Nerve growth factor modulates the proliferative capacity of the intrahepatic biliary epithelium in experimental cholestasis.
OBJECTIVE
We evaluated the expression of neurotrophins in rat cholangiocytes and the role and mechanisms by which nerve growth factor (NGF) modulates cholangiocyte proliferation.


METHODS
The expression of neurotrophins and their receptors was investigated by immunohistochemistry in liver sections and reverse-transcription polymerase chain reaction and immunoblots in isolated cholangiocytes. In vitro, the effect of NGF on cholangiocyte proliferation and signal transduction was investigated by immunoblotting for proliferating cell nuclear antigen, phosphorylated AKT (p-AKT), phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2), phosphorylated c-jun-N-terminal kinase, and phosphorylated p38. In vivo, rats that had undergone bile duct ligation (BDL) were treated with an anti-NGF antibody to immunoneutralize NGF and bile duct mass, proliferation, apoptosis, and inflammation were investigated by immunohistochemistry.


RESULTS
NGF and its TrkA receptor were expressed by normal rat cholangiocytes and up-regulated following BDL. Cholangiocytes secrete NGF, and secretion is increased in proliferating BDL cholangiocytes. In vitro, NGF stimulated cholangiocyte proliferation, which was associated with enhanced p-AKT and p-ERK1/2 expression. NGF proliferation in vitro was partially blocked by the MEK inhibitor (UO126) and completely ablated by the phosphatidylinositol 3-kinase inhibitor (wortmannin). In vitro, NGF and estrogens have an additive effect on cholangiocyte proliferation by acting on phosphorylated TrkA and p-ERK1/2. In vivo, immunoneutralization of NGF decreased bile duct mass in BDL rats, which was associated with depressed proliferation and enhanced apoptosis and with increased portal inflammation.


CONCLUSIONS
Cholangiocytes secrete NGF and express NGF receptors. NGF induces cholangiocyte proliferation by activating the ERK and, predominantly, the phosphatidylinositol 3-kinase pathway and exerts an additive effect in combination with estrogens on proliferation.
Division of Gastroenterology, Department of Clinical Medicine, University of Rome La Sapienza, Italy.
Alessandro
A
Gigliozzi
Gianfranco
G
Alpini
Gianluca Svegliati
GS
Baroni
Luca
L
Marucci
Veronica Drudi
VD
Metalli
Shannon S
SS
Glaser
Heather
H
Francis
Maria Grazia
MG
Mancino
Yoshiyuki
Y
Ueno
Barbara
B
Barbaro
Antonio
A
Benedetti
Adolfo F
AF
Attili
Domenico
D
Alvaro
D000818:Animals; D001653:Bile Ducts, Intrahepatic / Q000166:cytology*; D002455:Cell Division; D002779:Cholestasis / Q000473:pathology*; D004847:Epithelial Cells / Q000166:cytology; D004958:Estradiol / Q000494:pharmacology; D007150:Immunohistochemistry; D020935:MAP Kinase Signaling System; D008297:Male; D020932:Nerve Growth Factor / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D051381:Rats; D011916:Rats, Inbred F344; D020917:Receptor, trkA / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction
D004958:Estradiol; D020932:Nerve Growth Factor; D019869:Phosphatidylinositol 3-Kinases; D020917:Receptor, trkA