Familial Mediterranean fever (FMF) is a prototypical autoinflammatory syndrome associated with phagocytic cell activation. Pyrin mutations are the genetic basis of this disease, and its expression has been shown in monocytes, granulocytes, dendritic cells, and synovial fibroblasts. Pyrin functions as a cytosolic pattern recognition receptor and forms a distinct pyrin inflammasome. The phagocyte-specific protein S100A12 is predominantly expressed in granulocytes and belongs to the group of damage associated molecular patterns (DAMP). S100A12 can be detected at massively elevated levels in the serum of FMF patients, even in clinically inactive disease. Whether this is crucial for FMF pathogenesis is as yet unknown, and we therefore investigated the mechanisms of S100A12 release from granulocytes of FMF patients presenting clinically inactive. We demonstrate that FMF neutrophils from patients in clinical inactive disease possess an intrinsic activity leading to cell death even in exogenously unstimulated neutrophils. Cell death resembles NETosis and is dependent on ROS and pore forming protein gasdermin D (GSDMD), as inhibitors for both are capable of completely block cell death and S100A12 release. When pyrin-activator TcdA (Clostridium difficile toxin A) is used to stimulate, neutrophilic cell death and S100A12 release are significantly enhanced in neutrophils from FMF patients compared to neutrophils from HC. We are able to demonstrate that activation threshold of neutrophils from inactive FMF patients is decreased, most likely by pre-activated pyrin. FMF neutrophils present with intrinsically higher ROS production, when cultured ex vivo. This higher baseline ROS activity leads to increased GSDMD cleavage and subsequent release of, e.g., S100A12, and to increased cell death with features of NETosis and pyroptosis. We show for the first time that cell death pathways in neutrophils of inactive FMF patients are easily triggered and lead to ROS- and GSDMD-dependent activation mechanisms and possibly pathology. This could be therapeutically addressed by blocking ROS or GSDMD cleavage to decrease inflammatory outbreaks when becoming highly active.

中文翻译：

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家族性地中海热中吞噬细胞死亡导致促炎性 S100A12 释放增强

家族性地中海热（FMF）是一种与吞噬细胞激活相关的典型自身炎症综合征。Pyrin突变是这种疾病的遗传基础，其表达已在单核细胞、粒细胞、树突状细胞和滑膜成纤维细胞中显示出来。Pyrin 作为胞质模式识别受体发挥作用，并形成独特的 Pyrin 炎性小体。吞噬细胞特异性蛋白 S100A12 主要在粒细胞中表达，属于损伤相关分子模式 (DAMP) 组。即使在临床非活动性疾病中，FMF 患者的血清中也可以检测到 S100A12 水平大幅升高。这对于 FMF 发病机制是否至关重要尚不清楚，因此我们研究了临床上不活跃的 FMF 患者粒细胞释放 S100A12 的机制。我们证明，来自临床非活动性疾病患者的 FMF 中性粒细胞具有导致细胞死亡的内在活性，即使在外源性未刺激的中性粒细胞中也是如此。细胞死亡类似于 NETosis，并且依赖于 ROS 和孔形成蛋白gasdermin D (GSDMD)，因为两者的抑制剂能够完全阻止细胞死亡和 S100A12 释放。当使用吡啶激活剂 TcdA（艰难梭菌毒素 A）刺激时，与 HC 患者的中性粒细胞相比，FMF 患者的中性粒细胞死亡和 S100A12 释放显着增强。我们能够证明，不活动的 FMF 患者的中性粒细胞激活阈值降低，很可能是由于预激活的吡啶所致。当离体培养时，FMF 中性粒细胞本质上具有较高的 ROS 产量。这种较高的基线 ROS 活性导致 GSDMD 裂解增加，随后释放例如 S100A12，并导致具有 NETosis 和细胞焦亡特征的细胞死亡增加。我们首次表明，不活动的 FMF 患者中性粒细胞的细胞死亡途径很容易被触发，并导致 ROS 和 GSDMD 依赖性激活机制以及可能的病理学。这个问题可以通过阻断 ROS 或 GS​​DMD 裂解来减少炎症在高度活跃时的爆发来解决。