Neurotrophins in Pancreas Development

描述（由申请人提供）：神经营养因子是肽生长因子，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得到了最好的研究。然而，神经营养因子也与一些非神经元组织的发育和功能有关，包括心血管系统、免疫系统和内分泌系统。在胰腺中，体外研究表明，神经营养因子，神经生长因子（NGF）调节胰岛素生成细胞的存活和功能。NGF还能延长移植小鼠胰岛的体外和体内存活。这些研究暗示了NGF信号在胰岛发育和再生中的作用。然而，到目前为止，还没有尝试使用缺乏NGF或其受体酪氨酸激酶TrkA的转基因小鼠来解决神经营养因子信号在胰腺，特别是胰岛发育中的体内作用。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。在成年杂合子NGF+/-小鼠中，胰岛体积减小，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信号的直接需求或间接由于支配胰腺的NGF依赖性神经元的死亡而引起的。根据我们的初步结果，这项建议的目标是双重的；(1)利用基因工程小鼠模型研究胰岛发育过程中细胞对NGF-TrkA信号的自主需求；(2)通过结合体外神经元-胰腺共培养试验和缺乏交感神经支配的突变小鼠胰腺发育的体内分析，确定交感神经元对胰腺发育的贡献。通过关注胰腺发育中神经营养因子信号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。了解调节胰岛发育的外在信号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，并提高移植后胰岛的存活。

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.