Circulation：復旦大學趙健元研究團隊突破維生素代謝難題

2017年3月16日，國際心血管病頂級學術期刊《Circulation》發表復旦大學生命科學學院趙健元研究團隊題為Lower Circulating Folate Induced by a Fidgetin Intronic Variant is Associated with Reduced Congenital Heart Disease Susceptibility的研究論文，研究發現與葉酸代謝不直接相關的Fidgetin(FIGN)基因內含子的遺傳變異同時與低水準的血漿葉酸濃度和降低的CHD患病風險顯著相關，

表明CHD罹患風險的決定因素是葉酸利用效率，而非血液中游離葉酸濃度。復旦大學附屬兒科醫院王丹博士、王鳳博士和安徽醫科大學二附院心胸外科主任石開虎教授為本文的共同第一作者。趙健元副研究員和復旦大學附屬婦產科醫院王紅豔教授和趙世民教授為本文的共同通訊作者。

維生素失調是很多疾病的原因，

但是臨床對界定維生素失調卻時常缺乏客觀指標。比如，葉酸(folic acid，又稱為維生素B9或者Bc)是包括出生缺陷、心腦血管疾病、腫瘤等在內的獨立風險因數，葉酸補服可以明確預防先天性心臟病(CHD)等出生缺陷的發生。然而，多年來困擾臨床的一個問題是，血液葉酸水準並不是一個好的出生缺陷預防/診斷指標。醫生很難通過血液葉酸濃度高低來預測疾病風險和判斷預後。

研究發現，

與葉酸代謝不直接相關的Fidgetin(FIGN)基因內含子的遺傳變異同時與低水準的血漿葉酸濃度和降低的CHD患病風險顯著相關。這一現象與傳統理論“缺葉酸導致CHD”相悖，卻與許多臨床中發現的“血漿葉酸水準與CHD相關性差”相符，提示FIGN可能在葉酸代謝中發揮未知作用。研究人員在分子機理研究中發現，FIGN基因內含子的遺傳變異在其下游序列形成了一個新的轉錄起始點，阻止抑制子cAMP反應原件結合蛋白CREB1的結合並招募rna合成酶，進而啟動基因的可變轉錄(圖1)。進一步，表達升高的FIGN蛋白通過抑制蛋白酶體，積累還原型葉酸受體1和二氫葉酸還原酶蛋白，促進葉酸的跨膜轉運和膜內利用(圖2)，在降低血漿葉酸濃度的同時降低CHD罹患風險。該發現既肯定了葉酸與CHD的關係，還提示在臨床評估葉酸代謝狀態時不僅要測定外周血葉酸水準，還應當檢測受試個體的葉酸利用效率來確定病人的葉酸狀況。

圖1、FIGN遺傳變異啟動可變轉錄

圖2、FIGN促進葉酸跨膜轉運

原文連結：

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 geneticpolymorphisms 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 expressionbecause 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.

作者：趙健元 點擊：次