Osteogenic protein-1 (OP-1, BMP-7) induces osteoblastic cell differentiation of the pluripotent mesenchymal cell line C2C12

Effect of gamma and Ultraviolet-C sterilization on BMP-7 level of indigenously prepared demineralized freeze-dried bone allograft

The presence of bone morphogenetic proteins in demineralized freeze-dried bone allograft (DFDBA) are responsible for developing hard tissues in intraosseous defects. The most common mode of sterilization of bone allografts, i.e., Gamma rays, have dramatic effects on the structural and biological properties of DFDBA, leading to loss of BMPs. Ultraviolet-C radiation is a newer approach to sterilize biodegradable scaffolds, which is simple to use and ensures efficient sterilization. However, UV-C radiation has not yet been effectively studied to sterilize bone allografts. This study aimed to compare and evaluate the effectiveness of Gamma and Ultraviolet-C rays in sterilizing indigenously prepared DFDBA and assess their effect on the quantity of BMP-7 present in the allograft. DFDBA samples from non-irradiated, gamma irradiated, and UV-C irradiated groups were tested for BMP-7 level and samples sterilized with gamma and UV-C rays were analysed for sterility testing. The estimated mean BMP-7 level was highest in non-irradiated DFDBA samples, followed by UV-C irradiated, and the lowest in gamma irradiated samples. Our study concluded that UV-C rays effectively sterilized DFDBA as indicated by negative sterility test and comprised lesser degradation of BMP-7 than gamma irradiation.

Aging and Bone Metabolism

Changes in bone architecture and metabolism with aging increase the likelihood of osteoporosis and fracture. Age-onset osteoporosis is multifactorial, with contributory extrinsic and intrinsic factors including certain medical problems, specific prescription drugs, estrogen loss, secondary hyperparathyroidism, microenvironmental and cellular alterations in bone tissue, and mechanical unloading or immobilization. At the histological level, there are changes in trabecular and cortical bone as well as marrow cellularity, lineage switching of mesenchymal stem cells to an adipogenic fate, inadequate transduction of signals during skeletal loading, and predisposition toward senescent cell accumulation with production of a senescence-associated secretory phenotype. Cumulatively, these changes result in bone remodeling abnormalities that over time cause net bone loss typically seen in older adults. Age-related osteoporosis is a geriatric syndrome due to the multiple etiologies that converge upon the skeleton to produce the ultimate phenotypic changes that manifest as bone fragility. Bone tissue is dynamic but with tendencies toward poor osteoblastic bone formation and relative osteoclastic bone resorption with aging. Interactions with other aging physiologic systems, such as muscle, may also confer detrimental effects on the aging skeleton. Conversely, individuals who maintain their BMD experience a lower risk of fractures, disability, and mortality, suggesting that this phenotype may be a marker of successful aging. © 2023 American Physiological Society. Compr Physiol 13:4355-4386, 2023.

Exercise-Induced Myokines can Explain the Importance of Physical Activity in the Elderly: An Overview

Physical activity has been found to aid the maintenance of health in the elderly. Exercise-induced skeletal muscle contractions lead to the production and secretion of many small proteins and proteoglycan peptides called myokines. Thus, studies on myokines are necessary for ensuring the maintenance of skeletal muscle health in the elderly. This review summarizes 13 myokines regulated by physical activity that are affected by aging and aims to understand their potential roles in metabolic diseases. We categorized myokines into two groups based on regulation by aerobic and anaerobic exercise. With aging, the secretion of apelin, β-aminoisobutyric acid (BAIBA), bone morphogenetic protein 7 (BMP-7), decorin, insulin-like growth factor 1 (IGF-1), interleukin-15 (IL-15), irisin, stromal cell-derived factor 1 (SDF-1), sestrin, secreted protein acidic rich in cysteine (SPARC), and vascular endothelial growth factor A (VEGF-A) decreased, while that of IL-6 and myostatin increased. Aerobic exercise upregulates apelin, BAIBA, IL-15, IL-6, irisin, SDF-1, sestrin, SPARC, and VEGF-A expression, while anaerobic exercise upregulates BMP-7, decorin, IGF-1, IL-15, IL-6, irisin, and VEGF-A expression. Myostatin is downregulated by both aerobic and anaerobic exercise. This review provides a rationale for developing exercise programs or interventions that maintain a balance between aerobic and anaerobic exercise in the elderly.

Synthesis and Characterization of a Biocomposite Bone Bandage for Controlled Delivery of Bone-Active Drugs in Fracture Nonunions

Fracture nonunions are common in orthopedics and their treatment often involves multiple surgical interventions. The aim of this study was to fabricate and characterize a gelatin-nano-hydroxyapatite membrane (GM)-based bone bandage for controlled delivery of bio-active molecules; recombinant human bone morphogenic protein-2 (rhBMP-2) and zoledronic acid (ZA) to promote osteoinduction and prevent callus resorption, respectively. In vitro cell-material interaction experiments using MC3T3 cells seeded on the GM indicated good biocompatibility. rhBMP-2-functionalized GM promoted osteogenic differentiation of MC3T3 cells and the rhBMP-2 bio-activity thus remained, as indicated by increased levels of alkaline phosphatase compared to only GM. The GM released a small amount (1.1%) of rhBMP-2 in vitro over a period of 5 weeks, demonstrating a strong interaction of rhBMP-2 with the GM. In the first animal study, the GM specimens loaded with rhBMP-2 or with the combination of rhBMP-2 + ZA were placed in the abdominal muscle pouch of rats. In the GM + rhBMP-2 + ZA group, significantly higher bone volume (21.5 ± 5.9 vs 2.7 ± 1.0 mm³) and area (3.3 ± 2.3 vs 1.0 ± 0.4 mm²) of bone were observed compared to GM + rhBMP-2 after 4 weeks, as indicated by micro-computed tomography and histomorphometry, respectively. Finally, a nonunion model in rats was used to evaluate the efficacy of the GM bandage and bio-active molecules in healing of fracture nonunions. The GM functionalized with rhBMP-2 + ZA led to higher bone formation around the fracture (63.9 ± 19.0 vs 31.8 ± 3.7 mm³) and stronger fracture callus (110.8 ± 46.8 vs 45.6 ± 17.8 N) compared to the empty controls. However, the overall union rate was only marginally improved. The GM alone or combined with ZA did not aid in bone healing in this model. Thus, this study shows that controlled delivery of rhBMP-2 + ZA via the developed GM is a promising approach that could aid in earlier full load bearing in patients with nonunion.

The Role of Bone Morphogenetic Protein 7 (BMP-7) in Inflammation in Heart Diseases

Bone morphogenetic protein-7 is (BMP-7) is a potent anti-inflammatory growth factor belonging to the Transforming Growth Factor Beta (TGF-β) superfamily. It plays an important role in various biological processes, including embryogenesis, hematopoiesis, neurogenesis and skeletal morphogenesis. BMP-7 stimulates the target cells by binding to specific membrane-bound receptor BMPR 2 and transduces signals through mothers against decapentaplegic (Smads) and mitogen activated protein kinase (MAPK) pathways. To date, rhBMP-7 has been used clinically to induce the differentiation of mesenchymal stem cells bordering the bone fracture site into chondrocytes, osteoclasts, the formation of new bone via calcium deposition and to stimulate the repair of bone fracture. However, its use in cardiovascular diseases, such as atherosclerosis, myocardial infarction, and diabetic cardiomyopathy is currently being explored. More importantly, these cardiovascular diseases are associated with inflammation and infiltrated monocytes where BMP-7 has been demonstrated to be a key player in the differentiation of pro-inflammatory monocytes, or M1 macrophages, into anti-inflammatory M2 macrophages, which reduces developed cardiac dysfunction. Therefore, this review focuses on the molecular mechanisms of BMP-7 treatment in cardiovascular disease and its role as an anti-fibrotic, anti-apoptotic and anti-inflammatory growth factor, which emphasizes its potential therapeutic significance in heart diseases.

SPARCL1 promotes C2C12 cell differentiation via BMP7-mediated BMP/TGF-β cell signaling pathway

The extracellular matrix (ECM) is known to regulate tissue development and cell morphology, movement, and differentiation. SPARCL1 is an ECM protein, but its role in mouse cell differentiation has not been widely investigated. The results of western blotting and immunofluorescence showed that SPARCL1 is associated with the repair of muscle damage in mice and that SPARCL1 binds to bone morphogenetic protein 7 (BMP7) by regulating BMP/transforming growth factor (TGF)-β cell signaling. This pathway promotes the differentiation of C2C12 cells. Using CRISPR/Cas9 technology, we also showed that SPARCL1 activates BMP/TGF-β to promote the differentiation of C2C12 cells. BMP7 molecules were found to interact with SPARCL1 by immunoprecipitation analysis. Western blotting and immunofluorescence were performed to verify the effect of BMP7 on C2C12 cell differentiation. Furthermore, SPARCL1 was shown to influence the expression of BMP7 and activity of the BMP/TGF-β signaling pathway. Finally, SPARCL1 activation was accompanied by BMP7 inhibition in C2C12 cells, which confirmed that SPARCL1 affects BMP7 expression and can promote C2C12 cell differentiation through the BMP/TGF-β pathway. The ECM is essential for muscle regeneration and damage repair. This study intends to improve the understanding of the molecular mechanisms of muscle development and provide new treatment ideas for muscle injury diseases.

MicroRNA profiles of BMSCs induced into osteoblasts with osteoinductive medium

MicroRNA (miRNA) plays an important role in cell differentiation and functions as a regulator. Therefore, miRNA is important in the process of bone marrow mesenchymal stem cells (BMSCs) being induced into osteoblasts. In this study, mouse BMSCs were induced with osteoinductive medium, the indices related to osteoblastic differentiation were assayed, including alkaline phosphatase, the deposit of calcium and protein levels of osteocalcin. Using miRNA microarray and reverse transcription-quantitative polymerase chain reaction analyses, differentially expressed miRNAs in the cells, which were induced with osteoinductive medium, were selected and identified. The target genes of the differentially expressed miRNAs were then predicted using bioinformatics analysis. The results revealed that osteoinductive medium promoted osteoblastic differentiation of BMSCs, and let-7c-5p, miR-181c-3p, miR-3092-3p and miR-5132-3p were identified as differentially expressed miRNAs in the cells treated with osteoinductive medium for 14 and 21 days. Certain target genes and signal pathways related to osteoblastic differentiation of the four miRNAs were predicted. These findings indicated the four differently expressed miRNAs may be potential regulators of osteoblastic differentiation, providing a basis for further study on the regulation of miRNAs in the osteogenic differentiation of BMSCs.

Mollugin enhances the osteogenic action of BMP-2 via the p38-Smad signaling pathway

Bone morphogenetic protein 2 (BMP-2) has been used clinically to encourage bone regeneration; although, there can be major side effects with larger doses. Therefore, there is a need to identify new small molecules to potentiate the osteogenic action of BMP-2. In this study, we investigated the effect of mollugin on bone formation in murine bi-potential mesenchymal progenitor C2C12 cells by combination with BMP-2. We found mollugin could enhance the BMP-2-mediated osteoblast differentiation of C2C12 cells. This was accompanied by the induction of other osteogenic BMPs. We also found the enhancing potential of mollugin may involve activation of the p38-Smad1/5/8 signaling axis. Furthermore, mollugin promoted skeletal development in zebrafish. The combination of BMP-2 with small molecules, including mollugin, could minimize its clinical limitations, and these molecules might lead to the development of effective stem cell stimulants for bone regeneration and fracture healing.

Synergistic effects of BMP-2, BMP-6 or BMP-7 with human plasma fibronectin onto hydroxyapatite coatings: A comparative study

Design of new osteoinductive biomaterials to reproduce an optimized physiological environment capable of recruiting stem cells and instructing their fate towards the osteoblastic lineage has become a priority in orthopaedic surgery. This work aims at evaluating the bioactivity of BMP combined with human plasma fibronectin (FN/BMP) delivered in solution or coated onto titanium-hydroxyapatite (TiHA) surfaces. Herein, we focus on the comparison of in vitro osteogenic efficacy in mouse C2C12 pre-osteoblasts of three BMP members, namely: BMP-2, BMP-6 and BMP-7. In parallel, we evaluated the molecular binding strength between each BMP with FN using the Surface Plasmon Resonance (SPR) technology. The affinity of BMPs for FN was found totally different and dependent on BMP type. Indeed, the combination of FN with BMP-2 on TiHA surfaces potentiates the burst of gene-mediated osteogenic induction, while it prolongs the osteogenic activity of BMP-6 and surprisingly annihilates the BMP-7 one. These results correlate with FN/BMP affinity for TiHA, since BMP-6>BMP-2>BMP-7. In addition, by analyzing the osteogenic activity in the peri-implant environment, we showed that osteoinductive paracrine effects were significantly decreased upon (FN/BMP-6), as opposed to (FN/BMP-2) coatings. Altogether, our results support the use of FN/BMP-6 to develop a biomimetic microenvironment capable to induce osteogenic activity under physiological conditions, with minimum paracrine signalization.

STATEMENT OF SIGNIFICANCE

The originality of our paper relies on the first direct comparison of the in vitro osteogenic potential of three osteogenic BMPs (BMP-2, -6 and -7) combined with native human plasma fibronectin delivered in solution or coated by laser transfer onto titanium hydroxyapatite surfaces. We confirm that BMP association with fibronectin enhances the osteogenic activity of BMP-2, -6 and -7, but with essential discrepancies, depending on the BMP member, and in agreement with the affinity of BMPs for fibronectin. Moreover, we bring elements to explain the origin of the BMP-2 medical life-threatening side-effects by analyzing in vitro paracrine effects. Finally, this work supports the alternative use of FN/BMP-6 to induce osteogenic activity under physiological conditions, with minimum side effects.

Muscle as an osteoinductive niche for local bone formation with the use of a biphasic calcium sulphate/hydroxyapatite biomaterial

Objectives

We have observed clinical cases where bone is formed in the overlaying muscle covering surgically created bone defects treated with a hydroxyapatite/calcium sulphate biomaterial. Our objective was to investigate the osteoinductive potential of the biomaterial and to determine if growth factors secreted from local bone cells induce osteoblastic differentiation of muscle cells.

Materials and Methods

We seeded mouse skeletal muscle cells C2C12 on the hydroxyapatite/calcium sulphate biomaterial and the phenotype of the cells was analysed. To mimic surgical conditions with leakage of extra cellular matrix (ECM) proteins and growth factors, we cultured rat bone cells ROS 17/2.8 in a bioreactor and harvested the secreted proteins. The secretome was added to rat muscle cells L6. The phenotype of the muscle cells after treatment with the media was assessed using immunostaining and light microscopy.

Results

C2C12 cells differentiated into osteoblast-like cells expressing prominent bone markers after seeding on the biomaterial. The conditioned media of the ROS 17/2.8 contained bone morphogenetic protein-2 (BMP-2 8.4 ng/mg, standard deviation (sd) 0.8) and BMP-7 (50.6 ng/mg, sd 2.2). In vitro, this secretome induced differentiation of skeletal muscle cells L6 towards an osteogenic lineage.

Conclusion

Extra cellular matrix proteins and growth factors leaking from a bone cavity, along with a ceramic biomaterial, can synergistically enhance the process of ectopic ossification. The overlaying muscle acts as an osteoinductive niche, and provides the required cells for bone formation.

Cite this article: D. B. Raina, A. Gupta, M. M. Petersen, W. Hettwer, M. McNally, M. Tägil, M-H. Zheng, A. Kumar, L. Lidgren. Muscle as an osteoinductive niche for local bone formation with the use of a biphasic calcium sulphate/hydroxyapatite biomaterial. Bone Joint Res 2016;5:500–511. DOI: 10.1302/2046-3758.510.BJR-2016-0133.R1.

Growth Factor-Loaded Microparticles for Tissue Engineering: The Discrepancies of In Vitro Characterization Assays

Efficient and effective growth factor (GF) delivery is an ongoing challenge for tissue regeneration therapies. The accurate quantification of complex molecules such as GFs, encapsulated in polymeric delivery devices, is equally critical and just as complex as achieving efficient delivery of active GFs. In this study, GFs relevant to bone tissue formation, vascular endothelial growth factor (VEGF) and bone morphogenetic protein 7 (BMP-7), were encapsulated, using the technique of electrospraying, into poly(lactic-co-glycolic acid) microparticles that contained poly(ethylene glycol) and trehalose to assist GF bioactivity. Typical quantification procedures, such as extraction and release assays using saline buffer, generated a significant degree of GF interactions, which impaired accurate assessment by enzyme-linked immunosorbent assay (ELISA). When both dry BMP-7 and VEGF were processed with chloroform, as is the case during the electrospraying process, reduced concentrations of the GFs were detected by ELISA; however, the biological effect on myoblast cells (C2C12) or endothelial cells (HUVECs) was unaffected. When electrosprayed particles containing BMP-7 were cultured with preosteoblasts (MC3T3-E1), significant cell differentiation into osteoblasts was observed up to 3 weeks in culture, as assessed by measuring alkaline phosphatase. In conclusion, this study showed how electrosprayed microparticles ensured efficient delivery of fully active GFs relevant to bone tissue engineering. Critically, it also highlights major discrepancies in quantifying GFs in polymeric microparticle systems when comparing ELISA with cell-based assays.

Bone morphogenetic protein-7: Review of signalling and efficacy in fracture healing

Bone morphogenetic proteins (BMPs) are a group of signalling molecules that belong to the transforming growth factor-β superfamily of proteins. Initially identified for their ability to induce bone formation, recent advances in the understanding of cellular and molecular mechanisms regarding BMPs have led to the use of the growth factor to accelerate bone healing. Recent clinical trials have demonstrated that BMPs, BMP-7 in particular, may present an alternative line of treatment other than the gold standard, autogenous bone grafting, in the treatment of fracture nonunion. We performed a literature search in September 2014 of PubMed and Embase using search terms, including "bone morphogenetic proteins", "BMP-7", "non-union", "fracture healing" and "cost-effectiveness", reviewing the efficacy, safety, and cost of treatment of nonunions with BMP-7. The authors further canvassed the reference lists of selected articles and used online search tools, such as Google Scholar. BMP-7 uses both the canonical and noncanonical signalling pathways. The treatment of fracture nonunion with recombinant human BMP-7 (rhBMP-7) has a comparable efficacy with that of autogenous bone grafting with an average union rate of 87% compared with 93% for bone grafting. Furthermore, fewer complications have been described with the use of rhBMP-7 compared with traditional bone grafting. We describe the signalling pathways that BMP-7 uses to exert its effect on bone. In nonunions, rhBMP-7 has been shown to have a similar efficacy to bone grafting with fewer complications.

Skeletal tissue engineering using mesenchymal or embryonic stem cells: clinical and experimental data

INTRODUCTION

Mesenchymal stem cells (MSCs) can be obtained from a wide variety of tissues for bone tissue engineering such as bone marrow, adipose, birth-associated, peripheral blood, periosteum, dental and muscle. MSCs from human fetal bone marrow and embryonic stem cells (ESCs) are also promising cell sources.

AREAS COVERED

In vitro, in vivo and clinical evidence was collected using MEDLINE® (1950 to January 2014), EMBASE (1980 to January 2014) and Google Scholar (1980 to January 2014) databases.

EXPERT OPINION

Enhanced results have been found when combining bone marrow-derived mesenchymal stem cells (BMMSCs) with recently developed scaffolds such as glass ceramics and starch-based polymeric scaffolds. Preclinical studies investigating adipose tissue-derived stem cells and umbilical cord tissue-derived stem cells suggest that they are likely to become promising alternatives. Stem cells derived from periosteum and dental tissues such as the periodontal ligament have an osteogenic potential similar to BMMSCs. Stem cells from human fetal bone marrow have demonstrated superior proliferation and osteogenic differentiation than perinatal and postnatal tissues. Despite ethical concerns and potential for teratoma formation, developments have also been made for the use of ESCs in terms of culture and ideal scaffold.

Transcriptomic profile induced in bone marrow mesenchymal stromal cells after interaction with multiple myeloma cells: implications in myeloma progression and myeloma bone disease

Despite evidence about the implication of the bone marrow (BM) stromal microenvironment in multiple myeloma (MM) cell growth and survival, little is known about the effects of myelomatous cells on BM stromal cells. Mesenchymal stromal cells (MSCs) from healthy donors (dMSCs) or myeloma patients (pMSCs) were co-cultured with the myeloma cell line MM.1S, and the transcriptomic profile of MSCs induced by this interaction was analyzed. Deregulated genes after co-culture common to both d/pMSCs revealed functional involvement in tumor microenvironment cross-talk, myeloma growth induction and drug resistance, angiogenesis and signals for osteoclast activation and osteoblast inhibition. Additional genes induced by co-culture were exclusively deregulated in pMSCs and predominantly associated to RNA processing, the ubiquitine-proteasome pathway, cell cycle regulation, cellular stress and non-canonical Wnt signaling. The upregulated expression of five genes after co-culture (CXCL1, CXCL5 and CXCL6 in d/pMSCs, and Neuregulin 3 and Norrie disease protein exclusively in pMSCs) was confirmed, and functional in vitro assays revealed putative roles in MM pathophysiology. The transcriptomic profile of pMSCs co-cultured with myeloma cells may better reflect that of MSCs in the BM of myeloma patients, and provides new molecular insights to the contribution of these cells to MM pathophysiology and to myeloma bone disease.

In vitro and in vivo Bone-Forming Activity of Saururus chinensis Extract

Bone is maintained by osteoclast-mediated resorption and osteoblast-mediated formation. Recently, anti-osteoporotic activity of Saururus chinensis extract (SCE) and anti-osteoclastogenic activity of its components have been reported, but the effect of SCE on bone formation has not been studied well. Therefore, in this study, we investigated whether Saururus chinensis SCE exhibits in vitro osteogenic and in vivo bone-forming activity. extract strongly enhanced the bone morphogenetic protein (BMP)-2-stimulated induction of alkaline phosphatase, an early phase biomarker of osteoblast differentiation, in bi-potential mesenchymal progenitor C2C12 cells. In vitro osteogenic activity of SCE was accompanied by enhanced expression of BMP-2, BMP-4, BMP-7 and BMP-9 mRNA. In addition, a pharmacological inhibition study suggested the involvement of p38 activation in the osteogenic action of SCE. Moreover, the BMP dependency and the involvement of p38 activation in the osteogenic action of SCE were confirmed by the treatment of noggin, an antagonist of BMP. Saururus chinensis extract also exhibited to induce runt-related transcription factor 2 activation at the high concentration. Furthermore, the in vivo osteogenic activity of SCE was confirmed in zebrafish and mouse calvarial bone formation models, suggesting the possibility of its use for bone formation. In conclusion, we suggested that in vivo anti-osteoporotic activity of SCE could be because of its dual action in bone, anti-osteoclastogenic and anabolic activity.

Quinoline compound KM11073 enhances BMP-2-dependent osteogenic differentiation of C2C12 cells via activation of p38 signaling and exhibits in vivo bone forming activity

Recombinant human bone morphogenetic protein (rhBMP)-2 has been approved by the FDA for clinical application, but its use is limited due to high cost and a supra-physiological dose for therapeutic efficacy. Therefore, recent studies have focused on the generation of new therapeutic small molecules to induce bone formation or potentiate the osteogenic activity of BMP-2. Here, we show that [4-(7-chloroquinolin-4-yl) piperazino][1-phenyl-5-(trifluoromethyl)-1H-pyrazol-4-yl]methanone (KM11073) strongly enhances the BMP-2-stimulated induction of alkaline phosphatase (ALP), an early phase biomarker of osteoblast differentiation, in bi-potential mesenchymal progenitor C2C12 cells. The KM11073-mediated ALP induction was inhibited by the BMP antagonist noggin, suggesting that its osteogenic activity occurs via BMP signaling. In addition, a pharmacological inhibition study suggested the involvement of p38 activation in the osteogenic action of KM11073 accompanied by enhanced expression of BMP-2, -6, and -7 mRNA. Furthermore, the in vivo osteogenic activity of KM11073 was confirmed in zebrafish and mouse calvarial bone formation models, suggesting the possibility of its single use for bone formation. In conclusion, the combination of rhBMP-2 with osteogenic small molecules could reduce the use of expensive rhBMP-2, mitigating the undesirable side effects of its supra-physiological dose for therapeutic efficacy. Moreover, due to their inherent physical properties, small molecules could represent the next generation of regenerative medicine.

Calcifying vascular smooth muscle cells and osteoblasts: independent cell types exhibiting extracellular matrix and biomineralization-related mimicries

BACKGROUND

Ectopic vascular calcifications represent a major clinical problem associated with cardiovascular disease and mortality. However, the mechanisms underlying pathological vascular calcifications are largely unknown hampering the development of therapies to tackle this life threatening medical condition.

RESULTS

In order to gain insight into the genes and mechanisms driving this pathological calcification process we analyzed the transcriptional profile of calcifying vascular smooth muscle cells (C-VSMCs). These profiles were compared to differentiating osteoblasts, cells that constitute their physiological calcification counterparts in the body. Overall the transcriptional program of C-VSMC and osteoblasts did not overlap. Several genes, some of them relevant for bone formation, were distinctly modulated by C-VSMCs which did not necessarily lose their smooth muscle cell markers while calcifying. Bioinformatics gene clustering and correlation analysis disclosed limited bone-related mechanisms being shared by two cell types. Extracellular matrix (ECM) and biomineralization genes represented common denominators between pathological vascular and physiological bone calcifications. These genes constitute the strongest link between these cells and represent potential drivers for their shared end-point phenotype.

CONCLUSIONS

The analyses support the hypothesis that VSMC trans-differentiate into C-VSMCs keeping their own identity while using mechanisms that osteoblasts use to mineralize. The data provide novel insights into groups of genes and biological processes shared in MSC and VSMC osteogenic differentiation. The distinct gene regulation between C-VSMC and osteoblasts might hold clues to find cell-specific pathway modulations, opening the possibility to tackle undesired vascular calcifications without disturbing physiologic bone formation and vice versa.

Spatial patterning of BMP-2 and BMP-7 on biopolymeric films and the guidance of muscle cell fate

In the cellular microenvironment, growth factor gradients are crucial in dictating cell fate. Towards developing materials that capture the native microenvironment we engineered biomimetic films that present gradients of matrix-bound bone morphogenetic proteins (BMP-2 and BMP-7). To this end layer-by-layer films composed of poly(L-lysine) and hyaluronan were combined in a simple microfluidic device enabling spatially controlled growth factor diffusion along the film. Linear long-range gradients of both BMPs induced the trans-differentiation of C2C12 myoblasts towards the osteogenic lineage in a dose dependent manner with a different signature for each BMP. The osteogenic marker alkaline phosphatase (ALP) increased in a linear manner for BMP-7 and non-linearly for BMP-2. Moreover, an increased expression of the myogenic marker troponin T was observed with decreasing matrix-bound BMP concentration, providing a substrate that it is both osteo- and myo-inductive. Lastly, dual parallel matrix-bound gradients of BMP-2 and -7 revealed a complete saturation of the ALP signal. This suggested an additive or synergistic effect of the two BMPs. This simple technology allows for determining quickly and efficiently the optimal concentration of matrix-bound growth factors, as well as for investigating the presentation of multiple growth factors in their solid-phase and in a spatially controlled manner.

BMP7 gene transfer via gold nanoparticles into stroma inhibits corneal fibrosis in vivo

This study examined the effects of BMP7 gene transfer on corneal wound healing and fibrosis inhibition in vivo using a rabbit model. Corneal haze in rabbits was produced with the excimer laser performing -9 diopters photorefractive keratectomy. BMP7 gene was introduced into rabbit keratocytes by polyethylimine-conjugated gold nanoparticles (PEI2-GNPs) transfection solution single 5-minute topical application on the eye. Corneal haze and ocular health in live animals was gauged with stereo- and slit-lamp biomicroscopy. The levels of fibrosis [α-smooth muscle actin (αSMA), F-actin and fibronectin], immune reaction (CD11b and F4/80), keratocyte apoptosis (TUNEL), calcification (alizarin red, vonKossa and osteocalcin), and delivered-BMP7 gene expression in corneal tissues were quantified with immunofluorescence, western blotting and/or real-time PCR. Human corneal fibroblasts (HCF) and in vitro experiments were used to characterize the molecular mechanism mediating BMP7’s anti-fibrosis effects. PEI2-GNPs showed substantial BMP7 gene delivery into rabbit keratocytes in vivo (2×10⁴ gene copies/ug DNA). Localized BMP7 gene therapy showed a significant corneal haze decrease (1.68±0.31 compared to 3.2±0.43 in control corneas; p<0.05) in Fantes grading scale. Immunostaining and immunoblot analyses detected significantly reduced levels of αSMA (46±5% p<0.001) and fibronectin proteins (48±5% p<0.01). TUNEL, CD11b, and F4/80 assays revealed that BMP7 gene therapy is nonimmunogenic and nontoxic for the cornea. Furthermore, alizarin red, vonKossa and osteocalcin analyses revealed that localized PEI2-GNP-mediated BMP7 gene transfer in rabbit cornea does not cause calcification or osteoblast recruitment. Immunofluorescence of BMP7-transefected HCFs showed significantly increased pSmad-1/5/8 nuclear localization (>88%; p<0.0001), and immunoblotting of BMP7-transefected HCFs grown in the presence of TGFβ demonstrated significantly enhanced pSmad-1/5/8 (95%; p<0.001) and Smad6 (53%, p<0.001), and decreased αSMA (78%; p<0.001) protein levels. These results suggest that localized BMP7 gene delivery in rabbit cornea modulates wound healing and inhibits fibrosis in vivo by counter balancing TGFβ1-mediated profibrotic Smad signaling.

Dynamic regulation of bone morphogenetic proteins in engineered osteochondral constructs by biomechanical stimulation

Osteochondral tissue-engineered grafts are proposed to hold greater potential to repair/regenerate damaged cartilage through enhanced biochemical and mechanical interactions with underlying subchondral bone as compared to simple engineered cartilage. Additionally, biomechanical stimulation of articular chondrocytes (ACs) or osteoblasts (OBs) was shown to induce greater morphogenesis of the engineered tissues composed of these cells. In this report, to define the advantages of biomechanical stimulation to osteochondral grafts for tissue engineering, we examined whether (1) ACs and OBs in three-dimensional (3D) osteochondral constructs support functional development of each other at the molecular level, and (2) biomechanical stimulation of osteochondral constructs further promotes the regenerative potential of such grafts. Various configurations of cell/scaffold assemblies, including chondral, osseous, and osteochondral constructs, were engineered with mechano-responsive electrospun poly(ɛ-caprolactone) scaffolds. These constructs were subjected to either static or dynamic (10% cyclic compressive strain at 1 Hz for 3 h/day) culture conditions for 2 weeks. The expression of bone morphogenetic proteins (BMPs) was examined to assess the regenerative potential of each treatment on the cells. Biomechanical stimulation augmented a marked upregulation of Bmp2, Bmp6, and Bmp7 as well as downregulation of BMP antagonist, Bmp3, in a time-specific manner in the ACs and OBs of 3D osteochondral constructs. More importantly, the presence of biomechanically stimulated OBs was especially crucial for the induction of Bmp6 in ACs, a BMP required for chondrocytic growth and differentiation. Biomechanical stimulation led to enhanced tissue morphogenesis possibly through this BMP regulation, evident by the improved effective compressive modulus of the osteochondral constructs (710 kPa of dynamic culture vs. 280 kPa of static culture). Similar BMP regulation was observed in the femoral cartilages of the rats subjected to gentle exercise, demonstrating the physiological relevance of in vitro biomechanical stimulation of osteochondral constructs. Overall, our findings show that biomechanical stimulation may be critical for cross signaling between ACs and OBs to support chondrocytic growth in 3D osteochondral tissues.

Synergistic effect of recombinant human bone morphogenic protein-7 and osteogenic differentiation medium on human bone-marrow-derived mesenchymal stem cells in vitro

PURPOSE

The purpose of this study was to investigate the effect of recombinant human bone morphogenetic protein-7 (rhBMP-7) with or without osteogenic differentiation medium (ODM) on osteogenic differentiation of primary human bone-marrow-derived mesenchymal stem cells (hBMSCs) in vitro.

METHOD

The hBMSCs were isolated from medullary reaming tissue. At 80% confluence, hBMSCs were treated with different concentrations of rhBMP-7 with and without ODM. Alkaline phosphatase (ALP) activity, calcium deposition and messenger RNA (mRNA) expression of osteocalcin (OC) and osteopontin (OPN) were examined.

RESULTS

ALP activity and calcium deposits in hBMSC culture were significantly increased by rhBMP-7 at 0.1 μg/ml (0.23 ± 0.07 IU and 28.9 ± 4.2 mg/dl) and 1.0 μg/ml (0.32 ± 0.03 IU and 38.7 ± 3.0 mg/dl), respectively, in the presence of ODM, showing a clearly dose-dependent osteoblastic differentiation. However, the same dose of 0.1 μg/ml rhBMP-7 without ODM and ODM alone induced low level of ALP and calcium deposits, indicating a synergistic effect of rhBMP-7 and ODM on committed osteogenic differentiation. Quantitative real-time reverse-transcriptase polymerase chain reaction (RT-PCR) analysis showed up-regulated OC and OPN mRNA levels, corroborating the synergistic effect of rhBMP-7 and ODM.

CONCLUSION

Our study showed that rhBMP-7 with ODM created a synergistic effect on up-regulation of osteogenic genes as well as osteogenic differentiation of primary hBMSCs in vitro. In the presence of ODM, the lowest concentration of rhBMP-7 needed to induce significant osteogenic differentiation of hBMSCs was 0.1 μg/ml.

In vitro and in vivo osteogenic activity of licochalcone A

We investigated the in vitro and in vivo osteogenic activity of licochalcone A. At low concentrations, licochalcone A stimulated the differentiation of mouse pre-osteoblastic MC3T3-E1 subclone 4 (MC4) cells and enhanced the bone morphogenetic protein (BMP)-2-induced stimulation of mouse bi-potential mesenchymal precursor C2C12 cells to commit to the osteoblast differentiation pathway. This osteogenic activity of licochalcone A was accompanied by the activation of extracellular-signal regulated kinase (ERK). The involvement of ERK was confirmed in a pharmacologic inhibition study. Additionally, noggin (a BMP antagonist) inhibited the osteogenic activity of licochalcone A in C2C12 cells. Licochalcone A also enhanced the BMP-2-stimulated expression of various BMP mRNAs. This suggested that the osteogenic action of licochalcone A in C2C12 cells could be dependent on BMP signaling and/or expression. We then tested the in vivo osteogenic activity of licochalcone A in two independent animal models. Licochalcone A accelerated the rate of skeletal development in zebrafish and enhanced woven bone formation over the periosteum of mouse calvarial bones. In summary, licochalcone A induced osteoblast differentiation with ERK activation in both MC4 and C2C12 cells and it exhibited in vivo osteogenic activity in zebrafish skeletal development and mouse calvarial bone formation. The dual action of licochalcone A in stimulating bone formation and inhibiting bone resorption, as described in a previous study, might be beneficial in treating bone-related disorders.

Identification of differentially regulated secretome components during skeletal myogenesis

Myogenesis is a well-characterized program of cellular differentiation that is exquisitely sensitive to the extracellular milieu. Systematic characterization of the myogenic secretome (i.e. the ensemble of secreted proteins) is, therefore, warranted for the identification of novel secretome components that regulate both the pluripotency of these progenitor mesenchymal cells, and also their commitment and passage through the differentiation program. Previously, we have successfully identified 26 secreted proteins in the mouse skeletal muscle cell line C2C12 (1). In an effort to attain a more comprehensive picture of the regulation of myogenesis by its extracellular milieu, quantitative profiling employing stable isotope labeling by amino acids in cell culture was implemented in conjunction with two parallel high throughput online reverse phase liquid chromatography-tandem mass spectrometry systems. In summary, 34 secreted proteins were quantified, 30 of which were shown to be differentially expressed during muscle development. Intriguingly, our analysis has revealed several novel up- and down-regulated secretome components that may have critical biological relevance for both the maintenance of pluripotency and the passage of cells through the differentiation program. In particular, the altered regulation of secretome components, including follistatin-like protein-1, osteoglycin, spondin-2, and cytokine-induced apoptosis inhibitor-1, along with constitutively expressed factors, such as fibulin-2, illustrate dynamic changes in the secretome that take place when differentiation to a specific lineage occurs.

The role of BMP-7 in chondrogenic and osteogenic differentiation of human bone marrow multipotent mesenchymal stromal cells in vitro

This study addresses the role of bone morphogenetic protein-7 (BMP-7) in chondrogenic and osteogenic differentiation of human bone marrow multipotent mesenchymal stromal cells (BM MSCs) in vitro. BM MSCs were expanded and differentiated in the presence or absence of BMP-7 in monolayer and three-dimensional cultures. After 3 days of stimulation, BMP-7 significantly inhibited MSC growth in expansion cultures. When supplemented in commonly used induction media for 7-21 days, BMP-7 facilitated both chondrogenic and osteogenic differentiation of MSCs. This was evident by specific gene and protein expression analyses using real-time PCR, Western blot, histological, and immunohistochemical staining. BMP-7 supplementation appeared to enhance upregulation of lineage-specific markers, such as type II and type IX collagens (COL2A1, COL9A1) in chondrogenic and secreted phosphoprotein 1 (SPP1), osteocalcin (BGLAP), and osterix (SP7) in osteogenic differentiation. BMP-7 in the presence of TGF-beta3 induced superior chondrocytic proteoglycan accumulation, type II collagen, and SOX9 protein expression in alginate and pellet cultures compared to either factor alone. BMP-7 increased alkaline phosphatase activity and dose-dependently accelerated calcium mineralization of osteogenic differentiated MSCs. The potential of BMP-7 to promote adipogenesis of MSCs was restricted under osteogenic conditions, despite upregulation of adipocyte gene expression. These data suggest that BMP-7 is not a singular lineage determinant, rather it promotes both chondrogenic and osteogenic differentiation of MSCs by co-ordinating with initial lineage-specific signals to accelerate cell fate determination. BMP-7 may be a useful enhancer of in vitro differentiation of BM MSCs for cell-based tissue repair.

Physcion-8-O-beta-D-glucopyranoside enhances the commitment of mouse mesenchymal progenitors into osteoblasts and their differentiation: Possible involvement of signaling pathways to activate BMP gene expression

Here, we show the involvement of signaling pathways to induce the gene expression of bone morphogenetic protein (BMP) in the osteogenic activity of physcion-8-O-beta-D-glucopyranoside (physcion-Glu); it stimulated osteoblast differentiation in mouse osteoblast MC3T3-E1 subclone 4 cells and induced BMP-2 gene expression and activation of Akt and ERK/MAP kinases. Physcion-Glu-induced BMP-2 expression and mineralization were attenuated by LY294002, an inhibitor of PI3K that lies upstream of Akt and MAP kinases, suggesting that physcion-Glu induces osteoblast differentiation via PI3K-Akt/MAP kinase signaling pathways, which play important roles in inducing BMP-2 gene expression. Physcion-Glu also enhanced BMP-2-induced commitment of mouse bi-potential mesenchymal precursor C2C12 cells into osteoblasts while inducing the transcription of several osteogenic BMP isoforms, such as BMP-2, -4, -7, and -9. Osteogenic synergy between BMP-2 and physcion-Glu was supported by the fact that noggin inhibited BMP-2 and physcion-Glu-induced alkaline phosphatase expression and activity. Considering that physcion-Glu induced Runx2 activity and the nuclear translocation of p-Smad, physcion-Glu could act by enhancing the BMP signaling pathway that induces Smad activation and translocation to activate Runx2. In conclusion, physcion-Glu could enhance the commitment of mesenchymal progenitors into osteoblasts and their differentiation by activating signaling pathways to induce BMP gene expression.

Stromal derived factor-1 regulates bone morphogenetic protein 2-induced osteogenic differentiation of primary mesenchymal stem cells

Stromal derived factor-1 (SDF-1) is a chemokine signaling molecule that binds to its transmembrane receptor CXC chemokine receptor-4 (CXCR4). While we previously detected that SDF-1 was co-required with bone morphogenetic protein 2 (BMP2) for differentiating mesenchymal C2C12 cells into osteoblastic cells, it is unknown whether SDF-1 is similarly involved in the osteogenic differentiation of mesenchymal stem cells (MSCs). Therefore, here we examined the role of SDF-1 signaling during BMP2-induced osteogenic differentiation of primary MSCs that were derived from human and mouse bone marrow. Our data showed that blocking of the SDF-1/CXCR4 signal axis or adding SDF-1 protein to MSCs significantly affected BMP2-induced alkaline phosphatase (ALP) activity and osteocalcin (OCN) synthesis, markers of preosteoblasts and mature osteoblasts, respectively. Moreover, disrupting the SDF-1 signaling impaired bone nodule mineralization during terminal differentiation of MSCs. Furthermore, we detected that blocking of the SDF-1 signaling inhibited the BMP2-induced early expression of Runt-related factor-2 (Runx2) and osterix (Osx), two "master" regulators of osteogenesis, and the SDF-1 effect was mediated via intracellular Smad and Erk activation. In conclusion, our results demonstrated a regulatory role of SDF-1 in BMP2-induced osteogenic differentiation of MSCs, as perturbing the SDF-1 signaling affected the differentiation of MSCs towards osteoblastic cells in response to BMP2 stimulation. These data provide novel insights into molecular mechanisms underlying MSC osteogenesis, and will contribute to the development of MSC therapies for enhancing bone formation and regeneration in broad orthopaedic situations.

Tanshinone IIA enhances BMP-2-stimulated commitment of C2C12 cells into osteoblasts via p38 activation

In this study, we demonstrate a stimulatory effect of tanshinone IIA isolated from the root of Salvia miltiorrhiza on the commitment of bi-potential mesenchymal precursor C2C12 cells into osteoblasts in the presence of bone morphogenetic protein (BMP)-2. At low concentrations, tanshinone IIA enhanced BMP-2-stimulated induction of alkaline phosphatase (ALP), an early phase biomarker of osteoblast differentiation, and mRNA expression of BMPs. ALP induction was inhibited by the BMP antagonist noggin, suggesting that tanshinone IIA enhances the osteogenic activity of BMP signaling. Furthermore, considering the tanshinone IIA-mediated enhancement of BMP-2-stimulated Smad-Runx2 activities, tanshinone IIA could enhance the osteogenic activity of BMP-2 via acceleration of Smad-Runx2 activation. Additionally, pharmacologic inhibition studies suggest the possible involvement of p38 in the action of tanshinone IIA. The p38 inhibitor SB202190 strongly and dose-dependently inhibited tanshinone IIA-enhanced ALP induction. SB202190 also dose-dependently inhibited the tanshinone IIA-induced p38 activation and combined tanshinone IIA-BMP-2-induced Smad activation. In conclusion, tanshinone IIA enhances the commitment of C2C12 cells into osteoblasts and their differentiation through synergistic cross talk between tanshinone IIA-induced p38 activation and BMP-2-induced Smad activation. These activations could subsequently induce the activation of Runx2, which induces osteogenesis via regulation of the osteogenic factors BMP and ALP expression.

The synergistic effect of autograft and BMP-7 in the treatment of atrophic nonunions

Combining autologous bone graft and recombinant human bone morphogenetic protein-7 (BMP-7) to treat long-bone fracture aseptic atrophic nonunions theoretically could promote bone healing at higher rates than each of these grafting agents separately. We retrospectively reviewed prospectively collected data on patient general characteristics, clinical outcomes, and complications over 3 years to determine the healing rates and the incidence of complications and adverse events of this "graft expansion rationale." There were 45 patients (32 male) with a median age of 43 years (range, 19-76 years). Minimum followup was 12 months (mean, 24.5 months; range, 12-65 months). There were seven humeral, 19 femoral, and 19 tibial nonunions. The median number of prior operations was two (range, 1-7). All fractures united. Clinical and radiographic union occurred within a median of 5 months (range, 3-14 months) and 6 months (range, 4-16 months), respectively. Thirty-nine (87%) patients returned to their preinjury occupation at a mean of 4.2 months (range, 3-6 months). The median visual analog scale pain score was 0.9 (range, 0-2.8; maximum 10), and the median functional score was 86 (range, 67-95; maximum 100) at the final followup. BMP-7 as a bone-stimulating agent combined with conventional autograft resulted in a nonunion healing rate of 100% in these 45 patients.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Evaluation and management of osteoporosis and fragility fractures in the elderly

Osteoporosis is characterized by low bone mass and microarchitectural deterioration that leads to increased bone fragility and fracture. The medical, psychosocial and economic burden that fragility fractures have on individuals and society is staggering. As the geriatric segment of the population continues to expand, so to will the magnitude of this epidemic. There are multiple mechanisms influencing bone quality and bone loss with age. Fragility fracture is a composite of multiple intrinsic and extrinsic factors related to the individual and their environment. Fall prevention remains the cornerstone of management in this problem. The FRAX® fracture risk assessment program, which estimates the 10-year probability of a major osteoporotic fracture, is an exciting new tool in assessing risk. Novel therapeutics, including zoledronic acid, strontium and teriparatide, are now available to complement proven osteoporosis treatments and more effectively decrease fracture risk in vulnerable individuals. Agents in Phase III trials, including denosumab and lasofoxifene, will probably increase the armamentarium of tools clinicians can use to combat the growing problem of osteoporosis and its complications.

Progenitor and stem cells for bone and cartilage regeneration

Research in regenerative medicine is developing at a significantly quick pace. Cell-based bone and cartilage replacement is an evolving therapy aiming at the treatment of patients who suffer from limb amputation, damaged tissues and various bone and cartilage-related disorders. Stem cells are undifferentiated cells with the capability to regenerate into one or more committed cell lineages. Stem cells isolated from multiple sources have been finding widespread use to advance the field of tissue repair. The present review gives a comprehensive overview of the developments in stem cells originating from different tissues and suggests future prospects for functional bone and cartilage tissue regeneration.

Effect of rhBMP-7 combined with two bone grafts on human periodontal ligament cell differentiation

The purpose of this study was to evaluate the in vitro effect of recombinant human bone morphogenetic protein-7 (rhBMP-7) combined with demineralised freeze-dried bone allograft (DFDBA) and an inorganic bovine material with a synthetic peptide (PepGen P-15) on human periodontal ligament (hPDL) cell differentiation, in a time-dependent manner. hPDL cells were cultured and treated with: (1) 500 ng/ml of rhBMP-7, (2) 10 mg of DFDBA or PepGen P-15 and (3) their combination. Cell differentiation was estimated after 48 and 72 h by measuring alkaline phosphatase (ALPase) activity and osteocalcin (OC) secretion. The presence of rhBMP-7, DFDBA, PepGen P-15, rhBMP-7 + DFDBA and rhBMP-7+ PepGen P-15 promoted a significant increase of ALPase activity after 48 and 72 h. The combination of rhBMP-7 with DFDBA or PepGen P-15 did not lead to significant OC secretion. The results of this study imply that rhBMP-7 stimulates the early osteoblastic differentiation of hPDL cells and that DFDBA and PepGen P-15 could serve as carriers for rhBMP-7.

Myoblast sensitivity and fibroblast insensitivity to osteogenic conversion by BMP-2 correlates with the expression of Bmpr-1a

Background

Osteoblasts are considered to primarily arise from osseous progenitors within the periosteum or bone marrow. We have speculated that cells from local soft tissues may also take on an osteogenic phenotype. Myoblasts are known to adopt a bone gene program upon treatment with the osteogenic bone morphogenetic proteins (BMP-2,-4,-6,-7,-9), but their osteogenic capacity relative to other progenitor types is unclear. We further hypothesized that the sensitivity of cells to BMP-2 would correlate with BMP receptor expression.

Methods

We directly compared the BMP-2 sensitivity of myoblastic murine cell lines and primary cells with osteoprogenitors from osseous tissues and fibroblasts. Fibroblasts forced to undergo myogenic conversion by transduction with a MyoD-expressing lentiviral vector (LV-MyoD) were also examined. Outcome measures included alkaline phosphatase expression, matrix mineralization, and expression of osteogenic genes (alkaline phosphatase, osteocalcin and bone morphogenetic protein receptor-1A) as measured by quantitative PCR.

Results

BMP-2 induced a rapid and robust osteogenic response in myoblasts and osteoprogenitors, but not in fibroblasts. Myoblasts and osteoprogenitors grown in osteogenic media rapidly upregulated Bmpr-1a expression. Chronic BMP-2 treatment resulted in peak Bmpr-1a expression at day 6 before declining, suggestive of a negative feedback mechanism. In contrast, fibroblasts expressed low levels of Bmpr-1a that was only weakly up-regulated by BMP-2 treatment. Bioinformatics analysis confirmed the presence of myogenic responsive elements in the proximal promoter region of human and murine BMPR-1A/Bmpr-1a. Forced myogenic gene expression in fibroblasts was associated with a significant increase in Bmpr-1a expression and a synergistic increase in the osteogenic response to BMP-2.

Conclusion

These data demonstrate the osteogenic sensitivity of muscle progenitors and provide a mechanistic insight into the variable response of different cell lineages to BMP-2.

A comparative study on BMP-induced osteoclastogenesis and osteoblastogenesis in primary cultures of adult rat bone marrow cells

Bone remodeling is a process consisting of bone formation and resorption. The present study compared the relative osteoclastic and osteoblastic potency of bone morphogenetic proteins (BMP)-2, -4, -5, -6, and -7 in primary murine bone marrow cultures. All five BMPs stimulated, to varying degree, formation of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells in a time- and protein concentration-dependent manner. The TRAP staining intensity correlated positively with the number of nuclei per TRAP-positive cell and the mRNA levels of colony-stimulating factor (CSF-1), receptor activator of nuclear factor kappaB ligand (RANKL), TRAP, and cathepsin K. Under osteogenic conditions, all five BMPs stimulated AP activity and mineralized bone nodule formation in a protein concentration-dependent manner in the same primary murine bone marrow cell culture system. These findings should be useful in designing treatment strategies for bone regeneration.

New bone formation by murine osteoprogenitor cells cultured on corticocancellous allograft bone

The gold standard for bone grafting in orthopedics is autograft, however autograft has a limited supply and is associated with significant morbidity at the harvest site. One alternative, allograft bone, provides an osteoconductive scaffold, is in less limited supply, and it does not require a harvest from the patient. However, allograft lacks both osteogenic cells and osteoinductive proteins that make autograft bone so advantageous. This study provides a model to investigate strategies for augmentation of corticocancellous allograft bone discs with bone marrow-derived osteoprogenitor cells (OPCs) plus exogenous growth factors in vitro. In this model, allograft bone discs were created by cutting 1-mm thick slices from the distal femur and proximal tibia of euthanized mice. The allografts were sterilized and scanned by micro-computed tomography (microCT) to provide the pre-culture graft volume and trabecular characteristics. The discs were then seeded with OPCs harvested from murine bone marrow. The seeded grafts were placed in organ culture until harvest, after which they were re-scanned by microCT and the data compared to the corresponding pre-culture data. In addition, bone morphogenetic protein-7 (BMP-7, also know as osteogenic protein-1 or OP-1), basic fibroblast growth factor (bFGF), and OP-1 combined with bFGF were added on a daily basis to the cultures. After final microCT scanning, all grafts were sectioned and evaluated histologically after hematoxylin and eosin (H&E) staining. microCT scans of cultured allografts with cells at 3, 5, and 9 weeks showed a time-dependent, statistically significant increase in bone volume. The trabecular thickness (Tb.Th.) of grafts, from both groups that were augmented with OP-1, showed a statistically significant increase in trabecular thickness of allografts with OPCs. These data suggest that bone marrow-derived OPCs adhere to, and produce, new bone on corticocancellous allograft in vitro. When exogenous OP-1 is added to this model, an increase in the production of bone onto the corticocancellous allograft bone disc is seen. This model allows for the investigation of the effects of multiple growth factors, and other interventions, on OPCs seeded onto allograft bone in vitro.

BMP-2/4 and BMP-6/7 differentially utilize cell surface receptors to induce osteoblastic differentiation of human bone marrow-derived mesenchymal stem cells

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-beta superfamily of growth factors and are used clinically to induce new bone formation. The purpose of this study was to evaluate receptor utilization by BMP-2, BMP-4, BMP-6, and BMP-7 in primary human mesenchymal stem cells (hMSC), a physiologically relevant cell type that probably mediates the in vivo effects of BMPs. RNA interference-mediated gene knockdown revealed that osteoinductive BMP activities in hMSC are elicited through the type I receptors ACVR1A and BMPR1A and the type II receptors ACVR2A and BMPR2. BMPR1B and ACVR2B were expressed at low levels and were not found to play a significant role in signaling by any of the BMPs evaluated in this study. Type II receptor utilization differed significantly between BMP-2/4 and BMP-6/7. A greater reliance on BMPR2 was observed for BMP-2/4 relative to BMP-6/7, whereas ACVR2A was more critical to signaling by BMP-6/7 than BMP-2/4. Significant differences were also observed for the type I receptors. Although BMP-2/4 used predominantly BMPR1A for signaling, ACVR1A was the preferred type I receptor for BMP-6/7. Signaling by both BMP-2/4 and BMP-6/7 was mediated by homodimers of ACVR1A or BMPR1A. A portion of BMP-2/4 signaling also required concurrent BMPR1A and ACVR1A expression, suggesting that BMP-2/4 signal in part through ACVR1A/BMPR1A heterodimers. The capacity of ACVR1A and BMPR1A to form homodimers and heterodimers was confirmed by bioluminescence resonance energy transfer analyses. These results suggest different mechanisms for BMP-2/4- and BMP-6/7-induced osteoblastic differentiation in primary hMSC.

In vitro and in vivo optimization of impaction allografting by demineralization and addition of rh-OP-1

Impaction allografting is a bone tissue engineering technique currently used in lower limb reconstruction orthopedic surgery. Our hypothesis was that biological optimization can be achieved by demineralization and addition of osteogenic protein-1 (OP-1) to the allograft. The objective of our in vitro study was to evaluate human mesenchymal stem cell (MSC) proliferation (Alamar Blue assay, titrated thymidine assay, total DNA Hoechst 33258, and scanning electron microscopy) and osteogenic differentiation (alkaline phosphatase assay) in two types of impacted carrier, namely, demineralized bone matrix (DBM) and insoluble collagenous bone matrix (ICBM), with or without OP-1. The objective in vivo was to compare the osteogenic potential of impacted DBM with or without OP-1, with that of impacted fresh frozen allograft (FFA), again with or without OP-1. DBM + OP-1 optimized osteoinduction and significantly improved (p < 0.05) proliferation and differentiation in comparison to the majority of all other graft preparation in vitro. In addition, DBM + OP-1 was significantly superior, with regard to osteogenesis, compared to the impacted FFA alone (p < 0.001), FFA + OP-1 (p = 0.01) and DBM alone (p = 0.02) in vivo. We propose that partial demineralization and addition of OP-1 provides a good method for improving the osteoinductive properties of fresh allograft currently used in the impaction grafting technique.

Modulation of allograft incorporation by continuous infusion of growth factors over a prolonged duration in vivo

Morselized cancellous allograft bone is frequently used in the reconstruction of bone defects in cases of revision total joint replacement, trauma, spine fusion and treated infection. However, the initial lack of viable bone cells in morselized allograft bone significantly slows the process of graft incorporation compared to autograft bone. This study examined the effects of prolonged local infusion of the growth factors bone morphogenic protein-7 (BMP-7 or OP-1) and fibroblast growth factor-2 (FGF-2 or basic FGF) in the process of allograft incorporation using a rabbit tibial chamber model. New bone formation was evaluated by two indices, the activity of alkaline phosphatase and the level of birefringence. The markers of osteoclast-like cells were also measured. Without the infusion of the growth factors, lower levels of new bone formation were observed in the allograft group, compared to the autograft group. Infusion of growth factors FGF-2 and OP-1, singly or in combination, for 4 weeks, diminished this difference. The numbers of osteoclast-like cells were much higher in the allograft group before the growth factors were delivered. The infusion of FGF, singly, diminished this difference. However, the infusion of OP-1 or the combination of FGF and OP-1 did not decrease the number of osteoclast-like cells to a level comparable to autograft only. Local infusion of growth factors appears to be a useful adjunct to promote the incorporation of allograft bone in vivo.

A novel regulatory role for stromal-derived factor-1 signaling in bone morphogenic protein-2 osteogenic differentiation of mesenchymal C2C12 cells

Stromal-derived factor 1 (SDF-1) is a chemokine with important functions in development and postnatal tissue homeostasis. SDF-1 signaling via the G-protein-coupled receptor CXCR4 regulates the recruitment of stem and precursor cells to support tissue-specific repair or regeneration. In this study we examined the contribution of SDF-1 signaling to osteogenic differentiation of mesenchymal C2C12 cells induced by bone morphogenic protein 2 (BMP2). Blocking SDF-1 signaling before BMP2 stimulation by treatment with siRNA, antibodies against SDF-1 or CXCR4, or the G-protein-coupled receptor inhibitor pertussis toxin strongly suppressed BMP2 induction of osteogenic differentiation in C2C12 cells, as evidenced by an early decrease in the expression of the myogenesis inhibitor Id1, the osteogenic master regulators Runx2 and Osx, the osteoblast-associated transcription factors JunB, Plzf, Msx2, and Dlx5, and later of the bone marker proteins osteocalcin and alkaline phosphatase. Similarly, blocking SDF-1/CXCR4 signaling strongly inhibited BMP2-induced osteogenic differentiation of ST2 bone marrow stromal cells. Moreover, we found that the interaction between SDF-1 and BMP2 signaling was mediated via intracellular Smads and MAPK activation. Our data provide the first evidence for a co-requirement of the SDF-1/CXCR4 signaling axis in BMP2-induced osteogenic differentiation of C2C12 and ST2 cells and, thus, uncover a new potential target for modulation of osteogenesis.

Endoglin differentially modulates antagonistic transforming growth factor-beta1 and BMP-7 signaling

Transforming growth factor-beta1 (TGF-beta1) and BMP-7 (bone morphogenetic protein-7; OP-1) play central, antagonistic roles in kidney fibrosis, a setting in which the expression of endoglin (CD105), an accessory TGF-beta type III receptor, is increased. So far, endoglin is known as a negative regulator of TGF-beta/ALK-5 signaling. Here we analyzed the effect of BMP-7 on TGF-beta1 signaling and the role of endoglin for both pathways in endoglin-deficient L(6)E(9) cells. In this myoblastic cell line, TGF-beta1 and BMPs are opposing cytokines, interfering with myogenic differentiation. Both induce specific target genes of which Id1 (for BMPs) and collagen I (for TGF-beta1) are two examples. TGF-beta1 activated two distinct type I receptors, ALK-5 and ALK-1, in these cells. Although the ALK-5/Smad3 signaling pathway mediated collagen I expression, ALK-1/Smad1/Smad5 signaling mediated a transient Id1 up-regulation. In contrast, BMP-7 exclusively activated Smad1/Smad5 resulting in a more prolonged Id1 expression. Although BMP-7 had no impact on collagen I abundance, it antagonized TGF-beta1-induced collagen I expression and (CAGA)(12)-MLP-Luc activity, effects that are mediated by the ALK-5/Smad3 pathway. Finally, we found that the transient overexpression of endoglin, previously shown to inhibit TGF-beta1-induced ALK-5/Smad3 signaling, enhanced the BMP-7/Smad1/Smad5 pathway.

BMP-7 and CBFA1 in allograft bone in vivo bone formation and the influence of gamma-irradiation

An initial study showed that morselized human bone grafts were osteoconductive and osteoinductive when implanted in nude rat tibial window defects, and 25 kGy of gamma-irradiation significantly reduced those properties. The mechanism of the osteoinductivity and the influence of gamma-irradiation required further investigation. In this study we assessed the paraffin sections of seven morselized human bone grafts implanted into rat tibial defects for 3 weeks after being treated with 0, 15, or 25 kGy gamma-radiation respectively. Osteoclast-like cell counting and protein expressions of bone morphogenetic protein-7 (BMP-7), core binding factor alpha1 (CBFA1), and proliferating cell nuclear antigen (PCNA) were investigated and the positive signals were quantitatively analyzed. More new bone formation was observed in the 0 and 15 kGy groups compared with 25 kGy groups. The newly formed bones were found mainly from the intact cortex into the defects bridged by the implanted grafts. A dense staining of BMP-7 and CBFA1 was noted in the osteoblast-like cells in those areas. The BMP-7 and CBFA1 staining was also seen in the cells surrounding the implanted grafts in the centre areas of the defects in distance from the intact cortex. Quantitative analysis of immunohistochemical staining of the centre areas of the defects showed that gamma-irradiation (15 and 25 kGy) significantly reduced the expression of CBFA1 and BMP-7. In conclusion, morselized human bone grafts may contain some factors, which induced osteoblast lineage differentiation and bone formation and gamma-irradiation damages those bone inducing factors.

New technologies for the enhancement of skeletal repair

Although fracture healing is a well-optimized biological process that leads to healing, approximately 10-20% of fractures result in impaired or delayed healing and these fractures may benefit from the use of biotechnologies to enhance skeletal repair. Peptide signaling molecules such as the bone morphogenetic proteins have been shown to stimulate the healing of fresh fractures, nonunions, and spinal fusions and side effects from their use appear to be minimal. Other growth factors currently being studied for local application include growth and differentiation factor-5 (GDF-5), vascular endothelial growth factor (VEGF), transforming growth factor beta (TGFbeta), and platelet-derived growth factor (PDGF). Molecules such as prostaglandin E receptor agonists and the thrombin-related peptide, TP508, have shown promise in animal models of fracture repair. Gene therapy using various growth factors or combinations of factors might also aid in fracture repair, particularly as new methods for delivery that do not require viral vectors are developed. Systemic therapy with agents such as parathyroid hormone (PTH), growth hormone (GH), and the HMG-CoA reductase inhibitors are also under investigation. As these and other technologies are shown to be safe and effective, their use will become a part of the standard of care in managing skeletal injuries.

Callus formation enhanced by BMP-7 ex vivo gene therapy during distraction osteogenesis in rats

This study was designed to observe the effects of bone morphogenetic protein-7 (BMP-7) ex vivo gene therapy on callus formation during rat mandibular distraction osteogenesis (DO). Fifty-four Sprague-Dawley rats underwent osteodistraction of the right mandible and were then randomly divided into three groups. Immediately after distraction, autologous bone marrow mesenchymal stem cells (MSCs) transfected with BMP-7, MSCs untransfected with BMP-7, and physiological saline were injected into the distraction gaps of the mandibles in groups A, B, and C, respectively. Nine animals from each group were euthanized at 2 and 6 weeks after completion of distraction. The distracted mandibles were removed and processed for radiographic, histological, immunohistochemical, and scanning electron microscopic examinations as well as Ca/P ratio analysis. Group A animals showed greater bone formation and earlier mineralization in the distracted callus when compared with group B. Similarly increased callus formation was found in group B than group C. Positive immunostaining of BMP-7 was observed in the distracted callus in all groups. However, BMP-7 expression was much stronger in group A compared with groups B and C. The results of this study suggest that BMP-7-mediated ex vivo gene transfer based on MSCs may accelerate callus formation in distraction osteogenesis and facilitate consolidation. Local gene therapy may ultimately be an alternative or supplemental approach to DO enhancement, especially for patients whose osteogenic potentials are compromised by diseases such as osteoporosis, severe trauma, and postoncologic irradiation.

Simultaneous gene transfer of bone morphogenetic protein (BMP) -2 and BMP-7 by in vivo electroporation induces rapid bone formation and BMP-4 expression

BACKGROUND

Transcutaneous in vivo electroporation is expected to be an effective gene-transfer method for promoting bone regeneration using the BMP-2 plasmid vector. To promote enhanced osteoinduction using this method, we simultaneously transferred cDNAs for BMP-2 and BMP-7, as inserts in the non-viral vector pCAGGS.

METHODS

First, an in vitro study was carried out to confirm the expression of BMP-2 and BMP-7 following the double-gene transfer. Next, the individual BMP-2 and BMP-7 plasmids or both together were injected into rat calf muscles, and transcutaneous electroporation was applied 8 times at 100 V, 50 msec.

RESULTS

In the culture system, the simultaneous transfer of the BMP-2 and BMP-7 genes led to a much higher ALP activity in C2C12 cells than did the transfer of either gene alone. In vivo, ten days after the treatment, soft X-ray analysis showed that muscles that received both pCAGGS-BMP-2 and pCAGGS-BMP-7 had better-defined opacities than those receiving a single gene. Histological examination showed advanced ossification in calf muscles that received the double-gene transfer. BMP-4 mRNA was also expressed, and RT-PCR showed that its level increased for 3 days in a time-dependent manner in the double-gene transfer group. Immunohistochemistry confirmed that BMP-4-expressing cells resided in the matrix between muscle fibers.

CONCLUSION

The simultaneous transfer of BMP-2 and BMP-7 genes using in vivo electroporation induces more rapid bone formation than the transfer of either gene alone, and the increased expression of endogenous BMP-4 suggests that the rapid ossification is related to the induction of BMP-4.