Role of sex hormones in the modulation of cholangiocyte function

Over the last years,cholangiocytes,the cells that line the biliary tree,have been considered an important object of study for their biological properties which involves bile formation,proliferation,injury repair,fibrosis and angiogenesis.Cholangiocyte proliferation occurs in all pathologic conditions of liver injury where it is associated with inflammation and regeneration.During these processes,biliary cells start to secrete different cytokines,growth factors,neuropeptides and hormones which represent potential mechanisms for cross talk with other liver cells.Several studies suggest that hormones,and in particular,sex hormones,play a fundamental role in the modulation of the growth of this compartment in the injured liver which functionally conditions the progression of liver disease.Understanding the mechanisms of action and the intracellular pathways of these compounds on cholangiocyte pathophysiology will provide new potential strategies for the management of chronic liver diseases.The purpose of this review is to summarize the recent findings on the role of sex hormones in cholangiocyte proliferation and biology.

Cholangiocytes and blood supply

The microvascular supply of the biliary tree, the peribiliary plexus （PBP）, stems from the hepatic artery branches and flows into the hepatic sinusoids. A detailed three-dimensional study of the PBP has been performed by using the Scanning Electron Microscopy vascular corrosion casts （SEMvcc） technique. Considering that the PBP plays a fundamental role in supporting the secretory and absorptive functions of the biliary epithelium, their organization in either normalcy and pathology is explored. The normal liver shows the PBP arranged around extra-and intrahepatic biliary tree. In the small portal tract PBP was characterized by a single layer of capillaries which progressively continued with the extrahepatic PBP where it showed a morecomplex vascular network. After common duct ligation （BDL）, progressive modifications of bile duct and PBP proliferation are observed. The PBP presents a three-dimensional network arranged around many bile ducts and appears as bundles of vessels, composed by capillaries of homogeneous diameter with a typical round mesh structure. The PBP network is easily distinguishable from the sinusoidal network which appears normal. Considering the enormous extension of the PBP during BDL, the possible role played by the Vascular Endothelial Growth Factor （VEGF） is evaluated. VEGF-A,VEGF-C and their related receptors appeared highly immunopositive in proliferating cholangiocytes of BDL rats. The administration of anti-VEGF-A or anti-VEGF-C antibodies to BDL rats as well as hepatic artery ligation induced a reduced bile duct mass. The administration of rVEGF-A to BDL hepatic artery ligated rats prevented the decrease of cholangiocyte proliferation and VEGF-A expression as compared to BDL control rats. These data suggest the role of arterial blood supply of the biliary tree in conditions of cholangiocyte proliferation, such as it occurs during chronic cholestasis. On the other hand,the role played by VEGF as a tool of cross-talk between cholangiocytes and PBP endothelial cells suggests that manipulation of VEGF release and function could represent a therapeutic strategy for human pathological conditions characterized by damage of hepatic artery or the biliary tree.