title: Involvement of cytosolic phospholipase A2 alpha signalling pathway in spontaneous and transforming growth factor-beta-induced activation of rat hepatic stellate cells.
abstract: BACKGROUND
  Hepatic stellate cells (HSCs) are extracellular matrix-producing cells that play a pivotal role in liver fibrogenesis. During liver injury and when cells are placed in vitro, HSCs undergo phenotypic transition from quiescent retinoid-storing cells to activated retinoid-deficient myofibroblast-like cells. Although several mediators including reactive oxygen species, platelet derived growth factor, transforming growth factor-beta (TGF-β) and tumour necrosis factor-alpha (TNF-α) were implicated in HSC activation, the cellular signalling pathways that regulate this process remain incompletely defined.
  
  
  OBJECTIVE
  The objectives of this study were to evaluate the role of cytosolic phospholipase A(2) alpha (cPLA(2)α) and peroxisome proliferator-activated receptor-beta/delta (PPAR-β/δ) in HSC activation.
  
  
  METHODS
  Rat HSCs were isolated, purified, cultured and stimulated with TGF-β1 in the presence or absence of the selective cPLA(2)α inhibitor, arachidonyltrifluoromethyl ketone (AACOCF(3)). The activation status of HSC was evaluated by immunofluorescent staining of alpha-smooth muscle actin (α-SMA) and by measuring the expression of cPLA(2)α, cyclooxygenase 2 (COX-2) and PPAR-β/δ using western blot analysis.
  
  
  RESULTS
  Rapid and significant increase in cPLA(2)α expression was observed during activation of HSCs. These events preceded the elevation of PPAR-β/δ and the expression of α-SMA. Elevated expression of cPLA(2)α, but not COX-2, was also observed during TGF-β-induced HSC activation. The TGF-β-induced α-SMA expression was blocked by AACOCF(3). Furthermore, transfection of a cPLA(2)α expression vector enhanced the transcription activity of PPAR-β/δ and the expression of α-SMA in HSCs.
  
  
  CONCLUSIONS
  cPLA(2)α-mediated induction of PPAR-β/δ is a novel intracellular signalling pathway in spontaneous and TGF-β induced activation of HSCs and could be a potential therapeutic target for the treatment of liver fibrosis.
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Calgary and Calgary Laboratory Services, Calgary, AB, Canada.
authors.forename: Liena
authors.initials: L
authors.lastname: Zhao
authors.forename: Chandrashekhar R
authors.initials: CR
authors.lastname: Gandhi
authors.forename: Zu-hua
authors.initials: ZH
authors.lastname: Gao
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D001095:Arachidonic Acids; D015153:Blotting, Western; D005455:Fluorescent Antibody Technique; D005822:Genetic Vectors; D054513:Group IV Phospholipases A2 / Q000378:metabolism*; D055166:Hepatic Stellate Cells / Q000166:cytology* / Q000378:metabolism*; D047494:PPAR delta / Q000378:metabolism*; D048068:PPAR-beta / Q000378:metabolism*; D051381:Rats; D015398:Signal Transduction / Q000502:physiology*; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism*
chemical_list: D000199:Actins; D001095:Arachidonic Acids; D054513:Group IV Phospholipases A2; D047494:PPAR delta; D048068:PPAR-beta; D016212:Transforming Growth Factor beta; C104956:arachidonyl-diazomethyl ketone; C498862:Acta2 protein, rat