Mechanisms of Asbestos-Induced Alveolar Epithelial Cell Injury

描述(由申请人提供)： 石棉导致石棉肺(继发于石棉的肺纤维化)和恶性肿瘤(肺癌和间皮瘤)，其机制尚未完全阐明。肺泡上皮细胞(AEC)损伤和修复的程度是石棉等有毒物质致纤维化潜力的关键决定因素。以前的研究，包括我们小组的研究，已经确定了导致石棉不利影响的一些重要因素以及具有保护作用的策略。我们已经证明，线粒体电子传输链(ETC)中的铁源性活性氧物种(ROS)通过P53和线粒体调节的(内在)死亡途径介导石棉诱导的AEC DNA损伤和凋亡。我们最近的数据暗示了一个特定的p53依赖的转录分子Noxa的重要作用，以及一个新的机制，线粒体人8-氧鸟嘌呤-DNA糖基酶1(mt-hOgg1)通过保存线粒体乌头酸酶来防止氧化剂诱导的内源性AEC凋亡。尽管Bcl2家族成员在调节细胞凋亡中起着至关重要的作用，但目前尚不清楚特定的Bcl2蛋白如何调控石棉诱导的AEC凋亡，以及下游促凋亡的Bax/Bak激活是否对介导石棉肺起关键作用。在这次更新中，我们研究了石棉诱导血管内皮细胞内源性凋亡的分子机制。我们的假设是，线粒体hOgg1和乌头酸酶在减轻石棉诱导的AEC mtDNA损伤中起重要作用，这些损伤是由线粒体ROS的产生导致P53(Noxa)激活、Bax/Bak固有的AEC凋亡和肺纤维化引起的。我们将在未来4年研究的具体目标包括：(1)确定线粒体hOgg1保存乌头酸酶是否对于减轻石棉诱导的AEC mtDNA损伤是否重要，石棉诱导的AEC mtDNA损伤导致P53(NoxA)激活和内在凋亡。我们还将评估Ogg1-/-小鼠是否更容易患石棉肺。(2)确定石棉诱导的AEC线粒体ROS是否激活P53(NoxA)依赖的转录，从而导致线粒体(Bax/Bak)调控的细胞凋亡。我们还将确定线粒体ROS是否对石棉暴露后的肺纤维化起关键作用。(3)确定石棉诱导的AEC P53(Noxa)激活是否导致Mcl-1丢失，从而导致Bax/Bak介导的细胞凋亡。我们将确定肺泡上皮Bax/Bak有条件缺失的小鼠是否对石棉肺具有保护作用。这些研究有几个直接和长期的好处。首先，他们应该深入了解石棉诱导的AEC DNA损伤、P53激活、线粒体功能障碍和细胞凋亡的潜在机制，以及这些事件是如何导致肺纤维化的。其次，这些研究将表征线粒体hOgg1保存乌头酸酶在防止石棉诱导的AEC线粒体功能障碍、P53激活和内源性凋亡中的作用。最后，也许最重要的是，我们的发现可能提供关于其他慢性肺部疾病的病理生理事件的新信息，这将确定新的治疗方法。旨在减少线粒体ROS产生和保持线粒体DNA完整性的策略可能被证明在预防肺纤维化和/或肺癌暴露于各种肺部毒素(例如石棉、香烟烟雾、空气颗粒物等)方面有用。

DESCRIPTION (provided by applicant): Asbestos causes asbestosis (pulmonary fibrosis secondary to asbestos) and malignancies (bronchogenic carcinoma and mesothelioma) by mechanisms that are not fully elucidated. The extent of alveolar epithelial cell (AEC) injury and repair are critical determinants of the fibrogenic potential of toxic agents such as asbestos. Previous studies, including ones from our group, have identified some of the important factors contributing to the adverse effects of asbestos as well as strategies that are protective. We have shown that iron-derived reactive oxygen species (ROS) from the mitochondria electron transport chain (ETC) mediate asbestos-induced AEC DNA damage and apoptosis by a p53- and mitochondria-regulated (intrinsic) death pathway. Our more recent data implicate an important role for a specific p53-dependent transcriptional molecule, Noxa, as well as a novel mechanism by which mitochondrial human 8-oxoguanine-DNA glycosylase 1 (mt-hOgg1) prevents oxidant-induced intrinsic AEC apoptosis by preserving mitochondrial aconitase. Although Bcl-2 family members are crucial for regulating apoptosis, it is unclear how specific Bcl-2 proteins modulate asbestos-induced AEC apoptosis and whether downstream proapoptotic Bax/Bak activation is essential for mediating asbestosis. In this renewal, we investigate the molecular mechanisms underlying asbestos-induced AEC intrinsic apoptosis. Our HYPOTHESIS is that mitochondrial hOgg1 and aconitase are important for attenuating asbestos- induced AEC mtDNA damage resulting from mitochondrial ROS production that leads to p53 (Noxa) activation, Bax/Bak intrinsic AEC apoptosis and pulmonary fibrosis. Our SPECIFIC OBJECTIVES that will be examined over the next 4 years include: (1) To determine whether mitochondrial hOgg1 preservation of aconitase is important in attenuating asbestos- induced AEC mtDNA damage that results in p53 (Noxa) activation and intrinsic apoptosis. We will also assess whether Ogg1-/- mice are more susceptible to asbestosis. (2) To determine whether asbestos-induced ROS from AEC mitochondria activate p53 (Noxa)-dependent transcription that causes mitochondria (Bax/Bak)-regulated apoptosis. We will also determine whether mitochondrial ROS are crucial for mediating pulmonary fibrosis following asbestos exposure. (3) To determine whether asbestos-induced AEC p53 (Noxa) activation results in the loss of Mcl-1 leading to Bax/Bak-mediated apoptosis. We will determine whether mice with conditional loss of Bax/Bak at the alveolar epithelium are protected against asbestosis. There are several immediate and long-range benefits from these studies. First, they should provide insight into the mechanisms underlying asbestos-induced AEC DNA damage, p53 activation, mitochondrial dysfunction, and apoptosis as well as how these events cause pulmonary fibrosis. Second, these studies will characterize the role of mitochondrial hOgg1 preservation of aconitase in preventing asbestos-induced AEC mitochondrial dysfunction, p53 activation, and intrinsic apoptosis. Finally, and perhaps most importantly, our findings may provide new information about the pathophysiologic events of other chronic lung diseases that will identify novel management approaches. Strategies aimed at reducing mitochondrial ROS production and preserving mitochondrial DNA integrity may prove useful in preventing pulmonary fibrosis and/or lung cancer from exposure to various pulmonary toxins (e.g. asbestos, cigarette smoke, air-borne particulate matter etc).