魏勝娟,昝林森＊,2,王洪寶,2

(1.西北農(nóng)林科技大學動物科技學院,陜西 楊凌 712100;2.國家肉牛改良中心,陜西 楊凌 712100)

動物脂肪酸轉(zhuǎn)運蛋白1的研究進展

魏勝娟1,昝林森＊1,2,王洪寶1,2

(1.西北農(nóng)林科技大學動物科技學院,陜西 楊凌 712100;2.國家肉牛改良中心,陜西 楊凌 712100)

脂肪含量對人類和動物健康以及動物肉品質(zhì)均有重要影響。脂肪酸轉(zhuǎn)運蛋白1(fatty acid transport protein 1,FA TP1)是整合的跨膜蛋白,屬于脂肪酸轉(zhuǎn)運蛋白家族(FATPs)成員,參與脂肪酸跨膜轉(zhuǎn)運及脂肪酸代謝,是影響脂肪含量的關(guān)鍵基因之一,近年來引起了越來越多的關(guān)注。本文就FATP1的結(jié)構(gòu)特點與組織分布、功能、表達調(diào)控以及遺傳變異等方面做一綜述,以期對今后的研究提供參改。

脂肪酸轉(zhuǎn)運蛋白1;FA TP1;S LC27a1;研究進展

脂肪酸轉(zhuǎn)運蛋白1,全稱長鏈脂肪酸轉(zhuǎn)運蛋白1,又名SLC27a1(solute carrier family 27 member 1),由Schaffer等(1994)[1]通過表達克隆技術(shù)在小鼠3T 3-L1脂肪細胞中首次發(fā)現(xiàn),定位于質(zhì)膜;參與長鏈脂肪酸跨膜轉(zhuǎn)運及脂肪酸代謝。至今為止,已在鼠、人、牛、雞等多物種中發(fā)現(xiàn),是至今發(fā)現(xiàn)的脂肪酸轉(zhuǎn)運蛋白家族FA TP1-6的六個成員中發(fā)現(xiàn)最早,也是研究最多的一個基因。

FA TP1通過調(diào)控脂肪酸攝取和代謝,從而間接影響脂質(zhì)分布與沉積,對動物肉質(zhì)改良有著非常重要的意義。此外,激素等調(diào)控FA TP1活性在機體穩(wěn)態(tài)及代謝性疾病中起著重要作用,有望成為基因治療中新的靶基因。不論對動物肉質(zhì)改良還是對人類和動物健康,FA TP1都起著非常重要的作用。

1 FATP1的結(jié)構(gòu)特點與組織分布

1.1 FATP1的定位與結(jié)構(gòu)特點

人的FATP1(NC 000019.9)定位于19號染色體,全長35678 bp,含 12個外顯子,編碼646個氨基酸;小鼠的FATP1(NC 000074)定位于8號染色體,全長17782 bp,含 14個外顯子,編碼646個氨基酸;牛的FA TP1(NC 007305.3)定位于7號染色體,全長39189 bp,含13個外顯子,同樣編碼 646個氨基酸。

FA TP1是63-k Da的質(zhì)膜蛋白,有 6個預測 α-螺旋的跨膜區(qū)[1,2]。Lew is等(2001)[3]研究顯示,FA TP1是至少有一個跨膜區(qū)和多個膜相關(guān)區(qū)域的膜蛋白(見圖1)。

圖1 FATP1的拓撲學模型示意圖[3]

Stuhlsatz-Krouper等[4](1998)通過比較人類、鼠類和酵母的FATP氨基酸序列,發(fā)現(xiàn)了一個高度保守的模序IYTSG T TGXPK,該模序在形成腺嘌呤核苷酸中間產(chǎn)物的一些蛋白中均以發(fā)現(xiàn)。成熟的脂肪酸轉(zhuǎn)運蛋白的該模序中引入250位丙氨酸取代絲氨酸的突變,致使產(chǎn)生適量表達的代謝突變型FATP,抑制了長鏈脂肪酸的轉(zhuǎn)運和與AT P的結(jié)合。FATP參與ATP的結(jié)合取決于IYTSG TTGXPK模序中250位的絲氨酸,胞內(nèi) A TP的耗盡能顯著降低FATP所調(diào)控的長鏈脂肪酸的攝取。Stuhlsatz-Krouper等[5](1999)通過分別定點突變了中心的250位絲氨酸和252位蘇氨酸殘基并在成纖維細胞中表達后發(fā)現(xiàn),突變后脂肪酸的攝入和疊氮基的結(jié)合均變?nèi)酢?50位絲氨酸和252位蘇氨酸對FATP的功能非常關(guān)鍵,且FATP的功能機制涉及到這些氨基酸殘基所決定的核苷酸的結(jié)合。?

1.2 FATP1的組織分布

FA TP1的分布比較廣泛,主要在脂肪和肌肉組織中表達,其組織特異性分布在各個物種中有類似也有區(qū)別。

人類FATP1存在于機體所有利用脂肪酸的組織中[6-8],Geneviève Martina等[9](2000)研究發(fā)現(xiàn),人類肌肉和脂肪組織中FATP1m RNA表達水平較高,小腸中等水平,肝臟中幾乎沒有;Schaffer等[1](1994)證實了小鼠的脂肪、心臟和肌肉組織中均有表達;束剛等[10](2006)發(fā)現(xiàn)豬的脂肪和心臟組織高豐度表達;Ordovás L等[11]發(fā)現(xiàn)牛的FATP1m RNA在心臟、睪丸、神經(jīng)和肌肉組織中含量很高,在肝臟組織中的含量很低,與人和小鼠差別較大的是,牛的脂肪組織中的FATP1的mRNA含量很低,在蛋白水平上,心臟、皮下組織和脂肪組織中均檢測到了該基因蛋白的表達,而在睪丸、神經(jīng)組織及肝臟中卻沒有檢測到。Song等[12](2008)研究發(fā)現(xiàn),黃羽肉雞胸肌和皮下脂肪在22、29和42日齡3個階段均能檢測到FATP1m RNA的恒定表達;骨骼肌42日齡的表達量明顯高于前兩個階段;公雞的腹部脂肪的FATP1m RNA表達量隨日齡明顯增多,而母雞于42日齡表達量急劇下降。這些研究表明了FATP1分布的組織特異性與性別特異性。

2 FATP1的功能

2.1 促進脂肪酸跨膜轉(zhuǎn)運,參與脂肪酸代謝

FA TP1是整合跨膜蛋白,引導外源性脂肪酸進入細胞,參與脂肪酸的攝入和酯化,對細胞內(nèi)甘油三酯的合成具有重要作用。Schaffer等[1](1994)在哺乳動物中表達FATP1能明顯促進長鏈脂肪酸的攝取。Mario Marottaa等[13](2004)研究發(fā)現(xiàn)大鼠中脂肪含量高的肌肉細胞FATP1的表達也高。Chiu等[14](2005)通過在心臟特異性過表達FATP1的轉(zhuǎn)基因小鼠研究發(fā)現(xiàn),心肌攝取脂肪酸的能力增大了4倍,細胞內(nèi)脂肪酸的沉積和代謝均增大了2倍。Wu等[15](2006)研究表明,小鼠FA TP1被敲除后,脂肪細胞中甘油三酯的含量顯著降低。FAT P1有脂酰輔酶A的活性,與長鏈?；o酶A合成酶相互作用,促進哺乳動物脂肪酸攝取[16,17];但此酶活是否對驅(qū)動脂肪酸攝取是必須的仍然未知[18]。

2.2 參與能量代謝

越來越多的研究證明,FATP1在能量代謝中起著重要作用。Wu等[19](2006)研究發(fā)現(xiàn),FA TP1在棕色脂肪組織的非戰(zhàn)栗產(chǎn)熱中起作用。Sebastián等[20](2009)證實,與FAT36相似,FATP1基因與線粒體相關(guān)且對肌肉細胞線粒體脂肪酸氧化起作用。Wiczer等(2009)[21]通過蛋白組學方法沉默了3T 3-L1脂肪細胞的FATP1基因,發(fā)現(xiàn)三羧酸循環(huán)活性增強,細胞的NAD(+)/NADH增多,脂肪酸氧化作用增強,乳酸產(chǎn)量增加,暗示了FA TP1的新的作用,即調(diào)控三羧酸循環(huán)活性及線粒體代謝的功能。Mitchell等(2009)[22]轉(zhuǎn)染FATPsiRNA于HEK293細胞,發(fā)現(xiàn)FA TP1能夠調(diào)控心磷脂的重新合成。Guitart等(2009)[23]通過亞細胞成分的免疫印記和FATP1-GFP融合蛋白的免疫細胞學發(fā)現(xiàn),在培養(yǎng)的肌管細胞中,FATP1定位于線粒體中并能提高丙酮酸脫氫酶的活性。

3 FATP1表達調(diào)控

FATP1主要受過氧化物酶體增生物激活受體,激素(研究較多的是胰島素),細胞因子等多種物質(zhì)調(diào)控,與其他調(diào)節(jié)因子共同調(diào)節(jié)長鏈脂肪酸的轉(zhuǎn)運,維持機體穩(wěn)態(tài)。

3.1 FATP的正向調(diào)控

FATP的上游區(qū)域-458到-474存在功能性過氧化物酶體增生物激活受體(PPARs)反應元件且能被PPA Rа和PPARγ激活物上調(diào)[24-27],因此在脂肪細胞分化過程中增加。此外,磺碘喹等藥物能通過維甲酸X受體上調(diào)FA TP的表達[28]。

3.2 FATP的負向調(diào)控

FATP m RNA表達水平還受胰島素等調(diào)控。在培養(yǎng)的3T 3-L1脂肪細胞中,胰島素下調(diào)FATP mRNA表達水平[1]。Northern blot顯示,FATP mRNA水平在3T 3-L1前脂肪細胞分化中增大了5～7倍,而胰島素在培養(yǎng)的脂肪細胞中能下調(diào)10倍。在短期禁食的動物試驗中,FA TP m RNA在成熟脂肪組織中增加了11倍[29]。Berk等[30](1997)證實,在胰島素抵抗Zucker鼠中,FATP m RNA的水平比正常鼠增大了5倍。Kim等[31](2004),FA TP1失活能預防骨骼肌中脂肪誘導的胰島素抵抗。Qiw ei等[32](2006)通過體內(nèi)試驗證明胰島素能通過調(diào)節(jié)FA TP1調(diào)控長鏈脂肪酸的攝取,FATPs決定了飲食中攝取的脂質(zhì)的組織分布,參與飲食誘導的肥胖。胰島素對FATP調(diào)控快速、可逆,主要通過定位于-1353和-1347的順式磷酸烯醇丙酮酸羧激酶類似元件[33],在轉(zhuǎn)錄水平負調(diào)控成熟脂肪細胞中FA TP基因的表達[25]。Wiczer等[34](2009)證明,在脂肪細胞中,胰島素誘導的脂肪酸攝入是通過FATP1基因調(diào)控AMPK途徑并通過潛在的調(diào)控機制調(diào)控從葡萄糖代謝新生成的脂肪酸的量的平衡,且在此過程中,脂肪酸的攝入通過乙酰輔酶A羧化酶的磷酸化進行。此外,內(nèi)毒素、腫瘤壞死因子a和白介素l等也能負向調(diào)控FAT P1的表達[35]。

4 FATP1的遺傳變異

Meirhaeghe等[36](2000)通過SSCP技術(shù)對1144個法國人的FAT P1基因多態(tài)性進行研究,首次發(fā)現(xiàn)了人類FATP1基因的內(nèi)含子8和內(nèi)含子9的3個SNPs(single nucleotide polymorphisms),分別為內(nèi)含子8的G/A+48,及內(nèi)含子9的G/A和G/T。發(fā)現(xiàn)內(nèi)含子8 SNP中A等位基因與較高的甘油三酯水平相關(guān),顯示了其對脂質(zhì)代謝的影響。2005年,Meirhaeghe等[37]通過進一步分析1195個法國人FATP1內(nèi)含子8發(fā)現(xiàn),G/A+48多態(tài)性與代謝綜合癥沒有顯著相關(guān),暗示該SNP可能對代謝綜合癥不起重要作用。

Gertow等[38](2003)通過對1054個瑞典人內(nèi)含子8的G/A48多態(tài)性與禁食和食后血脂、血漿脂蛋白變化的關(guān)系研究發(fā)現(xiàn),SNP與食后血脂及低密度脂蛋白顆粒大小分布的改變相關(guān),與禁食后血漿中TG含量無關(guān)。電遷移率和報告基因研究顯示,內(nèi)含子8不同等位基因核因子和轉(zhuǎn)錄活性不同。FATP1通過非酯化脂肪酸運輸,可能在食后脂代謝和心血管疾病中起作用。

Laura Ordovas等[39](2008)通過基因微測序技術(shù)首次研究FATP-1的多態(tài)性與乳脂含量的關(guān)系,發(fā)現(xiàn)該基因在荷斯坦奶牛中有14個SNPs,其中1個在啟動子,7個在內(nèi)含子,6個在外顯子。SNPs對荷斯坦奶牛乳脂率的高低影響不顯著,暗示了S LC27A 1與乳脂含量無關(guān)或影響很弱。

張龍等[40](2009)利用PCR-SSCP技術(shù)對381只大恒優(yōu)質(zhì)雞的FATP1基因研究發(fā)現(xiàn),FATP1的遺傳變異與部分屠體性狀和腹脂率存在相關(guān)性。

5 展望

FATP1是FATPs中重要成員之一,參與脂肪酸及能量代謝,對脂肪沉積及二型糖尿病的治療有著重要作用。雖然FATP1的結(jié)構(gòu)、組織分布、功能及表達調(diào)控等的研究均取得了一系列的進展,但FA TP1對動物肉質(zhì)的影響方面的報道還不是很多。進一步研究FATP1的遺傳變異與肉質(zhì)相關(guān)性及對脂肪細胞的影響等有著非常重要的意義。

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Advances in the Research of Animal Fatty Acid Transport Protein 1

WEI Sheng-juan1,ZAN Lin-sen＊1,2,WANG Hong-bao1,2

(1.College of Animal Science and Tech no logy,Northwest A&F University,Yang ling,Shaanxi 712100,China;2.National Beef Cattle Improvement Center in China,Y ang ling,Shaan xi 712100,China)

Fat content has an import ant role on the health of human and animals and the meat quality of animals.Fatty acid transport protein 1(FATP1)is an integral membrane protein.As one member of the family of the fatty acid transport proteins,FATP1 is involved in the transport of long chain fatty acids across the plasma membrane and the metabolism of fatty acids.It is one of the key genes which have an influence on fat content and has abstracted more and more attentions in recent years.In this paper,structural features and tissue distribution,gene expression and regulation and genetic variation of the gene FATP1 have been summarized for better research in the future.

fatty acid transport protein1;fATP1;sLC27a1;research advance

S823

A

1001-9111(2011)04-0047-05

2010-11-03

2010-12-10

國家“863”計劃(2010AA10Z101,2008AA 101010),“十一五”科技支撐計劃(2006BAD01A 10-3)。

魏勝娟(1987-),女,河南滑縣人,在讀碩士,主要從事生物技術(shù)與家畜育種研究。

＊通訊作者:昝林森(1963-),男,陜西扶風人,教授,主要從事動物生長發(fā)育調(diào)控及牛遺傳育種與繁殖研究。