The attenuation of ischemic injury by transglutaminase 2

本应用的重点是阐明转谷氨酰胺酶2 （TG2）调节缺氧诱导因子（HIF）信号和减轻缺血诱导的细胞死亡的分子机制。在对缺血的反应中，基因的上调可以促进细胞存活或细胞死亡。细胞存活或延迟细胞死亡是最终结果取决于表达的缺血诱导基因的补体，这取决于诸如损伤的持续时间和严重程度以及调节蛋白的存在等变量。HIF由氧敏感的HIF1亚基和组成性表达的HIF12组成，是主要负责缺氧反应基因上调的转录因子。我们已经证明TG2结合HIF12，减弱HIF信号，减弱特定HIF应答基因的表达，并保护免受缺血性损伤。此外，我们有令人信服的数据表明，在小鼠中风模型中，人类TG2的神经元表达显著减少梗死体积。该应用的中心假设是TG2是缺氧诱导的转录信号的调节因子，并且TG2在保护神经元免受缺血诱导的细胞死亡中起着基本作用。本提案的目标将通过测试假设的三个具体目标来实现：(1) TG2介导的HIF信号抑制依赖于TG2在细胞核中的定位，与转胺活性无关，需要与HIF12相互作用；(2)TG2对缺血诱导的细胞死亡的保护作用与转胺活性无关，但需要核定位；进一步说，TG2与HIF1¿的相互作用是TG2对缺血损伤的保护作用所必需的。(3) TG2在体内可减轻脑卒中后发生的延迟细胞死亡。总的来说，这是一个综合的、机械的、整体的方案。在我们的研究中，我们将使用重组蛋白来定义TG2和HIF1之间的相互作用域，使用细胞模型来了解TG2如何调节HIF依赖的转录事件并减轻缺血诱导的细胞死亡，以及使用小鼠模型来描述神经元TG2在减少中风损伤中的作用。我们相信，通过使用这些完整的方法，我们将能够更全面地了解TG2在改善缺血诱导的细胞死亡中的作用。这些令人兴奋和创新的研究不仅为理解TG2的功能定义了一个新的框架，而且还为缺血诱导的细胞死亡过程的调控提供了新的见解。

The focus of this application is on elucidating the molecular mechanisms by which transglutaminase 2 (TG2) regulates hypoxia inducible factor (HIF) signaling and attenuates ischemic-induced cell death. In response to ischemia there is an upregulation of genes that can facilitate either cell survival or cell death. Whether cell survival or delayed cell death is the final outcome is dependent on the complement of ischemia-induced genes expressed, which can differ depending on variables such as duration and severity of the insult and the presence of regulatory proteins. HIF, which is composed of the oxygen sensitive HIF1 subunit and the constitutively expressed HIF12, is the transcription factor that is primarily responsible for the upregulation of hypoxic responsive genes. We have demonstrated that TG2 binds HIF12, attenuates HIF signaling, attenuates the expression of specific HIF- responsive genes and protects against ischemic insult. Furthermore, we have compelling data demonstrating that neuronal expression of human TG2 significantly reduces infarct volume in a mouse stroke model. The central hypothesis of this application is that TG2 is a regulator of hypoxic-induced transcriptional signaling, and that TG2 plays a fundamental role in protecting neurons against ischemia-induced cell death. The objectives of this proposal will be met through three specific aims that test the hypotheses: (1) that the TG2- mediated suppression of HIF signaling is dependent on the localization of TG2 to the nucleus, independent of transamidating activity and requires interaction with HIF12, (2) that the protective effects of TG2 against ischemic-induced cell death are independent of transamidating activity, but require nuclear localization and further, that the interaction of TG2 with HIF1¿ is necessary for the protective role of TG2 against ischemic insult, and (3) that TG2 attenuates the delayed cell death that occurs in response to stroke in vivo. Overall, this is an integrated, mechanistic and holistic proposal. In our studies we will be using recombinant proteins to define the interacting domains between TG2 and HIF1¿, cell models to understand how TG2 modulates HIF dependent transcriptional events and attenuates ischemia-induced cell death, and mouse models to delineate the role of neuronal TG2 in decreasing stroke damage. We believe that by using this full complement of approaches we will be able to more completely understand the role of TG2 in ameliorating ischemia-induced cell death. These are exciting and innovative studies in that they not only define a new framework for understanding the function of TG2, but that they also are providing new insights into the regulation of ischemia-induced cell death processes.