Low-intensity pulsed ultrasound regulates osteoblast-osteoclast crosstalk via EphrinB2/EphB4 signaling for orthodontic alveolar bone remodeling.

Background: The limited regenerative potential of periodontal tissue remains a challenge in orthodontic treatment, especially with respect to alveolar bone remodeling. The dynamic balance between the bone formation of osteoblasts and the bone resorption of osteoclasts controls bone homeostasis. The osteogenic effect of low-intensity pulsed ultrasound (LIPUS) is widely accepted, so LIPUS is expected to be a promising method for alveolar bone regeneration. Osteogenesis is regulated by the acoustic mechanical effect of LIPUS, while the cellular perception, transduction mode and response regulation mechanism of LIPUS stimuli are still unclear. This study aimed to explore the effects of LIPUS on osteogenesis by osteoblast-osteoclast crosstalk and the underlying regulation mechanism. Methods: The effects of LIPUS on orthodontic tooth movement (OTM) and alveolar bone remodeling were investigated via rat model by histomorphological analysis. Mouse bone marrow mesenchymal stem cells (BMSCs) and bone marrow monocytes (BMMs) were purified and used as BMSC-derived osteoblasts and BMM-derived osteoclasts, respectively. The osteoblast-osteoclast co-culture system was used to evaluate the effect of LIPUS on cell differentiation and intercellular crosstalk by Alkaline phosphatase (ALP), Alizarin Red S (ARS), tartrate-resistant acid phosphatase (TRAP) staining, real-time quantitative PCR, western blotting and immunofluorescence. Results: LIPUS was found to improve OTM and alveolar bone remodeling in vivo, promote differentiation and EphB4 expression in BMSC-derived osteoblasts in vitro, particularly when cells were directly co-cultured with BMM-derived osteoclasts. LIPUS enhanced EphrinB2/EphB4 interaction between osteoblasts and osteoclasts in alveolar bone, activated the EphB4 receptor on osteoblasts membrane, transduced LIPUS-related mechanical signals to the intracellular cytoskeleton, and gave rise to the nuclear translocation of YAP in Hippo signaling pathway, thus regulating cell migration and osteogenic differentiation. Conclusions: This study shows that LIPUS modulates bone homeostasis by osteoblast-osteoclast crosstalk via EphrinB2/EphB4 signaling, which benefits the balance between OTM and alveolar bone remodeling.

Natural Plant Tissue with Bioinspired Nano Amyloid and Hydroxyapatite as Green Scaffolds for Bone Regeneration.

Bone defects have been increasingly prevalent around the globe and traditional bone substitutes are constantly limited by low abundance and biosafety due to their animal-based resources. Plant-based scaffolds are currently studied as a green candidate but the bioinertia of cellulose to mammalian cells leads to uncertain bone regeneration. Inspired by the cross-kingdom adhesion of plants and bacteria, this work proposes a concept of a novel plant bone substitute, involving coating decellularized plant with nano amyloids and nano hydroxyapatites, to bridge the plant scaffold and animal tissue regeneration. Natural microporosity of plants can guide alignment of mammalian cells into various organ-like structures. Taking advantage of the bioactive nano amyloids, the scaffolds drastically promote cell adhesion, viability, and proliferation. The enhanced bio-affinity is elucidated as positively charged nano amyloids and serum deposition on the nanostructure. Nano-hydroxyapatite crystals deposited on amyloid further prompt osteogenic differentiation of pre-osteoblasts. In vivo experiments prove successful trabeculae regeneration in the scaffold. Such a hierarchical design leverages the dedicated microstructure of natural plants and high bioactivity of nano amyloid/hydroxyapatite coatings, and addresses the abundant resource of bone substitutes. Not limited to their current application, plant materials functionalized with nano amyloid/hydroxyapatite coatings allow many cross-kingdom tissue engineering and biomedical applications.

Nanotopography on titanium promotes osteogenesis via autophagy-mediated signaling between YAP and ß-catenin.

Nanostructured titanium implants are recognized for inducing osteogenesis, but the cell signal transductions related to topography are not fully understood. Implant topography is associated with the functionality of osteogenic transcription factors directed by ß-catenin in the nucleus, and autophagic flux in the cytoplasm; YAP (Yes-associated protein) is implicated in the destruction of ß-catenin in the cytoplasm and is susceptible to autophagic flux. This study investigated whether surface topography of the titanium implant modulates autophagy-lysosome degradation of cytoplasmic YAP. Titanium surfaces were modified with smooth, micro, or nanotopographies. Compared with the smooth and micro surfaces, nanotopography was associated with higher ß-catenin nuclear translocation, osteogenic differentiation, and autophagy, and less cytoplasmic YAP. Blockade of the autophagy-lysosome pathway resulted in YAP retention in MC3T3-E1 cells. Cytoplasmic YAP restricted ß-catenin nuclear translocation. In the nano surface group, ß-catenin accumulation in the nucleus and expression of osteogenesis genes was improved. However, in the absence of cell-cell (confluent) contact, manipulation of YAP and ß-catenin localization associated with topography-induced autophagy was lost. In summary, the osteogenesis observed in response to titanium implants with nanotopography involves a signaling link between YAP and ß-catenin. STATEMENT OF SIGNIFICANCE: Titanium with rough topographical surfaces is extensively applied in orthopedic and dental clinics. However, the cellular response to topographies that promotes osteogenesis and underlying mechanisms are not fully understood. In this study, we modified titanium surfaces to produce smooth, micro, or nano topographies. Experiments indicated that the nanotopography induced a stronger autophagic response, leading to degraded cytoplasmic YAP. With the lower levels of YAP, ß-catenin transported and accumulated in the nucleus to activate TCF/LEF transcription factors, resulting in stronger osteogenesis. Additionally, cell-cell contact was essential in the autophagy-mediated signaling link between YAP and ß-catenin. Consequently, our investigation revealed a novel signal transduction in nanotopography-regulated osteogenesis, and supports the modification of biomaterial surfaces to maximize osseointegration.