SM22α抑制大鼠基质重构相关分子的表达及其在血管肥厚中的意义

 目的：探讨平滑肌蛋白22α（smooth muscle protein 22 alpha,SM22α）对大鼠血管肥厚及基质重构相关分子表达的影响。方法：采用SM22α及其突变体的腺病毒表达载体感染大鼠颈总动脉;利用血管紧张素II（angiotensin II,Ang II）微渗泵植入大鼠皮下复制高血压模型;用HE及免疫组化方法分别观察大鼠颈总动脉肥厚及基质重构相关分子在血管壁的表达情况。结果：Ang II显著升高大鼠的血压;颈总动脉过表达SM22α及其非磷酸化突变体S181A后,显著抑制Ang II诱导的血管肥厚,同时伴有MMP-2、MMP-9、 ICAM-1和VCAM-1的表达减少。结论：SM22α及其非磷酸化突变体显著抑制血管肥厚,该过程可能与其抑制基质重构相关的MMP及黏附分子的表达有关。     

PLGF参与Ang II诱导的心脏成纤维细胞激活

 目的：探讨胎盘生长因子（PLGF）在血管紧张素II（Ang II）激活心脏成纤维细胞(CFs)中的表达及其作用。方法：原代分离培养并鉴定新生SD大鼠CFs。蛋白免疫印迹检测α-平滑肌肌动蛋白（α-SMA）、PLGF和磷酸化ERK1/2(p-ERK1/2),免疫荧光观察α-SMA的表达,WST-1法检测细胞增殖,RT-PCR检测PLGF、I型和III型胶原蛋白的mRNA表达水平。结果：(1)Ang II组PLGF mRNA 表达明显高于对照组（P<0．01),联用替米沙坦后,PLGF mRNA表达水平下降;Ang  II组PLGF蛋白表达水平高于对照组（P<0.05); (2)PLGF诱导CFs增殖及α-SMA蛋白表达增加（P<0.05）;PLGF干预CFs 60 min后,p-ERK1/2蛋白水平表达明显高于对照组（P<0.01);(3)Ang II+anti-PLGF组与Ang II组比较,细胞增殖和α-SMA蛋白表达水平下降（P<0.05）,I型和III型胶原蛋白mRNA表达水平亦下调（P<0.05）。结论：PLGF可能参与Ang II诱导的CFs增殖和纤维化过程。     

大豆异黄酮对大鼠血管平滑肌细胞增殖和表型转化的影响

目的:观察大豆异黄酮对大鼠血管平滑肌细胞增殖和表型转化的影响。方法:采用酶消化法原代培养大鼠血管平滑肌细胞,传至第3～6代,加入含不同浓度(0、0.1、0.2、0.4、0.8μmol/L)大豆异黄酮的DMEM培养基作用24 h,采用MTT法检测大鼠血管平滑肌细胞增殖率,采用RT-PCR法检测平滑肌22α(SM22α)mRNA、骨桥蛋白mRNA的表达,采用Western blot法检测SM22α、骨桥蛋白的表达。结果:0.1～0.8μmol/L的大豆异黄酮随浓度增加其抑制大鼠血管平滑肌细胞增殖的作用增强(P<0.05);SM22αmRNA及SM22α蛋白表达增加,骨桥蛋白mRNA及骨桥蛋白表达降低,各组间有明显差异(P<0.05)。结论:大豆异黄酮抑制大鼠血管平滑肌细胞增殖,同时使大鼠血管平滑肌细胞从合成表型向收缩表型转化。     

沉默HIF-1α基因表达对大鼠肝癌细胞增殖的影响

 目的： 探讨沉默缺氧诱导因子　1α（HIF-1α）基因表达对缺氧状态下肝癌细胞增殖的影响。方法：选用大鼠CBRH-7919肝癌细胞株作为研究对象,利用氯化钴（CoCl2）建立缺氧模型。制备3组特异性较强的HIF-1α siRNA-脂质体复合物,转染于肝癌细胞。利用real-time RT-PCR、Western blotting等方法分别检测肝癌细胞HIF-1α、血管内皮生长因子(VEGF)、p21和cyclin D1在mRNA和（或）蛋白水平的表达。MTT及BrdU 掺入实验检测细胞增殖的变化。结果：缺氧条件下,肝癌细胞的HIF-1α和VEGF mRNA及蛋白表达显著增多（P<0.05）。HIF-1α基因表达沉默后,HIF-1α、VEGF及cyclin D1 mRNA和（或）蛋白表达明显减少（P<0.05）,p21蛋白表达明显增加（P<0.05）。HIF-1α siRNA转染组的BrdU阳性细胞比例明显少于对照组(P<0.05)。结论：沉默HIF-1α基因表达对缺氧状态下肝癌细胞的增殖有显著抑制作用。     

巨噬细胞移动抑制因子经Rho激酶途径促进人胚肺成纤维细胞表型转化

 目的：观察重组巨噬细胞移动抑制因子（rMIF）对人胚肺成纤维细胞（MRC-5）表型转换的作用,探讨哮喘气道重塑的发生机制。方法：不同浓度的rMIF (25~100 μg/L)分别作用于MRC-5细胞24 h或48 h,RT-PCR法检测α-平滑肌肌动蛋白（α-SMA）  mRNA表达,Western blotting检测α-SMA蛋白合成;100 μg/L rMIF刺激MRC-5细胞48 h,刺激前0.5 h加入Rho拮抗剂Y27632,RT-PCR法检测α-SMA mRNA表达,Western blotting法检测α-SMA表达;100 μg/L rMIF分别刺激MRC-5 6 h、12 h、24 h或48 h,Western blotting检测磷酸化肌球蛋白磷酸酶目标亚单位1（p-MYP1）蛋白合成。结果：刺激MRC-5 24 h,不同浓度的rMIF对α-SMA mRNA转录未见显著影响（P>0.05）。刺激MRC-5细胞48 h,rMIF可呈剂量依赖地促进α-SMA mRNA （r=0.697,P<0.01）和蛋白（r=0.957,P<0.01）表达。Y27632预刺激后,显著抑制rMIF100 μg/L促进α-SMA mRNA和蛋白表达的作用（均P<0.01）。rMIF刺激6 h后,p-MYPT1表达显著增加（P<0.01）,12 h达到高峰（P<0.01）,24 h开始下降,但24 h和48 h其水平仍高于对照组（均P<0.01）。结论：rMIF通过Rho信号通路刺激成纤维细胞表型转化,可能在哮喘气道重塑的发病机制中发挥关键作用。     

TGF-β1介导的RhoA/ROCK通路在大鼠肺肌成纤维细胞分化中的调节作用

 目的：探讨转化生长因子β1 (TGF-β1)介导的RhoA/Rho相关卷曲螺旋形成蛋白激酶(ROCK)通路在调控肺成纤维细胞向肌成纤维细胞分化过程中的作用。方法：胰酶消化法获得原代培养的肺成纤维细胞,进行以下实验：(1) 观察TGF-β1诱导肺成纤维细胞不同时间后p-RhoA、ROCK、磷酸化肌球蛋白磷酸酶靶亚基(p-MBS)、血清应答因子(SRF)、α-平滑肌肌动蛋白(α-SMA)、I型和III型胶原蛋白表达变化;(2) 将细胞分为对照组、TGF-β1诱导分化组和Y-27632（ROCK通路阻滞剂）干预组,免疫细胞化学染色与Western blotting法分别观察与检测ROCK、p-MBS、SRF、α-SMA、I型和III型胶原蛋白在细胞内的定位分布与表达。结果：（1）经TGF-β1诱导24 h后,大鼠肺成纤维细胞胞体内出现大量平行或交叉排列的α-SMA抗体标记的肌丝。随着TGF-β1诱导刺激时间的延长,p-RhoA、ROCK、p-MBS、SRF、α-SMA、I型和III型胶原蛋白表达逐渐增高,其中RhoA/ROCK信号（p-RhoA、ROCK、p-MBS）、SRF和α-SMA蛋白分别在诱导后6 h、12 h和24 h达到高峰。I型胶原和III型胶原蛋白表达均在24 h达高峰,分别为诱导前的2.19和3.04倍（P<0.05）。 (2)与TGF-β1诱导分化组比较,当给予Y-27632干预后,在相应时点ROCK、p-MBS、SRF、α-SMA、I型和III型胶原蛋白表达均明显降低,差异有统计学意义（P<0.05）。结论：TGF-β1通过ROCK信号转导通路的活化,刺激了大鼠肺成纤维细胞向肌成纤维细胞分化,进而促进了胶原蛋白的合成,可能在（矽）肺纤维化形成过程中发挥着重要作用。     

MEF2C调控DOK5基因的表达

目的 研究MEF2C对DOK5的表达调控机制。方法 用RT-PCR法检测小鼠中DOK5组织表达谱,检测P19CL6向心肌细胞分化过程中DOK5和MEF2C的表达。MEF2C与DOK5启动子报告基因共转染P19CL6细胞或将DOK5启动子上的MEF2结合位点突变后,观察报告基因活性的变化。结果DOK5在小鼠的脑、心脏、骨骼肌等高表达。DOK5和MEF2C在P19CL6向心肌细胞分化过程中mRNA表达水平升高 (p<0.05)。过表达MEF2C可以激活DOK5启动子区的报告基因活性,而MEF2结合位点突变则抑制DOK5启动子区报告基因活性。结论 MEF2C可以通过作用于DOK5启动子区的MEF2结合位点,调节DOK5的转录活性。     

核仁素在血管紧张素Ⅱ诱导的血管平滑肌细胞表型转化中的作用

目的:探讨核仁素在血管紧张素Ⅱ(AngⅡ)诱导的血管平滑肌细胞(VSMCs)表型转化中的作用。方法:以AngⅡ诱导大鼠VSMCs表型转化为模型,观察AngⅡ对VSMCs表型转化标志物α-平滑肌肌动蛋白(α-SMA)、钙调理蛋白(calponin)、平滑肌蛋白22α(SM22α)和骨桥蛋白(OPN)mRNA和蛋白表达的影响,并观察VSMCs表型转化时核仁素mRNA和蛋白的时空表达模式;进一步采用核仁素基因转染及RNA干扰技术观察核仁素对上述VSMCs表型转化标志物mRNA和蛋白表达的影响。结果:不同浓度的AngⅡ刺激VSMCs不同时间后,VSMCs收缩表型标志物α-SMA、calponin和SM22α的mRNA和蛋白表达逐渐减少,而合成表型标志物OPN的mRNA和蛋白表达逐渐增加(P0.05);不同浓度AngⅡ刺激VSMCs不同时间后,随着时间和剂量增加,核仁素的mRNA和蛋白表达在一定程度上逐渐升高;AngⅡ可诱导核仁素从细胞核向细胞浆移位;核仁素过表达可促进Ang II诱导的VSMCs表型转化,核仁素表达下调后,其促进表型转化作用被解除。结论:核仁素具有促进Ang II诱导的VSMCs表型转化的作用,核仁素的表达上调和移位参与Ang II诱导的VSMCs表型转化。     

磷酸化修饰的反义TGF-β1寡核苷酸抑制血管损伤后内膜增殖

 目的：探讨反义转化生长因子β1（TGF-β1)寡核苷酸对血管损伤后血管平滑肌细胞（VSMCs）表型转变的影响及对内膜增殖的作用。方法：在跨过TGF-β1 cDNA序列的起始密码区ATG范围内,设计含15个碱基、无修饰或硫代磷酸化修饰的反义TGF-β1寡核苷酸（AS TGF-β1）及对照的正义（与反义寡核苷酸互补）寡核苷酸（S TGF-β1）。球囊导管损伤SD大鼠颈总动脉,术后7 d取出正常或损伤的血管进行VSMCs的培养,RT-PCR及蛋白印迹分别检测VSMCs生物学标志平滑肌22α蛋白（SM22α）、基质Gla蛋白和骨桥蛋白,以及TGF-β1和纤维连结蛋白（fibronectin,FN）mRNA和蛋白质的表达。采用ALZET 泵皮下注射硫代磷酸化修饰AS TGF-β1及S TGF-β1（90 μg·kg-1·d-1）,连续给药28 d后测定血管内膜与中膜的面积比（I/M）。结果：（1）AS TGF-β1对血管损伤后VSMCs TGF-β1 mRNA表达并无明显作用,但呈浓度依赖性抑制TGF-β1蛋白质的表达,而S TGF-β1不影响TGF-β1mRNA和蛋白质的表达。（2）AS TGF-β1呈浓度依赖性抑制血管损伤后VSMCs DNA的合成,而不管是AS TGF-β1还是S TGF-β1对正常VSMCs DNA的合成均无明显的量效作用;同时AS TGF-β1显著抑制了血管损伤后VSMCs FN的合成。（3）AS TGF-β1显著促进了VSMCs SM22α mRNA的表达,但抑制了基质Gla蛋白和骨桥蛋白mRNA的表达,这种相反的作用在001及01 μmol/L的水平最为明显。（4）硫代磷酸化修饰的AS TGF-β1治疗28 d后,显著抑制了颈动脉损伤后新生内膜的增殖,I/M比对照组下降了68%。结论：AS TGF-β1特异性抑制了VSMCs TGF-β1蛋白的表达,抑制血管损伤后VSMCs增殖及合成、分泌FN,减轻血管损伤后新生内膜的增殖。上述作用可能与逆转血管损伤后VSMCs的表型转变有关。     

Rho激酶在血管紧张素Ⅱ刺激大鼠心肌成纤维细胞增殖和胶原合成中的作用

目的： 探讨Rho激酶在血管紧张素Ⅱ（AngⅡ）刺激心肌成纤维细胞（CFBs）增殖和胶原合成中的作用。方法： 采用胰酶消化、差速贴壁法培养新生Sprague-Dawley (SD) 大鼠CFBs，并用AngⅡ诱导CFBs增殖和胶原合成。采用四氮唑盐（MTT）比色法测定细胞增殖,羟脯氨酸法测定CFBs胶原含量, RT-PCR检测Rho激酶mRNA表达，Western blotting检测肌球蛋白结合亚基磷酸化（MBS-P）表达作为Rho激酶功能活化的标志。结果：（1）AngⅡ（10-７ mol/L）刺激48h可诱导CFBs增殖和胶原合成(均P<0.01)；（2) AngⅡ（10-7 mol/L）可显著上调新生SD大鼠CFBs的Rho激酶mRNA表达并诱导Rho激酶快速活化；（3）在一定浓度范围内，Rho激酶特异性抑制剂hydroxyfasudil (H4413)对AngⅡ（10-7 mol/L）刺激的CFBs增殖与胶原合成具有明显的抑制作用(P<0.05或P<0.01)。结论： AngⅡ可诱导新生SD大鼠CFBs的Rho激酶mRNA转录并活化Rho激酶，抑制Rho激酶活化对AngⅡ刺激的CFBs增殖与胶原合成具有明显的抑制作用，提示Rho激酶在调控AngⅡ刺激大鼠CFBs增殖与胶原合成中可能具有重要作用。     

降钙素基因相关肽对血管平滑肌细胞心肌素表达及细胞表型改变的作用

目的:研究降钙素基因相关肽(CGRP)对血管平滑肌细胞(VSMCs)心肌素表达的影响及对细胞表型改变的调节作用。方法:取大鼠胸主动脉,以组织块贴壁培养法获得VSMCs,分为对照组、血管紧张素Ⅱ(AngⅡ)组(加入AngⅡ处理)、CGRP组(加入AngⅡ和CGRP处理)和CGRP8-37组(在AngⅡ和CGRP基础上加入CGRP8-37)。Western blot法检测VSMCs中心肌素及细胞表型标志蛋白α-平滑肌肌动蛋白(α-SMA)和骨桥蛋白(OPN)表达情况。结果:在VSMCs培养中,细胞心肌素表达水平随着培养时间延长逐渐降低,细胞培养48 h和72h时心肌素表达水平较基线水平显著降低(P0.05);而加入CGRP处理后,心肌素表达水平逐渐增加,与基线水平比较,加入CGRP培养后48 h和72 h时细胞心肌素水平显著增加(P0.05)。同时,在VSMCs培养48 h时,AngⅡ组细胞心肌素水平较对照组下降(P0.05),且α-SMA表达亦相应下降(P0.05),而OPN表达水平显著增加(P0.05);CGRP组VSMCs心肌素水平较AngⅡ组增加,伴随着α-SMA表达水平增加(P0.05),相反地OPN表达水平下降(P0.05);CGRP8-37组心肌素和α-SMA表达水平较CGRP+AngⅡ组降低(P0.05),而OPN表达较CGRP组增加(P0.05)。结论:CGRP通过促进VSMCs心肌素的表达而抑制细胞表型转换,使细胞维持收缩表型,且这一作用是CGRP通过与其受体结合后实现的。     

27nt-miRNA对血管平滑肌细胞SM22α表达的调节及其对细胞活力、迁移和表型改变的影响

目的:探讨27nt-微小RNA(27nt-miRNA)对血管平滑肌细胞(VSMCs)中平滑肌22α蛋白(SM22α表达的调节及其对细胞活力、迁移和表型改变的影响。方法:构建27nt-miRNA高表达、反义序列(anti-27nt-miRNA)以及阴性对照的表达质粒,经慢病毒包装后分别转染大鼠原代VSMCs,加入血小板源性生长因子BB(PDGF-BB)诱导VSMCs表型转换。MTT实验检测细胞活力,划痕实验检测细胞迁移能力,RT-PCR、Western blot和免疫细胞化学染色法检测细胞中SM22α的mRNA和蛋白表达情况。结果:与正常组相比,PDGF-BB组的细胞活力上升(P 0.05)、迁移能力上升(P 0.05),SM22α的mRNA及蛋白表达量下降(P 0.05);与阴性对照慢病毒组相比,27nt-miRNA高表达组的细胞活力下降(P 0.05),迁移能力下降(P 0.05),SM22α的mRNA及蛋白表达量明显升高(P 0.05);而anti-27nt-miRNA组细胞的细胞活力上升(P 0.05),迁移能力上升(P 0.05),SM22α的mRNA及蛋白表达量下降(P 0.05)。结论:27nt-miRNA促进SM22α表达,同时抑制VSMCs的活力及迁移,并有可能抑制VSMCs从收缩型转变为合成型。     

Regulation on RhoA in Vascular Smooth Muscle Cells Under Inflammatory Stimulation Proposes a Novel Mechanism Mediating the Multiple-Beneficial Action of Acetylsalicylic Acid

Recent studies have revealed the additional beneficial effects of acetylsalicylic acid (aspirin) in the medication of cardiovascular diseases. The small GTPase RhoA as an important signaling factor is implicated in a wide range of cell functions. This study aimed to investigate the regulatory effect of acetylsalicylic acid on RhoA in vascular smooth muscle cells (VSMCs). We found that aspirin at 300 μM suppressed VSMCs proliferation stimulated by LPS, and this inhibitory effect was partially mediated by inhibiting the iNOS/NO pathway. RhoA overexpression was downregulated by aspirin (both 30 and 300 μM) because of enhanced degradation of RhoA protein. The effect of LPS on increasing active RhoA level was significantly attenuated by aspirin (300 μM), which exerted no effect on RhoA translocation. The promoted RhoA phosphorylation under LPS stimulation, coupled with RhoA protein expression, was greatly decreased by aspirin treatment. No effect of aspirin was found on the expression, activation, and phosphorylation of RhoA in VSMCs devoid of inflammatory stimulation. Our investigation indicates that the regulation of RhoA by aspirin in VSMCs under inflammatory stimulus could be a novel mechanism via which aspirin, apart from the COX-dependent action, exerted the multiple beneficial effects.     

卡维地洛与压力负荷心衰大鼠心室重塑和Rho激酶表达的关系

目的研究卡维地洛(α1肾上腺素受体阻断剂、β肾上腺素受体非选择性阻断剂)对升主动脉缩窄压力超负荷心力衰竭大鼠心室重塑、RhoA、Rho激酶表达的影响,探讨卡维地洛改善心力衰竭的新机制。方法将升主动脉缩窄术后心力衰竭Wistar雌性大鼠随机分为2组,一组为心力衰竭组,给予生理盐水灌胃,每日2次(n=10);一组为卡维地洛组,12.5mg/Kg卡维地洛灌胃,每日2次(n=10),治疗12周。同时制备模型设置假手术组作为对照(n=10),不予处置。观察各组大鼠各项指标变化。结果与假手术组相比,心力衰竭大鼠心肌肥厚指数增加,HE染色心肌排列紊乱,血液动力学指标明显异常,心肌细胞RhoA、Rho激酶表达显著升高(P<0.05);药物治疗12w后,与心力衰竭组对比,卡维地洛治疗组心肌肥厚指数降低,HE染色示心肌重塑不明显,血液动力学参数改善,RhoA、Rho激酶表达显著降低。结论卡维地洛可通过对心肌细胞α-Gq-RhoA/Rho激酶通路表达干预,明显缓解心力衰竭症状、改善心室重塑,卡维地洛这种α1肾上腺素受体阻断剂可能对心力衰竭更有利。     

PDGF-BB对血管平滑肌细胞表型标志物表达的影响

目的:观察血小板源性生长因子BB(PDGF-BB)对血管平滑肌细胞(VSMCs)增殖及分化相关基因表达的影响,探讨其可能的机制。方法:分离体外培养的SD大鼠胸腹主动脉VSMCs,分为空白对照组和不同浓度PDGF-BB处理组。分别采用MTT法、流式细胞术和伤口愈合实验检测PDGF-BB对VSMCs增殖、细胞周期和迁移活性的影响;用W estern b lotting分析检测VSMCs表型标志物的表达;用免疫沉淀和免疫共沉淀分析检测Krüppel样因子4(KLF4)磷酸化及与其它转录因子的相互作用。结果:PDGF-BB促进VSMCs增殖和迁移;上调增殖相关蛋白PCNA的表达,下调增殖抑制蛋白p27、分化相关蛋白SM22α的表达。PDGF-BB诱导KLF4的表达和磷酸化,促进KLF4与NF-κB的相互作用,抑制KLF4与Sm ad3、HDAC2的结合。结论:PDGF-BB可能通过影响KLF4磷酸化及其与不同转录调节因子的相互作用而诱导VSMCs表型转化。     

IQGAP1 promotes the phenotypic switch of vascular smooth muscle by myocardin pathway: a potential target for varicose vein

Recently, the architectural remodeling of venous vessel wall ranks as the basis of varicose veins development based on the phenotypic state of vascular smooth muscle cells (VSMCs). In this study, we firstly demonstrated an obvious up-regulation of IQ-domain GTPase-activating protein 1 (IQGAP1) in patients with varicose veins. Importantly, following stimulation with PDGF-BB for 4 h, a common inducer of phenotypic switch in VSMCs, a dramatically time-dependent increase in IQGAP1 expression was observed in human venous smooth muscle cells (HUVSMCs), concomitant with the down-regulation of SMC markers [including α-smooth muscle actin (SMA), smooth muscle calponin (CNN), SM22α (SM22)], suggesting a critical function of IQGAP1 during the switch of synthetic VSMC phenotype. Further analysis ascertained that IQGAP1 overexpression significantly inhibited the expression of SMA, SM and CNN, while its silencing dramatically promoted their expression levels. Moreover, the elevated IQGAP1 enhanced cell proliferation, migration and rearrangement. Mechanism assay confirmed that IQGAP1 overexpression notably blocked myocardin levels. Importantly, after transfection with myocardin siRNA, IQGAP1 down-regulation-induced decrease in cell proliferation, migration and cell rearrangement was remarkably attenuated. Together, these results demonstrated that IQGAP1 may regulate the phenotypic switch of VSMCs by myocardin pathway, which is critical for the pathological progression of varicose vein. Therefore, this study supports a prominent insight into how IQGAP1 possesses its benefit function in varicose veins development by regulating vascular remodeling.     

RhoA-Mediated Signaling in Mechanotransduction of Osteoblasts

Osteoblasts play a pivotal role in load-driven bone formation by activating Wnt signaling through a signal from osteocytes as a mechanosensor. Osteoblasts are also sensitive to mechanical stimulation, but the role of RhoA, a small GTPase involved in the regulation of cytoskeleton adhesion complexes, in mechanotransduction of osteoblasts is not completely understood. Using MC3T3-E1 osteoblast-like cells under 1 hr flow treatment at 10 dyn/cm², we examined a hypothesis that RhoA signaling mediates the cellular responses to flow-induced shear stress. To test the hypothesis, we conducted genome-wide pathway analysis and evaluated the role of RhoA in molecular signaling. Activity of RhoA was determined with a RhoA biosensor, which determined the activation state of RhoA based on a fluorescence resonance energy transfer between CFP and YFP fluorophores. A pathway analysis indicated that flow treatment activated phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) signaling as well as a circadian regulatory pathway. Western blot analysis revealed that in response to flow treatment phosphorylation of Akt in PI3K signaling and phosphorylation of p38 and ERK1/2 in MAPK signaling were induced. FRET measurement showed that RhoA was activated by flow treatment, and an inhibitor to a Rho kinase significantly reduced flow-induced phosphorylation of p38, ERK1/2, and Akt as well as flow-driven elevation of the mRNA levels of osteopontin and cyclooxygenase-2. Collectively, the result demonstrates that in response to 1 hr flow treatment to MC3T3-E1 cells at 10 dyn/cm², RhoA plays a critical role in activating PI3K and MAPK signaling as well as modulating the circadian regulatory pathway.     

RhoA-Mediated Signaling in Mechanotransduction of Osteoblasts

Osteoblasts play a pivotal role in load-driven bone formation by activating Wnt signaling through a signal from osteocytes as a mechanosensor. Osteoblasts are also sensitive to mechanical stimulation, but the role of RhoA, a small GTPase involved in the regulation of cytoskeleton adhesion complexes, in mechanotransduction of osteoblasts is not completely understood. Using MC3T3-E1 osteoblast-like cells under 1 hr flow treatment at 10 dyn/cm(2), we examined a hypothesis that RhoA signaling mediates the cellular responses to flow-induced shear stress. To test the hypothesis, we conducted genome-wide pathway analysis and evaluated the role of RhoA in molecular signaling. Activity of RhoA was determined with a RhoA biosensor, which determined the activation state of RhoA based on a fluorescence resonance energy transfer between CFP and YFP fluorophores. A pathway analysis indicated that flow treatment activated phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) signaling as well as a circadian regulatory pathway. Western blot analysis revealed that in response to flow treatment phosphorylation of Akt in PI3K signaling and phosphorylation of p38 and ERK1/2 in MAPK signaling were induced. FRET measurement showed that RhoA was activated by flow treatment, and an inhibitor to a Rho kinase significantly reduced flow-induced phosphorylation of p38, ERK1/2, and Akt as well as flow-driven elevation of the mRNA levels of osteopontin and cyclooxygenase-2. Collectively, the result demonstrates that in response to 1 hr flow treatment to MC3T3-E1 cells at 10 dyn/cm(2), RhoA plays a critical role in activating PI3K and MAPK signaling as well as modulating the circadian regulatory pathway.