DataSheet1_Elevated levels of damage-associated molecular patterns HMGB1 and S100A8/A9 coupled with toll-like receptor-triggered monocyte activation are associated with inflammation in patients with myelofibrosis.pdf

Inflammation plays a pivotal role in the pathogenesis of primary and post-essential thrombocythemia or post-polycythemia vera myelofibrosis (MF) in close cooperation with the underlying molecular drivers. This inflammatory state is induced by a dynamic spectrum of inflammatory cytokines, although recent evidence points to the participation of additional soluble inflammatory mediators. Damage-associated molecular patterns (DAMPs) represent endogenous signals released upon cell death or damage which trigger a potent innate immune response. We assessed the contribution of two prototypical DAMPs, HMGB1 and S100A8/A9, to MF inflammation. Circulating HMGB1 and S100A8/A9 were elevated in MF patients in parallel to the degree of systemic inflammation and levels increased progressively during advanced disease stages. Patients with elevated DAMPs had higher frequency of adverse clinical features, such as anemia, and inferior survival, suggesting their contribution to disease progression. Monocytes, which are key players in MF inflammation, were identified as a source of S100A8/A9 but not HMGB1 release, while both DAMPs correlated with cell death parameters, such as serum LDH and cell-free DNA, indicating that passive release is an additional mechanism leading to increased DAMPs. HMGB1 and S100A8/A9 promote inflammation through binding to Toll-like receptor (TLR) 4, whereas the former also binds TLR2. Monocytes from MF patients were shown to be hyperactivated at baseline, as reflected by higher CD11b and tissue factor exposure and increased expression levels of proinflammatory cytokines IL-1β and IL-6. Patient monocytes showed preserved TLR4 and TLR2 expression and were able to mount normal or even exacerbated functional responses and cytokine upregulation following stimulation of TLR4 and TLR2. Elevated levels of endogenous TLR ligands HMGB1 and S100A8/A9 coupled to the finding of preserved or hyperreactive TLR-triggered responses indicate that DAMPs may promote monocyte activation and cytokine production in MF, fueling inflammation. Plasma IL-1β and IL-6 were elevated in MF and correlated with DAMPs levels, raising the possibility that DAMPs could contribute to cytokine generation in vivo. In conclusion, this study highlights that, in cooperation with classic proinflammatory cytokines, DAMPs represent additional inflammatory mediators that may participate in the generation of MF inflammatory state, potentially providing novel biomarkers of disease progression and new therapeutic targets.

炎症与潜在分子驱动因素协同作用，在原发性骨髓纤维化、原发性血小板增多症后骨髓纤维化及真性红细胞增多症后骨髓纤维化（myelofibrosis, MF）的发病机制中发挥关键作用。这种炎症状态由一系列动态变化的炎性细胞因子介导，不过最新研究证据表明，另有可溶性炎性介质参与其中。损伤相关分子模式（Damage-associated molecular patterns, DAMPs）是细胞死亡或损伤时释放的内源性信号，可触发强烈的固有免疫应答。本研究评估了两种典型损伤相关分子模式——高迁移率族蛋白B1（HMGB1）和S100A8/A9——对骨髓纤维化炎症的调控作用。骨髓纤维化患者外周血中的HMGB1与S100A8/A9水平随全身炎症程度升高而上升，且在疾病晚期阶段呈进行性升高。损伤相关分子模式水平升高的患者，贫血等不良临床特征的发生率更高，生存预后更差，提示这类分子可能参与疾病进展。作为骨髓纤维化炎症的核心效应细胞，单核细胞被证实是S100A8/A9的释放来源，但并非HMGB1的释放来源；而两种损伤相关分子模式均与细胞死亡相关指标（如血清乳酸脱氢酶（lactate dehydrogenase, LDH）和游离DNA）呈正相关，表明被动释放是导致损伤相关分子模式水平升高的另一机制。HMGB1与S100A8/A9可通过结合Toll样受体4（Toll-like receptor 4, TLR4）介导炎症反应，其中HMGB1还可结合Toll样受体2（Toll-like receptor 2, TLR2）。骨髓纤维化患者的单核细胞在基线状态下即呈过度活化状态，具体表现为CD11b与组织因子表达升高、促炎细胞因子IL-1β和IL-6的表达水平上调。骨髓纤维化患者的单核细胞仍可维持Toll样受体4与Toll样受体2的表达，且在Toll样受体4、Toll样受体2刺激后，可产生正常甚至更强的功能应答与细胞因子上调反应。内源性Toll样受体配体HMGB1与S100A8/A9水平升高，加之单核细胞Toll样受体触发的应答仍可维持甚至呈高反应性，这两点共同表明，损伤相关分子模式可能促进骨髓纤维化患者单核细胞活化与细胞因子产生，进而加剧炎症反应。骨髓纤维化患者血浆中的IL-1β与IL-6水平升高，且与损伤相关分子模式水平呈正相关，提示损伤相关分子模式可能在体内参与细胞因子的产生。综上，本研究表明，损伤相关分子模式可与经典促炎细胞因子协同作用，参与骨髓纤维化炎症状态的形成，有望成为疾病进展的新型生物标志物与治疗靶点。