BILIARY SECRETORY PATHWAYS IN CYSTIC FIBROSIS

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Cystic fibrosis (CF) is the most common lethal inherited diseases in white population. As CF patients live longer, liver disease has become the second leading cause of death. The development of CF disease is believed to result from the secretory defects in the bile ducts leading to the obstructions of bile ductules by tenacious bile secretions, thereby secreting in focal periportal biliary fibrosis/cirrhosis. This explanation in addition to the recent finding that CFTR is only expressed on bile duct cells, but not on hepatocytes, suggest that studying biliary secretion is crucial to understanding the pathophysiology and developing therapeutic strategies for CF liver. A novel polarized isolated bile duct unit (IBDU) prepared from rat liver has demonstrated to be an ideal tool to study bile ductular secretion but the lack of CF rat model limited its use in CF studies. By applying these isolation methods, recently, IBDUs have been isolated from normal and CF mice. Therefore, the aims of this research are to further characterize bile duct cells (BDC) and IBDU from normal and CF knockout mice, to characterize ion transporters in BDC, and to study the actions and mechanisms of various secretagogues including neuroendocrine peptides in biliary secretion in order to find ways to activate alternative, cAMP-independent biliary secretory pathways in CF mice. Preliminary experiments to isolate IBDU from normal mouse yielded intact polarized functional IBDU that responds to secretin, vasoactive intestinal peptide, and DBcAMP-IBMX. Similar IBDUs were also isolated from CF mice but need further characterization. Quantitative videomicroscopy will be used to screen potential secretagogues to stimulate biliary secretion in normal and CF mice and to characterize their underlying ion transporters by using ion substitutions and inhibitor studies. These ion transporters will be further studied by BCECF dual ratio methods for measuring pH, micropuncture, and patch clamping techniques. Signal transduction systems involved in their action will be studied by monitoring changes in the concentrations of secondary messengers. Understanding transport systems and their underlying mechanisms of biliary secretion in normal and CF mice will help to formulate therapeutic approaches to overcome the CFTR defect. This project, in turn, will provide the candidate with an excellent opportunity to broaden and develop research and cognitive skills to become independent researcher, as well as help to successfully compete for future research grants.