Mechanisms of necrosis regulation of hematopoietic stem cell function

正常的造血需要严格控制新细胞的产生（增殖）和去除衰老 程序性细胞死亡（Programmed Cell Death）患有骨髓衰竭疾病的患者，如 骨髓增生异常综合征（MDS）的骨髓程序性细胞死亡增加， 死亡诱导细胞因子，如TNF α。过去几年的发现表明， 除了细胞凋亡外，TNF α还激活一种新的细胞死亡形式，即程序性坏死。凋亡细胞 内爆在半胱天冬酶驱动和免疫沉默过程中，而坏死细胞爆炸在Rip激酶驱动 过程，释放细胞内容物（DAMPS）并引发免疫反应。我们发现Rip 1增加 在70%的MDS患者样品中检测到激酶表达，表明坏死性凋亡在MDS中被激活。我们 还发现来自小鼠模型的骨髓携带在MDS中发现的已知遗传突变（Asxl 1-/-， Asxl 1-/-Tet 2-/-）显示Rip 1激酶增加，表明MDS遗传/表观遗传改变导致 导致骨髓细胞死亡的坏死性凋亡信号增加。大量数据表明， MDS是一种克隆干细胞病症（Graubert等人，2012; Walter等人，2011; Walter等人，2012; Walter等人， 2013年）。MDS中固有的矛盾是，尽管MDS繁殖克隆增加了竞争力， 能力，它的扩张最终导致骨髓衰竭。MDS干细胞的存在和死亡 祖细胞赋予共存的正常干细胞降低的功能，这表明MDS干细胞和 祖细胞产生杀死正常造血干细胞的骨髓环境。在我们 在具有不受限制的造血坏死的小鼠模型中，小鼠死于骨髓衰竭，其中大多数 人类MDS的特征。此外，这些小鼠的骨髓表现出更强的竞争性， 但是移植的小鼠在四岁时死于骨髓衰竭， 尽管野生型骨髓的持续存在，但这些坏死的HSC和祖细胞仍然存在， 细胞可以杀死野生型HSC，导致骨髓衰竭。因此，我们的小鼠揭示了MDS克隆如何 导致骨髓衰竭：我们的总体假设是MDS细胞的程序性坏死引发了骨髓衰竭。 炎症反应杀死正常的造血干细胞。这就使得突变的茎和 祖细胞扩张并接管骨髓，从而导致骨髓衰竭。中断 细胞死亡信号通路或改变炎症信号通路有可能阻止细胞凋亡。 死亡和重建骨髓稳态以获得治疗益处。目的1：评估细胞死亡和 细胞因子信号传导在无限制的坏死性凋亡的遗传小鼠模型中，以及MDS突变，以确定 分子决定驱动因素，以及这些驱动因素如何改变骨髓细胞死亡目标2：将决定 无论是抑制上述小鼠模型中HSC和祖细胞中的坏死还是炎症信号传导 通过抑制坏死信号传导（Rip 1/Rip 3抑制剂）或抑制炎症信号传导（Jak 1/2抑制剂）， 重置造血稳态和预防MDS骨髓衰竭。影响：目标是确定如何 携带MDS突变的HSC和祖细胞执行细胞死亡，以及它们如何杀死正常HSC， 确定是否中断这种细胞死亡可以挽救骨髓功能。

Normal hematopoiesis requires stringent control of production of new cells (proliferation) and removal of aging or damaged cells (programmed cell death). Patients with bone marrow failure disorders such as Myelodysplastic syndrome (MDS) have increased bone marrow programmed cell death, and increased levels of death-inducing cytokines such as TNFa. Discoveries in the last several years have demonstrated that in addition to apoptosis, TNFa also activates a novel form of cell death, programmed necrosis. Apoptotic cells implode in caspase-driven and immune silent process, whereas necrotic cells explode in a Rip kinase-driven process, releasing cellular contents (DAMPS) and eliciting an immune response. We find increased Rip1 kinase expression in 70% of MDS patient samples tested suggesting that necroptosis is activated in MDS. We also find that bone marrow from mouse models harboring known genetic mutations found in MDS (Asxl1-/-, Asxl1-/-Tet2-/-) display increased Rip1 kinase, suggesting that MDS genetic/epigenetic alterations result in increased necroptosis signaling that contributes to bone marrow cell death. Substantial data demonstrate that MDS is a clonal stem cell disorder(Graubert et al., 2012; Walter et al., 2011; Walter et al., 2012; Walter et al., 2013). A paradox inherent in MDS is that although the MDS-propagating clone has increased competitive ability, its expansion ultimately results in bone marrow failure. The presence of MDS stem cells and dying progenitor cells confers decreased function to the coexisting normal stem cells, suggesting that MDS stem and progenitor cells create a bone marrow environment that is killing normal hematopoietic stem cells. In our mouse model with unrestrained hematopoietic necrosis, mice die of bone marrow failure with the majority of the features of human MDS. Furthermore, bone marrow from these mice displayed increased competitive repopulating ability against wild type bone marrow, but transplanted mice die of bone marrow failure at four months despite the persistence of wild type bone marrow, suggesting that these necrotic HSC and progenitor cells can kill wild type HSCs to cause bone marrow failure. Our mice thus shed light on how an MDS clone can cause bone marrow failure: Our overarching hypothesis is that programmed necrosis in MDS cells triggers an inflammatory response that kills normal hematopoietic stem cells. This in term enables mutant stem and progenitor cells to expand and take over the bone marrow, thus driving bone marrow failure. Interrupting the cell death signaling pathway or altering the inflammatory signaling pathway has the potential to prevent cell death and re establish bone marrow homeostasis for therapeutic benefit. Aim 1: Will evaluate cell death and cytokine signaling in genetic mouse models of unrestrained necroptosis, as well as MDS mutations, to identify the molecular decision drivers, and how these drivers alter bone marrow cell death Aim 2: Will determine whether inhibiting necrosis or inflammatory signaling in HSC and progenitor cells in the above mouse models by inhibiting necrosis signaling (Rip1/Rip3 inhibitors) or inhibiting inflammatory signaling (Jak1/2 inhibitors) can reset hematopoietic homeostasis and prevent MDS bone marrow failure. Impact: The goal is to identify how HSCs and progenitor cells harboring MDS mutations execute cell death, and how they kill normal HSCs, and determine whether interrupting this cell death can rescue bone marrow function.