Concerted roles of PTEN and ATM in controlling hematopoietic stem cell fitness and dormancy. 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. Overall design: 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.