SAMe, RXRalpha-mediated Pathways and ALD

描述(申请人提供)：本项目的目标是研究核受体维甲酸X受体ET(RXR-α)介导的调节S-腺苷-L-蛋氨酸(SAME)动态平衡的机制。主要的假说是RXR-α介导的途径直接或间接地控制肝脏中谷胱甘肽和磷脂酰胆碱的合成，从而在酒精性肝病(ALD)的发生发展中发挥关键作用。大多数视黄醇和酒精研究依赖于给动物喂食过量的视黄醇，或引入缺乏视黄醇的饮食。用维甲酸喂养动物可能是有毒的。视黄醇缺乏也会导致许多不必要的影响。基因敲除技术避免了这些潜在的问题。组织特异性基因敲除进一步允许以细胞类型特异性的方式研究基因的功能，而不会系统地影响基因的功能。我们已经建立了一个动物模型，RXR-α基因只在肝细胞中被敲除。RXR-α在肝脏中高度表达，几乎所有核受体介导的途径都需要RXR-α。因此，肝细胞RXR-α缺陷小鼠是研究酒精性肝病中维甲酸信号转导的良好模型。当肝细胞RXR-α缺乏时，肝脏维甲酸升高，酒精清除率增加，酒精性肝损伤加重。此外，同一途径中涉及的十多个编码酶的基因的表达也发生了变化。这些数据表明，RXR-α、SAME和ALD之间存在错综复杂的联系。为了研究RXR-α对体内稳态的直接和间接影响，我们提出了两个特定的目标。首先是研究RXR-α介导的途径如何调节酒精代谢，这可能间接控制同样的合成并影响ALD的发展。其次是研究RXR-α介导的途径如何调控同一途径中的编码酶基因，并直接控制同一途径的内稳态。RXR-α介导的途径包括PPARcz、3‘和RXR-α同源二聚体等。将分析这些核受体配体在调节相同合成方面的作用。这项拟议的研究不仅让我们了解核受体是如何调节体内平衡的，也为确定ALD的潜在治疗靶点和治疗剂提供了机会。

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.