Receptor-mediated regulation of differentiation and proliferation of hepatocytes by synthetic polymer model of asialoglycoprotein.

Morphology and responses of hepatocytes are investigated using an artificial asialoglycoprotein model polymer--lactose-carrying polystyrene (PVLA) as a culture substratum, especially in focusing on the effect of the surface density of the PVLA substratum. The surface density of PVLA on polystyrene dishes was determined using fluorescein-labeled PVLA as a probe under a fluorescence laser microscope. PVLA-coated surfaces were observed by scanning electron microscope and atomic force microscopies under air and water, which showed that PVLA molecules were adsorbed patchily on low density surfaces and uniformly concentrated all over the dish on high density surfaces. It is suggested from the requirement of the Ca2+ ion, inhibition of galactosyl substances, and localization of receptors that the adhesion of hepatocytes to both low and high PVLA-density surfaces is mediated by galactose-specific interactions between PVLA and asialoglycoprotein receptors. At low PVLA densities (0.07 micrograms cm-2), the hepatocytes were flat and expressed high levels of 3H-thymidine uptake and low levels of bile acid secretion. Contrastingly, at high PVLA densities (1.08 micrograms cm-2), they were round and expressed a low level of 3H-thymidine uptake and a high level of bile acid secretion. The shapes, proliferation, and differentiation of hepatocytes could be regulated by varying the densities of PVLA adsorbed to polystyrene dishes. We assume that there are two recognition mechanisms operating between PVLA and hepatocytes: (1) adhesion through highly concentrated or clustered galactose-specific interaction; and (2) responses in shape, proliferation, and differentiation by PVLA-coating densities.