Ability Of Bone Morphogenetic Protein Research Articles

Germline/soma distinction in Drosophila embryos requires regulators of zygotic genome activation.

In Drosophila melanogaster embryos, somatic versus germline identity is the first cell fate decision. Zygotic genome activation (ZGA) orchestrates regionalized gene expression, imparting specific identity on somatic cells. ZGA begins with a minor wave that commences at nuclear cycle (NC)8 under the guidance of chromatin accessibility factors (Zelda, CLAMP, GAF), followed by the major wave during NC14. By contrast, primordial germ cell (PGC) specification requires maternally deposited and posteriorly anchored germline determinants. This is accomplished by a centrosome coordinated release and sequestration of germ plasm during the precocious cellularization of PGCs in NC10. Here, we report a novel requirement for Zelda and CLAMP during the establishment of the germline/soma distinction. When their activity is compromised, PGC determinants are not properly sequestered, and specification is disrupted. Conversely, the spreading of PGC determinants from the posterior pole adversely influences transcription in the neighboring somatic nuclei. These reciprocal aberrations can be correlated with defects in centrosome duplication/separation that are known to induce inappropriate transmission of the germ plasm. Interestingly, consistent with the ability of bone morphogenetic protein (BMP) signaling to influence specification of embryonic PGCs, reduction in the transcript levels of a BMP family ligand, decapentaplegic (dpp), is exacerbated at the posterior pole.

Targeting chemoresistant colorectal cancer via systemic administration of a BMP7 variant

Despite intense research and clinical efforts, patients affected by advanced colorectal cancer (CRC) have still a poor prognosis. The discovery of colorectal (CR) cancer stem cell (CSC) as the cell compartment responsible for tumor initiation and propagation may provide new opportunities for the development of new therapeutic strategies. Given the reduced sensitivity of CR-CSCs to chemotherapy and the ability of bone morphogenetic proteins (BMP) to promote colonic stem cell differentiation, we aimed to investigate whether an enhanced variant of BMP7 (BMP7v) could sensitize to chemotherapy-resistant CRC cells and tumors. Thirty-five primary human cultures enriched in CR-CSCs, including four from chemoresistant metastatic lesions, were used for in vitro studies and to generate CR-CSC-based mouse avatars to evaluate tumor growth and progression upon treatment with BMP7v alone or in combination with standard therapy or PI3K inhibitors. BMP7v treatment promotes CR-CSC differentiation and recapitulates the cell differentiation-related gene expression profile by suppressing Wnt pathway activity and reducing mesenchymal traits and survival of CR-CSCs. Moreover, in CR-CSC-based mouse avatars, BMP7v exerts an antiangiogenic effect and sensitizes tumor cells to standard chemotherapy regardless of the mutational, MSI, and CMS profiles. Of note, tumor harboring PIK3CA mutations were affected to a lower extent by the combination of BMP7v and chemotherapy. However, the addition of a PI3K inhibitor to the BMP7v-based combination potentiates PIK3CA-mutant tumor drug response and reduces the metastatic lesion size. These data suggest that BMP7v treatment may represent a useful antiangiogenic and prodifferentiation agent, which renders CSCs sensitive to both standard and targeted therapies.

Repair of large segmental bone defects in rabbits using BMP and FGF composite xenogeneic bone.

The objective of this study was to determine the ability of bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) to repair large segmental radial bone defects in rabbits. We treated calf cancellous bones with 3 mg/L BMP (Group A), 5 μg/L FGF (Group B), or 3 mg/L BMP plus 5 μg/L FGF (Group C). A bone damage model was established using healthy radii from rabbits. The complexes were implanted in the areas of the bone defects in the radii. After successful transplantation, the rabbits underwent radiographic imaging, and bone graft specimens were detected by histopathology methods. Biomechanical indexes were also assessed in order to observe the healing status of the bone defects. Our results indicated that the repair of bone defects was significantly better in Group C compared to the other 2 groups. Therefore, we concluded that combining BMP and FGF significantly promoted bone defect repair and achieved effects that were superior to the use of BMP alone.

Long-Term Effects of Bone Morphogenetic Protein- Based Treatments in Humans

Bone morphogenetic proteins (BMPs) are low-molecular-weight proteins of the transforming growth factor-beta (TGF-β) superfamily. In recent years, these growth and differentiation factors have been extensively researched for their multifunctional properties ranging from embryonic development to postnatal homeostasis. The defining ability of BMPs is the role they play in skeletal development and maintenance, especially the powerful osteoinductive activity for which these proteins are currently sought after. There are over 20 BMPs that have been discovered, with BMP-2 and BMP-7 currently being the only proteins of the group that are approved by the US Food and Drug Administration for clinical use as an autograft substitute for lumbar spinal interbody fusion procedures and for open tibial fractures with intramedullary nail fixation. BMP-2 has also been approved for use in dental bone grafting indications. However, a significant amount of off-label usage of these proteins has been reported, which has led to an industry approaching a billion dollars annually. In this review, we examine the long-term effects of BMPs as evidenced from in vitro, preclinical, and clinical studies.

Recombinant human bone morphogenetic protein‐7 enhances fracture healing in an ischemic environment

Ischemia predisposes orthopedic trauma patients to delayed fracture healing or nonunion. The goal of this study was to test the ability of bone morphogenetic protein 7 (BMP7) to stimulate fracture repair in an ischemic environment. Ischemic fractures were generated in male adult mice by resecting the femoral artery prior to the creation of a nonstabilized tibia fracture. Recombinant human BMP7 (rhBMP7, 50 microg) was injected into the fracture site immediately after surgery. At 7 days after injury, more tissue vascularization was observed in rhBMP7 treated fractures. Histomorphometric analyses revealed that rhBMP7 induced more cartilage at day 7, more callus and bone at days 14 and 28, and more adipose tissue and fibrous tissue at days 7, 14, and 28 compared to controls (n=5/group/time). At day 28, all fractures treated with rhBMP7 (50 microg, n=5) healed, whereas only three of five control fractures exhibited slight bony bridging. In addition, we found that rhBMP7 (both 10 and 50 microg) significantly increased the amount of cartilage compared to controls in stabilized fractures, confirming its chondrogenic effect. Lastly, using bone marrow transplantation, we determined that no donor-derived osteocytes or chondrocytes were present in rhBMP7-treated fractures, suggesting rhBMP7 did not recruit mesenchymal stem cells from the bone marrow to the fracture site. In conclusion, our results indicate that rhBMP7 is a promising treatment for fractures with severely disrupted blood supply.

Bone morphogenetic protein‐2 enhances Wnt/β‐catenin signaling‐induced osteoprotegerin expression

Wnt/beta-catenin signaling plays an important role in the developing skeletal system. Our previous studies demonstrated that Wnt/beta-catenin signaling inhibits the ability of bone morphogenetic protein (BMP)-2 to suppress myotube formation in the multipotent mesenchymal cell line C2C12 and that this inhibition is mediated by Id1. In this study, we examined the role of intracellular signaling by Wnt/beta-catenin and BMP-2 in regulating the expression of osteoprotegerin (OPG) and of the receptor activator of NFkappaB ligand (RANKL). OPG expression was induced by Wnt/beta-catenin signaling in C2C12 cells and osteoblastic MC3T3-E1 cells. Silencing of glycogen synthase kinase-3beta also increased OPG expression. In contrast, R expression was suppressed by Wnt/beta-catenin signaling. In a transfection assay, beta-catenin induced the activity of a reporter gene, a 1.5 kb fragment of the 5'-flanking region of the OPG gene. Deletion and mutation analysis revealed that Wnt/beta-catenin signaling regulates transcription of OPG via a promoter region containing two Wnt/beta-catenin responsive sites. BMP-2 enhanced Wnt/beta-catenin-dependent transcriptional activation of the OPG promoter. In response to BMP-2 stimulation, Smad 1 and 4 interacted with Wnt/beta-catenin responsive sites. These results show that the regulation of OPG expression is mediated through two transcription pathways that involve the OPG promoter.

NDST-1 modulates BMPR and PTHrP signaling during endochondral bone formation in a gene knockout model

GlcNAc N-deacetylase/ N-sulfotransferase-1 (NDST-1), a member of the enzyme family catalyzing the first modification step in the biosynthesis of heparan sulfate (HS), was knocked out in mice to investigate its role in embryonic development. NDST-1 null mice exhibited delayed endochondral bone formation including shortened calcified zones in limbs, delayed chondrocyte and osteogenetic differentiation, and increased chondrocyte proliferation. In situ HS binding assay revealed that the binding ability of bone morphogenetic protein (BMP) -2, -4, and -6 to endogenous HS was decreased in mutant phalanges, while that of fibroblast growth factor-1 (FGF-1) was not affected. Up-regulation of BMPR-IA, Phospho-Smad1 (P-Smad1) and parathyroid-hormone related protein (PTHrP), but not the Indian hedgehog, Gli1, Gli3, Patched, and FGFR-3, was observed. Furthermore, block of BMPR signaling with noggin rescued the delayed chondrocyte hypertrophic differentiation in NDST-1 (−/−) mice and recovered the expression of both P-Smad1 and PTHrP proteins. These results suggested that NDST-1-dependent heparan sulfate might negatively modulate BMP and its downstream PTHrP signaling, and thus affect endochondral bone development.

The role of bone morphogenetic proteins in articular cartilage development, homeostasis and repair

Bone morphogenetic proteins (BMPs) are members of the TGF-beta superfamily of secreted ligands. BMPs regulate a diverse range of developmental processes during embryogenesis and postnatal development, and control the differentiation of several musculoskeletal tissues including bone, cartilage, tendon and ligaments. The ability of BMPs to modulate the phenotype of cells in these tissue lineages suggests that these factors could be valuable for musculoskeletal tissue regeneration. In fact, BMPs-2 and -7 are already in clinical use for bone regeneration. This review addresses the signaling mechanisms by which BMPs regulate cellular processes, the role of BMPs in articular cartilage development and joint formation, and the data that supports the use of BMPs for in vitro phenotypic support of articular chondrocyte cultures, chondrogenic differentiation of mesenchymal stem cells (MSCs) and articular cartilage repair. Given the documented importance of BMP activity for normal joint formation, articular cartilage development and maintenance, the chondrogenic activity of BMPs when applied to MSC cultures and the encouraging outcomes of several in vivo cartilage repair studies, BMP therapies hold considerable promise for effective cartilage repair and/or regeneration. Future advances in the control of BMP elution from biocompatible matrices and prolonged, dose-controlled BMP expression by genetically engineered cells should substantially improve cartilage repair strategies using BMPs and similar chondro-protective proteins.

Bmpr1a and Bmpr1b have overlapping functions and are essential for chondrogenesis in vivo.

Previous studies have demonstrated the ability of bone morphogenetic proteins (BMPs) to promote chondrogenic differentiation in vitro. However, the in vivo role of BMP signaling during chondrogenesis has been unclear. We report here that BMP signaling is essential for multiple aspects of early chondrogenesis. Whereas mice deficient in type 1 receptors Bmpr1a or Bmpr1b in cartilage are able to form intact cartilaginous elements, double mutants develop a severe generalized chondrodysplasia. The majority of skeletal elements that form through endochondral ossification are absent, and the ones that form are rudimentary. The few cartilage condensations that form in double mutants are delayed in the prechondrocytic state and never form an organized growth plate. The reduced size of mutant condensations results from increased apoptosis and decreased proliferation. Moreover, the expression of cartilage-specific extracellular matrix proteins is severely reduced in mutant elements. We demonstrate that this defect in chondrocytic differentiation can be attributed to lack of Sox9, L-Sox5, and Sox6 expression in precartilaginous condensations in double mutants. In summary, our study demonstrates that BMPR1A and BMPR1B are functionally redundant during early chondrogenesis and that BMP signaling is required for chondrocyte proliferation, survival, and differentiation in vivo.

A 2-year follow-up pilot study evaluating the safety and efficacy of op-1 putty (rhbmp-7) as an adjunct to iliac crest autograft in posterolateral lumbar fusions

The ability of bone morphogenetic proteins (BMPs) to induce bone formation has led to a multitude of investigations into their use as bone graft substitutes in spinal surgery. The purpose of this multi-center clinical pilot study was to evaluate the safety and efficacy of BMP-7 (osteogenic protein 1, OP-1), in the form of a putty, combined with autograft for intertransverse process fusion of the lumbar spine in patients with symptomatic spinal stenosis and degenerative spondylolisthesis following spinal decompression. Twelve patients with spinal stenosis and degenerative lumbar spondylolisthesis underwent a laminectomy and partial or complete medial facetectomy as required for decompression of the neural elements, followed by an intertransverse process fusion by placing iliac crest autograft and OP-1 putty between the decorticated transverse processes. No instrumentation was used. Patients were followed clinically using the Oswestry scale and SF-36 outcome forms, and radiographically using static and dynamic radiographs to assess their fusion status over a 2-year period. Independent and blinded radiologists assessed the films for the presence of bridging bone between the transverse processes and measured translation and angulation on dynamic films using digital calipers. Radiographic outcome was compared to a historical control (autograft alone fusion without instrumentation for the treatment of degenerative spondylolisthesis). All adverse events were recorded prospectively. The results showed eight of the nine evaluable patients (89%) obtained at least a 20% improvement in their preoperative Oswestry score, while five of ten patients (50%) with radiographic follow-up achieved a solid fusion by the criteria used in this study. Bridging bone on the anteroposterior film was observed in seven of the ten patients (70%). No systemic toxicity, ectopic bone formation, recurrent stenosis or other adverse events related to the OP-1 putty implant were observed. A successful fusion was observed in slightly over half the patients in this study, using stringent criteria without adjunctive spinal instrumentation. This study did not demonstrate the statistical superiority of OP-1 combined with autograft over an autograft alone historical control, in which the fusion rate was 45%. There were no adverse events related to the OP-1 putty implant in this study, which supports findings in other studies suggesting the safety of bone morphogenetic proteins in spinal surgery.

Multiple functions of BMPs in chondrogenesis.

The ability of bone morphogenetic proteins (BMPs) to promote chondrogenesis has been investigated extensively over the past two decades. Although BMPs promote almost every aspect of chondrogenesis, from commitment to terminal differentiation is well known, the mechanisms of BMP action in discrete aspects of endochondral bone formation have only recently begun to be investigated. In this review, we focus on in vivo studies that have identified interactions between BMP signaling pathways and key downstream targets of BMP action in chondrogenesis. We also discuss evidence regarding the potential roles of BMP receptors in mediating distinct aspects of chondrogenesis, and studies investigating the intersection of BMP pathways with other pathways known to coordinate the progression of chondrocytes through the growth plate. These studies indicate that both Smad-dependent and -independent BMP pathways are required for chondrogenesis, and that BMPs exert essential roles via regulation of the Indian hedgehog (IHH)/parathyroid hormone-related protein (PTHrP) and fibroblast growth factor (FGF) pathways in the growth plate.

Bone morphogenetic protein 2 induces dental follicle cells to differentiate toward a cementoblast/osteoblast phenotype.

When triggered appropriately, dental follicle cells are considered to be able to differentiate toward a cementoblast/osteoblast phenotype. However, factors and mechanisms regulating follicle cell differentiation remain undefined. This study focused on determining the ability of bone morphogenetic protein (BMP) 2 to promote the differentiation of follicle cells and periodontal ligament (PDL) cells along a cementoblast/ osteoblast pathway. Follicle cells and PDL cells were isolated from the first molar region of CD-1 mice and immortalized with SV40. Both cell types expressed BMP-4 and BMP receptors (BMPR) IA and II, but only follicle cells expressed BMP-2 mRNA. Cells were exposed to recombinant human BMP (rhBMP)-2 (0-100 ng/ml) and Northern blots were used to determine the expression of mineral-associated markers. BMP-2, in a dose- and time-dependent manner, induced cementoblast/osteoblast differentiation of follicle cells, as reflected by enhanced core binding factor alpha (Cbfal), bone sialoprotein (BSP), and osteocalcin (OCN) mRNA expression and enhanced mineral formation. U0126, a specific inhibitor of MEK-1/2 members of the MAPK family, abolished BMP-2-mediated expression of BSP and OCN. In contrast, exposure of PDL cells to BMP-2 resulted in modest expression of OCN and minimal promotion of mineralization. These results suggest that BMP-2 triggers follicle cells to differentiate toward a cementoblast/osteoblast phenotype and that the MAPK pathway is involved.

Antagonistic drivers share BuMPy pathway

Seemingly confounding and contradictory, the ability of bone morphogenetic proteins (BMPs) to promote both proliferation and terminal differentiation (and even apoptosis!) of neuronal stem cells—to both expand and limit precursor cell numbers—now makes perfectly good sense. At least it does in light of the conclusions drawn by Ronald McKay, David Panchision, and colleagues (National Institutes of Health, Bethesda, MD), who postulate a mechanism by which BMP ligands control both the production and fate of neural precursor cells. Figure Too much BMPR-IB (right) causes widespread cell death. Panchision attributes this “dynamic process” to the sequential and linked expression and function of two BMP receptors, BMPR-IA and BMPR-IB. In this model, “the BMP-mediated induction of receptor IB accounts for features of stem cell proliferation, identity, differentiation, and death,” says McKay. Expression of mutant BMP receptors in CNS stem cells in vitro and in transgenic mice led to the startling discovery of a “feed-forward” mechanism. Activation of the BMPR-IA receptor early in development promotes proliferation of neural precursor cells and determines their dorsal identity. But BMPR-IA also induces the expression of Bmpr-1b. BMPR-IB activation then mediates mitotic arrest, resulting in either apoptosis (early in development, perhaps to control cell numbers) or terminal differentiation (later in development, for those cells that are left). Additional competence signals must be required to interpret the BMPR-IB signal into an apopototic or differentiation response. An induction–termination sequence could, suggests Panchision, be a general property of signaling in stem cells. It is unclear whether this self-limiting sequential mechanism, which dead-ends at terminal differentiation or cell death, could be reactivated on demand to regenerate tissues, say during wound healing or limb amputation. McKay envisions using knowledge of the linked receptor model to control stem cell proliferation and differentiation, with an eye toward potential applications in cell therapy and cancer therapeutics. ▪ Reference: Panchision, D.M., et al. 2001. Genes Dev. 15:2094–2110. [PubMed]

Biological mediators for periodontal regeneration.

A review of the literature on the use of growth-regulatory molecules in the oral cavity permits a model in which to consider approaches to oral tissue engineering. These concepts apply to periodontal regeneration and to regeneration of alveolar bone. In either case, the formation of tissues is complex but proceeds in a deliberate and orderly sequence. In these sequence of events resulting in either bone or cementum formation, periodontal ligament and bone can be stimulated at various points. Different signals can apparently be used to stimulate tissue formation including mitogenic signals and differentiation factors. Additionally, both hard and soft tissue stimulatory molecules appear to be permissive. Classic receptor-mediated peptides or extracellular matrix molecules for soft and hard tissues appear to allow stimulation of tissue formation cascades. Importantly, it also appears that the stimulatory event is transitory (that is, short-lived) and leads itself to a sequence of cellular events. These cellular events in turn stimulate a number of subsequent events (such as chemotaxis, proliferation, differentiation or angiogenesis), which lead to further progression of tissue formation. While a solid scientific rationale exists for the use of a variety of growth and attachment factors in regeneration of oral tissues, only a small number are being pursued clinically. Many therapeutic regimens have failed in preclinical testing or have resulted in limited regenerative capacity. The mitogenic polypeptides that stimulate soft tissue growth (such as platelet-derived growth factor) and both hard and soft tissue growth (such as transforming growth factor-beta) appear to have not led to successful enough outcomes to facilitate further work towards regulatory approval. The demonstrated ability of bone morphogenetic proteins to generate substantial quantities of bone suggest many applications in the oral cavity where this is the only tissue desired. Another therapeutic candidate is enamel matrix derivative, a set of matrix proteins. Enamel matrix derivative appears to stimulate first acellular cementum formation, which may allow for functional periodontal ligament formation. It will be of interest in the future to determine whether the protein matrix contains classic mitogenic or differentiation factors as well as the amelogenins. It is also evident that the bone morphogenetic proteins permit periodontal ligament formation. The conditions for stimulating predictable periodontal ligament tissues with bone morphogenetic proteins however are not known. It is clear that the bone morphogenetic proteins are excellent molecules for stimulating oral bone formation. The results of all these studies will determine the future therapeutic potential for these growth molecules such that they may be used to optimally stimulate and direct specific points along tissue formation cascades.