Sympathetic innervation in pancreatic development and function

描述（由申请人提供）：已知自主神经系统通过调节成人胰腺中的激素释放来调节葡萄糖稳态。朗格汉斯胰岛受自主神经系统交感神经的丰富支配，神经支配的开始与胰腺发育中胰岛生长和成熟的阶段一致。然而，交感神经支配是否参与胰腺器官发生至今尚未明确。我们最近报道，在小鼠的发育过程中，交感神经的消融会导致胰岛形状和细胞结构的严重缺陷（Borden et. al, 2013）。交感神经切除小鼠在以后的生活中表现出胰岛素分泌减少和葡萄糖耐受不良。因此，本研究的总体目标是阐明交感神经元促进胰岛形成和功能成熟的分子机制。基于初步发现，我们假设神经来源的信号是神经递质去甲肾上腺素，它通过胰腺肾上腺素能受体促进细胞迁移和胰岛组织。因此，我们将通过评估缺乏去甲肾上腺素能神经传递的突变小鼠体内的胰岛形成，以及通过检查去甲肾上腺素对体外细胞迁移和聚集的影响，来确定去甲肾上腺素对胰岛结构是否必要和充分（目的1）。在目标2中，我们将确定去甲肾上腺素信号影响胰岛结构的分子机制。通过对交感神经切除胰岛的深度测序分析，我们观察到PTTG1（垂体肿瘤转化基因1）的显著下调，该基因编码一种据报道具有细胞骨架调节功能的蛋白质。因此，我们将确定PTTG1是否是去甲肾上腺素信号的转录靶点。此外，我们将利用PTTG1敲除小鼠来评估PTTG1是否是细胞迁移的重要调节因子。最后，我们将通过检查去甲肾上腺素对葡萄糖感知机制和胰岛素颗粒在细胞中运输的影响来阐明神经源性信号影响胰岛成熟的机制（目的3）。我们的研究的意义在于，它是第一个解决神经系统如何控制胰岛发育的研究，也将为目前治疗胰腺功能障碍的转化努力开辟一条新的研究路线。

DESCRIPTION (provided by applicant): The autonomic nervous system is known to regulate glucose homeostasis by modulating hormone release in the adult pancreas. Pancreatic islets of Langerhans are richly innervated by sympathetic nerves of the autonomic nervous system and the onset of innervation is coincident with stages of islet growth and maturation in the developing pancreas. Yet, whether, sympathetic innervation contributes to pancreas organogenesis has not been defined so far. We recently reported that ablation of sympathetic nerves results in profound defects in the shape and cyto-architecture of islets during development in mice (Borden et. al, 2013). Sympathectomized mice exhibit reduced insulin secretion and glucose intolerance later in life. Thus, the overall goal of this proposal is to elucidate the molecular mechanisms by which sympathetic neurons promote islet formation and the acquisition of functional maturity. Based on preliminary findings, we hypothesize that the nerve-derived signal is the neurotransmitter, norepinephrine, that acts via pancreatic �-adrenergic receptors to promote �-cell migration and islet organization. Thus, we will determine if norepinephrine is necessary and sufficient for islet architecture by assessing islet formation i vivo in mutant mice that lack noradrenergic neurotransmission, as well as by examining the effects of norepinephrine on �-cell migration and aggregation in vitro (Aim 1). In Aim 2, we will identify the molecular mechanisms by which norepinephrine signaling influences islet architecture. By deep sequencing-based profiling of sympathectomized islets, we observed a dramatic down-regulation of PTTG1 (pituitary tumor-transforming gene 1), that encodes for a protein reported to have cytoskeleton-regulatory functions. Thus, we will determine if PTTG1 is a transcriptional target of norepinephrine signaling. Additionally, we will assess whether PTTG1 is an essential regulator of �-cell migration, employing available PTTG1 knockout mice. Finally, we will elucidate the mechanisms by which nerve-derived signaling influences islet maturation by examining the effects of norepinephrine on the glucose-sensing machinery and insulin granule trafficking in �-cells (Aim 3). The significance of our studies is that it is the first to address how the nervous system controls islet development and will also initiate a new line of research in current translational efforts to treat pancreatic dysfunction.