Colony stimulating factor-1 receptor signaling networks inhibit macrophage inflammatory responses by induction of microRNA-21

Macrophage polarization between the M2 (repair, pro-tumorigenic) and M1 (inflammatory) phenotypes is seen as a continuum of states. The detailed transcriptional events and signals downstream of CSF-1R that contribute to amplification of the M2 phenotype and suppression of the M1 phenotype are largely unknown. Macrophage CSF-1R pTyr-721 signaling promotes cell motility and enhancement of tumor cell invasion in vitro. Combining analysis of cellular systems for CSF-1R gain-of-function and loss-of-function with bioinformatic analysis of the macrophage CSF-1R pTyr-721-regulated transcriptome, we uncovered miR-21 as a downstream molecular switch controlling macrophage activation and identified ERK1/2 and NF-B as CSF-1R pTyr-721-regulated signaling nodes. We show that CSF-1R pTyr-721 signaling suppresses the proinflammatory phenotype, predominantly by induction of miR-21. Profiling of the miR-21-regulated mRNAs revealed that 80% of the CSF-1-regulated canonical miR-21 targets are pro-inflammatory molecules. Additionally, miR-21 positively regulates M2 marker expression. Moreover, miR-21 feeds back to positively regulate its own expression and to limit CSF-1R-mediated activation of ERK1/2 and NF-B. Consistent with an anti-inflammatory role of miRNA-21, intraperitoneal injection of mice with a miRNA-21 inhibitor increases the recruitment of inflammatory monocytes and enhances the peritoneal monocyte/macrophage response to lipopolysaccharide (LPS).

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Caescu CI, Guo X, Tesfa L, Bhagat TD, Verma A, Zheng D, Stanley ER