Tumor-associated macrophages (TAM) are immunosuppressive cells that contribute to impaired anti-cancer immunity. Iron plays a critical role in regulating macrophage function. However, it is still elusive whether it can drive the functional polarization of macrophages in the context of cancer and how tumor cells affect the iron-handing properties of TAM. In this study, using hepatocellular carcinoma (HCC) as a study model, we aimed to explore the effect and mechanism of reduced ferrous iron in TAM. TAM from HCC patients and mouse HCC tissues were collected to analyze the level of ferrous iron. Quantitative real-time PCR was used to assess M1 or M2 signature genes of macrophages treated with iron chelators. A co-culture system was established to explore the iron competition between macrophages and HCC cells. Flow cytometry analysis was performed to determine the holo-transferrin uptake of macrophages. HCC samples from The Cancer Genome Atlas (TCGA) were enrolled to evaluate the prognostic value of transferrin receptor (TFRC) and its relevance to tumor-infiltrating M2 macrophages. We revealed that ferrous iron in M2-like TAM is lower than that in M1-like TAM. In vitro analysis showed that loss of iron-induced immunosuppressive M2 polarization of mouse macrophages. Further experiments showed that TFRC, the primary receptor for transferrin-mediated iron uptake, was overexpressed on HCC cells but not TAM. Mechanistically, HCC cells competed with macrophages for iron to upregulate the expression of M2-related genes via induction of HIF-1α, thus contributing to M2-like TAM polarization. We further clarified the oncogenic role of TFRC in HCC patients by TCGA. TFRC is significantly increased in varieties of malignancies, including HCC, and HCC patients with high TFRC levels have considerably shortened overall survival. Also, TFRC is shown to be positively related to tumor-infiltrating M2 macrophages. Collectively, we identified iron starvation through TFRC-mediated iron competition drives functional immunosuppressive polarization of TAM, providing new insight into the interconnection between iron metabolism and tumor immunity.

中文翻译：

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肿瘤细胞施加的铁限制驱动肿瘤相关巨噬细胞的免疫抑制极化


肿瘤相关巨噬细胞（TAM）是免疫抑制细胞，会导致抗癌免疫力受损。铁在调节巨噬细胞功能中起着至关重要的作用。然而，它是否可以在癌症中驱动巨噬细胞的功能极化以及肿瘤细胞如何影响 TAM 的铁处理特性仍然是难以捉摸的。本研究以肝细胞癌（HCC）为研究模型，旨在探讨TAM中还原亚铁的作用及其机制。收集 HCC 患者和小鼠 HCC 组织的 TAM 来分析亚铁的水平。使用定量实时 PCR 评估铁螯合剂处理的巨噬细胞的 M1 或 M2 特征基因。建立共培养体系来探索巨噬细胞和肝癌细胞之间的铁竞争。进行流式细胞术分析以确定巨噬细胞的全转铁蛋白摄取。来自癌症基因组图谱 (TCGA) 的 HCC 样本被纳入评估转铁蛋白受体 (TFRC) 的预后价值及其与肿瘤浸润 M2 巨噬细胞的相关性。我们发现，M2 类 TAM 中的亚铁含量低于 M1 类 TAM 中的亚铁含量。体外分析表明，铁的缺失会诱导小鼠巨噬细胞的免疫抑制性 M2 极化。进一步的实验表明，TFRC（转铁蛋白介导的铁摄取的主要受体）在 HCC 细胞上过度表达，但 TAM 则不然。从机制上讲，HCC细胞与巨噬细胞竞争铁，通过诱导HIF-1α上调M2相关基因的表达，从而促进类似M2的TAM极化。我们通过 TCGA 进一步阐明了 TFRC 在 HCC 患者中的致癌作用。 TFRC 在包括 HCC 在内的多种恶性肿瘤中显着增加，并且 TFRC 水平高的 HCC 患者的总生存期显着缩短。此外，TFRC 与肿瘤浸润的 M2 巨噬细胞呈正相关。总的来说，我们发现铁饥饿是通过 TFRC 介导的铁竞争驱动 TAM 的功能性免疫抑制极化，为铁代谢与肿瘤免疫之间的相互联系提供了新的见解。