破骨细胞的研究进展

健康成人的骨骼在不断地重建，旧骨吸收和新骨形成处于动态平衡状态，破骨细胞在骨骼的形成和骨量的调节方面起着关键作用。近年来，破骨细胞的研究取得了相当大的进展。在破骨细胞增殖和分化过程中RANKL和M—CSF起到了重要的作用。骨吸收过程中破骨细胞与骨基质接触，在它自身与骨表面之间形成一个独立的微环境。破骨细胞对于骨的识别受到整合素的调控。PU．1基因、转录因子c-Fos、Fra-1、c-Jun可以通过调节破骨细胞前体的分化和成熟发挥吸收骨的作用。通过来源于脾干细胞的破骨细胞样细胞的诱导生成及其培养，可以获得大量的破骨细胞，从而用于实验室内分子生物学研究。     

唑来膦酸盐治疗Paget病的研究进展

Paget病,以骨骼一个或多个区域破骨细胞介导的骨吸收增加伴有骨骼修复不良,进而导致骨重建失调和骨转换增加为主要特征.发病具有一定的年龄和地域差异,我国少见.其发病受环境和遗传的影响.目前,双膦酸盐是Paget病的主要治疗药物.通过多种途径抑制骨吸收从而达到治疗目的.唑来膦酸盐是第三代双膦酸盐,给药方式为单剂注射,临床实验证明能快速持久地缓解病情,具有高效性和安全性,并能提高患者生活质量,具有良好的应用前景.     

骨髓间充质干细胞成骨分化中信号转导途径与雌激素受体的关系

<正>妇女在绝经后由于体内雌激素生成及分泌减少,骨髓间充质干细胞(BMSCs)成骨分化能力减弱,导致成骨细胞生成减少,骨骼不能对适度负荷产生足够的适应性骨重建,容易引起骨质疏松,甚至发生骨折。雌激素可以通过直接调节、旁分泌和细胞凋亡等机制作用于成骨细胞和破骨细胞而发挥作用,促进成骨细胞及抑制破骨细胞增殖,影响骨代谢,防治骨质疏松〔1〕。对于预防及治疗绝经后妇女骨质疏松,保持体内雌激素水平尤为重要〔2〕。     

唑来膦酸盐治疗Paget病的研究进展

Paget病,以骨骼一个或多个区域破骨细胞介导的骨吸收增加伴有骨骼修复不良,进而导致骨重建失调和骨转换增加为主要特征。发病具有一定的年龄和地域差异,我国少见。其发病受环境和遗传的影响。目前,双膦酸盐是Paget病的主要治疗药物。通过多种途径抑制骨吸收从而达到治疗目的。唑来膦酸盐是第三代双膦酸盐,给药方式为单剂注射,临床实验证明能快速持久地缓解病情,具有高效性和安全性,并能提高患者生活质量,具有良好的应用前景。     

p38丝裂素活化蛋白激酶在氟骨症发病机制中的作用

适量的氟对人体具有重要的生理功能,但长期摄入过量的氟则可能引起慢性全身中毒性病变,即慢性氟中毒[1].氟中毒损伤各个系统的器官组织,尤以损伤骨骼和牙齿最为严重,表现为氟斑牙和氟骨症.其病理表现主要是骨形成和骨吸收平衡破坏,骨转换加速[2],成骨细胞与破骨细胞相互调节组成了持续不断的骨重建过程.长期小剂量氟可以促进骨形成,大剂量则可引起骨质疏松或骨质硬化[3].     

骨细胞与骨代谢的关系

骨细胞呈星形或树突状,是骨中数量最丰富的细胞.其作为机械应力感受细胞,通过产生一些调节成骨细胞和破骨细胞活性的因子参与骨组织的改建.骨细胞凋亡是骨质疏松发病机制之一,而骨细胞蛋白产物抑骨素、成纤维细胞生长因子23(FGF23)、牙本质基质蛋白1(DMP1)等在维持骨正常代谢中起重要作用.因此,骨细胞与骨代谢之间关系密切.对骨细胞凋亡及其蛋白产物的进一步研究,可为防治骨代谢疾病提供新思路和新的药物靶点.     

鸢尾素参与骨稳态调节的研究进展

<正>骨骼由细胞(成骨细胞、破骨细胞和骨细胞)和细胞外基质组成^[1],具有机械支持、肌肉附着、钙磷储存等功能。骨骼的正常代谢对矿物质稳态、骨骼结构的完整性及功能状态的维持至关重要。骨稳态是成骨细胞介导的骨形成和破骨细胞介导的骨吸收之间的动态平衡。骨稳态失衡是导致绝经后及老年性骨质疏松症、骨关节炎等多种骨骼疾病的根本原因之一。鸢尾素(irisin)是一种肌源性因子，     

成骨细胞与破骨细胞的相互作用对骨重塑的调节

骨骼是一个动态活性组织,它通过持续的重塑来维持其矿化平衡及自身的结构完整。在骨重塑的过程中,协调成骨细胞,骨细胞和破骨细胞之间的活性,能保持骨重塑过程的动态耦联平衡,其中成骨细胞（骨形成功能）和破骨细胞（骨吸收功能）在骨重塑过程中起关键作用。成骨细胞和破骨细胞之间的相互调节在骨重塑过程实现骨形成和骨吸收平衡的基础。两组细胞实现细胞间相互作用主要有三种方式：直接接触,分泌旁分泌因子及细胞与骨基质作用,成骨细胞和破骨细胞之间3种相互作用方式对骨重塑过程起重要调节作用。     

P2X7受体介导骨质疏松症的机制研究进展

骨质疏松症是以骨吸收和骨重建的偶联出现缺陷,导致人体的钙磷代谢不平衡,骨密度逐渐减少的全身代谢性疾病。嘌呤能离子通道型7（P2X7）受体广泛表达在各种骨细胞上,用于调节骨骼系统连续的吸收和重建。P2X7受体激活与破骨细胞的形成和再吸收功能,成骨细胞的分化有关,还可通过在炎症反应期间刺激免疫细胞来影响骨质流失。本文回顾了近年来P2X7受体参与骨质疏松症的相关研究进展,为骨质疏松症的发病机制及新型药物研发提供依据。     

嘌呤能离子通道型受体7介导骨质疏松症机制的研究进展

骨质疏松症是因骨吸收和骨重建的偶联出现缺陷,导致人体的钙磷代谢不平衡、骨密度逐渐减少的全身代谢性疾病。嘌呤能离子通道型受体7(P2X7R)广泛表达在各种骨细胞上,用于调节骨骼系统连续的吸收和重建。P2X7R激活与破骨细胞的形成和再吸收功能及成骨细胞的分化有关,还可通过在炎症反应期间刺激免疫细胞来影响骨质流失。本文回顾了近年来P2X7R参与骨质疏松症的相关研究进展,为骨质疏松症的发病机制及新型药物研发提供依据。     

骨细胞与骨代谢的关系

骨细胞呈星形或树突状,是骨中数量最丰富的细胞。其作为机械应力感受细胞,通过产生一些调节成骨细胞和破骨细胞活性的因子参与骨组织的改建。骨细胞凋亡是骨质疏松发病机制之一,而骨细胞蛋白产物抑骨素、成纤维细胞生长因子23（FGF23）、牙本质基质蛋白1（DMP1）等在维持骨正常代谢中起重要作用。因此,骨细胞与骨代谢之间关系密切。对骨细胞凋亡及其蛋白产物的进一步研究,可为防治骨代谢疾病提供新思路和新的药物靶点。     

The Osteocyte as an Orchestrator of Bone Remodeling: An Engineer’s Perspective

Bone is adapted to mechanical loading. The trabeculae in cancellous bone and the osteons in cortical bone are aligned to the mechanical loading direction. Our bones are constantly remodeled by bone-resorbing osteoclasts and bone-forming osteoblasts, cooperating in so-called basic multicellular units or BMUs. In cortical bone, osteoclasts dig tunnels through solid bone, while in cancellous bone, they dig trenches across the trabecular surface. Osteoblasts fill these tunnels and trenches, creating osteons and hemi-osteons, respectively. How mechanical forces guide these cells is still uncertain, but mechanosensitive osteocytes are believed to orchestrate bone remodeling by sending signals to the cells at the bone surface. Computer simulations have demonstrated that local remodeling regulated by mechanosensitive osteocytes indeed produces load-aligned trabeculae and osteons. The strains around a BMU resorption cavity are concentrated at the lateral sides, away from the loading axis. Strain-induced osteocyte signals from these regions likely repel osteoclasts, forcing them to resorb bone in the loading direction, and at the same time, such signals could recruit osteoblasts to start bone formation. Thus, mechanosensitive osteocytes likely regulate the steering of and coupling within BMUs. A region of osteocyte death (therefore, lacking osteoclast-repelling signals) near the path of the BMU redirects its course to resorb this region. This may provide a mechanism for damage removal, because osteocyte death is associated with microdamage. BMUs may also function with disuse-induced osteocyte signals that recruit osteoclasts to the relatively unloaded region in front of the BMU and inhibit osteoblastic bone formation by osteoblast-inhibiting signals such as sclerostin when the tunnel or trench is sufficiently filled.     

Osteocyte function, osteocyte death and bone fracture resistance

The function of the most numerous cell in bone, the osteocyte, has until recently been mysterious and at times controversial. There is now an emerging consensus that osteocytes modulate signals arising from mechanical loading and so direct the appearance and disappearance of bone tissue at the microscopic level, which allows bone as an organ both to grow and to adapt efficiently to the body's mechanical needs for strength with lightness. Osteocytes appear to use some molecular signalling pathways that are familiar from other tissues, such as the generation of nitric oxide and prostaglandins as well as directing cell-cell communication via gap junctions. They may also direct the removal of damaged or redundant bone through mechanisms linked to their own apoptosis or via the secretion of specialised cellular attachment proteins such as osteopontin. Osteocytes possess receptors for parathyroid hormone/parathyroid hormone related peptide and both oestrogen receptors alpha and beta. They also express molecules which in nerve cells are involved with glutamate neuro-transmission. At least some of these receptors and their ligands may regulate osteocyte apoptosis and modulate osteocyte signalling.     

Mechanisms of action of antiresorptive therapies of postmenopausal osteoporosis

In the treatment of osteoporosis, the aim of the antiresorptive therapy is to restore bone density by decreasing bone remodeling. The process of bone remodeling plays a role in plasma calcium homeostasis and serves to modify bone architecture in order to meet changing mechanical needs, to maintain osteocyte viability, and to repair microdamage in bone matrix. Estrogen deficiency results in a number of detrimental effects on bone, including suppression of osteocyte survival as well as impairment of osteoblast response to mechanical stimuli and repair of ageing bone. In this review, effects of available antiresorptive therapies on endocrine regulations of bone metabolism in postmenopausal osteoporosis are compared. The aim of antiresorptive treatment is to ensure adequate bone remodeling, reparation of microdamage of bone, and increased bone strength. Ideally, this effect should be maintained long-term. Several agents are approved for the treatment of osteoporosis. Calcitonin transiently inhibits osteoclast activity without decreasing osteoblast collagen synthesis. Aminobisphosphonates decrease bone remodeling by decreasing osteoclast activity and by inducing osteoclast apoptosis. This allows more time for secondary mineralization to proceed to completion in the existing bone tissue mass, so increasing the mechanical resistance of bone to loading. Estrogens and raloxifene (a selective estrogen receptor modulator that acts as an estrogen agonist in bone) suppress bone remodeling to the premenopausal range, maintaining the function of osteoblasts and osteocytes. In the placebo-controlled osteoporosis treatment trials, all the above treatments reduced the risk of fractures. Raloxifene therapy was also associated with a favorable or neutral effect in the cardiovascular system, and a reduced incidence of breast cancer. Selection of appropriate drug for treatment of postmenopausal osteoporosis should take into account the long-term effect of the antiresorptive agent on bone. Moreover, the effects on other tissues ++should also be considered, and this encompasses both safety concerns, as well as the potentially beneficial effects on other tissues. Further investigation is needed to evaluate the different modes of action of these agents, and their long-term effects on bone and other tissues.     

Osteocytes: Mechanosensors of Bone and Orchestrators of Mechanical Adaptation

Significant progress has been made in the field of mechanotransduction in bone cells. The knowledge about the role of osteocytes as the professional mechanosensor cells of bone as well as the lacuno-canalicular porosity as the structure that mediates mechanosensing is increasing. New insights might result in a paradigm for understanding the bone formation response to mechanical loading, and the bone resorption response to disuse. Under physiological loading conditions the strain-derived flow of interstitial fluid through the lacuno-canalicular porosity seems to mechanically activate the osteocytes, which subsequently alter the bone remodeling activity of osteoblasts and/or osteoclasts. Fatigue loading results in local microdamage, disruption of normal flow patterns, and osteocyte apoptosis. Apoptotic osteocytes likely attract osteoclasts to resorb the damaged bone. This concept allows explanation of local bone gain and loss, as well as remodeling in response to fatigue damage, as processes supervised by mechanosensitive osteocytes. Uncovering the cellular and mechanical basis of the osteocyte’s response to loading would greatly contribute to our understanding of the cellular basis for bone remodeling, and could contribute to the discovery of new treatment modalities for bone mass disorders, such as osteoporosis.     

The structural and biomechanical basis of the gain and loss of bone strength in women and men.

Structural failure (fracture) is a problem in biomechanics. Its solution resides, in part, in identifying the material and structural properties of bone that determine its mechanical resistance to structural failure. Bones must be stiff so that they do not bend when loaded, otherwise movement against gravity would not be possible. However, bones must also be flexible, otherwise their ability to absorb energy by elastic and plastic deformation will decrease and the energy imparted will be dissipated only by microdamage or complete fracture. Thus, failure may occur if bones deform too much (exceeding their peak strain) or too little (exceeding their peak stress). Phylogeny and ontogeny make bone "just right" for the functions it is predicted to perform, but the genetic material was not warned about the increased longevity the female enjoys after ovarian failure. Age-related and menopause-related abnormalities in bone remodeling produce loss of the material and structural properties that no longer keep bone "just right". High remodeling reduces the mineral content of bone tissue resulting in loss of stiffness (resistance to shortening in compression and lengthening in tension when loaded). Sex hormone deficiency increases the volume of bone resorbed and reduces the volume of bone formed in each BMU. Solutions to the biomechanic problem will emerge provided that the material and structural properties of bone that determine its strength are measured and studied. Drugs are available to reduce remodeling rate so that there is more time for completion of secondary mineralization to restore bone stiffness. If remodeling is suppressed too much the production of microdamage may increase as homogeneous and highly mineralized bone is less resistant to microdamage progression while reduced remodeling targeted to microdamage may result in microdamage accumulation. Drugs are available to reduce osteoclastic bone resorption and increase osteoblastic bone formation, which together will restore bone balance in the BMU and so prevent further loss of bone mass, prevent thinning and loss of trabeculae, thinning of cortices, and progression of porosity. These approaches prevent the progression of fragility but will not restore bone architecture. Even if a positive BMU balance is achieved, drugs that reduce remodeling are unlikely to reverse the structure damage. Slow remodeling means there are too few remodeling foci depositing their small net positive bone volume to progressively thicken cortices or trabeculae. Agents that are anabolic, that increase bone formation on the periosteal and endosteal surfaces are needed to restore the structure of bone. Other articles in this volume address this challenge. We do not understand the proportional contributions made by differences in bone size, cortical thickness, trabecular number, thickness, connectivity, tissue mineral content, microdamage burden, osteocyte density, porosity, to differences in spine and hip fracture rates within a sex, between sexes, between races, or between treatment, and control arms in clinical trials. The challenge for the future is to measure these specific materials and structural determinants of bone strength. Whether a combination of these material and structural properties will more accurately identify women likely to sustain fractures, or improve approaches to drug therapy is unknown. The quest to eliminate fragility fractures is a distant horizon seen through a glass darkly at this time.     

软骨下骨成骨细胞在骨性关节炎中的作用与机制

骨性关节炎是一种骨组织代谢疾病,软骨下骨成骨细胞直接参与骨性关节炎的病理过程。成骨细胞表达异常的生物学表型与软骨下骨结构和功能改变密切相关,其可使软骨承受更高的应力;软骨下骨成骨细胞产生的代谢调节因子通过骨和软骨间微结构直接促进软骨细胞退变。免疫和脂类代谢通过成骨细胞调节骨组织代谢,参与骨性关节炎病变过程。进一步阐明软骨下骨成骨细胞在骨性关节炎病变过程中的作用和机制,可为骨性关节炎研究和治疗提供新方法和思路。     

The effects of antifracture therapies on the components of bone strength: assessment of fracture risk today and in the future

OBJECTIVE: To summarize the current knowledge regarding the impact of the most common antifracture medications on the various determinants of bone strength. METHODS: Relevant English-language articles acquired from Medline from 1966 to January 2005 were reviewed. Searches included the keywords bone AND 1 of the following: strength, remodeling, microcrack, structure, mineralization, collagen, organic, crystallinity, osteocyte, porosity, diameter, anisotropy, stress risers, or connectivity AND alendronate, estrogen, etidronate, hormone replacement therapy, parathyroid hormone, risedronate, OR teriparatide. Abstracts from relevant conference proceedings were also reviewed for pertinent information. RESULTS: Antiresorptive therapies increase bone strength through decreasing bone turnover. This lower bone turnover results in a higher mean mineralization and decreases the number of active resorption pits within bone at any given time. These resorption pits are speculated to be areas of focal weakness and a higher number of them would, if all other things were equal, result in greater fragility. Parathyroid hormone therapy increases the rate of bone remodeling, which introduces many resorption pits, but this source of strength loss is thought to be compensated by rapid increases in bone mass. CONCLUSIONS: Both the antiresorptives, particularly bisphosphonates, and the parathyroid hormone therapy increase bone strength; however, the changes that are elicited to achieve this differ significantly.     

Evaluation of bone quality in terms of degree of mineralization

Quantification of degree of mineralization has recently drawn considerable attention as an evaluation method of bone quality. Degree of mineralization of bone is a main determinant factor for tissue material property of bone, and also closely associated with bone remodeling, fatigue process, and mechanical environment of bone.