCs express mRNAs of key components of nonphagocytic NADPH oxidase. Ang II phosphorylated p47phox, a regulatory subunit of NADPH oxidase, and induced reactive oxygen species formation via NADPH oxidase activity. Ang II phosphorylated AKT and MAPKs and increased AP-1 DNA binding in a redox-sensitive manner. Ang II stimulated DNA synthesis, cell migration, procollagen alpha1(I) mRNA expression, and secretion of TGF-beta1 and inflammatory cytokines. These effects were attenuated by N-acetylcysteine and diphenylene iodonium, an NADPH oxidase inhibitor. Moreover, Ang II induced upregulation of genes potentially involved in hepatic wound-healing response in a redox-sensitive manner, as assessed by microarray analysis. HSCs isolated from p47phox 2 /2 mice displayed a blunted response to Ang II compared with WT cells. We also assessed the role of NADPH oxidase in experimental liver fibrosis. After bile duct ligation, p47phox 2 /2 mice showed attenuated liver injury and fibrosis compared with WT counterparts. Moreover, expression of smooth muscle alphaactin and expression of TGF-beta1 were reduced in p47phox 2 /2 mice. Thus, NADPH oxidase mediates the actions of Ang II on HSCs and plays a critical role in liver fibrogenesis. [Abstract reproduced by permission of J Clin Invest 2003;112:1383–94] A long-running popular TV game show in the US, ‘Jeopardy’ has the unique premise of providing the answers to unknown questions and asking contestants to provide the correct question. In a sense, the recent outstanding paper by Bataller and colleagues in the Journal of Clinical Investigation offers a similar scenario [1]. The importance of the angiotensin pathway in regulating blood pressure and vascular resistance has been apparent for decades, yet a fuller spectrum of its biologic activity is only apparent now that the correct questions are being asked. This work has identified converging pathways that involve key determinants of fibrogenesis, and provides ample justification for targeting this pathway in antifibrotic strategies. Angiotensin II (Ang II) is a potent vasoconstrictor that is a key mediator of renal vasoconstriction [2] and has been implicated in portal blood flow regulation as well [3]. Bataller and colleagues have mounted a growing body of evidence implicating hepatic stellate cells as a major target of these liver-specific activities. Stellate cells, a major source of extracellular matrix in liver injury by virtue of their capacity to activate into contractile fibroblasts, are perfectly positioned to regulate sinusoidal blood flow through their perisinusoidal foot processes. Indeed, a host of contractile mediators can stimulate stellate cell contraction and relaxation, including endothelin, nitric oxide, prostaglandins, catecholamines and carbon monoxide [4]. Four years ago, Bataller [5] and others [6] identified Ang II receptors on stellate cells. Like many other cytokine receptors [7], these were upregulated during cellular activation, amplifying Ang II activities by enhancing its responsiveness to the growth factor, leading to increased proliferation and contraction [5]. In vivo studies using Ang II antagonists followed logically from these culture studies, confirming an antifibrotic activity in animal models [8–10]. As with many other mediators regulating stellate cell activation, an autocrine source of Ang II has subsequently become apparent, indicating that stellate cells Journal of Hepatology 40 (2004) 1050–1052 www.elsevier.com/locate/jhep