MANF/CDNF與神經(jīng)系統(tǒng)疾病

劉淼,王偉,喻志源

華中科技大學(xué)同濟(jì)醫(yī)學(xué)院附屬同濟(jì)醫(yī)院神經(jīng)科,武漢430030

1 概述

神經(jīng)營(yíng)養(yǎng)因子是一類小分子分泌蛋白,通過(guò)與相應(yīng)的受體結(jié)合,調(diào)節(jié)神經(jīng)細(xì)胞的生長(zhǎng)、發(fā)育、成熟與存活,尤其在調(diào)控神經(jīng)元的數(shù)量、突起的分支、突觸的形成和神經(jīng)細(xì)胞表型的成熟等發(fā)面發(fā)揮重要作用。神經(jīng)營(yíng)養(yǎng)因子還有促進(jìn)損傷后神經(jīng)元再生,治療慢性神經(jīng)系統(tǒng)疾病的功能[1-3]。中腦星形膠質(zhì)細(xì)胞源性神經(jīng)營(yíng)養(yǎng)因子(mesencephalic astrocyte-derived neurotrophic factor,MANF)是 Petrova等[4]于2003年首次在體外傳代培養(yǎng)的大鼠中腦Ⅰ型星形膠質(zhì)細(xì)胞的培養(yǎng)基中分離到的一種能促進(jìn)體外多巴胺神經(jīng)元存活的神經(jīng)營(yíng)養(yǎng)因子,分子量為18 kD,也被稱為ARMET(arginine rich,mutated in early stage of tumurs)或 ARP(arginine-rich protein)。脊椎動(dòng)物中存在的另一種神經(jīng)營(yíng)養(yǎng)因子保守型多巴胺神經(jīng)營(yíng)養(yǎng)因子(conserved dopamine neurotrophic factor,CDNF),是MANF的同類物[5],二者的同源性＞59%[6],都屬于含8個(gè)半胱氨酸殘基保守序列的蛋白家族[4,5,7]。

哺乳動(dòng)物的MANF/CDNF mRNA和蛋白廣泛表達(dá)于中樞神經(jīng)系統(tǒng)[5,8],在大腦皮質(zhì)、海馬及小腦浦肯野細(xì)胞中相對(duì)高表達(dá)[8];在肺、肌肉、睪丸和胃等一些組織中也有豐富的表達(dá)[5,8]。MANF/CDNF的基因在進(jìn)化上高度保守,從線蟲到人的各級(jí)動(dòng)物中均有表達(dá),是迄今在無(wú)脊椎動(dòng)物中發(fā)現(xiàn)的唯一一個(gè)神經(jīng)營(yíng)養(yǎng)因子家族[6]。但序列分析發(fā)現(xiàn)脊椎動(dòng)物中同時(shí)含CDNF和MANF 2種基因[5],無(wú)脊椎動(dòng)物中卻只含有1種與MANF更具相關(guān)性的同源基因[6]。MANF基因缺失的果蠅會(huì)因多巴胺神經(jīng)元的數(shù)量和多巴胺水平的減少而死亡,給予人源性的MANF可以發(fā)揮替代功能[6]。這也表明該神經(jīng)營(yíng)養(yǎng)因子在2種動(dòng)物中可能采用相同或相似的信號(hào)傳導(dǎo)機(jī)制來(lái)完成神經(jīng)營(yíng)養(yǎng)功能,而且在漫長(zhǎng)的生命進(jìn)化過(guò)程中這一功能不可替代。

2 MANF/CDNF的生物結(jié)構(gòu)特點(diǎn)

傳統(tǒng)的神經(jīng)營(yíng)養(yǎng)因子主要分為3個(gè)超家族[9,10]:①神經(jīng)營(yíng)養(yǎng)因子超家族:神經(jīng)生長(zhǎng)因子(nerve growth factor,NGF),腦源性神經(jīng)營(yíng)養(yǎng)因子(brain derived neurophic factor,BDNF),神經(jīng)營(yíng)養(yǎng)因子-3(neurotrophin-3,NT-3),神經(jīng)營(yíng)養(yǎng)因子-4/5/6/7(NT-4/5/6/7);②神經(jīng)生成細(xì)胞因子超家族:睫狀神經(jīng)營(yíng)養(yǎng)因子(ciliary neurotrophic factor,CNTF),白介素-6(interleukin-6,IL-6),心肌營(yíng)養(yǎng)因子-1(cardiotrophin-1,CT-1);③膠質(zhì)細(xì)胞源性神經(jīng)營(yíng)養(yǎng)因子超家族:膠質(zhì)細(xì)胞源性神經(jīng)營(yíng)養(yǎng)因子(glial cell line derived neurotrophic factor,GDNF),neurturin(NRTN),artemin(ARTN),persephin(PSPN)。但哺乳動(dòng)物中MANF/CDNF的蛋白結(jié)構(gòu)與以往任何一種神經(jīng)營(yíng)養(yǎng)因子相比都大不同,因此被列為一類新型的神經(jīng)營(yíng)養(yǎng)因子家族[9]。

最初的研究發(fā)現(xiàn)MANF基因的氨基末端是一段富含精氨酸的序列,該序列在多種腫瘤的早期存在單個(gè)核苷酸突變[7,11,12],因此被認(rèn)為與腫瘤的發(fā)生有關(guān)。而隨后的研究卻發(fā)現(xiàn),成熟的MANF上并未發(fā)現(xiàn)該段精氨酸富集區(qū)的表達(dá)[4,13],MANF基因中出現(xiàn)的這種突變非腫瘤所特有,而是屬于正?；虻亩鄳B(tài)性[14,15]。目前的研究表明,MANF/CDNF的結(jié)構(gòu)由2個(gè)區(qū)域組成[16]:氨基末端是疏水的saposin樣結(jié)構(gòu)域,其表面含有數(shù)個(gè)保守的精氨酸和賴氨酸殘基,帶有豐富的正電荷,可能與膜磷脂表面或脂質(zhì)受體的負(fù)電荷產(chǎn)生靜電作用[9,10,16,17],推測(cè)其與神經(jīng)營(yíng)養(yǎng)活性的發(fā)揮有關(guān);羧基末端是一個(gè)可溶性結(jié)構(gòu)[18],含有由8個(gè)保守的半胱氨酸殘基形成的4個(gè)二硫鍵[5],組成2個(gè)CXXC的模序結(jié)構(gòu)[18],這一結(jié)構(gòu)與胞內(nèi)催化二硫鍵形成的硫醇類氧化還原酶的結(jié)構(gòu)相類似[9],而且該末端的KDEL樣序列表明MANF/CDNF在內(nèi)質(zhì)網(wǎng)腔內(nèi)有表達(dá)[13,19,20],推測(cè)MANF/CDNF可能與內(nèi)質(zhì)網(wǎng)中蛋白質(zhì)的氧化折疊有關(guān)。MANF/CDNF是否有氧化還原活性有待進(jìn)一步研究證實(shí)。另外,MANF的羧基末端區(qū)域與Ku70的SAP結(jié)構(gòu)域同源,因此它可能是促凋亡蛋白Bax的另一個(gè)抑制因子[21]。

3 MANF/CDNF的生理功能

早在上世紀(jì)90年代,Omalley等[22]就發(fā)現(xiàn)體外培養(yǎng)的黑質(zhì)膠質(zhì)細(xì)胞能促進(jìn)多巴胺神經(jīng)元的存活,隨后在體外培養(yǎng)細(xì)胞的培養(yǎng)基中分離到MANF和CDNF[4,5],并證實(shí)它們能選擇性地保護(hù)多巴胺神經(jīng)元,而對(duì)5-羥色胺能 、γ-氨基丁酸(gamma-aminobutyric acid,GABA)能及周圍神經(jīng)元無(wú)影響[4,5]。又有研究顯示MANF與內(nèi)質(zhì)網(wǎng)膜和高爾基體膜蛋白均有共定位現(xiàn)象,用布雷菲德菌素A(Brefeldin A,BFA)阻斷內(nèi)質(zhì)網(wǎng)和高爾基體之間的蛋白運(yùn)輸,致使內(nèi)質(zhì)網(wǎng)中的該類蛋白增多而培養(yǎng)基中的量卻減少[19];隨后在MANF基因缺失的果蠅中觀察到多巴胺神經(jīng)元軸突的退變、多巴胺水平下降和幼蟲的死亡[6],這些證據(jù)支持MANF是一種多巴胺神經(jīng)元營(yíng)養(yǎng)因子。現(xiàn)在有學(xué)者認(rèn)為MANF/CDNF可能是膠質(zhì)細(xì)胞通過(guò)旁分泌的形式對(duì)其周圍的神經(jīng)元起營(yíng)養(yǎng)作用[5],但它發(fā)揮營(yíng)養(yǎng)神經(jīng)元功能的受體和下游機(jī)制目前還不清楚。

有研究證明實(shí)際上僅有很小一部分 MANF/CDNF被分泌到細(xì)胞外[19],在內(nèi)質(zhì)網(wǎng)腔內(nèi)它們也有豐富的表達(dá)[13,19,20],說(shuō)明MANF/CDNF不僅有營(yíng)養(yǎng)神經(jīng)細(xì)胞的作用,還參與細(xì)胞內(nèi)的其它生命過(guò)程。內(nèi)質(zhì)網(wǎng)是真核細(xì)胞的重要細(xì)胞器,與各種膜蛋白、分泌蛋白、磷脂、膽固醇等的代謝過(guò)程密切相關(guān)。在疾病或有害因素的影響下,內(nèi)質(zhì)網(wǎng)發(fā)生功能紊亂,導(dǎo)致內(nèi)質(zhì)網(wǎng)腔內(nèi)未折疊蛋白或錯(cuò)誤折疊蛋白的堆積等,即為內(nèi)質(zhì)網(wǎng)應(yīng)激。許多神經(jīng)系統(tǒng)疾病的早期都會(huì)發(fā)生內(nèi)質(zhì)網(wǎng)應(yīng)激,應(yīng)激信號(hào)能通過(guò)內(nèi)質(zhì)網(wǎng)膜傳遞到細(xì)胞核中,繼而引起未折疊蛋白反應(yīng)[23],處理異常蛋白的集聚,促使細(xì)胞存活[24];但長(zhǎng)時(shí)間的內(nèi)質(zhì)網(wǎng)應(yīng)激可引起細(xì)胞凋亡。越來(lái)越多的證據(jù)表明MANF是一種內(nèi)質(zhì)網(wǎng)應(yīng)激反應(yīng)蛋白[13,19,25,26],高表達(dá)MANF能增強(qiáng)細(xì)胞對(duì)無(wú)糖狀態(tài)和其它內(nèi)質(zhì)網(wǎng)應(yīng)激誘因的耐受性[19],而對(duì)MANF基因的體外 RNAi或者在體敲除可使細(xì)胞或有機(jī)體在內(nèi)質(zhì)網(wǎng)應(yīng)激時(shí)發(fā)生死亡[19]。因此,MANF上調(diào)可能是細(xì)胞在內(nèi)質(zhì)網(wǎng)應(yīng)激時(shí)的一種內(nèi)源性神經(jīng)保護(hù)機(jī)制的激活,其具體分子機(jī)制目前尚在研究中。Mizobuchi等[13]初步研究認(rèn)為內(nèi)質(zhì)網(wǎng)應(yīng)激是通過(guò)內(nèi)質(zhì)網(wǎng)應(yīng)激反應(yīng)元素Ⅱ來(lái)上調(diào)MANF的表達(dá)量,MANF可能通過(guò)降解錯(cuò)誤折疊蛋白、或處理未折疊蛋白、或調(diào)控內(nèi)質(zhì)網(wǎng)應(yīng)激感受器活性來(lái)參與未折疊蛋白反應(yīng)[19],改善細(xì)胞生理狀態(tài)。然而CDNF的表達(dá)量在內(nèi)質(zhì)網(wǎng)應(yīng)激時(shí)未發(fā)生明顯變化[19],推測(cè)它可能是內(nèi)質(zhì)網(wǎng)的結(jié)構(gòu)蛋白質(zhì)之一。

MANF/CDNF在胞外有神經(jīng)營(yíng)養(yǎng)因子活性,在胞內(nèi)參與內(nèi)質(zhì)網(wǎng)應(yīng)激反應(yīng)保護(hù)細(xì)胞,這兩種功能之間是否相互關(guān)聯(lián),還有待進(jìn)一步研究。

4 MANF/CDNF與神經(jīng)系統(tǒng)疾病

4.1 MANF/CDNF與帕金森病 帕金森病是一種神經(jīng)退行性疾病,對(duì)帕金森病的治療目前仍以藥物對(duì)癥治療為主,可改善患者的生活質(zhì)量,但并不能減慢或阻止疾病的進(jìn)展。促進(jìn)多巴胺神經(jīng)元存活或重建多巴胺能神經(jīng)系統(tǒng)正常功能的治療方法意義重大。某些神經(jīng)營(yíng)養(yǎng)因子在帕金森病患者黑質(zhì)中表達(dá)量不足[16,17],多種帕金森治療藥物也表現(xiàn)出調(diào)節(jié)神經(jīng)營(yíng)養(yǎng)因子的現(xiàn)象。許多神經(jīng)營(yíng)養(yǎng)因子在體外培養(yǎng)細(xì)胞中已顯示出多巴胺神經(jīng)元保護(hù)作用,目前在動(dòng)物模型中顯示出治療作用的神經(jīng)營(yíng)養(yǎng)因子并不多,包括 GDNF、BDNF、NRTN 和 MANF/CDNF等[10]。其中GDNF、NRTN已經(jīng)進(jìn)入臨床研究階段,但其 Ⅱ期臨床雙盲試驗(yàn)的有效率并不明顯[9,29,30]。應(yīng)用GDNF治療還出現(xiàn)血清反應(yīng)和小腦損傷等一系列嚴(yán)重的副反應(yīng)[29-31],使其臨床應(yīng)用價(jià)值受到質(zhì)疑。近年來(lái)研究證明,膠質(zhì)細(xì)胞中MANF/CDNF基因缺失會(huì)導(dǎo)致動(dòng)物體內(nèi)多巴胺神經(jīng)元缺失和多巴胺不足引起的一系列病理反應(yīng)[6]。在6-羥基多巴胺(6-hydroxydopamine,6-OHDA)誘導(dǎo)的大鼠帕金森模型中,通過(guò)紋狀體內(nèi)注射MANF/CDNF不但能保護(hù)中腦多巴胺神經(jīng)元和紋狀體多巴胺神經(jīng)纖維,而且能加強(qiáng)存活神經(jīng)元的功能、修復(fù)受損的黑質(zhì)-紋狀體多巴胺系統(tǒng)[5,9,32],減少帕金森大鼠的運(yùn)動(dòng)障礙,具有預(yù)防和治療的雙重潛在作用。與GDNF、NRTN相比,MANF/CDNF具有以下優(yōu)點(diǎn):對(duì)細(xì)胞外基質(zhì)親和力低[32,33],擴(kuò)散范圍較大;選擇性作用于多巴胺神經(jīng)元,對(duì)周圍運(yùn)動(dòng)、感覺(jué)神經(jīng)元和交感神經(jīng)元無(wú)影響[4,5],副作用小;在低、中藥物濃度時(shí)的選擇性較GDNF和BDNF高[4,9]。這些特點(diǎn)顯示出MANF/CDNF在帕金森病防治中較大的應(yīng)用前景。

4.2 MANF/CDNF與腦缺血損傷 神經(jīng)保護(hù)是治療缺血性腦血管的有效方法之一。腦缺血時(shí),神經(jīng)營(yíng)養(yǎng)因子能夠維持細(xì)胞內(nèi)環(huán)境的Ca2+和自由基代謝的穩(wěn)定,阻止因興奮毒性或過(guò)氧化所致皮質(zhì)或海馬的神經(jīng)元死亡或凋亡。MANF不僅存在于中腦多巴胺神經(jīng)元中,在大腦皮質(zhì)和海馬組織中也有豐富的表達(dá)[8];腦缺血會(huì)引起海馬和大腦皮質(zhì)MANF表達(dá)的變化[8,19,34]。一過(guò)性或永久性腦缺血會(huì)引起異常蛋白在內(nèi)質(zhì)網(wǎng)內(nèi)的積聚[35],發(fā)生內(nèi)質(zhì)網(wǎng)應(yīng)激,激活未折疊蛋白反應(yīng),上調(diào)神經(jīng)元中MANF/CDNF的表達(dá)量[8,19],并增強(qiáng)其免疫活性[19],可減少缺血區(qū)神經(jīng)元的過(guò)多凋亡和壞死[36]。MANF預(yù)處理可以減小腦缺血大鼠梗死灶的體積,有利于行為學(xué)功能的恢復(fù)[36],這可能和缺血灶中反應(yīng)性增生的膠質(zhì)細(xì)胞減少有關(guān),此假說(shuō)與MANF抑制體外培養(yǎng)細(xì)胞的增殖相一致[19]。另外,腦缺血后MANF的表達(dá)在神經(jīng)元和膠質(zhì)細(xì)胞中發(fā)生重新分布,推測(cè)可能和MANF神經(jīng)營(yíng)養(yǎng)功能有關(guān)。CDNF在動(dòng)物腦缺血后有無(wú)保護(hù)作用還在研究中。

4.3 其他 MANF/CDNF在其它神經(jīng)系統(tǒng)疾病中的研究較少。Lindholm等[8]利用電刺激誘導(dǎo)小鼠癲癇持續(xù)狀態(tài)后,會(huì)引起海馬顆粒細(xì)胞層、丘腦網(wǎng)狀核和大腦皮質(zhì)某些區(qū)域的MANF mRNA表達(dá)一過(guò)性增高,提示MANF與癲癇發(fā)生、發(fā)展或恢復(fù)存在某些聯(lián)系。

5 前景展望

哺乳動(dòng)物的MANF/CDNF表達(dá)范圍廣泛,基因進(jìn)化保守,在多種腦損傷后其表達(dá)量與蛋白分布均受到不同程度的調(diào)節(jié)[8,32,36],提示其在生理和病理狀態(tài)下都發(fā)揮重要作用。MANF/CDNF作為一類分泌蛋白,在內(nèi)質(zhì)網(wǎng)應(yīng)激時(shí)表達(dá)上調(diào),該特點(diǎn)可使其作為亞健康狀態(tài)或疾病早期的一個(gè)預(yù)警信號(hào)。MANF/CDNF不僅以胞外分泌的形式起到營(yíng)養(yǎng)神經(jīng)元的功能,在胞內(nèi)也發(fā)揮著普遍的細(xì)胞保護(hù)作用;又由于這類神經(jīng)營(yíng)養(yǎng)因子與以往神經(jīng)營(yíng)養(yǎng)因子的結(jié)構(gòu)大不相同,可能是通過(guò)一種新的信號(hào)途徑來(lái)起作用[21],因此對(duì)其深入研究可能為臨床神經(jīng)系統(tǒng)疾病的綜合治療提供支持。

[1]Evans JR,Barker RA.Neurotrophic factors as a therapeutic target for Parkinson's disease[J].Expert Opin Ther Targets,2008,12(4):437-447.

[2]Huang EJ,Reichardt LF.Neurotrophins:Roles in neuronal development and function[J].Annu Rev Neurosci,2001,24:677-736.

[3]Airaksinen MS,Saarma M.The GDNF family:Signalling,biological functions and therapeutic value[J].Nat Rev Neurosci,2002,3(5):383-394.

[4]Petrova P,Raibekas A,Pevsner J,et al.MANF:a new mesencephalic,astrocyte-derived neurotrophic factor with selectivity for dopaminergic neurons[J].J Mol Neurosci,2003,20(2):173-188.

[5]Lindholm P,Voutilainen MH,Lauren J,et al.Novel neurotrophic factor CDNF protects and rescues midbrain dopamine neurons in vivo[J].Nature,2007,448(7149):73-77.

[6]Palgi M,Lindstrom R,Peranen J,et al.Evidence that DmMANF is an invertebrate neurotrophic factor supporting dopaminergic neurons[J].PNAS,2009,106(7):2429-2434.

[7]Shridhar V,Rivard S,Shridhar R.A gene from human chromosomal band 3p21.1 encodes a highly conserved arginine-rich protein and is mutated in renal cell carcinomas[J].Oncogene,1996,12(9):1931-1939.

[8]Lindholm P,Peranen J,Andressoo JO,et al.M ANF is widely expressed in mammalian tissues and differently regulated after ischemic and epileptic insults in rodent brain[J].Mol Cell Neurosci,2008,39(3):356-371.

[9]Lindholm P,Saarma M.Novel CDNF/MANF Family of Neurotrophic Factors[J].Dev Neurobiol,2010,70(5):360-371.

[10]Parkash V.Neurotrophic factors and their receptors[M].Helsinki:Helsinki University press,2009.

[11]Shridhar R,Shridhar V,Rivard S,et al.Mutations in the arginine-rich protein gene,in lung,breast,and prostate cancers,and in squamous cell carcinoma of the head and neck[J].Cancer Res,1996,56(24):5576-5578.

[12]Shridhar V,Rivard S,Wang XH,et al.Mutations in the arginine-rich protein gene(ARP)in pancreatic cancer[J].Oncogene,1997,14(18):2213-2216.

[13]Mizobuchi N,Hoseki J,Kubota H,et al.A RM ET is a soluble ER protein induced by the unfolded protein response via ERSE-II element[J].Cell Struct Funct,2007,32(1):41-50.

[14]Evron E,Cairns P,Halachmi N,et a1.Normal poly-morphism in the incomplete trinucleotide repeat of the arginine-rich protein gene[J].Cancer Res,1997,57(14):2888-2889.

[15]Tanaka H,Shimada Y,Harada H,et al.Polymorphic variation of the ARP gene on 3p21 in Japanese esophageal cancer patients[J].Oncology Rep,2000,7(3):591-593.

[16]Parkash V,Lindholm P,Peranen J,et al.The structure of the conserved neurotrophic factors MANF and CDNF explains why they are bifunctional[J].Protein Eng Des Sel,2009,22(4):233-241.

[17]Bruhn H.A short guided tour through functional and structural features of saposin-like proteins[J].Biochem J,2005,389:249-257.

[18]Hoseki J,Sasakawa H,Yamaguchi Y,et al.Solution structure and dynamics of mouse ARMET[J].FEBS Lett,2010,584(8):1536-1542.

[19]Apostolou A,Shen Y,Liang Y,et al.Armet,a UPR-upregulated protein,inhibits cell proliferation and ER stress-induced cell death[J].Exp Cell Res,2008,314(13):2454-2467.

[20]Raykhel I,Alanen H,Salo K,et al.A molecular specificity code for the three mammalian KDEL receptors[J].J Cell Biol,2007,179(6):1193-1204.

[21]Hellman M,Arumae U,Yu LY,et al.Mesencephalic Astrocyte-derived Neurotrophic Factor(MANF)Has a Unique Mechanism to Rescue Apoptotic Neurons[J].J Biol Chem,2011,286(4):2675-2680.

[22]Omalley EK,Sieber BA,Black IB,et al.Mesencephalic type I astrocytes mediate the survival of substantia nigra dopaminergic neurons in culture[J].Brain Res,1992,582(1):65-70.

[23]Marciniak SJ,Ron D.Endoplasmic reticulum stress signaling in disease[J].Physiol Rev,2006,86(4):1133-1149.

[24]Szegezdi E,Logue SE,Gorman AM,et al.M ediators of endoplasmic reticulum stress-induced apoptosis[J].EMBO Rep,2006,7(9):880-885.

[25]Lee AH,Iwakoshi NN,Glimcher LH.XBP-1 regulates a subset of endoplasmic reticulum resident chaperone genes in the unfolded protein response[J].Mol Cell Biol,2003,23(21):7448-7459.

[26]Tadimalla A,Belmont PJ,Thuerauf DJ.Mesencephalic astrocyte-derived neurotrophic factor is an ischemiainducible secreted endoplasmic reticulum stress response protein in the heart[J].Circ Res,2008,103(11):1249-1258.

[27]Mogi M,Togari A,Kondo T,et al.Brain-derived growth factor and nerve growth factor concentrations are decreased in the substantia nigra in Parkinson's disease[J].Neurosci Lett,1999,270(1):45-48.

[28]Chauhan NB,Siegel GJ,Lee JM.Depletion of glial cell line-derived neurotrophic factorin substantia nigra neurons of Parkinson's disease brain[J].J Chem Neuroanat,2001,21(4):277-288.

[29]Lang AE,Gill S,Patel NK,et al.Randomized controlled trial of intraputamenal glial cell line-derived neurotrophic factor infusion in Parkinson disease[J].Ann Neurol,2006,59(3):459-466.

[30]Peterson AL,Nutt JG.Treatment of Parkinson's disease with trophic factors[J].Neurotherapeutics,2008,5(2):270-280.

[31]Hovland DN Jr,Boyd RB,Butt MT,et al.Six-month continuous intraputamenal infusion toxicitystudy of recombinant methionyl human glial cell line-derived neurotrophic factor(r-metHuGDNF)in rhesus monkeys[J].Toxicol Pathol,2007,35(7):1013-1029.

[32]Voutilainen MH,Back S,Porsti E,et al.Mesencephalic astrocyte-derived neurotrophic factor is neurorestorative in rat model of Parkinson's disease[J].J Neurosci,2009,29(30):9651-9659.

[33]Bespalov M M,Saarma M.GDNF family receptor complexes are emerging drug targets[J].Trends Pharmacol Sci,2007,28(2):68-74.

[34]Yu YQ,Liu LC,Wang FC,et al.Induction profile of MANF/ARM ET by cerebral ischemia and its implication for neuron protection[J].J Cereb Blood Flow Metab,2010,30(1):79-91.

[35]DeGracia DJ,Montie HL.Cerebral ischemia and the unfolded protein response[J].J Neurochem,2004,91(1):1-8.

[36]Airavaara M,Shen H,Kuo CC,et al.Mesencephalic astrocyte-derived neurotrophic factor reduces ischemic brain injury and promotes behavioral recovery in rats[J].J Comp Neurol,2009,515(1):116-124.