Equine Amniotic Microvesicles and Their Anti-Inflammatory Potential in a Tenocyte Model in Vitro

Administration of horse amniotic mesenchymal cells (AMCs) and their conditioned medium (AMC-CM) improves the in vivo recovery of spontaneous equine tendon lesions and inhibits in vitro proliferation of peripheral blood mononuclear cells (PBMC). This process may involve microvesicles (MVs) as an integral component of cell-to-cell communication during tissue regeneration. In this study, the presence and type of MVs secreted by AMCs were investigated and the response of equine tendon cells to MVs was studied using a dose-response curve at different concentrations and times. Moreover, the ability of MVs to counteract in vitro inflammation of tendon cells induced by lipopolysaccharide was studied through the expression of some proinflammatory genes such as metallopeptidase (MPP) 1, 9, and 13 and tumor necrosis factor-α (TNFα), and expression of transforming growth factor-β (TGF-β). Lastly, the immunomodulatory potential of MVs was investigated. Results show that AMCs secrete MVs ranging in size from 100 to 200 nm. An inverse relationship between concentration and time was found in their uptake by tendon cells: the maximal uptake occurred after 72 h at a concentration of 40 × 106 MVs/mL. MVs induced a downregulation of MMP1, MMP9, MMP13, and TNFα expression without affecting PBMC proliferation, contrary to CM and supernatant. Our data suggest that MVs contribute to in vivo healing of tendon lesions, alongside soluble factors in AMC-CM.