BMP and BMP Inhibitors in Bone

The Role of Neuromodulation and Potential Mechanism in Regulating Heterotopic Ossification

Heterotopic ossification (HO) is a pathological process characterized by the aberrant formation of bone in muscles and soft tissues. It is commonly triggered by traumatic brain injury, spinal cord injury, and burns. Despite a wide range of evidence underscoring the significance of neurogenic signals in proper bone remodeling, a clear understanding of HO induced by nerve injury remains rudimentary. Recent studies suggest that injury to the nervous system can activate various signaling pathways, such as TGF-β, leading to neurogenic HO through the release of neurotrophins. These pathophysiological changes lay a robust groundwork for the prevention and treatment of HO. In this review, we collected evidence to elucidate the mechanisms underlying the pathogenesis of HO related to nerve injury, aiming to enhance our understanding of how neurological repair processes can culminate in HO.

Regulation mechanism of endochondral ossification in Rana zhenhaiensis during metamorphosis based on histomorphology and transcriptome analyses

Endochondral ossification plays a crucial role in the limb development of amphibians. This study explored the ossification sequence in the hindlimb of Rana zhenhaiensis tadpoles and the correlation between thyroid hormones (THs) and endochondral ossification via histomorphology and transcriptional analyses. Our results suggest that ossification of the femur and tibiofibula was initiated during the period of high THs activity (metamorphosis climax). In addition, the results of differentially expressed gene analyses in the hindlimb and tail showed that systemic factors, transcription factors, and locally secreted factors interacted with each other during the metamorphosis climax to regulate the occurrence of endochondral ossification. These results will enrich the morphological data of anurans and provide scientific reference for the evolutionary history of vertebrates.

GREM2 inactivation increases trabecular bone mass in mice

Osteoporosis is a common skeletal disease affecting millions of individuals world-wide, with an increased risk of fracture, and a decreased quality of life. Despite its well-known consequences, the etiology of osteoporosis and optimal treatment methods are not fully understood. Human genetic studies have identified genetic variants within the FMN2/GREM2 locus to be associated with trabecular volumetric bone mineral density (vBMD) and vertebral and forearm fractures, but not with cortical bone parameters. GREM2 is a bone morphogenetic protein (BMP) antagonist. In this study, we employed Grem2-deficient mice to investigate whether GREM2 serves as the plausible causal gene for the fracture signal at the FMN2/GREM2 locus. We observed that Grem2 is moderately expressed in bone tissue and particularly in osteoblasts. Complete Grem2 gene deletion impacted mouse survival and body growth. Partial Grem2 inactivation in Grem2+/- female mice led to increased trabecular BMD of femur and increased trabecular bone mass in tibia due to increased trabecular thickness, with an unchanged cortical thickness, as compared with wildtype littermates. Furthermore, Grem2 inactivation stimulated osteoblast differentiation, as evidenced by higher alkaline phosphatase (Alp), osteocalcin (Bglap), and osterix (Sp7) mRNA expression after BMP-2 stimulation in calvarial osteoblasts and osteoblasts from the long bones of Grem2-/- mice compared to wildtype littermates. These findings suggest that GREM2 is a possible target for novel osteoporotic treatments, to increase trabecular bone mass and prevent osteoporotic fractures.

Proteomics of CKD progression in the chronic renal insufficiency cohort

Progression of chronic kidney disease (CKD) portends myriad complications, including kidney failure. In this study, we analyze associations of 4638 plasma proteins among 3235 participants of the Chronic Renal Insufficiency Cohort Study with the primary outcome of 50% decline in estimated glomerular filtration rate or kidney failure over 10 years. We validate key findings in the Atherosclerosis Risk in the Communities study. We identify 100 circulating proteins that are associated with the primary outcome after multivariable adjustment, using a Bonferroni statistical threshold of significance. Individual protein associations and biological pathway analyses highlight the roles of bone morphogenetic proteins, ephrin signaling, and prothrombin activation. A 65-protein risk model for the primary outcome has excellent discrimination (C-statistic[95%CI] 0.862 [0.835, 0.889]), and 14/65 proteins are druggable targets. Potentially causal associations for five proteins, to our knowledge not previously reported, are supported by Mendelian randomization: EGFL9, LRP-11, MXRA7, IL-1 sRII and ILT-2. Modifiable protein risk markers can guide therapeutic drug development aimed at slowing CKD progression.

Between a rock and a hard place: Regulation of mineralization in the periodontium

The periodontium supports and attaches teeth via mineralized and nonmineralized tissues. It consists of two, unique mineralized tissues, cementum and alveolar bone. In between these tissues, lies an unmineralized, fibrous periodontal ligament (PDL), which distributes occlusal forces, nourishes and invests teeth, and harbors progenitor cells for dentoalveolar repair. Many unanswered questions remain regarding periodontal biology. This review will focus on recent research providing insights into one enduring mystery: the precise regulation of the hard-soft tissue borders in the periodontium which define the interfaces of the cementum-PDL-alveolar bone structure. We will focus on advances in understanding the molecular mechanisms that maintain the unmineralized PDL "between a rock and a hard place" by regulating the mineralization of cementum and alveolar bone.

A Process for the Design and Development of Novel Bone Morphogenetic Protein-7 (BMP-7) Mimetics With an Example: THR-184

Growth Factors have been evaluated as therapeutic targets for the treatment of a broad spectrum of diseases. Because they are proteins with pleiotropic effects, the quest to harness their beneficial effects has presented challenges. Most Growth Factors operate at the extracellular-receptor level and have natural feedback mechanisms that modulate their effects. As proteins, they are difficult and expensive to manufacture. Frequently proteins must be administered parenterally, may invoke an immune response, and may be neutralized by naturally occurring inhibitors. To circumvent these limitations, we have undertaken an effort to develop mimetics for the Bone Morphogenetic Protein (BMP) signaling pathway effects that incorporate the beneficial effects, eliminate the deleterious effects, and thereby create effective drug-like compounds.To this end, we have designed and tested a family of small peptide BMP mimetics. The design used the three-dimensional structure of BMP-7 to identify likely active surface regions. Lead sequences were then optimized based on in vitro assays that examine the selective binding to BMP receptors, demonstrate the phosphorylation of Smad-1,5,8, detect anti-apoptosis and anti-inflammation, and block the epithelial to mesenchymal transition (EMT) in renal tubular epithelial cells. These sequences were further optimized using in vivo assays of the attenuation of acute kidney injury in a rat-model of unilateral clamp ischemic reperfusion. This process uses a Structure Variance Analysis algorithm (SVA) to identify structure/activity relationships. One member of this family, THR-184, is an agonist of BMP signaling and a potent antagonist of TGFβ signaling. This small peptide mimetic inhibits inflammation, apoptosis, fibrosis and reverses epithelial to mesenchymal transition (EMT) by regulating multiple signaling pathways involved in the cellular injury of multiple organs. Its effects have been shown to control Acute Kidney Injury (AKI). THR-184 has progressed through phase I and II clinical trials for the prevention of Cardio-Vascular Surgery (CVS) associated AKI. This work provides a roadmap for the development of other growth factor mimetics and demonstrates how we might harness their therapeutic potential.

Fabrication of an ordered micro-/nanotextured titanium surface to improve osseointegration

Ordered microscale titanium (Ti) surface topography with homogeneous cell-sized microholes (20 µm in diameter) was fabricated using simple electrochemical etching. The as-prepared surface imposed with uniform titania nanotubes (TNTs, 70 nm in diameter) through electrochemical anodization showed no considerable change in the initial microscale morphology. Bone marrow mesenchymal stem cells (BMSCs) were used in evaluating the bioactivity. Compared with polished Ti and unordered microtextured Ti, the ordered microtextured Ti formed by electrochemical etching remarkably promoted cell attachment, alkaline phosphatase activity, collagen secretion, extracellular matrix mineralization, and osteogenesis-related gene expression but considerably inhibited cell proliferation. After TNTs were introduced to the ordered microtextured Ti, cell attachment and osteogenic differentiation indexes were further enhanced, and cell proliferation recovered over time. The ordered micro-/nanotextured Ti surface was more conducive to the cell attachment, proliferation, and osteogenesis of BMSCs than polished Ti with and without TNTs, unordered microtextured Ti with and without TNTs, and unitary ordered microtextured Ti. Thus, the novel ordered bio-inspired micro-/nanotextured structure composed of cell-sized microholes and TNTs on the Ti surface possessed a favorable interfacial environment that improved osseointegration, potentially optimizing Ti implant surface topography.

Signaling network regulating osteogenesis in mesenchymal stem cells

Osteogenesis is an important developmental event that results in bone formation. Bone forming cells or osteoblasts develop from mesenchymal stem cells (MSCs) through a highly controlled process regulated by several signaling pathways. The osteogenic lineage commitment of MSCs is controlled by cell-cell interactions, paracrine factors, mechanical signals, hormones, and cytokines present in their niche, which activate a plethora of signaling molecules belonging to bone morphogenetic proteins, Wnt, Hedgehog, and Notch signaling. These signaling pathways individually as well as in coordination with other signaling molecules, regulate the osteogenic lineage commitment of MSCs by activating several osteo-lineage specific transcription factors. Here, we discuss the key signaling pathways that regulate osteogenic differentiation of MSCs and the cross-talk between them during osteogenic differentiation. We also discuss how these signaling pathways can be modified for therapy for bone repair and regeneration.

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.

Therapeutic potential of triptolide in autoimmune diseases and strategies to reduce its toxicity

With the increasing epidemiology of autoimmune disease worldwide, there is an urgent need for effective drugs with low cost in clinical treatment. Triptolide, the most potent bioactive compound from traditional Chinese herb Tripterygium Wilfordii Hook F, possesses immunosuppression and anti-inflammatory activity. It is a potential drug for the treatment of various autoimmune diseases, but its clinical application is still restricted due to severe toxicity. In this review, the pharmacodynamic effects and pharmacological mechanisms of triptolide in autoimmune diseases are summarized. Triptolide exerts therapeutic effect by regulating the function of immune cells and the expression of cytokines through inflammatory signaling pathways, as well as maintaining redox balance and gut microbiota homeostasis. Meanwhile, the research progress on toxicity of triptolide to liver, kidney, reproductive system, heart, spleen, lung and gastrointestinal tract has been systematically reviewed. In vivo experiments on different animals and clinical trials demonstrate the dose- and time- dependent toxicity of triptolide through different administration routes. Furthermore, we focus on the strategies to reduce toxicity of triptolide, including chemical structural modification, novel drug delivery systems, and combination pharmacotherapy. This review aims to reveal the potential therapeutic prospect and limitations of triptolide in treating autoimmune diseases, thus providing guiding suggestions for further study and promoting its clinical translation.

USF2 reduces BMP3 expression via transcriptional activation of miR-34a, thus promoting osteogenic differentiation of BMSCs

INTRODUCTION

Osteoporosis is the most susceptible disease for people over 60. The main cause of osteoporosis is the decreased osteogenic differentiation of mesenchymal stem cells (MSCs). Here we showed that upstream stimulatory factor 2 (USF2)/microRNA-34a (miR-34a)/bone morphogenetic protein 3 (BMP3) axis regulated osteogenic differentiation of BMSCs.

MATERIALS AND METHODS

USF2 and miR-34a expression were examined using qPCR. Protein levels of BMP3 and osteogenic markers expression were evaluated using both western blot and qPCR. Activity of ALP was determined by ALP assay kit. Mineralization capacity of hBMSCs was assessed using ARS. Besides, CHIP assay was employed to verify whether USF2 could bind to miR-34a promoter. Finally, RIP assay and dual-luciferase reporter assay were employed to verify whether miR-34a directly bound to BMP3.

RESULTS

Our results suggested that miR-34a was upregulated during osteogenic differentiation of BMSCs, and miR-34a overexpression could enhance osteogenic differentiation of BMSCs. USF2 could positively regulate miR-34a expression by interacting with its promoter. USF2 overexpression enhanced osteogenic differentiation of BMSCs, while miR-34a inhibition reversed the effect. Besides, BMP3 was the target of miR-34a. MiR-34a overexpression enhanced osteogenic differentiation of BMSCs, which was abolished by BMP3 overexpression.

CONCLUSION

Taken together, USF2 enhanced osteogenic differentiation of BMSCs via downregulating BMP3 by interacting with miR-34a promoter.

Role of Inhibitor SMADs in Stage 3 Grade B periodontitis before and after periodontal treatment

OBJECTIVE

This study aimed to examine the levels of transforming growth factor-beta (TGF-β) and inhibitory-Smads (I-Smads) in saliva and gingival crevicular fluid (GCF) in patients with Stage 3 Grade B periodontitis before and after non-surgical periodontal treatment.

BACKGROUND

Recently, it has been stated that Smads play an active role in all conditions where TGF-β is involved, including periodontal inflammation.

METHODS

Twenty healthy participants (control) and 20 patients with Stage 3, Grade B periodontitis were recruited. GCF and saliva samples and clinical periodontal recordings were investigated at the baseline and 1 month after treatment. TGF-β and I-Smads (Smads 6 and 7) were determined by ELISA.

RESULTS

Salivary Smad6 and Smad7 levels were significantly lower in the periodontitis group than healthy controls (p < .05), while there was no difference in salivary TGF-β levels between groups at baseline (p > .05). The total amounts and concentrations of GCF TGF-β, Smad6, and Smad7 were significantly lower in the periodontitis group than healthy controls at baseline (p < .05), and then decreased in concentration levels with treatment (p < .001). Positive correlations were found between total amounts and concentrations of GCF TGF-β, Smad6, and Smad7 (p < .05).

CONCLUSION

Our findings revealed that Smad6 and Smad7 in GCF and saliva decreased in periodontitis and then increased after periodontal treatment. Our study suggests that I-Smads act in parallel with TGF-β in periodontal inflammation and may have a role in the development of periodontitis.

Craniosynostosis: current conceptions and misconceptions

Cranial bones articulate in areas called sutures that must remain patent until skull growth is complete. Craniosynostosis is the condition that results from premature closure of one or more of the cranial vault sutures, generating facial deformities and more importantly, skull growth restrictions with the ability to severely affect brain growth. Typically, craniosynostosis can be expressed as an isolated event, or as part of syndromic phenotypes. Multiple signaling mechanisms interact during developmental stages to ensure proper and timely suture fusion. Clinical outcome is often a product of craniosynostosis subtypes, number of affected sutures and timing of premature suture fusion. The present work aimed to review the different aspects involved in the establishment of craniosynostosis, providing a close view of the cellular, molecular and genetic background of these malformations.

Effect of interleukin-1β on bone morphogenetic protein-9-induced osteoblastic differentiation of human periodontal ligament fibroblasts

Bone morphogenetic protein-9 (BMP-9) has been shown to potently induce osteoblastic differentiation of periodontal ligament fibroblasts (PDLFs) and may be a candidate therapeutic agent for periodontal tissue healing/regeneration, but the effect of the inflammatory environment of periodontitis on such approaches is unclear. We investigated whether interleukin-1β (IL-1β) affected BMP-9-mediated osteoblastic differentiation of human (h) PDLFs. IL-1β suppressed BMP-9-induced osteogenic differentiation of hPDLFs, as evidenced by reduced alkaline phosphatase (ALP) activity and mineralization, and the downregulated expression of BMP-9-mediated bone-related genes, RUNX2, SP7, IBSP, and SPP1. In hPDLFs, with or without BMP-9, IL-1β increased the protein expression of activin A, a BMP-9 antagonist, and decreased follistatin protein, an antagonist of activin A. Similarly, IL-1β upregulated the expression of the activin A gene and downregulated that of the follistatin gene. Notably, follistatin re-established BMP-9-induced ALP activity suppressed by IL-1β. Activin A inhibited the expression of BMP-9-responsive genes and BMP-9-induced ALP activity, while follistatin re-established them. Finally, extracellular signal-regulated kinase 1/2 (ERK1/2), p38, and nuclear factor-kappa B (NF-κB) inhibition significantly blocked IL-1β-induced activin A gene expression. Our data indicate that IL-1β inhibits BMP-9-induced osteoblastic differentiation of hPDLFs, possibly by promoting activin A production via the ERK1/2, p38, and NF-κB pathways.

Identification of key genes and pathways of BMP-9-induced osteogenic differentiation of mesenchymal stem cells by integrated bioinformatics analysis

Background

The purpose of present study was to identify the differentially expressed genes (DEGs) associated with BMP-9-induced osteogenic differentiation of mesenchymal stem cells (MSCs) by using bioinformatics methods.

Methods

Gene expression profiles of BMP-9-induced MSCs were compared between with GFP-induced MSCs and BMP-9-induced MSCs. GSE48882 containing two groups of gene expression profiles, 3 GFP-induced MSC samples and 3 from BMP-9-induced MSCs, was downloaded from the Gene Expression Omnibus (GEO) database. Then, DEGs were clustered based on functions and signaling pathways with significant enrichment analysis. Pathway enrichment analysis using the Kyoto Encyclopedia of Genes and Genomes (KEGG) demonstrated that the identified DEGs were potentially involved in cytoplasm, nucleus, and extracellular exosome signaling pathway.

Results

A total of 1967 DEGs (1029 upregulated and 938 downregulated) were identified from GSE48882 datasets. R/Bioconductor package limma was used to identify the DEGs. Further analysis revealed that there were 35 common DEGs observed between the samples. GO function and KEGG pathway enrichment analysis, among which endoplasmic reticulum, protein export, RNA transport, and apoptosis was the most significant dysregulated pathway. The result of protein-protein interaction (PPI) network modules demonstrated that the Hspa5, P4hb, Sec61a1, Smarca2, Pdia3, Dnajc3, Hyou1, Smad7, Derl1, and Surf4 were the high-degree hub nodes.

Conclusion

Taken above, using integrated bioinformatical analysis, we have identified DEGs candidate genes and pathways in BMP-9 induced MSCs, which could improve our understanding of the key genes and pathways for BMP-9-induced osteogenic of MSCs.

Enhanced BMP signalling causes growth plate cartilage dysrepair in rats

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

Morphogens and growth factor signalling in the myeloma bone-lining niche

Multiple myeloma is a malignancy caused by the clonal expansion of abnormal plasma cells. Myeloma cells have proven to be incredibly successful at manipulating their microenvironment to promote growth and to evade modern therapies. They have evolved to utilise the integral signalling pathways of the bone and bone marrow to drive disease progression. The bone marrow is often described in the context of a single structure that fills the bone cavity and supports normal haematopoiesis. However, within that structure exists two anatomically different niches, the perivascular niche and the endosteal niche. These contain different cell types functioning to support normal immune and blood cell production as well as healthy bone. These cells secrete numerous signalling molecules that can influence myeloma cell biology and behaviour. The endosteal niche is home to specific bone cell lineages and plays a pivotal role in myeloma cell establishment and survival. This review will concentrate on some of the signalling pathways that are hijacked by myeloma cells to shape a favourable environment, and the different influences myeloma cells are exposed to depending on their spatial location within the bone marrow.

Bone Morphogenetic Protein-2 Induces Non-Canonical Inflammatory and Oxidative Pathways in Human Retinal Endothelial Cells

The mechanisms of diabetic retinopathy (DR), are not yet fully understood. We previously demonstrated an upregulation of retinal bone morphogenetic protein-2 (BMP2) in experimental diabetes and in retinas of diabetic human subjects. The purpose of current study was to investigate the role of non-canonical inflammatory pathway in BMP2-induced retinal endothelial cell (REC) barrier dysfunction. For this purpose, we used RT-PCR and western blotting to evaluate the levels of BMP2 signaling components (BMP2, BMP4, BMP receptors), VEGF, phosphorylated p38 MAPK and NFκB, and oxidative stress markers in cultured human retinal endothelial cells (HRECs) subjected to BMP2 (50ng/ml) for up to 24 h. Also, effect of high glucose (HG, 30mM D-glucose) on the expression of BMP2 and its downstream genes was examined in HRECs. H2-DCF is a fluorogenic dye that measures the levels of cellular reactive oxygen species (ROS) was used to measure the pro-oxidative effect of BMP2. Moreover, we evaluated the effect of inhibiting p38 and VEGF signaling on BMP2-induced HRECs barrier dysfunction by measuring the trans-endothelial cell electrical resistance (TER) using electric cell-substrate impedance sensing (ECIS). We also tested the effect of HG on the integrity of HRECs barrier in the presence or absence of inhibitors of BMP2 signaling. Our data reveals that BMP2 and high glucose upregulates BMP components of the BMP signaling pathway (SMAD effectors, BMP receptors, and TGFβ ligand itself) and induces phosphorylation of p38 MAPK and NFκB with nuclear translocation of NFκB. Inhibition of p38 or NFκB attenuated BMP2-induced VEGF expression and barrier dysfunction in HRECs. Also, inhibition of VEGFR2 attenuated BMP2-induced barrier dysfunction. Moreover, BMP2 induces generation of ROS and endothelial nitric oxide synthase (eNOS) expression and activity in HRECs. Finally, HG upregulated BMP2 and its downstream genes (SMAD, BMP4, ALKs, and TGF-β) in HRECs and BMP2 inhibitors attenuated HG-induced HRECs barrier dysfunction. Our results suggest that in addition to the regular canonical SMAD signaling BMP2 induces non-canonical inflammatory pathway in HRECs via activation of p38/NFκB pathway that causes the upregulation of VEGF and the disruption of HRECs. Inhibition of BMP2 signaling is a potential therapeutic intervention to preserve endothelial cell barrier function in DR.

Integrated In Silico-In Vitro Identification and Optimization of Bone Morphogenic Protein-2 Armpit Epitope as Its Antagonist Binding Site

Bone morphogenic protein-2 (BMP-2) is the most documented member of BMP family and plays a crucial role in bone formation and growth. In this study, we systematically analyze and compare the complex crystal structures and interaction properties of BMP-2 with its cognate receptors BMPR-I/BMPR-II and with its natural antagonist crossveinless-2 (CV-2) using an integrated in silico-in vitro strategy. It is found that the antagonist-binding site is not fully overlapped with the two receptor-binding sites on BMP-2 surface; the antagonist can competitively disrupt BMP-2-BMPR-II interaction using a blocking-out-of-site manner, but has no substantial influence on BMP-2-BMPR-I interaction. Here, the antagonist-binding site is assigned as a new functional epitope armpit to differ from the traditional conformational epitope wrist and linear epitope knuckle at receptor-binding sites. Structural analysis reveals that the armpit comprises three sequentially discontinuous, structurally vicinal peptide segments, separately corresponding to a loop region and two β-strands crawling on the protein surface. The three segments cannot work independently when splitting from the protein context, but can restore binding capability to CV-2 if they are connected to a single peptide. A systematic combination of different-length polyglycine linkers between these segments obtains a series of designed single peptides, from which several peptides that can potently interact with the armpit-recognition site of CV-2 with high affinity and specificity are identified using energetic analysis and fluorescence assay; they are expected to target BMP-2-CV-2 interaction in a self-inhibitory manner.

Discovery, synthesis and characterization of a series of 7-aryl-imidazo[1,2-a]pyridine-3-ylquinolines as activin-like kinase (ALK) inhibitors

The activin-like kinases are a family of kinases that play important roles in a variety of disease states. Of this class of kinases, ALK2, has been shown by a gain-of-function to be the primary driver of the childhood skeletal disease fibrodysplasia ossificans progressiva (FOP) and more recently the pediatric cancer diffuse intrinsic pontine glioma (DIPG). Herein, we report our efforts to identify a novel imidazo[1,2-a]pyridine scaffold as potent inhibitors of ALK2 with good in vivo pharmacokinetic properties suitable for future animal studies.

Extracellular BMP Antagonists, Multifaceted Orchestrators in the Tumor and Its Microenvironment

The bone morphogenetic proteins (BMPs), a subgroup of the transforming growth factor-β (TGF-β) superfamily, are involved in multiple biological processes such as embryonic development and maintenance of adult tissue homeostasis. The importance of a functional BMP pathway is underlined by various diseases, including cancer, which can arise as a consequence of dysregulated BMP signaling. Mutations in crucial elements of this signaling pathway, such as receptors, have been reported to disrupt BMP signaling. Next to that, aberrant expression of BMP antagonists could also contribute to abrogated signaling. In this review we set out to highlight how BMP antagonists affect not only the cancer cells, but also the other cells present in the microenvironment to influence cancer progression.

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.

Effect of inducible bone morphogenetic protein 2 expression on the osteogenic differentiation of dental pulp stem cells in vitro

Bone morphogenetic protein 2 (BMP-2) is a member of the transforming growth factor-β superfamily, it is known to be a factor involved in skeletal development and capable of inducing in vitro osteogenic differentiation of mesenchymal stem cells (MSCs). Dental pulp stem cells (DPSCs) isolated from extracted third molar teeth are an ideal resource for bone tissue engineering and regeneration applications, due to their convenient isolation, safe cryopreservation, and easy maintenance in cell cultures. The aims of this study were to deliver BMP-2 under control of the tetracycline-inducible (tet-on) promoter into dental pulp stem cells and to examine whether these BMP-2 expressing cell lines are capable of promoting osteogenic differentiation in vitro. BMP-2 gene was cloned into the lentiviral transfer plasmid pTet-IRES-EGFP and used to establish the DPSC-BMP-2 cell line. DPSC, DPSC-GFP (mock) and DPSC-BMP-2 cell lines were cultured in growth medium or osteogenic medium in the presence or absence of 100 ng/ml doxycycline. To assess differentiation, alkaline phosphatase activity, calcium accumulation and gene transcription levels of different genes involved in osteogenic differentiation (BMP-2, Runx2, alkaline phosphatase, and noggin) were measured. Doxycycline-induced BMP-2 expression induced the differentiation of DPSCs into the preosteoblastic stage but could not favor the further maturation into osteoblasts and osteocytes. We found that while Runx2 gene transcription was continuously upregulated in doxycycline-treated DPSC-BMP-2 cells, the alkaline phosphatase activity and the accumulation of minerals were reduced. As a result of the increased BMP-2 expression, the transcription level of the BMP antagonist noggin was also upregulated, and probably caused the observed effects regarding alkaline phosphatase (ALP) activity and mineral deposition. Our study shows that this system is effective in controlling transgene expression in DPSC cell line. Exploration of all known factors affecting osteogenic differentiation and their interactions is of major importance for the field of regenerative medicine. As the metabolic reaction to the upregulated transgene transcription appears to be cell line-specific, a wrongly selected target gene and/or regulation system could have adverse effects on differentiation.

A Bone Morphogenetic Protein (BMP)-derived Peptide Based on the Type I Receptor-binding Site Modifies Cell-type Dependent BMP Signalling

Bone morphogenetic proteins (BMPs) are multifunctional cytokines of the transforming growth factor β (TGFβ) superfamily with potential therapeutic applications due to their broad biological functionality. Designing BMP mimetics with specific activity will contribute to the translational potential of BMP-based therapies. Here, we report a BMP9 peptide mimetic, P3, designed from the type I receptor binding site, which showed millimolar binding affinities for the type I receptor activin receptor like kinase 1 (ALK1), ALK2 and ALK3. Although showing no baseline activity, P3 significantly enhanced BMP9-induced Smad1/5 phosphorylation as well as ID1, BMPR2, HEY1 and HEY2 gene expression in pulmonary artery endothelial cells (hPAECs), and this activity is dependent on its alpha helix propensity. However, in human dermal microvascular endothelial cells, P3 did not affect BMP9-induced Smad1/5 phosphorylation, but potently inhibited ALK3-dependent BMP4-induced Smad1/5 phosphorylation and gene expression. In C2C12 mouse myoblast cells, P3 had no effect on BMP9-induced osteogenic signalling, which is primarily mediated by ALK2. Interestingly, a previously published peptide from the knuckle region of BMP9 was found to inhibit BMP4-induced Smad1/5 phosphorylation. Together, our data identify a BMP9-derived peptide that can selectively enhance ALK1-mediated BMP9 signalling in hPAECs and modulate BMP9 and BMP4 signalling in a cell type-specific manner.

Enhancement of MicroRNA-200c on Osteogenic Differentiation and Bone Regeneration by Targeting Sox2-Mediated Wnt Signaling and Klf4

MicroRNA (miR)-200c functions in antitumorigenesis and mediates inflammation and osteogenic differentiation. In this study, we discovered that miR-200c was upregulated in human bone marrow mesenchymal stromal cells (hBMSCs) during osteogenic differentiation. Inhibition of endogenous miR-200c resulted in downregulated osteogenic differentiation of hBMSCs and reduced bone volume in the maxilla and mandible of a transgenic mouse model. Overexpression of miR-200c by transfection of naked plasmid DNA (pDNA) encoding miR-200c significantly promoted the biomarkers of osteogenic differentiation in hBMSCs, including alkaline phosphatase, Runt-related transcription factor 2, osteocalcin, and mineral deposition. The pDNA encoding miR-200c also significantly enhanced bone formation and regeneration in calvarial defects of rat models. In addition, miR-200c overexpression was shown to downregulate SRY (sex determining region Y)-box 2 (Sox2) and Kruppel-like factor 4 by directly targeting 3'-untranslated regions and upregulate the activity of Wnt signaling inhibited by Sox2. These results strongly indicated that miR-200c may serve as a unique osteoinductive agent applied for bone healing and regeneration.

The Bone Morphogenetic Protein Signaling Inhibitor LDN-193189 Enhances Metastasis Development in Mice

Breast cancer with bone metastasis is essentially incurable with current anticancer therapies. The bone morphogenetic protein (BMP) pathway is an attractive therapeutic candidate, as it is involved in the bone turnover and in cancer cell formation and their colonization of distant organs such as the bone. We previously reported that in breast cancer cells, the ZNF217 oncogene drives BMP pathway activation, increases the metastatic growth rate in the bone, and accelerates the development of severe osteolytic lesions in mice. In the present study, we aimed at investigating the impact of the LDN-193189 compound, a potent inhibitor of the BMP type I receptor, on metastasis development in vivo. ZNF217-revLuc cells were injected into the left ventricle of nude mice (n = 16) while control mice (n = 13) were inoculated with control pcDNA6-revLuc cells. Mice from each group were treated or not with LDN-193189 for 35 days. We found that systemic LDN-193189 treatment of mice significantly enhanced metastasis development, by increasing both the number and the size of metastases. In pcDNA6-revLuc-injected mice, LDN-193189 also affected the kinetics of metastasis emergence. Altogether, these data suggest that in vivo, LDN-193189 might affect the interaction between breast cancer cells and the bone environment, favoring the emergence and development of multiple metastases. Hence, our report highlights the importance of the choice of drugs and therapeutic strategies used in the management of bone metastases.

Bone morphogenetic proteins: Their role in regulating osteoclast differentiation

The ability to create recombinant bone morphogenetic proteins (BMPs) in recent years has led to their rise as a common clinical adjuvant. Their application varies, from spinal fixation to repairing palatal clefts, to coating implants for osseointegration. In recent years questions have been raised as to the efficacy of BMPs in several of these procedures. These questions are due to the unwanted side effect of BMPs on other cell types, such as osteoclasts which can resorb bone at the graft/implant site. However, most BMP research focuses on the anabolic osteoinductive effects of BMPs on osteoblasts rather than its counterpart- stimulation of the osteoclasts, which are cells responsible for resorbing bone. In this review, we discuss the data available from multiple in-vitro and in-vivo BMP-related knockout models to elucidate the different functions BMPs have on osteoclast differentiation and activity.

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BMPs can act directly on osteoclasts to regulate differentiation and activity.

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Osteoclasts express multiple BMP signaling components.

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BMPs signal through both SMAD independent and dependent mechanisms in osteoclasts.

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SMAD dependent BMP signaling regulates osteoclast-osteoblast coupling factors.

Convergence of TGFβ and BMP signaling in regulating human bone marrow stromal cell differentiation

Targeting regulatory signaling pathways that control human bone marrow stromal (skeletal or mesenchymal) stem cell (hBMSC) differentiation and lineage fate determination is gaining momentum in the regenerative medicine field. Therefore, to identify the central regulatory mechanism of osteoblast differentiation of hBMSCs, the molecular phenotypes of two clonal hBMSC lines exhibiting opposite in vivo phenotypes, namely, bone forming (hBMSC^+bone) and non-bone forming (hBMSC^−Bone) cells, were studied. Global transcriptome analysis revealed significant downregulation of several TGFβ responsive genes, namely, TAGLN, TMP1, ACTA2, TGFβ2, SMAD6, SMAD9, BMP2, and BMP4 in hBMSC^−Bone cells and upregulation on SERPINB2 and NOG. Transcriptomic data was associated with marked reduction in SMAD2 protein phosphorylation, which thereby implies the inactivation of TGFβ and BMP signaling in those cells. Concordantly, activation of TGFβ signaling in hBMSC^−Bone cells using either recombinant TGFβ1 protein or knockdown of SERPINB2 TGFβ-responsive gene partially restored their osteoblastic differentiation potential. Similarly, the activation of BMP signaling using exogenous BMP4 or via siRNA-mediated knockdown of NOG partially restored the differentiation phenotype of hBMSC^−Bone cells. Concordantly, recombinant NOG impaired ex vivo osteoblastic differentiation of hBMSC^+Bone cells, which was associated with SERBINB2 upregulation. Our data suggests the existence of reciprocal relationship between TGFB and BMP signaling that regulates hBMSC lineage commitment and differentiation, whilst provide a plausible strategy for generating osteoblastic committed cells from hBMSCs for clinical applications.

The BMP Pathway and Its Inhibitors in the Skeleton

Bone morphogenetic proteins (BMPs) constitute the largest subdivision of the transforming growth factor-β family of ligands. BMPs exhibit widespread utility and pleiotropic, context-dependent effects, and the strength and duration of BMP pathway signaling is tightly regulated at numerous levels via mechanisms operating both inside and outside the cell. Defects in the BMP pathway or its regulation underlie multiple human diseases of different organ systems. Yet much remains to be discovered about the BMP pathway in its original context, i.e., the skeleton. In this review, we provide a comprehensive overview of the intricacies of the BMP pathway and its inhibitors in bone development, homeostasis, and disease. We frame the content of the review around major unanswered questions for which incomplete evidence is available. First, we consider the gene regulatory network downstream of BMP signaling in osteoblastogenesis. Next, we examine why some BMP ligands are more osteogenic than others and what factors limit BMP signaling during osteoblastogenesis. Then we consider whether specific BMP pathway components are required for normal skeletal development, and if the pathway exerts endogenous effects in the aging skeleton. Finally, we propose two major areas of need of future study by the field: greater resolution of the gene regulatory network downstream of BMP signaling in the skeleton, and an expanded repertoire of reagents to reliably and specifically inhibit individual BMP pathway components.

Transcriptome analysis of mantle tissues reveals potential biomineralization-related genes in Tectus pyramis Born

The marine mollusk Tectus pyramis is a valuable shellfish primarily distributed in the tropical waters of the South China Sea, as well as in the Indo-Pacific Ocean and areas near the southern portion of the Japanese Peninsula. Despite major economic interest in this mollusk, limited genomic resources are available for this species, which has prevented studies of the molecular mechanism, such as biomineralization. Here, we report the first comprehensive transcript dataset of T. pyramis mantle tissue. From a total of 16,801,141 reads, 173,671 unique transcripts were assembled, which provides new genomic resources for the understanding of biomineralization in T. pyramis. The most abundant unique sequences of the top 30 most highly expressed genes were annotated as shematrin, while other highly expressed genes included glycine-rich protein and shematrin-1. Based on transcriptome annotation and Gene Ontology classification, 130 biomineralization-related genes were found including members of the BMP (bone morphogenetic proteins), calmodulin, perlucin, and shematrin families, as well as mantle genes, nacrein, and MSI60. The results of qPCR showed that 14 of 24 examined genes were highly expressed in the mantle. A phylogenetic tree of BMP, perlucin, shematrin proteins revealed conservation of their structure and functions and indicated that some members participated in biomineralization in T. pyramis. Taken together, the results presented herein will be useful in studies of molecular mechanisms and pathways of biomineralization in T. pyramis, as well as provide new insight into the mechanisms of biomineralization in gastropods.

PLGA-based control release of Noggin blocks the premature fusion of cranial sutures caused by retinoic acid

Craniosynostosis (CS), the premature and pathological fusion of cranial sutures, is a relatively common developmental disorder. Elucidation of the pathways involved and thus therapeutically targeting it would be promising for the prevention of CS. In the present study, we examined the role of BMP pathway in the all-trans retinoic acid (atRA)-induced CS model and tried to target the pathway in vivo via PLGA-based control release. As expected, the posterior frontal suture was found to fuse prematurely in the atRA subcutaneous injection mouse model. Further mechanism study revealed that atRA could repress the proliferation while promote the osteogenic differentiation of suture-derived mesenchymal cells (SMCs). Moreover, BMP signal pathway was found to be activated by atRA, as seen from increased expression of BMPR-2 and pSMAD1/5/9. Recombinant mouse Noggin blocked the atRA-induced enhancement of osteogenesis of SMCs in vitro. In vivo, PLGA microsphere encapsulated with Noggin significantly prevented the atRA-induced suture fusion. Collectively, these data support the hypothesis that BMP signaling is involved in retinoic acid-induced premature fusion of cranial sutures, while PLGA microsphere-based control release of Noggin emerges as a promising strategy for prevention of atRA-induced suture fusion.

Mucin 1 (Muc1) Deficiency in Female Mice Leads to Temporal Skeletal Changes During Aging

Mucin1 (MUC1) encodes a glycoprotein that has been demonstrated to have important roles in cell-cell interactions, cell-matrix interactions, cell signaling, modulating tumor progression and metastasis, and providing physical protection to cells against pathogens. In this study, we investigated the bone phenotype in female C57BL/6 Muc1 null mice and the impact of the loss of Muc1 on osteoblasts and osteoclasts. We found that deletion of Muc1 results in reduced trabecular bone volume in 8-week-old mice compared with wild-type controls, but the trabecular bone volume fraction normalizes with increasing age. In mature female mice (16 weeks old), Muc1 deletion results in stiffer femoral bones with fewer osteoblasts lining the trabecular surface but increased endosteal mineralized surface and bone formation rate. The latter remains higher compared with wild-type females at age 52 weeks. No difference was found in osteoclast numbers in vivo and in bone marrow osteoblast or osteoclast differentiation capacity or activity in vitro. Taken together, these results suggest that Muc1 depletion causes a transiently reduced trabecular bone mass phenotype in young mice, and later in life reduced numbers of osteoblasts with increased endocortical mineralization activity coincides with unaffected total bone mass and increased stiffness. In conclusion, our results show, for the first time to our knowledge, a role for Muc1 in bone mass and mineralization in mice in a time-dependent manner. © 2018 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Inhibitory Effects of Human Primary Intervertebral Disc Cells on Human Primary Osteoblasts in a Co-Culture System

Spinal fusion is a common surgical procedure to address a range of spinal pathologies, like damaged or degenerated discs. After the removal of the intervertebral disc (IVD), a structural spacer is positioned followed by internal fixation, and fusion of the degenerated segment by natural bone growth. Due to their osteoinductive properties, bone morphogenetic proteins (BMP) are applied to promote spinal fusion. Although spinal fusion is successful in most patients, the rates of non-unions after lumbar spine fusion range from 5% to 35%. Clinical observations and recent studies indicate, that the incomplete removal of disc tissue might lead to failure of spinal fusion. Yet, it is still unknown if a secretion of BMP antagonists in intervertebral disc (IVD) cells could be the reason of inhibition in bone formation. In this study, we co-cultured human primary osteoblasts (OB) and IVD cells i.e., nucleus pulposus (NPC), annulus fibrosus (AFC) and cartilaginous endplate cells (CEPC), to test the possible inhibitory effect from IVD cells on OB. Although we could see a trend in lower matrix mineralization in OB co-cultured with IVD cells, results of alkaline phosphatase (ALP) activity and gene expression of major bone genes were inconclusive. However, in NPC, AFC and CEPC beads, an up-regulation of several BMP antagonist genes could be detected. Despite being able to show several indicators for an inhibition of osteoinductive effects due to IVD cells, the reasons for pseudarthrosis after spinal fusion remain unclear.

The Dual Role of Bone Morphogenetic Proteins in Cancer

Bone morphogenetic proteins (BMPs) are a diverse class of molecules with over 20 growth factor proteins that belong to the transforming growth factor-β (TGF-β) family and are highly associated with bone formation and disease development. Aberrant expression of various BMPs has been reported in several cancer tissues. Biological function studies have elicited the dual role of BMPs in both cancer development and suppression. Furthermore, a variety of BMP antagonists, ligands, and receptors have been shown to reduce or enhance tumorigenesis and metastasis. Knockout mouse models of BMP signaling components have also revealed that the suppression of BMP signaling impairs cancer metastasis. Herein, we highlight the basic clinical background and involvement of BMPs in modulating cancer progression and their dynamic interactions (e.g., with microRNAs) in the tumor microenvironment in addition to their mutations and roles in chemoprevention. We also suggest that BMPs should be considered a powerful putative therapeutic target in tumorigenesis and bone metastasis.

The role of ClpX in erythropoietic protoporphyria

Hemoglobin is an essential biological component of human physiology and its production in red blood cells relies upon proper biosynthesis of heme and globin protein. Disruption in the synthesis of these precursors accounts for a number of human blood disorders found in patients. Mutations in genes encoding heme biosynthesis enzymes are associated with a broad class of metabolic disorders called porphyrias. In particular, one subtype - erythropoietic protoporphyria - is caused by the accumulation of protoporphyrin IX. Erythropoietic protoporphyria patients suffer from photosensitivity and a higher risk of liver failure, which is the principle cause of morbidity and mortality. Approximately 90% of these patients carry loss-of-function mutations in the enzyme ferrochelatase (FECH), while 5% of cases are associated with activating mutations in the C-terminus of ALAS2. Recent work has begun to uncover novel mechanisms of heme regulation that may account for the remaining 5% of cases with previously unknown genetic basis. One erythropoietic protoporphyria family has been identified with inherited mutations in the AAA+ protease ClpXP that regulates ALAS activity. In this review article, recent findings on the role of ClpXP as both an activating unfoldase and degrading protease and its impact on heme synthesis will be discussed. This review will also highlight the role of ClpX dysfunction in erythropoietic protoporphyria.

BMP3 expression by osteoblast lineage cells is regulated by canonical Wnt signaling

Bone morphogenetic protein (BMP) and canonical Wnt (cWnt) signaling factors are both known to regulate bone mass, fracture risk, fracture repair, and osteoblastogenesis. BMP3 is the most abundant BMP and negatively regulates osteoblastogenesis and bone mass. Thus, identifying the mechanism by which BMP3 acts to depress bone formation may allow for the development of new therapeutics useful in the treatment for osteopenia and osteoporosis. Here, we report that cWnt signaling stimulates BMP3 expression in osteoblast (OB) lineage cells. The expression of BMP3 increases with OB differentiation. Treatment of cells with various cWnt proteins stimulated BMP3 expression. Mice with enhanced cWnt signaling had high expression levels of BMP3. Our data suggest that reduction in BMP3 levels may contribute beneficially to the positive effect of cWnt agonists on bone mass.

Efficient in vitro delivery of Noggin siRNA enhances osteoblastogenesis

Several types of serious bone defects would not heal without invasive clinical intervention. One approach to such defects is to enhance the capacity of bone-formation cells. Exogenous bone morphogenetic proteins (BMP) have been utilized to positively regulate matrix mineralization and osteoblastogenesis, however, numerous adverse effects are associated with this approach. Noggin, a potent antagonist of BMPs, is an ideal candidate to target and decrease the need for supraphysiological doses of BMPs. In the current research we report a novel siRNA-mediated gene knock-down strategy to down-regulate Noggin. We utilized a lipid nanoparticle (LNP) delivery strategy in pre-osteoblastic rat cells. In vitro LNP-siRNA treatment caused inconsequential cell toxicity and transfection was achieved in over 85% of cells. Noggin siRNA treatment successfully down-regulated cellular Noggin protein levels and enhanced BMP signal activity which in turn resulted in significantly increased osteoblast differentiation and extracellular matrix mineralization evidenced by histological assessments. Gene expression analysis showed that targeting Noggin specifically in bone cells would not lead to a compensatory effect from other BMP negative regulators such as Gremlin and Chordin. The results from this study support the notion that novel therapeutics targeting Noggin have the clinically relevant potential to enhance bone formation without the need for toxic doses of exogenous BMPs. Such treatments will undeniably provide safe and economical treatments for individuals whose poor bone repair results in permanent morbidity and disability.

Celecoxib inhibits osteoblast differentiation independent of cyclooxygenase activity

Non-steroidal anti-inflammatory drugs (NSAIDs) exert their effects primarily by inhibiting the activity of cyclooxygenase (COX), thus suppressing prostaglandin synthesis. Some NSAIDs are known to perform functions other than pain control, such as suppressing tumour cell growth, independent of their COX-inhibiting activity. To identify NSAIDs with COX-independent activity, we examined various NSAIDs for their ability to inhibit osteoblastic differentiation using the mouse pre-osteoblast cell line MC3T3-E1. Only celecoxib and valdecoxib strongly inhibited osteoblastic differentiation, and this effect was not correlated with COX-inhibiting activity. Moreover, 2,5-dimethyl (DM)-celecoxib, a celecoxib analogue that does not inhibit COX activity, also inhibited osteoblastic differentiation. Celecoxib and DM-celecoxib inhibited osteoblastic differentiation induced by bone morphogenetic protein (BMP)-2 in C2C12 mouse myoblast cell line. Although celecoxib suppresses the growth of some tumour cells, the viability and proliferation of MC3T3-E1 cells were not affected by celecoxib or DM-celecoxib. Instead, celecoxib and DM-celecoxib suppressed BMP-2-induced phosphorylation of Smad1/5, a major downstream target of BMP receptor. Although it is well known that COX plays important roles in osteoblastic differentiation, these results suggest that some NSAIDs, such as celecoxib, have targets other than COX and regulate phospho-dependent intracellular signalling, thereby modifying bone remodelling.

Bone healing capabilities of recombinant human bone morphogenetic protein-9 (rhBMP-9) with a chitosan or collagen carrier in rat calvarial defects

The aim of this study was to examine the effects of recombinant human BMP-9 (rhBMP-9) with chitosan sponge (ChiS) or absorbable collagen sponge (ACS) on bone formation in rat calvarial defects. The defects were treated by one of the following implantations: ChiS, rhBMP-9/ChiS, ACS, rhBMP-9/ACS and no implantation. The animals were euthanized at 8 weeks for histological evaluation. The percentage of defect closure (DC) in the rhBMP-9/ACS group was significantly greater than that in the ACS group. The rhBMP-9/ACS group demonstrated the highest level of DC among all the groups. The newly formed bone area (NBA) and NBA/total area in the ChiS-implanted groups and in the rhBMP-9/ACS group were significantly greater compared with those in the ACS group. It can be concluded that rhBMP-9/ACS has a potential to induce bone formation in rat calvarial defects. Further studies are required to elucidate the mechanism of bone formation induced by rhBMP-9.

Cell-laden hydrogels for osteochondral and cartilage tissue engineering

Despite tremendous advances in the field of regenerative medicine, it still remains challenging to repair the osteochondral interface and full-thickness articular cartilage defects. This inefficiency largely originates from the lack of appropriate tissue-engineered artificial matrices that can replace the damaged regions and promote tissue regeneration. Hydrogels are emerging as a promising class of biomaterials for both soft and hard tissue regeneration. Many critical properties of hydrogels, such as mechanical stiffness, elasticity, water content, bioactivity, and degradation, can be rationally designed and conveniently tuned by proper selection of the material and chemistry. Particularly, advances in the development of cell-laden hydrogels have opened up new possibilities for cell therapy. In this article, we describe the problems encountered in this field and review recent progress in designing cell-hydrogel hybrid constructs for promoting the reestablishment of osteochondral/cartilage tissues. Our focus centers on the effects of hydrogel type, cell type, and growth factor delivery on achieving efficient chondrogenesis and osteogenesis. We give our perspective on developing next-generation matrices with improved physical and biological properties for osteochondral/cartilage tissue engineering. We also highlight recent advances in biomanufacturing technologies (e.g. molding, bioprinting, and assembly) for fabrication of hydrogel-based osteochondral and cartilage constructs with complex compositions and microarchitectures to mimic their native counterparts.

STATEMENT OF SIGNIFICANCE

Despite tremendous advances in the field of regenerative medicine, it still remains challenging to repair the osteochondral interface and full-thickness articular cartilage defects. This inefficiency largely originates from the lack of appropriate tissue-engineered biomaterials that replace the damaged regions and promote tissue regeneration. Cell-laden hydrogel systems have emerged as a promising tissue-engineering platform to address this issue. In this article, we describe the fundamental problems encountered in this field and review recent progress in designing cell-hydrogel constructs for promoting the reestablishment of osteochondral/cartilage tissues. Our focus centers on the effects of hydrogel composition, cell type, and growth factor delivery on achieving efficient chondrogenesis and osteogenesis. We give our perspective on developing next-generation hydrogel/inorganic particle/stem cell hybrid composites with improved physical and biological properties for osteochondral/cartilage tissue engineering. We also highlight recent advances in biomanufacturing and bioengineering technologies (e.g. 3D bioprinting) for fabrication of hydrogel-based osteochondral and cartilage constructs.

Comparison of the effects of recombinant human bone morphogenetic protein-2 and -9 on bone formation in rat calvarial critical-size defects

OBJECTIVES

Among bone morphogenetic protein (BMP) family members, BMP-2 and BMP-9 have demonstrated potent osteoinductive potential. However, in vivo differences in their potential for bone regeneration remain unclear. The present study aimed to compare the effects of recombinant human (rh) BMP-2 and rhBMP-9 on bone formation in rat calvarial critical-size defects (CSD).

MATERIALS AND METHODS

Twenty-eight Wistar rats surgically received two calvarial defects bilaterally in each parietal bone. Defects (n = 56) were allocated into four groups: absorbable collagen sponge (ACS) alone, rhBMP-2 with ACS (rhBMP-2/ACS), rhBMP-9/ACS, or sham surgery (control), on the condition that the treatments of rhBMP-2/ACS and rhBMP-9/ACS, or the same treatments were not included in the same animal. Animals were sacrificed at 2 and 8 weeks post-surgery. The calvarial defects were analyzed for bone volume (BV) by micro-computed tomography and for percentages of defect closure (DC/DL), newly formed bone area (NBA/TA), bone marrow area (BMA/NBA), adipose tissue area (ATA/NBA), central bone height (CBH), and marginal bone height (MBH) by histomorphometric analysis.

RESULTS

The BV in the rhBMP-2/ACS group (5.44 ± 3.65 mm³, n = 7) was greater than the other groups at 2 weeks post-surgery, and the rhBMP-2/ACS and rhBMP-9/ACS groups (18.17 ± 2.51 and 16.30 ± 2.46 mm³, n = 7, respectively) demonstrated significantly greater amounts of BV compared with the control and ACS groups (6.02 ± 2.90 and 9.30 ± 2.75 mm³, n = 7, respectively) at 8 weeks post-surgery. The rhBMP-2/ACS and rhBMP-9/ACS groups significantly induced new bone formation compared to the control and ACS groups at 8 weeks post-surgery. However, there were no statistically significant differences found between the rhBMP-2/ACS and rhBMP-9/ACS groups in any of the histomorphometric parameters. The ATA/NBA in the rhBMP-2/ACS group (9.24 ± 3.72%, n = 7) was the highest among the treatment groups at 8 weeks post-surgery.

CONCLUSIONS

Within the limits of this study, it can be concluded that rhBMP-2/ACS induced a slight early increase in new bone formation at 2 weeks and that rhBMP-9/ACS provided comparable new bone formation to rhBMP-2/ACS with less adipose tissues after a healing period of 8 weeks in rat CSD.

CLINICAL RELEVANCE

RhBMP-9/ACS treatment provided new bone formation with less adipose tissues compared with rhBMP-2/ACS.

Absorbable collagen sponges loaded with recombinant bone morphogenetic protein 9 induces greater osteoblast differentiation when compared to bone morphogenetic protein 2

The use of growth factors for the regeneration of soft and hard tissues has been utilized extensively in dental medicine over the past decade. Recently our group found that recombinant human bone morphogenetic protein 9 (rhBMP9) was more osteopromotive than recombinant human bone morphogenetic protein 2 (rhBMP2) when combined with a deprotenized bovine bone mineral bone grafting material. The aim of the present in vitro study was to evaluate the regenerative potential of an absorbable collagen sponge(ACS) specifically designed for extraction socket healing loaded with rhBMP9 when compared to rhBMP2. The adsorption and release kinetics of rhBMP2 and rhBMP9 were first investigated by enzyme-linked immunosorbent assay quantification. Then, the cellular effects of stromal cell line (ST2) preosteoblasts were investigated utilizing four groups including rhBMP2 and rhBMP9 at both low(10 ng/ml) and high(100 ng/ml) concentrations loaded onto ACS. Cellular attachment(8 hours) and proliferation(1, 3, and 5 days) as well as osteoblast differentiation were investigated by real-time polymerase chain reaction (PCR) at 3 and 14 days, alkaline phosphatase (ALP) activity at 7 days, and alizarin red staining at 14 days. ACS fully adsorbed both rhBMP2 and rhBMP9 that were slowly released up to 10 days. Although neither rhBMP2 nor rhBMP9 had any effects on cell attachment or proliferation, pronounced effects were observed on osteoblast differentiation. ALP activity was increased seven-fold with rhBMP2-high, whereas a marked 10-fold and 20-fold increase was observed with rhBMP9-low and high loaded to ACS, respectively. Furthermore, mRNA levels of collagen1, ALP, bone sialoprotein, and osteocalcin were all significantly higher for rhBMP9 when compared to control or rhBMP2 groups. Alizarin red staining further confirmed that rhBMP9-low and high demonstrated marked increases in mineralization potential when compared to rhBMP2-high. The results demonstrate the marked effect of rhBMP9 on osteoblast differentiation when combined with ACS in comparison to rhBMP2 at doses as much as 10 times lower. Further in vivo studies are necessary to investigate whether the regenerative potential is equally as potent.

Osteoblast Differentiation and Bone Matrix Formation In Vivo and In Vitro

We review the characteristics of osteoblast differentiation and bone matrix synthesis. Bone in air breathing vertebrates is a specialized tissue that developmentally replaces simpler solid tissues, usually cartilage. Bone is a living organ bounded by a layer of osteoblasts that, because of transport and compartmentalization requirements, produce bone matrix exclusively as an organized tight epithelium. With matrix growth, osteoblasts are reorganized and incorporated into the matrix as living cells, osteocytes, which communicate with each other and surface epithelium by cell processes within canaliculi in the matrix. The osteoblasts secrete the organic matrix, which are dense collagen layers that alternate parallel and orthogonal to the axis of stress loading. Into this matrix is deposited extremely dense hydroxyapatite-based mineral driven by both active and passive transport and pH control. As the matrix matures, hydroxyapatite microcrystals are organized into a sophisticated composite in the collagen layer by nucleation in the protein lattice. Recent studies on differentiating osteoblast precursors revealed a sophisticated proton export network driving mineralization, a gene expression program organized with the compartmentalization of the osteoblast epithelium that produces the mature bone matrix composite, despite varying serum calcium and phosphate. Key issues not well defined include how new osteoblasts are incorporated in the epithelial layer, replacing those incorporated in the accumulating matrix. Development of bone in vitro is the subject of numerous projects using various matrices and mesenchymal stem cell-derived preparations in bioreactors. These preparations reflect the structure of bone to variable extents, and include cells at many different stages of differentiation. Major challenges are production of bone matrix approaching the in vivo density and support for trabecular bone formation. In vitro differentiation is limited by the organization and density of osteoblasts and by endogenous and exogenous inhibitors.

Role of Recombinant Human Bone Morphogenetic Protein-2 on Hindfoot Arthrodesis

Despite advances in understanding bone healing physiology and surgical techniques, delayed union and nonunion still occur after the treatment of hindfoot arthrodesis. There is increasing appeal of bone morphogenetic proteins (BMPs) owing to the innate osteoinductive abilities of BMPs. Effective treatment with BMPs has been shown in animal studies. Human clinical studies have also shown success. The only study investigating the use of recombinant human BMP (rhBMP)-2 in hindfoot arthrodesis found a significant increase in fusion rate. Treatment cost effective. Complications from their use remain low. rhBMP-2 is a safe and effective bone-healing adjunct in hindfoot arthrodesis surgery.

BMPR1A antagonist differentially affects cartilage and bone formation during fracture healing

A soluble form of BMP receptor type 1A (mBMPR1A-mFC) acts as an antagonist to endogenous BMPR1A and has been shown to increase bone mass in mice. The goal of this study was to examine the effects of mBMPR1A-mFC on secondary fracture healing. Treatment consisted of 10 mg/kg intraperitoneal injections of mBMPR1A-mFC twice weekly in male C57BL/6 mice. Treatment beginning at 1, 14, and 21 days post-fracture assessed receptor function during endochondral bone formation, at the onset of secondary bone formation, and during coupled remodeling, respectively. Control animals received saline injections. mBMPR1A-mFC treatment initiated on day 1 delayed cartilage maturation in the callus and resulted in large regions of fibrous tissue. Treatment initiated on day 1 also increased the amount of mineralized tissue and up-regulated many bone-associated genes (p = 0.002) but retarded periosteal bony bridging and impaired strength and toughness at day 35 (p < 0.035). Delaying the onset of treatment to day 14 or 21 partially mitigated these effects and produced evidence of accelerated coupled remodeling. These results indicate that inhibition of the BMPR1A-mediated signaling has negative effects on secondary fracture healing that are differentially manifested at different stages of healing and within different cell populations. These effects are most pronounced during the endochondral period and appear to be mediated by selective inhibition of BMPRIA signaling within the periosteum. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:2096-2105, 2016.

Hyaluronic Acid Gel-Based Scaffolds as Potential Carrier for Growth Factors: An In Vitro Bioassay on Its Osteogenic Potential

Hyaluronic acid (HA) has been utilized for a variety of regenerative medical procedures due to its widespread presence in connective tissue and perceived biocompatibility. The aim of the present study was to investigate HA in combination with recombinant human bone morphogenetic protein 9 (rhBMP9), one of the most osteogenic growth factors of the BMP family. HA was first combined with rhBMP9 and assessed for the adsorption and release of rhBMP9 over 10 days by ELISA. Thereafter, ST2 pre-osteoblasts were investigated by comparing (1) control tissue culture plastic, (2) HA alone, and (3) HA with rhBMP9 (100 ng/mL). Cellular proliferation was investigated by a MTS assay at one, three and five days and osteoblast differentiation was investigated by alkaline phosphatase (ALP) activity at seven days, alizarin red staining at 14 days and real-time PCR for osteoblast differentiation markers. The results demonstrated that rhBMP9 adsorbed within HA scaffolds and was released over a 10-day period in a controlled manner. While HA and rhBMP9 had little effect on cell proliferation, a marked and pronounced effect was observed for cell differentiation. rhBMP9 significantly induced ALP activity, mRNA levels of collagen1α2, and ALP and osteocalcin (OCN) at three or 14 days. HA also demonstrated some ability to induce osteoblast differentiation by increasing mRNA levels of OCN and increasing alizarin red staining at 14 days. In conclusion, the results from the present study demonstrate that (1) HA may serve as a potential carrier for various growth factors, and (2) rhBMP9 is a potent and promising inducer of osteoblast differentiation. Future animal studies are now necessary to investigate this combination approach in vivo.

Osteogenic potential of recombinant human bone morphogenetic protein-9/absorbable collagen sponge (rhBMP-9/ACS) in rat critical size calvarial defects

OBJECTIVES

It has been reported that bone morphogenetic protein (BMP)-9 has potent osteoinductive properties among the BMP family by adenovirus-transfection experiments. We very recently reported that absorbable collagen sponge (ACS) as a carrier for recombinant human (rh) BMP-9, compared with chitosan sponge, was suitable for inducing bone healing/regeneration by BMP-9 in a rat calvarial defect model. The aim of this study was to evaluate different doses of rhBMP-9/ACS on new bone formation in rat critical size calvarial defects.

MATERIALS AND METHODS

Bilateral calvarial defects (n = 32) were surgically created in 16 wistar rats and randomly filled with one of the following materials: (1) absorbable collagen sponge (ACS) alone; (2) 1 μg-rhBMP-9/ACS (L-rhBMP-9/ACS); (3) 5 μg-rhBMP-9/ACS (H-rhBMP-9/ACS); and (4) blank defects (control). The animals were sacrificed 8 weeks postsurgery for radiographic and histomorphometric analyses.

RESULTS

Bone volume and defect closure were statistically higher in the rhBMP-9/ACS-implanted (L-rhBMP-9/ACS and H-rhBMP-9/ACS) groups when compared with ACS-alone group (p < 0.05). Furthermore, defects filled with H-rhBMP-9/ACS showed the highest levels of newly formed bone area (NBA) and NBA/total defect area among all groups. No significant differences in any of the radiographic and histometric parameters could be observed between both concentrations of rhBMP-9.

CONCLUSIONS

Within the limits of this study, it can be concluded that rhBMP-9/ACS-induced bone formation can be reached with as little as 1 μg/site in rat critical size calvarial defects.

CLINICAL RELEVANCE

RhBMP-9 could be a potential therapeutic growth factor for future bone regenerative procedures.