Immunoregulatory Role of MicroRNA-21 in Macrophages in Response to Bacillus Calmette-Guerin Infection Involves Modulation of the TLR4/MyD88 Signaling Pathway.

BACKGROUND/AIMS: The purpose of this study is to explore the immunoregulatory role of microRNA-21 (miR-21) targeting of the TLR4/MyD88 signaling pathway in macrophages in response to Bacillus Calmette-Guerin (BCG) infection.

METHODS: After infection with BCG, mouse RAW246.7 cells were assigned into control, BCG, miR-21 mimic + BCG, mimic-negative control (NC) + BCG, miR-21 inhibitor + BCG, inhibitor-NC + BCG, BCG + TAK242 (an inhibitor of the TLR4 signaling pathway), and miR-21 inhibitor + TAK242 + BCG groups. Western blotting and qRT-PCR were used to detect the expression of miR-21, TLR4 and MyD88. The levels of TNF-a, IL-6 and IL-10 were detected by enzyme-linked immunosorbent assay (ELISA). Cell viability was measured using an MTT assay. Cell apoptosis and necrosis rates were detected using flow cytometry.

RESULTS: Compared with the control group, miR-21 expression and levels of TNF-a, IL-6 and IL-10, as well as cell apoptosis and necrosis rates, were elevated, while expression of TLR4 and MyD88, as well as cell viability, were reduced in BCG infection groups. Compared with the BCG group, miR-21 expression was increased in the miR-21 mimic + BCG group but decreased in the miR-21 inhibitor + BCG and miR-21 inhibitor + TAK242 + BCG groups. The expression of TLR4 and MyD88, as well as the cell viability, were decreased, while levels of TNF-a, IL-6 and IL-10, as well as cell apoptosis and necrosis rates, were increased in the miR-21 mimic + BCG and TAK242 + BCG groups. The opposite trends were found in the miR-21 inhibitor + BCG group. Compared with the TAK242 + BCG group, the miR-21 inhibitor + TAK242 + BCG group had higher expression of TLR4 and MyD88 as well as higher cell viability and lower levels of TNF-a, IL-6, IL-10, cell apoptosis and necrosis rates. However, the miR-21 inhibitor + TAK242 + BCG group exhibited the opposite trends when compared with the miR-21 inhibitor + BCG group.

CONCLUSION: Our results suggest that miR-21 can negatively modulate the TLR4/MyD88 signaling pathway, resulting in decreased cell viability, increased cell apoptosis and increased levels of inflammatory factors following BCG infection in macrophages.