
摘 "要""盡管小腦體積只占人腦總量的10%, 但包含超半數(shù)的神經(jīng)元。此前, 小腦一直被認(rèn)為主要控制肢體的運(yùn)動(dòng)協(xié)調(diào), 但近年來(lái)越來(lái)越多的證據(jù)表明小腦與學(xué)習(xí)、注意、語(yǔ)言等高級(jí)認(rèn)知功能密切相關(guān), 參與多種非運(yùn)動(dòng)功能的調(diào)節(jié)。與此同時(shí), 小腦異常發(fā)育與多種神經(jīng)發(fā)育疾病密切相關(guān), 其中包括孤獨(dú)癥譜系障礙(Autism spectrum disorder, ASD), 或稱自閉癥、孤獨(dú)癥, 是一類典型的神經(jīng)發(fā)育疾病, 以社交障礙、重復(fù)刻板行為和語(yǔ)言障礙為主要特征, 并常伴有感覺(jué)異常。臨床研究發(fā)現(xiàn), ASD患者通常伴有小腦結(jié)構(gòu)與功能的改變。有意思的是, 在ASD動(dòng)物模型中也發(fā)現(xiàn)與人類似的小腦異常表型。重要的是, 特異敲除小腦神經(jīng)元中ASD易感基因可導(dǎo)致模式動(dòng)物表現(xiàn)出典型的孤獨(dú)癥樣行為, 提示小腦異常發(fā)育是導(dǎo)致ASD的關(guān)鍵病理機(jī)制之一。將從臨床及基礎(chǔ)研究?jī)蓚€(gè)方面簡(jiǎn)要概括小腦與ASD的關(guān)系, 為ASD的診斷和治療提供了新的視角。
關(guān)鍵詞""孤獨(dú)癥, 小腦, 結(jié)構(gòu)功能, 模式動(dòng)物
分類號(hào)""B845
1""引言
孤獨(dú)癥譜系障礙(Autism Spectrum Disorder, ASD)是一種神經(jīng)系統(tǒng)發(fā)育異常的疾病, 其核心臨床特征包括社交障礙、重復(fù)刻板行為、語(yǔ)言障礙以及感覺(jué)異常(Hirota amp; King, 2023)。全球范圍內(nèi), ASD的發(fā)病率呈逐年上升趨勢(shì), 影響全球1%以上人口(Bouzy et al., 2023)。研究者普遍認(rèn)為, 兒童ASD的發(fā)病率男性高于女性(胡格格"等, 2022; Alaerts et al., 2016)。ASD的確切原因尚不完全清楚, 研究表明遺傳和環(huán)境因素在其發(fā)展中起著關(guān)鍵作用(Cheroni et al., 2020)。盡管如此, 臨床上有效的診斷和治療策略仍然不足, 給患者家庭和社會(huì)帶來(lái)了巨大的負(fù)擔(dān)。因此, 深入研究ASD的病理機(jī)制具有重要的臨床和現(xiàn)實(shí)意義。
小腦在傳統(tǒng)觀念中主要被視為協(xié)調(diào)自主運(yùn)動(dòng)、步態(tài)和姿勢(shì)等功能的中樞神經(jīng)系統(tǒng)(Carey, 2024)。然而, 越來(lái)越多的研究證據(jù)表明, 小腦也參與調(diào)節(jié)多種高級(jí)認(rèn)知功能, 包括認(rèn)知、注意力、
記憶、語(yǔ)言交流、情緒調(diào)節(jié)以及執(zhí)行能力等(Prati et al., 2024)。因此, 有研究者認(rèn)為, 小腦可能是與ASD發(fā)生發(fā)展密切相關(guān)的病理腦區(qū)之一(Stoodley et al., 2017)。初步的臨床和動(dòng)物模型研究顯示, ASD患者和小鼠模型中存在運(yùn)動(dòng)協(xié)調(diào)和學(xué)習(xí)困難的表現(xiàn), 進(jìn)一步支持了小腦在ASD病理中的作用(武文佼, 張鵬, 2016)。本文將簡(jiǎn)要綜述小腦異常發(fā)育與ASD的相關(guān)研究進(jìn)展, 并展望了未來(lái)研究的方向。
2""小腦的基本結(jié)構(gòu)及其與大腦的連接
小腦位于腦干后部, 由兩個(gè)半球組成, 左右對(duì)稱。它主要由表面的灰質(zhì)和內(nèi)部的白質(zhì)組成。小腦核位于小腦灰質(zhì)的中央, 包括頂核、球狀核、栓狀核和齒狀核。小腦皮質(zhì)分為三層, 包括分子層(Molecular layer, ML)、浦肯野細(xì)胞層(Purkinje cell layer, PCL)以及顆粒細(xì)胞層(Granule layer, GCL)。皮層中含有多種神經(jīng)元, 包括星狀細(xì)胞(Stellate SC)、籃狀細(xì)胞(Basket cells, BC)、浦肯野細(xì)胞(Purkinje cell, PC)、高爾基氏細(xì)胞(Golgi cells, GoC)和顆粒細(xì)胞(Granule cells, GrC)等(Farini et"al., 2021)。主要輸入途徑是苔蘚纖維(Mossy Fiber, MF)和攀緣纖維(Climbing Fiber, CF)。顆粒細(xì)胞的軸突向上伸至分子層, 在分子層呈T字形分成兩支, 以相反的方向沿著葉片的長(zhǎng)軸走行, 被稱為平行纖維(Parallel fiber, PF) (Pijpers et al., 2006)。在小腦皮層形成的過(guò)程中, 特定部位的顆粒細(xì)胞增殖速度加快, 沿著浦肯野神經(jīng)元的軸突向內(nèi)牽引, 小腦皮層在該部位形成向內(nèi)的凹陷。隨著小腦皮層向外的發(fā)育, 逐漸形成了小腦葉片狀結(jié)構(gòu)。
小腦與大腦通過(guò)多條神經(jīng)通路連接, 包括小腦腦干通路、小腦核團(tuán)與大腦皮層的神經(jīng)纖維束連接, 以及小腦通過(guò)腦干傳輸信息到大腦皮層并接收返回信息的雙向通路(Sokolov et al., 2014)。這些連接不僅涉及運(yùn)動(dòng)控制, 還對(duì)認(rèn)知、情緒和其他高級(jí)神經(jīng)功能的調(diào)節(jié)至關(guān)重要, 使小腦成為整體神經(jīng)系統(tǒng)高效運(yùn)作的關(guān)鍵組成部分(王多浩"等, 2020)。ASD患者的大腦顯示出非典型的功能連接模式, 特別是遠(yuǎn)距離連接降低和局部連接增強(qiáng)(張芬"等, 2015)。同時(shí), 大腦與小腦之間的連接也呈現(xiàn)異常。
3 "ASD個(gè)體小腦異常及運(yùn)動(dòng)障礙
ASD個(gè)體的小腦結(jié)構(gòu)異常通常涉及小腦體積異常、小腦蚓部缺失, 以及浦肯野神經(jīng)元數(shù)量減少和神經(jīng)元大小變化(Courchesne et al., 2004)。盡管通常認(rèn)為ASD個(gè)體的小腦體積普遍較小, 但Piven及其同事卻發(fā)現(xiàn)部分ASD個(gè)體的小腦體積增大, 這表明ASD個(gè)體的小腦體積異常并非普遍存在選擇性縮小的情況(Piven et al., 1997)。磁共振成像技術(shù)(MRI)自20世紀(jì)80年代以來(lái)被廣泛用于分析ASD個(gè)體的腦部結(jié)構(gòu)。ASD個(gè)體的MRI"(Magnetic Resonance Imaging)影像顯示小腦的多個(gè)區(qū)域, 特別是小葉VI和VII, 面積普遍較小。這種小腦區(qū)域的減小通常被認(rèn)為是先天發(fā)育不全的結(jié)果, 而不是后天的萎縮或惡化。因此, 這種局部的發(fā)育異常可以被視為一個(gè)時(shí)間標(biāo)記, 用來(lái)識(shí)別在ASD中影響大腦發(fā)育的具體事件或過(guò)程(Courchesne et al., 1988; Hodgdon et"al., 2024)。在ASD個(gè)體中, 小腦結(jié)構(gòu)異??赡苤苯佑绊戇\(yùn)動(dòng)和認(rèn)知功能, 因?yàn)樾∧X與腦干、下丘腦和丘腦之間存在重要連接, 這些連接的異常可能間接影響涉及運(yùn)動(dòng)、認(rèn)知和感覺(jué)的小腦?大腦環(huán)路系統(tǒng)的正常發(fā)育(Strick et al., 2009)。小腦與大腦功能連接的異常對(duì)ASD個(gè)體的核心癥狀, 如社交和溝通障礙以及重復(fù)和刻板行為, 具有重要作用, 這提示異常的小腦?大腦功能連接可能是導(dǎo)致ASD認(rèn)知和感覺(jué)障礙的潛在神經(jīng)機(jī)制之一(Zhang et al., 2022)。小腦異??赡芷茐腁SD個(gè)體特定的小腦?腦環(huán)路結(jié)構(gòu)和功能優(yōu)化。在ASD患者中, 小腦與大腦之間的連接異常表現(xiàn)為連接不足或過(guò)度連接, 可能導(dǎo)致信息傳遞受限或處理混亂, 進(jìn)而影響認(rèn)知、社交和感知功能(van der Heijden et al., 2021)。具體來(lái)說(shuō), 小腦與感覺(jué)運(yùn)動(dòng)皮層之間的連接強(qiáng)度增加, 而與認(rèn)知功能相關(guān)的大腦皮層區(qū)域之間的連接強(qiáng)度減少(Noonan et al., 2009; Khan et al., 2015)。這種異常的連接通常是由于小腦發(fā)育障礙引起的, 可能會(huì)導(dǎo)致ASD的神經(jīng)發(fā)育障礙。
ASD的主要特征之一是重復(fù)刻板行為, 例如反復(fù)拍手、跺腳、舔舌頭和旋轉(zhuǎn)物體等。與ASD相似, 小腦蚓部缺失、小腦體積減少以及小腦發(fā)育不全的個(gè)體也常出現(xiàn)類似的刻板重復(fù)行為(Hampson amp; Blatt, 2015)。小腦病變個(gè)體通常表現(xiàn)出運(yùn)動(dòng)協(xié)調(diào)障礙, 如共濟(jì)失調(diào)和辨距不良(Flament amp; Hore, 1986)。在ASD個(gè)體中同樣觀察到與小腦病變個(gè)體類似的運(yùn)動(dòng)協(xié)調(diào)障礙。ASD個(gè)體的運(yùn)動(dòng)障礙表現(xiàn)為運(yùn)動(dòng)發(fā)育的延遲和缺陷, 包括粗大和精細(xì)運(yùn)動(dòng)方面的延遲, 在運(yùn)動(dòng)學(xué)習(xí)、平衡協(xié)調(diào)和步態(tài)方面也存在缺陷(Thomas et al., 2022)。高達(dá)80%的ASD兒童顯示出運(yùn)動(dòng)協(xié)調(diào)障礙, 這與ASD的嚴(yán)重程度和智商水平高度相關(guān)(Rudolph et al., 2023)。研究指出, ASD兒童常難以進(jìn)行熟練的動(dòng)作, 這可能與基本運(yùn)動(dòng)技能的需求、運(yùn)動(dòng)表征知識(shí), 以及將這些表征轉(zhuǎn)化為運(yùn)動(dòng)計(jì)劃相關(guān)聯(lián)。這些現(xiàn)象表明, ASD個(gè)體的思維障礙可能與空間表征的形成受損、表征的轉(zhuǎn)碼和執(zhí)行相關(guān)。這可能與跨頂葉、前運(yùn)動(dòng)和運(yùn)動(dòng)環(huán)路的異常分布及其連接異常有關(guān)(Dowell et al., 2009)。ASD的這些運(yùn)動(dòng)障礙可能直接或間接與小腦異常相關(guān), 盡管相關(guān)機(jī)制尚不完全清楚。
4""小腦病變者的ASD樣癥狀
Schmahmann等人指出, 小腦損傷可能導(dǎo)致小腦認(rèn)知情感綜合征(cerebellar cognitive affective syndrome, CCAS), 其特征包括執(zhí)行功能、語(yǔ)言處理、空間認(rèn)知和情感調(diào)節(jié)的缺陷, 這些特征與ASD的核心癥狀有重疊(Casartelli et al., 2018; Schmahmann amp; Sherman, 1998)。小腦異常, 如先天性小腦畸形、小腦腫瘤、Joubert's綜合征、小腦發(fā)育遲緩和小腦萎縮等, 增加了兒童神經(jīng)發(fā)育障礙的風(fēng)險(xiǎn), 并可能導(dǎo)致類似ASD的行為表現(xiàn)(Bolduc et al., 2012)。先天性小腦畸形患兒中普遍存在的神經(jīng)發(fā)育延遲和ASD譜系障礙, 有學(xué)者在對(duì)一定樣本量的先天性小腦畸形患者進(jìn)行統(tǒng)計(jì)分析后發(fā)現(xiàn), 這些患者中ASD的發(fā)生率為12% (Pinchefsky et al., 2019)。此外, 約25%的Joubert's綜合征患兒被診斷為ASD, 其中小腦蚓部發(fā)育不全是一個(gè)顯著特征(Geschwind amp; Levitt, 2007)。后顱窩綜合征患兒的小腦纖維損傷同樣與ASD樣行為的發(fā)生率升高密切相關(guān)(Catsman-Berrevoets amp; Aarsen, 2010)。小腦萎縮是ASD個(gè)體中最常見(jiàn)的神經(jīng)異常, 早期的小腦萎縮與增加的ASD發(fā)病率和風(fēng)險(xiǎn)密切相關(guān), 尤其是在早產(chǎn)兒中普遍存在。隨著醫(yī)療技術(shù)的進(jìn)步, 早產(chǎn)兒的生存率逐年提升, 這進(jìn)一步增加了其罹患ASD的風(fēng)險(xiǎn)(Rout amp; Dhossche, 2008)。因此, 深入研究小腦異常發(fā)育與ASD的關(guān)聯(lián)顯得尤為重要。
5""小腦異常發(fā)育與ASD的小鼠模型
盡管臨床影像學(xué)研究提示小腦異常發(fā)育與ASD存在緊密的相關(guān)性, 但目前的研究仍缺乏直接的因果關(guān)系證據(jù)。利用模式生物可以更直接地探索因果聯(lián)系, 并在基因分子和細(xì)胞環(huán)路層面初步解析其機(jī)制。實(shí)際上, 在嚙齒類動(dòng)物的ASD模型中觀察到小腦多種異常的改變, 包括小腦形態(tài)的改變、小葉數(shù)量增多(Yang et al., 2015)、浦肯野細(xì)胞丟失(Sudarov amp; Joyner, 2007)、顆粒神經(jīng)元異常增殖(Wefers et al., 2017)以及突觸連接異常(Lai et al., 2021)等。此外, 特異地影響小鼠小腦神經(jīng)發(fā)育可以導(dǎo)致類似ASD的表型, 這提示小腦發(fā)育異常可能是引發(fā)ASD的關(guān)鍵因素之一。
5.1""小鼠ASD模型存在小腦形態(tài)與功能的改變
丙戊酸(VPA)是一種廣泛用于治療癲癇和驚厥的藥物, 對(duì)成年人耐受性好且安全性高。然而, 有研究表明, VPA具有強(qiáng)致畸性作用, 可能導(dǎo)致輕度的神經(jīng)發(fā)育障礙甚至先天性畸形(Chen et al., 2024)。特別是, 產(chǎn)前暴露于VPA已被發(fā)現(xiàn)可增加兒童患ASD的風(fēng)險(xiǎn)(Gholipour et al., 2024)。因此, VPA產(chǎn)前暴露已成為一種常見(jiàn)的非轉(zhuǎn)基因ASD動(dòng)物模型, 在斑馬魚(yú)和嚙齒類動(dòng)物中得到廣泛應(yīng)用。針對(duì)大鼠的研究表明, VPA暴露后, 小腦蚓部和半球中浦肯野細(xì)胞數(shù)量顯著減少, 同時(shí)部分研究發(fā)現(xiàn)VPA暴露后大鼠小腦深部核團(tuán)核面積縮小、核長(zhǎng)度減短、核細(xì)胞數(shù)目增多(Wang et al., 2018)。此外, VPA暴露還導(dǎo)致大鼠小腦中小膠質(zhì)細(xì)胞密度的改變, 小膠質(zhì)細(xì)胞作為大腦中的免疫細(xì)胞, 通常對(duì)損傷和病理發(fā)展起反應(yīng)(Gifford et al., 2022)。
母體免疫激活(MIA)的動(dòng)物模型越來(lái)越被用于研究免疫介導(dǎo)的神經(jīng)發(fā)育障礙性疾病, 如ASD譜系障礙。最近的研究顯示, 母親孕期感染與子代ASD發(fā)病存在一定關(guān)聯(lián)性(Tartaglione et al., 2022)。實(shí)驗(yàn)中使用Poly (I)處理孕鼠模擬母體免疫激活, 觀察到其子代表現(xiàn)出社交行為減少和重復(fù)刻板行為增加等ASD樣行為。進(jìn)一步的研究揭示, Poly (I)處理孕鼠導(dǎo)致子代小鼠出現(xiàn)小腦浦肯野細(xì)胞缺失和顆粒細(xì)胞遷移延遲, 這對(duì)小腦的形態(tài)和各種運(yùn)動(dòng)及非運(yùn)動(dòng)行為產(chǎn)生了持久影響(Shi et al., 2009)??傮w而言, 這些研究表明MIA是ASD發(fā)生的一個(gè)風(fēng)險(xiǎn)因素, 但其與小腦之間的具體關(guān)聯(lián)還需要進(jìn)一步深入的探索和研究。
此外, 一些保守的ASD易感基因同樣對(duì)小鼠的小腦發(fā)育有顯著影響。例如, CNTNAP2基因在小腦浦肯野細(xì)胞中廣泛表達(dá), 調(diào)節(jié)其形態(tài), 其突變可以導(dǎo)致小鼠小腦畸形, 并表現(xiàn)出輕度小腦共濟(jì)失調(diào)行為障礙(Fernández et al., 2021)。另外, 前列腺素E2是一種生物活性信號(hào)分子, 通過(guò)環(huán)氧化酶-2 (COX-2)的酶活性從磷脂膜代謝而來(lái)。同樣, COX-2點(diǎn)突變小鼠顯示小腦神經(jīng)元樹(shù)突和樹(shù)突棘形態(tài)的改變, 伴隨出現(xiàn)ASD樣行為, 包括社交缺陷、重復(fù)行為和焦慮行為(Kissoondoyal et al., 2021)。
5.2""小腦特異性基因敲除可導(dǎo)致小鼠ASD樣表型
為了進(jìn)一步驗(yàn)證小腦對(duì)ASD的影響, 研究人員利用小鼠模型進(jìn)行了系統(tǒng)分析, 通過(guò)小腦特異性基因缺失或突變進(jìn)行研究。目前已知, 特定小腦基因的敲除確實(shí)可以導(dǎo)致小鼠表現(xiàn)出ASD樣表型, 這些基因包括TSC、PTEN、SHANK、CHD8、AUTS2、SCN8A等。
節(jié)性硬化癥(TSC)是一種常染色體顯性遺傳疾病, 可導(dǎo)致中樞神經(jīng)系統(tǒng)和非神經(jīng)組織的良性腫瘤。研究表明, TSC患者可能與小腦結(jié)節(jié)相關(guān), 影響小腦發(fā)育, 并增加患ASD的風(fēng)險(xiǎn)。TSC1或TSC2基因突變會(huì)影響mTOR信號(hào)通路, 與ASD相關(guān)。在小鼠模型中, 小腦浦肯野細(xì)胞中"Tsc1的雜合和純合缺失可導(dǎo)致ASD樣行為, 如社交互動(dòng)異常和重復(fù)行為(Tsai et al., 2012)。而雷帕霉素治療可預(yù)防這些行為異常。這些發(fā)現(xiàn)揭示了Tsc1在小腦功能中的作用, 為理解ASD等認(rèn)知障礙提供了新的分子基礎(chǔ)。
PTEN (抑癌磷酸酶和張力蛋白同系物)通過(guò)抑制PI3K/AKT/mTOR信號(hào)傳導(dǎo)通路, 在細(xì)胞生長(zhǎng)、蛋白質(zhì)合成和增殖中發(fā)揮重要作用。其功能通常會(huì)影響突觸可塑性和神經(jīng)元細(xì)胞結(jié)構(gòu)(Tilot et al., 2015)。在小鼠模型中, PTEN的缺失或功能障礙與神經(jīng)功能障礙及ASD樣行為相關(guān), 包括社交能力改變、重復(fù)行為和焦慮等表型, 這些與人類ASD相關(guān)(Clipperton-Allen amp; Page, 2020)。研究表明, 大約2%~5%的ASD患兒存在PTEN基因突變, 特別是在具有巨頭癥的ASD個(gè)體中, 這一比例可能更高(Kaymakcalan et al., 2021), 進(jìn)一步證明了PTEN在ASD發(fā)病中的高危因素地位。PTEN缺失在胚胎階段通常是致命的。研究發(fā)現(xiàn), 小腦特異性PTEN缺失會(huì)導(dǎo)致運(yùn)動(dòng)協(xié)調(diào)障礙, 這可能與小腦顆粒細(xì)胞的肥大有關(guān)。浦肯野細(xì)胞中PTEN的缺失(PTEN-KO PC)會(huì)引起類似ASD的特征, 包括社交能力減退、重復(fù)行為和運(yùn)動(dòng)學(xué)習(xí)缺陷。突變的浦肯野細(xì)胞表現(xiàn)為細(xì)胞體肥大、樹(shù)突和軸突結(jié)構(gòu)異常、興奮性降低, 以及平行纖維和攀緣纖維突觸的中斷, 最終導(dǎo)致細(xì)胞遲發(fā)性死亡。這些結(jié)果揭示了PTEN在浦肯野細(xì)胞功能中的新作用, 并驗(yàn)證了PTEN缺失與ASD樣病變之間的密切聯(lián)系。PTEN在小腦星形膠質(zhì)細(xì)胞中的缺失導(dǎo)致了Lhermitte-Duclos病樣病理和行為表型, 證明了PTEN在調(diào)節(jié)小腦細(xì)胞生長(zhǎng)和遷移中的重要作用, 并與ASD樣行為相關(guān)(Kwon et al., 2001)。
研究表明, 浦肯野細(xì)胞中PTEN的缺失(PTEN-"KO PC)導(dǎo)致類似于ASD譜系障礙的表型特征, 包括社交能力減退、重復(fù)行為和運(yùn)動(dòng)學(xué)習(xí)缺陷。此外, 突變的浦肯野細(xì)胞顯示出細(xì)胞體肥大、樹(shù)突和軸突結(jié)構(gòu)異常、興奮性降低, 以及平行纖維和攀緣纖維突觸的中斷, 最終導(dǎo)致細(xì)胞的遲發(fā)性死亡。這些研究結(jié)果揭示了PTEN在浦肯野細(xì)胞功能中的新作用, 進(jìn)一步驗(yàn)證了PTEN在浦肯野細(xì)胞中缺失與ASD樣病變發(fā)生之間的密切聯(lián)系(Cupolillo et al., 2016)。
SHANK家族蛋白在小腦中表達(dá)豐富, 在神經(jīng)元突觸形成、神經(jīng)元信號(hào)傳遞和小腦功能的調(diào)節(jié)中發(fā)揮重要作用(Sato et al., 2012; Uemura et al., 2004)。SHANK1、SHANK2和SHANK3組成了一個(gè)支架蛋白家族, 它們是谷氨酸能突觸后密度(PSD)的一部分, 并起到連接受體與肌動(dòng)蛋白細(xì)胞骨架的作用(Sala et al., 2015)。SHANK1和SHANK2在小腦的浦肯野細(xì)胞及其樹(shù)突中表達(dá)豐富, 而SHANK3則主要在顆粒細(xì)胞中表達(dá)(B?ckers"et al., 2004)。有研究發(fā)現(xiàn), 在小鼠的浦肯野細(xì)胞中特異性敲除SHANK2會(huì)導(dǎo)致ASD樣行為, 包括重復(fù)行為、超聲波發(fā)聲受損和平衡障礙(Peter et al., 2016)。這表明SHANK2在小腦細(xì)胞中的缺失可能與ASD的發(fā)生有關(guān)。
染色質(zhì)域解旋酶DNA結(jié)合蛋白8(CHD8)的基因突變是ASD譜系障礙的高度風(fēng)險(xiǎn)因素。其在小鼠小腦中的敲除可能導(dǎo)致小腦發(fā)育不全和運(yùn)動(dòng)協(xié)調(diào)障礙, 進(jìn)而影響社交和行為表型(Kawamura et al., 2021)。研究發(fā)現(xiàn), 小鼠小腦顆粒神經(jīng)元祖細(xì)胞特異性的CHD8敲除會(huì)導(dǎo)致在社交和光/暗試驗(yàn)中表現(xiàn)出異常的表型(Chen et al., 2022)。這些發(fā)現(xiàn)強(qiáng)調(diào)了CHD8在小腦發(fā)育中的關(guān)鍵作用, 并且對(duì)理解小腦在ASD發(fā)病機(jī)制中的具體貢獻(xiàn)具有重要意義。
ASD易感候選基因2(AUTS2)是與ASD譜系障礙相關(guān)的風(fēng)險(xiǎn)基因, 主要影響大腦的發(fā)育過(guò)程。AUTS2在小腦中也有廣泛的表達(dá)(Bedogni et al., 2010), 特別是在出生后發(fā)育過(guò)程中定位于浦肯野細(xì)胞和高爾基細(xì)胞。研究顯示, 條件性敲除小鼠的AUTS2基因會(huì)導(dǎo)致小腦體積減小、浦肯野細(xì)胞(PC)成熟延遲及突觸發(fā)育異常。這些小鼠在運(yùn)動(dòng)學(xué)習(xí)和聲音交流方面的能力也明顯下降, 表現(xiàn)出與ASD相關(guān)的小腦功能障礙特征(Yamashiro et al., 2020)。因此, AUTS2的損傷可能對(duì)小腦的功能發(fā)育起到重要影響, 進(jìn)而與ASD的發(fā)病機(jī)制相關(guān)聯(lián)。
此外, 小腦浦肯野細(xì)胞中的SCN8A表達(dá)缺失也被發(fā)現(xiàn)會(huì)導(dǎo)致小腦的變性以及與ASD譜系障礙相關(guān)的行為異常。SCN8A基因編碼電壓門(mén)控鈉通道8A, 在染色體12q13位點(diǎn)上, 共包含26個(gè)外顯子, 廣泛表達(dá)于中樞神經(jīng)系統(tǒng)和外周神經(jīng)系統(tǒng)的神經(jīng)元中。其基因表達(dá)變化與多種神經(jīng)系統(tǒng)疾病的發(fā)病機(jī)制密切相關(guān)。SCN8A基因突變常常表現(xiàn)為常染色體顯性遺傳, 已知與早發(fā)性癲癇性腦病伴智力缺陷有關(guān)。研究結(jié)果顯示, 小腦浦肯野細(xì)胞中敲除SCN8A基因的小鼠表現(xiàn)出明顯的小腦浦肯野細(xì)胞喪失和分子層變薄, 導(dǎo)致整體小腦體積減小。此外, 這些小鼠在神經(jīng)行為學(xué)上也顯示出社交障礙以及運(yùn)動(dòng)協(xié)調(diào)和運(yùn)動(dòng)學(xué)習(xí)能力的缺陷(Yang et al., 2022)。因此, 可以推測(cè)SCN8A在小腦中的表達(dá)缺失可能會(huì)導(dǎo)致類似于ASD的行為異常。
這些研究結(jié)果強(qiáng)調(diào)了小腦在ASD發(fā)病機(jī)制中的重要作用, 并為理解ASD的神經(jīng)生物學(xué)基礎(chǔ)提供了關(guān)鍵見(jiàn)解。
6""總結(jié)與展望
小腦異常發(fā)育與ASD之間存在密切的關(guān)聯(lián), 盡管具體的病理生理機(jī)制尚需進(jìn)一步研究, 但這一關(guān)聯(lián)為深入理解ASD的發(fā)病機(jī)制提供了新的視角。本文從臨床研究和嚙齒類動(dòng)物模型兩方面獲得的關(guān)鍵證據(jù)顯示, 小腦在ASD的病理生理中扮演著關(guān)鍵角色。不同遺傳或環(huán)境因素的影響可能導(dǎo)致小腦早期損傷, 進(jìn)而顯著改變小腦神經(jīng)環(huán)路的結(jié)構(gòu)和功能, 從而引發(fā)運(yùn)動(dòng)和認(rèn)知功能的障礙。小腦作為廣泛連接的神經(jīng)環(huán)路的一部分, 與其他腦區(qū)共同調(diào)控ASD個(gè)體的社交和刻板行為。可見(jiàn), 小腦異常發(fā)育在ASD的發(fā)生發(fā)展中具有重要的作用(見(jiàn)圖1)。
目前, 針對(duì)小腦作為ASD治療靶點(diǎn)的研究和臨床實(shí)驗(yàn)正在逐步展開(kāi)。早期研究表明, 改善小
腦功能和結(jié)構(gòu)可以顯著改善ASD患者的社交和認(rèn)知功能。神經(jīng)調(diào)節(jié)和藥物干預(yù)措施被認(rèn)為可能通過(guò)調(diào)節(jié)小腦神經(jīng)環(huán)路的活動(dòng)來(lái)改善ASD癥狀。神經(jīng)反饋技術(shù), 如深腦刺激和神經(jīng)回路調(diào)節(jié), 已經(jīng)在某些ASD患者中顯示出一定的效果。這些技術(shù)通過(guò)電刺激或神經(jīng)調(diào)節(jié)裝置對(duì)小腦區(qū)域進(jìn)行干預(yù), 改善神經(jīng)環(huán)路的功能和整合, 從而緩解ASD患者的核心癥狀。
在未來(lái), 基于小腦的個(gè)性化治療策略將是ASD治療的前沿。隨著對(duì)小腦神經(jīng)環(huán)路和功能的進(jìn)一步理解, 未來(lái)的研究將集中于開(kāi)發(fā)更加個(gè)性化和精準(zhǔn)的治療策略。結(jié)合基因組學(xué)和腦成像技術(shù), 可以精確識(shí)別ASD患者中小腦特異性異常的亞型, 并針對(duì)性地選擇最有效的治療手段??鐚W(xué)科研究團(tuán)隊(duì)的合作將推動(dòng)小腦與ASD之間關(guān)系的全面解析, 神經(jīng)科學(xué)、遺傳學(xué)、心理學(xué)和臨床醫(yī)學(xué)的結(jié)合將為理解ASD復(fù)雜的神經(jīng)發(fā)育機(jī)制提供新的視角和治療路徑。
當(dāng)然, 小腦作為ASD治療靶點(diǎn)具有一定的局限性。首先, 其與ASD相關(guān)的神經(jīng)發(fā)育異常涉及多個(gè)腦區(qū)的復(fù)雜互動(dòng), 僅僅依賴于小腦治療可能無(wú)法全面解決病因和癥狀。其次, ASD患者的個(gè)體差異和異質(zhì)性意味著針對(duì)小腦的治療效果會(huì)有所不同, 而目前治療策略的長(zhǎng)期效果和安全性仍需驗(yàn)證。未來(lái)的研究應(yīng)繼續(xù)探索多因素治療策略, 包括個(gè)性化和綜合考慮多腦區(qū)的干預(yù), 以提升治療效果和生活質(zhì)量。
綜上所述, 小腦作為ASD治療的靶點(diǎn)具有重要的理論和臨床意義。未來(lái)的研究將進(jìn)一步探索小腦在ASD發(fā)病機(jī)制中的詳細(xì)作用, 并開(kāi)發(fā)出更加精準(zhǔn)和有效的治療策略, 為改善ASD患者的生活質(zhì)量提供新的希望和機(jī)會(huì)。
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The relationship between abnormal cerebellar development and Autism Spectrum Disorder
TU Haixia1,2, WENG Xuchu3, XU Bo1,2
(1"School of Physical Education and Health Care, East China Normal University, Shanghai 200241,"China)(2"Key Laboratory of Adolescent Health Assessment and Exercise Intervention of Ministry of Education, East China Normal University, Shanghai 200241,"China) (3"Institute of Brain Research and Rehabilitation, South China Normal University, Guangzhou 510898,"China)
Abstract: Despite occupying only 10% of the total volume of the human brain, the cerebellum contains over half of its neurons. Traditionally viewed as primarily responsible for coordinating motor movements, increasing evidence in recent years suggests that the cerebellum is closely associated with higher cognitive functions such as learning, attention, memory, and language, participating in the regulation of various non- motor functions. Concurrently, abnormal cerebellar development has been closely linked to several neurodevelopmental disorders, including Autism Spectrum Disorder (ASD), characterized by social impairments,"repetitive behaviors, and language deficits, often accompanied by sensory abnormalities. Clinical studies have found structural and functional alterations in the cerebellum of individuals with autism. Interestingly, similar cerebellar phenotypes have been observed in animal models of autism spectrum disorders. Importantly, specific knockout of autism susceptibility genes in cerebellar neurons can induce typical autism-like behaviors in model animals, suggesting that abnormal cerebellar development is a key pathological mechanism underlying autism spectrum disorders. The relationship between the cerebellum and ASD will be briefly summarized from both clinical and basic research perspectives, providing new insights for the diagnosis and treatment of ASD.
Keywords:"Autism spectrum disorder, cerebellum, structural and functional, model animals