Characterization of scaffold carriers for BMP9-transduced osteoblastic progenitor cells in bone regeneration

Frontiers of Hydroxyapatite Composites in Bionic Bone Tissue Engineering

Bone defects caused by various factors may cause morphological and functional disorders that can seriously affect patient's quality of life. Autologous bone grafting is morbid, involves numerous complications, and provides limited volume at donor site. Hence, tissue-engineered bone is a better alternative for repair of bone defects and for promoting a patient's functional recovery. Besides good biocompatibility, scaffolding materials represented by hydroxyapatite (HA) composites in tissue-engineered bone also have strong ability to guide bone regeneration. The development of manufacturing technology and advances in material science have made HA composite scaffolding more closely related to the composition and mechanical properties of natural bone. The surface morphology and pore diameter of the scaffold material are more important for cell proliferation, differentiation, and nutrient exchange. The degradation rate of the composite scaffold should match the rate of osteogenesis, and the loading of cells/cytokine is beneficial to promote the formation of new bone. In conclusion, there is no doubt that a breakthrough has been made in composition, mechanical properties, and degradation of HA composites. Biomimetic tissue-engineered bone based on vascularization and innervation show a promising future.

Argonaute (AGO) proteins play an essential role in mediating BMP9-induced osteogenic signaling in mesenchymal stem cells (MSCs)

As multipotent progenitor cells, mesenchymal stem cells (MSCs) can renew themselves and give rise to multiple lineages including osteoblastic, chondrogenic and adipogenic lineages. It's previously shown that BMP9 is the most potent BMP and induces osteogenic and adipogenic differentiation of MSCs. However, the molecular mechanism through which BMP9 regulates MSC differentiation remains poorly understood. Emerging evidence indicates that noncoding RNAs, especially microRNAs, may play important roles in regulating MSC differentiation and bone formation. As highly conserved RNA binding proteins, Argonaute (AGO) proteins are essential components of the multi-protein RNA-induced silencing complexes (RISCs), which are critical for small RNA biogenesis. Here, we investigate possible roles of AGO proteins in BMP9-induced lineage-specific differentiation of MSCs. We first found that BMP9 up-regulated the expression of Ago1, Ago2 and Ago3 in MSCs. By engineering multiplex siRNA vectors that express multiple siRNAs targeting individual Ago genes or all four Ago genes, we found that silencing individual Ago expression led to a decrease in BMP9-induced early osteogenic marker alkaline phosphatase (ALP) activity in MSCs. Furthermore, we demonstrated that simultaneously silencing all four Ago genes significantly diminished BMP9-induced osteogenic and adipogenic differentiation of MSCs and matrix mineralization, and ectopic bone formation. Collectively, our findings strongly indicate that AGO proteins and associated small RNA biogenesis pathway play an essential role in mediating BMP9-induced osteogenic differentiation of MSCs.

Stem Cell-Friendly Scaffold Biomaterials: Applications for Bone Tissue Engineering and Regenerative Medicine

Bone is a dynamic organ with high regenerative potential and provides essential biological functions in the body, such as providing body mobility and protection of internal organs, regulating hematopoietic cell homeostasis, and serving as important mineral reservoir. Bone defects, which can be caused by trauma, cancer and bone disorders, pose formidable public health burdens. Even though autologous bone grafts, allografts, or xenografts have been used clinically, repairing large bone defects remains as a significant clinical challenge. Bone tissue engineering (BTE) emerged as a promising solution to overcome the limitations of autografts and allografts. Ideal bone tissue engineering is to induce bone regeneration through the synergistic integration of biomaterial scaffolds, bone progenitor cells, and bone-forming factors. Successful stem cell-based BTE requires a combination of abundant mesenchymal progenitors with osteogenic potential, suitable biofactors to drive osteogenic differentiation, and cell-friendly scaffold biomaterials. Thus, the crux of BTE lies within the use of cell-friendly biomaterials as scaffolds to overcome extensive bone defects. In this review, we focus on the biocompatibility and cell-friendly features of commonly used scaffold materials, including inorganic compound-based ceramics, natural polymers, synthetic polymers, decellularized extracellular matrix, and in many cases, composite scaffolds using the above existing biomaterials. It is conceivable that combinations of bioactive materials, progenitor cells, growth factors, functionalization techniques, and biomimetic scaffold designs, along with 3D bioprinting technology, will unleash a new era of complex BTE scaffolds tailored to patient-specific applications.

Nanocomposite Films of Chitosan-Grafted Carbon Nano-Onions for Biomedical Applications

The design of scaffolding from biocompatible and resistant materials such as carbon nanomaterials and biopolymers has become very important, given the high rate of injured patients. Graphene and carbon nanotubes, for example, have been used to improve the physical, mechanical, and biological properties of different materials and devices. In this work, we report the grafting of carbon nano-onions with chitosan (CS-g-CNO) through an amide-type bond. These compounds were blended with chitosan and polyvinyl alcohol composites to produce films for subdermal implantation in Wistar rats. Films with physical mixture between chitosan, polyvinyl alcohol, and carbon nano-onions were also prepared for comparison purposes. Film characterization was performed with Fourier Transformation Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Tensile strength, X-ray Diffraction Spectroscopy (XRD), and Scanning Electron Microscopy (SEM). The degradation of films into simulated body fluid (SBF) showed losses between 14% and 16% of the initial weight after 25 days of treatment. Still, a faster degradation (weight loss and pH changes) was obtained with composites of CS-g-CNO due to a higher SBF interaction by hydrogen bonding. On the other hand, in vivo evaluation of nanocomposites during 30 days in Wistar rats, subdermal tissue demonstrated normal resorption of the materials with lower inflammation processes as compared with the physical blends of ox-CNO formulations. SBF hydrolytic results agreed with the in vivo degradation for all samples, demonstrating that with a higher ox-CNO content increased the stability of the material and decreased its degradation capacity; however, we observed greater reabsorption with the formulations including CS-g-CNO. With this research, we demonstrated the future impact of CS/PVA/CS-g-CNO nanocomposite films for biomedical applications.

DKK1 and TNF-alpha influence osteogenic differentiation of adBMP9-infected-rDFCs

OBJECTIVES

Rat dental follicle cells (rDFCs) function as precursor cells of periodontal tissues. Bone morphogenetic protein (BMP9) plays an important role in proliferation and differentiation. Tumour necrosis factor-alpha (TNF-alpha) is an important contributor to bone resorption. Wnt canonical pathway can be inhibited by Dickkopf 1 (DKK1). The aim of the study was to enhance the osteogenesis of BMP9 treated rDFCs in an inflammatory environment and elucidate the mechanism.

MATERIALS AND METHODS

rDFCs were infected by adenoviruses expressing BMP9 (adBMP9). Expression levels of proteins and genes were measured by Western blotting and qPCR. The effect on osteogenesis was evaluated by measuring the activity of alkaline phosphatase (ALP), observation of Alizarin Red S and haematoxylin and eosin staining.

RESULTS

TNF-alpha activated the canonical Wnt pathway and inhibited the non-canonical pathway. DKK1 suppressed the canonical pathway and promoted the non-canonical pathway. Addition of TNF-alpha or DKK1 inhibited BMP9/Smad pathway. However, this inhibition was reduced by the addition of DKK1 with TNF-alpha.

CONCLUSIONS

DKK1 reduces the inhibitory effects of TNF-alpha in adBMP9-infected-rDFCs, possibly through interaction with the Smad signalling pathway and Wnt pathways. These findings may lead to a novel approach for the treatment of periodontitis-related alveolar bone defects.

Preparation of Chitosan/Poly(Vinyl Alcohol) Nanocomposite Films Incorporated with Oxidized Carbon Nano-Onions (Multi-Layer Fullerenes) for Tissue-Engineering Applications

Recently, tissue engineering became a very important medical alternative in patients who need to regenerate damaged or lost tissues through the use of scaffolds that support cell adhesion and proliferation. Carbon nanomaterials (carbon nanotubes, fullerenes, multi-wall fullerenes, and graphene) became a very important alternative to reinforce the mechanical, thermal, and antimicrobial properties of several biopolymers. In this work, five different formulations of chitosan/poly(vinyl alcohol)/oxidized carbon nano-onions (CS/PVA/ox-CNO) were used to prepare biodegradable scaffolds with potential biomedical applications. Film characterization consisted of Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), tension strength, Young's modulus, X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). The degradation in a simulated body fluid (FBS) demonstrated that all the formulations lost between 75% and 80% of their weight after 15 days of treatment, but the degradation decreased with the ox-CNO content. In vivo tests after 90 days of subdermal implantation of the nanocomposite films in Wistar rats' tissue demonstrated good biocompatibility without allergenic reactions or pus formation. There was a good correlation between FBS hydrolytic degradation and degradation in vivo for all the samples, since the ox-CNO content increased the stability of the material. All these results indicate the potential of the CS/PVA/ox-CNO nanocomposite films in tissue engineering, especially for long-term applications.

Thermoresponsive Injectable Microparticle-Gel Composites with Recombinant BMP-9 and VEGF Enhance Bone Formation in Rats

Bone morphogenetic protein-9 (BMP-9) has been shown to be the most osteogenic BMP. Most of these experiments, however, involve an adenovirus-transfection strategy. Here, we used the scaffold-based strategy to study the bone forming ability of recombinant BMP-9 combined with vascular endothelial growth factor (VEGF). A robust, injectable, multicomponent-releasing scaffold in the form of a composite gel was developed by combining chitosan microparticles (MPs) with thermosensitive gel (MPs-gel). The MPs acted as the carriers for BMP-9 and the gel was loaded with VEGF. The developed gel consisted of hydrophobic chains of methyl cellulose (MC) and the cross-linked structures of alginate (Alg) and calcium. Gelation was achieved at physiological temperature and thus facilitated the injection and localization of MPs enabling an increased efficacy of incorporated growth factors at the target site. A release profile of incorporated growth factors over a two-week period showed higher release of VEGF at each time point compared to that of BMP-9. Human mesenchymal stem cells (hMSCs) encapsulated within the MPs-gel maintained their viability. BMP-9 enhanced the proliferation of hMSCs along the surface of MPs. Furthermore, BMP-9 potently induced the osteogenic differentiation of encapsulated hMSCs elucidated by the increased alkaline phosphatase (ALP) activity and the higher expression of ALP, collagen 1, and osteocalcin genes. In addition, in vivo experiments demonstrated that MPs-gel with the combination of BMP-9-VEGF could significantly enhance both subcutaneous and cranial bone formation (p < 0.05). Taken together, the results here strongly suggest that BMP-9-VEGF incorporated MPs-gel holds promise as an injectable bone tissue engineering platform.

The healing of alveolar bone defects with novel bio-implants composed of Ad-BMP9-transfected rDFCs and CHA scaffolds

Cells, scaffolds, and growth factors play important roles in bone regeneration. Bone morphogenetic protein 9 (BMP9), a member of BMP family, could facilitate osteogenesis by regulating growth factors and promoting angiogenesis. Similar to other stem cells, rat dental follicle stem cells (rDFCs), the precursor cells of cementoblasts, osteoblasts and periodontal ligament cells, can self-renew and exhibit multipotential capacity. Coralline hydroxyapatite (CHA) has good biocompatibility and conductivity required for bone tissue engineering. Here, we reported that BMP9 could enhance the osteogenic differentiation of rDFCs in cell culture. Moreover, our results suggested that BMP9 acted through the Smad1/5/8 signaling pathway. We also produced a novel scaffold that encompasses bio-degradable CHA seeded with recombinant adenoviruses expressing BMP9-transfected rDFCs (Ad-BMP9-transfected rDFCs). With this implant, we achieved more alveolar bone regeneration in the alveolar bone defect compared to blank group, CHA group and rDFCs group. Our results provided a novel bio-implants composed of Ad-BMP9-transfected rDFCs and CHA scaffolds and its mechanism is regarding the activation of Smad1/5/8 signaling pathway in BMP9-induced rDFCs osteogenesis.

Bone morphogenetic protein 9 stimulates callus formation in osteoporotic rats during fracture healing

Fracture healing involves the coordinated actions of multiple cytokines. Bone morphogenetic protein 9 (BMP9) is an important factor in bone formation. The present study aimed to investigate the osteogenic potential of bone marrow stem cells (BMSCs) in response to adenoviral (Ad)BMP9, and the early fracture repair properties of AdBMP9 in surgically-created fractures in osteoporotic rats. Alkaline phosphatase (ALP) activity was assayed and matrix mineralization was examined by Alizarin Red S staining. mRNA and protein expression levels of BMP9, runt-related transcription factor 2 (RUNX2) and type 1 collagen (COL-1) were detected in vitro and in vivo. Femoral bone mineral density was assessed for osteoporosis in ovariectomized rats. An open femora fracture was subsequently created, and gelatin sponges containing AdBMP9 were implanted. The femora were harvested for radiographical, micro-computed tomography, biomechanical and histological analysis 4 weeks later. BMP9 successfully increased ALP activity and induced mineralized nodule formation in BMSCs. BMP9 in gelatin sponges demonstrated marked effects on microstructural parameters and the biomechanical strength of bone callus. In addition, it upregulated the expression levels of RUNX2 and COL-1. AdBMP9 in gelatin sponges significantly mediated callus formation, and increased bone mass and strength in osteoporotic rats with femora fractures. The results of the present study suggested that BMP9 enhanced callus formation and maintained early mechanical stability during fracture healing in osteoporotic rats, implicating it as a potential novel therapeutic target for fracture healing.

Nanoparticulate Mineralized Collagen Scaffolds and BMP-9 Induce a Long-Term Bone Cartilage Construct in Human Mesenchymal Stem Cells

Engineering the osteochondral junction requires fabrication of a microenvironment that supports both osteogenesis and chondrogenesis. Multiphasic scaffold strategies utilizing a combination of soluble factors and extracellular matrix components are ideally suited for such applications. In this work, the contribution of an osteogenic nanoparticulate mineralized glycosaminoglycan scaffold (MC-GAG) and a dually chondrogenic and osteogenic growth factor, BMP-9, in the differentiation of primary human mesenchymal stem cells (hMSCs) is evaluated. Although 2D cultures demonstrate alkaline phosphatase activity and mineralization of hMSCs induced by BMP-9, MC-GAG scaffolds do not demonstrate significant differences in the collagen I expression, osteopontin expression, or mineralization. Instead, BMP-9 increases expression of collagen II, Sox9, aggrecan (ACAN), and cartilage oligomeric protein. However, the hypertrophic chondrocyte marker, collagen X, is not elevated with BMP-9 treatment. In addition, histologic analyses demonstrate that while BMP-9 does not increase mineralization, BMP-9 treatment results in an increase of sulfated glycosaminoglycans. Thus, the combination of BMP-9 and MC-GAG stimulates chondrocytic and osteogenic differentiation of hMSCs.

Chitosan based biocomposite scaffolds for bone tissue engineering

The clinical demand for scaffolds and the diversity of available polymers provide freedom in the fabrication of scaffolds to achieve successful progress in bone tissue engineering (BTE). Chitosan (CS) has drawn much of the attention in recent years for its use as graft material either as alone or in a combination with other materials in BTE. The scaffolds should possess a number of properties like porosity, biocompatibility, water retention, protein adsorption, mechanical strength, biomineralization and biodegradability suited for BTE applications. In this review, CS and its properties, and the role of CS along with other polymeric and ceramic materials as scaffolds for bone tissue repair applications are highlighted.

BMP9-induced osteogenic differentiation is partially inhibited by miR-30a in the mesenchymal stem cell line C3H10T1/2

In the bone morphogenetic protein (BMP) family, BMP9 is the strongest inducer of osteogenic differentiation in mesenchymal stem cells. Recent studies have suggested that the miR-30 family regulates cell proliferation and osteoblastic differentiation. In the present study, we found that expression of only one miR-30 family member, miR-30a, first decreased and then increased during BMP9-induced osteogenic differentiation. Cell proliferation assays revealed that miR-30a had no effect on the proliferation of C3H10T1/2 cells. However, over-expression of miR-30a led to expression of an early osteogenic marker and a reduction in Runx2 expression. In addition, we observed decreases in the expression of late osteogenic markers and osteopontin, as well as calcium deposition. Dual-luciferase reporter assays indicated that this process might be mediated by suppressing Runx2 protein expression. In vivo stem cell implantation revealed inhibition of BMP9-induced ectopic bone formation and matrix mineralization by miR-30a. This study provides a better understanding of the molecular mechanisms through which miR-30a negatively regulates BMP9-induced osteogenic differentiation.