脊髓小膠質(zhì)細(xì)胞在神經(jīng)病理性疼痛發(fā)生發(fā)展過程中的作用機(jī)制研究進(jìn)展

周于然，李瑛(遵義醫(yī)學(xué)院，貴州遵義653000；遵義醫(yī)學(xué)院附屬醫(yī)院)

脊髓小膠質(zhì)細(xì)胞在神經(jīng)病理性疼痛發(fā)生發(fā)展過程中的作用機(jī)制研究進(jìn)展

周于然1，李瑛2
(1遵義醫(yī)學(xué)院，貴州遵義653000；2遵義醫(yī)學(xué)院附屬醫(yī)院)

脊髓小膠質(zhì)細(xì)胞是神經(jīng)病理性疼痛的發(fā)生過程中發(fā)揮重要的關(guān)鍵細(xì)胞之一。脊髓小膠質(zhì)細(xì)胞中單核細(xì)胞趨化蛋白-1、趨化因子配體-2、基質(zhì)金屬蛋白酶-9 和 絲裂原激活蛋白激酶類家族蛋白參與了脊髓小膠質(zhì)細(xì)胞激活進(jìn)而導(dǎo)致神經(jīng)病理性疼痛產(chǎn)生的過程。

神經(jīng)病理性疼痛；小膠質(zhì)細(xì)胞；脊髓；單核細(xì)胞趨化蛋白1；趨化因子配體2；基質(zhì)金屬蛋白酶9 ；絲裂原激活蛋白激酶類家族蛋白

慢性疼痛是疼痛刺激因素消除之后而疼痛持續(xù)存在的一種病理狀態(tài)，主要包括炎性痛和神經(jīng)病理性疼痛。神經(jīng)病理性疼痛，常發(fā)生于神經(jīng)損傷或某些疾病之后，比如癌癥、感染、自身免疫性疾病、創(chuàng)傷和糖尿病。神經(jīng)病理性疼痛不僅僅是疾病的一個癥狀，更可能是神經(jīng)系統(tǒng)功能紊亂導(dǎo)致的結(jié)果[1]。除了自發(fā)性疼痛和痛覺過敏，神經(jīng)病理性疼痛患者對正常的無傷害性刺激也會產(chǎn)生痛覺過敏。神經(jīng)病理性疼痛患者痛覺超敏的發(fā)生不僅有神經(jīng)元的參與，小膠質(zhì)細(xì)胞亦參與其中[2]。近年研究發(fā)現(xiàn)，脊髓小膠質(zhì)細(xì)胞是神經(jīng)病理性疼痛發(fā)生過程中的關(guān)鍵細(xì)胞之一。脊髓小膠質(zhì)細(xì)胞中的單核細(xì)胞趨化蛋白1(MCP-1)、趨化因子配體2(CCL2)和基質(zhì)金屬蛋白酶9 (MMP-9)、絲裂原激活蛋白激酶類家族(MAPKs)參與其中。現(xiàn)綜述如下。

1 MCP-1

趨化因子和趨化因子受體廣泛表達(dá)于中樞神經(jīng)系統(tǒng)，趨化因子信號通路在神經(jīng)炎癥反應(yīng)調(diào)解中發(fā)揮關(guān)鍵作用。脊髓小膠質(zhì)細(xì)胞表達(dá)的CCR2在痛覺過敏的發(fā)生和維持過程中發(fā)揮著積極作用[3]。CCR2基因敲除小鼠機(jī)械性結(jié)扎坐骨神經(jīng)后小鼠沒有出現(xiàn)觸誘發(fā)痛[3]，而MCP-1過表達(dá)可以增加疼痛的敏感性[4]，藥物阻斷CCR2可以抑制痛覺超敏[5]。研究證實(shí)正常大鼠鞘內(nèi)注射MCP-1也可以激活脊髓小膠質(zhì)細(xì)胞[6]。神經(jīng)元表達(dá)的MCP-1以活性依賴地方式釋放到脊髓背角[6]，趨化因子依賴性小膠質(zhì)細(xì)胞的激活是神經(jīng)病理性疼痛的發(fā)病機(jī)制，脊髓背角包含表達(dá)CCR2的小膠質(zhì)細(xì)胞[7]。為了進(jìn)一步確認(rèn)CCR2信號通路在慢性疼痛中的作用，Zhang等[8]研究發(fā)現(xiàn)在CCR2基因敲除小鼠不能形成慢性疼痛模型，可能是因為CCR2基因敲除小鼠鞘內(nèi)注射MCP-1不能引起小膠質(zhì)細(xì)胞激活。CCR2激活小膠質(zhì)細(xì)胞觸發(fā)促疼痛介質(zhì)和物質(zhì)的釋放，隨后引起星形膠質(zhì)細(xì)胞激活，最終有助于慢性疼痛的形成[4]。

CCL2和MCP-1一樣，是趨化因子家族的成員，可以特異性引導(dǎo)單核細(xì)胞到炎癥、感染、創(chuàng)傷、毒素暴露與缺血部位。CCL2主要存在于小型和中型的脊髓和背根神經(jīng)節(jié)神經(jīng)元，尤其是那些含有P物質(zhì)和降鈣素基因相關(guān)肽(CGRP)的神經(jīng)元；在延髓，CCL2表達(dá)于神經(jīng)元和星形膠質(zhì)細(xì)胞[9]。CCL2可以與多種受體結(jié)合，包括CCR1、CCR2和CCR4，其中CCL2的生物學(xué)效應(yīng)主要由CCR2介導(dǎo)[10]。CCL2-CCR2信號通路參與調(diào)解神經(jīng)炎癥和慢性疼痛。研究表明延髓背角CCL2和CCR2參與調(diào)解三叉神經(jīng)病理性疼痛[11]。在神經(jīng)病理條件下，脊髓CCL2表達(dá)也上調(diào)[6]。Thacker等[6]研究證實(shí)L5脊神經(jīng)結(jié)扎切斷模型中，損傷的L5脊神經(jīng)和未損傷的L4脊神經(jīng)背根神經(jīng)節(jié)均產(chǎn)生CCL2。臨床研究證實(shí)CCL2在腰椎間盤突出患者疼痛維持中發(fā)揮著重要作用[12]。動物實(shí)驗也證實(shí)背根神經(jīng)節(jié)和脊髓的CCL2和CCR2信號通路在大鼠腰椎間盤突出癥模型疼痛維持中發(fā)揮關(guān)鍵作用，CCL2/CCR2信號通路直接參與大鼠脊髓調(diào)解傷害性信息的傳遞[13]。此外，在神經(jīng)病理性疼痛模型中脊髓小膠質(zhì)細(xì)胞和星形膠質(zhì)細(xì)胞CCL2表達(dá)上調(diào)[3，13]。小膠質(zhì)細(xì)胞的特異性抑制劑米諾環(huán)素不僅可以有效緩解坐骨神經(jīng)損傷引起的神經(jīng)病理性疼痛，而且還降低神經(jīng)損傷引起的脊髓CCL2和CCR2表達(dá)水平升高[14]。Thacker等[6]發(fā)現(xiàn)脊髓內(nèi)注射CCL2可以引起同側(cè)脊髓背角小膠質(zhì)細(xì)胞的廣泛激活，表明CCL2/CCR2信號通路參與神經(jīng)元-小膠質(zhì)細(xì)胞的相互作用。盡管以上研究證實(shí)CCL2可通過神經(jīng)元、星形膠質(zhì)細(xì)胞和小膠質(zhì)細(xì)胞上的CCR2受體調(diào)解神經(jīng)病理性疼痛的敏感性，但具體機(jī)制仍有待進(jìn)一步研究。

2 MMP-9

基質(zhì)金屬蛋白酶(MMPs)家族由一大類內(nèi)肽酶組成，它們需要Zn2+維持酶的活性。MMPs通過裂解細(xì)胞外基質(zhì)蛋白、細(xì)胞因子和趨化因子在炎癥調(diào)解過程中發(fā)揮著至關(guān)重要的作用[15]。研究證實(shí)正常大鼠鞘內(nèi)注射MMP-9可以激活小膠質(zhì)細(xì)胞[6]，其機(jī)制可能與趨化因子、白介素1β(IL-1β)和腫瘤壞死因子α有關(guān)[16]。Kawasaki等[17]研究結(jié)果表明抑制MMP-9有利于緩解神經(jīng)病理性疼痛。米諾環(huán)素除了影響內(nèi)源性強(qiáng)啡肽水平，還強(qiáng)烈抑制MMP-9 mRNA的表達(dá)，可能是其發(fā)揮鎮(zhèn)痛和神經(jīng)保護(hù)效應(yīng)的機(jī)制[18]。鞘內(nèi)注射MMP-9抑制劑可以減弱CCI模型大鼠的機(jī)械痛和熱痛，效果類似于注射米諾環(huán)素[19]。坐骨神經(jīng)擠壓后MMP-9表達(dá)上調(diào)，降解髓鞘堿性蛋白導(dǎo)致神經(jīng)脫髓鞘病變[20]。脊神經(jīng)結(jié)扎(SNL)引起背根神經(jīng)節(jié)MMP-9快速(< 1 d)而短暫(< 3 d))的表達(dá)上調(diào)，MMP-9抑制劑可以減輕神經(jīng)病理性疼痛；相反，鞘內(nèi)注射MMP-9可以誘發(fā)類似機(jī)械性觸誘發(fā)痛神經(jīng)癥狀[17]。MMP-9 和 IL-1β共表達(dá)在背根神經(jīng)節(jié)相同神經(jīng)元上，MMP-9似乎通過IL-1β誘導(dǎo)神經(jīng)病理性疼痛癥狀[17]，因為中和抗體可部分阻斷MMP-9誘導(dǎo)的異常性疼痛。此外，MMP-9引起的脊髓神經(jīng)元連接異常在神經(jīng)病理性疼痛的發(fā)生中也非常重要[21]。

3 MAPKs

小膠質(zhì)細(xì)胞內(nèi)的P2X4受體蛋白主要位于溶酶體內(nèi)，在溶酶體的蛋白水解環(huán)境中P2X4受體蛋白仍保持穩(wěn)定狀態(tài)[22]。研究表明CCL2通過CCR2增加小膠質(zhì)細(xì)胞表面P2X4受體蛋白表達(dá)水平，但不影響其總表達(dá)量[23]。因此，CCL2可能通過胞外分泌方式上調(diào)了小膠質(zhì)細(xì)胞表面P2X4受體蛋白的表達(dá)。利用單分子成像技術(shù)追蹤小膠質(zhì)細(xì)胞P2X4受體蛋白的表達(dá)過程，研究發(fā)現(xiàn)激活態(tài)小膠質(zhì)細(xì)胞內(nèi)P2X4受體蛋白的橫向移動能力被p38增強(qiáng)，p38為絲裂原激活蛋白激酶類家族(MAPKs)的一個成員[24]。在不同類型神經(jīng)病理性疼痛模型中均發(fā)現(xiàn)脊髓小膠質(zhì)細(xì)胞p38被激活。注射p38抑制劑可以減弱外周神經(jīng)損傷[25]和糖尿病[26]引起的觸覺誘發(fā)疼痛。因此，p38的激活在神經(jīng)病理性疼痛的發(fā)病機(jī)理中占據(jù)重要地位。在周圍神經(jīng)損傷之前用布比卡因阻滯坐骨神經(jīng)，可以阻止脊髓小膠質(zhì)細(xì)胞p38的激活[27]。組織蛋白酶S鞘內(nèi)注射后迅速誘導(dǎo)脊髓小膠質(zhì)細(xì)胞磷酸化，這種效應(yīng)依賴于趨化因子和其受體信號通路[28]。此外，此外，嘌呤P2Y12R也可能參與脊髓小膠質(zhì)細(xì)胞p38的激活[29]。

MAPKs家族的另外一個成員胞外信號調(diào)節(jié)蛋白酶ERK，神經(jīng)損傷后不久首先出現(xiàn)在脊髓背角神經(jīng)元，幾天后主要出現(xiàn)在小膠質(zhì)細(xì)胞，3周后則出現(xiàn)在星形膠質(zhì)細(xì)胞[30]。Xu等[31]研究發(fā)現(xiàn)db/db小鼠ERK激活發(fā)生在脊髓神經(jīng)元和星形膠質(zhì)細(xì)胞，抑制ERK可以減弱機(jī)械性觸覺誘發(fā)疼痛。促炎性因子，IL-1b、IL-6和腫瘤壞死因子被認(rèn)為可能是MAPKs調(diào)解疼痛的中介分子[32]。

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李瑛(E-mail： 359062449@qq.com )

10.3969/j.issn.1002-266X.2017.11.034

R741.02

A

1002-266X(2017)11-0105-03

2016-09-22)