Marques Oriana, Horvat Natalie K, Zechner Laura, Colucci Silvia, Sparla Richard, Zimmermann Stefan, Neufeldt Christopher J, Altamura Sandro, Qiu Ruiyue, Müdder Katja, Weiss Günter, Hentze Matthias W, Muckenthaler Martina U
Department of Pediatric Hematology, Oncology, and Immunology, University of Heidelberg, Heidelberg, Germany.
Molecular Medicine Partnership Unit, University of Heidelberg, Heidelberg, Germany.
Blood. 2025 Feb 20;145(8):866-880. doi: 10.1182/blood.2023023417.
Anemia of inflammation is a prevalent comorbidity in patients with chronic inflammatory disorders. Inflammation causes hypoferremia and iron-restricted erythropoiesis by limiting ferroportin (FPN)-mediated iron export from macrophages that recycle senescent erythrocytes. Macrophage cell surface expression of FPN is reduced by hepcidin-induced degradation and/or by repression of FPN (Slc40a1) transcription via cytokine and Toll-like receptor (TLR) stimulation. Although the mechanisms underlying hepcidin-mediated control of FPN have been extensively studied, those inhibiting Slc40a1 messenger RNA (mRNA) expression remain unknown. We applied targeted RNA interference and pharmacological screens in macrophages stimulated with the TLR2/6 ligand FSL1 and identified critical signaling regulators of Slc40a1 mRNA repression downstream of TLRs and NF-κB signaling. Interestingly, the NF-κB regulatory hub is equally relevant for Slc40a1 mRNA repression driven by the TLR4 ligand lipopolysaccharide, the cytokine tumor necrosis factor β/lymphotoxin-alpha (LTA), and heat-killed bacteria. Mechanistically, macrophage stimulation with heat-killed Staphylococcus aureus recruits the histone deacetylases (HDACs) HDAC1 and HDAC3 to the antioxidant response element (ARE) located in the Slc40a1 promoter. Accordingly, pretreatment with a pan-HDAC inhibitor abrogates Slc40a1 mRNA repression in response to inflammatory cues, suggesting that HDACs act downstream of NF-κB to repress Slc40a1 transcription. Consistently, recruitment of HDAC1 and HDAC3 to the Slc40a1 ARE after stimulation with heat-killed S aureus is dependent on NF-κB signaling. These results support a model in which the ARE integrates the transcriptional responses of Slc40a1 triggered by signals from redox, metabolic, and inflammatory pathways. This work identifies the long-sought mechanism of Slc40a1 transcriptional downregulation upon inflammation, paving the way for therapeutic interventions at this critical juncture.
炎症性贫血是慢性炎症性疾病患者中普遍存在的一种合并症。炎症通过限制铁转运蛋白（FPN）介导的衰老红细胞循环利用巨噬细胞中的铁输出，导致低铁血症和铁限制性红细胞生成。铁调素诱导的降解和/或通过细胞因子和Toll样受体（TLR）刺激抑制FPN（Slc40a1）转录，从而降低巨噬细胞表面FPN的表达。尽管铁调素介导的FPN调控机制已得到广泛研究，但抑制Slc40a1信使核糖核酸（mRNA）表达的机制仍不清楚。我们在经TLR2/6配体FSL1刺激的巨噬细胞中应用靶向RNA干扰和药理学筛选，确定了TLRs和NF-κB信号下游Slc40a1 mRNA抑制的关键信号调节因子。有趣的是，NF-κB调节枢纽对于由TLR4配体脂多糖、细胞因子肿瘤坏死因子β/淋巴毒素-α（LTA）和热灭活细菌驱动的Slc40a1 mRNA抑制同样重要。从机制上讲，用热灭活的金黄色葡萄球菌刺激巨噬细胞会将组蛋白脱乙酰酶（HDAC）HDAC1和HDAC3募集到位于Slc40a1启动子中的抗氧化反应元件（ARE）。因此，用泛HDAC抑制剂预处理可消除炎症信号刺激下的Slc40a1 mRNA抑制，这表明HDAC在NF-κB下游发挥作用以抑制Slc40a1转录。一致地，热灭活金黄色葡萄球菌刺激后HDAC1和HDAC3募集到Slc40a1 ARE依赖于NF-κB信号。这些结果支持了一种模型，其中ARE整合了由氧化还原、代谢和炎症途径的信号触发的Slc40a1转录反应。这项工作确定了炎症时Slc40a1转录下调这一长期寻找的机制，为在这一关键节点进行治疗干预铺平了道路。
