Equine Mesenchymal Stromal Cells retain a pericyte-like phenotype

Mesenchymal Stem/Stromal Cells (MSCs) have been used in human and equine regenerative medicine, and interest in exploiting their potential has increased dramatically over the years. Despite significant effort to characterize equine MSCs, the actual origin of these cells and how much of their native phenotype is maintained in culture have not been determined. In this study, we investigated the relationship between MSCs, derived from adipose tissue (AT) and bone marrow (BM), and pericytes in the horse. Both pericyte (CD146, NG2 and αSMA) and MSC (CD29, CD90 and CD73) markers were detected in equine adipose tissue and co-localized around blood vessels. Importantly, as assessed by flow cytometry, both pericyte (CD146, NG2 and αSMA) and MSC (CD29, CD44, CD90 and CD105) markers were present in a majority (≥90%) of cells in cultures of AT- and BM-MSCs, however, levels of pericyte markers were variable within each of those populations. Moreover, the expression of pericyte markers was maintained for at least 8 passages in both AT- and BM-MSCs. Hematopoietic (CD45) and endothelial (CD144) markers were also detected at low levels in MSCs by qPCR. Finally, in co-culture experiments, AT-MSCs closely associated with networks produced by endothelial cells, resembling the natural perivascular location of pericytes in vivo. Our results indicate that equine MSCs originate from perivascular cells and, moreover, maintain a pericyte-like phenotype in culture. Therefore, we suggest that, in addition to classical MSC markers, pericyte markers such as CD146 could also be used when assessing and characterising equine MSCs.