Turning up the heat: The effects of thermal acclimation on the kinetics of hsp70 gene expression in the eurythermal goby, Gillichthys mirabilis

The beneficial effect of nanomethionine supplementation on growth performance, gene expression profile, and histopathology of heat-stressed broiler chicken

This study investigated the effects of nanomethionine (nano-meth) on performance, antioxidants, and gene expression of HSP70, HSP90 and Heat Shock factor-1 (HSF-1) from the liver, and TLR4 from the jejunum, of broiler chickens reared under normal temperatures or under heat stress. Three hundred 1-day-old chicks were randomly assigned to 5 treatment groups. Group 1 served as control. Under normal temperature, birds in group 2 received nano-meth (10 mL/L of drinking water) from d1 until the experiment ended. Group 3 birds were heat-stressed (HS) and did not receive any supplementation. Group 4 received nano-meth in the same dose from d1 old until experiment ended, and the birds were exposed to HS. Group 5 birds were HS and received supplementation of nano-meth during the HS period only. Nano-meth improved (P < 0.0001) final body weight, weight gain, feed conversion ratio, and also decreased (P < 0.0001) the effect of HS on growth performance. Reduction (P < 0.0001) in malondialdehyde and changes in antioxidant enzymes GPX and CAT activity indicated the antioxidant effect of nano-meth. Nano-meth supplementation caused an increase in the expression of HSP70 , HSP90 and HSF1, and a downregulation of TLR4 gene expression. Additionally, nano-meth-supplemented groups showed marked improvement in the histological liver structure, intestinal morphology and villus height compared to control or HS groups.

The heat shock response shows plasticity in embryonic lake whitefish (Coregonus clupeaformis) exposed to repeated thermal stress

We examined the impact of repeated thermal stress on the heat shock response (HSR) of thermally sensitive lake whitefish (Coregonus clupeaformis) embryos. Our treatments were designed to mimic temperature fluctuations in the vicinity of industrial thermal effluents. Embryos were either maintained at control temperatures (3 ^oC) or exposed to a repeated thermal stress (TS) of 3 or 6 ^oC above control temperature every 3 or 6 days throughout embryonic development. At 82 days post-fertilisation, repeated TS treatments were stopped and embryos received either a high level TS of 12, 15, or 18 ^oC above ambient temperature for 1 or 4 h, or no additional TS. These treatments were carried out after a 6 h recovery from the last repeated TS. Embryos in the no repeated TS group responded, as expected, with increases in hsp70 mRNA in response to 12, 15 and 18 ^oC high-level TS. However, exposure to repeated TS of 3 or 6 ⁰C every 6 days also resulted in a significant upregulation of hsp70 mRNA relative to the controls. Importantly, these repeated TS events and the associated elevations in hsp70 attenuated the upregulation of hsp70 in response to a 1 h, high-level TS of 12 ^oC above ambient, but not to either longer (4 h) or higher (15 or 18 ^oC) TS events. Conversely, hsp90α mRNA levels were not consistently elevated in the no repeated TS groups exposed to high-level TS. In some instances, hsp90α levels appeared to decrease in embryos exposed to repeated TS followed by a high-level TS. The observed attenuation of the HSR in lake whitefish embryos demonstrates that embryos of this species have plasticity in their HSR and repeated TS may protect against high-level TS, but the response differs based on repeated TS treatment, high-level TS temperature and duration, and the gene of interest.

Cloning and identification of grass carp transcription factor HSF1 and its characterization involving the production of fish HSP70

In mammals, heat shock transcription factor 1 (HSF1) is well documented as the critical transcript factor to regulate heat shock protein 70 (HSP70) expression under different stresses, such as heat shock or bacterial infection. In fish, Hsf1 responses to physiological and environmental stresses and regulates Hsp70 expression under thermal exposure. However, the functional role of Hsf1 in Hsp70 production is still elusive under bacterial infection. In the present study, a coding sequence of grass carp hsf1 (gchsf1) gene was cloned and identified. Using Ctenopharyngodon idellus kidney (CIK) cells as the model, we found that lipopolysaccharide (LPS) exerted stimulatory effects on the expression of grass carp hsp70 (gchsp70) and hsf1, implying possible relationship of Hsp70 and Hsf1 under immune stimulation in fish. To validate the hypothesis, overexpression of gcHsf1 was performed in CIK cells, and the effects of overexpressing gcHsf1 on the expression of gcHsp70 in the absence or presence of LPS were examined. Results showed that LPS significantly upregulated the transcription and protein synthesis of gcHsp70, and these stimulatory effects were further amplified when overexpression of gcHsf1 was performed. Furthermore, luciferase reporter assays in CIK cells revealed that both overexpression of Hsf1 and LPS upregulated gchsp70 transcription, and their combined treatment further enhanced the gchsp70 promoter activity. Moreover, the regions responsive to these treatments were mapped to the promoter of gchsp70. Besides transcriptional level and cellular protein contents, gcHsp70 secretion was measured by competitive ELISA, uncovering that gcHsf1 enhanced the release of gcHsp70 induced by LPS in the same cells. These data not only demonstrated the enhancement of Hsf1 in Hsp70 production but also initially revealed the involvement of Hsf1-Hsp70 axis in mediating inflammatory response in fish.

The ghost of temperature past: interactive effects of previous and current thermal conditions on gene expression in Manduca sexta

High temperatures can negatively impact the performance and survival of organisms, particularly ectotherms. While an organism's response to high temperature stress clearly depends on current thermal conditions, its response may also be affected by the temporal pattern and duration of past temperature exposures. We used RNA sequencing of Manduca sexta larvae fat body tissue to evaluate how diurnal temperature fluctuations during development affected gene expression both independently and in conjunction with subsequent heat stress. Additionally, we compared gene expression between two M. sexta populations, a lab colony and a genetically related field population that have been separated for >300 generations and differ in their thermal sensitivities. Lab-adapted larvae were predicted to show increased expression responses to both single and repeated thermal stress, whereas recurrent exposure could decrease later stress responses for field individuals. We found large differences in overall gene expression patterns between the two populations across all treatments, as well as population-specific transcriptomic responses to temperature; more differentially expressed genes were upregulated in the field compared with lab larvae. Developmental temperature fluctuations alone had minimal effects on long-term gene expression patterns, with the exception of a somewhat elevated stress response in the lab population. Fluctuating rearing conditions did alter gene expression during exposure to later heat stress, but this effect depended on both the population and the particular temperature conditions. This study contributes to increased knowledge of molecular mechanisms underlying physiological responses of organisms to temperature fluctuations, which is needed for the development of more accurate thermal performance models.

The cellular stress response and temperature: Function, regulation, and evolution

The cellular stress response (CSR) is critical for enabling organisms to cope with thermal damage to proteins, nucleic acids, and membranes. It is a graded response whose properties vary with the degree of cellular damage. Molecular damage has positive, as well as negative, function-perturbing effects. Positive effects include crucial regulatory interactions that orchestrate involvement of the different components of the CSR. Thermally unfolded proteins signal for rapid initiation of transcription of genes encoding heat shock proteins (HSPs), central elements of the heat shock response (HSR). Thermal disruption of messenger RNA (mRNA) secondary structures in untranslated regions leads to the culling of the mRNA pool: thermally labile mRNAs for housekeeping proteins are degraded by exonucleases; heat-resistant mRNAs for stress proteins like HSPs then can monopolize the translational apparatus. Thus, proteins and RNA function as "cellular thermometers," and evolved differences in their thermal stabilities enable rapid initiation of the CSR whenever cell temperature rises significantly above the normal thermal range of a species. Covalent DNA damage, which may result from increased production of reactive oxygen species, is temperature-dependent; its extent may determine cellular survival. High levels of stress that exceed capacities for molecular repair can lead to proteolysis, inhibition of cell division, and programmed cell death (apoptosis). Onset of these processes may occur later in the stress period, after initiation of the HSR, to allow HSPs opportunity to restore protein homeostasis. Delay of these energy costly processes may also result from shortfalls in availability of adenosine triphosphate and reducing power during times of peak stress.

The expression pattern of hsp70 plays a critical role in thermal tolerance of marine demersal fish: Multilevel responses of Paralichthys olivaceus and its hybrids (P. olivaceus ♀ × P. dentatus ♂) to chronic and acute heat stress

Ocean warming has multifaceted impacts on marine organisms. This study investigated the different responses of Paralichthys olivaceus and the hybrids (P. olivaceus ♀ × P. dentatus ♂) to chronic and acute heat stress. By comparing their survival, behavioural and histological changes, we found that the hybrids possess a better thermal tolerance with a higher cumulative survival rate (CSR), relatively fewer behavioural changes and less gill damage. Moreover, we analysed the relationship between thermal tolerance and the hsp70 expression pattern and found that thermal tolerant species (the hybrids) exhibited higher threshold induction temperature, shorter durations, stronger magnitudes and a delay in hsp70 expression. We speculated that the expression mode of hsp70, rather than itself, plays a critical role in thermal tolerance. These findings would improve the understanding of hsp70 in future marine climate research and help clarify the profound effects of rising temperature on marine demersal fishes.

Long-Term Acclimation to Different Thermal Regimes Affects Molecular Responses to Heat Stress in a Freshwater Clam Corbicula Fluminea

Global climate change (GCC) can negatively affect freshwater ecosystems. However, the degree to which freshwater populations can acclimate to long-term warming and the underlying molecular mechanisms are not yet fully understood. We used the cooling water discharge (CWD) area of a power plant as a model for long-term warming. Survival and molecular stress responses (expression of molecular chaperones, antioxidants, bioenergetic and protein synthesis biomarkers) to experimental warming (20–41 °C, +1.5 °C per day) were assessed in invasive clams Corbicula fluminea from two pristine populations and a CWD population. CWD clams had considerably higher (by ~8–12 °C) lethal temperature thresholds than clams from the pristine areas. High thermal tolerance of CWD clams was associated with overexpression of heat shock proteins HSP70, HSP90 and HSP60 and activation of protein synthesis at 38 °C. Heat shock response was prioritized over the oxidative stress response resulting in accumulation of oxidative lesions and ubiquitinated proteins during heat stress in CWD clams. Future studies should determine whether the increase in thermal tolerance in CWD clams are due to genetic adaptation and/or phenotypic plasticity. Overall, our findings indicate that C. fluminea has potential to survive and increase its invasive range during warming such as expected during GCC.

Multiple Stressors in a Changing World: The Need for an Improved Perspective on Physiological Responses to the Dynamic Marine Environment

Abiotic conditions (e.g., temperature and pH) fluctuate through time in most marine environments, sometimes passing intensity thresholds that induce physiological stress. Depending on habitat and season, the peak intensity of different abiotic stressors can occur in or out of phase with one another. Thus, some organisms are exposed to multiple stressors simultaneously, whereas others experience them sequentially. Understanding these physicochemical dynamics is critical because how organisms respond to multiple stressors depends on the magnitude and relative timing of each stressor. Here, we first discuss broad patterns of covariation between stressors in marine systems at various temporal scales. We then describe how these dynamics will influence physiological responses to multi-stressor exposures. Finally, we summarize how multi-stressor effects are currently assessed. We find that multi-stressor experiments have rarely incorporated naturalistic physicochemical variation into their designs, and emphasize the importance of doing so to make ecologically relevant inferences about physiological responses to global change.

Transcriptional responses, metabolic activity and mouthpart deformities in natural populations of Chironomus riparius larvae exposed to environmental pollutants

Biomarkers are an important tool in laboratory assays that link exposure or effect of specific toxicants to key molecular and cellular events, but they have not been widely used in invertebrate populations exposed to complex mixtures of environmental contaminants in their natural habitats. The present study focused on a battery of biomarkers and their comparative analysis in natural populations of the benthic larvae of Chironomus riparius (Diptera), sampled in three differentially polluted rivers (the Con, Sar, and Louro in Galicia, Spain). In our study, some parameters were identified, such as hsp70 gene activity, GST enzymatic activity, total glycogen content and mouthpart deformities, which showed significant differences among populations from the three rivers that differed in the levels and types of sedimentary contaminants analyzed (metals, organic-chlorine pesticides, alkylphenols, pharmaceutical, and personal care products). In contrast to these sensitive biomarkers, other parameters showed no significant differences (hsc70 gene, EcR gene, P450 gene, RNA:DNA ratio, total protein content), and were stable even when comparing field and nonexposed laboratory populations. The hsp70 gene seems to be particularly sensitive to conditions of pollutant exposure, while its constitutive counterpart hsc70 showed invariable expression, suggesting that the hsc70/hsp70 ratio may be a potential indicator of polluted environments. Although further studies are required to understand the correlation between molecular responses and the ecological effects of pollutants on natural populations, the results provide new data about the biological responses to multiple-stressor environments. This field study adds new molecular endpoints, including gene expression, as suitable tools that, complementing other ecotoxicological parameters, may help to improve the methodologies of freshwater monitoring under the increasing burden of xenobiotics.

Fever, immunity, and molecular adaptations

The heat shock response (HSR) is an ancient and highly conserved process that is essential for coping with environmental stresses, including extremes of temperature. Fever is a more recently evolved response, during which organisms temporarily subject themselves to thermal stress in the face of infections. We review the phylogenetically conserved mechanisms that regulate fever and discuss the effects that febrile-range temperatures have on multiple biological processes involved in host defense and cell death and survival, including the HSR and its implications for patients with severe sepsis, trauma, and other acute systemic inflammatory states. Heat shock factor-1, a heat-induced transcriptional enhancer is not only the central regulator of the HSR but also regulates expression of pivotal cytokines and early response genes. Febrile-range temperatures exert additional immunomodulatory effects by activating mitogen-activated protein kinase cascades and accelerating apoptosis in some cell types. This results in accelerated pathogen clearance, but increased collateral tissue injury, thus the net effect of exposure to febrile range temperature depends in part on the site and nature of the pathologic process and the specific treatment provided.

Natural thermal adaptation increases heat shock protein levels and decreases oxidative stress

Heat shock proteins (HSPs), originally identified as heat-inducible gene products, are a family of highly conserved proteins that respond to a wide variety of stress including oxidative stress. Although both acute and chronic oxidative stress have been well demonstrated to induce HSP responses, little evidence is available whether increased HSP levels provide enhanced protection against oxidative stress under elevated yet sublethal temperatures. We studied relationships between oxidative stress and HSPs in a physiological model by using Garra rufa (doctor fish), a fish species naturally acclimatized to different thermal conditions. We compared fish naturally living in a hot spring with relatively high water temperature (34.4±0.6°C) to those living in normal river water temperature (25.4±4.7°C), and found that levels of all the studied HSPs (HSP70, HSP60, HSP90, HSC70 and GRP75) were higher in fish living in elevated water temperature compared with normal river water temperature. In contrast, indicators of oxidative stress, including protein carbonyls and lipid hydroperoxides, were decreased in fish living in the elevated temperature, indicating that HSP levels are inversely associated with oxidative stress. The present results provide evidence that physiologically increased HSP levels provide protection against oxidative stress and enhance cytoprotection.

Investigating hsp gene expression in liver of Channa striatus under heat stress for understanding the upper thermal acclimation

Changes in hsp gene expression profiles in murrel Channa striatus experimentally exposed to temperature stress (36°C) for 4, 15, and 30 days were investigated; fish collected from aquaculture ponds and maintained in laboratory at the pond temperature (25 ± 1°C) served as control. Channa collected from a hot spring runoff (36°C) was included in the study to examine the hsp profiles beyond 30 days of exposure. Gene expression analyses of a battery of hsps in liver tissues were carried out by quantitative RT-PCR and protein expressions were analyzed by immunoblotting. hsps could be grouped into three clusters based on similarity in response to heat stress: hsp70, hsp78, and hsp60, whose transcript level continued to increase with duration of exposure; hsp90 and hsp110 that increased to a much higher level and then decreased; hsp27 and hsp47 that did not significantly vary as compared to control. The results suggest that Hsp70, Hsp78, and Hsp60 are involved in thermal acclimation and long term survival at high temperature. Fish living in the hot spring runoff appears to continuously express hsps that can be approximated by long term induction of hsps in farmed fish if temperature of their environment is raised to 36°C.

Influence of acclimation temperature on the induction of heat-shock protein 70 in the catfish Horabagrus brachysoma (Günther)

Every organism responds to heat stress by synthesizing a group of evolutionarily conserved proteins called the heat-shock proteins (HSPs) that, by acting as molecular chaperones, protect the cell against the aggregation of denatured proteins and play a significant role in adaptation to temperature. The present study aimed to investigate the critical thermal maxima (CTMax) and the expression of HSP70 in different tissues (gill, brain, muscle and liver) of an endemic catfish Horabagrus brachysoma acclimated at either 20 or 30°C for 30 days. To understand the HSP70 response, fish acclimated to the two temperatures were exposed to preset temperatures (26, 30, 34, 36 and 38°C for 20°C acclimated fish and 32, 34, 36, 38 and 40°C for 30°C acclimated fish) for 2 h, followed by 1 h recovery at their respective acclimation temperatures. The HSP70 levels in the gill, brain, muscle and liver tissues were determined by Western blotting of one-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis. A significant (P < 0.05) increase in the CTMax values was observed for fish acclimated at 30°C (41.86 ± 0.39°C) than those acclimated at 20°C (39.13 ± 0.18°C). HSP70 was detected in all the tissues with the highest level in the liver followed by intermediate levels in muscle and brain, and lowest level in gill tissue, irrespective of the acclimation temperatures (20 or 30°C). The HSP70 levels were significantly higher (P < 0.05) in the tissues of fish acclimated at 30°C than those acclimated at 20°C. The mean induction temperature of HSP70 in all the tissues of fish acclimated at either 20 or 30°C was 30 and 34°C, respectively. The optimum temperature for HSP70 induction in all the tissues of fish acclimated at 20°C was 36°C, whereas for fish acclimated at 30°C was 36°C for gill and 38°C for brain, muscle and liver. Decreased levels of HSP70 were noted in all the tissues of fish when exposed to temperatures that exceeded the optimum temperatures for HSP70 inductions. Overall results indicated that acclimation temperature influences both temperature tolerance and induction of HSP70 in H. brachysoma.

The gene expression response of the catadromous perciform barramundi Lates calcarifer to an acute heat stress

The acute heat-shock response of the tropical estuarine fish species barramundi Lates calcarifer as indicated by the expression of genes within stress (hsp 90AA, hsp 90AB, hsp 70 and hsc 70), metabolic (cisy, cco II and ldh) and growth (igf1 and mstn 1) related pathways was examined following an increase in water temperature from 28 to 36° C over 30 min. Lates calcarifer were maintained at the acute stress temperature of 36° C for 1 h before being returned to 28° C and allowed to recover at this temperature for a further 2 weeks. Muscle tissue sampling over the experimental period allowed for the expression quantification of stress, metabolic and growth-related genes via quantitative real-time polymerase chain reaction (qrt-PCR) where a robust and reliable normalization approach identified both α-tub and Rpl8 as appropriate genes for the analysis of gene expression in response to an acute heat stress. hsp90AA and hsp70 of the inducible heat-shock response pathway showed a massive up-regulation of gene expression in response to heat stress, whilst the constitutive heat-shock genes hsp90AB and hsp70 showed no change over the course of the experiment and a small increase after 2 weeks of recovery, respectively. Of the three genes representing the metabolic pathway (cisy, cco II and ldh) only cco II changed significantly showing a decrease in gene expression, which may suggest a small suppression of aerobic metabolism. igf1 of the growth pathway showed no significant differences in response to an acute heat stress, whilst mstn1 increased at the beginning of the heat stress but returned to basal levels soon after. Overall, the results demonstrate that an acute heat stress in L. calcarifer caused a significant increase in the expression of genes from the stress response pathway and a possible decrease in aerobic metabolism with only relatively minor changes to the growth pathway highlighting the hardy nature of L. calcarifer and its resilience in coping with sudden temperature changes routinely encountered within its natural environment.

Effects of thermal acclimation on transcriptional responses to acute heat stress in the eurythermal fish Gillichthys mirabilis (Cooper)

The capacities of eurythermal ectotherms to withstand wide ranges of temperature are based, in part, on abilities to modulate gene expression as body temperature changes, notably genes encoding proteins of the cellular stress response. Here, using a complementary DNA microarray, we investigated the sequence in which cellular stress response-linked genes are expressed during acute heat stress, to elucidate how severity of stress affects the categories of genes changing expression. We also studied how prior acclimation history affected gene expression in response to acute heat stress. Eurythermal goby fish ( Gillichthys mirabilis ) were acclimated to 9 ± 0.5, 19 ± 0.5, and 28 ± 0.5°C for 1 mo. Then fish were given an acute heat ramp (4°C/h), and gill tissues were sampled every +4°C to monitor gene expression. The average onset temperature for a significant change in expression during acute stress increased by ∼2°C for each ∼10°C increase in acclimation temperature. For some genes, warm acclimation appeared to obviate the need for expression change until the most extreme temperatures were reached. Sequential expression of different categories of genes reflected severity of stress. Regardless of acclimation temperature, the gene encoding heat shock protein 70 ( HSP70) was upregulated strongly during mild stress; the gene encoding the proteolytic protein ubiquitin ( UBIQ) was upregulated at slightly higher temperatures; and a gene encoding a protein involved in cell cycle arrest and apoptosis, cyclin-dependent kinase inhibitor 1B ( CDKN1B), was upregulated only under extreme stress. The tiered, stress level-related expression patterns and the effects of acclimation on induction temperature yield new insights into the fundamental mechanisms of eurythermy.

Response of mice to continuous 5-day passive hyperthermia resembles human heat acclimation

Chronic repeated exposure to hyperthermia in humans results in heat acclimation (HA), an adaptive process that is attained in humans by repeated exposure to hyperthermia and is characterized by improved heat elimination and increased exercise capacity, and acquired thermal tolerance (ATT), a cellular response characterized by increased baseline heat shock protein (HSP) expression and blunting of the acute increase in HSP expression stimulated by re-exposure to thermal stress. Epidemiologic studies in military personnel operating in hot environments and elite athletes suggest that repeated exposure to hyperthermia may also exert long-term health effects. Animal models demonstrate that coincident exposure to mild hyperthermia or prior exposure to severe hyperthermia can profoundly affect the course of experimental infection and injury, but these models do not represent HA. In this study, we demonstrate that CD-1 mice continuously exposed to mild hyperthermia (ambient temperature ~37°C causing ~2°C increase in core temperature) for 5 days and then exposed to a thermal stress (42°C ambient temperature for 40 min) exhibited some of the salient features of human HA, including (1) slower warming during thermal stress and more rapid cooling during recovery and (2) increased activity during thermal stress, as well as some of the features of ATT, including (1) increased baseline expression of HSP72 and HSP90 in lung, heart, spleen, liver, and brain; and (2) blunted incremental increase in HSP72 expression following acute thermal stress. This study suggests that continuous 5-day exposure of CD-1 mice to mild hyperthermia induces a state that resembles the physiologic and cellular responses of human HA. This model may be useful for analyzing the molecular mechanisms of HA and its consequences on host responsiveness to subsequent stresses.

Larval excretory-secretory products from the parasite Schistosoma mansoni modulate HSP70 protein expression in defence cells of its snail host, Biomphalaria glabrata

Synthesis of heat shock proteins (HSPs) following cellular stress is a response shared by many organisms. Amongst the HSP family, the approximately 70 kDa HSPs are the most evolutionarily conserved with intracellular chaperone and extracellular immunoregulatory functions. This study focused on the effects of larval excretory-secretory products (ESPs) from the parasite Schistosoma mansoni on HSP70 protein expression levels in haemocytes (defence cells) from its snail intermediate host Biomphalaria glabrata. S. mansoni larval stage ESPs are known to interfere with haemocyte physiology and behaviour. Haemocytes from two different B. glabrata strains, one which is susceptible to S. mansoni infection and one which is resistant, both showed reduced HSP70 protein levels following 1 h challenge with S. mansoni ESPs when compared to unchallenged controls; however, the reduction observed in the resistant strain was less marked. The decline in intracellular HSP70 protein persisted for at least 5 h in resistant snail haemocytes only. Furthermore, in schistosome-susceptible snails infected by S. mansoni for 35 days, haemocytes possessed approximately 70% less HSP70. The proteasome inhibitor, MG132, partially restored HSP70 protein levels in ESP-challenged haemocytes, demonstrating that the decrease in HSP70 was in part due to intracellular degradation. The extracellular signal-regulated kinase (ERK) signalling pathway appears to regulate HSP70 protein expression in these cells, as the mitogen-activated protein-ERK kinase 1/2 (MEK1/2) inhibitor, U0126, significantly reduced HSP70 protein levels. Disruption of intracellular HSP70 protein expression in B. glabrata haemocytes by S. mansoni ESPs may be a strategy employed by the parasite to manipulate the immune response of the intermediate snail host.

Transcriptional responses to thermal acclimation in the eurythermal fish Gillichthys mirabilis (Cooper 1864)

Thermal acclimation (acclimatization) capacity may be critical for determining how successfully an ectotherm can respond to temperature change, and adaptive shifts in gene expression may be pivotal for mediating these acclimatory responses. Using a cDNA microarray, we examined transcriptional profiles in gill tissue of a highly eurythermal goby fish, Gillichthys mirabilis , following 4 wk of acclimation to 9°C, 19°C, or 28°C. Overall, gill transcriptomes were not strikingly different among acclimation groups. Of the 1,607 unique annotated genes on the array, only 150 of these genes (9%) were significantly different in expression among the three acclimation groups (ANOVA, false discovery rate < 0.05). Principal component analysis revealed that 59% of the variation in expression among these genes was described by an expression profile that is upregulated with increasing acclimation temperature. Gene ontology analysis of these genes identified protein biosynthesis, transport, and several metabolic categories as processes showing the greatest change in expression. Our results suggest that energetic costs of macromolecular turnover and membrane-localized transport rise with acclimation temperature. The upregulation of several classes of stress-related proteins, e.g., heat shock proteins, seen in the species' response to acute thermal stress was not observed in the long-term 28°C-acclimated fish. The transcriptional differences found among the acclimation groups thus may reflect an acclimation process that has largely remedied the effects of acute thermal stress and established a new steady-state condition involving changes in relative energy costs for different processes. This pattern of transcriptional alteration in steady-state acclimated fish may be a signature of eurythermy.

Expression of heat shock proteins in anoxic crucian carp (Carassius carassius): support for cold as a preparatory cue for anoxia

The crucian carp ( Carassius carassius ) tolerates anoxia for days to months depending on temperature. During episodes of stress, heat shock proteins (HSPs) are important for limiting cellular damage, mainly by ensuring protein function. Accordingly, we hypothesized that anoxia would change the expression of HSPs and that this response would be temperature dependent. Real-time RT-PCR was used to investigate the effects of 1 and 7 days anoxia (A1 and A7) on the expression of HSP70a, HSP70b, HSC70, HSP90, and HSP30 in the brain and heart of 8°C- and 13°C-acclimated crucian carp. In general, the expression of all HSPs changed in response to anoxia, although varying in size and direction, and with organ and temperature. HSP70a expression increased drastically (∼10-fold) in A7 brains and hearts at 13°C but not at 8°C. HSC70 and HSP90 expression decreased in A7 brains (by 60–70%), but not in A7 hearts. HSC70 expression increased in A1 brains and hearts at both temperatures (by 60–160%), and HSP30 expression decreased in A7 brains and hearts at both temperatures (by 50–80%). Notably, normoxic fish showed 7- and 11-fold higher HSP70a expression in the brain and heart at 8°C compared with 13°C. This difference disappeared during anoxia, suggesting that cold may function as a cue for preconditioning the crucian carp's HSP70a expression to the approaching anoxic winter period.

Thermal sensitivity of mitochondrial respiration efficiency and protein phosphorylation in the clam Mercenaria mercenaria

The mitochondria of intertidal invertebrates continue to function when organisms are exposed to rapid substantial shifts in temperature. To test if mitochondrial physiology of the clam Mercenaria mercenaria is compromised under elevated temperatures, we measured mitochondrial respiration efficiency at 15 degrees C, 18 degrees C, and 21 degrees C using a novel, high-throughput, microplate respirometry methodology developed for this study. Though phosphorylating (state 3) and resting (state 4) respiration rates were unaffected over this temperature range, respiratory control ratios (RCRs: ratio of state 3 to state 4 respiration rates) decreased significantly above 18 degrees C (p < 0.05). The drop in RCR was not associated with reduction of phosphorylation efficiency, suggesting that, while aerobic scope of mitochondrial respiration is limited at elevated temperatures, mitochondria continue to efficiently produce adenosine triphosphate. We further investigated the response of clam mitochondria to elevated temperatures by monitoring phosphorylation of mitochondrial protein. Three proteins clearly demonstrated significant time- and temperature-specific phosphorylation patterns. The protein-specific patterns of phosphorylation may suggest that a suite of protein kinases and phosphatases regulate mitochondrial physiology in response to temperature. Thus, while aerobic scope of clam mitochondrial respiration is reduced at moderate temperatures, specific protein phosphorylation responses reflect large shifts in function that are initiated within the organelle at higher temperatures.

Hyperthermia in the febrile range induces HSP72 expression proportional to exposure temperature but not to HSF-1 DNA-binding activity in human lung epithelial A549 cells

Expression of heat shock proteins (HSPs) is classically activated at temperatures above the physiologic range (>or=42 degrees C) via activation of the stress-activated transcription factor, heat shock factor-1 (HSF-1). Several studies suggest that less extreme hyperthermia, especially within the febrile range, as occurs during fever and exertional/environmental hyperthemia, can also activate HSF-1 and enhance HSP expression. We compared HSP72 protein and mRNA expression in human A549 lung epithelial cells continuously exposed to 38.5 degrees C, 39.5 degrees C, or 41 degrees C or exposed to a classic heat shock (42 degrees C for 2 h). We found that expression of HSP72 protein and mRNA increased linearly as incubation temperature was increased from 37 degrees C to 41 degrees C, but increased abruptly when the incubation temperature was raised to 42 degrees C. A similar response in luciferase activity was observed using A549 cells stably transfected with an HSF-1-responsive luciferase reporter plasmid. However, activation of intranuclear HSF-1 DNA-binding activity was comparable at 38.5 degrees C, 39.5 degrees C, and 41 degrees C and only modestly greater at 42 degrees C but the mobility of HSF1 protein on a denaturing gel was altered with increasing exposure temperature and was distinctly different at 42 degrees C. These findings indicate that the proportional changes in HSF-1-dependent HSP72 expression at febrile-range temperatures are dependent upon exposure time and temperature but not on the degree of HSF-1 DNA-binding activity. Instead, HSF-1-mediated HSP expression following hyperthermia and heat shock appears to be mediated, in addition to HSF-1 activation, by posttranslational modifications of HSF-1 protein.

Exercise-heat acclimation in humans alters baseline levels and ex vivo heat inducibility of HSP72 and HSP90 in peripheral blood mononuclear cells

The induction of cellular acquired thermal tolerance (ATT) during heat acclimation (HA) in humans is not well described. This study determined whether exercise-HA modifies the human heat shock protein (HSP)72 and HSP90 responses and whether changes are correlated with physiological adaptations to HA. Using a 10-day HA protocol comprising daily exercise (treadmill walking) in a hot environment ( Ta = 49°C, 20% RH), we analyzed baseline and ex vivo heat-induced expression of HSP72 and HSP90 in peripheral blood mononuclear cells (PBMCs) isolated prior to exercise from eight subjects on day 1 and 10 of the HA protocol. Classical physiological responses to HA were observed, including significantly reduced heart rate and core body temperature, and significantly increased sweating rate. Baseline levels of HSP72 and HSP90 were significantly increased following acclimation by 17.7 ± 6.1% and 21.1 ± 6.5%, respectively. Ex vivo induction of HSP72 in PBMCs exposed to heat shock (43°C) was blunted on day 10 compared with day 1. A correlation was identified ( r2 = 0.89) between changes in core temperature elevation and ex vivo HSP90 responses to heat shock between days 1 and 10, indicating that volunteers demonstrating the greatest physiological HA tended to exhibit the greatest blunting of ex vivo HSP induction in response to heat shock. In summary, 1) exercise-HA resulted in increased baseline levels of HSP72 and HSP90, 2) ex vivo heat inducibility of HSP72 was blunted after HA, and 3) volunteers demonstrating the greatest physiological HA tended to exhibit the greatest blunting of ex vivo HSP induction in response to heat shock. These data demonstrate that physiological adaptations in humans undergoing HA are accompanied by both increases in baseline levels and changes in regulation of cytoprotective HSPs.

Field and laboratory investigations of the thermal influence on tissue-specific Hsp70 levels in common carp (Cyprinus carpio)

Thermal discharge from power stations can affect normal environmental conditions and change in heat shock proteins expression of native fish with increasing temperature. In this study, we investigated levels of Hsp70 in the heart, kidney, brain and gill of the common carp Cyprinus carpio both in long-term heat discharge environment and after 24 h acute heat shock exposure. In laboratory exposure experiments, fish acclimated at 10 degrees C were exposed to various elevated temperatures (20, 24 and 28 degrees C). Hsp70 concentrations were determined in tissues by Western blotting analysis after one dimensional SDS-PAGE separation. In the field study, the level of Hsp70 in the gill of the carp remained at control values, and Hsp70 expression in the heart, kidney and brain underwent a 2.8 to 3.7-fold increase. A lower thermal sensitivity of the Hsp70 response of the brain, compared with the heart, kidney and gill, was observed in the laboratory experiments. Our data show that these tissues had different levels of Hsp70 responses to thermal influence both in acute exposure and long-term acclimation. The pattern of tissue Hsp70 expression may have a close relationship with the thermal tolerance of the carp and allows the fish to survive long-term thermal pollution.

Effects of the Natural Tidal Cycle and Artificial Temperature Cycling on Hsp Levels in the Tidepool SculpinOligocottus maculosus

The rocky intertidal zone is characterized by a predictable cycle of environmental change cued by the ebb and flow of the tides. Tidepools are thus an excellent environment in which to determine whether predictability of environmental change can entrain an endogenous rhythmicity in heat shock protein (Hsp) levels. In this study, we monitored changes in Hsp mRNA and protein levels that occurred over the tidal cycle in tidepool sculpins and investigated whether there was an endogenous tidal rhythm in Hsp expression that persisted once the sculpins were transferred to a stable environment. Fluctuations in the tidepool environment increased hsc70, hsp70, and hsp90 mRNA levels, which translated into increased Hsc/Hsp70 and Hsp90 protein levels; however, this was not due to an endogenous tidal rhythm in Hsp levels because sculpins held under constant conditions did not show any rhythmicity in the expression of these genes. By exposing sculpins to an artificial temperature cycling regime that mimicked the temperature changes of a mid-intertidal pool, we were able to account for the direct role of temperature in regulating Hsp expression. However, there are additional extrinsic factors that likely integrate with temperature and result in differences between the hsp induction profiles that were observed in sculpins inhabiting their natural environment and those in cycling conditions in the laboratory.

Physiological basis for diurnal activity in dispersing juvenile Bufo granulosus in the Caatinga, a Brazilian semi-arid environment

Diurnal activity is characteristic of many toad species, including Bufo granulosus from the Brazilian semi-arid biome called the Caatinga. Because of their patterns of activity, juvenile toads are exposed to hot and dehydrating conditions. Our investigation focuses on temperature and water relationships, and is based on the prediction that anuran diurnal activity in a semi-arid environment must be associated with morphological, physiological and behavioral traits enhancing thermal tolerances, capacity for performance at high temperatures and water balance. To test specific hypothesis related with this prediction, we investigated postmetamorphic B. granulosus and collected data on thermal tolerances and preferences, thermal safety margins, thermal dependence of locomotor behavior, thermal and kinetic properties of citrate synthase (CS), and skin morphophysiology. This information was compared with additional data from adult conspecifics and adult toads from sympatric species or from species from more moderate environments. We found that juvenile B. granulosus exhibit the highest critical maximum temperature reported for toads (44.2 degrees C) and are well suited to move at high temperatures. However, and in contrast with juveniles of other Bufo species, they do not show thermal preferences in a gradient and appear to hydroregulate more than thermoregulate. The CS of adult and juvenile toads shows typical patterns of thermal sensibility, but the thermal stability of this enzyme is much higher in juveniles than in adult Bufo of any other species studied. The inguinal skin exhibits a complex folding pattern and seems highly specialized for capillary water uptake. Diurnal activity in juvenile B. granulosus is possible given high thermal tolerances, keen ability to detect and uptake water, and avoidance behaviors.