楊風(fēng)英 劉效磊 牛燕媚 傅力
1 天津醫(yī)科大學(xué)康復(fù)與運(yùn)動(dòng)醫(yī)學(xué)系(天津 300070)
2 天津體育學(xué)院研究生部
人口統(tǒng)計(jì)學(xué)研究顯示,到2050年,全世界60歲以上人口數(shù)量將達(dá)到20億,比2000年增長(zhǎng)逾3倍[1]。老齡人口的增多使與衰老相關(guān)疾病的發(fā)病率隨之增加,給社會(huì)經(jīng)濟(jì)和醫(yī)療等方面帶來(lái)沉重負(fù)擔(dān),因此對(duì)衰老及其相關(guān)疾病的研究越來(lái)越為人們所關(guān)注。目前,關(guān)于衰老過(guò)程調(diào)控的具體機(jī)制尚不明了,但可以確定的是,衰老的進(jìn)程不是由單一因素所調(diào)控,而是受遺傳和環(huán)境因素的共同影響。流行病學(xué)調(diào)查顯示,長(zhǎng)期高能量膳食以及缺乏適當(dāng)運(yùn)動(dòng)等不良生活習(xí)慣是肥胖、冠心病、2型糖尿病以及癌癥等與衰老密切相關(guān)疾病的重要誘發(fā)因素[2-4]。哺乳動(dòng)物雷帕霉素靶蛋白(Mammalian Target of Rapamycin,mTOR)是機(jī)體細(xì)胞內(nèi)的一種絲/蘇氨酸蛋白激酶,能夠感受細(xì)胞外營(yíng)養(yǎng)、能量水平以及生長(zhǎng)因子等信號(hào)變化,并通過(guò)調(diào)控下游相應(yīng)效應(yīng)蛋白,參與調(diào)節(jié)細(xì)胞生長(zhǎng)、分化、增殖以及蛋白質(zhì)合成等過(guò)程[5]。近年來(lái)研究表明,mTOR在機(jī)體細(xì)胞內(nèi)的異常表達(dá)可以引起癌癥、神經(jīng)退行性變以及代謝性相關(guān)疾病等,并且也與衰老過(guò)程密切相關(guān)[2-4]。研究顯示,飲食限制(Dietary Restriction,DR)以及適當(dāng)?shù)倪\(yùn)動(dòng)均能夠減少機(jī)體的能量供應(yīng),進(jìn)而使機(jī)體通過(guò)調(diào)控能量敏感性相關(guān)信號(hào)通路的活性延緩衰老及預(yù)防衰老相關(guān)疾病的發(fā)生[1,6,7]。本文歸納和總結(jié)了有氧運(yùn)動(dòng)及DR對(duì)mTOR信號(hào)通路的影響機(jī)制及其與衰老關(guān)系的研究現(xiàn)狀,提出亟需解決的問(wèn)題,為進(jìn)一步深入研究指出方向。
mTOR分子量為300 kDa,屬于磷脂酰肌醇激酶相關(guān)蛋白激酶家族。作為細(xì)胞內(nèi)高度保守的營(yíng)養(yǎng)狀態(tài)以及能量水平感受器,mTOR活性受細(xì)胞生長(zhǎng)因子、營(yíng)養(yǎng)素以及能量敏感相關(guān)信號(hào)通路的調(diào)節(jié),并通過(guò)其下游效應(yīng)蛋白如S6K1(Ribosomal Protein S6 Kinase,Polypeptide 1)以及4E-BP1(Eukaryotic Initiation Factor eIF4E Binding Protein 1)參與調(diào)節(jié)細(xì)胞生長(zhǎng)、分化、增殖以及蛋白合成等生物過(guò)程[7,8]。研究表明,能量過(guò)剩導(dǎo)致的mTOR過(guò)度激活可引起S6K1 Thr421/Ser424位點(diǎn)磷酸化活性增加,進(jìn)而提高胰島素受體底物1(Insulin Receptor Substrate 1,IRS-1)Ser636/639位點(diǎn)磷酸化水平,產(chǎn)生抑制胰島素信號(hào)轉(zhuǎn)導(dǎo)的效應(yīng)[9]。因而,S6K1不僅可以通過(guò)mTOR 接受其上游營(yíng)養(yǎng)、能量、生長(zhǎng)因子等信號(hào)通路的調(diào)控,參與調(diào)節(jié)細(xì)胞蛋白質(zhì)合成,其本身還存在一種反饋調(diào)節(jié)機(jī)制,即通過(guò)影響細(xì)胞內(nèi)胰島素的信號(hào)轉(zhuǎn)導(dǎo),參與調(diào)節(jié)細(xì)胞糖、脂以及能量代謝過(guò)程。另外,當(dāng)mTOR/S6K1信號(hào)通路的活性過(guò)高時(shí)還能導(dǎo)致過(guò)氧化物酶體增殖物激活受體輔激活因子1-(Peroxisome Proliferator-Activated Receptor-Coactivator 1,PGC-1)活性下降,從而引起細(xì)胞線粒體功能紊亂、能源物質(zhì)氧化代謝功能下降,進(jìn)而誘發(fā)肥胖以及胰島素抵抗(Insulin Resistance,IR)[10]。由此可見(jiàn),mTOR在細(xì)胞中主要發(fā)揮兩方面作用:一方面,作為營(yíng)養(yǎng)素、能量狀態(tài)的感受器參與調(diào)節(jié)細(xì)胞糖、脂等能量代謝;另一方面,促進(jìn)mRNA的翻譯,進(jìn)而促進(jìn)蛋白質(zhì)合成。
除此之外,mTOR信號(hào)通路還與衰老過(guò)程關(guān)系密切[11]。在以酵母、線蟲(chóng)以及果蠅等無(wú)脊椎生物為模型的研究中發(fā)現(xiàn),TOR可促進(jìn) mRNA 翻譯和細(xì)胞產(chǎn)生溶酶體小泡,這兩者均與衰老過(guò)程具有潛在的聯(lián)系[12]。無(wú)論采用基因工程手段還是藥物干預(yù),對(duì)于TOR信號(hào)通路相關(guān)因子,如S6K1、翻譯起始因子、核糖體蛋白等的抑制均可以延長(zhǎng)機(jī)體壽命[13-15]。近期研究表明,哺乳動(dòng)物mTOR信號(hào)通路活性與其壽命同樣密切相關(guān),并且發(fā)現(xiàn)當(dāng)使用mTOR抑制劑——雷帕霉素(Rapamycin) 以后,小鼠平均及最長(zhǎng)壽命均顯著延長(zhǎng)[16,17]。Selman等人的研究發(fā)現(xiàn),相對(duì)于野生型小鼠,S6K1基因敲除小鼠平均壽命延長(zhǎng)了80天,并且最長(zhǎng)壽命也顯著提高[18]。以上證據(jù)都支持mTOR及其下游效應(yīng)蛋白活性與機(jī)體衰老過(guò)程的調(diào)控具有密切關(guān)系。但是目前關(guān)于mTOR參與衰老過(guò)程調(diào)控的具體機(jī)制尚不明確。由于mTOR與機(jī)體腫瘤、神經(jīng)退行性變、代謝及各種心腦血管疾病等之間存在的密切聯(lián)系[4-6],我們推測(cè)通過(guò)mTOR信號(hào)通路而延緩衰老的效用可能是通過(guò)改善各種與衰老相關(guān)疾病的進(jìn)程而實(shí)現(xiàn)的。
DR在大量動(dòng)物模型的研究中被認(rèn)為是延長(zhǎng)平均及最長(zhǎng)壽命最有效的干預(yù)手段,并且DR還可有效抑制衰老相關(guān)疾病的發(fā)生[2,3,19]。Colman[20]等人最近研究表明,DR顯著延緩了靈長(zhǎng)類動(dòng)物恒河猴的衰老過(guò)程,并且降低了糖尿病、癌癥、各種心血管疾病等與衰老密切相關(guān)疾病的發(fā)病率。DR降低了機(jī)體能量供應(yīng),因而機(jī)體可能通過(guò)調(diào)節(jié)能量信號(hào)通路來(lái)影響衰老及其相關(guān)疾病的變化。胰島素信號(hào)通路是細(xì)胞感受并調(diào)節(jié)能量代謝的重要途徑[5,8,9]。研究表明,敲除胰島素樣生長(zhǎng)因子受體(IGF-1 Receptor,IGF-1R)基因的雜合子小鼠、脂肪組織胰島素受體(Insulin Receptor,IR)基因敲除小鼠、胰島素受體底物1(Insulin Receptor Substrate 1,IRS1)以及IRS2基因敲除小鼠模型的壽命均顯著長(zhǎng)于野生型對(duì)照組小鼠[21-23]。也有研究發(fā)現(xiàn),轉(zhuǎn)基因長(zhǎng)壽模型小鼠常常伴有局部組織(如脂肪組織、大腦等)或系統(tǒng)的輕微胰島素抵抗,并出現(xiàn)葡萄糖耐量降低現(xiàn)象[24]。因此,胰島素信號(hào)通路與衰老過(guò)程密切相關(guān)。一磷酸腺苷活化蛋白激酶(AMP-activated Protein Kinase,AMPK)是另一個(gè)細(xì)胞內(nèi)高度保守的能量狀態(tài)感受器,AMPK 是異源三聚體蛋白激酶,由一個(gè)催化亞基()和兩個(gè)調(diào)節(jié)亞基(和)構(gòu)成,可以在細(xì)胞高AMP狀態(tài)時(shí)被激活[25],因而也可能是參與DR延緩衰老的重要介導(dǎo)信號(hào)分子。研究表明,AMPK催化亞基AAK-2基因敲除線蟲(chóng)相對(duì)野生型壽命縮短12%,而其過(guò)表達(dá)轉(zhuǎn)基因生物模型壽命則顯著延長(zhǎng)[26]。Greer[27]等人的研究發(fā)現(xiàn),DR顯著延長(zhǎng)了線蟲(chóng)壽命,而對(duì)AAK-2基因敲除線蟲(chóng)的壽命則沒(méi)有顯著影響。由此可見(jiàn),AMPK在DR延緩衰老過(guò)程中發(fā)揮著重要作用。
衰老不僅受機(jī)體代謝相關(guān)途徑的影響,而且與細(xì)胞蛋白質(zhì)合成過(guò)程密切相關(guān)。研究表明,通過(guò)對(duì)轉(zhuǎn)錄起始因子、核糖體蛋白的抑制可顯著延長(zhǎng)線蟲(chóng)的壽命[14,15,28,29],因而推測(cè),與蛋白質(zhì)合成以及代謝密切相關(guān)的mTOR信號(hào)通路可能在機(jī)體衰老過(guò)程中起關(guān)鍵調(diào)節(jié)作用。胰島素以及AMPK信號(hào)通路都是mTOR重要的上游調(diào)節(jié)通路。在基礎(chǔ)狀態(tài)下,胰島素以及生長(zhǎng)因子等通過(guò)調(diào)節(jié)mTOR活性而促進(jìn)蛋白質(zhì)合成;而在 DR 或能量供應(yīng)不足時(shí),AMPK的激活又可以通過(guò)抑制mTOR活性,減少蛋白質(zhì)合成,從而使機(jī)體主要生命活動(dòng)由生長(zhǎng)轉(zhuǎn)向維持,以維持機(jī)體內(nèi)環(huán)境能量穩(wěn)態(tài)[30]。另外的研究發(fā)現(xiàn),S6K1基因敲除小鼠肌細(xì)胞AMPK活性顯著升高[31],并且S6K1基因敲除長(zhǎng)壽小鼠與服用AMPK激活劑——AICAR小鼠的基因表達(dá)譜具有極高相似性[18]。
由此可見(jiàn),長(zhǎng)期DR可以通過(guò)作用于胰島素以及AMPK信號(hào)通路抑制mTOR信號(hào)通路的活性,而在各種動(dòng)物模型的研究中已經(jīng)證實(shí),mTOR活性下降可以明顯延緩衰老[16-18]。因而進(jìn)一步證明,mTOR信號(hào)通路可能在DR延緩機(jī)體衰老過(guò)程中發(fā)揮著核心作用。
能量過(guò)剩及缺乏適當(dāng)運(yùn)動(dòng)被認(rèn)為是肥胖、冠心病、2型糖尿病以及癌癥等與衰老密切相關(guān)疾病的重要誘發(fā)因素[19]。DR已被廣泛證實(shí)可以通過(guò)作用于mTOR信號(hào)通路而顯著延緩衰老,大量研究證實(shí)運(yùn)動(dòng)也可以抑制mTOR信號(hào)通路的活性[32],但對(duì)于運(yùn)動(dòng)在延緩衰老方面的作用效果則頗具爭(zhēng)議。Holloszy等人研究認(rèn)為,長(zhǎng)期有氧運(yùn)動(dòng)對(duì)大鼠的最長(zhǎng)壽命無(wú)影響,但顯著延長(zhǎng)了其平均壽命,并且降低了與衰老相關(guān)疾病的發(fā)病率[33,34]。但Craig等人研究顯示,運(yùn)動(dòng)雖然使大鼠體脂含量明顯下降,但對(duì)其壽命并無(wú)明顯影響[35]。
mTOR是機(jī)體細(xì)胞內(nèi)相對(duì)保守的能量狀態(tài)感受器,其在細(xì)胞能量供應(yīng)不足狀態(tài)下,通過(guò)抑制其下游4E-BP1和S6K1活性而抑制細(xì)胞蛋白質(zhì)合成,從而維持細(xì)胞內(nèi)能量穩(wěn)態(tài)[8]。AMPK是 mTOR信號(hào)通路重要的上游調(diào)節(jié)因子,運(yùn)動(dòng)時(shí)細(xì)胞內(nèi)AMP/ADP明顯升高,AMPK被激活進(jìn)而抑制mTOR信號(hào)通路的活性[7,25,36]。此外,研究發(fā)現(xiàn),運(yùn)動(dòng)可使小鼠骨骼肌AMPK基因表達(dá)及其Thr172位點(diǎn)磷酸化增加,進(jìn)而通過(guò)磷酸化mTOR Thr2446位點(diǎn)或磷酸化mTOR 結(jié)合蛋白R(shí)aptor的Ser722/792位點(diǎn)抑制mTOR/S6K1 信號(hào)通路的活性[32,37-39]。Yaspelkis等人的研究還發(fā)現(xiàn),高脂飲食使得mTOR活性顯著增強(qiáng),而有氧運(yùn)動(dòng)則完全逆轉(zhuǎn)了這一趨勢(shì)[40,41]。我們的前期研究也發(fā)現(xiàn),6周有氧運(yùn)動(dòng)顯著降低了胰島素抵抗小鼠mTOR、S6K1 mRNA及蛋白表達(dá)水平,并且S6K1 Thr38位點(diǎn)磷酸化水平也顯著降低[32,42]。
由此可見(jiàn),mTOR也是一條運(yùn)動(dòng)敏感型通路,有氧運(yùn)動(dòng)對(duì)mTOR 信號(hào)轉(zhuǎn)導(dǎo)起著負(fù)向調(diào)控作用。目前研究表明,mTOR信號(hào)通路在機(jī)體衰老過(guò)程中發(fā)揮核心作用[11-18],而有氧運(yùn)動(dòng)則可以抑制 mTOR活性[32-41],這提示有氧運(yùn)動(dòng)可能通過(guò)抑制mTOR活性而在一定程度上起到延緩衰老的作用,但這一研究假設(shè)還需要進(jìn)一步實(shí)驗(yàn)來(lái)證實(shí)。
越來(lái)越多的證據(jù)表明,mTOR信號(hào)通路在機(jī)體衰老調(diào)控過(guò)程中起著核心作用,并已證實(shí)對(duì)mTOR信號(hào)活性的抑制可以有效延緩衰老。而mTOR作為細(xì)胞內(nèi)能量狀態(tài)重要的感受器,對(duì)機(jī)體的營(yíng)養(yǎng)狀態(tài)以及運(yùn)動(dòng)刺激非常敏感,因而其將成為研究限食與有氧運(yùn)動(dòng)延緩衰老的重要介導(dǎo)通路。對(duì)于限食及有氧運(yùn)動(dòng)與衰老以及mTOR信號(hào)轉(zhuǎn)導(dǎo)通路相互關(guān)系的深入研究,不僅有助于我們對(duì)機(jī)體生命衰老機(jī)制的全面理解,還將為采用合理飲食和運(yùn)動(dòng)手段促進(jìn)健康、延緩衰老提供寶貴的理論依據(jù)。
[1]KoopmanR,van Loon LJ. Aging,exercise,and muscle protein metabolism. J Appl Physiol,2009,106(6):2040-8.
[2]Spilman P,Podlutskaya N,Hart M,et al. Inhibition of mTOR by rapamycin abolishes cognitive de ficits and reduces amyloid-levels in a mouse model of Alzheimer's disease. PLoS One,2010,5(4):e9979.
[3]Wagner AJ,Malinowska-Kolodziej I,Morgan JA,et al. Clinical activity of mTOR inhibition with sirolimus in malignant perivascular epithelioid cell tumors:targeting the pathogenic activation of mTORC1 in tumors. J Clin Oncol,2010,28(5):835-40.
[4]Düvel K,Yecies JL,Menon S,et al. Activation of a metabolic gene regulatory network downstream of mTOR complex 1. Mol Cell,2010,39(2):171-83.
[5]劉曉磊,牛燕媚,傅力. mTOR/S6K1信號(hào)通路研究進(jìn)展. 中國(guó)運(yùn)動(dòng)醫(yī)學(xué)雜志,2010,29(1):118-121.
[6]Rockenfeller P,Madeo F,Ageing and eating. Biochim Biophys Acta,2010,1803(4):499-506.
[7]Masoro EJ. Overview of caloric restriction and ageing.Mech Ageing Dev,2005,126(9):913-22.
[8]Zid BM,Rogers AN,Katewa SD,et al. 4E-BP extends lifespan upon dietary restriction by enhancing mitochondrial activity in drosophila. Cell,2009,139(1):149-60.
[9]Khamzina L,Veilleux A,Marette A,et al. Increased acitivation of the mammalian target of rapamycin pathway in liver and skeletal muscle of obese rats:possible involvement in obesity-linked insulin resistance. Endocrinology,2005,146(3):1473-81.
[10]Atherton PJ,Babraj J,Smith K,et al. Selective activation of AMPK-PGC-1alpha or PKB-TSC2-mTOR signaling can explain speci fic adaptive responses to endurance or resistance training-like electrical muscle stimulation.FASEB J,2005,19(7):786-8.
[11]Sharp ZD,Strong R. The role of mTOR signaling in controlling mammalian life span:what a fungicide teaches us about longevity. J Gerontol A Biol Sci Med Sci,2010,65(6):580-9.
[12]Kaeberlein M,Kennedy BK. A midlife longevity drug?Nature,2010,460(16):331-332.
[13]Powers RW,Kaeberlein M,Caldwell SD,et al.Extension of chronological life span in yeast by decreased TOR pathway signaling. Genes Dev,2006,20(2):174-84.
[14]Stanfel MN,Shamieh LS,Kaeberlein M,et al. The TOR pathway comes of age. Biochim Biophys Acta,2009,1790(10):1067-74.
[15]Kaeberlein M. Lessons on longevity from budding yeast.Nature,2010,464(7288):513-9.
[16]Harrison DE,Strong R,Sharp ZD,et al. Rapamycin fed late in life extends lifespan in genetically heterogeneous mice. Nature,2009,460(7253):392-5.
[17]Kaeberlein M. Resveratrol and rapamycin:are they antiaging drugs? Bioessays,2010,32(2):96-9.
[18]Selman C,Tullet JM,Wieser D,et al. Ribosomal protein S6 kinase 1 signaling regulates mammalian life span.Science,2009,326(5949):140-4.
[19]Fontana L,Klein S,Holloszy JO. Effects of long-term calorie restriction and endurance exercise on glucose tolerance,insulin action,and adipokine production. Age(Dordr),2010,31(1):97-108.
[20]Colman RJ,Anderson RM,Johnson SC,et al. Caloric restriction delays disease onset and mortality in rhesus monkeys. Science,2009,325(5937):201-4.
[21]Bluher M,Kahn BB,Kahn CR. Extended longevity in mice lacking the insulin receptor in adipose tissue. Science,2003,299(5606):572-4.
[22]Taguchi A,Wartschow LM,White MF. Brain IRS2 signaling coordinates life span and nutrient homeostasis.Science,2007,317(5836):369-72.
[23]Selman C,Lingard S,Choudhury AI,et al. Evidence for lifespan extension and delayed age-related biomarkers in insulin receptor substrate 1 null mice. FASEB J,2008,22(3):807-18.
[24]Chen YF,Wu CY,Kirby R,et al. A role for the CISD2 gene in lifespan control and human disease. Ann N Y Acad Sci,2010,1201(7):58-64.
[25]Cheung PC,Salt IP,Davies SP,et al. Characterization of AMP-activated protein kinase gamma-subunit isoforms and their role in AMP binding. Biochem J,2000,346(Pt 3):659-69.
[26]Apfeld J,O'Connor G,McDonagh T,et al. The AMP-activated protein kinase AAK-2 links energy levels and insulin-like signals to lifespan in C. elegans. Genes Dev,2004,18(24):3004-9.
[27]Greer EL,Dowlatshahi D,Banko MR,et al. An AMPK-FOXO pathway mediates longevity induced by a novel method of dietary restriction in C. elegans. Curr Biol,2007,17(19):1646-56.
[28]Pan KZ,Palter JE,Rogers AN,et al. Inhibition of mRNA translation extends lifespan in Caenorhabditis elegans. Aging Cell,2007,6(1):111-9.
[29]Syntichaki P,Troulinaki K,Tavernarakis N. eIF4E function in somatic cells modulates ageing in Caenorhabditis elegans. Nature,2007,445(7130):922-6.
[30]Onken B,Driscoll M. Metformin induces a dietary restriction-like state and the oxidative stress response to extend C. elegans Healthspan via AMPK,LKB1,and SKN-1. PLoS One,2010,5(1):e8758.
[31]Aguilar V,Alliouachene S,Sotiropoulos A,et al. S6 kinase deletion suppresses muscle growth adaptations tonutrient availability by activating AMP kinase. Cell Metab,2007,5(6):476-87.
[32]牛燕媚,苑虹,劉彥輝,等. 有氧運(yùn)動(dòng)和飲食干預(yù)對(duì)胰島素抵抗小鼠骨骼肌脂聯(lián)素—腺苷酸活化蛋白激酶信號(hào)系統(tǒng)的影響研究. 中國(guó)運(yùn)動(dòng)醫(yī)學(xué)雜志,2009,28(4):402-6.
[33]Holloszy JO. Exercise increases average longevity of female rats despite increased food intake and no growth retardation. J Gerontol,1993,48(3):B97-100.
[34]Lee IM,Paffenbarger RS Jr,Hennekens CH. Physical activity,physical fitness and longevity. Aging(Milano),1997,9(1-2):2-11.
[35]Craig BW,Garthwaite SM,Holloszy JO. Adipocyte insulin resistance:effects of aging,obesity,exercise,and food restriction. J Appl Physiol,1987,62(1):95-100.
[36]Matsakas A,Narkar VA. Endurance exercise mimetics in skeletal muscle. Curr Sports Med Rep,2010,9(4):227-32.
[37]Cheng SW,F(xiàn)ryer LG,Carling D,et al. Thr2446 is a novel mammalian target of rapamycin(mTOR) phosphorylation site regulated by nutrient status. J Biol Chem,2004,279(16):15719-22.
[38]Gwinn DM,Shackelford DB,Egan DF,et al. AMPK phosphorylation of raptor mediates a metabolic checkpoint. Mol Cell,2008,30(2):214-26.
[39]Pauli JR,Ropelle ER,Cintra DE,et al. Acute exercise reverses aged-induced impairments in insulin signaling in rodent skeletal muscle. Mech Ageing Dev,2010,131(5):323-9.
[40]Rivas DA,Yaspelkis BB 3rd,Hawley JA,et al. Lipidinduced mTOR activation in rat skeletalmuscle reversed by exercise and 5’-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside. J Endocrinol,2009,202(3):441-51.
[41]Yaspelkis Iii BB,Kvasha IA,Lessard SJ,et al. Aerobic training reverses high-fat diet-induced pro-in flammatory signalling in rat skeletal muscle. Eur J Appl Physiol,2010,110(4):779-88.
[42]苑紅,牛燕媚,劉彥輝,等. mTOR/S6K1信號(hào)通路與有氧運(yùn)動(dòng)改善小鼠高脂飲食誘導(dǎo)胰島素抵抗間的關(guān)系. 中國(guó)康復(fù)醫(yī)學(xué)雜志,2009,24(4):297-302.
中國(guó)運(yùn)動(dòng)醫(yī)學(xué)雜志2011年5期