張闊軍,顧勤蘭,王明慧,趙麗,楊侃,王進(jìn)欣*(. 中國(guó)藥科大學(xué)江蘇省藥物分子設(shè)計(jì)與成藥性優(yōu)化重點(diǎn)實(shí)驗(yàn)室,江蘇 南京 0009;.中國(guó)藥科大學(xué)高等職業(yè)技術(shù)學(xué)院,江蘇 南京0009;.中國(guó)藥科大學(xué)生理教研室,江蘇 南京 0009)
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酸性鞘磷脂酶/神經(jīng)酰胺通路在疾病發(fā)生發(fā)展中作用機(jī)制的研究進(jìn)展
張闊軍1,顧勤蘭2,王明慧1,趙麗3,楊侃1,王進(jìn)欣1*
(1. 中國(guó)藥科大學(xué)江蘇省藥物分子設(shè)計(jì)與成藥性優(yōu)化重點(diǎn)實(shí)驗(yàn)室,江蘇 南京 210009;2.中國(guó)藥科大學(xué)高等職業(yè)技術(shù)學(xué)院,江蘇 南京210009;3.中國(guó)藥科大學(xué)生理教研室,江蘇 南京 210009)
[摘要]酸性鞘磷脂酶/神經(jīng)酰胺通路可介導(dǎo)細(xì)胞凋亡、炎癥和自噬等多種細(xì)胞活動(dòng),與心腦血管疾病、代謝類疾病、肺部和肝部疾病以及神經(jīng)系統(tǒng)疾病等多種疾病的發(fā)生、發(fā)展密切相關(guān)。酸性鞘磷脂酶現(xiàn)已成為多種疾病的臨床生物標(biāo)記物和潛在的治療靶點(diǎn)。綜述酸性鞘磷脂酶/神經(jīng)酰胺通路在各種疾病中的生物學(xué)功能和作用機(jī)制最新研究進(jìn)展,旨在為相關(guān)疾病的治療提供新思路。
[關(guān)鍵詞]酸性鞘磷脂酶;神經(jīng)酰胺;細(xì)胞凋亡;疾病
接受日期:2015-10-20
項(xiàng)目資助:國(guó)家自然科學(xué)基金面上項(xiàng)目(No. 81473231)
研究方向: 基于天然產(chǎn)物的新藥設(shè)計(jì)與合成研究;
Tel:025-83271414;E-mail: jinxinwang@163.com
Research Progress in Acidic Sphingomyelinase/ Ceramide Pathway: Its Role and Mechanism in
Development of Related Diseases
ZHANG Kuojun1, GU Qinlan2, WANG Minghui1, ZHAO Li3, YANG Kan1, WANG Jinxin1
(1. Key Laboratory of Drug Design and Optimization of Jiangsu Provinve, China Pharmaceutical University, Nangjing 210009, China; 2. Altitude Vocational School, China Pharmaceutical University, Nanjing 210009, China;3. Department of Physiology, China Pharmaceutical University, Nanjing 210009, China)
[Abstract] Acidic sphingomyelinase (ASMase)/ceramide (CE) pathway mediates various cellular processes including cell apoptosis, inflammation and autophagy, and is closely associated with the development of many human diseases, including cardiovascular and cerebrovascular, metabolic, pulmonary, hepatic and neurological disorders. ASMase has been regarded as a promising clinical biomarker and potential therapeutic target for many diseases. The recent progress in investigations on the biological functions and mechanisms of ASMase/CE pathway in these diseases was reviewed, so as to provide new ideas for the treatment of related diseases.
[Key words] acid sphingomyelinase; ceramide; apoptosis; disease
酸性鞘磷脂酶(acid sphingomyelinase,ASMase)是鞘脂類物質(zhì)代謝的一種關(guān)鍵酶,可催化鞘磷脂(sphingomyelin,SM)生成神經(jīng)酰胺(ceramide,CE)。雖然CE在體內(nèi)也可由其他生物途徑合成,但ASMase生成途徑是體內(nèi)CE生成最快、最直接的途徑。CE還可進(jìn)一步代謝生成鞘氨醇(sphingosine)、鞘氨醇-1-磷酸(sphingosine-1-phosphate,S1P)等一系列生物活性脂質(zhì),CE及其下游代謝物參與多種細(xì)胞活動(dòng),包括細(xì)胞增殖、凋亡、衰老、轉(zhuǎn)移、血管生成、炎癥、自噬、感染和蛋白運(yùn)輸?shù)萚1]。
ASMase的編碼基因SMPD1,能同時(shí)產(chǎn)生兩種ASMase,即溶酶體酸性鞘磷脂酶(lysosomal acid sphingomyelinase,L-ASMase)和分泌型酸性鞘磷脂酶(secretory acid sphingomyelinase,S-ASMase),兩者的分布位置和結(jié)構(gòu)均有差異,且發(fā)揮不同的生物學(xué)效應(yīng)。L-ASMase分布于溶酶體內(nèi)側(cè),與高甘露糖低聚糖糖基化,且不需額外的Zn2+激活;S-ASMase位于細(xì)胞外,需要Zn2+激活,具有復(fù)雜的糖基化模式,體內(nèi)半衰期較長(zhǎng)[2]。ASMase最初是因尼曼皮克?。∟iemann-Pick disease,NPD)患者體內(nèi)該酶缺乏導(dǎo)致鞘磷脂在溶酶體內(nèi)大量聚積而為大家所熟識(shí)。近年來,多項(xiàng)研究表明ASMase/CE通路在受體信號(hào)分子(如CD95、CD40)、細(xì)胞毒試劑(如順鉑、阿霉素)、病原體(如細(xì)菌、病毒)、輻射(如紫外線輻射、電離輻射)、氧化應(yīng)激、缺血再灌注等各種理化刺激下激活,參與細(xì)胞凋亡、炎癥和自噬等相關(guān)信號(hào)通路的調(diào)控[2-4],在心腦血管疾病、代謝類疾病、肝部和肺部疾病以及神經(jīng)系統(tǒng)疾病等多種疾病的發(fā)生、發(fā)展過程中起關(guān)鍵作用(見圖1)。本文就ASMase/CE通路在多種疾病中的生物學(xué)功能和作用機(jī)制研究的最新進(jìn)展進(jìn)行綜述。
圖1 AMSmase/CE通路生物學(xué)機(jī)制Figure 1 Biological mechanism of ASMase/CE pathway
1.1動(dòng)脈粥樣硬化
研究表明,ASMase/CE通路激活在動(dòng)脈粥樣硬化(arteriosclerosis,AS)發(fā)生、發(fā)展的各個(gè)環(huán)節(jié)均發(fā)揮重要作用。Schissel等最早發(fā)現(xiàn)粥樣硬化斑塊損傷處提取的低密度脂蛋白(low density lipoprotein,LDL)與血漿中的LDL相比,SM和CE含量均明顯增高。該課題組進(jìn)一步研究發(fā)現(xiàn):①AS動(dòng)物模型和患者的斑塊損傷處均有S-ASMase表達(dá),其可在生理(中性)pH條件下水解動(dòng)脈粥樣硬化LDL表面的SM生成CE,導(dǎo)致LDL顆粒聚集融合,增強(qiáng)LDL對(duì)動(dòng)脈壁蛋白聚糖的親和力,造成LDL內(nèi)皮下聚集和滯留[5],而LDL聚集后更易被巨噬細(xì)胞攝入,從而誘導(dǎo)泡沫細(xì)胞形成[6];②AS過程始終伴隨炎癥反應(yīng),損傷處的血管壁本身含有高水平的促炎因子,導(dǎo)致局部炎癥反應(yīng),促炎因子激活A(yù)SMase/CE通路,而CE又可刺激促炎因子進(jìn)一步表達(dá),最終造成內(nèi)膜增厚和斑塊破裂,介導(dǎo)AS炎癥過程[7]。最近,Deevska等[8]也證實(shí)了S-ASMase在LDL聚集中的重要作用。研究表明,在外界刺激(如死亡受體CD95)下,L-ASMase轉(zhuǎn)移至細(xì)胞膜外葉,水解細(xì)胞膜SM,釋放大量CE,CE自我聯(lián)結(jié),形成CE富集的膜平臺(tái),加速NADPH氧化酶亞基的聚集和激活,刺激活性氧(reactive oxygen species,ROS)的產(chǎn)生,引發(fā)氧化應(yīng)激,降低NO生物活性,最終導(dǎo)致內(nèi)皮細(xì)胞功能失調(diào)[9-11]。另外,血管平滑肌細(xì)胞的增殖和凋亡均促進(jìn)AS病變的發(fā)展,而ASMase/CE通路激活可同時(shí)參與平滑肌細(xì)胞增殖和凋亡的調(diào)控過程。
值得注意的是,盡管大量證據(jù)表明ASMase/CE通路激活促進(jìn)AS病理發(fā)展,但臨床研究結(jié)果卻表明A型和B型NPD患者(ASMase缺陷)患冠狀動(dòng)脈粥樣硬化的風(fēng)險(xiǎn)較大[12]。最近也有文獻(xiàn)報(bào)道,動(dòng)物模型中ASMase具有抗AS作用,比如腺病毒誘導(dǎo)ASMase表達(dá)、分泌至血液循環(huán),但并沒有加重載脂蛋白E(apolipoprotein E,apoE)缺陷小鼠(apoE-/-)粥樣硬化斑塊損傷,反而降低了損傷[13]。特別是L-ASMase被報(bào)道具有抗AS作用,其可能的機(jī)制:①L-ASMase水解溶酶體中SM,釋放出膽固醇,加速膽固醇運(yùn)輸至細(xì)胞外,阻止膽固醇在巨噬細(xì)胞溶酶體中的聚集[14];②L-ASMase通過調(diào)節(jié)自噬(autophagy)成熟過程發(fā)揮其抗AS效應(yīng)[15-16]。因此,L-ASMase與S-ASMase在AS中的作用及機(jī)制完全不同,兩者在上述過程中的確切調(diào)控機(jī)制尚未明確,還需進(jìn)一步深入研究。
1.2缺血再灌注損傷
大量體外、離體和體內(nèi)試驗(yàn)結(jié)果表明,ASMase/CE通路激活是缺血再灌注(ischemia/reperfusion,I/R)損傷產(chǎn)生的機(jī)制之一,I/R誘導(dǎo)ASMase/CE通路激活,導(dǎo)致細(xì)胞凋亡或介導(dǎo)炎癥因子的產(chǎn)生造成細(xì)胞損傷。例如,大鼠左冠狀動(dòng)脈閉塞模型中,缺血后CE的水平升高,再灌注后CE升高更加顯著,CE誘導(dǎo)心肌細(xì)胞凋亡[17-18];家兔左冠狀動(dòng)脈閉塞模型中,CE明顯升高,而缺血前靜脈注射D609(抑制ASMase和CE的生成)可減少心肌細(xì)胞凋亡和心肌梗死面積[19];局灶性腦缺血導(dǎo)致野生型小鼠(ASMase+/+)ASMase/CE通路激活,產(chǎn)生大量促炎因子,而ASMase-/-小鼠或ASMase+/+小鼠預(yù)先給予D609可有效降低腦部損傷程度,減小梗死面積,提高神經(jīng)功能,改善腦缺血再灌注后的中風(fēng)癥[20]。Usta等[21]采用人類心肌活檢,發(fā)現(xiàn)CE介導(dǎo)心麻痹和I/R中心肌細(xì)胞凋亡,而缺血前給予ASMase功能性抑制劑阿米替林,人心肌細(xì)胞凋亡現(xiàn)象明顯降低,預(yù)示ASMase抑制劑可應(yīng)用于臨床減輕I/R損傷。
缺血預(yù)處理(ischemic preconditioning,IP)可使I/R心肌細(xì)胞凋亡減輕,心肌梗死面積減小,心律失常發(fā)生率降低,并促進(jìn)再灌注后心肌功能的恢復(fù)等,但其機(jī)制尚不完全明確。Cui等[22]研究表明,IP 可短暫性激活A(yù)SMase,生成一定量的CE,而CE進(jìn)一步代謝生成S1P,最終CE減少、S1P增加。S1P與CE不同,具有抗凋亡效應(yīng),從而產(chǎn)生心肌保護(hù)作用,而在IP之前用ASMase功能性抑制劑去郁敏抑制ASMase活性則會(huì)抑制預(yù)處理的心肌保護(hù)作用。另外,Der等[23]研究表明IP可通過降低CE的生成而使內(nèi)皮一氧化氮合成酶(endothelial nitric oxide synthase,eNOS)從小窩蛋白-1 (caveolin 1,Cav-1)中釋放出來,生成心肌可利用的NO,從而降低心肌損傷。由此可見,ASMase、CE以及CE下游的代謝物共同參與IP的調(diào)控過程,但它們?cè)谠撨^程的具體調(diào)節(jié)機(jī)制尚需進(jìn)一步研究。
糖尿?。╠iabetes mellitus)分為1型糖尿病和2型糖尿病兩種類型,CE在兩種類型糖尿病的發(fā)病機(jī)制中發(fā)揮多方面的作用,主要包括誘導(dǎo)β-細(xì)胞凋亡、胰島素抵抗以及降低胰島素基因的表達(dá)[24]。例如,鏈脲霉素誘導(dǎo)的糖尿病小鼠模型中,腎臟和血漿中的CE含量升高,血漿中S-ASMase活性增加,提示CE介導(dǎo)糖尿病小鼠的腎臟損傷[25];2型糖尿病患者中CE含量升高,且CE含量與胰島素的敏感性呈負(fù)相關(guān)[22]。另外,有研究表明ASMase/CE通路在糖尿病并發(fā)癥中起關(guān)鍵作用,如糖尿病視網(wǎng)膜病變(diabetic retinopathy,DR)等[26]。Busik課題組發(fā)現(xiàn):①在視網(wǎng)膜內(nèi)皮細(xì)胞(體外)和1型糖尿病小鼠模型(體內(nèi))中,ASMase活性升高,介導(dǎo)視網(wǎng)膜血管炎癥,ASMase基因敲除或二十二碳六烯酸(docosahexaenoic acid,DHA)抑制ASMase活性,可有效抑制視網(wǎng)膜微血管炎癥及非細(xì)胞微血管的形成[27];②在2型糖尿病小鼠模型中,視網(wǎng)膜和內(nèi)皮祖細(xì)胞(一種血管內(nèi)皮損傷修復(fù)細(xì)胞)ASMase活性均升高,而DHA抑制視網(wǎng)膜內(nèi)皮細(xì)胞ASMase活性可抑制視網(wǎng)膜炎癥、血管損傷,抑制內(nèi)皮祖細(xì)胞ASMase活性可恢復(fù)內(nèi)皮祖細(xì)胞的血管修復(fù)功能[28],因此,ASMase在糖尿病視網(wǎng)膜病變的血管退化階段發(fā)揮重要作用,抑制ASMase既可抑制血管退化,又可恢復(fù)血管修復(fù)功能,提示ASMase是治療DR的潛在有效靶點(diǎn)。
3.1囊性纖維化
囊性纖維化(cystic fibrosis,CF)會(huì)累及身體多處器官,其中肺部所受的影響最為嚴(yán)重,主要表現(xiàn)為肺部慢性炎癥,反復(fù)性、持續(xù)性肺部感染以及肺部纖維化。大量證據(jù)表明,在CF細(xì)胞和動(dòng)物模型以及患者中存在ASMase/CE通路異常、CE聚集的現(xiàn)象[4, 29-30]。銅綠假單胞菌(Pseudomonas aeruginosa)感染是CF患者死亡的主要原因,Teichgr?ber等[4]研究發(fā)現(xiàn)不同品種CF小鼠模型以及CF患者肺部標(biāo)本的CE水平升高,促進(jìn)了肺部炎癥、內(nèi)皮細(xì)胞死亡、增加支氣管DNA沉積,從而增加了對(duì)P. aeruginosa感染的敏感性。抑制ASMase活性或者ASMase基因雜合小鼠(ASMase+/-),可使CE水平恢復(fù)正常,并阻止上述所有病理表現(xiàn),降低細(xì)菌感染。Brodlie等[30]也證實(shí)CE聚集出現(xiàn)在CF患者中。鑒于ASMase基因敲除和系統(tǒng)性抑制ASMase可能會(huì)給機(jī)體組織帶來副作用,Becker等[31]研究了CF小鼠肺部局部吸入ASMase抑制劑的影響,結(jié)果表明,ASMase抑制劑局部吸入與ASMase基因敲除和系統(tǒng)性抑制ASMase產(chǎn)生相似效果。另外,Ziobro等[32]研究表明CE促進(jìn)肺纖維化,長(zhǎng)時(shí)間給予阿米替林可減慢肺纖維化進(jìn)程。
3.2肺水腫和急性肺損傷
金黃色葡萄球菌(Staphylococcus aureus)引起的肺水腫模型中,ASMase/CE通路通過產(chǎn)生超氧化物破壞緊密連接蛋白(tight junctions,TJs)在肺水腫中起重要作用。阿米替林抑制ASMase活性或敲除ASMase基因均可抑制感染小鼠的肺水腫,但不能減少細(xì)菌的數(shù)量;而給予抗生素可減少細(xì)菌的數(shù)量,但不能抑制小鼠肺水腫。因此,抗生素與ASMase抑制劑合用既可抑制肺水腫,又可減少細(xì)菌數(shù)量,從而保護(hù)小鼠免受致命的敗血癥和肺功能障礙[33]。
新生兒肺部急性炎癥模型中,ASMase/CE通路激活,使血管通透性增加,表面活性劑鈍化,肺泡上皮細(xì)胞凋亡,誘發(fā)肺水腫。給予外源性表面活性劑對(duì)肺部功能只能起暫時(shí)性保護(hù)作用,而將ASMase功能性抑制劑丙米嗪與表面活性劑同時(shí)給予一次打擊誘發(fā)的新生幼豬急性肺損傷模型,可改善其肺部功能,且在灌洗液中其白細(xì)胞計(jì)數(shù)和白細(xì)胞介素-8(interleukin-8,IL-8)濃度均降低[34]。在后續(xù)研究中,研究者們采用三次打擊誘發(fā)的新生幼豬急性肺損傷模型,將表面活性劑與ASMase抑制劑磷脂酰肌醇-3,5-雙磷酸(phosphatidylinositol-3,5-bisphosphate,PIP2)或肌醇-1,2,6-三磷酸(inositol-1,2,6-trisphosphate,IP3)合用,能明顯改善肺部功能,抑制肺水腫的發(fā)生;分離的肺部組織中ASMase活性和CE濃度降低,各種炎癥因子、轉(zhuǎn)化生長(zhǎng)因子表達(dá)降低,粒細(xì)胞的浸潤(rùn)減輕,表面活性劑的表面張力也降低[35-36]。
血小板激活因子(platelet-activating factor,PAF)能迅速增加血管通透性,是肺水腫發(fā)生的重要調(diào)節(jié)因子。G?ggel等[37]研究表明PAF引發(fā)肺水腫包括兩種機(jī)制:ASMase激活產(chǎn)生 CE以及環(huán)氧合酶(cyclooxygenase,COX)激活產(chǎn)生前列腺素E2(prostaglandin E2,PGE2)。在此基礎(chǔ)上,研發(fā)人員進(jìn)一步研究發(fā)現(xiàn),PAF引起ASMase激活,產(chǎn)生大量CE,促進(jìn)各種信號(hào)分子包括Cav-1、eNOS、經(jīng)典瞬時(shí)受體電位-6(transient receptor potential classical 6,TRPC6)等募集至內(nèi)皮細(xì)胞的小窩。這一方面導(dǎo)致eNOS與Cav-1結(jié)合,減少NO的合成;另一方面促進(jìn)了Ca2+內(nèi)流,血管通透性增加,最終誘導(dǎo)肺水腫的發(fā)生[38- 39]。
4.1脂肪性肝炎
脂肪性肝炎(Steatohepatitis,SH)是脂肪性肝疾病的中間階段,主要包括酒精性脂肪性肝炎(alcoholic steatohepatitis,ASH)和非酒精性脂肪性肝炎(nonalcoholic steatohepatitis steatohepatitis,NASH)。有研究表明,ASH和NASH患者血清中ASMase水平升高,提示ASMase有望成為慢性肝疾病的新標(biāo)志物[40]。Fernández-Checa課題組的研究表明,ASH和NASH患者以及動(dòng)物模型中ASMase激活,可介導(dǎo)內(nèi)質(zhì)網(wǎng)應(yīng)激(endoplasmic reticulum stress,ER stress)、自噬和溶酶體膜透化作用(lysosomal membrane permeabilization,LMP),導(dǎo)致胰島素抵抗、脂肪變性、脂毒性、凋亡以及纖維化,從而促進(jìn)ASH和NASH的發(fā)展進(jìn)程[41-43]。給予ASMase+/+小鼠阿米替林,可抑制高脂肪食物引起的脂肪變性、纖維化和肝臟損傷,提示阿米替林可能成為NASH的有效治療方法[43]。另外,ASMase激活導(dǎo)致蛋氨酸代謝失常,如降低S-腺苷-L-蛋氨酸(S-adenosyl-L-methionine,SAM)和卵磷脂(phosphatidylcholine,PC)的水平,破壞甲基化反應(yīng)、抗氧化防御作用以及膜的完整性,從而促進(jìn)ASH和NASH病變發(fā)展。
4.2其他肝臟損傷
在腫瘤壞死因子α(tumor necrosis factorα,TNF-α)[44]、I/R[45]以及Wilson病[46]等誘導(dǎo)的肝細(xì)胞凋亡與ASMase/CE通路密切相關(guān)。Llacuna等[45]發(fā)現(xiàn),ASMase在小鼠肝臟I/R中被激活而釋放大量CE,CE激活下游的氨基末端激酶(Jun N-terminal kinase,JNK)通路,促進(jìn)促凋亡蛋白BimL(Bcl-2 interacting mediator of cell death L)磷酸化,并轉(zhuǎn)移至線粒體,從而誘導(dǎo)線粒體凋亡途徑,造成肝損傷。丙米嗪抑制ASMase活性以及siRNA沉默ASMase基因,可降低血清中丙氨酸氨基轉(zhuǎn)移酶(alanine aminotransferase,ALT)的水平,減輕肝細(xì)胞壞死和凋亡,使肝損傷程度明顯降低。Wilson病是一種由銅代謝障礙引起的常染色體隱性遺傳性疾病,臨床表現(xiàn)為肝損害、錐體外系癥狀以及貧血等。Lang等[46]研究表明大量的Cu2+聚集,激活A(yù)SMase/CE通路,一方面誘導(dǎo)肝細(xì)胞凋亡、促進(jìn)肝硬化的發(fā)生,另一方面促進(jìn)紅細(xì)胞膜上磷脂酰絲氨酸的外露,從而使紅細(xì)胞易被其他細(xì)胞內(nèi)化而造成貧血。給予Wilson小鼠丙米嗪,可阻止肝硬化、肝損傷,增加小鼠的生存率,并抑制貧血的發(fā)生。另外,Moles 等[47]發(fā)現(xiàn)ASMase/CE通路激活,可通過調(diào)節(jié)組織蛋白酶B(cathepsinB,CtsB)和組織蛋白酶D(cathepsinD,CtsD)的蛋白酶水解過程進(jìn)而促進(jìn)肝星狀細(xì)胞(hepatic stellate cell,HSC)的激活和增殖,促進(jìn)肝纖維化進(jìn)程。丙米嗪、阿米替林抑制ASMase活性、siRNA沉默ASMase基因或ASMase雜合小鼠(ASMase+/-),均可使CtsB/D的水解處理過程鈍化,HSC的激活和增殖受到抑制??傊?,抑制ASMase/CE通路激活具有雙重效應(yīng),既可抑制肝細(xì)胞凋亡而減輕肝臟損傷,又可抑制HSC激活而抑制肝纖維化進(jìn)程,因此,ASMase有望成為治療慢性肝疾病的新靶點(diǎn)。
5.1阿爾茨海默病
阿爾茨海默?。ˋlzheimer's disease,AD)是一種神經(jīng)退行性疾病,主要病理特征為β-淀粉樣蛋白(amyloid β peptide,Aβ)沉積形成老年斑(senile plaques,SPs)和tau蛋白過度磷酸化形成神經(jīng)元纖維纏結(jié)(neurofibrillary tangles,NFTs)。Malaplate-Armand等[48]研究表明Aβ寡聚體激活磷脂酶A2(phospholipase A2,cPLA2)-花生四烯酸(arachidonic acid,AA)-ASMase-CE通路可引起神經(jīng)元細(xì)胞凋亡,而CE下游代謝物S1P通過抑制ASMase活性進(jìn)而抑制Aβ寡聚體引起的細(xì)胞凋亡,是很強(qiáng)的神經(jīng)保護(hù)因子。He等[49]對(duì)AD患者大腦標(biāo)本中ASMase、CE及其下游的酸性神經(jīng)酰胺酶(acid ceramidase,AC)、鞘氨醇、S1P的水平進(jìn)行了全面分析,結(jié)果表明ASMase以及AC活性增加,CE、鞘氨醇水平升高,S1P降低,可共同促進(jìn)神經(jīng)元細(xì)胞凋亡。提示,ASMase的激活和S1P的降低與Aβ沉積和過度磷酸化的tau蛋白水平密切相關(guān)。自噬(autophagy)功能障礙或受限是AD發(fā)病的重要原因。Lee等[50]發(fā)現(xiàn)AD小鼠模型中ASMase激活,導(dǎo)致溶酶體活性降低、自噬功能障礙,進(jìn)而促進(jìn)AD病變的發(fā)展。ASMase基因部分敲除或阿米替林鹽酸鹽抑制AD小鼠ASMase活性,可使溶酶體自噬功能恢復(fù)正常,Aβ沉積減少,小鼠的認(rèn)知功能和記憶力得到改善。另有研究表明,CE還可通過穩(wěn)定β-分泌酶1(β-site APP cleaving enzyme 1,BACE1)進(jìn)而促進(jìn)Aβ的生成,造成Aβ過量沉積[51]。
5.2重度抑郁癥
重度抑郁癥(major depressive disorder,MDD)是一種嚴(yán)重的情緒障礙,終生患病率超過10%,而MDD的發(fā)病原因和機(jī)制到目前為止尚不明確。Gulbins課題組的研究表明ASMase/CE通路在MDD的發(fā)病機(jī)制中起核心作用[52]:①M(fèi)DD患者腦內(nèi)ASMase活性和CE水平均明顯異常升高[53];②三環(huán)類抗抑郁藥,例如阿米替林、氟西汀等通過抑制ASMase/CE通路激活發(fā)揮其抗抑郁功效,證實(shí)ASMase是抗抑郁的潛在靶點(diǎn)[54];③CE可抑制多巴胺轉(zhuǎn)運(yùn)體(dopamine transporter,DAT)活性,導(dǎo)致多巴胺轉(zhuǎn)運(yùn)受阻而血清素轉(zhuǎn)運(yùn)增加,從而引發(fā)抑郁癥[55]。
多種疾病的發(fā)生、發(fā)展與ASMase/CE通路激活密切相關(guān),ASMase抑制劑可下調(diào)ASMase的表達(dá)和活性,進(jìn)而降低CE水平,對(duì)相關(guān)疾病的預(yù)防和治療具有重要意義。目前,報(bào)道的ASMase抑制劑主要有兩種類型:功能性抑制劑和直接抑制劑[56]。ASMase功能性抑制劑是一類促使ASMase從溶酶體膜上脫落而與蛋白水解酶結(jié)合,導(dǎo)致ASMase降解失活的化合物[57],目前主要為三環(huán)類抗抑郁藥,如丙咪嗪、去郁敏、阿米替林等。但該類抑制劑會(huì)抑制其他溶酶體水解酶,選擇性較差[58];無組織特異性,會(huì)產(chǎn)生不良反應(yīng);起效濃度高,高劑量必然會(huì)導(dǎo)致一定的毒副作用。ASMase直接抑制劑是一類直接作用于ASMase而使之失活的化合物,目前主要有底物類似物、磷酸酯類和天然產(chǎn)物類[58]。底物類似物雖然活性較好,但對(duì)中性鞘磷脂酶也有抑制作用,故選擇性較差;磷酸酯類對(duì)磷脂酶A1、 A2、C和D不穩(wěn)定,且不易透過細(xì)胞膜,應(yīng)用受到限制;Okudaira 等[59]發(fā)現(xiàn),藤黃屬植物中分離得到的3個(gè)氧雜蒽酮化合物(α-mangostin、cowanin和cowanol)對(duì)ASMase具有較高的抑制活性。迄今為止,ASMase蛋白晶體結(jié)構(gòu)尚未見報(bào)道,基于受體的藥物設(shè)計(jì)無法進(jìn)行,ASMase直接抑制劑的研究任重道遠(yuǎn)。本課題組近期研究發(fā)現(xiàn)了一些結(jié)構(gòu)新穎、抑制活性較好的ASMase直接抑制劑[60],將有助于ASMase相關(guān)疾病的預(yù)防和治療藥物的研究與開發(fā)。
綜上所述,ASMase/CE通路在多種疾病中的作用及機(jī)制研究已取得重要進(jìn)展,充分證實(shí)ASMase/CE通路在相關(guān)疾病中的重要作用。但目前大多數(shù)研究只是針對(duì)細(xì)胞和動(dòng)物模型,相關(guān)臨床研究較少,ASMase/CE通路在病理生理中的確切調(diào)控機(jī)制以及CE下游代謝產(chǎn)物的確切變化規(guī)律尚需進(jìn)一步的深入研究。另外,由于高效、高選擇性的ASMase抑制劑嚴(yán)重缺乏,大多數(shù)研究只能使用基因敲除或RNA干擾技術(shù),疾病發(fā)展過程中ASMase的拓?fù)鋵W(xué)問題也尚未解決。隨著研究方法和技術(shù)的成熟,以及高效、高選擇性抑制劑的發(fā)現(xiàn),ASMase/CE通路生物學(xué)機(jī)制逐步被闡明,將為心腦血管疾病、肺部和肝部疾病以及神經(jīng)系統(tǒng)疾病等人類重大疾病的預(yù)防和治療提供新思路、新策略。
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*通訊作者:王進(jìn)欣,教授;
[中圖分類號(hào)]R363.2+1
[文獻(xiàn)標(biāo)志碼]A
[文章編號(hào)]1001-5094(2015)11-0838-08