Precoce and opposite response of proteasome activity after acute or chronic exposure of C. elegans to γ-radiation

Aronia melanocarpa extract extends the lifespan and health-span of Caenorhabditis elegans via mitogen-activated protein kinase 1

Aging is a highly complex process and one of the largest risk factors for many chronic diseases. Aronia melanocarpa (AM) is rich in bioactive phytochemicals with antioxidant, anti-inflammatory, and anticancer properties. However, little is known about its effects on aging. The objective of this study was to evaluate the effects of AM extract on lifespan and health-span using Caenorhabditis elegans as a representative model. The mechanisms of its effects were explored using transcriptomics and untargeted metabolomics. Results showed that the lifespan of C. elegans was significantly extended by 22.2% after high-dose AM treatment. AM improved the behavior and physiological functions of C. elegans by increasing the pharyngeal pumping rate, decreasing lipofuscin accumulation and the reactive oxygen species level, enhancing resistance to oxidative stress, and increasing the activities of superoxide dismutase and catalase. Transcriptome analysis showed that the pmk-1 gene (mitogen-activated protein kinase 1), which is involved in the MAPK signaling pathway, was the gene with the largest fold change after AM intervention. However, in the C. elegans pmk-1(km25) mutant, the beneficial effect of AM in improving nematode senescence disappeared. An untargeted metabolomics study showed that the levels of 4-hydroxyproline, rhamnose, and cysteine were increased after AM supplementation, and their extending effect on the lifespan and health-span of C. elegans were partly dependent on the pmk-1 gene. In conclusion, our results revealed that AM can promote the lifespan and health-span of C. elegans via the PMK-1 pathway, highlighting the potential of AM as a dietary supplement to delay aging.

Host defense alteration in Caenorhabditis elegans after evolution under ionizing radiation

BACKGROUND

Adaptation to a stressor can lead to costs on other traits. These costs play an unavoidable role on fitness and influence the evolutionary trajectory of a population. Host defense seems highly subject to these costs, possibly because its maintenance is energetically costly but essential to the survival. When assessing the ecological risk related to pollution, it is therefore relevant to consider these costs to evaluate the evolutionary consequences of stressors on populations. However, to the best of our knowledge, the effects of evolution in irradiate environment on host defense have never been studied. Using an experimental evolution approach, we analyzed fitness across 20 transfers (about 20 generations) in Caenorhabditis elegans populations exposed to 0, 1.4, and 50.0 mGy.h- 1 of 137Cs gamma radiation. Then, populations from transfer 17 were placed in the same environmental conditions without irradiation (i.e., common garden) for about 10 generations before being exposed to the bacterial parasite Serratia marcescens and their survival was estimated to study host defense. Finally, we studied the presence of an evolutionary trade-off between fitness of irradiated populations and host defense.

RESULTS

We found a lower fitness in both irradiated treatments compared to the control ones, but fitness increased over time in the 50.0 mGy.h- 1, suggesting a local adaptation of the populations. Then, the survival rate of C. elegans to S. marcescens was lower for common garden populations that had previously evolved under both irradiation treatments, indicating that evolution in gamma-irradiated environment had a cost on host defense of C. elegans. Furthermore, we showed a trade-off between standardized fitness at the end of the multigenerational experiment and survival of C. elegans to S. marcescens in the control treatment, but a positive correlation between the two traits for the two irradiated treatments. These results indicate that among irradiated populations, those most sensitive to ionizing radiation are also the most susceptible to the pathogen. On the other hand, other irradiated populations appear to have evolved cross-resistance to both stress factors.

CONCLUSIONS

Our study shows that adaptation to an environmental stressor can be associated with an evolutionary cost when a new stressor appears, even several generations after the end of the first stressor. Among irradiated populations, we observed an evolution of resistance to ionizing radiation, which also appeared to provide an advantage against the pathogen. On the other hand, some of the irradiated populations seemed to accumulate sensitivities to stressors. This work provides a new argument to show the importance of considering evolutionary changes in ecotoxicology and for ecological risk assessment.

Ionizing radiation affects the demography and the evolution of Caenorhabditis elegans populations

Ionizing radiation can reduce survival, reproduction and affect development, and lead to the extinction of populations if their evolutionary response is insufficient. However, demographic and evolutionary studies on the effects of ionizing radiation are still scarce. Using an experimental evolution approach, we analyzed population growth rate and associated change in life history traits across generations in Caenorhabditis elegans populations exposed to 0, 1.4, and 50.0 mGy.h^-1 of ionizing radiation (gamma external irradiation). We found a higher population growth rate in the 1.4 mGy.h^-1 treatment and a lower in the 50.0 mGy.h^-1 treatment compared to the control. Realized fecundity was lower in both 1.4 and 50.0 mGy.h^-1 than control treatment. High irradiation levels decreased brood size from self-fertilized hermaphrodites, specifically early brood size. Finally, high irradiation levels decreased hatching success compared to the control condition. In reciprocal-transplant experiments, we found that life in low irradiation conditions led to the evolution of higher hatching success and late brood size. These changes could provide better tolerance against ionizing radiation, investing more in self-maintenance than in reproduction. These evolutionary changes were with some costs of adaptation. This study shows that ionizing radiation has both demographic and evolutionary consequences on populations.

Male frequency in Caenorhabditis elegans increases in response to chronic irradiation

Outcrossing can be advantageous in a changing environment because it promotes the purge of deleterious mutations and increases the genetic diversity within a population, which may improve population persistence and evolutionary potential. Some species may, therefore, switch their reproductive mode from inbreeding to outcrossing when under environmental stress. This switch may have consequences on the demographic dynamics and evolutionary trajectory of populations. For example, it may directly influence the sex ratio of a population. However, much remains to be discovered about the mechanisms and evolutionary implications of sex ratio changes in a population in response to environmental stress. Populations of the androdioecious nematode Caenorhabditis elegans, are composed of selfing hermaphrodites and rare males. Here, we investigate the changes in the sex ratio of C. elegans populations exposed to radioactive pollution for 60 days or around 20 generations. We experimentally exposed populations to three levels of ionizing radiation (i.e., 0, 1.4, and 50 mGy.h^-1). We then performed reciprocal transplant experiments to evaluate genetic divergence between populations submitted to different treatments. Finally, we used a mathematical model to examine the evolutionary mechanisms that could be responsible for the change in sex ratio. Our results showed an increase in male frequency in irradiated populations, and this effect increased with the dose rate. The model showed that an increase in male fertilization success or a decrease in hermaphrodite self-fertilization could explain this increase in the frequency of males. Moreover, males persisted in populations after transplant back into the control conditions. These results suggested selection favoring outcrossing under irradiation conditions. This study shows that ionizing radiation can sustainably alter the reproductive strategy of a population, likely impacting its long-term evolutionary history. This study highlights the need to evaluate the impact of pollutants on the reproductive strategies of populations when assessing the ecological risks.

The endophytic fungus Penicillium oxalicum isolated from Ligusticum chuanxiong Hort possesses DNA damage-protecting potential and increases stress resistance properties in Caenorhabditis elegans

The chemical composition and antioxidant activity of extracts (POE) of Penicillium oxalate isolated from Ligusticum chuanxiong Hort have been investigated. However, the biological activity of POE is limited, and its antioxidant, stress resistance and DNA protection effects in vivo are unclear. The current study aims to explore the beneficial effects of POE on DNA damage protection in pBR322 plasmid and lymphocytes and stress resistance in Caenorhabditis elegans. The results showed that POE increased the survival rate of C. elegans under 35°C, UV and H₂O₂ stress, attenuated ROS and MDA accumulation, and enhanced the activity of some important enzymes (SOD, CTA, and GSH-PX). In addition, the POE-mediated stress resistance involved the upregulation of the expression of the sod-3, sod-5, gst-4, ctl-1, ctl-2, daf-16, hsp-16.1, hsp-16.2, and hsf-1 genes and acted dependently on daf-16 and hsf-1 rather than skn-1. Moreover, POE also reduced lipofuscin levels, but did not prolong the lifespan or damage the growth, reproduction and locomotion of C. elegans. Furthermore, POE showed a protective effect against DNA scission in the pBR322 plasmid and lymphocytes. These results suggested that P. oxalate extracts have significant anti-stress and DNA protection potential and could be potential drug candidates in the pharmaceutical field, thus greatly broadening the understanding of the biological effects of the endophytic fungus P. oxalate.

Adverse outcome pathways (AOPs) for radiation-induced reproductive effects in environmental species: state of science and identification of a consensus AOP network

BACKGROUND

Reproductive effects of ionizing radiation in organisms have been observed under laboratory and field conditions. Such assessments often rely on associations between exposure and effects, and thus lacking a detailed mechanistic understanding of causality between effects occurring at different levels of biological organization. The Adverse Outcome Pathway (AOP), a conceptual knowledge framework to capture, organize, evaluate and visualize the scientific knowledge of relevant toxicological effects, has the potential to evaluate the causal relationships between molecular, cellular, individual, and population effects. This paper presents the first development of a set of consensus AOPs for reproductive effects of ionizing radiation in wildlife. This work was performed by a group of experts formed during a workshop organized jointly by the Multidisciplinary European Low Dose Initiative (MELODI) and the European Radioecology Alliance (ALLIANCE) associations to present the AOP approach and tools. The work presents a series of taxon-specific case studies that were used to identify relevant empirical evidence, identify common AOP components and propose a set of consensus AOPs that could be organized into an AOP network with broader taxonomic applicability.

CONCLUSION

Expert consultation led to the identification of key biological events and description of causal linkages between ionizing radiation, reproductive impairment and reduction in population fitness. The study characterized the knowledge domain of taxon-specific AOPs, identified knowledge gaps pertinent to reproductive-relevant AOP development and reflected on how AOPs could assist applications in radiation (radioecological) research, environmental health assessment, and radiological protection. Future advancement and consolidation of the AOPs is planned to include structured weight of evidence considerations, formalized review and critical assessment of the empirical evidence prior to formal submission and review by the OECD sponsored AOP development program.

Deciphering Differential Life Stage Radioinduced Reproductive Decline in Caenorhabditis elegans through Lipid Analysis

Wildlife is chronically exposed to various sources of ionizing radiations, both environmental or anthropic, due to nuclear energy use, which can induce several defects in organisms. In invertebrates, reproduction, which directly impacts population dynamics, has been found to be the most radiosensitive endpoint. Understanding the underlying molecular pathways inducing this reproduction decrease can help in predicting the effects at larger scales (i.e., population). In this study, we used a life stage dependent approach in order to better understand the molecular determinants of reproduction decrease in the roundworm C. elegans. Worms were chronically exposed to 50 mGy·h⁻¹ external gamma ionizing radiations throughout different developmental periods (namely embryogenesis, gametogenesis, and full development). Then, in addition to reproduction parameters, we performed a wide analysis of lipids (different class and fatty acid via FAMES), which are both important signaling molecules for reproduction and molecular targets of oxidative stress. Our results showed that reproductive defects are life stage dependent, that lipids are differently misregulated according to the considered exposure (e.g., upon embryogenesis and full development) and do not fully explain radiation induced reproductive defects. Finally, our results enable us to propose a conceptual model of lipid signaling after radiation stress in which both the soma and the germline participate.

Review of Biological Effects of Acute and Chronic Radiation Exposure on Caenorhabditis elegans

Knowledge regarding complex radiation responses in biological systems can be enhanced using genetically amenable model organisms. In this manuscript, we reviewed the use of the nematode, Caenorhabditis elegans (C. elegans), as a model organism to investigate radiation’s biological effects. Diverse types of experiments were conducted on C. elegans, using acute and chronic exposure to different ionizing radiation types, and to assess various biological responses. These responses differed based on the type and dose of radiation and the chemical substances in which the worms were grown or maintained. A few studies compared responses to various radiation types and doses as well as other environmental exposures. Therefore, this paper focused on the effect of irradiation on C. elegans, based on the intensity of the radiation dose and the length of exposure and ways to decrease the effects of ionizing radiation. Moreover, we discussed several studies showing that dietary components such as vitamin A, polyunsaturated fatty acids, and polyphenol-rich food source may promote the resistance of C. elegans to ionizing radiation and increase their life span after irradiation.

Induction and Regulation of the Immunoproteasome Subunit β5i (PSMB8) in Laryngeal and Hypopharyngeal Carcinoma Cells

Background

The ubiquitin–proteasome pathway (UPP) is closely associated with the occurrence and progression of cancer, and the 5i immunoproteasome subunit is an important antitumor target in UPP. This study aimed to characterize the regulation of the immunoproteasome subunit β5i (PSMB8) in JHU-011 laryngeal carcinoma cells and FaDu hypopharyngeal carcinoma cells to explore a new target for the treatment of laryngeal and hypopharyngeal carcinomas.

Material/Methods

JHU-011 and FaDu cells were used as effector cells in this study. By means of ⁶⁰Co γ-irradiation, the construction of stable cell lines of the silenced proto-oncogene c-Abl, and the addition of exogenous tyrosine kinase inhibitor (TKI) and activator, the transcription and protein expression levels of PSMB8 and its alternatively spliced isoforms in both cell lines were detected by real-time fluorescence quantitative polymerase chain reaction (RT-PCR) and Western blot.

Results

Ionizing radiation upregulated the transcription level of the alternatively spliced isoform of PSMB8, E2, in both cell lines, thereby upregulating the mRNA and protein levels of PSMB8. The silencing of the proto-oncogene c-Abl and the activation and inhibition of its kinetic kinase product can affect the transcription and protein levels of PSMB8.

Conclusions

Ionizing radiation can significantly upregulate the mRNA and protein levels of PSMB8, which happens through the upregulation of its splicing isoform E2. The proto-oncogene c-Abl and its kinetic kinase protein product can regulate the transcription and protein expression levels of PSMB8 and its alternatively spliced isoforms.

In vivo assessment of reactive oxygen species production and oxidative stress effects induced by chronic exposure to gamma radiation in Caenorhabditis elegans

In the current study, effects of chronic exposure to ionizing gamma radiation were assessed in the radioresistant nematode Caenorhabditis elegans in order to understand whether antioxidant defences (AODs) could ameliorate radical formation, or if increased ROS levels would cause oxidative damage. This analysis was accompanied by phenotypical as well as molecular investigations, via assessment of reproductive capacity, somatic growth and RNA-seq analysis. The use of a fluorescent reporter strain (sod1::gfp) and two ratiometric biosensors (HyPer and Grx1-roGFP2) demonstrated increased ROS production (H₂O₂) and activation of AODs (SOD1 and Grx) in vivo. The data showed that at dose-rates ≤10 mGy h^-1 defence mechanisms were able to prevent the manifestation of oxidative stress. In contrast, at dose-rates ≥40 mGy h^-1 the continuous formation of radicals caused a redox shift, which lead to oxidative stress transcriptomic responses, including changes in mitochondrial functions, protein degradation, lipid metabolism and collagen synthesis. Moreover, genotoxic effects were among the most over-represented functions affected by chronic gamma irradiation, as indicated by differential regulation of genes involved in DNA damage, DNA repair, cell-cycle checkpoints, chromosome segregation and chromatin remodelling. Ultimately, the exposure to gamma radiation caused reprotoxic effects, with >20% reduction in the number of offspring per adult hermaphrodite at dose-rates ≥40 mGy h^-1, accompanied by the down-regulation of more than 300 genes related to reproductive system, apoptosis, meiotic functions and gamete development and fertilization.

Gamma radiation induces life stage-dependent reprotoxicity in Caenorhabditis elegans via impairment of spermatogenesis

The current study investigated life stage, tissue and cell dependent sensitivity to ionizing radiation of the nematode Caenorhabditis elegans. Results showed that irradiation of post mitotic L4 stage larvae induced no significant effects with respect to mortality, morbidity or reproduction at either acute dose ≤6 Gy (1500 mGy·h^-1) or chronic exposure ≤15 Gy (≤100 mGy·h^-1). In contrast, chronic exposure from the embryo to the L4-young adult stage caused a dose and dose-rate dependent reprotoxicity with 43% reduction in total brood size at 6.7 Gy (108 mGy·h^-1). Systematic irradiation of the different developmental stages showed that the most sensitive life stage was L1 to young L4. Exposure during these stages was associated with dose-rate dependent genotoxic effects, resulting in a 1.8 to 2 fold increase in germ cell apoptosis in larvae subjected to 40 or 100 mGy·h^-1, respectively. This was accompanied by a dose-rate dependent reduction in the number of spermatids, which was positively correlated to the reprotoxic effect (0.99, PCC). RNAseq analysis of nematodes irradiated from L1 to L4 stage revealed a significant enrichment of differentially expressed genes related to both male and hermaphrodite reproductive processes. Gene network analysis revealed effects related to down-regulation of genes required for spindle formation and sperm meiosis/maturation, including smz-1, smz-2 and htas-1. Furthermore, the expression of a subset of 28 set-17 regulated Major Sperm Proteins (MSP) required for spermatid production was correlated (R² 0.80) to the reduction in reproduction and the number of spermatids. Collectively these observations corroborate the impairment of spermatogenesis as the major cause of gamma radiation induced life-stage dependent reprotoxic effect. Furthermore, the progeny of irradiated nematodes showed significant embryonal DNA damage that was associated with persistent effect on somatic growth. Unexpectedly, these nematodes maintained much of their reproductive capacity in spite of the reduced growth.

Glochidion zeylanicum leaf extracts exhibit lifespan extending and oxidative stress resistance properties in Caenorhabditis elegans via DAF-16/FoxO and SKN-1/Nrf-2 signaling pathways

BACKGROUND

Glochidion zeylanicum (GZ), a common plant in Thailand and Eastern Asia, is rich in antioxidants. However, the possible anti-aging and oxidative stress resistance properties of GZ leaf extracts (hexane and methanol extracts) have not been reported.

PURPOSE

We aimed to provide the first science-based evidence of the beneficial effects of GZ on anti-aging and oxidative stress resistance in the Caenorhabditis elegans model.

METHODS

The phytochemical composition of the hexane and methanol extracts were analyzed using GLC-MS and LC-MS. Fingerprinting analysis of the extract was performed by RP-HPLC. We determined total phenolics, flavonoids, and antioxidant properties via DPPH and ABTS assays. Oxidative stress resistance, anti-aging and lifespan were studied in C. elegans treated with leaf extracts.

RESULTS

GZ leaf extracts protected the worms against oxidative stress and attenuated ROS accumulation. The expression of stress-response genes, such as SOD-3, and GST-4 were up-regulated, whereas HSP-16.2 was down-regulated after GZ treatment. The oxidative stress resistance properties of GZ possibly involved the DAF-16/FoxO and SKN-1/Nrf-2 transcription factors. GZ leaf extracts improved pharyngeal pumping function and autofluorescent pigment attenuation suggesting anti-aging properties. GZ leaf extracts modulated the lifespan extension in C. elegans.

CONCLUSION

This study reports novel anti-aging and antioxidant activities of GZ leaf extracts, suggesting a novel bioactivity for a medicinally important plant and supplementary drug against oxidative stress.

Differential modification of the C. elegans proteome in response to acute and chronic gamma radiation: Link with reproduction decline

Emission of ionizing radiation (IR) in the environment is a natural phenomenon which can be enhanced by human activities. Ecosystems are then chronically exposed to IR. But environmental risk assessment of chronic exposure suffers from a lack of knowledge. Extrapolation of data from acute to chronic exposure is not always relevant, and can lead to uncertainties as effects could be different between the two irradiation modes, especially regarding reproduction endpoint, which is an ecologically relevant parameter. In the present study, we decided to refine the understanding of the molecular mechanisms involved in response to acute and chronic γ-irradiation by a global proteome label free LC-MS/MS analysis. C. elegans were exposed to 3 common cumulated radiation doses for acute or chronic exposure condition and global modification of the proteome was studied. This analysis of protein expression has demonstrated the modulation of proteins involved in regulatory biological processes such as lipid transport, DNA replication, germ cell development, apoptosis, ion transport, cuticle development, and aging at lower doses than those for which individual effects on reproduction have been previously observed. Thus, these proteins could constitute early and sensitive markers of radio-induced reprotoxicity; more specifically HAT-1, RPS-19 in acute and VIT-3 for chronic conditions that are expressed in a dose-dependent manner. Finally, to focus on reproduction process, this analysis showed either repression or overexpression of 12 common proteins in organisms exposed to acute or chronic irradiation, respectively. These proteins include the vitellogenin cluster notably involved in lipid transport and oocyte maturation and proteins involved in cuticle development and molting i.e. COL-14, GLF-1, NOAH-1, NOAH-2, ACN-1. These results show that protein expression modulation is a sensitive and predictive marker of radio-induced reproductive effects, but also highlight limitation of data extrapolation from acute to chronic exposure for environmental risk assessment.

Interplay between ionizing radiation effects and aging in C. elegans

Living species are chronically exposed to environmental ionizing radiations from sources that can be overexpressed by nuclear accidents. In invertebrates, reproduction is the most radiosensitive studied endpoint, likely to be connected with aging. Surprisingly, aging is a sparsely investigated endpoint after chronic ionizing radiation, whereas understanding it is of fundamental interest in biology and medicine. Indeed, aging and aging-related diseases (e.g., cancer and degenerative diseases) cause about 90% of deaths in developed countries. Therefore, glp-1 sterile Caenorhabditis elegans nematode was used to assess the impact of chronic gamma irradiation on the lifespan. Analyses were performed, at the individual level, on aging and, in order to delve deeper into the mechanisms, at the molecular level, on oxidative damage (carbonylation), biomolecules (lipids, proteins and nucleic acids) and their colocalization. We observed that ionizing radiation accelerates aging (whatever the duration (3-19 days)/dose (0.5-24 Gy)/dose rate (7 and 52 mGy h^-1) tested) leading to a longevity value equivalent to that of wt nematode (∼25-30 days). Moreover, the level of protein oxidative damage (carbonylation) turned out to be good cellular biomarker of aging, since it increases with age. Conversely, chronic radiation treatments reduced carbonylation levels and induced neutral lipid catabolism whatever the dose rate and the final delivered dose. Finally, under some conditions a lipid-protein colocalization without any carbonyl was observed; this could be linked to yolk accumulation in glp-1 nematodes. To conclude, we noticed through this study a link between chronic gamma exposure, lifespan shortening and lipid level decrease associated with a decrease in the overall carbonylation.