畜牧兽医学报  2021, Vol. 52 Issue (5): 1247-1257. DOI: 10.11843/j.issn.0366-6964.2021.05.011    PDF    
miR-186-5p调控猪原代前体脂肪细胞增殖和分化的研究
蔡春波, 刘敏, 杨阳, 张万锋, 高鹏飞, 曹果清, 李步高, 郭晓红     
山西农业大学动物科学学院, 太谷 030801
摘要:旨在探究miR-186-5p对猪原代前体脂肪细胞增殖和成脂分化的调控作用及机制。本研究采集7日龄健康马身猪公猪的颈部皮下脂肪,分离培养马身猪原代前体脂肪细胞;猪原代前体脂肪细胞分为4组,分别转染miR-186-5p模拟物(mimics)及其对照组(mimics NC),miR-186-5p抑制剂(inhibitor)及其对照组(inhibitor NC),用CCK8和划痕试验分析猪原代前体脂肪细胞的增殖效果,油红O染色检测其成脂分化能力,qPCR检测其增殖和成脂分化相关基因的表达水平;预测miR-186-5p的靶基因,用双荧光素酶报告试验检测miR-186-5p与靶基因的相互作用。结果,当猪原代前体脂肪细胞中转染mimics时,miR-186-5p的表达量极显著升高(P < 0.01),细胞增殖能力和增殖相关基因:增殖细胞核抗原(proliferating cell nuclear antigen,PCNA)、周期蛋白依赖性激酶4(cyclin-dependent kinases 4,CDK4)的表达量以及预测靶基因去乙酰化酶2(sirtuins 2,SIRT2)的表达量都极显著降低(P < 0.01),而细胞成脂分化能力和成脂分化相关基因:过氧化物酶体增殖剂激活受体γ(peroxisome proliferators-activated receptor γ,PPARγ)、固醇调节元件结合转录因子1(sterol regulatory element binding transcription factor 1,SREBF1)、CCAAT增强子结合蛋白β(CCAAT enhancer binding protein β,C/EBPβ)、脂肪酸结合蛋白4(fatty acid-binding protein 4,FABP4)、脂蛋白脂肪酶(lipoprotein lipase,LPL)的表达量都极显著升高(P < 0.01);当猪原代前体脂肪细胞转染inhibitor时,miR-186-5p的表达量极显著降低(P < 0.01),细胞增殖能力以及增殖相关基因PCNACDK4的表达量、预测靶基因SIRT2的表达量都显著或极显著升高(P < 0.05、P < 0.01),而细胞成脂分化能力以及成脂分化相关基因PPARγSREBF1、C/EBPβFABP4、LPL的表达量都极显著降低(P < 0.01)。转染miR-186-5p mimics可以显著抑制SIRT2 3'UTR野生型双荧光素酶报告载体(SIRT2-Wt-psiCHECK-2)中荧光素酶的活性,但不影响SIRT2 3'UTR突变型双荧光素酶报告载体(SIRT2-Mut-psiCHECK-2)中荧光素酶的活性。miR-186-5p可以靶向结合SIRT2的3'UTR序列,降低SIRT2的表达,抑制马身猪原代前体脂肪细胞增殖,促进其成脂分化。
关键词miR-186-5p    马身猪    原代前体脂肪细胞    增殖    成脂分化    靶基因    
Regulation of miR-186-5p on Proliferation and Differentiation of Porcine Primary Preadipocytes
CAI Chunbo, LIU Min, YANG Yang, ZHANG Wanfeng, GAO Pengfei, CAO Guoqing, LI Bugao, GUO Xiaohong     
College of Animal Science, Shanxi Agricultural University, Taigu 030801, China
Abstract: The study aimed to explore the regulation and mechanism of miR-186-5p on the proliferation and adipogenic differentiation of porcine primary preadipocytes. The neck subcutaneous fat of 7-day-old healthy Mashen boar was collected and the primary preadipocytes were isolated and cultured. The primary preadipocytes were divided into 4 groups, which were transfected with miR-186-5p mimics (mimics) and its control group (mimics NC), miR-186-5p inhibitor (inhibitor) and its control group (inhibitor NC). CCK8 and scratch test were used to analyze the proliferation effect of porcine primary preadipocytes. Oil red O staining was used to detect the adipogenic differentiation ability. qPCR was used to detect the expression of proliferation and adipogenic differentiation related genes. The target genes of miR-186-5p were predicted, and the interaction between miR-186-5p and target genes was detected by dual luciferase reporter assay. When mimics were transfected into porcine primary preadipocytes, the expression of miR-186-5p significantly increased(P < 0.01); meanwhile the cell proliferation ability and expression of proliferation related genes, proliferating cell nuclear antigen (PCNA), cyclin-dependent kinases 4 (CDK4), and the target gene sirtuins 2 (SIRT2) significantly decreased(P < 0.01); however, the adipogenic differentiation ability and expression of adipogenic differentiation related genes, peroxisome proliferators-activated receptor γ (PPARγ), sterol regulatory element binding transcription factor 1 (SREBF1), CCAAT enhancer binding protein β (C/EBPβ), fatty acid-binding protein 4 (FABP4) and lipoprotein lipase (LPL) significantly increased(P < 0.01). When the primary preadipocytes were transfected with inhibitor, the expression of miR-186-5p significantly decreased(P < 0.01); meanwhile the cell proliferation ability and expression of PCNA, CDK4 and SIRT2 significantly increased(P < 0.05 or P < 0.01); while the adipogenic differentiation ability and expression of PPARγ, SREBF1, C/EBPβ, FABP4 and LPL significantly decreased(P < 0.01). Transfection of miR-186-5p mimics significantly inhibited the activity of luciferase in SIRT2-Wt-psiCHECK-2, but did not affect the activity of luciferase in SIRT2-Mut-psiCHECK-2. The results show that miR-186-5p can target the 3'UTR of SIRT2 and decrease the expression of SIRT2, which can inhibit the proliferation of Mashen pig primary preadipocytes and promote their adipogenic differentiation.
Key words: miR-186-5p    Mashen pigs    primary preadipocytes    proliferation    adipogenic differentiation    target gene    

肌内脂肪含量是评价猪肉品质的一个重要指标,而猪的背脂厚度与肌内脂肪含量呈明显的正相关,两者都与脂肪酸的合成相关[1]。此外,脂肪组织还能分泌多种蛋白类激素,例如瘦素和脂联素,通过组织液渗透和血液循环等方式运输到其他组织中,调控机体的新陈代谢[2]。脂肪组织的生成过程主要包括脂肪细胞数量的增多和甘油三酯的积累而导致的脂肪细胞的体积增大。筛选调控脂肪细胞增殖和成脂分化的关键因子对提高肌内脂肪含量和改良猪肉品质具有重要的意义。

microRNA(miRNA)是一类长约22 nt,具有调控基因表达功能的单链内源性非编码RNA。miRNA基因常以单拷贝、多拷贝或基因簇的形式存在于生物基因组中,广泛存在真核和原核生物体内。miRNA可以通过与互补的mRNA序列特异性地结合,从而降解mRNA或者抑制mRNA的翻译,进而参与机体相关生物学过程的调节。miRNA可通过调控靶基因的表达从而调控细胞的增殖、迁移[3-7]和分化[8-13]。miRNA对哺乳动物卵泡发育、卵母细胞成熟[14]和奶牛乳腺发育、乳脂合成[15]都具有重要的调控作用。miRNA对脂肪组织形成过程也具有重要的调控作用。研究表明,miR-331-3p能够抑制前体脂肪细胞的增殖,而且可以通过靶向二氢硫辛酰胺琥珀酰转移酶(dihydrolipoamide succinyltransferase,DLST)促进莱芜猪原代前体脂肪细胞成脂分化[16];miR-125b-5p能够抑制3T3-L1细胞的增殖,促进其成脂分化[17];miR-204-5p可以通过调节B淋巴细胞瘤-2(B-cell lymphoma-2,BCL-2)的表达,抑制前体脂肪细胞的增殖并诱导其凋亡,同时也可以通过靶向和抑制Kruppel样转录因子3(Kruppel-like factor 3,KLF3)的表达,促进前体脂肪细胞的分化[18]

miR-186-5p最先在小鼠中被发现,其种子序列在各物种间高度保守,它的主要功能是抑制癌细胞的增殖,如骨肉瘤[19]、大肠癌[20]、胆管癌[21]、神经母细胞瘤[22]、肺腺癌[23]。另外,miR-186-5p能够抑制骨桥蛋白(osteopontin,OPN)的表达,进而抑制骨髓间充质干细胞成骨分化[24];miR-186-5p能够抑制myogenin基因的表达,从而抑制C2C12细胞的成肌分化[25-26];在3T3-L1细胞中,miR-186-5p可抑制细胞增殖,而且还可以直接靶向结合无翅型MMTV整合位点家族成员5A(wingless type MMTV integration site family member 5A,WNT5A)和促分裂原活化蛋白激酶1(mitogen-activated protein kinase 1,Mapk1),促进细胞成脂分化[27]。目前,关于miR-186-5p对猪前体脂肪细胞的调控作用还未见报道。本研究以马身猪原代前体脂肪细胞为细胞模型,探究miR-186-5p对猪前体脂肪细胞增殖、迁移和成脂分化的调控作用和机制,进一步完善miRNA调控猪脂肪细胞分化的分子网络,为改良猪肉品质提供新的分子靶标。

1 材料与方法 1.1 试验材料

DMEM培养基(Hyclone,美国),胎牛血清FBS(Gibco,美国),油红O、地塞米松(DEX)、3-异丁基-1-甲基黄嘌呤(IBMX)和罗格列酮(RSG)(中国,索莱宝),TRIZOL® Reagent(Life Technologies,美国),PrimeScript®RT Master Mix(TaKaRa,日本),miRNA 1 st Strand cDNA Synthesis Kit (by stem-loop)、AceQ® Universal SYBR qPCR Master Mix和miRNA Universal SYBR qPCR Master Mix(诺唯赞,中国),miR-186-5p mimics、inhibitor、mimics NC和inhibitor NC委托上海吉玛公司合成,CCK8试剂盒(博士德生物,中国),psiCHECK-2载体和Dual-Luciferase® Reporter Assay System(Promega,美国)。

1.2 主要仪器

核酸蛋白测定仪(ND-1000,美国)、实时荧光定量PCR仪(7500 Real Time,美国)、全功能微孔板检测仪(SynerGyH1,美国)、细胞成像系统(EVOS FL Auto,美国)等。

1.3 试验方法

1.3.1 猪原代前体脂肪细胞的分离培养   采集7日龄健康马身猪公猪的颈部皮下脂肪组织,PBS清洗3次,剪碎后转移至Ⅰ型胶原酶溶液(1 g·L-1) 中,37 ℃振荡消化60 min,加入完全培养基(DMEM+10% FBS+1%双抗)终止消化;混合液经过400目细胞筛过滤,滤液离心后弃上清液,然后加入红细胞裂解液重悬细胞,室温下静置5 min,再次离心弃上清液,最后加入完全培养基重悬细胞,置入培养箱中培养;24 h后加入PBS缓冲液清洗细胞,然后加入完全培养基继续培养,每2 d换新鲜的完全培养基。

1.3.2 猪原代前体脂肪细胞转染   猪原代前体脂肪细胞的汇合度达到60%时,进行转染试验。首先将miR-186-5p的mimics (mimics NC、inhibitor和inhibitor NC的转染方法与mimics一致)稀释成终浓度为100 nmol·μL-1的工作液;20 μL mimics工作液中加入500 μL的DMEM培养基,混匀后静置5 min;10 μL的LipofectamineTM2000转染试剂中加入500 μL的DMEM培养基,混匀后静置5 min;将上述两种溶液混合后,室温静置20 min,加入3 mL的DMEM培养基,混匀后加入到铺有猪原代前体脂肪细胞的6孔板中,然后放置在培养箱中孵育,6 h后更换为完全培养基继续培养。

1.3.3 CCK8试验   将转染后的猪原代前体脂肪细胞接种至96孔细胞板中培养,分别培养0、24、48和72 h后加入10 μL的CCK8试剂,轻轻摇晃混匀,37 ℃静置孵育1 h,酶标仪检测450 nm波长下的OD值。

1.3.4 划痕试验   将转染后的猪原代前体脂肪细胞接种至96孔细胞板中,当细胞的汇合度达到100%后,在培养孔中轻轻划出痕迹,再将细胞置于培养箱中培养,0、24、36和72 h后观察划痕处细胞的生长状态。

1.3.5 RNA提取及cDNA合成   按RNA提取试剂盒的步骤提取猪原代前体脂肪细胞的总RNA。cDNA的合成分为两步:第一步,总RNA中加入DNA去除剂,再加入双蒸水至10 μL,42 ℃条件下反应2 min;第二步,混合液中加入反转录酶,通用引物和缓冲液,终体积为20 μL,37 ℃反应15 min,85 ℃反应5 s,保存于-20 ℃冰箱。

1.3.6 miRNA的反转录   按照miRNA 1 st Strand cDNA Synthesis Kit (by stem-loop)试剂盒的步骤对miRNA进行反转录。RNA溶液中加入DNA去除剂,加双蒸水至10 μL,42 ℃反应2 min;向混合液中加入反转录酶、缓冲液、miRNA和U6的反转录引物,终体积为20 μL,25 ℃反应5 min,55 ℃反应15 min,85 ℃反应5 min,产物保存于-20 ℃冰箱。

1.3.7 猪原代前体脂肪细胞成脂分化和油红O染色   当猪原代前体脂肪细胞的汇合度达到90%时,更换为成脂诱导分化培养基(完全培养基+ 5 μmol·L-1 INS + 1 μmol·L-1 DEX +0.5 mmol·L-1 IBMX + 1 μmol·L-1 RSG),每2 d换液;诱导分化4 d后,更换维持成脂分化培养基(完全培养基+ 5 μmol·L-1 INS),每2 d换液;维持成脂分化4 d后,进行油红O染色。细胞首先经过4%多聚甲醛固定45 min,PBS清洗3次,油红O工作液(饱和油红O∶蒸馏水=3∶2)染色30 min,蒸馏水冲洗干净,在显微镜下观察并拍照。然后加入异丙醇萃取细胞中的甘油三酯(triglyceride,TG),酶标仪测量波长为510 nm处的OD值。

1.3.8 SYBR荧光定量qPCR   qPCR的反应体系为10 μL:包括2×SYBR Mixture 5 μL,上游引物和下游引物各0.3 μL,模板cDNA 1 μL,RNase-free H2O 3.4 μL。qPCR反应程序:95 ℃预变性30 s;95 ℃变性10 s,60 ℃退火及延伸30 s,40个循环。引物序列见表 1,18SU6为内参基因。

表 1 引物序列 Table 1 Primer sequences

1.3.9 双荧光素酶报告试验   首先构建2种双荧光素酶报告载体:SIRT2 3′UTR野生型载体(SIRT2-Wt-psiCHECK-2)和SIRT2 3′UTR突变型载体(SIRT2-Mut-psiCHECK-2)。然后分为4组进行293T细胞共转染试验:SIRT2-Wt-psiCHECK-2 + mimics、SIRT2-Wt-psiCHECK-2 + mimics NC、SIRT2-Wt-psiCHECK-2 + inhibitor、SIRT2-Mut-psiCHECK-2+mimics。4组共转染293T细胞的方法一样,以SIRT2-Wt-psiCHECK-2 + mimics为例,简述转染方法。293T细胞的汇合度达到70%时进行转染试验;50 μL DMEM中加入2 μL mimics(100 nmol·μL-1)和1 μL SIRT2-Wt-psiCHECK-2(500 ng·μL-1)重组质粒,混匀后静置5 min;另取50 μL DMEM中加入1.5 μL LipofectamineTM2000溶液,混匀后静置5 min;将上述两种溶液混合,混匀后静置20 min;293T细胞的培养基更换为DMEM,然后加入上述混合溶液,混匀后置于培养箱中孵育6 h,然后更换为完全培养基继续培养;每组设3个重复,24 h后检测荧光素酶的活性。首先吸出293T细胞中培养基,PBS洗涤3次,加入100 μL细胞裂解缓冲液,吹打细胞至完全裂解,收集样品;然后将荧光素酶底物与缓冲液混合制成荧光素酶试剂,stop&Glo缓冲液与stop&Glo底物混合制成stop&Glo试剂;最后96孔板中加入20 μL样品和100 μL荧光素酶试剂,混匀后测量荧光值,再加入100 μL stop&Glo试剂,混匀后再次测量荧光值。

1.3.10 数据分析   试验均设置3个重复,试验数据均以“Mean ± SD”表示。数据使用GraphPad Prism7软件进行作图分析,两组比较采用独立样本t检验,多组间比较采用单因素方差分析(One-way ANOVA),并进行Duncan’s多重比较,以P < 0.05作为差异显著性的界值,P < 0.01作为差异极显著性的界值。

2 结果 2.1 miR-186-5p抑制猪原代前体脂肪细胞的增殖

猪原代前体脂肪细胞分为4组,分别转染miR-186-5p的mimics、mimics NC、inhibitor和inhibitor NC,通过CCK8试验检测各组细胞的增殖效果,qPCR检测细胞增殖相关基因的表达。与转染mimics NC组相比,转染miR-186-5p mimics组细胞中miR-186-5p的表达量极显著升高(P < 0.01,图 1A),24、48和72 h的细胞数量都极显著降低(P < 0.01,图 1B),细胞增殖相关基因PCNACDK4的表达量也极显著降低(P < 0.01,图 1C)。与inhibitor NC组相比,转染miR-186-5p inhibitor组细胞中miR-186-5p的表达量极显著降低(P < 0.01,图 1D),24、48和72 h的细胞数量都显著增加(P < 0.05,图 1B),细胞增殖相关基因PCNACDK4的表达量也极显著升高(P < 0.01,图 1C)。结果说明,miR-186-5p可以抑制猪原代前体脂肪细胞增殖。

A. mimics转染效率;B. 转染mimics后CCK8结果;C. 转染mimics后PCNACDK4基因的表达量;D. inhibitor转染效率;E. 转染inhibitor后CCK8结果;F. 转染inhibitor后PCNACDK4基因的表达量。*. P < 0.05,**. P < 0.01,下同 A. Mimics transfection efficiency; B. CCK8 results after mimics transfection; C. The expression of PCNA and CDK4 genes after mimics transfection; D. Inhibitor transfection efficiency; E. CCK8 results after inhibitor transfection; F. The expression of PCNA and CDK4 genes after inhibitor transfection; *. P < 0.05, **. P < 0.01, the same as below 图 1 miR-186-5p对猪原代前体脂肪细胞增殖的影响 Fig. 1 Effects of miR-186-5p on proliferation of porcine primary preadipocytes

对转染后的4组猪原代前体脂肪细胞进行划痕试验,通过观察划痕中长满细胞所需要的时间,检测每组细胞的增殖效果。转染miR-186-5p mimics组细胞培养72 h后,划痕处仍然具有明显的空隙(图 2A);而转染mimics NC组细胞培养36 h后,细胞基本铺满整个划痕(图 2B)。转染miR-186-5p inhibitor组细胞培养36 h后,细胞基本铺满整个划痕(图 2C);而转染inhibitor NC组细胞培养72 h后,划痕处仍然具有明显的空隙(图 2D)。结果说明,miR-186-5p可以抑制猪原代前体脂肪细胞的增殖。

A. 转染mimics;B. 转染mimics NC;C. 转染inhibitor;D. 转染inhibitor NC A. Transfected mimics; B. Transfected mimics NC; C. Transfected inhibitor; D. Transfected inhibitor NC 图 2 划痕试验的结果(50×) Fig. 2 The results of scratch test (50×)
2.2 miR-186-5p促进猪原代前体脂肪细胞成脂分化

对转染后的4组猪原代前体脂肪细胞进行成脂诱导分化,然后通过油红O染色和qPCR试验检测各组细胞的成脂分化状态。与转染mimics NC组相比,转染miR-186-5p mimics组细胞中miR-186-5p的表达量极显著升高(P < 0.01,图 3A),成脂分化相关基因PPARγSREBF1、C/EBPβFABP4和LPL的表达量都极显著升高(P < 0.01,图 3B),脂滴数量明显增加(图 3C),甘油三酯含量也极显著增加(P < 0.01,图 4D)。结果说明,miR-186-5p mimics可以促进猪原代前体脂肪细胞成脂分化。

A. mimics转染效率;B. 成脂相关基因的表达量;C. 油红O染色结果(50 ×);D. 异丙醇萃取结果 A. Mimics transfection efficiency; B. The expression of genes related to adipogenesis; C. Oil red O staining results (50 ×); D. Isopropanol extraction results 图 3 miR-186-5p mimics促进猪原代前体脂肪细胞成脂分化 Fig. 3 miR-186-5p mimics promote adipogenic differentiation of porcine primary preadipocytes
A. inhibitor转染效率;B. 成脂相关基因的表达量;C. 油红O染色结果(50 ×);D. 异丙醇萃取结果 A. Inhibitor transfection efficiency; B. The expression of genes related to adipogenesis; C. Oil red O staining results (50 ×); D. Isopropanol extraction results 图 4 miR-186-5p inhibitor抑制猪原代前体脂肪细胞成脂分化 Fig. 4 miR-186-5p inhibitor inhibit adipogenic differentiation of porcine primary preadipocytes

与转染inhibitor NC组细胞相比较,转染miR-186-5p inhibitor组细胞的miR-186-5p的表达量极显著降低(P < 0.01,图 4A),成脂分化相关基因PPARγSREBF1、C/EBPβFABP4和LPL的表达量都极显著降低(P < 0.01,图 4B),脂滴数量明显减少(图 4C),甘油三酯含量也显著降低(P < 0.05,图 4D)。结果说明,miR-186-5p inhibitor可以抑制猪原代前体脂肪细胞成脂分化。

2.3 miR-186-5p靶基因的检测

通过软件预测发现,miR-186-5p可以与SIRT2基因的3′UTR序列反向互补结合(图 5A),且miR-186-5p和SIRT2基因在猪原代前体脂肪细胞诱导成脂分化过程中表达趋势相反(图 5B5C)。猪原代前体脂肪细胞中过表达miR-186-5p后,SIRT2的表达量极显著降低(P < 0.01, 图 5D);抑制miR-186-5p后,SIRT2的表达量极显著的升高(P < 0.01,图 5E)。为进一步验证SIRT2与miR-186-5p的靶向关系,进行了双荧光素酶报告试验。检测结果显示(图 5F),与共转染mimics NC + SIRT2-Wt-psiCHECK-2野生型载体组和共转染inhibitor + SIRT2-Wt-psiCHECK-2野生型载体组细胞相比,共转染mimics + SIRT2-Wt-psiCHECK-2野生型载体组的293T细胞中荧光素酶的活性极显著降低(P < 0.01),说明miR-186-5p可以靶向结合SIRT2 3′UTR序列,抑制SIRT2基因的表达;而且与共转染mimics NC + SIRT2-Wt-psiCHECK-2野生型载体组细胞相比,共转染mimics + SIRT2-Mut-psiCHECK-2野生型载体组的293T细胞中荧光素酶的活性没有明显变化,说明SIRT2 3′UTR序列的突变消除了miR-186-5p对SIRT2基因表达的抑制作用,进一步说明miR-186-5p可以靶向结合SIRT2 3′UTR序列,抑制SIRT2基因的表达。

A. SIRT2 3′UTR的结合位点及突变位点;B、C. 猪原代前体脂肪细胞成脂分化过程中miR-186-5p与SIRT2的表达量;D、E. 过表达和抑制miR-186-5p时SIRT2的表达量;F. 双荧光素酶报告试验结果。标注不同大写字母表示差异极显著(P < 0.01),标注不同小写字母表示差异显著(P < 0.05) A. The binding site and mutation site of SIRT2 3′UTR; B, C. The expression of miR-186-5p and SIRT2 during adipogenic differentiation of porcine primary preadipocytes; D, E. The expression of SIRT2 after miR-186-5p overexpression and inhibition; F. The result of dual-luciferase reporter assay. Different capital letters indicate very significant difference (P < 0.01) and different lowercase letters indicate significant difference (P < 0.05) 图 5 miR-186-5p靶基因的检测 Fig. 5 Detection of miR-186-5p target gene
3 讨论

miRNA的长度约22 nt,属于单链内源性非编码RNA。miRNA序列较短,很容易通过化学合成的方式获得。构建特异性的miRNA载体和化学合成miRNA序列,然后转染到细胞中,都可以特异性增强或抑制内源性miRNA的表达。由于miRNA的序列较短,化学合成miRNA的成本较低,而且短序列的转染效率更高,操作也更加简单,减少了构建载体的步骤,因此,通过转染化学合成的miRNA,增强或抑制内源miRNA的表达,成为miRNA功能研究的主要方法。目前,化学合成的miRNA主要分为4种,分别是mimics、inhibitor、agomir和antagomir。mimics是化学合成的成熟双链miRNA,是miRNA的模拟物,能够增强内源miRNA的调控作用。agomir是经过特殊标记和化学修饰的双链小RNA,属于miRNA激动剂,通过模拟内源性miRNA来调节靶基因的生物学功能,作用效果持续时间长。inhibitor是化学修饰的成熟miRNA互补单链,属于miRNA抑制物,通过特异地靶向miRNA分子削弱内源miRNA的调控作用。antagomir是经过特殊标记和化学修饰的miRNA拮抗剂,特异性削弱内源miRNA的调控作用,具有更高的稳定性,作用效果持续时间长。agomir和antagomir都经过特殊化学修饰,虽然其作用效果更强,持续时间更久,但是其价格也较为昂贵,主要用于活体动物试验。本研究探讨miR-186-5p对猪原代脂肪前体细胞的调控作用,并没有在活体水平上研究其功能,所以采用miR-186-5p mimics和inhibitor。

miR-186-5p的主要功能是抑制癌细胞的增殖、迁移和侵袭。Zhu等[22]研究发现,miR-186-5p可以通过靶向抑制神经母细胞瘤中驱动蛋白5(kinesin-5,EG5)的表达,抑制肿瘤细胞的增殖。Feng等[23]发现,miR-186-5p可以通过靶向抑制磷脂酶和张力蛋白同源物(phosphatase and tensin homolog,PTEN)的表达促进肺腺癌细胞的增殖、迁移和侵袭。Cao等[28]发现,miR-186-5p可以抑制转导蛋白β样1X连锁受体1(transducin β like 1X-linked receptor 1,TBL1XR1)的表达,抑制骨肉瘤细胞的迁移和侵袭。这些研究说明,在不同的癌细胞中,miR-186-5p对癌细胞的调控作用并不一致。miR-186-5p也可以抑制绵羊黑色素细胞的增殖和迁移,减少黑色素的沉积[29]。猪属于脂肪沉积型动物,脂肪含量非常高。猪脂肪组织形成过程中,细胞增殖发挥着重要的作用,决定着成熟脂肪细胞的数量;而miR-186-5p对癌细胞的增殖和迁移过程具有重要的调控作用;因此,猜测miR-186-5p可能会通过调节猪前体脂肪细胞的增殖过程来调控成熟脂肪细胞的数量,进而最终影响猪的脂肪沉积。目前,关于miR-186-5p对猪脂肪沉积调控作用的研究还未见报道。因此,本研究以马身猪原代前体脂肪细胞为细胞模型,探讨miR-186-5p对猪前体脂肪细胞增殖和成脂分化的调控作用。本研究发现,miR-186-5p可以抑制马身猪原代前体脂肪细胞的增殖,促进其成脂分化。

miRNAs的主要作用方式是通过调控靶基因的表达,实现其对机体的调控。本研究通过软件预测SIRT2为miR-186-5p的靶基因。SIRT2是与酵母的沉默信息调节因子2(silent information regulator 2, SIR2)同源的去乙酰化酶,属于sirtuin蛋白家族成员,在脂肪细胞中大量表达[30]。SIRT2主要定位于细胞质,但在有丝分裂过程中可以从细胞质中转移到细胞核[31]。SIRT2能参与调节多种生物过程,包括细胞周期、卵泡发育、卵母细胞成熟、DNA修复、自噬等过程[32-34]。Jing等[35]发现,3T3-L1细胞中敲除SIRT2基因,叉头框转录因子O1 (forkhead box O1,FoxO1)的乙酰化和磷酸化水平都显著升高,导致细胞核中的FoxO1转移到细胞质中,减弱了FoxO1对PPARγ的抑制作用,从而促进细胞成脂分化。Wang和Tong[36]也发现,SIRT2可以通过抑制FoxO1的乙酰化,增强FoxO1对PPARγ的抑制作用,从而抑制3T3-L1细胞的成脂分化。刘炳婷等[37]发现,在猪原代前体脂肪细胞中过表达SIRT2可以抑制其成脂分化。本研究也发现, miR-186-5p可以靶向结合SIRT2的3′UTR序列,抑制SIRT2的表达,促进马身猪原代前体脂肪细胞的成脂分化。因此,miR-186-5p可以通过靶向抑制SIRT2的表达,增强FoxO1的乙酰化水平,促进PPARγ的表达,促进马身猪原代前体脂肪细胞成脂分化。

4 结论

本研究结果显示,miR-186-5p可以靶向结合SIRT2的3′UTR序列,降低SIRT2的表达,抑制马身猪原代前体脂肪细胞的增殖,促进其成脂分化。

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