Bonitz Katharina, Colucci Silvia, Qiu Ruiyue, Altamura Sandro, Sparla Richard, Mudder Katja, Zimmermann Stefan, Hentze Matthias W, Muckenthaler Martina U, Marques Oriana
Department of Pediatric Oncology, Hematology and Immunology Hopp Children's Cancer Center (KiTZ), University Hospital Heidelberg Heidelberg Germany.
Molecular Medicine Partnership Unit (MMPU) EMBL University of Heidelberg Heidelberg Germany.
Hemasphere. 2025 Apr 3;9(4):e70096. doi: 10.1002/hem3.70096. eCollection 2025 Apr.
Iron restriction is a critical pathomechanism underlying the Anemia of Inflammation and an innate immune response limiting the replication of extracellular pathogens. During infections, innate immune cells detect pathogen-associated molecular patterns (PAMPs) and produce proinflammatory cytokines. Among these, interleukin (IL)-6 is detected by hepatocytes, where it activates the production of the iron-regulated hormone hepcidin that inhibits iron export from macrophages. Consequently, macrophages accumulate iron and hypoferremia (low plasma iron) develops. Whether Toll-like receptors (TLRs) expressed on hepatocytes directly recognize PAMPs and contribute to hepcidin upregulation is still an open question. Stimulation of primary murine hepatocytes with a panel of PAMPs targeting TLRs 1-9 revealed that the TLR5 ligand flagellin and the TLR2:TLR6 ligand FSL1 upregulated hepcidin. Hepcidin was also induced upon treatment with heat-killed (HKSA) and (HKBA). The hepcidin response to flagellin, FSL1, HKSA, and HKBA started at an early time point, was independent of autocrine regulation by IL-6, and occurred through the TLR-mitogen-activated protein kinase (MAPK) axis. By analyzing a macrophage:hepatocyte co-culture, we additionally show that the hepcidin response was dependent on TLR2:TLR6 expression in hepatocytes and independent of macrophage cytokine secretion. Ex vivo liver perfusion of mice with FSL1 and HKSA further revealed that PAMPs and pathogens can pass the sinusoidal barrier and reach hepatocytes to cause hepcidin upregulation in a TLR2:TLR6-dependent manner. We conclude that hepatocytes can directly recognize PAMPs and pathogens and promote hepcidin upregulation in a macrophage and cytokine-independent manner. This positions hepatocytes in the spotlight as potential direct drivers of iron restriction.
铁限制是炎症性贫血潜在的关键病理机制，也是一种限制细胞外病原体复制的固有免疫反应。在感染期间，固有免疫细胞检测病原体相关分子模式（PAMPs）并产生促炎细胞因子。其中，肝细胞可检测到白细胞介素（IL）-6，它在肝细胞中激活铁调节激素铁调素的产生，铁调素会抑制巨噬细胞的铁输出。因此，巨噬细胞会积累铁，进而出现低铁血症（血浆铁含量低）。肝细胞上表达的Toll样受体（TLRs）是否能直接识别PAMPs并促进铁调素上调仍是一个悬而未决的问题。用一组靶向TLRs 1-9的PAMPs刺激原代小鼠肝细胞后发现，TLR5配体鞭毛蛋白和TLR2:TLR6配体FSL1可上调铁调素。用热灭活的金黄色葡萄球菌（HKSA）和大肠杆菌（HKBA）处理后也可诱导铁调素产生。铁调素对鞭毛蛋白、FSL1、HKSA和HKBA的反应在早期就开始了，与IL-6的自分泌调节无关，并且是通过TLR-丝裂原活化蛋白激酶（MAPK）轴发生的。通过分析巨噬细胞与肝细胞的共培养，我们还发现铁调素反应依赖于肝细胞中TLR2:TLR6的表达，且与巨噬细胞细胞因子分泌无关。用FSL1和HKSA对小鼠进行离体肝脏灌注进一步表明，PAMPs和病原体可以穿过肝血窦屏障并到达肝细胞，以TLR2:TLR6依赖的方式导致铁调素上调。我们得出结论，肝细胞可以直接识别PAMPs和病原体，并以巨噬细胞和细胞因子非依赖的方式促进铁调素上调。这使肝细胞成为铁限制潜在直接驱动因素的焦点。
