項永生 徐如祥
骨髓基質(zhì)干細胞在腦缺血疾病治療的新進展
項永生 徐如祥
成人骨髓基質(zhì)干細胞是源于骨髓的一種多潛能成體干細胞。它們的移植改善腦缺血模型和脊髓損傷模型的機制可能包括替換受損細胞,神經(jīng)功能保護作用,誘導(dǎo)軸突生長和促進新生血管形成。其應(yīng)用于細胞治療的主要優(yōu)勢在于其可以自體移植,因而不存在胚胎干細胞移植所存在的免疫排斥、倫理學(xué)及致瘤性等方面的限制;不像神經(jīng)干細胞主要位于腦室下帶、海馬等結(jié)構(gòu)中,因而細胞來源有限,獲得困難。因此,這種干細胞移植療法可能在未來的臨床治療具有重大意義。
骨髓基質(zhì)干細胞; 腦缺血性疾?。?干細胞治療
成人骨髓基質(zhì)干細胞 (human bone marrow stromal stem cells,hBMSCs)是源于骨髓的一種多潛能成體干細胞,其移植改善腦缺血模型和脊髓損傷模型的機制可能包括替換受損細胞、神經(jīng)功能保護作用、誘導(dǎo)軸突生長和促進新生血管形成。在成人腦卒中受試者中靜脈給予注射hBMSCs的初步臨床研究已經(jīng)開展,目前還在評估中。在這里,筆者回顧在中風(fēng)模型中hBMSCs移植用于細胞修復(fù)和神經(jīng)保護的特性,描述靜脈注射hBMSCs對腦卒中患者的影響,同時展望hBMSCs細胞移植的發(fā)展前景。
盡管缺血灶面積保持不變或擴大,腦卒中患者或動物模型在康復(fù)期間都會出現(xiàn)不同程度自發(fā)神經(jīng)功能恢復(fù)[1,2]。這些結(jié)果表明,隨著康復(fù)時間的延長,神經(jīng)可塑性代償或是大腦的重塑可能有助于神經(jīng)功能恢復(fù)。干細胞移植療法將有助于促進功能恢復(fù)或是提高內(nèi)源性自我修復(fù)過程[3]。而對神經(jīng)系統(tǒng)疾病的干細胞治療方法,早期的假設(shè)是干細胞將取代受傷的細胞。然而,目前的研究提出了幾種可能的作用機制,包括干細胞可以釋放或刺激釋放趨化因子、神經(jīng)保護、促進新生血管形成和軸突生成。這些不同的影響并不是相互排斥的,細胞療法可能是多種治療作用機制在不同的地點和時間點共同作用的結(jié)果。本文將闡述hBMSCs在治療腦卒中患者中的經(jīng)驗。
在胚胎發(fā)育過程中,中胚層含有多潛能祖細胞,能夠分化形成軟骨、骨、肌肉和其他的間充質(zhì)組織。研究表明,hBMSCs可以通過不同的信號通路分化為多個不同類型細胞系[4,5]。其他研究也證實hBMSCs具有自我更新和多分化潛能,分化成成骨細胞、脂肪細胞和軟骨細胞[6-10]。hBMSCs也被認為可以分化成神經(jīng)元和神經(jīng)膠質(zhì)細胞[7,11-14]。然而,有學(xué)者對hBMSCs是否能進入腦內(nèi)并分化成神經(jīng)元或是神經(jīng)膠質(zhì)細胞提出異議[15]。在體內(nèi),hBMSCs沒有明確的標記,并且局部微環(huán)境不同細胞特征混淆,因此對其鑒定比較困難[16]。
在本綜述中不討論hBMSCs的復(fù)雜性和特異性。只專注于通過流式細胞技術(shù)挑選CD34-、CD45-、CD73+和CD105+的hBMSCs移植對腦卒中患者潛在的修復(fù)能力[10,17]。
鼠腦缺血后hBMSCs移植幾小時到幾天即可減少梗死面積,改善神經(jīng)功能在鼠腦缺血模型[18-20]。靜脈注射hBMSCs后磁共振成像或組織切片均顯示梗塞灶體積的減小,并有功能性恢復(fù)(圖1)[17,21,22]。hBMSCs這些積極的作用機制包括神經(jīng)保護作用、血管生成、神經(jīng)再生和軸突發(fā)芽/再生[18,23,24]。
圖1 成人骨髓基質(zhì)干細胞注射后梗塞灶體積的減小并獲得功能性恢復(fù)
在腦缺血局灶區(qū),hBMSCs釋放生長因子和趨化因子或是刺激殘存的細胞釋放生長因子和趨化因子,加快缺血局灶區(qū)的修復(fù)或是重建,這對腦缺血區(qū)是有積極的意義[25]。事實上,在腦卒中模型中,給予靜脈注射hBMSCs能夠減少缺血局灶區(qū)細胞的凋亡,同時促進內(nèi)源性細胞的增殖[26]。在體外培養(yǎng)中,hBMSCs能夠分泌少量的多種神經(jīng)趨化因子;在體內(nèi)缺血局灶區(qū),移植的hBMSCs周圍也檢測出神經(jīng)趨化因子和血管生成因子。腦源性神經(jīng)趨化因子(brain derived neurotrophic factor,BDNF)在hBMSCs培養(yǎng)中發(fā)現(xiàn)少許表達,然而在鼠大腦中動脈栓塞模型中,靜脈給予注射hBMSCs能發(fā)現(xiàn)在缺血局灶區(qū)BDNF表達明顯增加[22,27]。BDNF基因改造的hBMSCs移植能顯著提高缺血局灶區(qū)BDNF表達水平及增強治療效果;在脊髓損傷模型中也觀察到同樣的效果,同時還發(fā)現(xiàn)脊髓神經(jīng)束軸突的再生[28]。這種以細胞為基礎(chǔ)的治療方法對損傷部位提供趨化因子相對于系統(tǒng)性全身給藥的不利影響具有潛在的優(yōu)勢。
傳統(tǒng)認為hBMSCs能夠分泌血管生成因子,包括血管內(nèi)皮生長因子(vascular endothelial growth factor,VEGF)和促血管生成素-1(angiopoietin-1,Ang-1)[29,30]。 VEGF 在腦組織中具有強大的血管生成能力及生成不成熟的新生血管[31,32]。然而,在腦缺血局灶區(qū)VEGF增強血管的通透性,血漿蛋白從血管內(nèi)漏出導(dǎo)致腦水腫[33]。直接注射VEGF到神經(jīng)系統(tǒng)中,能導(dǎo)致血腦屏障的開放[34]。在腦內(nèi),Ang-1參與血管的成熟、穩(wěn)定和血管的重塑,并促進血管的生成[30,35-37]。Ang-1保護血管的通透性,減少血漿蛋白的漏出,在缺血局灶區(qū)減少腦水腫,其作用機制是通過酪氨酸激酶受體Tie2受體家族信號通路促進新生血管的成熟及穩(wěn)定,減少滲漏(圖2)[38-41]。
圖2 自體骨髓間充質(zhì)干細胞原理流程圖
創(chuàng)傷性腦損傷后由于血腦屏障的破壞,血管通透性增加,細胞從血管壁游出,導(dǎo)致腦水腫[42]。同樣,腦卒中后,由于血腦屏障的破壞,血管通透性增強,細胞滲漏增加,水腫明顯,給予移植hBMSCs將可能通過Ang-1信號通路招募內(nèi)皮細胞穩(wěn)定微血管作用,減輕腦水腫。研究也證實,在腦缺血模型中,靜脈內(nèi)給予經(jīng)基因改造的Ang-1-hBMSCs比單獨給予hBMSCs更能產(chǎn)生更多新生血管和更好的神經(jīng)功能康復(fù)。相反,靜脈給予經(jīng)基因改造的VEGF-hBMSCs反而增加神經(jīng)功能的缺失,這和VEGF導(dǎo)致的血管通透性增加有關(guān)。然而,Miki等[43]研究卻認為給予經(jīng)基因改造的VEGF-hBMSCs比單獨給予hBMSCs有更大的治療作用。因此,VEGF表達水平具有潛在的治療意義。靜脈內(nèi)給予經(jīng)基因改造的Ang-1-VEGF-hBMSCs將會導(dǎo)致更多的新生血管形成和更好的神經(jīng)功能恢復(fù)。
周細胞是hBMSCs的主要來源之一[5,44]。假設(shè)腦缺血性損傷后,周細胞被破壞,hBMSCs的移植具有微血管修復(fù)作用,那么周細胞將是hBMSCs靶向治療微血管修復(fù)的重要靶點。
在側(cè)腦室室管膜下區(qū)(subventricular zone,SVZ)和齒狀回,成年哺乳動物的大腦能產(chǎn)生新的神經(jīng)元前體細胞[45]。這些細胞的一個亞群表達祖細胞的標記巢蛋白。在SVZ神經(jīng)前體細胞通過嘴側(cè)遷移流遷移到嗅球,然后分化成神經(jīng)元[46]。腦缺血后,在SVZ祖細胞的數(shù)量增加;研究表明hBMSCs移植增加祖細胞數(shù)量[3,26]。Shen等[24]研究表明,在hBMSCs移植治療缺血性腦損傷突觸素表達增加,提示軸突發(fā)芽的增加。
在一項可行性、療效、安全使用擴增培養(yǎng)的hBMSCs治療腦卒中患者的研究中,Bang等[47]按隨機化原則隨機分配30例大腦中動脈(middle cerebral artery,MCA)腦梗死患者,均表現(xiàn)出嚴重的神經(jīng)功能障礙。其中5例患者接受靜脈注射1×108hBMSCs。對照組和hBMSCs輸入組的預(yù)處理特征(臨床和放射學(xué))是一致的。入院后1周開始抽吸骨髓,分離出單個核細胞,等細胞貼壁后,選取貼壁細胞用含有胎牛血清的培養(yǎng)基進行擴增培養(yǎng)。表面標記物為CD34-、CD45-、SH2+和SH4+的細胞被定義為hBMSCs,在癥狀出現(xiàn)后4~5周和7~9周給予兩個靜脈輸注,每個輸注為5×107個細胞,并對2組患者進行1年的研究學(xué)習(xí)。
在Bang等[47]研究中,患者有大面積的MCA腦梗死缺血灶,隨訪影像資料為彌散加權(quán)成像的MRI進行記錄。采用巴塞爾指數(shù)測量方法進行評估,hBMSCs輸注組患者顯示更好的神經(jīng)功能恢復(fù),重要的是,hBMSCs輸注組患者無一例死亡、再次腦卒中或是更加嚴重的時間發(fā)生。本研究結(jié)果顯示hBMSCs運用的安全性和適度的神經(jīng)功能改善,但是由于患者數(shù)量較少,研究具有局限性。但是其5年隨訪也證實hBMSCs移植在腦卒中患者中沒有發(fā)生不良反應(yīng)事件[48]。
有報道描述一個Ⅰ期研究,12例腦卒中患者接受了靜脈注射自體hBMSCs[49]。安全性評估第1次在非人靈長類動物模型的建立[50]。本研究的總體結(jié)構(gòu)如圖3概述。在這項研究中患者入院后數(shù)周內(nèi),抽吸骨髓物,細胞貼壁后,取貼壁細胞與來自患者的血清進行培養(yǎng),這種培養(yǎng)方式具有很高的同質(zhì)性[10,51]。 這些患者的細胞表面抗原(CD34-,CD45-,CD73+和CD105+)具有很高的同質(zhì)性。這些細胞在體外進行擴增,安全性評估和抗原表型分析后,冷凍保存。同一天靜脈給予這些細胞。
12例患者行hBMSCs移植后對其進行1年多的MRI影像學(xué)觀察未發(fā)現(xiàn)腫瘤或異常細胞生成。細胞輸注后的第1周國家衛(wèi)生署腦卒中評分有改善,病灶體積有所縮??;有些患者細胞輸注后最初的2周神經(jīng)功能顯著改善(圖3)。此外,還有患者細胞輸注后最初的2周病灶體積變?。▓D3B),與病灶體積減少的是神經(jīng)功能改善(圖3C)[49]。相關(guān)評估顯示沒有嚴重的不良反應(yīng)。
作為一個臨床Ⅰ期研究,這個研究沒有進行雙盲也沒有安慰劑作對照,其結(jié)果不可靠。在這些患者中細胞輸注后,發(fā)生自發(fā)性的功能恢復(fù)不能排除。然而,在腦卒中患者接受細胞輸注的36~136 d里,缺血灶明顯縮小,神經(jīng)功能恢復(fù)明顯好轉(zhuǎn),這些均鼓勵進一步研究。
圖3 12例腦卒中患者靜脈注射自體骨髓基質(zhì)干細胞的數(shù)據(jù)統(tǒng)計
在一些神經(jīng)系統(tǒng)疾病中系統(tǒng)性給予hBMSCs細胞治療的研究已檢查并證實是相對安全的[47,49]。最佳的治療方案、移植細胞的數(shù)量、制備方式和移植的時間點都需要進一步研究。早期進行細胞輸注后,可通過調(diào)節(jié)hBMSCs釋放興奮因子(如BDNF)獲得有益的影響。hBMSCs還可以提供招募神經(jīng)元的營養(yǎng)支持,尤其是在半影中;抗炎反應(yīng)減少神經(jīng)腦水腫,從而導(dǎo)致增強腦組織的保護。隨著時間的增加,hBMSCs可促進新生血管形成、血管穩(wěn)定和血腦屏障的重塑,從而保護中樞神經(jīng)系統(tǒng)的組織和限制性腦水腫。hBMSCs也可以刺激缺血局灶區(qū)軸突出芽和新的突觸連接。而且,hBMSCs能夠招募缺血局灶區(qū)祖細胞有助于神經(jīng)髓鞘和軸突的發(fā)生。這些潛在的作用機制值得進一步研究。希望今后的臨床研究,可以最終確定治療干預(yù),通過細胞或無細胞的方法,在亞急性和慢性早期階段能夠積極影響細胞的存活和提高腦卒中的臨床觀察。
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(本文編輯:張麗)
項永生,徐如祥.骨髓基質(zhì)干細胞在腦缺血疾病治療的新進展[J/CD].中華神經(jīng)創(chuàng)傷外科電子雜志,2017,3(5):300-304.
New progress of bone marrow mesenchymal stem cells in the treatment of cerebral ischemic diseases
Xiang Yongsheng,Xu Ruxiang.Affiliated Bayi Brain Hospital,PLA General Hospital,Beijing 100700,China
Corresponding author:Xu Ruxiang,Email:xuruxiang1123@163.com
Adult bone marrow stromal stem cells(hBMSCs)is a kind of multi potential adult stem cells derived from bone marrow.The model mechanisms of transplantation to improve cerebral ischemia model and spinal cord injury model may include replacing damaged cells,protective effect of nerve function,the induction of axon growth,and the formation of new blood vessels.Its main advantage is that it can be used in cell therapy,so there is no limit to the immune rejection,ethical problems and tumorigenicity caused by embryonic stem cell transplantation;its material is easy to be obtained,unlike neural stem cells,which are mainly located in the lower zone of the brain and hippocampus,the cell source is limited,so it is difficult to obtained.Therefore,this stem cell transplantation therapy may be of great significance in the future clinical treatment.
Bone marrow stromal stem cells;Cerebral ischemic disease;Stem cell treatment
10.3877/cma.j.issn.2095-9141.2017.05.011
國家自然科學(xué)基金(81671189);全軍醫(yī)學(xué)科研十二五重點課題(BWS11J002)
100700北京,陸軍總醫(yī)院附屬八一腦科醫(yī)院
徐如祥,Email:zjxuruxiang@163.com