Reversibility of Defective Hematopoiesis Caused by Telomere Shortening in Telomerase Knockout Mice

Aparna Raval,Gregory K Behbehani,John Ramunas,Le Xuan Truong Nguyen,Garry P Nolan,Helen Blau,Brenda Kusler,Christopher Y Park,Colin Holbrook,Alina Garbuzov,Beverly S Mitchell,Steven E Artandi,Daniel Thomas,Gabriele Saretzki

doi:10.1371/journal.pone.0131722

Abstract

Telomere shortening is common in bone marrow failure syndromes such as dyskeratosis congenita (DC), aplastic anemia (AA) and myelodysplastic syndromes (MDS). However, improved knowledge of the lineage-specific consequences of telomere erosion and restoration of telomere length in hematopoietic progenitors is required to advance therapeutic approaches. We have employed a reversible murine model of telomerase deficiency to compare the dependence of erythroid and myeloid lineage differentiation on telomerase activity. Fifth generation Tert-/- (G5 Tert-/-) mice with shortened telomeres have significant anemia, decreased erythroblasts and reduced hematopoietic stem cell (HSC) populations associated with neutrophilia and increased myelopoiesis. Intracellular multiparameter analysis by mass cytometry showed significantly reduced cell proliferation and increased sensitivity to activation of DNA damage checkpoints in erythroid progenitors and in erythroid-biased CD150hi HSC, but not in myeloid progenitors. Strikingly, Cre-inducible reactivation of telomerase activity restored hematopoietic stem and progenitor cell (HSPC) proliferation, normalized the DNA damage response, and improved red cell production and hemoglobin levels. These data establish a direct link between the loss of TERT activity, telomere shortening and defective erythropoiesis and suggest that novel strategies to restore telomerase function may have an important role in the treatment of the resulting anemia.

Highlights

Telomeres are composed of repetitive TTAGGG sequences located at the ends of chromosomes [1, 2] and are essential for the preservation of genome integrity
Telomere shortening is common in dyskeratosis congenita (DC), AA and myelodysplastic syndromes (MDS) patients [30,31,32,33], but the specific consequences of telomere erosion for hematopoiesis have not been well-defined
Our data demonstrate that significant telomere shortening in late generation G5 Tert-/- mice results in impaired erythroid maturation and anemia and a significant reduction in both early and committed erythroid progenitors, as well as in the numbers of CD150hi-expressing hematopoietic stem cell (HSC) that are associated with erythroblast differentiation

Summary

Introduction

Telomeres are composed of repetitive TTAGGG sequences located at the ends of chromosomes [1, 2] and are essential for the preservation of genome integrity. Cell proliferation in the presence of very short telomeres can result in genomic instability, end-to-end chromosome fusions, translocations and aneuploidy [3, 4]. Critically shortened telomeres induce a DNA damage response (DDR) via the p53 pathway that may result in either senescence or apoptosis [5, 6]. Telomerase is expressed in embryonic stem cells and in highly proliferative cells like HSPC to prevent replicative senescence but is absent in most somatic cells, leading to progressive telomere shortening during cell division [10, 11]. A majority of cancer cells over-express telomerase, resulting in an “immortal” phenotype [12]

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