骨细胞的力学感受器

骨细胞是骨骼中最丰富和寿命最长的细胞,是骨重建的调节器。骨细胞在内分泌调节和钙磷酸盐代谢中发挥重要作用,也是力学刺激的主要响应者,感知力学刺激以直接或间接的方式对刺激做出反应。骨细胞中的力学转导是一个复杂而精细的调节过程,涉及细胞与其周围环境、相邻细胞以及细胞内部不同功能的力学感受器之间的相互作用。目前已知的骨细胞主要力学感受器包括初级纤毛、Piezo离子通道、整合素、细胞外基质以及基于连接蛋白的细胞间连接。这些力学感受器在骨细胞中发挥着至关重要的作用,它们能够感知并转导力学信号,进而调节骨稳态。本文对5种力学感受器进行系统的介绍,以期为理解骨细胞如何响应力学刺激和维持骨组织稳态提供新的视角和认识。     

初级纤毛/鞭毛转运系统介导力学反应性信号通路促骨髓基质干细胞成骨分化

背景：目前已证实力学刺激可以促进骨髓基质干细胞成骨分化，但其机制未完全明了。初级纤毛是重要的力学感受器并调控TGF-β1/BMP-2/SMAD等多种信号通路，很可能是骨髓基质干细胞力学调控的重要靶点。目的：探讨流体剪切力对骨髓基质干细胞成骨分化的影响及机制。方法：将大鼠骨髓基质干细胞分为对照组、力学刺激组(通过摇床施加流体剪切力学干预)、力学刺激+IFT88沉默组(力学刺激+使用siRNA沉默IFT88表达)，干预24 h后，采用qRT-PCR检测转化生长因子β1、骨形成蛋白2的表达、Western blot检测磷酸化SMAD2/3蛋白的表达，初级纤毛免疫荧光染色及形态学分析。结果与结论：剪切力刺激可促进骨髓基质干细胞的初级纤毛表达，转化生长因子β1及骨形成蛋白2基因转录激活，提高磷酸化SMAD2/3蛋白表达。siRNA干扰初级纤毛生成后，这一力学反应效应明显减低。骨髓基质干细胞的初级纤毛面积改变比值与转化生长因子β1及骨形成蛋白2基因转录增高比例具有Spearman相关性。结果表明：初级纤毛/鞭毛转运系统介导了流体剪切力反应性的TGF-β1/BMP-2/SMAD信号通路激活，促进骨髓...     

雌激素受体在骨生长、代谢及其力学响应中的作用和机制

力学信号在骨组织的生长、重建和疾病治疗中发挥着重要的作用。近年来的研究发现雌激素受体(estrogenreceptor,ER)能介导雌激素效应调节骨组织细胞的增殖、凋亡以及功能活性,从而影响骨形成和骨吸收,在骨组织生长、骨重建中发挥重要作用;同时参与骨组织及其细胞对力学刺激的响应过程。骨组织响应力学刺激的效应要受到ER数量和(或)功能活性的影响。这些研究提示了力学刺激和雌激素可能通过一些共同的信号通路来调节骨组织细胞的功能活性。本文着重关注ER在骨组织及其力学响应中的作用和机制。     

机体衰老对骨细胞力学响应的影响

骨骼是一个动态变化的器官,骨细胞的形态、结构和功能随力学刺激大小、方向、形式的不同而发生变化。适当的力学刺激是维持骨形成和骨吸收动态平衡的关键。随着年龄的增加,骨组织衰老会引起包括骨组织微环境、骨细胞形态、骨细胞内信号通路等在内的一系列变化,使骨骼力学响应能力减弱,进而引起骨质疏松等多种疾病。因此,研究衰老如何影响骨细胞的力学响应具有重要意义。重点讨论机体衰老对骨细胞力学响应的影响。     

载荷作用下骨细胞分泌因子对成骨细胞和破骨细胞的调节

骨细胞是骨组织主要的力学感受及转导细胞,它们通过众多突触结构相互连接,形成庞大的骨稳态细胞调控网络,联系着成骨细胞、破骨细胞等骨基质表面细胞。骨细胞通过旁分泌途径影响成骨细胞骨形成和破骨细胞骨吸收来调节骨代谢,维持骨更新。针对骨细胞在受到力学刺激后分泌或释放的一些信号分子或蛋白因子对成骨细胞和破骨细胞生长分化的影响,本文综述近年来关于受力学刺激的骨细胞如何与成骨/破骨细胞进行通讯,为骨细胞生物力学研究提供新思路。     

应力环境与骨折愈合

骨组织对应力刺激有良好的适应性，骨折愈合的好坏与其力学环境密切相关。接骨板固定、骨外固定的力学性能不同，构成的力学环境有异，因而对骨折愈合的影响亦不相同。     

力学刺激通过microRNA调控骨重建的研究进展

骨骼结构完整性和骨量的维持需要一定的力学刺激。研究表明,力学刺激可通过调控多种调节因子(例如激素、转录因子和信号分子等)参与骨重建过程。力学刺激可以通过调控微小RNA(microRNA,miRNA)表达在骨重建过程中起着至关重要的作用。然而,受力学刺激调控的miRNA在骨重建过程中的作用和机制尚不完全清楚。本文综述受力学刺激调控的miRNA在骨重建过程中的作用及其机制,并强调其在治疗骨质疏松中的潜在应用。     

初级纤毛在关节软骨中的生物力学效应

生物力学因素对于关节软骨的稳态维持具有至关重要的作用。初级纤毛是一种可同时感受力学信号和化学信号的细胞器，并于软骨细胞膜表面也存在有初级纤毛分布。其与多个信号转导通路相关，共同参与软骨细胞表型维持和物质代谢的过程。同时，初级纤毛的异常也关联到多种人类的骨关节类疾病。主要论述初级纤毛在软骨细胞力学微环境中的作用，以及与其他信号通路的交互作用机制，探讨其与骨关节疾病的联系，以期为骨科临床和基础科研提供一定的科学依据。     

力学刺激对成骨细胞作用机制的研究进展

力学环境在维持骨组织正常形态和功能活动中发挥着重要的影响,目前研究采用的细胞生物力学装置模拟了压应力、张应力及流体剪切力等不同应力模式对培养中细胞的作用.并发现成骨细胞对不同类型的力学刺激有不同的感受和应答机制,甲状旁腺素、应力的频率、大小等也影响着力学刺激对成骨细胞的作用效应.     

力学因素对骨髓间充质干细胞成骨分化的影响

近年来,组织工程学领域发展突飞猛进,已被列为一种修复或再生许多组织和器官的方法。骨髓间充质干细胞具有良好的成骨向分化潜能,在骨组织工程领域中具有广阔的应用前景。骨髓间充质干细胞增殖和成骨向分化受多种力学因素的影响,且不同性质的力学刺激对其定向分化的调节作用不尽相同。目前,许多学者致力于深入探讨力学因素影响骨髓间充质干细胞成骨向分化的具体途径,但其调控机制尚未完全明确。本文综述及讨论力学因素对骨髓间充质干细胞所产生的增殖、定向成骨分化等生物学效应的影响及可能涉及的力化学信号转导通路作用机制,以期丰富研究思路     

Development of a 'mechano-active' scaffold for tissue engineering

In this study. we investigate the potential for manipulating bone cell mechanotransducers in tissue engineering. Membrane ion channels such as voltage operated calcium channels (VOCC) have been shown to be a critical component of the bone cell transduction pathway with agonists and inhibitors of this pathway having profound effects on the load signal. By encapsulating a calcium channel agonist with slow release within a poly(L-lactide) (PLLA) scaffold, we can generate a 'mechano-active' scaffold for use in skeletal tissue engineering. PLLA scaffolds with and without a calcium channel agonist, BAY K8644, were seeded with primary human bone cells or the human MG63 bone cell line and cultured for 13 weeks followed by mechanical stimulation with a four-point bending model. Our results show that addition of the agonist for slow release is sufficient to enhance the load-related responses in bone cells within the scaffolds. Specifically, collagen type I expression and the ratio of alkaline phosphatase to protein are elevated in response to cyclical mechanical stimulation of approximately 1000 microstr which is then further enhanced in the mechano-active' scaffolds. As the agonists only act when the calcium channels are open by attenuating the calcium flux, the stimulation is specifically targeted to scaffolds subjected to load either in vitro or ultimately in vivo. Our results suggest that manipulating the VOCC and attenuating the opening of the calcium channels may be an effective technique to amplify matrix production via mechanical stimulation which may be applied to bone tissue engineering and potentially engineering of other load-bearing connective tissues.     

Factors that influence primary cilium length

Almost all mammalian cells carry one primary cilium that functions as a biosensor for chemical and mechanical stimuli. Genetic damages that compromise cilia formation or function cause a spectrum of disorders referred to as ciliapathies. Recent studies have demonstrated that some pharmacological agents and extracellular environmental changes can alter primary cilium length. Renal injury is a well-known example of an environmental insult that triggers cilia length modification. Lithium treatment causes primary cilia to extend in several cell types including neuronal cells;this phenomenon is likely independent of glycogen synthase kinase-3β inhibition. In renal epithelial cell lines, deflection of the primary cilia by fluid shear shortens them by reducing the intracellular cyclic AMP level, leading to a subsequent decrease in mechanosensitivity to fluid shear. Primary cilium length is also influenced by the dynamics of actin filaments and microtubules through the levels of soluble tubulin in the cytosol available for primary cilia extension. Thus, mammalian cells can adapt to the extracellular environment by modulating the primary cilium length, and this feedback system utilizing primary cilia might exist throughout the mammalian body. Further investigation is required concerning the precise molecular mechanisms underlying the control of primary cilium length in response to environmental factors.     

Primary Cilia: Cellular Sensors for the Skeleton

The primary cilium is a solitary, immotile cilium that is present in almost every mammalian cell type. Primary cilia are thought to function as chemosensors, mechanosensors, or both, depending on cell type, and have been linked to several developmental signaling pathways. Primary cilium malfunction has been implicated in several human diseases, the symptoms of which include vision and hearing loss, polydactyly, and polycystic kidneys. Recently, primary cilia have also been implicated in the development and homeostasis of the skeleton. In this review, we discuss the structure and formation of the primary cilium and some of the mechanical and chemical signals to which it could be sensitive, with a focus on skeletal biology. We also raise several unanswered questions regarding the role of primary cilia as mechanosensors and chemosensors and identify potential research avenues to address these questions. Anat Rec, 291:1074–1078, 2008. © 2008 Wiley‐Liss, Inc.     

骨骼肌通过力学刺激对骨重建的影响

骨骼与骨骼肌作为运动系统最重要的组织,两者之间存在密切的联系。骨肌单元的概念提出已久,运动产生的力学负荷将两者紧密地联系在一起。骨骼为骨骼肌施力提供力学支撑,而骨骼肌收缩带动机体的运动。在机体运动过程中,骨骼肌充当力学负荷与骨骼之间的中间媒介,并通过内分泌因子以及力学信号调节骨骼的代谢活动,与机体内持续不断的骨重建密切相关,并维持骨骼良好的结构和功能。主要综述近年来骨骼肌通过对骨骼施加力学刺激影响骨重建作用的研究进展,为预防和治疗骨代谢疾病提供新的思路。     

Effects of substrate characteristics on bone cell response to the mechanical environment

The effect of substrate characteristics on primary human bone cell response to mechanical loading was investigated in this study. The substrates comprised organic and inorganic materials with a range of hydrophilic and hydrophobic features. Substrate surface topography varied from smooth to particulate to porous. It was found that hydrophilic substrates such as borosilicate glass facilitated bone cell adhesion, in contrast to hydrophobic substrates such as poly(L-lactic acid), in which clumps of cells grew unevenly across the substrate surface. All primary bone cells cultured in the various collagen-coated substrates were responsive to mechanical stimulation. The study showed that, at a low strain level of 1000μstrain, mechanical stimulation enhanced bone cell differentiation rather than proliferation. Coating the substrates with collagen type l enhanced cell adhesion and promoted an elongated cell morphology, indicating that the presence of specific binding sites on a substrate may be more important than its hydrophilic properties, regardles of the substrate topography.     

The Primary Cilium of Connective Tissue Cells: Imaging by Multiphoton Microscopy

Although the role of the primary cilium as a sensory organelle in epithelial cells has been elucidated significantly over the past decade, the function of primary cilia in connective tissue cells has been studied less extensively. Primary cilia have been implicated as mechanotransducers in connective tissues, but the mechanisms by which the cells sense loads and convert them to biochemical signals for tissue formation and adaptation are poorly understood. Before hypotheses regarding the function of the primary cilium in connective tissue cells can be tested, methods for quantitation of incidence as well as three‐dimensional visualization of primary cilia with respect to the extracellular matrix (ECM) are needed. The objective of this study was to develop a rapid method for visualizing primary cilia in their native ECM in a wide range of connective tissues. Whole‐mount immunohistochemical and multiphoton microscopy techniques were developed to simultaneously image primary cilia, cell nuclei, and collagen and their relationships to each other in situ. Axonemes of primary cilia projecting into the ECM were successfully visualized in thick sections of growth plate cartilage, tendon, ligament, meniscus, intervertebral disc, and perichondrium. These methodologies will allow analysis of the incidence and three‐dimensional orientation of primary cilia and enable investigation of the role of primary cilia in normal and pathological growth and adaptation in a variety of musculoskeletal tissues. Anat Rec, 291:1062–1073, 2008. © 2008 Wiley‐Liss, Inc.