The NFKB inducing kinase (NIK) modulates hematopoiesis during stress. Mus musculus

The genetic programs that maintain hematopoiesis during steady state in physiologic conditions are different from those activated during stress. Here we show that hematopoietic stem cells (HSCs) with deficiencies in components of the alternative NFkB pathway (the NFkB inducing kinase, NIK, and the downstream molecule NFkB2) had a defect in response to stressors such as supraphysiological doses of cytokines, chemotherapy and hematopoietic transplantation. NIK-deficient mice had peripheral blood and bone marrow leukocyte numbers within normal ranges (except for the already reported defects in B-cell maturation), however, HSCs showed significantly slower expansion capacity in in vitro cultures compared to wild type HSCs. This was due to a delayed cell cycle and increased apoptosis. In vivo experiments showed that NIK-deficient HSCs did not recover at the same pace as controls when challenged with myeloablative chemotherapy. Finally, NIK-deficient HSCs showed a significantly decreased competitive repopulation capacity in vivo. Using HSCs from mice deficient in one of two downstream targets of NIK, i.e., either NFkB2 or c-Rel, only NFkB2 deficiency recapitulated the defects detected with NIK-deficient HSCs. Our results underscore the role of NIK and the alternative NFkB pathway for the recovery of normal levels of hematopoiesis after stress. Overall design: To explore the consequences of the defective NIKaly/aly protein in alternative NFKB signalling in HSCs, we investigated the gene expression profile of highly purified fresh LSK cells isolated from NIKWT and NIKaly/aly mice. We performed microarray analysis using total RNA from sorted LSK population using Agilent Whole Mouse Genome Oligo Microarrays.

生理稳态下维持造血功能的遗传程序，与应激状态下激活的遗传程序存在显著差异。本研究发现，携带非经典NF-κB通路（alternative NF-κB pathway）组分缺陷的造血干细胞（hematopoietic stem cells, HSCs）——其缺陷涉及NF-κB诱导激酶（NIK）与下游分子NF-κB2——对超生理剂量细胞因子、化疗及造血移植等应激原的应答存在缺陷。NIK缺陷小鼠的外周血与骨髓白细胞计数处于正常范围（除已有报道的B细胞成熟缺陷外），但与野生型HSCs相比，NIK缺陷HSCs的体外扩增能力显著降低，该缺陷源于细胞周期进程延缓与凋亡水平升高。体内实验显示，当接受清髓性化疗刺激时，NIK缺陷HSCs的恢复速度显著慢于对照组。此外，NIK缺陷HSCs的体内竞争性重建造血能力显著下降。通过使用携带NIK两个下游靶标（NF-κB2或c-Rel）其中之一缺陷的HSCs开展实验，仅NF-κB2缺陷可重现NIK缺陷HSCs所表现出的全部缺陷表型。本研究结果证实，NIK及非经典NF-κB通路在应激后正常造血功能恢复过程中发挥关键作用。实验整体设计：为探究缺陷型NIKaly/aly蛋白对HSCs中非经典NF-κB信号通路的影响，我们对从NIK野生型（NIKWT）及NIKaly/aly小鼠体内分离的高纯度新鲜LSK细胞进行基因表达谱分析。本研究采用安捷伦（Agilent）全小鼠基因组寡核苷酸微阵列，对分选得到的LSK细胞群体的总RNA进行微阵列分析。