Circulation：复旦大学赵健元研究团队突破维生素代谢难题

2017年3月16日，国际心血管病顶级学术期刊《Circulation》发表复旦大学生命科学学院赵健元研究团队题为Lower Circulating Folate Induced by a Fidgetin Intronic Variant is Associated with Reduced Congenital Heart Disease Susceptibility的研究论文，研究发现与叶酸代谢不直接相关的Fidgetin(FIGN)基因内含子的遗传变异同时与低水平的血浆叶酸浓度和降低的CHD患病风险显著相关，表明CHD罹患风险的决定因素是叶酸利用效率，而非血液中游离叶酸浓度。复旦大学附属儿科医院王丹博士、王凤博士和安徽医科大学二附院心胸外科主任石开虎教授为本文的共同第一作者。赵健元副研究员和复旦大学附属妇产科医院王红艳教授和赵世民教授为本文的共同通讯作者。

维生素失调是很多疾病的原因，但是临床对界定维生素失调却时常缺乏客观指标。比如，叶酸(folic acid，又称为维生素B9或者Bc)是包括出生缺陷、心脑血管疾病、肿瘤等在内的独立风险因子，叶酸补服可以明确预防先天性心脏病(CHD)等出生缺陷的发生。然而，多年来困扰临床的一个问题是，血液叶酸水平并不是一个好的出生缺陷预防/诊断指标。医生很难通过血液叶酸浓度高低来预测疾病风险和判断预后。

研究发现，与叶酸代谢不直接相关的Fidgetin(FIGN)基因内含子的遗传变异同时与低水平的血浆叶酸浓度和降低的CHD患病风险显著相关。这一现象与传统理论“缺叶酸导致CHD”相悖，却与许多临床中发现的“血浆叶酸水平与CHD相关性差”相符，提示FIGN可能在叶酸代谢中发挥未知作用。研究人员在分子机理研究中发现，FIGN基因内含子的遗传变异在其下游序列形成了一个新的转录起始点，阻止抑制子cAMP反应原件结合蛋白CREB1的结合并招募rna合成酶，进而激活基因的可变转录(图1)。进一步，表达升高的FIGN蛋白通过抑制蛋白酶体，积累还原型叶酸受体1和二氢叶酸还原酶蛋白，促进叶酸的跨膜转运和膜内利用(图2)，在降低血浆叶酸浓度的同时降低CHD罹患风险。该发现既肯定了叶酸与CHD的关系，还提示在临床评估叶酸代谢状态时不仅要测定外周血叶酸水平，还应当检测受试个体的叶酸利用效率来确定病人的叶酸状况。

图1、FIGN遗传变异激活可变转录

图2、FIGN促进叶酸跨膜转运

原文链接：

Lower Circulating Folate Induced by a Fidgetin Intronic Variant is Associated with Reduced Congenital Heart Disease Susceptibility

原文摘要：

Background—Folate deficiency is an independent risk factor for congenital heart disease (CHD); however, the maternal plasma folate level is paradoxically not a good diagnostic marker. Genome-wide surveys have identified variants of non-folate metabolic genes associated with the plasma folate level, suggesting that these genetic polymorphisms are potential risk factors for CHD.

Methods—To examine the effects of folate concentration-related variations on CHD risk in the Han Chinese population, we performed three independent case-control studies including a total of 1,489 CHD patients and 1,745 controls. The expression of the Fidgetin (FIGN) was detected in human cardiovascular and decidua tissue specimens using qRT-PCR and Western Blotting. The molecular mechanisms were investigated by luciferase reporter assays, surface plasmon resonance, and chromatin immunoprecipitation. FIGN-interacting proteins were confirmed by tandem affinity purification and co-immunoprecipitation. Proteasome activity and metabolite concentrations in the folate pathway were quantified using a commercial proteasome activity assay and immunoassays, respectively.

Results—The +94762G>C (rs2119289) variant in intron 4 of the FIGN gene was associated with significant reduction in CHD susceptibility (P=5.1 × 10-14 for the allele, P=8.5 × 10-13 for the genotype). Analysis of combined samples indicated that CHD risks in individuals carrying heterozygous (GC) or homozygous (CC) genotypes were reduced by 44% (odds ratio [OR]=0.56, 95% confidence interval [CI]=0.47-0.67) and 66% (OR=0.34, 95% CI=0.23-0.50), respectively, compared to those with the major GG genotype. Minor C allele carriers who had decreased plasma folate levels exhibited significantly increased FIGN expression because the transcription suppressor CREB1 did not bind the alternative promoter of FIGN isoform X3. Mechanistically, increased FIGN expression led to the accumulation of both reduced folate carrier 1 (RFC1) and dihydrofolate reductase (DHFR) via inhibition of their proteasomal degradation, which promoted folate absorption and metabolism.

Conclusions—We report a previously undocumented finding that decreased circulating folate levels induced by increased folate transmembrane transport and utilization, as determined by the Fidgetin intronic variant, serves as a protective mechanism against CHD. Our results may explain why circulating folate levels do not have a good diagnostic value.

doi:10.1161/CIRCULATIONAHA.116.025164

作者：赵健元 点击：次