Study on the molecular basis of the response of the digestive tract evoked by nutrients/functional food factors

1.转录因子参与发育过程中消化吸收相关基因的表达：在围产期，大鼠小肠组织中细胞视黄醇结合蛋白II(CRBPII)的表达急剧增加。伴随而来的是绒毛细胞核中RXR、α和hnf-4的协调和显著表达。RALDH1和RALDH2参与维甲酸生成的基因在出生前在肝脏和小肠中的表达增加。出生前获取的小肠器官培养结果显示，在RXRα配体存在的情况下，CRBPII基因被诱导。与小肠消化吸收相关的转录因子的表达及其磷酸化诱导的调控：饲喂高脂饲料的大鼠从绒毛底部到绒毛顶端CRBPII的表达水平较高。在这些动物中，PPARα和hnf-4的基因表达协同上调，而PPARδ的基因表达降低。用C2BBe1对PPARδ靶基因的蛋白质组学分析表明，δ配体诱导了HMG-CoA合成酶和谷胱甘肽S转移酶的表达。Forsklin诱导的HNF-4的磷酸化导致HNF-4与CRBPII基因启动子上的DR-1元件结合活性降低。这些结果表明，CRBPII的基本表达是由hnf-4维持的，其水平受RXRα配体的调节。消化吸收相关基因表达日变化的机制：CRBPII在大鼠空肠中的表达表现为转录水平的日变化，这种变化依赖于饲料中的脂肪含量，而在饲喂脱脂饲料的大鼠中表达缺失。这些结果表明，饮食中的脂肪酸可能在饮食诱导的CRBPII基因表达的日变化中起作用。

1. Transcription factors involved in the expression of digestion/absorption-related genes during development: In the perinatal period, the expression of cellular retinol-binding protein, type II (CRBPII) was abruptly elevated in rat small intestine. This was accompanied by a coordinated and marked expression of RXR α and HNF-4 in the nuclei of villus cells. The gene expression of RALDH1 and RALDH2 involved in the generation of retinoic acid was elevated in the liver and small intestine just before birth. The organ culture of the small intestine obtained just before birth showed an induction of CRBPII gene in the presence of RXR α ligand.2. The expression of transcription factors related to digestion and absorption in the small intestine and the modulation induced by phosphorylation.: Rats fed a high-fat diet showed a greater expression of CRBPII from the base to the tip of the villi. In these animals, the gene expression of PPAR α and HNF-4 were coordinately elevated, while that of PPAR δ was reduced. The proteomics analysis of PPAR δ target genes using C2BBe1 revealed that HMG-CoA synthase and glutathione S transferase were induced by PPAR δ ligand. The forskolin-induced phosphorylation of HNF-4 caused the reduction of the binding activity of HNF-4 to the DR-1 element on the CRBPII gene promoter. These results suggest that the basic expression of CRBPII is maintained by HNF-4, and its level is modulated by RXR α ligand.3. Mechanism involved in the diurnal variation of the expression of digestion/absorption-related genes: The expression of CRBPII in rat jejunum showed a diurnal variation at a transcriptional level, which depended on the dietary fat content, and lost in rats fed a fat-free diet. These results suggest that dietary fatty acids may play a role in the diet-induced diurnal variation of CRBPII gene expression.