SAMe, RXRalpha-mediated Pathways and ALD

描述（由申请人提供）：本项目的目的是研究核受体维甲酸x受体et（RXR-α）介导的途径调节S-腺苷-L-甲硫氨酸（SAMe）稳态的机制。主要假设是RXR-α介导的途径直接或间接控制SAMe合成，并改变肝脏中谷胱甘肽和磷脂酰胆碱的水平，从而在酒精性肝病（ALD）的发展中发挥关键作用。大多数视黄醇和酒精研究依赖于用过量的类维生素A喂养动物或用视黄醇缺乏的饮食引入动物。用类维生素A喂养动物可能有毒。 维生素A缺乏也会引起许多不必要的影响。敲除技术避免了这些潜在的问题。组织特异性敲除还允许以细胞类型特异性方式研究基因的功能，而不系统地影响基因功能。我们已经建立了一种动物模型，其中RXR-α基因仅在肝细胞中被敲除。RXR-α在肝脏中高度表达，并且是几乎所有核受体介导的途径所必需的。因此，肝细胞RXR-α缺陷型小鼠是研究酒精性肝病中类维生素A信号传导的良好模型。当肝细胞RXR-α缺乏时，肝脏视黄酸升高，酒精清除率增加，酒精诱导的肝损伤变得更加严重。此外，超过10个基因编码的酶参与SAMe途径的表达被改变。这些数据表明，RXR-α，SAMe和ALD是错综复杂地相互关联的。提出了两个具体的目标来研究RXR-α对SAMe稳态的直接和间接影响。首先是研究RXR-α介导的途径如何调节酒精代谢，这可能间接控制SAMe合成并影响ALD的发展。其次是表征RXR-α介导的途径如何调节SAMe途径中编码酶的基因并直接控制SAMe稳态。将研究RXR-α介导的途径，包括PPARcz和3'和RXR-α同源二聚体等。将分析这些核受体配体对调节SAMe合成的作用。这项拟议的研究不仅使我们能够了解核受体如何调节SAMe稳态，还为确定ALD的潜在治疗靶点和治疗药物提供了机会。

DESCRIPTION (provided by applicant): The goal of this project is to study the mechanism underlying nuclear receptor retinoid x receptor et (RXR-alpha)-mediated pathways on regulating S-adenosyl-L-methionine (SAMe) homeostasis. The main hypothesis is that RXR-alpha-mediated pathways either directly or indirectly control SAMe synthesis and alter the levels of glutathione and phosphatidylcholine in the liver, which consequently play a crucial role in the development of alcoholic liver disease (ALD). Most of the retinol and alcohol studies rely on either feeding animals with excess amount of retinoids or introducing animals with retinol deficient diet. Feeding animals with retinoids can be toxic. Retinol deficiency can also cause many unwanted effects. Knockout technology avoids these potential problems. Tissue specific knockout further allows studying the function of the gene in a cell type specific manner without affecting the gene function systemically. We have established an animal model in that the RXR-alpha gene is knocked out only in the hepatocyte. RXR-alpha is highly expressed in the liver and is required for almost all the nuclear receptor-mediated pathways. Therefore, hepatocyte RXR-alpha deficient mouse serves as an excellent model for studying retinoid signaling in alcoholic liver disease. When hepatocyte RXR-alpha is deficient, liver retinoic acid is elevated, alcohol elimination rate is increased and alcohol-induced liver damage becomes more severe. In addition, the expression of more than ten genes encoding enzymes involved in the SAMe pathway is altered. Those data indicate that RXR-alpha, SAMe and ALD are intricately interlinked. Two specific aims are proposed to study the direct and indirect effect of RXR-alpha on SAMe homeostasis. First is to examine how RXR-alpha-mediated pathways regulate alcohol metabolism, which may indirectly control SAMe synthesis and affect the development of ALD. Second is to characterize how RXR-alpha-mediated pathways regulate genes encoding enzymes in the SAMe pathway and directly control SAMe homeostasis. RXR-alpha-mediated pathways including PPARcz and 3' and RXR-alpha homodimer and others will be studied. The effect of those nuclear receptor ligands on regulating SAMe synthesis will be analyzed. The proposed study not only allows us to understand how nuclear receptors regulate SAMe homeostasis, it also provides an opportunity to identify potential therapeutical targets and treatment agents for ALD.