于文嬌 楊巍巍,3,4 李 昕,3,4 李旭冉 陳 敏 于 順,3,4*
(1.首都醫(yī)科大學(xué)宣武醫(yī)院神經(jīng)生物學(xué)研究室,北京市老年病醫(yī)療研究中心,北京 100053;2.首都醫(yī)科大學(xué)帕金森病臨床診療與研究中心,北京 100053;3.帕金森病北京市重點(diǎn)實(shí)驗(yàn)室和教育部神經(jīng)變性病重點(diǎn)實(shí)驗(yàn)室,北京 100053;4.國家老年疾病臨床醫(yī)學(xué)研究中心,北京 100053;5.桂林醫(yī)學(xué)院附屬醫(yī)院神經(jīng)科學(xué)實(shí)驗(yàn)室,廣西桂林 541001)
·Alpha-突觸核蛋白的致病機(jī)制·
α-突觸核蛋白通過Rab5B下調(diào)海馬神經(jīng)元膜表面NMDA受體含量及其介導(dǎo)的Ca2+內(nèi)流和內(nèi)向電流
于文嬌1, 2楊巍巍1, 2,3,4李 昕1, 2,3,4李旭冉1, 2陳 敏1, 5*于 順1, 2,3,4*
(1.首都醫(yī)科大學(xué)宣武醫(yī)院神經(jīng)生物學(xué)研究室,北京市老年病醫(yī)療研究中心,北京 100053;2.首都醫(yī)科大學(xué)帕金森病臨床診療與研究中心,北京 100053;3.帕金森病北京市重點(diǎn)實(shí)驗(yàn)室和教育部神經(jīng)變性病重點(diǎn)實(shí)驗(yàn)室,北京 100053;4.國家老年疾病臨床醫(yī)學(xué)研究中心,北京 100053;5.桂林醫(yī)學(xué)院附屬醫(yī)院神經(jīng)科學(xué)實(shí)驗(yàn)室,廣西桂林 541001)
目的研究α-突觸核蛋白(α-synuclein,α-Syn)對原代海馬神經(jīng)元膜表面N-甲基-D-天門冬氨酸(N-methyl-D-aspartate,NMDA)受體含量和功能的影響及其機(jī)制。方法細(xì)胞外添加基因重組α-Syn,使其進(jìn)入原代培養(yǎng)神經(jīng)元細(xì)胞內(nèi),觀察敲減Rab5B基因前后神經(jīng)元膜表面NMDA受體(NMDAR)和Rab5B表達(dá)的變化;NMDA激活NMDAR,活細(xì)胞工作站測定神經(jīng)元Ca2+內(nèi)流變化,全細(xì)胞膜片鉗記錄內(nèi)向跨膜電流變化。結(jié)果α-Syn增加神經(jīng)元Rab5B的表達(dá),減少膜表面NMDAR含量,并因而抑制NMDA引起的Ca2+內(nèi)流及內(nèi)向跨膜電流;敲減Rab5B可逆轉(zhuǎn)α-Syn對NMDAR的下膜作用及功能的影響。結(jié)論α-Syn通過上調(diào)Rab5B而下調(diào)海馬神經(jīng)元膜表面NMDAR含量及其介導(dǎo)的Ca2+內(nèi)流及內(nèi)向電流。
α-突觸核蛋白;NMDA受體;Rab5B;神經(jīng)元;海馬
α-突觸核蛋白(α-synuclein,α-Syn)異常表達(dá)存在于老化和某些神經(jīng)系統(tǒng)退行性疾病如阿爾茨海默病(Alzheimer’s disease,AD)、帕金森病(Parkinson’s disease,PD)、路易體癡呆(dementia with Lewy body,DLB)患者的腦中[1]。老化和上述變性腦均存在記憶功能下降或障礙的表現(xiàn)[2]。海馬是與記憶密切相關(guān)的神經(jīng)結(jié)構(gòu)。以往研究[3-6]表明,海馬神經(jīng)元表面與記憶密切相關(guān)的谷氨酸受體——N-甲基-D-天門冬氨酸受體(N-methyl-D-aspartate receptors,NMDARs)在老化和變性腦中發(fā)生顯著的變化,但其機(jī)制不清楚。筆者以往研究[7]表明,α-Syn的異常表達(dá)可以促進(jìn)多巴胺神經(jīng)元膜表面NMDARs的內(nèi)在化,導(dǎo)致膜表面NMDARs減少,這一作用與α-Syn上調(diào)Rab5B表達(dá)有關(guān)。Rab5B是一種小的GTPases蛋白,是NMDARs內(nèi)在化所必需的蛋白[8]。鑒于老化和變性腦的海馬結(jié)構(gòu)存在α-Syn的異常積聚,筆者推測,海馬神經(jīng)元膜表面NMDARs的變化可能與α-Syn有關(guān)。本研究將利用原代培養(yǎng)大鼠海馬神經(jīng)元觀察α-Syn對神經(jīng)元膜表面NMDARs內(nèi)在化及功能的影響,并分析Rab5B的作用。
健康出生12 h內(nèi)Wistar新生大鼠,購自中國人民解放軍軍事醫(yī)學(xué)科學(xué)實(shí)驗(yàn)動物中心,實(shí)驗(yàn)動物許可證號:SCXK-2014-004。杜恩斯組織勻漿器(Wheaton Kimble公司,美國);Neurobasal A培養(yǎng)基、B27、DMEM培養(yǎng)基(Gibco公司,美國);胎牛血清(FBS,Berlin公司,美國);NMDA、MK-801(Sigma公司,美國);Rab5B反義寡核苷酸(百恩維公司,中國);NMDAR NR1抗體(Abcam公司,美國);Rab5B抗體(Santa Cruz公司,美國);Fluo4-AM(東仁化學(xué)公司,日本)。
Hank’s平衡鹽溶液A(HBSS,不含Ca2+、Mg2+)(mmol/L):NaCl 0.14,KCl 0.54×10-2,葡萄糖0.006,KH2PO40.44×10-3,Na2HPO40.33×10-3,調(diào)整pH至7.2;Hank’s平衡鹽溶液B(HBSS,不含Mg2+)(mmol/L):NaCl 0.14,KCl 0.54×10-2,葡萄糖 1,KH2PO40.44×10-3,Na2HPO40.33×10-3,CaCl20.13×10-2,調(diào)整pH至7.2。電極內(nèi)液(mmol/L):CsCl 70,NaCl 10,4-羥乙基哌嗪乙磺酸(HEPES)10,EGTA 10,ATP 2,GTP 0.2,調(diào)整pH至7.3;細(xì)胞外液(mmol/L):NaCl 150,KCl 5,CaCl21.4,葡萄糖 10,HEPES 5,河豚毒素(TTX)0.000 3,木防儀苦毒素(picrotoxin)0.1,NBQX 0.01,士的寧(trychnine)0.1,調(diào)整pH至7.3,調(diào)整滲透壓至330 mOsm。
活細(xì)胞工作站(Leica公司,德國);玻璃微電極拉制儀(Narishige公司,日本);膜片鉗放大器(Multiclamp 700B)(HEKA公司,德國),數(shù)據(jù)采樣板(Digidata 1322A)和數(shù)據(jù)采集分析軟件(pClamp 9.2)(Molecular Devices公司,美國);MiniAnalysis軟件包(Synaptosoft公司,美國)。
1.2.1 重組人α-Syn的制備
基因重組人α-Syn的表達(dá)和純化根據(jù)本室已建立的方法進(jìn)行[7]。純化后的蛋白分別用SDS-PAGE和Western blotting法進(jìn)行鑒定,BCA法定量后備用。
1.2.2 海馬原代神經(jīng)元培養(yǎng)
原代神經(jīng)元培養(yǎng)方法根據(jù)已建立的方法[9]進(jìn)行:將新生鼠斷頭,剝離鼠腦后于顯微鏡下分離并剪碎雙側(cè)海馬,胰蛋白酶消化30 min后,用含10%(體積分?jǐn)?shù))FBS的DMEM培養(yǎng)基終止消化。玻璃滴管火焰拋光后,輕柔吹打分散細(xì)胞,計數(shù)細(xì)胞密度。以2 × 105個/cm2密度接種到多聚賴氨酸包被的35 mm培養(yǎng)皿中,于37 ℃,5%(體積分?jǐn)?shù)) CO2的培養(yǎng)箱內(nèi)培養(yǎng)。待神經(jīng)元貼壁后,改用Neurobasal A、B27無血清培養(yǎng)基繼續(xù)培養(yǎng),每3 d換半液,培養(yǎng)10~12 d。
1.2.3 Rab5B反義寡核苷酸的制備
Rab5B反義寡核苷酸(antisense sequence,AS)及擾亂順序的寡核苷酸(scrambled sequence,SS),其序列分別是:5′-GCTGTGCTTCTGCTAGTCATTTCAAGAG AATGACTAGCAGAAGCACAGCTTTTTTCTCGAGG-3′和5′-GATCCCTCGAGAAAAAAGCTGTGCTTCTGCTA GTCATTCTCTTGAAATGACTAGCAGAAGCACAGC-3′。
1.2.4 細(xì)胞免疫熒光檢測
細(xì)胞用PBS漂洗后,預(yù)冷的4%(質(zhì)量分?jǐn)?shù))多聚甲醛固定細(xì)胞30 min,含有1%(體積分?jǐn)?shù))Triton-X 100的PBST溶液室溫孵育30 min,1%(質(zhì)量分?jǐn)?shù)) BSA封閉1 h。加入抗NMDAR NR1抗體(1∶1 000)或抗Rab5B抗體(1∶1 000),于4 ℃反應(yīng)過夜。PBST洗3次,每次10 min。加入熒光二抗(1∶5 000),室溫反應(yīng)2 h。PBST洗3次,每次10 min。激光共聚焦顯微鏡觀察。
1.2.5 細(xì)胞內(nèi)Ca2+濃度的測定
細(xì)胞培養(yǎng)皿置于活細(xì)胞工作站載物臺上,激發(fā)光波長為488 nm,發(fā)射光波長為515 nm,固定參數(shù)后每10 s掃描一次,掃描180s作為基線。加入NMDA(100μmol/L)及甘氨酸(10μmol/L),繼續(xù)掃描目的細(xì)胞內(nèi)的Ca2+熒光強(qiáng)度改變,圖像由隨機(jī)軟件分析處理(Leica公司,德國)。胞內(nèi)的Ca2+熒光強(qiáng)度變化用Fluo-4與Ca2+結(jié)合后的熒光強(qiáng)度比值表示。計算公式:熒光強(qiáng)度變化=Ft/F0(Ft:添加NMDA后第t秒神經(jīng)元內(nèi)的熒光復(fù)合物的熒光強(qiáng)度,F(xiàn)0:基線水平的神經(jīng)細(xì)胞內(nèi)的熒光復(fù)合物的熒光強(qiáng)度[7])。
1.2.6 全細(xì)胞膜片鉗記錄細(xì)胞膜電流及給藥
采用常規(guī)全細(xì)胞記錄模式[10],記錄細(xì)胞的電信號,輸入膜片鉗放大器,而后經(jīng)由模數(shù)轉(zhuǎn)換儀輸入到計算機(jī),經(jīng)10 Hz濾波,采樣頻率為2~3 Hz。記錄信號的監(jiān)測、儲存及通過記錄點(diǎn)擊給予細(xì)胞的指令電壓以及分析處理由Axon軟件pClamp 8.0和Clampfit 8.0完成。全細(xì)胞記錄在22~24 ℃室溫環(huán)境下進(jìn)行,連續(xù)記錄30 min以上。
通過軟件控制正壓給藥系統(tǒng)(DAD-12 Superfusion System)的通道灌注NMDA(100 μmol/L)、Glycine(10 μmol/L)。使用HL-2型恒流泵進(jìn)行細(xì)胞外灌注沖洗細(xì)胞,以終止藥物作用。
免疫熒光標(biāo)記顯示,沒有α-Syn處理的神經(jīng)元(PBS組),NR1主要分布于神經(jīng)元的膜表面。外加α-Syn處理后,神經(jīng)元膜表面NR1顯著減少,胞質(zhì)中的NR1明顯增多,提示NR1發(fā)生內(nèi)在化。單純轉(zhuǎn)染Rab5B SS和Rab5B AS的神經(jīng)細(xì)胞,NR1也主要分布于神經(jīng)元的膜上。用α-Syn處理Rab5B SS轉(zhuǎn)染神經(jīng)元,膜表面的NR1顯著減少,胞質(zhì)中的NR1明顯增多,而在Rab5B AS轉(zhuǎn)染神經(jīng)元,α-Syn使NR1內(nèi)在化的作用消失,提示α-Syn促進(jìn)NMDAR NR1的內(nèi)在化的作用需要Rab5B的參與(圖1)。
活細(xì)胞工作站結(jié)果顯示(n=5),NMDA引起 [Ca2+]i快速而顯著增加,NMDA的這一作用被NMDA受體特異性阻斷劑MK-801完全阻斷。事先用α-Syn處理神經(jīng)元后,則 NMDA引起的[Ca2+]i增加的作用明顯受到抑制,而用Rab5B-AS抑制Rab5B表達(dá)后,α-Syn抑制[Ca2+]i增加的作用被消除(圖2)。
將鉗制電壓設(shè)定為-75 mV條件下時,NMDA受體介導(dǎo)的內(nèi)向電流隨受體特異性激動劑NMDA濃度的增加而增加(圖3)。α-Syn處理細(xì)胞后,NMDA受體介導(dǎo)的內(nèi)向電流受到抑制,且此抑制作用在Rab5B AS轉(zhuǎn)染細(xì)胞后消失(圖4)。
本研究結(jié)果表明,利用外加重組α-Syn處理海馬神經(jīng)元后,可使神經(jīng)元膜表面NMDARs亞單位NR1減少,胞質(zhì)含量增加。鑒于NR1是構(gòu)成NMDAR的必需亞單位,其在神經(jīng)元膜表面的減少意味著完整的具有功能的NMDARs發(fā)生了內(nèi)在化。筆者以往的研究[11]表明,將α-Syn添加到細(xì)胞外,α-Syn可以迅速進(jìn)入細(xì)胞并引起細(xì)胞內(nèi)α-Syn含量增加,由此推測,細(xì)胞外添加α-Syn導(dǎo)致的NMDARs的內(nèi)在化,很可能是α-Syn進(jìn)入細(xì)胞內(nèi)引起的。作為支持這一推測的證據(jù),在α-Syn過表達(dá)的神經(jīng)細(xì)胞中,NMDARs也發(fā)生內(nèi)在化。由于Rab5B蛋白是內(nèi)吞機(jī)制中的關(guān)鍵蛋白,能夠促進(jìn)細(xì)胞膜表面蛋白的內(nèi)在化[8],筆者推測,α-Syn引起的海馬神經(jīng)元膜表面NMDARs的內(nèi)在化可能有Rab5B的參與。為了證明這一點(diǎn),筆者利用小干擾RNA敲減Rab5B,觀察α-Syn對NMDARs內(nèi)在化的影響。結(jié)果顯示,敲減Rab5B后,α-Syn引起的NMDARs內(nèi)在化明顯受到抑制。
如前所述,神經(jīng)元膜表面NR1亞單位的減少意味著膜表面功能性NMDARs的減少。由于NMDARs在通道開放情況下可以介導(dǎo)Na+和Ca2+的內(nèi)流和由此引起的內(nèi)向電流,筆者分別利用活細(xì)胞工作站和膜片鉗技術(shù)研究了α-Syn處理和非處理神經(jīng)元NMDARs特異性激動劑NMDA對Ca2+內(nèi)流和內(nèi)向跨膜電流的影響。在無α-Syn處理的神經(jīng)元,NMDA引起細(xì)胞內(nèi)Ca2+濃度快速而顯著增加,同時可以記錄到NMDARs介導(dǎo)的內(nèi)向電流,NMDA的這一作用呈濃度依賴性。而在α-Syn處理神經(jīng)元,NMDA引起細(xì)胞內(nèi)Ca2+濃度增加以及NMDAR介導(dǎo)的內(nèi)向電流明顯受到抑制。這一結(jié)果提示,α-Syn引起了NMDARs功能的變化,這一變化很可能是通過促進(jìn)NMDARs的內(nèi)在化從而導(dǎo)致神經(jīng)元膜表面功能性的NMDARs減少。由于α-Syn的上述作用可因敲減Rab5B而被明顯抑制,因此推測Rab5B參與了α-Syn引起的NMDARs內(nèi)在化過程。
圖1 Rab5B在α-Syn所致細(xì)胞膜表面NR1內(nèi)在化中的作用Fig.1 The role of Rab5B in α-Syn-induced NR1 internalization
Representative immunofluorescence images showing NR1 (red),Rab5B SS or AS (green),and DAPI (blue).Cells were incubated separately with α-Syn (10 μmol/L) for 24 h or LV-GFP-Rab5B AS for 3 days,with or without added α-Syn.Other batches of cells were treated with corresponding vehicles,PBS and LV-GFP-Rab5B SS,either in the presence or absence of α-Syn.Each batch of cells was then stained for immunofluorescence microscopy and nuclei were counterstained with DAPI.Images were captured under a 100×objective with equal exposure times to allow direct comparison.Each of the three independent replicates was assessed from three to ten random fields of view.n=5 in each group,bar=10 μm.NR1: N-methyl-D-aspartate receptors1;PBS: phosphate buffered saline;α-Syn: α-synuclein;SS: scrambled sequence;AS: antisense sequence;GFP: green fluorescent protein.
圖2 α-Syn對于NMDA引起的[Ca2+]i增加的影響Fig.2 Effect of α-Syn on NMDA-induced elevation of [Ca2+]i
Cells were transfected with Rab5B SS or Rab5B AS for three days,and then treated with α-Syn (10μmol/L) for 24 h before observing NMDAR-mediated Ca2+influx.Cells were stained Ca2+indicator fluo4-AM.A: Dynamic changes in [Ca2+]i as indicated by fluorescence intensity (Ft/F0);B: Statistical peak values of [Ca2+]i before and after NMDA stimulation.n=5 in each group;*P<0.05,**P<0.01;α-Syn: α-synuclein;NMDA:N-methyl-D-aspartate;HBSS:Hank’s balanced salt solution;SS: scrambled sequence;AS: antisense sequence;Ft: fluorescence of the indicator at t second;F0: fluorescence of the indicator at 0 second;[Ca2+]i: Ca2+influx.
圖3 α-Syn對不同濃度的NMDA誘發(fā)內(nèi)向跨膜電流的影響Fig.3 The effect of α-Syn on currents evoked by NMDA of different concentrations
Whole cell patch clamp experiments were used to record NMDA receptor-mediated currents in cultured hippocampal neurons.Batches of cells were treated as described above.A,BCurrents in α-Syn-treated cells(10 μmol/L) were decreased at a range of agonist concentrations (0,10,20,50,100,200 and 500μmol/L) and returned to robust levels on addition of LV-GFP-AS (n=5,*P<0.05,**P<0.01vsPBS-treated group,#P<0.05vsα-Syn group);α-Syn: α-synuclein;NMDA:N-methyl-D-aspartate;SS: scrambled sequence;PBS: phosphate buffered saline;AS: antisense sequence.
圖4 α-Syn抑制NMDA受體介導(dǎo)的內(nèi)向電流Fig.4 α-Syn reduced NMDAR-mediated inward currents
A: Trace of NMDA receptor-mediated currents in each batch of cells.B: Bar graphs shows the normalized currents after NMDA stimulation.n=5 in each group;*P<0.05;α-Syn: α-synuclein;NMDA:N-methyl-D-aspartate;PBS: phosphate buffered saline;SS: scrambled sequence;AS: antisense sequence.
本研究為老化和某些神經(jīng)退行性疾病腦的海馬神經(jīng)元膜表面NMDARs變化的機(jī)制提供了實(shí)驗(yàn)依據(jù)。
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α-SynucleinreducessurfaceexpressionsofNMDAreceptorsandNMDA-invokedCa2+influxandinwardcurrentbyupregulationofRab5Binculturedprimaryhippocampalneurons
Yu Wenjiao1,2,Yang Weiwei1,2,3,4,Li Xin1,2,3,4,Li Xuran1,2,Chen Min1,5*,Yu Shun1,2,3,4*
(1.DepartmentofNeurobiology,XuanwuHospital,CapitalMedicalUniversity,BeijingInstituteofGeriatrics,Beijing100053,China;2.ClinicalCenterforParkinson’sDisease,CapitalMedicalUniversity,Beijing100053,China;3.BeijingKeyLaboratoryforParkinson’sDiseaseandKeyLaboratoryofNeurodegenerativeDiseases,MinistryofEducation,Beijing100053,China;4.NationalClinicalResearchCenterforGeriatricDisorders,Beijing100053;5.LaboratoryofNeuroscience,AffiliatedHospitalofGuilinMedicalUniversity,Guilin541001,GuangxiZhuangAutonomousRegion,China)
ObjectiveTo investigate the effects of α-synuclein(α-Syn) on surface expressions and functions of N-methyl-D-aspartate (NMDA) receptors (NMDARs) in cultured primary hippocampal neurons.MethodsIncreased intracellular α-Syn levels were realized by extracellular addition of recombinant human α-Syn to the culture medium of rat primary hippocampal neurons.Expressions of surface NMDARs and Rab5B were observed by fluorescence immunocytochemistry and Western blotting.Rab5B antisense oligonucleotides were applied to suppress Rab5B expression.Live cell imaging system and whole-cell patch-clamp recording were used to record NMDA-evoked Ca2+influx and inward currents.ResultsNeurons treated with α-Syn displayed increased Rab5B,decreased surface NMDARs,and reduced NMDA-evoked Ca2+influx and inward currents.The above α-Syn effects were inhibited by suppression of Rab5B expression.Conclusionα-Syn reduces the surface expression and functions of NMDARs by increasing Rab5B expression.
α-synuclein;NMDA receptor;Rab5B;neuron;hippocampus
國家自然科學(xué)基金(81371200,81071014,81401042),北京市醫(yī)院管理局“使命”計劃專項(xiàng)經(jīng)費(fèi)資助(SML20150803),北京市科學(xué)技術(shù)委員會資助(Z161100005116011,Z171100000117013),北京市衛(wèi)生和計劃生育委員會“老年重大疾病關(guān)鍵技術(shù)研究”(PXM2017_026283_000002),廣西自然科學(xué)基金(2014GXNSFAA118197)。This study was supported by National Natural Science Foundation of China (81371200,81071014,81401042),Beijing Municipal Administration of Hospitals’ Mission Plan (SML20150803),Beijing Municipal Science &Technology Commission (Z161100005116011,Z171100000117013),Beijing Municipal Commission of Health and Family Planning (PXM2017_026283_000002),Natural Science Foundation of Guangxi (2014GXNSFAA118197).
*Corresponding authors,E-mail:yushun103@163.com,chenmin790830@163.com
時間:2017-12-13 21∶29
http://kns.cnki.net/kcms/detail/11.3662.R.20171213.2129.066.html
10.3969/j.issn.1006-7795.2017.06.018]
Q189
2017-10-23)
編輯 陳瑞芳