楊卓瑾,張玉向,楊茜茜,高菲菲,楊婧思,閻春霞
組蛋白去甲基化酶KDM7家族在腦疾病中研究進(jìn)展
楊卓瑾1,2,3,張玉向1,2,3,楊茜茜1,2,3,高菲菲1,2,3,楊婧思1,2,3,閻春霞1,2,3
1. 西安交通大學(xué)法醫(yī)學(xué)院, 西安 710061 2. 國家衛(wèi)生健康委員會法醫(yī)學(xué)重點(diǎn)實(shí)驗(yàn)室(西安交通大學(xué)),西安 710061 3. 西安交通大學(xué)西部科技創(chuàng)新港生物證據(jù)研究院,西安 712000
組蛋白去甲基化酶KDM7家族包括KDM7A、KDM7B、KDM7C三種蛋白,主要通過去除與轉(zhuǎn)錄沉默相關(guān)的特定組蛋白賴氨酸甲基化修飾,進(jìn)而對基因轉(zhuǎn)錄發(fā)揮調(diào)控作用。目前,對KDM7家族的研究主要集中于其在神經(jīng)分化、腫瘤發(fā)生發(fā)展等過程中的作用,而對其在腦神經(jīng)疾病中的作用卻知之甚少。本文從該蛋白家族表觀遺傳調(diào)控機(jī)制、結(jié)構(gòu)生物學(xué)及其在腦神經(jīng)疾病中的作用等方面進(jìn)行了綜述,以期為研究其在腦神經(jīng)疾病中的功能機(jī)制提供參考,為理解腦神經(jīng)疾病分子病理機(jī)制以及探索基于該機(jī)制的有效治療靶點(diǎn)帶來新的啟示。
組蛋白去甲基化酶;KDM7;H3K9me2;H3K27me2
隨著近年來工業(yè)化、城鎮(zhèn)化及人口老齡化的加速發(fā)展,智力障礙、精神分裂癥、藥物成癮等疾病已經(jīng)成為嚴(yán)重威脅公眾健康、阻礙人口素質(zhì)提升的重要腦神經(jīng)系統(tǒng)疾病?!读~刀》雜志發(fā)布的2019年《全球疾病負(fù)擔(dān)(global burden of disease, GBD)報(bào)告》[1]顯示,精神障礙疾病是全世界十大疾病負(fù)擔(dān)之一,全世界14.3%的死亡,即每年約800萬例死亡是由精神障礙造成的[2];其中精神分裂癥影響著全世界至少2600萬人口,并間接影響了周邊1~2倍人口的生活[3]。此外,《2021年世界毒品報(bào)告》[4]顯示,2020年全球每年約有2.75億人吸毒,超過3600萬人患有毒品成癮,僅2010~ 2019年期間,吸毒人數(shù)增加了22%,因吸毒而死亡的人數(shù)急劇上升[1]。為此,有關(guān)腦疾病與腦科學(xué)問題已經(jīng)在全球范圍內(nèi)被提升至戰(zhàn)略高度。
目前,對于這些腦神經(jīng)疾病認(rèn)識依然不足,探究并發(fā)掘疾病進(jìn)展過程中新的調(diào)控分子,有望為藥物研發(fā)提供新的治療靶點(diǎn)。近年來,越來越多的研究發(fā)現(xiàn)表觀遺傳修飾在智力障礙、精神分裂癥、藥物成癮和其他腦神經(jīng)疾病的病因?qū)W和病理生理學(xué)中起作用[5,6]。其中,組蛋白去甲基化酶KDM7家族被發(fā)現(xiàn)在大腦發(fā)育過程中可以消除染色質(zhì)沉默標(biāo)記,對大腦正常發(fā)育至關(guān)重要[7]。本文主要結(jié)合表觀遺傳調(diào)控、組蛋白甲基化機(jī)制,從結(jié)構(gòu)生物學(xué)和分子生物學(xué)角度介紹了近年來KDM7家族成員調(diào)控腦神經(jīng)疾病的研究進(jìn)展,期望為腦神經(jīng)疾病的防治和干預(yù)提供新思路。
表觀遺傳(epigenetics)是指基因組核苷酸序列無變化的前提下,基因表達(dá)或細(xì)胞表型發(fā)生可穩(wěn)定遺傳的改變,組蛋白修飾(histone modification)是最常見的表觀遺傳修飾之一[8]。
組蛋白(histone, H)主要有H1、H2A、H2B、H3和H4五種亞型,每種組蛋白特別是其柔性尾巴能發(fā)生各種類型的共價(jià)修飾,稱為組蛋白記號(histone mark)或組蛋白密碼(histone code),是調(diào)控DNA復(fù)制、轉(zhuǎn)錄和修復(fù)的重要機(jī)制[9]。
組蛋白修飾包括甲基化(methylation)、乙?;?acetylation)、磷酸化(phosphorylation)、泛素化(ubiquitination)、SUMO化(sumoylation)、ADP-核糖基化(ADP-ribosylation)、生物素化(biotinylation)、巴豆?;?crotonylation)、乳酸化(lactylation)、異丁基化(isobutyrylation)等類型[10~13]。不同類型和位點(diǎn)的修飾由不同的酶催化產(chǎn)生或消除,并可被特異的效應(yīng)蛋白識別。根據(jù)酶的調(diào)控狀態(tài),組蛋白修飾始終處于高度動態(tài)中。大多數(shù)情況下,這幾種形式的組蛋白修飾并不是獨(dú)立存在的,而是通過組合識別(combinatorial readout)來共同介導(dǎo)基因的轉(zhuǎn)錄增強(qiáng)或抑制[14]。KDM7家族主要通過去除與轉(zhuǎn)錄沉默相關(guān)的組蛋白H3賴氨酸9、賴氨酸27及組蛋白H4賴氨酸20上的甲基化修飾起轉(zhuǎn)錄激活作用[15]。
組蛋白甲基化是指在組蛋白甲基轉(zhuǎn)移酶(histone methyltransferase, HMT)催化下,組蛋白H3或H4的N端賴氨酸(lysine,K)或者精氨酸(arginine,R)殘基發(fā)生甲基化[16],是最具特征的組蛋白修飾之一[17],常發(fā)生在H3K4、H3K9、H3K27、H3K36、H4K12等位點(diǎn)[18,19]。HMT包括賴氨酸特異性和精氨酸特異性甲基化轉(zhuǎn)移酶兩個(gè)家族[20],賴氨酸可以被單甲基化(me1)、雙甲基化(me2)或三甲基化(me3),精氨酸可以被單甲基化或發(fā)生對稱或非對稱雙甲基化[21]。組蛋白甲基化通過被修飾的特定氨基酸殘基來決定轉(zhuǎn)錄的激活或是抑制[22],從而調(diào)控遺傳印跡、神經(jīng)干細(xì)胞增殖及分化和細(xì)胞有絲分裂等重要發(fā)育過程[23,24]。
目前已有大量研究表明組蛋白甲基化修飾與腦神經(jīng)疾病存在相關(guān)性。Burgold等[25]的細(xì)胞實(shí)驗(yàn)結(jié)果表明組蛋白修飾是小鼠胚胎干細(xì)胞分化成為神經(jīng)干細(xì)胞的必要條件,是控制神經(jīng)發(fā)生的關(guān)鍵調(diào)節(jié)器。其次,腦內(nèi)H3K27的甲基化可使染色質(zhì)濃縮,進(jìn)而抑制基因表達(dá),從而調(diào)控酒精成癮過程中的炎性反應(yīng)[26]。組蛋白甲基轉(zhuǎn)移酶G9a通過對常染色質(zhì)區(qū)域組蛋白H3K9和H3K27位點(diǎn)的甲基化來控制基因表達(dá),此過程與嗎啡、可卡因、酒精等藥物成癮和精神發(fā)育遲緩等各類腦疾病有關(guān)。Chaudhury等[27]選用在情感反應(yīng)上表現(xiàn)出穩(wěn)定差異的高反應(yīng)(high responder, HR)和低反應(yīng)(low responder, LR)大鼠品系進(jìn)行研究,其中LR傾向于焦慮和抑郁樣表型,HR傾向于成癮表型,兩類大鼠的海馬、杏仁核和伏隔核中H3K9me3基礎(chǔ)水平存在顯著差異,提示表型與表觀遺傳的基礎(chǔ)差異有關(guān),進(jìn)一步研究顯示成纖維細(xì)胞生長因子2 (fibroblast growth factor 2, FGF2)可以改變這種表觀遺傳基礎(chǔ)差異。具體而言,F(xiàn)GF2通過降低LR大鼠海馬、杏仁核及伏隔核中H3K9me3水平及其與FGF2啟動子的結(jié)合,使LR大鼠在各腦區(qū)中的H3K9me3水平更接近于HR大鼠。相反,海馬中FGF2敲除可以提高HR的焦慮行為和H3K9me3水平,使它們在各腦區(qū)中的H3K9me3水平更接近于LR。這些發(fā)現(xiàn)表明FGF2是與情緒反應(yīng)相關(guān)的表觀遺傳機(jī)制的修飾因子,H3K9me3是調(diào)節(jié)情感脆弱性的關(guān)鍵因素。
細(xì)胞周期蛋白依賴激酶5(cyclin-dependent kinase 5,Cdk5)在神經(jīng)系統(tǒng)中高度表達(dá),可以調(diào)節(jié)中邊緣獎賞回路中的多巴胺信號,在獎賞形成中發(fā)揮作用。Heller等[28]選擇人工鋅指蛋白(zinc finger protein,ZFP)轉(zhuǎn)錄因子靶向Cdk5啟動子來修飾該位點(diǎn)的組蛋白,并在體內(nèi)雙向調(diào)節(jié)Cdk5基因表達(dá)。當(dāng)靶向Cdk5基因的ZFP與甲基轉(zhuǎn)移酶G9a融合時(shí)會富集H3K9me2,抑制Cdk5的基因表達(dá),從而減弱可卡因誘導(dǎo)的運(yùn)動行為和條件性位置偏愛(conditioned place preference,CPP)。以上研究為H3K9me2參與控制獎賞和應(yīng)激反應(yīng)提供了科學(xué)證據(jù)。
組蛋白的甲基化水平同時(shí)受到去甲基化酶(histone lysine demethylase, KDM)調(diào)控。迄今為止已發(fā)現(xiàn)兩類組蛋白去甲基化酶,KDM1家族又稱賴氨酸特異性脫甲基酶(lysine-specific histone demethylase,LSD)家族,是與單胺氧化酶(monoamine oxidase,MAOs)密切相關(guān)的黃素依賴性酶[42],它只作用于單甲基賴氨酸和雙甲基賴氨酸。賴氨酸特異性組蛋白去甲基化酶1 (LSD1)是一種驅(qū)動組蛋白修飾的關(guān)鍵酶,參與調(diào)控受體介導(dǎo)的基因轉(zhuǎn)錄,并分別維持染色質(zhì)的活性和非活性狀態(tài),從而調(diào)節(jié)組蛋白和其他蛋白的相互作用,并影響基因轉(zhuǎn)錄的激活、抑制和染色體失活等過程。LSD1通過特異性地去除H3K4和H3K9位點(diǎn)上的單甲基化和雙甲基化基團(tuán),在重塑獎賞通路中起重要作用[43]。另一個(gè)家族含有Jumonji C (JmjC)結(jié)構(gòu)域,包括KDM2~7,是鐵(II)和2-酮戊二酸(2OG)依賴性雙加氧酶,這類酶可去除與轉(zhuǎn)錄沉默相關(guān)的組蛋白H3賴氨酸9(H3K9me2/1)、賴氨酸27(H3K27me2/1)和H4K20me1的甲基化[7]。研究表明KDMs參與調(diào)控干細(xì)胞自我更新、分化增殖、應(yīng)激反應(yīng)和基因組穩(wěn)定性等過程[44]。截至目前,在人類中已發(fā)現(xiàn)超過50種HMT以及30種KDM。表1總結(jié)了KDM7家族調(diào)控的H3K9me2、H3K27me2和H3K4me3在腦神經(jīng)疾病中的研究結(jié)果,據(jù)此推斷這些修飾可能通過KDM7家族調(diào)控,但還需做進(jìn)一步的研究進(jìn)行驗(yàn)證。
KDM7家族成員大約由1000個(gè)氨基酸組成,主要由PHD、JmjC結(jié)構(gòu)域以及連接二者的linker蛋白和末端的卷曲螺旋coiled coil region (cc)組成。
KDM7家族是一類重要的轉(zhuǎn)錄激活因子,目前已發(fā)現(xiàn)有KDM7A、KDM7B、KDM7C三個(gè)成員,它們均有N末端植物同源結(jié)構(gòu)域(plant homeodomain,PHD)和JmjC結(jié)構(gòu)域[45](圖1)。PHD結(jié)構(gòu)域是真核生物中的一種鋅指結(jié)構(gòu)域,是組蛋白甲基化修飾“閱讀器”, PHD結(jié)構(gòu)域參與蛋白質(zhì)之間的相互作用,可以識別結(jié)合H3K4me3,通過結(jié)合H3K4me3,組蛋白甲基化酶KDM7家族在細(xì)胞內(nèi)才可以催化H3K9me2和H3K27me2的去甲基化[46];而活性JmjC結(jié)構(gòu)域包含幾個(gè)保守氨基酸和四個(gè)α-螺旋,氨基酸決定關(guān)鍵輔因子Fe2+和α-酮戊二酸的正確結(jié)合,JmjC羧基末端區(qū)域的α-螺旋保證了結(jié)構(gòu)域的活性。序列的相似決定催化底物的相似,KDM7家族成員主要催化H3K9me2/1、H3K27me2/1和H4K20me1中賴氨酸殘基的去甲基化[47,48]。
表1 KDM7家族調(diào)控的常見組蛋白甲基化修飾類型與腦神經(jīng)疾病關(guān)系
“↑”表示上調(diào);“↓”表示下調(diào);“—”表示未有研究報(bào)道。
圖1 KDM7家族成員的結(jié)構(gòu)域和氨基酸數(shù)量
研究表明,KDM7家族主要在魚類和小鼠的大腦以及哺乳動物的神經(jīng)元中表達(dá),在大腦發(fā)育過程中起著消除染色質(zhì)沉默標(biāo)記的作用,參與多種病理過程,包括各類癌癥和精神發(fā)育遲滯等。Tsukada等[7]發(fā)現(xiàn)抑制斑馬魚的KDM7直系同源物會導(dǎo)致發(fā)育性腦缺陷,提示KDM7對斑馬魚大腦的發(fā)育至關(guān)重要。圖2總結(jié)了KDM7家族的分子調(diào)控機(jī)制。
KDM7A又稱JHDM1D或KIAA1718,主要表達(dá)在胃、肝、肺、玻璃體、乳房等器官。作為抑制性標(biāo)記的擦除器, KDM7A主要通過催化去除靶基因啟動子上的雙甲基化標(biāo)記H3K9me2和H3K27me2及單甲基化標(biāo)記H4K20me1調(diào)節(jié)成纖維細(xì)胞生長因子4(fibroblast growth factor 4, FGF4)的表達(dá),從而在大腦發(fā)育、細(xì)胞分化、周期和增殖中發(fā)揮重要調(diào)控作用[7, 49]。KDM7A還作為潛在的腫瘤抑制因子發(fā)揮阻斷腫瘤生長和血管生成的作用[50]。
與KDM7B和KDM7C比較,KDM7A分子構(gòu)象更為伸展,其PHD結(jié)構(gòu)域在結(jié)合H3K4me3后失去催化H3K9me2去甲基化的活性,而更專注于催化H3K27me2的去甲基化;在無H3K4me3的情況下,KDM7A可催化H3K9me2的去甲基化。此外,KDM7A通常和其他KDM家族成員協(xié)同發(fā)揮效應(yīng)。例如,內(nèi)皮細(xì)胞上KDM7A與KDM6A通過腫瘤壞死因子(tumour necrosis factor-α, TNF-α)信號通路協(xié)同調(diào)控炎癥反應(yīng)。KDM7A與KDM6A同時(shí)受到新型microRNA,即miR-3679-5p的抑制。miR-3679-5p通過與靶mRNA分子堿基互補(bǔ)配對,形成miRNA-mRNA復(fù)合分子,從而抑制靶分子(KDM7A與KDM6A)的表達(dá);而KDM7A通過調(diào)控組蛋白H3K9me2作用于NF-κB通路,從而調(diào)控炎癥反應(yīng)。上述KDM7A一系列調(diào)控作用關(guān)系均受到基因組的三維空間結(jié)構(gòu)——染色質(zhì)構(gòu)象改變的影響,染色質(zhì)構(gòu)象可以精準(zhǔn)調(diào)控真核細(xì)胞的復(fù)制、修復(fù)和轉(zhuǎn)錄表達(dá)等過程[51]。
圖2 KDM7家族成員分子調(diào)控機(jī)制
KDM7A主要表達(dá)在腦、肝臟、肺、胃等;KDM7B主要表達(dá)在腦、肺、血漿等;KDM7C主要表達(dá)在腦、視網(wǎng)膜、T細(xì)胞等。KDM家族成員在多數(shù)已知的腦神經(jīng)疾病中多伴隨突變或功能減弱。
KDM7A是影響胚胎發(fā)育的關(guān)鍵因子。Rissi等[52]發(fā)現(xiàn)KDM7A基因敲除損害早期豬胚胎發(fā)育,-/-改變H3K9和H3K27的甲基化水平,降低胚泡期的胚胎發(fā)育和總細(xì)胞數(shù),并改變胚泡中ICM/總細(xì)胞數(shù)的比率,表明KDM7A是豬胚胎正常發(fā)育所必需的關(guān)鍵因子。此外,該研究還證明KDM7A可調(diào)節(jié)控制細(xì)胞多能性相關(guān)基因表達(dá),但尚不清楚KDM7A是通過調(diào)節(jié)H3K9和H3K27的甲基化直接調(diào)節(jié)NANOG、OCT4和CDX2等轉(zhuǎn)錄因子的表達(dá)活動,還是通過調(diào)節(jié)這些基因的其他轉(zhuǎn)錄調(diào)節(jié)器間接調(diào)節(jié)NANOG、OCT4和CDX2的表達(dá)。
KDM7A是促進(jìn)神經(jīng)分化的關(guān)鍵酶。神經(jīng)誘導(dǎo)是中樞神經(jīng)系統(tǒng)發(fā)育起始步驟,指的是外胚層特異性發(fā)育為胚胎神經(jīng)板。在雞胚發(fā)育早期階段,KDM7A主要位于原條的上胚層細(xì)胞。雞胚中KDM7A過表達(dá)導(dǎo)致神經(jīng)板擴(kuò)張,而敲低KDM7A則影響了神經(jīng)板正常發(fā)育,而這一調(diào)控主要通過FGF4發(fā)揮作用[53]。在神經(jīng)分化過程中,KDM7A過表達(dá)通過促進(jìn)FGF4的轉(zhuǎn)錄激活,加快了神經(jīng)分化[54]。Smith等[55]采用改良的流式細(xì)胞技術(shù)和細(xì)胞固定等技術(shù)手段,在健康成年大鼠腦組織的mRNA層面發(fā)現(xiàn)在中樞神經(jīng)系統(tǒng)星形膠質(zhì)細(xì)胞中表達(dá)最低,在神經(jīng)元中最高。此外,McMichael等[56]通過對183例腦癱患兒全基因組測序,發(fā)現(xiàn)他們的基因發(fā)生錯(cuò)義突變,進(jìn)一步提示KDM7A與神經(jīng)系統(tǒng)疾病密切相關(guān),但具體分子機(jī)制仍不清楚。
KDM7A可通過調(diào)節(jié)Hox基因調(diào)節(jié)小鼠脊柱發(fā)育。Hox基因又稱同源異型盒基因,是生物體中一類專門調(diào)控生物形體的基因,不同Hox基因在胚胎發(fā)育的不同階段“打開”或者“關(guān)閉”不同分子開關(guān),導(dǎo)致脊椎動物出現(xiàn)千差萬別的體型。Hox基因的特點(diǎn)之一是其排列順序與其作用位置相關(guān),具有時(shí)空共線性。如近3′端的基因調(diào)控身體頭部發(fā)育,近5′端基因調(diào)控身體尾部發(fā)育。Higashijima等[57]對出生1天的野生小鼠和突變小鼠進(jìn)行骨骼拍片,發(fā)現(xiàn)所有野生型小鼠的軸向骨骼結(jié)構(gòu)正常,而所有突變小鼠則顯示出脊椎的前向同源異型轉(zhuǎn)化,表明KDM7A通過去甲基化活性控制后部Hox基因的轉(zhuǎn)錄,從而調(diào)節(jié)小鼠的脊柱發(fā)育。
KDM7B又稱PHF8,分布在血漿、肺、胎盤、睪丸等組織器官。在成年小鼠中,KDM7B蛋白存在于整個(gè)新皮層、海馬和腹側(cè)紋狀體的前腦神經(jīng)元中。KDM7B通過催化去除靶基因啟動子上的單甲基化標(biāo)記H3K9me1、H4K20me1和雙甲基化標(biāo)記H3K9me2、H3K27me2來對靶基因進(jìn)行激活。KDM7B和KDM7A之間的差異主要在于它們的PHD結(jié)構(gòu)域與Jmjc結(jié)構(gòu)域之間linker柔性和長度不同,結(jié)構(gòu)的不同決定二者功能不同,KDM7B上連接PHD和JmjC的linker結(jié)構(gòu)域相較于KDM7A更短也更為靈活,使得KDM7B的PHD結(jié)構(gòu)域在結(jié)合H3K4me3后在柔性linker的幫助下共同催化H3K9me2去甲基化[49,58],因此,H3K4me3- H3K9me2組合更易成為KDM7B催化底物。KDM7B優(yōu)先作用于H3K9me2/1和H4K20me1,而KDM7A主要催化H3K9me2/1和H3K27me2/1去甲基化。
KDM7B與X染色體連鎖精神發(fā)育遲滯(X-linked mental retardation,XLMR)具有相關(guān)性。XLMR是一種高度異質(zhì)的遺傳疾病,是由于X染色體上的多個(gè)基因突變所導(dǎo)致的認(rèn)知能力發(fā)育障礙。2005年Laumonnier等[59]發(fā)現(xiàn)KDM7B基因在兩個(gè)表型為唇裂的XLMR的家庭中發(fā)現(xiàn)了可產(chǎn)生截短蛋白的突變,這種關(guān)聯(lián)表明KDM7B在胚胎中線形成和認(rèn)知能力發(fā)展方面具有重要功能。2007年Koivisto等[60]通過對18名XLMR患者進(jìn)行基因編碼區(qū)和剪接位點(diǎn)測序,在芬蘭一位多發(fā)性XLMR男性患者親屬身上發(fā)現(xiàn)了基因的新的突變。同年,Abidi等[61]報(bào)道發(fā)現(xiàn)在KDM7B上的一個(gè)新的無義突變導(dǎo)致XLMR,進(jìn)一步支持了KDM7B蛋白在認(rèn)知功能和胚胎中線形成中可能起重要作用的假設(shè)。2009年Loenarz等[62]發(fā)現(xiàn)基因上的另一個(gè)無義突變與輕度智力障礙、輕度畸形特征有關(guān)。
KDM7B在胚胎發(fā)育及神經(jīng)元分化中起重要作用。Walsh等[63]建立KDM7B敲除小鼠胚胎,發(fā)現(xiàn)與野生小鼠相比,KDM7B的缺失損害了小鼠胚胎成纖維細(xì)胞(mouse embryonic fibroblast,MEF)、神經(jīng)祖細(xì)胞(neural progenitor cells, NPCs)和胚胎干細(xì)胞(embryonic stem cell,ESCs)的增殖潛能,表明KDM7B在體外調(diào)節(jié)多種原代細(xì)胞類型的生長潛力;同時(shí)發(fā)現(xiàn)紋狀體體積顯著減小,提示KDM7B可能通過調(diào)控紋狀體導(dǎo)致智力殘缺等異常表型;此外,一系列行為學(xué)實(shí)驗(yàn)結(jié)果表明KDM7B敲除小鼠對焦慮和抑郁樣行為具有顯著抵抗力,且和血清素受體(包括5-HT1A、5-HT1B和5-HT2A)表達(dá)增加之間有著直接聯(lián)系,提示KDM7B顯著抑制血清素受體表達(dá),從而參與調(diào)控人類焦慮和抑郁行為。Qiu等[64]通過實(shí)驗(yàn)證明在小鼠胚胎癌細(xì)胞P19中敲除KDM7B會損害視黃酸(all-trans retinoic acid,RA)誘導(dǎo)的神經(jīng)元分化,表明KDM7B調(diào)節(jié)的組蛋白去甲基化在神經(jīng)元分化中起著關(guān)鍵作用。
KDM7B是學(xué)習(xí)記憶的關(guān)鍵因子。Chen等[65]發(fā)現(xiàn)KDM7B敲除小鼠表現(xiàn)出學(xué)習(xí)記憶受損,同時(shí)伴隨海馬長時(shí)程增強(qiáng)(long-term potentiation,LTP)異常。在KDM7B敲除小鼠中,哺乳動物雷帕霉素靶蛋白(mammalian target of rapamycin, mTOR)信號通路在海馬中過度活躍,KDM7B對H4K20me1的去甲基化導(dǎo)致核糖體S6蛋白激酶1(ribosomal S6 protein kinase type 1, RSK1)的轉(zhuǎn)錄抑制和mTOR信號穩(wěn)態(tài)破壞;而使用雷帕霉素對mTOR信號通路進(jìn)行抑制后,KDM7B敲除小鼠恢復(fù)了正常的LTP和認(rèn)知表型。表明KDM7B敲除后通過調(diào)控組蛋白修飾破壞mTOR信號通路,進(jìn)而引起學(xué)習(xí)和記憶障礙。
KDM7C又稱PHF2, 表達(dá)在血液中的CD8+T淋巴細(xì)胞、視網(wǎng)膜、胰腺、胎盤等組織器官。與其他KDM7酶類似,KDM7C的PHD結(jié)構(gòu)域也可結(jié)合H3K4me3,唯一不同的是KDM7C的JmjC結(jié)構(gòu)域上Fe的第5配體是酪氨酸(tyrosine, Tyr)而不是組氨酸,體積龐大的Tyr321會影響酶的功能,導(dǎo)致KDM7C酶的氧結(jié)合效率低下[15,66]。因此相比KDM7A、KDM7B,KDM7C顯示出極其微量的去甲基化酶活性,僅催化H3K9me2/1的去甲基化[45]。
研究發(fā)現(xiàn)KDM7C在胚胎神經(jīng)管形成和神經(jīng)節(jié)中大量表達(dá)[67],參與包括成骨和成脂在內(nèi)的多種生物學(xué)過程[50]。此外,KDM7C主要抑制腫瘤,參與乳腺癌、頭頸鱗狀細(xì)胞癌、結(jié)腸癌、胃癌等腫瘤進(jìn)展過程[68]。
組蛋白去甲基化酶KDM7家族相關(guān)分子的表觀遺傳調(diào)控異常,在腦神經(jīng)疾病的發(fā)生發(fā)展過程中扮演了重要角色。基于分子基礎(chǔ)差異,KDM7家族成員在組蛋白修飾中扮演著不同的角色,KDM7A更長的linker結(jié)構(gòu)域使它主要催化H3K9和H3K27的去甲基化;KDM7B作用于H3K9和H4K20;而由于JmjC結(jié)構(gòu)域上Fe的第5配體是酪氨酸,KDM7C僅能催化H3K9me2/1的去甲基化。KDM7家族成員在大腦發(fā)育、神經(jīng)分化、抑制腫瘤等方面發(fā)揮重要作用,其表觀遺傳調(diào)控異常會導(dǎo)致智力障礙、焦慮抑郁表型及學(xué)習(xí)記憶障礙等,還會造成發(fā)育異常導(dǎo)致畸形。
雖然已經(jīng)有很多研究結(jié)果表明KDMs家族與腦神經(jīng)疾病之間存在相關(guān)性,但由于腦神經(jīng)環(huán)路復(fù)雜、神經(jīng)網(wǎng)絡(luò)連接多變等不可調(diào)控的因素,KDMs家族在腦神經(jīng)疾病發(fā)生發(fā)展中的研究仍處于起步階段,尤其是KDMs家族在阿爾茲海默癥等機(jī)體老化和老化相關(guān)的神經(jīng)退行性疾病中的作用研究更是寥寥無幾,目前僅發(fā)現(xiàn)KDM4A與阿爾茲海默癥可能具有相關(guān)性[69]。未來的研究可借助正向遺傳學(xué)、基因組測序等研究手段,多組學(xué)聯(lián)合病毒干預(yù)、轉(zhuǎn)基因動物等分子生物學(xué)研究方法,進(jìn)一步深入研究腦神經(jīng)疾病表觀遺傳學(xué)機(jī)制,為理解腦神經(jīng)疾病分子病理機(jī)制以及探索基于該機(jī)制的有效治療靶點(diǎn)帶來新的啟示。
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The role of histone demethylases of KDM7 family in brain-related disorders
Zhuojin Yang1,2,3, Yuxiang Zhang1,2,3, Xixi Yang1,2,3, Feifei Gao1,2,3, Jingsi Yang1,2,3, Chunxia Yan1,2,3
The histone demethylases of KDM7 family, including KDM7A, KDM7B and KDM7C,regulate transcription through acting on specific histone lysines.Previous studies have shown that these family members are functionally important for the processes of neural differentiation and tumor development, and little is known about their roles in brain neurological diseases. In this review, we summarize the latest research progress of KDM7 family on their epigenetic regulation mechanisms, their protein structures and their functions in brain-related diseases, which will likely advance our understanding of the molecular mechanisms of neurological diseases.
histone lysine demethylases; KDM7; H3K9me2; H3K27me2
2021-10-01;
2021-12-21;
2022-01-04
國家自然科學(xué)基金項(xiàng)目(編號:81971792,81901920),中國博士后基金(編號:2019M663746)和陜西省自然科學(xué)研究計(jì)劃項(xiàng)目(編號: 2020JQ-091)資助[Supported by the National Natural Science Foundation of China (Nos. 81971792, 81901920), the China Postdoctoral Science Foundation (No. 2019M663746), and the Natural Science Basic Research Program of Shaanxi Province (No. 2020JQ-091)]
楊卓瑾,在讀碩士研究生,專業(yè)方向:法醫(yī)病理學(xué)及藥物成癮等腦疾病。E-mail: cloris_sunshine@stu.xjtu.edu.cn
張玉向,博士,副教授,研究方向:法醫(yī)病理學(xué)及藥物成癮等腦疾病。E-mail: yuxiangzhang@xjtu.edu.cn
閻春霞,博士,教授,研究方向:法醫(yī)病理學(xué)及藥物成癮等腦疾病。E-mail: yanchunxia@mail.xjtu.edu.cn
10.16288/j.yczz.21-280
(責(zé)任編委: 李海濤)