IL-16 regulates macrophage polarization as a target gene of mir-145-3p

Interleukin 16 is an immunomodulatory chemokine that signals through CD4 + T cells, monocytes, macrophages and dendritic cells. Its expression in immune-related cells enhances the antimicrobial effect and inhibits HIV replication in macrophages. However, the role of IL-16 in macrophage polarization is uncertain. Mir-145 was reported to regulate IL-10 expression by targeting histone deacetylase 11 and promotes alternatively activated macrophage (M2) polarization. Mir-145 was also predicted to target IL-16 mRNA. We aimed to explore the roles of IL-16 and mir-145 in macrophage polarization and antimicrobial functions.

THP1 monocytes were employed in this study, and their cell activity when incubated with different concentrations of IL-16 was evaluated using the CCK-8 cell counting kit. To obtain polarized macrophages, THP-1 cells were induced by IL-4 and IL-13 following PMA incubation (M2 polarized macrophages) or induced by IFN-gamma and LPS (M1 classical macrophage activation). The influence of IL-16 on macrophage phagocytosis was quantified by the amount of chicken red blood cell phagocytized. IL-16, IL-10 and miR-145 expression in THP1 monocytes and induced macrophages was quantified by quantitative PCR. The miR-145 and IL-16 targeting relationship was verified by the dual luciferase reporter assay. The influence of IL-16 and mir-145 on macrophage polarization was evaluated by M1 and M2 macrophage characterized marker gene expression.

The M0 macrophage subtype was induced by PMA. The M1 and M2 subtypes of macrophage were successfully induced by M1- and M2-specific induction. M1 macrophages express higher levels of IL-16 than M2 macrophages but express lower levels of IL-10 and mir-145 than M2 cells. IL-16 with a concentration up to 150 ng/mL has no influence on THP-1 cell proliferation but improves macrophage phagocytosis ability with the down-expression of IL-10 and up-expression of pro-inflammatory cytokines such as IL-1a and IL-6. Knockdown with its target siRNA is beneficial for macrophage maintenance but reduces phagocytosis ability. Mir-145 specifically targets the IL-16 3'UTR verified by the dual luciferase reporter assay. Mir-145 downregulates IL-16 expression and upregulates IL-10 expression, thereby promoting M2 macrophage polarization.

IL-16 modulates macrophage polarization through regulating IL-10, IL-1a and IL-6 expression. Mir-145 is involved in M2 macrophage polarization by targeting IL-16 and enhancing IL-10 expression.