The regulatory functions of mesenchymal stromal cells (MSC) in the immune system are the subject of increasing interest and of widening clinical applications. Prior to exert immunomodulation, the MSC effects relies on the presence of inflammatory mediators in the microenvironment. This process of MSC 'licensing' can occur by the presence of pro-inflammatory cytokines (IFN-γ and TNF-α), and by the action of inflammatory effector cells which culminates on MSC apoptosis, crucial for its immunomodulatory property. The nature of these MSC effects has been under extensive studies, and initial evidence has shown that extracellular vesicles (EV) are important functional elements from MSC secretome. However, little is known about the influence of MSC environment on EV release and content. We hypothesised that different licensing of MSC could generate EV with distinct molecular and functional profiles. To test this hypothesis, we studied the EV population derived from untreated MSC, from MSC licensed by pro-inflammatory cytokines and from MSC undergoing apoptosis.Our results indicate that the different MSC licensing affect the profile and cargo of the released EV. Apoptotic MSC release a higher number of small and large vesicles and possibly of different biogenesis than viable cells. Moreover, the cytokine-mediated and apoptosis-induced licensing generated EV with a distinct ‘molecular signature’. By analysing the profile of EV isolated from patients with GvHD who received MSC infusions, we confirmed that the
in vitro EV profile identified in MSC exposed to acute inflammation could also be detected
in vivo. Moreover, the analysis of EV cargo revealed that many of the molecules correlated to immunosuppressive effects of MSC were enclosed in EV released by licensed MSC, and the incorporation of MSC-derived EV upregulated immunosuppressive features in activated monocytes. Finally, we verified that EV released by apoptotic cells contains pro-apoptotic molecules that can promote apoptosis in sensitive target cells. As an effect, sensitive cells can release more EV and induce apoptosis in neighbouring cells. However, some target cells are resistant to EV uptake and/or apoptosis-induction promoted by these EV. In conclusion, our findings highlight the influence of microenvironment in the EV release. Moreover, this is the first study evaluating EV released by apoptotic MSC.
The effects of inflammation on mesenchymal stromal cell-derived extracellular vesicles
Minani Bertolino, G. (Author). 1 Jan 2021
Student thesis: Doctoral Thesis › Doctor of Philosophy