In vivo, cells are organized in complex tissue architecture with various extracellular matrix (ECM) and cellular signals governing cell behavior. In vitro models of tissue that mimic this 3 dimensional arrangement of ECM and different cell type offer the potential of capturing the complex signaling environment found in vivo. In the liver, hepatocytes and endothelial cells are arranged in layers with the space of Disse separating the two cell types. In our system, this architecture was mimicked by encapsulating primary rat hepatocytes in collagen and overlaying rat microvascular endothelial cells on top of the collagen. The effect of layering endothelial cells on top of hepatocytes was evaluated by measuring albumin as the marker of hepatic function. Albumin secretion by hepatocytes in the layered structure was dramatically increased during the first week of culture in comparison to collagen encapsulated hepatocytes. Enhanced albumin function was also observed in collagen encapsulated hepatocytes that were exposed to endothelial cells conditioned medium. However, hepatocytes cultured on top of collagen gel and exposed to conditioned medium showed a transient increase and then decrease in albumin secretion during first week of culture. This suggests that the soluble factors secreted by the endothelial cells in combination with collagen on top of hepatocytes lead to sustained hepatic function enhancement in the layered co-culture. Inhibition of growth factors and cytokines such as HGF, and TNFá in the co-culture had no effect, on the other hand supplementing conditioned medium with matrix metalloproteinase 3 (MMP3) reduced albumin secretion suggesting a role for ECM secreted by endothelial cells in hepatic function improvement.

Extended Abstract Status: Not Uploaded