| The proinflammatory cytokine tumor necrosis factor α (TNFα) is increased in the sera of patients with a variety of chronic liver diseases including hepatitis B and hepatitis C viral infections, alcoholic hepatitis, hepatocellular carcinoma, α1-antitrypsin deficiency and hereditary hemochromatosis. In contrast, TNFα has been shown to function in normal physiological processes, including regeneration of the liver following injury. Although it has been clearly demonstrated that TNFα is an important mediator of liver biology and pathobiology, the exact role of this cytokine and the mechanisms by which it exerts its effects are poorly understood.; In vivo, hepatocytes exist in G0of the cell cycle, but retain the capacity to proliferate to replace the lost liver mass resulting from partial hepatectomy, chemically induced necrosis or living donor liver transplant. In contrast to many other cell types, proliferation of the liver parenchyma results directly from division of hepatocytes and does not require differentiation from a stem cell precursor. To date, a number of cytokines have been identified that act as complete mitogens for hepatocytes including hepatocyte growth factor, epidermal growth factor (EGF), transforming growth factor a and acidic fibroblast growth factor. In addition, numerous agents act as priming factors for hepatocyte proliferation, capable of modulating the response of the cells to growth factors, including 30% partial hepatectomy and TNFα. Evidence exists for a mitogenic role for TNFα in hepatocyte proliferation. It has been demonstrated that mice deficient in TNF receptor 1 exhibit a severe defect in liver regeneration following partial hepatectomy, suggesting a possible role for TNFα as a complete hepatocyte mitogen. Despite this evidence, the possibility that TNFα acts as a primary mitogen for hepatocytes has never been directly investigated.; Our laboratory has previously described a system in which primary rat hepatocytes can be maintained in serum-free, long term dimethyl sulfoxide (DMSO) culture. Cells in this system retain highly differentiated liver specific functions including albumin production. Use of this system to investigate the mitogenic potential of TNFα is advantageous because the direct effect of the cytokine on hepatocytes can be examined, which cannot be accomplished in vivo.; In the present study, we have modified the long term DMSO culture system so that EGF is excluded from the culture media (-EGF), thus enabling us to examine the ability of TNFα to induce DNA synthesis in primary rat hepatocytes in the absence of known hepatocyte mitogens. (Abstract shortened by UMI.)... |
