Lam, Kwok Lim. / "October 2010." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 142-173). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

囊性纖維化（CF）是由囊性纖維化跨膜電導調節器（CFTR）的突變引起的一種隱性遺傳病。CF病人的肺、肝、胰腺、腸道與生殖道受到嚴重影響，其中有50%的成年病人患有糖尿病。由CF引起的糖尿病被稱為CF相關糖尿病（CFRD）, 关于它的病因至今仍然存有爭議。2007年，人們發現CFTR在分泌胰島素的胰島β細胞上有表達。儘管如此，β細胞上的CFTR与糖尿病发病的关系却一直被忽略。我們的研究目標是闡述β細胞上的CFTR在胰島素分泌中的作用。 / 在β細胞上，葡萄糖刺激的胰島素分泌伴隨著複雜的電活動，這種電活動被描述為細胞膜電位去极化疊加的動作電位的爆發。葡萄糖引起的ATP敏感的鉀離子通道（K[subscript Asubscript Tsubscript P]）的關閉被普遍認為是β細胞去極化的初始事件，初始的去極化啟動了電壓依賴的鈣離子通道，由此產生的鈣離子內流成為構成動作電位的去極化電流，引起了細胞內鈣離子的震盪，從而引起胰島素的釋放。雖然氯離子電流被認為參與了β細胞去極化電流，但是，人們仍然不能確定是哪一種氯離子通道介導了這個去極化電流。在我們研究的第一部分，CFTR被證明功能性的表達在β細胞上，並且可以被葡萄糖激活。CFTR可以被葡萄糖激活这一性质，在CFTR超表達的CHO 细胞上被進一步驗證。在原代培養的β細胞與β細胞株RIN-5F细胞中的葡萄糖引起的全細胞電流、膜電位的去極化、動作電位的幅度與頻率、鈣震盪和胰島素的分泌可以被CFTR的抑制劑或缺陷所降低。與野生型小鼠相比，CFTR基因敲除的小鼠，禁食之後，具有更高的血糖濃度，然而其胰島素的濃度低。 / 我們研究中的第二部分，利用了數學模型去闡明CFTR 在胰島素分泌的電活動中的角色。結果顯示， CFTR電導的減低可以使細胞的細胞膜去極化，從而導致需要更高的電刺激去引發動作電位，这些結果證明了CFTR對於维持細胞膜電位的貢獻。同時增加細胞內氯離子濃度和CFTR的電導可以引起更大頻率的膜電位的震盪，這一點證明了氯離子對於細胞膜電位震盪有著重要的作用。在数学模型中，CFTR電導的降低可以消除通過改變ATP/ADP值所引起的電火花， 這與我們在試驗中發現的CFTR參與了葡萄糖引起的動作電位是一致的。總而言之，我們的数学模型證明了CFTR對於胰島素的分泌是非常重要的，它通過介導氯離子外流對細胞膜電位的產生貢獻並且參與了電火花的產生，所有這些都進一步驗證了我們在實驗部分的發現。 / 综上所述，現有的研究揭示了CFTR，通過對β細胞膜電位作用與参与了動作電位的產生，在葡萄糖刺激胰島素分泌过程中的鮮為人知的重要角色。這個發現為揭示CFRD的病理機制提供了全新的視角，並且可能為開發治療CFRD的方法帶来了曙光。 / Cystic fibrosis (CF) is a recessive autosomal genetic disease resulted from mutations of cystic fibrosis transmembrane conductance regulator (CFTR). CF affects critically the lung, liver, pancreas, intestine and reproductive tract. CF patients also exhibit a high percentage of diabetes, which almost reach 50% in adult. The pathological cause of diabetes in CF patients, also called CF related diabetes (CFRD), is still controversial. It has been reported that CFTR expressed in the islet β cells, which is responsible for insulin secretion. However, the exact role of CFTR in islet β-cell and its relation to diabetes have been ignored. The present study aims to elucidate the role of CFTR in the process of insulin secretion by pancreatic islet β cells. / Glucose-stimulated insulin secretion is associated with a complex electrical activity in the pancreatic islet β-cell, which is characterized by a slow membrane depolarization superimposed with bursts of action potentials. Closing ATP-sensitive K⁺ channels (K[subscript Asubscript Tsubscript P]) in response to glucose increase is generally considered the initial event that depolarizes the β-cell membrane and activates the voltage-dependent Ca²⁺ channels, which constitutes the major depolarizing component of the bursting action potentials giving rise to the cytosolic calcium oscillations that trigger insulin release. While Cl⁻ has been implicated in an unknown depolarization current of the β-cell, the responsible Cl⁻ channel remains unidentified. In the first part of our study, we show functional expression of CFTR and its activation by glucose in the β-cell. Activation of CFTR by glucose was also demonstrated in CHO cell over-expression system. The glucose-elicited whole-cell currents, membrane depolarization, electrical bursts (both magnitude and frequency), Ca²⁺ oscillations and insulin secretion could be abolished or reduced by inhibitors/knockdown of CFTR in primary mouse β-cells or RIN-5F β-cell line, or significantly attenuated in isolated mouse islet β-cells from CFTR mutant mice compared to that of wildtype. Significantly increased blood glucose level accompanied with reduced level of insulin is found in CFTR mutant mice compared to the wildtype. The results strongly indicate a role of CFTR in the process of insulin secretion. / In the second part of our study, mathematical model is built up to clarify the role of CFTR in the electrical activity during insulin secretion. It is shown that reduction of CFTR conductance hyperpolarizes the membrane of the β-cell, for which it requires a larger electrical stimulus to evoke an action potential, indicating the contribution of CFTR to the membrane potential as demonstrated by our experimental results. Increase in intracellular Cl⁻ concentration and the conductance of CFTR result in higher frequency of membrane potential oscillations, demonstrating that Cl⁻ is crucial for the membrane potential oscillations. The electrical spikes induced by increase of ATP/ADP in the model are abolished by decreasing CFTR conductance, which is consistent with our findings that CFTR is involved in the generation of action potentials induced by glucose. In other word, our model demonstrates that CFTR is crucial for insulin secretion by its contribution to membrane potential and participating in the generation of electrical spikes via conducting Cl⁻ efflux, which confirms our findings in the experimental study. / Taken together, the present study reveals a previously unrecognized important role of CFTR in glucose-stimulated insulin secretion via contributing to the membrane potential and the participating in the generation of action potential in islet β cells. This finding sheds new light into the understanding of the pathogenesis of CFRD and may provide grounds for the development of new therapeutic approaches for CFRD. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Guo, Jinghui. / "December 2012." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 156-164). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Abstract --- p.i / 摘要： --- p.iii / Acknowledgement: --- p.v / LIST OF PUBLICATIONS --- p.vi / Declaration --- p.viii / ABBREVIATIONS --- p.xi / LIST OF FIGURES --- p.xiii / Chapter Chapter 1: --- General introduction --- p.1 / Chapter 1.1 --- The function of islet β cells and diabetes --- p.1 / Chapter 1.1.1 --- The introduction of the pancreas --- p.1 / Chapter 1.1.2. --- Glucose metabolism and blood glucose regulation --- p.6 / Chapter 1.1.2.2 --- Blood glucose regulation --- p.7 / Chapter 1.1.3 --- Insulin secretion by the islet β cell --- p.10 / Chapter 1.1.4 --- Diabetes --- p.14 / Chapter 1.2 --- Cystic fibrosis-related diabetes --- p.17 / Chapter 1.2.1 --- Cystic fibrosis --- p.17 / Chapter 1.2.2 --- CFTR --- p.19 / Chapter 1.3 --- Mathematical model for insulin secretion --- p.25 / Chapter 1.4 --- Aim and hypothesis --- p.27 / Chapter 1.4.1 --- CFTR may be activated by glucose --- p.27 / Chapter 1.4.2 --- Activation of CFTR may depolarize the membrane potential --- p.28 / Chapter 1.4.3 --- CFTR-mediating Cl-efflux may be involved in the generation of electrical spikes --- p.28 / Chapter 1.4.4 --- Calcium oscillation depends on CFTR --- p.28 / Chapter 1.4.5 --- Insulin secretion --- p.29 / Chapter 1.5 --- Approaches to test the hypothesis --- p.29 / Chapter Chapter 2: --- Materials and Methods --- p.31 / Chapter 2.1 --- Cell culture --- p.31 / Chapter 2.1.1 --- RIN-5F cell --- p.31 / Chapter 2.1.2 --- CHO cell --- p.31 / Chapter 2.2 --- Islet isolation and culture --- p.32 / Chapter 2.3 --- CFTR knockdown --- p.33 / Chapter 2.4 --- Western blot --- p.35 / Chapter 2.5 --- Immunofluorescence --- p.37 / Chapter 2.6 --- Membrane potential (Vm) measurement --- p.38 / Chapter 2.7 --- Intracellular chloride imaging --- p.39 / Chapter 2.8 --- Intracellular calcium imaging --- p.40 / Chapter 2.9 --- Patch-clamp --- p.40 / Chapter 2.10 --- Blood glucose measurement --- p.42 / Chapter 2.11 --- Insulin ELISA --- p.42 / Chapter 2.12 --- Statistics --- p.42 / Chapter Chapter 3: --- Contribution of CFTR on the eletrophysiological properties in insulin secretion --- p.43 / Chapter 3.1 --- Introduction --- p.43 / Chapter 3.2 --- Results --- p.45 / Chapter 3.2.1 --- Functional expression of CFTR in mouse islet β cells --- p.45 / Chapter 3.2.2 --- CFTR activation by glucose --- p.46 / Chapter 3.2.3 --- Involvement of CFTR in the maintenance of membrane potential of islet β cells --- p.47 / Chapter 3.2.4 --- CFTR is involved in the generation of spikes induced by glucose --- p.50 / Chapter 3.2.5 --- Generation of spikes burst in the β cell depends on intracellular chloride. --- p.52 / Chapter 3.2.6 --- Inhibition/mutation of CFTR attenuates calcium oscillation induced by glucose --- p.53 / Chapter 3.2.7 --- Inhibition/mutation of CFTR impairs insulin secretion --- p.53 / Chapter 3.3 --- Discussion --- p.71 / Chapter Chapter 4: --- Mathematical model for the role of CFTR in the process of insulin secretion in islet β cell --- p.74 / Chapter 4.1 --- Introduction to the mathematical modeling in the process of insulin secretion --- p.74 / Chapter 4.2 --- Methods --- p.77 / Chapter 4.2.1 --- Components in the model --- p.77 / Chapter 4.2.2 --- Assumptions and approaches in modeling --- p.78 / Chapter 4.2.3 --- Modeling ion channels and transporters --- p.79 / Chapter 4.2.3.1 --- KATP channel --- p.79 / Chapter 4.2.3.2 --- Sodium channel --- p.82 / Chapter 4.2.3.3 --- Voltage Dependent calcium channel --- p.83 / Chapter 4.2.3.4 --- NCX --- p.84 / Chapter 4.2.3.5 --- Na-K pump --- p.85 / Chapter 4.2.3.6 --- Kv channel --- p.87 / Chapter 4.2.3.7 --- Ca pump --- p.88 / Chapter 4.2.3.9 --- CFTR --- p.90 / Chapter 4.2.3.10 --- NKCC --- p.91 / Chapter 4.3 --- Results --- p.93 / Chapter 4.3.1 --- Role CFTR in regulation of the basal membrane potential in β cells --- p.93 / Chapter 4.3.2 --- Role of intracellular chloride concentration in the burst spikes induced by glucose --- p.95 / Chapter 4.3.3 --- Role of CFTR in the burst spikes induced by glucose --- p.96 / Chapter 4.4 --- Discussion --- p.105 / Chapter Chapter 5: --- General discussion and conclusion --- p.109 / Chapter 5.1 --- General discussion --- p.109 / Chapter 5.1.1 --- Role of CFTR in endocrine pancreas and diabetes --- p.109 / Chapter 5.1.2 --- Role of CFTR as a cell metabolic sensor --- p.111 / Chapter 5.1.3 --- Role of CFTR in excitable cells --- p.113 / Chapter 5.2 --- Conclusion --- p.114 / Appendix A --- p.115 / Appendix B --- p.118 / Reference: --- p.156