The influence of proteostasis loss in aging hematopoietic stem cells on leukemia initiation

摘要 这项建议的目标是了解蛋白质稳态(蛋白稳态)的丧失在衰老的造血过程中是如何 造血干细胞(HSCs)施加选择性压力，促进白血病的发生。损失 蛋白质平衡是最不为人所知的衰老标志之一，特别是当它与恶性肿瘤有关时 转型。随着生物体的衰老，错误折叠的蛋白质可能会在有丝分裂后的细胞中积累，或者在 很大程度上是静止的。这会给细胞带来压力，并可能推动重新平衡所需的适应性变化 蛋白质平衡。肝星状细胞特别容易失去蛋白平衡。成人造血干细胞的蛋白质含量很低。 相对于更频繁地分裂血统的血祖细胞的合成。这有助于保持 通过阻止错误折叠的蛋白质的生物发生来维持蛋白稳定，并需要维持成年HSC的自我 续订能力。然而，我们发现，衰老的HSC在体内经历了显著的蛋白质应激， 蛋白质的稳定必须通过基因表达和应激反应的改变来积极维持。 维持HSC自我更新活动和长寿的途径。在这方面，我们已经生成了初步数据。 证明了HSF1，一种关键的蛋白质平衡传感器，动态地重构蛋白质平衡网络 对应激的反应在老化的HSCs中被激活，在那里它需要减弱蛋白质的合成和 保留HSC自我更新能力。这些数据表明，衰老的HSCs必须主动维持蛋白质平衡，以 保持功能，蛋白平衡的丧失可能会产生促进克隆性造血的选择性压力 和白血病的启动。基于这些数据，我们假设蛋白质稳定性的丧失和维持的压力 衰老HSCs中的蛋白质平衡促进老年人克隆性造血和急性髓系白血病(AML)的启动 成年人。我们提出了两个目的来检验这一假设。在第一个目标中，我们将使用Aarssti/sti小鼠，它们有一个 TRNA编辑活性缺陷，破坏年轻和老年成年小鼠的蛋白质平衡。我们将测试一下 在衰老的背景下，蛋白质平衡的干扰加速了克隆性造血和AML的启动 Dnmt3aR878H和Tet2D/D突变。在第二个目标中，我们将测试HSF1的正常年龄相关激活是否会产生 在老化的造血干细胞中启动急性髓系白血病的许可环境。我们将有条件地删除年轻人和老年人中的HSF1 在Dnmt3aR878H突变和NrasG12D协同突变的情况下检测HSC 它促进了克隆性造血的出现，增加了老年人AML的发病率。这些 研究将开启新的调查路线，以了解以前未被认识到的与年龄相关的肥胖之间的联系 蛋白质平衡(衰老的一个标志)和白血病的发生。缓解蛋白平衡功能障碍的治疗方法可能 在以后的生命中保存HSC的克隆多样性，同时降低对AML的易感性。

ABSTRACT The goal of this proposal is to understand how loss of protein homeostats (proteostasis) in aging blood-forming hematopoietic stem cells (HSCs) applies a selective pressure that promotes leukemia initiation. Loss of proteostasis is one of the least understood hallmarks of aging, particularly as it relates to malignant transformation. As an organism ages, misfolded proteins can accumulate in post-mitotic cells, or in cells that are largely quiescent. This stresses the cell and can drive adaptive changes that are required to rebalance proteostasis. HSCs are particularly susceptible to a loss of proteostasis. Adult HSCs have low rates of protein synthesis relative to more frequently dividing lineage-committed blood progenitors. This helps maintain proteostasis by preventing the biogenesis of misfolded proteins, and it is required to maintain adult HSC self- renewal capacity. However, we have discovered that aged HSCs experience significant protein stress in vivo, and proteostasis must be actively maintained through changes in gene expression and stress-response pathways to sustain HSC self-renewal activity and longevity. In this regard, we have generated preliminary data demonstrating that Hsf1, a critical proteostasis sensor that dynamically remodels the proteostasis network in response to stress, is activated within aging HSCs where it is required to attenuate protein synthesis and preserve HSC self-renewal capacity. These data indicate that aged HSCs must actively maintain proteostasis to remain functional, and loss of proteostasis may create a selective pressure that promotes clonal hematopoiesis and leukemia initiation. Based on these data, we hypothesize that a loss of proteostasis and pressure to maintain proteostasis in aging HSCs promotes clonal hematopoiesis and acute myeloid leukemia (AML) initiation in older adults. We propose two aims to test this hypothesis. In the first aim, we will use Aarssti/sti mice, which have a defect in tRNA editing activity, to disrupt proteostasis in young and old adult mice. We will test whether proteostasis disruption accelerates clonal hematopoiesis and AML initiation during aging in the setting of Dnmt3aR878H and Tet2D/D mutations. In the second aim, we will test if normal age-related activation of Hsf1 creates a permissive context for AML initiation in aging HSCs. We will conditionally delete Hsf1 in young and old adult HSCs in the setting of a Dnmt3aR878H mutation with and without a cooperating NrasG12D mutation to determine if it contributes to the emergence of clonal hematopoiesis and increased incidence of AML in older adults. These studies will open new lines of investigation into a previously unappreciated link between age-related loss of proteostasis (a hallmark of aging) and leukemia initiation. Therapies that mitigate proteostasis dysfunction could preserve HSC clonal diversity later in life while reducing susceptibility to AML.