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，基于它在大鼠垂体细胞培养中刺激腺苷酸环化酶的能力。PACAP以38个（PACAP38）和27个（PACAP27）氨基酸的两种修饰形式存在，PACAP38是组织中的主要形式。PACAP是一种多效肽，具有促垂体激素、神经递质和神经调节剂的作用。更重要的是，它作为一种神经营养因子，调节胚胎大脑中的神经元发育，并防止成人大脑中的神经元损伤。在亚皮摩尔浓度下，PACAP能够完全抑制gp120在神经元/胶质共培养中诱导的细胞死亡。尽管PACAP对神经元培养具有直接的神经营养作用，但这种作用需要纳米或亚纳摩尔浓度的肽。我们的研究表明，静脉注射PACAP38可以防止大鼠大脑中动脉闭塞后海马CA1区锥体细胞的损失，并减少因局灶性缺血引起的梗死体积，即使延迟治疗也是如此。尽管PACAP可以从血液中穿过血脑屏障进入大脑，其效率比其他多肽甚至吗啡都要高，但全身给药后在大脑中可以达到的水平似乎没有达到纳摩尔浓度，而只能达到亚皮摩尔浓度。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激活星形胶质细胞，可能还有小胶质细胞，它们表达特定的PACAP受体（PAC1-R）。据推测，亚皮摩尔PACAP和PAC1-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。我们建议通过多种体外模型对这些假设进行验证，并确定PACAP的信号通路以及参与其神经保护作用的关键效应分子。更好地了解PACAP38的神经保护作用机制，将有助于最大限度地发挥全身给药PACAP38对脑卒中及其他中枢神经系统疾病所致神经元损伤的治疗效果。

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.