Regulatory effects of miR-155 and miR-146a on repolarization and inflammatory cytokine secretion in human alveolar macrophages in vitro

Abstract

Macrophages play an important role in inflammatory responses; however, miRNA-mediated repolarization of macrophages is essential for fulfilling this function. To clarify a series of changes at the RNA level in alveolar macrophages under normal and inflammatory conditions, bronchial alveolar lavage liquid (BALF) was collected from healthy volunteers or patients with pneumonia. This approach, which differs from that used in previously, provides more accurate information about the states of macrophages in different lung microenvironments. In this study, the density plots of macrophage subtypes (M1 and M2) in the BALF of healthy volunteers differed from that of the patients with pneumonia. The M2 subtype dominated in healthy volunteers and was rapidly repolarized to M1 in response to miRNA-mediated gene regulation. Differential miRNA expression in the two macrophage subtypes revealed lower expression of miR-155 and MIR-146a in patients with pneumonia compared with healthy volunteers; this may be related to inflammation and the use of anti-inflammatory drugs. We also found increased TNF-α and IL-6 expression at the RNA level, while macrophage galactose-type C-type lectin 1 (MGL-1) expression decreased with downregulation of miR-155 and miR-146a expression. These results indicate that the gene regulation mediated by miR-155 and miR-146a contributes to human alveolar macrophage phenotype repolarization, thus leading to an early switch from pro-inflammatory to anti-inflammatory cytokine production.