Contribution of microbially synthesized vitamers to folate status and impact on inflammatory bowel diseases

炎症性肠道疾病（IBD）的特征是活动过程呈波动性，病变自发缓解率低，并且不断存在复发的威胁。IBD的发病率随着社会的发展而显著增加，但其病因尚不清楚。虽然IBD患者的遗传易感性已经明确，但环境因素是IBD发病机制的必要因素。微生物生态失调是IBD受试者的标志。叶酸是参与正常细胞功能，生长和发育的关键维生素之一。亚临床但生化相关的叶酸缺乏症发生在40%的IBD患者。叶酸缺乏症可能与粘膜损伤的程度直接相关，或者是由于摄入不足、炎症引起的营养需求增加、药物摄入或遗传异常所致。参与叶酸代谢的FOLH 1基因的表达失调被认为是回肠克罗恩病（CD）表型的预测生物标志物。虽然越来越多的证据表明细菌来源的叶酸可能会影响宿主的叶酸状态，但它们在肠道中的生产在很大程度上被忽视了。在接种了叶酸生产菌的结肠炎小鼠模型中进行的初步研究表明，细菌合成的叶酸可能与减轻炎症有关，但其作用机制尚未阐明。我们的假设是，回肠CD受试者的血清叶酸缺乏反映了由于宿主和/或胃肠道微生物群成分导致的胃肠道叶酸代谢改变。此外，我们假设胃肠道中叶酸代谢的改变有助于回肠CD患者的微生物生态失调和炎症增加。在本项目中，我们将使用自上而下的方法，首先确定从具有不同血清叶酸状态的回肠CD患者获得的粪便叶酸维生素的数量以及不同形式，并使用下一代测序技术表征微生物群组成。在第二阶段，我们将通过发酵接种不同叶酸前体的粪便样品，研究具有高和低血清叶酸状态的回肠CD患者的粪便微生物群合成叶酸维生素的潜力，并通过焦磷酸测序表征微生物变化。本研究可能的后续研究包括使用接种了来自先前入组患者的粪便微生物群的回肠CD小鼠模型，以评价粪便微生物群对叶酸状态和炎症的影响。这些结果应该会导致对细菌合成叶酸的作用有更好的理解，并将促进改变肠道微生物群的策略的发展，以改善叶酸状态并预防或抑制宿主炎症。

Inflammatory bowel diseases (IBD) are characterized by an undulating course of activity, with a low rate of spontaneous remission of the lesions and a constant threat of relapsing attacks. Incidence rates of IBD increased dramatically in parallel with social development but etiology of the disease is unclear. Although genetic predisposition in IBD patients has been clearly established, environmental factors are necessary contributors to IBD pathogenesis. Microbial dysbiosis is a hallmark in IBD subjects. Folate is one of the key vitamins involved in normal cellular function, growth, and development. Subclinical but biochemically relevant folate deficiency occurs in 40% of IBD patients. Folate deficiency may be directly related to the extent of the mucosal damage or result from inadequate intake, increased nutritional requirements due to the inflammatory condition, intake of medication, or genetic abnormalities. Dysregulation of the expression of the FOLH1 gene involved in folate metabolism has been suggested to be a predictive biomarker for the ileal Crohn s disease (CD) phenotype. Although evidence is accumulating that bacterially derived folates could impact the folate status of the host, their production in the gut has been largely ignored. Preliminary study in a mouse model of colitis inoculated with a folate producer bacterial commensal indicated that bacterially synthesized folates could be linked to the reduction of inflammation, but mechanisms of action were not elucidated. Our hypothesis is that serum folate deficiency in ileal CD subjects reflects an altered folate metabolism in the gastrointestinal tract due to a host and/or a gastrointestinal microbiota component. Furthermore, we hypothesize that altered folate metabolism in the gastrointestinal tract contribute to microbial dysbiosis and increased inflammation in ileal CD patients.With the present project, we will use a top down-approach, to first define the quantity as well as the different forms of fecal folate vitamers obtained from ileal CD patients with different serum folate status, and to characterize microbiota composition using Next Generation sequencing technologies. In a second stage, we will investigate the potential of the fecal microbiota of ileal CD patients with high and low serum folate status to synthesize folate vitamers by performing fermentation of fecal samples inoculated with different folate precursors and characterize microbial changes by pyrosequencing. Possible follow up of this study include the use of a mouse model of ileal CD inoculated with fecal microbiota from previously enrolled patients, in order to evaluate the impact of the fecal microbiota on both folate status and inflammation. The results should lead to a greater understanding of the role of bacterially synthesized folates and will facilitate the development of strategies to alter the gut microbiota in an effort to improve folate status and to prevent or suppress host inflammation.