Bile acids induce hepatic stellate cell proliferation via activation of the epidermal growth factor receptor.
OBJECTIVE
Hepatic stellate cell (HSC) proliferation is a key event in the development of liver fibrosis. In many liver diseases, HSCs are exposed to inflammatory cytokines, reactive oxygen species, and bile acids. Although inflammatory cytokines and reactive oxygen species are known to promote proliferation of HSCs, nothing is known about the effects of bile acids on HSC proliferation or apoptosis. The aim of this study was to investigate the effects of bile acids on HSC proliferation.


METHODS
HSCs were exposed to bile acids with different hydrophobicity (5-200 micromol/L). HSC proliferation and cell cycle-related events were assessed by bromodeoxyuridine incorporation, cell counting and proliferating cell nuclear antigen and cyclin E expression, apoptosis by caspase-3 activity assay, immunocytochemistry for active caspase-3 and acridine orange staining, and activation of signal transduction pathways by Western blot using phospho-specific antibodies. Uptake of bile acids was investigated using fluorescent bile acids.


RESULTS
All bile acids, at concentrations >25 micromol/L, induce a 2.5- to 3-fold increase in HSC proliferation via activation of the epidermal growth factor receptor. Bile acid-induced proliferation is mediated by activation of a protein kinase C/extracellular signal-regulated kinase/p70S6K-dependent pathway. Bile acids did not induce apoptosis in HSCs. HSCs do not take up fluorescent bile acids and do not express the bile acid importer ntcp.


CONCLUSIONS
Bile acids at levels reached in cholestatic conditions are an independent profibrogenic factor. Bile acids induce HSC proliferation via the activation of the epidermal growth factor receptor, whereas HSCs are protected against bile acid-induced apoptosis by excluding bile acids.
Svegliati-Baroni
Gianluca
G
Department of Gastroenterology, University of Ancona, Italy.
Ridolfi
Francesco
F
Hannivoort
Rebekka
R
Saccomanno
Stefania
S
Homan
Manon
M
De Minicis
Samuele
S
Jansen
Peter L M
PL
Candelaresi
Cinzia
C
Benedetti
Antonio
A
Moshage
Han
H
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001647:Bile Acids and Salts / Q000493:pharmacokinetics / Q000494:pharmacology*; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D024042:Collagen Type I / Q000235:genetics; D016213:Cyclins / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D066246:ErbB Receptors / Q000378:metabolism*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005453:Fluorescence; D008099:Liver / Q000166:cytology* / Q000201:enzymology / Q000378:metabolism / Q000502:physiology; D008297:Male; D026901:Membrane Transport Proteins / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D029363:Organic Anion Transporters, Sodium-Dependent; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D027981:Symporters; D016212:Transforming Growth Factor beta / Q000235:genetics
D001647:Bile Acids and Salts; D024042:Collagen Type I; D016213:Cyclins; D026901:Membrane Transport Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; D047428:Protein Kinase Inhibitors; D012333:RNA, Messenger; D027981:Symporters; D016212:Transforming Growth Factor beta; C071908:sodium-bile acid cotransporter; D019869:Phosphatidylinositol 3-Kinases; D066246:ErbB Receptors; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D048049:Extracellular Signal-Regulated MAP Kinases; D048052:Mitogen-Activated Protein Kinase 3