Expression of CCAAT/enhancer binding protein family genes in monolayer and sandwich culture of hepatocytes: induction of stress-inducible GADD153

Enhanced glucose synthesis in three-dimensional hepatocyte collagen matrix

Three-dimensional (3D) cell culture model offers a unique opportunity to study hepatocytes that require extracellular matrix to keep the cells at the differentiated state. In this report, we cultured isolated mouse hepatocytes in a 3D collagen matrix system and developed a protocol to measure glucose production at 3h, 6h, 18h and 24h after culture. The results demonstrated that hepatocytes cultured under 3D collagen matrix condition consistently produced glucose at 240-290 mg/10(6) cells for up to 24h. Contrarily, hepatocytes cultured under traditional monolayer condition produced less than 50 mg/10(6) cells glucose. We demonstrated higher expression of phosphoenolpyruvate carboxykinase (PEPCK), a key enzyme for the synthesis of glucose from pyruvate, and CCAAT/enhancer-binding protein alpha (C/EBPalpha), an important liver-specific transcription factor, under the 3D collagen matrix culture condition in comparison to the monolayer condition. Thus, the 3D collagen matrix system preserved metabolic function of hepatocytes and can be used as an in vitro model for studying hepatocyte glucose production and gluconeogenesis.

Interferon-gamma induces reactive oxygen species and endoplasmic reticulum stress at the hepatic apoptosis

Interferon-gamma (IFN-gamma) induces cell-cycle arrest and p53-independent apoptosis in primary cultured hepatocytes. However, the detailed mechanism, including regulating molecules, is still unclear. In this study, we found that IFN-gamma induced generation of reactive oxygen species (ROS) in primary hepatocytes and that pyrrolidinedithiocarbamate (PDTC), an anti-oxidant reagent, completely suppressed IFN-gamma-induced hepatic apoptosis. PDTC blocked apoptosis downstream from IRF-1 and upstream from caspase activation, suggesting that the generation of ROS occurred between these stages. However, IFN-gamma also induced the generation of ROS in IRF-1-deficient hepatocytes, cells insensitive to IFN-gamma-induced apoptosis. Moreover, a general cyclooxygenase (COX) inhibitor, indomethacin (but not the cyclooxygenase 2-specific inhibitor, NS-398) also inhibited the apoptosis without blocking the generation of ROS. Both PDTC and indomethacin also blocked IFN-gamma-induced release of cytochrome c from mitochondria. These results suggest that ROS are not the only or sufficient mediators of IFN-gamma-induced hepatic apoptosis. In contrast, we also found that IFN-gamma induced endoplasmic reticulum (ER) stress proteins, CHOP/GADD153 and caspase 12, in wild-type primary hepatocytes, but induced only caspase 12 and not CHOP/GADD153 protein in IRF-1-deficient hepatocytes. These results suggest that IFN-gamma induces ER stress in primary hepatocytes. Both the ROS and ER stress induced by IFN-gamma may be complementary mediators that induce apoptosis in primary hepatocytes.