Horse adipose-derived mesenchymal stromal cells constitutively produce membrane vesicles: a morphological study

Mesenchymal stromal cells (MSCs) are multipotent somatic cells that can differentiate into a variety of mature cell types. Over recent years, their biological in vitro and in vivo properties have elicited great expectations in the field of regenerative medicine, immunotherapy and tumour treatment. An increasing number of experimental observations suggest that their biological effects are probably related to a paracrine mechanism via the release of trophic factors and cytokines as well as through the production of membrane vesicles (MVs). These are nanometric membrane-bound structures, comprising shedding vesicles (SV) and exosomes (Ex), that enclose and transfer signalling molecules to target cells. We hypothesized that MVs may be implicated in the biological effects of MSCs from horse adipose tissue (E-AdMSCs), a type of MSC that has been extensively studied in recent years for its remarkable efficacy in tissue regeneration. By means of electron microscopy, we ascertained, for the first time, that equine adipose-derived MSCs constitutively produce MVs (E-Ad-MSCs). The analysis of MVs separated by ultracentrifugation allowed us to describe their general morphological features. Through the examination of cell monolayers by TEM, additionally, we distinguished the different pathways of SV and Ex formation, demonstrating that both fractions are produced by E-AdMSC. The accurate description of MV heterogeneous morphological characteristics led us to emphasize the possible implications of the relationship between different morphologies versus different functions. The data presented in this paper has an additional value, as they can be noteworthy for horses as well as for other mammalian species, including humans.