李倩曉 于勤 那榮妹 劉百亭
[摘要] 目的 研究miR-1與miR-499在心肌細(xì)胞增殖與凋亡中的調(diào)控作用及其機(jī)制。 方法 通過(guò)脂質(zhì)體2000轉(zhuǎn)染試劑將miR-1 mimics、miR-499 inhibitor轉(zhuǎn)染至H9C2心肌細(xì)胞。設(shè)置空白對(duì)照組、H2O2組(未進(jìn)行轉(zhuǎn)染的H9C2心肌細(xì)胞)、干預(yù)組A(miR-1 mimics轉(zhuǎn)染的H9C2心肌細(xì)胞)、干預(yù)組B(miR-499 inhibitor轉(zhuǎn)染的H9C2心肌細(xì)胞)、干預(yù)組C(miR-1 mimics+miR-499 inhibitor轉(zhuǎn)染的H9C2心肌細(xì)胞)。通過(guò)H2O2誘導(dǎo)建立H9C2心肌細(xì)胞氧化應(yīng)激模型。采用CCK-8法檢測(cè)細(xì)胞增殖情況,流式細(xì)胞儀檢測(cè)細(xì)胞凋亡情況,Western Blot檢測(cè)Bim、Mcl-1蛋白表達(dá)水平。 結(jié)果 與空白對(duì)照組比較,H2O2組細(xì)胞增殖顯著降低而細(xì)胞凋亡率顯著升高,差異有統(tǒng)計(jì)學(xué)意義(P<0.05)。與H2O2組相比,干預(yù)組A、干預(yù)組B細(xì)胞增殖進(jìn)一步降低而細(xì)胞凋亡率進(jìn)一步升高,這種改變?cè)诟深A(yù)組C中更加顯著,差異有統(tǒng)計(jì)學(xué)意義(P<0.05)。與空白對(duì)照組比較,H2O2組Bim蛋白表達(dá)水平明顯升高,Mcl-1蛋白表達(dá)水平明顯降低,差異有統(tǒng)計(jì)學(xué)意義(P<0.05)。與H2O2組相比,干預(yù)組A、干預(yù)組B的Bim蛋白表達(dá)水平進(jìn)一步升高,Mcl-1蛋白表達(dá)水平進(jìn)一步降低,這種改變?cè)诟深A(yù)組C中更加顯著,差異有統(tǒng)計(jì)學(xué)意義(P<0.05)。 結(jié)論 miR-1與miR-499在心肌細(xì)胞增殖與凋亡中發(fā)揮重要調(diào)控作用,miR-1可能通過(guò)上調(diào)Bim、下調(diào)Mcl-1蛋白表達(dá)促進(jìn)心肌細(xì)胞凋亡,miR-499則通過(guò)下調(diào)Bim、上調(diào)Mcl-1蛋白表達(dá)抑制心肌細(xì)胞凋亡。
[關(guān)鍵詞] miR-1;miR-499;調(diào)控;心肌細(xì)胞;凋亡
[中圖分類(lèi)號(hào)] R587.2? ? ? ? ? [文獻(xiàn)標(biāo)識(shí)碼] A? ? ? ? ? [文章編號(hào)] 1673-9701(2020)17-0037-04
A study of the regulatory effect of miR-1 and miR-499 on the proliferation and apoptosis of cardiomyocytes and the mechanism
LI Qianxiao1? ?YU Qin2? ?NA Rongmei2? ?LIU Baiting2
1.Department of Cardiology,Zhejiang Integrated Traditional and Western Medicine Hospital,Hangzhou? ?310000,China; 2.Department of Cardiology,Affiliated Zhongshan Hospital of Dalian University,Dalian? ?116001,China
[Abstract] Objective To study the regulatory effect of miR-1 and miR-499 on the proliferation and apoptosis of cardiomyocytes and the mechanism. Methods MiR-1 mimics and miR-499 inhibitor were transfected into H9C2 cardiomyocytes by liposome 2000 transfection reagent. Those groups were set up such as the blank control group, the H2O2 group(H9C2 cardiomyocytes not transfected),the intervention group A(H9C2 cardiomyocytes transfected by miR-1 mimics), the intervention group B(H9C2 cardiomyocytes transfected by miR-499 inhibitor), and the intervention group C(H9C2 cardiomyocytes transfected by miR-1 mimic+miR-499 inhibitor). The oxidative stress model of H9C2 cardiomyocytes was established by H2O2 induction. The cell proliferation was detected by the CCK-8 method, the cell apoptosis was detected by flow cytometer,and Bim and Mcl-1 protein expression levels were detected by Western Blot. Results Compared with that in the blank control group, the proliferation of cells in the H2O2 group was significantly reduced while the apoptosis rate of cells was significantly increased, with statistically significant differences(P<0.05). Compared with that in the H2O2 group,the proliferation of cells in the intervention group A and the intervention group B further decreased while the apoptosis rate of cells in the two groups further increased, and the correspondent changes were more significant in the intervention group C, with statistically significant differences(P<0.05). Compared with those in the blank control group,the Bim protein expression level in the H2O2 group significantly increased and the Mcl-1 protein expression level significantly decreased, with statistically significant differences(P<0.05). Compared with those in the H2O2 group, the Bim protein expression level in the intervention group A and the intervention group B further increased and the Mcl-1 protein expression level further decreased, and the correspondent changes were more significant in the intervention group C,with statistically significant differences(P<0.05). Conclusion MiR-1 and miR-499 play important regulatory roles in the proliferation and apoptosis of cardiomyocytes. MiR-1 may promote the apoptosis of cardiomyocytes by up-regulating Bim protein expression and down-regulating Mcl-1 protein expression, while miR-499 may inhibit the apoptosis of cardiomyocytes by down-regulating Bim protein expression and up-regulating Mcl-1 protein expression.
[Key words] miR-1;miR-499;Regulation;Cardiomyocyte;Apoptosis
心肌細(xì)胞凋亡與心臟疾病密切相關(guān),包括心肌缺血再灌注損傷、缺血性心臟病、心力衰竭、心肌病等[1]。近年來(lái),關(guān)于微小RNA(microRNA,miRNA)調(diào)控心肌細(xì)胞凋亡的研究已成為熱點(diǎn),為心臟疾病的診治提供了重要方向[2]。本研究將miR-1 mimics、miR-499 inhibitor轉(zhuǎn)染至H2O2處理的心肌細(xì)胞,探討miR-1與miR-499在心肌細(xì)胞增殖與凋亡過(guò)程中的調(diào)控作用及其機(jī)制,現(xiàn)報(bào)道如下。
1 材料與方法
1.1 材料來(lái)源
大鼠H9C2心肌細(xì)胞株,購(gòu)自中科院上海細(xì)胞庫(kù);胎牛血清、DMEM培養(yǎng)基、0.05%胰酶/EDTA(美國(guó)Hycloneo公司);miR-1 mimics、miR-499 inhibitor、競(jìng)爭(zhēng)性短核糖核苷酸陰性對(duì)照序列(scramble-NC)、miR-499、miR-1和U6引物序列(上海吉?jiǎng)P基因化學(xué)技術(shù)有限公司);H2O2、CCK-8、Annexin V-FITC/PI細(xì)胞凋亡檢測(cè)試劑盒(中國(guó)碧云天試劑公司);β-actin、Bim、Mcl-1單抗(美國(guó)Epitmics公司);ECL化學(xué)發(fā)光試劑盒(美國(guó)millipore公司);脂質(zhì)體2000轉(zhuǎn)染試劑(美國(guó)Invitrogen公司);二喹啉甲酸(BCA)試劑盒(美國(guó)Thermo公司);miRNeasy Serum/plasma Kit、miScript SYBR Green PCR Kit、RNase-free ddH2O、逆轉(zhuǎn)錄試劑盒(德國(guó)QIAGEN公司)。RT-PCR檢測(cè)儀(美國(guó)ABI公司),流式細(xì)胞儀(美國(guó)BD公司),酶標(biāo)儀(美國(guó)Bio-Tek公司)。
1.2 細(xì)胞培養(yǎng)
配置含10%胎牛血清的DMEM培養(yǎng)基,加入H9C2心肌細(xì)胞,置于37℃、5%CO2培養(yǎng)箱中培養(yǎng)。每隔2~3 d細(xì)胞傳代1次。在實(shí)驗(yàn)前24 h取對(duì)數(shù)生長(zhǎng)期的H9C2心肌細(xì)胞換液備用。
1.3 細(xì)胞分組及轉(zhuǎn)染
將培養(yǎng)好的H9C2心肌細(xì)胞分為空白對(duì)照組、陰性對(duì)照組、miR-1 mimics組、miR-499 inhibitor組。除空白對(duì)照組外,其余三組H9C2心肌細(xì)胞分別采用隨機(jī)合成的miRNA片段、miR-1 mimics片段、miR-499 inhibitor片段通過(guò)脂質(zhì)體2000轉(zhuǎn)染試劑進(jìn)行轉(zhuǎn)染,濃度均為200 nm,處理時(shí)間均為6 h。轉(zhuǎn)染結(jié)束后將細(xì)胞置于37℃、5%CO2培養(yǎng)箱中培養(yǎng),48 h后收集細(xì)胞。
1.4 RT-PCR檢測(cè)轉(zhuǎn)染情況
采用miRNeasy Serum/plasma Kit試劑盒提取血清RNA,并檢測(cè)RNA的純度。采用逆轉(zhuǎn)錄試劑盒將miRNA逆轉(zhuǎn)錄為特定的cDNA,并置于-80℃冰箱保存?zhèn)溆?。RT-PCR反應(yīng):應(yīng)用制備好的cDNA作為模板,分別配置空白對(duì)照組、陰性對(duì)照組、miR-1 mimics組、miR-499 inhibitor組反應(yīng)管,以U6作內(nèi)參。采用ABI 7500軟件分析熔解曲線,用2-△Ct計(jì)算miRNA基因相對(duì)表達(dá)量。
1.5 實(shí)驗(yàn)分組及H2O2處理
設(shè)置空白對(duì)照組、H2O2組(未進(jìn)行轉(zhuǎn)染的H9C2心肌細(xì)胞)、干預(yù)組A(miR-1 mimics轉(zhuǎn)染的H9C2心肌細(xì)胞)、干預(yù)組B(miR-499 inhibitor轉(zhuǎn)染的H9C2心肌細(xì)胞)、干預(yù)組C(miR-1 mimics+miR-499 inhibitor轉(zhuǎn)染的H9C2心肌細(xì)胞)。除空白對(duì)照組外,其余四組H9C2心肌細(xì)胞均采用200 μmol/L的H2O2處理6 h。
1.6 CCK-8法檢測(cè)細(xì)胞增殖情況
取對(duì)數(shù)生長(zhǎng)期的H9C2心肌細(xì)胞,接種到96孔板中(1×104個(gè)細(xì)胞/孔),置于37℃、5%CO2培養(yǎng)箱中,培養(yǎng)24 h,待細(xì)胞貼壁后,將H2O2處理后的各組細(xì)胞加入貼壁均勻的96孔板中,用CCK-8進(jìn)行處理后,繼續(xù)置于37℃、5%CO2培養(yǎng)箱中。孵育2 h后,測(cè)定各組細(xì)胞光密度(optical density,OD)值。
1.7 流式細(xì)胞儀檢測(cè)細(xì)胞凋亡情況
取H2O2處理后的各組細(xì)胞,經(jīng)PBS洗滌后,消化,離心,收集細(xì)胞。在收集到的細(xì)胞沉淀中加入200 μL binding buffer并吹打成單細(xì)胞懸液,再分別加入濃度為250 μg/mL的Annexin V-FITC和PI試劑各5 μL,避光室溫下反應(yīng)5~15 min,在1 h內(nèi)采用流式細(xì)胞儀檢測(cè)細(xì)胞凋亡率。
1.8 Western Blot檢測(cè)Bim、Mcl-1蛋白表達(dá)水平
取H2O2處理后的各組細(xì)胞,加入裂解液處理30 min,收集蛋白并用BCA法測(cè)定蛋白濃度,煮沸10 min使蛋白變性,上樣,按20 μg/泳道蛋白量經(jīng)12%SDS-PAGE電泳后轉(zhuǎn)至PVDF膜,以5%脫脂奶粉封閉60 min,分別加入β-actin、Bim、Mcl-1特異性抗體(均按照1:1000稀釋),4℃孵育過(guò)夜。次日用PBS-T液洗膜后加入辣根過(guò)氧化物酶標(biāo)記的羊抗兔二抗,室溫孵育2 h后,電化學(xué)發(fā)光(Electro-chemi-luminescence,ECL)顯影,采用圖像分析軟件測(cè)定目的條帶灰度值,用甘油醛-3-磷酸脫氫酶(Glyceraldehyde-3-phosphate dehydrogenase,GAPDH)條帶灰度值作為對(duì)照進(jìn)行校正,分別計(jì)算出各樣本相對(duì)表達(dá)量。計(jì)算方法:目的蛋白相對(duì)表達(dá)量=目的蛋白條帶灰度值/GAPDH條帶灰度值。
1.9 統(tǒng)計(jì)學(xué)方法
采用SPSS 23.0統(tǒng)計(jì)學(xué)軟件處理數(shù)據(jù),計(jì)量資料以均數(shù)±標(biāo)準(zhǔn)差(x±s)表示,多組間比較采用單因素方差分析,兩兩比較采用LSD-t檢驗(yàn),P<0.05為差異有統(tǒng)計(jì)學(xué)意義。
2 結(jié)果
2.1 轉(zhuǎn)染結(jié)果比較
與空白對(duì)照組和陰性對(duì)照組比較,miR-1 mimics組miR-1表達(dá)明顯升高,miR-499 inhibitor組miR-499表達(dá)明顯降低,差異有統(tǒng)計(jì)學(xué)意義(P<0.05)??瞻讓?duì)照組與陰性對(duì)照組間miR-1與miR-499表達(dá)均無(wú)顯著差異(P>0.05)。見(jiàn)表1。
注:與空白對(duì)照組和陰性對(duì)照組比較,*P<0.05;與空白對(duì)照組比較,▲P>0.05
2.2 各組心肌細(xì)胞增殖檢測(cè)結(jié)果比較
與空白對(duì)照組比較,H2O2組細(xì)胞增殖顯著降低,差異有統(tǒng)計(jì)學(xué)意義(P<0.05)。與H2O2組相比,干預(yù)組A、干預(yù)組B細(xì)胞增殖進(jìn)一步降低,這種改變?cè)诟深A(yù)組C中更加顯著,差異有統(tǒng)計(jì)學(xué)意義(P<0.05)。見(jiàn)表2。
注:與空白對(duì)照組比較,*P<0.05;與H2O2組比較,#P<0.05
2.3 各組心肌細(xì)胞凋亡檢測(cè)結(jié)果比較
與空白對(duì)照組比較,H2O2組細(xì)胞凋亡率顯著升高,差異有統(tǒng)計(jì)學(xué)意義(P<0.05)。與H2O2組相比,干預(yù)組A、干預(yù)組B細(xì)胞凋亡率進(jìn)一步升高,這種改變?cè)诟深A(yù)組C中更加顯著,差異有統(tǒng)計(jì)學(xué)意義(P<0.05)。見(jiàn)表3。
注:與空白對(duì)照組比較,*P<0.05;與H2O2組比較,#P<0.05
2.4 各組心肌細(xì)胞Bim、Mcl-1蛋白表達(dá)水平比較
與空白對(duì)照組比較,H2O2組Bim蛋白表達(dá)水平明顯升高,而Mcl-1蛋白表達(dá)水平明顯降低,差異有統(tǒng)計(jì)學(xué)意義(P<0.05)。與H2O2組相比,干預(yù)組A、干預(yù)組B的Bim蛋白表達(dá)水平進(jìn)一步升高,而Mcl-1蛋白表達(dá)水平進(jìn)一步降低,這種改變?cè)诟深A(yù)組C中更加顯著,差異有統(tǒng)計(jì)學(xué)意義(P<0.05)。見(jiàn)表4。
注:與空白對(duì)照組比較,*P<0.05;與H2O2組比較,#P<0.05
3 討論
心肌細(xì)胞凋亡由氧化應(yīng)激、缺血、缺氧、負(fù)荷過(guò)重、再灌注損傷等誘導(dǎo)[3]。心肌細(xì)胞凋亡機(jī)能異常是多種心臟疾病發(fā)生的重要機(jī)制[4]。細(xì)胞凋亡經(jīng)典通路主要包括線粒體凋亡通路和死亡受體凋亡通路[5]。B細(xì)胞淋巴瘤-2(B-cell lymphoma-2,Bcl-2)基因家族是一類(lèi)重要的凋亡調(diào)控蛋白,在線粒體凋亡通路中具有重要調(diào)節(jié)作用[6-8]。Bcl-2基因家族分為抗凋亡亞家族、促凋亡亞家族和僅含BH3結(jié)構(gòu)域的BH3-only亞家族[9]。Bcl-2相互作用細(xì)胞凋亡調(diào)節(jié)因子(Bcl-2 interacting mediator of cell death,Bim)是僅含BH3結(jié)構(gòu)域的BH3-only亞家族成員之一,與促凋亡亞家族成員高親和力結(jié)合,發(fā)揮促凋亡作用[10]。髓細(xì)胞白血病基因-1(myeloid cell leukaemia-1,Mcl-1)是抗凋亡亞家族成員之一,可調(diào)控細(xì)胞凋亡、分化和細(xì)胞周期[11]。
miRNA是一類(lèi)廣泛存在于真核生物中內(nèi)源性表達(dá)的小分子非編碼單鏈RNA,幾乎參與調(diào)控人類(lèi)生長(zhǎng)發(fā)育的各個(gè)階段[12,13]。miRNA在轉(zhuǎn)錄水平通過(guò)與靶基因mRNA特定序列互補(bǔ)結(jié)合,阻止靶基因mRNA翻譯或誘導(dǎo)其剪切,從而在基因調(diào)控中發(fā)揮重要作用,參與各種生物學(xué)過(guò)程和疾病的發(fā)生發(fā)展[14,15]。miRNA在心臟疾病的病理過(guò)程中具有重要調(diào)節(jié)作用[16]。研究發(fā)現(xiàn),miRNA可作為心臟疾病早期篩查的生物標(biāo)志物[17]。由于miRNA可同時(shí)調(diào)控細(xì)胞某一信號(hào)通路上與疾病相關(guān)的多個(gè)基因表達(dá),因此對(duì)miRNA進(jìn)行干預(yù)有望成為更理想的治療方法[18]。miR-499是與心肌細(xì)胞分化密切相關(guān)的miRNA,在心肌細(xì)胞中特異表達(dá)[19,20]。miR-1在調(diào)節(jié)心肌細(xì)胞增殖、心臟節(jié)律性、心臟電傳導(dǎo)等過(guò)程中具有重要作用[21]。本研究檢測(cè)了miR-1 mimics、miR-499 inhibitor轉(zhuǎn)染后心肌細(xì)胞增殖與凋亡情況,結(jié)果表明,上調(diào)miR-1表達(dá)或抑制miR-499表達(dá)后,心肌細(xì)胞增殖降低,而心肌細(xì)胞凋亡率升高。當(dāng)兩者同時(shí)進(jìn)行干預(yù)后,心肌細(xì)胞增殖進(jìn)一步降低,而心肌細(xì)胞凋亡率則進(jìn)一步升高。通過(guò)檢測(cè)促凋亡蛋白Bim與抗凋亡蛋白Mcl-1,發(fā)現(xiàn)轉(zhuǎn)染miR-1 mimics、miR-499 inhibitor心肌細(xì)胞,Bim蛋白表達(dá)水平明顯升高,Mcl-1蛋白表達(dá)水平明顯降低,而聯(lián)合干預(yù)組Bim蛋白表達(dá)水平升高幅度及Mcl-1蛋白表達(dá)水平降低幅度更為顯著,提示miR-1可能是通過(guò)上調(diào)Bim、下調(diào)Mcl-1蛋白發(fā)揮促進(jìn)心肌細(xì)胞凋亡作用,而miR-499則通過(guò)下調(diào)Bim、上調(diào)Mcl-1蛋白發(fā)揮抑制心肌細(xì)胞凋亡作用。
總而言之,miRNA的發(fā)現(xiàn)為心臟疾病的診斷與治療提供了一個(gè)新的研究方向,但目前相關(guān)機(jī)制研究仍處于起步階段,尚有待今后進(jìn)一步深入探索。
[參考文獻(xiàn)]
[1] Xia P,Liu Y,Cheng Z. Signaling pathways in cardiac myocyte apoptosis[J]. Biomed Res Int,2016,2016(19):1-22.
[2] Chen-Scarabelli C,Saravolatz L,Murad Y,et al. A critical review of the use of carvedilol in ischemic heart disease[J]. Am J Cardiovasc Drugs,2012,12(6):391-401.
[3] Vila-Petroff M,Salas MA,Said M,et al. CaMKⅡ inhibition protects against necrosis and apoptosis in irreversible ischemia-reperfusion injury[J]. Cardiovasc Res,2007,73(4):689-698.
[4] Bergmann MW,Rechner C,F(xiàn)reund C,et al. Statins inhibit reoxygenation induced cardiomyocyte apoptosis:Role for glycogen synthase kinase 3 and transcription factor β catenin[J]. J Molec Cell Cardiol,2004,37(5):681-690.
[5] Martinez BA,Petersen DA,Gaeta AL,et al. Dysregulation of the mitochondrial unfolded protein response induces non-apoptotic dopaminergic neurodegeneration in C.elegans models of Parkinson's disease[J]. J Neurosci,2017,37(46):11085-11100.
[6] Zhu Y,Tchkonia T,F(xiàn)uhrmann-Stroissnigg H,et al. Identification of a novel senolytic agent,navitoclax,targeting the Bcl-2 family of anti-apoptotic factors[J]. Aging Cell,2016,15(3):428-435.
[7] Grancara S,Ohkubo S,Artico M,et al. Milestones and recent discoveries on cell death mediated by mitochondria and their inter actions with biologically active amines[J]. Amino Acids,2016,48(10):2313-2326.
[8] Zheng JH,Viacava FA,Kriwacki RW,et al. Discoveries and controversies in BCL-2 protein-mediated apoptosis[J].Febs Journal,2016,283(14):2690-2700.
[9] Aira LE,Villa E,Colosetti P,et al. The oncogenic tyrosine kinase Lyn impairs the pro-apoptotic function of Bim[J]. Oncogene,2018,37(16):2122-2136.
[10] Shukla S,Saxena S,Singh BK,et al. BH3-only protein BIM:an emerging target in chemotherapy[J]. European Journal of Cell Biology,2017,96(8):728-738.
[11] Petros AM,Swann SL,Song D,et al. Fragment-based discovery of potent inhibitors of the anti-apoptotic Mcl-1 protein[J]. Bioorg Med Chem Lett,2014,24(6):1484-1488.
[12] Navickas R,Gal D,Laucevi?ius A,et al. Identifying circulating microRNAs as biomarkers of cardiovascular disease:A systematic review[J]. Cardiovasc Res,2016, 111(4):322-337.
[13] Ye Y,Perez-polo JR,Qian J,et al. The role of microRNA in modulating myocardial ischemia-reperfusion injury[J]. Physiol Genomics,2011,43(10):534-542.
[14] Gurha P. Noncoding RNAs in cardiovascular diseases[J]. Curr Opin Cardiol,2019,34(3):241-245.
[15] Seeley JJ,Baker RG,Mohamed G,et al. Induction of innate immune memory via microRNA targeting of chromatin remodelling factors[J]. Nature,2018,559(7712):114-119.
[16] Li R,Geng HH,Xiao J,et al. MiR-7a/b attenuates post-myocardial infarction remodeling and protects H9C2 cardiomyoblast against hypoxia-induced apoptosis involving Sp1 and PARP-1[J]. Sci Rep,2016,6(1):1-11.
[17] Mayr B,Muller EE,Schafer C,et al. Exercise responsive micro ribonucleic acids identify patients with coronary artery disease[J]. Eur J Prev Cardiol,2019,26(4):348-355.
[18] Vegter EL,Ovchinnikova ES,van Veldhuisen DJ,et al. Low circulating microRNA levels in heart failure patients are associated with atherosclerotic disease and cardiovascular-related rehospitalizations[J]. Clin Res Cardiol,2017, 106(8):598-609.
[19] Sluijter JP,van Mil A,van Vliet P,et al. MicroRNA-1 and -499 regulate differentiation and proliferation in human-derived cardiomyocyte progenitor cells[J]. Arterioscler Thromb Vasc Biol,2010,30(4):859-868.
[20] Bell ML,Buvoli M,Leinwand LA. Uncoupling of expression of an intronic microRNA and its myosin host gene by exon skipping[J]. Mol Cell Biol,2010,30(8):1937-1945.
[21] Barwari T,Joshi A,Mayr M. MicroRNAs in cardiovascular disease[J]. J Am Coll Cardiol,2016,68(23):2577-2584.
(收稿日期:2020-03-11)