Aspp1 Preserves Hematopoietic Stem Cell Pool Integrity and Prevents Malignant Transformation

Quiescent hematopoietic stem cells (HSCs) are prone to mutagenesis, and accumulation of mutations can result in hematological malignancies. The mechanisms through which HSCs prevent such detrimental accumulation, however, are unclear. Here, we show that Aspp1 coordinates with p53 to maintain the genomic integrity of the HSC pool. Aspp1 is preferentially expressed in HSCs and restricts HSC pool size by attenuating self-renewal under steady state conditions. After genotoxic stress, Aspp1 promotes HSC cycling and induces p53-dependent apoptosis in cells with persistent DNA damage foci. Beyond these p53-dependent functions, Aspp1 attenuates HSC self-renewal and accumulation of DNA damage in p53-null HSCs. Consequently, concomitant loss of Aspp1 and p53 leads to the development of hematological malignancies, especially T-cell leukemia and lymphoma. Together, these data highlights coordination between Aspp1 and p53 in regulating HSC self-renewal and DNA damage tolerance, and suggest that HSCs possess specific mechanisms that prevent accumulation of mutations and malignant transformation. 8-week-old WT, Aspp1-/-, Mx1-Cre(+)p53flox/flox and Mx1-Cre(+)Aspp1-/-p53flox/flox mice were intraperitoneally administered with 400 μg pIpC five times every other day to obtain WT, Aspp1-/-, p53-/- and Aspp1-/-p53-/- bone marrow. 4 weeks after pIpC treatment, bone marrow lineage(-) Sca-1(+) cKit(+) cells were isolated. RNA was extracted and pooled from 3 independent mice per genotype. RNA samples were then amplified, labeled, and hybridized to independent arrays.

静息态造血干细胞（Quiescent hematopoietic stem cells, HSCs）易发生诱变，突变积累可引发血液系统恶性肿瘤。然而，造血干细胞防止此类有害突变积累的机制尚不清楚。本研究证实，Aspp1与p53协同维持造血干细胞池的基因组完整性。Aspp1在造血干细胞中优先表达，并通过在稳态条件下减弱自我更新来限制造血干细胞池的大小。在遗传毒性应激后，Aspp1促进造血干细胞周期进程，并在存在持续性DNA损伤灶的细胞中诱导p53依赖性凋亡。除上述p53依赖性功能外，Aspp1还可在p53缺失的造血干细胞中减弱其自我更新并减少DNA损伤积累。因此，Aspp1与p53共同缺失会导致血液系统恶性肿瘤的发生，尤其是T细胞白血病和淋巴瘤。综上，本研究结果揭示了Aspp1与p53在调控造血干细胞自我更新及DNA损伤耐受中的协同作用，表明造血干细胞具备特定机制以阻止突变积累与恶性转化。

我们对8周龄的野生型（WT）、Aspp1基因敲除（Aspp1-/-）、Mx1-Cre(+)p53flox/flox及Mx1-Cre(+)Aspp1-/-p53flox/flox小鼠，每隔一天腹腔注射400 μg聚肌胞苷酸（pIpC），共注射5次，以获得野生型、Aspp1-/-、p53基因敲除（p53-/-）及Aspp1-/-p53-/-骨髓细胞。聚肌胞苷酸处理4周后，分离骨髓谱系阴性（Lin⁻）、Sca-1阳性（Sca-1(+)）、cKit阳性（cKit(+)）细胞。提取各基因型3只独立小鼠的RNA并混合，随后对RNA样本进行扩增、标记，并分别与独立的基因芯片进行杂交。