Homocysteine, ER stress and alcoholic liver injury

描述（由申请人提供）：尽管最近取得了相当大的进展，但酒精性肝病（ALD）的发病机制仍不确定。我们提出了一个新的假设，建立在已知的影响，酒精对同型半胱氨酸代谢的联系，这对ER应激反应和随之而来的脂肪肝，坏死和凋亡，我们已经观察到在胃内乙醇喂养的小鼠模型。我们的初步结果表明，饲料甜菜碱逆转高同型半胱氨酸血症，内质网应激和肝脏病理学响应酒精。提出了五个目标，建立在这个假设和初步结果。首先，我们将完成一个详细的表征乙醇诱导的ER应激，包括细胞和区域区室化酒精小鼠肝脏，乙醇对ER应激和凋亡信号的敏感性的影响，以及ER应激对TNF的敏感性的影响。第二，我们将尝试通过利用具有ER应激反应的特定组分（例如SREBP-1、CHOP、半胱天冬酶12）或用于调节SREBP的其他信号传导机制的基因缺失的各种小鼠（LXRa缺失小鼠）来确定ER应激反应的关键组分对酒精性肝病的贡献。第三，我们将通过评估底物池的大小、同型半胱氨酸代谢酶的表达和示踪动力学来确定乙醇引起高同型半胱氨酸血症的机制。这些研究将使我们能够确定肝脏是同型半胱氨酸的主要来源，以及是否减少再甲基化和/或转硫作用是导致同型半胱氨酸过量的主要原因。第四，我们将确定同型半胱氨酸在乙醇诱导的内质网应激中的作用。我们将采用几种不同的策略来加强同型半胱氨酸和ER对乙醇的应激反应之间联系的证据。我们将确定是否同时提高同型半胱氨酸与过量的饮食蛋氨酸或胍乙酸或使用胱硫醚合酶+/-小鼠增强酒精性肝损伤。此外，我们将评估SAMe喂养对同型半胱氨酸、ER应激和肝损伤的影响，并通过评估TNF-R1基因敲除小鼠对乙醇喂养的应答中同型半胱氨酸和ER应激来确定TNF是否在同型半胱氨酸上游起作用。第五，我们将通过比较甜菜碱与牛磺酸、二甲基磺基丙酸盐以及通过确定甜菜碱是否在MAT 1A缺陷小鼠中提供保护来确定甜菜碱喂养在保护免受乙醇侵害方面的作用机制。此外，我们将评估甜菜碱喂养对肝脏基因表达的整体影响，以寻找甜菜碱替代效应的线索，这也可能有助于其保护作用。我们期望我们将获得重要的新知识，可应用于ALD的预防和治疗

DESCRIPTION (provided by applicant): The pathogenesis of alcoholic liver disease (ALD) remains uncertain despite considerable recent progress. We present a new hypothesis which builds upon the known effect of alcohol on homocysteine metabolism by linking this to the ER stress response and consequent fatty liver, necrosis, and apoptosis which we have observed in the intragastric ethanol fed mouse model. Our preliminary results indicate that feeding betaine reverses the hyperhomocysteinemia, ER stress and liver pathology in response to alcohol. Five aims are proposed which build on this hypothesis and preliminary results. First, we will complete a detailed characterization of ethanol-induced ER stress including the cellular and zonal compartmentation alcoholic mouse liver, the effect of ethanol on the susceptibility to ER stress and apoptotic signaling, and the effect of ER stress on susceptibility to TNF. Second, we will attempt to ascertain the contribution of key components of the ER stress response to alcoholic liver disease by exploiting various mice which have gene deletions of specific components of the ER stress response (e.g. SREBP-1, CHOP, caspase 12) or other signaling mechanisms for regulating SREBP (LXRa null mice). Third, we will determine the mechanism of hyperhomocysteinemia in response to ethanol by assessing substrate pool sizes, homocysteine metabolizing enzyme expression and tracer kinetics. These studies will allow us to determine that the liver is the major source of homocysteine and whether decreased remethylation and/or transulfuration are primarily responsible for excess homocysteine. Fourth, we will determine the role of homocysteine in ethanol-induced ER stress. We will employ several different strategies to strengthen the evidence for linkage of homocysteine and the ER stress response to ethanol. We will determine if alcoholic liver injury is potentiated by concomitantly raising homocysteine with either excess dietary methionine or guanidinoacetate or use of cystathionine ¿- synthase +/- mice. In addition, we will assess the effect of SAMe feeding on homocysteine, ER stress and liver injury and determine if TNF acts upstream of homocysteine by assessing homocysteine and ER stress in response to ethanol feeding in TNF-R1 null mice. Fifth, we will determine the mechanism of action of betaine feeding in protecting against ethanol by comparing it to taurine, dimethlysulfoniopropriate, and by determining if betaine protects in MAT1A null mice. In addition, we will assess the global effects of betaine feeding on hepatic gene expression to look for clues of alternative effects of betaine which might also contribute to its protective action. We anticipate that we will obtain important new knowledge which can be applied to the prevention and treatment of ALD