Homeostatic Regulation of Folate Metabolism

描述(由申请人提供)：我们建议阐明在DNA合成位置调节从头合成胸腺酸(DTMP)的生化、遗传和营养因素，并建立这一途径中潜在的损伤机制。叶酸和维生素B12依赖的一碳(1C)代谢受损与许多常见的病理有关，但机制尚未建立。最近，我们报道了Shmt-/+小鼠模型在DNA中积累尿嘧啶，并对肠道肿瘤和神经管缺陷敏感。SHMT1是唯一报道的叶酸依赖酶，其破坏会导致叶酸反应神经管缺陷。我们的发现表明，细胞核和线粒体DTMP的生物合成是叶酸和维生素B12相关疾病的基础。作为这些研究的结果，我们将建立对细胞核和线粒体中1C通路的基本理解，阐明它们由特定的维生素和代谢物调节，并确定它们在维持基因组完整性中的作用。这些研究还将确定核从头合成DTMP生物合成和对DNA的表观遗传修饰之间是否存在代谢相互作用。这一结果将为未来的人类研究提供信息，这些研究将转化为预防和治疗叶酸和维生素B12相关疾病的医疗实践和公共卫生政策。有待研究的三个相关和重叠的领域是：目的I.确定MTHFD1和KDM1酶对维生素B12和叶酸介导的细胞核1C代谢的贡献。这些研究将确定和表征两种叶酸利用酶MTHFD1和KDM1作为合成DTMP并与DNA复制机制相关的核多酶复合体的组成部分的作用。这些研究还将确定核DTMP生物合成和表观遗传染色质修饰是否通过使用叶酸辅助因子而相互依赖。目的II.阐明核内DTMP合成调控的决定因素和机制。这些研究将确定核叶酸依赖酶在DTMP合成中的作用、调节和贡献。研究包括对控制核DTMP生物合成和基因组稳定性的营养、代谢和遗传因素的调查。目的III.阐明线粒体DTMP合成调控的决定因素和机制。这些研究将确定线粒体叶酸依赖酶在DTMP合成中的作用、调节和贡献，包括控制线粒体DTMP生物合成和线粒体基因组稳定性的营养、代谢和遗传因素。 公共卫生相关性：与叶酸和维生素B12相关的病理很常见，但其潜在机制和途径尚不清楚，仅补充叶酸不足以降低或消除这些疾病的风险，而且可能会造成伤害。本申请中提出的实验建立在我们实验室最近的发现基础上，即几种与叶酸和维生素B12相关的病理是胸腺嘧啶酸生物合成受损的结果。这些实验的结果将为未来的人体研究提供信息，并最终转化为预防和治疗叶酸和维生素B12相关疾病的医疗实践和公共卫生政策。

DESCRIPTION (provided by applicant): We propose to elucidate the biochemical, genetic and nutritional factors that regulate de novo thymidylate (dTMP) synthesis at the sites of DNA synthesis, and establish the mechanisms underlying impairments in this pathway. Impaired folate- and vitamin B12-dependent one-carbon (1C) metabolism is associated with numerous common pathologies, but mechanisms have yet to be established. Recently, we reported that the Shmt-/+ mouse model accumulates uracil in DNA and is sensitized to intestinal tumors and neural tube defects. SHMT1 is the only reported folate-dependent enzyme whose disruption results in folate-responsive neural tube defects. Our findings indicate that nuclear and mitochondrial dTMP biosynthesis underlies folate- and vitamin B12-related disease. As a result of these studies, our fundamental understanding of 1C pathways in the nucleus and mitochondria will be established, their regulation by specific vitamins and metabolites elucidated, and their role in maintaining genome integrity characterized. These studies will also determine if there are metabolic interactions between nuclear de novo dTMP biosynthesis and epigenetic modifications to DNA. The results will inform future human studies that translate into medical practice and public health policy for the prevention and treatment of folate- and vitamin B12-associated pathologies. The three related and overlapping areas to be investigated are: Aim I. Determine the contributions of the enzymes MTHFD1 and KDM1 to vitamin B12- and folate-mediated 1C metabolism in the nucleus. These studies will identify and characterize the role of two folate-utilizing enzymes, MTHFD1 and KDM1, as components of a nuclear multienzyme complex that synthesizes dTMP and associates with the DNA replication machinery. These studies will also determine if nuclear dTMP biosynthesis and epigenetic chromatin modifications are interdependent through their use of folate cofactors. Aim II. Elucidate the determinants and mechanisms of nuclear dTMP synthesis regulation. These studies will determine the role, regulation and contribution of nuclear folate-dependent enzymes in dTMP synthesis. Studies include investigations into the nutritional, metabolic and genetic factors that govern nuclear dTMP biosynthesis and genome stability. AIM III. Elucidate the determinants and mechanisms of mitochondrial dTMP synthesis regulation. These studies will determine the role, regulation and contribution of mitochondrial folate-dependent enzymes in dTMP synthesis, including the nutritional, metabolic and genetic factors that govern mitochondrial dTMP biosynthesis and mitochondrial genome stability. PUBLIC HEALTH RELEVANCE: Folate- and vitamin B12-associated pathologies are common but their underlying mechanisms and pathways are not understood, and folic acid supplementation alone is not sufficient to reduce or eliminate risk of these pathologies and may do harm. The experiments proposed in this application build on recent findings from our laboratory that several folate- and vitamin B12- related pathologies result from impaired thymidylate biosynthesis. The results from these experiments will inform future human studies and ultimately translate into medical practice and public health policy for the prevention and treatment of folate- and vitamin B12-associated pathologies.