The global clonal complexity of the murine blood system declines throughout life and after serial transplantation

Abstract

Although many recent studies describe the emergence and prevalence of “clonal hematopoiesis of indeterminate potential” in aged human populations, a systematic analysis of the numbers of clones supporting steady-state hematopoiesis throughout mammalian life is lacking. Previous efforts relied on transplantation of “barcoded” hematopoietic stem cells (HSCs) to track the contribution of HSC clones to reconstituted blood. However, ex vivo manipulation and transplantation alter HSC function and thus may not reflect the biology of steady-state hematopoiesis. Using a noninvasive in vivo color-labeling system, we report the first comprehensive analysis of the changing global clonal complexity of steady-state hematopoiesis during the natural murine lifespan. We observed that the number of clones (ie, clonal complexity) supporting the major blood and bone marrow hematopoietic compartments decline with age by ∼30% and ∼60%, respectively. Aging dramatically reduced HSC in vivo–repopulating activity and lymphoid potential while increasing functional heterogeneity. Continuous challenge of the hematopoietic system by serial transplantation provoked the clonal collapse of both young and aged hematopoietic systems. Whole-exome sequencing of serially transplanted aged and young hematopoietic clones confirmed oligoclonal hematopoiesis and revealed mutations in at least 27 genes, including nonsense, missense, and deletion mutations in Bcl11b, Hist1h2ac, Npy2r, Notch3, Ptprr, and Top2b.

In vivo dynamics of human hematopoietic stem cells: novel concepts and future directions

“…Recently, reduction of HSC clones and lymphoid potential was observed in HSPC compartments of aged vs young mice through in vivo labeling of HSPC. 66 Interestingly, stress induced by serial transplantations resulted in clonal collapse in both groups of animals, implying that continuous challenging of the hematopoietic compartment during the entire life of a subject would be one of the major drivers of HSPC aging.…”

Clones assemble! The clonal complexity of blood during ontogeny and disease

“…Interestingly, we also observed an expansion and contraction of clonal pools over the life span of individual mice, supporting a model of PB clonal instability and/or clonal succession during native hematopoiesis. Finally, the clonal complexity of HSCs mirrors that of MPPs throughout life, but diverges significantly from that of downstream HSPCs with aging, suggesting that apex HSCs consistently give rise to MPPs throughout aging, but that downstream progenitors behave more stochastically in terms of their lineage output with age [87].…”

“…[87] is the only current study to follow the clonal complexity of the hematopoietic system throughout the mammalian lifespan. Here, the Confetti reporter allele (as described in the previous section) [37] was utilized to label hematopoietic clones during embryogenesis and then track global clonal complexity from 2 to 26 months of age utilizing statistical modeling [87]. Clonal complexity in the peripheral blood (PB) dropped by 30% by 26 months of age.…”

“…They confirmed that steady-state hematopoiesis in humans results from many clones that originate during embryonic development [49,50,84] and that 50,000−200,000 clones contribute to native hematopoiesis in adulthood [94] (dynamics similar to those seen in mice by Ganuza et al . [87]). The authors also report the existence of hematopoietic clones with persistent myeloid and B-lymphocyte output throughout life, whereas the clonal dynamics of T lymphocytes were less clear [94].…”

Quantifying Hematopoietic Stem Cell Clonal Diversity by Selecting Informative Amplicon Barcodes

“…HSC clonal diversity has important implications for the study of hematopoiesis and blood disorders [2][3][4][5][6] . Methods for estimating HSC clonal diversity include counting viral integration sites in transduced bone marrow 7 , single-cell or limiting dilution transplantation [8][9][10][11] , sequencing transposon insertion sites 12 , SNP analysis in genomic 13,14 or mtDNA 15 , and genetic barcoding using CRISPR/Cas9 or Cre-Lox-based recombination [16][17][18][19][20][21][22][23][24] . An ideal method would sample a large fraction of the HSCs in an organism, be able to discriminate many clones with little or no ambiguity, and would mark HSC clones without causing any alteration in cell function.…”