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]

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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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