Characterization of Exosomes Released from Mycobacterium abscessus-infected Macrophages

Extracellular vesicles, such as exosomes, play a critical role in cell-to-cell communication and have been found to modulate cellular processes, including metabolic and inflammatory pathways, in recipient cells. Non-tuberculous Mycobacteria (NTM), such as Mycobacterium abscessus (M.ab), are a group of environmental bacteria that can cause severe lung infections in populations with pre-existing lung conditions, such as cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD). There is limited knowledge of the engagement of extracellular vesicles in the host-pathogen interactions in the context of NTM infections. In this study, we found that M.ab infection increased the release of a subpopulation of exosomes (CD9, CD63 and/or CD81 positive) by mouse macrophages but did not affect exosome morphology. Proteomic analysis of the vesicles demonstrated that M.ab infection affects the enrichment of host proteins in exosomes released by macrophages. When compared to exosomes from uninfected macrophages, exosomes released by M.ab-infected macrophages significantly improved M.ab growth and downregulated the intracellular level of glutamine in recipient macrophages in cell culture. Interestingly, the protein abundance of the glutamine transporters Slc1a5 and Slc38a2 were found to be enriched in exosomes from M.ab-infected macrophages compared to those from uninfected macrophages. Increasing glutamine concentration in the medium rescued intracellular glutamine levels and inhibited M.ab growth in recipient macrophages treated with exosomes from M.ab-infected macrophages. Taken together, our results indicate that exosomes may serve as extracellular glutamine eliminators that interfere with glutamine-dependent M.ab killing in recipient macrophages. This suggests that the development of exosome-targeting therapies may have the potential to augment current treatments for mycobacterial infections.