Cell-matrix interaction in bone: type I collagen modulates signal transduction in osteoblast-like cells

Engineering approaches to manipulate osteoclast behavior for bone regeneration

Extensive research has delved into the multifaceted roles of osteoclasts beyond their traditional function in bone resorption in recent years, uncovering their significant influence on bone formation. This shift in understanding has spurred investigations into engineering strategies aimed at leveraging osteoclasts to not only inhibit bone resorption but also facilitate bone regeneration. This review seeks to comprehensively examine the mechanisms by which osteoclasts impact bone metabolism. Additionally, it explores various engineering methodologies, including the modification of bioactive material properties, localized drug delivery, and the introduction of exogenous cells, assessing their potential and mechanisms in aiding bone repair by targeting osteoclasts. Finally, the review proposes current limitations and future routes for manipulating osteoclasts through biological and material cues to facilitate bone repair.

Proton Transport Across Collagen Fibrils and Scaffolds: The Role of Hydroxyproline

Collagen is one of the most studied proteins due to its fundamental role in creating fibrillar structures and supporting tissues in our bodies. Accordingly, collagen is also one of the most used proteins for making tissue-engineered scaffolds for various types of tissues. To date, the high abundance of hydroxyproline (Hyp) within collagen is commonly ascribed to the structure and stability of collagen. Here, we hypothesize a new role for the presence of Hyp within collagen, which is to support proton transport (PT) across collagen fibrils. For this purpose, we explore here three different collagen-based hydrogels: the first is prepared by the self-assembly of natural collagen fibrils, and the second and third are based on covalently linking between collagen via either a self-coupling method or with an additional cross-linker. Following the formation of the hydrogel, we introduce here a two-step reaction, involving (1) attaching methanesulfonyl to the -OH group of Hyp, followed by (2) removing the methanesulfonyl, thus reverting Hyp to proline (Pro). We explore the PT efficiency at each step of the reaction using electrical measurements and show that adding the methanesulfonyl group vastly enhances PT, while reverting Hyp to Pro significantly reduces PT efficiency (compared with the initial point) with different efficiencies for the various collagen-based hydrogels. The role of Hyp in supporting the PT can assist in our understanding of the physiological roles of collagen. Furthermore, the capacity to modulate conductivity across collagen is very important to the use of collagen in regenerative medicine.

Significance of mechanical loading in bone fracture healing, bone regeneration, and vascularization

In 1892, J.L. Wolff proposed that bone could respond to mechanical and biophysical stimuli as a dynamic organ. This theory presents a unique opportunity for investigations on bone and its potential to aid in tissue repair. Routine activities such as exercise or machinery application can exert mechanical loads on bone. Previous research has demonstrated that mechanical loading can affect the differentiation and development of mesenchymal tissue. However, the extent to which mechanical stimulation can help repair or generate bone tissue and the related mechanisms remain unclear. Four key cell types in bone tissue, including osteoblasts, osteoclasts, bone lining cells, and osteocytes, play critical roles in responding to mechanical stimuli, while other cell lineages such as myocytes, platelets, fibroblasts, endothelial cells, and chondrocytes also exhibit mechanosensitivity. Mechanical loading can regulate the biological functions of bone tissue through the mechanosensor of bone cells intraosseously, making it a potential target for fracture healing and bone regeneration. This review aims to clarify these issues and explain bone remodeling, structure dynamics, and mechano-transduction processes in response to mechanical loading. Loading of different magnitudes, frequencies, and types, such as dynamic versus static loads, are analyzed to determine the effects of mechanical stimulation on bone tissue structure and cellular function. Finally, the importance of vascularization in nutrient supply for bone healing and regeneration was further discussed.

Aging exacerbates the morphological and mechanical response of mineralized collagen fibrils in murine cortical bone to disuse

Mineralized collagen fibrils (MCFs) are the fundamental building blocks of bone tissue and contribute significantly to the mechanical behavior of bone. However, it is still largely unknown how the collagen network in bone responds to aging and the disuse normally accompanying it. Utilizing atomic force microscopy, nanoindentation and Raman spectroscopy, age-related alterations in the microstructure and mechanical properties of murine cortical tibia at multiple scales were investigated in this study. The potential difference in the responses of bone to disuse at different ages was studied. The results indicated that the age- and disuse-related alterations in bone initiate from MCFs in the bone matrix. The D-periodic spacing, radial elastic modulus of a single MCF and the mineral-to-matrix ratio on the cortical bone surface were larger in aged mice than in adult mice. Disuse, on the other hand, mainly has a major influence on aged mice, particularly on the morphology and mechanical properties of MCFs, but it only has modest effects on adult bone. These findings revealed insights into the morphological and mechanical adaptation of mineralized collagen fibrils in murine cortical bone to aging and disuse. STATEMENT OF SIGNIFICANCE: Bone is a complex structured composite material consisting of an interwoven framework of collagen fibrils reinforced by mineral particles and embedded in an extrafibrillar mineralized matrix. Utilizing atomic force microscopy, nanoindentation and Raman spectroscopy, this study suggests that the effects of aging, as well as the accompanying disuse, on the morphology and mechanical properties of bone initiate from the mineralized collagen fibril level. More interestingly, the MCF in the bone of aged mice seems to be more sensitive to disuse than that in adult mice. These findings significantly further the current understanding of the adaptation process of bone to aging at the mineralized collagen fibril level and provide direct insights into the physiological response of bone to aging and the abnormal mechanical environment.

Remotely Temporal Scheduled Macrophage Phenotypic Transition Enables Optimized Immunomodulatory Bone Regeneration

Precise timing of macrophage polarization plays a pivotal role in immunomodulation of tissue regeneration, yet most studies mainly focus on M2 macrophages for their anti-inflammatory and regenerative effects while the essential proinflammatory role of the M1 phenotype on the early inflammation stage is largely underestimated. Herein, a superparamagnetic hydrogel capable of timely controlling macrophage polarization is constructed by grafting superparamagnetic nanoparticles on collagen nanofibers. The magnetic responsive hydrogel network enables efficient polarization of encapsulated macrophage to the M2 phenotype through the podosome/Rho/ROCK mechanical pathway in response to static magnetic field (MF) as needed. Taking advantage of remote accessibility of magnetic field together with the superparamagnetic hydrogels, a temporal engineered M1 to M2 transition course preserving the essential role of M1 at the early stage of tissue healing, as well as enhancing the prohealing effect of M2 at the middle/late stages is established via delayed MF switch. Such precise timing of macrophage polarization matching the regenerative process of injured tissue eventually leads to optimized immunomodulatory bone healing in vivo. Overall, this study offers a remotely time-scheduled approach for macrophage polarization, which enables precise manipulation of inflammation progression during tissue healing.

Review on material parameters to enhance bone cell function in vitro and in vivo

Bone plays critical roles in support, protection, movement, and metabolism. Although bone has an innate capacity for regeneration, this capacity is limited, and many bone injuries and diseases require intervention. Biomaterials are a critical component of many treatments to restore bone function and include non-resorbable implants to augment bone and resorbable materials to guide regeneration. Biomaterials can vary considerably in their biocompatibility and bioactivity, which are functions of specific material parameters. The success of biomaterials in bone augmentation and regeneration is based on their effects on the function of bone cells. Such functions include adhesion, migration, inflammation, proliferation, communication, differentiation, resorption, and vascularization. This review will focus on how different material parameters can enhance bone cell function both in vitro and in vivo.

Bone Healing and Inflammation: Principles of Fracture and Repair

Bones comprise a significant percentage of human weight and have important physiologic and structural roles. Bone remodeling occurs when healthy bone is renewed to maintain bone strength and maintain calcium and phosphate homeostasis. It proceeds through four phases: (1) cell activation, (2) resorption, (3) reversal, and (4) bone formation. Bone healing, on the other hand, involves rebuilding bone following a fracture. There are two main types of bone healing, primary and secondary. Inflammation plays an integral role in both bone remodeling and healing. Therefore, a tightly regulated inflammatory response helps achieve these two processes, and levels of inflammation can have detrimental effects on bone healing. Other factors that significantly affect bone healing are inadequate blood supply, biomechanical instability, immunosuppression, and smoking. By understanding the different mechanisms of bone healing and the factors that affect them, we may have a better understanding of the underlying principles of bony fixation and thereby improve patient care.

Use of in vitro bone models to screen for altered bone metabolism, osteopathies, and fracture healing: challenges of complex models

Approx. every third hospitalized patient in Europe suffers from musculoskeletal injuries or diseases. Up to 20% of these patients need costly surgical revisions after delayed or impaired fracture healing. Reasons for this are the severity of the trauma, individual factors, e.g, the patients’ age, individual lifestyle, chronic diseases, medication, and, over 70 diseases that negatively affect the bone quality. To investigate the various disease constellations and/or develop new treatment strategies, many in vivo, ex vivo, and in vitro models can be applied. Analyzing these various models more closely, it is obvious that many of them have limits and/or restrictions. Undoubtedly, in vivo models most completely represent the biological situation. Besides possible species-specific differences, ethical concerns may question the use of in vivo models especially for large screening approaches. Challenging whether ex vivo or in vitro bone models can be used as an adequate replacement for such screenings, we here summarize the advantages and challenges of frequently used ex vivo and in vitro bone models to study disturbed bone metabolism and fracture healing. Using own examples, we discuss the common challenge of cell-specific normalization of data obtained from more complex in vitro models as one example of the analytical limits which lower the full potential of these complex model systems.

A Preshaped Titanium Mesh for Guided Bone Regeneration with an Equine-Derived Bone Graft in a Posterior Mandibular Bone Defect: A Case Report

One of the most often used bone augmentation techniques is the guided bone regeneration procedure. The authors report the case of a 75-year-old man with an atrophic right posterior mandible who underwent bone augmentation through guided bone regeneration with a preshaped titanium mesh adapted on a stereolithographic model of the patient’s jaw. The graft volume was simulated with a light-curing resin. The actual site was grafted with a mixture of autogenous and equine-derived bone. Five months later, the mesh was retrieved, three cylindrical implants were positioned, and a bone biopsy was collected for histomorphometric analysis. A provisional prosthesis was delivered three and a half months later. Definitive rehabilitation was accomplished after one additional month. The graft allowed for effective bone formation (newly formed bone, residual biomaterial, and medullar spaces were, respectively, 39%, 10%, and 51% of the core volume). The patient has functioned successfully throughout six and a half years of follow-up. Using the preshaped titanium mesh in association with the enzyme-treated equine bone substitute provided effective bone regeneration.

Chemical, Clinical and Histomorphometric Comparison between Equine Bone Manufactured through Enzymatic Antigen-Elimination and Bovine Bone Made Non-Antigenic Using a High-Temperature Process in Post-Extractive Socket Grafting. A Comparative Retrospective Clinical Study

Enzyme-deantigenic equine bone (EDEB) and anorganic bovine bone (ABB) are two xenografts made non-antigenic through different processing methods. This study aimed to characterize them for the presence of native bone collagen and other proteins and to compare their histomorphometric outcome when they were used to graft post-extractive sockets. The records of 46 patients treated with EDEB (n = 22) or ABB (n = 24) and followed-up for at least four months after delayed implant placement, were retrospectively collected. Samples of EDEB and ABB were analyzed using Attenuated Total Reflection Fourier Transform Infrared and Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis for the presence of collagen and other proteins. For histomorphometric analysis on bone specimens, newly formed bone and residual biomaterial percentages were calculated. Results of the present study show that EDEB contains type I bone collagen in its native conformation, while no proteins were detected in ABB. Grafting EDEB resulted in a significantly greater quantity of newly formed bone and less residual biomaterial. Our findings suggest that the manufacturing process can greatly affect the graft behavior and a process preserving collagen in its native form may favor bone tissue regeneration.

Effects of nicotine on the metabolism and gene expression profile of Sprague‑Dawley rat primary osteoblasts

Smoking is a risk factor associated with bone and oral diseases, particularly periodontitis. Nicotine, the major toxic component of tobacco, is able to affect the quality and quantity of bone. Osteoblasts serve an important role in bone formation. Thus far, the effects of nicotine on metabolism‑associated gene and protein expression in osteoblasts have been controversial and the mechanisms remain unclear. The present study assessed alterations in osteogenic activity by performing a Cell Counting kit‑8 assay to investigate proliferation, Annexin V‑fluorescein isothiocyanate/propidium iodide staining to investigate apoptosis, alizarin red staining to investigate the formation of mineralized nodules, reverse transcription‑quantitative polymerase chain reaction and western blotting to investigate the mRNA and protein levels of collagen I, alkaline phosphatase, bone osteocalcin, bone sialoprotein and osteopontin; and mRNA microarray expression analysis, Kyoto Encyclopedia of Genes and Genomes and Gene Ontology analysis to investigate the whole genome expression profile of Sprague‑Dawley (SD) rat primary osteoblasts following treatment with different concentrations of nicotine. The results demonstrated that nicotine inhibited proliferation, promoted early apoptosis and inhibited mineralized nodule formation in a dose‑dependent manner by regulating alkaline phosphatase activity and the expression of osteoblast metabolism‑associated genes and proteins. According to microarray analysis, several genes associated with bone metabolism and genes in the Hedgehog and Notch signaling pathways were downregulated significantly in nicotine‑treated osteoblasts. The results of the present study indicated that nicotine may serve an inhibitory, dose‑dependent role in SD rat primary osteoblasts that may be caused by the perturbation of genes and signaling pathways associated with bone formation. These results may provide a theoretical basis for future research regarding bone metabolism and targeted treatment of oral diseases associated with smoking.

Age-related collagen turnover of the interstitial matrix and basement membrane: Implications of age- and sex-dependent remodeling of the extracellular matrix

The extracellular matrix (ECM) plays a vital role in maintaining normal tissue function. Collagens are major components of the ECM and there is a tight equilibrium between degradation and formation of these proteins ensuring tissue health and homeostasis. As a consequence of tissue turnover, small collagen fragments are released into the circulation, which act as important biomarkers in the study of certain tissue-related remodeling factors in health and disease. The aim of this study was to establish an age-related collagen turnover profile of the main collagens of the interstitial matrix (type I and III collagen) and basement membrane (type IV collagen) in healthy men and women. By using well-characterized competitive ELISA-assays, we assessed specific fragments of degraded (C1M, C3M, C4M) and formed (PINP, Pro-C3, P4NP7S) type I, III and IV collagen in serum from 617 healthy men and women ranging in ages from 22 to 86. Subjects were divided into 5-year age groups according to their sex and age. Groups were compared using Kruskal-Wallis adjusted for Dunn's multiple comparisons test and Mann-Whitney t-test. Age-specific changes in collagen turnover was most profound for type I collagen. PINP levels decreased in men with advancing age, whereas in women, the level decreased in early adulthood followed by an increase around the age of menopause (age 40-60). Sex-specific changes in type I, III and IV collagen turnover was present at the age around menopause (age 40-60) with women having an increased turnover. In summary, collagen turnover is affected by age and sex with the interstitial matrix and the basement membrane being differently regulated. The observed changes needs to be accounted for when measuring ECM related biomarkers in clinical studies.

A WNT protein therapeutic improves the bone-forming capacity of autografts from aged animals

Autografts tend to be unreliable in older patients. Some of these age-related skeletal changes appear to be attributable to a decline in endogenous WNT signaling. We used a functional in vivo transplantation assay to demonstrate that the bone-forming capacity of an autograft can be traced back to a Wnt-responsive cell population associated with the mineralized bone matrix fraction of a bone graft. Micro-CT imaging, flow cytometry and quantitative analyses demonstrate that this mineralized fraction declines with age, along with a waning in endogenous Wnt signaling; together these factors contribute to the age-related deterioration in autograft efficacy. Using a lipid formulation to stabilize the hydrophobic WNT3A protein, we demonstrate that osteogenic capacity can be restored by incubating the bone graft ex vivo with WNT3A. Compared to control bone grafts, WNT-treated bone grafts give rise to three times more bone. These preclinical results establish a pivotal role for WNT signaling in the age-related decline of autologous bone grafting efficacy, and demonstrate a means to restore that efficacy via local, transient amplification of endogenous Wnt signaling.

Preserving the Bone Profile in Anterior Maxilla using an Equine Cortical Bone Membrane and an Equine Enzyme-treated Bone Graft: A Case Report with 5-year Follow-up

AIM

This study aimed to report a well-succeeded use of equine enzyme-deantigenic cortical membrane and bone granules for guided bone regeneration (GBR) in the esthetic zone concomitant with implant placement.

BACKGROUND

In the anterior maxilla, where patients typically have the highest expectations for implant-supported restorations, bone resorption in the wake of tooth loss often leads to a lack of soft tissue support and ultimately to unsatisfactory esthetic results. Buccal bone augmentation at the time of implant placement has thus become common. This is usually accomplished following GBR principles and employing membranes made from various materials to serve as a barrier between the soft tissue and graft material. One of the more recently introduced membrane materials is made from thin, flexible equine cortical bone, i.e., rendered nonantigenic in an enzymatic process that preserves native bone collagen.

CASE REPORT

This report describes the treatment of a patient who received an equine enzyme-deantigenic graft and membrane in conjunction with placement of an implant in the right maxillary lateral incisor site.

CONCLUSION

After 5 years of follow-up, the patient was very satisfied with her appearance. A cone-beam computed tomography scan showed that the peri-implant bone levels and ridge thickness had been maintained, and the cortical layer in the pristine ridge had also undergone remodeling.

CLINICAL SIGNIFICANCE

Guided bone regeneration with the concomitant use of enzyme-deantigenic membrane and graft is a valuable and suitable option for effective implant-supported prosthetic rehabilitation in the esthetic zone.

Nanotopography Induced Human Bone Marrow Mesangiogenic Progenitor Cells (MPCs) to Mesenchymal Stromal Cells (MSCs) Transition

Mesangiogenic progenitor cells (MPCs) are a very peculiar population of cells present in the human adult bone marrow, only recently discovered and characterized. Owing to their differentiation potential, MPCs can be considered progenitors for mesenchymal stromal cells (MSCs), and for this reason they potentially represent a promising cell population to apply for skeletal tissue regeneration applications. Here, we evaluate the effects of surface nanotopography on MPCs, considering the possibility that this specific physical stimulus alone can trigger MPC differentiation toward the mesenchymal lineage. In particular, we exploit nanogratings to deliver a mechanical, directional stimulus by contact interaction to promote cell morphological polarization and stretching. Following this interaction, we study the MPC-MSC transition by i. analyzing the change in cell morphotype by immunostaining of the key cell-adhesion structures and confocal fluorescence microscopy, and ii. quantifying the expression of cell-phenotype characterizing markers by flow cytometry. We demonstrate that the MPC mesengenic differentiation can be induced by the solely interaction with the NGs, in absence of any other external, chemical stimulus. This aspect is of particular interest in the case of multipotent progenitors as MPCs that, retaining both mesengenic and angiogenic potential, possess a high clinical appeal.

Sika Deer Antler Collagen Type I-Accelerated Osteogenesis in Bone Marrow Mesenchymal Stem Cells via the Smad Pathway

Deer antler preparations have been used to strengthen bones for centuries. It is particularly rich in collagen type I. This study aimed to unravel part of the purported bioremedial effect of Sika deer antler collagen type I (SDA-Col I) on bone marrow mesenchymal stem cells. The results suggest that SDA-Col I might be used to promote and regulate osteoblast proliferation and differentiation. SDA-Col I might potentially provide the basis for novel therapeutic strategies in the treatment of bone injury and/or in scaffolds for bone replacement strategies. Finally, isolation of SDA-Col I from deer antler represents a renewable, green, and uncomplicated way to obtain a biomedically valuable therapeutic.

Biocompatibility of Novel Type I Collagen Purified from Tilapia Fish Scale: An In Vitro Comparative Study

Type I collagen (COL-1) is the prevailing component of the extracellular matrix in a number of tissues including skin, ligament, cartilage, bone, and dentin. It is the most widely used tissue-derived natural polymer. Currently, mammalian animals, including pig, cow, and rat, are the three major sources for purification of COL-1. To reduce the risk of zoonotic infectious diseases transmission, minimize the possibility of immunogenic reaction, and avoid problems related to religious issues, exploration of new sources (other than mammalian animals) for the purification of type I collagen is highly desirable. Hence, the purpose of the current study was to investigate the in vitro responses of MDPC-23 to type I collagen isolated from tilapia scale in terms of cellular proliferation, differentiation, and mineralization. The results suggested that tilapia scale collagen exhibited comparable biocompatibility to porcine skin collagen, indicating it might be a potential alternative to type I collagen from mammals in the application for tissue regeneration in oral-maxillofacial area.

Impaired extracellular matrix structure resulting from malnutrition in ovariectomized mature rats

Bone loss is a symptom related to disease and age, which reflects on bone cells and ECM. Discrepant regulation affects cell proliferation and ECM localization. Rat model of osteoporosis (OVX) was investigated against control rats (Sham) at young and old ages. Biophysical, histological and molecular techniques were implemented to examine the underlying cellular and extracellular matrix changes and to assess the mechanisms contributing to bone loss in the context of aging and the widely used osteoporotic models in rats. Bone loss exhibited a compromised function of bone cells and infiltration of adipocytes into bone marrow. However, the expression of genes regulating collagen catabolic process and adipogenesis was chronologically shifted in diseased bone in comparison with aged bone. The data showed the involvement of Wnt signaling inhibition in adipogenesis and bone loss due to over-expression of SOST in both diseased and aged bone. Further, in the OVX animals, an integrin-mediated ERK activation indicated the role of MAPK in osteoblastogenesis and adipogenesis. The increased PTH levels due to calcium and estrogen deficiency activated osteoblastogenesis. Thusly, RANKL-mediated osteoclastogenesis was initiated. Interestingly, the data show the role of MEPE regulating osteoclast-mediated resorption at late stages in osteoporotic bone. The interplay between ECM and bone cells change tissue microstructure and properties. The involvement of Wnt and MAPK pathways in activating cell proliferation has intriguing similarities to oncogenesis and myeloma. The study indicates the importance of targeting both pathways simultaneously to remedy metabolic bone diseases and age-related bone loss.

Biology of Bone Tissue: Structure, Function, and Factors That Influence Bone Cells

Bone tissue is continuously remodeled through the concerted actions of bone cells, which include bone resorption by osteoclasts and bone formation by osteoblasts, whereas osteocytes act as mechanosensors and orchestrators of the bone remodeling process. This process is under the control of local (e.g., growth factors and cytokines) and systemic (e.g., calcitonin and estrogens) factors that all together contribute for bone homeostasis. An imbalance between bone resorption and formation can result in bone diseases including osteoporosis. Recently, it has been recognized that, during bone remodeling, there are an intricate communication among bone cells. For instance, the coupling from bone resorption to bone formation is achieved by interaction between osteoclasts and osteoblasts. Moreover, osteocytes produce factors that influence osteoblast and osteoclast activities, whereas osteocyte apoptosis is followed by osteoclastic bone resorption. The increasing knowledge about the structure and functions of bone cells contributed to a better understanding of bone biology. It has been suggested that there is a complex communication between bone cells and other organs, indicating the dynamic nature of bone tissue. In this review, we discuss the current data about the structure and functions of bone cells and the factors that influence bone remodeling.

Guided Bone Regeneration of an Atrophic Mandible with a Heterologous Bone Block

The aim of this work was to test the effectiveness of using enzymatically deantigenated equine bone block as a scaffold for guided bone regeneration (GBR) during a horizontal augmentation of the lower jaw. A partially edentulous atrophic mandible was augmented using an equine-derived block with an expanded polytetrafluoroethylene membrane. After 8.5 months, two bone core samples were collected at the augmentation site, and implants were placed. A definitive prosthesis delivered 6 months after implant placement provided excellent functional and aesthetic rehabilitation throughout the follow-up period. Histological and histomorphometrical analysis of the biopsies showed newly formed bone to be present and the residual biomaterial was still undergoing remodeling. Comparison of cone beam computed tomography scans taken before augmentation and 26 months later showed maintenance of ridge width and possible corticalization of the vestibular augmented ridge side. The equine-derived bone block placed in accordance with GBR principles provided a successful clinical, radiographic, and histological outcome.

Horizontal-guided Bone Regeneration using a Titanium Mesh and an Equine Bone Graft

AIM

The present work describes a horizontal ridge augmentation in which a titanium mesh was preshaped by adapting it to a stereolithographic model of the patient's jaw that was fabricated from CT scans.

BACKGROUND

Guided bone regeneration (GBR) involves covering the augmentation site with a long-lasting barrier to protect it from the invasion of surrounding soft tissues. Among barriers, titanium meshes may provide a successful outcome, but the intraoperatory time needed to shape them is a disadvantage.

CASE DESCRIPTION

The 54-year-old patient, missing the right mandibular second bicuspid, first molar, and second molar, had her atrophic ridge augmented with a 30:70 mixture of autogenous bone and equine, enzyme-deantigenic collagen-preserved bone substitute. Two conical implants were inserted concomitantly in the second bicuspid and first molar positions, and the site was protected with the preshaped mesh. Four months later, the titanium mesh was retrieved, a bone sample was collected, and histological and histomorphometric analyses were performed. Provisional and definitive prostheses were then delivered, and follow-up controls were performed for up to 24 months.

CONCLUSION

Preshaping the mesh on a model of the patient's mandible shortened the surgical time and enabled faster mesh placement. Two years after surgery, the implants were perfectly functional, and the bone width was stable over time as shown by radiographic controls. Histological analysis of the bone sample showed the heterologous biomaterial to be biocompatible and undergoing advanced remodeling and replacement with newly formed bone.

CLINICAL SIGNIFICANCE

Preshaping a titanium mesh over a stereolithographic model of the patient's jaw allowed for a significant reduction of the intraoperative time and may be therefore, advisable in routine practice.

Clinical utility of locally-delivered collagen-based biodegradable tetracycline fibers in periodontal therapy: an in vivo study

AIM

The purpose of the present investigation was to evaluate and compare the efficacy of resorbable collagen-based tetracycline fibers (Periodontal Plus AB fibers) given as an adjunct to scaling and root planing, with the clinical effects of scaling and root planning delivered as a monotherapy, in the treatment of chronic periodontitis.

METHODS

A split-mouth design was used to conduct this study. Forty patients with periodontal pockets ranging from ≥ 5 mm to ≤ 7 mm, with minimum of two sites in two non-adjacent quadrants, were selected for the study. The treatment sites in each patient were randomly divided into the control and experimental groups. All of the selected sites were treated with scaling and root planning, and then collagen-based resorbable tetracycline fibers were placed adjunctively in the experimental sites at the same visit. Baseline and follow-up measurements in both treatment groups included plaque index, sulcus bleeding index, probing pocket depth, and relative attachment level.

RESULTS

Although significant clinical benefits were obtained in both treatment groups, the adjunctive antimicrobial use of tetracycline fibers demonstrated better results compared to the control group over the 3-month observational period.

CONCLUSIONS

The delivery of antimicrobial agent tetracycline in a collagen matrix was found to improve the benefits of scaling and root planing by a larger magnitude in patients with moderate-to-deep pockets.

Impact of extracellular matrix derived from osteoarthritis subchondral bone osteoblasts on osteocytes: role of integrinβ1 and focal adhesion kinase signaling cues

INTRODUCTION

Our recent study indicated that subchondral bone pathogenesis in osteoarthritis (OA) is associated with osteocyte morphology and phenotypic abnormalities. However, the mechanism underlying this abnormality needs to be identified. In this study we investigated the effect of extracellular matrix (ECM) produced from normal and OA bone on osteocytic cells function.

METHODS

De-cellularized matrices, resembling the bone provisional ECM secreted from primary human subchondral bone osteoblasts (SBOs) of normal and OA patients were used as a model to study the effect on osteocytic cells. Osteocytic cells (MLOY4 osteocyte cell line) cultured on normal and OA derived ECMs were analyzed by confocal microscopy, scanning electron microscopy (SEM), cell attachment assays, zymography, apoptosis assays, qRT-PCR and western blotting. The role of integrinβ1 and focal adhesion kinase (FAK) signaling pathways during these interactions were monitored using appropriate blocking antibodies.

RESULTS

The ECM produced by OA SBOs contained less mineral content, showed altered organization of matrix proteins and matrix structure compared with the matrices produced by normal SBOs. Culture of osteocytic cells on these defective OA ECM resulted in a decrease of integrinβ1 expression and the de-activation of FAK cell signaling pathway, which subsequently affected the initial osteocytic cell's attachment and functions including morphological abnormalities of cytoskeletal structures, focal adhesions, increased apoptosis, altered osteocyte specific gene expression and increased Matrix metalloproteinases (MMP-2) and -9 expression.

CONCLUSION

This study provides new insights in understanding how altered OA bone matrix can lead to the abnormal osteocyte phenotypic changes, which is typical in OA pathogenesis.

Variation in type I collagen fibril nanomorphology: the significance and origin

Although the axial D-periodic spacing is a well-recognized nanomorphological feature of type I collagen fibrils, the existence of a distribution of values has been largely overlooked since its discovery seven decades ago. Studies based on single fibril measurements occasionally noted variation in D-spacing values, but accredited it with no biological significance. Recent quantitative characterizations supported that a 10-nm collagen D-spacing distribution is intrinsic to collagen fibrils in various tissues as well as in vitro self-assembly of reconstituted collagen. In addition, the distribution is altered in Osteogenesis Imperfecta and long-term estrogen deprivation. Bone collagen is organized into lamellar sheets of bundles at the micro-scale, and D-spacings within a bundle of a lamella are mostly identical, whereas variations among different bundles contribute to the full-scale distribution. This seems to be a very general phenomenon for the protein as the same type of D-spacing/bundle organization is observed for dermal and tendon collagen. More research investigation of collagen nanomorphology in connection to bone biology is required to fully understand these new observations. Here we review the data demonstrating the existence of a D-spacing distribution, the impact of disease on the distribution and possible explanations for the origin of D-spacing variations based on various collagen fibrillogenesis models.

Surface characteristics and osteoblastic cell response of alkali-and heat-treated titanium-8tantalum-3niobium alloy

Purpose

The aim of the present study was to evaluate the biological response of alkali- and heat-treated titanium-8tantalum-3niobium surfaces by cell proliferation and alkaline phosphatase (ALP) activity analysis.

Methods

Commercial pure titanium (group cp-Ti) and alkali- and heat-treated titanium-8tantalum-3niobium (group AHT) disks were prepared. The surface properties were evaluated using scanning electron microscopy, energy dispersed spectroscopy and X-ray photoelectron spectroscopy (XPS). The surface roughness was evaluated by atomic force microscopy and a profilometer. The contact angle and surface energy were also analyzed. The biological response of fetal rat calvarial cells on group AHT was assessed by cell proliferation and ALP activity.

Results

Group AHT showed a flake-like morphology microprofile and dense structure. XPS analysis of group AHT showed an increased amount of oxygen in the basic hydroxyl residue of titanium hydroxide groups compared with group cp-Ti. The surface roughness (Ra) measured by a profilometer showed no significant difference (P>0.05). Group AHT showed a lower contact angle and higher surface energy than group cp-Ti. Cell proliferation on group AHT surfaces was significantly higher than on group cp-Ti surfaces (P<0.05). In comparison to group cp-Ti, group AHT enhanced ALP activity (P<0.05).

Conclusions

These results suggest that group AHT stimulates osteoblast differentiation.

Altered cell motility and attachment with titanium surface modifications

BACKGROUND

Titanium implants are widely used in dentistry to replace lost teeth. Various surface modifications have been used to improve implant retention and osseointegration. This study is designed to compare the ability of three titanium surfaces to promote cell attachment and cell motility of cells relevant to periodontal tissues.

METHODS

Three clinically relevant surfaces were tested: 1) machined titanium; 2) a titanium surface roughened through acid etching (dual thermal-etched titanium [DTET]); and 3) a titanium surface roughened with nanometer-scale calcium phosphate deposition (nanoscale calcium phosphate-impregnated titanium [NCPIT]). Cell attachment and migration were examined for four cell types: rat osteosarcoma cells, human osteoblasts, and gingival and periodontal ligament (PDL) fibroblasts.

RESULTS

All four cell types attached to each of the three titanium surfaces equally by 2 hours, and the PDL and gingival fibroblasts generally displayed less attachment than the osteosarcoma cells and osteoblasts. The cells displayed differential motility and long-term attachment to each of the titanium surfaces. Osteosarcoma cells displayed preferential motility on NCPIT, whereas PDL fibroblasts were more motile on machined titanium, and gingival fibroblasts moved more rapidly on both DTET and NCPIT. Osteoblasts displayed little motility on any of the titanium surfaces and lost viability on NCPIT after 24 hours. Gingival fibroblasts lost attachment to machined titanium.

CONCLUSIONS

Periodontal cells displayed differential motility and long-term attachment to titanium surfaces. Selective modification of titanium surface properties in various regions of an implant may be useful in guiding specific cell populations to specific locations where they might best aid in osseointegration and soft tissue remodeling.

Ascorbic acid regulates osterix expression in osteoblasts by activation of prolyl hydroxylase and ubiquitination-mediated proteosomal degradation pathway

Mouse genetic studies reveal that ascorbic acid (AA) is essential for osteoblast (OB) differentiation and that osterix (Osx) was a key downstream target of AA action in OBs. To determine the molecular pathways for AA regulation of Osx expression, we evaluated if AA regulates Osx expression by regulating production and/or actions of local growth factors and extracellular matrix (ECM) proteins. Inhibition of actions of IGFs by inhibitory IGFBP-4, BMPs by noggin, and ECM-mediated integrin signaling by RGD did not block AA effects on Osx expression in OBs. Furthermore, blockade of components of MAPK signaling pathway had no effect on AA-induced Osx expression. Because AA is required for prolyl hydroxylase domain (PHD) activity and because PHD-induced prolyl-hydroxylation targets proteins to proteosomal degradation, we next tested if AA effect on Osx expression involves activation of PHD to hydroxylate and induce ubiquitin-proteosome-mediated degradation of transcriptional repressor(s) of Osx gene. Treatment of OBs with dimethyloxallyl glycine and ethyl 3, 4-dihydroxybenzoate, known inhibitors of PHD, completely blocked AA effect on Osx expression and OB differentiation. Knockdown of PHD2 expression by Lentivirus-mediated shRNA abolished AA-induced Osx induction and alkaline phosphatase activity. Furthermore, treatment of OBs with MG115, inhibitor of proteosomal degradation, completely blocked AA effects on Osx expression. Based on these data, we conclude that AA effect on Osx expression is mediated via a novel mechanism that involves PHD2 and proteosomal degradation of a yet to be identified transcriptional repressor that is independent of BMP, IGF-I, or integrin-mediated signaling in mouse OBs.

Small peptide (P-15) bone substitute efficacy in a rabbit cancellous bone model

P-15 is a synthetic 15-amino acid residue identical to the cell binding domain of type I collagen. P-15 can be adsorbed onto anorganic bovine bone mineral (ABM) and will enhance cell attachment and subsequent cell activation. Although ABM/P-15 has been studied as a bone graft substitute in the oral cavity, its use in orthopedic models has been limited. Thus, this study investigated the efficacy of ABM/P-15 treatment in a rabbit model of long bone cancellous healing. Defects were created in the distal femurs and proximal medial tibiae of rabbits and were filled with either ABMP/P-15 suspended in hydrogel, ABM alone suspended in hydrogel, hydrogel carrier alone, or no graft material. Rabbits were sacrificed at 1, 2, 4, or 8 weeks postsurgery, and the femurs and tibiae were harvested. Histomorphometric analyses indicated that defects treated with ABM/P-15 had significantly larger areas of new bone formation than the other three treatments at 2 and 8 weeks postsurgery. ABM/P-15 treated defects also had significantly more bone growth than defects left empty or filled with ABM alone at 4 weeks postsurgery. Furthermore, histological examination did not reveal acute inflammatory infiltrate cells in any of the treatment conditions. These results are consistent with the findings of ABM/P-15 use in human oral-maxillofacial studies and in large animal spine fusion models.

Collagen I gel can facilitate homogenous bone formation of adipose-derived stem cells in PLGA-beta-TCP scaffold

Cell-based tissue engineering is thought to be a new therapy for treatment of bone defects and nonunions after trauma and tumor resection. In this study, we explore the in vitro and in vivo osteogenesis of a novel biomimetic construct fabricated by using collagen I gel to suspend rabbit adipose-derived stem cells (rASCs) into a porous poly(lactic-co-glycolic)acid-beta-tricalcium phosphate (PLGA-beta-TCP) scaffold (rASCs-COL/PLGA-beta-TCP). In vitro and in vivo studies of the rASCs-COL/PLGA-beta-TCP composite (group A) were carried out compared with the single combination of rASCs and PLGA-beta-TCP (rASCs/PLGA-beta-TCP; group B), the combination of acellular collagen I gel and PLGA-beta-TCP (COL/PLGA-beta-TCP; group C), and the PLGA-beta-TCP scaffold (group D). Composites of different groups were cultured in vitro for 2 weeks in osteogenic medium and then implanted into the autologous muscular intervals for 8 weeks. After 2 weeks of in vitro culture, alkaline phosphatase activity and extracellular matrix mineralization in group A were significantly higher than in group B (p < 0.01, n = 4). In vivo osteogenesis was evaluated by radiographic and histological analyses. The calcification level was radiographically evident in group A, whereas no apparent calcification was observed in groups B, C and D (n = 4). In group A, woven bone with a trabecular structure was formed, while in group B, only osteoid tissue was observed. Meanwhile, the bone-forming area in group A was significantly higher than in group B (p < 0.01, n = 4). No bone formation was observed in groups C or D (n = 4). In conclusion, by using collagen I gel to suspend rASCs into porous PLGA-beta-TCP scaffold, osteogenic differentiation of rASCs can be improved and homogeneous bone tissue can be successfully formed in vivo.

Nuclear factor-E2-related factor-1 mediates ascorbic acid induction of osterix expression via interaction with antioxidant-responsive element in bone cells

We recently found that deletion of the gulonolactone oxidase gene, which is involved in the synthesis of ascorbic acid (AA), was responsible for the fracture phenotype in spontaneous fracture mice. To explore the molecular mechanisms by which AA regulates osteoblast differentiation, we examined the effect of AA on osterix expression via Nrf1 (NF-E2-related factor-1) binding to antioxidant-responsive element (ARE) in bone marrow stromal (BMS) cells. AA treatment caused a 6-fold increase in osterix expression in mutant BMS cells at 24 h, which was unaffected by pretreatment with protein synthesis inhibitor. Sequence analyses of mouse osterix promoter revealed a putative ARE located at -1762 to -1733 upstream of the transcription start site to which Nrf potentially binds. A gel mobility shift assay revealed that nuclear proteins from AA-treated BMS cells bound to radiolabeled ARE much more strongly than nuclear extracts from AA-untreated cells. A chromatin immunoprecipitation assay with Nrf1 antibody confirmed the interaction of Nrf1 with the mouse osterix promoter. A reporter assay demonstrated that the promoter activity of mouse osterix containing an ARE was stimulated 4-fold by a 48-h treatment with AA in spontaneous fracture BMS cells. Treatment of mutant BMS cells with AA resulted in a 3.9-fold increase in the nuclear accumulation of Nrf1. Transfection of mutant BMS cells with Nrf1 small interfering RNA decreased Nrf1 protein by 4.5-fold, blocked AA induction of osterix expression, and impaired BMS cell differentiation. Our data provided the first experimental evidence that AA modulated osterix expression via a novel mechanism involving Nrf1 nuclear translocation and Nrf1 binding to ARE to activate genes critical for cell differentiation.

Runx2/Cbfa1-genetically engineered skeletal myoblasts mineralize collagen scaffolds in vitro

Genetic engineering of progenitor and stem cells is an attractive approach to address cell sourcing limitations associated with tissue engineering applications. Bone tissue engineering represents a promising strategy to repair large bone defects, but has been limited in part by the availability of a sustained, mineralizing cell source. This study examined the in vitro mineralization potential of primary skeletal myoblasts genetically engineered to overexpress Runx2/Cbfa1, an osteoblastic transcriptional regulator essential to bone formation. These cells were viable at the periphery of 3D fibrous collagen scaffolds for 6 weeks of static culture. Exogenous Runx2 expression induced osteogenic differentiation and repressed myogenesis in these constructs relative to controls. Runx2-modified cells deposited significant amounts of mineralized matrix and hydroxyapatite, as determined by microcomputed tomography, histological analysis, and Fourier transform infrared spectroscopy, whereas scaffolds seeded with control cells exhibited no mineralized regions. Although mineralization by Runx2-engineered cells was confined to the periphery of the construct, colocalizing with cell viability, it was sufficient to increase the compressive modulus of constructs 30-fold relative to controls. This work demonstrates that Runx2 overexpression in skeletal myoblasts may address current obstacles of bone tissue engineering by providing a potent cell source for in vitro mineralization and construct maturation. Additionally, the use of genetic engineering methods to express downstream control factors and transcriptional regulators, in contrast to soluble signaling molecules, represents a robust strategy to enhance cellular activities for tissue engineering applications.

P253R fibroblast growth factor receptor-2 mutation induces RUNX2 transcript variants and calvarial osteoblast differentiation

Unregulated fibroblast growth factor 2 (FGF2) signaling caused by mutations in the fibroblast growth factor receptor (FGFR2) leads to human craniosynostosis such as the Apert syndrome. In an in vitro control model of calvarial osteoblasts from Apert patients carrying the FGFR2 P253R mutation, we studied the changes in cellular phenotype and evaluated the effects of FGF2. Compared with wild-type controls, osteocalcin mRNA was down-regulated in Apert osteoblasts, Runt-related transcription factor-2 (RUNX2) mRNA was differentially spliced, and FGF2 secretion was greater. Total protein synthesis, fibronectin and type I collagen secretion were up-regulated, while protease and glycosidase activities and matrix metalloproteinase-13 (MMP-13) transcription were decreased, suggesting an altered ECM turnover. Adding FGF2 increased protease and glycosidase activities and down-regulated fibronectin and type I collagen secretion in Apert osteoblasts. High affinity FGF2 receptors were up-regulated in Apert osteoblasts and analysis of signal transduction showed elevated levels of Grb2 tyrosine phosphorylation and the Grb2-p85 beta association, which FGF2 stimulation strongly reduced. All together these findings suggest increased constitutive receptor activity in Apert mutant osteoblasts and an autocrine loop involving the FGF2 pathway in modulation of Apert osteoblast behavior.

Enhanced cell attachment and osteoblastic activity by P-15 peptide-coated matrix in hydrogels

The cells in bone grow on a composite matrix made up of mineral and organic (mainly type-I collagen) components. In this study, anorganic bone mineral (ABM) particles were coated with a cell-binding domain of type-I collagen (P-15 peptide) to mimic the bone matrix components and suspended in injectable hyaluronate (Hy) hydrogels. The ABM/P-15/Hy was compared to ABM/Hy-the same matrix without P-15 peptide. Osteoblast-like HOS cells migrated through the hydrogels around ABM/P-15 or ABM particles; however, more cells adhered to ABM/P-15/Hy particles, and the cells formed better surface coverage and had more stress fibers on ABM/P-15/Hy. HOS cells cultured on ABM/P-15/Hy had increased osteogenic gene expression for alkaline phosphatase and bone morphogenetic proteins, and deposited more mineralized matrix. Studies with two different hydrogels (carboxymethylcellulose and sodium alginate) showed similar enhanced cell attachment and mineralization. The studies suggest that the ABM/P-15 in hydrogels can be used as an injectable biomimetic matrix to facilitate bone repair.

Bone matrix proteins: their function, regulation, and relationship to osteoporosis

Bone is a unique tissue composed of numerous cell types entombed within a mineralized matrix each with its own unique functions. While the majority of the matrix is composed of inorganic materials, study of the organic components has yielded most of the insights into the roles and regulation of cell and tissue specific functions. The goal of this review will be to describe some of the major known organic components of the bone matrix and discuss their functions as currently perceived. The potential usefulness of bone matrix protein assays for diagnosing the status of bone diseases and our current understanding of how these proteins could be related to diseases such as osteoporosis will also be reviewed.

An evaluation of accelerated Portland cement as a restorative material

Biocompatibility of two variants of accelerated Portland cement (APC) were investigated in vitro by observing the cytomorphology of SaOS-2 osteosarcoma cells in the presence of test materials and the effect of these materials on the expression of markers of bone remodelling. Glass ionomer cement (GIC), mineral trioxide aggregate (MTA) and unmodified Portland cement (RC) were used for comparison. A direct contact assay was undertaken in four samples of each test material, collected at 12, 24, 48 and 72 h. Cell morphology was observed using scanning electron microscopy (SEM) and scored. Culture media were collected for cytokine quantification using enzyme-linked immunosorbent assay (ELISA). On SEM evaluation, healthy SaOS-2 cells were found adhering onto the surfaces of APC variant, RC and MTA. In contrast, rounded and dying cells were observed on GIC. Using ELISA, levels of interleukin (IL)-1beta, IL-6, IL-18 and OC were significantly higher in APC variants compared with controls and GIC (p<0.01), but these levels of cytokines were not statistically significant compared with MTA. The results of this study provide evidence that both APC variants are non-toxic and may have potential to promote bone healing. Further development of APC is indicated to produce a viable dental restorative material and possibly a material for orthopaedic

The contribution of the organic matrix to bone's material properties

Bone is a two-phase porous composite material comprised primarily of collagen and mineral, which together provide its mechanical properties. The contribution of the mineral phase to bone's mechanical properties has dominated scientific thinking. Collagen's role has been underappreciated and not very well studied. However, there is evidence that changes in collagen content, or changes to inter- and intrafibrillar collagen cross-linking, can reduce the energy required to cause bone failure (toughness), and increase fracture risk. Although collagen may have less effect on bone's strength and stiffness than does mineral, it may have a profound effect on bone fragility. Collagen changes that occur with age and reduce bone's toughness may be an important factor in the risk of fracture in older women with low bone mass.

Collagen type I-coating of Ti6Al4V promotes adhesion of osteoblasts

The initial contact of osteoblasts with implant surfaces is an important event for osseointegration of implants. Osseointegration of Ti6Al4V may be improved by precoating of its surface with collagen type I. In this study, the adhesion of rat calvarial osteoblasts to uncoated and collagen type I-coated titanium alloy was investigated over a period of 24 h. Collagen type I-coating accelerates initial adhesion of osteoblasts in the presence of fetal calf serum. One hour after plating, no differences in the percentage of adherent cells between the surfaces investigated were found. Adhesion of osteoblasts to uncoated surfaces was reduced by the GRGDSP peptide by about 70%, whereas adhesion to collagen type I-coated surfaces remained unaffected by treatment of the cells with the peptide. Cell adhesion to coated materials was reduced by about 80% by anti-integrin beta1 antibody. The integrin beta1 antibody did not influence the adhesion to uncoated titanium alloy. The results suggest that osteoblasts adhere to collagen type I-coated materials via integrin beta1 but not by interacting with RGD peptides, whereas adhesion to uncoated titanium alloy is mediated by RGD sequences but not via integrin beta1. Fibronectin does not seem to be involved in the adhesion of osteoblasts to either coated or uncoated titanium alloy.

Regulation of no synthesis induced by inflammatory mediators in RAW264.7 cells: collagen prevents inhibition by osteopontin

Osteopontin has been shown to inhibit the induction of inducible nitric oxide synthase (iNOS, or NOS2) by lipopolysaccharide and interferon-gamma in the RAW264.7 mouse monocyte/macrophage line and in primary mouse proximal tubule epithelial cells. However, the RAW264.7 cells become refractory to the action of OPN after several subcultures or under dilute culture conditions, possibly because of changes in the composition of the extracellular matrix. We make this suggestion because if the cells are plated on a collagen type I or collagen type IV substrate the inhibitory action of OPN is completely suppressed; this is not the case on substrates consisting of laminin, fibronectin, poly-D-lysine, or poly-(2-hydroxyethylmethylacrylate). These observations imply that macrophages are sensitive to regulation by OPN only in certain physiological contexts. Both hyaluronate, which binds CD44, and rat IgGs are also able to inhibit the induction of NO synthesis by the inflammatory mediators. The similar actions of HA and OPN are consistent with the possibility that CD44 may be a receptor for OPN.

High-resolution morphometric analysis of human osteoblastic cell adhesion on clinically relevant orthopedic alloys

Understanding the cellular basis of osteoblastic cell-biomaterial interaction is crucial to the analysis of the mechanism of osseointegration, a requirement of long-term orthopedic implant stability. Clinically, the amount of bone ingrowth is variable, and cellular parameters that influence ingrowth have yet to be clearly determined. In this study, two clinically relevant orthopedic alloys, titanium Ti6A14V (Ti) and cobalt-chrome-molybdenum (CC), were used for a comparative analysis of primary human osteoblastic cell adhesion and spreading, where cell adhesion represents the initial interaction between cellular elements and the biomaterial surface. The kinetic profile of adhesion revealed enhanced cell attachment upon rough Ti surfaces relative to rough CC. Using confocal laser scanning microscopy (CLSM), we observed that, during the first 12 h of contact with the substratum, osteoblastic cells were relatively less spread on rough Ti, whereas cells appeared elongated with multiple cellular extensions on rough CC. Focal adhesion contacts, as indicated by vinculin immunostaining, were distributed throughout the cells adhering to Ti, but were relatively sparse and localized to cellular processes on CC. Furthermore, three-dimensional CLSM reconstruction analysis indicated the presence of vinculin at all membrane-to-surface contact points on both Ti and CC. On Ti, these contact points closely followed the surface contour, whereas, on CC, they were restricted to relative topographic peaks only. Actin cytoskeletal reorganization was prominent in cells cultured on Ti, with stress fibers arranged throughout the cell body, whereas, on CC, actin filaments were sparse and localized primarily to cellular extensions. Because cell attachment mechanisms are likely to influence signal transduction and regulation of gene expression, these early differential responses of osteoblastic cells on Ti and CC may have functional implications on subsequent extracellular matrix mineralization and bone ingrowth at the cell-biomaterial interface.

E-selectin gene expression is induced synergistically with the coexistence of activated classic protein kinase C and signals elicited by interleukin-1beta but not tumor necrosis factor-alpha

We have examined the effect of protein kinase C (PKC) on the expression of the E-selectin and intercellular adhesion molecule-1 (ICAM-1) mRNAs in human umbilical vein endothelial cells. The lower classic PKC activity on pretreatment with phorbol ester (phorbol 12-myristate 13-acetate (PMA)) for 24 h markedly decreased IL-1beta-induced E-selectin mRNA expression in the presence of fetal calf serum and basic fibroblast growth factor, although the induction of ICAM-1 mRNA expression was only influenced a little by the PKC down-regulation. On the other hand, tumor necrosis factor-alpha (TNFalpha)-induced gene expression of these adhesion molecules was unaffected by such PKC modulation. The intracellular signals generated by interleukin (IL)-1beta and TNFalpha themselves are not mediated through classic PKC activation, because the response to neither stimulant was inhibited by the PKC down-regulation in the absence of fetal calf serum and basic fibroblast growth factor. Simultaneous treatment with IL-1beta and PMA synergistically induced E-selectin gene expression but not when TNFalpha was substituted for IL-1beta. ICAM-1 mRNA expression was only additively induced on the cotreatment. The synergistic effect on E-selectin mRNA induction was independent of de novo protein synthesis and mediated by elevated transcriptional activity. Promoter analysis of E-selectin indicated that the NF-ELAM1/activating transcription factor element is critical for the synergistic effect of the cotreatment with IL-1beta and PMA.

Inactivation of kinase cascades in mesangial cells grown on collagen type I

Growth on collagen type I gels is known to suppress the mitogenic responsiveness of mesangial cells. Because these cells proliferate in some renal diseases and themselves synthesize collagen type I, we examined the influence of growth on collagen upon several kinase signaling cascades involved in mesangial cell proliferation. Quiescent mesangial cells grown on collagen type I and then stimulated with serum showed a markedly diminished induction of the protooncogene c-fos, compared with their counterparts on plastic or fibronectin. This effect was accompanied by decreased activation of mitogen-activated (Erk family) and Ca2+/calmodulin-dependent protein kinases. Cells on collagen showed lower basal protein kinase C (PKC) activity and diminished levels of PKC-alpha and -zeta isoforms. Global phosphorylation of tyrosine residues was diminished on collagen, and tyrosine phosphorylation of Erk and focal adhesion kinase in response to serum was not detected, in contrast to cells on plastic. We conclude that attachment of mesangial cells to collagen type I results in a broad suppression of protein phosphorylation that is reflected in diminished induction of the c-fos gene and probably underlies the conversion of cultured mesangial cells to a nonproliferative phenotype.