Three-dimensional mechanical microenvironment enhanced osteogenic activity of mesenchymal stem cells-derived exosomes

Exosomes derived from mesenchymal stem cells (MSCs) through the paracrine pathway have shown great potentials in cell-free therapy for regenerative medicine. Although MSCs have been recently known to respond to the mechanical microenvironment and thus orchestrate their behaviors and functions, the effects of such a biophysical cue on the paracrine pathway of MSCs, especially on the regulation of characteristics and bioactivity of MSC-derived exosomes have rarely been reported. In this study, we used periodontal ligament stem cells (PDLSCs), which were cultured in the three-dimensional(3D) microscale magnetically stretched collagen hydrogels, as the model MSCs to explore the changes in characteristics (e.g., morphology, size distribution, typical surface protein expression, miRNA content, and internalization) and bioactivity of MSC-derived exosomes in response to matrix strain. We found that the levels of 25 miRNAs in exosomes secreted by PDLSCs in the 3D strain microenvironment (SM-Exo) were dramatically different from those obtained from the 3D culture microenvironment (Exo). Next, the bioactivity of SM-Exo was significantly enhanced as reflected by the improved proliferation, migration, and osteogenic differentiation of target cells (e.g., BMSCs). This was further confirmed by in vivo studies, in which PDLSC-derived exosomes obtained from the 3D strain microenvironment showed stronger bioactivity to repair alveolar bone defects in SD rats. This study proposed a novel strategy to promote alveolar bone regeneration via altered PDLSC-derived exosomes in the 3D strain microenvironment, and such an engineered mechanical microenvironment would be an effective tool in other regenerative studies and clinical applications.