Serum α-1 Antitrypsin (AAT) antagonizes intrinsic apoptosis induction in neutrophils from patients with systemic inflammatory response syndrome

Excessive neutrophil activation accompanied by delayed apoptotic cell death in inflammatory conditions causes progressive damage of cells and tissues, leading to life-threatening multiple organ dysfunction syndrome. Previous work suggested that circulating serum factors during inflammation are critically involved in the suppression of neutrophil cell death although the identity of these antiapoptotic mediators remained elusive. In this study, we identified the acute phase protein α-1 Antitrypsin (AAT) as a potent suppressor of staurosporine (STS)-induced apoptosis in human neutrophils through a mechanism implicating caspases-independent pathways. We show here that serum levels of AAT, potentially in part released by stimulated neutrophils, are markedly elevated in major trauma patients suffering from systemic inflammatory response syndrome (SIRS). Notably, AAT depletion from serum increased sensitivity of human neutrophils for STS-induced cell death. In fact, AAT was demonstrated to confer intrinsic apoptosis resistance by preventing PKC/Akt inactivation and subsequent proteasomal degradation of antiapoptotic Mcl-1 protein in response to STS treatment. Neither MAP kinase ERK1/2 nor caspases were found to be involved in AAT-triggered antiapoptotic pathways in neutrophils. In summary, these results establish a novel pivotal role of circulating AAT in mediating survival by antagonizing the proapoptotic action of the PKC inhibitor STS and should be considered for AAT augmentation therapies in future.炎症状态下过度活化的中性粒细胞伴随凋亡细胞死亡延迟，会造成细胞与组织的进行性损伤，进而引发危及生命的多器官功能障碍综合征（multiple organ dysfunction syndrome）。既往研究表明，炎症过程中的循环血清因子可显著抑制中性粒细胞死亡，尽管此类抗凋亡介质（antiapoptotic mediators）的具体身份仍未明确。本研究中，我们鉴定出急性期蛋白α-1抗胰蛋白酶（α-1 Antitrypsin, AAT）是人类中性粒细胞中星形孢菌素（staurosporine, STS）诱导凋亡的强效抑制剂，其作用机制涉及半胱天冬酶非依赖通路。本研究显示，罹患全身炎症反应综合征（systemic inflammatory response syndrome, SIRS）的重度创伤患者体内，AAT的血清水平显著升高，其部分来源可能为活化中性粒细胞的释放。值得注意的是，去除血清中的AAT会增强人类中性粒细胞对星形孢菌素诱导的细胞死亡的敏感性。研究证实，AAT可通过阻断蛋白激酶C（PKC）/丝氨酸苏氨酸激酶B（Akt）的失活以及星形孢菌素处理后抗凋亡Mcl-1蛋白的后续蛋白酶体降解，赋予中性粒细胞内源性凋亡抵抗特性。研究未发现丝裂原活化蛋白激酶ERK1/2（MAP kinase ERK1/2）与半胱天冬酶（caspases）参与AAT介导的中性粒细胞抗凋亡通路。综上，本研究结果证实循环AAT通过拮抗PKC抑制剂星形孢菌素的促凋亡作用，在介导中性粒细胞存活中发挥全新的关键作用，未来可考虑将AAT补充疗法应用于相关临床治疗。