Romanowicz Jennifer, Leonetti Camille, Dhari Zaenab, Korotcova Ludmila, Ramachandra Shruti D, Saric Nemanja, Morton Paul D, Bansal Shivani, Cheema Amrita, Gallo Vittorio, Jonas Richard A, Ishibashi Nobuyuki
Children's National Heart Institute Children's National Health System Washington DC.
Center for Neuroscience Research Children's National Health System Washington DC.
J Am Heart Assoc. 2019 Aug 6;8(15):e012711. doi: 10.1161/JAHA.119.012711. Epub 2019 Jul 23.
Background Reduced oxygen delivery in congenital heart disease causes delayed brain maturation and white matter abnormalities in utero. No treatment currently exists. Tetrahydrobiopterin (BH4) is a cofactor for neuronal nitric oxide synthase. BH4 availability is reduced upon NOS activation, such as during hypoxic conditions, and leads to toxin production. We hypothesize that BH4 levels are depleted in the hypoxic brain and that BH4 replacement therapy mitigates the toxic effects of hypoxia on white matter. Methods and Results Transgenic mice were used to visualize oligodendrocytes. Hypoxia was introduced during a period of white matter development equivalent to the human third trimester. BH4 was administered during hypoxia. BH4 levels were depleted in the hypoxic brain by direct quantification (n=7-12). The proliferation (n=3-6), apoptosis (n=3-6), and developmental stage (n=5-8) of oligodendrocytes were determined immunohistologically. Total oligodendrocytes increased after hypoxia, consistent with hypoxia-induced proliferation seen previously; however, mature oligodendrocytes were less prevalent in hypoxia, and there was accumulation of immature oligodendrocytes. BH4 treatment improved the mature oligodendrocyte number such that it did not differ from normoxia, and accumulation of immature oligodendrocytes was not observed. These results persisted beyond the initial period of hypoxia (n=3-4). Apoptosis increased with hypoxia but decreased with BH4 treatment to normoxic levels. White matter myelin levels decreased following hypoxia by western blot. BH4 treatment normalized myelination (n=6-10). Hypoxia worsened sensory-motor coordination on balance beam tasks, and BH4 therapy normalized performance (n=5-9). Conclusions Suboptimal BH4 levels influence hypoxic white matter abnormalities. Repurposing BH4 for use during fetal brain development may limit white matter dysmaturation in congenital heart disease.
先天性心脏病中氧输送减少会导致子宫内脑成熟延迟和白质异常。目前尚无治疗方法。四氢生物蝶呤（BH4）是神经元型一氧化氮合酶的辅因子。在一氧化氮合酶激活时，如在缺氧条件下，BH4的可用性会降低，并导致毒素产生。我们假设缺氧脑内BH4水平会降低，且BH4替代疗法可减轻缺氧对白质的毒性作用。
使用转基因小鼠可视化少突胶质细胞。在相当于人类妊娠晚期的白质发育阶段引入缺氧。在缺氧期间给予BH4。通过直接定量法测定缺氧脑内的BH4水平（n = 7 - 12）。通过免疫组织化学法确定少突胶质细胞的增殖（n = 3 - 6）、凋亡（n = 3 - 6）和发育阶段（n = 5 - 8）。缺氧后少突胶质细胞总数增加，与之前观察到的缺氧诱导增殖一致；然而，成熟少突胶质细胞在缺氧时较少见，且存在未成熟少突胶质细胞的积累。BH4治疗可改善成熟少突胶质细胞数量，使其与常氧状态无差异，且未观察到未成熟少突胶质细胞的积累。这些结果在缺氧初始阶段之后仍然存在（n = 3 - 4）。凋亡随缺氧增加，但经BH4治疗后降至常氧水平。通过蛋白质印迹法检测，缺氧后白质髓鞘水平降低。BH4治疗可使髓鞘形成恢复正常（n = 6 - 10）。缺氧会使平衡木任务中的感觉运动协调性变差，而BH4治疗可使表现恢复正常（n = 5 - 9）。
BH4水平欠佳会影响缺氧性白质异常。在胎儿脑发育期间重新利用BH4可能会限制先天性心脏病中的白质发育异常。
