LONG-TERM EXPOSURE TO EPIDERMAL GROWTH-FACTOR RESULTS IN APOPTOSIS IN T51B CELLS

The major objective of this research was the development of an in vitro model for liver homeostasis that would allow the future study of early events in cell proliferation and cell death. The model that was set up involves growing T51B rat liver epithelial cells with a single dose of 1 nM epidermal growth factor (EGF). This results in a period of hyperplasia where the cells reach double the control cell numbers 2 days after EGF addition. This is then followed by a decrease in cell numbers and the cell density returns to around the confluent control level 5 days after EGF addition. The model was investigated to ascertain whether the decrease in cell numbers 3-5 days after EGF addition was due to an increase in apoptosis. The results from light and electron microscopy studies, electrophoresis of T51B cell DNA, and quantification of nuclear fragmentation indicated that the cells do die via an increase in apoptosis. The electron microscopy studies also show that healthy T51B cells can phagocytose apoptotic bodies. This suggests that the model is more physiological than other in vitro models of apoptosis. This work describes the development and characterization an in vitro model of liver homeostasis that closely parallels in vivo systems where animals are given mitogenic stimuli.