The BoneXpert Method for Automated Determination of Skeletal Maturity

Bone age rating is associated with a considerable variability from the human interpretation, and this is the motivation for presenting a new method for automated determination of bone age (skeletal maturity). The method, called BoneXpert, reconstructs, from radiographs of the hand, the borders of 15 bones automatically and then computes “intrinsic” bone ages for each of 13 bones (radius, ulna, and 11 short bones). Finally, it transforms the intrinsic bone ages into Greulich Pyle (GP) or Tanner Whitehouse (TW) bone age. The bone reconstruction method automatically rejects images with abnormal bone morphology or very poor image quality. From the methodological point of view, BoneXpert contains the following innovations: 1) a generative model (active appearance model) for the bone reconstruction; 2) the prediction of bone age from shape, intensity, and texture scores derived from principal component analysis; 3) the consensus bone age concept that defines bone age of each bone as the best estimate of the bone age of the other bones in the hand; 4) a common bone age model for males and females; and 5) the unified modelling of TW and GP bone age. BoneXpert is developed on 1559 images. It is validated on the Greulich Pyle atlas in the age range 2–17 years yielding an SD of 0.42 years [0.37; 0.47] 95% conf, and on 84 clinical TW-rated images yielding an SD of 0.80 years [0.68; 0.93] 95% conf. The precision of the GP bone age determination (its ability to yield the same result on a repeated radiograph) is inferred under suitable assumptions from six longitudinal series of radiographs. The result is an SD on a single determination of 0.17 years [0.13; 0.21] 95% conf.      

Effects of osteoprotegerin administration on osteoclast differentiation and trabecular bone structure in osteoprotegerin-deficient mice

Osteoprotegerin (OPG)-deficient mice exhibit severe bone loss including the destruction of growth plate cartilage. Using OPG-deficient mice, we attempted to clarify the differentiation and ultrastructure of osteoclasts located on the destroyed growth plate cartilage and trabecular bone matrix in long bones. In (-/-) homozygous OPG knockout mice, adjacent to the growth plate cartilage, the formation of bone trabeculae without a calcified cartilaginous core resulted in an irregular chondrocyte distribution in the growth plate cartilage. At the metaphyseal ossification center, TRAP-positive osteoclasts showed unusual localization on both type-II collagen-positive cartilage and type-I collagen-positive bone matrix. Osteoclasts located on cartilage matrix lacked a typical ruffled border structure, but formed resorption lacunae. During growth plate cartilage destruction, osteoclasts formed ruffled border structures on bone matrix deposited on the remaining cartilage surfaces. These findings suggest that, in OPG (-/-) mice, osteoclast structure differs, depending on the matrix of either cartilage or bone. Then, we examined the effects of OPG administration on the internal trabecular bone structure and osteoclast differentiation in OPG (-/-) mice. OPG administration to OPG (-/-) mice significantly inhibited trabecular bone loss and maintained the internal trabecular bone structure, but did not reduce the osteoclast number on bone trabeculae. For most osteoclasts, OPG administration caused disappearance or reduction of the ruffled border, but induced neither necrotic nor apoptotic damages. These results suggest that OPG administration is an effective means of maintaining the internal structure and volume of trabecular bone in metabolic bone diseases by inhibition of osteoclastic bone resorption.     

Injectable Biomimetic Hydrogel Guided Functional Bone Regeneration by Adapting Material Degradation to Tissue Healing

The treatment of irregular bone defects remains a clinical challenge since the current biomaterials (e.g., calcium phosphate bone cement (CPC)) mainly act as inert substitutes, which are incapable of transforming into a regenerated host bone (termed functional bone regeneration). Ideally, the implant degradation rate should adapt to that of bone regeneration, therefore providing sufficient physicochemical support and giving space for bone growth. This study aims to develop an injectable biomaterial with bone regeneration-adapted degradability, to reconstruct a biomimetic bone-like structure that can timely transform into new bone, facilitating functional bone regeneration. To achieve this goal, a hybrid (LP-CPC@gelatin, LC) hydrogel is synthesized via one-step incorporation of laponite (LP) and CPC into gelatin hydrogel, and the LC gel degradation rate is controlled by adjusting the LP/CPC ratio to match the bone regeneration rate. Such an LC hydrogel shows good osteoinduction, osteoconduction, and angiogenesis effects, with complete implant-to-new bone transformation capacity. This 2D nanoclay-based bionic hydrogel can induce ectopic bone regeneration and promote ligament graft osseointegration in vivo by inducing functional bone regeneration. Therefore, this study provides an advanced strategy for functional bone regeneration and an injectable biomimetic biomaterial for functional skeletal muscle repair in a minimally invasive therapy.     

Prediction of biomechanical properties of trabecular bone in MR images with geometric features and support vector regression

Whole knee joint MR image datasets were used to compare the performance of geometric trabecular bone features and advanced machine learning techniques in predicting biomechanical strength properties measured on the corresponding ex vivo specimens. Changes of trabecular bone structure throughout the proximal tibia are indicative of several musculoskeletal disorders involving changes in the bone quality and the surrounding soft tissue. Recent studies have shown that MR imaging also allows non-invasive 3-D characterization of bone microstructure. Sophisticated features like the scaling index method (SIM) can estimate local structural and geometric properties of the trabecular bone and may improve the ability of MR imaging to determine local bone quality in vivo. A set of 67 bone cubes was extracted from knee specimens and their biomechanical strength estimated by the yield stress (YS) [in MPa] was determined through mechanical testing. The regional apparent bone volume fraction (BVF) and SIM derived features were calculated for each bone cube. A linear multiregression analysis (MultiReg) and a optimized support vector regression (SVR) algorithm were used to predict the YS from the image features. The prediction accuracy was measured by the root mean square error (RMSE) for each image feature on independent test sets. The best prediction result with the lowest prediction error of RMSE = 1.021 MPa was obtained with a combination of BVF and SIM features and by using SVR. The prediction accuracy with only SIM features and SVR (RMSE = 1.023 MPa) was still significantly better than BVF alone and MultiReg (RMSE = 1.073 MPa). The current study demonstrates that the combination of sophisticated bone structure features and supervised learning techniques can improve MR-based determination of trabecular bone quality.     

A Bifunctional Biomaterial with Photothermal Effect for Tumor Therapy and Bone Regeneration

Malignant bone tumor is one of the major bone diseases. The treatment of such a bone disease typically requires the removal of bone tumor and regeneration of tumor‐initiated bone defects simultaneously. To address this issue, it is required that implanted biomaterials should combine the bifunctions of both therapy and regeneration. In this work, a bifunctional graphene oxide (GO)‐modified β‐tricalcium phosphate (GO‐TCP) composite scaffold combining a high photothermal effect with significantly improved bone‐forming ability is prepared by 3D‐printing and surface‐modification strategies. The prepared GO‐TCP scaffolds exhibit excellent photothermal effects under the irradiation of 808 nm near infrared laser (NIR) even at an ultralow power density of 0.36 W cm^?2, while no photothermal effects are observed for pure β‐TCP scaffolds. The photothermal temperature of GO‐TCP scaffolds can be effectively modulated in the range of 40–90 °C by controlling the used GO concentrations, surface‐modification times, and power densities of NIR. The distinct photothermal effect of GO‐TCP scaffolds induces more than 90% of cell death for osteosarcoma cells (MG‐63) in vitro, and further effectively inhibits tumor growth in mice. Meanwhile, the prepared GO‐TCP scaffolds possess the improved capability to stimulate the osteogenic differentiation of rabbit bone mesenchymal stem cells (rBMSCs) by upregulating bone‐related gene expression, and significantly promote new bone formation in the bone defects of rabbits as compared to pure β‐TCP scaffolds. These results successfully demonstrate that the prepared GO‐TCP scaffolds have bifunctional properties of photothermal therapy and bone regeneration, which is believed to pave the way to design and fabricate novel implanting biomaterials in combination of therapy and regeneration functions.     

Cocrystal Strategy toward Multifunctional 3D‐Printing Scaffolds Enables NIR‐Activated Photonic Osteosarcoma Hyperthermia and Enhanced Bone Defect Regeneration

Malignant bone tumors are one of the major serious diseases in clinic. Inferior reconstruction of new bone and rapid propagation of residual tumor cells are the main challenges to surgical intervention. Herein, a bifunctional DTC@BG scaffold for near‐infrared (NIR)‐activated photonic thermal ablation of osteosarcoma and accelerated bone defect regeneration is engineered by in situ growth of NIR‐absorbing cocrystal (DTC) on the surface of a 3D‐printing bioactive glass (BG) scaffold. The prominent photothermal conversion performance and outstanding bone regeneration capability of DTC@BG scaffolds originate from the precise tailoring of the bandgap between the electron donors and acceptors of DTC and promote new bone growth performance of BG scaffolds. DTC@BG scaffolds not only significantly promote tumor cell ablation in vitro, but also effectively facilitate bone tumor suppression in vivo. In particular, DTC@BG scaffolds exhibit excellent capability in stimulating osteogenic differentiation and angiogenesis, and finally promote newborn bone formation in the bone defects. This research represents the first paradigm for ablating osteosarcoma and facilitating new bone formation through precise modulation of electron donors and acceptors in the cocrystal, which offers a new avenue to construct high‐efficiency therapeutic platforms based on cocrystal strategy for ablation of malignant bone tumor.     

Bioinspired Mineral–Organic Bone Adhesives for Stable Fracture Fixation and Accelerated Bone Regeneration

The use of hydrogel‐based bone adhesives has the potential to revolutionize the clinical treatment of bone repairs. However, severe deficiencies remain in current products, including cytotoxicity concerns, inappropriate mechanical strength, and poor fixation performance in wet biological environments. Inspired by the unique roles of glue molecules in the robust mechanical strength and fracture resistance of bone, a design strategy is proposed using novel mineral–organic bone adhesives for strong water‐resistant fixation and guided bone tissue regeneration. The system leveraged tannic acid (TA) as a phenolic glue molecule to spontaneously co‐assemble with silk fibroin (SF) and hydroxyapatite (HA) in order to fabricate the inorganic–organic hybrid hydrogel (named SF@TA@HA). The combination of the strong affinity between SF and TA along with sacrificial coordination bonds between TA and HA significantly improves the toughness and adhesion strength of the hydrogel by increasing the amount of energy dissipation at the nanoscale. This in turn facilitated adequate and stable fixation of bone fracture in wet biological environments. Furthermore, SF@TA@HA promotes the regeneration of bone defects at an early stage in vivo. This work presents a type of bioinspired bone adhesive that is able to provide stable fracture fixation and accelerated bone regeneration during the bone remodeling process.     

Differentiation and function of osteoclasts cultured on bone and cartilage

We examined the differentiation and resorptive function of osteoclasts (OC) cultured on the slices of calcified bone, decalcified bone and hyaline cartilage, and found that OC differentiation depends on the co-cultured substratum, as well as osteoblast-derived factors. Bone marrow-derived macrophages (BMM) were formed from marrow cells of 5 week old ddY mice and cultured for 3 days on freeze-dried slices of calcified bone, decalcified bone or cartilage, all prepared from rabbit costal bone. BMM cultured on calcified bone slices exhibited tartrate-resistant acid phosphatase (TRAP) activity and were structurally characterized by multinucleation and ruffled border development. However, on decalcified bone slices, BMM seldom became multinucleated and exhibited weak TRAP activity. BMM cultured on cartilage slices were mononuclear, devoid of TRAP activity and structurally resembled mononuclear phagocytes. In SEM observations of co-cultured slices, resorption lacunae were formed only on calcified bone slices, and not on slices of decalcified bone and cartilage. Our results, therefore, indicated that BMM could differentiate into functional OC only on calcified bone slices, suggesting a key role of calcified components in the bone matrix for the terminal OC differentiation. Then, we cultured BMM on the same slices with yeast particles. In cultures with yeast particles, BMM exhibited intense TRAP activity, developed a ruffled border-like structure and formed resorption lacunae even on decalcified bone and cartilage slices. Vacuolar-type H+-ATPase was strongly expressed along the ruffled border membranes of these OC. Only the BMM that had not incorporated yeast particles developed a ruffled border, whereas the BMM that had incorporated yeast particles did not become multinucleated and lacked a ruffled border structure. Thus, our results further suggest that, even on uncalcified substrata, the terminal differentiation of BMM into functional OC is induced by an unidentified external stimulus, which may be contained in the cell membrane of yeast particles.     

Analysis of trabecular bone structure using Fourier transforms andneural networks

Hip fracture due to osteoporosis (OP) and hip osteoarthritis (OA) are both important causes of locomotor morbidity in the elderly population. In osteoporosis, bone mass gradually decreases until the skeleton is too fragile to support the body and a fracture occurs, typically in the femur, wrist or spine. In osteoarthritis, there is a proliferation of bone, leading to a stiffening of the tissue. Current clinical methods for assessment of bone changes in these disorders largely depend on assessing bone mineral density. However, this does not provide any information about bone structure, which is considered to be an equally important factor in assessing bone quality. This paper presents a novel approach for computer analysis of trabecular (or cancellous) bone structure. The technique uses a Fourier transform to generate a “spectral fingerprint” of an image. Principal components analysis is then applied to identify key features from the Fourier transform and this information is passed to a neural network for classification. Testing this on a series of 100 histological sections of trabecular bone from patients with OP and OA and a normal group correctly classified over 90% of the OP group with an overall accuracy of 77%-84%. Such high success rates on a small group suggest that this may provide a simple, but powerful, method for identifying alterations in bone structure     

Ex vivo assessment of trabecular bone structure from three-dimensional projection reconstruction MR micro-images

Magnetic resonance (MR) imaging has recently been proposed for assessing osteoporosis and predicting fracture risks. However, accurate acquisition techniques and image analysis protocols for the determination of the trabecular bone structure are yet to be defined. The aim of this study was to assess the potential of projection reconstruction (PR) MR microscopy in the analysis of the three-dimensional (3-D) architecture of trabecular bone and in the prediction of its biomechanical properties. High-resolution 3-D PR images (41 x 41 x 82 microm3 voxels) of 15 porcine trabecular bone explants were analyzed to determine the trabecular bone volume fraction (Vv), the mean trabecular thickness (Tb.Th), and the mean trabecular separation (Tb.Sp) using the method of directed secants. These parameters were then compared with those derived from 3-D conventional spin-echo microimages. In both cases, segmentation of the high-resolution images into bone and bone marrow was obtained using a spatial adaptive threshold. The contemporary inclusion of Vv, Tb.Th and 1/Tb.Sp in a multiple regression analysis significantly improved the prediction of Young's modulus (YM). The parameters derived from the PR spin-echo images were found to be stronger predictors of YM (R2 = 0.94, p = 0.004) than those derived from conventional spin-echo images (R2 = 0.79, p = 0.051). Our study indicates that projection reconstruction MR microscopy appears to be more accurate than the conventional Fourier transform method in the quantification of trabecular bone structure and in the prediction of its bioimechanical properties. The proposed PR approach should be readily adaptable to the in vivo MRI studies of osteoporosis.     

Effects of ovariectomy on bone morphology in maxillae of mature rats.

Postmenopausal oestrogen deficiency results in bone loss (osteoporosis) in humans and experimental animals. The loss of trabecular bone in the ovariectomized (OVX) rat provides a useful experimental model of post-menopausal osteoporosis. At 5 months after ovariectomy of 3-month-old female rats, the mid and distal femurs and maxillae were dissected and processed for quantitative backscattered electron microscopic examinations. Histomorphometric analysis of femurs in OVX rats showed significant loss in metaphyseal trabecular bone areas compared with sham-operated controls; no significant bone loss was observed in the cortical bone areas of mid-diaphyses in OVX rats. Net bone areas in the maxillae of OVX rats was similar to that of sham-operated controls. Bone structure of maxillae in OVX rats was also similar to that in controls. Our results suggest that, in this animal model of osteoporosis, prominent bone loss occurs mainly in the bone areas formed by endochondral ossification such as distal femurs, but those areas formed by intramembranous ossification such as mid-femurs and maxillae sustained less effects by OVX.     

Bioprinted Scaffold Remodels the Neuromodulatory Microenvironment for Enhancing Bone Regeneration

Herein, a 3D bioprinted scaffold is proposed, containing a calcitonin gene-related peptide (CGRP) and the β-adrenergic receptor blocker propranolol (PRN) as a new method to achieve effective repair of bone defects. By leveraging the neuromodulation mechanism of bone regeneration, CGRP and PRN loaded mesoporous silica nanoparticles are added into a hybrid bio-ink, which initially contains gelatin methacrylate, Poly (ethylene glycol) diacrylate and bone marrow mesenchymal stem cells (BMSCs). Subsequently, the optimized bio-ink is used for 3D bioprinting to create a composite scaffold with a pre-designed micro-nano hierarchical structure. The migration and tube formation of human umbilical vein endothelial cells (HUVECs) can be promoted by the scaffold, which is beneficial to the formation of a new capillary network during the bone repair process. With the release of CGRP from the scaffold, the secretion of neuropeptides by sensory nerves is simulated. Meanwhile, the release of PRN can inhibit the binding process of catecholamine to β-adrenergic receptor, co-promoting the osteogenic differentiation of BMSCs with CGRP and silicon ions, which will effectively enhance bone repair of a critical-sized cranial defect in a rat model. In conclusion, this study provides a promising strategy for bone defect repair by understanding the neuromodulatory mechanisms during bone regeneration.     

Noncompressible Hemostasis and Bone Regeneration Induced by an Absorbable Bioadhesive Self-Healing Hydrogel

Bone bleeding and bone defects arising from trauma or bone tumor resection pose a great threat to patients and they are challenging problems to orthopedic surgeons. Traditional hemostatic materials are not suitable for bone fractures where compression cannot be applied, neither are they effective during surgeries where large amounts of body fluids prevent them from adhering to the large and irregular bone wound sites. This research introduces a catechol-conjugated chitosan (CHI-C) multi-functional hydrogel with adhesion, self-healing, cytocompatibility, hemocompatibility, and blood cell coagulation capacity. The hydrogel can be injected into internal and irregular bleeding sites and bone defective areas, and then rapidly self-heals (within 2 min) to an integrated hydrogel that fully fills the defective sites and strongly sticks to bleeding areas in the presence of body fluids during surgery. In vivo experiments using a rabbit ilium bone defect model demonstrate quick hemostasis after the hydrogel is applied and the blood loss is only ¼ compared to the untreated injuries. In addition, the bone regeneration is not interfered by the hydrogel and the bone defect is no longer visible with disappearance of the hydrogel after 4 weeks. This multi-functional hydrogel is potentially valuable for clinical applications towards tissue adhesion, hemostasis, and bone regeneration.     

Injectable Hydrogel with NIR Light-Responsive,Dual-Mode PTH Release for Osteoregeneration in Osteoporosis

Effective treatments to overcome osteoblast/osteoclast imbalance are the key to achieving desirable bone regeneration for osteoporosis patients. When used for local bone repair, parathyroid hormone (PTH) often leads to either excessive osteoclasts under continuous exposure or insufficient osteoclasts with pulsatile release of PTH. Herein, an injectable multifunctional in situ-generated calcium phosphate nanoparticle (ICPN)-coordinated poly(dimethylaminoethyl methacrylate-co-2-hydroxyethyl methacrylate) (DHCP) hydrogel loaded with PTH for near-infrared (NIR)-stimulated release is developed to achieve bone regeneration in an ovariectomized (OVX) model. Photothermal-responsive poly(N-acryloyl glycinamide-co-acrylamide) PNAm-indocyanine green ICG-PTH microspheres (PIP MSs) endow a dual-mode release system with a sustained release at low concentrations, a pulse release of PTH, and in situ pore formation properties. The PIP MS-encapsulated DHCP hydrogel (DHCP-10PIP/d) is injected into the bone defects of OVX rats. Under NIR irradiation, the localized photothermal effects trigger on-demand PTH release and in situ micropores formation through the gel–sol transition of PIP MSs, and the repeated treatment is harmless to the bioactivity of PTH. This platform can enhance osteoblast and osteoclast activity at the same time both in vitro and in vivo and repair the cranial defects of OVX rats successfully. Overall, this work provides a promising strategy for PTH delivery to repair osteoporotic bone defects.     

Simulation of surface EMG signals for a multilayer volume conductor with a superficial bone or blood vessel

This study analytically describes surface electromyogram (EMG) signals generated by a planar multilayer volume conductor constituted by different subdomains modeling muscle, bone (or blood vessel), fat, and skin tissues. The bone is cylindrical in shape, with a semicircular section. The flat portion of the boundary of the bone subdomain is interfaced with the fat layer tissue, the remaining part of the boundary is in contact with the muscle layer. The volume conductor is a model of physiological tissues in which the bone is superficial, as in the case of the tibia bone, backbone, and bones of the forearm. The muscle fibers are considered parallel to the axes of the bone, so that the model is space invariant in the direction of propagation of the action potential. The proposed model, being analytical, allows faster simulations of surface EMG with respect to previously developed models including bone or blood vessels based on the finite-element method. Surface EMG signals are studied by simulating a library of single-fiber action potentials (SFAP) of fibers in different locations within the muscle domain, simulating the generation, propagation, and extinction of the action potential. The decay of the amplitude of the SFAPs in the direction transversal to the fibers is assessed. The decay in the direction of the bone has a lower rate with respect to the opposite direction. Similar results are obtained by simulating motor unit action potentials (MUAPs) constituted by 100 fibers with territory 5 mm2. M waves and interference EMG signals are also simulated based on the library of SFAPs. Again, the decay of the amplitude of the simulated interference EMG signals is lower approaching the bone with respect to going farther from it. The findings of this study indicate the effect of a superficial bone in enhancing the EMG signals in the transversal direction with respect to the fibers of the considered muscle. This increases the effect of crosstalk. The same mathematical method used to simulate a superficial bone can be applied to simulate other physiological tissues. For example, superficial blood vessels (e.g., basilic vein, brachial artery) can influence the recorded EMG signals. As the electrical conductivity of blood is high (it is of the same order as the longitudinal conductivity in the muscle), the effect on EMG signals is opposite compared to the effect of a superficial bone.     

A Novel Approach to Enhance Bone Regeneration by Controlling the Polarity of GaN/AlGaN Heterostructures

Rapid and effective bone regeneration is still a major challenge in the clinical treatment of various bone diseases. Although recently developed electroactive materials have demonstrated high bone regeneration potential, the instability of the electrical stimulation and the unclear effects of the charge polarity on osteogenic differentiation hinder their clinical applications. In this work, GaN/AlGaN materials with well-controlled polarity are used for the first time to induce endogenous electric stimulation and facilitate bone regeneration. By controlling the direction and magnitude of the piezoelectric and spontaneous polarization in the functional layer (GaN), charged GaN/AlGaN surfaces of opposite polarity, whose zeta potentials are within the range of the physiological potential, are obtained. Compared with N-polarity GaN/AlGaN (with a positively charged surface), Ga-polarity GaN/AlGaN (with a negatively charged surface) nanofilms show rapid and superior bone repair in vivo. In addition, the Ga-polarity GaN/AlGaN hetero-structures significantly promote the attachment, spreading, recruitment, and osteogenic differentiation of bone mesenchymal stem cells in vitro. Moreover, the bone morphogenetic protein-6 (BMP6) expression profile in the early stages of osteogenic differentiation reveals that BMP6 may be an electrically sensitive osteogenic protein. This work sheds light on the application of III-nitride materials in bone regeneration.     

Selenoprotein-Regulated Hydrogel for Ultrasound-Controlled Microenvironment Remodeling to Promote Bone Defect Repair

Abnormal levels of reactive oxygen species (ROS) and the hypoxic microenvironment within bone defects are important factors that impede bone repair processes. Herein, an innovative ultrasound-modulatable hydrogel platform with selenoprotein-mediated antioxidant effects to promote bone injury repair is presented. This hydrogel platform encapsulates oxygen-enriched selene-incorporated thin-shell silicon within methacrylate gelatin (O₂-PSSG). The resultant construct orchestrates the modulation of the bone-defect microenvironment, thereby expediting the course of bone regeneration. Ultrasound (US) is used to regulate the pore size of the hydrogel to release selenium-containing nanoparticles and promote the in situ synthesis of efficient intracellular selenoproteins and hydrogen peroxide consumption. As expected, O₂-PSSG rapidly releases selenocystine ([Sec]₂) under US control to scavenge reactive oxygen species and maintain the homeostasis of bone marrow mesenchymal stem cells (BMSCs). Over time, the action of the system by selenoprotein increases the activation of Wnt/β-catenin pathways and promotes the differentiation of BMSCs. Consequently, O₂-PSSG potentiates the antioxidant proficiency of BMSCs both in vitro and in vivo, alleviates hypoxic environments, promotes osteogenic differentiation, and expedites cranial bone repair in rat models. In summary, this study suggests that the designed and constructed US-responsive antioxidant hydrogel is a promising prospective strategy for addressing bone defects and fostering bone regeneration.     

Regulatory mechanism of osteoclast activation

Osteoclasts are multinucleated, terminally differentiated cells which play an essential role in bone resorption. Osteoclasts exhibit high expression of the alpha(v)beta3 integrin, which binds to a variety of extracellular matrix proteins, including vitronectin, osteopontin and bone sialoprotein. RGD (Aug-Gly-Asp)-containing peptides, RGD-mimetics and blocking antibodies to alpha(v)beta3 integrin were shown to inhibit bone resorption in vitro and in vivo, suggesting that this integrin plays an important role in regulating osteoclast function. A number of signalling molecules were found to be involved in the alpha(v)beta3 integrin-dependent signalling pathway, including c-Src, Pyk2 and p130Cas. Both Pyk2 and p130Cas localize to the sealing zone of actively resorbing osteoclasts, suggesting their role in linking the adhesion of osteoclasts to the bone matrix, to cytoskeletal organization, and to the polarization and activation of these cells for bone resorption. In this article, we review the regulatory mechanism of osteoclast activation.     

Osteoprotegerin administration reduces femural bone loss in ovariectomized mice via impairment of osteoclast structure and function

Osteoprotegerin (OPG) is a novel osteoblast-derived secreted member of the tumour necrosis factor receptor superfamily that inhibits osteoclastogenesis. We examined the effects of OPG administration on the distribution, ultrastructure and vacuolar-type H+-ATPase expression of osteoclasts and resulting trabecular bone loss in the femurs of ovariectomized (OVX) mice. Two-month-old female ddY mice were allocated to the following groups: (1) pretreatment base-line controls; (2) untreated sham-operated controls; (3) untreated OVX; and (4) OPG-administered OVX mice. Postoperatively, OPG (0.3 mg kg(-1) day(-1)) was intraperitoneally administered daily to OVX mice for 7 days. On postoperative day 7, all mice were sacrificed, and the dissected femurs were examined by means of light and immunoelectron microscopy and quantitative backscattered-electron image analysis. Backscattered-electron examination revealed that trabecular bone area/unit medullary area in untreated OVX mice was significantly lower than that of base-line control and sham-operated control mice. Compared with untreated OVX mice, OPG administration to OVX mice significantly increased trabecular bone area, which was similar to that of sham-operated control mice. Surprisingly, the number of TRAP-positive osteoclasts along the trabecular bone surfaces in OPG-administered OVX mice was not significantly decreased compared with that of sham-operated control and untreated OVX mice. Ultrastructurally, OPG administration caused disappearance of ruffled borders in most osteoclasts, but induced neither necrotic nor apoptotic changes. In addition, the expression of vacuolar-type H+-ATPase in osteoclasts was decreased by OPG administration. Our results suggest that low-dose OPG administration significantly reduces trabecular bone loss in OVX mice via impairment of the structure and bone resorbing activity of osteoclasts.