Division of Intramural Research, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD, USA.
Transgenic Mouse Core, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD, USA.
Hum Mol Genet. 2018 Oct 15;27(20):3627-3640. doi: 10.1093/hmg/ddy267.
In humans, poor nutrition, malabsorption and variation in cobalamin (vitamin B12) metabolic genes are associated with hematological, neurological and developmental pathologies. Cobalamin is transported from blood into tissues via the transcobalamin (TC) receptor encoded by the CD320 gene. We created mice carrying a targeted deletion of the mouse ortholog, Cd320. Knockout (KO) mice lacking this TC receptor have elevated levels of plasma methylmalonic acid and homocysteine but are otherwise healthy, viable, fertile and not anemic. To challenge the Cd320 KO mice we maintained them on a vitamin B12-deficient diet. After 5 weeks on this diet, reproductive failure develops in Cd320 KO females but not males. In vitro, homozygous Cd320 KO embryos from cobalamin-deficient Cd320 KO dams develop normally to embryonic day (E) 3.5, while in vivo, few uterine decidual implantation sites are observed at E7.5, suggesting that embryos perish around the time of implantation. Dietary restriction of vitamin B12 induces a severe macrocytic anemia in Cd320 KO mice after 10-12 months while control mice on this diet are anemia-free up to 2 years. Despite the severe anemia, cobalamin-deficient KO mice do not exhibit obvious neurological symptoms. Our results with Cd320 KO mice suggest that an alternative mechanism exists for mice to transport cobalamin independent of the Cd320 encoded receptor. Our findings with deficient diet are consistent with historical and epidemiological data suggesting that low vitamin B12 levels in humans are associated with infertility and developmental abnormalities. Our Cd320 KO mouse model is an ideal model system for studying vitamin B12 deficiency.
在人类中，营养不良、吸收不良和钴胺素（维生素 B12）代谢基因的变异与血液、神经和发育病理学有关。钴胺素通过 CD320 基因编码的转钴胺素（TC）受体从血液转运到组织中。我们创建了携带靶向小鼠同源物 Cd320 缺失的小鼠。缺乏这种 TC 受体的敲除（KO）小鼠血浆甲基丙二酸和同型半胱氨酸水平升高，但其他方面健康、有活力、可育且不贫血。为了挑战 Cd320 KO 小鼠，我们让它们维持在维生素 B12 缺乏饮食中。在用这种饮食喂养 5 周后，Cd320 KO 雌性小鼠出现生殖失败，但雄性小鼠没有。在体外，来自钴胺素缺乏的 Cd320 KO 母鼠的纯合子 Cd320 KO 胚胎在 E3.5 时正常发育，而在体内，在 E7.5 时很少观察到子宫蜕膜着床部位，表明胚胎在着床时死亡。维生素 B12 的饮食限制在 10-12 个月后会在 Cd320 KO 小鼠中引起严重的巨幼细胞性贫血，而在用这种饮食喂养的对照小鼠中，这种贫血在 2 年内不会发生。尽管贫血严重，但缺乏钴胺素的 KO 小鼠没有表现出明显的神经症状。我们对 Cd320 KO 小鼠的研究结果表明，小鼠存在一种替代机制来运输钴胺素，而不需要 Cd320 编码的受体。我们用缺乏饮食的研究结果与历史和流行病学数据一致，这些数据表明人类维生素 B12 水平低与不孕和发育异常有关。我们的 Cd320 KO 小鼠模型是研究维生素 B12 缺乏的理想模型系统。
