Hedgehog信号通路与骨质疏松症

Hedgehog信号通路是一条保守而重要的信号通路,涉及到多种细胞的增殖和分化活动。近年研究发现,Hedgehog信号通路可以通过上调Runx2和Osx等主要转录因子的表达促进间充质干细胞（mesenchymalstemcells,MSCs）向成骨细胞分化,并且抑制MSCs向脂肪细胞分化。Hedgehog信号通路还可以通过调节细胞周期蛋白促进成骨细胞增殖。本文综述总结了Hedgehog信号通路调节成骨细胞增殖分化的作用机制,认为Hedgehog信号通路通过促进成骨细胞增殖分化参与调节骨代谢,为骨质疏松症的治疗提供一种新思路。     

表皮生长因子受体信号通路对骨折愈合的生物学作用

骨折愈合过程中,骨髓间充质干细胞、软骨细胞、成骨细胞及破骨细胞都有各自特定的作用,任何一类细胞的功能异常都会影响骨折愈合。目前一些研究显示,EGFR信号通路参与调节骨髓间充质干细胞、软骨细胞、成骨细胞及破骨细胞的增殖、分化及凋亡等多种生物学过程,在此,作者对EGFR信号通路对骨折愈合过程中相关骨组织细胞的影响做一综述。     

BMSC向成骨细胞分化的信号传导通路

骨髓间充质干细胞(bone mesenchymal stem cell,BMSC)是一种多潜能干细胞,具有向成骨细胞分化的能力.在BMSC向成骨细胞分化中,有膜内成骨和软骨内成骨2条途径,而且受到众多信号传导通路调控.本文结合相关文献,简要介绍BMWSmads、Runx2/osterix、Hedgehog、Wnt/β-Catenin和MAPK信号传导通路.     

ERK途径在转化生长因子-β3诱导骨髓基质干细胞向软骨分化过程中的作用

目的 观察丝裂原活化蛋白激酶(MAPK)信号途径中细胞外信号调节的激酶ERK途径在转化生长因子(TGF)-β3诱导的骨髓基质干细胞(MSCs)向软骨分化的过程中的作用.方法 在体外培养大鼠的MSCs,在含有TGF-β3的诱导培养基中向软骨方向诱导分化,在诱导分化的不同时间点,分别用Western blot测定ERK1/2的表达和磷酸化.确定ERK1/2在分化过程中的变化,同时测定在分化的过程中MSCs与软骨分化相关基因的表达,之后用ERK1/2的抑制剂U0126,观察ERK1/2信号传导通路阻断后对软骨分化的影响.结果 在TGF-β3促使MSCs向软骨方向分化的过程中,ERK1/2参与了细胞的分化和相关软骨基质的合成,ERK1/2抑制剂的使用削弱和减缓了上述过程的发生.结论 ERK1/2途径在软骨分化过程中起重要作用.     

流体剪切应力促进成骨细胞增殖的机制

成骨细胞是骨组织中重要的的刺激感受细胞和效应细胞,参与多种力学刺激下骨的修复及重建。流体剪切应力是人体内骨组织受到的最直接的力学刺激,已有大量研究证明流体剪切应力可以通过激活Wnt信号通路、BMP-Smad依赖性信号通路或BMP-非Smad依赖性信号通路促进成骨细胞增殖分化。近年来,越来越多的研究发现流体剪切应力还可以通过激活ERK5信号通路、PI3K/AKT激酶信号通路等途径抑制成骨细胞凋亡,这为流体剪切应力促进成骨细胞增殖提供了一个新的研究方向。本文就近年来流体剪切应力促进成骨细胞增殖的影响机制作一综述,希望能为骨科相关疾病的防治及研究提供参考。     

NO-CGMP信号途径在干细胞诱导分化中的作用

一氧化氮-环磷鸟苷(Nitric oxide–cyclic guanosine monophosphate,NO-cGMP)信号途径介导了机体内各系统的重要生理功能的实现。大量研究表明,NO-cGMP信号通路在干细胞向心肌细胞、神经细胞等的诱导分化中发挥重要的作用。此外,NO-cGMP信号通路还能促进神经轴突的延伸。本文就NO-cGMP信号途径在胚胎干细胞(Embryonicstem cells,ESCs)、间充质干细胞(Mesenchymal stem cells,MSCs)、神经干细胞(Neural stem cells,NSCs)等诱导分化中的作用进行综述。     

Hedgehog信号通路调控骨形成探讨中药防治骨质疏松症的研究进展

Hedgehog信号通路是一种高度保守而重要的信号通路，参与多种细胞的增殖和分化。骨质疏松症是一种常见的以骨量减少、骨组织微结构破坏为特征，导致骨质脆性增加和易于骨折的全身性骨代谢疾病，给社会造成了巨大的负担。骨质疏松症的发生发展受多种信号通路调控。近年来，国内外研究发现，Hedgehog通路是一个很有前途的参与骨形成和骨稳态的信号通路。已有研究证实，Hedgehog信号通路可能通过增加骨形成相关因子的表达，诱导骨髓间充质干细胞成骨分化，促进成骨细胞增殖分化，对防治骨质疏松症具有重要意义。本文综述了目前Hedgehog信号通路在骨形成调节中的作用机制及中医药的干预作用，旨在为促进骨形成、防治骨质疏松症提供新的作用靶点。     

BMPs及其相关microRNAs在MSC向成骨细胞 分化过程中的作用

目的间充质干细胞(MSCs)向成骨细胞分化是目前组织工程和骨愈合研究的热点。已有大 量文献报道骨诱导形成蛋白（BMP)在该过程中的作用,随着微小RNA( microRNA,miRNA)的发现,其 对BMP在MSC向成骨细胞诱导分化过程中所起的调控作用也日益受到重视。作者归纳总结了 BMIP及其相关miRNA在MSC向成骨细胞分化过程中的作用,以及一些常用生物材料在诱导MSCs 向成骨细胞分化过程中,对BMP及相关miRNA的影响。为进一步的研究提供了借鉴和参考。     

骨髓脂肪细胞与成骨细胞分化的信号转导调控机制

骨髓基质干细胞具有多向分化潜能和自我增殖能力.在不同调节因子的作用下分化为多种细胞,如成骨细胞、软骨细胞、脂肪细胞、成肌细胞、神经细胞和血管内皮细胞等.近年研究发现,骨质疏松的发生可能与骨髓内环境中骨髓基质干细胞向成骨细胞分化能力的减弱,使得骨髓脂肪细胞的数量增多,脂肪细胞与成骨细胞的比例失调有关.骨髓基质干细胞纵向分化为成熟骨髓脂肪细胞及成骨细胞的过程受到多种通路的调控和影响,而分化成熟的成骨细胞和脂肪细胞在一定条件下也可以相互转化,这提示我们以后是否可以通过药物或其他手段来抑制BMS向脂肪细胞的分化、增殖能力进而使更多成骨细胞生成,甚至通过脂肪细胞去分化再分化为成骨细胞,从而有效地刺激骨形成,以达到治疗骨丢失和骨代谢异常的目的.基于此,本文结合最新研究进展,重点叙述骨髓基质干细胞向成熟脂肪细胞与成骨细胞分化过程中的信号转导调节机制以及两条信号转导间信号转导因子的相互影响.同时叙述了成熟骨髓脂肪细胞和成骨细胞在一定条件下相互转化可能的机制,希望可以为以后研究开发骨组织合成代谢药物提供新思路.     

Wnt/β-catenin信号通路主要因子与成骨细胞研究进展

经典Wnt/β-catenin信号通路在成骨细胞的增殖、分化及骨形成过程中起关键作用.Wnt信号通路中主要因子Wnt配体、β-catenin及转录因子Runx2表达与功能的改变,将会影响成骨细胞的增殖、分化、骨基质的形成和矿化,进而导致骨量的变化.通路中不同因子在成骨细胞分化与成熟的过程中所起作用又有所不同,而且在此过程中又会受到其它因素的影响,进而增强或减弱成骨细胞分化与成熟的进程.     

Rap1b Is an Effector of Axin2 Regulating Crosstalk of Signaling Pathways During Skeletal Development

Recent identification and isolation of suture stem cells capable of long‐term self‐renewal, clonal expanding, and differentiating demonstrate their essential role in calvarial bone development, homeostasis, and injury repair. These bona fide stem cells express a high level of Axin2 and are able to mediate bone regeneration and repair in a cell autonomous fashion. The importance of Axin2 is further demonstrated by its genetic inactivation in mice causing skeletal deformities resembling craniosynostosis in humans. The fate determination and subsequent differentiation of Axin2+ stem cells are highly orchestrated by a variety of evolutionary conserved signaling pathways including Wnt, FGF, and BMP. These signals are often antagonistic of each other and possess differential effects on osteogenic and chondrogenic cell types. However, the mechanisms underlying the interplay of these signaling transductions remain largely elusive. Here we identify Rap1b acting downstream of Axin2 as a signaling interrogator for FGF and BMP. Genetic analysis reveals that Rap1b is essential for development of craniofacial and body skeletons. Axin2 regulates Rap1b through modulation of canonical BMP signaling. The BMP‐mediated activation of Rap1b promotes chondrogenic fate and chondrogenesis. Furthermore, by inhibiting MAPK signaling, Rap1b mediates the antagonizing effect of BMP on FGF to repress osteoblast differentiation. Disruption of Rap1b in mice not only enhances osteoblast differentiation but also impairs chondrocyte differentiation during intramembranous and endochondral ossifications, respectively, leading to severe defects in craniofacial and body skeletons. Our findings reveal a dual role of Rap1b in development of the skeletogenic cell types. Rap1b is critical for balancing the signaling effects of BMP and FGF during skeletal development and disease. © 2017 American Society for Bone and Mineral Research.     

Notch Signaling in Skeletal Stem Cells

The skeleton originates from stem cells residing in the sclerotome and neural crest that undergo proliferation, migration, and commitment. The development of the skeletal stem cells is influenced by many signaling pathways that govern cell fate determination, proliferation, differentiation, and apoptosis. This review will focus on Notch signaling functions in regulating the different cell types that form the skeletal system as well as the interplay between them to maintain homeostasis. Osteochondroprogenitors require Notch signaling to maintain multipotency and to prevent premature differentiation into osteoblasts. Subsequently, overactivation of Notch signaling suppresses osteoblast maturation. Moreover, Notch signaling in osteochondroprogenitors is required for chondrocyte proliferation and hypertrophy and suppresses terminal differentiation. Translational studies demonstrated a crucial role of Notch signaling in osteosarcoma and osteoarthritis, where concepts derived from developmental pathways are often recapitulated. This brings hope of taking advantage of the molecular mechanisms learned from development to approach the pathological processes underlying abnormal bone/cartilage metabolism or tumorigenesis. Pharmacological agents that target Notch receptors or ligands in a tissue-specific fashion would offer new opportunities for treating bone/cartilage diseases caused by dysregulation of Notch signaling.     

骨质疏松症中miRNA调控骨种子细胞分化的研究

骨质疏松症与骨稳态失衡密切相关。骨稳态主要由骨种子细胞(成骨细胞、破骨细胞、间充质干细胞、单核/巨噬细胞)维持,可受多种信号通路调控。近年来微小RNA(miRNA)被证实在改善骨质疏松症方面的疗效,可能通过多种途径调控骨种子细胞的分化。该文拟对骨质疏松症中miRNA调控骨种子细胞分化的研究进展进行综述。     

Activation of c‐Jun NH2‐terminal kinase 1 increases cellular responsiveness to BMP‐2 and decreases binding of inhibitory Smad6 to the type 1 BMP receptor

Bone morphogenetic protein 2 (BMP‐2) plays a critical role in the differentiation of precursor cells and has been approved for clinical application to induce new bone formation. To date, unexpectedly high doses of recombinant BMP‐2 have been required to induce bone healing in humans. Thus, enhancing cellular responsiveness to BMP‐2 potentially has critically important clinical implications. BMP responsiveness may be modulated in part by cross‐talk with other signaling pathways, including mitogen‐activated protein kinases (MAPKs). c‐Jun NH₂‐terminal kinase (JNK) is a MAPK that has been reported to be required for late‐stage differentiation of preosteoblasts and BMP‐2‐induced differentiation of preosteoblasts and pleuripotent cells. In this study we determined that MC3T3‐E1‐clone 24 cells (MC‐24) can be induced by BMP‐2 to differentiate into mineralizing osteoblast cultures. Using this inducible system, we employed both JNK loss‐of‐function and gain‐of‐function reagents to make three key observations: (1) JNK is required for phosphorylation of Smad1 by BMP‐2 and subsequent activation of Smad1 signaling and osteoblast differentiation, (2) JNK1, but not JNK2, is required for BMP‐2‐induced formation of mineralized nodules, and (3) JNK1 activation decreases binding of inhibitory Smad6 to the type I BMP receptor (BMPR‐I) and reciprocally increases binding of Smad1, both observations that would increase responsiveness to BMP‐2. Understanding this and other pathways that lead to increased cellular responsiveness to BMPs could greatly aid more cost‐effective and safe clinical delivery of these important molecules. © 2011 American Society for Bone and Mineral Research.     

Glycogen synthase kinase‐3α/β inhibition promotes in vivo amplification of endogenous mesenchymal progenitors with osteogenic and adipogenic potential and their differentiation to the osteogenic lineage

Small molecules are attractive therapeutics to amplify and direct differentiation of stem cells. They also can be used to understand the regulation of their fate by interfering with specific signaling pathways. Mesenchymal stem cells (MSCs) have the potential to proliferate and differentiate into several cell types, including osteoblasts. Activation of canonical Wnt signaling by inhibition of glycogen synthase kinase 3 (GSK‐3) has been shown to enhance bone mass, possibly by involving a number of mechanisms ranging from amplification of the mesenchymal stem cell pool to the commitment and differentiation of osteoblasts. Here we have used a highly specific novel inhibitor of GSK‐3, AR28, capable of inducing β‐catenin nuclear translocation and enhanced bone mass after 14 days of treatment in BALB/c mice. We have shown a temporally regulated increase in the number of colony‐forming units–osteoblast (CFU‐O) and –adipocyte (CFU‐A) but not colony‐forming units–fibroblast (CFU‐F) in mice treated for 3 days. However, the number of CFU‐O and CFU‐A returned to normal levels after 14 days of treatment, and the number of CFU‐F was decreased significantly. In contrast, the number of osteoblasts increased significantly only after 14 days of treatment, and this was seen together with a significant decrease in bone marrow adiposity. These data suggest that the increased bone mass is the result of an early temporal wave of amplification of a subpopulation of MSCs with both osteogenic and adipogenic potential, which is driven to osteoblast differentiation at the expense of adipogenesis. © 2011 American Society for Bone and Mineral Research.     

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。     

Downregulation of Wnt signaling by increased expression of Dickkopf-1 and -2 is a prerequisite for late-stage osteoblast differentiation of KS483 cells.

We examined the role of Wnt/beta-catenin signaling in successive stages of osteoblast differentiation. It has been shown that Wnt signaling in mature osteoblasts needs to be downregulated to enable the formation of a mineralized matrix. Using RNA interference, we showed that this is, at least in part, accomplished by upregulation of the Wnt antagonists Dickkopf-1 and -2. INTRODUCTION: The role of Wnt signaling in the initiation of osteoblast differentiation has been well studied. However, the role during late-stage differentiation is less clear. We have examined the role of Wnt/beta-catenin signaling in successive stages of osteoblast differentiation. MATERIALS AND METHODS: We treated murine bone marrow and mesenchymal stem cell-like KS483 cells with either LiCl or Wnt3A during several stages of osteoblast differentiation. In addition, we generated stable KS483 cell lines silencing either the Wnt antagonist Dkk-1 or -2 RESULTS: Activation of Wnt signaling by LiCl inhibits the formation of a mineralized bone matrix in both cell types. Whereas undifferentiated KS483 cells respond to Wnt3A by inducing nuclear beta-catenin translocation, differentiated cells do not. This is at least in part accomplished by upregulated expression of Dkk-1 and -2 during osteoblast differentiation. Using RNA interference, we showed that Dkk-1 plays a crucial role in blunting the BMP-induced alkaline phosphatase (ALP) response and in the transition of an ALP+ osteoblast in a mineralizing cell. In contrast, Dkk-2 plays a role in osteoblast proliferation and the initiation of osteoblast differentiation. CONCLUSIONS: Our data suggest that Wnt signaling in maturing osteoblasts needs to be downregulated to enable the formation of a mineralized bone matrix. Furthermore, they suggest that Dkk-1 and Dkk-2 may have distinct functions in osteoblast differentiation.