胰臟內分泌細胞分化的調控事件的研究揭示了胰島素分泌細胞的形成。這一原理既有利於體外誘導用於移植的胰島素分泌細胞，又可應用于糖尿病病人自體胰島素分泌細胞的再生。正在發育的組織和器官中，發現了腎素血管緊張素（RAS）成員，揭示了他們在發育過程中的潛在調控作用。另外，對 RAS 信號系統做出應答的活性氧化物質（ROS），被認為是第二信使，通過對轉錄調控因子的氧化還原的修飾促進分化。作為 ROS 的主要來源，NADPH 已被證實在各類細胞和組織中參與了祖細胞的分化。儘管如此，依賴於 NADPH 氧化酶的 ROS對于胰腺內分泌細胞分化的調控作用仍不清楚。基於這個背景，本研究致力於揭示 RAS 和 NADPH 氧化酶依賴性 ROS 在胰腺內分泌細胞分化中的作用。本實驗將在小鼠胰臟原基培養物和尿鏈黴素（STZ）誘導的新生大鼠上進行。 結果顯示，經典 RAS 成員中的血管緊張素 2 型受體（AT₂R）分佈於內分泌祖細胞的細胞核，之後穿梭定位於胰島素分泌細胞的細胞質。阻斷 AT₂R 功能抑制了Ngn3，胰島素的表達以及 β 細胞的增值。在不同的胚胎期 ROS 的水平發生了改變。對于培養的胰臟原基施加適當的外源 ROS，刺激了內分泌細胞的分化。同時，ROS 清除劑減弱了胰島細胞分化和成熟的標記基因的表達。NOX4 以及其相關的亞基 p22phox 是 NADPH 氧化酶成員，其在胰臟發育過程中的變化同 ROS 水平的變化相似，並且持續表達與內分泌細胞系統。在 NGN3 高表達的胚胎期15.5 天，它們定位于表達 NGN3 的細胞；在 NGN3 表達下調，且胰島素表達升高的胚胎期 17.5 天，它們分佈於胰島素表達細胞。而且，NADPH 氧化酶的抑製劑 DPI 削弱了胰臟培養物中的內分泌祖細胞的分化, 外源 H₂O₂ 的加入扭轉了這一現象。 / 另一方面，在 STZ 誘導的新生大鼠的研究中，DPI 負調節 β 細胞的再生。血糖失調，胰島結構毀壞以及血清胰島素匱乏的現象發生在了 DPI 處理組。另外，DPI 減弱了 NGN3 的表達而並非 Ki67, 顯示 β 細胞的分化而並非增值對於 ROS 的刺激進行了應答。在體內和體外的實驗中，DPI 也抑制了 NGN3 的轉綠調控因子 SOX9 在胰腺祖細胞中的表達。有趣的是，過表達 SOX9 可以恢復 DPI 引發的對於 NGN3 的抑制 。結合以上數據，本研究顯示 NADPH 氧化酶依賴性ROS 誘導的信號通路參與了胰腺祖細胞到胰島素分泌細胞的分化。 / Investigations into the regulatory events that modulate pancreatic endocrine cell differentiation shed light on the generation of sufficient insulin-producing cells in vitro for transplantation or regeneration of β cells in patients with diabetes. The expression of renin-angiotensin system (RAS) components has been detected in development tissue and organs, implicating their regulatory role in developmental processes. On the other hand, reactive oxygen species (ROS) are responsive to RAS signaling pathways and act as second messengers to promote differentiation through redox modification of transcriptional factors essential for differentiation. As a major source of ROS, NADPH oxidase has been shown to participate in the progenitor differentiation in a variety of cells and tissues. Despite this finding, the role of NADPH oxidase-dependent ROS in regulating pancreatic endocrine cell differentiation remains ambiguous. Against this background, the study was aimed at elucidating the roles of RAS components and NADPH oxidase-derived ROS during differentiation of pancreatic endocrine cells using mouse pancreatic rudiments and streptozotocin-treated neonatal rats. / Results showed that angiotensin II type 2 receptor (AT₂R), a major component of the classical RAS, was localized within the nuclei of endocrine progenitors in the cultured pancreatic rudiments; following the differentiation of endocrine progenitors into insulin producing cells, it translocated to cytoplasm. Blockade of AT₂R impeded the expression of Ngn3 and insulin as well as proliferation of β-cells. In addition, the dynamic changes of ROS levels were found in mouse pancreata at different embryonic days, concomitant with induction of endocrine cell differentiation induced by modest exogenous ROS in pancreatic rudiment cultures. Moreover, scavenger of ROS diminished the expression of islet cell markers for differentiation and maturation. NOX4 and its associated subunit p22phox, which are the member of NADPH oxidase, exhibited similar changes of expression to that of ROS levels during pancreas development and persisted in the endocrine lineage; they were located in NGN3⁺ cells at E15.5 during the burst of NGN3 expression and then distributed in insulin⁺ cell at E17.5, the latter being the phase that has a decline in NGN3 expression with an increase of insulin. Furthermore, administration of NADPH oxidase inhibitor, diphenylene iodonium (DPI) attenuated the differentiation of endocrine progenitors in rudiment cultures, while exogenous ROS reversed this effect. / On the other hand, studies performed in streptozotocin-induced neonatal rats showed that β cell regeneration was negatively affected by DPI treatments; consistently, impaired blood glucose control, disturbed islet architecture and deficient serum insulin were observed in DPI-treated groups. In addition, DPI treatments blunted NGN3 expression, but not Ki67-labeling beta-cells, suggesting that differentiation beyond proliferation of β-cells was accountable in response to ROS stimulation. Administration of DPI also suppressed the levels of SOX9, a transcriptional regulator of NGN3, in pancreatic progenitor cells, as evidenced by both in vivo and in vitro studies. Interestingly, over-expression of SOX9 could restore the repression of NGN3 induced by DPI. Taken all these data together, our results indicate that NADPH oxidase-dependent ROS-induced signaling pathway is involved in the differentiation of pancreatic endocrine progenitors into insulin-producing β cells. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Liang, Juan. / Thesis (Ph.D.) Chinese University of Hong Kong, 2014. / Includes bibliographical references (leaves 171-205). / Abstracts also in Chinese.
| Identifer | oai:union.ndltd.org:cuhk.edu.hk/oai:cuhk-dr:cuhk_1077737 |
| Date | January 2014 |
| Contributors | Liang, Juan (author.), Leung, Po Sing (thesis advisor.), Chinese University of Hong Kong Graduate School. Division of Biomedical Sciences. (degree granting institution.) |
| Source Sets | The Chinese University of Hong Kong |
| Language | English, Chinese |
| Detected Language | English |
| Type | Text, bibliography, text |
| Format | electronic resource, electronic resource, remote, 1 online resource (xix, 205 leaves) : illustrations, computer, online resource |
| Rights | Use of this resource is governed by the terms and conditions of the Creative Commons “Attribution-NonCommercial-NoDerivatives 4.0 International” License (http://creativecommons.org/licenses/by-nc-nd/4.0/) |
Page generated in 0.0024 seconds