Differential Effects of Low and High Radiation Dose Rates on Mouse Spermatogenesis

Potential radiosensitive germline biomarkers in the testes of wild mice after the Fukushima accident

We investigated potential germline-specific radiosensitive biomarkers in the testes of large Japanese field mice (Apodemus speciosus) exposed to low-dose-rate (LDR) radiation after the Fukushima accident. Fukushima wild mice testes were analysed via RNA-sequencing to identify genes differentially expressed in the breeding and non-breeding seasons when compared to controls. Results revealed significant changes during the breeding season, with Lsp1 showing a considerable upregulation, while Ptprk and Tspear exhibited significant reductions. Conversely, in the non-breeding season, Fmo2 and Fmo2 (highly similar) were significantly upregulated in radiation-exposed Fukushima mice. qPCR analysis results were consistent with transcriptome sequencing, detecting Lsp1 and Ptprk regulation in the testes of Fukushima mice. While differences in gene expression were observed, these do not imply any causal association between the identified biomarkers and chronic LDR exposure, as other factors such as the environment and developmental age may contribute. This study provides valuable insights into the reproductive biology is affected by environmental radiation and highlights the value of assessing the effects of chronic LDR radiation exposure on testicular health in wild mice.

Inverse dose protraction effects of low-LET radiation: Evidence and significance

Biological effects of ionizing radiation vary not merely with total dose but also with temporal dose distribution. Sparing dose protraction effects, in which dose protraction reduces effects of radiation have widely been accepted and generally assumed in radiation protection, particularly for stochastic effects (e.g., solid cancer). In contrast, inverse dose protraction effects (IDPEs) in which dose protraction enhances radiation effects have not been well recognized, nor comprehensively reviewed. Here, we review the current knowledge on IDPEs of low linear energy transfer (LET) radiation. To the best of our knowledge, since 1952, 157 biology, epidemiology or clinical papers have reported IDPEs following external or internal low-LET irradiation with photons (X-rays, γ-rays), β-rays, electrons, protons or helium ions. IDPEs of low-LET radiation have been described for biochemical changes in cell-free macromolecules (DNA, proteins or lipids), DNA damage responses in bacteria and yeasts, DNA damage, cytogenetic changes, neoplastic transformation and cell death in mammalian cell cultures of human, rodent or bovine origin, mutagenesis in silkworms, cytogenetic changes, induction of cancer (solid tumors and leukemia) and non-cancer effects (male sterility, cataracts and diseases of the circulatory system), tumor inactivation and survival in non-human mammals (rodents, rabbits, dogs and pigs), and induction of cancer and non-cancer effects (skin changes and diseases of the circulatory system) in humans. In contrast to a growing body of phenomenological evidence for manifestations of IDPEs, there is limited knowledge on mechanistic underpinnings, but proposed mechanisms involve cell cycle-dependent resensitization and low dose hyper-radiosensitivity. These necessitate continued studies for further mechanistic developments and assessment of implications of scientific evidence for radiation protection (e.g., in terms of a dose rate effectiveness factor).

Testicular exposure to ionizing radiation and sperm epigenetic alterations as possible mechanisms of hereditary effects: perspectives from the viewpoint of radiation protection

PURPOSE

Since the genotoxicity of ionizing radiation was demonstrated in the 1920s, its hereditary effects have remained a serious concern for human society. The International Commission on Radiological Protection has highlighted the need for appropriate protection against hereditary effects of radiation in humans. In this paper, we review the literature on the possible multigenerational and transgenerational effects following testicular exposure to radiation, focusing on sperm epigenetic alterations as possible mechanisms.

RESULTS

This mini-review highlights that hereditary effects following testicular exposure occur via epigenetic changes of germ cells in animal models, providing implications on human radiation protection.

CONCLUSIONS

A great amount of epigenomic research data has emerged rapidly since the beginning of this century; thus, a revision of the radiological protection protocols against the hereditary effects of radiation would be no longer inevitable. The collection and analysis of evidence on these effects must be enhanced and further accelerated to formulate appropriate protection protocols in the future.

Transgenerational Effects on Lifespan and Pathology of Paternal Pre-conceptional Exposure to Continuous Low-dose-rate Gamma Rays in C57BL/6J Mice

The present work investigates the multigenerational effects of paternal pre-conceptional exposure to continuous low-dose-rate gamma rays in C56BL/6J mice. Male C57BL/6J (F0 sires) mice were exposed to low dose rates of 20, 1, and 0.05 mGy/day for 400 days, to total accumulated doses of 8,000, 400, and 20 mGy, respectively. Upon completion of the radiation exposure, the F0 male mice were immediately bred to non-irradiated 8-week-old C57BL/6J females (F0 dams) to produce the first-generation (F1) mice. Randomly selected F1 males and females were then bred to produce the second-generation (F2) mice. All the mice, except the F0 dams, were subjected to pathological examination upon natural death. Reproductive parameters, lifespan, causes of death, neoplasm incidences and non-neoplastic disease incidences were used as parameters to evaluate the biological effects of continuous pre-conceptional exposure of the sires (F0) to continuous low-dose-rate radiation. There were no significant differences in the pregnancy and weaning rates among the parent (F0) generation. Average litter size and average number of weaned pups (F1) from dams bred to males (F0) exposed to 20 mGy/day were significantly decreased compared to the non-irradiated controls. Significant lifespan shortening in the sires (F0) was observed only in the 20 mGy/day group due to early death from malignant lymphomas. Life shortening was also observed in the F1 progeny of sires (F0) exposed to 20 and 1 mGy/day, but could not be attributed to a specific cause. No significant differences in the causes of death were found between dose groups in any generation. The number of primary tumors per mouse was significantly increased only in the F0 males exposed to 20 mGy/day. Except for the increased incidence rate for Harderian gland neoplasms in sires (F0) exposed to 20 mGy/day, there was no significant difference in neoplasm incidences and tumor spectra in all 3 generations in each sex regardless of radiation exposure. No multi- or transgenerational effects in the parameters examined were observed in the F1 and F2 progeny of sires exposed to 0.05 mGy/day for 400 days.

DCAF2 regulates the proliferation and differentiation of mouse progenitor spermatogonia by targeting p21 and thymine DNA glycosylase

DDB1-Cullin-4-associated factor-2 (DCAF2, also known as DTL or CDT2), a conserved substrate recognition protein of Cullin-RING E3 ligase 4 (CRL4), recognizes and degrades several substrate proteins during the S phase to maintain cell cycle progression and genome stability. Dcaf2 mainly expressed in germ cells of human and mouse. Our study found that Dcaf2 was expressed in mouse spermatogonia and spermatocyte. The depletion of Dcaf2 in germ cells by crossing Dcaf2fl/fl mice with stimulated by retinoic acid gene 8(Stra8)-Cre mice caused a reduction in progenitor spermatogonia and differentiating spermatogonia, eventually leading to the failure of meiosis initiation and male infertility. Further studies showed that depletion of Dcaf2 in germ cells caused abnormal accumulation of the substrate proteins, cyclin-dependent kinase inhibitor 1A (p21) and thymine DNA glycosylase (TDG), decreasing of cell proliferation, increasing of DNA damage and apoptosis. Overexpression of p21 or TDG attenuates proliferation and increases DNA damage and apoptosis in GC-1 cells, which is exacerbated by co-overexpression of p21 and TDG. The findings indicate that DCAF2 maintains the proliferation and differentiation of progenitor spermatogonia by targeting the substrate proteins p21 and TDG during the S phase.

Radiotherapy and Testicular Function: A Comprehensive Review of the Radiation-Induced Effects with an Emphasis on Spermatogenesis

This comprehensive review explores the existing literature on the effects of radiotherapy on testicular function, focusing mainly on spermatogenic effects, but also with a brief report on endocrine abnormalities. Data from animal experiments as well as results on humans either from clinical studies or from accidental radiation exposure are included to demonstrate a complete perspective on the level of vulnerability of the testes and their various cellular components to irradiation. Even relatively low doses of radiation, produced either from direct testicular irradiation or more commonly from scattered doses, may often lead to detrimental effects on sperm count and quality. Leydig cells are more radioresistant; however, they can still be influenced by the doses used in clinical practice. The potential resultant fertility complications of cancer radiotherapy should be always discussed with the patient before treatment initiation, and all available and appropriate fertility preservation measures should be taken to ensure the future reproductive potential of the patient. The topic of potential hereditary effects of germ cell irradiation remains a controversial field with ethical implications, requiring future research.

Ultrastructural Analysis of Large Japanese Field Mouse (Apodemus speciosus) Testes Exposed to Low-Dose-Rate (LDR) Radiation after the Fukushima Nuclear Power Plant Accident

Since the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, great attention has been paid to the impact of chronic low-dose-rate (LDR) radiation exposure on biological systems. The reproductive system is sensitive to radiation, with implications connected to infertility. We investigated the testis ultrastructure of the wild large Japanese field mouse (Apodemus speciosus) from three areas contaminated after the FDNPP accident, with different levels of LDR radiation (0.29 µSv/h, 5.11 µSv/h, and 11.80 µSv/h). Results showed good preservation of the seminiferous tubules, comparable to the unexposed animals (controls), except for some ultrastructural modifications. Increases in the numerical density of lipid droplet clusters in spermatogenic cells were found at high levels of LDR radiation, indicating an antioxidant activity rising due to radiation recovery. In all groups, wide intercellular spaces were found between spermatogenic cells, and cytoplasmic vacuolization increased at intermediate and high levels and vacuolated mitochondria at the high-level. However, these findings were also related to the physiological dynamics of spermatogenesis. In conclusion, the testes of A. speciosus exposed to LDR radiation associated with the FDNPP accident showed a normal spermatogenesis, with some ultrastructural changes. These outcomes may add information on the reproductive potential of mammals chronically exposed to LDR radiation.

In utero exposure to ionizing radiation and metabolic regulation: perspectives for future multi- and trans-generation effects studies

PURPOSE

The radiation protection community has been particularly attentive to the risks of delayed effects on offspring from low dose or low dose-rate exposures to ionizing radiation. Despite this, the current epidemiologic studies and scientific data are still insufficient to provide the necessary evidence for improving risk assessment guidelines. This literature review aims to inform future studies on multigenerational and transgenerational effects. It primarily focuses on animal studies involving in utero exposure and discusses crucial elements for interpreting the results. These elements include in utero exposure scenarios relative to the developmental stages of the embryo/fetus, and the primary biological mechanisms responsible for transmitting heritable or hereditary effects to future generations. The review addresses several issues within the contexts of both multigenerational and transgenerational effects, with a focus on hereditary perspectives.

CONCLUSIONS

Knowledge consolidation in the field of Developmental Origins of Health and Disease (DOHaD) has led us to propose a new study strategy. This strategy aims to address the transgenerational effects of in utero exposure to low dose and low dose-rate radiation. Within this concept, there is a possibility that disruption of epigenetic programming in embryonic and fetal cells may occur. This disruption could lead to metabolic dysfunction, which in turn may cause abnormal responses to future environmental challenges, consequently increasing disease risk. Lastly, we discuss methodological limitations in our studies. These limitations are related to cohort size, follow-up time, model radiosensitivity, and analytical techniques. We propose scientific and analytical strategies for future research in this field.

Low dose rate radiation impairs early follicles in young mice

Low-dose radiation is generally considered less harmful than high-dose radiation. However, its impact on ovaries remains debated. Since previous reports predominantly employed low-dose radiation delivered at a high dose rate on the ovary, the effect of low-dose radiation at a low dose rate on the ovary remains unknown. We investigated the effect of low-dose ionizing radiation delivered at a low dose rate on murine ovaries. Three- and ten-week-old mice were exposed to 0.1 and 0.5 Gy of radiation at a rate of 6 mGy/h and monitored after 3 and 30 days. While neither body weight nor ovarian area showed significant changes, ovarian cells were damaged, showing apoptosis and a decrease in cell proliferation after exposure to 0.1 and 0.5 Gy radiation. Follicle numbers decreased over time in both age groups proportionally to the radiation dose. Younger mice were more susceptible to radiation damage, as evidenced by decreased follicles in 3-week-old mice after 30 days of 0.1 Gy exposure, while 10-week-old mice showed reduced follicles only following 0.5 Gy exposure. Primordial or primary follicles were the most vulnerable to radiation. These findings suggest that even low-dose radiation, delivered at a low dose rate, can adversely affect ovarian function, particularly in the early follicles of younger mice.

Dose rate dependent reduction in chromatin accessibility at transcriptional start sites long time after exposure to gamma radiation

Ionizing radiation (IR) impact cellular and molecular processes that require chromatin remodelling relevant for cellular integrity. However, the cellular implications of ionizing radiation (IR) delivered per time unit (dose rate) are still debated. This study investigates whether the dose rate is relevant for inflicting changes to the epigenome, represented by chromatin accessibility, or whether it is the total dose that is decisive. CBA/CaOlaHsd mice were whole-body exposed to either chronic low dose rate (2.5 mGy/h for 54 d) or the higher dose rates (10 mGy/h for 14 d and 100 mGy/h for 30 h) of gamma radiation (60Co, total dose: 3 Gy). Chromatin accessibility was analysed in liver tissue samples using Assay for Transposase-Accessible Chromatin with high-throughput sequencing (ATAC-Seq), both one day after and over three months post-radiation (>100 d). The results show that the dose rate contributes to radiation-induced epigenomic changes in the liver at both sampling timepoints. Interestingly, chronic low dose rate exposure to a high total dose (3 Gy) did not inflict long-term changes to the epigenome. In contrast to the acute high dose rate given to the same total dose, reduced accessibility at transcriptional start sites (TSS) was identified in genes relevant for the DNA damage response and transcriptional activity. Our findings link dose rate to essential biological mechanisms that could be relevant for understanding long-term changes after ionizing radiation exposure. However, future studies are needed to comprehend the biological consequence of these findings.

The role of HIF-1α-mediated autophagy in ionizing radiation-induced testicular injury

Testis, as a key organ for maintaining male fertility, are extremely sensitive to ionizing radiation (IR). IR-induced testicular dysfunction and infertility are common adverse effects of radiation therapy in patients with pelvic cancer. To study the phenotype and mechanism of IR-induced testicular injury, the mice were irradiated with different radiation doses (0, 2 and 5 Gy) below the semi-lethal dose for one month. Our present results showed that testicular weight and the serum testosterone levels significantly decreased with the structural injury of the testis in an IR dose-dependent manner, indicating that IR caused not only the structural damage of the testis, but also the functional damage. Further analysis by TUNEL staining and Western blotting found that IR induced the apoptosis in a dose-dependent manner as indicated by increased expressions of cleaved caspase3, p53 and Bax on Day 15 after IR treatment. Combined with significantly increased oxidative stress, these results indicated that IR-induced testicular damage may be a long-term, progressively aggravated process, accompanied by apoptosis. Given the role of autophagy in apoptosis, the present study also detected and analyzed the localization and expressions of autophagy-related proteins LC-3I/II, beclin1, p62 and Atg12 in testicular cells, and found that LC-3II, beclin1 and Atg12 expressions significantly increased in the testicular cells of mice irradiated with 2 Gy and 5 Gy, while p62 expression significantly decreased with 5 Gy, implying autophagy was involved in the apoptosis of testicular cells induced by IR. Furthermore, the expressions of HIF-1α and BNIP3 were significantly enhanced in the testis cells of mice irradiated with 2 Gy and 5 Gy, suggesting the potential role of HIF-1α/BNIP3-mediated autophagy in the apoptosis of testicular cells induced by IR. Taken together, our findings demonstrated that HIF-1α/BNIP3-mediated autophagy not only plays a protective effect on the testicular cells of mice irradiated with 2 Gy, but also induces the apoptosis of the testicular cells of mice irradiated with 5 Gy, indicating the double effects on apoptosis, which will help us further understanding the molecular mechanisms of IR-induced testicular injury, and will facilitate us further studies on testicular radioprotection.

Treatment progress of cryptozoospermia with Western Medicine and traditional Chinese medicine: A literature review

Background and Aims

Cryptozoospermia is an extreme oligozoospermia with an unsatisfactory treatment effect, with an incidence rate of approximately 8.73% in male infertility, whose effective solution has become the call of the times. Western Medicine has achieved certain effects through drugs, surgery, and assisted reproductive therapy, but this is still not ideal. Traditional Chinese medicine (TCM) has made many achievements in other disciplines; however, there is still a lack of evidence-based medical evidence to improve sperm production.

Methods

The relevant literatures from the China National Knowledge Internet (CNKI) and PubMed in the past 10 years were collected in this article, of which the mechanisms, advantages, or current controversies of various treatment methods of Western Medicine and TCM were analyzed, to find new treatment methods and research directions.

Results

With the development of modern science and technology, medical treatments for cryptozoospermia have become increasingly abundant; however, there is still no universally recognized unified and effective guiding plan. Although TCM has not been fully verified by evidence-based medicine, most TCM combined with Western Medicine can achieve unexpected results.

Conclusion

The combination of TCM and Western Medicine may become a bane for cryptozoospermia and bring good news to infertile men worldwide.

A Brief Overview of Radiation-Induced Effects on Spermatogenesis and Oncofertility

Simple Summary

Spermatogenesis is one of the most important processes for the propagation of life; however, the testes’ ability to form sperm via this differentiation process is highly radiosensitive and easily impacted by exposure to environmental, occupational, or therapeutic radiation. Furthermore, the possibility that radiation effects on the gonads can be passed on from generation to generation should not be overlooked. This review focuses on the radiation-induced effects on spermatogenesis and the transgenerational effects. We also explore the potential of novel radiobiological approaches to improve male fertility preservation during radiotherapy.

Abstract

The genotoxicity of radiation on germ cells may be passed on to the next generation, thus its elucidation is not only a scientific issue but also an ethical, legal, and social issue in modern society. In this article, we briefly overview the effects of radiation on spermatogenesis and its associated genotoxicity, including the latest findings in the field of radiobiology. The potential role of transgenerational effects is still poorly understood, and further research in this area is desirable. Furthermore, from the perspective of oncofertility, we discuss the historical background and clinical importance of preserving male fertility during radiation treatment and the potential of microbeam radiotherapy. We hope that this review will contribute to stimulating further discussions and investigations for therapies for pediatric and adolescent/young adult patients.