Pulmonary Division, Faculty of Medicine, Université de Sherbrooke, Sherbrooke, QC, Canada.
Centre de recherche du CHUS (CRCHUS), Sherbrooke, QC, Canada.
Front Immunol. 2021 Sep 20;12:675315. doi: 10.3389/fimmu.2021.675315. eCollection 2021.
Neutrophil extracellular trap (NET) formation has emerged as an important response against various pathogens; it also plays a role in chronic inflammation, autoimmunity, and cancer. Despite a growing understanding of the mechanisms underlying NET formation, much remains to be elucidated. We previously showed that in human neutrophils activated with different classes of physiological stimuli, NET formation features both early and late events that are controlled by discrete signaling pathways. However, the nature of these events has remained elusive. We now report that PAD4 inhibition only affects the early phase of NET generation, as do distinct signaling intermediates (TAK1, MEK, p38 MAPK). Accordingly, the inducible citrullination of residue R2 on histone H3 is an early neutrophil response that is regulated by these kinases; other arginine residues on histones H3 and H4 do not seem to be citrullinated. Conversely, elastase blockade did not affect NET formation by several physiological stimuli, though it did so in PMA-activated cells. Among belated events in NET formation, we found that chromatin decondensation is impaired by the inhibition of signaling pathways controlling both early and late stages of the phenomenon. In addition to chromatin decondensation, other late processes were uncovered. For instance, unstimulated neutrophils can condition themselves to be poised for rapid NET induction. Similarly, activated neutrophils release endogenous proteic factors that promote and largely mediate NET generation. Several such factors are known RAGE ligands and accordingly, RAGE inbibition largely prevents both NET formation and the conditioning of neutrophils to rapidly generate NETs upon stimulation. Our data shed new light on the cellular processes underlying NET formation, and unveil unsuspected facets of the phenomenon that could serve as therapeutic targets. In view of the involvement of NETs in both homeostasis and several pathologies, our findings are of broad relevance.
中性粒细胞胞外诱捕网（NET）的形成已成为抵御各种病原体的重要反应；它在慢性炎症、自身免疫和癌症中也发挥作用。尽管人们对 NET 形成的机制有了越来越多的了解，但仍有许多问题需要阐明。我们之前曾表明，在被不同生理刺激激活的人类中性粒细胞中，NET 的形成具有由离散信号通路控制的早期和晚期事件。然而，这些事件的性质仍然难以捉摸。我们现在报告称，PAD4 抑制仅影响 NET 生成的早期阶段，而独特的信号转导介体（TAK1、MEK、p38 MAPK）也是如此。因此，组蛋白 H3 残基 R2 上的诱导性瓜氨酸化是一种早期中性粒细胞反应，受这些激酶调节；组蛋白 H3 和 H4 上的其他精氨酸残基似乎不会瓜氨酸化。相反，弹性蛋白酶阻断不会影响几种生理刺激诱导的 NET 形成，尽管它会影响 PMA 激活的细胞。在 NET 形成的晚期事件中，我们发现，控制该现象早期和晚期阶段的信号通路的抑制会损害染色质去凝聚。除了染色质去凝聚外，还发现了其他晚期过程。例如，未受刺激的中性粒细胞可以使自身处于快速 NET 诱导的准备状态。同样，激活的中性粒细胞释放促进并在很大程度上介导 NET 生成的内源性蛋白因子。已知有几种这样的因子是 RAGE 配体，因此，RAGE 抑制在很大程度上阻止了 NET 的形成以及中性粒细胞在受到刺激时快速生成 NET 的条件。我们的数据为 NET 形成的细胞过程提供了新的见解，并揭示了该现象的一些意想不到的方面，这些方面可能成为治疗靶点。鉴于 NET 参与了体内平衡和几种病理学，我们的发现具有广泛的相关性。
