Book Description

[Truncated abstract] There is great interest in the field of liver progenitor (oval) cells which are a bipotential compartment of cells responding to chronic liver damage. Oval cells have enormous potential to treat patients with liver disease by a cell therapy approach but their use is limited by their scarcity and number of donor livers from which they can be derived. Knowledge is lacking in the origin of oval cells as well as the mechanisms which drive their activation, proliferation and differentiation which is required for their therapeutic potential to be realised. Bone marrow may be a suitable source of liver progenitor cells which could circumvent both disadvantages of using liver-derived material. Derivation of oval cells from bone marrow has been examined in rodents using hepatotoxins and partial hepatectomy to create liver damage. These protocols induce oval cell proliferation however they do not mimic the disease conditions that occur in humans. The first aim of this thesis was therefore to evaluate the contribution of bone marrow cells to oval cells in conditions that more closely mimic human liver disease pathophysiology using a choline-deficient, ethionine-supplemented (CDE) diet which causes fatty liver and virus-induced hepatitis. To determine the contribution of bone marrow cells to CDE and viral-hepatitis injury, lacZ transgenic bone marrow cells were transplanted into congenic mice, liver injury was induced and the movement of bone marrow cells to the liver monitored. Cells originating from donor BM were identified by x-gal staining and their phenotype was determined by immunohistochemical staining with cell type specific markers. Bone marrow-derived oval cells were observed in response to the CDE diet and viral injury but represented a minor fraction (0-1.6%) of the oval cell compartment. The combination of the CDE diet and viral infection produced more severe liver damage with larger numbers of proliferating oval cells; however the proportion of oval cells generated from BM did not increase. In all situations only rare, individual BM-derived oval cells were observed. We hypothesized that the BM cells may replenish oval cells that are expended by protracted liver injury and regeneration, however experiments involving a subsequent episode of chronic liver injury failed to induce proliferation of the BM-derived oval cells which appeared as a result of the first episode. BM-derived hepatocytes were also observed in all injury models and controls in numbers unrelated to that of oval cells. We conclude that during chronic liver disease induced by agents also responsible for human disease the contribution of BM cells to hepatocytes either via oval cell or by independent mechanisms is minimal and that the majority of oval cells responding to this injury are sourced from the liver. The second aim of this thesis was to advance knowledge of the mechanisms which govern oval cell behaviour. The transcriptional profile of oval cells freshly isolated from CDE-fed mice was analysed by microarray to obtain evidence of their relationship to hematopoietic cells and to establish changes in pattern of gene expression following their differentiation into hepatocytes...