Soluble Stimuli

In the liver, regional variations in hepatocyte morphology and function are known to exist along the sinusoid. These zones of hepatocyte specialization (termed ‘zonation') are regulated not only by gradients of adhesive factors (see cell-cell and cell-matrix interactions ) but also by soluble factors such as oxygen, growth factors, and paracrine signals.

Oxygen gradients have been shown to play a particularly important role in zonation of in vitro hepatocyte cultures. We have developed a biomimetic flat-plate bioreactor system that allows the formation of steady-state oxygen gradients over a monolayer of hepatocytes or hepatocyte-stromal co-cultures. Using a mathematical model of oxygen transport in this bioreactor, we can predict the distribution of oxygen along the surface of the cells. Figure 1 shows a contour plot and schematic of the oxygen concentration in a cross section of the bioreactor. In bioreactor cultures, physiological oxygen gradients contributed to the induction of prototypic zonation markers, including cytochrome P450 2B (CYP2B, downstream), observed in vivo (see Fig. 2 Western blot). Allen & Bhatia, 2003.

Our laboratory is interested in characterizing the effect of oxygen gradients on hepatocellular function, both independently and in combination with other soluble stimuli. These studies may improve our understanding of fundamental liver biology, as well as aid in the design of improved bioartificial support systems or cell-based therapies for liver disease.

Fig. 1

Fig. 2