Fibronectin regulates calvarial osteoblast differentiation

Clinical potential of plasma-functionalized graphene oxide ultrathin sheets for bone and blood vessel regeneration: Insights from cellular and animal models

Graphene and graphene oxide (GO), due to their unique chemical and physical properties, possess biochemical characteristics that can trigger intercellular signals promoting tissue regeneration. Clinical applications of thin GO-derived sheets have inspired the development of various tissue regeneration and repair approaches. In this study, we demonstrate that ultrathin sheets of plasma-functionalized and reduced GO, with the oxygen content ranging from 3.2 % to 22 % and the nitrogen content from 0 % to 8.3 %, retain their essential mechanical and molecular integrity, and exhibit robust potential for regenerating bone tissue and blood vessels across multiple cellular and animal models. Initially, we observed the growth of blood vessels and bone tissue in vitro using these functionalized GO sheets on human adipose-derived mesenchymal stem cells and umbilical vein endothelial cells. Remarkably, our study indicates a 2.5-fold increase in mineralization and two-fold increase in tubule formation even in media lacking osteogenic and angiogenic supplements. Subsequently, we observed the initiation, conduction, and formation of bone and blood vessels in a rat tibial osteotomy model, evident from a marked 4-fold increase in the volume of low radio-opacity bone tissue and a significant elevation in connectivity density, all without the use of stem cells or growth factors. Finally, we validated these findings in a mouse critical-size calvarial defect model (33 % higher healing rate) and a rat skin lesion model (up to 2.5-fold increase in the number of blood vessels, and 35 % increase in blood vessels diameter). This study elucidates the pro-osteogenic and pro-angiogenic properties of both pristine and plasma-treated GO ultrathin films. These properties suggest their significant potential for clinical applications, and as valuable biomaterials for investigating fundamental aspects of bone and blood vessel regeneration.

Contemporary Concepts in Osseointegration of Dental Implants: A Review

In a society highly conscious of esthetics, prosthetic rehabilitation of lost teeth with tissue-integrated implants has gained wide acceptance and demand by patients and clinicians. The backbone of these tissue-integrated implants is the biotechnical process of osseointegration. Although the concept has been introduced and discussed for ages, the deepening knowledge about its cellular and molecular mechanisms has led the researchers to borrow further into the factors influencing the process of osseointegration. This has aided in the hastening and improving the process of osseointegration by exploiting several, even the minutest, details and events taking place in this natural process. Recently, due to the high esthetic expectations of the patients, the implants are being loaded immediately, which demands a high degree of implant stability. Implant stability, especially secondary stability, largely depends on bone formation and integration of implants to the osseous tissues. Various factors that influence the rate and success of osseointegration can either be categorized as those related to implant characteristics like the physical and chemical macro- and microdesign of implants or the bone characteristics like the amount and quality of bone and the local and systemic host conditions, or the time or protocol followed for the functional loading of the dental implant. To address the shortcomings in osseointegration due to any of the factors, it is mandatory that continuous and reliable monitoring of the status of osseointegration is done. This review attempts to encompass the mechanisms, factors affecting, and methods to assess osseointegration, followed by a discussion on the recent advances and future perspectives in dental implantology to enhance the process of osseointegration. The review was aimed at igniting the inquisitive minds to usher further the development of technology that enhances osseointegration.

Bone Tissue Engineering Using Osteogenic Cells: From the Bench to the Clinical Application

The use of tissue engineering to restore and to build new bone tissue is under active research at present. The following review summarizes the latest studies and clinical trials related to the use of osteogenic cells, biomaterials, and scaffolds to regenerate bone defects in the human jaws. Bone tissue engineering (BTE) combined with scaffolds have provided a range of advantages not only to transport the target cells to their desired destination but also to support the early phases of the mineralization process. The mechanical, chemical, and physical properties of scaffolds have been evaluated as they affect the quantity of bone regeneration, particularly in the oral cavity. This review also highlighted the mechanisms underlying bone homeostasis, including the key transcription factors and signaling pathways responsible for regulating the differentiation of osteoblast lineage. Furthering understanding of the mechanisms of cellular signaling in skeletal remodeling with the use of mesenchymal stem cells and the proper scaffold properties are key-factors to enable the incorporation of new and effective treatment methods into clinical practice for bone tissue regeneration using BTE. Impact Statement The use of mesenchymal stem cells able to differentiate in osteoblast lineage for bone tissue engineering (BTE) remains a major challenge. Viable cells and signaling pathways play an essential role in bone repair and regeneration of critical size defects. Recent advances in scaffolds and biological factors such as growth factors (e.g., cytokines and hormones) controlling the osteogenic signaling cascade are now becoming new players affecting the osteogenic potential of cells. Such techniques will significantly impact the maxillofacial bone tissue replacement, repair, and regeneration for patients without having to rely on donor banks or other surgical sites.

Function and Mechanism of RGD in Bone and Cartilage Tissue Engineering

Bone and cartilage injury is common, tissue engineered scaffolds are potential means to repair. Because most of the scaffold materials used in bone and cartilage tissue engineering are bio-inert, it is necessary to increase the cellular adhesion ability of during tissue engineering reconstruction. The Arginine - Glycine - Aspartic acid (Arg-Gly-Asp, RGD) peptide family is considered as a specific recognition site for the integrin receptors. Integrin receptors are key regulators of cell-cell and cell-extracellular microenvironment communication. Therefore, the RGD polypeptide families are considered as suitable candidates for treatment of a variety of diseases and for the regeneration of various tissues and organs. Many scaffold material for tissue engineering and has been approved by US Food and Drug Administration (FDA) for human using. The application of RGD peptides in bone and cartilage tissue engineering was reported seldom. Only a few reviews have summarized the applications of RGD peptide with alloy, bone cements, and PCL in bone tissue engineering. Herein, we summarize the application progress of RGD in bone and cartilage tissue engineering, discuss the effects of structure, sequence, concentration, mechanical stimulation, physicochemical stimulation, and time stimulation of RGD peptide on cells differentiation, and introduce the mechanism of RGD peptide through integrin in the field of bone and cartilage tissue engineering.

Decellularized Extracellular Matrix for Cell Biology

The extracellular matrix (ECM) is an architecture that supports the cells in our bodies and regulates various cell functions. The ECM is composed of many proteins and carbohydrates, and these molecules activate various intracellular signaling pathways orchestrated to decide cell fates. Therefore, it is not enough to study the role of single ECM molecules to understand the roles of the ECM in the regulation of cell functions; it is necessary to understand how the ECM, as an assembly of various molecules, regulates cell functions as a whole. For this purpose, in vitro ECM models mimicking native ECM are required. Here, a decellularization technique is presented to reconstitute native ECM in vitro. In this article, methods for preparing decellularized ECM (dECM) are described for use in tumor and stem cell biology. Additionally, a method for confirmation of decellularization and a dECM modification method are described. These dECM types will be useful for comprehensive studies of ECM roles. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Preparation of in vitro extracellular matrix (ECM) models mimicking native ECM in different malignant tumor tissues Basic Protocol 2: Preparation of in vitro ECM models mimicking native ECM surrounding myoblasts differentiating into myotubes at each myogenic stage Support Protocol 1: Confirmation of myogenic stages by myogenic stages by myogenic gene expression analysis Basic Protocol 3: Confirmation of cell removal Basic Protocol 4: Reduction of chondroitin sulfate chains in cultured cell-derived decellularized ECM Support Protocol 2: Quantification of chondroitin sulfate chain amounts in the decellularized ECM.

Hypothalamic and ovarian transcriptome profiling reveals potential candidate genes in low and high egg production of white Muscovy ducks (Cairina moschata)

In China, the low egg production rate is a major challenge to Muscovy duck farmers. Hypothalamus and ovary play essential role in egg production of birds. However, there are little or no reports from these tissues to identify potential candidate genes responsible for egg production in White Muscovy ducks. A total of 1,537 laying ducks were raised; the egg production traits which include age at first egg (days), number of eggs at 300 d, and number of eggs at 59 wk were recorded. Moreover, 4 lowest (LP) and 4 highest producing (HP) were selected at 59 wk of age, respectively. To understand the mechanism of egg laying regulation, we sequenced the hypothalamus and ovary transcriptome profiles in LP and HP using RNA-Seq. The results showed that the number of eggs at 300 d and number of eggs at 59 wk in the HP were significantly more (P < 0.001) than the LP ducks. In total, 106.98G clean bases were generated from 16 libraries with an average of 6.68G clean bases for each library. Further analysis showed 569 and 2,259 differentially expressed genes (DEGs) were identified in the hypothalamus and ovary between LP and HP, respectively. The KEGG pathway enrichment analysis revealed 114 and 139 pathways in the hypothalamus and ovary, respectively which includes Calcium signaling pathway, ECM-receptor interaction, Focal adhesion, MAPK signaling pathway, Apoptosis and Apelin signaling pathways that are involved in egg production. Based on the GO terms and KEGG pathways results, 10 potential candidate genes (P2RX1, LPAR2, ADORA1, FN1, AKT3, ADCY5, ADCY8, MAP3K8, PXN, and PTTG1) were identified to be responsible for egg production. Further, protein-protein interaction was analyzed to show the relationship between these candidate genes. Therefore, this study provides useful information on transcriptome of hypothalamus and ovary of LP and HP Muscovy ducks.

Freeze-Dried Secretome (Lyosecretome) from Mesenchymal Stem/Stromal Cells Promotes the Osteoinductive and Osteoconductive Properties of Titanium Cages

Titanium is one of the most frequently used materials in bone regeneration due to its good biocompatibility, excellent mechanical properties, and great osteogenic performance. However, osseointegration with host tissue is often not definite, which may cause implant failure at times. The present study investigates the capacity of the mesenchymal stem cell (MSC)-secretome, formulated as a ready-to-use and freeze-dried medicinal product (the Lyosecretome), to promote the osteoinductive and osteoconductive properties of titanium cages. In vitro tests were conducted using adipose tissue-derived MSCs seeded on titanium cages with or without Lyosecretome. After 14 days, in the presence of Lyosecretome, significant cell proliferation improvement was observed. Scanning electron microscopy revealed the cytocompatibility of titanium cages: the seeded MSCs showed a spread morphology and an initial formation of filopodia. After 7 days, in the presence of Lyosecretome, more frequent and complex cellular processes forming bridges across the porous surface of the scaffold were revealed. Also, after 14 and 28 days of culturing in osteogenic medium, the amount of mineralized matrix detected by alizarin red was significantly higher when Lyosecretome was used. Finally, improved osteogenesis with Lyosecretome was confirmed by confocal analysis after 28 and 56 days of treatment, and demonstrating the production by osteoblast-differentiated MSCs of osteocalcin, a specific bone matrix protein.

Biohybrid Bovine Bone Matrix for Controlled Release of Mesenchymal Stem/Stromal Cell Lyosecretome: A Device for Bone Regeneration

SmartBone® (SB) is a biohybrid bone substitute advantageously proposed as a class III medical device for bone regeneration in reconstructive surgeries (oral, maxillofacial, orthopedic, and oncology). In the present study, a new strategy to improve SB osteoinductivity was developed. SB scaffolds were loaded with lyosecretome, a freeze-dried formulation of mesenchymal stem cell (MSC)-secretome, containing proteins and extracellular vesicles (EVs). Lyosecretome-loaded SB scaffolds (SBlyo) were prepared using an absorption method. A burst release of proteins and EVs (38% and 50% after 30 min, respectively) was observed, and then proteins were released more slowly with respect to EVs, most likely because they more strongly adsorbed onto the SB surface. In vitro tests were conducted using adipose tissue-derived stromal vascular fraction (SVF) plated on SB or SBlyo. After 14 days, significant cell proliferation improvement was observed on SBlyo with respect to SB, where cells filled the cavities between the native trabeculae. On SB, on the other hand, the process was still present, but tissue formation was less organized at 60 days. On both scaffolds, cells differentiated into osteoblasts and were able to mineralize after 60 days. Nonetheless, SBlyo showed a higher expression of osteoblast markers and a higher quantity of newly formed trabeculae than SB alone. The quantification analysis of the newly formed mineralized tissue and the immunohistochemical studies demonstrated that SBlyo induces bone formation more effectively. This osteoinductive effect is likely due to the osteogenic factors present in the lyosecretome, such as fibronectin, alpha-2-macroglobulin, apolipoprotein A, and TGF-β.

Fibronectin 1 activates WNT/β-catenin signaling to induce osteogenic differentiation via integrin β1 interaction

Osteoporosis (OP) is a systemic skeletal disease leading to fragility fractures and is a major health issue globally. WNT/β-catenin signaling regulates bone-remodeling processes and plays vital roles in OP development. However, the underlying regulatory mechanisms behind WNT/β-catenin signaling in OP requires clarification, as further studies are required to identify novel alternate therapeutic agents to improve OP. Here we report that fibronectin 1 (FN-1) promoted differentiation and mineralization of osteoblasts by activating WNT/β-catenin pathway, in cultured pre-osteoblasts. With isobaric tags for relative and absolute quantitation labeling proteomics analysis, we investigated protein changes in bone samples from OP patients and normal controls. FN-1 accumulated in osteoblasts in bone samples from OP patients and age-related OP mice compared to control group. In addition, we observed that integrin β1 (ITGB1) acts as an indispensable signaling molecule for the interplay between FN-1 and β-catenin, and that FN-1 expression increased, but ITGB1 expression decreased in osteoblasts during OP progression. Therefore, our study reveals a novel explanation for WNT/β-catenin pathway inactivation in OP pathology. Supplying of FN-1 and ITGB1 may provide a potential therapeutic strategy in improving bone formation during OP.

Review of Integrin-Targeting Biomaterials in Tissue Engineering

The ability to direct cell behavior has been central to the success of numerous therapeutics to regenerate tissue or facilitate device integration. Biomaterial scientists are challenged to understand and modulate the interactions of biomaterials with biological systems in order to achieve effective tissue repair. One key area of research investigates the use of extracellular matrix-derived ligands to target specific integrin interactions and induce cellular responses, such as increased cell migration, proliferation, and differentiation of mesenchymal stem cells. These integrin-targeting proteins and peptides have been implemented in a variety of different polymeric scaffolds and devices to enhance tissue regeneration and integration. This review first presents an overview of integrin-mediated cellular processes that have been identified in angiogenesis, wound healing, and bone regeneration. Then, research utilizing biomaterials are highlighted with integrin-targeting motifs as a means to direct these cellular processes to enhance tissue regeneration. In addition to providing improved materials for tissue repair and device integration, these innovative biomaterials provide new tools to probe the complex processes of tissue remodeling in order to enhance the rational design of biomaterial scaffolds and guide tissue regeneration strategies.

Decellularized extracellular matrices derived from cultured cells at stepwise myogenic stages for the regulation of myotube formation

The regulation of stem cell differentiation is key for muscle tissue engineering and regenerative medicine. To this end, various substrates mimicking the native extracellular matrix (ECM) have been developed with consideration of the mechanical, topological, and biochemical properties. However, mimicking the biochemical properties of the native ECM is difficult due to its compositional complexity. To develop substrates that mimic the native ECM and its biochemical properties, decellularization is typically used. Here, substrates mimicking the native ECM at each myogenic stage are prepared as stepwise myogenesis-mimicking matrices via the in vitro myogenic culture of C2C12 myoblasts and decellularization. Cells adhered to the stepwise myogenesis-mimicking matrices at similar levels. However, the matrices derived from cells at the myogenic early stage suppressed cell growth and promoted myogenesis. This promotion of myogenesis was potentially due to the suppression of the activation of endogenous BMP signaling following the suppression of the expression of the myogenic-inhibitory factors, Id2 and Id3. Our stepwise myogenesis-mimicking matrices will be suitable ECM models for basic biological research and myogenesis of stem cells. Further, these matrices will provide insights that improve the efficacy of decellularized ECM for muscle repair.

Macrophage-Derived Extracellular Vesicles as Carriers of Alarmins and Their Potential Involvement in Bone Homeostasis

Extracellular vesicles are a heterogeneous group of cell-derived membranous structures, which facilitate intercellular communication. Recent studies have highlighted the importance of extracellular vesicles in bone homeostasis, as mediators of crosstalk between different bone-resident cells. Osteoblasts and osteoclasts are capable of releasing various types of extracellular vesicles that promote both osteogenesis, as well as, osteoclastogenesis, maintaining bone homeostasis. However, the contribution of immune cell-derived extracellular vesicles in bone homeostasis remains largely unknown. Recent proteomic studies showed that alarmins are abundantly present in/on macrophage-derived EVs. In this review we will describe these alarmins in the context of bone matrix regulation and discuss the potential contribution macrophage-derived EVs may have in this process.

Design of fibronectin type III domains fused to an elastin-like polypeptide for the osteogenic differentiation of human mesenchymal stem cells

Extracellular matrix (ECM) including fibronectin (FN) and elastin plays a pivotal role in providing a microenvironment to support tissue regeneration in stem cell therapy. To develop a novel biomimetic ECM for stem cell differentiation, we engineered FN type III 9 and 10 domains fused to elastin-like polypeptides (FN-ELPs). The recombinant FN-ELP fusion protein was expressed in Escherichia coli and purified by inverse transition cycling. Human mesenchymal stem cells (hMSCs) cultured on plates coated with FN-ELP had significantly greater adhesion activity and proliferation than cells grown on non-coated plates. FN-ELP induced the osteogenic differentiation by elevating alkaline phosphatase (ALP) and mineralization activity of hMSCs. Furthermore, the osteogenic marker gene expressions of ALP, collagen type I (Col I), osteopontin (OPN), and transcriptional coactivator with a PDZ-binding motif (TAZ) were increased in hMSCs cultured on plates coated with FN-ELP. We reported a novel biomimetic ECM with potential for bone regeneration that promotes the osteogenic differentiation of hMSCs.

The Bone Extracellular Matrix as an Ideal Milieu for Cancer Cell Metastases

Bone is a preferential site for cancer metastases, including multiple myeloma, prostate, and breast cancers.The composition of bone, especially the extracellular matrix (ECM), make it an attractive site for cancer cell colonization and survival. The bone ECM is composed of living cells embedded within a matrix composed of both organic and inorganic components. Among the organic components, type I collagen provides the tensile strength of bone. Inorganic components, including hydroxyapatite crystals, are an integral component of bone and provide bone with its rigidity. Under normal circumstances, two of the main cell types in bone, the osteoblasts and osteoclasts, help to maintain bone homeostasis and remodeling through cellular communication and response to biophysical signals from the ECM. However, under pathological conditions, including osteoporosis and cancer, bone remodeling is dysregulated. Once in the bone matrix, disseminated tumor cells utilize normal products of bone remodeling, such as collagen type I, to fuel cancer cell proliferation and lesion outgrowth. Models to study the complex interactions between the bone matrix and metastatic cancer cells are limited. Advances in understanding the interactions between the bone ECM and bone metastatic cancer cells are necessary in order to both regulate and prevent metastatic cancer cell growth in bone.

Angiogenic and Osteogenic Synergy of Human Mesenchymal Stem Cells and Human Umbilical Vein Endothelial Cells Cocultured on a Nanomatrix

To date, bone tissue regeneration strategies lack an approach that effectively provides an osteogenic and angiogenic environment conducive to bone growth. In the current study, we evaluated the osteogenic and angiogenic response of human mesenchymal stem cells (hMSCs) and green fluorescent protein-expressing human umbilical vein endothelial cells (GFP-HUVECs) cocultured on a self-assembled, peptide amphiphile nanomatrix functionalized with the cell adhesive ligand RGDS (PA-RGDS). Analysis of alkaline phosphatase activity, von Kossa staining, Alizarin Red quantification, and osteogenic gene expression, indicates a significant synergistic effect between the PA-RGDS nanomatrix and coculture that promoted hMSC osteogenesis. In addition, coculturing on PA-RGDS resulted in enhanced HUVEC network formation and upregulated vascular endothelial growth factor gene and protein expression. Though PA-RGDS and coculturing hMSCs with HUVECs were each previously reported to individually enhance hMSC osteogenesis, this study is the first to demonstrate a synergistic promotion of HUVEC angiogenesis and hMSC osteogenesis by integrating coculturing with the PA-RGDS nanomatrix. We believe that using the combination of hMSC/HUVEC coculture and PA-RGDS substrate is an efficient method for promoting osteogenesis and angiogenesis, which has immense potential as an efficacious, engineered platform for bone tissue regeneration.

Non-sutural basicranium-derived cells undergo a unique mineralization pathway via a cartilage intermediate in vitro

The basicranium serves as a key interface in the mammalian skull, interacting with the calvarium, facial skeleton and vertebral column. Despite its critical function, little is known about basicranial bone formation, particularly on a cellular level. The goal of this study was therefore to cultivate a better understanding of basicranial development by isolating and characterizing the osteogenic potential of cells from the neonatal murine cranial base. Osteoblast-like basicranial cells were isolated, seeded in multicellular aggregates (designated micromasses), and cultured in osteogenic medium in the presence or absence of bone morphogenetic protein-6 (BMP6). A minimal osteogenic response was observed in control osteogenic medium, while BMP6 treatment induced a chondrogenic response followed by up-regulation of osteogenic markers and extensive mineralization. This response appears to be distinct from prior analyses of the calvarium and long bones, as basicranial cells did not mineralize under standard osteogenic conditions, but rather required BMP6 to stimulate mineralization, which occurred via an endochondral-like process. These findings suggest that this site may be unique compared to other cranial elements as well as the limb skeleton, and we propose that the distinct characteristics of these cells may be a function of the distinct properties of the basicranium: endochondral ossification, dual embryology, and complex loading environment.

Delivery of cellular factors to regulate bone healing

Bone tissue has a strong intrinsic regenerative capacity, thanks to a delicate and complex interplay of cellular and molecular processes, which tightly involve the immune system. Pathological settings of anatomical, biomechanical or inflammatory nature may lead to impaired bone healing. Innovative strategies to enhance bone repair, including the delivery of osteoprogenitor cells or of potent cytokines/morphogens, indicate the potential of 'orthobiologics', but are not fully satisfactory. Here, we review different approaches based on the delivery of regenerative cues produced by cells but in cell-free, possibly off-the-shelf configurations. Such strategies exploit the paracrine effect of the secretome of mesenchymal stem/stromal cells, presented in soluble form, shuttled through extracellular vesicles, or embedded within the network of extracellular matrix molecules. In addition to osteoinductive molecules, attention is given to factors targeting the resident immune cells, to reshape inflammatory and immunity processes from scarring to regenerative patterns.

Differentiated osteoblasts derived decellularized extracellular matrix to promote osteogenic differentiation

Background

The extracellular matrix (ECM) can directly or indirectly influence on regulation of cell functions such as cell adhesion, migration, proliferation and differentiation. The cell derived ECM (CD-ECM) is a useful in vitro model for studying the comprehensive functions of CD-ECM because it maintains a native-like structure and composition. In this study, the CD-ECM is obtained and a test is carried out to determine the effectiveness of several combinations of decellularized methods. These methods were used to regulate the optimal ECM compositions to be induced by osteogenic differentiation using primary isolated osteoblasts.

Result

We investigated the effect of osteoblasts re-seeded onto normal osteoblast ECM under the growth medium (GM-ECM) and the osteogenic differentiation medium (OD-ECM). The osteoblasts were then cultured statically for 1, 2, and 4 weeks in a growth medium or differentiation medium. Before osteoblast culture, we performed immunostaining with filamentous actin and nuclei, and then performed DNA quantification. After each culture period, the osteogenic differentiation of the osteoblasts re-seeded on the OD-ECMs was enhanced osteogenic differentiation which confirmed by alkaline phosphatase staining and quantification, Alizarin Red S staining and quantification, and von Kossa staining. The OD-ECM-4 W group showed more effective osteogenic differentiation than GM-ECM and OD-ECM-2 W.

Conclusions

The OD-ECM-4 W has a better capacity in a microenvironment that supports osteogenic differentiation on the GM-ECM and OD-ECM-2 W. The ECM substrate has a wide range of applications as cell culture system or direct differentiation of stem cell and excellent potential as cell-based tissue repair in orthopedic tissue engineering.

The extracellular matrix protein Edil3 stimulates osteoblast differentiation through the integrin α5β1/ERK/Runx2 pathway

Epidermal growth factor-like repeats and discoidin I-like domain 3 (Edil3) is an extracellular matrix protein containing an Arg-Gly-Asp (RGD) motif that binds integrin. Recently, Edil3 has been implicated in various biological processes, including angiogenesis and cellular differentiation. It can inhibit inflammatory bone destruction. The objective of this study was to explore the role of Edil3 in osteoblast differentiation and its underlying molecular mechanisms. In wild-type mice, high expression levels of Edil3 mRNA were observed in isolated calvaria and tibia/femur bones. Immunohistochemical analysis showed that Edil3 protein was localized along periosteum and calcified regions surrounding bone tissues. When murine calvaria-derived MC3T3-E1 cells were cultured in osteogenic medium containing 50 μg/ml ascorbic acid and 5 mM β-glycerophosphate, Edil3 mRNA and protein expression levels were increased. Treatment with Edil3 protein in growth media increased expression levels of alkaline phosphatase and osteocalcin gene and phosphorylation level of extracellular signal-regulated kinase (ERK). Edil3 treatment with osteogenic medium induced mineralization. Treatment with a neutralizing antibody against α5β1 and MEK inhibitor U0126 inhibited Edil3-enhanced osteogenic marker gene expression and mineral deposition. Edil3 increased protein expression levels of transcription factor runt-related transcription factor2 (Runx2). Edil3-induced Runx2 protein expression was suppressed by pretreatment with U0126. Taken together, these results suggest that Edil3 may stimulate osteoblast differentiation and matrix mineralization by increasing expression of Runx2 through α5β1 integrin /ERK pathway.

Biomimetic matrix fabricated by LMP-1 gene-transduced MC3T3-E1 cells for bone regeneration

Bone healing is regulated by multiple microenvironmental signals provided by the extracellular matrix (ECM). This study aimed to mimic the native osteoinductive microenvironment by developing an ECM using gene-transduced cells. The LIM mineralization protein-1 (LMP-1) gene was transferred to murine pre-osteoblast cells (MC3T3-E1) using lentiviral vectors. Western blotting assay indicated that the MC3T3-E1 cells expressed an increased level of bone morphologic protein-2, -4 and -7 (BMP-2, -4 and -7) after LMP-1 gene transduction. The transduced cells were then seeded into calcined bovine bone scaffolds and cultured for 7, 14, and 21 days to construct ECMs on the scaffolds. The ECM-scaffold composites were then decellularized using the freeze-drying method. Scaffolds without ECM deposition were used as controls. The composites and controls were implanted into critical-sized bone defects created in the distal femurs of New Zealand rabbits. Twelve weeks after the surgery, both microcomputed tomography and histologic results indicated that the 7-day-cell-modified ECM-scaffold composites induced bone regeneration with significantly larger volume, trabecular thickness and connectivity than the controls. However, the 14- and 21-day-cell-modified ECM-scaffold composites triggered sustained inflammation response even at 12 weeks after the surgery and showed less bone ingrowth and integration than their 7-day-cell-modified counterparts. In conclusion, these results highlight the viable gene transfer techniques for manipulating cells in a constructed microenvironment of ECM for bone regeneration. However, the unresolved inflammation relating to the duration of ECM modification needs to be considered.

Molecular modeling to predict peptide accessibility for peptide-functionalized hydrogels

Peptide-functionalized (PF) hydrogels are being widely investigated by the tissue engineering and regenerative medicine communities for a broad range of applications because of their unique potential to mimic the natural extracellular matrix and promote tissue regeneration. In order for these complex material systems to perform their intended bioactive function (e.g., cell signaling), the peptides that are tethered to the hydrogel matrix must be accessible at the hydrogel surface for cell-receptor binding. The factors influencing the surface accessibility of the tethered peptide mainly include the length of the tethers, the loading (i.e., concentration) of the peptide, and the association between the tethered peptide and the hydrogel matrix. In the present work, the authors developed coarse-grained molecular models based on the all-atom polymer consistent force field for a type of poly(ethylene glycol)-based PF hydrogel and conducted molecular simulations to investigate the distribution of the peptide within the hydrogel and its surface accessibility as a function of tether length and peptide concentration. The calculated results of the effects of these design parameters on the surface accessibility of the peptide agree very well with corresponding experimental measurements in which peptide accessibility was quantified by the number of cells attached to the hydrogel surface per unit area. The developed modeling methods are able to provide unique insights into the molecular behavior of PF hydrogels and the distribution of the tethered peptides, which can serve as a guide for hydrogel design optimization.

In situ examination of osteoblast biomineralization on sulfonated polystyrene-modified substrates using Fourier transform infrared microspectroscopy

Osteoporosis is a skeletal disorder that is characterized by the loss of bone mineral density (BMD) resulting in increased risk of fracture. However, it has been shown that BMD is not the only indicator of fracture risk, as the strength of bone depends on a number of factors, including bone mass, architecture and material properties. Physiological mineral deposition requires the formation of a properly developed extracellular matrix (ECM), which recruits calcium and phosphate ions into the synthesis of apatite crystals. Temporal and spatial compositional and structural changes of biological apatite greatly depend on the properties of the crystals initially formed. As such, Fourier-transform infrared microspectroscopy (FTIRM) is capable of examining adaptive remodeling by providing compositional information such as the level of mineralization and carbonate substitution, as well as quality and perfection of the mineral phase. The objective of this study was to evaluate the in vitro mineralization development of MC3T3-E1 murine calvarial preosteoblasts cultured on different substrata by comparing FTIRM measurements from two subclones (mineralizing subclone 4 and nonmineralizing subclone 24) maintained in culture for up to 21 days. The results showed that modulation of the substrate surface using a thin coating of sulfonated polystyrene (SPS) provided favorable conditions for the development of a mineralizable ECM and that the mineral formed by the osteoblasts was similar to that of fully mineralized bone tissue. Specifically, the mineralizing subclone produced significantly more mineral phosphate when cultured on SPS-coated substrates for 21 days, compared to the same culture on bare substrates. In contrast, the level of mineralization in nonmineralizing subclone was low on both SPS-coated and uncoated substrates. The mineralizing subclone also produced comparable amounts of collagen on both substrates; however, mineralization was significantly higher in the SPS culture. The nonmineralizing subclone produced comparable amounts of collagen on day 1 but much less on day 21. Collagen maturity ratio increased in the mineralizing subclone from day 1 to day 21, but remained unchanged in the nonmineralizing subclone. These results suggest that SPS-treatment of the substrate surface may alter collagen remodeling; however, other factors may also influence osteoblast mineralization in the long term.

EDA-Fibronectin Originating from Osteoblasts Inhibits the Immune Response against Cancer

Osteoblasts lining the inner surface of bone support hematopoietic stem cell differentiation by virtue of proximity to the bone marrow. The osteoblasts also modify their own differentiation by producing various isoforms of fibronectin (FN). Despite evidence for immune regulation by osteoblasts, there is limited knowledge of how osteoblasts modulate cells of the immune system. Here, we show that extra domain A (EDA)-FN produced by osteoblasts increases arginase production in myeloid-derived cells, and we identify α5β1 as the mediating receptor. In different mouse models of cancer, osteoblasts or EDA-FN was found to up-regulate arginase-1 expression in myeloid-derived cells, resulting in increased cancer growth. This harmful effect can be reduced by interfering with the integrin α5β1 receptor or inhibiting arginase. Conversely, in tissue injury, the expression of arginase-1 is normally beneficial as it dampens the immune response to allow wound healing. We show that EDA-FN protects against excessive fibrotic tissue formation in a liver fibrosis model. Our results establish an immune regulatory function for EDA-FN originating from the osteoblasts and identify new avenues for enhancing the immune reaction against cancer.

Osteoblasts produce an isoform of fibronectin (EDA-fibronectin) that acts on myeloid cells to increase arginase-1 expression and protect against fibrosis. However, it can also enhance cancer growth; interfering with the interaction between EDA-fibronectin and its receptor diminishes this effect.

Osteoblasts, which are the cells that produce bone, line the inner surface of the bone and are adjacent to the marrow that generates all the different blood cells. Osteoblasts have a close relationship with hematopoiesis, and it has been shown that a transient elimination of osteoblasts leads to the decrease of hematopoietic stem cells and progenitor cells. Fibronectin (FN) is an extracellular matrix protein with a known role in hematopoiesis in vitro that is secreted by osteoblasts. Here, we analyze the role of FN in hematopoiesis and find that an isoform that contains the extra domain A (EDA) and is produced by the osteoblasts affects both the number and future behavior of a subset of immune cells. EDA-FN protects against excessive fibrotic tissue formation in a liver fibrosis model. The same process, however, is detrimental in cancer, because it prevents the organism from mounting a potent immune response against the cancer and induces an increase of cancer growth. Mechanistically, we find that the EDA domain binds to the cell surface receptor α5β1 integrin and enhances the production of the anti-inflammatory and immunosuppressive factor arginase-1. We conclude that EDA-FN production by osteoblasts modulates immune cell behavior, and that interfering with this mechanism opens up new possibilities for enhancing an immune reaction against cancer.

Use of a biological reactor and platelet-rich plasma for the construction of tissue-engineered bone to repair articular cartilage defects

Articular cartilage defects are a major clinical burden worldwide. Current methods to repair bone defects include bone autografts, allografts and external fixation. In recent years, the repair of bone defects by tissue engineering has emerged as a promising approach. The present study aimed to assess a novel method using a biological reactor with platelet-rich plasma to construct tissue-engineered bone. Beagle bone marrow mesenchymal stem cells (BMSCs) were isolated and differentiated into osteoblasts and chondroblasts using platelet-rich plasma and tricalcium phosphate scaffolds cultured in a bioreactor for 3 weeks. The cell scaffold composites were examined by scanning electron microscopy (SEM) and implanted into beagles with articular cartilage defects. The expression of osteogenic markers, alkaline phosphatase and bone γ-carboxyglutamate protein (BGLAP) were assessed using polymerase chain reaction after 3 months. Articular cartilage specimens were observed histologically. Adhesion and distribution of BMSCs on the β-tricalcium phosphate (β-TCP) scaffold were confirmed by SEM. Histological examination revealed that in vivo bone defects were largely repaired 12 weeks following implantation. The expression levels of alkaline phosphatase (ALP) and BGLAP in the experimental groups were significantly elevated compared with the negative controls. BMSCs may be optimum seed cells for tissue engineering in bone repair. Platelet-rich plasma (PRP) provides a rich source of cytokines to promote BMSC function. The β-TCP scaffold is advantageous for tissue engineering due to its biocompatibility and 3D structure that promotes cell adhesion, growth and differentiation. The tissue-engineered bone was constructed in a bioreactor using BMSCs, β-TCP scaffolds and PRP and displayed appropriate morphology and biological function. The present study provides an efficient method for the generation of tissue-engineered bone for cartilage repair, compared with previously used methods.

Strontium ranelate increases osteoblast activity

Strontium ranelate (SR) is the first generation of a new class of medication for osteoporosis, which is capable of inducing bone formation and, to a certain extent, inhibiting bone resorption. The aim of this study was to evaluate the in vitro effects of SR on osteoblastic cell cultures. MC3TE-E1 cells were seeded in 24-well plates at a density of 2×10(4) cells/well and exposed to SR at 0.05, 0.1, and 0.5mM. The following parameters were assayed: 1) Cell proliferation by hemocytometer counting after 24, 48 and 72h, 2) Cell viability by MTT assay after 24, 48 and 72h, 3) Type I Collagen and Osteopontin (OPN) quantification by Western Blotting, ELISA, and Real Time PCR after 48h, 3) Immunolocalization of fibronectin (FN) by epifluorescence, and 4) matrix mineralization by Alizarin Red staining after 14days. After 24, 48 and 72h, the cell proliferation and viability were not affected by SR at 0.05 and 0.1mM (p>0.05). However, cell cultures exposed to SR at 0.5mM exhibited a decrease in both cell proliferation and cell viability in all time points assayed (p<0.05). High levels of protein and mRNA for Type I Collagen and OPN were detected in cultures exposed to SR, particularly at 0.5mM (p<0.05). SR allowed the expression of FN in osteoblastic cell cultures as observed by epifluorescence analysis. The mineralized bone-like nodule formation was affected in a concentration-dependent manner by SR, with large bone-like nodules being detected in osteoblastic cell cultures exposed to SR at 0.5mM. In conclusion, these results suggest that SR can accelerate acquisition of the osteoblastic phenotype, which explains, at least in part, the rebalancing of bone turnover in favor of bone formation.

Curcumin and epithelial-mesenchymal transition in breast cancer cells transformed by low doses of radiation and estrogen

Breast cancer is a major cause of global mortality in women. Curcumin exerts anti-proliferative, anti-migratory and apoptotic effects. The aim of this study was to evaluate gene expression involved in epithelial-mesenchymal transition (EMT). An in vitro model was developed with the MCF-10F immortalized breast epithelial cell line exposed to low radiation doses of high LET (linear energy transfer) α-particles (150 keV/µm) and cultured in the presence of 17β-estradiol (estrogen). The following cell lines were used: i) MCF-10F, normal; ii) Alpha5, pre-tumorigenic, and iii) Tumor2 derived from Alpha5 injected into the nude mice. Our previous results have shown that Alpha5 and Tumor2 increased cell proliferation, anchorage independency, invasive capabilities and tumor formation in nude mice in comparison to control. Results indicated that curcumin decreased expression of EMT-related genes in Tumor2 cell line when compared to its counterpart as E-cadherin, N-cadherin, ZEB2, Twist1, Slug, Axl, vimentin, STAT-3, fibronectin; and genes p53 and caveolin-1, as well as apoptotic genes caspase-3, caspase-8, and others such as cyclin D1 and NFκB. All these changes induced a decrease in migratory and invasive capabilities of such a cell line. Thus, it seems that curcumin may impinge upon apoptosis and metastatic properties of the malignant cells exerting antitumor activity in breast cancer cells transformed by low doses of α-particles and estrogen in vitro.

Hypergravity-induced enrichment of β1 integrin on the cell membranes of osteoblast-like cells via caveolae-dependent endocytosis

In bone cells, integrins on the cellular surface are the primary sensors of their mechanical environment. Although gravitational changes are known to affect the adhesion and functions of bone cells, whether integrins respond to hypergravity in osteoblasts remains unclear. In this work, we demonstrate that exposure to a hypergravitational environment (20 × g via centrifugation) resulted in the concentration of β1, but not β3, integrin on the cell membrane of osteoblast-like (MC3T3-E1) cells. Notably, the total expression of both integrins was unaffected by the hypergravitational environment. In addition, caveolin-dependent endocytosis was discovered to be involved in the regulation of the enrichment of β1 integrin on the cell surface after stimulation by hypergravity. These findings could aid in the improvement of our understanding of the mechanisms underlying the effects of different gravitational forces on the human body.

Design of an osteoinductive extracellular fibronectin matrix protein for bone tissue engineering

Integrin-mediated cell-matrix interactions play an important role in osteogenesis. Here, we constructed a novel osteoinductive fibronectin matrix protein (oFN) for bone tissue engineering, designed to combine the integrin-binding modules from fibronectin (iFN) and a strong osteoinductive growth factor, bone morphogenetic protein-2. Compared with iFN, the purified oFN matrix protein caused a significant increase in cell adhesion and osteogenic differentiation of pre-osteoblast MC3T3-E1 cells (p < 0.05).

Revealing cytokine-induced changes in the extracellular matrix with secondary ion mass spectrometry

Cell-secreted matrices (CSMs), where extracellular matrix (ECM) deposited by monolayer cell cultures is decellularized, have been increasingly used to produce surfaces that may be reseeded with cells. Such surfaces are useful to help us understand cell-ECM interactions in a microenvironment closer to the in vivo situation than synthetic substrates with adsorbed proteins. We describe the production of CSMs from mouse primary osteoblasts (mPObs) exposed to cytokine challenge during matrix secretion, mimicking in vivo inflammatory environments. Time-of-flight secondary ion mass spectrometry data revealed that CSMs with cytokine challenge at day 7 or 12 of culture can be chemically distinguished from one another and from untreated CSM using multivariate analysis. Comparison of the differences with reference spectra from adsorbed protein mixtures points towards cytokine challenge resulting in a decrease in collagen content. This is supported by immunocytochemical and histological staining, demonstrating a 44% loss of collagen mass and a 32% loss in collagen I coverage. CSM surfaces demonstrate greater cell adhesion than adsorbed ECM proteins. When mPObs were reseeded onto cytokine-challenged CSMs they exhibited reduced adhesion and elongated morphology compared to untreated CSMs. Such changes may direct subsequent cell fate and function, and provide insights into pathological responses at sites of inflammation.

Serotonin (5-HT) inhibits Factor XIII-A-mediated plasma fibronectin matrix assembly and crosslinking in osteoblast cultures via direct competition with transamidation

Serotonin (5-HT)--a monoamine with a variety of physiological functions--has recently emerged as a major regulator of bone mass. 5-HT is synthesized in the brain and the gut, and gut-derived 5-HT contributes to circulating 5-HT levels and is a negative modulator of bone mass and quality. 5-HT's negative effects on the skeleton are considered to be mediated via its receptors and transporter in osteoblasts and osteoclasts; however, 5-HT can also incorporate covalently into proteins via a transglutaminase-mediated serotonylation reaction, which in turn can alter protein function. Plasma fibronectin (pFN)--a major component of the bone extracellular matrix that regulates bone matrix quality in vivo--is a major transglutaminase substrate in bone and in osteoblast cultures. We have recently demonstrated that pFN assembly into osteoblast culture matrix requires a Factor XIII-A (FXIII-A) transglutaminase-mediated crosslinking step that regulates both quantity and quality of type I collagen matrix in vitro. In this study, we show that 5-HT interferes with pFN assembly into the extracellular matrix in osteoblast cultures, which in turn has major consequences on matrix assembly and mineralization. 5-HT treatment of MC3T3-E1 osteoblast cultures dramatically decreased both pFN fibrillogenesis as analyzed by immunofluorescence microscopy and pFN levels in DOC-soluble and DOC-insoluble matrix fractions. This was accompanied by an increase in pFN levels in the culture media. Analysis of the media showed covalent incorporation of 5-HT into pFN. Minor co-localization of pFN with 5-HT was also seen in extracellular fibrils. 5-HT also showed co-localization with FXIII-A on the cell surface and inhibited its transamidation activity directly. 5-HT treatment of osteoblast cultures resulted in a discontinuous pFN matrix and impaired type I collagen deposition, decreased alkaline phosphatase and lysyl oxidase activity, and delayed mineralization of the cultures. Addition of excess exogenous pFN to cultures treated with 5-HT resulted in a significant rescue of pFN fibrillogenesis as well as type I collagen deposition and mineralization. In summary, our study presents a novel mechanism on how increased peripheral extracellular 5-HT levels might contribute to the weakening of bone by directly affecting the stabilization of extracellular matrix networks.

Integrin mediated adhesion of osteoblasts to connective tissue growth factor (CTGF/CCN2) induces cytoskeleton reorganization and cell differentiation

Pre-osteoblast adhesion and interaction with extracellular matrix (ECM) proteins through integrin receptors result in activation of signaling pathways regulating osteoblast differentiation. Connective tissue growth factor (CTGF/CCN2) is a matricellular protein secreted into the ECM. Prior studies in various cell types have shown that cell adhesion to CTGF via integrin receptors results in activation of specific signaling pathways that regulate cell functions, such as differentiation and cytoskeletal reorganization. To date, there are no studies that have examined whether CTGF can serve as an adhesive substrate for osteoblasts. In this study, we used the MC3T3-E1 cell line to demonstrate that CTGF serves as an adhesive matrix for osteoblasts. Anti-integrin blocking experiments and co-immunoprecipitation assays demonstrated that the integrin α_vβ₁ plays a key role in osteoblast adhesion to a CTGF matrix. Immunofluorescence staining of osteoblasts cultured on a CTGF matrix confirmed actin cytoskeletal reorganization, enhanced spreading, formation of focal adhesions, and activation of Rac1. Alkaline phosphatase (ALP) staining and activity assays, as well as Alizarin red staining demonstrated that osteoblast attachment to CTGF matrix enhanced maturation, bone nodule formation and matrix mineralization. To investigate whether the effect of CTGF on osteoblast differentiation involves integrin-mediated activation of specific signaling pathways, we performed Western blot, chromatin immunoprecipitation (ChIP) and qPCR assays. Osteoblasts cultured on a CTGF matrix showed increased total and phosphorylated (activated) forms of focal adhesion kinase (FAK) and extracellular signal-regulated kinase (ERK). Inhibition of ERK blocked osteogenic differentiation in cells cultured on a CTGF matrix. There was an increase in runt-related transcription factor 2 (Runx2) binding to the osteocalcin gene promoter, and in the expression of osteogenic markers regulated by Runx2. Collectively, the results of this study are the first to demonstrate CTGF serves as a suitable matrix protein, enhancing osteoblast adhesion (via α_vβ₁ integrin) and promoting cell spreading via cytoskeletal reorganization and Rac1 activation. Furthermore, integrin-mediated activation of ERK signaling resulted in increased osteoblast differentiation accompanied by an increase in Runx2 binding to the osteocalcin promoter and in the expression of osteogenic markers.

Effect of microgrooved surface topography on osteoblast maturation and protein adsorption

Microgrooved surfaces have been used extensively to influence cell contact guidance. Guiding cell growth, extracellular matrix deposition, and mineralization is important for bone implant longevity. In this study, we investigated the osteoblast response to microgrooved metallic surfaces in serum-supplemented medium. Groove spacing was comparable with the spread osteoblast size. Focal adhesions were observed to confine to the intervening ridge/groove boundaries. Osteoblasts bridged over the grooves and were unable to conform to the concave shape of the underlying grooves. Microgrooved surfaces induced higher osteoblast proliferation and metabolic activity after 14 days in osteogenic medium compared with as-received surfaces, resulting in higher mineralization and alignment of cell-secreted collagen after 28 days. To establish whether preferential cell attachment at the ridge/groove boundaries was influenced by the adhesion proteins contained in the serum-supplemented media, fluorescently labeled fibronectin was adsorbed onto the microgrooved substrates at low concentrations, mimicking the concentrations found in blood serum. Fibronectin was found to selectively adsorb onto the ridge/groove boundaries, the osteoblast focal adhesion sites, suggesting that protein adsorption may have influenced the cell attachment pattern.

Heparin-induced conformational changes of fibronectin within the extracellular matrix promote hMSC osteogenic differentiation

Heparin switches the conformation of relaxed fibrillar fibronectin. This conformation upregulates osteogenic differentiation of hMSCs, but only when locked-in by fixation.

The effect of conditional inactivation of beta 1 integrins using twist 2 Cre, Osterix Cre and osteocalcin Cre lines on skeletal phenotype

Skeletal development and growth are complex processes regulated by multiple microenvironmental cues, including integrin-ECM interactions. The β1 sub-family of integrins is the largest integrin sub-family and constitutes the main integrin binding partners of collagen I, the major ECM component of bone. As complete β1 integrin knockout results in embryonic lethality, studies of β1 integrin function in vivo rely on tissue-specific gene deletions. While multiple in vitro studies indicate that β1 integrins are crucial regulators of osteogenesis and mineralization, in vivo osteoblast-specific perturbations of β1 integrins have resulted in mild and sometimes contradictory skeletal phenotypes. To further investigate the role of β1 integrins on skeletal phenotype, we used the Twist2-Cre, Osterix-Cre and osteocalcin-Cre lines to generate conditional β1 integrin deletions, where Cre is expressed primarily in mesenchymal condensation, pre-osteoblast, and mature osteoblast lineage cells respectively within these lines. Mice with Twist2-specific β1 integrin disruption were smaller, had impaired skeletal development, especially in the craniofacial and vertebral tissues at E19.5, and did not survive beyond birth. Osterix-specific β1 integrin deficiency resulted in viable mice which were normal at birth but displayed early defects in calvarial ossification, incisor eruption and growth as well as femoral bone mineral density, structure, and mechanical properties. Although these defects persisted into adulthood, they became milder with age. Finally, a lack of β1 integrins in mature osteoblasts and osteocytes resulted in minor alterations to femur structure but had no effect on mineral density, biomechanics or fracture healing. Taken together, our data indicate that β1 integrin expression in early mesenchymal condensations play an important role in skeletal ossification, while β1 integrin-ECM interactions in pre-osteoblast, odontoblast- and hypertrophic chondryocyte-lineage cells regulate incisor eruption and perinatal bone formation in both intramembranously and endochondrally formed bones in young, rapidly growing mice. In contrast, the osteocalcin-specific β1 integrin deletion had only minor effects on skeletal phenotype.

Biointerface control of electrospun fiber scaffolds for bone regeneration: engineered protein link to mineralized surface

Control over the interface of biomaterials that favors the initial adhesion and subsequent differentiation of stem cells is one of the key strategies in bone tissue engineering. Here we engineer the interface of biopolymer electrospun fiber matrices with a fusion protein of fibronectin 9-10 domain (FNIII9-10) and osteocalcin (OCN), aiming to stimulate mesenchymal stem cell (MSC) functions, including initial adhesion, growth and osteogenic differentiation. In particular, a specific tethering of FNIII9-10-OCN protein was facilitated by the hydroxyapatite (HA) mineralization of the biopolymer surface through a molecular recognition of OCN to the HA crystal lattice. The FNIII9-10-OCN anchorage to the HA-mineralized fiber was observed to be highly specific and tightly bound to preserve stability over a long period. Initial cell adhesion levels, as well as the spreading shape and process, of MSCs within 24h were strikingly different between the fibers linked with and without fusion protein. Significant up-regulations in the mRNA expression of adhesion signaling molecules occurred with the fusion protein link, as analyzed by the reverse transcriptase polymerase chain reaction. The expression of a series of osteogenic-related genes at later stages, over 2-3weeks, was significantly improved in the fusion protein-tailored fiber, and the osteogenic protein levels were highly stimulated, as confirmed by immunofluorescence imaging and fluorescence-activated cell sorting analyses. In vivo study in a rat calvarium model confirmed a higher quantity of new bone formation in the fiber linked with fusion protein, and a further increase was noticed when the MSCs were tissue-engineered with the fusion protein-linked fiber. Collectively, these results indicate that FN-OCN fusion protein links via HA mineralization is a facile tool to generate a biointerface with cell-attractive and osteogenic potential, and that the engineered fibrous matrix is a potential bone regenerative scaffold.

Transglutaminase regulation of cell function

Transglutaminases (TGs) are multifunctional proteins having enzymatic and scaffolding functions that participate in regulation of cell fate in a wide range of cellular systems and are implicated to have roles in development of disease. This review highlights the mechanism of action of these proteins with respect to their structure, impact on cell differentiation and survival, role in cancer development and progression, and function in signal transduction. We also discuss the mechanisms whereby TG level is controlled and how TGs control downstream targets. The studies described herein begin to clarify the physiological roles of TGs in both normal biology and disease states.

Novel biomimetic tripolymer scaffolds consisting of chitosan, collagen type 1, and hyaluronic acid for bone marrow-derived human mesenchymal stem cells-based bone tissue engineering

Human bone marrow-derived mesenchymal stem cells (hMSCs) are an ideal osteogenic cell source for bone tissue engineering (BTE). A scaffold, in the context of BTE, is the extracellular matrix (ECM) that provides the unique microenvironment and play significant role in regulating cell behavior, differentiation, and development in an in vitro culture system. In this study, we have developed novel biomimetic tripolymer scaffolds for BTE using an ECM protein, collagen type 1; an ECM glycosaminoglycan, hyaluronic acid; and a natural osteoconductive polymer, chitosan. The scaffolds were characterized by scanning electron microscopy (SEM) and swelling ratio. The scaffolds were seeded with hMSCs and tested for cytocompatibility and osteogenic potential. The scaffolds supported cell adhesion, enhanced cell proliferation, promoted cell migration, showed good cell viability, and osteogenic potential. The cells were able to migrate out from the scaffolds in favorable conditions. SEM, alkaline phosphatase assay, and immunofluorescent staining confirmed the differentiation of hMSCs to osteogenic lineage in the scaffolds. In conclusion, we have successfully developed biomimetic scaffolds that supported the proliferation and differentiation of hMSCs. These scaffolds hold great promise as a cell-delivery vehicle for regenerative therapies and as a support system for enhancing bone regeneration.

Circulating fibronectin controls tumor growth

Fibronectin is ubiquitously expressed in the extracellular matrix, and experimental evidence has shown that it modulates blood vessel formation. The relative contribution of local and circulating fibronectin to blood vessel formation in vivo remains unknown despite evidence for unexpected roles of circulating fibronectin in various diseases. Using transgenic mouse models, we established that circulating fibronectin facilitates the growth of bone metastases by enhancing blood vessel formation and maturation. This effect is more relevant than that of fibronectin produced by endothelial cells and pericytes, which only exert a small additive effect on vessel maturation. Circulating fibronectin enhances its local production in tumors through a positive feedback loop and increases the amount of vascular endothelial growth factor (VEGF) retained in the matrix. Both fibronectin and VEGF then cooperate to stimulate blood vessel formation. Fibronectin content in the tumor correlates with the number of blood vessels and tumor growth in the mouse models. Consistent with these results, examination of three separate arrays from patients with breast and prostate cancers revealed that a high staining intensity for fibronectin in tumors is associated with increased mortality. These results establish that circulating fibronectin modulates blood vessel formation and tumor growth by modifying the amount of and the response to VEGF. Furthermore, determination of the fibronectin content can serve as a prognostic biomarker for breast and prostate cancers and possibly other cancers.

Transglutaminase activity arising from Factor XIIIA is required for stabilization and conversion of plasma fibronectin into matrix in osteoblast cultures

Circulating plasma fibronectin (pFN), produced by hepatocytes, is a major component of the noncollagenous bone matrix where it was recently shown in vivo in mice to control the biomechanical quality as well as the mineral-to-matrix ratio in bone. FN fibrillogenesis is a process generally requiring FN binding to cellular integrins, and cellular tension to elongate and assemble the molecule. Whether soluble pFN undergoes cell-mediated assembly in bone is not fully established. FN is a well-known substrate for transglutaminases (TGs), which are protein-crosslinking enzymes capable of stabilizing macromolecular structures. The role of this modification regarding the function of FN in bone matrix has remained unknown. Osteoblasts express two TGs-transglutaminase 2 and Factor XIIIA-and we have shown that Factor XIIIA is the main TG active during osteoblast differentiation. In the present study, conducted using MC3T3-E1 osteoblast cultures and bone marrow stromal cells, we demonstrate that pFN requires a TG-mediated crosslinking step to form osteoblast matrix in vitro. This modification step is specific for pFN; cellular FN (EDA-FN) does not serve as a TG substrate. Inhibition of pFN assembly using a TG inhibitor, or depletion of pFN from cell culture serum, dramatically decreased total FN matrix assembly in the osteoblast cultures and affected both the quantity and quality of the type I collagen matrix, and decreased lysyl oxidase and alkaline phosphatase levels, resulting in decreased mineralization. Experiments with isozyme-specific substrate peptides showed that FXIIIA is responsible for the crosslinking of pFN. Addition of exogenous preactivated FXIIIA to osteoblast cultures promoted pFN assembly from the media into matrix. Exogenous TG2 had no effect. Analysis of pFN and EDA-FN fibrils by immunofluorescence microscopy demonstrated that they form distinct matrix network, albeit with minor overlap, suggesting different functions for the two FN forms. Further analysis using EDA-FN blocking antibody showed that it regulated preosteoblast proliferation whereas pFN depletion from the serum had no effect on this process. In conclusion, our study shows that pFN assembly into bone matrix in vitro requires FXIIIA transglutaminase activity making pFN assembly an active, osteoblast-mediated process.

Comparison of osteogenic differentiation of embryonic stem cells and primary osteoblasts revealed by responses to IL-1β, TNF-α, and IFN-γ

There are well-established approaches for osteogenic differentiation of embryonic stem cells (ESCs), but few show direct comparison with primary osteoblasts or demonstrate differences in response to external factors. Here, we show comparative analysis of in vitro osteogenic differentiation of mouse ESC (osteo-mESC) and mouse primary osteoblasts. Both cell types formed mineralized bone nodules and produced osteogenic extracellular matrix, based on immunostaining for osteopontin and osteocalcin. However, there were marked differences in the morphology of osteo-mESCs and levels of mRNA expression for osteogenic genes. In response to the addition of proinflammatory cytokines interleukin-1β, tumor necrosis factor-α, and interferon-γ to the culture medium, primary osteoblasts showed increased production of nitric oxide (NO) and prostaglandin E2 (PGE2) at early time points and decreases in cell viability. In contrast, osteo-mESCs maintained viability and did not produce NO and PGE2 until day 21. The formation of bone nodules by primary osteoblasts was reduced markedly after cytokine stimulation but was unaffected in osteo-mESCs. Cell sorting of osteo-mESCs by cadherin-11 (cad-11) showed clear osteogenesis of cad-11(+) cells compared to unsorted osteo-mESCs and cad-11(-) cells. Moreover, the cad-11(+) cells showed a significant response to cytokines, similar to primary osteoblasts. Overall, these results show that while osteo-mESC cultures, without specific cell sorting, show characteristics of osteoblasts, there are also marked differences, notably in their responses to cytokine stimuli. These findings are relevant to understanding the differentiation of stem cells and especially developing in vitro models of disease, testing new drugs, and developing cell therapies.

Stem cell culture using cell-derived substrates

There have been great efforts to develop cell culture systems using chemically-fixed cells or decellularized matrices to regulate stem cell functions.