Synergistic effects of different bone morphogenetic protein type I receptors on alkaline phosphatase induction

The extracts of osteoblast developed from adipose-derived stem cell and its role in osteogenesis

Cell-based therapy has become an achievable choice in regenerative medicines, particularly for musculoskeletal disorders. Adipose-derived stem cells (ASCs) are an outstanding resource because of their ability and functions. Nevertheless, the use of cells for treatment comes with difficulties in operation and safety. The immunological barrier is also a major limitation of cell therapy, which can lead to unexpected results. Cell-derived products, such as cell extracts, have gained a lot of attention to overcome these limitations. The goal of this study was to optimize the production of ASC-osteoblast extracts as well as their involvement in osteogenesis. The extracts were prepared using a freeze-thaw method with varying temperatures and durations. Overall, osteogenic-associated proteins and osteoinductive potential of the extracts prepared from the osteogenic-induced ASCs were assessed. Our results demonstrated that the freeze-thaw approach is practicable for cell extracts production, with minor differences in temperature and duration having no effect on protein concentration. The ASC-osteoblast extracts contain a significant level of essential specialized proteins that promote osteogenicity. Hence, the freeze-thaw method is applicable for extract preparation and ASC-osteoblast extracts may be beneficial as an optional facilitating biologics in bone anabolic treatment and bone regeneration.

Self-oxygenation of engineered living tissues orchestrates osteogenic commitment of mesenchymal stem cells

Oxygenating biomaterials can alleviate anoxic stress, stimulate vascularization, and improve engraftment of cellularized implants. However, the effects of oxygen-generating materials on tissue formation have remained largely unknown. Here, we investigate the impact of calcium peroxide (CPO)-based oxygen-generating microparticles (OMPs) on the osteogenic fate of human mesenchymal stem cells (hMSCs) under a severely oxygen deficient microenvironment. To this end, CPO is microencapsulated in polycaprolactone to generate OMPs with prolonged oxygen release. Gelatin methacryloyl (GelMA) hydrogels containing osteogenesis-inducing silicate nanoparticles (SNP hydrogels), OMPs (OMP hydrogels), or both SNP and OMP (SNP/OMP hydrogels) are engineered to comparatively study their effect on the osteogenic fate of hMSCs. OMP hydrogels associate with improved osteogenic differentiation under both normoxic and anoxic conditions. Bulk mRNAseq analyses suggest that OMP hydrogels under anoxia regulate osteogenic differentiation pathways more strongly than SNP/OMP or SNP hydrogels under either anoxia or normoxia. Subcutaneous implantations reveal a stronger host cell invasion in SNP hydrogels, resulting in increased vasculogenesis. Furthermore, time-dependent expression of different osteogenic factors reveals progressive differentiation of hMSCs in OMP, SNP, and SNP/OMP hydrogels. Our work demonstrates that endowing hydrogels with OMPs can induce, improve, and steer the formation of functional engineered living tissues, which holds potential for numerous biomedical applications, including tissue regeneration and organ replacement therapy.

Activin receptor-like kinase 3: a critical modulator of development and function of mineralized tissues

Mineralized tissues, such as teeth and bones, pose significant challenges for repair due to their hardness, low permeability, and limited blood flow compared to soft tissues. Bone morphogenetic proteins (BMPs) have been identified as playing a crucial role in mineralized tissue formation and repair. However, the application of large amounts of exogenous BMPs may cause side effects such as inflammation. Therefore, it is necessary to identify a more precise molecular target downstream of the ligands. Activin receptor-like kinase 3 (ALK3), a key transmembrane receptor, serves as a vital gateway for the transmission of BMP signals, triggering cellular responses. Recent research has yielded new insights into the regulatory roles of ALK3 in mineralized tissues. Experimental knockout or mutation of ALK3 has been shown to result in skeletal dysmorphisms and failure of tooth formation, eruption, and orthodontic tooth movement. This review summarizes the roles of ALK3 in mineralized tissue regulation and elucidates how ALK3-mediated signaling influences the physiology and pathology of teeth and bones. Additionally, this review provides a reference for recommended basic research and potential future treatment strategies for the repair and regeneration of mineralized tissues.

Carrier systems for bone morphogenetic proteins: An overview of biomaterials used for dentoalveolar and maxillofacial bone regeneration

Different types of biomaterials have been used to fabricate carriers to deliver bone morphogenetic proteins (BMPs) in both dentoalveolar and maxillofacial bone regeneration procedures. Despite that absorbable collagen sponge (ACS) is considered the gold standard for BMP delivery, there is still some concerns regarding its use mainly due to its poor mechanical properties. To overcome this, novel systems are being developed, however, due to the wide variety of biomaterial combination, the heterogeneous assessment of newly formed tissue, and the intended clinical applications, there is still no consensus regarding which is more efficient in a particular clinical scenario. The combination of two or more biomaterials in different topological configurations has allowed specific controlled-release patterns for BMPs, improving their biological and mechanical properties compared with classical single-material carriers. However, more basic research is needed. Since the BMPs can be used in multiple clinical scenarios having different biological and mechanical needs, novel carriers should be developed in a context-specific manner. Thus, the purpose of this review is to gather current knowledge about biomaterials used to fabricate delivery systems for BMPs in both dentoalveolar and maxillofacial contexts. Aspects related with the biological, physical and mechanical characteristics of each biomaterial are also presented and discussed.

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Strategies for bone formation and regeneration are a major concern in dentistry.

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Topical delivery of bone morphogenetic proteins (BMPs) allows rapid bone formation.

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BMPs requires proper carrier system to allow controlled and sustained release.

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Carrier should also fulfill mechanical requirements of bone defect sites.

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By using complex composites, it would be possible to develop new carriers for BMPs.

Factors affecting the induction of uncoupling protein 1 in C2C12 myogenic cells

Brown/beige adipocytes, which are derived from skeletal muscle/smooth muscle-lineage cells, consume excess energy as heat through the expression of mitochondrial uncoupling protein 1 (UCP1). Previous studies have shown that forced expression of PR/SET domain (PRDM)-16 or early B-cell factor (EBF)-2 induced UCP1-positive adipocytes in C2C12 myogenic cells. Here, we explored the culture conditions to induce Ucp1 expression in C2C12 cells without introducing exogenous genes. Treatment with rosiglitazone (a peroxisome proliferator-activated receptor (PPAR)-γ agonist), GW501516 (a PPARδ agonist), and bone morphogenetic protein (BMP)-7 for 8 days efficiently increased Ucp1 expression in response to treatment with forskolin, an activator of the protein kinase A pathway. BMP7 dose-dependently increased forskolin-induced Ucp1 expression in the presence of rosiglitazone and GW501516; however, GW501516 was not required for Ucp1 induction. Additionally, the structurally related proteins, BMP6 and BMP9, efficiently increased forskolin-induced Ucp1 expression in rosiglitazone-treated cells. UCP1 protein was localized in cells with lipid droplets, but adipocytes were not always positive for UCP1. Continuous treatment with BMP7 was needed for the efficient induction of Ucp1 by forskolin treatment. Significant expression of Prdm16 was not detected, irrespective of the treatment, and treatment with rosiglitazone, GW501516, and BMP7 did not affect the expression levels of Ebf2. Fibroblast growth factor receptor (Fgfr)-3 expression levels were increased by BMP9 in rosiglitazone-treated cells, and molecules that upregulate Fgfr3 transcription partly overlapped with those that stimulate Ucp1 transcription. The present results provide basic information on the practical differentiation of myogenic cells to brown adipocytes.

Advances in pharmacotherapy for acute kidney injury

INTRODUCTION

Acute kidney injury (AKI) is a clinically critical disease exhibiting an acute decline in renal function. The lack of an effective prevention and treatment method equates to a high morbidity and mortality rate. Consequently, over the past few decades, many therapeutic drugs with different mechanisms of action have been proposed and gradually applied to the clinic. The involved drug mechanisms evaluated have included hemodynamic modulation, anti-inflammatory, antioxidant, repair agents, metabolic derangement and mitochondrial function.

AREAS COVERED

The authors of this review provide the reader with a reference point for the latest advances in pharmacotherapy in acute kidney injury. This is achieved by the evaluation of the latest data collected on potential therapeutic drugs with different mechanisms of action, as well as their preclinical and clinical impact on AKI.

EXPERT OPINION

Presently, the vast majority of drugs are still in clinical development, which is a huge challenge. Nevertheless, in addition to current chemical drugs and gene therapy strategies, the advent of mesenchymal stem cell treatments and other emerging pharmaceutical strategies could enable clinicians to better treat AKI. Due to the nonselective distribution and low bioavailability of some of the latest pharmaceutical strategies, there is hope that these treatment options may provide more efficacious avenues.

Differential bioactivity of four BMP-family members as function of biomaterial stiffness

While a soft film itself is not able to induce cell spreading, BMP-2 presented via such soft film (so called "matrix-bound BMP-2") was previously shown to trigger cell spreading, migration and downstream BMP-2 signaling. Here, we used thin films of controlled stiffness presenting matrix-bound BMPs to study the effect of four BMP members (BMP-2, 4, 7, 9) on cell adhesion and differentiation of skeletal progenitors. We performed automated high-content screening of cellular responses, including cell number, cell spreading area, SMAD phosphorylation and alkaline phosphatase activity. We revealed that the cell response to bBMPs is BMP-type specific, and involved certain BMP receptors and beta chain integrins. In addition, this response is stiffness-dependent for several receptors. The basolateral presentation of the BMPs allowed us to discriminate the specificity of cellular response, especiallyd the role of type I and II BMP receptors and of β integrins in a BMP-type and stiffness-dependent manner. Notably, BMP-2 and BMP-4 were found to have distinct roles, while ALK5, previously known as a TGF-β receptor was revealed to be involved in the BMP-pathway.

SPARC-related modular calcium binding 1 regulates aortic valve calcification by disrupting BMPR-II/p-p38 signalling

Aims

Aortic valve calcification is more prevalent in chronic kidney disease accompanied by hypercalcemia. Secreted protein acidic and rich in cysteine (SPARC)-related modular calcium binding 1 (SMOC1) is a regulator of BMP2 signalling, but the role of SMOC1 in aortic valve calcification under different conditions has not been studied. This study aimed to investigate the roles of SMOC1 in aortic valve calcification under normal and high calcium conditions, focusing on the effects on aortic valve interstitial cells (AVICs).

Methods and results

SMOC1 was expressed by aortic valve endothelial cells and secreted into the extracellular matrix in non-calcific valves and downregulated in calcific aortic valves. In vitro studies demonstrated that HUVEC secreted SMOC1 could enter the cytoplasm of AVICs. Overexpression of SMOC1 attenuated warfarin-induced AVIC calcification but promoted high calcium/phosphate or vitamin D-induced AVIC and aortic valve calcification by regulating BMP2 signalling both in vitro and in vivo. Co-immunoprecipitation revealed that SMOC1 binds to BMP receptor II (BMPR-II) and inhibits BMP2-induced phosphorylation of p38 (p-p38) via amino acids 372–383 of its EF-hand calcium-binding domain. Inhibition of p-p38 by the p38 inhibitor SB203580 blocked the effects of SMOC1 on BMP2 signalling and AVIC calcification induced by high calcium/phosphate medium. In high-calcium-treated AVICs, SMOC1 lost its ability to bind to BMPR-II, but not to caveolin-1, promoting p-p38 and cell apoptosis due to increased expression of BMPR-II and enhanced endocytosis.

Conclusions

These observations support that SMOC1 works as a dual-directional modulator of AVIC calcification by regulating p38-dependent BMP2 signalling transduction according to different extracellular calcium concentrations.

Correlation between growth differentiation factor 5 (rs143383) gene polymorphism and knee osteoarthritis: an updated systematic review and meta-analysis

Background

A great deal of evidence has supported that growth differentiation factor 5 (GDF5) is associated with the occurrence of knee osteoarthritis (KOA), while their results are not consistent. In the present study, we aimed to explore the association between GDF5 gene polymorphism and KOA for a more credible conclusion.

Methods

Comprehensive literature searches were carried out in English databases, including PubMed, Embase, Web of Science (WOS), and Cochrane, and Chinese databases, including China National Knowledge Infrastructure (CNKI), WANFANG, and VIP database. After the data were extracted from the required studies, the odds ratios (ORs) and their 95% confidence intervals (CIs) were determined to assess the correlation between GDF5 gene polymorphism and KOA. The publication bias was evaluated by funnel plot.

Results

According to the inclusion and exclusion criteria, 15 studies on the correlation between GDF5 gene polymorphism and KOA occurrence were eligible for meta-analysis. Among these articles, four studies showed no apparent correlation, while the other 11 studies indicated an obvious correlation. Meanwhile, we also carried out a subgroup analysis of the population. Due to the inevitable heterogeneity, three genetic models were finally selected for analysis. With the allele model (C versus T: OR = 0.79, 95% CI = 0.73~0.87), recessive model (CC versus CT + TT: OR = 0.76, 95% CI = 0.68~0.86), and homozygous model (CC versus TT: OR = 0.66, 95% CI = 0.58~0.76), GDF5 gene polymorphism decreased the risk of KOA. Besides, a significant association was observed in Caucasians, Asians, and Africans. Meanwhile, the protective effect of genotype C (or CC) in the Asian group was little obvious than that in the Caucasian group and the African group. Although the quality of the included studies was above medium-quality, we obtained results with a low level of evidence.

Conclusions

The results of the meta-analysis showed that the genotype C (or CC) of GDF5 protected against KOA occurrence in Caucasian, Asian, and African populations.

Bone morphogenetic protein receptors: Structure, function and targeting by selective small molecule kinase inhibitors

Bone morphogenetic proteins (BMPs) are secreted cytokines that control the fate and function of many different cell types. They exert their cellular responses via heteromeric complexes of specific BMP type I and type II serine/threonine kinase receptors, e.g. BMPRIA and BMPRII. Three type II and four type I receptors, also termed activin receptor-like kinases (ALKs), have been identified. The constitutively active type II kinase phosphorylates the type I receptor, which upon activation initiates intracellular signaling by phosphorylating SMAD effectors. Auxiliary cell surface receptors without intrinsic enzymatic motifs, such as Endoglin and Repulsive guidance molecules (RGM), can fine-tune signaling by regulating the interaction of the BMP ligands with the BMPRs. The functional annotation of the BMPR encoding genes has helped to understand underlying mechanisms of diseases in which these genes are mutated. Loss of function mutations in BMPRII, Endoglin or RGMc are causally linked to pulmonary arterial hypertension, hereditary hemorrhagic telangiectasia and juvenile hemochromatosis, respectively. In contrast, gain of function mutations in ACVR1, encoding ALK2, are linked to Fibrodysplasia ossificans progressiva and diffuse intrinsic pontine glioma. Here, we discuss BMPR identification, structure and function in health and disease. Moreover, we highlight the therapeutic promise of small chemical compounds that act as selective BMPR kinase inhibitors to normalize overactive BMPR signaling.

Application of Cytokines of the Bone Morphogenetic Protein (BMP) Family in Spinal Fusion - Effects on the Bone, Intervertebral Disc and Mesenchymal Stromal Cells

Low back pain is a prevalent socio-economic burden and is often associated with damaged or degenerated intervertebral discs (IVDs). When conservative therapy fails, removal of the IVD (discectomy), followed by intersomatic spinal fusion, is currently the standard practice in clinics. The remaining space is filled with an intersomatic device (cage) and with bone substitutes to achieve disc height compensation and bone fusion. As a complication, in up to 30% of cases, spinal non-fusions result in a painful pseudoarthrosis. Bone morphogenetic proteins (BMPs) have been clinically applied with varied outcomes. Several members of the BMP family, such as BMP2, BMP4, BMP6, BMP7, and BMP9, are known to induce osteogenesis. Questions remain on why hyper-physiological doses of BMPs do not show beneficial effects in certain patients. In this respect, BMP antagonists secreted by mesenchymal cells, which might interfere with or block the action of BMPs, have drawn research attention as possible targets for the enhancement of spinal fusion or the prevention of non-unions. Examples of these antagonists are noggin, gremlin1 and 2, chordin, follistatin, BMP3, and twisted gastrulation. In this review, we discuss current evidence of the osteogenic effects of several members of the BMP family on osteoblasts, IVD cells, and mesenchymal stromal cells. We consider in vitro and in vivo studies performed in human, mouse, rat, and rabbit related to BMP and BMP antagonists in the last two decades. We give insights into the effects that BMP have on the ossification of the spine. Furthermore, the benefits, pitfalls, and possible safety concerns using these cytokines for the improvement of spinal fusion are discussed.

Allergen-induced asthma, chronic rhinosinusitis and transforming growth factor-β superfamily signaling: mechanisms and functional consequences

Introduction: Often co-associated, asthma and chronic rhinosinusitis (CRS) are complex heterogeneous disease syndromes. Severity in both is related to tissue inflammation and abnormal repair (termed remodeling). Understanding signaling factors that can modulate, integrate the activation, and regulation of such key processes together is increasingly important. The transforming growth factor (TGF)-β superfamily of ligands comprise a versatile system of immunomodulatory molecules that are gaining recognition as having an essential function in the immunopathogenesis of asthma. Early data suggest an important role in CRS as well. Abnormal or dysregulated signaling may contribute to disease pathogenesis and severity.Areas covered: The essential biology of this complex family of growth factors in relation to the excess inflammation and remodeling that occurs in allergic asthma and CRS is reviewed. The need to understand the integration of signaling pathways together is highlighted. Studies in human airway tissue are evaluated and only selected key animal models relevant to human disease discussed given the highly context-dependent signaling and function of these ligands.Expert opinion: Abnormal or dysregulated TGF-β superfamily signaling may be central to the excess inflammation and tissue remodeling in asthma, and possibly CRS. Therefore, the TGF-β superfamily signaling pathways represent an emerging and attractive therapeutic target.

Minimum structural requirements for BMP-2-binding of heparin oligosaccharides

Bone morphogenetic proteins (BMPs) are essential during tissue repair and remodeling after injury. Glycosaminoglycan (GAG) sugars are known to enhance BMP activity in vitro and in vivo; here the interactions of BMP-2 with various glycosaminoglycan classes were compared and shown to be selective for heparin over other comparable saccharides. The minimal chain lengths and specific sulfate moieties required for heparin-derived oligosaccharide binding to BMP-2, and the ability of such oligosaccharides to promote BMP-2-induced osteogenic differentiation in vitro were then determined. BMP-2 could bind to heparin hexasaccharides (dp6) and octasaccharides (dp8), but decasaccharides (dp10) were the minimum chain length required for both efficient binding of BMP-2 and consequent heparin-dependent cell responses. N-sulfation is the most important, and 6-O-sulfation moderately important for BMP-2 binding and activity, whereas 2-O-sulfation was much less critical. Bone formation assays in vivo further confirmed that dp10, N-sulfated heparin oligosaccharides were the minimal requirement for effective enhancement of BMP-2-induced bone formation. Such information is necessary for the rational design of the next generations of heparan-based devices for bone tissue repair.

Interaction between orexin A and bone morphogenetic protein system on progesterone biosynthesis by rat granulosa cells

The involvement of orexins in reproductive function has been gradually uncovered. However, the functional role of orexins in ovarian steroidogenesis remains unclear. In the present study, we investigated the effects of orexin A on ovarian steroidogenesis by using rat primary granulosa cells that express both OX1 and OX2 receptors for orexins. Treatment with orexin A enhanced progesterone, but not estradiol, biosynthesis induced by FSH, whereas it did not affect basal levels of progesterone or estradiol. In accordance with the effects on steroidogenesis, orexin A increased the mRNA levels of progesterogenic enzymes, including StAR, P450scc and 3βHSD, but not P450arom, and cellular cAMP synthesis induced by FSH. Under the condition of blockage of endogenous BMP actions by noggin or BMP-signaling inhibitors, orexin A failed to increase levels of progesterone synthesis induced by FSH treatment, suggesting that endogenous BMP activity in granulosa cells might be involved in the enhancement of progesterone synthesis by orexin A. Treatment with orexin A impaired Smad1/5/9 activation as well as Id-1 mRNA expression stimulated by BMP-6 and BMP-7, the latter of which was reversed by treatment with an OX1 antagonist. It was also found that orexin A suppressed the mRNA expression of both type-I and -II receptors for BMPs and increased that of inhibitory Smad6 and Smad7 in granulosa cells. On the other hand, treatments with BMP-6 and -7 suppressed the expression of OX1 and OX2. Collectively, the results indicated that orexin A enhances FSH-induced progesterone production, at least in part, by downregulating BMP signaling in granulosa cells. Thus, a new role of orexin A in facilitating progesterone synthesis and functional interaction between the orexin and BMP systems in granulosa cells were revealed.

Combinatorial Analysis of Growth Factors Reveals the Contribution of Bone Morphogenetic Proteins to Chondrogenic Differentiation of Human Periosteal Cells

Successful application of cell-based strategies in cartilage and bone tissue engineering has been hampered by the lack of robust protocols to efficiently differentiate mesenchymal stem cells into the chondrogenic lineage. The development of chemically defined culture media supplemented with growth factors (GFs) has been proposed as a way to overcome this limitation. In this work, we applied a fractional design of experiment (DoE) strategy to screen the effect of multiple GFs (BMP2, BMP6, GDF5, TGF-β1, and FGF2) on chondrogenic differentiation of human periosteum-derived mesenchymal stem cells (hPDCs) in vitro. In a micromass culture (μMass) system, BMP2 had a positive effect on glycosaminoglycan deposition at day 7 (p < 0.001), which in combination with BMP6 synergistically enhanced cartilage-like tissue formation that displayed in vitro mineralization capacity at day 14 (p < 0.001). Gene expression of μMasses cultured for 7 days with a medium formulation supplemented with 100 ng/mL of BMP2 and BMP6 and a low concentration of GDF5, TGF-β1, and FGF2 showed increased expression of Sox9 (1.7-fold) and the matrix molecules aggrecan (7-fold increase) and COL2A1 (40-fold increase) compared to nonstimulated control μMasses. The DoE analysis indicated that in GF combinations, BMP2 was the strongest effector for chondrogenic differentiation of hPDCs. When transplanted ectopically in nude mice, the in vitro-differentiated μMasses showed maintenance of the cartilaginous phenotype after 4 weeks in vivo. This study indicates the power of using the DoE approach for the creation of new medium formulations for skeletal tissue engineering approaches.

Tissue-specific regulation of BMP signaling by Drosophila N-glycanase 1

Mutations in the human N-glycanase 1 (NGLY1) cause a rare, multisystem congenital disorder with global developmental delay. However, the mechanisms by which NGLY1 and its homologs regulate embryonic development are not known. Here we show that Drosophila Pngl encodes an N-glycanase and exhibits a high degree of functional conservation with human NGLY1. Loss of Pngl results in developmental midgut defects reminiscent of midgut-specific loss of BMP signaling. Pngl mutant larvae also exhibit a severe midgut clearance defect, which cannot be fully explained by impaired BMP signaling. Genetic experiments indicate that Pngl is primarily required in the mesoderm during Drosophila development. Loss of Pngl results in a severe decrease in the level of Dpp homodimers and abolishes BMP autoregulation in the visceral mesoderm mediated by Dpp and Tkv homodimers. Thus, our studies uncover a novel mechanism for the tissue-specific regulation of an evolutionarily conserved signaling pathway by an N-glycanase enzyme.

DNA carries the information needed to build and maintain an organism, and units of DNA known as genes contain coded instructions to build other molecules, including enzymes. Sometimes, genes can become faulty and develop mutations that can affect how an embryo develops and lead to diseases. For example, people with mutations in the gene that encodes an enzyme called N-glycanase 1 experience many problems with their nervous system, gut and other organs.

Normally, N-glycanase 1 helps the body remove specific sugar molecules from some proteins in the cells, and is also thought to be important during embryonic development. As an embryo develops, its cells undergo a series of transformations, which is regulated by different molecules and signaling pathways. For example, a pathway known as BMP signaling plays an important role in many tissues. Problems with this pathway can lead to many diseases throughout the body, including the gut, where it helps cells to develop.

Previous research has shown that fruit flies lacking the gene that codes for an equivalent N-glycanase enzyme (which is called Pngl in flies) cannot develop properly into adults. However, until now it was not known what type of cells need the N-glycanase enzyme in any organism, or if NGLY1 is essential for important signaling pathways like BMP signaling. Now, Galeone et al. have used genetically modified flies to test how losing Pngl affected their development.

The results first showed that engineering Pngl-deficient fruit flies to produce the human enzyme eliminated their problems; these flies developed and survived like normal flies. This confirmed that that the human and fly enzymes can perform equivalent roles. Galeone et al. then discovered that Pngl plays two distinct roles in a group of cells that surround the fruit fly’s gut tissue and give rise to the cells that eventually form the muscle layer in the gut. In the larvae, Pngl was required to empty the gut, which is a necessary step before the larvae can develop into an adult. Moreover, Pngl is needed for BMP signaling in the gut, and when flies had the enzyme removed, some parts of their gut could not from properly.

This study will provide a framework to improve our understanding of how BMP signaling is regulated in humans. A next step will be to test if some of the symptoms experienced by patients without a working copy of the gene for N-glycanase 1 are caused by a faulty BMP-signaling system in specific tissues. If this is the case, it could provide new opportunities to treat some of these symptoms.

RhBMP-2 and -7 combined with absorbable collagen sponge carrier enhance ectopic bone formation: An in vivo bioassay

Background: Recombinant human bone morphogenetic proteins (rhBMPs) have been characterized especially chondrogenic and osteogenic activity both in vitro and in vivo studies. However, delivery of more than one growth factor by sustained release carrier to orthopedic site has yet been questionable in terms of efficacy and synergism.

Objective: Evaluate osteoinductivity and synergistic effect of rhBMP-2 and -7 using absorbable collagen sponge (ACS) carrier system in vivo.

Methods: cDNA of BMP-2 and -7 active domains were cloned and expressed in Escherichia coli BL21 StarTM (DE3) using pRSETc expression system. Then, the purified rhBMPs were loaded onto ACS and evaluated by in vivo rat subcutaneous bioassay. Two and eight weeks postoperatively, all treated groups were histologically verified for evidence of new bone formation and neovascularization by hematoxylin-eosin staining and light microscopy.

Results: The Wistar rat treated with rhBMP-2 or -7/ACS exhibited new bone formation, compared to ACS control. The group treated with ACS supplemented with both rhBMP-2 and -7 significantly showed the osteoid matrix very well-organized into trabeculae-like structure with significant blood vessel invasion.

Conclusion: The osteogenic induction of rhBMPs was combined with ACS carrier in the in vivo bioassay. In addition, the combination of both two potent recombinant osteoinductive cytokines, rhBMP-2 and -7, with ACS carrier demonstrated synergistic effect and might be a more promising and effective choice for therapeutic applications.

Regulation of hepcidin expression by inflammation-induced activin B

Activin B is induced in response to inflammation in the liver and enhances hepcidin expression, but the source of activin B and the molecular mechanism underlying hepcidin induction are not clear yet. Lipopolysaccharide (LPS)-induced inflammation induced inhibin βB but not inhibin α or inhibin βA expression in the liver, implicating activin B induction. Immunoreactive inhibin βB was detected in endothelial cells and Kupffer cells in LPS-treated liver. Activin B, but not activin A or activin AB, directly increased hepcidin expression. Activin B induced phosphorylation and activation of Smad1/5/8, the BMP-regulated (BR)-Smads. The stimulation of hepcidin transcription by activin B was mediated by ALK2 and ActRIIA, receptors for the TGF-β family. Unexpectedly, activin B-induced hepcidin expression and BR-Smad phosphorylation were resistant to the effects of LDN-193189, an ALK2/3/6 inhibitor. ALK2 and ActRIIA complex formation in response to activin B may prevent the approach of LDN-193189 to ALK2 to inhibit its activity. Activin B also induced phosphorylation of Smad2/3, the TGF-β/activin-regulated (AR)-Smad, and increased expression of connective tissue growth factor, a gene related to liver fibrogenesis, through ALK4 and ActRIIA/B. Activin B-induced activation of the BR-Smad pathway was also detected in non-liver-derived cells. The present study reveals the broad signaling of activin B, which is induced in non-parenchymal cells in response to hepatic inflammation, in hepatocytes.

Bone Morphogenetic Proteins and Their Receptors in the Eye

The human genome encodes at least 42 different members of the transforming growth factor-β superfamily of growth factors. Bone morphogenetic proteins (BMPs) are the largest subfamily of proteins within the transforming growth factor-β superfamily and are involved in numerous cellular functions including development, morphogenesis, cell proliferation, apoptosis, and extracellular matrix synthesis. This article first reviews BMPs and BMP receptors, BMP signaling pathways, and mechanisms controlling BMP signaling. Second, we review BMP and BMP receptor expression during embryonic ocular development/ differentiation and in adult ocular tissues. Lastly, future research directions with respect to BMP, BMP receptors, and ocular tissues are suggested.

An investigation of BMP-7 mediated alterations to BMP signalling components in human tenocyte-like cells

The incidence of tendon re-tears post-surgery is an ever present complication. It is suggested that the application of biological factors, such as bone morphogenetic protein 7 (BMP-7), can reduce complication rates by promoting tenogenic characteristics in in vitro studies. However, there remains a dearth of information in regards to the mechanisms of BMP-7 signalling in tenocytes. Using primary human tenocyte-like cells (hTLCs) from the supraspinatus tendon the BMP-7 signalling pathway was investigated: induction of the BMP associated Smad pathway and non-Smad pathways (AKT, p38, ERK1/2 and JNK); alterations in gene expression of BMP-7 associated receptors, Smad pathway components, Smad target gene (ID1) and tenogenic marker scleraxis. BMP-7 increases the expression of specific BMP associated receptors, BMPR-Ib and BMPR-II, and Smad8. Additionally, BMP-7 activates significantly Smad1/5/8 and slightly p38 pathways as indicated by an increase in phosphorylation and proven by inhibition experiments, where p-ERK1/2 and p-JNK pathways remain mainly unresponsive. Furthermore, BMP-7 increases the expression of the Smad target gene ID1, and the tendon specific transcription factor scleraxis. The study shows that tenocyte-like cells undergo primarily Smad8 and p38 signalling after BMP-7 stimulation. The up-regulation of tendon related marker genes and matrix proteins such as Smad8/9, scleraxis and collagen I might lead to positive effects of BMP-7 treatment for rotator cuff repair, without significant induction of osteogenic and chondrogenic markers.

Biodegradable Mg-Cu alloys with enhanced osteogenesis, angiogenesis, and long-lasting antibacterial effects

A series of biodegradable Mg-Cu alloys is designed to induce osteogenesis, stimulate angiogenesis, and provide long-lasting antibacterial performance at the same time. The Mg-Cu alloys with precipitated Mg2Cu intermetallic phases exhibit accelerated degradation in the physiological environment due to galvanic corrosion and the alkaline environment combined with Cu release endows the Mg-Cu alloys with prolonged antibacterial effects. In addition to no cytotoxicity towards HUVECs and MC3T3-E1 cells, the Mg-Cu alloys, particularly Mg-0.03Cu, enhance the cell viability, alkaline phosphatase activity, matrix mineralization, collagen secretion, osteogenesis-related gene and protein expressions of MC3T3-E1 cells, cell proliferation, migration, endothelial tubule forming, angiogenesis-related gene, and protein expressions of HUVECs compared to pure Mg. The favorable osteogenesis and angiogenesis are believed to arise from the release of bioactive Mg and Cu ions into the biological environment and the biodegradable Mg-Cu alloys with osteogenesis, angiogenesis, and long-term antibacterial ability are very promising in orthopedic applications.

Bone morphogenetic proteins and their antagonists: current and emerging clinical uses

Bone morphogenetic proteins (BMPs) are members of the TGFβ superfamily of secreted cysteine knot proteins that includes TGFβ1, nodal, activins and inhibins. BMPs were first discovered by Urist in the 1960s when he showed that implantation of demineralized bone into intramuscular tissue of rabbits induced bone and cartilage formation. Since this seminal discovery, BMPs have also been shown to play key roles in several other biological processes, including limb, kidney, skin, hair and neuronal development, as well as maintaining vascular homeostasis. The multifunctional effects of BMPs make them attractive targets for the treatment of several pathologies, including bone disorders, kidney and lung fibrosis, and cancer. This review will summarize current knowledge on the BMP signalling pathway and critically evaluate the potential of recombinant BMPs as pharmacological agents for the treatment of bone repair and tissue fibrosis in patients.

Bone Morphogenetic Protein-6 (BMP-6) Stimulates the Antrum Formation by the Regulation of its Signalling Pathway in Caprine Pre-antral Follicles Cultured In Vitro

BMP-6 has been found to be important to ovarian cells and oocyte, as well as to uterus. Thus, this study investigated the effect of bone morphogenetic protein (BMP-6) and recombinant follicle-stimulating hormone (rFSH) alone or in combination on the in vitro culture (IVC) of isolated caprine secondary follicles (Experiment 1) and the mRNA levels for BMP receptors/Smad signalling pathway (BMPR1A, BMPR2, SMAD1, SMAD4, SMAD5, SMAD6, SMAD7 and SMAD8) in vivo and in vitro using BMP-6 (Experiment 2). Secondary follicles were cultured in αMEM(+) alone (control medium) or supplemented with BMP-6 at 1 or 10 ng/ml and rFSH alone or the combination of both BMP-6 concentrations and rFSH. The results from Experiment 1 showed that the antrum formation rate was higher in the BMP-6 at 1 ng/ml (p < 0.05) than in MEM. In Experiment 2, the mRNA expression for BMPR2, SMAD1, SMAD5 and SMAD6 was detected in non-cultured control and after in vitro culture (MEM and 1 ng/ml BMP-6); while the expression of SMAD7 and SMAD8 mRNA was only detected after IVC, SMAD4 was only detected in the BMP-6 at 1 ng/ml treatment. In conclusion, the low BMP-6 concentration positively influenced antrum formation and ensured normal mRNA expression for BMP receptor and Smads after IVC of caprine secondary follicles.

Expression of bone morphogenetic protein 2, 4, and related components of the BMP signaling pathway in the mouse uterus during the estrous cycle

The objective was to investigate the expression of bone morphogenetic protein (BMP) family members in the mouse uterus during the estrous cycle by real-time polymerase chain reaction (PCR) and immunohistochemistry. Uterine samples from Swiss ICR mice were collected and dissected free of surrounding tissue. One uterine horn was snap frozen in liquid nitrogen immediately after collection and stored at -80 °C for RNA extraction, and the other was fixed in 40 mg/ml paraformaldehyde at room temperature for immunolocalization of BMP2 protein. Real-time PCR analysis showed that the expression level of Bmp2 was significantly higher at proestrus than at estrus and metestrus (P<0.05). The relative abundance of Bmp4 exhibited significant fluctuations, but there were no statistically significant differences between the expression levels of Bmp2 and Bmp4 (P>0.05). The expression levels of Bmpr1a and Bmpr2 remained unchanged during estrous cycles. However, the level of Bmpr1b mRNA decreased significantly at estrus (P<0.05), increasing subsequently at metestrus. Furthermore, the level of Bmpr1b mRNA was significantly lower than those of Bmpr1a and Bmpr2 mRNA at the corresponding stages (P<0.05). All three receptor-regulated Smads (R-Smads) detected were differentially expressed in the mouse uterus and the expression levels of Smad1 and Smad5 were significantly higher than that of Smad8 (P<0.05). In addition, the expression level of Smad4 did not change substantially throughout the estrous cycle. Immunohistochemical experiments revealed that BMP2 protein was differentially expressed and localized mainly in the uterine luminal and glandular epithelial cells throughout the estrous cycle. In conclusion, our results provide information about the variation in the mRNA levels of Bmp2 and Bmp4 and related components of the BMP signaling pathway. The data provide quantitative and useful information about the roles of endometrial BMP proposed and demonstrated by others, such as the degradation and remodeling of the endometrium.

Co-operative Bmp- and Fgf-signaling inputs convert skin wound healing to limb formation in urodele amphibians

Urodele amphibians have remarkable organ regeneration capability, and their limb regeneration capability has been investigated as a representative phenomenon. In the early 19th century, nerves were reported to be an essential tissue for the successful induction of limb regeneration. Nerve substances that function in the induction of limb regeneration responses have long been sought. A new experimental system called the accessory limb model (ALM) has been established to identify the nerve factors. Skin wounding in urodele amphibians results in skin wound healing but never in limb induction. However, nerve deviation to the wounded skin induces limb formation in ALM. Thus, nerves can be considered to have the ability to transform skin wound healing to limb formation. In the present study, co-operative Bmp and Fgf application, instead of nerve deviation, to wounded skin transformed skin wound healing to limb formation in two urodele amphibians, axolotl (Ambystoma mexicanum) and newt (Pleurodeles waltl). Our findings demonstrate that defined factors can induce homeotic transformation in postembryonic bodies of urodele amphibians. The combination of Bmp and Fgf(s) may contribute to the development of novel treatments for organ regeneration.

Can OP-1 stimulate union in a rat model of pathological fracture post treatment for soft tissue sarcoma?

The goal of soft tissue sarcoma management in the extremities is limb preservation, often combining surgery and external beam radiation. In patients who have undergone this therapy in the thigh, pathologic fracture is a serious, late complication. Non-union rates of 80-90% persist. No reliable biologic solution exists. A rat model combining one 18 Gy dose of radiation and diaphyseal periosteal excision reliably generates atrophic non-union of femoral fractures. We hypothesized that augmentation with OP-1 would increase union rate. Female Sprague-Dawley retired breeder rats were randomized to Control, Disease (external beam radiotherapy and periosteal stripping), Control + OP-1 (80 µg) and Disease + OP-1 groups. Animals underwent prophylactic fixation and controlled left femur fracture. Twenty-eight, 35, and 42 days post-fracture were end-points. Femora were analyzed using MicroCT, Back Scattered Electron Microscopy, and Histomorphometry. We observed a 2% union rate in the Disease groups (±OP-1 treatment). The union rate in Control groups was 97%. MicroCT demonstrated a lack of callus volume in Disease groups. Heterotopic ossification was observed in some OP-1 treated animals. The ineffectiveness of OP-1 in stimulating fracture union in this model suggests the endogenous repair mechanism has been compromised beyond the capabilities of osteoinductive biologics.

Structure-activity relationship of 3,5-diaryl-2-aminopyridine ALK2 inhibitors reveals unaltered binding affinity for fibrodysplasia ossificans progressiva causing mutants

There are currently no effective therapies for fibrodysplasia ossificans progressiva (FOP), a debilitating and progressive heterotopic ossification disease caused by activating mutations of ACVR1 encoding the BMP type I receptor kinase ALK2. Recently, a subset of these same mutations of ACVR1 have been identified in diffuse intrinsic pontine glioma (DIPG) tumors. Here we describe the structure–activity relationship for a series of novel ALK2 inhibitors based on the 2-aminopyridine compound K02288. Several modifications increased potency in kinase, thermal shift, or cell-based assays of BMP signaling and transcription, as well as selectivity for ALK2 versus closely related BMP and TGF-β type I receptor kinases. Compounds in this series exhibited a wide range of in vitro cytotoxicity that was not correlated with potency or selectivity, suggesting mechanisms independent of BMP or TGF-β inhibition. The study also highlights a potent 2-methylpyridine derivative 10 (LDN-214117) with a high degree of selectivity for ALK2 and low cytotoxicity that could provide a template for preclinical development. Contrary to the notion that activating mutations of ALK2 might alter inhibitor efficacy due to potential conformational changes in the ATP-binding site, the compounds demonstrated consistent binding to a panel of mutant and wild-type ALK2 proteins. Thus, BMP inhibitors identified via activity against wild-type ALK2 signaling are likely to be of clinical relevance for the diverse ALK2 mutant proteins associated with FOP and DIPG.

A medium-throughput analysis of signaling pathways involved in early stages of stem cell reprogramming

The induction of pluripotency from adult cells has enormous potential in regenerative medicine. While initial efforts to study mechanisms and improve efficiency of induced pluripotent stem cell (iPSC) reprogramming focused on the direct roles of transcriptional regulators, increasing evidence indicates that cellular signal transduction pathways can modulate this process. Here, we present a medium-throughput system to study the effect of signaling pathways on the early stages of reprogramming. We generated a set of lentiviral vectors encoding 38 genes that upregulate or downregulate major signal transduction pathways and quantified each signaling factor's effect on reprogramming. This approach confirmed the role of several factors previously implicated in reprogramming, as well as identified several GTPases-factors that to date have not been largely studied in reprogramming-that improve or hinder iPSC reprogramming. In addition, this methodology is useful in determining new targets for enhancing pluripotency reprogramming, lineage reprogramming, and/or cell differentiation.

CD44 and hyaluronan promote the bone morphogenetic protein 7 signaling response in murine chondrocytes

OBJECTIVE

Cell-matrix interactions promote cartilage homeostasis. We previously found that Smad1, the transcriptional modulator of the canonical bone morphogenetic protein 7 (BMP-7) pathway, interacted with the cytoplasmic domain of CD44, the principal hyaluronan receptor on chondrocytes. To elucidate the physiologic function of CD44-Smad1 interactions, as well as the role of hyaluronan, we studied the response of chondrocytes isolated from CD44(-/-) and BALB/c (wild-type [WT]) mice to stimulation with BMP-7.

METHODS

In primary murine chondrocytes, CD44 expression was decreased by small interfering RNA (siRNA) transfection or was enhanced by plasmid transfection. Pericellular hyaluronan was removed by hyaluronidase treatment, or its endogenous synthesis was inhibited. Changes in response to BMP-7 stimulation were evaluated by Western blotting of Smad1 phosphorylation and aggrecan messenger RNA (mRNA) expression.

RESULTS

Chondrocytes from CD44(-/-) mice and WT mice transfected with CD44 siRNA were less responsive than untransfected chondrocytes from WT mice to BMP-7. CD44(-/-) mouse chondrocytes transfected with pCD44 showed increased sensitivity to BMP-7. Significant increases in aggrecan mRNA were observed in WT mouse chondrocytes in response to 10 ng/ml of BMP-7, whereas at least 100 ng/ml of BMP-7 was required for CD44(-/-) mouse chondrocytes. However, in chondrocytes from CD44(-/-) and WT mice, hyaluronidase treatment decreased cellular responses to BMP-7. Treatment of both bovine and murine chondrocytes with 4-methylumbelliferone to reduce the synthesis of endogenous hyaluronan confirmed that hyaluronan promoted BMP-7 signaling.

CONCLUSION

Taken together, these investigations into the mechanisms underlying BMP-7 signaling in chondrocytes revealed that while hyaluronan-dependent pericellular matrix is critical for BMP-7 signaling, the expression of CD44 promotes the cellular response to lower concentrations of BMP-7.

Positive selection for bone morphogenetic protein receptor type-IB promotes differentiation and specification of human adipose-derived stromal cells toward an osteogenic lineage

BACKGROUND

Adipose tissue represents an abundant and easily accessible source of multipotent cells that may serve as an excellent building block for tissue engineering. However, adipose-derived stromal cells (ASCs) are a heterogeneous group and subpopulations may be identified with enhanced osteogenic potential.

METHODS

Human ASC subpopulations were prospectively isolated based on expression of bone morphogenetic protein receptor type-IB (BMPR-IB). Unsorted, BMPR-IB(+), and BMPR-IB(-) cells were analyzed for their osteogenic capacity through histological staining and gene expression. To evaluate their in vivo osteogenic potential, critical-sized calvarial defects were created in immunocompromised mice and treated with unsorted, BMPR-IB(+), or BMPR-IB(-) cells. Healing was assessed using microcomputed tomography and pentachrome staining of specimens at 8 weeks.

RESULTS

Increased osteogenic differentiation was noted in the BMPR-IB(+) subpopulation, as demonstrated by alkaline phosphatase staining at day 7 and extracellular matrix mineralization with Alizarin red staining at day 14. This was also associated with increased expression for osteocalcin, a late marker of osteogenesis. Radiographic analysis demonstrated significantly enhanced healing of critical-sized calvarial defects treated with BMPR-IB(+) ASCs compared with unsorted or BMPR-IB(-) cells. This was confirmed through pentachrome staining, which revealed more robust bone regeneration in the BMPR-IB(+) group.

CONCLUSION

BMPR-IB(+) human ASCs have an enhanced ability to form bone both in vitro and in vivo. These data suggest that positive selection for BMPR-IB(+) and manipulation of the BMP pathway in these cells may yield a highly osteogenic subpopulation of cells for bone tissue engineering.

BMP activation and Wnt-signalling affect biochemistry and functional biomechanical properties of cartilage tissue engineering constructs

OBJECTIVES

Bone morphogenetic protein (BMP-) and Wnt-signalling play crucial roles in cartilage homeostasis. Our objective was to investigate whether activation of the BMP-pathway or stimulation of Wnt-signalling cascades effectively enhances cartilage-specific extracellular matrix (ECM) accumulation and functional biomechanical parameters of chondrocyte-seeded tissue engineering (TE)-constructs.

DESIGN

Articular chondrocytes were cultured in collagen-type-I/III-matrices over 6 weeks to create a biomechanical standard curve. Effects of stimulation with 100 ng/mL BMP-4/-7 heterodimer or 10 mM lithium chloride (LiCl) on ECM-deposition was quantified and characterized histologically. Biomechanical parameters were determined by the Very Low Rubber Hardness (VLRH) method and under confined compression stress relaxation.

RESULTS

BMP-4/-7 treatment resulted in stronger collagen type-II staining and significantly enhanced glycosaminoglycan (GAG) deposition (3.2-fold; *P < 0.01) correlating with improved hardness (∼1.7-fold; *P = 0.001) reaching 83% of native cartilage values after 28 days, a value not reached before 9 weeks without stimulation. LiCl treatment enhanced VLRH slightly, but significantly (∼1.3-fold; *P = 0.016) with a trend to more ECM-deposition. BMP-4/-7 treatment significantly enhanced the E Modulus (105.7 ± 34.1 kPa; *P = 0.000001) compared to controls (8.0 ± 4.2 kPa). Poisson's ratio was significantly improved by BMP-4/-7 treatment (0.0703 ± 0.0409; *P = 0.013) vs controls (0.0432 ± 0.0284) and a significantly lower permeability (5.8 ± 2.1056 × 10(-14) m4/N.s; *P = 0.00001) was detected compared to untreated scaffolds (4.4 ± 3.1289 × 10(-13) m4/N.s).

CONCLUSIONS

While Wnt-activation is less effective, BMP-4/-7 heterodimer stimulation approximated native cartilage features in less than 50% of standard culture time representing a promising strategy for functional cartilage TE to improve biomechanical parameters of engineered cartilage.

Deletion of the sequence encoding the tail domain of the bone morphogenetic protein type 2 receptor reveals a bone morphogenetic protein 7-specific gain of function

The bone morphogenetic protein (BMP) type II receptor (BMPR2) has a long cytoplasmic tail domain whose function is incompletely elucidated. Mutations in the tail domain of BMPR2 are found in familial cases of pulmonary arterial hypertension. To investigate the role of the tail domain of BMPR2 in BMP signaling, we generated a mouse carrying a Bmpr2 allele encoding a non-sense mediated decay-resistant mutant receptor lacking the tail domain of Bmpr2. We found that homozygous mutant mice died during gastrulation, whereas heterozygous mice grew normally without developing pulmonary arterial hypertension. Using pulmonary artery smooth muscle cells (PaSMC) from heterozygous mice, we determined that the mutant receptor was expressed and retained its ability to transduce BMP signaling. Heterozygous PaSMCs exhibited a BMP7‑specific gain of function, which was transduced via the mutant receptor. Using siRNA knockdown and cells from conditional knockout mice to selectively deplete BMP receptors, we observed that the tail domain of Bmpr2 inhibits Alk2‑mediated BMP7 signaling. These findings suggest that the tail domain of Bmpr2 is essential for normal embryogenesis and inhibits Alk2‑mediated BMP7 signaling in PaSMCs.

Fluoride promotes viability and differentiation of osteoblast-like Saos-2 cells via BMP/Smads signaling pathway

The BMP/Smad signaling pathway plays an important role in the viability and differentiation of osteoblast; however, it is not clear whether this pathway is involved in the fluoride-induced osteoblast differentiation. In this study, we investigated the role of BMP/Smad signaling pathway in fluoride-induced osteoblast-like Saos-2 cells differentiation. Cells were exposed to fluoride of different concentrations (0, 0.1, 0.2, 0.4, 0.8, and 1.6 mM), and cell proliferation was determined using WST assays. The expression of osteoblast marker genes such as osteocalcin (BGP) and bone alkaline phosphatase (BALP) were detected by qRT-PCR. We found that fluoride enhanced the proliferation of Saos-2 cells in a dose-dependent manner and 0.2 mM of fluoride resulted in a higher expression of osteoblast marker genes. In addition, immunofluorescence analysis showed that the promotion effects of 0.2 mM of fluoride on Saos-2 cells differentiation were associated with the activation of the BMP/Smad pathway. Expression of phosphorylated Smad1/5(p-Smad1/5) was higher in cells exposed to 0.2 mM of fluoride. Plasmid expression vectors encoding the short hairpin RNA (shRNA) targeting Smad4 gene were used to block the BMP/Smad pathway, which resulted in a significantly reduced expression of BGP and BALP as well as their corresponding mRNA. The mRNA levels after transfection remained low even in the presence of fluoride. The present results reveal that BMP/Smad signaling pathway was altered during the period of osteogenesis, and that the activities of p-Smad1/5 were required for Saos-2 cells viability and differentiation induced by fluoride.

N-acylated glucosamines for bone and joint disorders: effects of N-butyryl glucosamine on ovariectomized rat bone

The benefit of glucosamine (GlcN) in bone and joint disorders remains controversial. N-acetylation and other N-acylations of GlcN alter its biological properties fundamentally. We have shown previously that N-butyryl glucosamine (GlcNBu) preserved strikingly the subchondral bone structure in a destructive arthritis rat model. Here, we examine whether GlcNBu preserves bone in the ovariectomized (OVX) rat, a model for postmenopausal osteoporosis. Rats were randomized into 4 groups: group 1, sham OVX glucose (Glc) fed; group 2, sham OVX GlcNBu fed; group 3, OVX Glc fed; and group 4, OVX GlcNBu fed. A single, oral, 200-mg/kg dose of GlcNBu or Glc was administered daily for 6 months. Bone mineral content (BMC) and bone mineral density, and biomechanical properties of the femurs and spines were determined by standardized techniques. Two-way analysis of variance with a Bonferroni post hoc test was used for statistical analysis. Ovariectomy in group 3 resulted either in significant or highly significant effects in a number of the tests. For spinal BMCs the interaction between GlcNBu and OVX was significant. For the femurs, this interaction was also seen in energy to failure, and ultimate displacement and ultimate strain tests. In general, ovariectomy was necessary to show significant preventive effects of GlcNBu on mineral content and some biomechanical properties. We conclude that GlcNBu feeding in the OVX rat preserves bone mineral and some biomechanical properties. Translationally, GlcNBu can be positioned between nutriceuticals and pharmaceuticals for the prevention and treatment of osteoporosis. Advantages include low production costs and a favorable safety profile.

Bone morphogenetic proteins-immobilized polydioxanone porous particles as an artificial bone graft

Bone morphogenetic proteins (BMPs)-immobilized polydioxanone (PDO)/Pluronic F127 porous particles were prepared as a bone graft using a melt-molding particulate-leaching method, and the sequential binding of heparin and BMPs (BMP-2 and BMP-7, single or dual) onto the porous particles. The prepared PDO/Pluronic F127 porous particles gradually degraded with time, with ∼30% of the initial particle weight remaining after 16 weeks. The degradation rate of the PDO/Pluronic F127 porous particles may parallel the bone-healing rate. The BMPs were easily immobilized onto the pore surfaces of PDO/Pluronic F127 particles via heparin binding and were released in a sustained manner for up to 21 days, regardless of BMP type. The BMPs (single BMP-2 or dual BMP-2/BMP-7)-immobilized porous particles were effective for in vitro osteogenesis of bone marrow stem cells (BMSCs), as analyzed by alkaline phosphatase activity, calcium content, time polymerase chain reaction using specific markers for osteogenesis (Type I collagen, osteocalcin, osteopotin, and RunX2), and immunohistochemical staining. The BMPs (single BMP-2 or dual BMP-2/BMP-7)-immobilized porous particles were also effective in promoting new bone formation, as analyzed by the preliminary animal study using a full-thickness skull defect model of Sprague-Dawley rats (microcomputed tomography). The synergistic effect of dual BMPs on the osteogenesis of BMSCs and bone regeneration was not significant in our system. The BMP-2 or dual BMPs (BMP-2/BMP-7)-immobilized PDO/Pluronic F127 porous particles may be a promising candidate as a bone graft for the delayed and insufficient bone healing in clinical fields.

Addition of bone morphogenetic protein type 2 to ascorbate and β-glycerophosphate supplementation did not enhance osteogenic differentiation of human adipose-derived stem cells

Bone morphogenetic protein type 2 (BMP-2) is a potent local factor, which promotes bone formation and has been used as an osteogenic supplement for mesenchymal stem cells.

Pathogenic mutation of ALK2 inhibits induced pluripotent stem cell reprogramming and maintenance: mechanisms of reprogramming and strategy for drug identification

Fibrodysplasia ossificans progressiva (FOP) is a rare congenital disorder characterized by progressive ossification of soft tissues. FOP is caused by mutations in activin receptor-like kinase 2 (ALK2) that cause its constitutive activation and result in dysregulation of BMP signaling. Here, we show that generation of induced pluripotent stem cells (iPSCs) from FOP-derived skin fibroblasts is repressed because of incomplete reprogramming and inhibition of iPSC maintenance. This repression was mostly overcome by specific suppression of ALK2 expression and treatment with an ALK2 inhibitor, indicating that the inhibition of iPSC generation and maintenance observed in FOP-derived skin fibroblasts results from constitutive activation of ALK2. Using this system, we identified an ALK2 inhibitor as a potential candidate for future drug development. This study highlights the potential of the inhibited production and maintenance of iPSCs seen in diseases as a useful phenotype not only for studying the molecular mechanisms underlying iPS reprogramming but also for identifying drug candidates for future therapies.

Involvement of bone morphogenetic protein activity in somatostatin actions on ovarian steroidogenesis

Somatostatin is expressed in the hypothalamus, pancreas and gastrointestinal tracts and it inhibits the secretion of various hormones in vivo. In the rodent ovary, somatostatin receptor (SSTR) subtypes 2 and 5 are expressed in granulosa cells and oocytes. Somatostatin analogs have been clinically used for treatment of endocrine tumors. For this purpose, relatively high-dose or long-term treatments of somatostatin analogs are necessary; however, the direct and continuous impact of somatostatin analogs on gonadal functions has yet to be elucidated. In the present study, we investigated the effects of somatostatin analogs (octreotide and pasireotide) on ovarian steroidogenesis by rat primary granulosa cell culture. The expression levels of SSTR2 and SSTR5 in granulosa cells were upregulated by FSH treatment. Treatment with somatostatin analogs decreased FSH-induced estradiol production with reduction in aromatase mRNA expression, while the treatment also suppressed FSH-induced progesterone production with reduction of mRNAs levels of StAR, P450scc and 3βHSD2 in granulosa cells. This trend was also observed in a granulosa/oocyte co-culture condition. The effect of pasireotide was more potent than that of octreotide. FSH-induced synthesis of steroids and cAMP was also suppressed by somatostatin analog treatment. Notably, pretreatment with a BMP-binding protein, noggin reversed the suppressive effects of somatostatin analogs on progesterone and cAMP production, suggesting that the endogenous BMP system is functionally involved in the SSTR effects in granulosa cells. Treatment with BMP-2, -4, -6 and -7 decreased the mRNA expression of inhibitory Smads6 and 7, leading to enhancement of BMP actions detected by Id-1 transcription in granulosa cells. Collectively, the results revealed that SSTR activation modulates ovarian steroidogenesis by upregulating endogenous BMP activity in growing follicles.

ALK2 and BMPR2 knockdown and endothelin-1 production by pulmonary microvascular endothelial cells

BACKGROUND

Many cases of pulmonary arterial hypertension (PAH) are heritable and related to gene mutations in bone morphogenic receptor-2 (BMPR2). These patients consequently may have a signaling imbalance within the transforming growth factor beta (TGFβ) receptor superfamily. The causes of increased endothelin-1 (ET-1), which contributes to PAH, are unknown, and we therefore studied the contribution of various BMPs and their receptors on ET-1 production in vitro, after knockdown of BMPR2 in human pulmonary microvascular endothelial cells (HMVEC-LBl).

METHODOLOGY/PRINCIPAL FINDINGS

Receptor knockdown in HMVEC-LBl was performed using siRNA to BMPR2, and activin like-kinases 1 and 2 (ALK1, ALK2). ET-1 and TGFβ levels in the medium were measured by ELISA. In some experiments, cells were exposed to TGFβ or BMP7 or FK506 (tacrolimus). Using Western blotting, levels of BMPR2, endothelin ET(B) receptor, phosphorylated SMAD 2 (pSMAD 2), phosphorylated SMAD 1,5 (pSMAD 1,5), ALK1, ALK2, ALK5, TGFβ receptor 2, plasminogen activator inhibitor-1 (PAI-1) and ID1 were measured. BMPR2 knockdown significantly increased ET-1 levels. It did not affect ET(B) receptor or TGFβ levels. TGFβ increased ET-1 levels, with or without BMPR2 knockdown. BMPR2 knockdown did not affect TGFβ (pSMAD 2 and PAI-1) signaling. BMP7 increased ET-1 levels after BMPR2 knockdown but this was prevented by ALK2 knockdown as was the increase in ID1 caused by BMPR2 knockdown. FK506, which interacts with ALK2, increased ET-1 levels and ID1 levels, and this was blocked by ALK2 knockdown.

CONCLUSION/SIGNIFICANCE

ALK2 may be an important receptor in ET-1 production during BMPR2 knockdown.

Mullerian inhibiting substance recruits ALK3 to regulate Leydig cell differentiation

Müllerian inhibiting substance (MIS) not only induces Müllerian duct regression during male sexual differentiation but also modulates Leydig cell steroidogenic capacity and differentiation. MIS actions are mediated through a complex of homologous receptors: a type II ligand-binding receptor [MIS type II receptor (MISRII)] and a tissue-specific type I receptor that initiates downstream signaling. The putative MIS type I receptors responsible for Müllerian duct regression are activin A type II receptor, type I [Acvr1/activin receptor-like kinase 2 (ALK2)], ALK3, and ALK6, but the one recruited by MIS in Leydig cells is unknown. To identify whether ALK3 is the specific type I receptor partner for MISRII in Leydig cells, we generated Leydig cell-specific ALK3 conditional knockout mice using a Cre-lox system and compared gene expression and steroidogenic capacity in Leydig cells of ALK3(fx/fx)Cyp17(cre+) and control mice (ALK3(fx/fx)Cyp17(cre-) or ALK3(fx/wt)Cyp17(cre-) littermates). We found reduced mRNA expression of the genes encoding P450c17, StAR, and two enzymes (17βHSD-III and 3βHSD-VI) that are expressed in differentiated adult Leydig cells and increased expression of androgen-metabolizing enzymes (3α-HSD and SRD5A2) and proliferating cell nuclear antigen (PCNA) in Leydig cells of ALK3(fx/fx)Cyp17(cre+) mice. Despite down-regulation of steroidogenic capacity in ALK3(fx/fx)Cyp17(cre+) mice, the loss of MIS signaling also stimulates Leydig cell proliferation such that plasma testosterone and androstenedione concentrations are comparable to that of control mice. Collectively, these results indicate that the phenotype in ALK3 conditional knockout mice is similar to that of the MIS-knockout mice, confirming that ALK3 is the primary type I receptor recruited by the MIS-MISRII complex during Leydig cell differentiation.

Effect of endoglin overexpression during embryoid body development

Increasing evidence points to endoglin (Eng), an accessory receptor for the transforming growth factor-β superfamily commonly associated with the endothelial lineage, as an important regulator of the hematopoietic lineage. We have shown that lack of Eng results in reduced numbers of primitive erythroid colonies as well as downregulation of key hematopoietic genes. To determine the effect of Eng overexpression in hematopoietic development, we generated a doxycycline-inducible embryonic stem cell line. Our results demonstrate that induction of Eng during embryoid body differentiation leads to a significant increase in the frequency of hematopoietic progenitors, in particular, the erythroid lineage, which correlated with upregulation of Scl, Gata1, Runx1, and embryonic globin. Interestingly, activation of the hematopoietic program happened at the expense of endothelial and cardiac cells, as differentiation into these mesoderm lineages was compromised. Eng-induced enhanced erythroid activity was accompanied by high levels of Smad1 phosphorylation. This effect was attenuated by addition of a bone morphogenetic protein (BMP) signaling inhibitor to these cultures. Among the BMPs, BMP4 is well known for its role in hematopoietic specification from mesoderm by promoting expression of several hematopoietic genes, including Scl. Because Scl is considered the master regulator of the hematopoietic program, we investigated whether Scl would be capable of rescuing the defective hematopoietic phenotype observed in Eng(-/-) embryonic stem cells. Scl expression in Eng-deficient embryonic stem cells resulted in increased erythroid colony-forming activity and upregulation of Gata1 and Gata2, positioning Eng upstream of Scl. Taken together, these findings support the premise that Eng modulates the hematopoietic transcriptional network, most likely through regulation of BMP4 signaling.

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.

Bone morphogenetic protein-3b (BMP-3b) inhibits osteoblast differentiation via Smad2/3 pathway by counteracting Smad1/5/8 signaling

Despite the involvement of BMP-3b (also called GDF-10) in osteogenesis, embryogenesis and adipogenesis, the functional receptors and intracellular signaling of BMP-3b have yet to be elucidated. In the present study, we investigated the cellular mechanism of BMP-3b in osteoblast differentiation using mouse myoblastic C2C12 cells. BMP-3b stimulated activin/TGF-β-responsive promoter activities. The stimulatory actions of BMP-3b on activin/TGF-β-responsive activities were suppressed by co-treatment with BMP-2. BMP-responsive promoter activities stimulated by BMP-2 were significantly inhibited by treatment with BMP-3b. BMP-3b suppressed the expression of osteoblastic markers including Runx2, osteocalcin and type-1 collagen induced by BMP-2, -4, -6 and -7. BMP-2-induced Smad1/5/8 phosphorylation and mRNA levels of the BMP target gene Id-1 were suppressed by co-treatment with BMP-3b, although BMP-3b failed to activate Smad1/5/8 signaling. Of interest, the BMP-3b suppression of BMP-2-induced Id-1 expression was not observed in cells overexpressing Smad4 molecules. On the other hand, BMP-3b directly activated Smad2/3 phosphorylation and activin/TGF-β target gene PAI-1 mRNA expression, while BMP-2 suppressed BMP-3b-induced Smad2/3 signal activation. BMP-2 inhibition of BMP-3b-induced PAI-1 expression was also reversed by overexpression of Smad4. Analysis using inhibitors for BMP-Smad1/5/8 pathways revealed that these BMP-3b effects were mediated via receptors other than ALK-2, -3 and -6. Furthermore, results of inhibitory studies using extracellular domains for BMP receptor constructs showed that the activity of BMP-3b was functionally facilitated by a combination of ALK-4 and ActRIIA. Collectively, BMP-3b plays an inhibitory role in the process of osteoblast differentiation, in which BMP-3b and BMP-2 are mutually antagonistic possibly by competing with the availability of Smad4.

Surface immobilization of bone morphogenetic protein 2 via a self-assembled monolayer formation induces cell differentiation

Bone extracellular matrix consists of a network of proteins in which growth factors, like bone morphogenetic protein 2 (BMP-2), are embedded and released upon matrix turnover and degradation. Recombinant human (rh)BMP-2 shows promise in enhancing bone fracture repair, although issues regarding finding a suitable delivery system still limit its extensive clinical use. The aim of this study is to determine which cell activities are triggered by the presentation of immobilized rhBMP-2. For this purpose gold surfaces were first decorated with a self-assembled monolayer consisting of a hetero-bifunctional linker. rhBMP-2 was covalently bound to the surfaces via this linker and used to investigate the cellular responses of C2C12 myoblasts. We show that covalently immobilized rhBMP-2 (iBMP-2) initiates short-term signaling events. Using a BMP-responsive reporter gene assay and western blotting to monitor phosphorylation of Smad1/5/8 we prove that iBMP-2 activates BMP-dependent signal transduction. Furthermore, we demonstrate that iBMP-2 suppresses myotube formation and promotes the osteoblast phenotype in C2C12 cells. The bioactivity of surface-bound rhBMP-2 presented in this study is not due to its release into the medium. As such, our simple approach paves the way for the controlled local presentation of immobilized growth factors, limiting degradation while still maintaining biological activity.

New insights into the molecular mechanism of multiple synostoses syndrome (SYNS): mutation within the GDF5 knuckle epitope causes noggin-resistance

Growth and differentiation factor 5 (GDF5), a member of the bone morphogenetic protein (BMP) family, is essential for cartilage, bone, and joint formation. Antagonists such as noggin counteract BMP signaling by covering the ligand's BMP type I (BMPRI) and type II (BMPRII, ActRII, ActRIIB) interaction sites. The mutation GDF5-S94N is located within the BMPRII interaction site, the so-called knuckle epitope, and was identified in patients suffering from multiple synostoses syndrome (SYNS). SYNS is characterized by progressive symphalangism, carpal/tarsal fusions, deafness and mild facial dysmorphism. Here we present a novel molecular mechanism of a GDF5 mutation affecting chondrogenesis and osteogenesis. GDF5-S94N exhibits impaired binding to BMPRII causing alleviated Smad and non-Smad signaling and reduced chondrogenic differentiation of ATDC5 cells. Surprisingly, chondrogenesis in mouse micromass cultures was strongly enhanced by GDF5-S94N. By using quantitative techniques (SPR, reporter gene assay, ALP assay, qPCR), we uncovered that this gain of function is caused by strongly reduced affinity of GDF5-S94N to the BMP/GDF antagonist noggin and the consequential lack of noggin inhibition. Thus, since noggin is upregulated during chondrogenic differentiation, GDF5-S94N exceeds the GDF5 action, which results in the phenotypic outcome of SYNS. The detailed molecular characterization of GDF5-S94N as a noggin-resistant growth factor illustrates the potential of GDF5 mutants in applications with defined therapeutical needs.