溫芳芳, 徐 竹, 劉樂平, 楊建靜, 丁賽丹
(溫州醫(yī)科大學(xué)附屬第一醫(yī)院,浙江省神經(jīng)老化與疾病研究重點(diǎn)實(shí)驗(yàn)室, 浙江 溫州 325000)
多巴胺通過mTOR-EAAT2通路影響星形膠質(zhì)細(xì)胞谷氨酸攝取能力*
溫芳芳, 徐 竹, 劉樂平, 楊建靜, 丁賽丹△
(溫州醫(yī)科大學(xué)附屬第一醫(yī)院,浙江省神經(jīng)老化與疾病研究重點(diǎn)實(shí)驗(yàn)室, 浙江 溫州 325000)
目的研究多巴胺(dopamine,DA)對星形膠質(zhì)細(xì)胞谷氨酸(glutamate,Glu)攝取能力的影響,以及DA通過哺乳動物雷帕霉素靶蛋白(mTOR)-興奮性氨基酸轉(zhuǎn)運(yùn)體2(EAAT2)信號通路對星形膠質(zhì)細(xì)胞Glu攝取能力的影響。方法采用Amplex Red谷氨酸測定試劑盒檢測經(jīng)過干預(yù)的原代皮層星形膠質(zhì)細(xì)胞對Glu攝取含量的變化,RT-qPCR、Western blot和免疫熒光染色等檢測EAAT2和mTOR mRNA 和蛋白質(zhì)相對表達(dá)量,mTOR拮抗劑雷帕霉素或mTOR興奮劑MHY1485干預(yù)在DA中共培養(yǎng)的星形膠質(zhì)細(xì)胞,檢測mTOR和EAAT2的表達(dá)情況,以及培養(yǎng)上清液Glu的含量。結(jié)果DA干預(yù)的原代星形膠質(zhì)細(xì)胞中mTOR表達(dá)下調(diào),EAAT2表達(dá)下調(diào),培養(yǎng)上清液Glu水平上升;雷帕霉素干預(yù)后,EAAT2表達(dá)下調(diào),培養(yǎng)上清液中Glu的含量增加;MHY1485干預(yù)后,EAAT2表達(dá)上調(diào),培養(yǎng)上清液中Glu的含量下降。結(jié)論DA通過與星形膠質(zhì)細(xì)胞mTOR-EAAT2通路相互作用,減弱星形膠質(zhì)細(xì)胞攝取Glu的能力,引起細(xì)胞外Glu蓄積,最終損傷星形膠質(zhì)細(xì)胞的功能。
多巴胺; 谷氨酸; 星形膠質(zhì)細(xì)胞
多巴胺(dopamine,DA)是α、β腎上腺素受體和多巴胺受體的激動劑。谷氨酸(glutamate,Glu)是大腦內(nèi)主要的興奮性神經(jīng)遞質(zhì),在學(xué)習(xí)和記憶上有著重要作用。Glu是哺乳動物的中樞神經(jīng)系統(tǒng)中主要的興奮性神經(jīng)遞質(zhì),但是過度刺激Glu受體反而會造成興奮性中毒[1]。Glu中毒已知參與很多神經(jīng)系統(tǒng)疾病包括阿爾茨海默癥,缺血性腦卒,帕金森綜合征,癲癇癥和抑郁癥[2-4]。
活化的星形膠質(zhì)細(xì)胞既具有保護(hù)神經(jīng)元的作用,又能分泌細(xì)胞毒因子、炎癥因子和補(bǔ)體蛋白而損害神經(jīng)元[5]。我們前期實(shí)驗(yàn)證實(shí)DA蓄積會誘導(dǎo)兒茶酚氧位甲基轉(zhuǎn)移酶(catechol-O-methyltransferase,COMT)抑制劑表達(dá)上調(diào)[6]。COMT是多巴胺(dopamine,DA)的降解酶,本課題組前期實(shí)驗(yàn)中采用DA干預(yù),發(fā)現(xiàn)星形膠質(zhì)細(xì)胞分泌TNF-α并導(dǎo)致神經(jīng)元凋亡[7],后又發(fā)現(xiàn)DA抑制神經(jīng)元中學(xué)習(xí)記憶通路Glu-NO-cGMP的活性[8],因此推測腦組織DA含量增加可能導(dǎo)致細(xì)胞外Glu累積。突觸間隙的興奮性氨基酸轉(zhuǎn)運(yùn)體2(excitatory amino acid transporter 2, EAAT2)能清除谷氨酸,哺乳動物類雷帕霉素靶蛋白(mammalian target of rapamycin, mTOR)被報(bào)道可以調(diào)控Glu轉(zhuǎn)運(yùn)體表達(dá)[3]。Glu誘導(dǎo)的興奮性中毒可能在DA干預(yù)的星形膠質(zhì)細(xì)胞功能損傷中扮演著重要角色。本研究探索DA是否會減弱星形膠質(zhì)細(xì)胞對Glu的攝取能力,闡明DA和信號通路協(xié)同損傷星形膠質(zhì)細(xì)胞的分子機(jī)制。
1藥物、儀器與試劑
微量滲析探針和微量泵購自BAS;mTOR拮抗劑雷帕霉素、mTOR興奮劑MHY1485、辣根過氧化物酶、 L-谷氨酸氧化酶、 谷氨酸丙酮酸氧基轉(zhuǎn)移酶、丙氨酸和6-羧基熒光素購自Sigma-Aldrich; Amplex Red谷氨酸測定試劑盒、RNA-Easy試劑盒、低聚糖(dT)、dNTP、 DTT、莫羅尼鼠白血病病毒逆轉(zhuǎn)錄酶、RNaseOUT和5×FS緩沖液購自Invitrogen;EAAT2和mTOR引物由Invitrogen合成。ABI-棱柱7700序列檢測系統(tǒng)購自Applied Biosystems。iTaqTM超高速與ROX購自Bio-Rad。
2實(shí)驗(yàn)方法
2.1原代皮層星形膠質(zhì)細(xì)胞(primary cortical astrocytes,PCAs)的分離和干預(yù)[9]取新生24 h內(nèi)的SD乳鼠,大腦皮層組織用機(jī)械消化得到細(xì)胞懸液。細(xì)胞鋪板在75 cm2的細(xì)胞培養(yǎng)瓶,將1.5×106個(gè)細(xì)胞培養(yǎng)在1 mL含1% 血清的DMEM/F12培養(yǎng)基中,培養(yǎng)72 h。之后,PCAs分別以每孔1.5×106培養(yǎng)在6孔培養(yǎng)板中。mTOR拮抗劑雷帕霉素(100 μmol/L)或mTOR興奮劑MHY1485(10 μmol/L)與DA(最終濃度為10 μmol/L)共培養(yǎng)星形膠質(zhì)細(xì)胞,對照加同樣量的緩沖液,3個(gè)重復(fù)。
2.2細(xì)胞外Glu攝取含量檢測 通過Amplex Red谷氨酸測定試劑盒檢測經(jīng)過干預(yù)后PCAs對Glu攝取含量的變化。在DA(10 μmol/L)干預(yù)PCAs 12 h之后,由含500 μmol/L谷氨酸的HEPES緩沖液替代,在每隔相同時(shí)間,取50 μL上清液轉(zhuǎn)入96孔板中,接著與50 μL混合物(100 mmol/L Amplex Red,250 U/L辣根過氧化物酶,80 U/L L-谷氨酸氧化酶,500 U/L谷氨酸丙酮酸氧基轉(zhuǎn)移酶和200 μL丙氨酸)混合后,37℃溫浴 30 min。酶標(biāo)儀在波長為530 nm處(對比參考波長為590 nm)測定吸光度。谷氨酸含量代入谷氨酸標(biāo)準(zhǔn)曲線計(jì)算得到。
2.3實(shí)時(shí)熒光定量PCR(RT-qPCR)實(shí)驗(yàn) 用RNA-Easy試劑盒提取總RNA。采用相對定量法定量靶基因,以 β-actin 為內(nèi)參照,計(jì)算待測EAAT2和mTOR mRNA 相對表達(dá)量。引物序列:EAAT2的上游引物為5′-ATGCTCCTCATTCTCACAG-3′,下游引物為5′-CTACATTGACCGAAGTTCTC-3′;mTOR的上游引物為5’-CTGGGACTCAAATGTGTGCAGTTC-3’,下游引物為5’-GAACAATAGGGTGAATGATCCGGG-3’;β-actin的上游引物為5′-GCTGAGAGGGAAATCGTGCGTGAC-3′ ,下游引物為5′-GGAGGAAGAGGATGCGGCAGTGG-3′。qPCR用ABI-棱柱7700序列系統(tǒng)檢測,mRNA水平采用2-ΔΔCt法計(jì)算。
2.4Western blot分析 原代星形膠質(zhì)細(xì)胞裂解,勻漿,離心后取上清液進(jìn)行蛋白變性,以15% SDS聚丙烯酰胺凝膠電泳分離蛋白,將分離的蛋白轉(zhuǎn)移至硝酸纖維素膜,5% 脫脂奶粉封閉1 h,加EAAT2、mTOR和β-actin抗體,4 ℃孵育過夜,用TBST充分洗滌后,加入辣根過氧化物酶標(biāo)記 II 抗37 ℃孵育1 h,TBST 充分洗滌,ECL 發(fā)光顯影;用CIS 凝膠圖像處理系統(tǒng)進(jìn)行分析。
3統(tǒng)計(jì)學(xué)處理
應(yīng)用SPSS 16.0統(tǒng)計(jì)分析軟件,研究結(jié)果以均數(shù)±標(biāo)準(zhǔn)差(mean±SD)表示,計(jì)量資料用完全隨機(jī)設(shè)計(jì)單因素方差分析(one-way ANOVA);計(jì)數(shù)資料用χ2檢驗(yàn);以P<0.05為差異有統(tǒng)計(jì)學(xué)意義。
1DA對星形膠質(zhì)細(xì)胞EAAT2表達(dá)的影響
RT-qPCR的結(jié)果顯示DA干預(yù)的PCAs中EAAT2的mRNA水平顯著減少,并且呈時(shí)間依賴性;Western blot實(shí)驗(yàn)結(jié)果顯示,DA干預(yù)的PCAs中EAAT2蛋白表達(dá)水平也隨時(shí)間逐漸減少,見圖1。
Figure 1. The change of EAAT2 mRNA (A) and protein (B) expression in the PCAs after treatment with DA. Mean±SD.n=3.*P<0.05,**P<0.01vs0 h.
圖1DA干預(yù)PCAs后EAAT2的mRNA和蛋白表達(dá)水平的變化
2DA對星形膠質(zhì)細(xì)胞mTOR表達(dá)的影響
RT-qPCR的結(jié)果顯示,DA干預(yù)的PCAs中mTOR的mRNA水平顯著減少,并且呈時(shí)間依賴性;Western blot實(shí)驗(yàn)結(jié)果與mRNA結(jié)果趨勢一致,mTOR蛋白表達(dá)水平顯著減少,并且呈時(shí)間依賴性,見圖2。
Figure 2. The change of mTOR mRNA (A) and protein (B) expression in the PCAs after treatment with DA. Mean±SD.n=3.*P<0.05,**P<0.01vs0 h.
圖2DA干預(yù)PCAs后mTOR的mRNA和蛋白表達(dá)水平的變化
3DA對mTOR抑制/激活后的PCAsEAAT2表達(dá)的影響
mTOR拮抗劑雷帕霉素與DA干預(yù)的PCAs共培養(yǎng)后的RT-qPCR和Western blot實(shí)驗(yàn)分析結(jié)果顯示,EAAT2的mRNA水平和蛋白表達(dá)都顯著降低;mTOR激活劑MHY1485與DA干預(yù)的PCAs共培養(yǎng)后,EAAT2的mRNA水平和蛋白表達(dá)顯著上升,見圖3。
Figure 3. The change of EAAT2 mRNA (A) and protein (B) expression in the PCAs after treatment with rapamycin/MHY1485 and DA. Mean±SD.n=3.*P<0.05,**P<0.01vsDA alone.
圖3雷帕霉素/MHY1485與DA干預(yù)PCAs后EAAT2的mRNA和蛋白表達(dá)水平的變化
4DA對mTOR抑制/激活后的PCAs對Glu攝取能力的影響
如圖4所示,雷帕霉素與DA干預(yù)的PCAs共培養(yǎng)后,細(xì)胞外的Glu水平顯著上升。MHY1485與DA干預(yù)的PCAs共培養(yǎng)后,其細(xì)胞外的Glu含量顯著下降。
Figure 4. The Glu content in the culture supernatant of the PCAs after treated with rapamycin/MHY1485 and DA. Mean±SD.n=3.*P<0.05,**P<0.01vsDA alone.
圖4雷帕霉素/MHY1485與DA干預(yù)PCAs后上清液Glu含量的比較
谷氨酸是大腦主要的興奮性神經(jīng)遞質(zhì),過多的Glu蓄積在細(xì)胞間隙會引起神經(jīng)興奮性中毒而受損,將會引發(fā)多種神經(jīng)退行性疾病。星形膠質(zhì)細(xì)胞能夠通過突觸間隙的EAAT2清除排到細(xì)胞外大約90%的谷氨酸[10]。已有報(bào)道星形膠質(zhì)細(xì)胞mTOR分子水平的改變與星形膠質(zhì)細(xì)胞EAAT2表達(dá)水平和功能相關(guān)[11]。
維持Glu內(nèi)穩(wěn)態(tài)的主要通路是通過EAAT1和EAAT2再攝取[12],Glu釋放入突觸間隙后,在神經(jīng)元活動期間需要通過興奮性氨基酸轉(zhuǎn)運(yùn)體快速攝取,EAAT1和EAAT2會優(yōu)先清除位于星形膠質(zhì)細(xì)胞外大部分的Glu[12]。這些轉(zhuǎn)運(yùn)體在控制興奮信號和阻止細(xì)胞外Glu興奮毒性聚集方面起著至關(guān)重要的作用[12-13],所以EAAT1和EAAT2的失活可能會導(dǎo)致Glu異常的累積,從而損傷星形膠質(zhì)細(xì)胞。已有報(bào)道表明,EAAT2的長期損傷會促進(jìn)中樞神經(jīng)系統(tǒng)功能紊亂[14]。非選擇性的EAATs抑制劑會誘導(dǎo)EAAT2功能紊亂,明顯影響行為反應(yīng)[15]和誘發(fā)神經(jīng)退行性病變[16]。在我們的實(shí)驗(yàn)結(jié)果中,EAAT2的mRNA和蛋白質(zhì)表達(dá)因DA干擾顯著降低,與Danbolt等[12]所報(bào)道的EAAT2蛋白表達(dá)降低后干擾Glu的清除相符。我們的實(shí)驗(yàn)結(jié)果顯示Glu的清除能力會因DA干擾減弱?;诖竽X釋放增加的DA會導(dǎo)致大腦興奮性氨基酸轉(zhuǎn)運(yùn)異常的現(xiàn)象,我們觀測到DA干預(yù)星形膠質(zhì)細(xì)胞對Glu攝取的最明顯改變是EAAT2的翻譯和轉(zhuǎn)運(yùn)功能下降,從而降低對Glu攝取能力。前期實(shí)驗(yàn)中我們已經(jīng)發(fā)現(xiàn)DA通過誘導(dǎo)星形膠質(zhì)細(xì)胞中NADPH氧化酶活化產(chǎn)生活性氧,導(dǎo)致蛋白質(zhì)酪氨酸酸化,改變星形膠質(zhì)細(xì)胞功能[17]。
DA干預(yù)下的星形膠質(zhì)細(xì)胞mTOR表達(dá)降低[18];mTOR可以調(diào)控Glu轉(zhuǎn)運(yùn)體在星形膠質(zhì)細(xì)胞的表達(dá)[18],mTOR可能涉及DA介導(dǎo)的EAAT2的下調(diào)。DA干預(yù)星形膠質(zhì)細(xì)胞后協(xié)同mTOR下調(diào)EAAT2,從而降低Glu清除能力而導(dǎo)致Glu水平增加。已知雷帕霉素為mTOR競爭者,能夠調(diào)節(jié)Glu的清除能力[11]。因此mTOR在DA誘導(dǎo)的過量Glu的釋放中有著重要的作用。DA可以降低星形膠質(zhì)細(xì)胞mTOR的表達(dá),這會造成mTOR/EAAT2受損及伴隨著Glu清除的受阻。
綜上所述,本次我們闡明DA是通過mTOR-EAAT2這一信號通路影響Glu的攝取從而誘導(dǎo)Glu的蓄積,Glu在細(xì)胞間隙聚集會引起神經(jīng)興奮毒性,從而使星形膠質(zhì)細(xì)胞受損,這涉及很多的神經(jīng)退行性疾病[19-20]。我們的實(shí)驗(yàn)研究DA體外干預(yù)星形膠質(zhì)細(xì)胞,明確DA抑制星形膠質(zhì)細(xì)胞對Glu的攝取,引起膠質(zhì)細(xì)胞興奮中毒,且星形膠質(zhì)細(xì)胞作為中樞神經(jīng)系統(tǒng)中含量最豐富的細(xì)胞在阿爾茨海默癥的發(fā)病過程中起十分重要的作用[21],可以更好地確定DA對腦內(nèi)谷氨酸攝取能力的影響及相關(guān)疾病的發(fā)病機(jī)制。
鑒于星形膠質(zhì)細(xì)胞在多種神經(jīng)退行性疾病中的作用越來越受到重視,后續(xù)我們還需要進(jìn)一步了解DA體內(nèi)干預(yù)大鼠海馬組織的星形膠質(zhì)細(xì)胞的具體機(jī)制,將有助于改善和治療神經(jīng)退行性疾病。
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(責(zé)任編輯: 盧 萍, 羅 森)
Effectofdopamineonglutamate-uptakeabilityofastrocytesbyregulatingmTOR-EAAT2pathway
WEN Fang-fang, XU Zhu, LIU Le-ping, YANG Jan-jing, DING Sai-dan
(ZhejiangProvincialKeyLaboratoryofAgingandNeurologicalDiseaseResearch,TheFirstAffiliatedHospitalofWenzhouMedicalUniversity,Wenzhou325000,China.E-mail:firstdsdan@hotmail.com)
AIM: To investigate the effect of dopamine (DA) on the glutamate (Glu)-uptake ability of astrocytes, and the role of mammalian target of rapamycin (mTOR)-excitatory amino acid transporter 2(EAAT2) pathway in this process.METHODSExtracellular Glu levels in DA-treated primary cortical astrocytes (PCAs) were measured by a fluorimetric method. The relative expression of EAAT2 and mTOR at mRNA and protein levels was measured by RT-qPCR and Western blot. PCAs stimulated with or without DA in the presence or absence of mTOR antagonist rapamycin or mTOR agonist MHY1485 were used to determine the expression of mTOR and EAAT2, and Glu content in the culture supernatant was also measured.RESULTSThe expression of mTOR in DA-treated PCAs was decreased, the expression of EAAT2 was also decreased. Extracellular Glu levels of DA-treated PCAs were elevated significantly. When the PCAs were stimulated with DA in the presence of rapamycin, the expression of EAAT2 was decreased, and the levels of extracellular Glu was significantly increased. In the presence of MHY1485, the expression of EAAT2 was elevated, and significant decrease in the levels of extracellular Glu was also observed.CONCLUSIONDA interacts with mTOR-EAAT2 pathway to reduce the Glu-uptake ability of the astrocytes, and causes extracellular Glu accumulation, ultimately destroys the function of astrocytes.
Dopamine; Glutamate; Astrocytes
R741; R363
A
10.3969/j.issn.1000- 4718.2017.10.003
1000- 4718(2017)10- 1746- 05
2017- 01- 22
2017- 03- 27
國家自然科學(xué)基金資助項(xiàng)目(No. 81671042; No. 81300308)
△通訊作者 Tel: 15888209333; E-mail: firstdsdan@hotmail.com
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