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Stress-triggered hematopoietic stem cell proliferation relies on Primpol-mediated repriming

ABSTRACT: Stem cell division is linked to tumorigenesis by yet-elusive mechanisms. The hematopoietic system reacts to stress by triggering stem and progenitor cell (HSPC) proliferation, which can be accompanied by chromosomal breakage in activated haematopoietic stem cells (HSCs). However, whether these lesions persist in their downstream progeny and induce a canonical DNA damage response (DDR) remained unclear. Inducing HSPC proliferation by simulated viral infection, we report that the associated DNA damage is restricted to HSCs and that proliferating HSCs rewire their DDR upon endogenous and clastogen-induced damage. Combining transcriptomics, single-cell and single-molecule assays on murine bone marrow cells, we found accelerated fork progression in stimulated HSPCs, reflecting engagement of Primpol-dependent repriming, at the expense of replication fork reversal. Ultimately, competitive bone marrow transplantation revealed the requirement of Primpol for efficient HSC amplification and bone marrow reconstitution. Hence, fine-tuning replication fork plasticity is essential to support stem cell functionality upon proliferation stimuli.

ORGANISM(S): Mus musculus

PROVIDER: GSE212580 | GEO | 2023/06/14

REPOSITORIES: GEO

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Project description:Activation of the MLL-ENL-ERtm oncogene initiates aberrant proliferation of myeloid progenitors. Here, we show induction of a fail-safe mechanism mediated by the DNA damage response (DDR) machinery that results in activation of the ATR/ATM-Chk1/Chk2-p53/p21 checkpoint and cellular senescence at early stages of cellular transformation caused by a regulatable MLL-ENL-ERtm in mice. Furthermore, we identified the transcription program underlying this intrinsic anti-cancer barrier, and DDR-induced inflammatory regulators that fine-tune the signaling towards senescence, thereby modulating the fate of MLL-ENL-immortalized cells in a tissue-environment-dependent manner. Our results indicate that DDR is a rate-limiting event for acquisition of stem cell-like properties in MLL-ENL-ERtm-mediated transformation, as experimental inhibition of the barrier accelerated the transition to immature cell states and acute leukemia development. We created a mouse model wherein the protein function of the MLL-ENL oncogene depends on tamoxifen due to fusion with the mutated estrogen-binding domain of the estrogen receptor (ERtm). After 7 months of tamoxifen administration, the MLL-ENL-ERtm mice developed a myeloproliferative disease, which progressed into the terminal stage after a long period (mean survival: 592 ± 112 days) of continuous tamoxifen provision. We have profiled gene expression at three time-points of tamoxifen treatment corresponding to three distinct cellular states of the MLL-ENL-ERtm-induced myeloproliferation in the bone marrow: 1. 7 months - high proliferation state with low DDR signaling (4 biological replicates), 2. 7-8 months - the transition period of lower proliferation and high DDR activity (4 biogical replicates) and 3. 8 months - the senescence (3 biological replicates). Time-matched tamoxifen-treated wild-type bone marrow analysed in 4 biological replicates. We have profiled gene expression in three disease stages in the spleen: 1. 7 months - early stage - induced proliferation and DDR (3 biological replicates), 2. 9-10 months - progression - partial senescence and DDR is maintained (3 biological replicates) and 3. 16-23 months - terminal stage - proliferation, low or absent DDR and no senescence (3 biological replicates). Time-matched tamoxifen-treated and age-matched wild-type spleens analysed in 5 biological replicates.

Project description:Background—Diabetes is a prevalent public health problem that affects about one third of the U.S. population and leads to serious vascular complications with increased risk for coronary artery disease. How bone marrow hematopoiesis contributes to diabetes complications is incompletely understood. We thus investigated the role of bone marrow endothelial cells in diabetic regulation of inflammatory myeloid cell production. Methods and Results—In three types of mouse diabetes, we observed enhanced proliferation of hematopoietic stem and progenitor cells (HSPC) leading to augmented circulating myeloid cell numbers. Analysis of bone marrow niche cells revealed that endothelial cells in diabetic mice expressed less Cxcl12, a retention factor promoting HSPC quiescence. Transcriptome-wide analysis of bone marrow endothelial cells demonstrated enrichment of genes involved in epithelial growth factor receptor (EGFR) signaling in mice with diet-induced diabetes. To explore whether endothelial EGFR plays a functional role in myelopoiesis, we generated mice with endothelial-specific deletion of EGFR (Cdh5Cre EGFRfl/fl). Unexpectedly, we found enhanced HSPC proliferation and increased myeloid cell production in Cdh5Cre EGFRfl/fl mice compared to wild type mice with diabetes. Disrupted EGFR signaling in endothelial cells decreased their expression of the HSPC retention factor angiopoietin-1. We tested the functional relevance of these findings for wound healing and atherosclerosis, both implicated in complications of diabetes. Inflammatory myeloid cells accumulated more in skin wounds of diabetic Cdh5Cre EGFRfl/fl mice, significantly delaying wound closure. Atherosclerosis accelerated in Cdh5Cre EGFRfl/fl mice, leading to larger and more inflamed atherosclerotic lesions in the aorta. Conclusions—In diabetes, bone marrow endothelial cells participate in the dysregulation of bone marrow hematopoiesis and promote cardiovascular complications via leukocyte overproduction. Specifically, diabetes reduces endothelial production of Cxcl12, a quiescence-promoting niche factor that reduces stem cell proliferation. We also describe a previously unknown counter-regulatory pathway, in which protective endothelial EGFR signaling curbs HSPC proliferation and myeloid cell production via angiopoietin-1.

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Stress-triggered hematopoietic stem cell proliferation relies on Primpol-mediated repriming

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