Cyclooxygenase-2 gene disruption promotes proliferation of murine calvarial osteoblasts in vitro

Cyclooxygenase-2 (COX-2) is highly expressed in osteoblasts, and COX-2 produced prostaglandins (PGs) can increase osteoblastic differentiation in vitro. The goal of this study was to examine effects of COX-2 expression on calvarial osteoblastic proliferation and apoptosis. Primary osteoblasts (POBs) were cultured from calvariae of COX-2 wild-type (WT) and knockout (KO) mice. POB proliferation was evaluated by (3)H-thymidine incorporation and analysis of cell replication and cell cycle distribution by flow cytometry. POB apoptosis was evaluated by annexin and PI staining on flow cytometry. As expected, PGE(2) production and alkaline phosphatase (ALP) activity were increased in WT cultures compared to KO cultures. In contrast, cell numbers were decreased in WT compared to KO cells by day 4 of culture. Proliferation, measured on days 3-7 of culture, was 2-fold greater in KO than in WT POBs and associated with decreased Go/G1 and increased S cell cycle distribution. There was no significant effect of COX-2 genotype on apoptosis under basal culture conditions on day 5 of culture. Cell growth was decreased in KO POBs by the addition of PGE(2) or a protein kinase A agonist and increased in WT POBs by the addition of NS398, a selective COX-2 inhibitor. In contrast, differentiation and cell growth in marrow stromal cell (MSC) cultures, evaluated by ALP and crystal violet staining respectively, were increased in MSCs from WT mice compared to MSCs from KO mice, and exogenous PGE(2) increased cell growth in KO MSC cultures. We conclude that PGs secondary to COX-2 expression decrease osteoblastic proliferation in cultured calvarial cells but increase growth of osteoblastic precursors in MSC cultures.     

Fibroblast growth factor-2 is an immediate-early gene induced by mechanical stress in osteogenic cells.

Fifteen minutes of physiological MS induces FGF-2 in osteogenic cells. Here, we show that MS induced proliferation in both MC3T3-E1 and BMOp cells isolated from Fgf2(+/+) mice; Fgf2(-/-) BMOp cells required exogenous FGF-2 for a normal proliferation response. The induction of fgf-2 is mediated by PKA and ERK pathways. INTRODUCTION: Mechanical stress (MS) induces gene expression and proliferation of osteogenic MC3T3-E1 cells. We have previously shown that physiological levels of MS in MC3T3-E1 cells causes extracellular signal-regulated kinase (ERK)1/2 phosphorylation. Here we evaluate the induction and importance of fibroblast growth factor-2 (FGF-2) for MS-induced proliferation. MATERIALS AND METHODS: We characterized the MS induction of fgf-2 using a 15-minute pulse of 120 mustrain and studied the stability of fgf-2 message using actinomycin D. Bone marrow stromal cells (BMOp) isolated from Fgf2(-/-) and Fgf2(+/+) mice were used to study the importance of FGF-2 in MS-induced proliferation. RESULTS: We found that the induction of fgf-2 by MS is dependent on both protein kinase A (PKA) and ERK pathways. MS transiently induces fgf-2 within 30 minutes. FGF-2 receptor (FGFR2) was also significantly increased within 1 h. All three isoforms of FGF-2 (24, 22, and 18 kDa) were significantly increased by MS. The MS-mediated increase of fgf-2 mRNA was caused by new synthesis and not stabilization. Pretreatment of MC3T3-E1 cells with cycloheximide showed that the induction of fgf-2 did not require new protein synthesis. Pretreating MC3T3-E1 cells with the mitogen-activated protein kinase (MAPK)/ERK kinase 1/2 (MEK1/2) inhibitor, U0126, or H-89, a PKA inhibitor, significantly inhibited the induction of fgf-2, showing that mechanical induction of fgf-2 is dependent on ERK and PKA signaling pathways. The downstream consequence of a single 15-minute stress pulse was a 3.5-fold increase in cell number in MC3T3-E1 compared with growth in nonstressed control cells. In studies using bone marrow osteoprogenitor cells (BMOp) isolated from Fgf2(+/+)and Fgf2(-/-) mice, we found that FGF-2 was necessary for a full proliferative response to MS. CONCLUSIONS: These studies show that FGF-2 is an immediate-early gene induced by MS, and its expression is mediated by both the PKA and MAPK signal transduction pathways. FGF-2 was required for a full proliferative response.     

流体剪切力抑制肿瘤坏死因子α诱导鼠成骨样细胞MC3T3-E1凋亡的实验研究

目的研究流体剪切力(fluid shear stress,FSS)对肿瘤坏死因子α(TNF-α)诱导鼠成骨样细胞MC3T3-E1凋亡的影响。方法将MC3T3-E1分为TNF-α干预组(实验组)和无TNF-α干预组(对照组),TNF-α(10ng/ml)×4h诱导MC3T3-E1凋亡后,四个实验组分别加载12dyn/cm2FSS作用0,15,30,60min。应用四甲基偶氮唑蓝(MTT)法、荧光显微镜和流式细胞技术(FΑCS)检测细胞的增殖能力和凋亡,免疫印迹法检测半胱氨酸蛋白激酶9(caspase9)和凋亡蛋白酶活化因子1(Αpaf-1)蛋白的表达。采用SPSS16.0软件包对数据进行单因素方差分析。结果TNF-α(10ng/ml)×4h能诱导明显的凋亡信号,FSS(12dyn/cm2)能明显抑制这种凋亡,而且随着刺激时间的增加,从0min逐渐延长至60min,细胞活性逐渐增加,凋亡细胞数逐渐减少,实验组与对照组单因素方差分析及各组间LSD两两比较有显著性差异(P0.05),同时caspase9和Αpaf-1蛋白的表达也逐渐增加。结论生理范围的FSS能够抑制TNF-α诱导的MC3T3-E1细胞的凋亡,作为线粒体通路的关键蛋白,caspase9和Αpaf-1在凋亡时增加而FSS后表达减少,说明FSS抑制这种凋亡至少部分是减弱了凋亡的线粒体通路。     

ERK5信号通路介导流体剪切力对MC3T3-E1成骨细胞MMPs、TIMPs表达的影响

目的观察流体剪切力(fluid shear stress,FSS)作用下,MC3T3-E1成骨细胞中细胞基质金属蛋白酶(matrix metalloproteinases,MMPs)和基质金属蛋白酶抑制剂(tissue inhibitors of metalloproteinases,TIMPs)的表达情况,并探讨ERK5信号通路在其中的作用。方法对MC3T3-E1成骨细胞进行不同的处理,分为正常组、XMD8-92组、FSS组和FSS+XMD8-92组,对FSS组施加12 dyn/cm~2流体剪切力,采用蛋白免疫印迹法分别检测P-ERK5、ERK5、MMPs和TIMPs蛋白水平的变化。结果生理强度(12 dyn/cm~2)的流体剪切力作用于MC3T3-E1成骨细胞45 min后能显著上调MMPs的表达,下调TIMPs的表达,但此效应可被ERK5高选择性抑制剂XMD8-92阻断。结论 ERK5信号通路调控流体剪切力对成骨细胞MMPs、TIMPs蛋白的表达。     

Osteotropic agents induce the differential secretion of granulocyte-macrophage colony-stimulating factor by the osteoblast cell line MC3T3-E1

Osteoblasts play a central role in the regulation of bone remodeling. Not only are they responsible for the formation of new bone, but they also regulate bone resorption. These cells also exert regulatory influences outside the bone in that they are able to regulate hematopoiesis. However, obtaining pure populations of osteoblasts devoid of contaminating cell types remains problematic. One approach to this problem is the use of cloned osteoblastic cell lines. To this end we have used MC3T3-E1, a cloned murine osteoblast cell line of C57BL/6 origin. We report that MC3T3-E1 cells respond to lipopolysaccharide (LPS) and, to a lesser extent, parathyroid hormone (PTH) by the secretion of granulocyte-macrophage colony-stimulating factor (GM-CSF). However, 1,25-(OH)2D3, a potent activator of osteoblasts, fails to induce these cells to secrete GM-CSF. These results suggest that MC3T3-E1 cells respond to osteotropic agents in a hierarchical fashion. Secretion of GM-CSF is not constitutive but rather requires active induction of the cells. MC3T3 cells fail to secrete detectable levels of interleukin-2 (IL-2), IL-3, or IL-4, regardless of whether or not the cells are activated. The data indicate that MC3T3-E1 cells secrete cytokines in response to osteotropic agents in a way similar to that of normal primary osteoblasts. Therefore, MC3T3-E1 cells may serve as a good in vitro model for primary osteoblasts.     

续苓健骨汤含药血清对MC3T3-E1细胞分化及增殖的影响

目的探讨续苓健骨汤含药血清对MC3T3-E1成骨细胞分化及增殖的影响。方法制备续苓健骨汤含药血清,实验分为空白对照组、含药血清低剂量组、中剂量组和高剂量组。采用CCK-8法和流式细胞术检测续苓健骨汤含药血清对MC3T3-E1细胞增殖和细胞周期的影响;碱性磷酸酶(ALP)活性测定MC3T3-E1细胞的成骨分化能力;茜素红染色检测MC3T3-E1细胞的矿化能力;实时荧光定量PCR检测成骨分化基因Runx2、OC、Bmp2、Col1a1mRNA水平。结果与空白对照组比较,中、高剂量续苓健骨汤含药血清能促进MC3T3-E1细胞增殖、S期细胞比率和细胞增殖指数,并且呈现一定的剂量依赖性;同时中高剂量续苓健骨汤含药血清组能明显提高MC3T3-E1细胞ALP活性(P0.01)和钙化能力(P0.01),促进Runx2、OC、Bmp2、Col1a1 mRNA的表达(P0.05)。结论续苓健骨汤含药血清能促进成骨细胞MC3T3-E1的增殖,并通过上调骨形成相关基因Runx2、OC、BMP2、Col1a1的表达水平,提高MC3T3-E1细胞的成骨能力。     

震荡流体剪切力通过ERK5信号通路促进成骨细胞增殖

目的探讨震荡流体剪切力(oscillatory shear stress,OSS)通过ERK5信号通路在诱导成骨细胞增殖中发挥的作用。方法对成骨MC3T3-E1细胞进行不同的处理,分为正常组、OSS组、XMD8-92组和OSS+XMD8-92组。采用MTT实验分别测定4组细胞的增殖活性并绘制生长曲线;蛋白免疫印迹法分别检测P-ERK5、ERK5和Cyclin D1等蛋白水平变化。结果 OSS可显著增加成骨MC3T3-E1细胞增殖活性,但此效应可被ERK5高选择性抑制剂XMD8-92阻断。OSS可显著上调Cyclin D1的表达,而XMD8-92可显著下调OSS诱导的Cyclin D1的表达。结论 OSS通过激活ERK5信号通路促进成骨细胞增殖,Cyclin D1是ERK5信号通路下游的重要靶点基因。     

Insulin-like growth factor-I and insulin-like growth factor-II induce c-fos in mouse osteoblastic cells

Summary We investigated the expression of c-fos in mouse osteoblast-like cultures treated with insulin-like growth factor (IGF)-I and IGF-II. The IGFs are present in bone, are produced by osteoblast-like cells in culture, and stimulate osteoblast cell proliferation. Quiescent, subconfluent cultures of the clonal osteoblast-like mouse calvarial cell line, MC3T3-E1, were treated with 10 ng/ml of IGF-I or IGF-II. RNA was extracted at 0, 15, 30, 60, 120 and 240 minutes, and c-fos messenger RNA (mRNA) was analyzed on Northern blots. Both IGFs transiently increased c-fos mRNA levels 25–28 fold at 15–30 min. To determine if c-fos induction was unique to the MC3T3-E1 cell line, effects of IGF-1 and IGF-II (3 ng/ml) were also tested in quiescent, serum-free primary mouse calvarial cells. Levels of c-fos mRNA were increased at 15 and 30 minutes (40-fold with IGF-I and 5-fold with IGF-II). These results indicate that IGF-I and IGF-II caused a rapid and transient induction of c-fos mRNA in murine osteoblasts.     

The Thyroid Hormone Receptor (TR) β-Selective Agonist GC-1 Inhibits Proliferation But Induces Differentiation and TR β mRNA Expression in Mouse and Rat Osteoblast-Like Cells

Previous studies showed anabolic effects of GC-1, a triiodothyronine (T3) analogue that is selective for both binding and activation functions of thyroid hormone receptor (TR) β1 over TRα1, on bone tissue in vivo. The aim of this study was to investigate the responsiveness of rat (ROS17/2.8) and mouse (MC3T3-E1) osteoblast-like cells to GC-1. As expected, T3 inhibited cellular proliferation and stimulated mRNA expression of osteocalcin or alkaline phosphatase in both cell lineages. Whereas equimolar doses of T3 and GC-1 equally affected these parameters in ROS17/2.8 cells, the effects of GC-1 were more modest compared to those of T3 in MC3T3-E1 cells. Interestingly, we showed that there is higher expression of TRα1 than TRβ1 mRNA in rat (~20–90%) and mouse (~90–98%) cell lineages and that this difference is even higher in mouse cells, which highlights the importance of TRα1 to bone physiology and may partially explain the modest effects of GC-1 in comparison with T3 in MC3T3-E1 cells. Nevertheless, we showed that TRβ1 mRNA expression increases (~2.8- to 4.3-fold) as osteoblastic cells undergo maturation, suggesting a key role of TRβ1 in mediating T3 effects in the bone forming cells, especially in mature osteoblasts. It is noteworthy that T3 and GC-1 induced TRβ1 mRNA expression to a similar extent in both cell lineages (~2- to 4-fold), indicating that both ligands may modulate the responsiveness of osteoblasts to T3. Taken together, these data show that TRβ selective T3 analogues have the potential to directly induce the differentiation and activity of osteoblasts.     

健骨胶囊对成骨样细胞MC3T3-E1增殖及分化作用机制

目的 探讨国医大师刘柏龄“健骨胶囊”对MC3T3-E1成骨细胞分化及增殖的影响。方法 制备健骨胶囊水提物,采用CCK-8法和细胞迁移实验检测健骨胶囊提取物对MC3T3-E1细胞增殖和细胞迁移的影响;茜素红染色检测MC3T3-E1细胞的矿化能力;实时荧光定量PCR检测成骨分化基因Runx2、OCN、OPN、Col1a1、ALP、Bcl2、RASSF1A等mRNA表达水平;蛋白质印迹法Western blot检测Col1a1、Bcl2的蛋白表达水平。结果 通过实验结果比对得出,健骨胶囊提取物能促进MC3T3-E1细胞增殖、使细胞迁移率提高;同时健骨胶囊提取物组能明显提高MC3T3-E1细胞钙化能力(P＜0.01),促进Runx2、OCN、OPN、Col1a1、ALP、Bcl2的mRNA表达(P＜0.05),上调Col1a1、Bcl2蛋白量的表达。结论 健骨胶囊能促进成骨细胞MC3T3-E1的增殖及细胞迁移能力,并通过上调成骨基因的表达水平如Runx2、OCN、OPN、Col1a1、ALP、Bcl2等,提高MC3T3-E1细胞的成骨能力。     

Activation of extracellular-signal regulated kinase (ERK1/2) by fluid shear is Ca(2+)- and ATP-dependent in MC3T3-E1 osteoblasts

To determine the role of Ca2+ signaling in activation of the Mitogen-Activated Protein Kinase (MAPK) pathway, we subjected MC3T3-E1 pre-osteoblastic cells to inhibitors of Ca2+ signaling during application of fluid shear stress (FSS). FSS only activated ERK1/2, rapidly inducing phosphorylation within 5 min of the onset of shear. Phosphorylation of ERK1/2 (pERK1/2) was significantly reduced when Ca2+i was chelated with BAPTA or when Ca2+ was removed from the flow media. Inhibition of both the L-type voltage-sensitive Ca2+ channel and the mechanosensitive cation-selective channel blocked FSS-induced pERK1/2. Inhibition of phospholipase C with U73122 significantly reduced pERK1/2. This inhibition did not result from blockage of intracellular Ca2+ release, but a loss of PKC activation. Recent data suggests a role of ATP release and purinergic receptor activation in mechanotransduction. Apyrase-mediated hydrolysis of extracellular ATP completely blocked FSS-induced phosphorylation of ERK1/2, while the addition of exogenous ATP to static cells mimicked the effects of FSS on pERK1/2. Two P2 receptors, P2Y2 and P2X7, have been associated with the anabolic responses of bone to mechanical loading. Using both iRNA techniques and primary osteoblasts isolated from P2X7 knockout mice, we found that the P2X7, but not the P2Y2, purinergic receptor was involved in ERK1/2 activation under FSS. These data suggest that FSS-induced ERK1/2 phosphorylation requires Ca2+-dependent ATP release, however both increased Ca2+i and PKC activation are needed for complete activation. Further, this ATP-dependent ERK1/2 phosphorylation is mediated through P2X7, but not P2Y2, purinergic receptors.     

Ghrelin stimulates proliferation and differentiation and inhibits apoptosis in osteoblastic MC3T3-E1 cells

Ghrelin is a 28-amino-acid peptide identified in the stomach as an endogenous ligand of the growth hormone secretagogue receptor (GHS-R) that strongly stimulates the release of growth hormone at the hypothalamus and pituitary level. Although GHS-Rs are expressed in a variety of peripheral tissues, little is known about its effect on bone independent of GH/IGF-1 axis. This study was undertaken to investigate whether ghrelin exerts a direct effect on osteoblasts. We identified mRNA and protein expression of GHS-R in primary osteoblasts as well as a number of osteoblastic cell lines, including MC3T3-E1, ROS 17/2.8, UMR-106, MG63, and SaOS2 cells. Treatment of ghrelin (10(-11) to 10(-7) M) to MC3T3-E1 cells showed dose-dependent stimulation of proliferation, which was abrogated by treatment with [d-Lys]-GHRP-6 (10(-3) M), a selective antagonist of the ghrelin receptor. Ghrelin activated ERK1/2 MAPK and pretreatment with MAPK kinase inhibitors, PD98059 attenuated the ghrelin-induced cell proliferation. Ghrelin also inhibited TNFalpha-induced apoptosis and suppressed caspase-3 activation that occurs in response to TNFalpha as well as during in vitro differentiation process. Moreover, ghrelin treatment enhanced in vitro osteoblast differentiation as evidenced by matrix mineralization, alkaline phosphatase activity, and osteoblast-specific gene expression. These results suggest that ghrelin promotes proliferation and differentiation and inhibits apoptosis of osteoblasts.     

THSD4基因在小鼠间充质干细胞及MC3T3-E1细胞成骨分化中的作用

目的 探讨THSD4基因对小鼠间充质干细胞和MC3T3-E1细胞成骨分化的影响。方法 提取绝经后骨质疏松症患者的骨髓间充质干细胞进行基因测序分析,与骨关节炎患者的骨髓间充质干细胞进行比较,分析基因表达差异。通过提取不同分化阶段的小鼠骨髓间充质干细胞（M-BMSC）及MC3T3-E1细胞的mRNA来检测THSD4 基因以及成骨分化的标志性基因（ALP、Runx2、Osx）的表达水平。通过构建慢病毒表达载体来实现对M-BMSC及MC3T3-E1细胞中THSD4的敲减及过表达,并观察其对M-BMSC及MC3T3-E1细胞成骨分化能力的影响。结果 THSD4基因在绝经后骨质疏松症患者骨髓间充质干细胞中明显下调,且通过KEGG以及GO富集分析发现THSD4基因可能与PI3K-AKT信号通路及Wnt信号通路相关。随着成骨诱导分化时间的延长,THSD4 mRNA和成骨分化标志性基因（ALP、Runx2、Osx）mRNA在MC3T3-E1以及M-BMSC中表达量均逐渐增加。过表达THSD4可以增强MC3T3-E1细胞和M-BMSC的成骨分化能力,而敲减THSD4则减弱了MC3T3-E1细胞和M-BMSC的成骨分化能力。结论 THSD4基因在绝经后骨质疏松症患者骨髓间充质干细胞中明显下调,且THSD4基因可以增强MC3T3-E1细胞以及M-BMSC的成骨分化能力。     

二甲双胍调控PI3K/Akt/mTOR通路减轻糖皮质激素诱导的成骨细胞凋亡

目的探讨二甲双胍(Met)调控磷脂酰肌醇3激酶(PI3K)/蛋白激酶B(Akt)/哺乳动物雷帕霉素靶蛋白(m TOR)信号通路对糖皮质激素地塞米松(Dex)诱导的成骨细胞凋亡的影响。方法将体外培养的小鼠胚胎成骨细胞前体细胞MC3T3-E1分为对照组(正常培养)、Dex组(以Dex处理)、Met组(以Dex和Met共同处理)、Met+IGF-1组(以Dex、Met和PI3K/Akt/m TOR通路活化剂IGF-1共同处理)、Met+NVP-BEZ235组(以Dex、Met和PI3K/Akt/m TOR通路抑制剂NVP-BEZ235共同处理),采用免疫印迹法(WB)检测MC3T3-E1细胞中PI3K、Akt、磷酸化(p)-Akt、m TOR和p-mTOR蛋白表达水平,通过噻唑蓝(MTT)法检测MC3T3-E1细胞存活率、流式细胞术检测MC3T3-E1细胞凋亡率、实时荧光定量PCR检测MC3T3-E1细胞中Bcl-2和Bax mRNA表达水平、Caspase-3活性测定试剂盒检测MC3T3-E1细胞Caspase-3活性、JC-1探针检测MC3T3-E1细胞线粒体膜电位变化。结果与对照组比较,Dex组细胞中PI3K、p-Akt、p-mTOR蛋白表达水平和细胞存活率、Bcl-2 mRNA表达水平以及线粒体膜电位均明显降低,而细胞凋亡率、Bax mRNA表达水平和Caspase-3活性均明显升高(P0.05);与Dex组比较,Met组细胞中PI3K、p-Akt、p-mTOR蛋白表达水平和细胞存活率、Bcl-2 mRNA表达水平以及线粒体膜电位均明显升高,而细胞凋亡率、Bax mRNA表达水平、Caspase-3活性明显降低(P0.05);给予IGF-1作用后Met对MC3T3-E1细胞的作用效果明显增强,而给予NVP-BEZ235作用后Met对MC3T3-E1细胞的作用效果明显减弱(P0.05)。结论 Met可通过激活PI3K/Akt/m TOR通路抑制线粒体凋亡途径,减轻糖皮质激素Dex诱导的成骨细胞凋亡。     

Differential expression of neuroleukin in osseous tissues and its involvement in mineralization during osteoblast differentiation.

Osteoblast differentiation is a multistep process that involves critical spatial and temporal regulation of cellular processes marked by the presence of a large number of differentially expressed molecules. To identify key functional molecules, we used differential messenger RNA (mRNA) display and compared RNA populations isolated from the defined transition phases (proliferation, matrix formation, and mineralization) of the MC3T3-E1 osteoblast-like cell line. Using this approach, a complementary DNA (cDNA) fragment was isolated and identified as neuroleukin (NLK), a multifunctional cytokine also known as autocrine motility factor (AMF), phosphoglucose isomerase (PGI; phosphohexose isomerase [PHI]), and maturation factor (MF). Northern analysis showed NLK temporal expression during MC3T3-E1 cell differentiation with a 3.5-fold increase during matrix formation and mineralization. Immunocytochemical studies revealed the presence of NLK in MC3T3-E1 cells as well as in the surrounding matrix, consistent with a secreted molecule. In contrast, the NLK receptor protein was detected primarily on the cell membrane. In subsequent studies, a high level of NLK expression was identified in osteoblasts and superficial articular chondrocytes in bone of 1-, 4-, and 8-month-old normal mice, as well as in fibroblasts, proliferating chondrocytes, and osteoblasts within a fracture callus. However, NLK was not evident in hypertrophic chondrocytes or osteocytes. In addition, treatment of MC3T3 cells with 6-phosphogluconic acid (6PGA; a NLK inhibitor) resulted in diminishing alkaline phosphatase (ALP) activity and mineralization in MC3T3-E1 cells, especially during the matrix formation stage of differentiating cells. Taken together, these data show specific expression of NLK in discrete populations of bone and cartilage cells and suggest a possible role for this secreted protein in bone development and regeneration.