Regulation of activation-associated microRNA accumulation rates during monocyte-to-macrophage differentiation [Cell Biology]

August 22nd, 2014 by Eigsti, R. L., Sudan, B., Wilson, M. E., Graff, J. W.

Circulating monocytes recruited to tissues can differentiate into macrophages and adopt unique gene expression programs in response to environmental cues. We recently described the regulated expression of several microRNAs (miRNAs) in polarized human monocyte-derived macrophages (MDMs). Basal expression of these activation-associated miRNAs was low in monocytes relative to MDMs. As development occurs in the context of specific cellular environments, we hypothesized that the rate of miRNA accumulation would be modified in the presence of microbial or cellular products during monocyte-to-macrophage differentiation. Indeed, LPS treatment augmented the accumulation of miR-146a and miR-155 while IL-4 treatment augmented the accumulation of miR-193b and miR-222 during development. In contrast, some stimuli repressed accumulation of specific miRNAs including interferons (IFN) (miR-27a, miR-125a-5p, miR-222), IL-4 (miR-125a-5p), or LPS (miR-27a). RT-PCR-based expression profiling of monocytes differentiated with distinct methods showed that activation-associated miRNAs and markers of macrophage polarization were substantially altered in MDMs differentiated in the presence of non-monocytic peripheral blood mononuclear cells, due in part to NF-κB and STAT1 pathway activation. Expression of several of these miRNAs was regulated at a pre-processing step, since the expression of the primary miRNAs, but not Dicer, correlated with mature miRNA expression. We conclude that a set of miRNAs are regulated during MDM differentiation and the rate is uniquely modified for each miRNA by environmental factors. The low basal expression of activation-associated miRNAs in monocytes and their dynamic rates of accumulation during MDM differentiation permit monocytes to tailor miRNA profiles in peripheral tissues during differentiation to macrophages.