神經(jīng)遞質(zhì)對(duì)神經(jīng)干細(xì)胞增殖的調(diào)控

陳四化 劉吉星 任海軍

(蘭州大學(xué)第二醫(yī)院神經(jīng)外科，甘肅 蘭州 730000)

·綜述·

神經(jīng)遞質(zhì)對(duì)神經(jīng)干細(xì)胞增殖的調(diào)控

陳四化 劉吉星 任海軍*

(蘭州大學(xué)第二醫(yī)院神經(jīng)外科，甘肅 蘭州 730000)

神經(jīng)遞質(zhì); 神經(jīng)干細(xì)胞; 增殖; 調(diào)控

一、引言

在過(guò)去的幾年中，許多研究報(bào)道了在成人中樞神經(jīng)系統(tǒng)中神經(jīng)干細(xì)胞(neural stem cells,NSCs)能夠分化成新的神經(jīng)元，即星形膠質(zhì)細(xì)胞和少突膠質(zhì)細(xì)胞。這一發(fā)現(xiàn)推翻了在出生后中樞神經(jīng)系統(tǒng)不能再生的中心假設(shè)，同時(shí)也為理解神經(jīng)分化的分子原理基礎(chǔ)以及神經(jīng)組織修復(fù)新療法的開(kāi)發(fā)奠定了基礎(chǔ)[1]。NSCs的增殖分化受細(xì)胞外環(huán)境信號(hào)和細(xì)胞內(nèi)基因有序表達(dá)的雙重控制。神經(jīng)遞質(zhì)作為細(xì)胞外環(huán)境信號(hào)中一員的，不僅介導(dǎo)神經(jīng)元之間、神經(jīng)元和效應(yīng)器之間的信息傳遞，還在調(diào)節(jié)成人神經(jīng)干細(xì)胞的增殖，分化和突觸融合，以及成人神經(jīng)發(fā)生中發(fā)揮重要作用[2]。本文旨對(duì)幾種重要的神經(jīng)遞質(zhì)對(duì)位于哺乳動(dòng)物大腦腦室下區(qū)(subventricular zone,SVZ)和顆粒下層(subgranular zone,SGZ)的前體細(xì)胞增殖的調(diào)控作一綜述。

二、神經(jīng)遞質(zhì)作用于SVZ和SGZ受體對(duì)神經(jīng)干細(xì)胞增殖調(diào)控

1.多巴胺(dopamine,DA)：DA是兒茶酚胺類物質(zhì)，由黑質(zhì)腹側(cè)被蓋區(qū)和下丘腦的神經(jīng)元合成。DA受體為G蛋白偶聯(lián)受體，分為D1樣和D2樣。D1樣受體激活腺苷酸環(huán)化酶，D2樣受體抑制腺苷酸環(huán)化酶。D1樣受體存在于細(xì)胞質(zhì)中而不是存在于短暫擴(kuò)增細(xì)胞和成纖維細(xì)胞膜上，D2樣受體主要在短暫擴(kuò)增細(xì)胞膜上表達(dá)，少量在SVZ星形膠質(zhì)細(xì)胞膜上表達(dá)。短暫擴(kuò)增細(xì)胞表達(dá)D3受體而神經(jīng)母細(xì)胞和SVZ的膠質(zhì)細(xì)胞卻不表達(dá)D3受體[3]。嚙齒類動(dòng)物中，通過(guò)注射的選擇性神經(jīng)毒素，如6-羥基多巴胺或1-甲基4-苯基-1,2,3,6-四氫吡啶消融中腦多巴胺神經(jīng)元，可以減少SVZ前體細(xì)胞的增殖和神經(jīng)發(fā)生[4]。然而，在另一研究中，DA受體拮抗劑氟哌啶醇給藥14 d導(dǎo)致SVZ神經(jīng)前體細(xì)胞數(shù)目的增加[5]。對(duì)于上述不同研究結(jié)果表明同樣的神經(jīng)遞質(zhì)可能對(duì)NSCs的增殖發(fā)揮相反的作用。這一作用可能是DA不同受體亞型的激活所介導(dǎo)。長(zhǎng)期激活DA受體可能會(huì)抑制NSCs的增殖，然而短期內(nèi)激活DA受體促進(jìn)NSCs的增殖。DA受體介導(dǎo)的調(diào)控NSCs增殖依賴于睫狀神經(jīng)營(yíng)養(yǎng)因子，而已知睫狀神經(jīng)營(yíng)養(yǎng)因子能夠促進(jìn)SVZ神經(jīng)干細(xì)胞的增殖[6]。最近的一項(xiàng)研究提出，激活的DA受體主要通過(guò)Akt和細(xì)胞外信號(hào)調(diào)節(jié)激酶1/2(extracellular signal-regulated kinase,ERK1/2)信號(hào)促進(jìn)NSCs增殖[7]。而其它的研究表明，激活的DA受體可以刺激表皮生長(zhǎng)因分泌從而促進(jìn)NSCs增殖[7]。

2.谷氨酸(glutamic acid,GAA)：在中樞神經(jīng)系統(tǒng)中，GAA是一種興奮性神經(jīng)遞質(zhì)，它有幾種不同的受體亞型：即離子型的N-甲基-D-天門冬氨(N-methyl-D-aspartate,NMDA)受體、(2-氨基-3-3-羥基-5-甲基-異惡唑-哌啶-4-基)丙酸[2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propanoic acid]，AMPA受體、紅藻氨酸 (kamate,KA) 受體以及代謝型谷氨酸受體(metabotropic glutamate receptor,mGluR)[8]。電生理和免疫組化研究顯示各種谷氨酸受體在成年側(cè)腦室的SVZ和齒狀回SGZ的神經(jīng)前體細(xì)胞中均有表達(dá)[9]。GAA無(wú)論作用于代謝型或離子型受體都為神經(jīng)前體細(xì)胞的動(dòng)員提供了重要信號(hào)[8]。已經(jīng)檢測(cè)到代謝型谷氨酸受體mGluR3、mGluR4和mGluR5在成年海馬神經(jīng)祖細(xì)胞上表達(dá)和mGluR5在放射狀膠質(zhì)細(xì)胞樣細(xì)胞上表達(dá)[9]。生理?xiàng)l件下，NMDA受體激動(dòng)劑抑制表達(dá)mGluR5的放射狀膠質(zhì)細(xì)胞樣細(xì)胞增殖[9]。而在腦損傷條件下，NMDA受體激動(dòng)劑促進(jìn)放射狀膠質(zhì)細(xì)胞樣細(xì)胞增殖[10]。NMDA受體通過(guò)抑制神經(jīng)膠質(zhì)細(xì)胞上游堿性環(huán)-螺旋-(basic-helix-loop-helix,bHLH)的Hes1基因和DNA結(jié)合抑制因子2(inhibitor of DNA binding 2,Id2 )的表達(dá)和促進(jìn)轉(zhuǎn)錄因子神經(jīng)源性分化(neurogenic differentiation,NeuroD)的表達(dá)誘導(dǎo)成年海馬祖細(xì)胞的增殖[10]。

在SVZ，體內(nèi)的放射狀膠質(zhì)細(xì)胞樣細(xì)胞或在短暫擴(kuò)充細(xì)胞上都尚未發(fā)現(xiàn)谷氨酸受體表達(dá)。Platel等已證實(shí)代謝型谷氨酸受體和KA受體在SVZ的神經(jīng)母細(xì)胞上表達(dá)[10]。在體外，谷氨酸促進(jìn)來(lái)源于SVZ神經(jīng)祖細(xì)胞的增殖[5]。在體內(nèi)敲除NMDA受體基因?qū)е律窠?jīng)母細(xì)胞凋亡，表明NMDA受體對(duì)神經(jīng)母細(xì)胞的存活至關(guān)重要[10]。紅藻氨酸受體GLUK5在腦室下區(qū)神經(jīng)母細(xì)胞的遷移過(guò)程中被完全激活，而這種激活降低神經(jīng)母細(xì)胞遷移速度[8]。眾所周知谷氨酸鹽信號(hào)通過(guò)介導(dǎo)神經(jīng)營(yíng)養(yǎng)因子，如腦源性神經(jīng)營(yíng)養(yǎng)因子，神經(jīng)生長(zhǎng)因子和成纖維細(xì)胞生長(zhǎng)因子的分泌促進(jìn)神經(jīng)干細(xì)胞增殖[2]。在成人大腦GAA介導(dǎo)祖細(xì)胞增殖調(diào)控的下游機(jī)制還沒(méi)有被廣泛研究。

3.γ-氨基丁酸(γ-aminobutyric acid,GABA)：GABA在成年脊椎動(dòng)物大腦內(nèi)是主要的抑制性神經(jīng)遞質(zhì)，它通過(guò)激活離子型配體門控GABAA、GABAB或GABAC受體和G蛋白偶聯(lián)受體發(fā)揮作用。研究發(fā)現(xiàn)，成年小鼠海馬神經(jīng)干細(xì)胞及其后代表達(dá)GABAB受體[11]。GABAB受體的藥物抑制刺激NSCs增殖和在體內(nèi)GABAB1受體亞基基因的缺失促進(jìn)NSCs增殖和神經(jīng)母細(xì)胞的分化[11]。Song等結(jié)合光遺傳學(xué)和克隆譜系跟蹤技術(shù)研究發(fā)現(xiàn)在齒狀回的GABA由表達(dá)小清蛋白的中間神經(jīng)元釋放和通過(guò)激活含γ2亞基-GABAA受體抑制靜態(tài)放射狀膠質(zhì)細(xì)胞樣細(xì)胞的活化[12]。

在成年SVZ，GABA由神經(jīng)母細(xì)胞以鈣依賴性非囊泡形式合成釋放，通過(guò)GABAA受體激活去極化神經(jīng)母細(xì)胞并抑制神經(jīng)母細(xì)胞增殖[13]。在成年SVZ激活GABAA受體誘導(dǎo)組蛋白H2AX的磷酸化，抑制細(xì)胞周期中DNA的合成，進(jìn)而發(fā)揮GABA對(duì)該區(qū)域的細(xì)胞周期的抑制效果[13]。Alfonso等[14]研究發(fā)現(xiàn)，在SVZ神經(jīng)母細(xì)胞表達(dá)能夠結(jié)合地西泮結(jié)合抑制劑的GABAA受體亞單位，抵消GABA釋放對(duì)神經(jīng)神經(jīng)干細(xì)胞的抑制作用。

4.5-羥色胺 (5-hydroxytryptamine,5-HT)：5-HT是SVZ的中縫核神經(jīng)元合成的單胺類物質(zhì)[5]。在腦室下區(qū)5-HT受體的表達(dá)模式仍存在爭(zhēng)議。Councill[15]等提出從SVZ組織的逆轉(zhuǎn)錄聚合酶鏈反應(yīng)表明5-HT受體，如5-HT1A，5-HT1B,5-HT1D,5-HT2A,5-HT2B,5-HT2C,5-HT3A和5-HT6在SVZ神經(jīng)元上廣泛表達(dá)，但是只有受體5-HT1A，5-HT2A和5-HT2C在腦室下區(qū)神經(jīng)元上表達(dá)文獻(xiàn)已報(bào)到。普遍認(rèn)為5-HT 對(duì)腦室下區(qū)神經(jīng)發(fā)生產(chǎn)生積極影響，因?yàn)樵隗w內(nèi)注射5-HT會(huì)促進(jìn)腦室下區(qū)神經(jīng)球產(chǎn)生.Tegenge等[16]通過(guò)特異性受體激動(dòng)劑急性或慢性激活5-HT受體5-HT1A和5-HT2發(fā)現(xiàn)腦室下區(qū)和嗅球5-溴脫氧尿嘧啶核苷(5-bromo-2-deoxyuridine,BrdU)標(biāo)記的神經(jīng)干細(xì)胞數(shù)量增多，而對(duì)神經(jīng)膠質(zhì)細(xì)胞和新生神經(jīng)元的比例沒(méi)有影響。然而，慢性激活5HT1A可能阻止新生神經(jīng)元向嗅球的遷移。

5.一氧化氮(nitric oxide,NO)：NO是一種非典型性神經(jīng)遞質(zhì)，它不被存儲(chǔ)在囊泡或通過(guò)胞吐作用釋放出來(lái)，而是在合成位置釋放，并通過(guò)擴(kuò)散穿透細(xì)胞膜進(jìn)入鄰近的細(xì)胞。在大腦中， NO是由三種不同的一氧化氮合酶 (nitric oxide synthases,NOSs)，神經(jīng)元一氧化氮合酶(neuronal NOS,nNOS)內(nèi)皮一氧化氮合酶(endothelial NOS,eNOS)和誘導(dǎo)型一氧化氮合酶(inducible NOS,iNOS)合成。nNOS是由靠近腦室下區(qū)和齒狀回的神經(jīng)元表達(dá)。在生理?xiàng)l件下， NO抑制神經(jīng)干細(xì)胞增殖，而在腦損傷條件下NO促進(jìn)神經(jīng)干細(xì)胞增殖[5]。在生理?xiàng)l件下，2個(gè)月小鼠腦室下區(qū)和齒狀回中缺乏功能性的nNOS促進(jìn)神經(jīng)干細(xì)胞增殖[17]。體外研究表明 NO通過(guò)作用于表皮生長(zhǎng)因子受體抑制神經(jīng)干細(xì)胞增殖[18]。Carreira等[19〗研究表明，在腦損傷條件下NO能先后激活兩條獨(dú)立的信號(hào)途徑細(xì)胞外信號(hào)調(diào)控激酶(extracellular signal -regulated kinase,EPK)/絲裂原活化蛋白激酶(mitogen-activated protein,MAPK)和鳥(niǎo)苷酸環(huán)化酶(guanylate cyclase,GC)/環(huán)磷酸鳥(niǎo)苷(cyclic guanosine monophosphate,cGMP)/cGMP依賴蛋白激酶G(cGMP-dependent protein kinase G,PKG)促進(jìn)神經(jīng)干細(xì)胞增殖。

6.乙酰膽堿(acetylcholine,Ach)：輸入到齒狀回的膽堿能來(lái)自內(nèi)側(cè)隔核。用離子型乙酰膽堿受體激動(dòng)劑煙堿長(zhǎng)期治療已經(jīng)顯示在齒狀回減少增殖[20]。在成人大腦膽堿能神經(jīng)元的消融導(dǎo)致顆粒下層區(qū)神經(jīng)干細(xì)胞增殖的減少，同時(shí)也損害空間記憶[21]。膽堿能藥物對(duì)SVZ和SGZ神經(jīng)干細(xì)胞增殖發(fā)揮不同的調(diào)節(jié)作用[22]。在顆粒下層區(qū)的放射狀膠質(zhì)細(xì)胞樣細(xì)胞和聚唾液酸-神經(jīng)細(xì)胞黏附分子陽(yáng)性細(xì)胞上毒蕈堿型乙酰膽堿受體表達(dá)已經(jīng)被確定[23]。給予乙酰膽堿藥10 d通過(guò)激活毒蕈堿M1受體促進(jìn)顆粒下層區(qū)神經(jīng)干細(xì)胞增殖，而通過(guò)激活煙堿受體發(fā)揮相反的作用。在嚙齒類動(dòng)物，功能性a4b2煙堿型膽堿能受體(nicotinic acetylcholine receptors,nAChR)通過(guò)促進(jìn)Math1基因的表達(dá)，決定神經(jīng)干細(xì)胞增殖和分化[23]。

三、總結(jié)與展望

神經(jīng)干細(xì)胞移植治療腦中風(fēng)已成為當(dāng)研究的熱點(diǎn)。移植后的神經(jīng)干細(xì)胞在一定條件下能夠分化成具有形態(tài)學(xué)和電生理特性的神經(jīng)元。神經(jīng)遞質(zhì)作為細(xì)胞外環(huán)境的一員參與調(diào)控神經(jīng)干細(xì)胞在體內(nèi)外的增殖和分化。深入研究神經(jīng)遞質(zhì)對(duì)腦室下區(qū)和顆粒下層區(qū)神經(jīng)干細(xì)胞增殖調(diào)控機(jī)制，為研究神經(jīng)遞質(zhì)和神經(jīng)遞質(zhì)受體藥理機(jī)制奠定了基礎(chǔ)。

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1671-2897(2016)15-558-03

國(guó)家自然科學(xué)基金資助項(xiàng)目(C030307)

陳四化，碩士，E-mail:354409914@qq.com

*通訊作者：任海軍，主任醫(yī)師，E-mail:baiyunguan@hotmail.com

R 651

A

2014-09-02；

2015-01-30)