Hematopoietic stem cells are acutely sensitive to Acd shelterin gene inactivation
Morgan Jones, … , Catherine E. Keegan, Ivan Maillard
Morgan Jones, … , Catherine E. Keegan, Ivan Maillard
Published December 9, 2013
Citation Information: J Clin Invest. 2014;124(1):353-366. https://doi.org/10.1172/JCI67871.
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Research Article Hematology

Hematopoietic stem cells are acutely sensitive to Acd shelterin gene inactivation

Abstract

The shelterin complex plays dual functions in telomere homeostasis by recruiting telomerase and preventing the activation of a DNA damage response at telomeric ends. Somatic stem cells require telomerase activity, as evidenced by progressive stem cell loss leading to bone marrow failure in hereditary dyskeratosis congenita. Recent work demonstrates that dyskeratosis congenita can also arise from mutations in specific shelterin genes, although little is known about shelterin functions in somatic stem cells. We found that mouse hematopoietic stem cells (HSCs) are acutely sensitive to inactivation of the shelterin gene Acd, encoding TPP1. Homozygosity for a hypomorphic acd allele preserved the emergence and expansion of fetal HSCs but led to profoundly defective function in transplantation assays. Upon complete Acd inactivation, HSCs expressed p53 target genes, underwent cell cycle arrest, and were severely depleted within days, leading to hematopoietic failure. TPP1 loss induced increased telomeric fusion events in bone marrow progenitors. However, unlike in epidermal stem cells, p53 deficiency did not rescue TPP1-deficient HSCs, indicating that shelterin dysfunction has unique effects in different stem cell populations. Because the consequences of telomere shortening are progressive and unsynchronized, acute loss of shelterin function represents an attractive alternative for studying telomere crisis in hematopoietic progenitors.

Authors

Morgan Jones, Gail Osawa, Joshua A. Regal, Daniel N. Weinberg, James Taggart, Hande Kocak, Ann Friedman, David O. Ferguson, Catherine E. Keegan, Ivan Maillard

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Figure 9

p53 inactivation does not rescue the survival and function of Acd-deficient HSCs.

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p53 inactivation does not rescue the survival and function of Acd-defic...
(A) Experimental design: lethally irradiated B6-CD45.1 mice were transplanted with BM from Mx-Cre+Acd+/–p53+/+, Mx-Cre+Acd+/–p53–/–, Mx-Cre+Acdfl/–p53+/+, or Mx-Cre+Acdfl/–p53–/– B6-CD45.2+ and WT B6-CD45.1 competitor mice (5 × 105 cells each, 1:1 ratio). After 6 weeks to allow for hematopoietic reconstitution, poly(I:C) was administered. (B) Flow cytometric analysis of peripheral blood 2–16 weeks after poly(I:C), administration showing a rapid drop in contribution of the CD45.2+Mx-Cre+Acdfl/–p53+/+ and Mx-Cre+Acdfl/–p53–/– grafts to the myeloid (CD11b+GR1+), T cell (CD3+), and B cell (CD19+B220+) compartments. Baseline chimerism was normalized to 100% in each mouse. The percentage of Mx-Cre+Acdfl/–p53+/+ and Mx-Cre+Acdfl/–p53–/–graft output differed significantly from Mx-Cre+Acd+/–p53+/+and Mx-Cre+Acd+/–p53–/– output in the myeloid compartment by week 2 (P < 0.001), in the T cell compartment by week 12 (P < 0.01), and in the B cell compartment by week 8 (P < 0.01). Data represent the mean ± SD (n ≥4 per group). (C) CD45.2/CD45.1 chimerism in CD150+CD48–Lin–Sca-1hicKithi LT-HSCs 16 weeks after poly(I:C) administration, showing no residual CD45.2+Mx-Cre+Acdfl/–p53+/+ or Mx-Cre+Acdfl/–p53–/– HSCs. Representative flow cytometry plots are shown. Numbers indicate the percentage of cells in each gate.