Mechanisms of TLR4-mediated impairment of murine and human HSC function

描述(由申请人提供)：血细胞生产受损与发病率和死亡率有关。血细胞补充的经典模型正在发生变化，人们意外地意识到，造血干细胞(HSCs)通过Toll样受体(Toll-like Receptor，TLRs)直接感知病原体并对其做出反应。在TLR刺激后，小鼠HSC增殖，并优先进行髓系特异性分化。对TLR配体的直接感应被认为使HSCs能够立即补充在急性感染期间迅速耗尽的固有免疫细胞。与短期激活HSC的潜在好处相比，慢性 刺激TLR显著损害HSC的长期功能。我们最近发现，在体内长期暴露于低剂量TLR4激动剂的小鼠HSCs失去淋巴潜能，变得精疲力竭，无法自我更新。这些发现很重要，因为TLRs可以被肥胖时升高的内源性脂肪酸激活，也可以被慢性感染患者中存在的血浆内毒素或细菌16S rDNA激活。与小鼠HSCs一样，体外研究表明，人HSCs在TLR刺激后被激活并表现出髓系偏向。然而，TLR刺激对体内人HSC功能的影响尚未确定。同样未知的是慢性TLR刺激扰乱HSC功能的机制(S)。在目标1中，我们在人源化的小鼠模型中检测了TLR4刺激对体内人HSCs自我更新和多谱系重建能力的影响。在目标2中，我们研究了TLR4驱动的HSC偏斜的机制。这些研究将首次在临床前模型中建立慢性TLR刺激对人类HSC能力的影响，并建立TLR刺激损害HSC功能的机制(S)。

DESCRIPTION (provided by applicant): Impaired production of blood cells is associated with morbidity and mortality. The classical model for blood cell replenishment is changing with the unexpected realization that hematopoietic stem cells (HSCs) directly sense and respond to pathogens via toll-like receptors (TLRs). Following TLR stimulation, murine HSCs proliferate and preferentially undergo myeloid-specific differentiation. Direct sensing of TLR ligand is thought to enable HSCs to immediately replenish innate immune cells that are rapidly depleted during acute infection. In contrast to the potential benefits of short-term HSC activation, chronic TLR stimulation dramatically impairs long-term HSC function. We have recently shown that murine HSCs chronically exposed to low-dose TLR4 agonist in vivo lose lymphoid potential, become exhausted, and fail to self renew. These findings are important because TLRs can be activated by endogenous fatty acids that are elevated in obesity as well as by plasma LPS or bacteria 16S rDNA which are present in patients with chronic infections. Like murine HSCs, in vitro studies show that human HSCs become activated and exhibit myeloid bias following TLR stimulation. However, the impact of TLR stimulation to human HSC function in vivo has not been established. Also unknown is the mechanism(s) by which chronic TLR stimulation perturbs HSC function. In Aim 1, we examine the impact of TLR4 stimulation to the self-renewal and multi-lineage reconstitution potential of human HSCs in vivo in a humanized mouse model. In Aim 2, we examine the mechanisms underlying TLR4-driven HSC skewing. These studies will be the first to establish the consequences of chronic TLR stimulation to human HSC competence in a pre-clinical model, and to establish the mechanism(s) by which TLR stimulation impairs HSC function.