B Cell Development in Aging

说明(申请人提供)：老龄化与疫苗接种效果降低以及肺炎球菌、流感和西尼罗河病毒等病原体感染后发病率和死亡率增加有关。多个获得性缺陷可能导致老年人产生针对新遇到的病原体的保护性抗体的能力降低。在老年小鼠中，负责产生对初次感染的保护性抗体的滤泡(FO)B细胞的数量减少，这与造血干细胞(HSCs)的FO B细胞的生成能力降低有关。因此，B淋巴细胞生成减少可能是与衰老相关的对新发现的病原体的体液免疫下降的原因。类似的缺陷似乎也存在于人类身上，来自老年成人捐赠者的移植骨髓(BM)干细胞往往无法产生B细胞。这种B淋巴更年期的分子基础尚不清楚。我们的长期目标是了解这一缺陷并开发出纠正它的方法。尽管老年小鼠比年轻小鼠含有明显更多的HSCs，但这些细胞表现出基因转录失调和产生B细胞的选择性损害。HSCs的造血细胞发育通过转录因子的有序表达/功能序列进行，转录因子控制着谱系的指定、承诺和进展。这一系列事件在一定程度上是由参与这些过程的基因的染色质可及性控制的。染色质的可及性由组蛋白修饰(如乙酰化、甲基化、磷酸化等)调节。和DNA CpG二核苷酸的甲基化。关于影响早期造血步骤的组蛋白修饰和DNA甲基化的模式，以及这些模式在衰老过程中可能如何改变，人们知之甚少。在这里，我们建议解决这样的假设，即老年HSCs转录失调和缺陷B细胞的产生能力是表观遗传学变化和随之而来的基因组不稳定的结果。我们的方法将涉及使用体外HSC以及来自免疫老年或年轻小鼠的有条件转化的HSC系。后者保留了原始成体干细胞的功能表型，并为生化研究提供了无限的材料。此外，可以对这些细胞进行遗传操作，以确定特定变化在HSC缺陷中的作用。这些造血干细胞的B细胞发育将在体内和OP9培养系统中进行研究，在该培养系统中，与衰老相关的B淋巴细胞缺陷被复制。与公共卫生相关：一定比例的老年人由于后天免疫缺陷而生活质量不佳，这些缺陷降低了他们抵抗感染的能力。这些人需要更多的医疗护理和住院治疗，主要是在经济方面影响公共健康。我们的研究将试图确定这种免疫力下降的基础和纠正它的策略。

DESCRIPTION (provided by applicant): Aging is associated with decreased efficacy of vaccination, and increased morbidity and mortality following infection by agents such as pneumococcus, influenza and West Nile virus. Multiple acquired defects may contribute to the reduced ability of elderly individuals to produce protective antibodies against newly encountered pathogens. In aged mice, follicular (FO) B cells responsible for generation of protective antibodies to primary infection are reduced in numbers, and this is correlated with reduction in the FO B cell generative capacity of hematopoietic stem cells (HSCs). Thus, decreased B lymphopoiesis may be causal in the aging- associated decline in humoral immunity to newly encountered pathogens. A similar defect appears to exist in humans where transplanted bone marrow (BM) stem cells from older adult human donors often fail to give rise to B cells. The molecular basis of this B lymphopause is unknown. It is our long-term goal to understand this defect and develop approaches to correct it. Although aged mice contain significantly more HSCs than their young counterparts, these cells exhibit dysregulation of gene transcription and selective impairment in the ability to give rise to B cells. Hematopoietic cell development from HSCs proceeds through an ordered sequence of expression/function of transcription factors, which control lineage specification, commitment and progression. This sequence of events is controlled, in part, by chromatin accessibility of the genes involved in these processes. Chromatin accessibility is regulated by histone modification (e.g. acetylation, methylation, phosphorylation, etc.) and methylation of DNA CpG dinucleotides. Little is known regarding the patterns of histone modification and DNA methylation that impact early steps in hematopoiesis, and how these patterns might be altered during aging. Here we propose to address the hypotheses that dysregulation of transcription and defective B cell generative capacity of aged HSCs is the consequence of epigenetic changes and attendant genomic destabilization. Our approach will involve the use of ex vivo HSCs as well as conditionally transformed HSC lines derived from immunologically aged or young mice. The latter retain the functional phenotype of the originating adult stem cells, and provide an unlimited supply of material for biochemical studies. Further, these cells can be manipulated genetically to establish the role of specific alterations in HSC defects. B cell development from these HSCs will be studied both in vivo and in the OP9 culture system in which aging-associated B lymphopoietic defects are replicated. PUBLIC HEALTH RELEVANCE: A proportion of aged individuals suffer poor quality of life due to acquired immune defects that reduce their ability to fight infection. Such people require increased medical care and hospitalization, impacting public health primarily in economic terms. Our studies will attempt to define the basis of this immune decline and strategies to correct it.