毛湘冰 黃志清 陳小玲 余 冰 陳代文

瘦肉率和生長(zhǎng)速度一直以來(lái)都是豬生產(chǎn)中的重要目標(biāo)性狀,而其與骨骼肌的含量及骨骼肌內(nèi)蛋白質(zhì)沉積的能力有很大關(guān)系。哺乳動(dòng)物骨骼肌蛋白質(zhì)合成受到諸多因素的調(diào)節(jié),這些因素包括采食、體內(nèi)各種激素水平、運(yùn)動(dòng)、營(yíng)養(yǎng)物質(zhì)(如蛋白質(zhì)、氨基酸和葡萄糖等)水平等[1-2]。近年的大量研究表明,亮氨酸可以誘導(dǎo)骨骼肌蛋白質(zhì)合成,而在這一過(guò)程中,亮氨酸可作為一種調(diào)節(jié)因子來(lái)調(diào)控肌細(xì)胞內(nèi)信號(hào)通路,從而提高哺乳動(dòng)物骨骼肌蛋白質(zhì)的合成[1]。因此,本文總結(jié)了近年關(guān)于亮氨酸調(diào)節(jié)哺乳動(dòng)物(主要是鼠和豬)骨骼肌蛋白質(zhì)合成及其作用機(jī)制,為亮氨酸營(yíng)養(yǎng)的深入研究與亮氨酸在臨床和生產(chǎn)上的科學(xué)利用提供參考。

1 亮氨酸的概述

亮氨酸(leucine,又稱(chēng)白氨酸)是 Proust首先從奶酪中分離出來(lái)的,之后 Braconnot在肌肉、羊毛酸水解物中得到其結(jié)晶,分析出它的化學(xué)結(jié)構(gòu)為 α-氨基異己酸,并將其命名為亮氨酸。作為一種支鏈氨基酸,亮氨酸是機(jī)體內(nèi)的必需氨基酸,哺乳動(dòng)物自身不能合成,必須由飼糧提供,而亮氨酸也是目前飼糧中數(shù)量最大的必需氨基酸[3]。

亮氨酸的從頭合成限于植物和微生物中,在哺乳動(dòng)物體內(nèi)不能從頭合成。而哺乳動(dòng)物體內(nèi)亮氨酸的分解過(guò)程如下:起始步驟是轉(zhuǎn)氨,即亮氨酸在支鏈氨基酸轉(zhuǎn)氨酶(branched-chain aminotransferase,BCAT)催化下,生成 α-酮異己酸,其為一種支鏈酮酸(branched-chain ketoacid,BCKA),該反應(yīng)為可逆反應(yīng)[4];然后,α-酮異己酸在支鏈氨基酸脫氫酶(branched-chain dehydogense,BCDH)催化下發(fā)生不可逆的氧化脫羧反應(yīng),生成少 1個(gè)碳原子的酮酸與乙酰輔酶 A衍生物;最終,分解生成乙酰乙酸和乙酰輔酶 A進(jìn)入檸檬酸循環(huán),因此,亮氨酸是一種生酮氨基酸[5]。一般來(lái)說(shuō),哺乳動(dòng)物體內(nèi)絕大多數(shù)氨基酸代謝均在肝臟內(nèi)進(jìn)行,而亮氨酸的代謝則主要位于骨骼肌當(dāng)中,這與以上關(guān)鍵酶的分布有很大關(guān)系[5]。

關(guān)于亮氨酸功能的研究發(fā)現(xiàn),亮氨酸在機(jī)體中發(fā)揮著重要的營(yíng)養(yǎng)生理作用,概括起來(lái)主要包括 3個(gè)方面,即氧化供能、調(diào)節(jié)機(jī)體免疫功能和調(diào)節(jié)機(jī)體(尤其是骨骼肌)的蛋白質(zhì)代謝。

2 亮氨酸對(duì)骨骼肌蛋白質(zhì)合成的刺激作用

關(guān)于亮氨酸營(yíng)養(yǎng)生理作用的研究,近年多集中于其對(duì)哺乳動(dòng)物骨骼肌蛋白質(zhì)代謝(尤其是合成)的影響。

2.1 亮氨酸對(duì)健康動(dòng)物骨骼肌蛋白質(zhì)合成的影響

諸多以仔豬和大鼠為模型的試驗(yàn)均表明,亮氨酸可以刺激骨骼肌蛋白質(zhì)的合成。美國(guó)的Davis團(tuán)隊(duì)和 Kimball團(tuán)隊(duì)在這一方面最先進(jìn)行了大量的研究,這些研究主要集中在體內(nèi)急性試驗(yàn),他們通過(guò)給禁飼的大鼠灌服或新生仔豬靜脈注射一次性給予亮氨酸溶液(亮氨酸給予的劑量分別為1.35和 3.2 g/kg BW),結(jié)果發(fā)現(xiàn),與未給予亮氨酸的禁飼大鼠或新生仔豬相比,給予亮氨酸的大鼠或新生仔豬骨骼肌蛋白質(zhì)合成顯著增加,且發(fā)現(xiàn)補(bǔ)充亮氨酸時(shí)供給其他必需氨基酸更有利于氨基酸的利用與骨骼肌蛋白質(zhì)合成[6-12]。而法國(guó)的Balage研究小組則進(jìn)行了一些關(guān)于亮氨酸調(diào)節(jié)骨骼肌蛋白質(zhì)合成的長(zhǎng)期試驗(yàn)研究,所選用的試驗(yàn)對(duì)象為大鼠。 Dardevet等[13]和 Rieu等[14-15]分別使用添加 4.45%亮氨酸飼糧或通過(guò)不同蛋白質(zhì)來(lái)源配制飼糧進(jìn)行長(zhǎng)期飼喂發(fā)現(xiàn),提高的亮氨酸水平刺激了老齡大鼠骨骼肌蛋白質(zhì)合成,而且在停止飼喂添加亮氨酸飼糧后,這種作用依然得到延續(xù);但是,飼糧中亮氨酸水平的增加對(duì)成年大鼠骨骼肌蛋白質(zhì)的合成沒(méi)有顯著影響;另外,在進(jìn)一步的研究中,Debras等[16]發(fā)現(xiàn),飼糧中亮氨酸的缺乏有降低正常生長(zhǎng)大鼠骨骼肌蛋白質(zhì)合成的趨勢(shì),但差異不顯著。除此之外,Lynch等[17]通過(guò)飲水長(zhǎng)期供給生長(zhǎng)大鼠亮氨酸[(2.2～3.2)g/(kg BW?d)],也提高了其骨骼肌蛋白質(zhì)合成。Yin等[18]在斷奶仔豬為試驗(yàn)?zāi)Ｐ偷难芯恐邪l(fā)現(xiàn),在蛋白含量為16.9%的低蛋白飼糧中添加 0.27%或 0.55%的亮氨酸,可以顯著提高仔豬骨骼肌內(nèi)蛋白質(zhì)合成。對(duì)于其他哺乳動(dòng)物,亮氨酸調(diào)節(jié)骨骼肌蛋白質(zhì)合成也存在類(lèi)似的作用,桑丹等[19]給綿羊飼喂添加了 0.05%～0.15%瘤胃保護(hù)性亮氨酸的飼糧,發(fā)現(xiàn)亮氨酸的添加可以顯著提高綿羊骨骼肌蛋白質(zhì)的合成。而在人上的研究也發(fā)現(xiàn),給青年人提供過(guò)量的亮氨酸也可以提高其骨骼肌蛋白質(zhì)合成能力,并促進(jìn)骨骼肌蛋白質(zhì)的沉積[20]。

2.2 亮氨酸對(duì)疾病引起骨骼肌群流失的緩解作用

根據(jù)以上健康狀態(tài)動(dòng)物試驗(yàn)的研究結(jié)果,各國(guó)學(xué)者認(rèn)為亮氨酸在緩解骨骼肌群流失上可能具有相應(yīng)的作用,因此建立了目前引起骨骼肌蛋白質(zhì)流失的各種疾病模型,如敗血癥、癌癥和糖尿病等,并進(jìn)行了相應(yīng)的亮氨酸處理研究。Anthony等[21]利用丙酮二酰注射誘導(dǎo)大鼠產(chǎn)生糖尿病,并對(duì)其一次性灌服 1.35 g/kg BW的亮氨酸發(fā)現(xiàn),與灌服生理鹽水的對(duì)照組相比,亮氨酸的灌服可以顯著提高糖尿病大鼠的骨骼肌合成。Ventrucci等[22]先給大鼠飼喂添加 3%亮氨酸的飼糧,之后通過(guò)植入癌細(xì)胞誘導(dǎo)大鼠癌癥的發(fā)生,結(jié)果表明亮氨酸的添加可以顯著提高癌癥大鼠骨骼肌蛋白質(zhì)合成能力,減輕癌癥引起的骨骼肌群流失。Vary[23]通過(guò)手術(shù)給大鼠腹腔植入大腸桿菌和脆弱類(lèi)桿菌誘導(dǎo)慢性敗血癥,繼而進(jìn)行一次性灌服1.35 g/kg BW的亮氨酸,發(fā)現(xiàn)亮氨酸的添加可抑制敗血癥引起的骨骼肌蛋白質(zhì)合成減少,從而緩解其帶來(lái)的體重下降等負(fù)面效應(yīng)。

2.3 體外試驗(yàn)中亮氨酸的蛋白質(zhì)合成刺激作用

在以肌肉細(xì)胞為體外模型的研究中,研究者們也發(fā)現(xiàn)亮氨酸對(duì)于蛋白質(zhì)合成具有顯著刺激作用。Kimballs等[24]和 Mordier等[25]分別去除了L6和 C2C12肌管培養(yǎng)基中的亮氨酸后,發(fā)現(xiàn)肌管的蛋白質(zhì)合成顯著下降。而 Du等[26]和 Han等[27]分別在饑餓后的 C2C12成纖維細(xì)胞和原代肌肉衛(wèi)星細(xì)胞的培養(yǎng)基中添加了 2 mmol/L的亮氨酸進(jìn)行試驗(yàn),結(jié)果表明亮氨酸的添加顯著提高了細(xì)胞內(nèi)蛋白質(zhì)合成水平。

在研究亮氨酸刺激蛋白質(zhì)合成過(guò)程中,很多研究者還發(fā)現(xiàn)亮氨酸可在體內(nèi)和體外刺激某些特定蛋白質(zhì)的合成。Roh等[28]和 Lynch等[29]發(fā)現(xiàn),亮氨酸可以刺激脂肪細(xì)胞和組織產(chǎn)生和分泌瘦素。Tomiya等[30-31]也研究表明,亮氨酸可以刺激肝臟星狀細(xì)胞產(chǎn)生肝臟生長(zhǎng)因子。Ijichi等[32]的研究還發(fā)現(xiàn),在原代培養(yǎng)的肝上皮實(shí)質(zhì)細(xì)胞的培養(yǎng)基中添加亮氨酸,可以刺激其白蛋白合成。另外,Mao等[33]通過(guò)亮氨酸處理 C2C12肌管發(fā)現(xiàn),亮氨酸可以顯著提高肌管內(nèi)瘦素受體的表達(dá)。

3 亮氨酸調(diào)節(jié)骨骼肌蛋白質(zhì)合成的機(jī)制

亮氨酸可作為能量來(lái)源。研究表明,1 mol亮氨酸完全氧化可產(chǎn)生 40 mol ATP,氧化產(chǎn)生 ATP的效率高于其他氨基酸[32,34]。這說(shuō)明亮氨酸可以為蛋白質(zhì)合成提供能量,且亮氨酸本身也是蛋白質(zhì)合成的重要基質(zhì)。除了這些之外,更重要的是,亮氨酸對(duì)于骨骼肌蛋白質(zhì)合成的促進(jìn)作用還在于其可以調(diào)節(jié)細(xì)胞內(nèi)各種信號(hào)通路。歸納近年的研究結(jié)果可以發(fā)現(xiàn),亮氨酸調(diào)節(jié)骨骼肌蛋白質(zhì)合成主要是通過(guò)哺乳動(dòng)物雷帕霉素靶蛋白(mammalian target of rapamycin,mTOR)依賴(lài)與非依賴(lài) 2條通路來(lái)進(jìn)行的。

3.1 亮氨酸對(duì) mTOR依賴(lài)的信號(hào)通路的調(diào)節(jié)

各國(guó)學(xué)者通過(guò)動(dòng)物或細(xì)胞為模型的研究發(fā)現(xiàn),亮氨酸調(diào)節(jié)骨骼肌蛋白質(zhì)合成機(jī)制主要是通過(guò)細(xì)胞內(nèi)轉(zhuǎn)錄后調(diào)節(jié)通路之一——mTOR信號(hào)通路,圖 1描述了亮氨酸通過(guò) mTOR信號(hào)通路刺激肌肉蛋白質(zhì)合成的可能信號(hào)轉(zhuǎn)導(dǎo)情況。

首先,亮氨酸分別激活磷脂酰肌醇 3激酶/蛋白激酶 B/40 ku的脯氨酸富集的蛋白激酶 B基質(zhì)(phosphatidylinositol 3-kinase/protein kinase B/proline-rich Akt substrate of 40 ku,PI3K/PKB/PRAS40)通路、一組鳥(niǎo)苷三磷酸酶(a family of four related small guanosine triphosphatases,Rag)或富集于大腦的 Ras同源物(Ras homolog enriched in brain,Rheb),進(jìn)而活化無(wú)活性的哺乳動(dòng)物雷帕霉素靶蛋白復(fù)合物 1(mammalian target of rapamycin complex 1,mTORC1),這一過(guò)程的表現(xiàn)即為,mTOR蛋白上某些位點(diǎn)的蘇氨酸和絲氨酸發(fā)生了磷酸化[35-37]。而 mTORC1的活化將促使其下游的 2個(gè)重要的效應(yīng)物——核糖體蛋白 S6激酶(ribosomal protein S6 kinase,p70S6K)和真核翻譯起始因子 4E結(jié)合蛋白 1(eukaryotic initiation factor 4E-binding protein-1,4E-BP1)發(fā)生磷酸化。4E-BP1磷酸化后釋放了真核翻譯起始因子 4E(eukaryotic initiation factor 4E,eIF4E),使 eIF4E與真核翻譯起始因子 4G(eukaryotic initiation factor 4G,eIF4G)結(jié)合,形成真核翻譯起始因子 4F(eukaryotic initiation factor 4F,eIF4F),進(jìn)而提高了 mRNA的穩(wěn)定性,促進(jìn)了 mRNA翻譯的起始[38]。而p70S6K的活化促使核糖體蛋白 S6(ribosomal protein S6,S6)的磷酸化,增加了 mRNA翻譯(特別是涉及到蛋白質(zhì)合成的編碼蛋白的mRNA)[39]。最終,亮氨酸激活了蛋白質(zhì)的合成。

3.2 亮氨酸對(duì)非 mTOR依賴(lài)信號(hào)通路的調(diào)節(jié)

在對(duì)亮氨酸提高骨骼肌蛋白質(zhì)合成機(jī)制的進(jìn)一步探討中,Anthony[40]利用 mTOR的特異性抑制劑(rapamycin)處理大鼠后,發(fā)現(xiàn) rapamycin并沒(méi)有完全的抑制亮氨酸對(duì)肌肉蛋白質(zhì)合成的增強(qiáng)作用,因此,推斷亮氨酸對(duì)于蛋白質(zhì)合成的調(diào)節(jié)作用還存在mTOR非依賴(lài)途徑。但是,目前相關(guān)研究很少。除此之外,近年的一些研究還發(fā)現(xiàn),亮氨酸可以促進(jìn)機(jī)體內(nèi)多種激素(如胰島素和瘦素等)的產(chǎn)生。而且,在進(jìn)一步研究亮氨酸與胰島素調(diào)節(jié)骨骼肌蛋白質(zhì)合成是否具有依賴(lài)關(guān)系中,O'Connor等[41]發(fā)現(xiàn),亮氨酸與胰島素刺激新生仔豬骨骼肌蛋白質(zhì)合成的作用并不具有相互依賴(lài)性;而以豬原代衛(wèi)星細(xì)胞為模型的研究中,亮氨酸與類(lèi)胰島素生長(zhǎng)因子 -Ⅰ刺激蛋白質(zhì)合成的作用可能具有協(xié)同效應(yīng),但對(duì)于 mTOR信號(hào)通路的激活作用并不具有協(xié)同作用[27]。另外,Sans等[42]以大鼠和小鼠為試驗(yàn)?zāi)Ｐ脱芯窟€發(fā)現(xiàn),亮氨酸可以通過(guò)mTOR信號(hào)通路激活胰腺腺泡內(nèi)的 mRNA翻譯機(jī)制,而這一過(guò)程不受膽囊收縮素和胰島素的影響。毛湘冰[43]以 C2C12肌管和 ob/ob小鼠為模型研究發(fā)現(xiàn),亮氨酸與瘦素在調(diào)節(jié)骨骼肌蛋白質(zhì)合成中具有協(xié)同作用,但沒(méi)有進(jìn)一步對(duì)相關(guān)的信號(hào)通路和機(jī)制進(jìn)行探討。

圖1 亮氨酸通過(guò)m TOR信號(hào)通路刺激肌肉蛋白質(zhì)合成的可能信號(hào)轉(zhuǎn)導(dǎo)圖Fig.1 Signaling events of mTOR signaling pathway in the stimulation of protein synthesis in muscle by leucine

4 小 結(jié)

雖然目前已有大量關(guān)于亮氨酸刺激骨骼肌蛋白質(zhì)合成以及相關(guān)機(jī)制的研究,但是還存在諸多方面需要開(kāi)展大量試驗(yàn)來(lái)進(jìn)一步探討。如近年的研究發(fā)現(xiàn)飼糧中亮氨酸的過(guò)量添加(≥5%)能夠刺激骨骼肌蛋白質(zhì)合成,卻會(huì)導(dǎo)致采食量下降,進(jìn)而影響機(jī)體的生長(zhǎng)[44-46],因此,亮氨酸的補(bǔ)充劑量或需要量需要進(jìn)一步確定。另外,關(guān)于補(bǔ)充亮氨酸的途徑和方式的研究也沒(méi)有得到一致的結(jié)果。而對(duì)于亮氨酸調(diào)節(jié)骨骼肌蛋白質(zhì)合成的機(jī)制方面,目前各國(guó)學(xué)者已公認(rèn) mTOR信號(hào)通路的調(diào)節(jié)作用,但是對(duì)于 mTOR上游的因子以及 mTOR非依賴(lài)信號(hào)通路的研究報(bào)道還是十分缺乏的。未來(lái)的研究必須在這些方面進(jìn)行深入,探明這些問(wèn)題,才能為亮氨酸在臨床和生產(chǎn)上的應(yīng)用提供堅(jiān)實(shí)的理論基礎(chǔ)。

[1] KIMBALL S R,FARRELL P A,JEFFERSON L S.Exercise effects on muscle insulin signaling and action invited review:role of insulin in translational control of protein synthesis in skeletal muscle by amino acids or exercise[J].Journal of Applied Physiology,2002,93:1168-1180.

[2] SAHA A K,XU X J,LAWSON E,et al.Downregulation of AMPK accompanies leucine-and glucoseinduced increases in protein synthesis and insulin resistance in rat skeletal muscle[J].Diabetes,2010,59:2426-2434.

[3] SCHADEWALDT P,WENDEL U.Metabolism of branched-chain amino acids in maple syrup urine disease[J].European Journal of Pediatrics,1997,156:S62-S66.

[4] DESANTIAGO S,TORRES N,SURYAWAN A,et al.Regulation of branched-chain amino acid metabolism in the lactating rat[J].The Journal of Nutrition,1998,128:1165-1171.

[5] SHIMOMURA Y,HONDA T,SHIRAKI M,et al.Branched-chain amino acid catabolism in exercise and liver disease[J].The Journal of Nutrition,2006,136:250S-253S.

[6] VARY T C,JEFFERSON L S,KIMBALL S R.A-mino acid-induced stimulation of translation initiation in rat skeletal muscle[J].American Journal of Physiology,1999,277:E 1077-E 1086.

[7] ANTHONY J C,YOSHIZAWA F,ANTHONY T G,et al.Leucine stimulates translation initiation in skeletal muscle of postabsorptive rats via arapamycinsensitive pathway[J].The Journal of Nutrition,2000,130:2413-2419.

[8] CROZIER S J,KIMBALL S R,EMMERT S W,et al.Oral leucine administration stimulates protein synthesis in rat skeletal muscle[J].The Journal of Nutrition,2005,135:376-382.

[9] SURYAWAN A,JEYAPALAN A S,ORELLANA R A,et al.Leucine stimulates protein synthesis in skeletal muscle of neonatal pigs by enhancing mTORC1 activation[J].American Journal of Physiology,2008,295:E868-E875.

[10] NORTON L E,LAYMAN D K,BUNPO P,et al.The leucine content of a complete meal directs peak activation but not duration of skeletal muscle protein synthesis and mammalian target of rapamycin signaling in rats[J].The Journal of Nutrition,2009,139:1103-1109.

[11] ESCOBAR J,FRANK JW,SURYAWAN A,et al.Leucine and-ketoisocaproic acid,but not norleucine,stimulate skeletal muscle protein synthesis in neonatal pigs[J].The Journal of Nutrition,2010,140:1418-1424.

[12] WILSON F A,SURYAWAN A,GAZZANEO M C,et al.Stimulation of muscle protein synthesis by prolonged parenteral infusion of leucine is dependent on amino acid availability in neonatal pigs[J].The Journal of Nutrition,2010,140:264-270.

[13] DARDEVET D,SORNET C,BAYLE G,et al.Postprandial stimulation of muscle protein synthesis in old rats can be restored by a leucine-supplemented meal[J].The Journal of Nutrition,2002,132:95-100.

[14] RIEU I,SORNET C,BAYLE G,et al.Leucinesupplemented meal feeding for ten days beneficially affects postprandial muscleprotein synthesis in old rats[J].The Journal of Nutrition,2003,133:1198-1205.

[15] RIEU I,BALAGEM,SORNET C,et al.Increased availability of leucine with leucine-rich whey proteins improves postprandial muscle protein synthesis in aging rats[J].Nutrition,2007,23:323-331.

[16] DEBRAS E,PROD'HOMME M,RIEU I,et al.Postprandial leucine deficiency failed to alter muscle protein synthesis in growing and adult rats[J].Nutrition,2007,23:267-276.

[17] LYNCH C J,HUTSON S M,PATSON B J,et al.Tissue-specific effects of chronic dietary leucine and norleucine supplementation on protein synthesis in rats[J].American Journal of Physiology,2002,283:E824-E835.

[18] YIN Y,YAO K,LIU Z,et al.Supplementing L-leucine to a low-protein diet increases tissue protein synthesis in weanling pigs[J].Amino Acids,2010,39:1477-1486.

[19] 桑丹,孫海洲,趙存發(fā),等.亮氨酸對(duì)綿羊機(jī)體蛋白質(zhì)合成的影響[J].動(dòng)物營(yíng)養(yǎng)學(xué)報(bào),2010,22(4):951-955.

[20] GLYNN E L,FRY C S,DRUMMOD MJ,et al.Excess leucine intake enhances muscle anabolic signaling but not net protein anabolism in young men and women[J].The Journal of Nutrition,2010,140:1970-1976.

[21] ANTHONY J C,REITER A K,ANTHONY T G,et al.Orally administered leucine enhances protein synthesis in skeletal muscle of diabetic rats in the absence of increases in 4E-BP1 or S6K 1 phosphorylation[J].Diabetes,2002,51:928-936.

[22] VENTRUCCI G,MELLO M A R,GOMES-MARCONDES M C C.Leucine-rich diet alters the eukaryotic translation initiation factors expression in skeletal muscle of tumour-bearing rats[J].BMC Cancer,2007,7:42.

[23] VARY T C.Acute oral leucine administration stimulates protein synthesis during chronic sepsis through enhanced association of eukaryotic initiation factor 4G with eukaryotic initiation factor 4E in rats[J].The Journal of Nutrition,2007,137:2074-2079.

[24] KIMBALLSR,SHANTZ L M,HORETSKY R L,et al.Leucine regulates translation of specific mRNAs in L6 myoblasts through mTOR-mediated changes in availability of eIF4E and phosphorylation of ribosomal protein S6[J].Journal of Biological Chemistry,1999,274:11647-11652.

[25] MORDIER S,DEVAL C,BéCHET D,et al.Leucine limitation induces autophagy and activation of lysosome-dependent proteolysis in C2C12 myotubes through a mammalian target of rapamycin-independent signaling pathway[J].Journal of Biological Chemistry,2000,275:29900-29906.

[26] DU M,SHEN Q,ZHU M,et al.Leucine stimulates mammalian target of rapamycin signaling in C2C12 myoblasts in part through inhibition of adenosine monophosphate-activated protein kinase[J].Journal of Animal Science,2007,85:919-927.

[27] HAN B,TONG J,ZHU M,et al.Insulin-like growth factor-1(IGF-1)and leucine activate pig myogenic satellite cells through mammalian target of rapamycin(mTOR)pathway[J].Molecular Reproduction and Development,2008,75:810-817.

[28] ROH C,HAN J R,TZATSOS A,et al.Nutrientsensing mTOR-mediated pathway regulates leptin production in isolated rat adipocytes[J].American Journal of Physiology,2003,284:E322-E 330.

[29] LYNCH C J,GERN B,LLOYD C,et al.Leucine in food mediates some of the postprandial rise in plasma leptin concentrations[J].American Journal of Physiology,2006,291:E621-E630.

[30] TOMIYA T,NISHIKAWA T,INOUE Y,et al.Leucine stimulates HGF production by hepatic stellate cells through mTOR pathway[J].Biochemical and Biophysical Research Communications,2007,358:176-180.

[31] TOMIYA T,INOUE Y,YANASE M,et al.Treatment with leucine stimulates the production of hepatocyte growth factor in vivo[J].Biochemical and Biophysical Research Communications,2004,322:772-777.

[32] IJICHI C,MATSUMURA T,TSUJI T,et al.Branched-chain amino acids promote albumin synthesis in rat primary hepatocytes through the mTOR signal transduction system[J].Biochemical and Biophysical Research Communications,2003,303:59-64.

[33] MAO X,ZENG X,WANG J,et al.Leucine promotes leptin receptor expression in mouse C2C12 myotubes through the mTOR pathway[J].Molecular Biology Reports,2010,DOI:10.1007/s11033-010-9992-6.

[34] ICHIHARA A.BCA,HGF,and proteasomes[J].Biochemical and Biophysical Research Communications,1999,266:647-651.

[35] KIM E,GORAKSHA-HICKSP,LI L,et al.Regulation of TORC1by Rag GTPases in nutrient response[J].Nature Cell Biology,2008,10:935-945.

[36] SANCAKY,PETERSON T R,SHAUL Y D,et al.The Rag GTPases bind raptor and mediate amino acid signaling to mTORC1[J].Science,2008,320:1496-1501.

[37] CANEDO C S,DEMEULDER B,GINION A,et al.Activation of the cardiac mTOR/p 70S6K pathway by leucine requires PDK 1 and correlates with PRAS40 phophorylation[J].American Journal of Physiology,2010,298:E761-E 769.

[38] PROUD C G.Amino acids and mTOR signalling in anabolic function[J].Biochemical Society Transactions,2007,35:1187-1190.

[39] LYNCH C J.Role of leucine in the regulation of mTOR by amino acids:Revelations from structure-activity studies[J].The Journal of Nutrition,2001,131:861S-865S.

[40] ANTHONY J C.Translation control of protein synthesis in skeletal muscle of post-absorptive rats following oral administration of leucine[D].Dissertation.Pennsylvania:Pennsylvania State University,2001.

[41] O'CONNOR PM J,BUSH J A,SURYAWAN A,et al.Insulin and amino acids independently stimulate skeletal muscle protein synthesis in neonatal pigs[J].American Journal of Physiology,2003,284:E110-E119.

[42] SANS M D,TASHIRO M,VOGEL N L,et al.Leucine activates pancreatic translational machinery in rats and mice through mTOR independently of CCK and insulin[J].The Journal of Nutrition,2006,136:1792-1799.

[43] 毛湘冰.亮氨酸與瘦素協(xié)同調(diào)節(jié)生長(zhǎng)鼠骨骼肌蛋白質(zhì)代謝的研究[D].博士學(xué)位論文.北京:中國(guó)農(nóng)業(yè)大學(xué),2010.

[44] MATSUZAKI K,KATO H,SAKAI R,et al.Transcriptomics and metabolomics of dietary leucine excess[J].The Journal of Nutrition,2005,135:1571S-1575S.

[45] EDMONDS M S,BAKER D H.Amino acid excesses for young pigs:effects of excess methionine,tryptophan,threonine or leucine[J].Journal of Animal Science,1987,64:1664-1671.

[46] ROPELLE E R,PAULI J R,FERNANDES M F A,et al.A central role for neuronal AMP-activated protein kinase(AMPK)and mammalian target of rapamycin(mTOR)in high-protein diet-induced weight loss[J].Diabetes,2008,57:594-605.