Bone Abstracts

Introduction: Despite the popularity of platet lysate (PL) treatments in orthopaedics, the mechanism of action and the effectiveness of this therapeutic tool is still controversial. So far, the activity of PL has been associated with different growth factors (GFs) released upon platelet degranulation. However, PL activity might also be due to the efficient cell to cell transport system of GF and other bioactive molecules by their encapsulation into exosomes. In this study, we characterized exosomes from human PL, and investigated their effect on MSC proliferation, migration and osteogenic differentiation in vitro.

Methods: Exosomes were isolated from human PL by differential ultracentrifugation. Their purity was assessed by electron microscopy and evaluating CD63 expression by western blot analysis. To test the effect of exosomes on MSC functions, bone marrow-derived MSC were cultured in presence of two different exosome concentrations or with PL. At specific time points, cell proliferation, migration, and osteogenic differentiation were evaluated by Alamar blue assay, Boyden chamber assay, and Alizarin red staining respectively.

Results: Electron microscopy revealed the presence of vesicles within the expected size range of exosomes (30–100 nm) which expressed the specific exosomal marker CD63. MSC treated with PL-derived exosomes showed a significant and dose-dependent increase of cell proliferation and migration. Furthermore, osteogenic differentiation assay demonstrated that exosome concentration differently affected the ability of MSC to deposit mineralized matrix.

Conclusions: In this study, we demonstrated that exosomes can be successfully isolated from human PL. PL-derived exosomes increase cell proliferation and migration at an higher extent than PL. In addition, exosome concentration affects osteogenic differentiation of MSC. Our results provide evidence of exosomes as putative effectors of PL, and highlight the importance of these vesicles as a potential nanodelivery system for cell-free regeneration therapies.