Role of phospholipase A2 in spinal cord secondary injury

描述(申请人提供)：磷脂酶A2在脊髓继发性损伤中的作用损伤后脊髓损伤有两种机制：一种是原发的机械性损伤，另一种是由多种损伤机制介导的继发性损伤。到目前为止，对脊髓损伤后的三种损伤机制，即炎症、氧化和兴奋性神经毒性进行了广泛的研究。由于涉及多个机制，阻断一个特定的机制不太可能显著阻止继发性脊髓损伤的进程。然而，这些不同的机制可能共享一条中心或汇聚途径来发挥其不利影响。如果是这样的话，阻断这样一条汇聚通路应该比阻断单一通路更能带来更大的解剖和功能恢复。磷脂酶A2(PLA2)是一种可以作为收敛介体的候选分子。磷脂酶A2是一个多种多样的酶家族，它能分解磷脂sn-2位的酯键，产生一种游离脂肪酸，如花生四烯酸(AA)和溶血磷脂。这些产品是生物活性二十烷基类化合物和血小板激活因子(PAF)的前体，这两种物质是众所周知的炎症、氧化和细胞毒性介质。此外，PLA2可以直接攻击细胞膜，诱导神经元和神经胶质细胞死亡。尽管PLA2的下游产物，如AA，已经得到了广泛的研究，但令我们惊讶的是，关于PLA2本身在创伤性脊髓损伤中的作用和机制还知之甚少。最近，我们首次证明了急性挫伤性脊髓损伤后总PLA2的活性和胞浆PLA2的表达(cPLA2；PLA2的一个亚型)显著增加(Liu等，Ann Neurol 59：606-619,2006)。值得注意的是，在小鼠脊髓损伤后30分钟给予cPLA2抑制剂AACOCF3显著减少了组织损伤并改善了行为恢复。在这里，我们提出了一个中心假设，即PLA2是一种汇聚分子，介导了与继发性脊髓损伤相关的多条损伤途径。如果我们的假设是正确的，阻断PLA2的激活应该会抑制多条损伤途径，从而促进脊髓损伤后更好的神经保护和功能恢复。由于cPLA2是参与受体介导的AA释放的最重要的PLA2同工酶，因此本文将重点介绍cPLA2在介导脊髓损伤中的作用和机制。因此，为了确定cPLA2是否作为一种汇聚分子来介导自由基、兴奋性氨基酸和炎性细胞因子的细胞毒性效应，2)cPLA2激活是否是介导继发性脊髓损伤的必要条件和充分条件，以及3)cPLA2介导继发性脊髓损伤的机制，我们提出了以下三个具体目标：1)cPLA2是否作为一个汇聚分子介导自由基、兴奋性氨基酸和炎性细胞因子的细胞毒作用；2)cPLA2激活是否既是必要的也是充分的，以介导继发性脊髓损伤，重点是线粒体功能障碍。这一应用的完成可能会导致新的有效策略的发展，旨在促进脊髓损伤后更大的解剖和功能恢复。 公共卫生相关性：这项应用将检验一个中心假设，即磷脂酶A2(PLA2)是一种汇聚分子，介导与继发性脊髓损伤(SCI)相关的多种损伤机制。为了验证这一假说，我们提出了三个具体的目标，以确定1)cPLA2是否作为一个汇聚分子介导自由基、兴奋性氨基酸和炎性细胞因子的细胞毒效应，2)cPLA2激活是否既是必要的又是充分的，以介导继发性脊髓损伤，以及3)cPLA2介导继发性脊髓损伤的机制，重点是线粒体功能障碍。我们希望，通过完成这一应用，我们将确定一个新的治疗干预靶点，旨在促进脊髓损伤后更大的解剖和功能恢复。

DESCRIPTION (provided by applicant): Role of phospholipase A2 in spinal cord secondary injury There are two mechanisms of damage to the spinal cord after injury: a primary mechanical injury and a secondary injury mediated by multiple injury mechanisms. To date, three injury mechanisms, i.e., inflammation, oxidation and excitatory neurotoxicity, are extensively studied following spinal cord injury (SCI). Since multiple mechanisms are involved, it is unlikely that blocking one particular mechanism would significantly prevent the course of secondary SCI. However, it is possible that these different mechanisms may share a central or convergence pathway to exert their detrimental effects. If so, blocking such a convergence pathway should result in greater anatomical and functional recovery than blocking a single pathway. A candidate molecule that could serve as a convergence mediator is the enzyme phospholipase A2 (PLA2). PLA2 is a diverse family of enzymes that hydrolyze the ester bond at the sn-2 position of phospholipids to produce a free fatty acid such as arachidonic acid (AA) and a lysophospholipid. These products are precursors of bioactive eicosanoids and platelet activating factor (PAF) that are well-known mediators of inflammation, oxidation and cytotoxicity. Additionally, PLA2 can attack cell membranes directly to induce neuronal and glial death. Although the downstream products of PLA2, such as AA, have been extensively studied, to our surprise, little is known concerning the role and mechanism of the PLA2 itself in traumatic SCI. Recently, we demonstrated, for the first time, that both the activity of total PLA2 and expression of cytosolic PLA2 (cPLA2; a subtype of PLA2) increased significantly following an acute contusive SCI (Liu et al., Ann Neurol 59:606-619, 2006). Remarkably, AACOCF3, a cPLA2 inhibitor, administered at 30 min post-SCI in mice significantly reduced tissue damage and improved behavioral recovery. Here, we propose a central hypothesis that PLA2 is a convergence molecule that mediates multiple injury pathways associated with the secondary SCI. If our hypothesis is correct, blocking PLA2 activation should induce inhibition of multiple injury pathways and, therefore, promotion of greater neuroprotection and functional recovery following SCI. Since cPLA2 is the most important PLA2 isozyme implicated in receptor-mediated release of AA, this application will focus on the role and mechanisms of cPLA2 action in mediating SCI. As such, the following three specific aims are proposed to determine 1) whether cPLA2 serves as a convergence molecule mediating the cytotoxic effects of free radicals, excitatory amino acids and inflammatory cytokines, 2) whether cPLA2 activation is both necessary and sufficient to mediate secondary SCI, and 3) the mechanism by which cPLA2 mediates secondary SCI with an emphasis being placed on the mitochondria dysfunction. Completion of this application may lead to the development of novel and effective strategies aimed at promoting greater anatomical and functional recoveries after SCI. PUBLIC HEALTH RELEVANCE: This application will test a central hypothesis that phospholipase A2 (PLA2) is a convergence molecule that mediates multiple injury mechanisms associated with secondary spinal cord injury (SCI). To test this hypothesis, we have proposed three specific aims to determine 1) whether cPLA2 serves as a convergence molecule that mediates the cytotoxic effects of free radicals, excitatory amino acids and inflammatory cytokines, 2) whether cPLA2 activation is both necessary and sufficient to mediate secondary SCI, and 3) the mechanism by which cPLA2 mediates secondary SCI with an emphasis being placed on the mitochondria dysfunction. We hope that, by completion of this application, we will identify a novel target for therapeutic intervention aimed at promoting greater anatomical and functional recoveries after SCI.