Gene-Nutrient Interactions in Neural Tube Defects

性状（由申请方提供）：核苷酸（嘌呤和dTMP）和S-腺苷甲硫氨酸（蛋氨酸）的合成需要叶酸代谢。叶酸代谢的破坏影响了DDMet和dTMP的合成，从而影响了DDMet依赖的甲基化反应和DNA中的尿嘧啶含量。DNA尿嘧啶和甲基化都影响DNA的稳定性，而染色质甲基化调节许多基因的表达。目前尚不清楚叶酸代谢中断与病理（包括某些癌症，心血管疾病）和发育异常（包括神经管缺陷（NTD））之间的关联是否是由改变的Met合成和/或dTMP合成引起的。最近，我们证明了酶细胞质丝氨酸羟甲基转移酶（cSHMT）是一种代谢开关，调节叶酸激活的一碳单位之间的dTMP和cSHMet生物合成途径的流量。在cSHMT和cSHMT-/-小鼠中观察到的cSHMT表达减少诱导胚胎NTD，使动物对结肠癌敏感，影响DNA中的尿嘧啶含量并增加cSHMT/cSHMT-/-比值。这是唯一的小鼠模型，表现出NTD的结果，叶酸依赖性酶的破坏，从而能够阐明叶酸响应性NTD的机制。CSHMT在已知与叶酸相关的病理/发育异常（包括NTD）相关的组织中表达。cSHMT的表达和活性受几种营养素的动态调节，因此cSHMT有可能导致叶酸相关疾病的病因学，并可能成为通过饮食预防的靶点。将确定饮食、胚胎和母体cSHMT基因型对NTD发生的贡献，并阐明cSHMT在NTD病因学中的代谢作用。具体目的是：1）确定基因-营养相互作用增加cSHMT缺陷小鼠NTD的风险。2)以确定与神经管闭合缺陷相关的代谢缺陷。3)以阐明cSHMT SUMO化对NTD频率的贡献。4)以确定cSHMT和MTHFR是否相互作用增加叶酸反应性NTD的风险。待检验的主要假设是：1）cSHMT表达通过改变叶酸代谢而导致叶酸反应性NTD风险。2)cSHMT SUMO化损伤影响dTMP和cSHMT合成以及NTD的风险。3)cSHMT和MTHFR基因相互作用，增加叶酸反应性NTD的风险。公共卫生相关性：该项目的长期目标是确定神经管闭合缺陷的潜在机制以及cSHMT在NTD预防中的作用。叶酸相关的病理，包括某些癌症，和发育缺陷，包括神经管缺陷，是常见的和复杂的疾病，涉及基因营养相互作用，但潜在的机制尚未建立。美国食品供应中的叶酸强化是为了降低出生缺陷的发生率，但人们仍然担心叶酸强化对癌症发病率的影响。本提案中概述的研究将调查叶酸相关出生缺陷的机制以及叶酸和其他饮食成分在第一个叶酸代谢紊乱导致的叶酸相关出生缺陷小鼠模型中预防这些缺陷的作用。

DESCRIPTION (provided by applicant): Folate metabolism is required for the synthesis of nucleotides (purines and dTMP) and S- adenosylmethionine (AdoMet). Disruption of folate metabolism affects AdoMet and dTMP syntheses and thereby influences AdoMet-dependent methylation reactions and uracil content in DNA. Both DNA uracil and methylation affect DNA stability, and chromatin methylation regulates the expression of many genes. It is not known if the associations between disruptions in folate metabolism and pathologies (including certain cancers, cardiovascular disease) and developmental anomalies (including neural tube defects (NTDs)) result from altered AdoMet synthesis and/or dTMP synthesis. Recently, we demonstrated that the enzyme cytoplasmic serine hydroxymethyltransferase (cSHMT) is a metabolic switch that regulates the flux of folate-activated one-carbon units between the dTMP and AdoMet biosynthetic pathways. Reduced expression of cSHMT, as observed in both cSHMT and cSHMT-/- mice, induces embryonic NTDs, sensitizes the animals to colon cancer, affects uracil content in DNA and increases the AdoMet/AdoHcy ratio. This is the only mouse model to exhibit NTDs as a result of the disruption of a folate-dependent enzyme, and thereby enables elucidation of the mechanisms underlying folate-responsive NTDs. CSHMT is expressed in tissues known to be associated with folate-related pathologies/developmental anomalies including NTDs. The expression and activity of cSHMT is dynamically regulated by several nutrients and therefore the cSHMT has the potential to contribute to the etiology of folate-related pathologies and may be a target for prevention through diet. The contributions of diet, embryonic and maternal cSHMT genotype to NTD occurrence will be determined, and the metabolic role of cSHMT in NTD etiology will be elucidated. The specific aims are: 1) to determine the gene-nutrient interactions that increase risk for NTDs in mice deficient in cSHMT. 2) to determine the metabolic defect associated with neural tube closure defects. 3) to elucidate the contribution of cSHMT SUMOylation to NTD frequency. 4) to determine if cSHMT and MTHFR interact to increase risk for folate-responsive NTDs. The principle hypotheses to be tested are that: 1) cSHMT expression contributes to folate-responsive NTD risk by altering folate metabolism. 2) impairments in cSHMT SUMOylation affect dTMP and AdoMet synthesis and risk for NTDs. 3) the cSHMT and MTHFR genes interact to increase risk for folate-responsive NTDs. PUBLIC HEALTH RELEVANCE: The long-term goals of this project is to determine the mechanisms underlying neural tube closure defects and the role of cSHMT in NTD prevention. Folate-related pathologies, including certain cancers, and developmental defects, including neural tube defects, are common and complex disorders involving gene nutrient interactions but the underlying mechanisms are not established. Folate-fortification of the US food supply was implemented to reduce incidence of birth defects, yet concerns remain regarding the effects of folate fortification on cancer incidence. The studies outlined in this proposal will investigate the mechanisms of folate-related birth defects and role of folate and other dietary components in preventing these defects in the first mouse model of folate-related birth defects resulting from disrupted folate metabolism.