title: Replication stress is a potent driver of functional decline in ageing haematopoietic stem cells.
abstract: Haematopoietic stem cells (HSCs) self-renew for life, thereby making them one of the few blood cells that truly age. Paradoxically, although HSCs numerically expand with age, their functional activity declines over time, resulting in degraded blood production and impaired engraftment following transplantation. While many drivers of HSC ageing have been proposed, the reason why HSC function degrades with age remains unknown. Here we show that cycling old HSCs in mice have heightened levels of replication stress associated with cell cycle defects and chromosome gaps or breaks, which are due to decreased expression of mini-chromosome maintenance (MCM) helicase components and altered dynamics of DNA replication forks. Nonetheless, old HSCs survive replication unless confronted with a strong replication challenge, such as transplantation. Moreover, once old HSCs re-establish quiescence, residual replication stress on ribosomal DNA (rDNA) genes leads to the formation of nucleolar-associated γH2AX signals, which persist owing to ineffective H2AX dephosphorylation by mislocalized PP4c phosphatase rather than ongoing DNA damage. Persistent nucleolar γH2AX also acts as a histone modification marking the transcriptional silencing of rDNA genes and decreased ribosome biogenesis in quiescent old HSCs. Our results identify replication stress as a potent driver of functional decline in old HSCs, and highlight the MCM DNA helicase as a potential molecular target for rejuvenation therapies.
authors: 1] The Eli and Edythe Broad Center for Regenerative Medicine and Stem Cell Research, Department of Medicine, Hem/Onc Division, University of California San Francisco, San Francisco, California 94143, USA [2] Institute of Experimental Cancer Research, Comprehensive Cancer Center, 89081 Ulm, Germany.
authors: Johanna
authors: J
authors: Flach
authors: The Eli and Edythe Broad Center for Regenerative Medicine and Stem Cell Research, Department of Medicine, Hem/Onc Division, University of California San Francisco, San Francisco, California 94143, USA.
authors: Sietske T
authors: ST
authors: Bakker
authors: The Eli and Edythe Broad Center for Regenerative Medicine and Stem Cell Research, Department of Medicine, Hem/Onc Division, University of California San Francisco, San Francisco, California 94143, USA.
authors: Mary
authors: M
authors: Mohrin
authors: Center for Chromosome Biology, School of Natural Sciences, National University of Ireland Galway, Galway, Ireland.
authors: Pauline C
authors: PC
authors: Conroy
authors: The Eli and Edythe Broad Center for Regenerative Medicine and Stem Cell Research, Department of Medicine, Hem/Onc Division, University of California San Francisco, San Francisco, California 94143, USA.
authors: Eric M
authors: EM
authors: Pietras
authors: The Eli and Edythe Broad Center for Regenerative Medicine and Stem Cell Research, Department of Medicine, Hem/Onc Division, University of California San Francisco, San Francisco, California 94143, USA.
authors: Damien
authors: D
authors: Reynaud
authors: Spanish National Cancer Research Centre (CNIO), E-28049 Madrid, Spain.
authors: Silvia
authors: S
authors: Alvarez
authors: Department of Pathology, University of California San Francisco, San Francisco, California 94143, USA.
authors: Morgan E
authors: ME
authors: Diolaiti
authors: Institute for the Biology of Stem Cells, Department of Biomolecular Engineering, University of California Santa Cruz, Santa Cruz, California 95064, USA.
authors: Fernando
authors: F
authors: Ugarte
authors: Institute for the Biology of Stem Cells, Department of Biomolecular Engineering, University of California Santa Cruz, Santa Cruz, California 95064, USA.
authors: E Camilla
authors: EC
authors: Forsberg
authors: Section of Hematology/Oncology and the Comprehensive Cancer Center, University of Chicago, Chicago, Illinois 60637, USA.
authors: Michelle M
authors: MM
authors: Le Beau
authors: Department of Pathology, University of California San Francisco, San Francisco, California 94143, USA.
authors: Bradley A
authors: BA
authors: Stohr
authors: Spanish National Cancer Research Centre (CNIO), E-28049 Madrid, Spain.
authors: Juan
authors: J
authors: Méndez
authors: Center for Chromosome Biology, School of Natural Sciences, National University of Ireland Galway, Galway, Ireland.
authors: Ciaran G
authors: CG
authors: Morrison
authors: The Eli and Edythe Broad Center for Regenerative Medicine and Stem Cell Research, Department of Medicine, Hem/Onc Division, University of California San Francisco, San Francisco, California 94143, USA.
authors: Emmanuelle
authors: E
authors: Passegué
mesh_terms: D000818:Animals; D049109:Cell Proliferation; D016922:Cellular Senescence / Q000235:genetics / Q000502:physiology*; D004249:DNA Damage / Q000235:genetics; D004261:DNA Replication / Q000502:physiology*; D004275:DNA, Ribosomal / Q000235:genetics; D005260:Female; D005786:Gene Expression Regulation; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000473:pathology*; D006657:Histones / Q000235:genetics / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D064110:Minichromosome Maintenance Proteins / Q000235:genetics; D013312:Stress, Physiological
chemical_list: D004275:DNA, Ribosomal; D006657:Histones; D064110:Minichromosome Maintenance Proteins; C475961:gamma-H2AX protein, mouse