ICAM-1 regulates macrophage polarization by suppressing MCP-1 expression via miR-124 upregulation.

Intercellular adhesion molecule-1 is the adhesion molecule mediating leukocyte firm adhesion to endothelial cells, plays a critical role in subsequent leukocyte transmigration. ICAM-1 is also expressed in other cells including macrophages; however, the role of this adhesion molecule in mediating macrophage functions remains enigmatic. We report that ICAM-1 regulates macrophage polarization by positively modulating miR-124 expression. We found higher expression levels of monocyte chemotactic protein-1 in lungs of mice lacking ICAM-1. Consistent with this result, siRNA mediated depletion of ICAM-1 in macrophage resulted in increased expression levels of MCP-1. Moreover, ICAM-1 controlled miR-124 expression and downregulated MCP-1 mRNA and protein expression by binding of miR-124 to MCP-1 3' untranslated region. ICAM-1 also induced the transcription factor Sp1 expression, which is important for miR-124 expressing in macrophages. Furthermore, ICAM-1 depletion led to M1 macrophage polarization, in contrast, miR-124 mimics promoted M2 macrophage polarization. Exogenous administration of miR-124 mimics into the lungs prevented lipopolysaccharide-induced myeloperoxidase activity