Polarization of Human Macrophages by Interleukin-4 Does Not Require ATP-Citrate Lyase.

Dmitry Namgaladze,Dominik Fuhrmann,Nina Kurrle,Bernhard Brüne,Frank Schnütgen,Ingrid Fleming,Sven Zukunft

doi:10.3389/fimmu.2018.02858

Abstract

Macrophages exposed to the Th2 cytokines interleukin (IL) IL-4 and IL-13 exhibit a distinct transcriptional response, commonly referred to as M2 polarization. Recently, IL-4-induced polarization of murine bone marrow-derived macrophages (BMDMs) has been linked to acetyl-CoA levels through the activity of the cytosolic acetyl-CoA-generating enzyme ATP-citrate lyase (ACLY). Here, we studied how ACLY regulated IL-4-stimulated gene expression in human monocyte-derived macrophages (MDMs). Although multiple ACLY inhibitors attenuated IL-4-induced target gene expression, this effect could not be recapitulated by silencing ACLY expression. Furthermore, ACLY inhibition failed to alter cellular acetyl-CoA levels and histone acetylation. We generated ACLY knockout human THP-1 macrophages using CRISPR/Cas9 technology. While these cells exhibited reduced histone acetylation levels, IL-4-induced gene expression remained intact. Strikingly, ACLY inhibitors still suppressed induction of target genes by IL-4 in ACLY knockout cells, suggesting off-target effects of these drugs. Our findings suggest that ACLY may not be the major regulator of nucleocytoplasmic acetyl-CoA and IL-4-induced polarization in human macrophages. Furthermore, caution should be warranted in interpreting the impact of pharmacological inhibition of ACLY on gene expression.

Highlights

Macrophages respond to changes in their environment, such as bacterial or viral infection, hormones, cytokines, or nutrients, with remodeling their transcriptome
Analyzing the list of top 50 IL-4 responsive genes sensitive to ATP-citrate lyase (ACLY) inhibition in murine bone marrow-derived macrophage (BMDM) [14], we found that only 5 genes (CCL17, FIGURE 1 | ACLY inhibitors attenuate IL-4-induced target gene expression. (A–D) Quantitative real time PCR (Q-PCR) analysis of mRNA expression of arachidonate 15-Lipoxygenase (ALOX15) in monocyte-derived macrophage (MDM) treated for 1 h with indicated concentrations of BMS 303141 (A), SB 204490 (B), MEDICA 16 (C), or hydroxycitrate (HC) (D) prior to 24-h treatment with 20 ng/mL IL-4. (E–I) Q-PCR analysis of mRNA expression of indicated genes in MDMs treated for 1 h with 5 μM BMS 303141, 25 μM SB 204490, 100 μM MEDICA 16 or 20 mM HC prior to 24-h treatment with 20 ng/mL IL-13 (E) or IL-4 (F–I). **p < 0.01 vs. IL-4
Our data contrast with observations in murine BMDMs, where ACLY was shown to significantly contribute to the induction of at least a subset of the IL-4-sensitive transcriptome by increasing histone acetylation [14]

Summary

Introduction

Macrophages respond to changes in their environment, such as bacterial or viral infection, hormones, cytokines, or nutrients, with remodeling their transcriptome. They alter their phenotype, a response known as macrophage polarization [1]. While metabolism primarily serves to provide energy and substrates to support macrophage functional responses, e.g., phagocytosis, several metabolites directly affect transcription through epigenetic mechanisms [6]. Acetyl-CoA is ATP-Citrate Lyase in Macrophages a metabolite with a distinct role in epigenetic and transcriptional regulation through its widespread use as a substrate for acetylation of histones and other proteins, including transcription factors [7]. Further studies reported epigenetic regulation through ACLY in adipocytes [9, 12] or myocytes [13]

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