Transient and localized expression of bone morphogenetic protein 4 messenger RNA during fracture healing

Case report: Focal heterotopic ossification in paravertebral muscles as a cause of neurogenic lameness in a dog

This case report describes a 17-month-old Pudelpointer with recurring motor impairment localized to the left thoracic limb. A neurological exam highlighted lameness in that limb, accompanied by pre-scapular swelling. Radiographs and magnetic resonance imaging detected an osseous structure in soft tissues close to the fifth cervical vertebra, and subsequent surgery uncovered adjacent cervical spinal nerve impingement. Histology of the bony structure revealed heterotopic ossification in paravertebral muscles. Mild bone re-formation at the operating site was detected after a 2-year period, but the patient was asymptomatic. This article reports the first case of heterotopic ossification with spinal nerve entrapment in a dog and adds a new differential diagnosis to the causes of neurogenic lameness in dogs.

Identification of bone morphogenetic protein 4 in the saliva after the placement of fixed orthodontic appliance

Background

This study was conducted in order to explore the effects of orthodontic tooth movement (OTM) on the changes of salivary proteome. This prospective observational pilot study recruited 12 healthy teenage boys with malocclusion treated with a fixed orthodontic appliance and 6 appropriate control participants. Saliva samples were collected a day before and at 0, 2, 7, and 30 days after initialization of treatment, corresponding to the initial, lag, and post-lag phases of OTM. Pooled samples were analyzed by liquid chromatography-mass spectrometry, ELISA, and Western blotting. To date, there is no published data on the presence of BMP molecules or their antagonists in the saliva or in the gingival cervical fluid related to orthodontic conditions.

Results

A total of 198 identified saliva proteins were classified based on their functional characteristics. Proteins involved in bone remodeling were observed exclusively 30 days post appliance placement, including bone morphogenetic protein 4 (BMP4), a BMP antagonist BMP-binding endothelial regulator, insulin-like growth factor-binding protein 3, cytoskeleton-associated protein 4, and fibroblast growth factor 5. Based on the analysis of protein interactions, BMP4 was found to have a central position in this OTM-related protein network.

Conclusions

The placement of a fixed orthodontic appliance induced occurrence of proteins involved in bone remodeling in the saliva at a time corresponding to the post-lag period of OTM. Limitations of this study include a relatively small sample size, limited time of monitoring patients, and the lack of interindividual variability assessment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40510-021-00364-6.

Role of rhBMP-7, Fibronectin, And Type I Collagen in Dental Implant Osseointegration Process: An Initial Pilot Study on Minipig Animals

Background: The biological factors involved in dental implant osseointegration need to be investigated to improve implant success. Methods: Twenty-four implants were inserted into the tibias of six minipigs. Bone samples were obtained at 7, 14, and 56 days. Biomolecular analyses evaluated mRNA of BMP-4, -7, Transforming Growth Factor-β2, Interleukin-1β, and Osteocalcin in sites treated with rhBMP-7, Type 1 Collagen, or Fibronectin (FN). Inflammation and osteogenesis were evaluated by histological analyses. Results: At 7 and 14 days, BMP-4 and BMP-7 increased in the sites prepared with rhBMP-7 and FN. BMP-7 remained greater at 56 days in rhBMP-7 and FN sites. BPM-4 at 7 and 14 days increased in Type 1 Collagen sites; BMP-7 increased from day 14. FN increased the TGF-β2 at all experimental times, whilst the rhBMP-7 only did so up to 7 days. IL-1β increased only in collagen-treated sites from 14 days. Osteocalcin was high in FN-treated sites. Neutrophilic granulocytes characterized the inflammatory infiltrate at 7 days, and mononuclear cells at 14 and 56 days. Conclusions: This initial pilot study, in a novel way, evidenced that Type 1 Collagen induced inflammation and did not stimulate bone production; conversely FN or rhBMP-7 showed neo-osteogenetic and anti-inflammatory properties when directly added into implant bone site.

Enhanced BMP signalling causes growth plate cartilage dysrepair in rats

Growth plate cartilage injuries often result in bony repair at the injury site and premature mineralisation at the uninjured region causing bone growth defects, for which underlying mechanisms are unclear. With the prior microarray study showing upregulated bone morphogenetic protein (BMP) signalling during the injury site bony repair and with the known roles of BMP signalling in bone healing and growth plate endochondral ossification, this study used a rat tibial growth plate drill-hole injury model with or without systemic infusion of BMP antagonist noggin to investigate roles of BMP signalling in injury repair responses within the injury site and in the adjacent "uninjured" cartilage. At days 8, 14 and 35 post-injury, increased expression of BMP members and receptors and enhanced BMP signalling (increased levels of phosphorylated (p)-Smad1/5/8) were found during injury site bony repair. After noggin treatment, injury site bony repair at days 8 and 14 was reduced as shown by micro-CT and histological analyses and lower mRNA expression of osteogenesis-related genes Runx2 and osteocalcin (by RT-PCR). At the adjacent uninjured cartilage, the injury caused increases in the hypertrophic zone/proliferative zone height ratio and in mRNA expression of hypertrophy marker collagen-10, but a decrease in chondrogenesis marker Sox9 at days 14 and/or 35, which were accompanied by increased BMP signalling (increased levels of pSmad1/5/8 protein and BMP7, BMPR1a and target gene Dlx5 mRNA). Noggin treatment reduced the hypertrophic zone/proliferative zone height ratio and collagen-10 mRNA expression, but increased collagen-2 mRNA levels at the adjacent growth plate. This study has identified critical roles of BMP signalling in the injury site bony repair and in the hypertrophic degeneration of the adjacent growth plate in a growth plate drill-hole repair model. Moreover, suppressing BMP signalling can potentially attenuate the undesirable bony repair at injury site and suppress the premature hypertrophy but potentially rescue chondrogenesis at the adjacent growth plate.

Ectopic transient overexpression of OCT-4 facilitates BMP4-induced osteogenic transdifferentiation of human umbilical vein endothelial cells

Limitation in cell sources for autologous cell therapy has been a recent focus in stem cell therapy and tissue engineering. Among various research advances, direct conversion, or transdifferentiation, is a notable and feasible strategy for the generation and acquirement of wanted cell source. So far, utilizing cell transdifferentiation technology in tissue engineering was mainly restricted at achieving single wanted cell type from diverse cell types with high efficiency. However, regeneration of a complete tissue always requires multiple cell types which poses an intrinsic complexity. In this study, enhanced osteogenic differentiation was achieved by transient ectopic expression of octamer-binding transcription factor 4 (OCT-4) gene followed by bone morphogenetic protein 4 treatment on human umbilical vein endothelial cells. OCT-4 transfection and bone morphogenetic protein 4 treatment resulted in enhanced expression of osteogenic markers such as core-binding factor alpha 1, alkaline phosphatase, and collagen 1 compared with bone morphogenetic protein 4 treatment alone. Furthermore, we employed gelatin-heparin cryogel in cranial defect model for in vivo bone formation. Micro-computed tomography and histological analysis of in vivo samples showed that OCT-4 transfection followed by bone morphogenetic protein 4 treatment resulted in efficient transdifferentiation of endothelial cells to osteogenic cells. These results suggest that the combination of OCT-4 and bone morphogenetic protein 4 on endothelial cells would be a reliable multicellular transdifferentiation model which could be applied for bone tissue engineering.

Bone morphogenetic protein 4 regulates immortalized chicken preadipocyte proliferation by promoting G1/S cell cycle progression

Bone morphogenetic protein 4 (BMP4) has been reported to regulate adipose development, but its role in preadipocyte proliferation has not been explored in vitro. Here, we investigated the effect of BMP4 on chicken preadipocyte proliferation using immortalized chicken preadipocytes (ICP1 cells) as a cell model. We report that BMP4 expression increases during preadipocyte proliferation. Overexpression and knockdown of BMP4 promotes and inhibits preadipocyte proliferation, respectively. In addition, overexpression of BMP4 decreased the number of preadipocytes at the G0/G1 phase of the cell cycle, and increased the proportion of cells at S phase. In contrast, knockdown of BMP4 increased the number of preadipocytes at the G0/G1 phase of the cell cycle, and decreased the proportion of cells at the S and G2 phases. Furthermore, overexpression of BMP4 promoted the expression of proliferating cell nuclear antigen (PCNA), Id2, cyclin E, and cyclin‐dependent kinase 2 (CDK2), while knockdown of BMP4 inhibited the expression of Id2, cyclin E, and CDK2. Finally, neither BMP4 overexpression nor BMP4 knockdown affected cell apoptosis. Taken together, our results suggest that BMP4 may promote proliferation of ICP1 cells by driving cell cycle transition from G1 to S phase.

Three-dimensional computational model simulating the fracture healing process with both biphasic poroelastic finite element analysis and fuzzy logic control

A dynamic model regulated by both biphasic poroelastic finite element analysis and fuzzy logic control was established. Fuzzy logic control was an easy and comprehensive way to simulate the tissue differentiation process, and it is convenient for researchers and medical experts to communicate with one another to change the fuzzy logic rules and improve the simulation of the tissue differentiation process. In this study, a three-dimensional fracture healing model with two different interfragmentary movements (case A: 0.25 mm and case B: 1.25 mm) was analysed with the new set-up computational model. As the healing process proceeded, both simulated interfragmentary movements predicted a decrease and the time that the decrease started for case B was later than that for case A. Compared with experimental results, both cases corresponded with experimental data well. The newly established dynamic model can simulate the healing process under different mechanical environments and has the potential to extend to the multiscale healing model, which is essential for reducing the animal experiments and helping to characterise the complex dynamic interaction between tissue differentiations within the callus region.

Variable signaling activity by FOP ACVR1 mutations

Most patients with fibrodysplasia ossificans progressiva (FOP), a rare genetic disorder of heterotopic ossification, have the same causative mutation in ACVR1, R206H. However, additional mutations within the ACVR1 BMP type I receptor have been identified in a small number of FOP cases, often in patients with disease of lesser or greater severity than occurs with R206H mutations. Genotype-phenotype correlations have been suggested in patients, resulting in classification of FOP mutations based on location within different receptor domains and structural modeling. However while each of the mutations induces increased signaling through the BMP-pSmad1/5/8 pathway, the molecular mechanisms underlying functional differences of these FOP variant receptors remained undetermined. We now demonstrate that FOP mutations within the ACVR1 receptor kinase domain are more sensitive to low levels of BMP than mutations in the ACVR1 GS domain. Our data additionally confirm responsiveness of cells with FOP ACVR1 mutations to both BMP and Activin A ligands. We also have determined that constructs with FOP ACVR1 mutations that are engineered without the ligand-binding domain retain increased BMP-pSmad1/5/8 pathway activation relative to wild-type ACVR1, supporting that the mutant receptors can function through ligand-independent mechanisms either directly through mutant ACVR1 or through indirect mechanisms.

Transfer of the bone morphogenetic protein 4 gene into rat periodontal ligament by in vivo electroporation

OBJECTIVE

Regulation of alveolar bone metabolism is required in clinical dentistry. The aim of the present study was to establish a method for gene transfer into the periodontal ligament (PDL) by in vivo electroporation with a plasmid vector and to investigate the effects of BMP-4 transfer into the PDL.

DESIGN

Plasmids containing mouse BMP-4 cDNA (pCAGGS-BMP4) were transfected into cultured rat PDL cells by in vitro electroporation, and BMP-4 production and secretion were detected by immunocytochemistry and western blotting. Next, pCAGGS-BMP4 was injected into the PDL of rats, and electroporation was performed in vivo, using original paired-needle electrodes. BMP-4 expression was examined by immunohistochemical staining 3, 7, 14, 21, and 28days after electroporation. Control groups were injected with pCAGGS by electroporation, injected with pCAGGS-BMP4 without electroporation, or subjected to neither injection nor electroporation.

RESULTS

In vitro-transfected rat PDL cells exhibited production and secretion of the mature-form BMP-4. After in vivo electroporation of pCAGGS-BMP4, site-specific BMP-4 expression peaked on day 3, gradually decreased until day 14, and was absent by day 21. We observed no unfavorable effects such as inflammation, degeneration, or necrosis.

CONCLUSIONS

Gene transfer by electroporation with plasmid DNA vectors has several advantages over other methods, including the non-viral vector, non-immunogenic effects, site-specific expression, simplicity, cost-effectiveness, and limited histological side effects. Our results indicate that the method is useful for gene therapy targeting the periodontal tissue, which regulates alveolar bone remodeling.

Expression analysis of bone morphogenetic protein 4 between fat and lean birds in adipose tissue and serum

The objectives of the present study were to characterize the tissue expression of chicken (Gallus gallus) bone morphogenetic protein 4 (BMP4) and compare differences in its expression in abdominal fat tissue and serum between fat and lean birds and to determine a potential relationship between the expression of BMP4 and abdominal fat tissue growth and development. The results showed that chicken BMP4 messenger RNA (mRNA) and protein were expressed in various tissues, and the expression levels of BMP4 transcript and protein were relatively higher in adipose tissues. In addition, the mRNA and protein expression levels of BMP4 in abdominal fat tissue of fat males were lower than those of lean males at 1, 2, 5, and 7 wk of age (P < 0.05). Furthermore, the serum BMP4 content of fat males was lower than that of lean males at 7 wk of age (P < 0.05). BMP4 mRNA expression levels were significantly higher in preadipocytes than those in mature adipocytes (P < 0.05), and the expression level decreased during differentiation in vitro (P < 0.05). These results suggested that chicken BMP4 might affect abdominal fat deposition through differences in its expression level. The results of this study will provide basic molecular information for studying the role of BMP4 in the regulation of adipogenesis in avian species.

Bone Morphogenetic Proteins

Bone morphogenetic proteins (BMPs), originally identified as osteoinductive components in extracts derived from bone, are now known to play important roles in a wide array of processes during formation and maintenance of various organs including bone, cartilage, muscle, kidney, and blood vessels. BMPs and the related "growth and differentiation factors" (GDFs) are members of the transforming growth factor β (TGF-β) family, and transduce their signals through type I and type II serine-threonine kinase receptors and their intracellular downstream effectors, including Smad proteins. Furthermore, BMP signals are finely tuned by various agonists and antagonists. Because deregulation of the BMP activity at multiple steps in signal transduction is linked to a wide variety of human diseases, therapeutic use of activators and inhibitors of BMP signaling will provide potential avenues for the treatment of the human disorders that are caused by hypo- and hyperactivation of BMP signals, respectively.

Methylsulfonylmethane enhances BMP‑2‑induced osteoblast differentiation in mesenchymal stem cells

As human lifespans have increased, the incidence of osteoporosis has also increased. Methylsulfonylmethane (MSM) affects the process of mesenchymal stem cell (MSC) differentiation into osteoblasts via the Janus kinase 2 (Jak2)/signal transducer and activator of transcription (STAT)5b signaling pathway, and bone morphogenetic protein 2 (BMP‑2) is also known to significantly affect bone health. In addition, the phosphorylation of small mothers against decapentaplegic (Smad)1/5/8 regulates the Runt‑related transcription factor 2 (Runx2) gene, which encodes a transcription factor for osteoblast differentiation markers. In the present study, the differentiation of MSCs treated with MSM, BMP‑2, and their combination were examined. The differentiation of osteoblasts was demonstrated through observation of morphological changes and mineralization, using alizarin red and Von Kossa staining. Western blotting analysis demonstrated that the combination of MSM and BMP-2 increased the phosphorylation of the BMP signaling-associated protein, Smad1/5/8. Combination of MSM and BMP-2 significantly increased osteogenic differentiation and mineralization of the MSCs compared with either MSM or BMP-2 alone. Additionally, reverse transcription-polymerase chain reaction analysis demonstrated that combination of MSM and BMP-2 increased the expression level of the Runx2 gene and the osteoblast differentiation marker genes, alkaline phosphatase, bone sialoprotein and osteocalcin, in MSCs compared with controls. Thus, the combination of MSM and BMP-2 may promote the differentiation of MSCs into osteoblasts.

Granting immunity to FOP and catching heterotopic ossification in the Act

The progressive transformation of one organ system into another is a fundamental signature of fibrodysplasia ossificans progressiva (FOP), the most catastrophic form of extraskeletal bone formation in humans. In all affected individuals, FOP is caused by heterozygous missense gain-of-function mutations in Activin receptor A type I (ACVR1), a bone morphogenetic protein (BMP) type I receptor. Loss of autoinhibition of the mutant receptor (mACVR1) results in dysregulated BMP pathway signaling, and is necessary for the myriad developmental features of FOP, but does not appear sufficient to induce the episodic flare-ups that lead to disabling post-natal heterotopic endochondral ossification (HEO) and that are a hallmark of the disease. Post-natal FOP flare-ups strongly implicate an underlying immunological trigger involving inflammation and the innate immune system. Recent studies implicate canonical and non-canonical TGFβ/BMP family ligands in the amplification of mACVR1 signaling leading to the formation of FOP lesions and resultant HEO. BMP and Activin ligands that stimulate mACVR1 signaling also have critical regulatory functions in the immune system. Cross-talk between the morphogenetic and immunological pathways that regulate tissue maintenance and wound healing identifies potential robust therapeutic targets for FOP. Here we review current evidence for an immunological trigger for flare-ups and HEO in FOP, propose a working schema for the pathophysiology of observed phenomena, and highlight outstanding questions under investigation.

Significance of the Immunohistochemical Expression of Bone Morphogenetic Protein-4 in Bone Maturation after Maxillary Sinus Grafting in Humans

BACKGROUND

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-β (TGFβ) protein superfamily and are known to be involved in bone and cartilage formation. Within this family, BMP-4 is one of the most studied members. It has been shown to induce osteogenic differentiation of osteoblasts and osteoprogenitor cells in vitro, but the intimate processes in which this protein promotes and regulates osseous repair still remains unclear.

PURPOSE

To assess whether the native cellular immunohistochemical expression of BMP-4 correlates with the maturation of bone samples obtained at 6 months after maxillary sinus augmentation.

MATERIALS AND METHODS

Histopathological and histomorphometrical analyses were performed in all the samples, which were obtained from a total of 58 patients. Immunohistochemical expression of BMP-4 was analyzed in 30 core biopsies obtained from maxillary sinuses grafted with a combination of anorganic bovine bone and autogenous cortical bone [1:1] (AB-group), and 18 biopsies from maxillary sinuses grafted solely with a cortico-cancellous particulate allograft (M-group), all of them after a 6-month healing period. Also, 10 biopsies of native pristine bone were obtained and used as control group (C-group).

RESULTS

Mild to moderate immunohistochemical expression of native granular BMP-4 was present in 56.8% (31.0% AB-group, 22.4% M-group, and 3.4% C-group) (p = 0.000, chi-square) of the specimens analyzed. BMP-4 expression was primarily located in the cytoplasm of osteoblasts, osteoclasts, and epithelial cells of the schneiderian membrane. Whereas significant differences were observed in the proportion of mineralized tissue and cellularity between sinuses grafted with anorganic bovine bone, allograft, or nongrafted sinuses, there were no statistically significant differences in the cellular expression of BMP-4 among groups.

CONCLUSION

Our findings suggest that the native expression of BMP-4 appears to be associated with normal bone homeostasis and reparation in grafted and nongrafted maxillary sites.

Hyaluronan inhibits BMP-induced osteoblast differentiation

Hyaluronan (HA), one of the major structural extracellular components in cartilage, regulates cellular responses via receptors such as CD44. However, the direct effects of HA on osteoblastic differentiation has not been studied in detail. Here, we investigated the effects of HA (molecular weight: 900-1200 kDa) on osteoblastic differentiation that was induced by bone morphogenetic protein (BMP) in C2C12 cells (mouse myoblastic cells) and ST2 cells (mouse bone marrow cells). BMP-induced osteoblastic differentiation and Smad1/Smad5/Smad8 phosphorylation were downregulated by HA. Use of the CD44-blocking antibody restored HA-induced inhibition of osteoblastic differentiation and Smad1/Smad5/Smad8 phosphorylation. Our results indicate that HA inhibits BMP-induced osteoblastic differentiation through the CD44 receptor.

Expression of noggin, an antagonist of bone morphogenetic protein, in schwannoma: A possible mechanism

Schwannoma is a benign peripheral nerve sheath tumor derived from Schwann cells. Bone scalloping, including spinal foramen enlargement, develops when the tumor is located adjacent to a bone and is a characteristic radiological feature. In the present study, to investigate the pathomechanism of bone resorption, the expression of noggin (a potent antagonist of bone morphogenetic protein) was analyzed in schwannoma tissues and compared with that observed in other soft tissue tumors. Quantitative polymerase chain reaction analysis revealed that the mRNA levels of noggin in schwannomas were significantly increased compared with the levels in other tumors. The gene product of noggin was only detected in a subset of schwannomas using immunohistochemistry and western blot analysis. Furthermore, the tissue extract from a noggin-producing schwannoma was found to inhibit osteoblastic differentiation in MC3T3 mouse osteoblastic cells in a dose-dependent manner. These findings indicate that bone scalloping in radiology may be induced by schwannoma-secreted noggin. In addition, noggin may have potential as a novel molecular and diagnostic marker for identifying certain types of schwannoma.

BMP-2 mRNA expression after endothelial progenitor cell therapy for fracture healing

PURPOSE

Endothelial progenitor cells (EPCs) represent a population of novel precursor cells with known ability to participate in angiogenesis. Our previous studies have shown that local EPC therapy significantly increased angiogenesis and osteogenesis to promote fracture healing in an animal bone defect model. However, the cellular and molecular mechanisms by which EPC therapy promotes fracture healing remain largely unknown. The purpose of this study was to quantify local bone morphogenetic protein (BMP-2) expression after EPC therapy for a rat segmental bone defect, in hopes of further defining the potential mechanisms by which EPCs promote fracture healing.

METHOD

EPCs were isolated from the bone marrow of syngeneic rats and cultured ex vivo for 7-10 days before transfer to the bone defect. A total of 56 rats were studied. The treatment group received 1 × 10 EPCs on a gelfoam scaffold at the bone defect, and control animals received gelfoam/saline only. Before euthanasia, radiographs of the femur were performed. Animals were euthanized at 1, 2, 3, and 10 weeks, and specimens from the fracture gap area were collected, pulverized, and total messenger RNA (mRNA) was extracted. BMP-2 mRNA was measured by reverse transcriptase-polymerase chain reaction and quantified by VisionWorksLS. All measurements were performed in triplicate.

RESULTS

All EPC-treated bone defects healed radiographically by 10 weeks, whereas control-treated defects developed a nonunion. The expression of BMP-2 mRNA was significantly elevated in EPC-treated defects relative to controls at week 1 (EPC, 0.59 ± 0.10; control, 0.31 ± 0.08; P = 0.05), week 2 (EPC, 0.40 ± 0.06; control, 0.23 ± 0.04; P = 0.04), and week 3 (EPC, 0.33 ± 0.06; control, 0.18 ± 0.03; P = 0.04), but not at week 10 (EPC, 0.31 ± 0.06; control, 0.21 ± 0.04, P = 0.15). The highest mean expression of BMP-2 in EPC-treated defects was observed at 1 week, with a progressive decline in BMP-2 expression noted thereafter.

CONCLUSIONS

These findings demonstrate that EPC-treated bone defects demonstrate both radiographic healing and elevated expression of BMP-2 relative to control-treated defects. These results provide further insight into the potential mechanisms by which EPC therapy may promote fracture healing and provide further evidence to suggest that the trophic actions of EPC therapy may be a critical factor in their contribution to fracture healing.

Polymorphisms in BMP4 and FGFR1 genes are associated with fracture non-union

Fracture healing is a complex process influenced by a multitude of factors and expression of several thousand genes. Polymorphisms in these genes can lead to an extended healing process and explain why certain patients are more susceptible to develop non-union. A total of 16 SNPs within five genes involved in bone repair pathogenesis (FAM5C, BMP4, FGF3, FGF10, and FGFR1) were investigated in 167 patients with long bone fractures, 101 with uneventful healing, and 66 presenting aseptic non-unions. Exclusion criteria were patients presenting pathological fractures, osteoporosis, hypertrophic and infected non-unions, pregnancy, and children. All genetic markers were genotyped using TaqMan real-time PCR. Chi-square test was used to compare genotypes, allele frequencies, and haplotype differences between groups. Binary logistic regression analyzed the significance of many covariates and the incidence of non-union. Statistical analysis revealed open fracture to be a risk factor for non-union development (p < 0.001, OR 3.6 [1.70-7.67]). A significant association of haplotype GTAA in BMP4 (p = 0.01) and FGFR1 rs13317 (p = 0.005) with NU could be observed. Also, uneventful healing showed association with FAM5C rs1342913 (p = 0.04). Our work supported the role of BMP4 and FGFR1 in NU fracture independently of the presence of previously described risk factors.

N-acetyl cysteine as an osteogenesis-enhancing molecule for bone regeneration

Bone regeneration often requires cues from osteogenesis-inducing factors for successful outcome. N-acetyl cysteine (NAC), an anti-oxidant small molecule, possibly modulates osteoblastic differentiation. This study investigated the potential of NAC as an osteogenesis-enhancing molecule in vitro and in vivo. Various concentrations of NAC (0, 2.5, 5.0, and 10 mM) were added to rat bone marrow stromal cell or osteoblastic cell culture in media with or without dexamethasone. The results showed marked enhancement of alkaline phosphatase activity and mineralized matrix formation together with consistent upregulation of bone-related gene markers such as collagen I, osteopontin, and osteocalcin in the osteoblastic culture with addition of 2.5 or 5.0 mM NAC regardless of the presence of dexamethasone. Micro-CT-based analysis and histological observation revealed that addition of NAC to a collagenous sponge implanted in a critical size cortical bone defect (3.0 mm × 5.0 mm) in rat femur yielded acceleration and completion of defect closure, with thick, compact, and contiguous bone after 6 weeks of healing. In contrast, with sponge alone, only sparse and incomplete bone regeneration was observed during the matching healing period. These results indicate that NAC can function as an osteogenesis-enhancing molecule to accelerate bone regeneration by activating differentiation of osteogenic lineages.

Sclerostin antibody increases bone volume and enhances implant fixation in a rat model

BACKGROUND

Previous studies have demonstrated that sclerostin blockade is anabolic for bone. This study examined whether systemic administration of sclerostin antibody would increase implant fixation and peri-implant bone volume in a rat model.

METHODS

Titanium cylinders were placed in the femoral medullary canal of ninety male Sprague-Dawley rats. One-half of the rats (n=45) received murine sclerostin antibody (Scl-Ab, 25 mg/kg, twice weekly) and the other one-half (n=45) received saline solution. Equal numbers of rats from both groups were sacrificed at two, four, or eight weeks after the implant surgery and the femora were examined by microcomputed tomography, mechanical pull-out testing, and histology.

RESULTS

Fixation strength in the two groups was similar at two weeks but was 1.9-fold greater at four weeks (p=0.024) and 2.2-fold greater at eight weeks (p<0.001) in the rats treated with sclerostin antibody. At two weeks, antibody treatment led to increased cortical area, with later increases in cortical thickness and total cross-sectional area. Significant differences in peri-implant trabecular bone were not evident until eight weeks but included increased bone volume per total volume, bone structure that was more plate-like, and increased trabecular thickness and number. Changes in bone architecture in the intact contralateral femur tended to precede the peri-implant changes. The peri-implant bone properties accounted for 61% of the variance in implant fixation strength, 32% of the variance in stiffness, and 63% of the variance in energy to failure. The implant fixation strength at four weeks was approximately equivalent to the strength in the control group at eight weeks.

CONCLUSIONS

Sclerostin antibody treatment accelerated and enhanced mechanical fixation of medullary implants in a rat model by increasing both cortical and trabecular bone volume.

Co-expression of BMPs and BMP-inhibitors in human fractures and non-unions

Bone morphogenetic proteins (BMPs) are increasingly being used clinically to enhance fracture repair and healing of non-unions. However, the potential efficacy of supraphysiological dosing for clinical results warrants further clarification of the BMP signaling pathway in human fracture healing. As BMP signaling can be fine-tuned at numerous levels, the role of BMP-inhibitors has become a major focus. The aim of the present study was to document co-expression of BMPs, pSmad 1/5/8, and BMP-inhibitors in human fracture callus and human non-unions. Using human tissue of fracture callus (n=14) and non-unions (n=4) we documented expression of BMPs (BMP2, BMP3 and BMP7), pSmad 1/5/8 and the BMP-inhibitors noggin, gremlin, chordin, Smad-6, Smad-7 and BAMBI. Co-expression of pSmad 1/5/8, BMPs and BMP-inhibitors was noted in the osteoblasts of fracture callus as well as of non-unions. Expression of BMP-inhibitors was generally stronger in non-unions than in fracture callus. The most pertinent differences were noted in the cartilaginous tissue components. Expression of BMP2 in chondrocytes was markedly decreased in non-unions compared to fracture callus and that of BMP7 was almost completely absent. Expression of BMP-inhibitors was almost the same in osteoblasts, chondrocytes and fibroblasts of fracture callus and well as in non-unions. Interestingly, although BMP ligands were present in the chondrocytes and fibroblasts of non-unions, they did not co-express pSmad 1/5/8 suggesting that BMP signaling may have been inhibited at some point before Smad 1/5/8 phosphorylation. These results suggest co-expression of BMP, pSmad 1/5/8 and BMP-inhibitors occurs in human fracture callus as well as non-unions but the relative expression of BMPs vs. BMP-inhibitors was different between these two tissue types. In contrast to our expectations, the expression of BMP inhibitors was comparable between fracture callus and non-unions, whereas the expression of BMPs was notably lower in the cartilaginous component of the non-unions in comparison to fracture callus. Based on these results, we believe that aberrations in the BMP-signaling pathway in the cartilaginous component of fracture healing could influence clinical fracture healing. An imbalance between the local presence of BMP and BMP-inhibitors may switch the direction towards healing or non-healing of a fracture.

Risk factors for posttraumatic heterotopic ossification of the elbow: case-control study

PURPOSE

Heterotopic ossification (HO) is well-known after surgical repair of elbow fractures, but little is known about risk factors for its development in these patients. The purpose of this study was to define factors associated with development of HO.

METHODS

We used a prospective fracture registry collected in 2 Level I trauma centers and medical chart review to examine all elbow fractures treated surgically between 2002 and 2009. We determined which of these patients developed HO with an impact on range of motion (Hastings class II and III). We conducted a matched case-control study to examine factors associated with risk of HO. We used conditional logistic regression to compare occurrences of risk factors between cases and controls, matched by fracture type, age, and sex.

RESULTS

Our database contained 786 elbow fractures treated surgically. Of these, 55 developed clinically relevant HO. The risk of HO varied among types of elbow fractures, with combined olecranon and radial head fractures having no HO and floating elbows (fractures on both sides of the elbow joint) having the highest incidence of HO at 36%. In multiple conditional logistic regression, risk factors for the development of HO were days to surgery, with subjects waiting 8 or more days having 12 times the odds of HO than subjects having surgery within a day of injury, and time to postoperative mobilization, with subjects who had at least 15 days to mobilization having greater odds of HO than those who had less than 7 days to mobilization.

CONCLUSIONS

Heterotopic ossification of the elbow occurs frequently after surgical repair of elbow fractures, with an incidence of 7% in this registry. In the case-control sample, conditions associated with development of HO included longer time to surgery and longer time to mobilization after surgery.

A new haplotype in BMP4 implicated in ossification of the posterior longitudinal ligament (OPLL) in a Chinese population

Previous genome-wide microarray analysis of candidate genes involved in the ossification of the posterior longitudinal ligament (OPLL) of the spine resulted in the identification of a novel, clinically relevant gene encoding bone morphogenetic protein 4 (BMP4) but was defined only by its expression patterns. The complete genomic BMP4 coding DNA from 450 patients with OPLL and 550 matched controls were sequenced and compared. We identified 18 SNPs, among which the minor alleles of SNP8 (C>T; p < 0.001; OR: 1.58), SNP13 (rs17563C>T; p < 0.001; OR: 1.76), and SNP14 (rs76335800A>T; p < 0.001; OR: 1.68) were associated with OPLL. Logistic regression analysis showed that the additive model of SNP8 (p < 0.001; OR: 3.48), SNP13 (p < 0.001; OR: 2.22), and SNP14 (p < 0.001; OR: 1.99) retained statistical significance. Linkage disequilibrium (LD) analysis identified a 3-kbp block of intense LD in BMP4 and 1 specific haplotype, TGGGCTT (p < 0.001, OR: 2.54), which was associated with OPLL-associated risk alleles and increased severity of OPLL, as shown by the distribution of ossified vertebrae in patients with OPLL (p = 0.002). Novel mutations in the BMP4 gene and a specific haplotype TGGGCTT appear to contribute to the risk of developing OPLL. Also the severity of OPLL seems to be mediated predominantly by genetic variations in this specific BMP4 gene region, but might be associated with other certain clinical and demographic characteristics in the Chinese population studied.

Microarray expression analysis of genes and pathways involved in growth plate cartilage injury responses and bony repair

The injured growth plate cartilage is often repaired by a bone bridge which causes bone growth deformities. Whilst previous studies have identified sequential inflammatory, fibrogenic, osteogenic and bone remodelling responses involved in the repair process, the molecular pathways which regulated these cellular events remain unknown. In a rat growth plate injury model, tissue from the injury site was collected across the time-course of bone bridge formation using laser capture microdissection and was subjected to Affymetrix microarray gene expression analysis. Real Time PCR and immunohistochemical analyses were used to confirm changes in levels of expression of some genes identified in microarray. Four major functional groupings of differentially expressed genes with known roles in skeletal development were identified across the time-course of bone bridge formation, including Wnt signalling (SFRP1, SFRP4, β-catenin, Csnk2a1, Tcf7, Lef1, Fzd1, Fzd2, Wisp1 and Cpz), BMP signalling (BMP-2, BMP-6, BMP-7, Chrd, Chrdl2 and Id1), osteoblast differentiation (BMP-2, BMP-6, Chrd, Hgn, Spp1, Axin2, β-catenin, Bglap2) and skeletal development (Chrd, Mmp9, BMP-1, BMP-6, Spp1, Fgfr1 and Traf6). These studies provide insight into the molecular pathways which act cooperatively to regulate bone formation following growth plate cartilage injury and highlight potential therapeutic targets to limit bone bridge formation.

BMP4 localization and PCNA expression during distraction osteogenesis of the porcine mandible

This study characterized sequential molecular and cellular events in the porcine mandibular distraction osteogenesis (DO) wound. Nineteen Yucatan minipigs were divided into three treatment groups: Group A, unilateral mandibular distraction with 0 day latency, 1mm/day rate for 12 days, 24 days fixation (n=16); Group B, acute lengthening 12 mm (n=2); Group C, sham control (n=1). Group A was further divided by death date: mid-DO (n=5), end-DO (n=4), mid-fixation (n=5) and end-fixation (n=2). Groups B and C were killed on postoperative day 36, corresponding to end-fixation. Specimens were stained for proliferating cell nuclear antigen (PCNA) and bone morphogenetic protein-4 (BMP4). Cellular proliferation (PCNA) was assessed quantitatively and BMP4 staining was assessed on a semi-quantitative scale. Progenitor cell proliferation was greatest during mid-DO and decreased from end-DO through end-fixation. Proliferation in the acute lengthening group was elevated relative to sham control and comparable to end-DO. BMP4 staining intensity (localized to the periosteal cambium layer) was greatest during mid- and end-DO, decreased at mid-fixation and was undetectable at end-fixation. Progenitor cell proliferation and BMP4 expression are greatest during mid-DO and decrease progressively thereafter. At the time of death of the acute lengthening group, only increased cell proliferation was demonstrated.

Loss of transcription factor early growth response gene 1 results in impaired endochondral bone repair

Transcription factors that play a role in ossification during development are expected to participate in postnatal fracture repair since the endochondral bone formation that occurs in embryos is recapitulated during fracture repair. However, inherent differences exist between bone development and fracture repair, including a sudden disruption of tissue integrity followed by an inflammatory response. This raises the possibility that repair-specific transcription factors participate in bone healing. Here, we assessed the consequence of loss of early growth response gene 1 (EGR-1) on endochondral bone healing because this transcription factor has been shown to modulate repair in vascularized tissues. Model fractures were created in ribs of wild type (wt) and EGR-1(-/-) mice. Differences in tissue morphology and composition between these two animal groups were followed over 28 post fracture days (PFDs). In wt mice, bone healing occurred in healing phases characteristic of endochondral bone repair. A similar healing sequence was observed in EGR-1(-/-) mice but was impaired by alterations. A persistent accumulation of fibrin between the disconnected bones was observed on PFD7 and remained pronounced in the callus on PFD14. Additionally, the PFD14 callus was abnormally enlarged and showed increased deposition of mineralized tissue. Cartilage ossification in the callus was associated with hyper-vascularity and -proliferation. Moreover, cell deposits located in proximity to the callus within skeletal muscle were detected on PFD14. Despite these impairments, repair in EGR-1(-/-) callus advanced on PFD28, suggesting EGR-1 is not essential for healing. Together, this study provides genetic evidence that EGR-1 is a pleiotropic regulator of endochondral fracture repair.

Progress and outlook of inorganic nanoparticles for delivery of nucleic acid sequences related to orthopedic pathologies: a review

The anticipated growth in the aging population will drastically increase medical needs of society; of which, one of the largest components will undoubtedly be from orthopedic-related pathologies. There are several proposed solutions being investigated to cost-effectively prepare for the future--pharmaceuticals, implant devices, cell and gene therapies, or some combination thereof. Gene therapy is one of the more promising possibilities because it seeks to correct the root of the problem, thereby minimizing treatment duration and cost. Currently, viral vectors have shown the highest efficacies, but immunological concerns remain. Nonviral methods show reduced immune responses but are regarded as less efficient. The nonviral paradigms consist of mechanical and chemical approaches. While organic-based materials have been used more frequently in particle-based methods, inorganic materials capable of delivery have distinct advantages, especially advantageous in orthopedic applications. The inorganic gene therapy field is highly interdisciplinary in nature, and requires assimilation of knowledge across the broad fields of cell biology, biochemistry, molecular genetics, materials science, and clinical medicine. This review provides an overview of the role each area plays in orthopedic gene therapy as well as possible future directions for the field.

Modularity of the oral jaws is linked to repeated changes in the craniofacial shape of african cichlids

The African cichlids of the East-African rift-lakes provide one of the most dramatic examples of adaptive radiation known. It has long been thought that functional decoupling of the oral and pharyngeal jaws in cichlids has facilitated their explosive evolution. Recent research has also shown that craniofacial evolution from radiations in lakes Victoria, Malawi, and Tanganyika has occurred along a shared primary axis of shape divergence, whereby the preorbital region of the skull changes in a manner that is, relatively independent from other head regions. We predicted that the preorbital region would comprise a variational module and used an extensive dataset from each lake that allowed us to test this prediction using a model selection approach. Our findings supported the presence of a preorbital module across all lakes, within each lake, and for Malawi, within sand and rock-dwelling clades. However, while a preorbital module was consistently present, notable differences were also observed among groups. Of particular interest, a negative association between patterns of variational modularity was observed between the sand and rock-dwelling clades, a patter consistent with character displacement. These findings provide the basis for further experimental research involving the determination of the developmental and genetic bases of these patterns of modularity.

Xenopus laevis as a novel model to study long bone critical-size defect repair by growth factor-mediated regeneration

We used the tarsus of an adult Xenopus laevis frog as an in vivo load-bearing model to study the regeneration of critical-size defects (CSD) in long bones. We found the CSD for this bone to be about 35% of the tarsus length. To promote regeneration, we implanted biocompatible 1,6 hexanediol diacrylate scaffolds soaked with bone morphogenetic proteins-4 and vascular endothelial growth factors. In contrast to studies that use scaffolds as templates for bone formation, we used scaffolds as a growth factor delivery vehicle to promote cartilage-to-bone regeneration. Defects in control frogs were filled with scaffolds lacking growth factors. The limbs were harvested at a series of time points ranging from 3 weeks to 6 months after implantation and evaluated using micro-computed tomography and histology. In frogs treated with growth factor-loaded scaffolds, we observed a cartilage-to-bone regeneration in the skeletal defect. Five out of eight defects were completely filled with cartilage by 6 weeks. Blood vessels had invaded the cartilage, and bone was beginning to form in ossifying centers. By 3 months, these processes were well advanced, and extensive ossification was observed in 6-month samples. In contrast, the defects in control frogs showed only formation of fibrous scar tissue. This study demonstrates the utility of a Xenopus model system for tissue engineering research and that the normal in vivo mechanism of endochondral bone development and fracture repair can be mimicked in the repair of CSD with scaffolds used as growth factor delivery mechanisms.

Consistent osteoblastic differentiation of human mesenchymal stem cells with bone morphogenetic protein 4 and low serum

Providing fully mature and functional osteoblasts is challenging for bone tissue engineering and regenerative medicine. Such cells could be obtained from multipotent bone marrow mesenchymal stem cells (MSCs) after induction by different osteogenic factors. However, there are some discrepancies in results, notably due to the use of sera and to the type of osteogenic factor. In this study, we compared the osteogenic differentiation of bone marrow MSCs induced by dexamethasone (Dex) or bone morphogenetic proteins (BMPs) by assessing phenotypes in vitro and functional osteoblasts in vivo. Reducing the content of fetal calf serum from 10% to 2% significantly increased the mineral deposition and expression of osteoblastic markers during osteogenesis. In comparison to Dex condition, the addition of BMP4 greatly improved the differentiation of MSCs into fully mature osteoblasts as seen by high expression of Osterix. These results were confirmed in different supportive matrixes, plastic flasks, or biphasic calcium phosphate biomaterials. In contrast to Dex-derived osteoblasts, BMP4-derived osteoblasts from MSCs were significantly able to produce new bone in subcutis of nude mice in accordance with in vitro results. In conclusion, we describe a convenient ex vivo method to produce consistently mature functional osteoblasts from human MSCs with use of BMP4 and low serum.

Growth factors and gene expression of stem cells: bone marrow compared with peripheral blood

PURPOSE

To evaluate and compare the presence of cytokines and growth factors in both bone marrow (BM) and peripheral blood.

MATERIAL

Samples of autogenous BM aspirate and peripheral blood (PB) from 7 patients ranging in age from 49 to 80 years were analyzed with real-time polymerase chain reaction technology to identify and compare selected gene expression for specific cytokines and growth factors. The genes selected for analysis included those involved in osteogenesis, hematogenesis, angiogenesis, extracellular matrix molecules, and cell-adhesion molecules. A maximum of 4 cc';s BM aspirate was taken from the anterior iliac crest and 0.5 mL of venous blood was drawn from each of 7 patients.

RESULTS

The results of the analysis indicate that both circulating blood and BM aspirate contain large quantities of a host of growth factors and cytokines. More platelet-derived growth factor is expressed in patient blood (PB) than in BM. Vascular endothelial growth factor alpha is expressed slightly greater in BM and vascular endothelial growth factor beta is slightly more prominent in PB. Transforming growth factors (TGFs) TGFA, TGFB1, and TGFB3 were equally expressed in BM and PB, and TGFB2 had a greater expression in PB. Bone morphogenetic proteins (BMPs) 1, 3, 7, 8B, R1A, and PR2 were almost equally expressed in BM and PB. BMPs 4 and 6 were expressed greater in PB. BMP2 was expressed more in BM. Extracellular matrix factors were equally expressed in PB and BM. Mesenchymal stem cell lineage markers varied in PB and BMA, and hematopoietic stem cell lineage markers were expressed more in PB than BM. Gene expression for angiogenic factors were equally expressed in PB and BM.

CONCLUSION

In this investigation, specific cytokines and growth factors in BM are compared with those in peripheral blood. Each has similar biologic effects and most expressed equally in BM and PB. However, BMP2 and vascular endothelial growth factor alpha had greater expression in BM.

An internal locking plate to study intramembranous bone healing in a mouse femur fracture model

In most murine fracture models, the femur is stabilized by an intramedullary implant and heals predominantly through endochondral ossification. The aim of the present study was to establish a mouse model in which fractures heal intra-membraneously. Femur fractures of 16 SKH-mice were stabilized by an internal locking plate. Femur fractures of another 16 animals were stabilized by an intramedullary screw. Bone repair was analyzed by radiographic, biomechanical, and histological methods. At 2 weeks, histological analysis showed a significantly smaller callus diameter and callus area after locking plate fixation. Cartilage formation within the callus could only be observed after screw fixation, but not after fracture stabilization with the locking plate. Radiological and biomechanical analysis after 2 and 5 weeks showed a significantly improved healing and a higher bending stiffness of fractures stabilized by the locking plate. Fractures stabilized by the locking plate healed exclusively by intramembranous ossification, which is most probably a result of the anatomical reduction and stable fixation. The fractures that healed by intramembranous ossification showed an increased stiffness compared to fractures that healed by endochondral ossification. This model may be used to study molecular mechanisms of intramembranous bone healing.

Stimulation of ectopic bone formation in response to BMP-2 by Rho kinase inhibitor: a pilot study

The small GTPase Rho and Rho-associated protein kinase (Rho kinase, ROCK) signal participates in a variety of biological functions including vascular contraction, tumor invasion, and penile erection. Evidence also suggests Rho-ROCK is involved in signaling for mesenchymal cellular differentiation. However, whether it is involved in osteoblastic differentiation is unknown. We therefore asked whether Rho-ROCK signaling participates in recombinant human bone morphogenetic protein (rhBMP-2)-induced osteogenesis both in vitro and in vivo. Continuous delivery of a specific ROCK inhibitor (Y-27632) enhanced ectopic bone formation induced by rhBMP-2 impregnated into an atelocollagen carrier in mice without affecting systemic bone metabolism. Treatment with Y-27632 also enhanced the osteoblastic differentiation of cultured murine neonatal calvarial cells. These effects were associated with increased expression of BMP-4 gene. Expression of a dominant negative mutant of ROCK in ST2 cells promoted osteoblastic differentiation, while a constitutively active mutant of ROCK attenuated osteoblastic differentiation and the ROCK inhibitor reversed this phenotype. Thus, ROCK inhibits osteogenesis, and a ROCK inhibitor in combination with the local delivery of rhBMP/collagen composite may be clinically applicable for stimulating bone formation.

Stem cell- and scaffold-based tissue engineering approaches to osteochondral regenerative medicine

In osteochondral tissue engineering, cell recruitment, proliferation, differentiation, and patterning are critical for forming biologically and structurally viable constructs for repair of damaged or diseased tissue. However, since constructs prepared ex vivo lack the multitude of cues present in the in vivo microenvironment, cells often need to be supplied with external biological and physical stimuli to coax them toward targeted tissue functions. To determine which stimuli to present to cells, bioengineering strategies can benefit significantly from endogenous examples of skeletogenesis. As an example of developmental skeletogenesis, the developing limb bud serves as an excellent model system in which to study how osteochondral structures form from undifferentiated precursor cells. Alongside skeletal formation during embryogenesis, bone also possesses innate regenerative capacity, displaying remarkable ability to heal after damage. Bone fracture healing shares many features with bone development, driving the hypothesis that the regenerative process generally recapitulates development. Similarities and differences between the two modes of bone formation may offer insight into the special requirements for healing damaged or diseased bone. Thus, endogenous fracture healing, as an example of regenerative skeletogenesis, may also inform bioengineering strategies. In this review, we summarize the key cellular events involving stem and progenitor cells in developmental and regenerative skeletogenesis, and discuss in parallel the corresponding cell- and scaffold-based strategies that tissue engineers employ to recapitulate these events in vitro.

Ex vivo analysis of rotational stiffness of different osteosynthesis techniques in mouse femur fracture

The various molecular mechanisms of cell regeneration and tissue healing can best be studied in mouse models with the availability of a wide range of monoclonal antibodies and gene-targeted animals. The influence of the mechanical stability of individual stabilization techniques on the molecular mechanisms of fracture healing has not been completely elucidated yet. Although during recent years several osteosynthesis techniques have been introduced in mouse fracture models, no comparative study on fracture stabilization is available yet. We therefore analyzed herein in a standardized ex vivo setup the rotational stiffness of seven different osteosynthesis techniques using osteotomized right cadaver femora of CD-1 mice. Uninjured femora without osteotomy served as controls. Femur stabilization with a locking plate or an external fixator resulted in a rotational stiffness almost similar to the intact femur. The use of a "pin-clip" device, a "locking nail," a "mouse nail," or an "intramedullary screw" produced a lower torsional stiffness, which, however, was still significantly higher than that achieved with the widely applied conventional pin. By the use of the presented data a more specific choice of stabilization technique will be possible according to the various questions concerning molecular aspects in fracture healing.

Comparison of osteogenic potentials of BMP4 transduced stem cells from autologous bone marrow and fat tissue in a rabbit model of calvarial defects

We compared bone marrow stem cells (BMSCs) and adipose-derived stem cells (ADSCs) of adult rabbits under identical conditions in terms of their culture characteristics, proliferation capacity, osteogenic differentiation potentials induced by adenovirus-containing bone morphogenetic protein 4 (Ad-BMP4) in vitro, and capacity to repair calvarial defects in the rabbit model by autologous transplantation ex vivo. According to the results of growth curve, cell cycle, and telomerase activity analysis, ADSCs possess a higher proliferation potential. Both of the Ad-BMP4 transduced MSCs expressed BMP4 mRNA and protein and underwent osteogenic differentiation. Up-regulated mRNA expression of all osteogenic genes was observed in differentiated BMSCs and ADSCs, but with different patterns confirmed by real-time RT-PCR. Deposition of calcified extracellular matrix was significantly greater in differentiated ADSCs compared with differentiated BMSCs. X-ray and histological examination indicated significant bone regeneration in the calvarial defects transplanted with Ad-BMP4 transduced autologous MSCs compared to the control groups. There was no significant difference in new bone formation in Ad-BMP4 transduced MSCs based on quantitative digital analysis of histological sections. The use of ADSCs often resulted in the growth of fat tissue structures in the control groups, and the fat tissue structures were not seen with BMSC cells. Our data demonstrate that BMP4 can be potently osteoinductive in vivo, resulting in bone repair. ADSCs may be an attractive alternative to BMSCs for bone tissue engineering under appropriate stimuli. But the easy adipogenic differentiation needs to be considered when choosing adipose tissue for specific clinical application.

Advances in the establishment of defined mouse models for the study of fracture healing and bone regeneration

The availability of a broad spectrum of antibodies and gene-targeted animals caused an increasing interest in mouse models for the study of molecular mechanisms of fracture healing and bone regeneration. In most murine fracture models, the tibia or the femur is fractured using a 3-point bending device (closed models) or is osteotomized using an open surgical approach (open models). For fracture studies in mice, the tibia has to be considered less appropriate compared with the femur because the stabilization of the fracture is more difficult due to its triangular, distally declining caliber and its bowed longitudinal axis. Biomechanical factors critically influence the bone healing process. Thus, the use of stable osteosynthesis techniques is also of interest in murine fracture models. To achieve stable fixation, several biomechanically standardized implants have recently been introduced, including a locking nail and an intramedullary compression screw. Other implants, such as a pin-clip, an external fixator, and a locking plate, additionally allow the stabilization of fractures with distinct gap sizes. This enables the study of healing of critical size defects and nonunions. The use of these implants further allows a rigid fixation of fractures in bridle bones, which is essential for fracture studies in animals suffering from metabolic bone diseases like osteoporosis. In general, the analysis of bone healing in these models includes different imaging techniques and histologic, immunohistochemical, biomechanical, and molecular methods. To evaluate the impact of different osteosynthesis techniques on physical activity and rehabilitation, gait analysis may additionally be performed. By this, the gait of the animals can be visualized and quantitatively analyzed using modified running wheels and dynamic high-resolution radiography systems. Taken together, a variety of different murine femur fracture models have become available, providing defined biomechanical conditions for fracture research. The use of these mouse models may now allow studying the influence of fracture stabilization techniques on molecular mechanisms of bone healing.

Developmental toxicity of indium: embryotoxicity and teratogenicity in experimental animals

Indium, a precious metal classified in group 13 (IIIB) in the periodic table, has been used increasingly in the semiconductor industry. Because indium is a rare metal, technology for indium recycling from transparent conducting films for liquid crystal displays is desired, and its safety evaluation is becoming increasingly necessary. The developmental toxicity of indium in experimental animals was summarized. The intravenous or oral administration of indium to pregnant animals causes growth inhibition and the death of embryos in hamsters, rats, and mice. The intravenous administration of indium to pregnant animals causes embryonic or fetal malformation, mainly involving digit and tail deformities, in hamsters and rats. The oral administration of indium also induces fetal malformation in rats and rabbits, but requires higher doses. No teratogenicity has been observed in mice. Caudal hypoplasia, probably due to excessive cell loss by increased apoptosis in the tailbud, in the early postimplantation stage was considered to account for indium-induced tail malformation as a possible pathogenetic mechanism. Findings from in vitro experiments indicated that the embryotoxicity of indium could have direct effects on the conceptuses. Toxicokinetic studies showed that the embryonic exposure concentration was more critical than the exposure time regarding the embryotoxicity of indium. It is considered from these findings that the risk of the developmental toxicity of indium in humans is low, unless an accidentally high level of exposure or unknown toxic interaction occurs because of possible human exposure routes and levels (i.e. oral, very low-level exposure).