IL-4/IL-13-Dependent and Independent Expression of miR-124 and Its Contribution to M2 Phenotype of Monocytic Cells in Normal Conditions and during Allergic Inflammation

Abstract

Monocytic cells exhibit a high level of heterogeneity and have two distinct modes of their activation: 1) classical M1 path associated with inflammation and tissue damage, and 2) alternative M2 path. Although it has been demonstrated that M2 macrophages play an important role in the regulation of the allergic immune responses, tissue maintenance and repair, little is known about the mechanisms that determine the M2 phenotype. We have previously shown that miR-124 is expressed in microglia that exhibit the M2 phenotype and overexpression of miR-124 in macrophages resulted in downregulation of a number of M1 markers (MHC class II, CD86) and up-regulation of several M2 markers (Fizz1, Arg1). We further investigated whether the polarization of macrophages towards the M2 phenotype induced miR-124 expression. We found that exposure of cells to IL-4 and IL-13 resulted in the upregulation of miR-124 in macrophages. We also demonstrated that IL-4 induced expression of three miR-124 precursor transcripts with predominant expression of pri-miR-124.3, suggesting regulation of miR-124 expression by IL-4 on a transcriptional level. Expression of miR-124 in microglia did not depend on IL-4 and/or IL-13, whereas expression of miR-124 in lung resident macrophages was IL-4 and IL-13-dependent and was upregulated by systemic administration of IL-4 or during allergic inflammation. Upregulation of several M2 markers (CD206, Ym1) and downregulation of the M1 markers (CD86, iNOS, TNF) in M2-polarized macrophages was abrogated by a miR-124 inhibitor, suggesting that this microRNA contributed to the M2 phenotype development and maintenance. Finally we showed that human CD14+CD16+ intermediate monocytes, which are found in increased numbers in patients with allergies and bronchial asthma, expressed high levels of miR-124 and exhibited other properties of M2-like cells. Thus, our study suggests that miR-124 serves as a regulator of the M2 polarization in various subsets of monocytic cells both in vitro and in vivo.

Suppressor of Cytokine Signaling (SOCS)1 Regulates Interleukin-4 (IL-4)-activated Insulin Receptor Substrate (IRS)-2 Tyrosine Phosphorylation in Monocytes and Macrophages via the Proteasome

“…asthmatic donors express marker genes of M2 polarization more highly than monocytes from healthy individuals (94,95). Therefore, dysregulation of these negative regulators of Th2 cytokine signaling represents another mechanism of pathogenesis that contributes to allergic inflammation.…”

miR-125b controls monocyte adaptation to inflammation through mitochondrial metabolism and dynamics

“…[61][62][63][64][65][66] In THP-1, the expression of miR-125b is upregulated in macrophages, either after PMA-induced differentiation or M1 polarizing conditions, as well as in monocytes after LPS stimulation. Several reports showed that miR-125b is enriched in macrophages and is an LPS-regulated miRNA.…”

Translational Nano-Medicines: Targeted Therapeutic Delivery for Cancer and Inflammatory Diseases

“…In addition, miRNAs have been reported to regulate macrophage polarization. Among various miRNAs, miR-124 has been reported to polarize macrophages toward the M2 phenotype (85). Overexpression of miR-124 in macrophages decreased expression of MHC class II and CD86 (M1 markers) and upregulation of Fizz1 and Arg1 (M2 markers).…”

“…However, expression of miR-124 in microglia does not depend on IL-4 and/or IL-13 pathway, whereas miR-124 expression in lung macrophages was IL-4 and IL-13-dependent. Upregulation of several M2 markers and downregulation of the M1 markers in M2-polarized macrophages was absent by transfecting the macrophages with a miR-124 inhibitor (85,86). miR-223 is another miRNA that regulates M2 macrophage activation (87).…”