Pathway and network analysis of genes related to osteoporosis.

As a common degenerative disease, osteoporosis (OS) is characterized by reduced bone mass and microarchitectural deterioration of bone tissue. Both genetic and environmental factors are involved in OS development. To date, ~300 genes have been confirmed to be involved in the pathogenesis of OS, a large majority of which have been independently investigated. As OS is a polygenetic disease, a comprehensive analysis focusing on the biological functions and interactions of OS­related genes would provide valuable information. In this study, OS related research deposited in PubMed was retrieved and genes related to OS were catalogued. Pathways with an enriched biological function for these genes were extracted, and the crosstalk between the enriched pathways was analyzed. A comprehensive network was constructed, and a minimal network was extracted using the Steiner minimal network algorithm. In this study, a total of 294 genes in were retrieved from PubMed. Biological processes found to be enriched included those related to bone metabolism and the immune system. In total, 58 pathways were enriched. Furthermore, the comprehensive network consisting of 3,943 nodes and 7,976 edges was constructed, among which 631 nodes and 2,581 edges contributed to the OS­specific molecular network. In this network, in excess of 300 potential genes associated with OS and two modules were identified. Thus, this study provides a mechanistic insight into OS and suggests more than 300 potential OS­related genes for future research.

The expression and crucial roles of BMP signaling in development of smooth muscle progenitor cells in the mouse embryonic gut.

Bone morphogenetic protein (BMP) signaling is essential for normal development of the gastrointestinal (GI) tract. BMPs also play multiple roles in vascular smooth muscle cells; however, the BMP signaling in the development of the GI musculature remains to be clarified. We investigated the expression of BMPs and their receptors in mouse embryonic GI tracts by immunohistochemistry and in situ hybridization. We demonstrated that BMP2, BMP receptor Ib and BMP receptor II were expressed in the smooth muscle progenitors from E12 to E13 for the first time. BMP signaling on smooth muscle differentiation was examined by implantation of agarose beads soaked with BMPs in the in vitro developmental model that is gut-like structures from mouse embryonic stem (ES) cells. BMP2 rather than BMP4 beads enhanced smooth muscle differentiation, and increased gut-like structures showing spontaneous contractions and expressing intensive alpha-smooth muscle actin immunoreactivity. This increase was confirmed by up-regulation of SM22 mRNA shown by real-time PCR. By addition of noggin beads or noggin to the medium at BMP2 bead implantation, the ratio of contractive gut-like structures decreased. Implantation of BMP2 beads at EB7 (EB--embryoid bodies) (corresponding to E12 or E13 of mouse embryo) showed the highest effects and up-regulation of transcription factors msx-1 after 24h. This increase was blocked by noggin, and msx-1 decreased to almost the control level after 60 h. BMP2 beads at EB7 increased platelet-derived growth factor-A (PDGF-A) in the differentiating smooth muscle cells. We have recently reported that PDGF-A is expressed in the developing inner circular smooth muscle and is crucial for the longitudinal smooth muscle differentiation. Taken together, BMP signaling was expressed for a short window in the smooth muscle progenitors and the signal, especially BMP2, plays an essential role in smooth muscle differentiation in cooperation with PDGF signaling.

Expression patterns of engrailed and dpp in the gastropod Lymnaea stagnalis.

We isolated the full-length cDNAs of engrailed and dpp-BMP2/4 orthologues from the pond snail Lymnaea stagnalis and examined their expression patterns during development by the whole mount in situ hybridization. At the gastrula and trochophore stages, engrailed is expressed in the peripheral ectoderm of the presumptive and invaginating shell gland, corroborating its role in the shell formation that is widely conserved among molluscs. At the same stages, dpp-BMP2/4 is expressed in the right-hand side ectoderm of the shell gland and in the invaginating stomodaeum. Unlike in the gastropod Patella vulgata, our results suggested that dpp-BMP2/4 has a role in the shell formation, rather than in the regional specification and that it could be involved in the specification pathway of the left-right asymmetry of the developing shell in L. stagnalis.

Bone morphogenetic proteins in tissue engineering: the road from the laboratory to the clinic, part I (basic concepts).

Discovered in 1965, bone morphogenetic proteins (BMPs) are a group of cytokines from the transforming growth factor-beta (TGFbeta) superfamily with significant roles in bone and cartilage formation. BMPs are used as powerful osteoinductive components of diverse tissue-engineering products for the healing of bone. Several BMPs with different physiological roles have been identified in humans. The purpose of this review is to cover the biological function of the main members of BMP family, the latest research on BMPs signalling pathways and advances in the production of recombinant BMPs for tissue engineering purposes.

Modulation of bone morphogenetic protein signaling in vivo regulates systemic iron balance.

Systemic iron balance is regulated by hepcidin, a peptide hormone secreted by the liver. By decreasing cell surface expression of the iron exporter ferroportin, hepcidin decreases iron absorption from the intestine and iron release from reticuloendothelial stores. Hepcidin excess has been implicated in the pathogenesis of anemia of chronic disease, while hepcidin deficiency has a key role in the pathogenesis of the iron overload disorder hemochromatosis. We have recently shown that hemojuvelin is a coreceptor for bone morphogenetic protein (BMP) signaling and that BMP signaling positively regulates hepcidin expression in liver cells in vitro. Here we show that BMP-2 administration increases hepcidin expression and decreases serum iron levels in vivo. We also show that soluble hemojuvelin (HJV.Fc) selectively inhibits BMP induction of hepcidin expression in vitro and that administration of HJV.Fc decreases hepcidin expression, increases ferroportin expression, mobilizes splenic iron stores, and increases serum iron levels in vivo. These data support a role for modulators of the BMP signaling pathway in treating diseases of iron overload and anemia of chronic disease.

[Bone morphogenetic proteins in the skeletal system]. / Bone Morphogenetic Proteins im Skelettsystem -- eine zusammenfassende Darstellung.

Bone morphogenetic proteins (BMPs) belong to the transforming growth factor-beta superfamily. Their potential for organ and tissue regeneration and repair has been intensively investigated in recent years. Studies on fetal development have demonstrated the important role of these proteins for the development and differentiation of different organs. Miss-expression or mutation of BMPs may lead to severe abnormalities or even abortion. However, a regenerative potential has also been recognized for the adult organism. BMPs support fracture healing and may contribute to treatment of joint diseases. Thus, BMP-7 is one of the first BMPs approved for clinical application in non-unions of bone fractures resistant to conventional therapy. In degenerative and inflammatory joint diseases, experimental data suggest a decrease of BMP expression in cartilage tissue. Therefore, BMPs could be promising therapeutic candidates in these diseases, although more detailed analyses are necessary. In this review we will focus on bone morphogenetic proteins and discuss present and putative future clinical applications.

BMP antagonists: their roles in development and involvement in pathophysiology.

Bone morphogenetic proteins (BMPs) are phylogenetically conserved signaling molecules that belong to the transforming growth factor (TGF)-beta superfamily, and are involved in the cascades of body patterning and morphogenesis. The activities of BMPs are precisely regulated by certain classes of molecules that are recently recognized as BMP antagonists. BMP antagonists function through direct association with BMPs, thus prohibiting BMPs from binding their cognate receptors. In this review, the classification and functions of BMP antagonists will be discussed, especially focusing on the new family of tissue-specific BMP antagonists composed of uterine sensitization-associated gene 1 (USAG-1) and sclerostin.

[Use of growth factors in the repair of bone]. / Utilisation de facteurs de croissance pour la réparation osseuse.

Osteoformation is induced by numerous growth factors that play an important role in bone repair such as fracture healing. They may serve as therapeutic agent in the treatment of squeletal injuries in the orthopeadic and maxillo-facial fields. Among these proteins, Bone Morphogenetic Proteins (BMP) are the only known osteoinductive growth factors. Unfortunately, they are highly susceptible to proteolysis in vivo and require a suitable delivery system to potentiate their biological activity in a local, controlled and durable manner. In this aim, three options are under investigations: (i) osteoinductive materials made of appropriate carrier to release the protein in situ, (ii) in vivo gene therapy in which the gene is directly transfected in cells of the patient or (iii) ex vivo gene therapy in which cells are harvested from the patient, transfected with DNA in culture and then implanted in the defect. These different kinds of BMP delivery will be discussed.

Bone morphogenetic protein-3 family members and their biological functions.

Bone morphogenetic protein-3 and 3b (BMP-3 and BMP-3b) together represent a unique subgroup of the BMP family. BMP-3b shares 82% amino acid identity with BMP-3 in the mature region (ligand domain), but only 37% in the pro-region (pro-domain). In osteoblasts, BMP-3 and 3b have similar antagonistic activity against BMP-2, but they are differentially regulated. In developing embryos, BMP-3 and 3b have different dorsalizing activities. BMP-3b triggers secondary head formation in an autonomous manner, whereas BMP-3 induces aberrant tail formation. Loss-of-function analysis demonstrates that coordinated activity of xBMP-3b and cerberus, a head inducer, are required for head formation in Xenopus embryos. At the molecular level, BMP-3b antagonizes both nodal-like proteins (Xnr1 and derriere) and ventralizing BMPs (BMP-2 and ADMP), whereas BMP-3 only antagonizes ventralizing BMPs. Moreover, BMP-3b, but not BMP-3, associates with the monomeric form of Xnr1, a nodal-like protein. These molecular features of BMP-3 and 3b are due to their distinct pro-regions. These findings suggest that the processing of precursor regions and assembly of BMP-3 and 3b are important in various developmental processes and organogenesis.

Molecular pathways needed for regeneration of spinal cord and muscle in a vertebrate.

The tail of the frog tadpole, comprising spinal cord, muscle, and notochord, regenerates following partial amputation. We show that, in Xenopus, this occurs throughout development, except for a "refractory period" between stages 45 and 47, when tails heal over without regeneration. Regeneration can be enabled during this refractory period by activation of either the BMP or Notch signaling pathways. Conversely, regeneration can be prevented during the later, regenerative, stages by inhibition of either pathway. BMP signaling will cause regeneration of all tissues, whereas Notch signaling activates regeneration of spinal cord and notochord, but not muscle. An activated form of Msx1 can promote regeneration in the same way as BMP signaling. Epistasis experiments suggest that BMP signaling is upstream of Notch signaling but exerts an independent effect on muscle regeneration. The results demonstrate that regenerative capability can be enabled by genetic modifications that reactivate specific components of the developmental program.

Osteogenic activity of the fourteen types of human bone morphogenetic proteins (BMPs).

BACKGROUND: Bone morphogenic proteins (BMPs) are known to promote osteogenesis, and clinical trials are currently underway to evaluate the ability of certain BMPs to promote fracture-healing and spinal fusion. The optimal BMPs to be used in different clinical applications have not been elucidated, and a comprehensive evaluation of the relative osteogenic activity of different BMPs is lacking. METHODS: To identify the BMPs that may possess the most osteoinductive activity, we analyzed the osteogenic activity of BMPs in mesenchymal progenitor and osteoblastic cells. Recombinant adenoviruses expressing fourteen human BMPs (BMP-2 to BMP-15) were constructed to infect pluripotent mesenchymal progenitor C3H10T1/2 cells, preosteoblastic C2C12 cells, and osteoblastic TE-85 cells. Osteogenic activity was determined by measuring the induction of alkaline phosphatase, osteocalcin, and matrix mineralization upon BMP stimulation. RESULTS: BMP-2, 6, and 9 significantly induced alkaline phosphatase activity in pluripotential C3H10T1/2 cells, while BMP-2, 4, 6, 7, and 9 significantly induced alkaline phosphatase activity in preosteoblastic C2C12 cells. In TE-85 osteoblastic cells, most BMPs (except BMP-3 and 12) were able to induce alkaline phosphatase activity. The results of alkaline phosphatase histochemical staining assays were consistent with those of alkaline phosphatase colorimetric assays. Furthermore, BMP-2, 6, and 9 (as well as BMP-4 and, to a lesser extent, BMP-7) significantly induced osteocalcin expression in C3H10T1/2 cells. In C2C12 cells, osteocalcin expression was strongly induced by BMP-2, 4, 6, 7, and 9. Mineralized nodules were readily detected in C3H10T1/2 cells infected with BMP-2, 6, and 9 (and, to a lesser extent, those infected with BMP-4 and 7). CONCLUSIONS: A comprehensive analysis of the osteogenic activity of fourteen types of BMPs in osteoblastic progenitor cells was conducted. Our results suggest an osteogenic hierarchical model in which BMP-2, 6, and 9 may play an important role in inducing osteoblast differentiation of mesenchymal stem cells. In contrast, most BMPs are able to stimulate osteogenesis in mature osteoblasts.

Consequences of knocking out BMP signaling in the mouse.

During the past two decades, a significant amount of data has been accumulated revealing the intriguing functions of bone morphogenetic proteins (BMPs) in all aspects of embryonic development and organogenesis. Numerous genes encoding BMPs, BMP receptors, and their downstream signal transducers have been mutated in the mouse through targeted mutagenesis. This review focuses on what is known about the role of BMP signaling in gastrulation, mesoderm formation, left-right asymmetry, neural patterning, skeletal and limb development, organogenesis, and gametogenesis as revealed by BMP-signaling mutants.

Recent outcomes and perspectives of the application of bone morphogenetic proteins in implant dentistry.

BACKGROUND: Since the discovery of bone morphogenetic proteins (BMPs), the number of related studies has increased substantially, and more recent outcomes have cast encouraging perspectives on their use in reconstructive surgery. PURPOSE: The aim of the present review was to summarize the present knowledge about the use of BMPs in conjunction with dental implants based on the literature. MATERIALS AND METHODS: Scientific articles dealing with the use of growth factors and bone healing with or without dental implants were searched for on MEDLINE and critically scrutinized. RESULTS: Thirty-nine scientific reports formed the base for the present review. Whereas the osteoinductive capability of BMPs is well documented, studies on their effects in implant dentistry are still incipient. Preclinical and clinical studies did not show outstandingly good outcomes of the application of BMPs compared with conventional treatments or controls. CONCLUSIONS: The number of studies in the field of dental implantology in which BMPs have been used is still too small for establishing clinical protocols of their use in order to improve a recipient bone bed prior to implant placement or to enhance the integration process of an implant.

Bone morphogenetic proteins: basic concepts.

The cellular and molecular events governing bone formation in the embryo, healing of a fractured bone, and induced bone fusion follow a similar pattern. Discovery, purification, and recombinant synthesis of bone morphogenetic proteins (BMPs) constitute a major milestone in the understanding of bone physiology. In this review the author discusses the mechanism of action, clinical applications, dosage, and optimum carriers for BMPs. The roles played by other growth factors are also discussed.

Therapeutic potential of bone morphogenetic proteins.

Recently, there has been substantial progress in the area of bone morphogenetic protein (BMP) research. This review serves as an up-to-date summary of the history of BMPs, the mechanisms of BMP signalling and the role of BMPs in adipose, kidney, liver, bone and nervous system. The potential of BMPs as therapeutic agents will also be discussed.

Proteínas morfogénicas / Morphogenic proteins

A partir del descubrimiento de las proteínas morfogénicas y sus propiedades inductivas en la formación de hueso, se han efectuado numerosas investigaciones que han permitido conocer toda una serie de funciones y propiedades de estas sustancias. Las posibilidades de aplicación de este conocimiento son innumerables en las diversas áreas de la odontología y la medicina. En este trabajo se hace una revisión de las proteínas morfogenéticas que comprende su descubrimiento, aislamiento, clasificación y los efectos inductivos en varios tejidos.

Bone morphogenetic proteins: an update on basic biology and clinical relevance.

The regeneration of bone is a remarkable, complex physiological process, and BMPs are a formidable clinical tool to promote its regeneration. By defining roles played by BMPs in developmental biology and bone regeneration, significant progress has been made to identify cell-signaling molecules and their regulators. For example, the regulators of BMPs that include noggin, chordin, cerberus, dan, and gremlin may be harnessed as therapies to offset calcification encountered after total hip arthroplasties. Furthermore, exploiting BMPs and Smads may generate new therapeutic options for bone repair. Another compelling clinical consideration is the trans-acting factor osteoblast-specific factor-2, which can promote osteoblast differentiation. Moreover, the affiliation of osteoblast-specific factor-2 with heritable disorders merits exploration. A recognized daunting challenge includes a carrier/delivery system for the powerful morphogenetic therapeutic tools, as well as osteoprogenitor cells and intracellular transduction and transcriptional factors. In addition, the long-term effects of administering superphysiological doses of rhBMPs to patients must be assessed systematically. A new generation carrier/delivery system may be the answer to offset dosing liabilities as well as to provide residence for exogenous, BMP-receptive osteoprogenitor cells (111,112). The areas highlighted in this review offer fertile territory for thought and research to develop rational clinical treatments to promote bone regeneration and to understand some of the biological roles of BMPs.

Crystal structure of human bone morphogenetic protein-2 at 2.7 A resolution.

Homodimeric bone morphogenetic protein-2 (BMP-2) is a member of the transforming growth factor beta (TGF-beta) superfamily that induces bone formation and regeneration, and determines important steps during early stages of embryonic development in vertebrates and non-vertebrates. BMP-2 can interact with two types of receptor chains, as well as with proteins of the extracellular matrix and several regulatory proteins. We report here the crystal structure of human BMP-2 determined by molecular replacement and refined to an R-value of 24.2 % at 2.7 A resolution. A common scaffold of BMP-2, BMP-7 and the TGF-betas, i.e. the cystine-knot motif and two finger-like double-stranded beta-sheets, can be superimposed with r. m.s. deviations of around 1 A. In contrast to the TGF-betas, the structure of BMP-2 shows differences in the flexibility of the N terminus and the orientation of the central alpha-helix as well as two external loops at the fingertips with respect to the scaffold. This is also known from the BMP-7 model. Small secondary structure elements in the loop regions of BMP-2 and BMP-7 seem to be specific for the respective BMP-subgroup. Two identical helix-finger clefts and two distinct cavities located around the central 2-fold axis of the dimer show characteristic shapes, polarity and surface charges. The possible function of these specific features in the interaction of BMP-2 with its binding partners is discussed.