Neurotrophins in Pancreas Development

说明(申请人提供)：神经营养因子是一种多肽生长因子，因其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而得到最好的研究。然而，神经营养因子也参与了几种非神经组织的发育和功能，包括心血管、免疫和内分泌系统。在胰腺，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生存和功能。NGF在体外和体内均能延长移植小鼠胰岛的存活时间。这些研究表明，NGF信号与胰岛的发育和再生有关。然而，到目前为止，还没有人尝试使用缺乏NGF或其受体酪氨酸激酶TrkA的转基因小鼠来研究神经营养素信号在胰腺中的体内作用，特别是胰岛的发育。利用缺乏NGF的小鼠，我们观察到发育中的胰岛组织紊乱，胰岛内内分泌细胞类型的正常空间排列被破坏。在成年NGF+/-杂合子小鼠中，胰岛体积缩小且碎片化。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对NGF信号的直接需求，也可能是由于支配胰腺的NGF依赖神经元的死亡。基于我们的初步结果，这项建议的目标有两个：(1)使用基因工程小鼠模型来检测胰岛发育中对NGF-TrkA信号的细胞自主需求，以及(2)通过结合使用体外神经元-胰腺共培养试验和对缺乏交感神经支配的突变小鼠胰腺发育的体内分析来确定交感神经元对胰腺发育的贡献。通过关注胰腺发育中对神经营养因子信号和神经衍生信号的体内需求，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。了解外源性信号调节胰岛发育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胰岛的存活，以及提高胰岛移植后的存活率。 公共卫生相关性：这项建议的目标是确定影响胰岛发育的新的外在生长因素。深入了解调控胰岛发育的外在信号对治疗I型糖尿病、促进损伤或疾病后的胰腺再生、延长胰岛移植后的存活具有重要意义。在这项研究中，我们重点关注神经营养因子，神经生长因子(NGF)，一种被研究为在发育中的神经系统中促进神经元存活和连接的可溶性生长因子。NGF及其受体TrkA也在胰腺中表达，NGF信号已被证明在体外促进胰岛细胞的存活。然而，到目前为止，还没有人尝试使用转基因小鼠来解决NGF信号在胰腺和特别是胰岛发育中的体内作用。本研究的目的是使用包括小鼠遗传学和神经-胰腺共培养在内的创新工具来研究NGF信号是通过胰腺内的信号直接影响胰腺发育，还是通过促进NGF反应性交感神经元的神经支配间接影响胰腺发育。总之，这些研究将对神经营养因子和神经衍生信号在胰岛发育中的影响这一以前未被描述的问题提供重要的见解。

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.