Induction of IL-4Rα–dependent microRNAs identifies PI3K/Akt signaling as essential for IL-4–driven murine macrophage proliferation in vivo

Abstract

Macrophage (M⌽) activation must be tightly controlled to preclude overzealous responses that cause self-damage. MicroRNAs promote classical M⌽ activation by blocking antiinflammatory signals and transcription factors but also can prevent excessive TLR signaling. In contrast, the microRNA profile associated with alternatively activated M⌽ and their role in regulating wound healing or antihelminthic responses has not been described. By using an in vivo model of alternative activation in which adult Brugia malayi nematodes are implanted surgically in the peritoneal cavity of mice, we identified differential expression of miR125b-5p, miR-146a-5p, miR-199b-5p, and miR-378-3p in helminth-induced M⌽. In vitro experiments demonstrated that miR-378-3p was specifically induced by IL-4 and revealed the IL-4-receptor/PI3K/Aktsignaling pathway as a target. Chemical inhibition of this pathway showed that intact Akt signaling is an important enhancement factor for alternative activation in vitro and in vivo and is essential for IL-4-driven M⌽ proliferation in vivo. Thus, identification of miR-378-3p as an IL-4R␣-induced microRNA led to the discovery that Akt regulates the newly discovered mechanism of IL-4-driven macrophage proliferation. Together, the data suggest that negative regulation of Akt signaling via microRNAs might play a central role in limiting M⌽ expansion and alternative activation during type 2 inflammatory settings. (Blood. 2012;120(11): 2307-2316) IntroductionMacrophages (M⌽) are involved centrally in recognizing and containing pathogens. Subsequently, they ensure the efficient induction and upkeep of a protective adaptive immune response. M⌽ also help to limit the ensuing immune reaction as well as clear apoptotic cells and other debris. 1 The adaption of M⌽ to these diverse roles is reflected in the multitude of activation phenotypes that have been described. 2 Classical (or M1) and IL-4R␣-driven alternative (or M2) activation represent the 2 most divergent phenotypes, with the former thought to be proinflammatory and important for the clearance of microbial pathogens, whereas the latter are predominantly found during helminth infections and are associated with wound healing and immunosuppression. [3][4][5][6] In either case, M⌽ activation must be closely controlled because excessive activation can lead to tissue destruction or fibrosis, respectively. 6,7 Control is achieved by external signals, including cytokines (eg,9 ) and hormones (eg, glucocorticoids 10 ) but also by M⌽-intrinsic mechanisms. For example, classically activated M⌽ become unresponsive to secondary stimulation with lipopolysaccharide (LPS) as the result, at least in part, of the induction of negative feedback loops blocking or limiting activating signaling cascades. 11 The possibility that microRNAs may mediate such feedback mechanisms has recently attracted considerable interest. 11 MicroRNAs (miRNA) are short (18-24 nt), noncoding RNAs that influence the translation of specific genes by binding to the 3Ј-untranslated region (3ЈUTR) of t...

A unique role for p53 in the regulation of M2 macrophage polarization

“…IL4 reportedly activates the PI3K/AKT signaling cascade, which is an important feature of M2 polarization. 16 Our data indicate that activation of PI3K/AKT phosphorylates (and thence activates) MDM2 at Ser166, which then binds to and promotes p53 ubiquitination, thereby limiting p53-mediated transactivation. The critical role of MDM2 in this process is clear from the ability of nutlin-3a, which destabilizes the p53/MDM2 interaction, to potentiate p53 accumulation and transactivation in M2-polarized cells.…”

“…17,18 The mechanism underlying this process is not clear, although PI3K/AKT signaling has been implicated. 16 Here we show that (i) in vitro, the low, basal level of p53 activity in IL4-polarized M2 macrophages is associated with significant cell proliferation and that loss of p53 potentiates, whereas pharmacological activation of p53 impairs M2-mediated proliferation, and (ii) in vivo, IL4 stimulation increased peritoneal macrophage cellularity, which was more marked in the absence of p53. In this manner, p53 is able to regulate M2 macrophage expansion.…”

MicroRNA-200a Affects the Proliferation of Airway Smooth Muscle Cells and Airway Remodeling by Targeting FOXC1 via the PI3K/AKT Signaling Pathway in Ovalbumin-Induced Asthmatic Mice

“…EOSs may be activated and recruited by Th2 cytokines (IL-4), inducing airway hyperreactivity [60,61]. miRs negatively target PI3K/AKT signaling, limiting IL-4-mediated murine macrophage proliferation [62]. IL-6 has been reported to promote the airway remodeling process, which could be enhanced by the PI3K/AKT signaling pathway [63].…”

A Critical Evaluation of Anti-IL-13 and Anti-IL-4 Strategies in Severe Asthma

“…The binding to theIL-13Rα1/IL-4Rα complex initiates the activation of multiple transduction pathways including tyrosine kinase 2 (Tyk-2) and Janus kinase 1 (JAK1), which are associated with the IL-13R subunit [29]. The activation of these transduction systems induces the phosphorylation and activation of the proteins, signal transducer and activator of transcription 6 (STAT6) and insulin receptor substrate 2 (IRS-2) [29], which move from the cytoplasm to the nucleus, and activate other transduction processes such as that of phosphatidylinositide 3-kinase (PI3-K) [30,31,32], serine-threonine protein kinase [33,34,35,36] and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) [37,38,39]. IL-13R has another receptor chain, IL-13Rα2, which does not activate transduction processes, but might play a regulatory role in IL-13-induced effects [40] and has been associated with human lung cancer as a potential target for novel therapies [41].…”