Neurotrophins in Pancreas Development

描述（由申请人提供）：神经营养因子是肽类生长因子，研究最多的是它们在发育中的神经系统中促进神经元存活和轴突生长的作用。然而，神经营养因子也涉及几种非神经元组织的发育和功能，包括心血管、免疫和内分泌系统。在胰腺中，体外研究表明，神经营养因子，神经生长因子（NGF）调节胰岛素产生细胞的存活和功能。NGF在体外和体内也能促进移植的小鼠胰岛的存活。这些研究暗示了NGF信号在胰岛发育和再生中的作用。然而，迄今为止，还没有尝试使用缺乏NGF或其受体酪氨酸激酶TrkA的遗传修饰小鼠来解决胰腺中神经营养因子信号传导的体内作用，特别是胰岛发育。使用缺乏NGF的小鼠，我们观察到发育中的胰岛是紊乱的，并且胰岛内分泌细胞类型的正常空间排列被破坏。在成年杂合子NGF+/-小鼠中，胰岛大小减小并碎裂。由于NGF及其受体TrkA在胰岛细胞中表达，这些缺陷可能是由于胰腺中直接需要NGF信号传导或间接由于神经支配胰腺的NGF依赖性神经元的死亡而引起的。根据我们的初步结果，这项建议的目标有两个：（1）使用基因工程小鼠模型来检查胰岛发育中NGF-TrkA信号传导的细胞自主需求，以及（2）通过采用体外神经元-胰腺共刺激的组合来确定交感神经元对胰腺发育的贡献，缺乏交感神经支配的突变小鼠中胰腺发育的培养测定和体内分析。通过关注胰腺发育中神经营养因子信号传导和神经源性信号的体内需求，我们的研究将为调节胰腺发育的外源性生长因子提供独特的见解。关于调节胰岛发育的外源性信号的知识将有助于设计更好的治疗策略，以促进I型糖尿病和损伤期间的胰岛存活，以及提高移植后的胰岛存活。 公共卫生相关性：该提案的目标是确定影响胰岛发育的新型外源性生长因子。深入了解调节胰岛发育的外源性信号对于治疗I型糖尿病、促进损伤或疾病后的胰腺再生以及延长移植后胰岛存活具有重要意义。在这项研究中，我们专注于神经营养因子，神经生长因子（NGF），可溶性生长因子最好的研究，其作用是促进神经元的存活和连接在发育中的神经系统。NGF及其受体TrkA也在胰腺中表达，并且已经显示NGF信号传导在体外促进胰岛细胞的存活。然而，迄今为止，还没有尝试使用基因修饰的小鼠来解决NGF信号传导在胰腺和特别是胰岛发育中的体内作用。本研究的目标是使用创新工具，包括小鼠遗传学和神经元胰腺共培养，以解决NGF信号是否通过胰腺内的信号直接影响胰腺发育，或间接通过促进NGF反应性交感神经元的神经支配。总之，这些研究将提供一个重要的洞察力，以前没有特点的问题，神经营养因子和神经源性信号在胰岛发育的影响。

DESCRIPTION (provided by applicant): Neurotrophins are peptide growth factors best studied for their roles in promoting neuronal survival and axonal growth in the developing nervous system. However, neurotrophins have also been implicated in development and function of several non-neuronal tissues including the cardiovascular, immune and endocrine systems. In the pancreas, in vitro studies have shown that the neurotrophin, Nerve Growth Factor, (NGF) regulates survival and function of insulin-producing ¿-cells. NGF also prolongs survival of transplanted mouse islets in vitro and in vivo. These studies implicate NGF signaling in pancreatic islet development and regeneration. However, to date, there have been no attempts to use genetically modified mice lacking NGF or its receptor tyrosine kinase, TrkA, to address the in vivo role of neurotrophin signaling in the pancreas, and specifically islet development. Employing mice deficient for NGF, we observed that developing pancreatic islets are disorganized and that the normal spatial arrangement of endocrine cell types within islets is disrupted. In adult heterozygous NGF+/- mice, pancreatic islets are reduced in size and fragmented. Since NGF and its receptor, TrkA, are expressed in islet cells, these deficits could arise due to a direct requirement for NGF signaling in the pancreas or indirectly due to the death of NGF-dependent neurons innervating the pancreas. Based on our preliminary results, the goal of this proposal is two-fold; (1) Use genetically engineered mouse models to examine the cell-autonomous requirement for NGF-TrkA signaling in islet development, and (2) determine the contribution of sympathetic neurons to pancreas development by employing a combination of in vitro neuron-pancreas co-culture assays and in vivo analyses of pancreas development in mutant mice lacking sympathetic innervation. By focusing on the in vivo requirement for neurotrophin signaling and nerve-derived signals in pancreas development, our studies will provide unique insight into extrinsic growth factors that regulate pancreas development. Knowledge about extrinsic signals regulating islet development will facilitate the design of better therapeutic strategies to promote islet survival during type I diabetes and injury, as well as enhance islet survival following transplantation. PUBLIC HEALTH RELEVANCE: The goal of this proposal is to identify novel extrinsic growth factors that influence development of pancreatic islets. Gaining insight into extrinsic signals regulating islet development has important implications for treatment of type I diabetes, promoting pancreatic regeneration following injury or disease, and prolonging islet survival after transplantation. In this study, we focus on the neurotrophin, Nerve Growth Factor (NGF), a soluble growth factor best studied for its role in promoting neuronal survival and connectivity in the developing nervous system. NGF and its receptor, TrkA, are also expressed in the pancreas and NGF signaling has been shown to promote survival of pancreatic islet cells, in vitro. However, to date, there have been no attempts to use genetically modified mice to address the in vivo role of NGF signaling in the pancreas and specifically islet development. The goal of this study is to use innovative tools including mouse genetics and neuron-pancreas co-cultures to address whether NGF signaling influences pancreas development directly by signaling within the pancreas, or indirectly via promoting innervation of NGF-responsive sympathetic neurons. Together, these studies will provide significant insight into a previously uncharacterized question of the influence of neurotrophins and nerve-derived signals in islet development.