Singhal Naveen Kumar, Li Shuo, Arning Erland, Alkhayer Kholoud, Clements Robert, Sarcyk Zachary, Dassanayake Rohan S, Brasch Nicola E, Freeman Ernest J, Bottiglieri Teodoro, McDonough Jennifer
Departments of Biological Sciences and.
Departments of Biological Sciences and Chemistry and Biochemistry, Kent State University, Kent, Ohio 44242.
J Neurosci. 2015 Nov 11;35(45):15170-86. doi: 10.1523/JNEUROSCI.4349-14.2015.
Mitochondrial changes, including decreased expression of electron transport chain subunit genes and impaired energetic, have been reported in multiple sclerosis (MS), but the mechanisms involved in these changes are not clear. To determine whether epigenetic mechanisms are involved, we measured the concentrations of methionine metabolites by liquid chromatography tandem mass spectrometry, histone H3 methylation patterns, and markers of mitochondrial respiration in gray matter from postmortem MS and control cortical samples. We found decreases in respiratory markers as well as decreased concentrations of the methionine metabolites S-adenosylmethionine, betaine, and cystathionine in MS gray matter. We also found expression of the enzyme betaine homocysteine methyltransferase in cortical neurons. This enzyme catalyzes the remethylation of homocysteine to methionine, with betaine as the methyl donor, and has previously been thought to be restricted to liver and kidney in the adult human. Decreases in the concentration of the methyl donor betaine were correlated with decreases in histone H3 trimethylation (H3K4me3) in NeuN+ neuronal nuclei in MS cortex compared with controls. Mechanistic studies demonstrated that H3K4me3 levels and mitochondrial respiration were reduced in SH-SY5Y cells after exposure to the nitric oxide donor sodium nitroprusside, and betaine was able to rescue H3K4me3 levels and respiratory capacity in these cells. Chromatin immunoprecipitation experiments showed that betaine regulates metabolic genes in human SH-SY5Y neuroblastoma cells. These data suggest that changes to methionine metabolism may be mechanistically linked to changes in neuronal energetics in MS cortex.
For decades, it has been observed that vitamin B12 deficiency and multiple sclerosis (MS) share certain pathological changes, including conduction disturbances. In the present study, we have found that vitamin B12-dependent methionine metabolism is dysregulated in the MS brain. We found that concentrations of the methyl donor betaine are decreased in MS cortex and are correlated with reduced levels of the histone H3 methyl mark H3K4me3 in neurons. Cell culture and chromatin immunoprecipitation-seq data suggest that these changes may lead to defects in mitochondria and impact neuronal energetics. These data have uncovered a novel pathway linking methionine metabolism with mitochondrial respiration and have important implications for understanding mechanisms involved in neurodegeneration in MS.
线粒体变化，包括电子传递链亚基基因表达降低和能量代谢受损，已在多发性硬化症（MS）中被报道，但这些变化所涉及的机制尚不清楚。为了确定表观遗传机制是否参与其中，我们通过液相色谱串联质谱法测量了蛋氨酸代谢物的浓度、组蛋白H3甲基化模式以及来自死后MS和对照皮质样本的灰质中线粒体呼吸的标志物。我们发现MS灰质中的呼吸标志物降低，以及蛋氨酸代谢物S-腺苷甲硫氨酸、甜菜碱和胱硫醚的浓度降低。我们还发现皮质神经元中存在甜菜碱同型半胱氨酸甲基转移酶的表达。这种酶催化同型半胱氨酸以甜菜碱作为甲基供体重新甲基化为蛋氨酸，并且此前一直被认为在成年人体内仅限于肝脏和肾脏。与对照组相比，MS皮质中甲基供体甜菜碱浓度的降低与NeuN +神经元细胞核中组蛋白H3三甲基化（H3K4me3）的降低相关。机制研究表明，在暴露于一氧化氮供体硝普钠后，SH-SY5Y细胞中的H3K4me3水平和线粒体呼吸降低，并且甜菜碱能够挽救这些细胞中的H3K4me3水平和呼吸能力。染色质免疫沉淀实验表明，甜菜碱调节人SH-SY5Y神经母细胞瘤细胞中的代谢基因。这些数据表明，蛋氨酸代谢的变化可能在机制上与MS皮质中神经元能量代谢的变化相关。
几十年来，人们观察到维生素B12缺乏症和多发性硬化症（MS）有某些共同的病理变化，包括传导障碍。在本研究中，我们发现维生素B12依赖的蛋氨酸代谢在MS大脑中失调。我们发现MS皮质中甲基供体甜菜碱的浓度降低，并且与神经元中组蛋白H3甲基标记H3K4me3的水平降低相关。细胞培养和染色质免疫沉淀测序数据表明，这些变化可能导致线粒体缺陷并影响神经元能量代谢。这些数据揭示了一条将蛋氨酸代谢与线粒体呼吸联系起来的新途径，并且对于理解MS神经退行性变所涉及的机制具有重要意义。
