Cd44-Hyaluronan Interaction Plays a Critical Role in Biliary Proliferation During the Development of Hepatic Cholestasis
Gordon D. Wu*1, Yao He1, Haimei Wang1, Hong Wang1, John M. Vierling2, Andrew S. Klein1
1Comprehensive Transplant Center, Cedars-Sinai Medical Center, Los Angeles, CA; 2Department of Hepatology, Baylor College of Medicine, Houston, TX
Background: High levels of CD44 and its ligand hyaluronic acid (HA) are present in cholestatic livers. The role of CD44-hyaluronic acid (HA) interaction in biliary pathology, however, is poorly undrstood.
Methods: A rat model of cholestatic liver induced by bile duct ligation (BDL) was employed for the studies. Histological distribution of CD44-expressing cells and disposition of extracellular hyaluronic acid (HA) were examined in cryostat sections of the livers with immunofluorescence or histochemistry. Biliary epithelial cells (BEC), hepatic stellate cells (HSC), CD31+ hepatic endothelial cells (HEC) and ED2+ Kupffer cells (KC) were isolated and examined for expression of CD44 standard (s) and variant (v) isoforms with quantitative real time PCR. The regulatory role of CD44-HA interaction in biliary proliferation was investigated in biliary epithelial cell (BEC) cultures.
Results: BDL livers developed intensive intrahepatic bile duct proliferation. Epithelia lining the proliferative bile ducts were strongly positive for CD44. CD44 expression by the proliferative BEC was associated with markedly increased interstitial HA accumulation. Quantitative PCR revealed that CD44 expressed by the cholestatic livers increased 26-fold over the control (p<0.01). BEC isolated from the cholestatic livers expressed high levels of CD44 mRNA, which was 3-fold, 17-fold, and 19-fold as that expressed by sinusoidal endothelia, Kupffer cells and hepatic stellar cells (P<0.01, respectively). BEC significantly increased expression of CD44 (p<0.01) and cell proliferation marker ki-67 (p<0.05) in responses to hyaluronan stimulation in cultures. Cellular proliferation assay demonstrated that cholangiocyte propagation accelerated upon HA stimulation, and was antagonized by anti-CD44 treatment (p<0.05).
Conclusion: The study provides compelling evidence to suggest that proliferative BEC lining the intrahepatic bile ducts are the major source of hepatic CD44. CD44-HA interaction, by enhancing biliary proliferation, plays a pathogenic role in the development of cholestatic liver diseases.
