Z Gastroenterol 2011; 49 - P452
DOI: 10.1055/s-0031-1285723

Ethanol sensitizes primary mouse hepatocytes for the apoptotic effects of transforming growth factor (TGF)-β

K Breitkopf-Heinlein 1, H Gaitantzi 1, C Meyer 1, Q Li 1, J Dzieran 1, S Schneider 1, A Müller 1, G Millonig 2, S Mueller 2, H Bantel 3, K Wahl 3, S Dooley 1
  • 1Medical Clinic II, University Hospital at Mannheim, University of Heidelberg, Molecular Hepatology – Alcohol Associated Diseases, Mannheim, Germany
  • 2Krankenhaus Salem; Universität Heidelberg, Innere Medizin, Gastroenterologie und Alkoholforschung, Heidelberg, Germany
  • 3Medizinische Hochschule Hannover, Gastroenterologie, Hepatologie und Endokrinologie, Hannover, Germany

We previously showed that TGF-β signalling is increased in ethanol fed mice and that a combination of ethanol plus TGF-β causes much more apoptosis of primary mouse hepatocytes than each stimulus alone. In the present study we further analyzed this apoptosis induction and show that ethanol strongly enhances TGF-β Smad-signalling in isolated hepatocytes. Apoptosis induction was accompanied by reduced basal activity of Akt along with increased TGF-β receptor type II (TβRII) expression. Blunting PI3K/Akt with the small molecule inhibitor LY294002 in hepatocytes blocked apoptosis and, similar to ethanol, led to increased TβRII expression, indicating a functional link between loss of activated Akt, TβRII expression and apoptosis by TGF-β. The ethanol/TGF-β mediated apoptosis pathway further included cytochrome-C release from mitochondria and depended on glycogen synthase kinase (GSK) activity as well as change of expression of Bcl2 protein family members. Acetaldehyde did not mimic ethanol effects and inhibition of alcohol metabolizing enzymes (ADH1 or Cyp2E1) did not block this apoptotic pathway. Application of oxidative stress to cultured hepatocytes showed similar effects as ethanol, e.g. increased TGF-β dependent apoptotis, induction of TβRII and in combination with TGF-β treatment down-regulated expression of Bcl-2. Acute treatment of mice with alcohol also resulted in rapid upregulation of TβRII expression in liver lysates, suggesting in vivo relevance of this finding and ethanol/TGF-β induced apoptosis was confirmed in fresh human liver slices that were treated ex vivo.

In summary, by causing oxidative stress, ethanol decreased phospho-Akt levels in hepatocytes leading to increased TβRII expression and strongly enhanced TGF-β dependent apoptosis. These results clearly indicate that under conditions of pre-damaged liver where TGF-β levels are already elevated (e.g. NASH or HCV) any alcohol consumption (even „moderate„) should be avoided.