Bone Morphogenetic Proteins: Promising Molecules for Bone Healing, Bioengineering, and Regenerative Medicine

BMP7-induced osteoblast differentiation requires hedgehog signaling and involves nuclear mechanisms of gene expression control

During the morphological changes occurring in osteoblast differentiation, Sonic hedgehog (Shh) plays a crucial role. While some progress has been made in understanding this process, the epigenetic mechanisms governing the expression of Hh signaling members in response to bone morphogenetic protein 7 (BMP7) signaling in osteoblasts remain poorly understood. To delve deeper into this issue, we treated pre-osteoblasts (pObs) with 100 ng/mL of BMP7 for up to 21 days. Initially, we validated the osteogenic phenotype by confirming elevated expression of well-defined gene biomarkers, including Runx2, Osterix, Alkaline Phosphatase (Alp), and bone sialoprotein (Bsp). Simultaneously, Hh signaling-related members Sonic (Shh), Indian (Ihh), and Desert (Dhh) Hedgehog (Hh) exhibited nuanced modulation over the 21 days in vitro period. Subsequently, we evaluated epigenetic markers, and our data revealed a notable change in the CpG methylation profile, considering the methylation/hydroxymethylation ratio. CpG methylation is a reversible process regulated by DNA methyltransferases and demethylases, including Ten-eleven translocation (Tets), which also exhibited changes during the acquisition of the osteogenic phenotype. Specifically, we measured the methylation pattern of Shh-related genes and demonstrated a positive Pearson correlation for GLI Family Zinc Finger 1 (Gli1) and Patched (Ptch1). This data underscores the significance of the epigenetic machinery in modulating the BMP7-induced osteogenic phenotype by influencing the activity of Shh-related genes. In conclusion, this study highlights the positive impact of epigenetic control on the expression of genes related to hedgehog signaling during the morphogenetic changes induced by BMP7 signaling in osteoblasts.

Development of cobalt (Co)-doped monetites for bone regeneration

Cobalt-doped monetite powders were synthesized by coprecipitation method under a cobalt nominal content between 2 and 20 mol % of total cation. Structural characterization of samples was performed by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy. XRD results indicated that the Co-doped samples exhibited a monetite single-phase with the cell parameters and crystallite size dependent on the amount of substitutional element incorporated into the triclinic crystalline structure. Cell viability and adhesion assays using pre-osteoblastic cells showed there is no toxicity and the RTqPCR analysis showed significant differences in the expression for osteoblastic phenotype genes, showing a potential material for the bone regeneration.

Helicobacter pylori-activated fibroblasts as a silent partner in gastric cancer development

The discovery of Helicobacter pylori (Hp) infection of gastric mucosa leading to active chronic gastritis, gastroduodenal ulcers, and MALT lymphoma laid the groundwork for understanding of the general relationship between chronic infection, inflammation, and cancer. Nevertheless, this sequence of events is still far from full understanding with new players and mediators being constantly identified. Originally, the Hp virulence factors affecting mainly gastric epithelium were proposed to contribute considerably to gastric inflammation, ulceration, and cancer. Furthermore, it has been shown that Hp possesses the ability to penetrate the mucus layer and directly interact with stroma components including fibroblasts and myofibroblasts. These cells, which are the source of biophysical and biochemical signals providing the proper balance between cell proliferation and differentiation within gastric epithelial stem cell compartment, when exposed to Hp, can convert into cancer-associated fibroblast (CAF) phenotype. The crosstalk between fibroblasts and myofibroblasts with gastric epithelial cells including stem/progenitor cell niche involves several pathways mediated by non-coding RNAs, Wnt, BMP, TGF-β, and Notch signaling ligands. The current review concentrates on the consequences of Hp-induced increase in gastric fibroblast and myofibroblast number, and their activation towards CAFs with the emphasis to the altered communication between mesenchymal and epithelial cell compartment, which may lead to inflammation, epithelial stem cell overproliferation, disturbed differentiation, and gradual gastric cancer development. Thus, Hp-activated fibroblasts may constitute the target for anti-cancer treatment and, importantly, for the pharmacotherapies diminishing their activation particularly at the early stages of Hp infection.

Effect of milk and whey on proliferation and differentiation of placental stromal cells

Fetal bovine serum (FBS), which is widely used in cell culture media, has the potential to cause medical and ethical problems. Here, an experimental study using milk or whey proteins containing essential nutrients and growth factors is presented to limit the use of FBS in cell culture media produced for cell and tissue regeneration. Study groups were formed by culturing human placenta mesenchymal stem cells, known to have high proliferation and differentiation capacity, with milk or whey solution at increasing concentrations, alone or in combination with FBS. Osteogenic and adipogenic differentiation capacities of proliferating cells were observed in FBS, milk or whey groups. Milk, whey or FBS groups obtained in P3 and after differentiation were separately analyzed for protein mRNA expression by reverse transcriptase-polymerase chain reaction (RT-qPCR). Fibroblast Growth Factor 2 (FGF2), Octamer-binding Transcription Factor 4 (OCT4), Bone Morphogenetic Protein 6 (BMP6), and adipogenic differentiation marker Peroxisome Proliferator-Activated Receptor Gamma (PPARG) were analysed by RT-qPCR. Proliferation was more pronounced in FBS alone and in its combinations with milk-whey compared to the groups in which only milk and whey were used. OCT4 mRNA and FGF2 mRNA expression decreased in differentiated cells. BMP6 mRNA expression increased with osteogenic and adipogenic stimuli. As expected, PPRG expression also increased with adipogenic stimulation. With this experimental study, evidence has been obtained that milk or whey can provide nutritional support to the culture media of repair cells and preserve the functional capacity of the cells, with a slightly more limited capacity than FBS.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s10616-023-00585-z.

Emerging role of RNA acetylation modification ac4C in diseases: Current advances and future challenges

The oldest known highly conserved modification of RNA, N4-acetylcytidine, is widely distributed from archaea to eukaryotes and acts as a posttranscriptional chemical modification of RNA, contributing to the correct reading of specific nucleotide sequences during translation, stabilising mRNA and improving transcription efficiency. Yeast Kre33 and human NAT10, the only known authors of ac4C, modify tRNA with the help of the Tan1/THUMPD1 adapter to stabilise its structure. Currently, the mRNA for N4-acetylcytidine (ac4C), catalysed by NAT10 (N-acetyltransferase 10), has been implicated in a variety of human diseases, particularly cancer. This article reviews advances in the study of ac4C modification of RNA and the ac4C-related gene NAT10 in normal physiological cell development, cancer, premature disease and viral infection and discusses its therapeutic promise and future research challenges.

Adenovirus-Based Gene Therapy for Bone Regeneration: A Comparative Analysis of In Vivo and Ex Vivo BMP2 Gene Delivery

Adenovirus-mediated gene therapy is a promising tool in bone regenerative medicine. In this work, gene-activated matrices (GAMs) composed of (1) polylactide granules (PLA), which serve as a depot for genetic constructs or matrices for cell attachment, (2) a PRP-based fibrin clot, which is a source of growth factors and a binding gel, and (3) a BMP2 gene providing osteoinductive properties were studied. The study aims to compare the effectiveness of in vivo and ex vivo gene therapy based on adenoviral constructs with the BMP2 gene, PLA particles, and a fibrin clot for bone defect healing. GAMs with Ad-BMP2 and MSC(Ad-BMP2) show osteoinductive properties both in vitro and in vivo. However, MSCs incubated with GAMs containing transduced cells showed a more significant increase in osteopontin gene expression, protein production, Alpl activity, and matrix mineralization. Implantation of the studied matrices into critical-size calvarial defects after 56 days promotes the formation of young bone. The efficiency of neoosteogenesis and the volume fraction of newly formed bone tissue are higher with PLA/PRP-MSC(Ad-BMP2) implantation (33%) than PLA/PRP-Ad-BMP2 (28%). Thus, ex vivo adenoviral gene therapy with the BMP2 gene has proven to be a more effective approach than the in vivo delivery of gene constructs for bone regeneration.

Modeling anabolic and antiresorptive therapies for fracture healing in a mouse model of osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a genetic bone fragility disorder that features frequent fractures. Bone healing outcomes are contingent on a proper balance between bone formation and resorption, and drugs such as bone morphogenetic proteins (BMPs) and bisphosphonates (BPs) have shown to have utility in modulating fracture repair. While BPs are used for OI to increase BMD and reduce pain and fracture rates, there is little evidence for using BMPs as local agents for fracture healing (alone or with BPs). In this study, we examined wild-type and OI mice (Col1a2^+/G610C ) in a murine tibial open fracture model with (i) surgery only/no treatment, (ii) local BMP-2 (10 µg), or (iii) local BMP-2 and postoperative zoledronic acid (ZA; 0.1 mg/kg total dose). Microcomputed tomography reconstructions of healing fractures indicated BMP-2 was less effective in an OI setting, however, BMP-2 +ZA led to considerable increases in bone volume (+193% WT, p < 0.001; +154% OI, p < 0.001) and polar moment of inertia (+125% WT, p < 0.01; +248% OI, p < 0.05). Tissue histology revealed a thinning of the neocortex of the callus in BMP-2 treated OI bone, but considerable retention of woven bone in the healing callus with BMP + ZA specimens. These data suggest a cautious approach may be warranted with the sole application of BMP-2 in an OI surgical setting as a bone graft substitute. However, this may be overcome by off-label BP administration.

Transgenic PDGF-BB sericin hydrogel potentiates bone regeneration of BMP9-stimulated mesenchymal stem cells through a crosstalk of the Smad-STAT pathways

Silk as a natural biomaterial is considered as a promising bone substitute in tissue regeneration. Sericin and fibroin are the main components of silk and display unique features for their programmable mechanical properties, biocompatibility, biodegradability and morphological plasticity. It has been reported that sericin recombinant growth factors (GFs) can support cell proliferation and induce stem cell differentiation through cross-talk of signaling pathways during tissue regeneration. The transgenic technology allows the productions of bioactive heterologous GFs as fusion proteins with sericin, which are then fabricated into solid matrix or hydrogel format. Herein, using an injectable hydrogel derived from transgenic platelet-derived GF (PDGF)-BB silk sericin, we demonstrated that the PDGF-BB sericin hydrogel effectively augmented osteogenesis induced by bone morphogenetic protein (BMP9)-stimulated mesenchymal stem cells (MSCs) in vivo and in vitro, while inhibiting adipogenic differentiation. Further gene expression and protein-protein interactions studies demonstrated that BMP9 and PDGF-BB synergistically induced osteogenic differentiation through the cross-talk between Smad and Stat3 pathways in MSCs. Thus, our results provide a novel strategy to encapsulate osteogenic factors and osteoblastic progenitors in transgenic sericin-based hydrogel for robust bone tissue engineering.

AAV-mediated BMP7 gene therapy counteracts insulin resistance and obesity

Type 2 diabetes, insulin resistance, and obesity are strongly associated and are a major health problem worldwide. Obesity largely results from a sustained imbalance between energy intake and expenditure. Therapeutic approaches targeting metabolic rate may counteract body weight gain and insulin resistance. Bone morphogenic protein 7 (BMP7) has proven to enhance energy expenditure by inducing non-shivering thermogenesis in short-term studies in mice treated with the recombinant protein or adenoviral vectors encoding BMP7. To achieve long-term BMP7 effects, the use of adeno-associated viral (AAV) vectors would provide sustained production of the protein after a single administration. Here, we demonstrated that treatment of high-fat-diet-fed mice and ob/ob mice with liver-directed AAV-BMP7 vectors enabled a long-lasting increase in circulating levels of this factor. This rise in BMP7 concentration induced browning of white adipose tissue (WAT) and activation of brown adipose tissue, which enhanced energy expenditure, and reversed WAT hypertrophy, hepatic steatosis, and WAT and liver inflammation, ultimately resulting in normalization of body weight and insulin resistance. This study highlights the potential of AAV-BMP7-mediated gene therapy for the treatment of insulin resistance, type 2 diabetes, and obesity.

Repeated Transient Transfection: An Alternative for the Recombinant Production of Difficult-to-Express Proteins Like BMP2

Human bone morphogenetic protein 2 (hBMP2) is routinely used in medical applications as an inducer of osteoformation. The recombinant production of BMP2 is typically performed using stable Chinese hamster ovary (CHO) cell lines. However, this process is inefficient, resulting in low product titers. In contrast, transient gene expression (TGE), which also enables the production of recombinant proteins, suffers from short production times and hence limited total product amounts. Here, we show that TGE-based BMP2 production is more efficient in HEKsus than in CHOsus cells. Independently of the cell lines, a bicistronic plasmid co-expressing EGFP and BMP2 facilitated the determination of the transfection efficiency but led to inferior BMP2 titers. Finally, we used a high cell density transient transfection (HCD-TGE) protocol to improve and extend the BMP2 expression by performing four rounds of serial transfections on one pool of HEKsus cells. This repeated transient transfection (RTT) process in HEKsus cells was implemented using EGFP as a reporter gene and further adapted for BMP2 production. The proposed method significantly improves BMP2 production (up to 509 ng/106 cells) by extending the production phase (96–360 h). RTT can be integrated into the seed train and is shown to be compatible with scale-up to the liter range.

Construction of tissue-engineered nucleus pulposus by stimulation with periodic mechanical stress and BMP-2

Intervertebral disc (IVD) degeneration, which is common among elderly individuals, mainly manifests as low back pain and is caused by structural deterioration of the nucleus pulposus (NP) due to physiological mechanical stress. NP mesenchymal stem cells (NPMSCs) around the IVD endplate have multidirectional differentiation potential and can be used for tissue repair. To define favorable conditions for NPMSC proliferation and differentiation into chondroid cells for NP repair, the present study simulated periodic mechanical stress (PMS) of the NP under physiological conditions using MSC chondrogenic differentiation medium and recombinant human BMP-2 (rhBMP-2). rhBMP-2 effectively promoted NPMSC proliferation and differentiation. To clarify the mechanism of action of rhBMP-2, integrin alpha 1 (ITG A1) and BMP-2 were inhibited. PMS regulated the BMP-2/Smad1/RUNX2 pathway through ITG A1 and promoted NPMSC proliferation and differentiation. During tissue-engineered NP construction, PMS can effectively reduce osteogenic differentiation and promote extracellular matrix protein synthesis to enhance structural NP recovery.

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Extraction of NPMSCs from degenerated nucleus pulposus

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NPMSCs cultured in vitro by simulating physiological mechanical stress

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ITG A1 to promote proliferation and differentiation of NPMSCs through BMP-2/Smad1/RUNX2

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Injectable tissue-engineered nucleus pulposus

Research progress on exosomal proteins as diagnostic markers of gastric cancer (review article)

Gastric cancer (GC) is one of the most common types of tumors and the most common cause of cancer mortality worldwide. The diagnosis of GC is critical to its prevention and treatment. Available tumor markers are the crucial step for GC diagnosis. Recent studies have shown that proteins in exosomes are potential diagnostic and prognostic markers for GC. Exosomes, secreted by cells, are cup-shaped with a diameter of 30–150 nm under the electron microscope. They are also surrounded by lipid bilayers and are widely found in various body fluids. Exosomes contain proteins, lipids and nucleic acid. The examination of exosomal proteins has the advantages of quickness, easy sampling, and low pain and cost, as compared with the routine inspection method of GC, which may lead to marked developments in GC diagnosis. This article summarized the exosomal proteins with a diagnostic and prognostic potential in GC, as well as exosomal proteins involved in GC progression.

The Role of BMP Signaling in Female Reproductive System Development and Function

Bone morphogenetic proteins (BMPs) are a group of multifunctional growth factors that belong to the transforming growth factor-β (TGF-β) superfamily of proteins. Originally identified by their ability to induce bone formation, they are now known as essential signaling molecules that regulate the development and function of the female reproductive system (FRS). Several BMPs play key roles in aspects of reproductive system development. BMPs have also been described to be involved in the differentiation of human pluripotent stem cells (hPSCs) into reproductive system tissues or organoids. The role of BMPs in the reproductive system is still poorly understood and the use of FRS tissue or organoids generated from hPSCs would provide a powerful tool for the study of FRS development and the generation of new therapeutic perspectives for the treatment of FRS diseases. Therefore, the aim of this review is to summarize the current knowledge about BMP signaling in FRS development and function.

Adrenergic receptor behaviors of mesenchymal stem cells obtained from different tissue sources and the effect of the receptor blockade on differentiation

In this study, it was aimed to analyze behavioral changes of adrenergic receptors (ARs) in first three passages and osteogenic/adipogenic differentiation of mesenchymal stem cells (MSCs) derived from placenta fetal membrane (FM) and bone marrow (BM). It was also aimed to evaluate effects of receptor blockade on differentiation. We obtained first three passages of MSCs from placenta and BM samples. For cell identification, the cells were analyzed by flow cytometry using CD34, CD45 and CD3, CD105 antibodies in each passage. The effects of propranolol and phenoxybenzamine at incremental doses were analyzed by MTT. In addition, cell cultures were separately maintained with the blockers or without after second passage. After each passage and differentiation, α1A, α1B, α2A, α2B, β1, β2, β3 AR-mRNA expressions analyzed by RT-qPCR technique. BMP6 and PPARG mRNA expressions only after differentiation and passage 3 were analyzed. A microscopic examination was also performed. Our results showed that AR expression behaviors were different in MSCs obtained from different tissue sources. In particular, α_1A-AR and α_2A-AR were expressed with considerably high coefficients in differentiation under blocker effect in BM-derived MSCs. No such coefficients were observed in any group of placental MSCs. In addition, it was found that the blockers stimulated adipogenesis in BM-derived MSCs during osteogenic differentiation. MSCs exhibit protein expressions that vary according to source of tissue and differentiation. Given that MSCs from different sources are used for repair and modulation, our study makes implications of this variable expression intriguing in the clinical practice.

NAT10 Promotes Osteogenic Differentiation of Mesenchymal Stem Cells by Mediating N4-Acetylcytidine Modification of Gremlin 1

Objective

To investigate the function of NAT10 in mesenchymal stem cell (MSC) osteogenic differentiation and study the mechanism by which NAT10 affects MSC osteogenesis by mediating Gremlin 1 N4-acetylcytidine (ac⁴C) modification.

Methods

Osteogenic differentiation of MSCs was induced, and the osteogenic ability was evaluated with alizarin red S (ARS) and alkaline phosphatase (ALP) assays. The NAT10 expression level during MSC osteogenesis was measured by western blot (WB). MSCs were transfected with lentiviruses to inhibit (Sh-NAT10) or overexpress NAT10 (Over-NAT10), and the osteogenic differentiation ability was assessed by ARS, ALP, and osteogenic gene marker assays. β-Catenin, Akt, and Smad signaling pathway component activation levels were assessed, and the expression levels of key Smad signaling pathway molecules were determined by PCR and WB. The Gremlin 1 mRNA ac⁴C levels were analyzed using RIP-PCR, and the Gremlin 1 mRNA degradation rate was determined. Sh-Gremlin 1 was transfected to further investigate the role of NAT10 and Gremlin 1 in MSC osteogenesis.

Results

During MSC osteogenesis, NAT10 expression, ARS staining, and the ALP level gradually increased. Decreasing NAT10 expression inhibited, and increasing NAT10 expression promoted MSC osteogenic differentiation. NAT10 affected the BMP/Smad rather than the Akt and β-Catenin signaling pathway activation by regulating Gremlin 1 expression. The Gremlin 1 mRNA ac⁴C level was positively regulated by NAT10, which accelerated Gremlin 1 degradation. Sh-Gremlin 1 abolished the promotive effect of NAT10 on MSC osteogenic differentiation.

Conclusion

NAT10 positively regulated MSC osteogenic differentiation through accelerating the Gremlin 1 mRNA degradation by increasing its ac⁴C level. These results may provide new mechanistic insight into MSC osteogenesis and bone metabolism in vivo.

Crosstalk between Bone and Nerves within Bone

For the past two decades, the function of intrabony nerves on bone has been a subject of intense research, while the function of bone on intrabony nerves is still hidden in the corner. In the present review, the possible crosstalk between bone and intrabony peripheral nerves will be comprehensively analyzed. Peripheral nerves participate in bone development and repair via a host of signals generated through the secretion of neurotransmitters, neuropeptides, axon guidance factors and neurotrophins, with additional contribution from nerve-resident cells. In return, bone contributes to this microenvironmental rendezvous by housing the nerves within its internal milieu to provide mechanical support and a protective shelf. A large ensemble of chemical, mechanical, and electrical cues works in harmony with bone marrow stromal cells in the regulation of intrabony nerves. The crosstalk between bone and nerves is not limited to the physiological state, but also involved in various bone diseases including osteoporosis, osteoarthritis, heterotopic ossification, psychological stress-related bone abnormalities, and bone related tumors. This crosstalk may be harnessed in the design of tissue engineering scaffolds for repair of bone defects or be targeted for treatment of diseases related to bone and peripheral nerves.

Modular genome-wide gene expression architecture shared by early traits of osteoporosis and atherosclerosis in the Young Finns Study

We analysed whole blood genome-wide expression data to identify gene co-expression modules shared by early traits of osteoporosis and atherosclerosis. Gene expression was profiled for the Young Finns Study participants. Bone mineral density and content were measured as early traits of osteoporosis. Carotid and bulbus intima media thickness were measured as early traits of atherosclerosis. Joint association of the modules, identified with weighted co-expression analysis, with early traits of the diseases was tested with multivariate analysis. Among the six modules significantly correlated with early traits of both the diseases, two had significant (adjusted p-values (p.adj) < 0.05) and another two had suggestively significant (p.adj < 0.25) joint association with the two diseases after adjusting for age, sex, body mass index, smoking habit, alcohol consumption, and physical activity. The three most significant member genes from the significant modules were NOSIP, GXYLT2, and TRIM63 (p.adj ≤ 0.18). Genes in the modules were enriched with biological processes that have separately been found to be involved in either bone metabolism or atherosclerosis. The gene modules and their most significant member genes identified in this study support the osteoporosis-atherosclerosis comorbidity hypothesis and can provide new joint biomarkers for both diseases and their dual prevention.

In Vitro and In Vivo Study of a Novel Nanoscale Demineralized Bone Matrix Coated PCL/β-TCP Scaffold for Bone Regeneration

Bone defects remains a challenge for surgeons. Bone graft scaffold can fill the defect and enhance the bone regeneration. Demineralized bone matrix (DBM) is an allogeneic bone graft substitute, which can only be used as a filling material rather than a structural bone graft. Coating of the scaffolds with nanoscale DBM may enhance the osteoinductivity or osteoconductivity. Herein the lyophilization method is presented to coat the nano-DBM on surface of the porous polycaprolactone (PCL)/β-tricalcium phosphate (β-TCP) scaffolds fabricated by 3D printing technology. The morphology, elastic modulus, in vitro cell biocompatibility, and in vivo performance are investigated. Scanning electron microscope (SEM) shows DBM particle clusters with size of 200-500 nm are observed on scaffolds fibers after coating. MC3T3-E1 cells on nano-DBM coated PCL/β-TCP scaffold show better activity than on PCL/β-TCP scaffold. In vivo tests show better infiltration of new bone tissue in nano-DBM coated PCL/β-TCP scaffold than PCL/β-TCP scaffold via the interface. These results show the presence of nano-DBM coating on PCL/β-TCP scaffold could enhance the attachment, proliferation, and viability of cells and benefit for the new bone formation surrounding and deep inside the scaffolds. Nano-DBM could potentially be used as a new kind of biomaterial for bone defect treatment.

Platelet microparticles load a repertory of miRNAs programmed to drive osteogenic phenotype

Autologous platelet-rich plasma accelerates bone healing by releasing biomolecules during their degranulation process, which are transported by vesicle-like structures called platelet microparticles (PMPs). However, the underlying mechanisms regulating the osteogenic differentiation by PMP-released miRs remain poorly understood and this prompted us to better address this issue. Thus, miRNAseq expression profiles (E-GEOD-76789) were downloaded from ArrayExpress database. GEO2R was performed to evaluate the differential expression, and mirnatap R package was used to find targets for differentially expressed miRNAs. An extend protein-protein (ePPI) network for osteogenic marker proteins was generated using String, and DAVID tools were used to perform gene ontology and KEGG pathway analysis from ePPI and miRNAs targets. Our data show that ePPI network was composed by 232 nodes and 2,175 edges, with a clustering coefficient of 0.546. MCODE was able to identify seven clusters contained in the ePPI network, and the two that presented a score above 10 were used in further analysis. Conversely, 15,944 different targets were found as down-expressed while 5,715 different targets were up-expressed. Among the downregulated 75 miRNAs, 70 have predicted targets present in the ePPI network, while the 21 upregulated miRNAs have 19 predicted targets in the ePPI network. Our study provides a registry of miRNAs that play a central role in regulating osteogenic phenotype, which might have potential therapeutic applications in bone regeneration and bone tissue engineering.

Zanthoxylum nitidum extract attenuates BMP-2-induced inflammation and hyperpermeability

Bone morphogenetic protein-2 (BMP-2) is commonly applied in spinal surgery to augment spinal fusion. Nevertheless, its pro-inflammatory potential could induce dangerous side effects such as vascular hyper-permeability, posing the need for manners against this condition. The present study aims to investigate the protective effect of Zanthoxylum nitidum (ZN) on BMP-2-related hyperpermeability and inflammation on the human umbilical vein endothelial cells (HUVECs). The results revealed that, in a concentration-dependent manner, BMP-2 enhanced the production of pro-inflammatory cytokines, including interleukin (IL)-1α, IL-1β, and tumor necrosis factor-α, which were, however, suppressed by ZN. ZN inhibited BMP-2-induced inflammatory response by suppressing the phosphorylation of NF-κBp65 and IκB, and the abnormal nuclear translocation of p65. Moreover, the inhibited expression intercellular tight junction protein VE-cadherin and Occludin caused by BMP-2 was blocked by ZN. The hyper-permeability of HUVECs induced by BMP-2, as expressed as the higher fluorescent intensity of dextran, was also reversed by ZN. Overall, these findings demonstrated that ZN antagonized BMP-2-induced inflammation and hyperpermeability. It could be a therapeutic candidate for the treatment of BMP-2-induced side effects during spinal fusion.

BMP7 overexpression in adipose tissue induces white adipogenesis and improves insulin sensitivity in ob/ob mice

BACKGROUND/OBJECTIVES

During obesity, hypertrophic enlargement of white adipose tissue (WAT) promotes ectopic lipid deposition and development of insulin resistance. In contrast, WAT hyperplasia is associated with preservation of insulin sensitivity. The complex network of factors that regulates white adipogenesis is not fully understood. Bone morphogenic protein 7 (BMP7) can induce brown adipogenesis, but its role on white adipogenesis remains to be elucidated. Here, we assessed BMP7-mediated effects on white adipogenesis in ob/ob mice.

METHODS

BMP7 was overexpressed in either WAT or liver of ob/ob mice using adeno-associated viral (AAV) vectors. Analysis of gene expression, histological and morphometric alterations, and metabolites and hormones concentrations were carried out.

RESULTS

Overexpression of BMP7 in adipocytes of subcutaneous and visceral WAT increased fat mass, the proportion of small-size adipocytes and the expression of adipogenic and mature adipocyte genes, suggesting induction of adipogenesis irrespective of fat depot. These changes were associated with reduced hepatic steatosis and improved insulin sensitivity. In contrast, liver-specific overproduction of BMP7 did not promote WAT hyperplasia despite BMP7 circulating levels were similar to those achieved after genetic engineering of WAT.

CONCLUSIONS

This study unravels a new autocrine/paracrine role of BMP7 on white adipogenesis and highlights that BMP7 may modulate WAT plasticity and increase insulin sensitivity.

Proteomics of regenerated tissue in response to a titanium implant with a bioactive surface in a rat tibial defect model

Due to their excellent mechanical and biocompatibility properties, titanium-based implants are successfully used as biomedical devices. However, when new bone formation fails for different reasons, impaired fracture healing becomes a clinical problem and affects the patient's quality of life. We aimed to design a new bioactive surface of titanium implants with a synergetic PEG biopolymer-based composition for gradual delivery of growth factors (FGF2, VEGF, and BMP4) during bone healing. The optimal architecture of non-cytotoxic polymeric coatings deposited by dip coating under controlled parameters was assessed both in cultured cells and in a rat tibial defect model (100% viability). Notably, the titanium adsorbed polymer matrix induced an improved healing process when compared with the individual action of each biomolecules. High-performance mass spectrometry analysis demonstrated that recovery after a traumatic event is governed by specific differentially regulated proteins, acting in a coordinated response to the external stimulus. Predicted protein interactions shown by STRING analysis were well organized in hub-based networks related with response to chemical, wound healing and response to stress pathways. The proposed functional polymer coatings of the titanium implants demonstrated the significant improvement of bone healing process after injury.

Electrospun Fibers Immobilized with BMP-2 Mediated by Polydopamine Combined with Autogenous Tendon to Repair Developmental Dysplasia of the Hip in a Porcine Model

Purpose

Developmental dysplasia of the hip (DDH) can increase the pressure between the joints, which causes secondary hip osteoarthritis. The aim of the present study was to fabricate poly(D, L-lactic acid)-poly(ethylene glycol)-poly(D, L-lactic acid) (PELA) electrospun fibrous scaffolds, immobilized with bone morphogenetic protein-2 (BMP-2), to repair the acetabulum defects.

Methods

The characteristics of PELA electrospun were analyzed using scanning electron microscopy, the release kinetics of BMP-2 in vitro were analyzed using enzyme-linked immunosorbent assays. Human mesenchymal stem cells (hMSCs) were used for in vitro experiments, the biocompatibility of the electrospinning materials was investigated using a cell counting kit-8 (CCK-8) kit, and osteogenic differentiation was tested via alkaline phosphatase (ALP) activity and relative gene expression. Eighteen miniature pig animal models were used in the in vivo experiment. The pigs were sacrificed at 24 weeks after surgery, and the reconstructed acetabulum was evaluated using histological sections.

Results

Structural analysis revealed that the diameter of the PELA electrospun fiber was 0.8195 ± 0.16 μm. The PELA electrospun fiber materials showed good hydrophilicity and biocompatibility and could continuously release BMP-2 within 27 days: 16.07 ± 0.11 ng of BMP-2 was released from the scaffold. A total of sixteen implants fully filled the defects, and hematoxylin and eosin staining and Goldner's trichrome staining showed that the simple tendon group (T group) was mostly fibrous tissues, lots of fibroblasts and small amounts of chondrocytes were observed in the polydopamine-coated electrospun fiber group (DP group). The DP plus BMP-2 (DPB) group showed a large number of chondrocytes and partial new bone tissues.

Conclusion

PELA electrospun fibrous scaffolds are good sustained-release carriers, which can not only induce implant differentiation into cartilage and bone but also are completely degraded without toxicity. Therefore, the material can be used for bone and cartilage regeneration.

Anti‑proliferative effect of honokiol on SW620 cells through upregulating BMP7 expression via the TGF‑β1/p53 signaling pathway

Honokiol (HNK), a natural pharmaceutically active component extracted from magnolia bark, has been used for clinical treatments and has anti‑inflammatory, antiviral and antioxidative effects. In recent years, anticancer research has become a major hotspot. However, the underlying molecular mechanisms of how HNK inhibits colorectal cancer have remained elusive. The present study focused on elucidating the effects of HNK on the expression of bone morphogenetic protein (BMP)7 and its downstream interaction with transforming growth factor (TGF)‑β1 and p53 in colon cancer. In in vitro assays, cell viability, cell cycle distribution and apoptosis were examined using Cell Counting Kit‑8, flow cytometry and reverse transcription‑quantitative PCR, respectively. In addition, the expression of BMP7, TGF‑β1 and relevant signaling proteins was determined by western blot analysis. In vivo, the anticancer effect of HNK was assessed in xenografts in nude mice. Furthermore, immunohistochemistry was performed to evaluate the association between BMP7 and TGF‑β1 expression in colon cancer. The results indicated that HNK inhibited the proliferation of colon cancer cell lines, with SW620 cells being more sensitive than other colon cancer cell lines. Furthermore, HNK markedly promoted the expression of BMP7 at the mRNA and protein level. Exogenous BMP7 potentiated the effect of HNK on SW620 cells, while knocking down BMP7 inhibited it. As a downstream mechanism, HNK increased the expression of TGF‑β1 and p53, which was enhanced by exogenous BMP7 in SW620 cells. In addition, immunohistochemical analysis indicated a positive association between BMP7 and TGF‑β1 expression. Hence, the present results suggested that HNK is a promising agent for the treatment of colon cancer and enhanced the expression TGF‑β1 and p53 through stimulating BMP7 activity via the non‑canonical TGF‑β signaling pathway.

BMP2 variants in the risk of ankylosing spondylitis

The purpose of the study was to explore the genetic effects of bone morphogenetic protein (BMP2) polymorphisms on the susceptibility to ankylosing spondylitis (AS) in Chinese Han population. The case-control study included 120 AS cases and 110 healthy controls. Hardy-Weinberg equilibrium test was performed in control group. BMP2 rs235768 and rs3178250 polymorphisms were analyzed by polymerase chain reaction and direct sequencing. Additionally, the χ²  test was used to estimate association strength between BMP2 genetic polymorphisms and AS susceptibility, and the results were assessed via odds ratio (OR) with the corresponding 95% confidence interval (95%CI). Results adjustment was performed using logistic regression analysis. AA, AT, TT genotype and A, T allele frequencies of BMP2 rs235768 polymorphism presented no significant differences between case and control groups (P > .05 for all). TC genotype of rs3178250 polymorphism showed significantly higher in case group than that in control group (P = .048). After adjusting, TC genotype was a risk factor for AS (OR = 2.095; 95%CI = 1.086-4.038; P = .027). BMP2 rs3178250 polymorphism may increase individual susceptibility to AS in Chinese Han population.

Specification of BMP Signaling

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

Reconstruction of a Large Posttraumatic Mandibular Defect Using Bone Tissue Engineering With Fresh-Frozen Humeral Allograft Seeded With Autologous Bone Marrow Aspirate and Vascularized With a Radial Forearm Flap

INTRODUCTION

Currently, vascularized autologous bone transplantation is considered the gold standard for large mandibular continuity defect reconstruction. Donor site morbidity is a major concern. Therefore, bone tissue engineering (BTE) seems to be the ideal solution. Fresh-frozen bone allograft is the closest material to autologous bone. The purpose of this clinical report is to show a new technique of large mandibular continuity defect reconstruction using a fresh-frozen humeral allograft seeded with autologous iliac bone marrow aspirate and vascularized with a radial forearm flap.

METHODS

A 33-year-old man presented with severe cranio-facial trauma resulting in several fractures of the facial skeleton including a comminuted mandibular fracture from left parasymphysis to left angle, which caused a large continuity defect.

RESULTS

Result at 6 months was aesthetically and functionally satisfactory with osseointegration of the bone graft.

DISCUSSION

The authors chose to use iliac bone marrow aspirate to seed the allograft scaffold since hematopoietic stem cells and mesenchymal stem cell are able to differentiate into osteoblasts, ease of harvest of the iliac crest and its low rate of morbidity. Contemporary biomaterials used for BTE are bioceramic but bone is still the better scaffold to engineer bone and only allografting avoids donor site morbidity. Vascularization is one of the main challenges of BTE; insertion of autologous vascular bundles from pedicle or free flaps is 1 solution. The authors chose the radial forearm flap since the pedicle is long and the authors did not need a great amount of soft tissue.

Glucocorticoid Enhanced the Expression of Ski in Osteonecrosis of Femoral Head: The Effect on Adipogenesis of Rabbit BMSCs

Glucocorticoid (GC)-induced osteonecrosis has been considered as the most serious side effect in long-term or over-dose steroid therapy. The decreased bone mass and increased marrow fat tissue demonstrated that GC can destroy the normal differentiation of bone marrow mesenchymal stem cells (BMSCs), which accelerates adipogenesis but not osteogenesis. However, the underlying mechanisms are still unclear. Ski, an evolutionary conserved protein, is a multifunctional transcriptional regulator that involved in regulating signaling pathways associated with adipogenesis differentiation, but the concrete function remains unclear. In this work, we first established a methylprednisolone (MPS)-induced osteonecrosis of femoral head (ONFH) rabbit model, in which the expression of Ski, PPAR-γ, and FABP4 was up-regulated compared with control group, and then we induced the isolated BMSCs from rabbit with dexamethasone (Dex) in vitro and the results showed that the Ski expression was up-regulated by Dex in a dose- and time-dependent manner. Therefore, we demonstrated that the expression of Ski was up-regulated in glucocorticoid-related osteonecrosis disease in vivo and in vitro. Moreover, the adipogenesis differentiation capacity of BMSCs was enhanced after induced by Dex, which was identified by Oil Red O staining, and the up-regulated PPAR-γ and FABP4 expression. To further study the function of Ski in BMSC after induced by Dex, Ski specific small interfering RNA (Ski-siRNA) was used. Results showed that knockdown of Ski obviously decreased adipogenesis differentiation evident by Oil Red O staining, and the expression of PPAR-γ and FABP4 was down-regulated simultaneously. Collectively, our findings suggest that Ski increased significantly during glucocorticoid-induced adipogenic differentiation of BMSCs, and the expression level was consistent with adipogenic-related proteins including PPAR-γ and FABP4. Based on the above data, we believe that Ski might become a new molecule in the treatment of GC-induced ONFH and our study could provide a basis for further study on the detailed function of Ski in ONFH.

Cell sheets of co-cultured BMP-2-modified bone marrow stromal cells and endothelial progenitor cells accelerate bone regeneration in vitro

Bone tissue engineering provides a substitute for bone transplantation to address various bone defects. However, bone regeneration involves a large number of cellular events. In addition, obtaining sufficient source material for autogenous bone or alloplastic bone substitutes remains an unsolved issue. In previous studies, it was confirmed that bone marrow stromal cells (BMSCs) and endothelial progenitor cells (EPCs) had the capacity to promote bone regeneration. Additionally, bone morphogenetic protein-2 (BMP-2) has been demonstrated to be an active inducer of osteoblast differentiation. Therefore, the aim of the present study was to produce an effective integration system, including a scaffold, reparative cells and growth factors, that may enhance bone regeneration. Firstly, bone marrow-derived BMSCs and EPCs were isolated and identified by flow cytometry. Cell proliferation ability, secreted BMP-2 levels and alkaline phosphatase (ALP) activity were highest in the cell sheets containing BMP-2-modified BMSCs and EPCs. In addition, the expression levels of osteogenesis-associated genes, including runt related transcription factor 2 (Runx2), distal-less homeobox 5 (Dlx5), ALP and integrin-binding sialoprotein (Ibsp), and osteogenesis-associated proteins, including Runx2, Dlx, ALP, Ibsp, vascular endothelial growth factor, osteonectin, osteopontin and type I collagen, gradually increased during the co-culture of ad-BMP-2-BMSCs/EPCs. The levels of these genes and proteins were increased compared with those observed in the BMSC, EPC and BMP-2-modified BMSC groups. Finally, scanning electron microscopy observation also demonstrated that the BMP2-modified BMSCs were able to combine well with EPCs to construct a cell sheet for bone formation. Collectively, these results describe an adenovirus (ad)-BMP2-BMSCs/EPCs co-culture system that may significantly accelerate bone regeneration compared with a BMSCs/EPCs co-culture system or ad-BMP2-BMSCs alone.

All-trans retinoic acid and COX-2 cross-talk to regulate BMP9-induced osteogenic differentiation via Wnt/β-catenin in mesenchymal stem cells

COX-2 specific inhibitor, which has been widely used, can delay bone fracture healing and reduce osteogenic potential of bone marrow stromal cells. However, it remains unknown how to prevent these side-effects of COX-2 inhibitor. In this study, we introduced BMP9-induced osteogenic differentiation as model to evaluate whether all-trans retinoic acid (ATRA) could ameliorate these adverse effects of COX-2 specific inhibitor on bone metabolism with in vitro and in vivo experiments, and uncover the possible mechanism underlying this process. Results showed that ATRA enhanced the potential of BMP9 to induce the osteogenic markers, such as alkaline phosphates (ALP) and mineralization; but retinoic acid receptor a (RARa) inhibitor showed the reversal effects. COX-2 specific inhibitor (NS398) reduced the osteogenic markers induced by BMP9, and ATRA almost eliminated the inhibitory effect of NS398. BMP9 up-regulated the protein level of β-catenin and promoted it translocate to nucleus, and both were reduced by NS398. On the contrary, ATRA notablely attenuated the inhibitory effect of NS398 on BMP9-increased β-catenin. Exogenous RXRa obviously ameliorated the inhibitory effect of silencing COX-2 on ectopic bone formation induced by BMP9. NS398 reduced the level of phosphorylated CREB, which was almost reversed by ATRA. Besides, RXRa interacted with phosphorylated CREB directly and both were recruited at β-catenin promoter region. Thus, we demonstrated that ATRA may reverse the side-effects of COX-2 inhibitor on bone metabolism through increasing the activation of Wnt/β-catenin pathway partly.

Comparison of osteogenic differentiation induced by siNoggin and pBMP-2 delivered by lipopolysaccharide-amine nanopolymersomes and underlying molecular mechanisms

Purpose: Gene therapies via Noggin small interfering (si)RNA (siNoggin) and bone morphogenetic protein (BMP)-2 plasmid DNA (pBMP-2) may be promising strategies for bone repair/regeneration, but their ideal delivery vectors, efficacy difference, and underlying mechanisms have not been explored, so these issues were probed here.

Methods: This study used lipopolysaccharide-amine nanopolymersomes (LNPs), an efficient cytosolic delivery vector developed by the research team, to mediate siNoggin and pBMP-2 to transfect MC3T3-E1 cells, respectively. The cytotoxicity, cell uptake, and gene knockdown efficiency of siNoggin-loaded LNPs (LNPs/siNoggin) were studied, then the osteogenic-differentiation efficacy of MC3T3-E1 cells treated by LNPs/pBMP-2 and LNPs/siNoggin, respectively, were compared by measuring the expression of osteogenesis-related genes and proteins, alkaline phosphatase (ALP) activity, and mineralization of the extracellular matrix at all osteogenic stages. Finally, the possible signaling pathways of the two treatments were explored.

Results: LNPs delivered siNoggin into cells efficiently to silence 50% of Noggin expression without obvious cytotoxicity. LNPs/siNoggin and LNPs/pBMP-2 enhanced the osteogenic differentiation of MC3T3 E1 cells, but LNPs/siNoggin was better than LNPs/pBMP-2. BMP/Mothers against decapentaplegic homolog (Smad) and glycogen synthase kinase (GSK)-3β/β-catenin signaling pathways appeared to be involved in osteogenic differentiation induced by LNPs/siNoggin, but GSK-3β/β-catenin was not stimulated upon LNPs/pBMP-2 treatment.

Conclusion: LNPs are safe and efficient delivery vectors for DNA and RNA, which may find wide applications in gene therapy. siNoggin treatment may be a more efficient strategy to enhance osteogenic differentiation than pBMP-2 treatment. LNPs loaded with siNoggin and/or pBMP-2 may provide new opportunities for the repair and regeneration of bone.

[Safety and efficacy of BMP-2 and BMP-7 use in dentistry]

The article deals with bone morphogenetic proteins BMP-2 and BMP-7 with high osteoinductive potential. The materials containing these proteins are considered. Their safety and efficacy for regeneration of maxillofacial bone defects are evaluated. The prospects of bone tissue regeneration technologies development based on the use of bone morphogenetic proteins are described.

Bone Morphogenetic Proteins (BMPs) and Bone Regeneration

Many research methods exist to elucidate the role of BMP-2 during bone regeneration. This chapter briefly reviews important animal models used in these studies and provides details on the rat femur defect model. This animal model is frequently utilized to measure the efficacy of osteogenic factors like BMP-2. Detailed information about delivery methods, dose range, and dose duration used in BMP-2-related studies are provided.

Apoptosis-associated speck-like protein containing a caspase-1 recruitment domain (ASC) contributes to osteoblast differentiation and osteogenesis

The role of apoptosis-associated speck-like protein containing a caspase-1 recruitment domain (ASC) in bone healing remains to be understood. To address this issue, we investigated the requirement of inflammasome-related genes in response to bone morphogenetic protein 7 (BMP7)-induced osteoblast differentiation in vitro. To validate the importance of ASC on osteogenesis, we subjected wild-type (WT) and ASC knockout C57BL/6 mice (ASC KO) to tibia defect to evaluate the bone healing process (up to 28 days). Our in vitro data showed that there is an involvement of ASC during BMP7-induced osteoblast differentiation, concomitant to osteogenic biomarker expression. Indeed, primary osteogenic cells from ASC KO presented a lower osteogenic profile than those obtained from WT mice. To validate this hypothesis, we evaluated the bone healing process of tibia defects on both WT and ASC KO mice genotypes and the ASC KO mice were not able to fully heal tibia defects up to 28 days, whereas WT tibia defects presented a higher bone de novo volume at this stage, evidencing ASC as an important molecule during osteogenic phenotype. In addition, we have shown a higher involvement of runt-related transcription factor 2 in WT sections during bone repair, as well as circulating bone alkaline phosphatase isoform when both were compared with ASC KO mice behavior. Altogether, our results showed for the first time the involvement of inflammasome during osteoblast differentiation and osteogenesis, which opens new avenues to understand the pathways involved in bone healing.

All-trans retinoic-acid inhibits heterodimeric bone morphogenetic protein 2/7-stimulated osteoclastogenesis, and resorption activity

Background

Bone regenerative heterodimeric bone morphogenetic protein 2/7 (BMP2/7) enhances but all-trans retinoic acid (ATRA) inhibits osteoclastogenesis. However, the effect of ATRA on physiological and/or BMP2/7-induced osteoclastogenesis in still unclear. In this study, we aimed to test the effect of combined treatment of BMP2/7 and ATRA on osteoclastogenesis, and resorption activity.

Results

All-trans retinoic acid (1 µM) ± BMP2/7 (5 or 50 ng/ml) was added in murine pre-osteoclasts cell line RAW264.7 or mouse bone marrow derived macrophages (BMM) cultures. Osteoclast marker gene expression, osteoclastogenesis, and resorption activity were analyzed. BMP2/7 robustly enhanced osteoclast maker gene expression, osteoclastogenesis, and resorption activity. Interestingly, ATRA completely inhibited osteoclast formation in presence or absence of BMP2/7. Pan-antagonist of retinoic acid receptors (RARs) and antagonist of RARα, β or γ failed to reverse the inhibitory effect of ATRA on osteoclastogenesis. ATRA strongly inhibited Rank and Nfatc1 expression.

Conclusions

All-trans retinoic acid inhibits BMP2/7-induced osteoclastogenesis, and resorption activity possibly via RANKL-RANK pathway. Our findings from previous and current study suggest that combination of ATRA and BMP2/7 could be a novel approach to treat hyperactive osteoclast-induced bone loss such as in inflammation-induced severe osteoporosis and bone loss caused by cancer metastasis to bone.

Involvement of FAK-mediated BMP-2/Smad pathway in mediating osteoblast adhesion and differentiation on nano-HA/chitosan composite coated titanium implant under diabetic conditions

Nanophase HA/CS composite coated porous titanium implant exhibited superior biological performance under diabetic conditions compared to pure Ti.

Strategies Developed to Induce, Direct, and Potentiate Bone Healing

Bone exhibits a great ability for endogenous self-healing. Nevertheless, impaired bone regeneration and healing is on the rise due to population aging, increasing incidence of bone trauma and the clinical need for the development of alternative options to autologous bone grafts. Current strategies, including several biomolecules, cellular therapies, biomaterials, and different permutations of these, are now developed to facilitate the vascularization and the engraftment of the constructs, to recreate ultimately a bone tissue with the same properties and characteristics of the native bone. In this review, we browse the existing strategies that are currently developed, using biomolecules, cells and biomaterials, to induce, direct and potentiate bone healing after injury and further discuss the biological processes associated with this repair.

Comparison of cell-based versus cell-free mammalian systems for the production of a recombinant human bone morphogenic growth factor

The human bone morphogenetic protein-2 (hBMP2) is a glycoprotein, which induces de novo bone formation. Here, recombinant production in stably transfected Chinese Hamster Ovary (CHO) cells is compared to transient expression in Human Embryo Kidney (HEK) cells and cell-free synthesis in CHO cell lysates containing microsomal structures as sites of post-translational processing. In case of the stably transfected cells, growth rates and viabilities were similar to those of the parent cells, while entry into the death phase of the culture was delayed. The maximum achievable rhBMP2 concentration in these cultures was 153 pg/mL. Up to 280 ng/mL could be produced in the transient expression system. In both cases the rhBMP-2 was found to interact with the producer cells, which presumably contributed to the low yields. In the cell-free system, hBMP2 yields could be increased to almost 40 μg/mL, reached within three hours. The cell-free system thus approached productivities for the active (renatured) protein previously only recorded for bacterial hosts, while assuring comprehensive post-translational processing.

Dose effects of beta-tricalcium phosphate nanoparticles on biocompatibility and bone conductive ability of three-dimensional collagen scaffolds

Three-dimensional collagen scaffolds coated with beta-tricalcium phosphate (β-TCP) nanoparticles reportedly exhibit good bioactivity and biodegradability. Dose effects of β-TCP nanoparticles on biocompatibility and bone forming ability were then examined. Collagen scaffold was applied with 1, 5, 10, and 25 wt% β-TCP nanoparticle dispersion and designated TCP1, TCP5, TCP10, and TCP25, respectively. Compressive strength, calcium ion release and enzyme resistance of scaffolds with β-TCP nanoparticles applied increased with β-TCP dose. TCP5 showed excellent cell-ingrowth behavior in rat subcutaneous tissue. When TCP10 was applied, osteoblastic cell proliferation and rat cranial bone augmentation were greater than for any other scaffold. The bone area of TCP10 was 7.7-fold greater than that of non-treated scaffold. In contrast, TCP25 consistently exhibited adverse biological effects. These results suggest that the application dose of β-TCP nanoparticles affects the scaffold bioproperties; consequently, the bone conductive ability of TCP10 was remarkable.

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.

Tcf12, A Member of Basic Helix-Loop-Helix Transcription Factors, Mediates Bone Marrow Mesenchymal Stem Cell Osteogenic Differentiation In Vitro and In Vivo

Several basic Helix-Loop-Helix transcription factors have recently been identified to regulate mesenchymal stem cell (MSC) differentiation. In the present study, Tcf12 was investigated for its involvement in the osteoblastic cell commitment of MSCs. Tcf12 was found highly expressed in undifferentiated MSCs whereas its expression decreased following osteogenic culture differentiation. Interestingly, Tcf12 endogenous silencing using shRNA lentivirus significantly promoted the differentiation ability of MSCs evaluated by alkaline phosphatase staining, alizarin red staining and expression of osteoblast-specific markers by real-time PCR. Conversely, overexpression of Tcf12 in MSCs suppressed osteoblast differentiation. It was further found that silencing of Tcf12 activated bone morphogenetic protein (BMP) signaling and extracellular signal-regulated kinase (Erk)1/2 signaling pathway activity and upregulated the expression of phospho-SMAD1 and phospho-Erk1/2. A BMP inhibitor (LDN-193189) and Erk1/2 signaling pathway inhibitor (U0126) reduced these findings in the Tcf12 silencing group. Following these in vitro results, a poly-L-lactic acid/Hydroxyappatite scaffold carrying Tcf12 silencing lentivirus was utilized to investigate the repair of bone defects in vivo. The use of Tcf12 silencing lentivirus significantly promoted new bone formation in 3-mm mouse calvarial defects as assessed by micro-CT and histological examination whereas overexpression of Tcf12 inhibited new bone formation. Collectively, these data indicate that Tcf12 is a transcription factor highly expressed in the nuclei of stem cells and its downregulation plays an essential role in osteoblast differentiation partially via BMP and Erk1/2 signaling pathways. Stem Cells 2017;35:386-397.

Heterodimeric BMP-2/7 for nucleus pulposus regeneration-In vitro and ex vivo studies

Intervertebral disc (IVD) degeneration is the leading trigger of low back pain, which causes disability and leads to enormous healthcare toll worldwide. Biological treatment with growth factors has evolved as potential therapy for IVD regeneration. Bone morphogenetic protein 2 (BMP-2) and BMP-7 have shown promise in this regard. In the current study, we evaluated the effect of BMP-2/7 heterodimer for disc regeneration both in vitro and in organ culture. Nucleus pulposus (NP) cells isolated from bovine caudal disc were cultured in a fibrin-hyaluronan (FBG-HA) hydrogel for up to 14 days. BMP-2/7 heterodimer covalently incorporated within the hydrogel up-regulated the aggrecan and type II collagen gene expression, and glycosaminoglycan synthesis of NP cells. The activity of the BMP-2/7 heterodimer was dose dependent. The higher dose of BMP-2/7 was further assessed in an IVD whole organ system. After 14 days of culture with cyclic dynamic load, the BMP-2/7 heterodimer delivered into the nucleotomized region showed potential to stimulate the gene expression and synthesis of proteoglycan in the remaining NP tissue after partial nucleotomy. The gene expression level of type I collagen and alkaline phosphatase in the native disc tissue were not affected by BMP-2/7 treatment, indicating no adverse fibroblastic or osteogenic effect on the disc tissue. Intradiscal delivery of BMP-2/7 heterodimer may be a promising therapeutic approach for NP regeneration. The current IVD whole organ partial nucleotomy model may be utilized for screening of other biomaterials or drugs to treat early degenerative disc disorders. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:51-60, 2017.

Fluoride affects bone repair differently in mice models with distinct bone densities

We grouped mice [strains: C57BL/6J (n=32) and C3H/HeJ (n=32)] to address the influence of bone density on fluoride's (F's) biological effects. These animals received low-fluoride food and water containing 0 (control group) or 50ppm of F for up to 28days. The upper left central incisor was extracted, and the left maxilla was collected at 7, 14, 21, and 28days for histological and histomorphometric analysis to estimate bone neoformation. Our results showed bone neoformation in all of the evaluated groups, with the presence of bone islets invading the center of the alveoli when replacing the existing connective tissue. Curiously, this biological phenomenon was more evident in the C57BL/6J strain. The histomorphometric analysis confirmed the histological findings in relation to the amount of new bone tissue and showed a decrease in C3H/HeJ mice (control group). Altogether, our results showed differential effects of fluoride bone metabolism, confirming a genetic component in susceptibility to the effects of fluoride.

Bone morphogenetic protein-2-mediated pain and inflammation in a rat model of posterolateral arthrodesis

BACKGROUND

Bone morphogenetic protein-2 (BMP-2) is a pleiotropic, secreted molecule with diverse effects. The potent ability of BMP-2 to stimulate bone growth prompted its widespread clinical use for arthrodesis (spine fusion). However, elevated post-operative pain in patients treated with BMP-2 has been increasingly reported. Determining whether BMP-2 induces pain directly or whether it induces neuroinflammation, which could lower the threshold for pain, is important for developing therapeutic interventions. We therefore modeled the clinical use of BMP-2 for posterior lumbar fusion by implanting absorbable collagen sponges soaked with either recombinant human BMP-2 (rhBMP-2) or vehicle above the L4-L5 transverse processes of rat spine.

RESULTS

Using microarray analysis we found that implantation of rhBMP-2-soaked absorbable collagen sponges resulted in altered expression of numerous pro-inflammatory genes in the adjacent dorsal root ganglia (DRG) showing that implantation of rhBMP-2/absorbable collagen sponges triggers potent neuroinflammatory responses in the DRG-2. Interestingly, direct BMP-2 treatment of DRG explants resulted in changes in gene expression that were not specifically pro-inflammatory. Rats implanted with rhBMP-2 in absorbable collagen sponges also exhibited a transient change in thermal and mechanical sensitivity indicating that rhBMP-2 applied to the lumbar spine could increase pain sensitivity. Immunohistochemical analysis indicated macrophage infiltration in the DRG and spinal nerve in rats implanted with rhBMP-2/absorbable collagen sponges or absorbable collagen sponges alone, but not in rats that underwent surgery without implantation of the absorbable collagen sponges suggesting that the sponges contributed to the biological response. Indeed, analysis of DRGs taken from rats implanted with absorbable collagen sponges without rhBMP-2 showed a significant change in gene expression distinct from DRGs from rats undergoing surgery only.

CONCLUSIONS

Our data indicate that implantation of rhBMP-2/absorbable collagen sponges on the lumbar spine triggers potent neuroinflammatory responses in the DRG. Importantly, however, these BMP-2 effects may be partially mediated through a response to the absorbable collagen sponges.

Implant Composed of Demineralized Bone and Mesenchymal Stem Cells Genetically Modified with AdBMP2/AdBMP7 for the Regeneration of Bone Fractures in Ovis aries

Adipose-derived mesenchymal stem cells (ADMSCs) are inducible to an osteogenic phenotype by the bone morphogenetic proteins (BMPs). This facilitates the generation of implants for bone tissue regeneration. This study evaluated the in vitro osteogenic differentiation of ADMSCs transduced individually and in combination with adenoviral vectors expressing BMP2 and BMP7. Moreover, the effectiveness of the implant containing ADMSCs transduced with the adenoviral vectors AdBMP2/AdBMP7 and embedded in demineralized bone matrix (DBM) was tested in a model of tibial fracture in sheep. This graft was compared to ewes implanted with untransduced ADMSCs embedded in the same matrix and with injured but untreated animals. In vivo results showed accelerated osteogenesis in the group treated with the AdBMP2/AdBMP7 transduced ADMSC graft, which also showed improved restoration of the normal bone morphology.