Neuronal Apoptosis Induced by DNA Damage

描述（申请人提供）：神经元凋亡在正常脑发育和神经退行性变中起重要作用。最近的研究结果表明，脑损伤后这种类型的神经元死亡优先通过caspase激活的内在途径进行。线粒体细胞色素c （Cyto-c）向细胞质的释放在这一途径中起着核心作用。细胞-c的释放是由Bcl-2家族的促凋亡成员介导的，这些成员在DNA损伤的损伤神经元中被诱导。另一方面，其他报道表明，线粒体中细胞c的释放不足以诱导内在凋亡途径。尽管有Cyto-c释放，但这一途径的进展受到细胞外信号调节蛋白激酶Erk1/2的抑制，Erk1/2能够阻断caspase-9的激活，并通过直接磷酸化procaspase-9促进细胞存活。在凋亡神经元中抑制这种保护机制的途径尚不清楚。在这个应用中，我们提出DNA损伤、线粒体中细胞c的释放、促存活Erk1/2的去磷酸化和失活、半胱天冬酶的激活和神经元死亡之间可能存在联系。我们的工作假设是，DNA损伤诱导的神经元凋亡的进展取决于p53介导的特异性双特异性磷酸酶（DUSPs）的激活，DUSPs能够通过选择性Erk1/2失活来促进procaspase-9的加工。如果我们的假设是正确的，那么神经元损伤后DUSP活性的抑制一定具有神经保护作用。为了解决这一假设，我们提出了两个相关的具体目标：(1)在体外和体内脑外伤后检测DUSP基因家族成员的神经元表达对DNA损伤的反应；(2)评估诱导DUSP在抑制Erk1/2、caspase激活和神经元死亡中的作用。本研究的结果可能对确定各种急性和慢性神经退行性疾病的新治疗策略具有根本性影响，其中DNA损伤和p53依赖性细胞凋亡对神经元丢失的贡献非常显著。

DESCRIPTION (provided by applicant): Neuronal apoptosis plays an essential role in normal brain development and neurodegeneration. Results of recent studies indicate that after brain injury this type of neuronal death preferentially proceeds through the intrinsic pathway of caspase activation. The release of mitochondrial cytochrome c (Cyto-c) to the cytoplasm plays a central role in this pathway. Cyto-c release is mediated by pro-apoptotic members of Bcl-2 family, which are induced in injured neurons in response to DNA damage. On the other hand, other reports indicate that the release of Cyto-c from mitochondria is not sufficient for the induction of the intrinsic apoptotic pathway. Despite of Cyto-c release, progression of this pathway is inhibited by the extracellular signal-regulated protein kinases Erk1/2 able to block activation of caspase-9 and promote cell survival by direct phosphorylation of procaspase-9. A pathway, which restrains this protective mechanism in apoptotic neurons, remains unknown. In this application we propose a possible link between DNA damage, the release of Cyto-c from mitochondria, dephosphorylation and inactivation of pro-survival Erk1/2, activation of caspases, and neuronal death. Our working hypothesis is that the progression of DNA damage-induced apoptosis in neurons depends on p53-mediated activation of specific dual specificity phosphatases (DUSPs) able to promote processing of procaspase-9 through selective Erk1/2 inactivation. If our hypothesis is correct, inhibition of DUSP activity after neuronal injury must be neuroprotective. To address the hypothesis, we propose 2 related Specific Aims: (1) To examine neuronal expression of DUSP gene family members in response to DNA damage in vitro and after brain trauma in vivo and (2) To assess a role for inducible DUSPs in inhibition of Erk1/2, caspase activation, and neuronal death. Results of this study may have fundamental impact on identifying novel treatment strategies for a wide variety of acute and chronic neurodegenerative conditions where the contribution of DNA damage and p53-dependent apoptosis to neuronal loss is highly significant.