Hypoxia and the Role of HIF-1 in the Ischemic Testis

说明(申请人提供)：氧气对所有需氧生物的生存都是必不可少的。哺乳动物细胞对氧气浓度的变化非常敏感，特别是局部氧气供应的减少(缺氧)。生物体依靠许多氧气感应机制来检测缺氧并刺激分子适应做出相应的反应。睾丸扭转是一种医学紧急情况，会造成睾丸缺血和缺氧，导致生殖细胞丢失和精子发生障碍。了解睾丸对缺氧的反应所涉及的分子机制对于了解细胞损伤是如何在缺血睾丸中发生的至关重要。低氧诱导因子-1(HIF-1)在许多组织中被认为是低氧反应和氧稳态的“主调节器”。HIF-1被低氧激活，是一种转录因子，能刺激编码蛋白的表达，这些蛋白参与了氧输送增加、代谢反应、细胞拯救和细胞死亡途径(包括细胞凋亡)等反应。HIF-1在对缺氧的反应以及中风、心脏病发作和其他形式的缺血性损伤的病理生理学中发挥着关键作用。本实验室以前的研究表明，HIF-1在大鼠睾丸中产生，并在缺血的睾丸中受到缺氧的快速刺激。我们的工作假设是，睾丸HIF-1激活了缺血睾丸中的抗凋亡和促凋亡通路，这取决于缺氧的程度和持续时间。这项工作的总体目标是研究HIF-1在缺血睾丸对缺氧的适应性反应中的潜在作用，并确定可能参与大鼠睾丸缺血期间细胞存活和细胞死亡反应的HIF-1靶基因。这一建议的具体目的是：(1)验证HIF-1在缺血大鼠睾丸中具有促凋亡作用的假说，这取决于氧债(通过缺氧缺氧)的持续时间和程度。(2)验证HIF-1在睾丸缺氧或缺氧条件下通过与肿瘤抑制蛋白P53相互作用而导致细胞损伤的假说。(3)验证抗凋亡基因(Mcl-1)和促凋亡基因(Bax，Nip3)是HIF-1在缺血睾丸中反式激活靶点的假说。从实验中获得的知识将有助于了解缺血睾丸对低氧的细胞和分子反应，并为HIF-1在低氧和睾丸缺血损伤的病理生理效应中的作用提供基本的见解。

DESCRIPTION (provided by applicant): Oxygen is essential for the survival of all aerobic organisms. Mammalian cells are extremely sensitive to changes in oxygen concentration, particularly decreases in local oxygen supply (hypoxia). Organisms rely on a number of oxygen sensing mechanisms to detect hypoxia and stimulate molecular adaptations to respond accordingly. Testicular torsion is a medical emergency creating testicular ischemia and hypoxia that can result in germ cell loss and impaired spermatogenesis. An understanding of the molecular mechanisms involved in the response to hypoxia in the testis is critically important for understanding how cellular damage occurs in the ischemic testis. Hypoxia-inducible factor-1 (HIF-1) is considered the "master regulator" of the response to hypoxia and oxygen homeostasis in many tissues. Activated by hypoxia, HIF-1 is a transcription factor that stimulates expression of genes encoding proteins involved in responses such as increased oxygen delivery, metabolic responses, and cell rescue and cell death pathways including apoptosis. HIF-1 performs critical functions in the response to hypoxia and the pathophysiology of stroke, heart attack and other forms of ischemic injury. Previous research in our laboratory has shown that HIF-1 is produced in the rat testis and rapidly stimulated by hypoxia in the ischemic testis. Our working hypothesis is that testicular HIF-1 activates anti-apoptotic as well as pro-apoptotic pathways in the ischemic testis depending on the extent and duration of hypoxia. The overall goal of the work described in this proposal is to examine potential roles of HIF-1 in the adaptive response to hypoxia in the ischemic testis and to identify HIF-1 target genes that may be involved in cell-survival and cell-death responses that occur during testis ischemia in a rat model. The specific aims of this proposal are: (1) To test the hypothesis that HIF-1 has a pro-apoptotic role in the ischemic rat testis depending on the duration and extent of oxygen debt {hypoxia through anoxia). (2) To test the hypothesis that HIF-1 contributes to cell damage in the ischemic rat testis by interacting with the tumor suppressor protein p53 under conditions of testicular hypoxia or anoxia. (3) To test the hypothesis that anti-apoptotic (Mcl-1) and pro-apoptotic (Bax, Nip3) genes are transactivation targets for HIF-1 in the ischemic testis. Knowledge gained from the proposed experiments will be relevant to understanding cellular and molecular responses to hypoxia in the ischemic testis and provide fundamental insight on the role of HIF-1 in pathophysiologic effects of hypoxia and testicular ischemic injury.