miR-146a-5p targets IRAK1/TRAF6 to promote bacillus Calmette-Guérin survival by exosome-mediated autocrine actions

Background

Exosomes carry signaling molecules between cells and play important roles in the interaction between macrophages and Mycobacterium tuberculosis (Mtb). This study aimed to examine the function and content of exosomes secreted by macrophages infected with Bacillus Calmette-Guérin (BCG).

Methods

THP-1 monocytes and HEK293T cells were used. Macrophages were infected with BCG. A Transwell system was used to evaluate the effect of the exosomes secreted by macrophages. Cells were transfected with the miR-146a-5p plasmid or inhibitor to examine the effects of miR-146a-5p overexpression or inhibition. qRT-PCR was employed to investigate the expression levels of miR-320a-5p, miR-27a-5p, miR-26a-5p, miR-146a-5p, and miR-223–5p and the mRNA expression of IL-6, TNF-α, and IL-1β. Western blot was used to investigate the protein expression of IRAK1, TRAF6, CD63, CD81, GRP94, Alix, TSG101, P65, and p-P65. A dual luciferase assay was performed to investigate whether miR-146a-5p targets IRAK1 and TRAF6.

Results

The infected cells contained high miR-146a-5p levels that could be secreted into exosomes. Exosomal miR-146a-5p promoted Mtb survival and proliferation after uptake by host cells. Bioinformatics showed that high miR-146a-5p levels were found in exosomes from BCG-infected macrophages and blood samples from patients with tuberculosis. The phagocytosis of exosomes containing miR-146a-5p by BCG-infected macrophages suppressed the expression of inflammatory factors by regulating the IRAK1-TRAF6-NF-κB signaling pathway, ultimately leading to the inhibition of inflammatory factor expression in macrophages and a decrease in the macrophage BCG killing capacity.

Conclusion

The findings indicate a new immune evasion mechanism of Mtb. miR-146a-5p secreted in exosomes by BCG-infected macrophages can decrease the bactericidal potential of macrophages. The results offer a novel theoretical basis and potential biomarkers for diagnosing, treating, and managing tuberculosis.