Control of the inflammatory macrophage transcriptional signature by miR-155

Classically activated (M1) macrophages protect from infection but can cause inflammatory disease and tissue damage while alternatively activated (M2) macrophages reduce inflammation and promote tissue repair. Modulation of macrophage phenotype may be therapeutically beneficial and requires further understanding of the molecular programs that control macrophage differentiation. A potential mechanism by which macrophages differentiate may be through microRNA (miRNA), which bind to messenger RNA and post-transcriptionally modify gene expression, cell phenotype and function. The inflammation-associated miRNA, miR-155, was rapidly up-regulated over 100-fold in M1, but not M2, macrophages. Inflammatory M1 genes and proteins iNOS, IL-1b and TNF-a were reduced up to 72% in miR-155 knockout mouse macrophages, but miR-155 deficiency did not affect expression of genes associated with M2 macrophages (e.g., Arginase-1). Additionally, a miR-155 oligonucleotide inhibitor efficiently suppressed iNOS and TNF-a gene expression in wild-type M1 macrophages. Comparative transcriptional profiling of unactivated (M0) and M1 macrophages derived from wild-type and miR-155 knockout (KO) mice revealed an M1 signature of approximately 1300 genes, half of which were dependent on miR-155. Real-Time PCR of independent datasets validated miR-155's contribution to induction of iNOS, IL-1b, TNF-a, IL-6 and IL-12, as well as suppression of miR-155 targets Inpp5d, Tspan14, Ptprj and Mafb. Overall, these data indicate that miR-155 plays an essential role in driving the differentiation and effector potential of inflammatory M1 macrophages.

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Jablonski KA, Gaudet AD, Amici SA, Popovich PG, Guerau-de-Arellano M