Cartilage-derived morphogenetic proteins and osteogenic protein-1 differentially regulate osteogenesis

Frameshift Mutation in a Chinese Patient with Brachydactyly Type C Involving the Third Metacarpal: A Case Report

Brachydactyly is a common feature of congenital hand anomalies characterized by shortening of the phalanges and/or metacarpals. Mutation of growth differentiation factor‐5 (GDF5) may result in loss of appearance and function in brachydactyly type C (BDC). Herein, we describe an 11 year‐old Chinese BDC patient with significant shortening of the 1st, 2nd, 3rd, and 5th digits. Notably, according to the analysis of metacarpophalangeal pattern profiles, we do not think the 4th digit appears unaffected as usual. In this patient a novel heterozygous frameshift mutation was identified (c.349delG) causing termination of translation after translating six amino acids from codon 117 (p.A117fs*6). This mutation is located in the propeptide region of GDF5, causing GDF5 haploinsufficiency in BDC. Considering our results expanding the genetic spectrum of BDC‐causing mutations, further molecular analysis to diagnose and reclassify isolated brachydactyly on the basis of genotype rather than phenotype is warranted.

Associations of Obesity with Linear Growth and Puberty

BACKGROUND

The prevalence of obesity in childhood has increased dramatically in recent decades with increased risk of developing cardiometabolic and other comorbidities. Childhood adiposity may also influence processes of growth and puberty.

SUMMARY

Growth patterns of obesity during childhood have been shown to be associated with increased linear growth in early childhood, leading to accelerated epiphyseal growth plate (EGP) maturation. Several hormones secreted by the adipose tissue may affect linear growth in the context of obesity, both via the growth hormone IGF-1 axis and via a direct effect on the EGP. The observation that children with obesity tend to mature earlier than lean children has led to the assumption that the degree of body fatness may trigger the neuroendocrine events that lead to pubertal onset. The most probable link between obesity and puberty is leptin and its interaction with the kisspeptin system, which is an important regulator of puberty. However, peripheral action of adipose tissue could also be involved in changes in the onset of puberty. In addition, nutritional factors, epigenetics, and endocrine-disrupting chemicals are potential mediators linking pubertal onset to obesity. In this review, we focused on interactions of obesity with linear growth and pubertal processes, based on basic research and clinical data in humans.

KEY MESSAGE

Children with obesity are subject to accelerated linear growth with risk of impaired adult height and early puberty, with its psychological consequences. The data highlight another important objective in combatting childhood obesity, for the prevention of abnormal growth and pubertal patterns.

Rat model of an autologous cancellous bone graft

Autologous cancellous bone (ACB) grafting is the "gold standard" treatment for delayed bone union. However, small animal models for such grafts are lacking. Here, we developed an ACB graft rat model. Anatomical information regarding the iliac structure was recorded from five rat cadavers (10 ilia). Additionally, 5 and 25 rats were used as controls and ACB graft models, respectively. A defect was created in rat femurs and filled with ACB. Post-graft neo-osteogenic potential was assessed by radiographic evaluation and histological analysis. Iliac bone harvesting yielded the maximum amount of cancellous bone with minimal invasiveness, considering the position of parailiac nerves and vessels. The mean volume of cancellous bone per rat separated from the cortical bone was 73.8 ± 5.5 mm³. Bone union was evident in all ACB graft groups at 8 weeks, and new bone volume significantly increased every 2 weeks (P < 0.001). Histological analysis demonstrated the ability of ACB grafts to act as a scaffold and promote bone union in the defect. In conclusion, we established a stable rat model of ACB grafts by harvesting the iliac bone. This model can aid in investigating ACB grafts and development of novel therapies for bone injury.

Biology of bone morphogenetic protein in bone repair and regeneration: A role for autologous blood coagulum as carrier

BMPs were purified from demineralized bone matrix based on their ability to induce new bone in vivo and they represent a large member of the TGF-β superfamily of proteins. BMPs serve as morphogenic signals for mesenchymal stem cell migration, proliferation and subsequently differentiation into cartilage and bone during embryonic development. A BMP when implanted with a collagenous carrier in a rat subcutaneous site is capable of inducing new bone by mimicking the cellular events of embryonic bone formation. Based on this biological principle, BMP2 and BMP7 containing collagenous matrix as carrier have been developed as bone graft substitutes for spine fusion and long bone fractures. Here, we describe a novel autologous bone graft substitute that contains BMP6 delivered within an autologous blood coagulum as carrier and summarize the biology of osteogenic BMPs in the context of bone repair and regeneration specifically the critical role that carrier plays to support osteogenesis.

Receptor binding competition: A paradigm for regulating TGF-β family action

The transforming growth factor (TGF)-β family is a group of structurally related, multifunctional growth factors, or ligands that are crucially involved in the development, regulation, and maintenance of animal tissues. In humans, the family counts over 33 members. These secreted ligands typically form multimeric complexes with two type I and two type II receptors to activate one of two distinct signal transduction branches. A striking feature of the family is its promiscuity, i.e., many ligands bind the same receptors and compete with each other for binding to these receptors. Although several explanations for this feature have been considered, its functional significance has remained puzzling. However, several recent reports have promoted the idea that ligand-receptor binding promiscuity and competition are critical features of the TGF-β family that provide an essential regulating function. Namely, they allow a cell to read and process multi-ligand inputs. This capability may be necessary for producing subtle, distinctive, or adaptive responses and, possibly, for facilitating developmental plasticity. Here, we review the molecular basis for ligand competition, with emphasis on molecular structures and binding affinities. We give an overview of methods that were used to establish experimentally ligand competition. Finally, we discuss how the concept of ligand competition may be fundamentally tied to human physiology, disease, and therapy.

Regenerative Response of Degenerate Human Nucleus Pulposus Cells to GDF6 Stimulation

Growth differentiation factor (GDF) family members have been implicated in the development and maintenance of healthy nucleus pulposus (NP) tissue, making them promising therapeutic candidates for treatment of intervertebral disc (IVD) degeneration and associated back pain. GDF6 has been shown to promote discogenic differentiation of mesenchymal stem cells, but its effect on NP cells remains largely unknown. Our aim was to investigate GDF6 signalling in adult human NP cells derived from degenerate tissue and determine the signal transduction pathways critical for GDF6-mediated phenotypic changes and tissue homeostatic mechanisms. This study demonstrates maintained expression of GDF6 receptors in human NP and annulus fibrosus (AF) cells across a range of degeneration grades at gene and protein level. We observed an anabolic response in NP cells treated with recombinant GDF6 (increased expression of matrix and NP-phenotypic markers; increased glycosaminoglycan production; no change in catabolic enzyme expression), and identified the signalling pathways involved in these responses (SMAD1/5/8 and ERK1/2 phosphorylation, validated by blocking studies). These findings suggest that GDF6 promotes a healthy disc tissue phenotype in degenerate NP cells through SMAD-dependent and -independent (ERK1/2) mechanisms, which is important for development of GDF6 therapeutic strategies for treatment of degenerate discs.

BMPR1A is necessary for chondrogenesis and osteogenesis, whereas BMPR1B prevents hypertrophic differentiation

BMP2 stimulates bone formation and signals preferably through BMP receptor (BMPR) 1A, whereas GDF5 is a cartilage inducer and signals preferably through BMPR1B. Consequently, BMPR1A and BMPR1B are believed to be involved in bone and cartilage formation, respectively. However, their function is not yet fully clarified. In this study, GDF5 mutants with a decreased affinity for BMPR1A were generated. These mutants, and wild-type GDF5 and BMP2, were tested for their ability to induce dimerization of BMPR1A or BMPR1B with BMPR2, and for their chondrogenic, hypertrophic and osteogenic properties in chondrocytes, in the multipotent mesenchymal precursor cell line C3H10T1/2 and the human osteosarcoma cell line Saos-2. Mutants with the lowest potency for inducing BMPR1A-BMPR2 dimerization exhibited minimal chondrogenic and osteogenic activities, indicating that BMPR1A is necessary for chondrogenic and osteogenic differentiation. BMP2, GDF5 and the GDF5 R399E mutant stimulated expression of chondrogenic and hypertrophy markers in C3H10T1/2 cells and chondrocytes. However, GDF5 R399E, which induces the dimerization of BMPR1B and BMPR2 more potently than GDF5 or BMP2, displayed reduced hypertrophic activity. Therefore, we postulate that stronger BMPR1B signaling, compared to BMPR1A signaling, prevents chondrocyte hypertrophy and acts as a cartilage stabilizer during joint morphogenesis.This article has an associated First Person interview with the first author of the paper.

Specification of BMP Signaling

Bone Morphogenetic Proteins (BMPs) together with the Growth and Differentiation Factors (GDFs) form the largest subgroup of the Transforming Growth Factor (TGF)β family and represent secreted growth factors, which play an essential role in many aspects of cell communication in higher organisms. As morphogens they exert crucial functions during embryonal development, but are also involved in tissue homeostasis and regeneration in the adult organism. Their involvement in maintenance and repair processes of various tissues and organs made these growth factors highly interesting targets for novel pharmaceutical applications in regenerative medicine. A hallmark of the TGFβ protein family is that all of the more than 30 growth factors identified to date signal by binding and hetero-oligomerization of a very limited set of transmembrane serine-threonine kinase receptors, which can be classified into two subgroups termed type I and type II. Only seven type I and five type II receptors exist for all 30plus TGFβ members suggesting a pronounced ligand-receptor promiscuity. Indeed, many TGFβ ligands can bind the same type I or type II receptor and a particular receptor of either subtype can usually interact with and bind various TGFβ ligands. The possible consequence of this ligand-receptor promiscuity is further aggravated by the finding that canonical TGFβ signaling of all family members seemingly results in the activation of just two distinct signaling pathways, that is either SMAD2/3 or SMAD1/5/8 activation. While this would implicate that different ligands can assemble seemingly identical receptor complexes that activate just either one of two distinct pathways, in vitro and in vivo analyses show that the different TGFβ members exert quite distinct biological functions with high specificity. This discrepancy indicates that our current view of TGFβ signaling initiation just by hetero-oligomerization of two receptor subtypes and transduction via two main pathways in an on-off switch manner is too simplified. Hence, the signals generated by the various TGFβ members are either quantitatively interpreted using the subtle differences in their receptor-binding properties leading to ligand-specific modulation of the downstream signaling cascade or additional components participating in the signaling activation complex allow diversification of the encoded signal in a ligand-dependent manner at all cellular levels. In this review we focus on signal specification of TGFβ members, particularly of BMPs and GDFs addressing the role of binding affinities, specificities, and kinetics of individual ligand-receptor interactions for the assembly of specific receptor complexes with potentially distinct signaling properties.

Widespread cis-regulatory convergence between the extinct Tasmanian tiger and gray wolf

The extinct marsupial Tasmanian tiger, or thylacine, and the eutherian gray wolf are among the most widely recognized examples of convergent evolution in mammals. Despite being distantly related, these large predators independently evolved extremely similar craniofacial morphologies, and evidence suggests that they filled similar ecological niches. Previous analyses revealed little evidence of adaptive convergence between their protein-coding genes. Thus, the genetic basis of their convergence is still unclear. Here, we identified candidate craniofacial cis-regulatory elements across vertebrates and compared their evolutionary rates in the thylacine and wolf, revealing abundant signatures of convergent positive selection. Craniofacial thylacine-wolf accelerated regions were enriched near genes involved in TGF beta (TGFB) and BMP signaling, both of which are key morphological signaling pathways with critical roles in establishing the identities and boundaries between craniofacial tissues. Similarly, enhancers of genes involved in craniofacial nerve development showed convergent selection and involvement in these pathways. Taken together, these results suggest that adaptation in cis-regulators of TGF beta and BMP signaling may provide a mechanism to explain the coevolution of developmentally and functionally integrated craniofacial structures in these species. We also found that despite major structural differences in marsupial and eutherian brains, accelerated regions in both species were common near genes with roles in brain development. Our findings support the hypothesis that, relative to protein-coding genes, positive selection on cis-regulatory elements is likely to be an essential driver of adaptive convergent evolution and may underpin thylacine-wolf phenotypic similarities.

TGFβ/BMP Signaling Pathway in Cartilage Homeostasis

Cartilage homeostasis is governed by articular chondrocytes via their ability to modulate extracellular matrix production and degradation. In turn, chondrocyte activity is regulated by growth factors such as those of the transforming growth factor β (TGFβ) family. Members of this family include the TGFβs, bone morphogenetic proteins (BMPs), and growth and differentiation factors (GDFs). Signaling by this protein family uniquely activates SMAD-dependent signaling and transcription but also activates SMAD-independent signaling via MAPKs such as ERK and TAK1. This review will address the pivotal role of the TGFβ family in cartilage biology by listing several TGFβ family members and describing their signaling and importance for cartilage maintenance. In addition, it is discussed how (pathological) processes such as aging, mechanical stress, and inflammation contribute to altered TGFβ family signaling, leading to disturbed cartilage metabolism and disease.

Therapeutic potential of growth differentiation factors in the treatment of degenerative disc diseases

Intervertebral disc (IVD) degeneration is a major contributing factor to chronic low back pain and disability, leading to imbalance between anabolic and catabolic processes, altered extracellular matrix composition, loss of tissue hydration, inflammation, and impaired mechanical functionality. Current treatments aim to manage symptoms rather than treat underlying pathology. Therefore, IVD degeneration is a target for regenerative medicine strategies. Research has focused on understanding the molecular process of degeneration and the identification of various factors that may have the ability to halt and even reverse the degenerative process. One such family of growth factors, the growth differentiation factor (GDF) family, have shown particular promise for disc regeneration in in vitro and in vivo models of IVD degeneration. This review outlines our current understanding of IVD degeneration, and in this context, aims to discuss recent advancements in the use of GDF family members as anabolic factors for disc regeneration. An increasing body of evidence indicates that GDF family members are central to IVD homeostatic processes and are able to upregulate healthy nucleus pulposus cell marker genes in degenerative cells, induce mesenchymal stem cells to differentiate into nucleus pulposus cells and even act as chemotactic signals mobilizing resident cell populations during disc injury repair. The understanding of GDF signaling and its interplay with inflammatory and catabolic processes may be critical for the future development of effective IVD regeneration therapies.

Bone regeneration strategies: Engineered scaffolds, bioactive molecules and stem cells current stage and future perspectives

Bone fractures are the most common traumatic injuries in humans. The repair of bone fractures is a regenerative process that recapitulates many of the biological events of embryonic skeletal development. Most of the time it leads to successful healing and the recovery of the damaged bone. Unfortunately, about 5-10% of fractures will lead to delayed healing or non-union, more so in the case of co-morbidities such as diabetes. In this article, we review the different strategies to heal bone defects using synthetic bone graft substitutes, biologically active substances and stem cells. The majority of currently available reviews focus on strategies that are still at the early stages of development and use mostly in vitro experiments with cell lines or stem cells. Here, we focus on what is already implemented in the clinics, what is currently in clinical trials, and what has been tested in animal models. Treatment approaches can be classified in three major categories: i) synthetic bone graft substitutes (BGS) whose architecture and surface can be optimized; ii) BGS combined with bioactive molecules such as growth factors, peptides or small molecules targeting bone precursor cells, bone formation and metabolism; iii) cell-based strategies with progenitor cells combined or not with active molecules that can be injected or seeded on BGS for improved delivery. We review the major types of adult stromal cells (bone marrow, adipose and periosteum derived) that have been used and compare their properties. Finally, we discuss the remaining challenges that need to be addressed to significantly improve the healing of bone defects.

Effect of Nutrition on Statural Growth

In children, proper growth and development are often regarded as a surrogate marker for good health. A complex system controls the initiation, rate, and cessation of growth, and thus gives a wonderful example of the interactions between genetics, epigenetics, and environmental factors (especially stress and nutrition). Malnutrition is considered a leading cause of growth attenuation in children. This review summarizes our current knowledge regarding the mechanisms linking nutrition and skeletal growth, including systemic factors, such as insulin, growth hormone, insulin-like growth factor-1, fibroblast growth factor-21, etc., and local mechanisms, including mTOR, miRNAs, and epigenetics. Studying the molecular mechanisms regulating skeletal growth may lead to the establishment of better nutritional and therapeutic regimens for more effective linear growth in children with malnutrition and growth abnormalities. 
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Brachdactyly Instigated as a Result of Mutation in GDF5 and NOG Genes in Pakistani Population

Objectives

Brachdactyly a genetic disorder associated with the abnormal development of metacarpals, phalanges or both which results in the shortening of hands and feet. Mutations in the contributing genes has been recognized with the majority of the investigated syndromic form of brachdactyly. The current study was proposed to examine mutation in NOG and GDF5 genes in a Pakistani family.

Methods

Poly Acrylamide Gel Electrophoresis and Polymerase Chain Reaction was used for the genomic screening and linkage analysis to observe the mutation in genes. The samples were collected from Luckki Marwat district, KPK, while the research study was conducted in the department of Biochemistry, Quaid-I-Azam University, Islamabad, Pakistan.

Results

After survey, family was identified with brachdactyly type A2 and investigated a heterozygous arginine to glutamine exchange in the growth demarcation factor 5 in all the victim persons. Different types of skeletal dysplasia resulted due to mutation in the GDF5 genes. Novel GDF5 genes mutations were reported with distinct limb malformation and sequencing of coding region revealed that the mildly affected individuals were heterozygous while the harshly affected individuals were homozygous.

Conclusion

The current study reported the genetic variability and concluded that the Brachdacytyly type A2 and type B2 resulted due to mutation in GDF5 and NOG genes respectively. A new subtype of brachydactyly (BDB2) was instigated as a result of novel mutations in NOG. The mutation has been reported for the first time in Pakistani population and especially in Pushtoon ethnic population.

Growth Differentiation Factor 6 Promotes Vascular Stability by Restraining Vascular Endothelial Growth Factor Signaling

OBJECTIVE

The assembly of a functional vascular system requires a coordinated and dynamic transition from activation to maturation. High vascular endothelial growth factor activity promotes activation, including junction destabilization and cell motility. Maturation involves junctional stabilization and formation of a functional endothelial barrier. The identity and mechanism of action of prostabilization signals are still mostly unknown. Bone morphogenetic protein receptors and their ligands have important functions during embryonic vessel assembly and maturation. Previous work has suggested a role for growth differentiation factor 6 (GDF6; bone morphogenetic protein 13) in vascular integrity although GDF6's mechanism of action was not clear. Therefore, we sought to further explore the requirement for GDF6 in vascular stabilization.

APPROACH AND RESULTS

We investigated the role of GDF6 in promoting endothelial vascular integrity in vivo in zebrafish and in cultured human umbilical vein endothelial cells in vitro. We report that GDF6 promotes vascular integrity by counteracting vascular endothelial growth factor activity. GDF6-deficient endothelium has increased vascular endothelial growth factor signaling, increased vascular endothelial-cadherin Y658 phosphorylation, vascular endothelial-cadherin delocalization from cell-cell interfaces, and weakened endothelial cell adherence junctions that become prone to vascular leak.

CONCLUSIONS

Our results suggest that GDF6 promotes vascular stabilization by restraining vascular endothelial growth factor signaling. Understanding how GDF6 affects vascular integrity may help to provide insights into hemorrhage and associated vascular pathologies in humans.

Knock-in human GDF5 proregion L373R mutation as a mouse model for proximal symphalangism

Proximal symphalangism (SYM1) is an autosomal dominant disorder, mainly characterized by bony fusions of the proximal phalanges of the hands and feet. GDF5 and NOG were identified to be responsible for SYM1. We have previously reported on a p.Leu373Arg mutation in the GDF5 proregion present in a Chinese family with SYM1. Here, we investigated the effects of the GDF-L373R mutation. The variant caused proteolysis efficiency of GDF5 increased in ATDC5 cells. The variant also caused upregulation of SMAD1/5/8 phosphorylation and increased expression of target genes SMURF1, along with COL2A1 and SOX9 which are factors associated with chondrosis. Furthermore, we developed a human-relevant SYM1 mouse model by making a Gdf5^L367R (the orthologous position for L373R in humans) knock-in mouse. Gdf5^L367R/+ and Gdf5^L367R/L367R mice displayed stiffness and adhesions across the proximal phalanx joint which were in complete accord with SYM1. It was also confirmed the joint formation and development was abnormal in Gdf5^L367R/+ and Gdf5^L367R/L367R mice, including the failure to develop the primary ossification center and be hypertrophic chondrocytes during embryonic development. This knock-in mouse model offers a tool for assessing the pathogenesis of SYM1 and the function of the GDF5 proregion.

Association of BMP-14 rs143383 ploymorphism with its susceptibility to osteoarthritis: A meta-analysis and systematic review according to PRISMA guideline

BACKGROUND

Osteoarthritis (OA) is a complex disease which can be caused by both environmental and genetic factors. A functional locus rs143383 of bone morphogenetic protein-14 (BMP-14) has been pointed out to be associated with OA etiology, but conflicting conclusions have been reached. To provide a more comprehensive conclusion about this issue, we performed this meta-analysis.

METHODS

Relevant studies were searched from electronic databases including PubMed, Chinese National Knowledge Infrastructure, Embase, and Wanfang. The strength of correlations was examined with pooled odds ratios (ORs) and 95% confidence intervals (95% CIs). Subgroup analyses stratified by ethnicity and source of control were carried out. All statistical analyses were performed with STATA software (version 12.0).

RESULTS

Overall, BMP-14 rs143383 polymorphism was negatively correlated with the susceptibility to knee OA and hand OA under genetic contrasts of CC versus TT, CC + TC versus TT, CC versus TT + TC, C versus T, TC versus TT (OR = 0.71, 95% CI = 0.65-0.79; OR = 0.81, 95% CI = 0.73-0.89; OR = 0.79, 95% CI = 0.71-0.86; OR = 0.85, 95% CI = 0.81-0.90; OR = 0.84, 95% CI = 0.75-0.93), and TC versus TT, CC versus TT + TC, C versus T (OR = 0.76, 95% CI = 0.65-0.89; OR = 0.79, 95% CI = 0.68-0.92; OR = 0.90, 95% CI = 0.85-0.95), respectively; similar results were observed in subgroups after stratification analyses. Additionally, the polymorphism also reduced hip OA risk in Asian group after stratified analysis by ethnicity.

CONCLUSION

BMP-14 rs143383 polymorphism may be a protective factor against OA occurrence.

Beta Palmitate Improves Bone Length and Quality during Catch-Up Growth in Young Rats

Palmitic acid (PA) is the most abundant saturated fatty acid in human milk, where it is heavily concentrated in the sn-2-position (termed beta palmitate, BPA) and as such is conserved in all women, regardless of their diet or ethnicity, indicating its physiological and metabolic importance. We hypothesized that BPA improves the efficiency of nutrition-induced catch up growth as compared to sn-1,3 PA, which is present in vegetable oil. Pre-pubertal male rats were subjected to a 17 days food restriction followed by re-feeding for nine days with 1,3 PA or BPA-containing diets. We measured bone length, epiphyseal growth plate height (EGP, histology), bone quality (micro-CT and 3-point bending assay), and gene expression (Affymetrix). The BPA-containing diet improved most growth parameters: humeri length and EGP height were greater in the BPA-fed animals. Further analysis of the EGP revealed that the hypertrophic zone was significantly higher in the BPA group. In addition, Affymetrix analysis revealed that the diet affected the expression of several genes in the liver and EGP. Despite the very subtle difference between the diets and the short re-feeding period, we found a small but significant improvement in most growth parameters in the BPA-fed rats. This pre-clinical study may have important implications, especially for children with growth disorders and children with special nutritional needs.

Articular cartilage tissue engineering: the role of signaling molecules

Effective early disease modifying options for osteoarthritis remain lacking. Tissue engineering approach to generate cartilage in vitro has emerged as a promising option for articular cartilage repair and regeneration. Signaling molecules and matrix modifying agents, derived from knowledge of cartilage development and homeostasis, have been used as biochemical stimuli toward cartilage tissue engineering and have led to improvements in the functionality of engineered cartilage. Clinical translation of neocartilage faces challenges, such as phenotypic instability of the engineered cartilage, poor integration, inflammation, and catabolic factors in the arthritic environment; these can all contribute to failure of implanted neocartilage. A comprehensive understanding of signaling molecules involved in osteoarthritis pathogenesis and their actions on engineered cartilage will be crucial. Thus, while it is important to continue deriving inspiration from cartilage development and homeostasis, it has become increasingly necessary to incorporate knowledge from osteoarthritis pathogenesis into cartilage tissue engineering.

Shape Ontogeny of the Distal Femur in the Hominidae with Implications for the Evolution of Bipedality

Heterochrony has been invoked to explain differences in the morphology of modern humans as compared to other great apes. The distal femur is one area where heterochrony has been hypothesized to explain morphological differentiation among Plio-Pleistocene hominins. This hypothesis is evaluated here using geometric morphometric data to describe the ontogenetic shape trajectories of extant hominine distal femora and place Plio-Pleistocene hominins within that context. Results of multivariate statistical analyses showed that in both Homo and Gorilla, the shape of the distal femur changes significantly over the course of development, whereas that of Pan changes very little. Development of the distal femur of Homo is characterized by an elongation of the condyles, and a greater degree of enlargement of the medial condyle relative to the lateral condyle, whereas Gorilla are characterized by a greater degree of enlargement of the lateral condyle, relative to the medial. Early Homo and Australopithecus africanus fossils fell on the modern human ontogenetic shape trajectory and were most similar to either adult or adolescent modern humans while specimens of Australopithecus afarensis were more similar to Gorilla/Pan. These results indicate that shape differences among the distal femora of Plio-Pleistocene hominins and humans cannot be accounted for by heterochrony alone; heterochrony could explain a transition from the distal femoral shape of early Homo/A. africanus to modern Homo, but not a transition from A. afarensis to Homo. That change could be the result of genetic or epigenetic factors.

Evolving New Skeletal Traits by cis-Regulatory Changes in Bone Morphogenetic Proteins

Changes in bone size and shape are defining features of many vertebrates. Here we use genetic crosses and comparative genomics to identify specific regulatory DNA alterations controlling skeletal evolution. Armor bone-size differences in sticklebacks map to a major effect locus overlapping BMP family member GDF6. Freshwater fish express more GDF6 due in part to a transposon insertion, and transgenic overexpression of GDF6 phenocopies evolutionary changes in armor-plate size. The human GDF6 locus also has undergone distinctive regulatory evolution, including complete loss of an enhancer that is otherwise highly conserved between chimps and other mammals. Functional tests show that the ancestral enhancer drives expression in hindlimbs but not forelimbs, in locations that have been specifically modified during the human transition to bipedalism. Both gain and loss of regulatory elements can localize BMP changes to specific anatomical locations, providing a flexible regulatory basis for evolving species-specific changes in skeletal form.

Cartilage Derived Morphogenetic Protein-2 Induces Cell Migration and Its Chondrogenic Potential in C28/I2 Cells

BACKGROUND

Intervertebral disc degeneration is a major cause of low back pain. Previous researches have demonstrated local administration of signalling molecules as potential biological therapies for disc regeneration. Our laboratory has published encouraging results for effectiveness of injection of the cartilage derived morphogenetic protein-2 (CDMP-2) into ovine discs following annular injury. To elucidate the mechanisms underpinning these in vivo effects, this project aimed to investigate the potential of CDMP-2 on cellular migration, proliferation and extracellular matrix production in a human chondrocytic cell line.

METHODS

To evaluate cell motility, cells were seeded into Boyden chambers and CDMP-2 as a chemo-attractant or a stimulant was placed into either the bottom or top chambers respectively. Cells that had completed migration through the porous membrane were visualized by immunocytochemical staining and analysed using Image J. The effect of CDMP-2 on cell proliferation, proteoglycan and collagen production, as well as chondrogenic gene expression in human chondrocytic cell line C28/I2 was also examined.

RESULTS

The results revealed that cells migrated significantly under the influence of CDMP-2 (200 ng/ml) stimulation compared to control (3-fold increase, p = 0.033) and demonstrated a significant chemotactic movement towards a solution of 200ng/ml CDMP-2 (>2-fold increase, p = 0.027). A 35% increase in C28/I2 proliferation was observed after CDMP-2 stimulation (p < 0.0001) compared to control, and in the presence of 100ng/ml CDMP-2, proteoglycan synthesis had an 8-fold increase (p = 0.048). Similarly, gene expression analysis demonstrated increased expression of aggrecan, collagen types II, X and XXVII, BMPR-1A and BMPR-2 when cells were treated with CDMP-2.

CONCLUSION

The study shows that C28/I2 cells can migrate under the influence of CDMP-2 as a chemoattractant or migration stimulator, suggestive of an effect on chondrocytic cells in the intervertebral disc. Further, CDMP-2 can stimulate C28/I2 cells to proliferate and synthesize key extracellular matrix proteins.

Tendon healing: an overview of physiology, biology, and pathology of tendon healing and systematic review of state of the art in tendon bioengineering

PURPOSE

Tendon injuries vary from acute rupture to chronic tendinopathy. For an optimal treatment of either condition, a profound knowledge is essential. Therefore, this article shall give an overview of physiology, biology, and pathology of tendon healing and state of the art in tendon bioengineering.

METHODS

For a preferably comprehensive survey, the current literature listed in PubMed and published in English peer-reviewed journals (March 2013) was systematically reviewed for tendon healing and tendon bioengineering including cytokine modulation, autologous sources of growth factors, biomaterials, gene therapy, and cell-based therapy. No differentiation was made between clinical and preclinical in vitro investigations.

RESULTS

Tendon healing happens in certain stadiums of inflammation, formation, and remodelling. An additional process of "collagen recycling" close to the healing site has been described recently. With increasing comprehension of physiology and pathology of tendon healing, several promising approaches in tendon bioengineering using growth factors, biomaterials, gene therapy, or cell-based therapy are described. However, only some of these are already used routinely in clinics.

CONCLUSION

Strong and resistant tendons are crucial for a healthy musculoskeletal system. The new approaches in tendon bioengineering are promising to aid physiological tendon healing and thus resulting in a stronger and more resistant tendon after injury. The growing knowledge in this field will need to be further taken into clinical studies so that especially those patients with prolonged courses, revision surgery, or chronic tendinopathy and high-demanding patients, i.e., professional athletes would benefit.

LEVEL OF EVIDENCE

II.

Growth without growth hormone: can growth and differentiation factor 5 be the mediator?

Growth without growth hormone (GH) is often observed in the setup of obesity; however, the missing link between adipocytes and linear growth was until now not identified. 3T3L1 cells were induced to differentiate into adipocytes and their conditioned medium (CM) (adipocytes CM, CMA) was added to metatarsals bone culture and compared to CM derived from undifferentiated cells. CMA significantly increased metatarsals bone elongation. Adipogenic differentiation increased the expression of growth and differentiation factor (GDF)-5, also found to be secreted into the CMA. GDF-5 significantly increased metatarsal length in culture; treatment of the CMA with anti-GDF-5 antibody significantly reduced the stimulatory effect on bone length. The presence of GDF-5 receptor (bone morphogenetic protein receptor; BMPR1) in metatarsal bone was confirmed by immunohistochemistry. Animal studies in rodents subjected to food restriction followed by re-feeding showed an increase in GDF-5 serum levels concomitant with nutritional induced catch up growth. These results show that adipocytes may stimulate bone growth and suggest an additional explanation to the growth without GH phenomenon.

Human chondrocytes respond discordantly to the protein encoded by the osteoarthritis susceptibility gene GDF5

A genetic deficit mediated by SNP rs143383 that leads to reduced expression of GDF5 is strongly associated with large-joint osteoarthritis. We speculated that this deficit could be attenuated by the application of exogenous GDF5 protein and as a first step we have assessed what effect such application has on primary osteoarthritis chondrocyte gene expression. Chondrocytes harvested from cartilage of osteoarthritic patients who had undergone joint replacement were cultured with wildtype recombinant mouse and human GDF5 protein. We also studied variants of GDF5, one that has a higher affinity for the receptor BMPR-IA and one that is insensitive to the GDF5 antagonist noggin. As a positive control, chondrocytes were treated with TGF-β1. Chondrocytes were cultured in monolayer and micromass and the expression of genes coding for catabolic and anabolic proteins of cartilage were measured by quantitative PCR. The expression of the GDF5 receptor genes and the presence of their protein products was confirmed and the ability of GDF5 signal to translocate to the nucleus was demonstrated by the activation of a luciferase reporter construct. The capacity of GDF5 to elicit an intracellular signal in chondrocytes was demonstrated by the phosphorylation of intracellular Smads. Chondrocytes cultured with TGF-β1 demonstrated a consistent down regulation of MMP1, MMP13 and a consistent upregulation of TIMP1 and COL2A1 with both culture techniques. In contrast, chondrocytes cultured with wildtype GDF5, or its variants, did not show any consistent response, irrespective of the culture technique used. Our results show that osteoarthritis chondrocytes do not respond in a predictable manner to culture with exogenous GDF5. This may be a cause or a consequence of the osteoarthritis disease process and will need to be surmounted if treatment with exogenous GDF5 is to be advanced as a potential means to overcome the genetic deficit conferring osteoarthritis susceptibility at this gene.

Enhanced reconstruction of long bone architecture by a growth factor mutant combining positive features of GDF-5 and BMP-2

Non healing bone defects remain a worldwide health problem and still only few osteoinductive growth factors are available for clinical use in bone regeneration. By introducing BMP-2 residues into growth and differentiation factor (GDF)-5 we recently produced a mutant GDF-5 protein BB-1 which enhanced heterotopic bone formation in mice. Designed to combine positive features of GDF-5 and BMP-2, we suspected that this new growth factor variant may improve long bone healing compared to the parent molecules and intended to unravel functional mechanisms behind its action. BB-1 acquired an increased binding affinity to the BMP-IA receptor, mediated enhanced osteogenic induction of human mesenchymal stem cells versus GDF-5 and higher VEGF secretion than BMP-2 in vitro. Rabbit radius defects treated with a BB-1-coated collagen carrier healed earlier and with increased bone volume compared to BMP-2 and GDF-5 according to in vivo micro-CT follow-up. While BMP-2 callus often remained spongy, BB-1 supported earlier corticalis and marrow cavity formation, showing no pseudojoint persistence like with GDF-5. Thus, by combining positive angiogenic and osteogenic features of GDF-5 and BMP-2, only BB-1 restored a natural bone architecture within 12 weeks, rendering this promising growth factor variant especially promising for long bone regeneration.

Alveolar ridge augmentation using implants coated with recombinant human growth/differentiation factor -5 (rhGDF-5). Radiographic observations

OBJECTIVES

Application of growth factors onto dental implant surfaces is being considered to support local bone formation. Bone morphogenetic protein-2 (BMP-2) and BMP-7 have been shown to support local bone formation, but are also associated with adverse events including seroma formation, extensive bone remodeling, and implant displacement captured in the radiographic evaluation. This report presents mineralized tissue formation and associated adverse events following implantation of recombinant human growth/differentiation factor-5 (rhGDF-5) coated onto a purpose-designed titanium porous-oxide implant surface.

MATERIAL AND METHODS

Twelve young adult Labrador dogs were used. Three 10-mm titanium implants/jaw quadrant were placed 5 mm into the alveolar ridge in the posterior mandible following surgical extraction of the premolar teeth and reduction of the alveolar ridge. Six animals received implants coated with rhGDF-5 at 30 or 60 μg/implant in contralateral jaw quadrants. Six animals received implants coated with rhGDF-5 at 120 μg/implant or uncoated implants (sham-surgery control) using the same split-mouth design. The mucoperiosteal flaps were advanced, adapted, and sutured to submerge the implants. Radiographic recordings were made immediately postsurgery (baseline), and at week 4 and 8 (end of study). Two masked examiners performed the analysis using computer enhanced radiographic images.

RESULTS

rhGDF-5 coated implants displayed mineralized tissue formation significantly exceeding that of the sham-surgery control in a dose-dependent order. The greatest increase was observed for implants coated with rhGDF-5 at 60 μg and 120 μg amounting to approximately 2.2 mm for both groups at 8 weeks. Importantly, none of the implants showed evidence of peri-implant bone remodeling, implant displacement, or seroma formation. The newly formed mineralized tissues assumed characteristics of the resident bone.

CONCLUSIONS

rhGDF-5 coated onto a titanium porous-oxide implant surface exhibits a dose-dependent potential to stimulate local mineralized tissue formation. Application of rhGDF-5 appears safe as it is associated with limited, if any, adverse events.

B2A as a positive BMP receptor modulator

B2A (B2A2-K-NS) is a synthetic multi-domain peptide that in vitro augments bone morphogenetic protein (BMP)-2-induced cell responsiveness and osteodifferentiation. Augmentation of endogenous BMP-2 is thought to ultimately improve bone repair, and has led to clinical evaluation of B2A in orthopedic applications. In this study, we show that B2A binds to BMP receptor (BMPR)-IB, BMPR-II, and BMPR-IA. B2A reduces the EC50 of rh-BMP-2, thus shifting the response curve to the left. B2A enhances the osteogenic activity of BMP-2, but not growth and differentiation factor-5, BMP-7, or BMP-9, indicating its action is highly BMP-2 selective. Additionally, B2A did not augment Wnt-3a- and retinoic acid-induced differentiation. All three functional domains (receptor-binding domain, hydrophobic-linker domain, heparin-binding domain) of B2A are required for optimal bioactivity. Collectively, the results suggest that B2A, via its unique sequence, acts in a manner consistent with a positive receptor modulator to selectively enhance BMP-2 osteodifferentiation, and yet in the absence of BMP-2, B2A is without cooperative effect.

Role of growth factors in rotator cuff healing

The histologic lesion underlying overuse rotator cuff tendinopathy is a failed healing response, with haphazard proliferation of tenocytes, disruption of tendon cells and collagen fibers, and increased noncollagenous extracellular matrix. Recent attention has focused on the biological pathways by which tendons heal, leading to the identification of several growth factors (GFs) involved in this process. No studies have been published on the time course of the various GFs during rotator cuff healing process in vivo, in humans. We review what is known about these GFs and their role in rotator cuff healing.

Bone Morphogenetic Protein functions as a context-dependent angiogenic cue in vertebrates

Bone Morphogenetic Protein (BMP) signaling has been implicated in diverse biological processes. Although how BMP signaling regulates behaviors of endothelial cells during angiogenesis are not fully understood, increasing evidence indicate functions of BMP signaling components are essential in developmental and pathological angiogenesis. Here we review recent advances in delineating the functions of BMP signaling during angiogenesis. In addition, we discuss downstream pathways that transduce BMP signaling in endothelial cells, and factors that modulate BMP signaling response in endothelial cells. Finally, we provide recent insight on how BMP signaling functions as a context dependent angiogenic cue.

Delayed fracture healing in growth differentiation factor 5-deficient mice: a pilot study

BACKGROUND

Growth differentiation factor-5 (GDF-5) is a key regulator of skeletogenesis and bone repair and induces bone formation in spinal fusions and nonunion applications by enhancing chondrocytic and osteocytic differentiation and stimulating angiogenesis. Elucidating the contribution of GDF-5 to fracture repair may support its clinical application in complex fractures.

QUESTIONS/PURPOSE

We therefore asked whether the absence of GDF-5 during fracture repair impaired bone healing as assessed radiographically, histologically, and mechanically.

METHODS

In this pilot study, we performed tibial osteotomies on 10-week-old male mice, stabilized by intramedullary and extramedullary nailing. Healing was assessed radiographically and histologically on Days 1 (n = 1 wild-type; n = 5 bp [brachopodism]), 5 (n = 3 wild-type; n = 3 bp), 10 (n = 6 wild-type; n = 3 bp), 14 (n = 6 wild-type; n = 6 bp), 21 (n = 6 wild-type; n = 6 bp), 28 (n = 7 wild-type; n = 6 bp), and 56 (n = 6 wild-type; n = 6 bp) after fracture. After 10 (n = 7 wild-type; n = 7 bp contralateral and n = 3 bp fractured tibiae), 14 (n = 6 wild-type; n = 6 bp), 21 (n = 6 wild-type; n = 6 bp), 28 (n = 6 wild-type; n = 3 bp), and 56 (n = 8 wild-type; n = 6 bp) days, the callus cross-sectional area was calculated. We characterized the mechanical integrity of the healing fracture by yield stress and Young's modulus at 28 (n = 6 wild-type; n = 3 bp) and 56 (n = 8 wild-type; n = 6 bp) days postfracture.

RESULTS

The absence of GDF-5 impaired cartilaginous matrix deposition in the callus and reduced callus cross-sectional area. After 56 days, the repaired bp fracture was mechanically comparable to that of controls.

CONCLUSIONS

Although GDF-5 deficiency did not compromise long-term fracture healing, a delay in cartilage formation and remodeling supports roles for GDF-5 in the early phase of bone repair.

CLINICAL RELEVANCE

Local delivery of GDF-5 to clinically difficult fractures may simulate cartilage formation in the callus and support subsequent remodeling.

Divergent activities of osteogenic BMP2, and tenogenic BMP12 and BMP13 independent of receptor binding affinities

Ectopic expression of recombinant human bone morphogenetic protein 2 (rhBMP2) induces osteogenesis, while ectopic expression of rhBMP12 and rhBMP13 induces the formation of tendon-like tissue. Despite their different in vivo activities, all three ligands bound to the type I bone morphogenic protein receptors (BMPRs), activin receptor-like kinase (ALK)-3 and ALK6, and to the type II BMPRs, activin receptor type-2A, activin receptor type-2B, and BMPR2, with similar affinities. Treatment of C3H10T1/2 cells with rhBMP2 activated SMAD signaling and induced expression of osteoblast markers including osteocalcin mRNA (Ocn). In contrast, treatment with rhBMP12 or rhBMP13 resulted in a dose-dependent induction of a tendon-specific gene (Thbs4) expression with no detectable activation of SMAD 1, 5, and 8. Differential regulation of Thbs4 and Ocn has potential utility as an in vitro biomarker for induction of tenogenic signaling. Such an assay also permits the ability to distinguish between the activities of different BMPs and may prove useful in studies on the molecular mechanisms of BMP tenogenic activity.

The effects of growth and differentiation factor 5 on bone marrow stromal cell transplants in an in vitro tendon healing model

The effects of growth differentiation factor-5 (GDF-5) and bone marrow stromal cells (BMSCs) on tendon healing were investigated under in vitro tissue culture conditions. BMSCs and GDF-5 placed in a collagen gel were interpositioned between the cut ends of dog flexor digitorum profundus tendons. The tendons were randomly assigned into four groups: 1) repaired tendon without gel; 2) repaired tendon with BMSC-seeded gel; 3) repaired tendon with GDF-5 gel without cells; and 4) repaired tendon with GDF-5 treated BMSC-seeded gel. At 2 and 4 weeks, the maximal strength of repaired tendons with GDF-5 treated BMSCs-seeded gel was significantly higher than in tendons without gel interposition. However, neither BMSCs nor GDF-5 alone significantly increased the maximal strength of healing tendons at 2 or 4 weeks. These results suggest that the combination of BMSCs and GDF-5 accelerates tendon healing, but either BMSCs or GDF-5 alone are not effective in this model.

Augmentation of zone II flexor tendon repair using growth differentiation factor 5 in a rabbit model

PURPOSE

Modulation of zone II flexor tendon repair healing using growth factors may reduce the incidence of complications, such as rupture and fibrosis. We hypothesized that sutures coated with growth differentiation factor 5 (GDF5) will stimulate the healing of zone II flexor tendon repairs.

METHODS

We created and immediately repaired zone II flexor tendon lacerations in the second and fourth toe of the right forepaw of 44 New Zealand White rabbits. One tendon was repaired with suture coated with GDF5, whereas the other tendon was repaired with suture without GDF5 (control). We randomized the allocation of GDF5 and control suture to either toe. A proximal tenotomy of the flexor digitorum profundus at the level of the wrist was performed to relieve tension on the more distal repairs. Rabbits were euthanized at 21 or 42 days after repair. Four rabbits (8 tendons) underwent histological analysis at each time point; the remaining repairs were tested biomechanically in a blinded fashion.

RESULTS

Control tendons demonstrated distinct borders at the transection site and less endogenous repair at 3 weeks. The Soslowsky histological score for collagen was better in the GDF5 group at both time points (p≤.003). All tendons failed at the repair site. The maximum load was significantly greater (p=.04) in the GDF5 group (11.6 ± 3.5 N) compared with control tendons (8.6 ± 3.0 N) at 3 weeks. The maximum load was not significantly different (p=.12) at 6 weeks. We observed no significant differences in stiffness at either time point (p>.11).

CONCLUSIONS

The results demonstrate that GDF5 has an early beneficial effect on tendon healing in zone II flexor tendon repairs in a rabbit flexor tendon injury model.

Chondrogenic differentiation of mouse bone marrow mesenchymal stem cells induced by cartilage-derived morphogenetic protein-2 in vitro

To study the cartilage differentiation of mouse mesenchymal stem cells (MSCs) induced by cartilage-derived morphogenetic proteins-2 in vitro, the MSCs were isolated from mouse bone marrow and cultured in vitro. The cells in passage 3 were induced into chondrogenic differentiation with different concentrations of recombinant human cartilage-derived morphogenetic proteins-2 (0, 10, 20, 50 and 100 ng/mL). After 14 days of induction, morphology of cells was observed under phase-contrast microscope. Collagen II mRNA and protein were examined with RT-PCR, Western blotting and immunocytochemistry respectively and the sulfate glycosaminoglycan was measured by Alcian blue staining. RT-PCR showed that CDMP-2 could promote expression of collagen II mRNA in an dose-dependant manner, especially at the concentration of 50 ng/mL and 100 ng/mL. Immunocytochemistry and Western blotting revealed a similar change. Alcian blue staining exhibited deposition of typical cartilage extracellular matrix. Our results suggest that mouse bone marrow mesenchymal stem cells can differentiate into chondrogenic phonotype with the induction of CDMP-2 in vitro, which provides a basis for further research on the role of CDMP-2 in chondrogenesis.

Evidence of association between GDF5 polymorphisms and congenital dislocation of the hip in a Caucasian population

OBJECTIVE

Congenital dislocation of the hip (CDH) is a multifactorial disease which involves genetic factors that are still unidentified. Recently, a functional polymorphism (rs143383) of the 5'-untranslated region of GDF5 (Growth/Differentiation Factor 5) - previously reported to be associated with osteoarthritis - has been associated with CDH in a Chinese population. The aim of our study was to determine whether GDF5, known to be involved in bone, joint and cartilage morphogenesis, is also associated with CDH in Caucasians.

DESIGN

We genotyped three tagSNPs (rs224334, rs143384, rs143383) in 239 cases and 239 controls from western Brittany (France) where CDH is frequent, and tested the association using both single-locus and haplotype-based approaches.

RESULTS

The most significant association was observed with rs143384. The T allele of this SNP was overrepresented in cases (65.9% vs 55.9%, P=0.002). Under a recessive model, carriers of the TT genotype had a 1.71-fold higher risk of developing CDH than carriers of the other genotypes (OR(TT vs CT+CC)=1.71, 95% CI: [1.18-2.48], P=0.005). At a nominal level, the association was also significant with rs143383 (OR(TT vs CT+CC)=1.52, 95% CI: [1.05-2.19], P=0.026). The haplotype carrying the susceptibility alleles of these SNPs was also more frequent in cases (65.9% vs 55.9%, OR=1.53, 95% CI: [1.18-1.98], P=0.002).

CONCLUSION

This study reports, for the first time, the association between GDF5 polymorphisms and CDH in Caucasians, and points out another polymorphism of interest that requires further investigation. Reduction in GDF5 expression might lead to developmental deficiency of ligaments and capsule in hip joint, and therefore contribute to CDH pathogenesis.

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.

BMP signaling in vascular development and disease

Genetic and functional studies indicate that common components of the bone morphogenetic protein (BMP) signaling pathway play critical roles in regulating vascular development in the embryo and in promoting vascular homeostasis and disease in the adult. However, discrepancies between in vitro and in vivo findings and distinct functional properties of the BMP signaling pathway in different vascular beds, have led to controversies in the field that have been difficult to reconcile. This review attempts to clarify some of these issues by providing an up to date overview of the biology and genetics of BMP signaling relevant to the intact vasculature.

Effects of cartilage-derived morphogenetic protein-3 on the expression of chondrogenic and osteoblastic markers in the pluripotent mesenchymal C3H10T1/2 cell line

CDMP-3/GDF-7/BMP-12 treatment of pluripotent mesenchymal C3H10T1/2 cells resulted in a dose- and time-dependent change in cell morphology and in the expression of alkaline phosphatase, mRNA expression of osteocalcin, and bone sialoprotein, as well as mineralized bone nodule formation. CDMP-3 also stimulated Alcian Blue staining indicative of extracellular matrix formation without affecting aggrecan expression. CDMP-3 downregulated mRNA expression of BMP-4 and BMP-8A. CDMP-3 stimulated mRNA expression of ALK-1, ALK-2(ActR-IA), ALK-3(BMPR-IA), and ALK-4 without affecting that of ALK-6(BMPR-IB), ALK-7, and BMPR-II. These findings suggest that, under the experimental conditions studied, CDMP-3 induces the pluripotent mesenchymal C3H10T1/2 cells to express both chondrocytic and osteoblastic markers. The results further reveal potential complex interplay between the different bone morphogenetic proteins and their receptors in these processes.

Differential effects of growth differentiation factor-5 on porcine dental papilla- and follicle-derived cells

In this study, the effect of growth differentiation factor-5 (GDF-5) on the growth and differentiation of porcine dental papilla- and follicle-derived cells was investigated. Furthermore, the effect was compared with that of BMP-2. Recombinant mouse GDF-5 (rmGDF-5) enhanced alkaline phosphatase (ALP) activity in dental papilla-derived cells in a dose-dependent manner, while ALP activity in dental follicle-derived cells was reduced. In rmGDF-5 stimulated dental papilla-derived cells, the expressions of odontoblast-marker genes were up-regulated. Conversely, recombinant human BMP-2 (rhBMP-2) enhanced ALP activity dose-dependently in both dental papilla- and follicle-derived cells. When combined, GDF-5 did not further enhance BMP-2-induced ALP activities. Rather, GDF-5 reduced BMP-2-induced ALP activities in both dental papilla- and follicle-derived cells. This suggests that affinity of GDF-5 to the shared receptors may be higher than that of BMP-2 in both cell types. These observations indicate that GDF-5 regulates differentiation of both dental papilla and follicle during odontogenesis, co-operatively with other growth factors such as BMP-2.

Large-scale analysis of association between GDF5 and FRZB variants and osteoarthritis of the hip, knee, and hand

OBJECTIVE

GDF5 and FRZB have been proposed as genetic loci conferring susceptibility to osteoarthritis (OA); however, the results of several studies investigating the association of OA with the rs143383 polymorphism of the GDF5 gene or the rs7775 and rs288326 polymorphisms of the FRZB gene have been conflicting or inconclusive. To examine these associations, we performed a large-scale meta-analysis of individual-level data.

METHODS

Fourteen teams contributed data on polymorphisms and knee, hip, and hand OA. For rs143383, the total number of cases and controls, respectively, was 5,789 and 7,850 for hip OA, 5,085 and 8,135 for knee OA, and 4,040 and 4,792 for hand OA. For rs7775, the respective sample sizes were 4,352 and 10,843 for hip OA, 3,545 and 6,085 for knee OA, and 4,010 and 5,151 for hand OA, and for rs288326, they were 4,346 and 8,034 for hip OA, 3,595 and 6,106 for knee OA, and 3,982 and 5,152 for hand OA. For each individual study, sex-specific odds ratios (ORs) were calculated for each OA phenotype that had been investigated. The ORs for each phenotype were synthesized using both fixed-effects and random-effects models for allele-based effects, and also for haplotype effects for FRZB.

RESULTS

A significant random-effects summary OR for knee OA was demonstrated for rs143383 (1.15 [95% confidence interval 1.09-1.22]) (P=9.4x10(-7)), with no significant between-study heterogeneity. Estimates of effect sizes for hip and hand OA were similar, but a large between-study heterogeneity was observed, and statistical significance was borderline (for OA of the hip [P=0.016]) or absent (for OA of the hand [P=0.19]). Analyses for FRZB polymorphisms and haplotypes did not reveal any statistically significant signals, except for a borderline association of rs288326 with hip OA (P=0.019).

CONCLUSION

Evidence of an association between the GDF5 rs143383 polymorphism and OA is substantially strong, but the genetic effects are consistent across different populations only for knee OA. Findings of this collaborative analysis do not support the notion that FRZB rs7775 or rs288326 has any sizable genetic effect on OA phenotypes.

A novel polymorphism of GDF5 gene and its association with body measurement traits in Bos taurus and Bos indicus breeds

Body measurement traits, influenced by genes and environmental factors, play numerous important roles in the value assessment of productivity and economy. Growth differentiate factor 5 (GDF5), involved in the development and maintenance of bone and cartilage, is an important candidate gene for body measurement traits selection through marker-assisted selection (MAS). In this study, based on the PCR-RFLP technology, we discovered and evaluated the potential association of the single nucleotide polymorphism (SNP) (T586C in exon 1) of the bovine GDF5 gene with body measurement traits in 985 Bos taurus breed, 42 Bos indicus breed and 76 Bos indicus x Bos taurus individuals. As the SNP marker, there were the significant effects on the Body length (BL) in the Bos taurus (BT) and Bos indicus x Bos taurus (BMY) populations (P < 0.05). In BT population, animals with the genotype TT had lower mean values for BL and Hip width (HW) than these with the TC and CC genotype (P < 0.01). In BMY population, animals with the genotype TC had lower mean values for BL than these with the genotype CC (P < 0.05). These results suggest that the SNP of the GDF5 gene could be a very useful genetic marker for body measurement traits in the bovine reproduction and breeding.

New insights into BMP-7 mediated osteoblastic differentiation of primary human mesenchymal stem cells

Bone Morphogenetic Proteins (BMPs) are members of the TGF-beta superfamily of growth factors. Several BMPs exhibit osteoinductive bioactivities, and are critical for bone formation in both developing and mature skeletal systems. BMP-7 (OP-1) is currently used clinically in revision of posterolateral spine fusions and long bone non-unions. The current study characterizes BMP-7 induced gene expression during early osteoblastic differentiation of human mesenchymal stem cells (hMSC). Primary hMSC were treated with BMP-7 for 24 or 120 h and gene expression across the entire human genome was evaluated using Affymetrix HG-U133 Plus 2.0 Arrays. 955 probe sets representing 655 genes and 95 ESTs were identified as differentially expressed and were organized into three major expression profiles (Profiles A, B and C) by hierarchical clustering. Genes from each profile were classified according to biochemical pathway analyses. Profile A, representing genes upregulated by BMP-7, revealed strong enrichment for established osteogenic marker genes, as well as several genes with undefined roles in osteoblast function, including MFI2, HAS3, ADAMTS9, HEY1, DIO2 and FGFR3. A functional screen using siRNA suggested roles for MFI2, HEY1 and DIO2 in osteoblastic differentiation of hMSC. Profile B contained genes transiently downregulated by BMP-7, including numerous genes associated with cell cycle regulation. Follow-up studies confirmed that BMP-7 attenuates cell cycle progression and cell proliferation during early osteoblastic differentiation. Profile C, comprised of genes continuously downregulated by BMP-7, exhibited strong enrichment for genes associated with chemokine/cytokine activity. Inhibitory effects of BMP-7 on cytokine secretion were verified by analysis of enriched culture media. Potent downregulation of CHI3L1, a potential biomarker for numerous joint diseases, was also observed in Profile C. A focused evaluation of BMP, GDF and BMP inhibitor expression elucidated feedback loops modulating BMP-7 bioactivity. BMP-7 was found to induce BMP-2 and downregulate GDF5 expression. Transient knockdown of BMP-2 using siRNA demonstrated that osteoinductive properties associated with BMP-7 are independent of endogenous BMP-2 expression. Noggin was identified as the predominant inhibitor induced by BMP-7 treatment. Overall, this study provides new insight into key bioactivities characterizing early BMP-7 mediated osteoblastic differentiation.

Crystal structure analysis reveals a spring-loaded latch as molecular mechanism for GDF-5-type I receptor specificity

Dysregulation of growth and differentiation factor 5 (GDF-5) signalling, a member of the TGF-beta superfamily, is strongly linked to skeletal malformation. GDF-5-mediated signal transduction involves both BMP type I receptors, BMPR-IA and BMPR-IB. However, mutations in either GDF-5 or BMPR-IB lead to similar phenotypes, indicating that in chondrogenesis GDF-5 signalling seems to be exclusively mediated through BMPR-IB. Here, we present structural insights into the GDF-5:BMPR-IB complex revealing how binding specificity for BMPR-IB is generated on a molecular level. In BMPR-IB, a loop within the ligand-binding epitope functions similar to a latch allowing high-affinity binding of GDF-5. In BMPR-IA, this latch is in a closed conformation leading to steric repulsion. The new structural data now provide also a molecular basis of how phenotypically relevant missense mutations in GDF-5 might impair receptor binding and activation.