Fig. 1

Hepatocyte culture and functions. a Hepatocyte culture configurations are critical to modeling in vitro functions. Several techniques are known to support not only increased levels of liver-specific gene expression, but also metabolic and physiological functions in long term culture. i) Sandwich culture provides long term physiological morphology and function and maintains epithelial structure and lateral, basal, and apical membrane domains. ii) Heterogeneous cell co-culture provides critical cell-cell heterotypic interactions between hepatocytes and supporting cells, like NIH 3T3-J2 fibroblasts that represent stellate cells and endothelial cells that represent liver sinusoidal endothelial cells, which together promotes liver functions. iii) Same as ii) except controlled cell co-culture, often using selective cell adhesion, micropatterning and microfabrication technology. iv) Liver cell aggregate culture (homogenous) enhances cell-cell contacts compared to cell matrix contacts and promotes liver function. v) Same as iv) except heterogeneous aggregate containing multiple supporting cell types that promote heterotypic cell-cell contacts. b Hepatocyte functions in culture. The liver is responsible for a number of important physiological and biochemical functions that can be analyzed within in vitro cultures. We depict two hepatocytes with preserved cell-cell junctional complexes, and membrane domains, including the basal, lateral, baso-lateral, and apical (bile canalicular) domains. The hepatocyte on the left demonstrates various metabolic activities of the liver, including protein, fat and carbohydrate metabolism. Glycogen storage, glycogenolysis, and gluconeogenesis refer to different metabolic processes for regulating whole body glucose levels, as well as the uptake and release of glucose for cellular metabolism. Lipids are also oxidized in the liver, and triglycerides are metabolized to produce energy. Lipoproteins, are also synthesized in the liver. Further, the liver regulates the deamination and transamination of amino acids (AA) into carbon skeletons and also regulates the removal of ammonia (N2) by urea synthesis. The liver contains many mitochondria that reduce oxygen and generate cellular energy via the electron transport chain. The liver has many other functions not shown. The cellular medium is critical, and must contain hormones, and growth factors that support these functions. The hepatocyte to the right depicts key hepatocellular functions like the synthesis and secretion of albumin, the expression of P450 microsomal enzymes for drug metabolism, expression of low density lipoprotein receptor (LDL), the expression of asialoglycoprotein receptor (ASGPR) for clearing asialyated proteins, and the expression of integrins for engaging extracellular matrix, particularly collagen Type IV in the basement membrane. The liver also synthesizes a majority of the clotting factors needed in blood coagulation