Spatial and temporal gene expression in chondrogenesis during fracture healing and the effects of basic fibroblast growth factor

Unique Spatial Transcriptomic Profiling of the Murine Femoral Fracture Callus: A Preliminary Report

Fracture callus formation is a dynamic stage of bone activity and repair with precise, spatially localized gene expression. Metastatic breast cancer impairs fracture healing by disrupting bone homeostasis and imparting an altered genomic profile. Previous sequencing techniques such as single-cell RNA and in situ hybridization are limited by missing spatial context and low throughput, respectively. We present a preliminary approach using the Visium CytAssist spatial transcriptomics platform to provide the first spatially intact characterization of genetic expression changes within an orthopedic model of impaired fracture healing. Tissue slides prepared from BALB/c mice with or without MDA-MB-231 metastatic breast cancer cells were used. Both unsupervised clustering and histology-based annotations were performed to identify the hard callus, soft callus, and interzone for differential gene expression between the wild-type and pathological fracture model. The spatial transcriptomics platform successfully localized validated genes of the hard (Dmp1, Sost) and soft callus (Acan, Col2a1). The fibrous interzone was identified as a region of extensive genomic heterogeneity. MDA-MB-231 samples demonstrated downregulation of the critical bone matrix and structural regulators that may explain the weakened bone structure of pathological fractures. Spatial transcriptomics may represent a valuable tool in orthopedic research by providing temporal and spatial context.

Application of dental pulp stem cells for bone regeneration

Bone defects resulting from severe trauma, tumors, inflammation, and other factors are increasingly prevalent. Stem cell-based therapies have emerged as a promising alternative. Dental pulp stem cells (DPSCs), sourced from dental pulp, have garnered significant attention owing to their ready accessibility and minimal collection-associated risks. Ongoing investigations into DPSCs have revealed their potential to undergo osteogenic differentiation and their capacity to secrete a diverse array of ontogenetic components, such as extracellular vesicles and cell lysates. This comprehensive review article aims to provide an in-depth analysis of DPSCs and their secretory components, emphasizing extraction techniques and utilization while elucidating the intricate mechanisms governing bone regeneration. Furthermore, we explore the merits and demerits of cell and cell-free therapeutic modalities, as well as discuss the potential prospects, opportunities, and inherent challenges associated with DPSC therapy and cell-free therapies in the context of bone regeneration.

Impact of elevated serum advanced glycation end products and exercise on intact and injured murine tendons

OVERVIEW

Delayed tendon healing is a significant clinical challenge for those with diabetes. We explored the role of advanced glycation end-products (AGEs), a protein modification present at elevated levels in serum of individuals with diabetes, on injured and intact tendons using a mouse model. Cell proliferation following tissue injury is a vital component of healing. Based on our previous work demonstrating that AGEs limit cell proliferation, we proposed that AGEs are responsible for the delayed healing process commonly observed in diabetic patients. Further, in pursuit of interventional strategies, we suggested that moderate treadmill exercise may support a healing environment in the presence of AGEs as exercise has been shown to stimulate cell proliferation in tendon tissue.

MATERIALS AND METHODS

Mice began receiving daily intraperitoneal injections of bovine serum albumin (BSA)-Control or AGE-BSA injections (200μg/ml) at 16-weeks of age. A tendon injury was created in the central third of both patellar tendons. Animals assigned to an exercise group began a moderate treadmill protocol one week following injury. The intact Achilles tendon and soleus muscle were also evaluated to assess the effect of BSA and AGE-BSA on un-injured muscle and tendon.

RESULTS

We demonstrate that our injection dosing and schedule lead to an increase in serum AGEs. Our findings imply that AGEs indeed modulate gene expression following a patellar tendon injury and have modest effects on gene expression in intact muscle and tendon.

CONCLUSIONS

While additional biomechanical analysis is warranted, these data suggest that elevated serum AGEs in persons with diabetes may impact tendon health.

Effect of Recombinant Human Bone Morphogenetic Protein-2 (rhBMP-2) with Hydroxyapatite Carrier in Induced Membrane Technique: A Retrospective Propensity Score-Matched Study

OBJECTIVES

To determine the effect of recombinant human bone morphogenetic protein-2 (rhBMP-2) with hydroxyapatite (HA) carrier augmentation in managing critical-sized bone defect (CSBD) with induced membrane technique (IMT).

DESIGN

Retrospective comparative study.

SETTING

Academic level I trauma center.

PATIENTS/PARTICIPANTS

The study included 14 patients who underwent rhBMP-2 with HA carrier (rhBMP-2/HA) augmentation in IMT for managing CSBD (BMP group). Moreover, 14 patients who underwent IMT without rhBMP-2 augmentation were matched by propensity score analysis (non-BMP group).

INTERVENTION

IMT with or without rhBMP-2/HA augmentation.

MAIN OUTCOME MEASUREMENT

Changes in quality and quantity measurements of grafted bone to regenerated bone using serial computed tomography.

RESULTS

In the BMP and non-BMP groups, the changes in densities from grafted bone to regenerated bone were +379.63 Hounsfield unit and +248.55 Hounsfield unit (P = 0.034), changes in dense bone percentage were +37.52% and +23.31% (P = 0.027), corticalization rates under the plate were 79.70% and 39.30% (P = 0.007), changes in volume were -20.77% and -23.35% (P = 0.812), union rates were 85.71% and 78.57% (P = 0.622), numbers of patients requiring additional procedures were 4 and 3 (P = 0.663), and time to union were 316.3 and 585.45 days (P = 0.040), respectively.

CONCLUSIONS

RhBMP-2/HA augmentation increases the density of regenerated bone, enhances corticalization under the plate, and shortens the time to union while managing CSBD with IMT.

LEVEL OF EVIDENCE

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

The Role of Growth Factors in Bioactive Coatings

With increasing obesity and an ageing population, health complications are also on the rise, such as the need to replace a joint with an artificial one. In both humans and animals, the integration of the implant is crucial, and bioactive coatings play an important role in bone tissue engineering. Since bone tissue engineering is about designing an implant that maximally mimics natural bone and is accepted by the tissue, the search for optimal materials and therapeutic agents and their concentrations is increasing. The incorporation of growth factors (GFs) in a bioactive coating represents a novel approach in bone tissue engineering, in which osteoinduction is enhanced in order to create the optimal conditions for the bone healing process, which crucially affects implant fixation. For the application of GFs in coatings and their implementation in clinical practice, factors such as the choice of one or more GFs, their concentration, the coating material, the method of incorporation, and the implant material must be considered to achieve the desired controlled release. Therefore, the avoidance of revision surgery also depends on the success of the design of the most appropriate bioactive coating. This overview considers the integration of the most common GFs that have been investigated in in vitro and in vivo studies, as well as in human clinical trials, with the aim of applying them in bioactive coatings. An overview of the main therapeutic agents that can stimulate cells to express the GFs necessary for bone tissue development is also provided. The main objective is to present the advantages and disadvantages of the GFs that have shown promise for inclusion in bioactive coatings according to the results of numerous studies.

Proteomics of regenerated tissue in response to a titanium implant with a bioactive surface in a rat tibial defect model

Due to their excellent mechanical and biocompatibility properties, titanium-based implants are successfully used as biomedical devices. However, when new bone formation fails for different reasons, impaired fracture healing becomes a clinical problem and affects the patient's quality of life. We aimed to design a new bioactive surface of titanium implants with a synergetic PEG biopolymer-based composition for gradual delivery of growth factors (FGF2, VEGF, and BMP4) during bone healing. The optimal architecture of non-cytotoxic polymeric coatings deposited by dip coating under controlled parameters was assessed both in cultured cells and in a rat tibial defect model (100% viability). Notably, the titanium adsorbed polymer matrix induced an improved healing process when compared with the individual action of each biomolecules. High-performance mass spectrometry analysis demonstrated that recovery after a traumatic event is governed by specific differentially regulated proteins, acting in a coordinated response to the external stimulus. Predicted protein interactions shown by STRING analysis were well organized in hub-based networks related with response to chemical, wound healing and response to stress pathways. The proposed functional polymer coatings of the titanium implants demonstrated the significant improvement of bone healing process after injury.

Bone callus formation is highly disrupted by dietary restriction in growing rats sustaining a femoral fracture1

PURPOSE

To evaluate the effects of food restriction on fracture healing in growing rats.

METHODS

Sixty-eight male Wistar rats were assigned to two groups: (1) Control and (2) Dietary restriction. After weaning the dietary restricted animals were fed ad libitum for 42 days with 50% of the standard chow ingested by the control group. Subsequently, the animals underwent bone fracture at the diaphysis of the right femur, followed by surgical stabilization of bone fragments. On days 14 and 28 post-fracture, the rats were euthanized, and the fractured femurs were dissected, the callus was analyzed by dual-energy X-ray absorptiometry, micro-computed tomography, histomorphometry, mechanical tests, and gene expression.

RESULTS

Dietary restriction decreased body mass gain and resulted in several phenotypic changes at the bone callus (a delay in cell proliferation and differentiation, lower rate of newly formed bone and collagen deposition, reductions in bone callus density and size, decrease in tridimensional callus volume, deterioration in microstructure, and reduction in bone callus strength), together with the downregulated expression of osteoblast-related genes.

CONCLUSION

Dietary restriction had detrimental effects on osseous healing, with a healing delay and a lower quality of bone callus formation.

Anabolic Strategies to Augment Bone Fracture Healing

PURPOSE OF REVIEW

The development of therapeutics that target anabolic pathways involved in skeletogenesis is of great importance with regard to disease resulting in bone loss, or in cases of impaired bone repair. This review aims to summarize recent developments in this area.

RECENT FINDINGS

A greater understanding of how drugs that modulate signaling pathways involved in skeletogenesis exert their efficacy, and the molecular mechanisms resulting in bone formation has led to novel pharmacological bone repair strategies. Furthermore, crosstalk between pathways and molecules has suggested signaling synergies that may be exploited for enhanced tissue formation. The sequential pharmacological stimulation of the molecular cascades resulting in tissue repair is a promising strategy for the treatment of bone fractures. It is proposed that a therapeutic strategy which mimics the natural cascade of events observed during fracture repair may be achieved through temporal targeting of tissue repair pathways.

Basic Fibroblast Growth Factor Fused with Tandem Collagen-Binding Domains from Clostridium histolyticum Collagenase ColG Increases Bone Formation

Basic fibroblast growth factor 2 (bFGF) accelerates bone formation during fracture healing. Because the efficacy of bFGF decreases rapidly following its diffusion from fracture sites, however, repeated dosing is required to ensure a sustained therapeutic effect. We previously developed a fusion protein comprising bFGF, a polycystic kidney disease domain (PKD; s2b), and collagen-binding domain (CBD; s3) sourced from the Clostridium histolyticum class II collagenase, ColH, and reported that the combination of this fusion protein with a collagen-like peptide, poly(Pro-Hyp-Gly)₁₀, induced mesenchymal cell proliferation and callus formation at fracture sites. In addition, C. histolyticum produces class I collagenase (ColG) with tandem CBDs (s3a and s3b) at the C-terminus. We therefore hypothesized that a bFGF fusion protein containing ColG-derived tandem CBDs (s3a and s3b) would show enhanced collagen-binding activity, leading to improved bone formation. Here, we examined the binding affinity of four collagen anchors derived from the two clostridial collagenases to H-Gly-Pro-Arg-Gly-(Pro-Hyp-Gly)₁₂-NH₂, a collagenous peptide, by surface plasmon resonance and found that tandem CBDs (s3a-s3b) have the highest affinity for the collagenous peptide. We also constructed four fusion proteins consisting of bFGF and s3 (bFGF-s3), s2b-s3b (bFGF-s2b-s3), s3b (bFGF-s3b), and s3a-s3b (bFGF-s3a-s3b) and compared their biological activities to those of a previous fusion construct (bFGF-s2b-s3) using a cell proliferation assay in vitro and a mouse femoral fracture model in vivo. Among these CB-bFGFs, bFGF-s3a-s3b showed the highest capacity to induce mesenchymal cell proliferation and callus formation in the mice fracture model. The poly(Pro-Hyp-Gly)₁₀/bFGF-s3a-s3b construct may therefore have the potential to promote bone formation in clinical settings.

Acceleration of Fracture Healing by Overexpression of Basic Fibroblast Growth Factor in the Mesenchymal Stromal Cells

In this study, we engineered mesenchymal stem cells (MSCs) to over‐express basic fibroblast growth factor (bFGF) and evaluated its effects on fracture healing. Adipose‐derived mouse MSCs were transduced to express bFGF and green fluorescence protein (ADSC^bFGF‐GFP). Closed‐femoral fractures were performed with osterix‐mCherry reporter mice of both sexes. The mice received 3 × 10⁵ ADSCs transfected with control vector or bFGF via intramuscular injection within or around the fracture sites. Mice were euthanized at days 7, 14, and 35 to monitor MSC engraftment, osteogenic differentiation, callus formation, and bone strength. Compared to ADSC culture alone, ADSC^bFGF increased bFGF expression and higher levels of bFGF and vascular endothelial growth factor (VEGF) in the culture supernatant for up to 14 days. ADSC^bFGF treatment increased GFP‐labeled MSCs at the fracture gaps and these cells were incorporated into the newly formed callus. quantitative reverse transcription polymerase chain reaction (qRT‐PCR) from the callus revealed a 2‐ to 12‐fold increase in the expression of genes associated with nervous system regeneration, angiogenesis, and matrix formation. Compared to the control, ADSC^bFGF treatment increased VEGF expression at the periosteal region of the callus, remodeling of collagen into mineralized callus and bone strength. In summary, MSC^bFGF accelerated fracture healing by increasing the production of growth factors that stimulated angiogenesis and differentiation of MSCs to osteoblasts that formed new bone and accelerated fracture repair. This novel treatment may reduce the time required for fracture healing. Stem Cells Translational Medicine2017;6:1880–1893

TNFα contributes to diabetes impaired angiogenesis in fracture healing

Diabetes increases the likelihood of fracture, interferes with fracture healing and impairs angiogenesis. The latter may be significant due to the critical nature of angiogenesis in fracture healing. Although it is known that diabetes interferes with angiogenesis the mechanisms remain poorly defined. We examined fracture healing in normoglycemic and streptozotocin-induced diabetic mice and quantified the degree of angiogenesis with antibodies to three different vascular markers, CD34, CD31 and Factor VIII. The role of diabetes-enhanced inflammation was investigated by treatment of the TNFα-specific inhibitor, pegsunercept starting 10days after induction of fractures. Diabetes decreased both angiogenesis and VEGFA expression by chondrocytes. The reduced angiogenesis and VEGFA expression in diabetic fractures was rescued by specific inhibition of TNF in vivo. In addition, the TNF inhibitor rescued the negative effect of diabetes on endothelial cell proliferation and endothelial cell apoptosis. The effect of TNFα in vitro was enhanced by high glucose and an advanced glycation endproduct to impair microvascular endothelial cell proliferation and tube formation and to stimulate apoptosis. The effect of TNF, high glucose and an AGE was mediated by the transcription factor FOXO1, which increased expression of p21 and caspase-3. These studies indicate that inflammation plays a major role in diabetes-impaired angiogenesis in endochondral bone formation through its effect on microvascular endothelial cells and FOXO1.

Bone fracture healing in mechanobiological modeling: A review of principles and methods

Bone fracture is a very common body injury. The healing process is physiologically complex, involving both biological and mechanical aspects. Following a fracture, cell migration, cell/tissue differentiation, tissue synthesis, and cytokine and growth factor release occur, regulated by the mechanical environment. Over the past decade, bone healing simulation and modeling has been employed to understand its details and mechanisms, to investigate specific clinical questions, and to design healing strategies. The goal of this effort is to review the history and the most recent work in bone healing simulations with an emphasis on both biological and mechanical properties. Therefore, we provide a brief review of the biology of bone fracture repair, followed by an outline of the key growth factors and mechanical factors influencing it. We then compare different methodologies of bone healing simulation, including conceptual modeling (qualitative modeling of bone healing to understand the general mechanisms), biological modeling (considering only the biological factors and processes), and mechanobiological modeling (considering both biological aspects and mechanical environment). Finally we evaluate different components and clinical applications of bone healing simulation such as mechanical stimuli, phases of bone healing, and angiogenesis.

Combined delivery of FGF-2, TGF-β1, and adipose-derived stem cells from an engineered periosteum to a critical-sized mouse femur defect

Critical-sized long bone defects suffer from complications including impaired healing and non-union due to substandard healing and integration of devitalized bone allograft. Removal of the periosteum contributes to the limited healing of bone allografts. Restoring a periosteum on bone allografts may provide improved allograft healing and integration. This article reports a polysaccharide-based tissue engineered periosteum that delivers basic fibroblast growth factor (FGF-2), transforming growth factor-β1 (TGF-β1), and adipose-derived mesenchymal stem cells (ASCs) to a critical-sized mouse femur defect. The tissue engineered periosteum was evaluated for improving bone allograft healing and incorporation by locally delivering FGF-2, TGF-β1, and supporting ASCs transplantation. ASCs were successfully delivered and longitudinally tracked at the defect site for at least 7 days post operation with delivered FGF-2 and TGF-β1 showing a mitogenic effect on the ASCs. At 6 weeks post implantation, data showed a non-significant increase in normalized bone callus volume. However, union ratio analysis showed a significant inhibition in allograft incorporation, confirmed by histological analysis, due to loosening of the nanofiber coating from the allograft surface. Ultimately, this investigation shows our tissue engineered periosteum can deliver FGF-2, TGF-β1, and ASCs to a mouse critical-sized femur defect and further optimization may yield improved bone allograft healing. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 900-911, 2017.

Biological Approaches to Bone Regeneration by Gene Therapy

Safe, effective approaches for bone regeneration are needed to reverse bone loss caused by trauma, disease, and tumor resection. Unfortunately, the science of bone regeneration is still in its infancy, with all current or emerging therapies having serious limitations. Unlike current regenerative therapies that use single regenerative factors, the natural processes of bone formation and repair require the coordinated expression of many molecules, including growth factors, bone morphogenetic proteins, and specific transcription factors. As will be developed in this article, future advances in bone regeneration will likely incorporate therapies that mimic critical aspects of these natural biological processes, using the tools of gene therapy and tissue engineering. This review will summarize current knowledge related to normal bone development and fracture repair, and will describe how gene therapy, in combination with tissue engineering, may mimic critical aspects of these natural processes. Current gene therapy approaches for bone regeneration will then be summarized, including recent work where combinatorial gene therapy was used to express groups of molecules that synergistically interacted to stimulate bone regeneration. Last, proposed future directions for this field will be discussed, where regulated gene expression systems will be combined with cells seeded in precise three-dimensional configurations on synthetic scaffolds to control both temporal and spatial distribution of regenerative factors. It is the premise of this article that such approaches will eventually allow us to achieve the ultimate goal of bone tissue engineering: to reconstruct entire bones with associated joints, ligaments, or sutures. Abbreviations used: BMP, bone morphogenetic protein; FGF, fibroblast growth factor; AER, apical ectodermal ridge; ZPA, zone of polarizing activity; PZ, progress zone; SHH, sonic hedgehog; OSX, osterix transcription factor; FGFR, fibroblast growth factor receptor; PMN, polymorphonuclear neutrophil; PDGF, platelet-derived growth factor; IGF, insulin-like growth factor; TGF-β, tumor-derived growth factor β; CAR, coxsackievirus and adenovirus receptor; MLV, murine leukemia virus; HIV, human immunodeficiency virus; AAV, adeno-associated virus; CAT, computer-aided tomography; CMV, cytomegalovirus; GAM, gene-activated matrix; MSC, marrow stromal cell; MDSC, muscle-derived stem cell; VEGF, vascular endothelial growth factor.

Molecular profiling of a simple rat model of open tibial fractures with hematoma and periosteum disruption

Bone fractures are a worldwide public health concern. Therefore, improving understanding of the bone healing process at a molecular level, which could lead to the discovery of potential therapeutic targets, is important. In the present study, a model of open tibial fractures with hematoma disruption, periosteal rupture and internal fixation in 6-month-old male Wistar rats was established, in order to identify expression patterns of key genes and their protein products throughout the bone healing process. A tibial shaft fracture was produced using the three-point bending technique, the hematoma was drained through a 4-mm incision on the medial aspect of the tibia and the fracture stabilized by inserting a needle into the medullary canal. Radiographs confirmed that the induced fractures were diaphyseal and this model was highly reproducible (kappa inter-rater reliability, 0.82). Rats were sacrificed 5, 14, 21, 28 and 35 days post-fracture to obtain samples for histological, immunohistochemical and molecular analysis. Expression of interleukin-1β (Il-1β), transforming growth factor-β2 (Tgf-β2), bone morphogenetic protein-6 (Bmp-6), bone morphogenetic protein-7 (Bmp-7) and bone γ-carboxyglutamic acid-containing protein (Bglap) genes was determined by reverse transcription quantitative polymerase chain reaction and protein expression was evaluated by immunohistochemistry, while histological examination allowed characterization of the bone repair process. Il-1β showed a biphasic expression, peaking 5 and 28 days post-fracture. Expression of Tgf-β2, Bmp-6 and Bmp-7 was restricted to the period 21 days post-fracture. Bglap expression increased gradually, peaking 21 days post-fracture, although it was expressed in all evaluated stages. Protein expression corresponded with the increased expression of their corresponding genes. In conclusion, a clear and well-defined expression pattern of the evaluated genes and proteins was observed, where their maximal expression correlated with their known participation in each stage of the bone healing process.

Bioinformatics and Microarray Analysis of miRNAs in Aged Female Mice Model Implied New Molecular Mechanisms for Impaired Fracture Healing

Impaired fracture healing in aged females is still a challenge in clinics. MicroRNAs (miRNAs) play important roles in fracture healing. This study aims to identify the miRNAs that potentially contribute to the impaired fracture healing in aged females. Transverse femoral shaft fractures were created in adult and aged female mice. At post-fracture 0-, 2- and 4-week, the fracture sites were scanned by micro computed tomography to confirm that the fracture healing was impaired in aged female mice and the fracture calluses were collected for miRNA microarray analysis. A total of 53 significantly differentially expressed miRNAs and 5438 miRNA-target gene interactions involved in bone fracture healing were identified. A novel scoring system was designed to analyze the miRNA contribution to impaired fracture healing (RCIFH). Using this method, 11 novel miRNAs were identified to impair fracture healing at 2- or 4-week post-fracture. Thereafter, function analysis of target genes was performed for miRNAs with high RCIFH values. The results showed that high RCIFH miRNAs in aged female mice might impair fracture healing not only by down-regulating angiogenesis-, chondrogenesis-, and osteogenesis-related pathways, but also by up-regulating osteoclastogenesis-related pathway, which implied the essential roles of these high RCIFH miRNAs in impaired fracture healing in aged females, and might promote the discovery of novel therapeutic strategies.

Extracellular matrix-inspired growth factor delivery systems for bone regeneration

Growth factors are very promising molecules to enhance bone regeneration. However, their translation to clinical use has been seriously limited, facing issues related to safety and cost-effectiveness. These problems derive from the vastly supra-physiological doses of growth factor used without optimized delivery systems. Therefore, these issues have motivated the development of new delivery systems allowing better control of the spatiotemporal release and signaling of growth factors. Because the extracellular matrix (ECM) naturally plays a fundamental role in coordinating growth factor activity in vivo, a number of novel delivery systems have been inspired by the growth factor regulatory function of the ECM. After introducing the role of growth factors during the bone regeneration process, this review exposes different issues that growth factor-based therapies have encountered in the clinic and highlights recent delivery approaches based on the natural interaction between growth factor and the ECM.

Role of c-Myb in chondrogenesis

The Myb locus encodes the c-Myb transcription factor involved in controlling a broad variety of cellular processes. Recently, it has been shown that c-Myb may play a specific role in hard tissue formation; however, all of these results were gathered from an analysis of intramembranous ossification. To investigate a possible role of c-Myb in endochondral ossification, we carried out our study on the long bones of mouse limbs during embryonic development. Firstly, the c-myb expression pattern was analyzed by in situ hybridization during endochondral ossification of long bones. c-myb positive areas were found in proliferating as well as hypertrophic zones of the growth plate. At early embryonic stages, localized expression was also observed in the perichondrium and interdigital areas. The c-Myb protein was found in proliferating chondrocytes and in the perichondrium of the forelimb bones (E14.5-E17.5). Furthermore, protein was detected in pre-hypertrophic as well as hypertrophic chondrocytes. Gain-of-function and loss-of-function approaches were used to test the effect of altered c-myb expression on chondrogenesis in micromass cultures established from forelimb buds of mouse embryos. A loss-of-function approach using c-myb specific siRNA decreased nodule formation, as well as downregulated the level of Sox9 expression, a major marker of chondrogenesis. Transient c-myb overexpression markedly increased the formation of cartilage nodules and the production of extracellular matrix as detected by intense staining with Alcian blue. Moreover, the expression of early chondrogenic genes such as Sox9, Col2a1 and activity of a Col2-LUC reporter were increased in the cells overexpressing c-myb while late chondrogenic markers such as Col10a1 and Mmp13 were not significantly changed or were downregulated. Taken together, the results of this study demonstrate that the c-Myb transcription factor is involved in the regulation and promotion of endochondral bone formation.

Antagonizing the αv β3 integrin inhibits angiogenesis and impairs woven but not lamellar bone formation induced by mechanical loading

Angiogenesis and osteogenesis are critically linked, although the role of angiogenesis is not well understood in osteogenic mechanical loading. In this study, either damaging or non-damaging cyclic axial compression was used to generate woven bone formation (WBF) or lamellar bone formation (LBF), respectively, at the mid-diaphysis of the adult rat forelimb. αv β3 integrin-targeted nanoparticles or vehicle was injected intravenously after mechanical loading. β3 integrin subunit expression on vasculature was maximal 7 days after damaging mechanical loading, but was still robustly expressed 14 days after loading. Accordingly, targeted nanoparticle delivery in WBF-loaded limbs was increased compared with non-loaded limbs. Vascularity was dramatically increased after WBF loading (+700% on day 14) and modestly increased after LBF loading (+50% on day 14). This increase in vascularity was inhibited by nanoparticle treatment in both WBF- and LBF-loaded limbs at days 7 and 14 after loading. Decreased vascularity led to diminished woven, but not lamellar, bone formation. Decreased woven bone formation resulted in impaired structural properties of the skeletal repair, particularly in post-yield behavior. These results demonstrate that αv β3 integrin-mediated angiogenesis is critical for recovering fracture resistance after bone injury but is not required for bone modeling after modest mechanical strain. © 2014 American Society for Bone and Mineral Research.

Role of angiogenesis in bone repair

Bone vasculature plays a vital role in bone development, remodeling and homeostasis. New blood vessel formation is crucial during both primary bone development as well as fracture repair in adults. Both bone repair and bone remodeling involve the activation and complex interaction between angiogenic and osteogenic pathways. Interestingly studies have demonstrated that angiogenesis precedes the onset of osteogenesis. Indeed reduced or inadequate blood flow has been linked to impaired fracture healing and old age related low bone mass disorders such as osteoporosis. Similarly the slow penetration of host blood vessels in large engineered bone tissue grafts has been cited as one of the major hurdle still impeding current bone construction engineering strategies. This article reviews the current knowledge elaborating the importance of vascularization during bone healing and remodeling, and the current therapeutic strategies being adapted to promote and improve angiogenesis.

Attenuation of limb loss in an experimentally induced hindlimb ischemic model by fibroblast growth factor-2/fragmin/protamine microparticles as a delivery system

Fibroblast growth factor-2 (FGF-2) is a well-characterized protein that is used in the treatment of healing-impaired wounds. We previously reported that fragmin/protamine microparticles (F/P MPs) are useful as biodegradable carriers for the controlled release of cytokines. We examined the ability of FGF-2-containing (FGF-2/) F/P MPs to prevent limb loss in an experimentally induced ischemic hindlimb model using adult Balb/c-nu/nu male mice. One day after inducing ischemia, intramuscular injections of 100 μL of FGF-2/F/P MPs turbid suspension (10 μg/mL FGF-2 and 6 mg/mL F/P MPs) were administered into eight sites of the ischemic hindlimb. A 100-μL suspension of each of the following-10 μg/mL FGF-2, 6 mg/mL F/P MPs, and phosphate-buffered saline (PBS; the control)-was similarly injected into the hindlimb. From 5 days onward after the injections, recovery from ischemia was observed in the FGF-2/F/P MP-treated group, but only partial recovery occurred in the FGF-2-treated group. The F/P MP-treated and PBS-treated groups (i.e., control) exhibited no recovery from the ischemia. The histological evaluations of the hindlimbs also confirmed that the capillary (i.e., mature vessels) density was significantly higher in the FGF-2/F/P MP-treated group than in the other groups. The mice injected with FGF-2/F/P MPs also recovered hindlimb blood flow, as reflected by oxygen saturation and surface temperature evaluation. Our present approach using FGF-2/F/P MPs could be considered a valuable option for the therapeutic treatment of peripheral ischemic diseases.

Angiogenesis in bone regeneration

Angiogenesis is a key component of bone repair. New blood vessels bring oxygen and nutrients to the highly metabolically active regenerating callus and serve as a route for inflammatory cells and cartilage and bone precursor cells to reach the injury site. Angiogenesis is regulated by a variety of growth factors, notably vascular endothelial growth factor (VEGF), which are produced by inflammatory cells and stromal cells to induce blood vessel in-growth. A variety of studies with transgenic and gene-targeted mice have demonstrated the importance of angiogenesis in fracture healing, and have provided insights into regulatory processes governing fracture angiogenesis. Indeed, in animal models enhancing angiogenesis promotes bone regeneration, suggesting that modifying fracture vascularization could be a viable therapeutic approach for accelerated/improved bone regeneration clinically.

Long bone fracture repair in mice harboring GFP reporters for cells within the osteoblastic lineage

GFP reporter mice previously developed to assess levels of osteoblast differentiation were employed in a tibial long bone fracture model using a histological method that preserves fluorescent signals in non-decalcified sections of bone. Two reporters, based on Col1A1 (Col3.6GFPcyan) and osteocalcin (OcGFPtpz) promoter fragments, were bred into the same mice to reflect an early and late stage of osteoblast differentiation. Three observations were apparent from this examination. First, the osteoprogenitor cells that arise from the flanking periosteum proliferate and progress to fill the fracture zone. These cells differentiate to osteoblasts, chondrocytes, to from the outer cortical shell. Second, the hypertrophic chondrocytes are dispersed and the cartilage matrix mineralized by the advancing Col3.6+ osteoblasts. The endochondral matrix is removed by the following osteoclasts. Third, a new cortical shell develops over the cartilage core and undergoes a remodeling process of bone formation on the inner surface and resorption on the outer surface. The original fractured cortex undergoes resorption as the outer cortical shell remodels inward to become the new diaphyseal bone. The fluorescent microscopy and GFP reporter mice used in this study provide a powerful tool for appreciating the molecular and cellular processes that control these fundamental steps in fracture repair, and may provide a basis for understanding fracture nonunion.

Prolonged endochondral bone healing in senescence is shortened by low-intensity pulsed ultrasound in a manner dependent on COX-2

To test whether mechanical loading produces faster healing in aged mice, fractured femurs of aged 1-year-old mice were subjected to low-intensity pulsed ultrasound (LIPUS), a treatment that is routinely used to help heal fractures in humans. Cyclooxygenase-2 knockout mice (COX-2(-/-)), which lack an immediate early mediator of mechanical stimulation, were also studied by histochemistry, microcomputed tomography and quantitative polymerase chain reaction to determine the role of COX-2. The healing in the aged COX-2(-/-) mice is slow during the endochondral bone remodeling (>30 d), a period generally prolonged in senescence. For aged wild-type mice, LIPUS halved the endochondral phase to about 10 d, whereas that was not the case for aged COX-2(-/-) mice, which showed no apparent shortening of the prolonged endochondral-phase healing time. Injecting prostaglandin E(2) receptor agonists, however, rescued the COX-2(-/-) callus from insensitivity to LIPUS. In conclusion, COX-2 is a limiting factor in the delayed endochondral bone healing and is induced by LIPUS, which normalizes healing rate to the wild-type level.

Healing of non-displaced fractures produced by fatigue loading of the mouse ulna

We developed a fatigue loading protocol in mice to produce a non-displaced ulnar fracture in vivo, and characterized the early healing response. Using adult (5 month) C57Bl/6 mice, we first determined that cyclic compression of the forelimb under load-control leads to increasing applied displacement and, eventually, complete fracture. We then subjected the right forelimbs of 80 mice to cyclic loading (2 Hz; peak force approximately 4N) and limited the displacement increase to 0.75 mm (60% of the average displacement increase at complete fracture). This fatigue protocol created a partial, non-displaced fracture through the medial cortex near the ulnar mid-shaft, and reduced ulnar strength and stiffness by >50%. Within 1 day, there was significant upregulation of genes related to hypoxia (Hif1a) and osteogenesis (Bmp2, Bsp) in loaded ulnae compared to non-loaded, contralateral controls. The gene expression response peaked in magnitude near day 7 (e.g., Osx upregulated 8-fold), and included upregulation of FGF-family genes (e.g., Fgfr3 up 6-fold). Histologically, a localized periosteal response was seen at the site of the fracture; by day 7 there was abundant periosteal woven bone surrounding a region of cartilage. From days 7 to 14, the woven bone became denser but did not increase in area. By day 14, the woven-bone response resulted in complete recovery of ulnar strength and stiffness, restoring mechanical properties to normal levels. In the future, the fatigue loading approach can be used create non-displaced bone fractures in transgenic and knockout mice to study the mechanisms by which the skeleton rapidly repairs damage.

Analytical approaches to uptake and release of hydrogel-associated FGF-2

Strategies to control the delivery of growth factors are critically important in the design of advanced biomaterials. In this study we investigated the binding and release of fibroblast growth factor 2 (FGF-2) to/from a biohybrid hydrogel matrix by four independent analytical methods: radioisotope and fluorescence labeling, amino acid analysis and Enzyme-Linked Immunosorbent Assays (ELISA). The compared analyses provided qualitatively similar uptake characteristics while the results of the FGF-2 quantification strongly depended on the particular experimental conditions. The release kinetics of FGF-2 from the gels could be monitored sensitively by (125)I labeling and by ELISA-techniques. The latter method was concluded to be advantageous since it permits the application of unmodified ("native") growth factors.

Controlled release of FGF-2 using fragmin/protamine microparticles and effect on neovascularization

Water-insoluble fragmin/protamine microparticles of about 0.5-1 mum in diameter were prepared by simple mixing of low-molecular-weight heparin (fragmin) with protamine. We investigated the capability of these microparticles to immobilize fibroblast growth factor (FGF)-2, to protect FGF-2 against degradation, to enhance FGF-2 activity, and to facilitate controlled release of FGF-2. FGF-2 bound to the fragmin/protamine microparticles with high affinity (Kd = 2.08 x 10(-9) M) and the half-life of FGF-2-activity was prolonged substantially through binding of FGF-2 to the microparticles, by protection of FGF-2 from inactivation by heat and proteolysis. After subcutaneous injection into the back of mice, the fragmin/protamine microparticles underwent biodegradation and disappeared in about 2 weeks. A similar injection of FGF-2-containing microparticles resulted in significant neovascularization and fibrous tissue formation near the injection site after 1 week. These results indicate that controlled release of biologically active FGF-2 occurs through both slow diffusion and biodegradation of the microparticles, with subsequent induction of neovascularization. (c) 2008 Wiley Periodicals, Inc. J Biomed Mater Res, 2009.

Effects of single and cyclical local injections of basic fibroblast growth factor on cancellous bone defects in rabbits

BACKGROUND

Local administration of basic fibroblast growth factor (bFGF) has anabolic effects on bone formation. A delivery system for local treatment is required to increase efficacy because of its short half-life. However, little is known about the effects of cyclical local injection of bFGF. We evaluated the effects of single and cyclical local injection of bFGF at a cancellous bone defect in the femoral condyle in rabbits.

METHODS

Using the "vehicle only" as a control, a single low dose (40 microg), single high dose (120 microg), or cyclical low dose (40 microg, three times) of bFGF was injected percutaneously into a bone defect implanted with a gelatin sponge. The rabbits were killed at 4 weeks after surgery and the femurs were harvested for evaluation.

RESULTS

Both single and cyclical administration of bFGF dose-dependently increased the amount of new bone formation in the bone defect using radiographs (P < 0.01) and bone mineral density (BMD) measurements (P < 0.01) compared to controls. However, only high-dose bFGF injection significantly increased the cancellous bone volume at the bone defect (P < 0.05) compared to controls, using bone histomorphometry. Cyclical injection of bFGF significantly increased the number of runt-related transcription factor-2 (Runx2)-positive cells compared to single low- and high-dose bFGF administration (P < 0.01 and P < 0.05, respectively), and single high-dose and cyclical administration significantly increased the number of osteopontin-positive cells compared to controls (P < 0.01), based on immunohistochemical analysis.

CONCLUSIONS

These results suggest that high-dose injection of bFGF, at the very early stage of cancellous bone healing, is more effective in increasing cancellous bone volume, and cyclical injection of bFGF may stimulate osteoprogenitor cells.

Evidence of enhanced expression of osteopontin in spinal hyperostosis of the twy mouse

STUDY DESIGN

Gene expression and protein localization of osteopontin (OPN) in spinal hyperostosis of the twy mouse by means of in situ hybridization, immunohistochemistry, and Northern blot analysis.

OBJECTIVE

To verify the involvement of OPN in spinal hyperostosis in the twy mouse and elucidate its ossification pattern at molecular levels.

SUMMARY OF BACKGROUND DATA

OPN is a molecule that consistently colocalizes with ectopic calcification in human pathologic conditions. The twy mouse, which shows ectopic calcification of the spinal ligament resulting in hind limb paralysis, is considered to be a model for human ossification of the posterior longitudinal ligament of the spine.

METHODS

Twenty-eight each of age-matched twy, heterozygote, and wild-type mice were killed at 2, 4, 8, 12, and 16 weeks old and subject to histologic and/or molecular analyses. Sections were hybridized with RNA probes for OPN and also stained with anti-OPN antibodies. Total cellular RNA was extracted from the cervicothoracic spine of each genotype at 2- and 16-week-old, and gene expression for OPN and COL10A1 was quantified by Northern blot analysis.

RESULTS

Enhanced expression of OPN mRNA was observed in spinal hyperostotic lesions of the twy mouse, specifically in cells of the spinal ligament and chondrogenic cells in the outer layer of the anulus fibrosus. These trends were also confirmed by immunohistochemical analyses. Northern blot analysis showed that a considerable amount of OPN transcripts was detected in all genotypes at 2 weeks old, but the robust expression of OPN mRNA was maintained only in twy mice at 16 weeks old. COL10A1 transcripts were hardly detected regardless of the genotype at 16 weeks old.

CONCLUSION

OPN was overexpressed in the hyperostotic spinal lesions of twy mice, and the hyperostosis was induced mainly by ectopic ossification of the spinal ligament. Because OPN is considered to be an inhibitor of calcification, further studies will be necessary to verify whether OPN overexpressed in the twy mouse is functional.

The systemic angiogenic response during bone healing

INTRODUCTION

Angiogenesis is known to be a critical and closely regulated step during bone formation and fracture healing driven by a complex interaction of various cytokines. Delays in bone healing or even nonunion might therefore be associated with altered concentrations of specific angiogenic factors. These alterations might in turn be reflected by changes in serum concentrations.

METHOD

To determine physiological time courses of angiogenic cytokines during fracture healing as well as possible changes associated with failed consolidation, we prospectively collected serum samples from patients who had sustained surgical treatment for a long bone fracture. Fifteen patients without fracture healing 4 months after surgery (nonunion group) were matched to a collective of 15 patients with successful healing (union group). Serum concentrations of angiogenin (ANG), angiopoietin 2 (Ang-2), basic fibroblast growth factor (bFGF), platelet derived growth factor AB (PDGF-AB), pleiotrophin (PTN) and vascular endothelial growth factor (VEGF) were measured using enzyme linked immunosorbent assays over a period of 24 weeks.

RESULTS

Compared to reference values of healthy uninjured controls serum concentrations of VEGF, bFGF and PDGF were increased in both groups. Peak concentrations of these cytokines were reached during early fracture healing. Serum concentrations of bFGF and PDGF-AB were significantly higher in the union group at 2 and 4 weeks after the injury when compared to the nonunion group. Serum concentrations of ANG and Ang-2 declined steadily from the first measurement in normal healing fractures, while no significant changes over time could be detected for serum concentrations of these factures in nonunion patients. PTN serum levels increased asymptotically over the entire investigation in timely fracture healing while no such increase could be detected during delayed healing.

CONCLUSION

We conclude that fracture healing in human subjects is accompanied by distinct changes in systemic levels of specific angiogenic factors. Significant alterations of these physiologic changes in patients developing a fracture nonunion over time could be detected as early as 2 (bFGF) and 4 weeks (PDGF-AB) after initial trauma surgery.

Fibroblast growth factor expression during skeletal fracture healing in mice

Fibroblast growth factors (FGFs) are important signaling molecules that regulate many stages of endochondral bone development. During the healing of a skeletal fracture, several features of endochondral bone development are reactivated. To better understand the role of FGFs in skeletal fracture healing, we quantitatively evaluated the temporal expression patterns of Fgfs, Fgf receptors (Fgfrs), and molecular markers of bone development over a 14-day period following long bone fracture in a mouse model. These studies identify distinct groups of FGFs that are differentially expressed and suggest active stage-specific roles for FGF signaling during the fracture repair process.

Tendon healing in vivo: gene expression and production of multiple growth factors in early tendon healing period

PURPOSE

The actions of growth factors during healing of injured flexor tendons are not well characterized, although information pertinent to some individual growth factors is available. We studied gene expression and protein production of a number of growth factors at several time points during the early healing period in a chicken model.

METHODS

Seventy-four long toes of 37 white Leghorn chickens were used. The flexor digitorum profundus tendons of 60 toes were surgically repaired after complete transection and were harvested for analysis 3, 5, 7, 9, 14, and 21 days after surgery. The expression of 6 growth factors was studied at 4 time points after surgery with real-time quantitative polymerase chain reactions, and production and distribution of 3 growth factors at all 6 time points were studied by immunohistochemical staining with antibodies. Fourteen tendons that had no surgery served as day 0 controls. Tendon healing status was also assessed histologically.

RESULTS

Throughout the early tendon healing period, connective tissue growth factor (CTGF) and transforming growth factor beta (TGF-beta) showed high levels of gene expression. Levels of gene expression of vascular endothelial growth factor (VEGF) and insulin-like growth factor 1 (IGF-1) were high or moderately high. Expression of the TGF-beta gene was upregulated after injury, whereas the basic fibroblast growth factor (bFGF) gene was downregulated at all postsurgical time points and expressed at the lowest levels among 6 growth factor genes 2 to 3 weeks after surgery. The platelet-derived growth factor B (PDGF-B) gene was also minimally expressed. Findings of immunohistochemistry corresponded to TGF-beta, bFGF, and IGF-1 gene expression.

CONCLUSIONS

In this model, up to 3 weeks after surgery, gene expression and production of TGF-beta are high and are upregulated in this healing period. However, expression of the bFGF gene and protein is low and decreases in the healing tendon. The CTGF, VEGF, and IGF-1 genes are expressed at high or moderately high levels, but PDGF-B is minimally expressed.

Molecular basis for affected cartilage formation and bone union in fracture healing of the streptozotocin-induced diabetic rat

Most studies have focused on the association between diabetes mellitus (DM) and impaired osseous healing, but there is also evidence that diabetes impairs cartilage formation during fracture healing. To investigate the molecular mechanisms by which diabetes affects endochondral ossification, experiments were performed in a model of rat closed fracture healing complicated with diabetes. Diabetic rats were created by a single intravenous injection of streptozotocin (STZ), while controls were treated with vehicle alone. Fractures were made 2 weeks after STZ injection. Animals were killed at 4, 7, 10, 14, 21, 28 and 42 days following fracture, and samples were subject to radiographic, histological and molecular analyses. In the DM group, a significantly smaller cartilaginous callus was formed compared with controls throughout healing, with the cartilage area being reduced rapidly after day 14. When the bone union rate was evaluated radiographically on day 28, DM calluses exhibited a lower rate than controls. However, when evaluated on day 42, both groups showed an equivalent union rate. Cellular proliferation of chondroprogenitor cells and proliferating chondrocytes in soft calluses of the DM group was significantly reduced during early stages of healing (days 4 and 7), but no longer reduced thereafter. Moreover, expression levels of collagen type II, type X and osteopontin (OPN) were constantly low in the DM group. These results show the molecular basis for diminished cartilage formation and delayed union in fracture healing of the STZ-induced diabetic rats.

Sequential biochemical and mechanical stimulation in the development of tissue-engineered ligaments

Application of stimuli in sequence to developing cultures in vitro offers the potential to intricately direct cell development and differentiation by following the template of native tissue behavior. We hypothesize that administration of mechanical stimulation at the peak of growth factor-induced cell activity will differentiate bone marrow stromal cells (BMSCs) along a fibroblast lineage and enhance in vitro ligament development through enhanced matrix ingrowth, matrix metalloproteinase-2 (MMP-2) production, collagen type I production, and extracellular matrix (ECM) alignment. BMSC-seeded silk matrices were cultured in a static growth-factor-free environment for 5 days prior to loading into bioreactor vessels to first establish an appropriate dynamic rotational regime, as determined through assessment of cell activity, histology, and surface topography. Once the regime was determined, seeded matrices initially cultured in basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), or growth-factor-free control medium for 5 days were loaded into the bioreactor for 9 days of mechanical stimulation. Our findings indicated that the sequential application of mechanical stimulation following growth factor supplemented static culture-induced cell differentiation toward a fibroblast lineage, enhancing matrix ingrowth, cell and ECM alignment, and total collagen type I produced compared to respective static cultures. The current results suggest a dynamic culturing regime in the development of engineered tissues.

Fracture repair: modulation of fracture-callus and mechanical properties by sequential application of IL-6 following PTH 1-34 or PTH 28-48

Fracture healing presents a sequence of three major stages: inflammation and granulation tissue formation, callus formation and remodeling. Our working hypothesis was that fracture-repair might be enhanced by stimulating proliferation of chondrocytes and osteoblasts in the early stages of fracture healing followed by sequential acceleration of the remodeling process. In the present study we employed a novel device developed by us implementing a standardized fracture in rat tibiae. We investigated the effect of PTH 28-48 or PTH 1-34 alone or in sequence combination with IL-6 together with its soluble receptor (IL-6sR) on fracture repair. PTH 28-48 or PTH 1-34 was applied locally into the hematoma of fractures on days 4, 5 and 6 and IL-6+ its soluble receptor on days 7, 9, and 11. Post-fracture callus volume as measured 14 days post-fracture was increased significantly only by PTH 1-34 (20%; P<0.01). When one of the PTH fragments and IL-6+IL-6sR were applied sequentially callus volume was increased significantly (33%; P<0.01). X-rays radiography at 5 weeks post-fracture showed enlarged callus volume following treatment by either PTH fragments alone, and complete union following the sequential injection of both PTH fragments and IL-6+IL-6sR, only. Only the combination of one of the PTH fragments with IL-6+IL-6sR, as measured 6 weeks post-fracture by three point bending, changed dramatically the quality of the regenerating bone as presented by a 300% increase in mechanical resistance when PTH 1-34 was combined and 200% when PTH 28-48 was combined relative to vehicle-treated fractured bones. We conclude that the sequential application of IL-6+IL-6sR with both PTH fragments has the potential of enhancing fracture healing in long bones and should be further explored in preclinical and in clinical studies.

Effects of a single percutaneous injection of basic fibroblast growth factor on the healing of a closed femoral shaft fracture in the rat

Recently, bioactive agents to stimulate bone formation have been available in the orthopedic field. We have shown previously that a single, local injection of basic fibroblast growth factor (bFGF) contributes to the formation of a larger cartilage (soft callus) but does not promote replacement of the cartilage by osseous tissue during experimental closed femoral fracture healing. Aiming at a clinical application, the present study was undertaken to clarify the effects of locally injected bFGF on bone (hard callus) formation and the mechanical properties of the callus in closed fracture healing in rats. Immediately after fracture, a carrier (200 muL of fibrin gel) containing 100 mug of bFGF or carrier alone was applied to the fracture site. At days 42 and 56 postfracture, the bone union rate, bone mineral density (BMD), and mechanical properties (strength and stiffness) of the callus were evaluated. Unexpectedly, with the exception of reduced stiffness in the FGF-injected callus at day 56, none of these parameters showed a significant difference between the control and the FGF-injected groups. Furthermore, the temporal expression pattern of OPN mRNA during healing was very similar between groups. We conclude that, in the healing of closed fractures of long bones, administration of bFGF forms a larger callus but does not necessarily accelerate the healing process.

Therapeutic angiogenesis induced by controlled release of fibroblast growth factor-2 from injectable chitosan/non-anticoagulant heparin hydrogel in a rat hindlimb ischemia model

The addition of non-anticoagulant heparin [periodate-oxidized (IO4) heparin] and fibroblast growth factor (FGF)-2 to a viscous water-soluble chitosan (CH-LA) aqueous solution produces an injectable FGF-2/CH-LA/IO4-heparin hydrogel. The purpose of this study was to examine the ability of the injected FGF-2/CH-LA/IO4-heparin hydrogel to induce vascularization and fibrous tissue formation. FGF-2/CH-LA/IO4-heparin hydrogels (100 microL of hydrogel consisting of 20 mg/mL of CH-LA, 2 mg/mL of IO4-heparin, and 50 microg/mL of FGF-2) were subcutaneously injected into the backs of wound healing-impaired diabetic (db/db) mice. Furthermore, the effect of percutaneous injection of FGF-2/CH-LA/IO4-heparin hydrogel at eight sites (25 microL/site) into ischemic left lower limbs of rats was examined from day 4 to at least day 28 postinjection. The injection of FGF-2/CH-LA/IO4-heparin hydrogels into the backs of db/db mice resulted in significant increases in blood vessel formation, significant vascularization, and fibrous tissue formation near the injection site. Injection of FGF-2/CH-LA/IO4-heparin hydrogel into ischemic left lower limbs of rats also significantly recovered and increased blood flow and blood oxygen in the calf and thigh. These results indicate that the controlled release of biologically active FGF-2 molecules from FGF-2/CH-LA/IO4-heparin induces angiogenesis and possibly collateral circulation in db/db mice and the ischemic limbs of rats.

Local application of recombinant human fibroblast growth factor-2 on bone repair: a dose-escalation prospective trial on patients with osteotomy

Based on preclinical evidence in animal models, the present study examined the clinical efficacy and safety of recombinant human fibroblast growth factor-2 (rhFGF-2) to accelerate bone repair in a dose-escalation prospective trial. One of three dosages (200, 400 or 800 microg) of rhFGF-2 in a biodegradable gelatin hydrogel was injected during surgery into the osteotomy site of 59 knee osteoarthritis patients undergoing high tibial osteotomy, and 57 of them were monitored for 16 weeks. The rhFGF-2 dose dependently increased the percentage of patients with radiographic bone union, and decreased the average time needed for such union. The percentages of patients with an absence of pain and full-weight bearing were also greater in the higher dosage groups than in the low dosage group, especially in the clinically critical periods 6, 8, and 10 weeks. Neither blood chemistries nor clinical adverse events were associated with the rhFGF-2 dosages. We therefore conclude that the rhFGF-2 in gelatin hydrogel dose dependently accelerated radiographic bone union of a surgical osteotomy with a safety profile at least at the dosages used, suggesting the clinical efficacy of this agent for bone repair.

Bioadjuvants for complex ankle and hindfoot reconstruction

Many reconstructive options exist for symptomatic hindfoot and ankle problems. Hindfoot and tibiotalar fusions are reliable procedures with consistent results. Unfortunately, many potential complications have been cited throughout the literature. Although the most important aspect in any fusion surgery is meticulous technique, advances in technology, including PRP, bone stimulators, and BMPs seem to be useful additions in the quest to achieve solid fusions with decreased complications.

Can we accelerate fracture healing? A critical analysis of the literature

The characterization of the molecular mediators regulating the fracture healing response over the past decade has vastly expanded our knowledge in this area at the molecular level. It is clear today that the physiological mechanisms governing the biology of bone repair and turnover are complex and far from being well understood. Several of the molecules implicated in the healing process have become available for use in the clinical setting thanks to advances made in recombinant technology. Current evidence of their effect in accelerating fracture healing in both experimental and clinical studies is promising. However, despite these findings, several factors require further investigation, including the ideal timing to administer these molecules, which is the most effective dose, and the factors affecting the lack of consistency in the experimental designs and animal models that have been used. In addition, the available evidence lacks phase III, level I studies. Until such studies become available, the results should be interpreted with caution.

Coordinated fibroblast growth factor and heparan sulfate regulation of osteogenesis

Growth and lineage-specific differentiation constitute crucial phases in the development of stem cells. Control over these processes is exerted by particular elements of the extracellular matrix, which ultimately trigger a cascade of signals that regulate uncommitted cells, by modulating their survival and cell cycle progression, to shape developmental processes. Uncontrolled, constitutive activation of fibroblast growth factor receptors (FGFR) results in bone abnormalities, underlining the stringent control over fibroblast growth factor (FGF) activity that must be maintained for normal osteogenesis to proceed. Mounting evidence suggests that FGF signalling, together with a large number of other growth and adhesive factors, is controlled by the extracellular glycosaminoglycan sugar, heparan sulfate (HS). In this review, we focus on FGF activity during osteogenesis, their receptors, and the use of HS as a therapeutic adjuvant for bone repair.

Gene expression for type-specific collagens in osteogenic protein-1 (rhBMP-7)-induced lumbar intertransverse process fusion in rabbits

To elucidate the molecular mechanism by which osteogenic protein (OP)-1 induces posterolateral lumbar spine fusion (PLF), we analyzed the process of OP-1-induced PLF in an established rabbit model by means of in situ hybridization (ISH). Intertransverse process lumbar fusions were performed at L5-L6 in rabbits using OP-1 (n= 18) or carrier alone (n= 9). The vertebrae were harvested at 2, 4, and 6 weeks postsurgery, and fusion masses evaluated using radiography, histology and ISH. In the OP-1 group, a contiguous fusion mass bridged the L5 and L6 transverse processes by 6 weeks postsurgery. At 2 weeks, collagen types II and X were expressed both near the transverse process and at the central portion of the intertransverse process area, corresponding to abundant, multifocal cartilage. After 4 weeks, endochondral ossification progressed from the transverse process toward the central portion. At 6 weeks, genes for collagen types II and X were restricted at the front of endochondral ossification. In carrier-alone group, no fusion mass was formed. The results demonstrate that OP-1 vigorously stimulates cells and induces chondrogenesis in the early phase of PLF. In the late phase, however, endochondral bone formation progressing toward the central portion became the major process, as was observed in PLF with autograft. In OP-1-induced PLF, therefore, osteogenic action of OP-1 seems to be quite intensive in the early phase but not in the late phase.

Controlled release of fibroblast growth factor-2 from an injectable 6-O-desulfated heparin hydrogel and subsequent effect onin vivo vascularization

We prepared a 6-O-desulfated (DS-) heparin (Hep) hydrogel as an excellent carrier for the controlled release of Hep-binding growth factors, such as fibroblast growth factor (FGF)-2. This material, which is partially derived from photoreactive groups, such as cinnamate, is easily crosslinked upon ultraviolet light (UV)-irradiation, resulting in a water-insoluble, viscous, and injectable hydrogel. In the present study, we examined the capacity of 6-O-DS-Hep hydrogel to immobilize FGF-2, as well as the controlled release of FGF-2 molecules from this hydrogel in vitro and in vivo. Only 10% of FGF-2 was gradually released from the FGF-2-containing 6-O-DS-Hep hydrogel (photocrosslinked 6-O-DS-Hep (4%; w/w) hydrogel containing 50 microg/mL FGF-2) into PBS (phosphate-buffered saline) within first 7 days. The 6-O-DS-Hep hydrogel in vitro maintained the original form through 1 weeks incubation in PBS, but it was gradually fragmented and could not maintain the original form by 2-3 week-washing. When the FGF-2-containing 6-O-DS-Hep hydrogel was subcutaneously injected into the back of rats, significant neovascularization and fibrous tissue formation were induced near the injected site from day 3 after the injection. And, the hydrogel had been biodegraded and completely disappeared from the injected sites in vivo within about 15-20 days after the injection. These findings indicate a controlled release of biologically active FGF-2 molecules together with fragmentation and biodegradation of 6-O-DS-Hep hydrogel and the subsequent induction of neovascularization in vivo.

Effects of low-dose, intermittent treatment with recombinant human parathyroid hormone (1-34) on chondrogenesis in a model of experimental fracture healing

Recent studies have demonstrated that intermittent administration of parathyroid hormone (PTH) enhances osteogenesis (hard callus formation) and increases mechanical strength in experimental fracture healing. Thus far, however, effects of PTH on chondrogenesis (soft callus formation) during fracture healing have not been fully elucidated. In the present study, we analyzed the underlying molecular mechanism by which exogenous PTH would affect chondrogenesis in a model of experimental fracture healing. Unilateral femoral fractures were produced in 2-month-old Sprague-Dawley rats. Daily subcutaneous injections of 10 microg/kg of recombinant human PTH(1-34) [rhPTH(1-34)] were administered over a 28-day period of fracture healing. Control animals were injected with vehicle solution (normal saline) alone. The results showed that, on day 14 after fracture, cartilage area in the PTH-treated group was significantly increased (1.4-fold) compared with the controls, but this increase was not observed at days 21 and 28. In the early stage of chondrogenesis (days 4-7), cell proliferation, expressed as the rate of proliferating cell nuclear antigen-positive cells, was increased in mesenchymal (chondroprogenitor) cells but not chondrocytes in the PTH-treated group compared with controls. In addition, gene expression of SOX-9 was up-regulated in the PTH-treated group on day 4 (1.4-fold), and this was accompanied by enhanced expression of pro-alpha1 (II) collagen (1.8-fold). After 14 days, there were no significant differences between groups in either cell proliferation or the expression levels of cartilage differentiation-related genes (SOX-9, pro-alpha1 (II) collagen, pro-alpha1 (X) collagen and osteopontin). These results suggest that intermittent treatment with low-dose rhPTH(1-34) induces a larger cartilaginous callus but does not delay chondrocyte differentiation during fracture healing.

Patterns and localization of gene expression during intramembranous bone regeneration in the rat femoral marrow ablation model

Tissue formation and repair are dependent upon cascades of biological events, but the signals involved and the possible gene coexpression patterns during intramembranous bone repair are only poorly understood. We sought to place this mode of regeneration in context by profiling quantitative gene expression for a panel of 39 genes between days 1 and 14 following rat femoral marrow ablation. In situ hybridization was employed to localize a subset of genes. Additionally, principal components analysis was conducted to identify underlying factors suggestive of coexpression patterns. During inflammation (days 1-5), several genes, including cyclooxygenase-1 and -2, showed downregulation. Other proinflammatory cytokines, tumor necrosis factor-alpha and interleukin-1beta, exhibited increasing levels around day 5. During repair (days 3-10), growth factors, receptors, and inhibitor genes for transforming growth factor- beta; basic fibroblast growth factor; bone morphogenetic proteins 2, 4, and 7; vascular endothelial growth factor; and insulin-like growth factor-I were upregulated. In addition, the gene for core binding factor-alpha1 and markers of osteoblast function such as alkaline phosphatase, collagen type I, osteonectin, osteopontin, and osteocalcin had peak expression at day 5 or 7. The remodeling phase (days 10-14) was characterized by peaks for cytokines associated with osteoclastic activity including receptor activator of nuclear factor-kappaB, receptor activator of nuclear factor-kappaB ligand (RANKL), cathepsin K, tumor necrosis factor-alpha, interleukin-6, and cyclooxygenase-2. In situ hybridization showed that the most common sites of increased signal were within osteoblastic cells on trabecular and endosteal surfaces. Principal components analysis identified eight underlying factors that together explained over 80% of the variance in the data.