Ammonia inhibits energy metabolism in astrocytes in a rapid and glutamate dehydrogenase 2-dependent manner.
Ammonia inhibits energy metabolism in astrocytes in a rapid and glutamate dehydrogenase 2-dependent manner.
复制标题
氨以快速和谷氨酸脱氢酶2依赖的方式抑制星形胶质细胞的能量代谢。
DOI：
10.1242/dmm.047134
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发表时间：
2020-11-04
影响因子：
4.3
通讯作者：
Reichert AS
中科院分区：
文献类型：
--
作者：
Drews L;Zimmermann M;Westhoff P;Brilhaus D;Poss RE;Bergmann L;Wiek C;Brenneisen P;Piekorz RP;Mettler-Altmann T;Weber APM;Reichert AS
星形胶质细胞功能障碍是肝性脑病（HE）的主要因素，在高氨血症下损害神经元活动。特别是，引起氨诱导的星形胶质细胞毒性的早期事件还没有得到很好的理解。使用已建立的细胞HE模型，我们表明，线粒体迅速经历碎片在高氨血症后，以可逆的方式。此外，在我们的分析中，在几分钟的时间尺度内，线粒体呼吸和糖酵解受到阻碍，这是以不依赖于pH的方式发生的。使用代谢组学，观察到葡萄糖和许多氨基酸（包括支链氨基酸）的积累。15 N标记的氨的代谢组学跟踪显示15 N快速掺入谷氨酸和谷氨酸衍生的氨基酸。下调人GLUD 2 [编码线粒体谷氨酸脱氢酶2（GDH 2）]，通过SIRT 4过表达抑制GDH 2活性，以及向细胞补充谷氨酸或谷氨酰胺减轻了氨诱导的线粒体呼吸抑制。13 C-谷氨酰胺的代谢组学追踪表明，高氨血症可以抑制三羧酸（TCA）循环中间产物的贫血。与其经典的贫血作用相反，我们发现，在高氨血症下，GDH 2通过α-酮戊二酸的还原胺化催化氨的去除，这有效且快速地抑制TCA循环。总的来说，我们提出了一个关键的GDH 2依赖性机制，在HE模型，有助于消除氨，但也损害线粒体的能量代谢迅速。总结：在这里，我们确定了肝性脑病的相关机制，谷氨酸脱氢酶2通过抑制星形胶质细胞中的TCA循环非常迅速地损害线粒体中的能量代谢。
Astrocyte dysfunction is a primary factor in hepatic encephalopathy (HE) impairing neuronal activity under hyperammonemia. In particular, the early events causing ammonia-induced toxicity to astrocytes are not well understood. Using established cellular HE models, we show that mitochondria rapidly undergo fragmentation in a reversible manner upon hyperammonemia. Further, in our analyses, within a timescale of minutes, mitochondrial respiration and glycolysis were hampered, which occurred in a pH-independent manner. Using metabolomics, an accumulation of glucose and numerous amino acids, including branched chain amino acids, was observed. Metabolomic tracking of 15N-labeled ammonia showed rapid incorporation of 15N into glutamate and glutamate-derived amino acids. Downregulating human GLUD2 [encoding mitochondrial glutamate dehydrogenase 2 (GDH2)], inhibiting GDH2 activity by SIRT4 overexpression, and supplementing cells with glutamate or glutamine alleviated ammonia-induced inhibition of mitochondrial respiration. Metabolomic tracking of 13C-glutamine showed that hyperammonemia can inhibit anaplerosis of tricarboxylic acid (TCA) cycle intermediates. Contrary to its classical anaplerotic role, we show that, under hyperammonemia, GDH2 catalyzes the removal of ammonia by reductive amination of α-ketoglutarate, which efficiently and rapidly inhibits the TCA cycle. Overall, we propose a critical GDH2-dependent mechanism in HE models that helps to remove ammonia, but also impairs energy metabolism in mitochondria rapidly. Summary: Here, we identified a mechanism relevant for hepatic encephalopathy by which glutamate dehydrogenase 2 impairs energy metabolism in mitochondria very rapidly via inhibiting the TCA cycle in astrocytes.