摘要
探究血清淀粉样蛋白A(SAA)对小胶质细胞迁移的影响及机制。采用Transwell小室法检测SAA诱导原代小胶质细胞和鼠源N9小胶质细胞的迁移能力。用Transwell检测甲酰肽受体2(FPR2)拮抗剂和TLR2中和抗体对SAA诱导N9小胶质细胞迁移的影响。实时荧光定量PCR检测SAA作用N9小胶质细胞后,FPR2和Toll样受体2(TLR2)的表达变化。Western blot检测SAA对N9小胶质细胞下游信号通路激酶表达的影响。用Transwell检测信号通路抑制剂对SAA诱导的N9小胶质细胞迁移的影响。结果显示:SAA以浓度依赖性方式促进原代小胶质细胞和N9小胶质细胞迁移。FPR2拮抗剂和TLR2中和抗体抑制了SAA诱导的N9小胶质细胞迁移。SAA促进了N9小胶质细胞内FPR2和TLR2受体的mRNA转录水平增加。SAA刺激N9小胶质细胞丝裂原活化蛋白激酶(MAPKs)和核因子κB(NF-κB)信号通路的激活,表现为细胞外调节蛋白激酶(ERK)、p38和c-Jun氨基末端激酶(JNK)磷酸化水平增加,IĸBα表达水平降低。p38、JNK和NF-κB信号通路抑制剂抑制了SAA诱导的N9小胶质细胞迁移。组间差异有统计学意义(P<0.05)。研究结果表明,SAA通过作用FPR2和TLR2受体,激活下游p38、JNK和NF-κB信号通路,进而诱导小胶质细胞迁移。
阿尔茨海默病(Alzheimer's disease,AD)是一种典型的中枢神经系统退行性疾病。脑内细胞外聚集的老年斑(以β amyloid,即Aβ为主要成分)和细胞内聚集的神经纤维缠结(主要由过度磷酸化的Tau蛋白构成)是AD的两大病理特
鼠源小胶质细胞系N9(上海生物科学研究院);Dulbecco's modified Eagle's medium(DMEM)培养基、Iscove's modified Dulbecco's medium(IMDM)培养基、胰酶、胎牛血清(美国Gibco公司);脂多糖(lipopolysaccharide,LPS)(来源Escherichia coli 0111:B4)、WRW4肽、TLR2中和抗体、多聚赖氨酸、ERK抑制剂PD98059、p38抑制剂SB203580、JNK抑制剂SP600125、NF-κB抑制剂SN50(美国Sigma公司);重组人apo-SAA蛋白(美国PeproTech公司);TRIzol试剂(美国Invitrogen公司);反转录试剂盒、实时荧光PCR试剂(日本东洋纺公司); Transwell小室、Falco
原代小胶质细胞分离及培养方法参考文献报
取孔径8 μm的小室,在下室加入各组溶液600 μL。收集原代小胶质细胞和对数生长期的N9小胶质细胞,用纯培养基稀释为每毫升5×1
用1 μmol/L SAA刺激N9小胶质细胞1,3,6,9和12 h。Trizol法提取总RNA,反转录为cDNA和qRT-PCR反应具体操作均按照说明书进行。PCR条件设定为预变性94 ℃ 3 min,94 ℃ 30 s,56 ℃退火45 s,72 ℃延伸30 s,共40个循环,接着再72 ℃ 10 min。基因表达的结果计算采用
用1 μmol/L SAA刺激N9小胶质细胞1,5,15,30,60 min后,收集各组细胞,然后采用RIPA裂解细胞。用10%浓度凝胶进行蛋白质电泳,电泳结束后使用NC膜进行转膜,5%脱脂奶粉在室温条件进行1 h封闭,分别加入一抗溶液(p-ERK1/2、ERK、p-p38、p38、p-JNK、JNK、IkBα和GAPDH),稀释比例均为1∶1 000,4 ℃孵育过夜。第2天采用TBST漂洗,加入对应二抗溶液(IRDy
采用Transwell检测SAA对原代小胶质细胞和N9小胶质细胞迁移能力影响。结果显示,SAA以浓度依赖性方式促进原代小胶质细胞和N9小胶质细胞的迁移,1 μmol/L SAA的作用效果最强,组间差异具有统计学意义。因为重组蛋白SAA含有微量LPS(小于1.2 ng/mL),因此为排除SAA内LPS的干扰,本研究设计了高于此剂量的LPS(2.5 ng/mL)作为对照组。结果显示此剂量的LPS对小胶质细胞的迁移并没有影响(

Figure 1 Serum amyloid A (SAA) induces migration of primary microglia and N9 microglia ()
A:Primary cultures of microglia and N9 microglia was treated with SAA (0.1-1 μmol/L)or LPS (2.5 ng/mL),and the migration was detected by Transwell assay; B:Quantitative analysis of SAA-induced migration of primary microglia; C:Quantitative analysis of SAA-induced migration of N9 microglia
因为FPR2和TLR2是SAA的两个主要受体,为验证SAA诱导小胶质细胞的迁移是否通过这两个受体,本研究加入FPR2受体拮抗剂WRW4和TLR2中和抗体检测SAA对N9小胶质细胞迁移能力影响。结果发现1,5,10 μmol/L的WRW4均能抑制SAA诱导的N9小胶质细胞迁移(

Figure 2 FPR2 antagonist and TLR2 neutralizing antibody inhibit SAA-induced migration of N9 microglia ()
A,B:Effect of FPR2 antagonist (WRW4) on SAA-induced migration of N9 microglia was detected by Transwell assay.(a) Control; (b)1 μmol/L SAA; (c) 1 μmol/L WRW4 + 1 μmol/L SAA; (d) 5 μmol/L WRW4 + 1 μmol/L SAA; (e) 10 μmol/L WRW4 + 1 μmol/L SAA; (f) 10 μmol/L WRW4; (g) 2.5 ng/mL LPS; (h)10 μmol/L WRW4 + 2.5 ng/mL LPS.C,D:Effect of TLR2 neutralizing antibody on SAA-induced migration of N9 microglia was detected by Transwell assay.(a) Control; (b) 1 μmol/L SAA; (c) 0.1 μg/mL Anti-mTLR2-IgG + 1 μmol/L SAA; (d) 0.5 μg/mL Anti-mTLR2-IgG + 1 μmol/L SAA; (e) 1 μg/mL Anti-mTLR2-IgG + 1 μmol/L SAA; (f) 1 μg/mL IgG + 1 μmol/L SAA; (g) 1 μg/mL Anti-mTLR2-IgG; (h) 2.5 ng/mL LPS; (i) 1 μg/mL Anti-mTLR2-IgG + 2.5 ng/mL LPS.
此外,本研究进一步检测SAA是否对这两种受体的表达有影响。使用实时荧光定量PCR方法检测SAA对N9小胶质细胞FPR2和TLR2受体mRNA表达的影响。结果发现SAA能够显著诱导N9小胶质细胞FPR2和TLR2 mRNA转录水平的增加,特别是FPR2受体。SAA诱导FPR2受体转录水平呈渐进式的升高,在9 h达到顶点,增加了约70倍(

Figure 3 SAA increases the mRNA levels of FPR2 (A) and TLR2 (B) in N9 microglia ()
***P<0.001 vs SAA (0 h) group;
因为FPR2和TLR2受体激活能够诱导下游丝裂原激活的蛋白激酶(MAPKs)和核因子κB(NF-κB)信号通路变化,因此采用Western blot检测SAA对N9小胶质细胞MAPKs和NF-κB信号通路的影响。结果发现SAA能够显著增加细胞外信号调节激酶(ERK)、p38和c-Jun氨基末端激酶(JNK)磷酸化水平,降低IĸBα表达水平,并且在15 min作用最明显(

Figure 4 SAA activates MAPKs and NF-κB signaling pathways in N9 microglia ()
A:Effect of SAA on the phosphorylation levels of MAPKs and NF-κB signaling pathway kinases in N9 microglia was examined by Western blot; B:Quantitative analysis of SAA-induced changes in the phosphorylation of ERK;C:Quantitative analysis of SAA-induced changes in the phosphorylation of p38;D:Quantitative analysis of SAA-induced changes in the phosphorylation of JNK;E:Quantitative analysis of SAA-induced changes in the expression of IĸBα
为验证SAA诱导小胶质细胞的迁移是否通过MAPKs和NF-κB信号通路,采用MAPKs和NF-κB信号通路抑制剂检测SAA对N9小胶质细胞迁移能力影响。结果发现ERK抑制剂PD98059不能有效抑制SAA诱导的N9小胶质细胞迁移。而p38抑制剂SB203580、JNK抑制剂SP600125及NF-κB抑制剂SN50均可以显著抑制SAA诱导的N9小胶质细胞迁移(

Figure 5 Inhibitor of p38,JNK,or NF-κB inhibits SAA-induced migration of N9 microglia ()
A,B:Effect of inhibitors of MAPKs (ERK,p38,and JNK)and NF-κB on SAA-induced migration of N9 microglia was detected by Transwell assay. (a) Control group; (b) 1 μmol/L SAA; (c) 20 μmol/L PD98059 + 1 μmol/L SAA; (d) 20 μmol/L SB203580 + 1 μmol/L SAA; (e) 20 μmol/L SP600125 + 1 μmol/L SAA; (f) 10 μmol/L SN50 + 1 μmol/L SAA; (g) 20 μmol/L PD98059; (h) 20 μmol/L SB203580; (i) 20 μmol/L SP600125; (j) 10 μmol/L SN50
外周血液循环中的血清淀粉样蛋白A主要是由急性期反应中的肝细胞合成的,而在肝外产生的SAA被认为与包括AD在内的慢性炎症疾病更为相
有研究报道AD患者脑脊液中SAA的浓度显著高于正常对照
研究表明SAA可以与多种受体结合,产生相应的生物学功能。对于中性粒细胞,SAA可以结合其细胞表面的FPR2和TLR2受体,进而激活细胞内的MAPKs、PI3K和NF-κB等信号通
此外,本研究还检测了SAA对N9小胶质细胞内MAPKs和NF-κB信号通路的影响。已有研究报道细胞迁移与MAPKs和NF-κB通路的激活密切相关。表皮生长因子(epidermal growth factor,EGF)和产促红细胞生成素肝细胞受体结合蛋白(erythropoietin-producing hepatocellular receptor interacting protein B1,ePhin B1)诱导的细胞迁移与JNK信号通路活化密切相
综上所述,本研究首次发现SAA能够促进小胶质细胞的迁移,其机制是通过作用于其细胞表面的FPR2和TLR2受体,激活下游的MAPKs和NF-κB信号通路。SAA还通过增加这两种受体的表达,进一步促进小胶质细胞迁移。本课题组之前的研究发现,SAA刺激小胶质细胞释放的白介素10(interleukin-10,IL-10)能够降低原代培养神经元由于LPS引起的Tau蛋白过度磷酸
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