Osteogenic response of mesenchymal stem cells to continuous mechanical strain is dependent on ERK1/2-Runx2 signaling

Mechanical stimuli are responsible for bone remodeling during orthodontic tooth movement. The role of mechanical stimulation in the regulation of the fate of bone mesenchymal stem cells (BMSCs) is of interest in bone regeneration and tissue engineering applications. However, the signaling pathway involved in strain-induced biochemical events in BMSCs is not well established and can be controversial. This study investigated strain-induced proliferation and differentiation of BMSCs, as well as the mechanism of mechanotransduction. BMSCs were exposed to continuous mechanical strain (CMS) of 10% at 1 Hz. The results showed that CMS reduced the proliferation of BMSCs and stimulated osteogenic differentiation by activating Runx2, followed by increased alkaline phosphatase (ALP) activity and mRNA expression of osteogenesis-related genes (ALP, collagen type I and osteocalcin). Furthermore, the phosphorylation level of extracellular regulated protein kinase (ERK)1/2 increased significantly at the onset of strain. However, the presence of U0126, a selective inhibitor of ERK1/2, blocked the induction of Runx2 and subsequent osteogenic events. These findings demonstrate that CMS regulated Runx2 activation and favored osteoblast differentiation through activation of the ERK1/2 signaling pathway. These results will contribute to a better understanding of strain-induced bone remodeling and will form the basis for the correct choice of applied force in orthodontic treatment.     

周期性牵张力介导BMP9通过PI3K/AKT信号通路调控人牙周膜成纤维细胞成骨分化

目的　研究在周期性牵张力介导下，骨形态发生蛋白9（bone morphogenetic proteins 9，BMP9）能否激活PI3K/AKT信号通路调控人牙周膜成纤维细胞（human periodontal ligament fibroblasts，hPDLFs）成骨分化。 方法　利用FlexCell系统对体外培养的hPDLFs加载正弦波、形变率10%、频率0.5 Hz的周期性牵张力，免疫荧光法检测细胞骨架蛋白的表达及分布，qPCR检测RUNX2、OCN、OPN、OSX mRNA的表达情况，免疫印迹法检测成骨标志蛋白OCN、OPN的表达，加入PI3K信号抑制剂LY294002后AKT、P-AKT以及OCN、OPN的变化。 结果　与对照组比较，6 h、12 h组的细胞骨架蛋白表达增多且呈受力方向分布，OCN、OPN表达上调，差异有统计学意义（P<0.05），qPCR检测mRNA的表达趋势与蛋白检测结果一致。 结论　周期性牵张力介导BMP9可以通过PI3K/AKT信号通路调控hPDLFs成骨分化。     

周期性牵张力介导BMP9通过PI3K/AKT信号通路调控人牙周膜成纤维细胞成骨分化

目的　研究在周期性牵张力介导下,骨形态发生蛋白9（bone morphogenetic proteins 9,BMP9）能否激活PI3K/AKT信号通路调控人牙周膜成纤维细胞（human periodontal ligament fibroblasts,hPDLFs）成骨分化。 方法　利用FlexCell系统对体外培养的hPDLFs加载正弦波、形变率10%、频率0.5 Hz的周期性牵张力,免疫荧光法检测细胞骨架蛋白的表达及分布,qPCR检测RUNX2、OCN、OPN、OSX mRNA的表达情况,免疫印迹法检测成骨标志蛋白OCN、OPN的表达,加入PI3K信号抑制剂LY294002后AKT、P-AKT以及OCN、OPN的变化。 结果　与对照组比较,6 h、12 h组的细胞骨架蛋白表达增多且呈受力方向分布,OCN、OPN表达上调,差异有统计学意义（P<0.05）,qPCR检测mRNA的表达趋势与蛋白检测结果一致。 结论　周期性牵张力介导BMP9可以通过PI3K/AKT信号通路调控hPDLFs成骨分化。     

正畸牙移动中牙周膜的力学-生物学行为研究进展

正畸牙移动（OTM）是一个相当复杂的力学-生物学过程,是通过力学手段使牙周组织发生改建而实现的.牙周膜作为连接牙槽骨与牙骨质的结缔组织,在对正畸力的感受和传导中起着非常重要的作用;同时,其在OTM过程中敏感的生物力学反应是介导和调控牙周组织发生改建的关键因素.就牙周膜在OTM过程中的具体作用及其力学-生物学行为作一综述.结合近年来最新的研究成果,从组织、细胞及分子水平阐明了牙周膜在OTM中的力学响应及生物学行为机制.     

Up-regulated osteogenic transcription factors during early response of human periodontal ligament stem cells to cyclic tensile strain

Introduction

As one group of periodontal ligament (PDL) cells, human periodontal ligament stem cells (hPDLSCs) have been isolated and identified as mesenchymal adult stem cells (MSCs) since 2004. It has been well accepted that PDL sensitively mediates the transmission of stress stimuli to the alveolar bone for periodontal tissue remolding. Besides, the direction of MSCs differentiation has been verified regulated by mechanical signals. Therefore, we hypothesized that tensile strain might act on hPDLSCs differentiation, and the early response to mechanical stress should be investigated.

Material and methods

The hPDLSCs were cultured in vitro and isolated via a magnetic activated CD146 cell sorting system. After investigation of surface markers and other experiments for identification, hPDLSCs were subjected to cyclic tensile strain at 3,000 µstrain for 3 h, 6 h, 12 h, and 24 h, without addition of osteogenic supplements. In the control groups, the cells were cultured in similar conditions without mechanical stimulation. Then osteogenic related genes and proteins were analyzed by RT-PCR and western blot.

Results

Cyclic tensile strain at 3,000 µstrain of 6 h, 12 h, and 24 h durations significantly increased mRNA and protein expressions of Satb2, Runx2, and Osx, which were not affected in unloaded hPDLSCs.

Conclusions

We indicate that hPDLSCs might be sensitive to cyclic tensile strain. The significant increase of Runx2, Osx and Satb2 expressions may suggest an early response toward osteogenic orientation of hPDLSCs.     

Cyclic tensile stretch modulates osteogenic differentiation of adipose-derived stem cells via the BMP-2 pathway

Introduction

Mechanical forces play critical roles in the development and remodelling process of bone. As an alternative cell source for bone engineering, adipose-derived stem cells (ASCs) should be fully investigated for their responses to mechanical stress and the mechanisms responsible for osteogenic induction in response to mechanical signals.

Material and methods

We hypothesized that appropriate application of uniaxial cyclic tensile strain to ASCs could increase bone morphogenetic protein-2 (BMP-2) expression and improve osteogenesis of ASCs. To test our hypothesis, ASCs from the same flask of the same donor were subjected to tensile strain with different patterns in order to eliminate the difference of donor site and passage. After surface markers investigation, the osteo-induced ASCs were subjected to uniaxial cyclic tensile stretch with the following two loading patterns: long duration continuous pattern (6 h, 1 HZ, 2000 µɛ) and short duration consecutive pattern (17 min every day for 10 consecutive days, 1 HZ, 2000 µɛ). Then osteogenic related genes were analysed by real-time PCR.

Results

The ASCs were positive for the markers STRO-1, CD90 and CD44 and negative for CD34. Cyclic tensile strain of 6 continuous h’ duration significantly increased gene expressions of BMP-2 and Runx2, and depressed OCN mRNA expression. In contrast, mechanical loading of 17 min every day did not significantly affect gene expression of BMP-2, Runx2, OCN or ALP.

Conclusions

We indicate that ASCs may sense mechanical loading in a duration-dependent manner and cyclic tensile stretch may modulate the osteogenic differentiation of ASCs via the BMP-2 signalling pathway.     

A comparative analysis of the osteogenic capacity of osteoblasts from newborn and two-week-old rats

AimTo compare the proliferation and osteogenic differentiation of osteoblasts between newborn rats (1d group) and two-week-old rats (14d group) and to clarify the mechanism underlying these effects.MethodThe endogenous expression of osteogenic marker genes was detected by qPCR, including ALP, OCN, Col1a1, and Runx2. The osteoblasts proliferation was evaluated by EdU assay and Western Blotting [PCNA and Cyclin D1]. ALP activities in osteoblasts were detected using a PNPP kit, ALP staining and qPCR. Mineralized nodule formation and intracellular calcium levels were assessed by Alizarin Red staining and calcium colorimetric assay respectively while OCN, Col1a1 and Runx2 levels in osteoblasts were analyzed by immunostaining. Osteogenesis-associated pathways including Wnt/β-Catenin, Akt/PPAR and Smad were analyzed via Western Blotting.ResultEndogenous ALP, OCN, Col1a1, and Runx2 expression levels were significantly higher in osteoblasts from 14d group than those from 1d group. After treatment with osteogenic induction medium, osteoblast proliferation, ALP activity, mineralized nodule formation, and intracellular calcium levels were markedly increased in osteoblasts from 1d group, with similar results also being observed for the expression of OCN, Col1a1, and Runx2. Wnt3a, β-catenin, p-Akt, p-Smad1/5/8, and p-Smad5 protein levels were also higher in osteoblasts from 1d group relative to those from 14d group, while the expression of PPARγ was lower.ConclusionThe superior osteogenic differentiation capacity in osteoblasts was associated with the higher activation levels of Wnt/β-Catenin, Akt/PPAR and Smad signaling pathways, and the enhanced proliferative activity in osteoblasts from 1d group.     

Co-culture with periodontal ligament stem cells enhanced osteoblastic differentiation of MC3T3-E1 cells and osteoclastic differentiation of RAW264.7 cells

Objectives: Periodontal ligament stem cells (PDLSCs) are characterized by having multipotential differentiation and immunoregulatory properties, which are the main mechanisms of PDLSCs-mediated periodontal regeneration. Periodontal or bone regeneration requires coordination of osteoblast and osteoclast, however, very little is known about the interactions between PDLSCs and osteoblast-like cells or osteoclast precursors. In this study, the indirect co-culture approach was introduced to preliminarily elucidate the effects of PDLSCs on differentiation of osteoblast-like cells and osteoclast precursors in vitro. Materials and methods: Human PDLSCs were obtained from premolars extracted and their stemness was identified in terms of their colony-forming ability, proliferative capacity, cell surface epitopes and multi-lineage differentiation potentials. A noncontact co-culture system of PDLSCs and preosteoblastic cell line MC3T3-E1 or osteoclast precursor cell line RAW264.7 was established, and osteoblastic differentiation of MC3T3-E1 and osteoclastic differentiation of RAW264.7 were evaluated. Results: PDLSCs exhibited features of mesenchymal stem cells. Further investigation through indirect co-culture system showed that PDLSCs enhanced ALP activity, expressions of ALP, Runx2, BSP, OPN mRNA and BSP, OPN proteins and mineralization matrix deposition in MC3T3-E1. Meanwhile, they improved maturation of osteoclasts and expressions of TRAP, CSTK, TRAF6 mRNA and TRAP, TRAF6 proteins in RAW264.7. Conclusions: PDLSCs stimulates osteoblastic differentiation of osteoblast precursors and osteoclastic differentiation of osteoclast precursors, at least partially, in a paracrine fasion.     

正畸加力后大鼠牙周组织中BMP的分布变化及其意义

本研究首次应用抗牛骨形成蛋白单克隆抗体（ｂＢＭＰ－ＭｃＡｂ）免疫组织化学染色法，观察加力后的大鼠上第一磨牙牙周组织中ＢＭＰ的分布，并与正常不加力组相比较。结果显示：ＢＭＰ在正常牙周组织中主要分布于牙周韧带中，尤其是牙槽骨和牙骨质表面，并与不同部位的骨改建活动相一致；正时加力后，张力区成骨活跃，ＢＭＰ染色较深（强阳性），压力区染色为阴性，只有活跃的破骨细胞染色较深；已接近成熟的新生牙槽骨及牙骨质则染色较弱。结果表明；ＢＭＰ可以作为骨改建活动的标志之一，在正畸骨改建中起着十分重要的作用。     

Electroporation-mediated transfer of Runx2 and Osterix genes to enhance osteogenesis of adipose stem cells

In the present study, we tested the hypothesis that electroporation-mediated transfer of Runx2, Osterix, or both genes enhances the in vitro and in vivo osteogenesis from adipose stem cells (ASCs). ASCs were transfected with Runx2, Osterix, or both genes using electroporation, and further cultured in monolayer or in PLGA scaffold under osteogenic medium for 14 days, then analyzed for in vitro osteogenic differentiation. Transfected ASC-PLGA scaffold hybrids were also implanted on nude mice to test for in vivo ectopic bone formation. Runx2 and Osterix genes were strongly expressed in ASCs transfected with each gene on day 7, decreasing rapidly on day 14. Runx2 protein was strongly expressed in ASCs transfected with the Runx2 gene, while Osterix protein was strongly expressed in ASCs transfected with either or both Runx2 and Osterix genes. Overexpression of Runx2 and Osterix significantly increased the gene expression of osteogenic differentiation markers (alkaline phosphatase [ALP], osteocalcin [OCN], type I collagen [COL1A1], and bone sialoprotein [BSP]) in ASCs. Transfection of Runx2 and Osterix genes enhanced the protein expression of OCN, type I collagen, and BSP, as demonstrated by Western blot analysis, and ALP activity as well as enhancing mineralization in the monolayer culture and ASC-PLGA scaffold hybrids. Runx2- or Osterix-transfected ASC-PLGA scaffold hybrids promoted bone formation in nude mice after 6 weeks of in vivo implantation.     

低氧条件下载二甲基草酰甘氨酸电纺纤维促血管化及成骨性能研究

目的 通过聚L-丙交酯-己内酯电纺纤维（PLCL）负载二甲基草酰甘氨酸（DMOG）,研究其在低氧和常氧成骨诱导过程中对大鼠骨髓间充质干细胞（BMSC）的血管化和体外成骨分化的作用。方法 本研究经静电纺丝技术制备PLCL电纺纤维（P）和负载DMOG的PLCL电纺纤维（PD）,通过扫描电镜观察电纺纤维形貌;通过细胞骨架染色观察BMSC在不同电纺纤维上的黏附和生长状态;通过碱性磷酸酶和茜素红染色检测在不同电纺纤维上的BMSC经常氧和低氧成骨诱导7 d后的碱性磷酸酶表达和14 d时的钙沉积情况;通过RT-PCR检测在不同电纺纤维上的BMSC经常氧和低氧成骨诱导7 d和14 d时的成骨相关基因（ALP、Runx2、Col1和OCN）和促血管化相关基因（VEGF）的表达情况。结果 扫描电镜结果表明,P和PD具有纤维状形态并呈现为多孔结构。细胞实验表明,BMSC可在P和PD表面黏附生长,且低氧条件下在PD上表现出更好的形态。与常氧条件相比,在低氧条件下,P和PD在7 d时的碱性磷酸酶表达减少。但低氧条件成骨诱导14 d时PD仍能促进钙的沉积。在常氧条件下,电纺纤维P可上调ALP、Runx2、Col1、OCN和VEGF的表达,但低氧条件下其对上述基因的上调作用不明显。而电纺纤维PD在常氧和低氧条件下均可促进ALP、Runx2、Col1、OCN和VEGF的表达。结论 本研究制备的负载DMOG的PLCL电纺纤维在低氧条件下具有良好的体外促血管化和促成骨分化性能,预期可作为一种较好的成骨修复材料。     

胰岛素样生长因子在正畸牙牙周组织改建中的作用

背景：正畸牙牙周组织改建主要是牙槽骨的改建。胰岛素样生长因子是牙周组织改建的重要因子,它在细胞的增殖、分化及个体的生长发育中发挥着重要的促进作用。 目的：综述胰岛素样生长因子在牙周组织改建中的作用。 方法：运用计算机检索PubMed,中国知网以及贵州省数字图书馆等数据库,查阅至今有关胰岛素样生长因子在牙周组织改建中作用的中英文文献。关键词“胰岛素样生长因子;牙周组织;改建;insulin-like growth factor;Periodontal tissue;remodeling”。纳入胰岛素样生长因子与牙周组织改建中作用相关的文献进行归纳分析。 结果与结论：胰岛素样生长因子属于胰岛素家族的一类多肽,对牙周膜中的成骨细胞、成纤维细胞以及诱导间充质细胞等,有促进其细胞迁移、增殖、分化、胶原和基质合成、增强碱性磷酸酶活性及在损伤修复中发挥着重要作用。在正畸治疗中,使用适宜矫治力的同时可适当运用能促进牙周组织改建的胰岛素样生长因子,加快正畸牙齿的移动,缩短患者的矫治时间。  中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程     

P2X7受体对牙周膜干细胞成骨分化的作用

背景：研究影响牙周膜干细胞成骨分化的相关离子通道。 目的：初步观察P2X7受体在人牙周膜干细胞成骨分化中的作用。 方法：分离培养人牙周膜干细胞,分为4组,分别添加成骨诱导液和100 nmol/L三磷酸腺苷、成骨诱导液、100 nmol/L三磷酸腺苷及普通培养基培养,于成骨诱导7,14 d,利用茜素红染色检测成骨效果,qRT-PCR,Western blot检测OCN、Runx2以及P2X7受体的表达。 结果与结论：茜素红染色显示成骨诱导液+三磷酸腺苷组牙周膜干细胞的成骨效果在7 d时显著好于成骨诱导液组,但在14 d时成骨诱导液组成骨效果显著好于成骨诱导液+三磷酸腺苷组(P < 0.05);在成骨诱导7 d时,qRT-PCR结果显示成骨诱导液+三磷酸腺苷组Runx2,OCN mRNA的表达达到峰值,而14 d时明显降低(P < 0.05)。成骨诱导7 d时,成骨诱导液+三磷酸腺苷组P2X7受体mRNA的表达量明显高于三磷酸腺苷组(P < 0.05),成骨诱导液组和对照组未见P2X7受体mRNA的表达,成骨诱导14 d时,成骨诱导液+三磷酸腺苷组表达量下降,明显低于三磷酸腺苷组,差异有显著性意义(P < 0.05)。Western blot结果显示,成骨诱导7 d时,成骨诱导液+三磷酸腺苷组P2X7受体的表达达到峰值,高于三磷酸腺苷组,而成骨诱导液组表达量低,对照组几乎没有表达;成骨诱导14 d时,成骨诱导液+三磷酸腺苷组P2X7受体的表达比7 d时明显下降,而三磷酸腺苷组P2X7受体的表达比7 d时有所增加。结果表明外源性三磷酸腺苷可在牙周膜干细胞成骨诱导前7 d明显提高成骨效果,但在7 d后,抑制成骨诱导效果,三磷酸腺苷可以激活牙周膜干细胞P2X7受体表达,且P2X7受体的表达与牙周膜干细胞的成骨效果正相关。中国组织工程研究杂志出版内容重点：干细胞;骨髓干细胞;造血干细胞;脂肪干细胞;肿瘤干细胞;胚胎干细胞;脐带脐血干细胞;干细胞诱导;干细胞分化;组织工程全文链接：     

骨髓脂肪细胞向成骨细胞的转分化

背景：骨髓脂肪细胞、成骨细胞共同来源于骨髓基质细胞,二者存在基因同源性,在一定的条件下可以相互转分化。 目的：观察骨髓细胞源性脂肪细胞在成骨诱导分化培养条件下转分化为成骨细胞的活性,探索股骨头坏死细胞水平治疗的新途径。 方法：将前脂肪细胞3T3-L1分别进行成骨诱导培养和成脂诱导培养。培养后不同时间点观察细胞形态的变化;并于诱导培养后5,21 d分别进行实时定量-聚合酶链反应检测成骨、成脂分化过程中,细胞中Runt相关基因转录因子2、氧化物增殖体激活物受体γ2、骨钙素和Ⅰ型胶原mRNA表达。并于成骨、成脂培养21 d后采用Wertern-blot法检测相关蛋白的表达。培养细胞爬片,分别进行碱性磷酸酶、钙结节茜素红、油红O染色,观察3T3-L1成骨转分化情况以及成骨细胞活性表达。 结果与结论：3T3-L1在成骨诱导培养5 d后,细胞由圆形逐渐演变成纺锤形和梭形;实时定量-聚合酶链反应检测结果与对照组相比,氧化物增殖体激活物受体γ2 mRNA表达减弱,而Runt相关基因转录因子2、骨钙素和Ⅰ型胶原mRNA表达微量增强。至21 d时,这种表达改变更加明显;Western-blot显示,Runt相关基因转录因子2、骨钙素和Ⅰ型胶原蛋白量增加,而氧化物增殖体激活物受体γ2微量甚至无表达;碱性磷酸酶染色阳性表达较多,茜素红钙结节染色可见多个散在分布的钙结节;油红O染色微量脂滴。提示小鼠骨髓基质细胞源性前脂肪细胞3T3-L1在成骨诱导培养下,可在一定程度上转分化为有生物活性的成骨细胞;小鼠骨髓基质细胞的脂肪细胞和成骨细胞二者之间存在着可塑性。     

Immunolocalization of lubricin in the rat periodontal ligament during experimental tooth movement

Lubricin is a protein which contributes to the boundary lubrication, facilitating low friction levels at the interfacing surfaces of joints. In tendons and ligaments it facilitates the relative movement of collagen bundles. Its expression is affected by mechanical signals and cytokines. During application of orthodontic forces to teeth, there is a transduction of mechanical forces to the cells of the periodontal ligament (PDL), which triggers several biological reactions causing the synthesis of prostaglandins, cytokines and growth factors. The aim of the present study was to examine the immunolocalization of lubricin and to evaluate if it is time-dependently and differentially detected within the PDL following the application of orthodontic forces to create areas of compression and tension. This was achieved by placing elastic bands between the maxillary first and second molars of 16 male Sprague-Dawley rats (each weighing 120-200 g) for 12 and 24 h. The molar-bearing segments were dissected and processed for histological and immunohistochemical examination. Binding of a monoclonal antibody was used to evaluate lubricin localization using an indirect streptavidin/biotin immunperoxidase technique. Lubricin, was constitutively expressed in the PDL of rat molars. After the experimental force was applied to the tooth, lubricin was down-regulated, on both sides (compression and tension) of the PDL, in a time-dependent fashion, although to a different extent, being at any time more expressed on the tension side. Furthermore, in every sample, almost all PDL cells in the adjacent tooth cementum and alveolar bone, were more heavily immunolabeled by lubricin antibody, contrary to those located in the central portion of the PDL. Lubricin expression therefore seems related to PDL remodeling and tooth displacement following the application of an orthodontic force, and it appears that lubricin may play an important role during tooth movement.