Altered microRNA expression patterns in irradiated hematopoietic tissues suggest a sex-specific protective mechanism

Hallmarks of sex bias in immuno-oncology: mechanisms and therapeutic implications

Sex differences are present across multiple non-reproductive organ cancers, with male individuals generally experiencing higher incidence of cancer with poorer outcomes. Although some mechanisms underlying these differences are emerging, the immunological basis is not well understood. Observations from clinical trials also suggest a sex bias in conventional immunotherapies with male individuals experiencing a more favourable response and female individuals experiencing more severe adverse events to immune checkpoint blockade. In this Perspective article, we summarize the major biological hallmarks underlying sex bias in immuno-oncology. We focus on signalling from sex hormones and chromosome-encoded gene products, along with sex hormone-independent and chromosome-independent epigenetic mechanisms in tumour and immune cells such as myeloid cells and T cells. Finally, we highlight opportunities for future studies on sex differences that integrate sex hormones and chromosomes and other emerging cancer hallmarks such as ageing and the microbiome to provide a more comprehensive view of how sex differences underlie the response in cancer that can be leveraged for more effective immuno-oncology approaches.

Time- and sex-dependent delayed effects of acute radiation exposure manifest via miRNA dysregulation

The detrimental effects of high-dose ionizing radiation on human health are well-known, but the influence of sex differences on the delayed effects of acute radiation exposure (DEARE) remains unclear. Here, we conducted six-month animal experiments using escalating radiation doses (7-9 Gy) on male and female C57BL/6 mice. The results show that female mice exhibited greater resistance to radiation, showing increased survival at six months post-total body irradiation. LD50/30 (lethal dose expected to cause 50% lethality in 30 days) for female mice is 8.08 Gy, while for male mice it is 7.76 Gy. DEARE causes time- and sex-dependent dysregulation of microRNA expression, processing enzymes, and the HOTAIR regulatory pathway. Differential regulation of molecular patterns associated with growth, development, apoptosis, and cancer is also observed in male and female mice. These findings shed light on the molecular basis of age and sex differences in DEARE response and emphasize the importance of personalized medicine for mitigating radiation-induced injuries and diseases.

Considerations of Medical Preparedness to Assess and Treat Various Populations During a Radiation Public Health Emergency

During a radiological or nuclear public health emergency, given the heterogeneity of civilian populations, it is incumbent on medical response planners to understand and prepare for a potentially high degree of interindividual variability in the biological effects of radiation exposure. A part of advanced planning should include a comprehensive approach, in which the range of possible human responses in relation to the type of radiation expected from an incident has been thoughtfully considered. Although there are several reports addressing the radiation response for special populations (as compared to the standard 18-45-year-old male), the current review surveys published literature to assess the level of consideration given to differences in acute radiation responses in certain sub-groups. The authors attempt to bring clarity to the complex nature of human biology in the context of radiation to facilitate a path forward for radiation medical countermeasure (MCM) development that may be appropriate and effective in special populations. Consequently, the focus is on the medical (as opposed to logistical) aspects of preparedness and response. Populations identified for consideration include obstetric, pediatric, geriatric, males, females, individuals of different race/ethnicity, and people with comorbidities. Relevant animal models, biomarkers of radiation injury, and MCMs are highlighted, in addition to underscoring gaps in knowledge and the need for consistent and early inclusion of these populations in research. The inclusion of special populations in preclinical and clinical studies is essential to address shortcomings and is an important consideration for radiation public health emergency response planning. Pursuing this goal will benefit the population at large by considering those at greatest risk of health consequences after a radiological or nuclear mass casualty incident.

Evaluating the Influences of Confounding Variables on Benchmark Dose using a Case Study in the Field of Ionizing Radiation

Purpose A vast amount of data regarding the effects of radiation stressors on transcriptional changes has been produced over the past few decades. These data have shown remarkable consistency across platforms and experimental design, enabling increased understanding of early molecular effects of radiation exposure. However, the value of transcriptomic data in the context of risk assessment is not clear and represents a gap that is worthy of further consideration. Recently, benchmark dose (BMD) modeling has shown promise in correlating a transcriptional point of departure (POD) to that derived using phenotypic outcomes relevant to human health risk assessment. Although frequently applied in chemical toxicity evaluation, our group has recently demonstrated application within the field of radiation research. This approach allows the possibility to quantitatively compare radiation-induced gene and pathway alterations across various datasets using BMD values and derive meaningful biological effects. However, before BMD modeling can confidently be used, an understanding of the impact of confounding variables on BMD outputs is needed. Methods: To this end, BMD modeling was applied to a publicly available microarray dataset (Gene Expression Omnibus #GSE23515) that used peripheral blood ex-vivo gamma-irradiated at 0.82 Gy/min, at doses of 0, 0.1, 0.5 or 2 Gy, and assessed 6 hours post-exposure. The dataset comprised six female smokers (F-S), six female non-smokers (F-NS), six male smokers (M-S), and six male non-smokers (M-NS). Results: A combined total of 412 genes were fit to models and the BMD distribution was noted to be bi-modal across the four groups. A total of 74, 41, 62 and 62 genes were unique to the F-NS, M-NS, F-S and M-S groups. Sixty-two BMD modeled genes and nine pathways were common across all four groups. There were no differential sensitivity of responses in the robust common genes and pathways. Conclusion: For radiation-responsive genes and pathways common across the study groups, the BMD distribution of transcriptional activity was unaltered by sex and smoking status. Although further validation of the data is needed, these initial findings suggest BMD values for radiation relevant genes and pathways are robust and could be explored further in future studies.

Suppression of HELLS by miR-451a represses mTOR pathway to hinder aggressiveness of SCLC

BACKGROUND

Uncovering molecular pathogenesis and mechanisms of small cell lung cancer (SCLC) will contribute to SCLC therapy. Multiple studies demonstrated that miR-451a acts as an anti-tumor miRNA in non-small cell lung cancer. However, the mechanism of miR-451a in SCLC was ambiguous.

OBJECTIVE

We aimed to explore the function of miR-451a in SCLC and decipher the underlying mechanisms.

METHODS

TargetScan and dual-luciferase reporter assays were used to analyze the target genes of miR-451a. Cell counting kit-8 and colony formation assays were performed to assess the roles of miR-451a on cell growth. Gene set enrichment analysis (GSEA) was utilized to enrich biological pathways. Western blot was used to measure protein expression.

RESULTS

MiR-451a expression was reduced dramatically in SCLC tissues and cell lines (NCI-H1688 and NCI-H446). Helicase, Lymphoid Specific (HELLS) was proved to be a target gene of miR-451a. In addition, cell proliferation assays in SCLC cells transfected with miR-451a mimic and/or HELLS revealed that miR-451a inhibited cell proliferation via targeting HELLS. Moreover, the roles of miR-451a/HELLS in expression of key proteins in mTOR and apoptosis signaling pathways suggested that miR-451a inactivated mTOR and activated apoptosis signaling pathway via directly silencing HELLS.

CONCLUSIONS

Our study indicated that miR-451a hinders SCLC cell proliferation in vitro through regulating mTOR and apoptosis signaling pathways via silencing HELLS, suggesting that miR-451a could be a promising tumor suppressor in SCLC. And there is a potential for miR-451a to be a drug target and biomarker for SCLC.

Development of a Model of the Acute and Delayed Effects of High Dose Radiation Exposure in Jackson Diversity Outbred Mice; Comparison to Inbred C57BL/6 Mice

Development of medical countermeasures against radiation relies on robust animal models for efficacy testing. Mouse models have advantages over larger species due to economics, ease of conducting aging studies, existence of historical databases, and research tools allowing for sophisticated mechanistic studies. However, the radiation dose-response relationship of inbred strains is inherently steep and sensitive to experimental variables, and inbred models have been criticized for lacking genetic diversity. Jackson Diversity Outbred (JDO) mice are the most genetically diverse strain available, developed by the Collaborative Cross Consortium using eight founder strains, and may represent a more accurate model of humans than inbred strains. Herein, models of the Hematopoietic-Acute Radiation Syndrome and the Delayed Effects of Acute Radiation Exposure were developed in JDO mice and compared to inbred C57BL/6. The dose response relationship curve in JDO mice mirrored the more shallow curves of primates and humans, characteristic of genetic diversity. JDO mice were more radioresistant than C57BL/6 and differed in sensitivity to antibiotic countermeasures. The model was validated with pegylated-G-CSF, which provided significantly enhanced 30-d survival and accelerated blood recovery. Long-term JDO survivors exhibited increased recovery of blood cells and functional bone marrow hematopoietic progenitors compared to C57BL/6. While JDO hematopoietic stem cells declined more in number, they maintained a greater degree of quiescence compared to C57BL/6, which is essential for maintaining function. These JDO radiation models offer many of the advantages of small animals with the genetic diversity of large animals, providing an attractive alternative to currently available radiation animal models.

Study logistics that can impact medical countermeasure efficacy testing in mouse models of radiation injury

PURPOSE

To address confounding issues that have been noted in planning and conducting studies to identify biomarkers of radiation injury, develop animal models to simulate these injuries, and test potential medical countermeasures to mitigate/treat damage caused by radiation exposure.

METHODS

The authors completed an intensive literature search to address several key areas that should be considered before embarking on studies to assess efficacy of medical countermeasure approaches in mouse models of radiation injury. These considerations include: (1) study variables; (2) animal selection criteria; (3) animal husbandry; (4) medical management; and (5) radiation attributes.

RESULTS

It is important to select mouse strains that are capable of responding to the selected radiation exposure (e.g. genetic predispositions might influence radiation sensitivity and proclivity to certain phenotypes of radiation injury), and that also react in a manner similar to humans. Gender, vendor, age, weight, and even seasonal variations are all important factors to consider. In addition, the housing and husbandry of the animals (i.e. feed, environment, handling, time of day of irradiation and animal restraint), as well as the medical management provided (e.g. use of acidified water, antibiotics, routes of administration of drugs, consideration of animal numbers, and euthanasia criteria) should all be addressed. Finally, the radiation exposure itself should be tightly controlled, by ensuring a full understanding and reporting of the radiation source, dose and dose rate, shielding and geometry of exposure, while also providing accurate dosimetry. It is important to understand how all the above factors contribute to the development of radiation dose response curves for a given animal facility with a well-defined murine model.

CONCLUSIONS

Many potential confounders that could impact the outcomes of studies to assess efficacy of a medical countermeasure for radiation-induced injuries are addressed, and recommendations are made to assist investigators in carrying out research that is robust, reproducible, and accurate.

Gender-dependent radiotherapy: The next step in personalised medicine?

Individuals do not react to radiation in a homogeneous manner. Recent radiogenomic research has proven that individual polymorphisms can correlate with treatment response most likely due to variation in the ability to recognise and repair DNA breaks. The difference in radiosensitivity between genders has been well documented, yet most radiotherapeutic guidelines are based solely on population averages rather than demographic subgroups such as age, race and gender. This paper is a review of the burgeoning literature available on the differences in efficacy and outcome of radiotherapy between genders. The work examines the effect of radiation on gender both from a tumour control as well as normal tissue toxicity perspective. While the literature reporting such findings is limited, the results show a small but significant difference in response to radiotherapy between sexes. Prospective and retrospective studies for evaluating these gender-specific differences are encouraged as a next step in personalised medicine.

Time-Dependent Measurement of Nrf2-Regulated Antioxidant Response to Ionizing Radiation Toward Identifying Potential Protein Biomarkers for Acute Radiation Injury

PURPOSE

Potential acute exposure to ionizing radiation in nuclear or radiological accidents presents complex mass casualty scenarios that demand prompt triage and treatment decisions. Due to delayed symptoms and varied response of radiation victims, there is an urgent need to develop robust biomarkers to assess the extent of injuries in individuals.

EXPERIMENTAL DESIGN

The transcription factor Nrf2 is the master of redox homeostasis and there is transcriptional evidence of Nrf2-dependent antioxidant response activation upon radiation. The biomarker potential of Nrf2-dependent downstream target enzymes is investigated by measuring their response in bone marrow extracted from C57Bl/6 and C3H mice of both genders for up to 4 days following 6 Gy total body irradiation using targeted MS.

RESULTS

Overall, C57Bl/6 mice have a stronger proteomic response than C3H mice. In both strains, male mice have more occurrences of upregulation in antioxidant enzymes than female mice. For C57Bl/6 male mice, three proteins show elevated abundances after radiation exposure: catalase, superoxide dismutase 1, and heme oxygenase 1. Across both strains and genders, glutathione S-transferase Mu 1 is consistently decreased.

CONCLUSIONS AND CLINICAL RELEVANCE

This study provides the basis for future development of organ-specific protein biomarkers used in diagnostic blood test for radiation injury.

Sex Difference of Radiation Response in Occupational and Accidental Exposure

Ionizing radiation is a well-established cause of deleterious effects on human health. Understanding the risks of radiation exposure is important for the development of protective measures and guidelines. Demographic factors such as age, sex, genetic susceptibility, comorbidities, and various other lifestyle factors influence the radiosensitivity of different subpopulations. Amongst these factors, the influence of sex differences on radiation sensitivity has been given very less attention. In fact, the International Commission on Radiological Protection (ICRP) has based its recommendations on a population average, rather than the data on the radiosensitivity of distinct subpopulations. In this study, we reviewed major human studies on the health risks of radiation exposure and showed that sex-related factors may potentially influence the long-term response to radiation exposure. Available data suggest that long-term radiosensitivity in women is higher than that in men who receive a comparable dose of radiation. The report on the biological effects of ionizing radiation (BEIR VII) published in 2006 by the National Academy of Sciences, United States emphasized that women may be at significantly greater risk of suffering and dying from radiation-induced cancer than men exposed to the same dose of radiation. We show that radiation effects are sex-specific, and long-term radiosensitivity in females is higher than that in males. We also discuss the radiation effects as a function of age. In the future, more systematic studies are needed to elucidate the sex differences in radiation responses across the life continuum - from preconception through childhood, adulthood, and old age - to ensure that boys and girls and men and women are equally protected across ages.

MicroRNA Functions in Thymic Biology: Thymic Development and Involution

During the entire processes of thymus organogenesis, maturation, and involution, gene regulation occurs post-transcriptionally via recently discovered microRNA (miRNA) transcripts. Numerous reports indicate that miRNAs may be involved in the construction of a normal thymic microenvironment, which constitutes a critical component to support T lymphocyte development. MiRNAs are also expressed in thymic stromal cells including thymic epithelial cells (TECs) during maturation and senescence. This review focuses on the function of miRNAs in thymic development and involution. A better understanding of these processes will provide new insights into the regulatory network of TECs and further comprehension of how genes control TECs to maintain the thymic microenvironment during thymus development and aging, thus supporting a normal cellular immune system.

Extracellular Vesicles Mediate Radiation-Induced Systemic Bystander Signals in the Bone Marrow and Spleen

Radiation-induced bystander effects refer to the induction of biological changes in cells not directly hit by radiation implying that the number of cells affected by radiation is larger than the actual number of irradiated cells. Recent in vitro studies suggest the role of extracellular vesicles (EVs) in mediating radiation-induced bystander signals, but in vivo investigations are still lacking. Here, we report an in vivo study investigating the role of EVs in mediating radiation effects. C57BL/6 mice were total-body irradiated with X-rays (0.1, 0.25, 2 Gy), and 24 h later, EVs were isolated from the bone marrow (BM) and were intravenously injected into unirradiated (so-called bystander) animals. EV-induced systemic effects were compared to radiation effects in the directly irradiated animals. Similar to direct radiation, EVs from irradiated mice induced complex DNA damage in EV-recipient animals, manifested in an increased level of chromosomal aberrations and the activation of the DNA damage response. However, while DNA damage after direct irradiation increased with the dose, EV-induced effects peaked at lower doses. A significantly reduced hematopoietic stem cell pool in the BM as well as CD4⁺ and CD8⁺ lymphocyte pool in the spleen was detected in mice injected with EVs isolated from animals irradiated with 2 Gy. These EV-induced alterations were comparable to changes present in the directly irradiated mice. The pool of TLR4-expressing dendritic cells was different in the directly irradiated mice, where it increased after 2 Gy and in the EV-recipient animals, where it strongly decreased in a dose-independent manner. A panel of eight differentially expressed microRNAs (miRNA) was identified in the EVs originating from both low- and high-dose-irradiated mice, with a predicted involvement in pathways related to DNA damage repair, hematopoietic, and immune system regulation, suggesting a direct involvement of these pathways in mediating radiation-induced systemic effects. In conclusion, we proved the role of EVs in transmitting certain radiation effects, identified miRNAs carried by EVs potentially responsible for these effects, and showed that the pattern of changes was often different in the directly irradiated and EV-recipient bystander mice, suggesting different mechanisms.

Emergence of miR-34a in radiation therapy

Expressions of many microRNAs (miRNAs) in response to ionizing radiation (IR) have already been investigated and some of them seem to play an important role in the tumor radioresistance, normal tissue radiotoxicity or as predictive biomarkers to radiation. miR-34a is an emerging miRNA in recent radiobiology studies. Here, we review this miR-34 family member by detailing its different roles in radiation response and we will discuss about the role that it can play in radiation treatment. Thus, we will show that IR regulates miR-34a by increasing its expression. We will also highlight different biological processes involved in cellular response to IR and regulated by miR-34a in order to demonstrate the role it can play in tumor radio-response or normal tissue radiotoxicity as a radiosensitizer or radioprotector. miR-34a is poised to assert itself as an important player in radiobiology and should become more and more important in radiation therapy management.

Human serum miR-34a as an indicator of exposure to ionizing radiation

Radiation exposure in industrial accidents or nuclear device attacks is a major public health concern. There is an urgent need for markers that rapidly identify people exposed to ionizing radiation (IR). Finding a blood-based marker is advantageous because of the ease of sample collection. This study was designed to test the hypothesis that serum miR-34a could serve as an indicator of exposure to IR. Therefore, 44 women with breast cancer, where radiotherapy was part of their therapeutic protocol, were investigated in this study. After demonstrating the appropriateness of our microRNA (miRNA) extraction efficiency and miRNA assay in human serum, we analyzed the miR-34a level in paired serum samples before and after radiotherapy. Fifty Gy X-ray irradiation in daily dose fractions of 2 Gy, 5 days per week, was used in this study. We demonstrated that IR significantly increased serum level of miR-34a. By measuring miR-34a in serum, we could distinguish irradiated patients with sensitivity of 65 % and specificity of 75 %. According to this study, serum miR-34a has the potential to be used as an indicator of radiation exposure.

Gamma-Tocotrienol Modulates Radiation-Induced MicroRNA Expression in Mouse Spleen

Ionizing radiation causes depletion of hematopoietic cells and enhances the risk of developing secondary hematopoietic malignancies. Vitamin E analog gamma-tocotrienol (GT3), which has anticancer properties, promotes postirradiation hematopoietic cell recovery by enhancing spleen colony-forming capacity, and provides protection against radiation-induced lethality in mice. However, the underlying molecular mechanism involved in GT3-mediated postirradiation survival is not clearly understood. Recent studies have shown that natural dietary products including vitamin E provide a benefit to biological systems by modulating microRNA (miR) expression. In this study, we show that GT3 differentially modulates the miR footprint in the spleen of irradiated mice compared to controls at early times (day 1), as well as later times (day 4 and 15) after total-body irradiation. We observed that miR expression was altered in a dose- and time-dependent manner in GT3-pretreated spleen tissues from total-body irradiated mice. GT3 appeared to affect the expression of a number of radiation-modulated miRs known to be involved in hematopoiesis and lymphogenesis. Moreover, GT3 pretreatment also suppressed the upregulation of radiation-induced p53, suggesting the function of GT3 in the prevention of radiation-induced damage to the spleen. In addition, we have shown that GT3 significantly reduced serum levels of Flt3L, a biomarker of radiation-induced bone marrow aplasia. Further in silico analyses of the effect of GT3 implied the association of p38 MAPK, ERK and insulin signaling pathways. Our study provides initial insight into the mechanism by which GT3 mediates protection of spleen after total-body irradiation.

Low dose irradiation profoundly affects transcriptome and microRNAme in rat mammary gland tissues

Ionizing radiation has been successfully used in medical tests and treatment therapies for a variety of medical conditions. However, patients and health-care workers are greatly concerned about overexposure to medical ionizing radiation and possible cancer induction due to frequent mammographies and/or CT scans. Diagnostic imaging involves the use of low doses of ionizing radiation, and its potential carcinogenic role creates a cancer risk concern for exposed individuals. In this study, the effects of X-ray exposure of different doses on the gene expression patterns and the micro-RNA expression patterns in normal breast tissue were investigated in rats. Our results revealed the activation of immune response pathways upon low dose of radiation exposure. These included natural killer mediated cytotoxicity pathways, antigen processing and presentation pathways, chemokine signaling pathways, and T- and B-cell receptor signaling pathways. Both high and low doses of radiation led to miRNA expression alterations. Increased expression of miR-34a may be linked to cell cycle arrest and apoptosis. Up-regulation of miR-34a was correlated with down-regulation of its target E2F3 and up-regulation of p53. This data suggests that ionizing radiation at specific high and low doses leads to cell cycle arrest and a possible initiation of apoptosis.

microRNA expression and biogenesis in cellular response to ionizing radiation

Increasing evidence demonstrates that the expression levels of microRNAs (miRNAs) significantly change upon ionizing radiation (IR) and play a critical role in cellular response to IR. Although several radiation responsive miRNAs and their targets have been identified, little is known about how miRNAs expression and biogenesis is regulated by IR-caused DNA damage response (DDR). Hence, in this review, we summarize miRNA expression and biogenesis in cellular response to IR and mainly elucidate the regulatory mechanisms of miRNA expression and biogenesis from different aspects including ataxia-telangiectasia mutated (ATM) kinase, p53/p63/p73 family and other potential factors. Furthermore, we focus on ΔNp73, which might be a potential regulator of miRNA expression and biogenesis in cellular response to IR. miRNAs could effectively activate the IR-induced DDR and modulate the radiation response and cellular radiosensitivity, which have an important potential clinical application. Therefore, thoroughly understanding the regulatory mechanisms of miRNAs expression and biogenesis in radiation response will provide new insights for clinical cancer radiotherapy.

Inhibition of microRNA-31-5p protects human colonic epithelial cells against ionizing radiation

MicroRNAs (miRNAs), endogenous non-coding small RNAs, are sensitive to environmental changes, and their differential expression is important for adaptation to the environment. However, application of miRNAs as a clinical prognostic or diagnostic tool remains unproven. In this study we demonstrate a chronic/persistent change of miRNAs from the plasma of a colorectal cancer susceptible mouse model (CPC;Apc) about 250 days after exposure to a simulated solar particle event (SPE). Differentially expressed miRNAs were identified compared to unirradiated control mice, including miR-31-5p, which we investigated further. To address the cellular function of miR-31-5p, we transfected a miR-31-5p mimic (sense) or inhibitor (antisense) into immortalized human colonic epithelial cells followed by gamma-irradiation. A miR-31-5p mimic sensitized but a miR-31-5p inhibitor protected colonic epithelial cells against radiation induced killing. We found that the miR-31-5p mimic inhibited the induction of hMLH1 expression after irradiation, whereas the miR-31-5p inhibitor increased the basal level of hMLH1 expression. The miR-31-5p inhibitor failed to modulate radiosensitivity in an hMLH1-deficient HCT116 colon cancer cell line but protected HCT116 3-6 and DLD-1 (both hMLH1-positive) colon cancer cell lines. Our findings demonstrate that miR-31-5p has an important role in radiation responses through regulation of hMLH1 expression. Targeting this pathway could be a promising therapeutic strategy for future personalized anti-cancer radiotherapy.

The microRNAs as potential biomarkers for predicting the onset of aflatoxin exposure in human beings: a review

The identification of aflatoxins as human carcinogens has stimulated extensive research efforts, which continue to the present, to assess potential health hazards resulting from contamination of the human food supply and to minimize exposure. The use of biomarkers that are mechanistically supported by toxicological studies will be important tools for identifying stages in the progression of development of the health effects of environmental agents. miRNAs are small non-coding mRNAs that regulate post-transcriptional gene expression. Also, they are molecular markers of cellular responses to various chemical agents. Growing evidence has demonstrated that environmental chemicals can induce changes in miRNA expression. miRNAs are good biomarkers because they are well defined, chemically uniform, restricted to a manageable number of species, and stable in cells and in the circulation. miRNAs have been used as serological markers of HCC and other tumors. The expression patterns of different miRNAs can distinguish among HCC-hepatitis viruses related, HCC cirrhosis-derivate, and HCC unrelated to either of them. The main objective of this review is to find unreported miRNAs in HCC related to other causes, so that they can be used as specific molecular biomarkers in populations exposed to aflatoxins and as early markers of exposure, damage/presence of HCC. Until today specific miRNAs as markers for aflatoxins-exposure and their reliability are currently lacking. Based on their elucidated mechanisms of action, potential miRNAs that could serve as possible markers of HCC by exposure to aflatoxins are miR-27a, miR-27b, miR-122, miR-148, miR-155, miR-192, miR-214, miR-221, miR-429, and miR-500. Future validation for all of these miRNAs will be needed to assess their prognostic significance and confirm their relationship with the induction of HCC due to aflatoxin exposure.

MicroRNA responses to focal cerebral ischemia in male and female mouse brain

Stroke occurs with greater frequency in men than in women across diverse ethnic backgrounds and nationalities. Work from our lab and others have revealed a sex-specific sensitivity to cerebral ischemia whereby males exhibit a larger extent of brain damage resulting from an ischemic event compared to females. Previous studies revealed that microRNA (miRNA) expression is regulated by cerebral ischemia in males; however, no studies to date have examined the effect of ischemia on miRNA responses in females. Thus, we examined miRNA responses in male and female brain in response to cerebral ischemia using miRNA arrays. These studies revealed that in male and female brains, ischemia leads to both a universal miRNA response as well as a sexually distinct response to challenge. Target prediction analysis of the miRNAs increased in male or female ischemic brain reveal sex-specific differences in gene targets and protein pathways. These data support that the mechanisms underlying sexually dimorphic responses to cerebral ischemia includes distinct changes in miRNAs in male and female brain, in addition to a miRNA signature response to ischemia that is common to both.

Epigenetics meets radiation biology as a new approach in cancer treatment

Cancer is a disease that results from both genetic and epigenetic changes. In recent decades, a number of people have investigated the disparities in gene expression resulting from variable DNA methylation alteration and chromatin structure modification in response to the environment. Especially, colon cancer is a great model system for investigating the epigenetic mechanism for aberrant gene expression alteration. Ionizing radiation (IR) could affect a variety of processes within exposed cells and, in particular, cause changes in gene expression, disruption of cell cycle arrest, and apoptotic cell death. Even though there is growing evidence on the importance of epigenetics and biological processes induced by radiation exposure in various cancer types including colon cancer, specific epigenetic alterations induced by radiation at the molecular level are incompletely defined. This review focuses on discussing possible IR-mediated changes of DNA methylation and histone modification in cancer.

Evidence relevant to untargeted and transgenerational effects in the offspring of irradiated parents

In this article we review health effects in offspring of human populations exposed as a result of radiotherapy and some groups exposed to chemotherapy. We also assess risks in offspring of other radiation-exposed groups, in particular those of the Japanese atomic bomb survivors and occupationally and environmentally exposed groups. Experimental findings are also briefly surveyed. Animal and cellular studies tend to suggest that the irradiation of males, at least at high doses (mostly 1Gy and above), can lead to observable effects (including both genetic and epigenetic) in the somatic cells of their offspring over several generations that are not attributable to the inheritance of a simple mutation through the parental germline. However, studies of disease in the offspring of irradiated humans have not identified any effects on health. The available evidence therefore suggests that human health has not been significantly affected by transgenerational effects of radiation. It is possible that transgenerational effects are restricted to relatively short times post-exposure and in humans conception at short times after exposure is likely to be rare. Further research that may help resolve the apparent discrepancies between cellular/animal studies and studies of human health are outlined.

Repression of ATR pathway by miR-185 enhances radiation-induced apoptosis and proliferation inhibition

Cellular responses to DNA damage induced by intrinsic and extrinsic genotoxic stresses are highly regulated by complex signaling pathways, such as activation of the phosphoinositide-3-kinase-like protein kinase family and their downstream genes. Disruption of these signaling pathways leads to genome instability and cell death, and thus may provide potential novel strategies for cancer therapy. Here, we find that the expression of a human microRNA (miRNA), hsa-miR-185, is downregulated in response to ionizing radiation. Elevation of miR-185 sensitizes renal cell carcinoma cells to X-rays both in vitro and in vivo. Bioinformatic analysis shows that the ATM- and Rad3-related (ATR) kinase, a master conductor of cellular responses to DNA damage and DNA replication stresses, is a target of miR-185. This prediction was validated by luciferase reporter and mutation assays. We also demonstrated that miR-185 negatively regulates ATR expression at post-transcriptional level. miR-185 enhances radiation-induced apoptosis and inhibition of proliferation by repressing ATR pathway. In conclusion, our findings indicate a previously unreported regulatory mechanism for ATR expression mediated by miR-185 and shed light on the potential application of miRNAs both as direct cancer therapeutics and as tools to sensitize tumor cells to radiotherapy.

Maternal stress induces epigenetic signatures of psychiatric and neurological diseases in the offspring

The gestational state is a period of particular vulnerability to diseases that affect maternal and fetal health. Stress during gestation may represent a powerful influence on maternal mental health and offspring brain plasticity and development. Here we show that the fetal transcriptome, through microRNA (miRNA) regulation, responds to prenatal stress in association with epigenetic signatures of psychiatric and neurological diseases. Pregnant Long-Evans rats were assigned to stress from gestational days 12 to 18 while others served as handled controls. Gestational stress in the dam disrupted parturient maternal behaviour and was accompanied by characteristic brain miRNA profiles in the mother and her offspring, and altered transcriptomic brain profiles in the offspring. In the offspring brains, prenatal stress upregulated miR-103, which is involved in brain pathologies, and downregulated its potential gene target Ptplb. Prenatal stress downregulated miR-145, a marker of multiple sclerosis in humans. Prenatal stress also upregulated miR-323 and miR-98, which may alter inflammatory responses in the brain. Furthermore, prenatal stress upregulated miR-219, which targets the gene Dazap1. Both miR-219 and Dazap1 are putative markers of schizophrenia and bipolar affective disorder in humans. Offspring transcriptomic changes included genes related to development, axonal guidance and neuropathology. These findings indicate that prenatal stress modifies epigenetic signatures linked to disease during critical periods of fetal brain development. These observations provide a new mechanistic association between environmental and genetic risk factors in psychiatric and neurological disease.

The secret language of destiny: stress imprinting and transgenerational origins of disease

Epigenetic regulation modulates gene expression without altering the DNA sequence to facilitate rapid adjustments to dynamically changing environmental conditions. The formation of an epigenetic memory allows passing on this information to subsequent generations. Here we propose that epigenetic memories formed by adverse environmental conditions and stress represent a critical determinant of health and disease in the F3 generation and beyond. Transgenerational programming of epigenetic regulation may represent a key to understand adult-onset complex disease pathogenesis and cumulative effects of life span and familial disease etiology. Ultimately, the mechanisms of generating an epigenetic memory may become of potentially promising diagnostic and therapeutic relevance due to their reversible nature. Exploring the role of environmental factors, such as stress, in causing variations in epigenetic profiles may lead to new avenues of personalized, preventive medicine based on epigenetic signatures and interventions.

Gene expression signatures of radiation exposure in peripheral white blood cells of smokers and non-smokers

PURPOSE

The issue of potential confounding factors is critical to the development of any approach to radiation biodosimetry, and has not been fully addressed for gene expression-based approaches.

MATERIALS AND METHODS

As a step in this direction, we have investigated the effect of smoking on the global radiation gene expression response in ex vivo-irradiated peripheral blood cells using microarray analysis. We also evaluated the ability of gene expression signatures to predict the radiation exposure level of ex vivo-exposed samples from smokers and non-smokers of both genders.

RESULTS

We identified eight genes with a radiation response that was significantly affected by smoking status, and confirmed an effect of smoking on the radiation response of the four and a half LIM domains 2 (FHL2) gene using quantitative real-time polymerase chain reaction. The performance of our previously defined 74-gene signature in predicting the radiation dose to samples in this study was unaffected by differences in gender or smoking status, however, giving 98% correct prediction of dose category. This is the same accuracy as that found in the original study from which the signature was derived, using different donors.

CONCLUSION

The results support the development of peripheral blood gene expression as a viable strategy for radiation biodosimetry.

The role of miRNA in the direct and indirect effects of ionizing radiation

This review focuses on a number of recent studies that have examined changes in microRNA (miRNA) expression profiles in response to ionizing radiation and other forms of oxidative stress. In both murine and human cells and tissues, a number of miRNAs display significant alterations in expression levels in response to both direct and indirect radiation exposure. In terms of direct irradiation, or exposure to agents that induce oxidative stress, miRNA array analyses indicate that a number of miRNAs are up- and down-regulated and, in particular, the let-7 family of miRNAs may well be critical in the cellular response to oxidative stress. In bystander cells that are not directly irradiated, but close to, or share media with directly irradiated cells or tissues, the miRNA expression profiles are also altered, but are somewhat distinct from the directly irradiated cells. Based on the results of these numerous studies, as well as our own data presented here, we conclude that miRNA regulation is a critical step in the cellular response to radiation and oxidative stress and that future studies should elucidate the mechanisms through which this altered regulation affects cell metabolism.

Cholinesterase-Targeting microRNAs Identified in silico Affect Specific Biological Processes

MicroRNAs (miRs) have emerged as important gene silencers affecting many target mRNAs. Here, we report the identification of 244 miRs that target the 3′-untranslated regions of different cholinesterase transcripts: 116 for butyrylcholinesterase (BChE), 47 for the synaptic acetylcholinesterase (AChE-S) splice variant, and 81 for the normally rare splice variant AChE-R. Of these, 11 and 6 miRs target both AChE-S and AChE-R, and AChE-R and BChE transcripts, respectively. BChE and AChE-S showed no overlapping miRs, attesting to their distinct modes of miR regulation. Generally, miRs can suppress a number of targets; thereby controlling an entire battery of functions. To evaluate the importance of the cholinesterase-targeted miRs in other specific biological processes we searched for their other experimentally validated target transcripts and analyzed the gene ontology enriched biological processes these transcripts are involved in. Interestingly, a number of the resulting categories are also related to cholinesterases. They include, for BChE, response to glucocorticoid stimulus, and for AChE, response to wounding and two child terms of neuron development: regulation of axonogenesis and regulation of dendrite morphogenesis. Importantly, all of the AChE-targeting miRs found to be related to these selected processes were directed against the normally rare AChE-R splice variant, with three of them, including the neurogenesis regulator miR-132, also directed against AChE-S. Our findings point at the AChE-R splice variant as particularly susceptible to miR regulation, highlight those biological functions of cholinesterases that are likely to be subject to miR post-transcriptional control, demonstrate the selectivity of miRs in regulating specific biological processes, and open new venues for targeted interference with these specific processes.

MicroRNA expression profiles distinguish the carcinogenic effects of riddelliine in rat liver

Pyrrolizidine alkaloids (PAs) are the most common plant constituents that poison livestock, wildlife and humans. Riddelliine is a prototype genotoxic PA and has been nominated to be classified as a reasonably anticipated human carcinogen by the US National Toxicology Program (NTP) in the 12th Report on Carcinogens. Riddelliine's nomination is due to the high incidence of liver tumours that were observed in both mice and rats in the NTP tumourigenicity bioassay study. In this current study, we explored whether riddelliine treatment could alter microRNA (miRNA) expression in rat liver and whether the possible deregulation of miRNA was related to mutagenicity and carcinogenicity of riddelliine. Groups of six rats were administered riddelliine at a mutagenic dose of 1 mg/kg body weight or with control vehicle 5 days a week for 12 weeks. A group of six rats treated with aristolochic acid, a renal carcinogen, was used as a tissue-specific negative control. The animals were sacrificed 1 day after the last treatment and the livers were isolated for miRNA expression analysis using miRNA microarrays. miRNA expression was significantly altered by riddelliine treatment. Principal component analysis and hierarchical clustering analysis showed that the miRNA expression profiles were clearly classified into two groups, riddelliine treatment versus other samples. Forty-seven miRNAs were significantly dysregulated by riddelliine treatment, among which 38 were up-regulated and 9 were down-regulated. Functional analysis of these differentially expressed miRNAs by riddelliine revealed that these miRNAs were involved in liver carcinogenicity and toxicity, such as liver proliferation, liver necrosis/cell death, hepatocellular carcinoma, liver hepatomegaly, liver inflammation and liver fibrosis. These results suggest that miRNAs actively respond to a mutagenic dose of riddelliine and the pattern of miRNA expression has the potential to be used as a biomarker of genotoxicity and carcinogenicity for riddelliine and possibly other PAs.

Non-targeted radiation effects-an epigenetic connection

Ionizing radiation (IR) is a pivotal diagnostic and treatment modality, yet it is also a potent genotoxic agent that causes genome instability and carcinogenesis. While modern cancer radiation therapy has led to increased patient survival rates, the risk of radiation treatment-related complications is becoming a growing problem. IR-induced genome instability has been well-documented in directly exposed cells and organisms. It has also been observed in distant 'bystander' cells. Enigmatically, increased instability is even observed in progeny of pre-conceptually exposed animals, including humans. The mechanisms by which it arises remain obscure and, recently, they have been proposed to be epigenetic in nature. Three major epigenetic phenomena include DNA methylation, histone modifications and small RNA-mediated silencing. This review focuses on the role of DNA methylation and small RNAs in directly exposed and bystander tissues and in IR-induced transgenerational effects. Here, we present evidence that IR-mediated effects are maintained by epigenetic mechanisms.

Sex-specific radiation-induced microRNAome responses in the hippocampus, cerebellum and frontal cortex in a mouse model

Ionizing radiation is an important treatment modality, but it is also a well-known genotoxic agent capable of damaging cells and tissues. Therefore radiation treatment can cause numerous side effects in exposed tissues and organs. Radiotherapy is a part of the front-line treatment regime for brain cancer patients, but can cause severe functional and morphological changes in exposed brain tissues. However, the mechanisms of radiation-induced effects in the brain are not well understood and are under-investigated. Recent data has implicated short RNAs, especially microRNAs, as important in radiation responses, yet nothing is known about radiation-induced changes in the brain microRNAome. We analyzed the effects of X-ray irradiation on microRNA expression in the hippocampus, frontal cortex, and cerebellum of male and female mice. Here, we report tissue-, time-, and sex-specific brain radiation responses, as well as show evidence of an interplay between microRNAs and their targets. Specifically, we show that changes in the expression of the miR-29 family may be linked, at least in part, to altered expression of de novo methyltransferase DNMT3a and changed global DNA methylation levels. Further, these sex-specific epigenetic changes may be correlated to the prevalence of radiation-induced cancers in males. We identified several microRNAs that can potentially serve as biomarkers of brain radiation exposure. In summary, our study may provide an important roadmap for further analysis of microRNA expression in different brain regions of male and female mice and for detailed dissection of radiation-induced brain responses.

MiR-34a in age and tissue related radio-sensitivity and serum miR-34a as a novel indicator of radiation injury

MiR-34a, a direct target of p53, has shown to exert potent anti-proliferative effects. It has also been found that miR-34a can be induced by irradiation in vitro and in vivo. However, the relationship between miR-34a and radio-sensitivity, and its potential diagnostic significance in radiation biology, remain unclear. This study found that differing responses to ionizing radiation (IR) of young and adult mice were related to miR-34a. First, we found that miR-34a could be induced in many organs by radiation of both young and adult mice. However, the level of miR-34a induced by young mice was much higher when compared to adult mice. Next, we found that miR-34a played a critical role in radio-sensitivity variations of different tissues by enhancing cell apoptosis and decreasing cell viability. We also found that the induction of miR-34a by radiation was in a p53 dependent manner and that one possible downstream target of miR-34a that lead to different radio-sensitivity was the anti-apoptosis molecular Bcl-2. However, over-expression of miR-34a and knockdown of Bcl-2 could significantly enhance the radio-sensitivity of different cells while inhibition of miR-34a could protect cells from radiation injury. Finally, we concluded that miR-34a could be stable in serum after IR and serve as a novel indicator of radiation injury. Taken together, this data strongly suggests that miR-34a may be a novel indicator, mediator and target of radiation injury, radio-sensitivity and radioprotection.

The elements of human cyclin D1 promoter and regulation involved

Cyclin D1 is a cell cycle machine, a sensor of extracellular signals and plays an important role in G1-S phase progression. The human cyclin D1 promoter contains multiple transcription factor binding sites such as AP-1, NF-қB, E2F, Oct-1, and so on. The extracellular signals functions through the signal transduction pathways converging at the binding sites to active or inhibit the promoter activity and regulate the cell cycle progression. Different signal transduction pathways regulate the promoter at different time to get the correct cell cycle switch. Disorder regulation or special extracellular stimuli can result in cell cycle out of control through the promoter activity regulation. Epigenetic modifications such as DNA methylation and histone acetylation may involved in cyclin D1 transcriptional regulation.

Detection of novel human MiRNAs responding to X-ray irradiation

Up to now, more than 1048 human miRNAs have been identified. However, the recognition of new human miRNAs is becoming more and more difficult. Based on the hypothesis that the expression of some miRNAs can be induced by ionizing radiation, total RNAs of HeLa cells were isolated 1 h after exposure to 2 Gy of X-rays, and total small RNAs were enriched and sequenced by PAGE and Solexa technology, respectively. As a result, 421 kinds of known miRNAs and 337 kinds of unknown sequences were identified, among which 10 novel miRNAs were characterized by bioinformatic approach and verified by qRT-PCR. Finally, putative targets of these miRNAs were predicted by TargetScan software and compared with known proteins down-regulated by radiation. It was confirmed that some of the targets of these novel miRNAs were radiation-related proteins. These results imply that these 10 novel miRNAs are radiation-related miRNAs. This study reveals a new way to find novel miRNAs.

Genomic analysis of microRNA time-course expression in liver of mice treated with genotoxic carcinogen N-ethyl-N-nitrosourea

BACKGROUND

Dysregulated expression of microRNAs (miRNAs) has been previously observed in human cancer tissues and shown promise in defining tumor status. However, there is little information as to if or when expression changes of miRNAs occur in normal tissues after carcinogen exposure.

RESULTS

To explore the possible time-course changes of miRNA expression induced by a carcinogen, we treated mice with one dose of 120 mg/kg N-ethyl-N-nitrosourea (ENU), a model genotoxic carcinogen, and vehicle control. The miRNA expression profiles were assessed in the mouse livers in a time-course design. miRNAs were isolated from the livers at days 1, 3, 7, 15, 30 and 120 after the treatment and their expression was determined using a miRNA PCR Array. Principal component analysis of the miRNA expression profiles showed that miRNA expression at post-treatment days (PTDs) 7 and 15 were different from those at the other time points and the control. The number of differentially expressed miRNAs (DEMs) changed over time (3, 5, 14, 32, 5 and 5 at PTDs 1, 3, 7, 15, 30 and 120, respectively). The magnitude of the expression change varied with time with the highest changes at PTDs 7 or 15 for most of the DEMs. In silico functional analysis of the DEMs at PTDs 7 and 15 indicated that the major functions of these ENU-induced DEMs were associated with DNA damage, DNA repair, apoptosis and other processes related to carcinogenesis.

CONCLUSION

Our results showed that many miRNAs changed their expression to respond the exposure of the genotoxic carcinogen ENU and the number and magnitude of the changes were highest at PTDs 7 to 15. Thus, one to two weeks after the exposure is the best time for miRNA expression sampling.

Low-dose radiation-induced responses: focusing on epigenetic regulation

PURPOSE

With the widespread use of ionising radiation, the risks of low-dose radiation have been increasingly highlighted for special attention. This review introduces the potential role of epigenetic elements in the regulation of the effects of low-dose radiation.

MATERIALS AND METHODS

The related literature has been analysed according to the topics of DNA methylation, histone modifications, chromatin remodelling and non-coding RNA modulation in low-dose radiation responses.

RESULTS

DNA methylation and radiation can reciprocally regulate effects, especially in the low-dose radiation area. The relationship between histone methylation and radiation mainly exists in the high-dose radiation area; histone deacetylase inhibitors show a promising application to enhance radiation sensitivity, both in the low-dose and high-dose areas; phosphorylated histone 2 AX (H2AX) shows a low sensitivity with 1-15 Gy irradiation as compared with lower dose radiation; and histone ubiquitination plays an important role in DNA damage repair mechanisms. Moreover, chromatin remodelling has an integral role in the repair of DNA double-strand breaks and the response of chromatin to ionising radiation. Finally, the effect of radiation on microRNA expression seems to vary according to cell type, radiation dose, and post-irradiation time point.

CONCLUSION

Small advances have been made in the understanding of epigenetic regulation of low-dose radiation responses. Many questions and blind spots deserve to be investigated. Many new epigenetic elements will be identified in low-dose radiation responses, which may give new insights into the mechanisms of radiation response and their exploitation in radiotherapy.

Heavy ions, radioprotectors and genomic instability: implications for human space exploration

The risk associated with space radiation exposure is unique from terrestrial radiation exposures due to differences in radiation quality, including linear energy transfer (LET). Both high- and low-LET radiations are capable of inducing genomic instability in mammalian cells, and this instability is thought to be a driving force underlying radiation carcinogenesis. Unfortunately, during space exploration, flight crews cannot entirely avoid radiation exposure. As a result, chemical and biological countermeasures will be an important component of successful extended missions such as the exploration of Mars. There are currently several radioprotective agents (radioprotectors) in use; however, scientists continue to search for ideal radioprotective compounds-safe to use and effective in preventing and/or reducing acute and delayed effects of irradiation. This review discusses the agents that are currently available or being evaluated for their potential as radioprotectors. Further, this review discusses some implications of radioprotection for the induction and/or propagation of genomic instability in the progeny of irradiated cells.

microRNAome changes in bystander three-dimensional human tissue models suggest priming of apoptotic pathways

The radiation-induced bystander effect (RIBE) is a phenomenon whereby unexposed cells exhibit molecular symptoms of stress exposure when adjacent or nearby cells are traversed by ionizing radiation (IR). Recent data suggest that RIBE may be epigenetically mediated by microRNAs (miRNAs), which are small regulatory molecules that target messenger RNA transcripts for translational inhibition. Here, we analyzed microRNAome changes in bystander tissues after α-particle microbeam irradiation of three-dimensional artificial human tissues using miRNA microarrays. Our results indicate that IR leads to a deregulation of miRNA expression in bystander tissues. We report that major bystander end points, including apoptosis, cell cycle deregulation and DNA hypomethylation, may be mediated by altered expression of miRNAs. Specifically, c-MYC-mediated upregulation of the miR-17 family was associated with decreased levels of E2F1 and RB1, suggesting a switch to a proliferative state in bystander tissues, while priming these cells for impending death signals. Upregulation of the miR-29 family resulted in decreased levels of its targets DNMT3a and MCL1, consequently affecting DNA methylation and apoptosis. Altered expression of miR-16 led to changes in expression of BCL2, suggesting modulation of apoptosis. Thus, our data clearly show that miRNAs play a profound role in the manifestation of late RIBE end points. In summary, this study creates a roadmap for understanding the role of microRNAome in RIBE and for developing novel RIBE biomarkers.

Small molecules with big effects: the role of the microRNAome in cancer and carcinogenesis

Small non-coding RNAs-microRNAs, are potent negative regulators of gene expression. MicroRNAs are involved in multiple biological processes, metabolic regulation, including cell proliferation, differentiation, and programmed cell death. Since the dysregulation of these processes is a hallmark of cancer, microRNAs can be viewed as major contributors to the pathogenesis of cancer, including initiation and progression of cancer. This review focuses on microRNA biogenesis and function, and their role in cancer, metastasis, drug resistance, and tumorigenesis.

Localization- and mutation-dependent microRNA (miRNA) expression signatures in gastrointestinal stromal tumours (GISTs), with a cluster of co-expressed miRNAs located at 14q32.31

The molecular biology and clinical behaviour of gastrointestinal stromal tumours (GISTs) are associated with their anatomical localization (stomach or intestine), and also with the mutation status of the receptor tyrosine kinases KIT and PDGFRA. Twelve GISTs were evaluated for differential miRNA expression signatures by use of microarrays representing 734 human miRNAs. Thirty-two miRNAs were found to be differentially expressed according to localization and mutation status. Differential expression was further analysed and confirmed for four miRNAs (miR-132, miR-221, miR-222, and miR-504) by qRT-PCR in 49 additional GISTs. Differentially expressed miRNAs were functionally mapped to KIT/PDGFRA signalling and G1/S-phase transition of the cell cycle, revealing 22 predicted miRNA/mRNA interactions for ten gene targets from KIT/PDGFRA signalling, and 12 interactions for 12 gene targets of G1/S-phase transition. Moreover, the expression of 44 miRNAs clustered in a genetically imprinted region at 14q32.31 was found to be strongly correlated in the microarray analysis. This was confirmed for two selected miRNAs (miR-134 and miR-370) from the 14q32.31 cluster by qRT-PCR in 49 additional GISTs, and the expression of these two miRNAs was significantly lower in GISTs with 14q loss, and also in GISTs with tumour progress. miRNA profiling may prove to be a key determinant of the biology and clinical features of GISTs.

Hypomethylation and genome instability in the germline of exposed parents and their progeny is associated with altered miRNA expression

Recent studies suggest that transgenerational genome instability may be epigenetic in nature and mediated via altered DNA methylation and microRNAome. Here, we investigated the nature and mechanisms underlying the disruption of DNA methylation and microRNA expression status in the germline and progeny of exposed parents. We have found that paternal irradiation leads to upregulation of the miR-29 family in the exposed male germline, which causes decreased expression of de novo methyltransferase, DNA methyltransferase 3a, and profound hypomethylation of long interspersed nuclear elements 1 (LINE1) and short interspersed nuclear elements B2 (SINE B2). Epigenetic changes in the male germline further resulted in deleterious effects in the somatic thymus tissue from the progeny of exposed animals, including hypomethylation of LINE1 and SINE B2. Hypomethylation of LINE1 and SINE B2 in the thymus tissue from the progeny was associated with a significant decrease in the levels of lymphoid-specific helicase (LSH) that is crucial for the maintenance of methylation and silencing of repetitive elements. Furthermore, we noted a significant upregulation of miR-468 that targets LSH and leads to its decreased expression in thymus in the progeny of exposed parents. We suggest that miR-468-mediated suppression of LSH leads to aberrant methylation of LINE1 and SINE B2. In summary, altered microRNAome and hypomethylation of retroelements constitute deleterious effects that may significantly influence genome stability of the parental germline and consequently cause genome instability in the progeny.

Memoirs of an insult: sperm as a possible source of transgenerational epimutations and genetic instability

Male transgenerational epigenetic effects have been discovered in the discipline of mouse radiation genetics, using genetic and non-genetic readouts. The mechanism to explain the origin of the transmission of epigenetic and genetic instability is still unknown. In a search for a hypothesis that could satisfy the data, we propose that regulation of chromosome structure in the germline, by the occupancy of matrix/scaffold associated regions, contains molecular memory function. The male germline is strikingly dynamic as to chromatin organization. This could explain why experience of irradiation stress leaves a persistent mark in the male germline only. To be installed, such memory requires both S-phase and chromatin reorganization during spermatogenesis and in the zygote, that likely also involves reorganization of loop domains. By this reorganization, another layer of information is added, needed to accommodate early embryonic development. Observations point at the involvement of DNA repair as inducer of transgenerational epigenetic modulation. Nuclear structure, chromatin composition and loop domain organization are aspects of human sperm variability that in many cases of assisted reproduction is increased due to inclusion of more incompletely differentiated/maturated sperm nuclei. Adjustment of loop domains in early embryo development can be anticipated and zygotic and cleavage stage S-phase repair activity will have to deal with potential paternal DNA lesions. Therefore, by changing male nucleus structure due to reproduction from impaired spermatogenesis, the transgenerational information content could be changed as well. We discuss aspects of male reproductive performance in the context of this hypothesis.

Ionizing radiation-induced bystander effects, potential targets for modulation of radiotherapy

Cells exposed to ionizing radiation show DNA damage, apoptosis, chromosomal aberrations or increased mutation frequency and for a long time it was generally accepted that these effects resulted from ionization of cell structures and the action of reactive oxygen species formed by water radiolysis. In the last few years, however, it has appeared that cells exposed to ionizing radiation and other genotoxic agents can release signals that induce very similar effects in non-targeted neighboring cells, phenomena known as bystander effects. These signals are transmitted to the neighboring non-hit cells by intercellular gap-junction communication or are released outside the cell, in the case of cultured cells into the medium. The signaling is mutual, and irradiated cells can also receive signals from non-irradiated neighbors. Most experiments show a decrease in survival of unirradiated bystander cells, but some studies of the influence of unirradiated or low dose-irradiated cells on those irradiated with higher doses show that intercellular bystander signaling can also increase the survival of irradiated cell populations. In the last few years, communication between irradiated and non-irradiated cells has attracted interest in many studies as a possible target for modulation of radiotherapy. Understanding the mechanisms underlying bystander effects is important for radiation risk assessment and for evaluation of protocols for cancer radiotherapy. In this review we describe different aspects of ionizing radiation-induced bystander effects: experimental examples, types of DNA damage, situations in vivo, and their possible role in adaptive response to irradiation, and we discuss their possible significance for anticancer therapy.