Circulating Hematopoietic Stem and Progenitor Cells in Aging Atomic Bomb Survivors

New perspective of skeletal stem cells

Tissue-resident stem cells are a group of stem cells distinguished by their capacity for self-renewal and multilineage differentiation capability with tissue specificity. Among these tissue-resident stem cells, skeletal stem cells (SSCs) were discovered in the growth plate region through a combination of cell surface markers and lineage tracing series. With the process of unravelling the anatomical variation of SSCs, researchers were also keen to investigate the developmental diversity outside the long bones, including in the sutures, craniofacial sites, and spinal regions. Recently, fluorescence-activated cell sorting, lineage tracing, and single-cell sequencing have been used to map lineage trajectories by studying SSCs with different spatiotemporal distributions. The SSC niche also plays a pivotal role in regulating SSC fate, such as cell-cell interactions mediated by multiple signalling pathways. This review focuses on discussing the spatial and temporal distribution of SSCs, and broadening our understanding of the diversity and plasticity of SSCs by summarizing the progress of research into SSCs in recent years.

Restoration of aged hematopoietic cells by their young counterparts through instructive microvesicles release

This study addresses the potential to reverse age-associated morbidity by establishing methods to restore the aged hematopoietic system. Parabiotic animal models indicated that young secretome could restore aged tissues, leading us to establish a heterochronic transwell system with aged mobilized peripheral blood (MPB), co-cultured with young MPB or umbilical cord blood (UCB) cells. Functional studies and omics approaches indicate that the miRNA cargo of microvesicles (MVs) restores the aged hematopoietic system. The in vitro findings were validated in immune deficient (NSG) mice carrying an aged hematopoietic system, improving aged hallmarks such as increased lymphoid:myeloid ratio, decreased inflammation and cellular senescence. Elevated MYC and E2F pathways, and decreased p53 were key to hematopoietic restoration. These processes require four restorative miRs that target the genes for transcription/differentiation, namely PAX and phosphatase PPMIF. These miRs when introduced in aged cells were sufficient to restore the aged hematopoietic system in NSG mice. The aged MPBs were the drivers of their own restoration, as evidenced by the changes from distinct baseline miR profiles in MPBs and UCB to comparable expressions after exposure to aged MPBs. Restorative natural killer cells eliminated dormant breast cancer cells in vivo, indicating the broad relevance of this cellular paradigm - preventing and reversing age-associated disorders such as clearance of early malignancies and enhanced responses to vaccine and infection.

Human Transcriptomic Response to Mixed Neutron-Photon Exposures Relevant to an Improvised Nuclear Device

In the possible event of a detonation of an improvised nuclear device (IND), the immediate radiation would consist of both photons (gamma rays) and neutrons. Since neutrons generally have a high relative biological effectiveness (RBE) for most physiological end points, it is important to understand the effect that neutrons would have on the biodosimetry methods that are being developed for medical triage purposes. We previously compared the transcriptomic response in human blood after neutron and photon irradiation. In this study, we analyzed the effect of mixed-field-neutron-photon radiation on gene expression responses in human peripheral blood, to elucidate the neutron contribution in the setting of a radiation exposure from an IND detonation. We used four combinations of mixed neutron-photon exposures, with increasing percentages of neutrons, to a cumulative dose of 3 Gy. The mixed-field exposures consisted of 0%, 5%, 15% and 25% of neutrons, where 0% corresponds to 3 Gy of pure X rays. A maximum neutron exposure, corresponding to 83% neutrons (0.75 Gy) was also used in the study. Increases were observed in both the number and expression level of genes, with increasing percentages of neutrons from 0% to 25% in the mixed-field exposures. Gene ontology analysis showed an overall predominance of TP53 signaling among upregulated genes across all exposures. Some TP53 regulated genes, such as EDA2R, GDF15 and VWCE, demonstrated increased expression with increasing neutron percentages in mixed-field exposures. Immune response, specifically natural-killer-cell mediated signaling, was the most significant biological process associated with downregulated genes. We observed significant suppression of T-cell-mediated signaling in mixed-field exposures, which was absent in the response to pure photons. In this first study investigating gene expression in human blood cells exposed to mixed neutron-photon fields similar to an actual IND explosion, we have identified a number of genes responding to the 3 Gy dose that showed increasing expression as the neutron percentage increased. Such genes may serve as better indicators of the expected biological damage than a report of total physical dose, and thus provide more relevant information for treating physicians.

Lifelong Residual bone Marrow Damage in Murine Survivors of the Hematopoietic Acute Radiation Syndrome (H-ARS): A Compilation of Studies Comprising the Indiana University Experience

Accurate analyses of the delayed effects of acute radiation exposure in survivors of the hematopoietic acute radiation syndrome are hampered by low numbers of mice for examination due to high lethality from the acute syndrome, increased morbidity and mortality in survivors, high cost of husbandry for long-term studies, biological variability, and inconsistencies of models from different laboratories complicating meta-analyses. To address this, a compilation of 38 similar hematopoietic acute radiation syndrome studies conducted over a 7-y period in the authors' laboratory, comprising more than 1,500 irradiated young adult C57BL/6 mice and almost 600 day-30 survivors, was assessed for hematopoietic delayed effects of acute radiation exposure at various times up to 30 mo of age. Significant loss of long-term repopulating potential of phenotypically defined primitive hematopoietic stem cells was documented in hematopoietic acute radiation syndrome survivors, as well as significant decreases in all hematopoietic lineages in peripheral blood, prominent myeloid skew, significantly decreased bone marrow cellularity, and numbers of lineage-negative Sca-1+ cKit+ CD150+ cells (KSL CD150+; the phenotype known to be enriched for hematopoietic stem cells), and increased cycling of KSL CD150+ cells. Studies interrogating the phenotype of bone marrow cells capable of initiation of suspension cultures and engraftment in competitive transplantation assays documented the phenotype of hematopoietic stem cells in hematopoietic acute radiation syndrome survivors to be the same as that in nonirradiated age-matched controls. This compilation study adds rigor and validity to our initial findings of persistent hematopoietic dysfunction in hematopoietic acute radiation syndrome survivors that arises at the level of the hematopoietic stem cell and which affects all classes of hematopoietic cells for the life of the survivor.

Radiation- and Age-Associated Changes in Peripheral Blood Dendritic Cell Populations among Aging Atomic Bomb Survivors in Japan

Previous immunological studies in atomic bomb survivors have suggested that radiation exposure leads to long-lasting changes, similar to immunological aging observed in T-cell-adaptive immunity. However, to our knowledge, late effects of radiation on dendritic cells (DCs), the key coordinators for activation and differentiation of T cells, have not yet been investigated in humans. In the current study, we hypothesized that numerical and functional decreases would be observed in relationship to radiation dose in circulating conventional DCs (cDCs) and plasmacytoid DCs (pDCs) among 229 Japanese A-bomb survivors. Overall, the evidence did not support this hypothesis, with no overall changes in DCs or functional changes observed with radiation dose. Multivariable regression analysis for radiation dose, age and gender effects revealed that total DC counts as well as subpopulation counts decreased in relationship to increasing age. Further analyses revealed that in women, absolute numbers of pDCs showed significant decreases with radiation dose. A hierarchical clustering analysis of gene expression profiles in DCs after Toll-like receptor stimulation in vitro identified two clusters of participants that differed in age-associated expression levels of genes involved in antigen presentation and cytokine/chemokine production in cDCs. These results suggest that DC counts decrease and expression levels of gene clusters change with age. More than 60 years after radiation exposure, we also observed changes in pDC counts associated with radiation, but only among women.

Relationship between spontaneous γH2AX foci formation and progenitor functions in circulating hematopoietic stem and progenitor cells among atomic-bomb survivors

Accumulated DNA damage in hematopoietic stem cells is a primary mechanism of aging-associated dysfunction in human hematopoiesis. About 70 years ago, atomic-bomb (A-bomb) radiation induced DNA damage and functional decreases in the hematopoietic system of A-bomb survivors in a radiation dose-dependent manner. The peripheral blood cell populations then recovered to a normal range, but accompanying cells derived from hematopoietic stem cells still remain that bear molecular changes possibly caused by past radiation exposure and aging. In the present study, we evaluated radiation-related changes in the frequency of phosphorylated (Ser-139) H2AX (γH2AX) foci formation in circulating CD34-positive/lineage marker-negative (CD34+Lin-) hematopoietic stem and progenitor cells (HSPCs) among 226Hiroshima A-bomb survivors. An association between the frequency of γH2AX foci formation in HSPCs and the radiation dose was observed, but the γH2AX foci frequency was not significantly elevated by past radiation. We found a negative correlation between the frequency of γH2AX foci formation and the length of granulocyte telomeres. A negative interaction effect between the radiation dose and the frequency of γH2AX foci was suggested in a proportion of a subset of HSPCs as assessed by the cobblestone area-forming cell assay (CAFC), indicating that the self-renewability of HSPCs may decrease in survivors who were exposed to a higher radiation dose and who had more DNA damage in their HSPCs. Thus, although many years after radiation exposure and with advancing age, the effect of DNA damage on the self-renewability of HSPCs may be modified by A-bomb radiation exposure.