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

Abstract

Key Points• Analysis of CSF-1R pTyrregulated messenger RNAs identifies novel signaling nodes and networks that can be targeted to modulate macrophage functions.• miR-21 is a novel CSF-1R pTyr-721-induced molecule that suppresses the macrophage M1 phenotype and enhances the M2 phenotype.Macrophage polarization between the M2 (repair, protumorigenic) and M1 (inflammatory) phenotypes is seen as a continuum of states. The detailed transcriptional events and signals downstream of colony-stimulating factor 1 receptor (CSF-1R) that contributes 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 microRNA-21 (miR-21) as a downstream molecular switch controlling macrophage activation and identified extracellular signal-regulated kinase 1/2 and nuclear factor-kB as CSF-1R pTyr-721-regulated signaling nodes. We show that CSF-1R pTyr-721 signaling suppresses the inflammatory phenotype, predominantly by induction of miR-21. Profiling of the miR-21-regulated messenger RNAs revealed that 80% of the CSF-1-regulated canonical miR-21 targets are proinflammatory 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 extracellular signal-regulated kinase 1/2 and nuclear factor-kB. 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. These results identify the CSF-1R-regulated miR-21 network that modulates macrophage polarization. (Blood. 2015;125(8):e1-e13) IntroductionMacrophages protect the host against infection and injury and facilitate tissue remodeling.1 However, they frequently accumulate in pathological settings, including cancers, 2 atherosclerosis, 3 metabolic disease, 4 and sepsis, 5 where they respond to microenvironmental cues that can be detrimental to the host. Two distinct extreme states of polarized activation have been described in macrophages:6,7 the classically activated (M1) and the alternatively activated (M2) macrophage phenotypes, each characterized by well-described markers. 5,6,[8][9][10][11] M1 macrophages produce proinflammatory cytokines, elevate the expression of inducible nitric oxide synthase 2 (iNOS) and major histocompatibility complex class II (MHC II), 12 and can play antitumorigenic roles. 5,9 In contrast, the M2 macrophages have increased expression of scavenger receptors, increased activation of the arginase pathway, low expression of interleukin-12 (IL-12), high expression of IL-10 and IL-1RA, and increased anti-inflammatory responses a...

Colony-Stimulating Factor-1 Receptor in the Polarization of Macrophages: A Target for Turning Bad to Good Ones?

“…Besides suppressing the proinflammatory phenotype in vitro, miR-21 attenuates the recruitment of Ly6C high (i.e., inflammatory) monocytes to the peritoneal cavity in response to LPS in vivo. Taken together, these results indicated that pTyr-721 signaling suppresses the macrophage proinflammatory phenotype [16].…”

“…Along this line, it was recently reported that pTyr-721 signaling downregulates proinflammatory genes, including IL-1β (a cytokine typically expressed by M1 polarized macrophages), while upregulating the expression of the M2 genes coding for Arginase (Arg1) and IL-10 [16]. Moreover, miR-21 emerged as a CSF-1-induced pTyr-721-and PI3K-dependent product involved in the regulation of macrophage activation.…”

CSF-1/CSF-1R targeting agents in clinical development for cancer therapy

“…In contrast, data from CCR2 À/À PyMT and CCR2DTR-PyMT breast cancer models indicate that mammary tissue macrophages and, to a lesser extent, TAM are constitutively repopulated by circulating monocytes [26]. Conversely, Caescu reported that CSF-1 supports polarization toward a pro-tumorigenic M2 phenotype via microRNA-21 by decreasing pro-inflammatory molecules together with up-regulation of M2-marker expression [27], whereas microRNA-511-3p limits the pro-tumoral function of TAM [28]. Overall, the origin and phenotype of TAM in patients requires in depth analysis and a systematic comparison to the respective mouse models.…”

miRNA in Macrophage Development and Function

“…M2c phenotype did not display any specific change in miRNA expression. Recent studies, including those from our laboratory, demonstrate a critical role of miR-21 in macrophage polarization (8,16). We reported that miR-21 is central in efferocytosis (engulfment of apoptotic cells)-mediated change in macrophage from a proinflammatory (M1) to proresolving (M2) phenotype (16).…”

“…The molecular signaling elicited by CSF-1R pathway has been shown to regulate macrophage polarization via PI3K/ERK/NFjB and activation miR-21. Inhibition of miR-21 directed macrophage toward the M1 phenotype, suggesting that sufficient miR-21 in macrophages is essential for their M2 polarization (8). A central role of miR-33 in regulation of cellular lipid metabolism by repressing genes involved in cholesterol efflux, and fatty acid oxidation, has been recognized (39).…”