DNA damage and differential gene expression associated with physical stress in gilthead seabream (Sparus aurata)

Investigating the effects of acute and chronic stress on DNA damage

A hallmark of the vertebrate stress response is a rapid increase in glucocorticoids and catecholamines; however, this does not mean that these mediators are the best, or should be the only, metric measured when studying stress. Instead, it is becoming increasingly clear that assaying a suite of downstream metrics is necessary in stress physiology. One component of this suite could be assessing double-stranded DNA damage (dsDNA damage), which has recently been shown to increase in blood with both acute and chronic stress in house sparrows (Passer domesticus). To further understand the relationship between stress and dsDNA damage, we designed two experiments to address the following questions: (1) how does dsDNA damage with chronic stress vary across tissues? (2) does the increase in dsDNA damage during acute stress come from one arm of the stress response or both? We found that (1) dsDNA damage affects tissues differently during chronic stress and (2) the hypothalamic-pituitary-adrenal axis influences dsDNA damage with acute stress, but the sympathetic-adreno-medullary system does not. Surprisingly, our data are not explained by studies on changes in hormone receptor levels with chronic stress, so the underlying mechanism remains unclear.

Effect of different temperature variations on the physiological state of catfish species: a systematic review

Catfish are a highly diverse group of fish that are found in various regions across the globe. The significance of catfish culture extends to various aspects, including food security, economic advancement, preservation of cultural legacy, and ecological stewardship. The catfish industry is presently encountering unprecedented challenges as a consequence of the variability in water temperature caused by climate change. Temperature is a significant abiotic component that regulates and restricts fish physiology throughout their life cycle. The impact of severe temperatures on various species of catfish is dependent upon the magnitude of the stressor and additional influencing factors. This paper presents an analysis of the effects of temperature fluctuations on various aspects of catfish species, including growth and survival, blood parameters, enzymatic and hormone response, oxygen consumption rates, sound generation and hearing skills, nutritional requirements, and other phenotypic attributes. While this review is certainly not exhaustive, it offers a broad synopsis of the ideal temperature ranges that are most favorable for several catfish species. In-depth research to investigate the interacting impacts of severe temperature occurrences in conjunction with other associated environmental stresses on a wider variety of catfish species is crucial in order to further our understanding of how catfish species will respond to the anticipated climate change in the future.

Background DNA damage is higher in summer than winter in both free-living and captive birds

Although stress can cause overall damage to the genome, it is currently unknown whether normal background damage to DNA varies throughout the annual cycle. If DNA damage did vary seasonally, it would have major implications on environmental-genomic interactions. We measured background DNA double-stranded breaks using the neutral comet assay in five tissues (nucleated red blood cells, abdominal fat, hippocampus, hypothalamus, and liver) in four cohorts of house sparrows (Passer domesticus): free-living summer, captives on a summer light cycle, free-living winter, and captives on a winter light cycle. The experiment was designed to answer three questions: (1) Is red blood cell DNA damage representative of other tissues? (2) Is DNA damage in captive birds representative of DNA damage in free-living birds? (3) Does DNA damage show seasonality? We found that (1) blood is a representative tissue, (2) captive animals are representative of free-living animals, and (3) DNA damage is higher in the summer than in the winter. These data indicate that red blood cells can be an index of DNA damage throughout the body and that background levels of DNA damage show substantial seasonal variation. The latter result suggests the possibility that underlying molecular mechanisms of DNA damage and/or repair also change seasonally.

Transcriptomic response in thermally challenged seahorses Hippocampus erectus: The effect of magnitude and rate of temperature change

Hippocampus erectus inhabiting the shallow coastal waters of the southern Gulf of Mexico are naturally exposed to marked temperature variations occurring in different temporal scales. Under such heterogeneous conditions, a series of physiological and biochemical adjustments take place to restore and maintain homeostasis. This study investigated the molecular mechanisms involved in the response of H. erectus to increased temperature using transcriptome analysis based on RNA-Seq technology. Data was obtained from seahorses after 0.5-h exposure to combinations of different target temperatures (26 °C: control, and increased to 30 and 33 °C) and rates of thermal increase (abrupt: < 5 min; gradual: 1-1.5 °C every 3 h). The transcriptome of seahorses was assembled de novo using Trinity software to obtain 29,211 genes and 30,479 transcripts comprising 27,520,965 assembled bases. Seahorse exposure to both 30 and 33 °C triggered characteristic processes of the cellular stress response, regardless of the rate of thermal change. The transcriptomic profiles of H. erectus suggest an arrest of muscle development processes, the activation of heat shock proteins, and a switch to anaerobic metabolism within the first 0.5 h of exposure to target temperatures to ensure energy supply. Interestingly, apoptotic processes involving caspase were activated principally in gradual treatments, suggesting that prolonged exposure to even sublethal temperatures results in the accumulation of deleterious effects that may eventually terminate in cellular death. Results herein validate 30 °C and 33 °C as potential upper limits of thermal tolerance for H. erectus at the southernmost boundary of its geographic distribution.

Metabolomic and Transcript Analysis Revealed a Sex-Specific Effect of Glyphosate in Zebrafish Liver

Glyphosate is a component of commonly used herbicides for controlling weeds in crops, gardens and municipal parks. There is increasing awareness that glyphosate-based herbicides, in addition to acting on plants, may also exert toxicity in wildlife and humans. In this study, male and female adult zebrafish were exposed to 700 µg/L of glyphosate (GLY), for 28 days. We used the metabolomic approach and UHPLC-ESI-MS to analyze liver samples to investigate the adverse effects of glyphosate on hepatic metabolism. The impact of GLY was found to be sex-specific. In female, GLY exposure affected purine metabolism by decreasing the levels of AMP, GMP and inosinic acid, consequently increasing uric acid levels with respect to the control (CTRL). Exposure to GLY also caused a decrease of UMP levels in the pyrimidine metabolism pathway. In male, GLY exposure decreased the aminoadipic acid within the lysine degradation pathway. Transcript analysis of genes involved in stress response, oxidative stress and the immune system were also performed. Results demonstrated an increased stress response in both sexes, as suggested by higher nr3c1 expression. However, the hsp70.2 transcript level was increased in female but decreased in male. The results demonstrated reduced sod1, sod2, and gpx1a in male following exposure to GLY, indicating an impaired oxidative stress response. At the same time, an increase in the cat transcript level in female was observed. mRNA levels of the pro-inflammatory interleukins litaf and cxcl8b.1 were increased in female. Taken together, the results provide evidence of disrupted nucleotide hepatic metabolism, increased stress inflammatory response in female and disruption of oxidative stress response in male.

Insights into early ontogenesis: characterization of stress and development key genes of pikeperch (Sander lucioperca) in vivo and in vitro

There are still numerous difficulties in the successful farming of pikeperch in the anthropogenic environment of various aquaculture systems, especially during early developmental steps in the hatchery. To investigate the physiological processes involved on the molecular level, we determined the basal expression patterns of 21 genes involved in stress and immune responses and early ontogenesis of pikeperch between 0 and 175 days post hatch (dph). Their transcription patterns most likely reflect the challenges of growth and feed conversion. The gene coding for apolipoprotein A (APOE) was strongly expressed at 0 dph, indicating its importance for yolk sac utilization. Genes encoding bone morphogenetic proteins 4 and 7 (BMP4, BMP7), creatine kinase M (CKM), and SRY-box transcription factor 9 (SOX9) were highly abundant during the peak phases of morphological changes and acclimatization processes at 4-18 dph. The high expression of genes coding for peroxisome proliferator-activated receptors alpha and delta (PPARA, PPARD) at 121 and 175 dph, respectively, suggests their importance during this strong growth phase of juvenile stages. As an alternative experimental model to replace further in vivo investigations of ontogenetically important processes, we initiated the first approach towards a long-lasting primary cell culture from whole pikeperch embryos. The present study provides a set of possible biomarkers to support the monitoring of pikeperch farming and provides a first basis for the establishment of a suitable cell model of this emerging aquaculture species.

Oxidative stress, cell cycle arrest, DNA damage and apoptosis in the mud crab (Scylla paramamosain) induced by cadmium exposure

Cadmium is one of the most common heavy metal pollutants in the aquatic environment. Mud crab (Scylla paramamosain) is considered a model organism to monitor the impact of heavy metals. However, knowledge about toxicological mechanism of cadmium in crustaceans still remains limited. In this study, mud crabs were exposed to different concentrations of cadmium (0, 1.25, 2.5, 5 and 10 mg/L) for 72 h. Cadmium exposure significantly decreased superoxide dismutase (SOD) activity, catalase (CAT) activity and total antioxidative capacity (T-AOC), and significantly increased malondialdehyde (MDA) and H2O2 levels. Aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) activity significantly increased after cadmium exposure. Moreover, integrated biological responses version 2 (IBRv2) analysis suggested that cadmium exposure exerted stronger toxicity on mud crab. Furthermore, oxidative stress induced by cadmium exposure could decrease total hemocyte count (THC), interrupt Ca2+ homeostasis, and lead to cytological damage. Cadmium exposure induced DNA damage, which activated DNA damage response signaling ATR-CHK1-p53 pathway. Our results also showed that cadmium exposure significantly increased the apoptosis and caspase-3 mRNA levels, which implied that cadmium induced apoptosis through a caspase-3 pathway.

Molecular cloning, expression HSP70 and its response to bacterial challenge and heat stress in Microptenus salmoides

The gene encoding HSP70 was isolated from Microptenus salmoides by homologous cloning and rapid amplification of cDNA ends (RACE). The HSP70 transcripts were 2116 bp long and contained 1953 open reading frames encoding proteins of 650 amino acids with a molecular mass of 71.2 kDa and theoretical isoelectric point of 5.22. The qRT-PCR analysis showed that the HSP70 gene was differentially expressed in various tissues under normal conditions, and the highest HSP70 level was observed in the spleen and the lowest levels in the muscle and heart. The clear time-dependent expression level of HSP70 was observed after bacterial challenge and heat stress. A significant increase in HSP70 expression level was detected and reached a maximum at 3 h and 6 h in liver, spleens and gill tissues after Aeromonas hydrophila infection and heat stress, respectively (P < 0.05). As time progressed, the expression of HSP70 transcript was downregulated and mostly dropped back to the original level at 48 h. The concentration of cortisol, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) increased as the time of stress progressed, with the highest level found on 3 h and later declined rapidly and reached to the control levels at the 48 h. Those results suggested that HSP70 was involved in the immune response to bacterial challenge and heat stress. The cloning and expression analysis of the HSP70 provide theoretical basis to further study the mechanism of anti-adverseness in Microptenus salmoides.

Comparison between Single- and Group-housed Pregnant Sows for Direct and Indirect Physiological, Reproductive, Welfare Indicators and Gene Expression Profiling

Single- and group-housed pregnant sows were assessed during 8 weeks (4th and 8th to 14th) with regard to physiological, reproductive, welfare indicators and gene expression profiling. Compared to single-housed sows, group-housed sows had decreased non-return to estrus at 56 days after artificial insemination (AI) (83% vs 92%) and farrowing rate (78% vs 88%), respectively. Furthermore, group-housed sows showed a higher degree (p < 0.01) of advantageous physiological indicators, such as albumin (odds ratio [OR] = 4.4), alkaline phosphatase (OR = 1.5), bactericidal (OR = 3.2) and complement (OR = 24.3), and disadvantageous for alanine amino transferase (OR = 0.5), bilirubin (OR = 0.4), lysozyme (OR = 0.3) and C-reactive protein compared to single-housed. Eighty-seven genes related to immune response were underexpressed (log fold change ≤ 1.5; p < 0.05) during the 8th to 14th weeks in the group compared to single-housed sows, which in turn showed an immunomodulatory reduction on the expression of 43 genes during the 11th to 14th compared to the 4th week. Overall, the results were interpreted as indicative of greater comfort state of the group compared to single-housed sows.

Beyond corticosterone: The acute stress response increases DNA damage in house sparrows

Although corticosterone (Cort) has been the predominant metric used to assess acute stress in birds, it does not always accurately reflect how an animal copes with a stressor. Downstream measurements may be more reliable. In the current study, we tested the hypothesis that acute increases in DNA damage could be used to assess stressor exposure. Studies have shown DNA damage increases in response to stress-related hormones in vitro; however, this has not yet been thoroughly applied in wild animals. We exposed house sparrows (Passer domesticus) to a 30- or 120-min restraint stressor and took blood samples at 0, 30, 60, and 120 min to measure Cort, DNA damage, and uric acid. Both treatments increased DNA damage and Cort, and decreased uric acid. It thus appears that DNA damage can reflect acute stressor exposure. To improve the usability of DNA damage as a metric for stress, we also tested the impacts of sample storage on DNA damage. Leaving red blood cells on ice for up to 24 hr, only slightly influenced DNA damage. Freezing blood samples for 1-4 weeks substantially increased DNA damage. These findings emphasize the importance of reducing variation between samples by assaying them together whenever possible. Overall, these results indicate that assessing DNA damage is a valid method of assessing acute stressor exposure that is suitable for both laboratory- and field-based studies; however, additional research is needed on the molecular dynamics of nucleated red blood cells, including whether and how their DNA is repaired.

Alterations to transcriptomic profile, histopathology, and oxidative stress in liver of pikeperch (Sander lucioperca) under heat stress

Pikeperch (Sander lucioperca) is an economically important cool-water fish. In recent years, its cultivation has become threatened by higher temperatures in summer. We previously investigated the effects of heat stress on pikeperch liver under different temperatures, but the molecular mechanism of the heat-stress response is still unknown. This study applied consistent heat stress (29 °C, 0-48 h) to pikeperch juveniles, and a transcriptomic profile of pikeperch liver under heat stress (29 °C, 0 h) was performed by RNA-Seq. The antioxidant status, changes in liver histology, and antioxidant gene expression at different time points were examined. We identified 403 differentially expressed genes (DEGs), many of which were enriched in KEGG pathways, including protein processing in endoplasmic reticulum (ER), insulin signaling, and immune-related pathways. Among these, the most significant heat-stress-related pathway was protein processing in ER, indicating that this pathway is critical for the heat-stress response. After consistent heat stress at 29 °C, the total antioxidant capacity (T-AOC), the activities of total superoxide dismutase (T-SOD) and catalase (CAT), and the mRNA expression of manganese SOD (Mn-SOD), CAT, and glutathione peroxidase 1 and 7 (GPx1 and GPx7) in the treated groups showed the same trend of first increasing and then decreasing. Levels of malondialdehyde (MDA) content did not show significant differences between samples at 0 h and 3 h, but significantly increased by 6 h, and thereafter decreased. The liver tissue was normal at 0 h (29 °C); however, it suffered histological damage with increased duration of the heat stress. Above all, heat stress at 29 °C seemed to cause oxidative damage and dysfunction in pikeperch liver between 3 h and 48 h. The present results indicate that pikeperch have the capacity to defend against heat stress and maintain relative balance of oxidation-reduction reactions mainly through activating the antioxidant system, protein processing in ER, the insulin-signaling pathway, and immune-related pathways.

Dietary diisononylphthalate contamination induces hepatic stress: a multidisciplinary investigation in gilthead seabream (Sparus aurata) liver

In this study, adult gilthead seabream (Sparus aurata) were exposed for 21 days to Di-iso-nonylphthalte (DiNP at 15 and 1500 μg kg^-1 bw day^-1) via the diet. This plastic additive has been recently introduced to replace the di-(2-ethylhexyl)phthalate, the toxicity of which has been demonstrated conclusively both in vivo and in vitro trials. An analysis of a set of biomarkers involved in stress and immune response provides evidence of hepatic toxicity by DiNP in the present study. Both hsp70 and gr mRNA levels were upregulated significantly by DiNP, while plasma cortisol increased only in fish fed with the lowest DiNP dose. The oxidative stress markers g6pdh, glut red, gpx1 and CAT were upregulated by DiNP; gst mRNA was induced by the high dose and gck mRNA was downregulated significantly by the low dose. The mRNA levels of genes involved in the immune response, such as pla2, 5-lox, tnfa and cox2, were upregulated significantly only by the high dose of DiNP, while il1 mRNA increases in both doses. These molecular evidences were complemented with features obtained by Fourier Transform Infrared Imaging (FTIRI) analysis regarding the hepatic distribution of the main biological macromolecules. The FTIRI analysis showed an alteration of biochemical composition in DiNP samples. In particular, the low dose of DiNP induced an increase of saturated and unsaturated lipids and phosphorylated proteins, and a decrease of glycogen levels. The levels of caspase did not change significantly in the study, suggesting that DiNP does not activate apoptosis. Finally, the results also suggested the onset of hepatic oxidative stress and the activation of immune response, adding new knowledge to the already described hepatic DiNP toxicity.

DNA damage as an indicator of chronic stress: Correlations with corticosterone and uric acid

Corticosterone does not change in consistent ways across species and contexts, making it challenging to use as an indicator of chronic stress. We assessed DNA damage as a potential metric that could be a more integrative stress measurement with direct links to health. We captured free-living house sparrows, took an immediate blood sample, and transferred them to the laboratory, exposing them to the chronic stress of captivity. Biweekly blood and weight samples were then taken for 4 weeks. We immediately assessed DNA damage in red blood cells using the comet assay and later quantified corticosterone. Uric acid was analyzed in a separate group of birds. We found that birds initially lost, but began to regain weight over the course of captivity. DNA damage peaked within the first 10 days of captivity, and mostly remained elevated. However, the cellular distribution of damage changed considerably over time; most cells showed low levels of damage early, a bimodal distribution of high and low DNA damage during the peak of damage, and a wide unimodal distribution of damage at the end of the 4 weeks. Furthermore, corticosterone increased and remained elevated and uric acid decreased and remained depleted over the same period. Although both a molecular (DNA damage) and an endocrine (corticosterone) marker showed similar response profiles over the 4 weeks, they were not correlated, suggesting they reflect different aspects of the underlying physiology. These data provide convincing preliminary evidence that DNA damage has potential to be an additional indicator of chronic stress.

Effects of high temperature on biochemical parameters, oxidative stress, DNA damage and apoptosis of pufferfish (Takifugu obscurus)

Water temperature is an important environmental factor that affects physiology and biochemical activities of fish. In this study, we investigated of high temperature on biochemical parameters, oxidative stress, DNA damage and apoptosis of pufferfish. Thermal stress could significantly increase the levels of AST, ALT, LDH, GLU and TG, whereas the levels of ALP and TP decrease significantly. In addition, thermal stress also decreased total blood cell count, inhibited cell viability, and subsequently lead to DNA damage and apoptosis. The mRNA levels of p53, caspase-9 and caspase-3 were up-regulated under thermal stress. These results suggested that caspase-dependent and p53 signaling pathways could play important roles in thermal stress-induced apoptosis in fish. Furthermore, the gene expression of SOD, CAT, HSP90 and C3 were induced by thermal stress. This study provides new insights into the mechanism whereby thermal stress affects physiological responses and apoptosis in pufferfish.

Insulin-like Growth Factor Binding Protein6 Associated with Neuronal Apoptosis Following Intracerebral Hemorrhage in Rats

The insulin-like growth factor (IGF) system is linked to CNS pathological states. The functions of IGFs are modulated by a family of binding proteins termed insulin-like growth factor binding proteins (IGFBPs). Here, we demonstrate that IGFBP-6 may be associated with neuronal apoptosis in the processes of intracerebral hemorrhage (ICH). We obtained a significant upregulation of IGFBP-6 in neurons adjacent to the hematoma following ICH with the results of Western blot, immunohistochemistry, and immunofluorescence. Increasing IGFBP-6 level was found to be accompanied by the upregulation of Bax, Bcl-2, and active caspase-3. Besides, IGFBP-6 co-localized well with active caspase-3 in neurons, indicating its potential role in neuronal apoptosis. Knocking down IGFBP-6 by RNA-interference in PC12 cells reduced active caspase-3 expression. Thus, IGFBP-6 may play a role in promoting the brain secondary damage following ICH.