Regulation of genes encoding enzymes involved in carnitine biosynthesis by peroxisome proliferator-activated receptor of alpha (PPARalpha)

最近的研究强烈支持这一假设，即编码参与胭脂碱合成的酶的基因直接受过氧化物酶体增殖物激活受体α（PPARα）的调节。过氧化物酶体增殖物激活受体α（PPARα）是一种配体激活的转录因子，在哺乳动物体内起着调节脂质代谢和能量平衡的重要作用。PPARα通过激活的PPAR/维甲酸X受体异二聚体与靶基因启动子周围的特异性DNA序列（称为过氧化物酶体增殖反应元件（PPRE））结合来介导基因的转录调节。启动子区域内是否存在功能性PPRE已被公认为是将基因分类为PPARα靶基因的最佳标准。到目前为止，还没有关于编码与肉毒碱生物合成有关的酶如三甲基赖氨酸双加氧酶（TMLD）、三甲基氨基醛脱氢酶（TMABA-DH）和γ-丁酰甜菜碱双加氧酶（γ-BBD）的基因的启动子的功能性PPRE的描述。因此，本研究的目的是探讨PPARα对TMLD、TMABA-DH和BBD的转录调控。为此，将进行野生型和突变型TMLD、TMABA-DH和BBD启动子报告基因截短构建体的报告基因测定、电泳迁移率变动测定和染色质免疫沉淀测定。本课题的研究具有独创性，将直接证明编码肉毒碱合成相关酶的基因是否是具有PPRE功能的PPARα靶基因。由于PPARα被认为是脂肪酸代谢和葡萄糖稳态的关键调节因子，本项目的结果将显示PPARα是否也直接作为肉毒碱合成的重要调节因子。

Recent studies strongly support the hypothesis that genes encoding enzymes involved incarnitine synthesis are directly regulated by peroxisome proliferator-activated receptor α(PPARα). PPARα is a ligand-activated transcription factor that acts as an important regulatorof lipid metabolism and energy homeostasis in mammals. Transcriptional regulation of genesby PPARα is mediated by binding of activated PPAR/retinoid X receptor heterodimers tospecific DNA sequences, called peroxisome proliferator response elements (PPRE) presentin and around the promoter of target genes. The presence of a functional PPRE within apromoter region has been accepted as the best criterion to classify a gene as a PPARαtarget gene. So far, functional PPRE have not yet been described for the promoters of genesencoding enzymes involved in carnitine biosynthesis such as trimethyllysine dioxygenase(TMLD), trimethylaminoaldehyde dehydrogenase (TMABA-DH) and γ-butyrobetainedioxygenase (γ-BBD). Therefore, the aim of this project is to explore the transcriptionalregulation of TMLD, TMABA-DH and BBD by PPARα. For this purpose, reporter gene assayswith wild-type and mutant TMLD, TMABA-DH and BBD promoter reporter truncationconstructs, electrophoretic mobility shift assays, and chromatin immuno-precipitation assayswill be performed. The investigations of the present project are original and will provide directproof whether genes encoding enzymes involved in carnitine synthesis are PPARα targetgenes with functional PPRE or not. Because PPARα has been mostly considered as a keyregulator of fatty acid catabolism and glucose homeostasis, the results of this project willshow whether PPARα also functions directly as an essential regulator of carnitine synthesis.