No abstract

An imbalance in bone homeostasis results in bone loss and poor healing in bone diseases and trauma. Osteoimmune interactions, as a key contributor to bone homeostasis, depend on the crosstalk between mesenchymal stem cell-osteoblast (MSC-OB) and monocyte-macrophage (MC-Mφ) lineages. Currently, extracellular vesicles (EVs) are considered to be involved in cell-to-cell communication and represent a novel avenue to enhance our understanding of bone homeostasis and to develop novel diagnostic and therapeutic options. In this comprehensive review, we aim to present recent advances in the study of the effect of MC-Mφ-derived EVs on osteogenesis and the regulatory effects of MSC-OB-derived EVs on the differentiation, recruitment and efferocytosis of Mφ. Furthermore, we discuss the role of EVs as crucial mediators of the communication between these cell lineages involved in the development of common bone diseases, with a focus on osteoporosis, osteoarthritis, bone fracture, and periodontal disease. Together, this review focuses on the apparent discrepancies in current research findings and future directions for translating fundamental insights into clinically relevant EV-based therapies for improving bone health.

Successful osseointegration involves the biological behavior of bone marrow stem cells (BMSCs) on an implant surface; however, the role of BMSC-derived extracellular vesicles (EVs)/exosomes in osseointegration is little known. This study aimed to: (i) explore the interaction force between exosomes (Exo) and cells on a titanium surface; (ii) discuss whether the morphology and biological behavior of BMSCs are affected by exosomes; and (iii) preliminarily investigate the mechanism by which exosomes regulate cells on Ti surface. Exosomes secreted by rat BMSCs were collected by ultracentrifugation and analyzed using transmission electron microscopy and nanoparticle tracking analysis. Confocal fluorescence microscopy, scanning electron microscopy, Cell Counting Kit-8 (CCK-8), quantitative real-time polymerase chain reaction techniques, and alkaline phosphatase bioactivity, Alizarin Red staining, and quantification were used to investigate the exosomes that adhere to the Ti plates under different treatments as well as the morphological change, adhesion, spread, and differentiation of BMSCs. We found that exosomes were efficiently internalized and could regulate cell morphology and promoted the adhesion, spreading, and osteogenic differentiation of BMSCs. These were achieved partly by activating the RhoA/ROCK signaling pathway. Our discovery presents a new insight into the positive regulatory effect of exosomes on the biological behaviors of BMSCs on Ti surface and provides a novel route to modify the surface of a Ti implant.

Osteomyelitis, which is characterized by progressive inflammatory bone destruction and resorption, is a difficult-to-treat infection. Staphylococcus aureus (S. aureus) is one of the major causes of this disease. This pathogenic microorganism possesses several characteristics, which facilitate its involvement in the occurrence and progression of osteomyelitis. A cell-permeable peptide inhibitor of the IκB kinase complex, the nuclear factor (NF)-κB essential modulator-binding domain (NBD) peptide, has been reported to block osteoclastogenesis and may be considered a potential strategy for preventing inflammatory bone resorption. However, it remains to be determined as to whether the NBD peptide can regulate inflammation and bone resorption in S. aureus-induced osteomyelitis. In order to investigate the role of NBD in S. aureus-induced osteomyelitis, the present study obtained the NBD peptide, and confirmed that it inhibited receptor activator of NF-κB ligand-induced osteoclastogenesis in vitro. Subsequently, a bone defect was generated and S. aureus was injected into the mandible of experimental animals, in order to establish an in vivo osteomyelitis model. The present study analyzed the following three experimental groups: Untreated, treated with debridement, and treated with debridement plus NBD peptide administration. The results revealed that treatment with the NBD peptide reduced the bone defect in a 3-dimensional manner, and reduced bone resorption. To the best of our knowledge, the present study is the first to demonstrate that, in a model of osteomyelitis caused by S. aureus, the NBD peptide serves a role in inhibiting osteolysis and promoting bone remodeling in the direction of osteogenesis. The effects were better than those produced by debridement alone, thus suggesting that it may have promising therapeutic potential in osteomyelitis.