Distinct metabolic responses to heme in inflammatory human and mouse macrophages - Role of nitric oxide. Distinct metabolic responses to heme in inflammatory human and mouse macrophages - Role of nitric oxide

Activation of inflammation is tightly associated with metabolic reprogramming in macrophages. The iron-containing tetrapyrrole heme can induce pro-oxidant and pro-inflammatory effects in murine macrophages, but has been associated with polarization towards an anti-inflammatory phenotype in human macrophages. In the current study, we compared the regulatory responses to heme and the prototypical Toll-like receptor (TLR)4 ligand lipopolysaccharide (LPS) in human and mouse macrophages with a particular focus on alterations of cellular bioenergetics. In human macrophages, bulk RNA-sequencing analysis indicated that heme led to an anti-inflammatory transcriptional profile, whereas LPS induced a classical pro-inflammatory gene response. Co-stimulation of heme with LPS caused opposing regulatory patterns of inflammatory activation and cellular bioenergetics in human and mouse macrophages. Specifically, in LPS-stimulated murine, but not human macrophages, heme led to a marked suppression of oxidative phosphorylation and an up-regulation of glycolysis. The species-specific alterations in cellular bioenergetics and inflammatory responses to heme were critically dependent on the availability of nitric oxide (NO) that is generated in inflammatory mouse, but not human macrophages. Accordingly, studies with an inducible nitric oxide synthase (iNOS) inhibitor in mouse, and a pharmacological NO donor in human macrophages, reveal that NO is responsible for the opposing effects of heme in these cells. Taken together, the current findings indicate that NO is critical for the immunomodulatory role of heme in macrophages. Overall design: To assess the comparative effects of heme and LPS on RNA expression, bulk transcriptomics was performed in human monocyte-derived macrophages (hMDMs) from four individual donors treated with either heme or LPS

炎症激活与巨噬细胞的代谢重编程紧密相关。含铁四吡咯的血红素（heme）可在小鼠巨噬细胞中诱导促氧化与促炎效应，但在人类巨噬细胞中则与抗炎表型极化相关。
本研究比较了人类与小鼠巨噬细胞对血红素及经典Toll样受体4（Toll-like receptor 4, TLR4）配体脂多糖（lipopolysaccharide, LPS）的调控应答，重点关注细胞生物能学的改变。
在人类巨噬细胞中，批量RNA测序分析显示，血红素可诱导抗炎性转录谱，而脂多糖则触发典型的促炎基因应答。血红素与脂多糖共刺激可在人类与小鼠巨噬细胞中引发炎症激活与细胞生物能学的相反调控模式。
具体而言，在经脂多糖刺激的小鼠巨噬细胞（而非人类巨噬细胞）中，血红素可显著抑制氧化磷酸化并上调糖酵解。
这种物种特异性的细胞生物能学改变及对血红素的炎症应答，关键依赖于炎症小鼠巨噬细胞（而非人类巨噬细胞）所产生的一氧化氮（nitric oxide, NO）的可获得性。
据此，通过在小鼠模型中使用诱导型一氧化氮合酶（inducible nitric oxide synthase, iNOS）抑制剂、在人类巨噬细胞中使用药理学一氧化氮供体开展的实验证实，一氧化氮是导致血红素在两类细胞中产生相反效应的核心原因。
综上，本研究结果表明，一氧化氮对于血红素在巨噬细胞中发挥的免疫调控作用至关重要。
整体实验设计：为评估血红素与脂多糖对基因转录表达的比较效应，本研究对4名独立供者来源的人类单核细胞衍生巨噬细胞（human monocyte-derived macrophages, hMDMs）分别施以血红素或脂多糖处理，并开展批量转录组学分析。