Dysregulated Hepatic Methionine Metabolism Drives Homocysteine Elevation in Diet-Induced Nonalcoholic Fatty Liver Disease.
Dysregulated Hepatic Methionine Metabolism Drives Homocysteine Elevation in Diet-Induced Nonalcoholic Fatty Liver Disease.
复制标题
DOI：
10.1371/journal.pone.0136822
复制
发表时间：
2015
期刊：
影响因子：
3.7
通讯作者：
Sanyal AJ
中科院分区：
文献类型：
--
作者：
Pacana T;Cazanave S;Verdianelli A;Patel V;Min HK;Mirshahi F;Quinlivan E;Sanyal AJ
蛋氨酸代谢在甲基化反应、谷胱甘肽和甲基精氨酸的产生以及调节同型半胱氨酸水平中起着核心作用。NAFLD影响这些功能的机制尚不完全清楚。目的是对饮食诱导的NAFLD的肝脏蛋氨酸代谢进行代谢组学、分子和表观遗传学分析。女性129 s1 / SvlmJ;C57Bl/6J小鼠分别饲喂周粮（n = 6）和高脂高胆固醇（HFHC）饲料（n = 8），连续52周。进行了代谢组学研究、酶表达和DNA甲基化分析。HFHC饮食导致体重增加，明显的脂肪变性和广泛的纤维化。在蛋氨酸循环中，肝脏蛋氨酸消耗（30%,p< 0.01）， s-腺苷蛋氨酸(SAM)/蛋氨酸比值（p< 0.05）、s-腺苷同型半胱氨酸（SAH） （35%, p< 0.01）和同型半胱氨酸（25%,p< 0.01）显著升高。SAH水解酶蛋白水平显著降低（p <0.01）。丝氨酸（同型半胱氨酸再甲基化和转硫化的底物）被耗尽（45%,p< 0.01）。在转硫途径中，半胱甘氨酸和半胱氨酸呈上升趋势，而谷胱甘肽呈显著下降趋势（p< 0.05）。在转甲基化途径中，肝脏中最丰富的甲基转移酶甘氨酸n -甲基转移酶（GNMT）水平下降。磷脂酰胆碱(PC)/磷脂酰乙醇胺（PE）比值极显著升高（p< 0.01），表明磷脂酰乙醇胺甲基转移酶（PEMT）活性升高。蛋白精氨酸甲基转移酶1 （PRMT1）蛋白水平显著升高，其产物单甲基精氨酸（MMA）和不对称二甲基精氨酸（ADMA）显著降低。循环ADMA升高，接近显著性（p< 0.06）。蛋氨酸腺苷转移酶1A、半胱硫氨酸β-合成酶、γ-谷氨酰半胱氨酸合成酶、甜菜碱-同型半胱氨酸甲基转移酶和蛋氨酸合成酶的蛋白表达保持不变。虽然DNA甲基转移酶Dnmt3a的基因表达降低，但整体DNA甲基化没有改变。在单个基因中，只有HMG-CoA还原酶（Hmgcr）发生了高甲基化，b细胞1、c-Jun、b细胞淋巴瘤2 （Bcl-2）和Caspase 3中脂肪酸合成酶（Fasn）、kappa轻多肽基因增强子核因子（Nfκb1）、Caspase 3未发生甲基化变化。NAFLD与肝蛋氨酸缺乏和同型半胱氨酸升高有关，主要由同型半胱氨酸再甲基化受损和甲基转移酶反应异常引起。尽管PRMT1表达增加，但肝脏ADMA减少，而循环ADMA增加，表明向循环输出增加。
Methionine metabolism plays a central role in methylation reactions, production of glutathione and methylarginines, and modulating homocysteine levels. The mechanisms by which these are affected in NAFLD are not fully understood. The aim is to perform a metabolomic, molecular and epigenetic analyses of hepatic methionine metabolism in diet-induced NAFLD. Female 129S1/SvlmJ;C57Bl/6J mice were fed a chow (n = 6) or high-fat high-cholesterol (HFHC) diet (n = 8) for 52 weeks. Metabolomic study, enzymatic expression and DNA methylation analyses were performed. HFHC diet led to weight gain, marked steatosis and extensive fibrosis. In the methionine cycle, hepatic methionine was depleted (30%, p< 0.01) while s-adenosylmethionine (SAM)/methionine ratio (p< 0.05), s-adenosylhomocysteine (SAH) (35%, p< 0.01) and homocysteine (25%, p< 0.01) were increased significantly. SAH hydrolase protein levels decreased significantly (p <0.01). Serine, a substrate for both homocysteine remethylation and transsulfuration, was depleted (45%, p< 0.01). In the transsulfuration pathway, cystathionine and cysteine trended upward while glutathione decreased significantly (p< 0.05). In the transmethylation pathway, levels of glycine N-methyltransferase (GNMT), the most abundant methyltransferase in the liver, decreased. The phosphatidylcholine (PC)/ phosphatidylethanolamine (PE) ratio increased significantly (p< 0.01), indicative of increased phosphatidylethanolamine methyltransferase (PEMT) activity. The protein levels of protein arginine methytransferase 1 (PRMT1) increased significantly, but its products, monomethylarginine (MMA) and asymmetric dimethylarginine (ADMA), decreased significantly. Circulating ADMA increased and approached significance (p< 0.06). Protein expression of methionine adenosyltransferase 1A, cystathionine β-synthase, γ-glutamylcysteine synthetase, betaine-homocysteine methyltransferase, and methionine synthase remained unchanged. Although gene expression of the DNA methyltransferase Dnmt3a decreased, the global DNA methylation was unaltered. Among individual genes, only HMG-CoA reductase (Hmgcr) was hypermethylated, and no methylation changes were observed in fatty acid synthase (Fasn), nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (Nfκb1), c-Jun, B-cell lymphoma 2 (Bcl-2) and Caspase 3. NAFLD was associated with hepatic methionine deficiency and homocysteine elevation, resulting mainly from impaired homocysteine remethylation, and aberrancy in methyltransferase reactions. Despite increased PRMT1 expression, hepatic ADMA was depleted while circulating ADMA was increased, suggesting increased export to circulation.