The Unfolded Protein Response After Brain Ischemia

描述（申请人提供）：在每年7万例心脏骤停复苏患者中，脑缺血再灌注损伤使90%以上的患者无法恢复正常生活。我们的长期目标是充分了解损伤机制，制定临床有效的治疗方法。脑再灌注过程中蛋白质合成的抑制与区域选择性易感性和神经元死亡相关，这是由于两个翻译起始因子的修饰：真核起始因子2 (eIF2alpha) α亚基的磷酸化和真核起始因子4G （eIF4G）的蛋白水解断裂。eIF2磷酸化和eIF4G片段化不仅影响整体蛋白质合成速率，还影响可用mrna合成的肽。此外，已知在脑缺血和再灌注后立即磷酸化eIF2alpha的激酶PERK仅被称为未折叠蛋白反应（UPR）的内质网应激信号系统激活。UPR可以发出适应性促生存反应的信号，也可以触发细胞死亡。因此，抑制蛋白质翻译可能是决定再灌注神经元最终命运的更全面的细胞反应的一部分。我们假设：(1)UPR在早期脑再灌注时被激活；(2)脆弱但不耐药，神经元无法解决UPR；(3)在早期再灌注期间，由于eIF2alpha磷酸化和eIF4G碎片化，仅合成有限数量的蛋白质，这可能决定神经元恢复或死亡的结果。我们的具体目标如下。目的通过表征UPR的三种效应物ATF6、IRE1alpha和PERK的激活，比较缺血和再灌注时UPR的易损和抗性脑区。Aim 2将检查缺血再灌注易感和抵抗脑区域的UPR是否被分解（通过测定促存活蛋白GRP78、XBP-1、GADD34和SERCA2b的合成是否发生），或者UPR是否无法分解（通过测定促细胞死亡蛋白ATF4和CHOP的合成是否发生）。目的3将鉴定在再灌注早期通过残馀翻译合成的蛋白质，并比较缺血和再灌注易损和抵抗脑区之间的蛋白质。该方法提供了脑缺血再灌注期间的综合检查：(1)UPR激活的发生和后果，(2)翻译起始因子改变对残余蛋白合成的影响，以及(3)这两个事件与脑对缺血再灌注损伤的选择性易感的关系。

DESCRIPTION (provided by applicant): Brain ischemia and reperfusion injury prevents greater than 90% of the 70,000 patients per year resuscitated from cardiac arrest from resuming their normal lives. Our long-term goal is sufficient understanding of the injury mechanisms to formulate clinically effective therapy. Inhibition of protein synthesis during brain reperfusion correlates with regional selective vulnerability and neuronal death, and is due to modification of two translation initiation factors: the phosphorylation of the alpha-subunit of eukaryotic initiation factor 2 (eIF2alpha), and the proteolytic fragmentation of eukaryotic initiation factor 4G (eIF4G). eIF2 phosphorylation and eIF4G fragmentation affect not only the overall protein synthesis rate, but also which peptides are synthesized from the available mRNAs. Moreover, the kinase that phosphorylates eIF2alpha immediately after brain ischemia and reperfusion, PERK, is known to be activated only by the endoplasmic reticulum stress signaling system termed the unfolded protein response (UPR). The UPR can signal either an adaptive pro-survival response, or it can trigger cell death. Thus suppression of protein translation is likely to be part of a more comprehensive cellular response that determines the ultimate fate of reperfused neurons. We hypothesize: (1) the UPR is activated during early brain reperfusion, (2) vulnerable, but not resistant, neurons fail to resolve the UPR, and (3) there is synthesis of only a limited number of proteins during early reperfusion, as a consequence of eIF2alpha phosphorylation and eIF4G fragmentation, that may determine the outcome of neuronal recovery or death. Our Specific Aims are the following. Aim I will compare in ischemia and reperfusion vulnerable and resistant brain regions the activation of the UPR by characterizing activation of its three effectors ATF6, IRE1alpha, and PERK. Aim 2 will examine in ischemia and reperfusion vulnerable and resistant brain regions whether the UPR is resolved (by determining if synthesis of the pro-survival proteins GRP78, XBP-1, GADD34 and SERCA2b occurs), or if the UPR fails to resolve (by determining if synthesis of the pro-cell death proteins ATF4 and CHOP occurs). Aim 3 will identify those proteins being synthesized by residual translation during the early hours of reperfusion and compare them between ischemia and reperfusion vulnerable and resistant brain regions. This approach provides an integrated examination during brain ischemia and reperfusion of: (1) the occurrence and the consequences of UPR activation, (2) the consequences of translation initiation factor alterations on residual protein synthesis, and (3) the relationship of these two events to the selective vulnerability of the brain to ischemia and reperfusion injury.