Extracellular Vesicles from Mesenchymal Stromal Cells Modulate Inflammatory Responses on Feline Mixed Glia

The extracellular vesicles (EVs) secreted by mesenchymal stromal cells (MSC-EVs) exhibit immunoregulatory functions dependent on their parent cells. MSC-EVs are promising candidates for treating neuroinflammation in neurological diseases due to their acellular nature and their ability to reach the central nervous system. However, the conditions of MSCs for producing EVs with the highest anti-inflammatory efficacy are still unknown. Therefore, the first objective was to study the characteristics of the EVs produced by MSCs cultured in different conditions. The second objective was to evaluate the <i>in vitro</i> anti-inflammatory properties of those EVs in feline stimulated mixed glia. Umbilical cord-derived MSCs were treated with serum-free (SF) media, inflammatory (IF) media, or media supplemented with 5% EV-depleted fetal bovine serum (FBS). The isolated MSC-EVs were characterized by particle size and yield, and their anti-inflammatory ability was evaluated in lipopolysaccharide (LPS) stimulated feline mixed glia. All EV isolates were <160 nm, and the primary mixed glia consisted of microglia, astrocytes, neurons, and endothelial cells. Our results indicate that IF-EVs statistically significantly decreased the production of interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-α) and downregulated the transcription of the, nuclear factor kappa B p65 subunit in inflammatory mixed glia after 48 hours. In addition, SF- and FBS-EVs significantly reduced <i>in vitro</i> the secretion of IL-6 after 48 hours<i>,</i> but only SF-EVs achieved a significant effect on inhibiting the expression of p65 at 48 hours. Moreover, messenger RNA (mRNA) levels of inducible nitric oxide synthase (iNOS) were significantly decreased following treatment with SF-EV for 24 hours. This study demonstrates that MSC culture conditions affect the therapeutic potential of the secreted EVs in feline mixed glia.