國 敏,崔 梅,董 強(qiáng)
?
缺氧誘導(dǎo)因子-1靶基因參與生酮飲食提高大腦中動(dòng)脈閉塞模型小鼠腦缺血耐受作用
國 敏,崔 梅,董 強(qiáng)
[摘要]目的 探究生酮飲食對(duì)大腦中動(dòng)脈閉塞(middle cerebral artery occlusion,MCAO)模型小鼠的作用及缺氧誘導(dǎo)因子-1靶基因參與機(jī)制。方法 小鼠隨機(jī)分為正常對(duì)照組及標(biāo)準(zhǔn)飲食組、高碳水化合物飲食組、生酮飲食組,建模前通過3周飲食干預(yù)后,飲食干預(yù)的3組小鼠建造MCAO模型,正常對(duì)照組給予標(biāo)準(zhǔn)飲食但不進(jìn)行MCAO造模。2,3,5-三苯基氯化四氮唑染色觀察腦梗死體積,Longa評(píng)分法對(duì)模型鼠進(jìn)行神經(jīng)功能評(píng)分,聚合酶鏈反應(yīng)檢測缺血區(qū)腦組織缺氧誘導(dǎo)因子-1下游靶基因紅細(xì)胞生成素、血管內(nèi)皮生長因子、葡萄糖轉(zhuǎn)運(yùn)體1、單羧酸轉(zhuǎn)運(yùn)體4的mRNA表達(dá)量。結(jié)果 生酮飲食組小鼠腦組織梗死體積更小,神經(jīng)功能評(píng)分更低,缺血區(qū)腦組織中紅細(xì)胞生成素、血管內(nèi)皮生長因子、葡萄糖轉(zhuǎn)運(yùn)體1、單羧酸轉(zhuǎn)運(yùn)體4的mRNA表達(dá)顯著增加。結(jié)論 生酮飲食可能是通過增加缺血區(qū)缺氧誘導(dǎo)因子-1靶基因表達(dá),從而提高M(jìn)CAO小鼠腦組織對(duì)缺血的耐受性。
[關(guān)鍵詞]生酮飲食;大腦中動(dòng)脈閉塞;缺氧誘導(dǎo)因子-1靶基因;卒中
[作者單位]200040上海,復(fù)旦大學(xué)附屬華山醫(yī)院神經(jīng)內(nèi)科(國敏,崔 梅,董 強(qiáng))
缺血性卒中通常由局部腦組織血流量降低引起,是目前世界范圍內(nèi)引起死亡和終身殘疾的主要原因之一[1]。腦組織對(duì)缺血、缺氧損傷敏感,但是研究發(fā)現(xiàn)預(yù)先給予非致死性缺血、缺氧刺激腦組織能夠產(chǎn)生內(nèi)源性保護(hù)機(jī)制,稱為耐受[2]。缺氧預(yù)適應(yīng)是目前研究較多的誘導(dǎo)局部或全腦缺血后缺血耐受的方法。將動(dòng)物暴露于輕度低氧環(huán)境,觀察到腦缺氧預(yù)適應(yīng)能減輕缺血性卒中動(dòng)物模型腦梗死體積[3-4]。缺氧誘導(dǎo)因子-1(hypoxia inducible factor-1,HIF-1)是缺氧預(yù)適應(yīng)時(shí)激活的關(guān)鍵因子[5-6],HIF-1作為轉(zhuǎn)錄因子可調(diào)節(jié)下游靶基因,如紅細(xì)胞生成素(erythropoietin,EPO)、血管內(nèi)皮生長因子(vascular endothelial growth factor,VEGF)、葡萄糖轉(zhuǎn)運(yùn)體1(glucose transporter 1,GLUT1)、單羧酸轉(zhuǎn)運(yùn)體4(monocarboxylate transporter 4,MCT4)的表達(dá),通過促進(jìn)代謝、血管生成、葡萄糖轉(zhuǎn)運(yùn)等作用參與損傷修復(fù),提高腦缺氧耐受[7-8]。盡管缺氧預(yù)適應(yīng)在實(shí)驗(yàn)中有效,但臨床上卒中對(duì)象為人,卒中發(fā)生時(shí)間也無法準(zhǔn)確預(yù)知,其應(yīng)用于臨床難以實(shí)施,亟待尋找臨床可行的其他干預(yù)方法。
生酮飲食為高脂肪、低碳水化合物飲食,供給機(jī)體代謝所需的碳水化合物較少,因此脂肪成為主要能量來源。生酮飲食最初作為癲癇的非藥物療法取得較好的臨床效果[9],后來研究發(fā)現(xiàn)其對(duì)阿爾茨海默病和癡呆均有臨床療效[10],但生酮飲食對(duì)缺血性卒中的作用仍有待闡明。有研究報(bào)道[11],生酮飲食可增加缺血腦組織HIF-1含量,但HIF-1下游靶基因在生酮飲食中作用機(jī)制仍需探究。為進(jìn)一步闡明生酮飲食對(duì)缺血性卒中HIF-1靶基因的影響,本研究擬采用大腦中動(dòng)脈閉塞(middle cerebral artery occlusion,MCAO)小鼠模型,探究生酮飲食對(duì)HIF-1下游靶基因的表達(dá)及腦缺血損傷的影響。
1.1實(shí)驗(yàn)動(dòng)物分組及處理 正常健康8~10周齡雌性C57BL/6小鼠24只[上海斯萊克實(shí)驗(yàn)動(dòng)物有限公司,SCXK-(滬)-2012-0002)],體質(zhì)量18~25 g,清潔級(jí)。小鼠隨機(jī)分為正常對(duì)照(normal control,NC)組、標(biāo)準(zhǔn)飲食(standard diet,SD)組、高碳水化合物飲食(high carbohydrate,HC)組、生酮飲食(ketogenic diet,KD)組4組(每組6只)。NC組給予標(biāo)準(zhǔn)飲食但不進(jìn)行MCAO造模,其他3組動(dòng)物飲食配比情況見表1。各組在進(jìn)行不同飲食干預(yù)前,所有小鼠饑餓處理18 h以平衡個(gè)體間血糖水平后,分別接受不同飲食干預(yù)3周[11]。
表1 小鼠飲食配比表
1.2方法
1.2.1MCAO模型 飲食處理3周后,SD組、HC組及KD組小鼠腹腔注射氯胺酮(65 mg/kg)和甲苯噻嗪(6mg/kg)進(jìn)行麻醉,頭部置于立體定位儀(KOPF,美國,Stoelting公司),四肢放置在加熱墊上,使體溫保持在37℃。將激光多普勒探頭置于顱骨前囟旁開5 mm、后開2 mm處,石蠟包被的尼龍線栓從頸外動(dòng)脈置入至大腦中動(dòng)脈,同時(shí)用激光多普勒血流儀觀察局部腦血流量降至基線水平的25%以下。45 min后取出尼龍線栓并頸外動(dòng)脈進(jìn)行永久性結(jié)扎,頸總動(dòng)脈暫時(shí)結(jié)扎后恢復(fù)灌注。只有缺血期血流降至基線水平的25%以下、灌注期血流恢復(fù)80%以上的小鼠納入后續(xù)實(shí)驗(yàn)。
1.2.2小鼠神經(jīng)功能評(píng)定 MCAO模型72 h后,用Longa評(píng)分法對(duì)模型小鼠神經(jīng)功能進(jìn)行評(píng)定。評(píng)價(jià)標(biāo)準(zhǔn):0級(jí),無缺陷;1級(jí),不能伸展對(duì)側(cè)前肢;2級(jí),對(duì)側(cè)前肢屈曲;3級(jí),輕度向?qū)?cè)轉(zhuǎn)圈;4級(jí),嚴(yán)重的轉(zhuǎn)圈;5級(jí),對(duì)側(cè)癱瘓。神經(jīng)功能3~4級(jí)小鼠為成功模型。
1.2.3腦梗死體積測量 MCAO模型小鼠腦梗死72 h后處死,將腦組織在-20℃冰凍20 min,用切片機(jī)切成5~6片、厚度2 mm。37℃下腦片置于2,3,5-三苯基氯化四氮唑(2,3,5-triphenyl tetrazolium chloride,TTC)染色測量腦梗死體積,TTC染液避光染色1 h,期間翻轉(zhuǎn)腦片數(shù)次使著色均勻。對(duì)每個(gè)腦片進(jìn)行拍照,Image J軟件計(jì)算梗死體積。
1.2.4HIF-1下游靶基因 MCAO模型小鼠腦梗死72 h后處死,斷頭取腦組織,取大腦中動(dòng)脈供血區(qū)腦皮質(zhì),組織勻漿,用RNA提取試劑盒(美國,Qiagen公司)提取總RNA,用SuperScriptⅢ試劑盒(美國,Invitrogen公司)合成互補(bǔ)DNA,聚合酶鏈反應(yīng)(polymease chain reaction,PCR)檢測HIF-1下游靶基因。PCR反應(yīng)采用SYBR GreenⅠMaster Mix試劑盒(美國,Biored公司),反應(yīng)體系含上、下游引物各1μL,各基因所用引物見表2,操作均按照說明書進(jìn)行。所有的樣品均設(shè)置副孔,并作標(biāo)準(zhǔn)曲線以計(jì)算各樣本基因表達(dá)量,結(jié)果以目的基因mRNA與β-actin mRNA表達(dá)量的比值(%)表示。
表2 目的基因引物序列
1.3統(tǒng)計(jì)學(xué)處理 應(yīng)用SPSS 20.0軟件,計(jì)量資料以均數(shù)±標(biāo)準(zhǔn)差(±s)表示,多組計(jì)量資料比較采用單因素方差分析(ANOVA),P<0.05為差異有統(tǒng)計(jì)學(xué)意義。
2.1腦梗死體積及神經(jīng)功能評(píng)分 MCAO模型建立72 h后不同飲食組小鼠的腦梗死體積測量(圖1),SD組梗死體積平均為47 mm3,HC組梗死體積平均為48 mm3,神經(jīng)功能評(píng)分均為3分(圖2)。與SD組和HC組相比,KD組腦梗死體積減小(P<0.05),平均為28mm3;KD組神經(jīng)功能評(píng)分降低(P<0.05),為2分。
圖1 MCAO模型腦梗死體積
圖2 MCAO模型神經(jīng)功能評(píng)分
2.2HIF-1下游靶基因mRNA表達(dá) 大腦中動(dòng)脈供血區(qū)腦皮質(zhì)HIF-1靶基因mRNA,與NC組相比,3個(gè)飲食組缺血腦組織中VEGF、EPO、GLUT1、MCT4 的mRNA表達(dá)均增加,但是KD組mRNA表達(dá)量更高(P<0.01)分別增至正常對(duì)照組的3.4倍、14倍、3倍和3.7倍;與SD組、HC組相比,KD組表達(dá)量的增加也有統(tǒng)計(jì)學(xué)意義(P<0.05,圖3)。
圖3 HIF-1下游靶基因mRNA表達(dá)量
生酮飲食是一種高脂肪、低碳水化合物飲食,脂肪代謝產(chǎn)生大量酮體包括β羥基丁酸、乙酰乙酸和丙酮,可經(jīng)單羧酸轉(zhuǎn)運(yùn)體轉(zhuǎn)運(yùn)入細(xì)胞,在葡萄糖缺乏時(shí)可作為腦組織的能量來源[10-12]。在MCAO小鼠模型股靜脈注射β羥基丁酸能通過提高缺血期腦組織能量代謝效率而減輕腦組織水腫,減輕梗死程度[11]。實(shí)驗(yàn)觀察到3周生酮飲食可減小MCAO小鼠腦梗死體積,神經(jīng)功能評(píng)分好轉(zhuǎn),說明生酮飲食可提高腦缺血耐受性。
HIF-1由HIF-1α亞基和HIF-1β亞基組成,HIF-1β亞基恒定表達(dá),而HIF-1α亞基在細(xì)胞缺氧時(shí)增加,從轉(zhuǎn)錄水平調(diào)節(jié)促細(xì)胞存活信號(hào)通路[7]。正常狀態(tài)下,HIF-1α表達(dá)后脯氨酸殘基被羥基化,通過泛素連接酶介導(dǎo)蛋白酶體迅速降解,細(xì)胞內(nèi)無HIF-1α亞基累積[13]。生酮飲食干預(yù)時(shí),酮體代謝使得細(xì)胞內(nèi)琥珀酸鹽含量增加[11],從而抑制脯氨酸羥化酶,未被羥基化的HIF-1α亞基逃脫蛋白酶體的降解,HIF-1α含量增加并與HIF-1β亞基結(jié)合為二聚體,形成有活性的HIF復(fù)合體。HIF-1作為轉(zhuǎn)錄因子可調(diào)節(jié)一系列下游基因,包括VEGF、EPO、GLUT1和MCT4。
VEGF可促進(jìn)血管生成,腦缺血、缺氧時(shí)VEGF在神經(jīng)元和星形膠質(zhì)細(xì)胞表達(dá)快速增加[14]。本研究也觀察到MCAO處理后,3組小鼠缺血腦組織中VEGFmRNA表達(dá)量均有增加。有研究報(bào)道,VEGF可減少低氧狀態(tài)培養(yǎng)的海馬神經(jīng)元死亡[15],局部補(bǔ)充VEGF減小梗死體積、減輕局部腦水腫[16],腦缺血損傷后48 h靜脈注射VEGF提高神經(jīng)功能預(yù)后[17]。生酮飲食干預(yù)也觀察到MCAO小鼠腦梗死體積下降、神經(jīng)功能評(píng)分好轉(zhuǎn),VEGF mRNA表達(dá)量較SD組和HC組更高,提示VEGF參與生酮飲食提高腦缺血耐受作用。
EPO表達(dá)也受HIF-1調(diào)節(jié),其作為紅細(xì)胞生長因子在缺血、缺氧損傷動(dòng)物模型中也具有增強(qiáng)血管生成的作用,且研究發(fā)現(xiàn)EPO及EPO受體在中樞均有表達(dá)[18-19]。免疫熒光雙染色顯示缺血損傷8 h 后EPO主要在神經(jīng)元表達(dá),1周后主要在星形膠質(zhì)細(xì)胞表達(dá)[20],星形膠質(zhì)細(xì)胞表達(dá)的EPO可作為旁分泌因子作用于神經(jīng)元。MCAO模型小鼠建模72 h前缺氧預(yù)適應(yīng)3 h,可使缺血1 h后腦EPO轉(zhuǎn)錄水平增加7倍[11],在體、離體實(shí)驗(yàn)均支持給予EPO干預(yù)對(duì)神經(jīng)元的缺氧損傷具有保護(hù)作用[3,21]。本研究觀察到MCAO缺血處理后,SD組及HC組小鼠EPO mRNA水平升高,而KD組升高約14倍,說明EPO在生酮飲食提高腦缺血耐受中也發(fā)揮作用。
GLUT1在內(nèi)皮細(xì)胞廣泛分布,是跨血腦屏障轉(zhuǎn)運(yùn)葡萄糖的主要轉(zhuǎn)運(yùn)體[22]。細(xì)胞外葡萄糖濃度很高時(shí),腦內(nèi)皮細(xì)胞GLUT1表達(dá)減少,跨血腦屏障葡萄糖轉(zhuǎn)運(yùn)減少[23]。MCT4屬于單羧酸轉(zhuǎn)運(yùn)體家族,可以跨細(xì)胞膜雙向轉(zhuǎn)運(yùn)乳酸,可攝取細(xì)胞外乳酸儲(chǔ)存作為能量,細(xì)胞內(nèi)乳酸增多時(shí)MCT4也可將其轉(zhuǎn)運(yùn)出細(xì)胞外,防止酸中毒。MCT4主要分布在星形膠質(zhì)細(xì)胞[24],缺氧時(shí)MCT4可經(jīng)HIF-1誘導(dǎo)表達(dá)增加[25],星形膠質(zhì)細(xì)胞通過糖酵解釋出乳酸被神經(jīng)元攝取作為能量來源,此過程依賴MCT4[26]。葡萄糖和氧氣剝奪條件下觀察到神經(jīng)元死亡,而神經(jīng)元和膠質(zhì)細(xì)胞共培養(yǎng)體系中神經(jīng)元存活[27]。所以,GLUT1、MCT4是腦缺血時(shí)增加神經(jīng)元能量供應(yīng)的重要分子。本實(shí)驗(yàn)觀察到缺血時(shí)GLUT1、MCT4的mRNA表達(dá)增加,KD組表達(dá)量更高,與其提高腦缺血耐受作用一致,說明GLUT1和MCT4可能通過增加神經(jīng)元供能而發(fā)揮保護(hù)作用。
綜上,本研究證實(shí)了生酮飲食能提高M(jìn)CAO大鼠腦缺血耐受性,其作用可能是通過上調(diào)HIF-1靶基因水平實(shí)現(xiàn),生酮飲食能否用于缺血性卒中患者仍需進(jìn)一步臨床研究。
【參考文獻(xiàn)】
[1]Lopez AD,Mathers CD,Ezzati M,et al.Global and regional burden of disease and risk factors,2001:systematic analysis of population health data[J].Lancet,2006,367(9524): 1747-1757.
[2]Kitagawa K,Matsumoto M,Tagaya M,et al.‘Ischemic tolerance'phenomenon found in the brain[J].Brain Res,1990,528(1):21-24.
[3]Prass K,Scharff A,Ruscher K,et al.Hypoxia-induced stroke tolerance in themouse ismediated by erythropoietin [J].Stroke,2003,34(8):1981-1986.
[4]Bernaudin M,Nedelec AS,Divoux D,et al.Normobaric hypoxia induces tolerance to focal permanent cerebral ischemia in association with an increased expression ofhypoxiainducible factor-1 and its target genes,erythropoietin and VEGF,in the adultmouse brain[J].JCereb Blood Flow Metab,2002,22(4):393-403.
[5]Taie S,Ono J,Iwanaga Y,et al.Hypoxia-inducible factor-1 alpha has a key role in hypoxic preconditioning[J].JClin Neurosci,2009,16(8):1056-1060.
[6]Wacker BK,Perfater JL,Gidday JM.Hypoxic preconditioning induces stroke tolerance in mice via a cascading HIF,sphingosine kinase,and CCL2 signaling pathway[J]. JNeurochem,2012,123(6):954-962.
[7]Semenza GL.HIF-1:mediator of physiological and pathophysiological responses tohypoxia[J].JAppl Physiol(1985),2000,88(4):1474-1480.
[8]Sharp FR,Bernaudin M.HIF1 and oxygen sensing in the brain[J].Nat Rev Neurosci,2004,5(6):437-448.
[9]Sinha SR,Kossoff EH.The ketogenic diet[J].Neurologist,2005,11(3):161-170.
[10]Gasior M,RogawskiMA,Hartman AL.Neuroprotective and disease-modifying effects of the ketogenic diet[J].Behav Pharmacol,2006,17(5/6):431-439.
[11]Puchowicz MA,Zechel JL,Valerio J,et al.Neuroprotection in diet-induced ketotic rat brain after focal ischemia[J].J Cereb Blood Flow Metab,2008,28(12):1907-1916.
[12]Pierre K,Pellerin L.Monocarboxylate transporters in the central nervous system:distribution,regulation and function[J].JNeurochem,2005,94(1):1-14.
[13]Huang LE,Gu J,Schau M,et al.Regulation of hypoxia-inducible factor 1alpha is mediated by an O2-dependent degradation domain via the ubiquitin-proteasome pathway [J].Proc Natl Acad Sci USA,1998,95(14):7987-7992.
[14]Pichiule P,Agani F,Chavez JC,et al.HIF-1 alpha and VEGF expression after transient global cerebral ischemia [J].Adv Exp Med Biol,2003,530:611-617.
[15]Jin KL,Mao XO,Nagayama T,et al.Induction of vascular endothelial growth factor receptors and phosphatidylinositol 3′-kinase/Akt signaling byglobal cerebral ischemia in the rat[J].Neuroscience,2000,100(4):713-717.
[16]Hayashi T,Abe K,Itoyama Y.Reduction of ischemic damage by application of vascular endothelial growth factor in rat brain after transient ischemia[J].J Cereb Blood Flow Metab,1998,18(8):887-895.
[17]Zhang ZG,Zhang L,Jiang Q,et al.VEGF enhances angiogenesis and promotes blood-brain barrier leakage in the ischemic brain[J].JClin Invest,2000,106(7):829-838.
[18]Morishita E,Masuda S,Nagao M,et al.Erythropoietin receptor is expressed in rat hippocampal and cerebral cortical neurons,and erythropoietin prevents in vitro glutamateinduced neuronal death[J].Neuroscience,1997,76(1): 105-116.
[19]Marti HH,Wenger RH,Rivas LA,et al.Erythropoietin gene expression in human,monkey and murine brain[J]. Eur JNeurosci,1996,8(4):666-676.
[20]Mu D,Chang YS,Vexler ZS,et al.Hypoxia-inducible factor 1alpha and erythropoietin upregulation with deferoxamine salvage after neonatal stroke[J].Exp Neurol,2005,195(2):407-415.
[21]Baranova O,Miranda LF,Pichiule P,et al.Neuron-specific inactivation of the hypoxia inducible factor 1 alpha increases brain injury in amousemodel of transient focal cerebral ischemia[J].JNeurosci,2007,27(23):6320-6332.
[22]Guo X,Geng M,Du G.Glucose transporter 1,distribution in the brain and in neural disorders:its relationship with transport of neuroactive drugs through the blood-brain barrier[J].Biochem Genet,2005,43(3/4):175-187.
[23]Alpert E,Gruzman A,Riahi Y,et al.Delayed autoregulation of glucose transport in vascular endothelial cells[J]. Diabetologia,2005,48(4):752-755.
[24]Lim KS,Lim KJ,Price AC,et al.Inhibition of monocarboxylate transporter-4 depletes stem-like glioblastoma cells and inhibits HIF transcriptional response in a lactate-independentmanner[J].Oncogene,2014,33(35):4433-4441.
[25]Ullah MS,Davies AJ,Halestrap AP.The plasmamembrane lactate transporter MCT4,but not MCT1,is up-regulated by hypoxia through a HIF-1alpha-dependent mechanism [J].JBiol Chem,2006,281(14):9030-9037.
[26]Rosafio K,Pellerin L.Oxygen tension controls the expression of themonocarboxylate transporter MCT4 in cultured mouse cortical astrocytes via a hypoxia-inducible factor-1α-mediated transcriptional regulation[J].Glia,2014,62 (3):477-490.
[27]Gao C,Zhou L,Zhu W,et al.Monocarboxylate transporterdependentmechanism confers resistance to oxygen-and glucose-deprivation injury in astrocyte-neuron co-cultures [J].Neurosci Lett,2015,594:99-104.
Ketogenic dietmay im prove ischem ic tolerance ofm idd le cerebral artery occlusion m ice through up-regulation of hypoxia inducible factor-1 target genes
GUO Min,CUIMei,DONGQiang
(Department of Neurology,Huashan Hospital,F(xiàn)udan University,Shanghai200040,China)
[Abstract]Objective To explore the effects of ketogenic diet on middle cerebral artery occlusion(MCAO)mice and the role of hypoxia inducible factor-1(HIF-1)target genes in this process.M ethods C57BL/6 mice were random ly allocated into four groups:standard diet group,high carbohydrate diet group,ketogenic diet group and control group.Mice of the 3 intervention groups were fed with corresponding diets for 3 weeks and were afterwards made into MCAO mice models.Control group was fed with standard diet for 3 weeks without MCAO treatment.Stroke volume wasmeasured by 2,3,5-triphenyl tetrazolium chloride(TTC)staining.Neurological function was accessed by Longa scoringmethod.Polymerase chain reaction(PCR)was used to detectmRNA expression quantity of HIF-1 downstream target genes including erythropoietin(EPO),vascular endothelial growth factor(VEGF),glucose transport 1(GLUT1)and monocarboxylic transporter 4 (MCT4)in the ischemic region.Results Compared with the other 3 groups,ketogenic diet group showed smaller stroke volume,better neurological score and higher mRNA expression quantity of HIT-1 downstream target genes.Conclusion Ketogenic dietmay improve brain ischemic tolerance of MCAOmice through up-regulation of HIF-1 target genes.
[Key words]Ketogenic diet;Middle cerebral artery occlusion(MCAO);Hypoxia inducible factor-1(HIF-1)target genes;Stroke
(收稿日期:2015-12-18 本文編輯:徐海琴)
[通訊作者]董 強(qiáng),E-mail:dong_qiang@fudan.edu.cn
[基金項(xiàng)目]國家自然科學(xué)基金(81271295)
doi:10.3969/j.issn.2095-3097.2016.01.002
[中圖分類號(hào)]R743.33-332
[文獻(xiàn)標(biāo)志碼]A
[文章編號(hào)]2095-3097(2016)01-0005-05