骨桥蛋白与骨质疏松症研究进展

骨桥蛋白作为体内广泛存在的细胞因子和趋化因子,在骨代谢中起到重要作用.骨桥蛋白可能刺激成骨细胞增殖、钙化,促进破骨细胞与骨基质的黏附并提高破骨细胞的溶骨活性,介导机械应力引起的骨代谢变化,并抑制骨组织的矿化过程.本文就骨桥蛋白在骨质疏松症的发病中所起作用作一综述.     

致敏淋巴细胞对破骨细胞分化及骨吸收的影响

目的研究致敏淋巴细胞对破骨细胞分化及骨吸收功能的影响.方法从被骨水泥单体甲基丙烯酸甲酯(MMA)致敏的新西兰兔外周血中分离淋巴细胞并提取培养介质(LCM),分离培养兔颅骨成骨细胞和兔骨髓细胞,通过抗酒石酸酸性磷酸酶(TrACP)染色和骨磨片扫描电镜观察对破骨细胞进行鉴定.在成骨细胞与骨髓细胞的培养体系中,分别在无LCM,未经MMA刺激的LCM和经MMA刺激的LCM等3种情况下,进行成熟破骨细胞计数和TrACP活性检测.结果骨髓细胞能够分化成破骨细胞并且能在骨磨片上形成骨吸收陷窝,致敏淋巴细胞培养介质能够明显促进破骨细胞数量的增加和TrACP的分泌,在加入MMA刺激后,这种作用更加显著.结论致敏淋巴细胞能够促进骨髓破骨细胞的分化和骨吸收能力.     

致敏淋巴细胞对破骨细胞分化及骨吸收的影响

目的；研究致敏淋巴细胞对破骨细胞分化及骨吸收功能的影响。方法：从被骨水泥单体甲基丙烯酸甲酯（MMA）致敏的新西兰兔外周血中分离淋巴细胞并提取培养介质（LCM），分离培养兔颅骨成骨细胞和兔骨髓细胞，通过抗酒石酸酸性磷酸酶（TrACP)染色和骨磨片扫描电镜观察对破骨细胞进行鉴定。在成骨细胞与骨髓细胞的培养体系中，分别在无LCM，未经MMA刺激的LCM和经MMA刺激的LCM等3种情况下，进行成熟破骨细胞计数和TrACP活性检测。结果：骨髓细胞能够分化成破骨细胞并且能在骨磨片上形成骨吸收陷窝，致敏淋巴细胞培养介质能够明显促进破骨细胞数量的增加和TrACP的分泌，在加入MMA刺激后，这种作用更加显著。结论：致敏淋巴细胞能够促进骨髓破骨细胞的分化和骨吸收能力。     

淫羊藿苷对破骨细胞活性的影响

目的:观察淫羊藿苷对破骨细胞骨吸收及凋亡的影响,探讨淫羊藿苷的抗骨质疏松作用机制。方法:体外分离、培养兔破骨细胞,与玻片及骨磨片共同培养,用10-7、10-6、5×10-6、10-5mol/L浓度的淫羊藿苷刺激破骨细胞,倒置相差显微镜下观察活体细胞、HE染色、TRAP染色及骨吸收陷窝甲苯胺蓝染色,鉴定破骨细胞,并进行骨吸收陷窝计数和面积测量,吖啶橙染色观察凋亡破骨细胞所占的比例。结果:与空白对照组比较,10-6、5×10-6、10-5mol/L浓度的淫羊藿苷组破骨细胞凋亡率均明显增高,骨吸收陷窝数目、面积明显减少,随浓度增加抑制作用增强,差异有显著性意义(P<0.05)。结论:淫羊藿苷可诱导破骨细胞凋亡,抑制骨吸收,并随浓度增加抑制作用增强。     

β转化生长因子在骨改建中的作用

β转化生长因子(TGF-β)在骨改建中起突出的作用。TGF-β刺激基质蛋白合成,对与骨形成及骨吸收有关的细胞有作用。TGF-β在骨及以骨为条件的介质中很丰富。根据骨细胞表型及其分化的阶段,TGF-β可以有多种作用。根据成骨细胞的类型,TGF-β可以引起分化或增殖。TGF-β抑制破骨细胞前身的形成,抑制骨吸收,高浓度时还抑制分离破骨细胞。TGF-β在骨吸收及骨形成之间起偶合作用。     

破骨细胞融合相关分子的研究进展

多核破骨细胞具有骨吸收功能,其过度活化会导致骨破坏。在多种刺激诱导下,破骨前体细胞在其表达的融合相关分子(如树突状细胞特异性跨膜蛋白、破骨细胞多次跨膜蛋白、白细胞分化抗原、ATP6vOd2、E-钙黏蛋白、轻链钙调蛋白结合蛋白等)作用下,融合形成多核破骨细胞。由于破骨细胞融合过程对破骨细胞成熟及发挥骨吸收功能至关重要,因此,基于调节破骨细胞融合相关分子的研究可为骨质疏松、类风湿性关节炎、肿瘤等诱导的骨破坏提供新的治疗思路和方法。本文对破骨细胞融合相关分子的研究进展进行综述,旨在为骨破坏相关疾病的预防和治疗提供新方向。     

流体剪切力对破骨细胞的影响

骨组织受到成骨细胞成骨作用和破骨细胞溶骨作用共同影响。与成骨细胞和骨细胞不同,破骨细胞起源于造血干细胞,由单核巨噬细胞发育而来,具有吞噬功能,能对多种刺激因素产生效应,其中机械刺激是始终存在的影响方式。机械刺激诱导的成骨细胞的正性调节对于骨生成、骨修复有至关重要的作用,而破骨细胞在这些方面的效应也十分关键。流体剪切力作为骨组织内机械刺激的一种常见形式,作用于成骨细胞和骨细胞的时候,通过对Ca2+、前列腺素、NO、RANKL和OPG等信号因子的影响,表现出介导破骨细胞迁移、分化、吸收和生存维持等现象的功能,这承载了骨代谢必不可少的一部分。同时这些因子相互交错,表现出复杂信息网络及阶段特异性。但总的来说,人们对流体剪切力调节破骨细胞生理及病理功能具体信号传导的了解还不是很深入,需要用更多的研究来阐明流体剪切力和破骨细胞之间的关系。本文就流体剪切力对破骨细胞相关分子信号影响做一综述,简要展示流体剪切力影响破骨细胞的相关机理。     

骨细胞对破骨细胞形成和功能的影响

破骨细胞的骨吸收作用和成骨细胞骨形成作用的交替进行维持了骨量的平衡。破骨细胞可以选择性吸收损伤部位的骨质,其激活和定位机制目前还未阐明。近年来的研究认为骨细胞是感知骨环境的基本单位,而且骨细胞还可以将所感知的信号传递给其它骨细胞,骨衬细胞,成骨细胞及破骨细胞等。对骨细胞和破骨细胞的研究中发现骨细胞可能在破骨细胞的激活和定位中起到了重要的作用,但是具体机制还有待研究。     

白细胞介素─1刺激骨吸收的体外实验研究

作者采用新生纯系小鼠颅骨体外培养模型，综合利用钙转换率和组织形态学观察等指标，客观地评价了白细胞介素－１（ＩＬ－１）调节骨吸收的作用。结果表明，ＩＬ－１具有强烈的刺激骨吸收的活性，其两种不同形式ＩＬ－１α和ＩＬ－１β的活性接近。２００～４０００ｎｇ／ｍｌ的白细胞介素－１受体拮抗剂（ＩＬ－ｌｒａ）能完全阻断２０ｎｇ／ｍｌＩＬ－１α刺激骨吸收的作用，即使是在加入ＩＬ－１α４小时后，再加入ＩＬ－ｌｒａ同样能阻断ＩＬ－１α诱导的骨吸收作用。此外发现，ＩＬ－１在其作用最初２４小时内，未能增加培养颅骨骨吸收活性；培养７２小时后组织学观察颅骨破骨细胞数量增多。揭示ＩＬ－１刺激骨吸收的作用机制是：刺激破骨细胞前体增殖分化成熟，增加破骨细胞数量，而对成熟破骨细胞缺乏直接作用。     

低氧及相关因子对破骨细胞形成与活性的调节作用

破骨细胞是具有多个核的骨吸收细胞,来源于单核-巨噬细胞谱系,在骨的正常发育和改建、骨折的愈合及病理性骨吸收中起重要作用.现有的研究表明,破骨细胞前体细胞和破骨细胞属氧感应细胞,其分化和功能发挥可受控于低氧环境及其诱导产生的调节因子.低氧发生于组织的血供减少或中断时,低氧及相关的细胞因子(VEGF、FGF-2、IGF-I、TNF-α、TGF-β等0可通过引起局部微环境的酸化、促进骨髓中破骨细胞前体细胞的生成、趋化破骨细胞前体细胞、刺激成骨细胞RANKL的表达、延长成熟破骨细胞的生存期、活化成熟的破骨细胞等多种机制来调节破骨细胞的形成和活性.     

Osteopontin posttranslational modifications, possibly phosphorylation, are required for in vitro bone resorption but not osteoclast adhesion.

Osteopontin (OPN), a phosphorylated bone matrix glycoprotein, is an Arg-Gly-Asp (RGD)-containing protein that interacts with integrins and promotes in vitro attachment of a number of cell types, including osteoclasts. Gene knockout experiments support the idea that OPN is important in osteoclastic activity. We hypothesize that posttranslational modifications (PTMs) of OPN can influence its physiological function. Previous studies have suggested that phosphorylation of OPN and bone sialoprotein (BSP) is necessary for promoting osteoclast adhesion. However, no reports have explored the importance of phosphoserines and other PTMs in OPN-promoted bone resorption. To study this question, we determined the activities of different forms of OPN and BSP in three in vitro assays: attachment of osteoclasts; formation of actin rings; and bone resorption. For each assay, cells were incubated for 4-24 h, in the presence or absence of RGDS or RGES peptides, to test the involvement of integrin binding. In addition to OPN, activities of milk OPN (fully phosphorylated) and recombinant OPN (rOPN, no phosphate) were compared. We purified two forms of OPN (OPN-2 and OPN-5), which differ in the level of phosphorylation, and compared their activities. For comparison, the activities of BSP and recombinant BSP (rBSP) were determined. All forms of OPN, including rOPN, significantly increased attachment of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts. BSP and rBSP also promoted cell attachment. After 4 h of incubation, the proportion of cells with actin rings was increased with OPN, milk OPN, and BSP. In the presence of RGDS peptide, osteoclast retraction and the disruption of actin rings were observed, whereas no effect was seen with RGES. In the resorption assay, the number of pits and the total resorbed area per slice were increased in the presence of OPN, milk OPN, and BSP. As in other assays, the OPN enhancement of resorption was inhibited by RGDS, but not RGES, peptides. Significantly, rOPN and rBSP did not promote bone resorption. OPN-5 promoted resorption to a greater extent than OPN-2, and milk OPN significantly stimulated resorption to a greater extent than OPN. Our data suggest that: (1) the RGD sequence of OPN is essential in OPN-mediated cell attachment, actin ring formation, and bone resorption; and (2) some form of PTM, possibly phosphorylation, is necessary for in vitro osteoclastic bone resorption, but not for cell attachment and actin ring formation.     

Colocalization of intracellular osteopontin with CD44 is associated with migration, cell fusion, and resorption in osteoclasts.

Although osteopontin (OPN) is recognized generally as a secreted protein, an intracellular form of osteopontin (iOPN), associated with the CD44 complex, has been identified in migrating fibroblastic cells. Because both OPN and CD44 are expressed at high levels in osteoclasts, we have used double immunofluorescence analysis and confocal microscopy to determine whether colocalization of these proteins has functional significance in the formation and activity of osteoclasts. Analysis of rat bone marrow-derived osteoclasts revealed strong surface staining for CD44 and beta1- and beta3-integrins, whereas little or no staining for OPN or bone sialoprotein (BSP) was observed in nonpermeabilized cells. In permeabilized perfusion osteoclasts and multinucleated osteoclasts, staining for OPN and CD44 was prominent in cell processes, including filopodia and pseudopodia. Confocal microscopy revealed a high degree of colocalization of OPN with CD44 in motile osteoclasts. In cells treated with cycloheximide (CHX), perinuclear staining for OPN and BSP was lost, but iOPN staining was retained within cell processes. In osteoclasts generated from the OPN-null and CD44-null mice, cell spreading and protrusion of pseudopodia were reduced and cell fusion was impaired. Moreover, osteoclast motility and resorptive activity were significantly compromised. Although the area resorbed by OPN-null osteoclasts could be rescued partially by exogenous OPN, the resorption depth was not affected. These studies have identified an intracellular form of OPN, colocalizing with CD44 in cell processes, that appears to function in the formation and activity of osteoclasts.     

Osteopontin is a negative regulator of proliferation and differentiation in MC3T3-E1 pre-osteoblastic cells

Osteopontin (OPN) is an important mediator of bone remodeling. However, the role of OPN in the process of bone formation is not fully understood. In previous studies, we have shown that MC3T3-E1 pre-osteoblastic cells at higher passage number exhibited weakened osteogenic capacity and elevated OPN mRNA expression. In this work, we investigated the role of OPN on proliferation and differentiation of low-passage MC3T3-E1 cells by studying stable cell lines overexpressing either OPN mRNA or its antisense RNA. Overexpression was verified by both Northern and Western blot analyses. Overexpression of OPN markedly inhibited proliferation as determined by daily cell counts, while overexpression of antisense RNA stimulated cellular proliferation. We also examined the effect of OPN level on BMP-2-induced alkaline phosphatase activity. Overexpression of OPN inhibited BMP-2 responsiveness while overexpression of antisense RNA enhanced the effect of BMP-2 on alkaline phosphatase activity. Increased OPN expression also caused decreases in expression of osteocalcin and bone sialoproteins while a reduction of OPN level caused the opposite. Furthermore, endogenous OPN expression in response to BMP-2 exhibited a biphasic pattern, that is, it was initially inhibited and then enhanced by the treatment of BMP-2, indicating that OPN might function as a negative feedback regulator for osteoblastic differentiation. Finally, overexpression of OPN inhibited mineral deposition. In contrast, overexpression of antisense RNA enhanced mineral deposition. These results indicate that OPN is a negative regulator of proliferation and differentiation in MC3T3-E1 cells.     

Interactions between osteopontin and vascular endothelial growth factor: Implications for skeletal disorders

Osteopontin (OPN) and vascular endothelial growth factor (VEGF) are characterized by a convergence in function for maintaining the homeostasis of the skeletal and renal systems (the bone–renal–vascular axis regulates bone metabolism). The two cytokines contribute to bone remodeling, dental healing, kidney function, and the adjustment to microgravity. Often, they are co-expressed or one molecule induces the other, however, in some settings OPN-associated pathways and VEGF-associated pathways are distinct. In bone remodeling, OPN and VEGF are regulated under the influence of growth factors and hormones, hypoxia and inflammation, the micro-environment, and various physical forces. Their abundance can be affected by drug treatment. OPN and VEGF are variably associated with kidney disease. Their balanced levels are critical for restoring endothelial cell function and ameliorating the adverse effects of microgravity. Here, we review the relevant 83 papers of 257 articles published, and listed in PubMed under the key words OPN and VEGF.     

Spatial and temporal distribution of CD44 and osteopontin in fracture callus

The multifunctional adhesion molecule CD44 is a major cell-surface receptor for hyaluronic acid (HUA). Recent data suggest that it may also bind the ubiquitous bone-matrix protein, osteopontin (OPN). Because OPN has been shown to be a potentially important protein in bone remodelling, we investigated the hypothesis that OPN interactions with the CD44 receptor on bone cells participate in the regulation of the healing of fractures. We examined the spatial and temporal patterns of expression of OPN and CD44 in healing fractures of rat femora by in situ hybridisation and immunohistochemistry. We also localised HUA in the fracture callus using biotinylated HUA-binding protein. OPN was expressed in remodelling areas of the hard callus and was found in osteocytes, osteoclasts and osteoprogenitor cells, but not in cuboidal osteoblasts which were otherwise shown to express osteocalcin. The OPN signal in osteocytes was not uniformly distributed, but was restricted to specific regions near sites where OPN mRNA-positive osteoclasts were attached to bone surfaces. In the remodelling callus, intense immunostaining for CD44 was detected in osteocyte lacunae, along canaliculi, and on the basolateral plasma membrane of osteoclasts, but not in the cuboidal osteoblasts. HUA staining was detected in fibrous tissues but little was observed in areas of hard callus where bone remodelling was progressing. Our findings suggest that OPN, rather than HUA, is the major ligand for CD44 on bone cells in the remodelling phase of healing of fractures. They also raise the possibility that such interactions may be involved in the communication of osteocytes with each other and with osteoclasts on bone surfaces. The interactions between CD44 and OPN may have important clinical implications in the repair of skeletal tissues.     

Breast cancer osteomimicry and its role in bone specific metastasis; an integrative,systematic review of preclinical evidence

Metastasis accounts for most of the deaths from breast cancer and the preference of invasive breast cancer metastasising to bone has been widely reported. However, the biological basis of breast cancer osteotropism is not fully understood. This paper provides, for the first time, an integrative, systematic review of evidence of molecular factors that have functional roles in the homing of metastatic breast cancer to the bone.Pubmed, Web of Science and EBSCOhost were searched using keywords and synonyms for molecular, metastasis, breast cancer and bone to identify articles published between January 2004 and August 2016. 4491 potentially relevant citations were retrieved. 63 articles met the inclusion criteria, which were primary studies reporting evidence of molecular factors that have functional roles in predisposing breast cancer bone metastasis in vivo. 12 of those 63 articles that additionally met quality criteria were included in the review. Extracted data were tabulated and key findings that indicated biological mechanisms involved in breast cancer metastasis to bone were synthesised.15 proteins expressed by breast cancer cells were identified as factors that mediate breast cancer bone metastasis: ICAM-1, cadherin-11, osteoactivin, bone sialoprotein, CCN3, IL-11, CCL2, CITED2, CXCR4, CTGF, OPN, CX₃CR1, TWIST1, adrenomedullin and Enpp1. Upregulation or overexpression of one or more of them by breast cancer cells resulted in increased breast cancer metastasis to bone in vivo, except for CCL2 where bone-metastatic cells showed a reduced expression of this factor. All factors identified, here expressed by breast cancer cells, are proteins that are normally expressed in the bone microenvironment and linked to physiologic bone functions. All have a functional role in one of more of the following: cell proliferation and differentiation, bone mineralization and remodelling, cell adhesion and/or chemokine signalling. Six of them (cadherin-11, ICAM-1, OPN, CX₃CR1, CCN3 and osteoactivin) have a reported function in cell adhesion and another eight (CCN3, osteoactivin, Enpp1, IL-11, CTGF, TWIST1, adrenomedullin and CITED2) are reported to be involved in cell proliferation and differentiation.This review collates and synthesises published evidence to increase our understanding of the biology of breast cancer osteomimicry in the development of bone metastasis. Findings of this review suggest that changes in expression of proteins in breast cancer cells that confer osteomimicry facilitate homing to bone to enable the development of bone metastasis.     

Impaired angiogenesis, early callus formation, and late stage remodeling in fracture healing of osteopontin-deficient mice.

OPN is an ECM protein with diverse localization and functionality. The role of OPN during fracture healing was examined using wildtype and OPN(-/-) mice. Results showed that OPN plays an important role in regulation of angiogenesis, callus formation, and mechanical strength in early stages of healing and facilitates late stage bone remodeling and ECM organization. INTRODUCTION: Osteopontin (OPN) is an extracellular matrix (ECM) protein with diverse localization and functionality that has been reported to play a regulatory role in both angiogenesis and osteoclastic bone remodeling, two vital processes for normal bone healing. MATERIALS AND METHODS: Bone repair in wildtype and OPN(-/-) mice was studied using a femoral fracture model. microCT was used for quantitative angiographic measurements at 7 and 14 days and to assess callus size and mineralization at 7, 14, 28, and 56 days. Biomechanical testing was performed on intact bones and on fracture specimens at 14, 28, and 56 days. Histology and quantitative RT-PCR were used to evaluate cellular functions related to ECM formation and bone remodeling. RESULTS: OPN deficiency was validated in the OPN(-/-) mice, which generally displayed normal levels of related ECM proteins. Intact OPN(-/-) bones displayed increased elastic modulus but decreased strength and ductility. Fracture neovascularization was reduced at 7 but not 14 days in OPN(-/-) mice. OPN(-/-) mice exhibited smaller fracture calluses at 7 and 14 days, as well as lower maximum torque and work to failure. At 28 days, OPN(-/-) mice had normal callus size but a persistent reduction in maximum torque and work to failure. Osteoclast differentiation occurred normally, but mature osteoclasts displayed reduced functionality, decreasing late stage remodeling in OPN(-/-) mice. Thus, at 56 days, OPN(-/-) fractures possessed increased callus volume, increased mechanical stiffness, and altered collagen fiber organization. CONCLUSIONS: This study showed multiple, stage-dependent roles of OPN during fracture healing. We conclude that OPN deficiency alters the functionality of multiple cell types, resulting in delayed early vascularization, altered matrix organization and late remodeling, and reduced biomechanical properties. These findings contribute to an improved understanding of the role of OPN in vivo and provide new insight into mechanistic control of vascularization and bone regeneration during fracture repair.     

TRACP as an osteopontin phosphatase.

TRACP is synthesized as a latent proenzyme requiring proteolytic processing to attain maximal phosphatase activity. Excision of an exposed loop domain abolishes the interaction between the loop residue Asp146 and a ligand to the redox-sensitive iron of the active site, most likely Asn91, providing a mechanism for the enzyme repression. Both cathepsin K and L efficiently cleave in the loop domain and activate the latent enzyme, and we propose that cathepsin K acts as a physiological activator of TRACP in osteoclasts, whereas cathepsin L might fulfill a similar role in different types of macrophages. Considering the rather broad substrate specificity of TRACP, a tight regulation of its activity in the cell appears warranted. Besides proteolytic cleavage, the enzyme should need a specific local environment with a slightly acidic pH and reducing equivalents to keep the enzyme fully active. Cellular subcompartments where these required conditions prevail are potential subcellular site(s) of TRACP action. Of bone phosphoproteins shown to be substrates for TRACP, both osteopontin and bone sialoprotein are colocalized with TRACP in the resorption lacuna of the osteoclasts, and dephosphorylation of OPN impair its ability to promote adhesion as well as migration of osteoclasts in vitro. A role for TRACP as an osteopontin phosphatase in bone is therefore suggested. The expression of TRACP as well as OPN in other tissues with possible interactions between the two could suggest a more general function for TRACP as a regulator of OPN phosphorylation and bioactivity.