NLRP1 activation induces deletion of hematopoietic progenitor cells

描述（由申请人提供）：尽管进行了抗菌治疗，但全身感染患者的外周血细胞减少是确定的致命结果的预测因素。本项目提案旨在解释脓毒症诱导的细胞减少的分子机制。我们已经确定了造血干细胞和祖细胞在感染诱导的细胞减少中caspase -1依赖性死亡（称为焦亡）的核心作用。我们建立了两个NLRP1突变小鼠模型，第一个是enu诱导的NLRP1a的功能获得突变（NLRP1aQ593P），第二个是NLRP1的所有三个亚型（NLRP1a， NLRP1b和NLRP1c）的缺陷。NLRP1aQ593P突变发生在核苷酸结合（NACHT， NB）结构域和富亮氨酸重复序列（LRR）之间的柔性连接体区域，在该区域发现了降低植物NB-LRR先天防御蛋白激活阈值的激活突变。Nlrp1aQ593P/Q593P小鼠可发生致死性脑膜脑炎、肺炎和心肌炎。这种疾病依赖于IL-1¿和Caspase-1，但不依赖于ASC或Caspase-11，并且意外地受到IL-18的负调控。当Nlrp1aQ593P/Q593P小鼠IL-1受体缺乏时，不会发生多器官炎性疾病，但小鼠白细胞减少，且在稳态下造血干细胞和祖细胞明显缺乏（表1）。在淋巴细胞性脉络丛脑膜炎病毒（LCMV）感染或化疗诱导的造血应激反应中，Nlrp1aQ593P/Q593P小鼠不能重建髓系、淋巴系和红系细胞。相反，nlrp1缺陷小鼠从LCMV感染和化疗中恢复增强。根据我们的初步数据，我们提出(1)在感染期间，造血祖细胞中NLRP1的全身性激活可诱导细胞减少，从而导致免疫抑制。我们还提出(2)NLRP1的生理作用之一是诱导受感染造血干细胞和祖细胞的caspase -1依赖性死亡，以防止感染传播到后代细胞。本研究旨在：A.研究NLRP1的生化调节因子，包括Bcl-2和SREBP-1a的作用，以确定体内调节NLRP1的新途径；B.通过竞争性骨髓移植、连续骨髓移植、体外克隆培养和活力测定，确定受NLRP1影响的特定造血干细胞和祖细胞群。C.在感染和化疗诱导的造血应激过程中，表征NLRP1在造血干细胞和祖细胞中的作用，以了解NLRP1激活的有益和病理作用

DESCRIPTION (provided by applicant): Peripheral blood cytopenias in patients with systemic infection are well-established predictors of fatal outcome despite antimicrobial therapy. This project proposal seeks to explain the molecular mechanism of sepsis- induced cytopenias. We have identified a central role for Caspase-1-dependent death, known as pyroptosis, of hematopoietic stem and progenitor cells in infection-induced cytopenias. We have generated two NLRP1 mutant mouse models, the first an ENU-induced gain-of-function mutation in NLRP1a (NLRP1aQ593P), and the second a deficiency in all three isoforms of NLRP1 (NLRP1a, NLRP1b and NLRP1c). The NLRP1aQ593P mutation occurs in the flexible linker region between the nucleotide-binding (NACHT, NB) domain and leucine- rich repeats (LRR), where activating mutations that reduce the threshold for activation of plant NB-LRR innate defense proteins are found. Nlrp1aQ593P/Q593P mice develop lethal meningoencephalitis, pneumonitis and myocarditis. This disease is dependent on IL-1¿ and Caspase-1 but not ASC or Caspase-11 and is unexpectedly, negatively regulated by IL-18. When Nlrp1aQ593P/Q593P mice are deficient in the IL-1 receptor, the multi-organ inflammatory disease does not develop but the mice are leukopenic and they display significant deficiencies in hematopoietic stem and progenitor cells at the steady state (Table 1). In response to hematopoietic stress induced by lymphocytic choriomeningitis virus (LCMV) infection or chemotherapy, Nlrp1aQ593P/Q593P mice fail to repopulate myeloid, lymphoid and erythroid cells. Conversely, NLRP1-deficient mice show enhanced recovery from LCMV infection and chemotherapy. Based on our preliminary data, we propose (1) that systemic activation of NLRP1 in hematopoietic progenitor cells during infection can induce cytopenia resulting in immunosuppression. We also propose that (2) one of the physiological roles of NLRP1 is to induce Caspase-1-dependent death of infected hematopoietic stem and progenitor cells to prevent dissemination of infection to progeny cells. This research seeks to: A. examine the role of biochemical regulators of NLRP1 including Bcl-2 and SREBP-1a to identify new avenues to modulate NLRP1 in vivo B. define specific hematopoietic stem and progenitor cell populations affected by NLRP1 using competitive bone marrow transplant, serial bone marrow transplant, and ex vivo clonal culture and viability assays. C. characterise the role of NLRP1 in hematopoietic stem and progenitor cells during hematopoietic stress induced by infection and chemotherapy, to understand beneficial and pathological roles for NLRP1 activation