Concerted roles of PTEN and ATM in controlling hematopoietic stem cell fitness and dormancy

In order to sustain proficient life-long hematopoiesis, hematopoietic stem cells (HSCs) must possess robust mechanisms to preserve their quiescence and genome integrity. DNA-damaging stress can perturb HSC homeostasis by affecting their survival, self-renewal and differentiation. Ablation of the kinase ATM, a master regulator of the DNA damage response, impairs HSC fitness. Paradoxically, we show here that loss of a single allele of Atm enhances HSC functionality in mice. To explain this observation, we explored a possible link between ATM and the tumor suppressor PTEN, which also regulates HSC function. We generated and analyzed a knock-in mouse line (PtenS398A/S398A), in which PTEN cannot be phosphorylated by ATM. Similar to Atm+/-, PtenS398A/S398A HSCs have enhanced hematopoietic reconstitution ability, accompanied by resistance to apoptosis induced by genotoxic stress. Single-cell transcriptomic analyses and functional assays revealed that dormant PtenS398A/S398A HSCs aberrantly tolerate elevated mitochondrial activity and the accumulation of reactive oxygen species, which are normally associated with HSC priming for self-renewal or differentiation. Our results unveil a molecular connection between ATM and PTEN, which couples the response to genotoxic stress and dormancy in HSC. Long-term hematopoietic stem cells (Lin-Sca1+cKit+CD48-CD150+) were sorted from pools of 3 male and 3 female mice per genotype (Pten+/+ and PtenS398A/S398A). Cells were sorted directly onto the cell loading inlet of the C1 chip. The raw data had a total of 280 cells. After quality control analyses, a total of 206 cells (116 Pten+/+ cells and 90 PtenS398A/S398A) were retained for further downstream analyses.