Department of Preclinical Development and Validation, Fraunhofer Institute for Cell Therapy and Immunology, Leipzig, Germany.
Fraunhofer Cluster of Excellence Immune-Mediated Diseases (CIMD), Leipzig, Germany.
Front Immunol. 2023 May 23;14:1156493. doi: 10.3389/fimmu.2023.1156493. eCollection 2023.
The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that regulates a broad range of target genes involved in the xenobiotic response, cell cycle control and circadian rhythm. AhR is constitutively expressed in macrophages (Mϕ), acting as key regulator of cytokine production. While proinflammatory cytokines, i.e., IL-1β, IL-6, IL-12, are suppressed through AhR activation, anti-inflammatory IL-10 is induced. However, the underlying mechanisms of those effects and the importance of the specific ligand structure are not yet completely understood.
Therefore, we have compared the global gene expression pattern in activated murine bone marrow-derived macrophages (BMMs) subsequently to exposure with either benzo[]pyrene (BaP) or indole-3-carbinol (I3C), representing high-affinity vs. low-affinity AhR ligands, respectively, by means of mRNA sequencing. AhR dependency of observed effects was proved using BMMs from AhR-knockout () mice.
In total, more than 1,000 differentially expressed genes (DEGs) could be mapped, covering a plethora of AhR-modulated effects on basal cellular processes, i.e., transcription and translation, but also immune functions, i.e., antigen presentation, cytokine production, and phagocytosis. Among DEGs were genes that are already known to be regulated by AhR, i.e., , , and . However, we identified DEGs not yet described to be AhR-regulated in Mϕ so far, i.e., , , and All six genes likely contribute to shifting the Mϕ phenotype from proinflammatory to anti-inflammatory. The majority of DEGs induced through BaP were not affected through I3C exposure, probably due to higher AhR affinity of BaP in comparison to I3C. Mapping of known aryl hydrocarbon response element (AHRE) sequence motifs in identified DEGs revealed more than 200 genes not possessing any AHRE, and therefore being not eligible for canonical regulation. Bioinformatic approaches modeled a central role of type I and type II interferons in the regulation of those genes. Additionally, RT-qPCR and ELISA confirmed a AhR-dependent expressional induction and AhR-dependent secretion of IFN-γ in response to BaP exposure, suggesting an auto- or paracrine activation pathway of Mϕ.
芳香烃受体 (AhR) 是一种配体激活的转录因子，可调节涉及外来物反应、细胞周期控制和昼夜节律的广泛靶基因。AhR 在巨噬细胞 (Mϕ) 中持续表达，作为细胞因子产生的关键调节剂。虽然 AhR 的激活会抑制促炎细胞因子，如 IL-1β、IL-6 和 IL-12，但会诱导抗炎细胞因子 IL-10。然而，这些影响的潜在机制以及特定配体结构的重要性尚不完全清楚。
因此，我们通过 mRNA 测序比较了随后用高亲和力 AhR 配体苯并[a]芘 (BaP) 或低亲和力 AhR 配体吲哚-3-羧酸 (I3C) 处理的激活的鼠骨髓来源巨噬细胞 (BMM) 的全基因组表达模式。使用 AhR 敲除 () 小鼠的 BMM 证实了观察到的效应的 AhR 依赖性。
总共可以映射到超过 1000 个差异表达基因 (DEG)，涵盖了大量 AhR 调节的对基础细胞过程的影响，例如转录和翻译，但也包括免疫功能，例如抗原呈递、细胞因子产生和吞噬作用。DEG 中包括已经已知受 AhR 调节的基因，即 、 、和 。然而，我们还鉴定了迄今为止尚未描述为在 Mϕ 中受 AhR 调节的 DEG，即 、 、和 。所有六个基因可能有助于将 Mϕ 表型从促炎转变为抗炎。通过 BaP 诱导的大多数 DEG 不受 I3C 暴露的影响，这可能是由于 BaP 与 I3C 相比具有更高的 AhR 亲和力。在鉴定的 DEG 中映射已知的芳香烃反应元件 (AHRE) 序列基序揭示了超过 200 个不具有任何 AHRE 的基因，因此不符合经典调节标准。生物信息学方法表明，I 型和 II 型干扰素在这些基因的调节中起核心作用。此外，RT-qPCR 和 ELISA 证实了 BaP 暴露后 IFN-γ 的 AhR 依赖性表达诱导和 AhR 依赖性分泌，表明 Mϕ 的自分泌或旁分泌激活途径。
