Comparison of Antibacterial and Immunological Properties of Mesenchymal Stem/Stromal Cells from Equine Bone Marrow, Endometrium, and Adipose Tissue.

Equine mesenchymal stem/stromal cells (MSCs) are multipotent cells that are widely used for treatment of musculoskeletal injuries, and there is significant interest in expanding their application to nonorthopedic conditions. MSCs possess antibacterial and immunomodulatory properties that may be relevant for combating infection; however, comparative studies using MSCs from different origins have not been carried out in the horse, and this was the focus of this study. Our results showed that MSC-conditioned media attenuated the growth of Escherichia coli, and that this effect was, on average, more pronounced for endometrium (EM)-derived and adipose tissue (AT)-derived MSCs than for bone marrow (BM)-derived MSCs. In addition, the antimicrobial lipocalin-2 was expressed at mean higher levels in EM-MSCs than in AT-MSCs and BM-MSCs, and the bacterial component lipopolysaccharide (LPS) stimulated its production by all three MSC types. We also showed that MSCs express interleukin-6 (IL-6), IL-8, monocyte chemoattractant protein-1, chemokine ligand-5, and Toll-like receptor 4, and that, in general, these cytokines were induced in all cell types by LPS. Low expression levels of the macrophage marker colony-stimulating factor 1 receptor were detected in BM-MSCs and EM-MSCs but not in AT-MSCs. Altogether, these findings suggest that equine MSCs from EM, AT, and BM have both direct and indirect antimicrobial properties that may vary between MSCs from different origins and could be exploited toward improvement of regenerative therapies for horses.

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 AT and colocalized 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-MSCs 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 eight passages in both AT-MSCs and BM-MSCs. Hematopoietic (CD45) and endothelial (CD144) markers were also detected at low levels in MSCs by quantitative polymerase chain reaction (qPCR). Finally, in coculture 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 be used when assessing and characterizing equine MSCs.