(from applicant): One of the long standing unanswered questions in one of the most frequently studied models of carcinogenesis, chemical hepatocarcinogenesis, is what is the cell of origin of hepatocellular carcinomas (HCC)? The classic cellular pathway, championed by Emmanuel Farber, is that HCC develop from altered hepatocytes progressively through foci and preneoplastic nodules. However, studies on oval cells, which appear early during hepatocarcinogenesis, indicate that HCC may arise from """"""""bipolar"""""""" liver progenitor cells located within terminal ducts or from pluripotent progenitor cells located adjacent to the ducts. In addition, recent studies on female mice and rats receiving bone marrow transplants from male donors indicated two possible origins of liver stem cells: from bipolar progenitor cells in the terminal ducts or from periductal stem cells. It is further postulated that these periductal progenitor cells may arise from circulating bone marrow stem cells either by differentiation into liver cells or that bone marrow cells may fuse with liver cells.
In Specific Aim 1, the applicant proposes to develop a transgenic Fischer rat line expressing EGFP which can be used as a donor for bone marrow transplantation studies.
In Specific Aim 2, three models of carcinogenesis: a. Continuous DEN, which features foci of altered hepatocytes preceding HCC with little or no oval cells will be used to determine if HCC arise from hepatocytes; b. Solt-Farber model, which features prominent proliferation of ductal oval cells to determine if HCC arise from bipolar ductal precursor cells; c. Choline-deficiency-ethionine, a model which features periductular proliferation of oval cells will be used to determine if preneoplastic lesions or HCC arise from periportal oval cells. In each of these protocols, DDPIV- (canalicular enzyme) female rats will receive a bone marrow transplant from DDPIV+, EGFP+, male donors. The origin of the populations of cells responding by proliferation will be identified by the presence of donor or recipient markers, and the types of cells identified through labeling with both liver lineage and littoral cell markers, when appropriate.
In Specific Aim 3, the possibility of fusion of donor bone marrow stem cells with recipient liver cells will be tested and the possibility of fusion in etiology, progression or metastasis of HCC determined. Knowledge of the cellular origin of cancer is critical for understanding how cancer evolves and for developing prevention strategies.
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