Therapeutic Effects of Human Mesenchymal Stem Cell–derived Microvesicles in Severe Pneumonia in Mice

Abstract

Rationale: Microvesicles (MVs) are anuclear fragments of cells released from the endosomal compartment or shed from surface membranes. We and other investigators demonstrated that MVs released by mesenchymal stem cells (MSCs) were as effective as the cells themselves in inflammatory injuries, such as after endotoxininduced acute lung injury. However, the therapeutic effects of MVs in an infectious model of acute lung injury remain unknown.Objectives: We investigated the effects of human MSC MVs on lung inflammation, protein permeability, bacterial clearance, and survival after severe bacterial pneumonia.Methods: We tested the effects of MVs derived from human MSCs on Escherichia coli pneumonia in mice. We also studied the interactions between MVs and human monocytes and human alveolar epithelial type 2 cells.Measurements and Main Results: Administration of MVs derived from human MSCs improved survival in part through keratinocyte growth factor secretion and decreased the influx of inflammatory cells, cytokines, protein, and bacteria in mice injured with bacterial pneumonia. In primary cultures of human monocytes or alveolar type 2 cells, the uptake of MVs was mediated by CD44 receptors, which were essential for the therapeutic effects. MVs enhanced monocyte phagocytosis of bacteria while decreasing inflammatory cytokine secretion and increased intracellular ATP levels in injured alveolar epithelial type 2 cells. Prestimulation of MSCs with a toll-like receptor 3 agonist further enhanced the therapeutic effects of the released MVs.Conclusions: MVs derived from human MSCs were as effective as the parent stem cells in severe bacterial pneumonia.

Mesenchymal Stromal Cells Modulate Macrophages in Clinically Relevant Lung Injury Models by Extracellular Vesicle Mitochondrial Transfer

“…This is consistent with the literature showing that MSC-derived EVs range from less than 100 nm to 1,000 nm (24,27). Further characterization demonstrated that EVs were more than 90% positive for MSC membrane and more than 90% negative for annexin V and propidium iodide staining, indicating minimal contamination with cell debris or apoptotic bodies and, importantly, that EVs demonstrated uniform expression of CD44 (.98% positive) ( Figure 3A).…”

“…MSCs were able to increase the proportion of phagocytic MDMs in the presence of LPS ( Figure 1D). This adds to the body of literature supporting the phagocytosis-enhancing effects of MSCs on both macrophages and monocytes (8,10,19,27).…”

“…MSC-derived EVs were isolated as previously described (27). Briefly, 15 3 10 6 cells were cultured in media supplemented with EV-depleted serum for 48 hours.…”

“…Additionally, the capacity of MSCs to induce polarization toward M2-type monocytes/macrophages, identified by CD206 expression, may serve as a biomarker for MSC efficacy in clinical samples. EVs have emerged as a major contributor to the therapeutic effects of MSCs in lung injury, capable of recapitulating many of the effects of the whole-cell therapy (25)(26)(27). CD44 expression on MSC-derived EVs was shown to be necessary for their uptake and therapeutic effect on target cells (27,50).…”

“…MSC-derived EVs may contain a diverse cargo, including proteins, mRNAs, microRNAs (miRNAs), and mitochondria, the functional effects of which remain largely unknown (9,(23)(24)(25). MSC-derived EVs alone are capable of recapitulating many of the beneficial effects of MSC whole-cell therapy (25)(26)(27)(28). Phinney and colleagues observed the transfer of MSC mitochondria and miRNAs via EVs to human macrophages in a model of silicosis and found that mitochondria enhanced macrophage bioenergetics, whereas miRNAs suppressed Toll-like receptor signaling (24).…”