Hematopoietic Stem Cell Senescence

描述(申请人提供)：衰老小鼠的造血干细胞(HSC)优先失去再生适应性免疫系统的能力。这种偏向于生产髓系细胞和其他HSC异常可能是人类免疫衰老的原因之一。也就是说，老年人对疫苗接种的反应质量可能很差或不合适。导致这些变化的环境和潜在机制在很大程度上是未知的。虽然HSC受到化疗、放射、DNA修复缺陷、端粒酶缺失和细胞因子升高的损害，但在这些情况下尚未见有选择性淋巴生成潜力丧失的报道。相比之下，我们发现反复暴露于极低剂量脂多糖的小鼠的HSC中出现了髓系扭曲、自我更新缺陷和其他与年龄相关的变化。尽管这些动物总体上健康状况良好，HSC数量也是正常的。这些值得注意的发现表明，持续的低级别感染和相关的病原体产物可能会导致HSC衰老，并最终损害免疫力。与组织损伤和肥胖相关的内源性Toll样受体(TLR)配体可能引起类似的HSC变化。我们现在将确定这种现象是否发生在其他TLR配体和炎症性肠病(IBD)的动物模型中。此外，我们还将探讨损害HSC的方法。预计这些发现将对正常衰老以及许多可能加速免疫衰老的慢性疾病，如艾滋病毒/艾滋病，提供信息。此外，也可能发现一些血液系统恶性肿瘤的模式随年龄的变化而改变的基础。 与公共卫生相关：我们的免疫系统在老年时会变得不那么有效，有新的证据表明，这可能是由低级别感染史造成的。更多的研究可能会揭示如何阻止甚至逆转这些衰老的后果。

DESCRIPTION (provided by applicant): Hematopoietic stem cells (HSC) in aging mice preferentially lose the ability to regenerate the adaptive immune system. This skewing towards production of myeloid cells and other HSC abnormalities may contribute to the immunosenescence seen in humans. That is, the quality of responses to vaccination can be poor or inappropriate in aged individuals. The circumstances that elicit these changes and the underlying mechanisms are largely unknown. While HSC are harmed by chemotherapy, radiation, DNA repair defects, loss of telomerase and elevated cytokines, selective loss of lymphopoietic potential has not been reported in those circumstances. In contrast, we have found myeloid skewing, defective self-renewal and other age-related changes in HSC recovered from mice repeatedly exposed to very low doses of lipopolysaccharide. This is despite the fact that the animals were in generally good health and numbers of HSC were normal. These remarkable findings suggest that persistent low-grade infections and associated pathogen products might cause HSC senescence and ultimately compromise immunity. It is possible that similar HSC changes are caused by endogenous Toll- like receptor (TLR) ligands associated with tissue damage and obesity. We will now determine if the phenomenon occurs with other TLR ligands and in an animal model of inflammatory bowel disease (IBD). Additionally, we will explore the means through which HSC are harmed. The findings are expected to be informative about normal aging as well as many chronic conditions such as HIV/AIDS that may accelerate immunosenescence. Also, a basis may be found for age-related shifts in patterns of some hematopoietic malignancies. PUBLIC HEALTH RELEVANCE: Our immune systems become less effective in old age, and there is new evidence to suggest this can result from a history of low-grade infections. More study could reveal how to block or even reverse these consequences of aging.