EphB4/ephrinB2逆向信号对RAW264．7破骨细胞分化中PDZ结构域蛋白表达变化的研究

Eph受体是酪氨酸蛋白激酶受体家族中最大的亚家族,ephrin(Eph受体相互作用蛋白)是其配体,它们是膜结合蛋白,相互依赖进行信号转导.内居蛋白(syntenin)与Pick1属于PDZ结构域(PSD-95/Dlg-/Zo-1 domain)蛋白,报道称能与ephrinB配体结合,但是否受Eph受体调控尚未见报道.以RAW264.7细胞株为研究对象,通过蛋白质印迹及/或免疫荧光分析显示RAW264.7细胞经RANKL诱导的破骨细胞表达ephrinB2、内居蛋白(syntenin)和Pick1三个蛋白质.将提前成簇的可溶性EphB4蛋白加入培养液,与ephrinB2配体结合,用来研究EphB4/ephrinB2逆向信号对syntenin和Pick1表达水平变化的影响.免疫印迹及Real-time RT-PCR分析结果显示,在EphB4-Fc实验组中Pick1的蛋白质及mRNA水平都有明显增加,然而在EphB4-Fc实验组与Fc对照组别间syntenin的蛋白质及mRNA水平未见明显变化.免疫共沉淀结果显示,syntenin和Pick1不能与ephrinB2共沉淀.以上结果初步探索了体外破骨细胞分化过程中,EphB4/ephrinB2逆向信号对PDZ结构域蛋白(ephrinB2配体潜在的下游信号分子)表达变化的调控.     

Eph受体家族及其配体的信号转导途径及功能

Eph受体是已知最大的酪氨酸蛋白激酶受体家族,Eph受体和其膜附着型配体（ephrin）在发育过程中呈现不同的表达模式,近来研究证明,Eph受体和其配体在包括神经网络形成,神经管和轴旁中胚层的成型（patterning）,细胞迁移导向和轴突路径导引,血管形成等许多的发育过程中起重要作用.Eph受体及其配体也与肿瘤发生有关,因此深入分析这些分子尤其在肿瘤细胞生长中的功能而应用于治疗具有重要的临床意义.     

Eph/ephrin对树突棘的调控与中枢神经系统疾病

树突棘是神经元树突上的功能性突起结构,通常作为突触后成份与投射来的轴突共同构成完整的突触连接。树突棘的形态与结构具有明显的可塑性,其变化通常会引起突触功能的改变。Eph受体酪氨酸激酶家族分子与其配体ephrin都是重要的神经导向因子,同时对树突棘结构也有直接的调控作用。Eph受体的活化可以促进树突棘的发生并影响树突棘的形态及内部结构;而Eph受体的异常也往往会损害正常的突触功能,甚至导致许多与树突棘结构异常相关的神经系统病变的发生。     

RANKL与骨重建

骨是一种动态更新的组织,它不断进行骨吸收（bone resorption）与骨形成（bone formation）的平衡,这个过程称之为骨重建（bone remodeling）．核因子κB受体活化因子配体（receptor activator of nuclear factor κB ligand,RANKL）是骨吸收和骨形成耦联的关键,具有诱导破骨细胞（osteoclast, OC）生成、活化,抑制破骨细胞凋亡的作用．RANKL最初发现于活化的T细胞,但骨重建过程中RANKL主要来源于骨细胞、成骨细胞和骨髓基质细胞．RANKL/核因子κB受体活化因子（receptor activator of nuclear factor κB,RANK）/骨保护素（osteoprotegerin, OPG）信号通路在成骨细胞调控破骨细胞生成的过程中起着重要的调节作用,是维持骨重建平衡的关键．本文就RANKL及其在骨中的分子作用机制作一综述.     

Eph-ephrin与突触可塑性

Eph受体酪氨酸激酶及其配体ephrin广泛参与神经系统的发育,如轴突导向、细胞迁移、体节形成和血管生成。最近研究显示的Ephephrin在突触的定位提示其与突触可塑性有关。Ephephrin对成年神经系统的可塑性、学习和记忆,以及神经损伤后的再生可能具有重要的调节作用。     

EphrinB2/EphB4 在血管生长中的作用及中医药研究展望*

近年来,有关ephrin及其Eph受体的作用研究已从神经系统方面逐步向血管生长扩展。已有研究表明ephrinB2/EphB4及其独特的双向信号转导几乎参与血管生长的每个方面,涉及血管发育过程中的动静脉分化、胚胎后血管新生包括内皮细胞增殖、迁移、粘附和分化等过程,且与VEGF、Notch等血管新生调控因子关系密切。另外,实验表明活血化瘀名方血府逐瘀汤显著的促血管新生作用与ephrinB2/EphB4相关,说明中医药促血管新生中ephrinB2/EphB4具有重要作用。本文部分总结了ephrinB2/EphB4在血管生长中的作用,并提出中医药在这方面的展望。     

Eph家族蛋白在阿尔茨海默症等神经精神疾病中的作用

促红细胞生成素产生肝细胞(erythropoietin-producing hepatomocellular, Eph)受体是受体酪氨酸激酶家族中数量最多的成员。Eph受体与其配体肝配蛋白(Eph receptor-interacting proteins, ephrin)被统称为Eph家族蛋白,通过独特的双向信号传递在调控正常学习和记忆中扮演重要角色。近年大量的研究发现,Eph家族蛋白在多种神经精神疾病中发挥复杂而又重要的作用,主要是通过改变突触效能,参与神经元形态发生和调控基因表达等方式影响上述疾病的进程。然而,目前靶向Eph家族蛋白对阿尔茨海默症(Alzheimer’s disease, AD)、焦虑症及恐惧症等疾病进行治疗的研究却为数甚微。同时,单纯以β样淀粉蛋白为靶点的抗AD药物开发均遭遇瓶颈。因此,探索Eph家族蛋白在上述疾病中的具体作用变得十分迫切。本文综述了Eph家族蛋白在AD、焦虑症和恐惧症中的最新研究进展,旨在为靶向Eph家族蛋白治疗相关疾病提供新的思路。     

骨重建逆转期细胞事件及偶联因子再归类

骨重建是由基本多细胞单位（basic multicellular units, BMUs）进行的维持骨体积、微观结构的细胞活动,包括三个在时间和空间上高度协调的过程：骨吸收期、逆转期和骨形成期。BMUs逆转期发生的细胞事件在时间上是吸收期与形成期的短暂连接,在功能上偶联骨吸收的关闭和骨形成的启动,是骨质疏松症等疾病发生的病理生理基础。依据骨重建模型重新归类逆转期纷繁复杂的细胞分泌或基质偶联因子,可为骨重建障碍的疾病如骨质疏松等,提供符合偶联规律的药物治疗周期和靶点。     

自噬对骨疾病调控作用的研究进展

骨疾病是指机体因先天或后天性因素破坏正常骨代谢,导致骨代谢障碍而发生的一类疾病。骨主要由负责骨吸收的破骨细胞和负责骨重建的成骨细胞以及骨细胞构成。正常成人的骨形成量基本等于骨吸收量,两者处于动态平衡状态,保证了骨结构和功能的完整性。自噬是一种重要的细胞内清除机制,通过形成自噬溶酶体降解其所包裹的受损细胞器或蛋白质,实现细胞代谢和细胞器的更新。自噬相关基因的缺失能够抑制破骨细胞的骨吸收和成骨细胞的骨重建,而药物、肿瘤坏死因子等能够使自噬相关基因过表达导致骨吸收异常增加,造成骨吸收和骨形成之间的动态平衡失调,从而引起骨代谢障碍,形成骨疾病。该文分别就自噬与破骨细胞、成骨细胞以及骨疾病之间的研究进展进行综述,希望可以为骨疾病的靶向治疗提供新的思路。     

DNA甲基化与骨代谢调节及骨质疏松症研究进展

骨质疏松症的根本病因是由于多种因素导致成骨细胞介导的骨形成与破骨细胞介导的骨吸收过程之间的负平衡,引起骨质进行性丢失,骨密度降低,骨脆性增加,进而导致骨折风险增加。越来越多的研究表明,DNA甲基化可通过调控相关基因表达调节成骨细胞/破骨细胞的分化与功能,进而影响骨形成/骨吸收平衡,介导骨质疏松症的发生、发展。现主要阐述DNA甲基化与骨代谢调节和骨质疏松症之间的关系,并对相关研究进展进行综述。     

Bone cell interactions through Eph/ephrin

Bones cannot properly form or be maintained without cell-cell interactions through ephrin ligands and Eph receptors. Cell culture analysis and evaluation of genetic mouse models and human diseases reveal various ephrins and Eph functions in the skeletal system. Migration, attachment and spreading of mesenchymal stem cells are regulated by ephrinB ligands and EphB receptors. ephrinB1 loss-of-function is associated with craniofrontonasal syndrome (CFNS) in humans and mice. In bone remodeling, ephrinB2 is postulated to act as a “coupling stimulator.” In that case, bidirectional signaling between osteoclastic ephrinB2 and osteoblastic EphB4 suppresses osteoclastic bone resorption and enhances osteoblastic bone formation, facilitating the transition between these two states. Parathyroid hormone (PTH) induces ephrinB2 in osteoblasts and enhances osteoblastic bone formation. In contrast to ephrinB2, ephrinA2 acts as a “coupling inhibitor,” since ephrinA2 reverse signaling into osteoclasts enhances osteoclastogenesis and EphA2 forward signaling into osteoblasts suppresses osteoblastic bone formation and mineralization. Furthermore, ephrins and Ephs likely modulate pathological conditions such as osteoarthritis, rheumatoid arthritis, multiple myeloma and osteosarcoma. This review focuses on ephrin/Eph-mediated cell-cell interactions in bone biology.     

Bone cell interactions through Eph/ephrin: Bone modeling,remodeling and associated diseases

Bones cannot properly form or be maintained without cell-cell interactions through ephrin ligands and Eph receptors. Cell culture analysis and evaluation of genetic mouse models and human diseases reveal various ephrins and Eph functions in the skeletal system. Migration, attachment and spreading of mesenchymal stem cells are regulated by ephrinB ligands and EphB receptors. ephrinB1 loss-of-function is associated with craniofrontonasal syndrome (CFNS) in humans and mice. In bone remodeling, ephrinB2 is postulated to act as a “coupling stimulator.” In that case, bidirectional signaling between osteoclastic ephrinB2 and osteoblastic EphB4 suppresses osteoclastic bone resorption and enhances osteoblastic bone formation, facilitating the transition between these two states. Parathyroid hormone (PTH) induces ephrinB2 in osteoblasts and enhances osteoblastic bone formation. In contrast to ephrinB2, ephrinA2 acts as a “coupling inhibitor,” since ephrinA2 reverse signaling into osteoclasts enhances osteoclastogenesis and EphA2 forward signaling into osteoblasts suppresses osteoblastic bone formation and mineralization. Furthermore, ephrins and Ephs likely modulate pathological conditions such as osteoarthritis, rheumatoid arthritis, multiple myeloma and osteosarcoma. This review focuses on ephrin/Eph-mediated cell-cell interactions in bone biology.     

Targeted disruption of ephrin B1 in cells of myeloid lineage increases osteoclast differentiation and bone resorption in mice

Disruption of ephrin B1 in collagen I producing cells in mice results in severe skull defects and reduced bone formation. Because ephrin B1 is also expressed during osteoclast differentiation and because little is known on the role of ephrin B1 reverse signaling in bone resorption, we examined the bone phenotypes in ephrin B1 conditional knockout mice, and studied the function of ephrin B1 reverse signaling on osteoclast differentiation and resorptive activity. Targeted deletion of ephrin B1 gene in myeloid lineage cells resulted in reduced trabecular bone volume, trabecular number and trabecular thickness caused by increased TRAP positive osteoclasts and bone resorption. Histomorphometric analyses found bone formation parameters were not changed in ephrin B1 knockout mice. Treatment of wild-type precursors with clustered soluble EphB2-Fc inhibited RANKL induced formation of multinucleated osteoclasts, and bone resorption pits. The same treatment of ephrin B1 deficient precursors had little effect on osteoclast differentiation and pit formation. Similarly, activation of ephrin B1 reverse signaling by EphB2-Fc treatment led to inhibition of TRAP, cathepsin K and NFATc1 mRNA expression in osteoclasts derived from wild-type mice but not conditional knockout mice. Immunoprecipitation with NHERF1 antibody revealed ephrin B1 interacted with NHERF1 in differentiated osteoclasts. Treatment of osteoclasts with exogenous EphB2-Fc resulted in reduced phosphorylation of ezrin/radixin/moesin. We conclude that myeloid lineage produced ephrin B1 is a negative regulator of bone resorption in vivo, and that activation of ephrin B1 reverse signaling inhibits osteoclast differentiation in vitro in part via a mechanism that involves inhibition of NFATc1 expression and modulation of phosphorylation status of ezrin/radixin/moesin.     

miR-214对骨形成的抑制作用

越来越多的研究表明microRNA广泛参与骨代谢的调控,调节骨髓间充质干细胞、成骨及破骨细胞的增殖及分化,调控骨形成与骨吸收之间的平衡,在维持骨代谢平衡中发挥重要作用。近年来有研究报道老年性骨质疏松、绝经后骨质疏松均与miR-214的高表达有关。miR-214通过靶向作用于Osterix、ATF-4、FGFR1、Pten以及LZTS1等基因调控骨髓间充质干细胞、成骨细胞以及破骨细胞等骨组织细胞的增殖及分化,进而抑制骨形成,促进骨吸收。本文主要综述了miR-214对骨髓间充质干细胞、成骨细胞以及破骨细胞分化的调控作用,旨在探讨miR-214对骨形成的抑制作用,为骨质疏松等骨疾病的诊断及治疗提供理论依据。     

Boning up on ephrin signaling

The activities of osteoclasts, which degrade bone, and osteoblasts, which form bone, are coordinated to maintain bone homeostasis. Zhao et al. (2006) now demonstrate bidirectional signaling between these two cell populations via the transmembrane ligand ephrinB2 expressed by osteoclasts and its receptor EphB4 expressed by osteoblasts. Such bidirectional signaling limits osteoclast activity while stimulating osteoblast differentiation.     

Eph-ephrin bidirectional signaling in physiology and disease

Receptor tyrosine kinases of the Eph family bind to cell surface-associated ephrin ligands on neighboring cells. The ensuing bidirectional signals have emerged as a major form of contact-dependent communication between cells. New findings reveal that Eph receptors and ephrins coordinate not only developmental processes but also the normal physiology and homeostasis of many adult organs. Imbalance of Eph/ephrin function may therefore contribute to a variety of diseases. The challenge now is to better understand the complex and seemingly paradoxical signaling mechanisms of Eph receptors and ephrins, which will enable effective strategies to target these proteins in the treatment of diseases such as diabetes and cancer.     

钙敏感受体在骨代谢中的研究进展

钙敏感受体感受细胞外的钙离子水平,调控一系列激素的释放以维持机体的钙稳态。钙稳态的调节过程与骨代谢相偶联,钙敏感受体通过直接或间接对破骨和成骨细胞的调控,动员或者抑制骨钙入血。虽然钙敏感受体已被证实调控骨代谢,但是详尽的调控机制仍在不断探究中。目前认为细胞外的高钙水平会激活钙敏感受体,抑制甲状旁腺激素分泌并促进降钙素释放,进而破骨细胞被抑制,成骨细胞动员,增加了骨质合成。本文就近年来关于钙敏感受体调控骨代谢的研究进展作一综述,为促进钙敏感受体及相关作用因子治疗骨代谢疾病的研究提供参考。