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

描述（由申请人提供）：血细胞产生受损与发病率和死亡率相关。血细胞补充的经典模型正在发生变化，造血干细胞（HSC）通过Toll样受体（TLR）直接感知和响应病原体。TLR刺激后，鼠HSC增殖并优先进行骨髓特异性分化。TLR配体的直接感测被认为使HSC能够立即补充在急性感染期间迅速耗尽的先天免疫细胞。与短期HSC活化的潜在益处相比，慢性HSC活化的潜在益处是长期的。 TLR刺激显著损害HSC的长期功能。我们最近的研究表明，长期暴露于低剂量TLR4激动剂的鼠HSC在体内失去了淋巴潜能，变得疲惫不堪，不能自我更新。这些发现是重要的，因为TLR可以被肥胖症中升高的内源性脂肪酸以及慢性感染患者中存在的血浆LPS或细菌16S rDNA激活。与鼠HSC一样，体外研究表明，人HSC在TLR刺激后变得活化并表现出髓样偏向。然而，TLR刺激对体内人HSC功能的影响尚未确定。慢性TLR刺激扰乱HSC功能的机制也是未知的。在目的1中，我们在人源化小鼠模型中检查TLR4刺激对人HSC体内自我更新和多谱系重建潜力的影响。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确定慢性TLR刺激对人HSC能力的影响，并确定TLR刺激损害HSC功能的机制。

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.