BILIARY SECRETORY PATHWAYS IN CYSTIC FIBROSIS

囊性纤维化（CF）是白人最常见的致命性遗传性疾病。随着CF患者寿命的延长，肝脏疾病已成为第二大死亡原因。CF疾病的发展被认为是由于胆管分泌缺陷导致胆管被顽强的胆汁分泌物阻塞，从而在局灶性门静脉周围胆道纤维化/肝硬化中分泌。这一解释，再加上最近发现CFTR仅在胆管细胞上表达，而不在肝细胞上表达，表明研究胆道分泌对于了解CF肝的病理生理和制定治疗策略至关重要。从大鼠肝脏制备的一种新型极化孤立胆管单元（IBDU）已被证明是研究胆管分泌的理想工具，但缺乏CF大鼠模型限制了其在CF研究中的应用。利用这些分离方法，近年来已从正常小鼠和CF小鼠中分离出IBDUs。因此，本研究的目的是进一步表征正常小鼠和CF敲除小鼠的胆管细胞（BDC）和IBDU，表征BDC中的离子转运体，研究包括神经内分泌肽在内的各种分泌物在胆道分泌中的作用和机制，以寻找激活CF小鼠胆道分泌通路的方法。从正常小鼠中分离IBDU的初步实验获得了完整的极化功能IBDU，该IBDU对分泌素、血管活性肠肽和DBcAMP-IBMX有反应。类似的IBDUs也从CF小鼠中分离出来，但需要进一步表征。定量视频显微镜将用于筛选潜在的促分泌剂来刺激正常和CF小鼠的胆道分泌，并通过离子取代和抑制剂研究来表征其潜在的离子转运体。这些离子转运体将通过BCECF双比值法测量pH值、微穿刺和贴片夹持技术进一步研究。参与其作用的信号转导系统将通过监测次级信使浓度的变化来研究。了解正常和CF小鼠胆道分泌的转运系统及其潜在机制将有助于制定克服CFTR缺陷的治疗方法。这个项目将为候选人提供一个极好的机会，拓宽和发展研究和认知技能，成为独立的研究人员，并有助于成功竞争未来的研究资助。

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.