Abstract：
Cystathionine beta-synthase-deficient homocystinuria (HCU) is a life-threatening disorder of sulfur metabolism. HCU can be treated by using betaine to lower tissue and plasma levels of homocysteine (Hcy). Here, we show that mice with severely elevated Hcy and potentially deficient in the folate species tetrahydrofolate (THF) exhibit a very limited response to betaine indicating that THF plays a critical role in treatment efficacy. Analysis of a mouse model of HCU revealed a 10-fold increase in hepatic levels of 5-methyl -THF and a 30-fold accumulation of formiminoglutamic acid, consistent with a paucity of THF. Neither of these metabolite accumulations were reversed or ameliorated by betaine treatment. Hepatic expression of the THF-generating enzyme dihydrofolate reductase (DHFR) was significantly repressed in HCU mice and expression was not increased by betaine treatment but appears to be sensitive to cellular redox status. Expression of the DHFR reaction partner thymidylate synthase was also repressed and metabolomic analysis detected widespread alteration of hepatic histidine and glutamine metabolism. Many individuals with HCU exhibit endothelial dysfunction. DHFR plays a key role in nitric oxide (NO) generation due to its role in regenerating oxidized tetrahydrobiopterin, and we observed a significant decrease in plasma NOx (NO2 + NO3) levels in HCU mice. Additional impairment of NO generation may also come from the HCU-mediated induction of the 20-hydroxyeicosatetraenoic acid generating cytochrome CYP4A. Collectively, our data shows that HCU induces dysfunctional one-carbon metabolism with the potential to both impair betaine treatment and contribute to multiple aspects of pathogenesis in this disease.
摘要：
蛋氨酸β-合酶缺陷型高半胱氨酸尿症（HCU）是一种威胁生命的硫代谢疾病。HCU可通过使用甜菜碱降低组织和血浆同型半胱氨酸(Hcy)水平来治疗。这里,我们显示Hcy严重升高且可能缺乏叶酸类四氢叶酸（THF）的小鼠对甜菜碱的反应非常有限，表明THF在治疗功效中起关键作用。对HCU小鼠模型的分析显示，5-甲基-THF的肝脏水平增加了10倍，甲氨基谷氨酸的积累增加了30倍，与THF的缺乏一致。甜菜碱治疗均未逆转或改善这些代谢物的积累。在HCU小鼠中，THF生成酶二氢叶酸还原酶（DHFR）的肝表达受到显着抑制，甜菜碱治疗并未增加表达，但似乎对细胞氧化还原状态敏感。DHFR反应伴侣胸苷酸合酶的表达也被抑制，代谢组学分析检测到肝组氨酸和谷氨酰胺代谢的广泛改变。许多患有HCU的个体表现出内皮功能障碍。DHFR在一氧化氮（NO）产生中起关键作用，因为它在氧化四氢生物蝶呤再生中的作用，我们观察到HCU小鼠血浆NOx（NO2NO3）水平显着降低。NO产生的其他损害也可能来自HCU介导的产生20-羟基二十碳四烯酸的细胞色素CYP4A的诱导。总的来说，我们的数据显示,HCU诱导功能失调的一碳代谢,有可能损害甜菜碱治疗,并导致本病发病机制的多个方面.
