Restoring bone marrow niche function rejuvenates aged hematopoietic stem cells by reactivating the DNA Damage Response [3]. Restoring bone marrow niche function rejuvenates aged hematopoietic stem cells by reactivating the DNA Damage Response [3]

The bone marrow (BM) niche comprised of BM endothelial cells (BMECs) and LepR+ mesenchymal stromal cells (MSCs), plays a critical role in preserving the fitness of hematopoietic stem cells (HSCs). Aging is associated with defects in the BM niche that impair their ability to support HSC activity. However, mechanisms underlying age-related defects in the BM niche remain poorly understood. In this study, we identify BM niche derived Netrin-1 (NTN1) as a critical regulator of BM niche cell fitness during aging. Conditional deletion of NTN-1 specifically within BM MSCs or BMECs of young mice resulted in premature aging phenotypes within the BM niche including increased vascular leakiness, hypoxia, DNA damage and adiposity. On the other hand, supplementation of aged mice with NTN1 resulted in restoration of these hallmark niche defects and a rejuvenation of HSC activity. Mechanistically, we identify NTN1 as a critical regulator of DNA Damage Response (DDR) within BM niche cells and HSCs. In this experiment, RNA Seq analysis was performed on BMECs derived from young (3 month old) and aged (18 month old) mice to characterize transcriptional alterations within BMECs during aging. Overall design: Comparative gene expression profiling analysis of BMECs derived from young (3 month old) and aged (18 month old) mice

由骨髓（BM）内皮细胞（BMECs）和瘦素受体阳性（LepR+）间充质基质细胞（MSCs）构成的骨髓龛，在维持造血干细胞（HSCs）的功能活性方面发挥关键作用。衰老与骨髓龛的功能缺陷密切相关，此类缺陷会削弱其支持造血干细胞活性的能力。然而，骨髓龛中与衰老相关的缺陷背后的分子机制仍不甚明晰。本研究鉴定出骨髓龛来源的Netrin-1（NTN1）是衰老过程中调控骨髓龛细胞功能稳态的关键因子。在年轻小鼠的骨髓间充质基质细胞或骨髓内皮细胞中特异性条件性敲除NTN1，可诱导骨髓龛出现早衰表型，具体包括血管渗漏、缺氧、DNA损伤及脂肪堆积。与之相反，对衰老小鼠补充NTN1，则能够修复上述标志性的骨髓龛缺陷，并使造血干细胞活性实现年轻化。从机制层面分析，本研究证实Netrin-1（NTN1）是骨髓龛细胞及造血干细胞内DNA损伤应答（DDR）的关键调控因子。本实验针对取自年轻（3月龄）及衰老（18月龄）小鼠的骨髓内皮细胞开展RNA测序（RNA Seq）分析，以解析衰老过程中骨髓内皮细胞内的转录组变化。整体实验设计：对取自年轻（3月龄）及衰老（18月龄）小鼠的骨髓内皮细胞进行比较基因表达谱分析。