Osteopontin on the Dental Implant Surface Promotes Direct Osteogenesis in Osseointegration

Mechanotransducive surfaces for enhanced cell osteogenesis, a review

Novel strategies employing mechano-transducing materials eliciting biological outcomes have recently emerged for controlling cellular behaviour. Targeted cellular responses are achieved by manipulating physical, chemical, or biochemical modification of material properties. Advances in techniques such as nanopatterning, chemical modification, biochemical molecule embedding, force-tuneable materials, and artificial extracellular matrices are helping understand cellular mechanotransduction. Collectively, these strategies manipulate cellular sensing and regulate signalling cascades including focal adhesions, YAP-TAZ transcription factors, and multiple osteogenic pathways. In this minireview, we are providing a summary of the influence that these materials, particularly titanium-based orthopaedic materials, have on cells. We also highlight recent complementary methodological developments including, but not limited to, the use of metabolomics for identification of active biomolecules that drive cellular differentiation.

Cleaved SPP1-rich extracellular vesicles from osteoclasts promote bone regeneration via TGFβ1/SMAD3 signaling

Bone remodeling is a tightly coupled process between bone forming osteoblasts (OBs) and bone resorbing osteoclasts (OCs) to maintain bone architecture and systemic mineral homeostasis throughout life. However, the mechanisms responsible for the coupling between OCs and OBs have not been fully elucidated. Herein, we first validate that secreted extracellular vesicles by osteoclasts (OC-EVs) promote osteogenic differentiation of mesenchymal stem cells (MSCs) and further demonstrate the efficacy of osteoclasts and their secreted EVs in treating tibial bone defects. Furthermore, we show that OC-EVs contain several osteogenesis-promoting proteins as cargo. By employing proteomic and functional analysis, we reveal that mature osteoclasts secrete thrombin cleaved phosphoprotein 1 (SPP1) through extracellular vesicles which triggers MSCs osteogenic differentiation into OBs by activating Transforming Growth Factor β1 (TGFβ1) and Smad family member 3 (SMAD3) signaling. In conclusion, our findings prove an important role of SPP1, present as cargo in OC-derived EVs, in signaling to MSCs and driving their differentiation into OBs. This biological mechanism implies a paradigm shift regarding the role of osteoclasts and their signaling toward the treatment of skeletal disorders which require bone formation.

Effect of Hydroxyapatite/β-Tricalcium Phosphate on Osseointegration after Implantation into Mouse Maxilla

In our previous study we established an animal model for immediately placed implants using mice and clarified that there were no significant differences in the chronological healing process at the bone-implant interface between immediately and delayed placed implants blasted with hydroxyapatite (HA)/β-tricalcium phosphate (β-TCP) (ratio 1:4). This study aimed to analyze the effects of HA/β-TCP on osseointegration at the bone-implant interface after immediately placed implants in the maxillae of 4-week-old mice. Right maxillary first molars were extracted and cavities were prepared with a drill and titanium implants, blasted with or without HA/β-TCP, were placed. The fixation was followed-up at 1, 5, 7, 14, and 28 days after implantation, and the decalcified samples were embedded in paraffin and prepared sections were processed for immunohistochemistry using anti-osteopontin (OPN) and Ki67 antibodies, and tartrate-resistant acid phosphatase histochemistry. The undecalcified sample elements were quantitatively analyzed by an electron probe microanalyzer. Bone formation occurred on the preexisting bone surface (indirect osteogenesis) and on the implant surface (direct osteogenesis), indicating that osseointegration was achieved until 4 weeks post-operation in both of the groups. In the non-blasted group, the OPN immunoreactivity at the bone-implant interface was significantly decreased compared with the blasted group at week 2 and 4, as well as the rate of direct osteogenesis at week 4. These results suggest that the lack of HA/β-TCP on the implant surface affects the OPN immunoreactivity on the bone-implant interface, resulting in decreased direct osteogenesis following immediately placed titanium implants.

Forskolin enhanced the osteogenic differentiation of human dental pulp stem cells in vitro and in vivo

Background/purpose

Human dental pulp stem cells (hDPSCs) are multipotent adult stem cells that can differentiate into various lineages such as odontoblasts, osteoblasts, and chondrocytes. Regulation of hDPSCs differentiation with small-molecule compounds can be a useful tool for tissue engineering and regenerative therapy. Forskolin is an agonist of adenylate cyclase that promotes cyclic adenosine monophosphate production. However, the role of Forskolin in regulating the osteogenic differentiation of hDPSCs is still unknown.

Materials and methods

A cell counting kit-8 (CCK-8) assay was performed to screen out the safety concentrations of Forskolin. Following, quantitative polymerase chain reaction (qPCR) and alizarin red staining were performed to detect bone-related gene expression and mineralized deposit formation. Furthermore, we prepared cell sheets which were followed by a 3D culture for cell pellet formation. Finally, the hDPSC cell pellets were transplanted into immunodeficient mice.

Results

CCK-8 assay showed 5 μM and 10 μM Forskolin had no significant inhibition on the proliferation of hDPSCs. The qPCR indicated Forskolin (5, 10 μM) enhanced osteogenic differentiation of hDPSCs by upregulating bone-related genes. Alizarin red staining and its quantification analysis demonstrated Forskolin in 5 μM and 10 μM similarly enhanced the mineralized deposit formation of hDPSCs in vitro. After six weeks of transplantation, immunohistochemical stains showed that osteopontin expression and bone formation were significantly boosted in the Forskolin-treated group than in the normal osteogenic inducing group.

Conclusion

Our results indicate Forskolin enhances osteogenic differentiation of hDPSCs in vitro and boosts bone formation in vivo.

Evaluation of the Biocompatibility and Osteogenic Properties of Metal Oxide Coatings Applied by Magnetron Sputtering as Potential Biofunctional Surface Modifications for Orthopedic Implants

Biomaterials with adequate properties to direct a biological response are essential for orthopedic and dental implants. The surface properties are responsible for the biological response; thus, coatings with biologically relevant properties such as osteoinduction are exciting options to tailor the surface of different bulk materials. Metal oxide coatings such as TiO₂, ZrO₂, Nb₂O₅ and Ta₂O₅ have been suggested as promising for orthopedic and dental implants. However, a comparative study among them is still missing to select the most promising for bone-growth-related applications. In this work, using magnetron sputtering, TiO₂, ZrO₂, Ta₂O₅, and Nb₂O₅ thin films were deposited on Si (100) substrates. The coatings were characterized by Optical Profilometry, Scanning Electron Microscopy, Energy-Dispersive X-ray Spectroscopy, X-ray Photoelectron Spectroscopy, X-ray Diffraction, Water Contact Angle measurements, and Surface Free Energy calculations. The cell adhesion, viability, proliferation, and differentiation toward the osteoblastic phenotype of mesenchymal stem cells plated on the coatings were measured to define the biological response. Results confirmed that all coatings were biocompatible. However, a more significant number of cells and proliferative cells were observed on Nb₂O₅ and Ta₂O₅ compared to TiO₂ and ZrO_2. Nevertheless, Nb₂O₅ and Ta₂O₅ seemed to induce cell differentiation toward the osteoblastic phenotype in a longer cell culture time than TiO₂ and ZrO₂.