Neuroprotection by PACAP in Stroke

垂体腺苷酸环化酶激活多肽（PACAP）最初是从下丘脑中分离出来的，基于其在大鼠垂体细胞培养中刺激腺苷酸环化酶的能力。 PACAP以两种酰胺化形式存在，分别含有38个（PACAP 38）和27个（PACAP 27）氨基酸，其中PACAP 38是组织中的主要形式。 PACAP是一种多效性肽，作为促垂体激素、神经递质和神经调质发挥作用。更重要的是，它作为一种神经营养因子，调节胚胎脑中的神经元发育，并防止成人脑中的神经元损伤。 在亚皮摩尔浓度下，PACAP能够完全抑制神经元/胶质细胞共培养物中由gp 120诱导的细胞死亡。 虽然PACAP对神经元培养物发挥直接的神经营养作用，但这种作用需要纳摩尔或亚纳摩尔浓度的肽。 我们的研究表明，静脉内施用PACAP 38防止了大鼠全脑缺血后海马CA 1区锥体细胞的损失，并减少了大脑中动脉闭塞后局灶性缺血引起的梗死体积，即使治疗延迟。 虽然PACAP可以从血液穿过血脑屏障进入大脑，其效率高于其他肽甚至吗啡，但全身给药后在大脑中可达到的水平似乎没有达到纳摩尔浓度，而仅达到亚皮摩尔浓度。基于这些发现，我们假设亚皮摩尔浓度的PACAP的神经保护作用需要活化表达特异性PACAP受体（PAC 1-R）的星形胶质细胞和可能的小胶质细胞。 已经假设亚皮摩尔PACAP和PAC 1-R变体之间的相互作用触发细胞内信号级联，导致神经营养因子的表达增加。 我们建议使用各种体外模型研究这些假设，并确定信号通路以及参与PACAP神经保护作用的关键效应分子。 更好地理解PACAP 38的神经保护作用的机制将有助于最大化全身施用PACAP 38对由中风和其它CNS病症引起的神经元损伤的治疗功效。

Pituitary adenylate cyclase activating polypeptide (PACAP) was originally isolated from the hypothalamus based on its ability to stimulate adenylate cyclase in rat pituitary cell cultures. PACAP exists in two amidated forms with 38 (PACAP38) and 27 (PACAP27) amino acids, and PACAP38 is the major form in tissues. PACAP is a pleiotropic peptide that acts as a hypophysiotropic hormone, neurotransmitter and neuromodulator. More important, it functions as a neurotrophic factor that regulates neuronal development in the embryonic brain, and prevents neuronal damage in the adult brain. PACAP, at subpicomolar concentrations, is able to completely suppress the cell death induced by gp120 in neuron/glia co-cultures. Although PACAP exerts a direct neurotrophic effect on neuron cultures, nano- or subnanomolar concentrations of the peptide are required for this effect. Our study showed that intravenously administered PACAP38 prevented loss of pyramidal cells in the CA1 field of the hippocampus following global ischemia and reduced the infarct volume due to focal ischemia following the middle cerebral artery occlusion in the rat, even when the treatment was delayed. Although PACAP can enter the brain from the blood across the blood-brain barrier with an efficiency greater than other peptides and even morphine, the level which can be reached in the brain after systemic administration does not seem to reach nanomolar concentrations, but only subpicomolar concentrations. Based on these findings, we have hypothesized that te neuroprotective effect of subpicomolar concentrations of PACAP requires activation of astrocytes, and possibly microglia, which express the specific PACAP receptor (PAC1-R). It has been assumed that an interaction between subpicomolar PACAP and a PAC1-R variant triggers an intracellular signaling cascade that leads to an increased expression of a neurotrophic factos(s). We propose to investigate these hypotheses using various in vitro models, and determine the signaling pathway as well as the key effector molecules involved in the neuroprotective action of PACAP. A better understanding of the mechanism of the neuroprotective action of PACAP38 will help to maximize the therapeutic efficacy of systemic administration of PACAP38 for neuronal damage resulting from stroke and other CNS disorders.