Experimental models to study cholangiocyte biology

Abstract

Cholangiocytes-the epithelial cells which line the bile ducts-are increasingly recognized as important transporting epithelia actively involved in the absorption and secretion of water, ions, and solutes. This recognition is due in part to the recent development of new experimental models. New biologic concepts have emerged including the identification and topography of receptors and flux proteins on the apical and/or basolateral membrane which are involved in the molecular mechanisms of ductal bile secretion. Individually isolated and/or perfused bile duct units from livers of rats and mice serve as new,physiologically relevant in vitro models to study cholangiocyte transport. Biliary tree dimensions and novel insights into anatomic remodeling of proliferating bile ducts have emerged from three-dimensional reconstruction using CT scanning and sophisticated software. Moreover, new pathologic concepts have arisen regarding the interaction of cholangiocytes with pathogens such as Cryptosporidium parvum. These concepts and associated methodologies may provide the framework to develop new therapies for the cholangiopathies, a group of important hepatobiliary diseases in which cholangiocytes are the target cell.

Figure 1

Experimental in vitro models of biliary epithelia. (a) A scanning electron micrograph of a group of isolated cholangiocytes after separation using immunomagnetic beads. Note that the prominent microvilli (arrowheads) are limited to one side of the cells. Mag = 4400. (b) A transmission electron micrograph cross-section of normal rat cholangiocytes in culture demonstrates characteristics of polarized cells with apical microvilli (arrowheads) and numerous basolateral intercellular interdigitations near the collagen coated filter denoted by *, (Bar = 2 mm, Mag = 7500). (c) (d) A transmission electron micrograph of apical (c) and basolateral (d) plasma membrane domains revealed similar homogenous vesiculated membranes of varied shapes and sizes without apparent contamination of other organelles (Bar = 0.5 mm, Mag = 22500). (e) A three-dimensional reconstructed image of the intrahepatic biliary tree isolated from normal rat liver. (f) A light micrograph of an unstained isolated bile duct unit from rat liver. After overnight culture, the two ends seal forming an enclosed unit. A single layer of epithelial cells with a thin outer layer of connective tissue surrounds the lumen. (g) A microperfused intrahepatic bile duct unit isolated from rat liver, manually dissected and cannulated with micropipettes. (h) Transmission electron micrograph of C. parvum infection of cultured human cholangiocytes. A parasitophorous vacuole contains a developing parasite stage which is intracellular but extracytoplasmic. A macrogamet is shown in the inset, demonstrating development of sexual stages of the parasite. Bar = 1 mm.