Norepinephrine induces hepatic fibrogenesis in leptin deficient ob/ob mice q Jude A. Oben, a Tania Roskams, b Shiqi Yang, a Huizhi Lin, a Nicoletta Sinelli, b Zhiping Li, a Michael Torbenson, c Steven A. Thomas, d and Anna Mae Diehl a, * a Department of Medicine, Johns Hopkins University, Baltimore, MD 21205, USA b Department of Pathology, University Hospitals, University of Leuven, Leuven 3000, Belgium c Department of Pathology, Johns Hopkins University, Baltimore, MD 21205, USA d Department of Pharmacology, School of Medicine, University of Pennsylvania, Philadelphia, PA, USA Received 2 July 2003 Abstract Leptin’s actions on certain cells require a leptin-inducible neurotransmitter, norepinephrine (NE). NE modulates hepatic fibrosis. Therefore, decreased NE may explain why leptin deficiency inhibits hepatic fibrosis. We manipulated adrenergic activity in leptin- deficient ob/ob mice, leptin-sufficient, dopamine b-hydroxylase deficient (Dbh = ) mice, and HSC cultures to determine if leptin requires NE to activate HSC and induce hepatic fibrosis. ob/ob mice have chronic liver injury, but reduced numbers of HSC. Supplemental leptin increases HSC, suggesting that leptin-dependent, injury-related factors permit expansion of HSC populations. NE also increases HSC numbers and activation, normalizing fibrogenesis. When fed hepatotoxic diets, NE-deficient Dbh = mice fail to accumulate activated HSC and have impaired fibrogenesis unless treated with adrenergic agonists. NE acts directly on HSC to modulate leptin’s actions because leptin increases HSC proliferation and prazosin, an a-adrenoceptor antagonist, inhibits this. Thus, leptin permits injury-related increases in adrenergic activity and requires NE to activate HSC and induce hepatic fibrogenesis. Ó 2003 Elsevier Inc. All rights reserved. Keywords: Fibrosis; ob/ob; Hepatic stellate cells; Collagen; TGF-b; Norepinephrine; Sympathetic nervous system Leptin is a pleiotropic hormone best described for its effects on energy homeostasis. Mice with mutations that prevent the synthesis of leptin (ob/ob = mice) or its cognate receptor (db/db = mice) have increased food intake due to unopposed orexigenic effects of hypotha- lamic hormones such as neuropeptide Y and agouti- related protein which are normally down-regulated by leptin [1–3]. Both leptin-deficient and leptin-resistant mice develop obesity, insulin-resistance, and fatty livers that are unusually vulnerable to injury from lipopoly- saccharide or ischemia–reperfusion. Exposure to these secondary stresses results in severe steatohepatitis, at least in part, because leptin deficiency dysregulates im- mune cells in the liver, leading to excessive hepatic production of pro-inflammatory cytokines [4]. Curi- ously, however, although more sensitive to steatohepa- titis, leptin-deficient mice are relatively protected from developing cirrhosis [5,6]. This finding suggests that leptin is a pro-fibrogenic factor. Recently, leptin was shown to be released from activated hepatic stellate cells (HSC), the liver’s principal matrix producing cells [7]. Some investigators argue that the pro-fibrogenic effects of leptin may be indirect and involve the release of TGF-b and, possibly, other undefined mediators [5]. Pertinent to the latter possibility is increasing evi- dence that many effects of leptin are mediated via the sympathetic nervous system (SNS) and its neurotrans- mitters. For example, SNS neurotransmitters are nec- essary for leptin’s catabolic effect on brown adipocyte Biochemical and Biophysical Research Communications 308 (2003) 284–292 www.elsevier.com/locate/ybbrc BBRC q Abbreviations: ASMA, Alpha smooth muscle actin; ANS, auto- nomic nervous system; DBH, dopamine b-hydroxylase; GFAP, glial fibrillary acidic protein; HSC, hepatic stellate cells; ISO, isoprenaline; MCD, methionine restricted, choline deficient; NE, norepinephrine; PRZ, prazosin; RPA, ribonuclease protection assay; SNS, sympathetic nervous system; TIMP, tissue inhibitor of metalloproteinases; TGF, transforming growth factor. * Corresponding author. Fax: 1-410-955-9677. E-mail address: amdiehl@jhmi.edu (A.M. Diehl). 0006-291X/$ - see front matter Ó 2003 Elsevier Inc. All rights reserved. doi:10.1016/S0006-291X(03)01360-3