Influence of bioenergetic stress on heat shock protein gene expression in nucleated red blood cells of fish

Study the change in the mosquito larvae (Culex pipiens) in water treated with short pulses electric filed

Electrical Pulsed Field (PEF), of pulse duration in 4 milliseconds, effect on mosquito larvae (Culex pipiens) as aquatic insects is assessed in this work. Mosquito larvae classes have been treated with electric field power values (66.66, 83.33, 100, 116.66 V/cm) with separate pulse number (60) and other classes of various pulse numbers have been treated (20, 40, 60, 80) with power of the electrical field 100 V/cm. The findings revealed that positively significant of increase of the applied electrical field strength or increase of the number of pulses. The rise in both cases leads to an increase in the mortality of 25%, 50%, and 75% of the mosquito larvae (P < .05). The impact was calculated with the bioassay system on mosque larvae, SDS-PAGE for whole body proteins, enzyme analysis and ultrastructural examination using TEM. The current study reveals that a low pulsed electric field can cause mosquito larvae genotoxic, changes in the insect's body proteins, which may affect the insect's ability to live. The increase in pulsed electric field parameters also activates oxidative stress in the insect cell by disrupting its secretion of enzymes that could affect the mosquito's capabilities in the future.

Advances in understanding the impacts of global warming on marine fishes farmed offshore: Sparus aurata as a case study

Monitoring variations in proteins involved in metabolic processes, oxidative stress responses, cell signalling and protein homeostasis is a powerful tool for developing hypotheses of how environmental variations affect marine organisms' physiology and biology. According to the oxygen- and capacity-limited thermal tolerance hypothesis, thermal acclimation mechanisms such as adjusting the activities of enzymes of intermediary metabolism and of antioxidant defence mechanisms, inducing heat shock proteins (Hsps) or activating mitogen-activated protein kinases may all shift tolerance windows. Few studies have, however, investigated the molecular, biochemical and organismal responses by fishes to seasonal temperature variations in the field to link these to laboratory findings. Investigation of the impacts of global warming on fishes farmed offsore, in the open sea, can provide a stepping stone towards understanding effects on wild populations because they experience similar environmental fluctuations. Over the last 30 years, farming of the gilthead sea bream Sparus aurata (Linnaeus 1758) has become widespread along the Mediterranean coastline, rendering this species a useful case study. Based on available information, the prevailing seasonal temperature variations expose the species to the upper and lower limits of its thermal range. Evidence for this includes oxygen restriction, reduced feeding, reduced responsiveness to environmental stimuli, plus a range of molecular and biochemical indicators that change across the thermal range. Additionally, close relationships between biochemical pathways and seasonal patterns of metabolism indicate a connection between energy demand and metabolic processes on the one hand, and cellular stress responses such as oxidative stress, inflammation and autophagy on the other. Understanding physiological responses to temperature fluctuations in fishes farmed offshore can provide crucial background information for the conservation and successful management of aquaculture resources in the face of global change.

Combined effect of pCO2 and temperature levels on the thermal niche in the early benthic ontogeny of a keystone species

We evaluated the effects of projected, near future ocean acidification (OA) and extreme events of temperature (warming or cooling) on the thermal tolerance of Concholepas concholepas, a coastal benthic keystone species. Three separate trials of an experiment were conducted by exposing juvenile C. concholepas for 1 month to one of two contrasting pCO₂ levels (~500 and ~1200 μatm). In addition, each pCO₂ level was combined with one of four temperature treatments. The control was 15 °C, whilst the other temperatures were 10 °C (Trial 1), 20 °C (Trial 2) and 25 °C (Trial 3). At the end of each trial, we assessed Critical Thermal maximum (CTmax) and minimum (CTmin) via self-righting success, calculated partial thermal tolerance polygons, measured somatic growth, determined transcription of Heat Shock Proteins 70 (HSP70) and measured oxygen consumption rates. Regardless of pCO₂ level, HSP70 transcript levels were significantly higher in juveniles after exposure to extreme temperatures (10 °C and 25 °C) indicating physiological stress. Oxygen consumption rates increased with increasing temperature from 10 °C to 20 °C though showed a decrease at 25 °C. This rate was not affected by pCO₂ or the interaction between temperature and pCO₂. Juveniles exposed to present-day and near future pCO₂ levels at 20 °C showed similar thermal tolerance polygonal areas; whilst changes in both CTmin and CTmax at 25 °C and 10 °C caused narrower and broader areas, respectively. Temperature affected growth, oxygen consumption and HSP70 transcription in small juvenile C. concholepas. Exposure to elevated pCO₂ did not affect thermal tolerance, growth or oxygen consumption at temperatures within the thermal range normally experienced by this species in northern Chile (15-20 °C). At elevated pCO₂ conditions, however, exposure to warmer (25 °C) or colder (10 °C) temperatures reduced or increased the thermal area, respectively. This study demonstrates the importance of examining the thermal-tolerance edges to better understand how OA and temperature will combine to physiologically challenge inter-tidal organisms.

The endemic and endangered Maugean Skate (Zearaja maugeana) exhibits short-term severe hypoxia tolerance

The endangered and range-restricted Maugean skate (Zearaja maugeana) is subjected to large environmental variability coupled with anthropogenic stressors in its endemic habitat, Macquarie Harbour, Tasmania. However, little is known about the basic biology/physiology of this skate, or how it may respond to future environmental challenges predicted from climate change and/or increases in human activities such as aquaculture. These skate live at a preferred depth of 5-15 m where the dissolved oxygen (DO) levels are moderate (~55% air saturation), but can be found in areas of the Harbour where DO can range from 100% saturation to anoxia. Given that the water at their preferred depth is already hypoxic, we sought to investigate their response to further decreases in DO that may arise from potential increases in anthropogenic stress. We measured oxygen consumption, haematological parameters, tissue-enzyme capacity and heat shock protein (HSP) levels in skate exposed to 55% dissolved O₂ saturation (control) and 20% dissolved O₂ saturation (hypoxic) for 48 h. We conclude that the Maugean skate appears to be an oxyconformer, with a decrease in the rate of O₂ consumption with increasing hypoxia. Increases in blood glucose and lactate at 20% O₂ suggest that skate are relying more on anaerobic metabolism to tolerate periods of very low oxygen. Despite these metabolic shifts, there was no difference in HSP70 levels between groups, suggesting this short-term exposure did not elicit a cellular stress response. The metabolic state of the skate suggests that low oxygen stress for longer periods of time (i.e. >48 h) may not be tolerable and could potentially result in loss of habitat or shifts in their preferred habitat. Given its endemic distribution and limited life-history information, it will be critical to understand its tolerance to environmental challenges to create robust conservation strategies.

High-throughput sequencing reveals microRNAs in response to heat stress in the head kidney of rainbow trout (Oncorhynchus mykiss)

Recently, the research of animal microRNAs (miRNAs) has attracted wide attention for its regulatory effect in the development process and the response to abiotic stresses. Rainbow trout is a commercially and cold water fish species, and usually encounters heat stress, which affects its growth and leads to a huge economic loss. But there were few investigations about the roles of miRNAs in heat stress in rainbow trout. In this study, miRNAs of rainbow trout which were involved in heat stress were identified by high-throughput sequencing of six small RNA libraries from head kidney tissues under control (18 °C) and heat-treated (24 °C) conditions. A total of 392 conserved miRNAs and 989 novel miRNAs were identified, of which 78 miRNAs were expressed in different response to heat stress. Ten of these miRNAs were further validated by quantitative real-time PCR. In addition to, including 393 negative correlation miRNA-target gene pairs, several important regulatory pathways were involved in heat stress of the potential target genes, including protein processing in endoplasmic reticulum, NOD-like receptor signaling pathway, and phagosome. Our data significantly advance understanding of heat stress regulatory mechanism of miRNA in the head kidney of rainbow trout, which provide a useful resource for the cultivation of rainbow trout.

Gene expression profiling of whole blood cells supports a more efficient mitochondrial respiration in hypoxia-challenged gilthead sea bream (Sparus aurata)

BACKGROUND

Acclimation to abiotic challenges, including decreases in O2 availability, requires physiological and anatomical phenotyping to accommodate the organism to the environmental conditions. The retention of a nucleus and functional mitochondria in mature fish red blood cells makes blood a promising tissue to analyse the transcriptome and metabolic responses of hypoxia-challenged fish in an integrative and non-invasive manner.

METHODS

Juvenile gilthead sea bream (Sparus aurata) were reared at 20-21 °C under normoxic conditions (> 85% O2 saturation) followed by exposure to a gradual decrease in water O2 concentration to 3.0 ppm (41-42% O2 saturation) for 24 h or 1.3 ppm (18-19% O2 saturation) for up to 4 h. Blood samples were collected at three different sampling points for haematological, biochemical and transcriptomic analysis.

RESULTS

Blood physiological hallmarks remained almost unaltered at 3.0 ppm, but the haematocrit and circulating levels of haemoglobin, glucose and lactate were consistently increased when fish were maintained below the limiting oxygen saturation at 1.3 ppm. These findings were concurrent with an increase in total plasma antioxidant activity and plasma cortisol levels, whereas the opposite trend was observed for growth-promoting factors, such as insulin-like growth factor I. Additionally, gene expression profiling of whole blood cells revealed changes in upstream master regulators of mitochondria (pgcβ and nrf1), antioxidant enzymes (gpx1, gst3, and sod2), outer and inner membrane translocases (tom70, tom22, tim44, tim10, and tim9), components of the mitochondrial dynamics system (mfn2, miffb, miro1a, and miro2), apoptotic factors (aifm1), uncoupling proteins (ucp2) and oxidative enzymes of fatty acid β-oxidation (acca2, ech, and hadh), the tricarboxylic acid cycle (cs) and the oxidative phosphorylation pathway. The overall response is an extensive reduction in gene expression of almost all respiratory chain enzyme subunits of the five complexes, although mitochondrial-encoded catalytic subunits and nuclear-encoded regulatory subunits of Complex IV were primarily increased in hypoxic fish.

CONCLUSIONS

Our results demonstrate the re-adjustment of mitochondrial machinery at transcriptional level to cope with a decreased basal metabolic rate, consistent with a low risk of oxidative stress, diminished aerobic ATP production and higher O2-carrying capacity. Taken together, these results suggest that whole blood cells can be used as a highly informative target tissue of metabolic condition.

High survivorship after catch-and-release fishing suggests physiological resilience in the endothermic shortfin mako shark (Isurus oxyrinchus)

The shortfin mako shark (Isurus oxyrinchus) is a species commonly targeted by commercial and recreational anglers in many parts of the developed world. In Australia, the species is targeted by recreational anglers only, under the assumption that most of the sharks are released and populations remain minimally impacted. If released sharks do not survive, the current management strategy will need to be revised. Shortfin mako sharks are commonly subjected to lengthy angling events; however, their endothermic physiology may provide an advantage over ectothermic fishes when recovering from exercise. This study assessed the post-release survival of recreationally caught shortfin mako sharks using Survivorship Pop-up Archival Transmitting (sPAT) tags and examined physiological indicators of capture stress from blood samples as well as any injuries that may be caused by hook selection. Survival estimates were based on 30 shortfin mako sharks captured off the south-eastern coast of Australia. Three mortalities were observed over the duration of the study, yielding an overall survival rate of 90%. All mortalities occurred in sharks angled for <30 min. Sharks experienced increasing plasma lactate with longer fight times and higher sea surface temperatures (SSTs), increased plasma glucose at higher SSTs and depressed expression of heat shock protein 70 and β-hydroxybutyrate at higher SSTs. Long fight times did not impact survival. Circle hooks significantly reduced foul hooking when compared with J hooks. Under the conditions of this study, we found that physical injury associated with hook choice is likely to have contributed to an increased likelihood of mortality, whereas the high aerobic scope associated with the species' endothermy probably enabled it to cope with long fight times and the associated physiological responses to capture.

Synergy of environmental variables alters the thermal window and heat shock response: an experimental test with the crab Pachygrapsus marmoratus

The intertidal zone is an extremely variable habitat, imposing stressful conditions on its inhabiting communities. Tolerance towards extremes of temperature, salinity and pH are crucial in these habitats. Despite the vast literature on stress tolerance, few studies have focused on the synergistic effects of several variables on thermal tolerance and HSP70 (heat shock protein 70 kDa) levels. In this work, the crabs were exposed to three experimental conditions 1) thermal ramp at standard pH (8) and saline conditions (35‰) (named T), 2) thermal ramp at standard pH (8) and hyposaline conditions (15‰) (named T plus HypoS), and 3) thermal ramp at lower pH (7) and standard saline conditions (35‰) (named T plus A). Two physiological parameters (Critical Thermal Maximum - CTMax, and osmolality) and a stress biomarker (HSP70) were chosen for this analysis. These parameters were measured in all of the aforementioned conditions. CTMax for each set of conditions was reached by exposing the organisms to a rate of temperature increase of 1 °C h(-1) until loss of equilibrium. Haemolymph samples were taken every 2 °C to quantify HSP70 and osmolality. Results showed that CTMax did not differ between crabs solely exposed to T stress and crabs exposed to T plus HypoS stress. However, HSP70 production was impaired in T plus HypoS stress. When crabs were exposed to T plus A stress, they showed a significantly higher CTMax, suggesting that short-term exposure to acidified conditions may alter the thermal window of this species. Nevertheless, in T plus A conditions HSP70 production was impaired as well. Regarding osmolality it decreased according to temperature increase in all tested stress conditions. This study showed that the heat stress response is altered by the synergistic effect of variables. Physiological end-points (i.e. CTMax) may vary and the expression of stress proteins such as HSP70 may be impaired.

Avian erythrocytes have functional mitochondria, opening novel perspectives for birds as animal models in the study of ageing

Background

In contrast to mammalian erythrocytes, which have lost their nucleus and mitochondria during maturation, the erythrocytes of almost all other vertebrate species are nucleated throughout their lifespan. Little research has been done however to test for the presence and functionality of mitochondria in these cells, especially for birds. Here, we investigated those two points in erythrocytes of one common avian model: the zebra finch (Taeniopygia guttata).

Results

Transmission electron microscopy showed the presence of mitochondria in erythrocytes of this small passerine bird, especially after removal of haemoglobin interferences. High-resolution respirometry revealed increased or decreased rates of oxygen consumption by erythrocytes in response to the addition of respiratory chain substrates or inhibitors, respectively. Fluorometric assays confirmed the production of mitochondrial superoxide by avian erythrocytes. Interestingly, measurements of plasmatic oxidative markers indicated lower oxidative stress in blood of the zebra finch compared to a size-matched mammalian model, the mouse.

Conclusions

Altogether, those findings demonstrate that avian erythrocytes possess functional mitochondria in terms of respiratory activities and reactive oxygen species (ROS) production. Interestingly, since blood oxidative stress was lower for our avian model compared to a size-matched mammalian, our results also challenge the idea that mitochondrial ROS production could have been one actor leading to this loss during the course of evolution. Opportunities to assess mitochondrial functioning in avian erythrocytes open new perspectives in the use of birds as models for longitudinal studies of ageing via lifelong blood sampling of the same subjects.

The impact of mitochondrial and thermal stress on the bioenergetics and reserve respiratory capacity of fish cell lines

Various stressors affect the health of wild and cultured fish and can cause metabolic disturbances that first manifest at the cellular level. Here, we sought to further our understanding of cellular metabolism in fish by examining the metabolic responses of cell lines derived from channel catfish Ictalurus puntatus (CCO), white bass Morone chrysops (WBE), and fathead minnow Pimephales promelas (EPC) to both mitochondrial and thermal stressors. Using extracellular flux (EF) technology, we simultaneously measured the oxygen consumption rate (OCR; a measure of mitochondrial function) and extracellular acidification rate (ECAR; a surrogate of glycolysis) in each cell type. We performed a mitochondrial function protocol whereby compounds modulating different components of mitochondrial respiration were sequentially exposed to cells. This provided us with basal and maximal OCR, OCR linked to ATP production, OCR from ion movement across the mitochondrial inner membrane, the reserve capacity, and OCR independent of the electron transport chain. After heat shock, EPC and CCO significantly decreased OCR and all three cell lines modestly increased ECAR. After heat shock, the reserve capacity, the mitochondrial energetic reserve used to cope with stress and increased bioenergetic demand, was unaffected in EPC and CCO and completely abrogated in WBE. These findings provide proof-of-concept experimental data that further highlight the utility of fish cell lines as tools for modeling bioenergetics.

Thermal tolerance of the crab Pachygrapsus marmoratus: intraspecific differences at a physiological (CTMax) and molecular level (Hsp70)

Temperature is one of the most important variables influencing organisms, especially in the intertidal zone. This work aimed to test physiological and molecular intraspecific differences in thermal tolerance of the crab Pachygrapsus marmoratus (Fabricius, 1787). The comparisons made focused on sex, size, and habitat (estuary and coast) differences. The physiological parameter was upper thermal limit, tested via the critical thermal maximum (CTMax) and the molecular parameter was total heat shock protein 70 (Hsp70 and Hsp70 plus Hsc70) production, quantified via an enzyme-linked imunosorbent assay. Results showed that CTMax values and Hsp70 production are higher in females probably due to different microhabitat use and potentially due to different hormonal regulation in males and females. Among females, non-reproducing ones showed a higher CTMax value, but no differences were found in Hsp70, even though reproducing females showed higher variability in Hsp70 amounts. As reproduction takes up a lot of energy, its allocation for other activities, including stress responses, is lower. Juveniles also showed higher CTMax and Hsp70 expression because they occur in greater shore heights and ageing leads to alterations in protein synthesis. Comparing estuarine and coastal crabs, no differences were found in CTMax but coastal crabs produce more Hsp70 than estuarine crabs because they occur in drier and hotter areas than estuarine ones, which occur in moister environments. This work shows the importance of addressing intraspecific differences in the stress response at different organizational levels. This study shows that these differences are key factors in stress research, climate research, and environmental monitoring.

Physiological adaptations of stressed fish to polluted environments: role of heat shock proteins

Fish are subjected to a wide variety of environmental stressors. Stressors affect fish at all life stages and the stress-specific responses that occur at the biochemical and physiological levels affect the overall health and longevity of such animals. In this review, the organ-specific alterations in fish that inhabit polluted environments are addressed in detail. Fish,like other vertebrates, have evolved strategies to counteract stress-mediated effects. Among the key strategies that fish have developed is the induction of HSPs. The primary functions of HSPs are to promote the proper folding or refolding of proteins, to prevent potentially damaging interactions with proteins, and aiding in the disassembly of formations of protein aggregates. Stress, a state of unbalanced tissue oxidation, causes a general disturbance in the cellular antioxidant and redox balance and evokes HSP70 overexpression. Distinct families of HSPs have diverse physiological functions, and their induction, which is regulated at the transcriptional level, is mediated by the activation of heat shock factors. Interestingly, HSPs also interact with a wide variety of signaling molecules that modulate stress-mediated apoptotic effects. Hence, HSP induction is of major importance for maintenance of cell homeostasis. HSP-mediated adaptation processes are regarded as a fundamental protective mechanism that decreases cellular sensitivity to damaging events. Thus, the adaptive expression of HSPs is a protective response that helps combat stress-induced conformational damage to proteins. Additional research is needed to gain further information on the functional significance and role of individual HSPs and to enhance the understanding of the molecular mechanisms by which they act. In addition, field studies are needed to allow comprehensive evaluation of the potential use of HSPs as biomarkers for environmental monitoring. Furthermore, the expression of HSPs in fish fluctuates in response to seasonal variation. Because HSPs serves as a tool for assessing the stressed state of individuals and/or populations, the impact of seasonal influences on constitutive and inducible factors of these proteins should also be elucidated. Such research will lead to a fundamental improvement in the understanding of the functional role of HSPs in response to natural environmental changes and may allow correlation of the action of HSPs at the molecular level with the whole organismal stress response, which, so far, remains unexplained.

The influence of ambient temperature and thermal acclimation on hearing in a eurythermal and a stenothermal otophysan fish

Being ectothermic, fish body temperature generally depends on ambient water temperature. Thus, ambient temperature might affect various sensory systems, including hearing, as a result of metabolic and physiological processes. However, the maintenance of sensory functions in a changing environment may be crucial for an animal's survival. Many fish species rely on hearing for acoustic orientation and communication. In order to investigate the influence of temperature on the auditory system, channel catfish Ictalurus punctatus was chosen as a model for a eurytherm species and the tropical catfish Pimelodus pictus as a model for a stenotherm fish. Hearing sensitivity was measured with animals acclimated or unacclimated to different water temperatures. Ambient water temperature significantly influenced hearing thresholds and the shape of auditory evoked potentials, especially at higher frequencies in I. punctatus. Hearing sensitivity of I. punctatus was lowest at 10 degrees C and increased by up to 36 dB between 10 degrees C and 26 degrees C. Significant differences were also revealed between acclimated and unacclimated animals after an increase in water temperature but not a decrease. By contrast, differences in hearing thresholds were smaller in P. pictus, even if a similar temperature difference (8 degrees C) was considered. However, P. pictus showed a similar trend as I. punctatus in exhibiting higher hearing sensitivity at the highest tested temperature, especially at the highest frequency tested. The results therefore suggest that the functional temperature dependence of sensory systems may differ depending upon whether a species is physiologically adapted to tolerate a wide or narrow temperature range.

Pollution induced nitrative stress and heat shock protein 70 overexpression in fish liver mitochondria

Exposure to heavy metals and organic pollutants in natural water bodies can have detrimental effects on fish health. A combination of biochemical and energy studies were used to observe the changes in fish liver mitochondria in response to environmental pollutant induced nitrative stress in natural field conditions. The fish samples Mugil cephalus were collected from polluted (Ennore) and unpolluted (Kovalam) estuaries for a period of two years. The results revealed elevated nitrite (NO2-) and nitrate (NO3-) levels, increased nitric oxide (NO) synthesis and 3-nitrotyrosine expression, decreased respiratory chain enzyme activities and ATP/ADP ratio, reduced mitochondrial superoxide dismutase (MnSOD), glutathione peroxidase (Gpx) levels, diminished thiol status that leads to alterations in the mitochondrial function and elevated mitochondrial heat shock protein 70 (mtHSP70) expression (30%) to a significant extent in fish from the polluted estuary than in the unpolluted estuary. The overexpression of HSP70 under stress may aid mitochondrial survival by protecting against nitrative stress induced damage. The results also reveal the percentage increase in fish liver mitochondrial HSP70 in response to cumulative effect of environmental pollutants.

Beta-adrenergic stimulation enhances the heat-shock response in fish

We have taken advantage of the unique properties of nucleated rainbow trout (Oncorhynchus mykiss) red blood cells (rbcs) to demonstrate that beta-adrenergic stimulation with the agonist, isoproterenol, significantly enhanced the heat-induced induction of heat-shock proteins (Hsps) in trout rbcs without affecting hsp expression on its own. Furthermore, this beta-adrenergic potentiation of hsp expression occurred only at physiologically relevant concentrations of adrenergic stimulation. In further experiments, we found that adrenaline increased 100-fold and noradrenaline increased 50-fold in trout after a 1-h heat shock at 25 degrees C, approximately 12 degrees C above acclimation temperature. This is the first time the adrenergic heat-shock response has been described for a temperate fish species. We conclude that beta-adrenergic stimulation enhances hsp expression in trout rbcs following heat stress, indicating physiological regulation of the cellular stress response in fish.

Tribute to R. G. Boutilier: Evidence of a high activity carbonic anhydrase isozyme in the red blood cells of an ancient vertebrate, the sea lamprey Petromyzon marinus

Carbonic anhydrase (CA) is a multi-functional enzyme that catalyzes the hydration/dehydration of carbon dioxide. In the red blood cell (rbc), CA is necessary to facilitate the transport of carbon dioxide out of the body. Results from earlier biochemical studies indicate that ancient vertebrates,such as agnathans, possess a low activity rbc CA isozyme, whereas more recently evolved vertebrates, such as teleost fish, possess a high activity isozyme. At present, however, the changes in the molecular structure that have resulted in this large increase in catalytic efficiency are unknown. The objective of the current study was therefore to determine the molecular structure of rbc CA in lampreys and compare it to that of teleosts in an effort to ascertain how this important enzyme became more efficient over evolutionary time. Isolation and sequencing of cytoplasmic CA from rbc and gill showed only a single isozyme of 789 bp (262 amino acids). This isozyme was also found in brain and kidney, with no evidence of additional cytoplasmic CA isozymes in other tissues. Phylogenetic analysis grouped this isozyme closely to vertebrate CA VII, which is ancestral to the rbc isozymes in other vertebrates. Interestingly, active site analysis revealed a structure similar to high activity isozymes. A comparative kinetic analysis of CA from rbc lysates and CA fusion proteins showed that the traditional method of determining the turnover number may not be appropriate for all vertebrate CAs. In contrast to previous evidence, lamprey CA was found to be a high activity isozyme. These results suggest that the critical functional characteristics of rbc CA have been highly conserved throughout vertebrate evolution.

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

Most organisms respond to temperature fluctuations by altering the expression of an evolutionarily conserved family of proteins known as heat shock proteins (Hsps). Studies have shown Hsp expression and the activation of HSF1, one of the primary regulators of Hsp transcription, are highly malleable, varying with the recent thermal history of the organism; however, the mechanisms that confer plasticity to the regulation of this ubiquitous response are not well-understood. This study furthers our knowledge in this area by characterizing the activation kinetics of HSF1 and the corresponding transcription of hsp70 in the liver of the eurythermal goby, Gillichthys mirabilis, following a month-long acclimation at 13, 21 or 28 degrees C. Our data revealed HSF1 DNA-binding kinetics varied as a function of acclimation temperature and magnitude/duration of exposure, with gobies acclimated at 21 degrees C exhibiting the most robust response. Hsp70 mRNA followed a similar pattern with induction first occurring in the 13 and 21 degrees C fish, and then most robustly in the 28 degrees C group at 36 degrees C. The hsp70 mRNA induction pattern was corroborated by levels of HSF1 DNA-binding activity in each group and may have been lowest in the 28 degrees C group due to the 2-fold greater levels of hsp70 protein prior to thermal exposure. This study illustrates the integral role of HSF1 as a key regulator of Hsp induction and helps explain the plasticity of this response in ectothermic organisms.

Influence of cyclic mechanical strain and heat of human tendon fibroblasts on HSP-72

Heat shock protein 72 (HSP-72) is a member of a superfamily of different proteins that are synthesized as a cytoprotective response following cellular stress. Mechanical strain is an important component in ligament and tendon healing. Up to the present point of time, the influence of mechanical strain on the expression of HSP-72 is unknown. Tendon fibroblasts from the patellar tendons of nine individuals were isolated and amplified in vitro. First, the effect of 15 or 60 min of heat exposition was studied immunohistochemically and by Western blotting. In a second experiment, the effects of 15 and 60 min of cyclic longitudinal stretching were investigated. Samples were taken after 2, 4 and 8 h. The heat exposition experiments indicate that HSP-72 accumulates in the nucleus and that there is a transient upregulation. This effect is more prominent after 60 min of heat exposure. The same reaction was found after stretching stimulation, however, to a lesser extent. There was a transient up regulation of HSP-72 after short-term stretching and a biphasic increase after 60 min of stretching. Upregulation of HSP-72 by heat and mechanical stress is a response in human fibroblasts which involves a nuclear translocation. The response differs with regard to the time points beyond 2 h after the application of either stress.

Cytoplasmic carbonic anhydrase isozymes in rainbow trout Oncorhynchus mykiss: comparative physiology and molecular evolution

It is well established that the gills of teleost fish contain substantial levels of cytoplasmic carbonic anhydrase (CA), but it is unclear which CA isozyme(s) might be responsible for this activity. The objective of the current study was to determine if branchial CA activity in rainbow trout was the result of a general cytoplasmic CA isozyme, with kinetic properties, tissue distribution and physiological functions distinct from those of the red blood cell (rbc)-specific CA isozyme. Isolation and sequencing of a second trout cytoplasmic CA yielded a 780 bp coding region that was 76% identical with the trout rbc CA (TCAb), although the active sites differed by only 1 amino acid. Interestingly, phylogenetic analyses did not group these two isozymes closely together, suggesting that more fish species may have multiple cytoplasmic CA isozymes. In contrast to TCAb, the second cytoplasmic CA isozyme had a wide tissue distribution with high expression in the gills and brain, and lower expression in many tissues, including the red blood cells. Thus, unlike TCAb, the second isozyme lacks tissue specificity and may be expressed in the cytoplasm of all cells. For this reason, it is referred to hereafter as TCAc (trout cytoplasmic CA). The inhibitor properties of both cytoplasmic isozymes were similar (Ki acetazolamide 1.21+/-0.18 nmol l(-1) and 1.34+/-0.10 nmol l(-1) for TCAc and TCAb, respectively). However, the turnover of TCAb was over three times greater than that of TCAc (30.3+/-5.83 vs 8.90+/-1.95 e4 s(-1), respectively), indicating that the rbc-specific CA isoform was significantly faster than the general cytoplasmic isoform. Induction of anaemia revealed differential expression of the two isozymes in the red blood cell; whereas TCAc mRNA expression was unaffected, TCAb mRNA expression was significantly increased by 30- to 60-fold in anaemic trout.

Do mitochondria regulate the heat-shock response in Saccharomyces cerevisiae?

A mild heat shock induces the synthesis of heat-shock proteins (hsps), which protect cells from damage during more extreme heat exposure. The nature of the signals that induce transcription of heat shock-regulated genes remains conjectural. In this work we studied the role of mitochondria in regulating hsps synthesis in Saccharomyces cerevisiae. The results obtained clearly indicate that a mild heat shock elicits a hyperpolarization of the inner mitochondrial membrane and such an event is one of several signals triggering the chain of reactions that activates the expression of the HSP104 gene and probably the expression of other heat shock-regulated genes in S. cerevisiae. The uncouplers or mitochondrial inhibitors which are capable of dissipating the potential on the inner mitochondrial membrane under particular experimental conditions prevent the synthesis of Hsp104 induced by mild heat shock and thus inhibit the development of induced thermotolerance. It is suggested that cAMP-dependent protein kinase A is participating in the mitochondrial regulation of nuclear genes.

Comparative physiology and molecular analysis of carbonic anhydrase from the red blood cells of teleost fish

This study investigates the early evolution of vertebrate red blood cell (rbc) carbonic anhydrase (CA) by examining the physiological and molecular properties of rbc CA in teleost fish. When representatives of four different families of teleosts were compared, it was found that differences in overall rbc CA activity were due to different concentrations of CA, rather than differences in the enzyme's kinetic properties. Additional molecular analysis of CA from the rbcs of rainbow trout provided further evidence that critical elements of the enzyme, such as the active site, have been highly conserved during vertebrate evolution. The active site of the trout CA differed from that of gar rbc CA at only two amino acid positions. The rainbow trout rbc CA sequence also showed high sequence homology with CA sequences from other fish tissues, and fits into an emerging group of fish CAs that are basal to mammalian CA I, II and III. Northern blot analysis of the tissue expression of the sequenced CA indicated that it is primarily found in the rbcs, but high amounts of cytosolic CA activity were also found in the gill, suggesting the presence of other cytosolic CA isozymes in this species.

Oxygen-dependent cellular functions--why fishes and their aquatic environment are a prime choice of study

Owing to the variability of oxygen tension in aquatic, especially the freshwater environment, oxygen has been a major force in the evolution of fishes. Their long evolutionary history, and the present different oxygen requirements between species, and acclimatory responses to hypoxic and hyperoxic conditions make fishes prime models in the study of oxygen-dependent cellular functions and their regulation. In the present article oxygen-dependent membrane transport, cellular signalling, energy metabolism, gene expression and apoptosis are reviewed with an emphasis on available results on fish. Available data on oxygen sensing are described and examples on the cascade from sensing oxygen to its physiological effects are given. From the data it is clear that hitherto fish have not been utilised in the study of oxygen-dependent cellular regulation as much as their evolutionary history and present oxygen requirements would give possibilities to. Even more generally, oxygen has hitherto seldom been a carefully controlled key variable in experimental cell biology.

Heat shock protein genes and their functional significance in fish

Despite decades of intensive investigation, important questions remain regarding the functional, ecological, and evolutionary roles of heat shock proteins. In this paper, we discuss the utility of fish as a model system to address these questions, and review the relevant studies of heat shock protein genes and the regulation of their expression in fish. Although molecular studies of the heat shock proteins in fish are still in their early descriptive phase, data are rapidly being collected. More is known about the biotic and abiotic factors regulating heat shock proteins. We briefly review these studies and focus on the role of heat shock proteins in development, their regulation by the endocrine system, and their importance in fish in nature. Functional genomics approaches will provide the tools necessary to gain a comprehensive understanding of the significance of heat shock proteins in the cellular stress response, in the physiological processes at higher levels of organization, and in the whole animal in its natural environment.

Going with the flow or life in the fast lane: contrasting mitochondrial responses to thermal change

Temperature is one of the most important environmental factors affecting the physiology of animals. Seasonal fluctuations in temperature are of particular importance in aquatic ectotherms since their body temperature is in equilibrium with their environment. When an organism faces adverse environmental conditions, it can either remain active or enter into metabolic depression, adopting the strategy that maximises its fitness. Physiological responses to environmental stress occur at many different levels of organisation in an animal. Here, we focus on mitochondria, given their central importance in cellular energy metabolism. We contrast the thermal biology of skeletal muscle mitochondria from cold-active species with that of species that spend their winters in a metabolically depressed state. Specifically, we examine the modifications of mitochondrial properties during thermal/seasonal acclimation and examine mechanisms by which these modifications can arise. While compensatory responses to cold acclimation include increases in mitochondrial abundance, in the oxidative capacities of individual mitochondria and adjustments of ADP affinities, metabolic depression can reduce tissue levels of mitochondrial enzymes and mitochondrial proton leak rates.

Regional distribution of ionic currents and membrane voltage responses of type II hair cells in the vestibular neuroepithelium

Basolateral ionic currents and membrane voltage responses were studied in pigeon vestibular type II hair cells using a thin slice through either the semicircular canal (SCC) crista or utricular macular epithelium. Whole cell tight-seal patch-clamp recording techniques were used. Current-clamp and voltage-clamp studies were carried out on the same cell. One hundred ten cells were studied in the peripheral (Zone I) and central (Zone III) zones of the SCC crista, and 162 cells were studied in the striolar (S Zone) and extrastriolar (ES Zone) zones of the utricular macula. One of the major findings of this paper is that hair cells with fast activation kinetics of their outward currents are found primarily in one region of the SCC crista and utricular macula, whereas hair cells with slow activation kinetics are found in a different region. In Zone I of the crista, 95% of the cells have fast activation kinetics ("fast" cells) and in Zone III of the crista, 86% of the cells have slow activation kinetics ("slow" cells). In the utricular macula slice, 100% of the cells from the S Zone are slow cells, whereas 86% of the cells from the ES Zones are fast cells. Oscillation frequency (f) and quality factor (Q) of the damped oscillations of the membrane potential during extrinsic current injections were studied in hair cells in the different regions. The slow cells in Zone III and in the S Zone have a statistically significantly lower f, as a function of the amplitude of injected current, when compared with the fast cells in Zone I and the ES Zone. Although Q varied over a small range and was <2.6 for all cells tested, there was a statistically significant difference between Q for the membrane oscillations of the slow cells and fast cells in response to a range of current injections.