Neuroprotection by PACAP in Stroke

垂体腺苷环化酶激活多肽(PACAP)最初是从下丘脑中分离出来的，其基础是在培养的大鼠脑垂体细胞中刺激腺苷环化酶。PACAP以两种酰胺化形式存在，分别含有38(PACAP38)和27(PACAP27)个氨基酸，其中PACAP38是组织中的主要形式。PACAP是一种多效肽，作为促垂体激素、神经递质和神经调节剂发挥作用。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，并防止成年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诱导的神经元/神经胶质细胞共培养的细胞死亡。虽然PACAP对神经元培养有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多肽。我们的研究表明，静脉注射PACAP38可以防止全脑缺血后大鼠海马区CA1区锥体细胞的丢失，并减少大鼠大脑中动脉闭塞后局灶性脑缺血所致的脑梗塞体积，即使治疗被推迟。虽然PACAP可以通过血脑屏障从血液进入大脑，比其他多肽甚至吗啡的效率更高，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，而只达到了亚皮摩尔浓度。基于这些发现，我们推测，亚皮下摩尔浓度的PACAP的神经保护作用需要激活星形胶质细胞，可能还有表达特异性PACAP受体(PAC1-R)的小胶质细胞。有人认为，亚皮下单分子PACAP和PAC1-R变体之间的相互作用触发了细胞内信号级联，导致神经营养因子表达增加(S)。我们建议使用不同的体外模型来研究这些假说，并确定PACAP的信号通路以及参与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全身应用PACAP38治疗中风和其他中枢神经系统疾病引起的神经元损伤。

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.