Metabolic Profile as a Potential Modifier of Long-Term Radiation Effects on Peripheral Lymphocyte Subsets in Atomic Bomb Survivors

Spermidine alleviates thymopoiesis defects and aging of the peripheral T-cell population in mice after radiation exposure

The T cell aging process can be modified by genotoxic factors, including ionizing radiation, and metabolic controls, such as caloric restriction; the former accelerates and the latter retards the process. However, the mechanisms by which these systemic factors interact to cause T cell aging remain unclear. This study investigated the naïve T-cell pool, thymic cellularity, and transcriptome in mice irradiated with 3.8 Gy at 5 weeks of age and treated 13 months later with 30 mM spermidine (SPD), a metabolism regulator. The number of conventional naïve CD4 and CD8 T cells in the peripheral blood decreased 14 months after irradiation whereas the number of virtual memory naïve T cells, which increased with age, further increased by irradiation. However, these radiation-related changes were not significant in similarly irradiated mice that were subsequently treated with SPD. The numbers of total, double-positive, and single-positive thymocytes were decreased by irradiation, whereas none were decreased in the irradiated mice treated with SPD. RNA sequencing of thymus cells revealed 803 upregulated genes in irradiated mice compared with those in non-irradiated control mice, with these genes enriched in leukocyte activation and inflammatory cytokine production. However, only 22 genes were upregulated in irradiated and SPD-treated mice, suggesting a reversal of many radiation-induced gene expression changes. These findings suggest that SPD may alleviate radiation-induced acceleration of T-cell aging, particularly by mitigating reduced thymopoiesis and inflammation. Further research is warranted to explore the rejuvenating potential of SPD and its mechanisms of action in accelerated T-cell aging.

Metaphase-Based Cytogenetic Approach Identifies Radiation-Induced Chromosome and Chromatid Aberrations in Zebrafish Embryos

Metaphase-based cytogenetic methods based on scoring of chromosome aberrations for the estimation of the radiation dose received provide a powerful approach for evaluating the associated risk upon radiation exposure and form the bulk of our current knowledge of radiation-induced chromosome damages. They mainly rely on inducing quiescent peripheral lymphocytes into proliferation and blocking them at metaphases to quantify the damages at the chromosome level. However, human organs and tissues demonstrate various sensitivity towards radiation and within them, self-proliferating progenitor/stem cells are believed to be the most sensitive populations. The radiation-induced chromosome aberrations in these cells remain largely unknown, especially in the context of an intact living organism. Zebrafish is an ideal animal model for research into this aspect due to their small size and the large quantities of progenitor cells present during the embryonic stages. In this study, we employ a novel metaphase-based cytogenetic approach on zebrafish embryos and demonstrate that chromosome-type and chromatid-type aberrations could be identified in progenitor cells at different cell-cycle stages at the point of radiation exposure. Our work positions zebrafish at the forefront as a useful animal model for studying radiation-induced chromosome structural changes in vivo.

Proactive strategy for long-term biological research aimed at low-dose radiation risk in Korea

PURPOSE

Since the 2011 Fukushima nuclear power plant accident, Korean radiation experts have agreed that reliable data on health risks of low-dose radiation (LDR) are needed to ease the anxiety of lay people. The intent of this study was to devise a sustainable biological program suited for the research environment in Korea and aimed at the health effects of radiation exposures <100 millisieverts (mSv). To address pressing public concerns over LDR risk, we investigated the current understanding of LDR effects by analyzing the previous reports of international authorities for radiation protection and research publications that appeared after the Chernobyl accident. A research program appropriate for societal and scientific inclinations of Korea was then devised based on input from Korean radiation scientists.

CONCLUSIONS

After review by our advisory committee, program priorities were set, calling for an agenda that focused on dose-response relationships in carcinogenesis, health span responses to lifestyle variations, and systemic metabolic changes. Our long-term biological research program may contribute scientific evidence to reduce the uncertainties of LDR health risks and help stakeholders formulate policies for radiation protection.