Why do cells require heat shock proteins to survive heat stress?

The cellular response to heat stress includes the induction of a group of proteins called the Heat Shock Proteins, whose functions include the synthesis of the thermoprotectant trehalose, refolding of denatured proteins, and ubiquitin- and proteasome-dependent degradation. Recent studies show that simply increasing the activity of ubiquitin- and proteasome-dependent degradation can replace the essential functions played by the induction of heat shock proteins during a heat stress. These results suggest that accumulation of denatured or aggregated proteins is the reason for the loss of cell viability due to heat stress.     

Does the chloroplast small heat shock protein protect photosystem II during heat stress in vitro?

It has been suggested that the function of the chloroplast-localized small heat shock protein (sHsp) is to protect photosystem II (PSII) from heat inactivation. This paper reports that addition of purified sHsp protein to isolated thylakoid membranes gave no protection of PSII and questions that there is any direct effect of the sHsp on PSII. The opinion is forwarded that the primary role for the chloroplast-localized sHsp may not even be protection of PSII.     

Effects of 72—hour heat stress on semen quality in boars

Three sibling pairs of six-month old boars of each of four breeding groups (Yorkshire, Poland, China and the reciprocal crosses) were maintained in an area held at or below 21.5°C with a 12-hour daily light cycle. After a three month acclimation period, a randomly selected boar of each pair was subjected to 33°C, 50% RH for 72 hours. Semen was collected from each boar once during the treatment and every fourth day for 64 days post-treatment (PT). There were significant (p < 0.05) decreases in sperm concentration per ml, and total sperm number. The inverse of the methylene blue reduction time and the per cent motile sperm and total motile sperm in the ejaculate were significantly decreased (p < 0.01). The percentages of primary and secondary morphologically abnormal spermatozoa were increased significantly (p < 0.01). Maximal pair differences occurred at days 28 to 32 PT; all had returned to pretreatment levels by day 64 PT.

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Zusammenfassung Drei Geschwisterpaare 6-Monate alter Saubären aus 4 Zuchtgruppen (Yorkshire, Polen, China und deren reziproken Kreuzungen) wurden bei 21, 5°C in einem 12-Stunden Lichtzyklus gehalten. Nach einer Akklimatisationsperiode von 3 Monaten wurde ein zufällig ausgewählter Saubären jedes Paares 72 Stunden bei 33°C und 50% RF exponiert und von jedem Tier Samenproben einmal während der Hitzebelastung und an jedem 4. Tag bis zum 64. Tag nach der Behandlung gesammelt. Die Samenkonzentration im ml und die Gesamtspermienzahl waren signifikant reduziert (p < 0,05). Die Umkehrung der Methylenblau-Reduktionszeit und die prozentuale und totale Anzahl motiler Spermien im Ejakulat waren signifikant reduziert (p < 0,01). Der prozentuale Anteil primär und sekundär morphologisch abnormer Spermien war signifikant erhöht (p < 0,01). Maximale Unterschiede zwischen den Paaren traten zwischen dem 28. und 32. Tag auf. Am 64. Tag waren die Unterschiede verschwunden.

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Resume On a soumis 3 paires de verrats frères âgés de 6 mois à une atmosphère de 21, 5°C et à un cycle lumineux de 12 heures. Ces animaux provenaient de 4 groupes d'élevage (Yorkshire, Polen, China et leurs croisements réciproques). Après une période d'adaptation de 3 mois, on a choisi au hasard une bête de chaque paire qui fut placée durant 72 heures à 33°C et à 50% d'humidité relative. On a alors prélevé de la semence de chaque animal et cela durant la période de contrainte thermique, puis tous les 4 jours jusqu'au 64ème après l'essai. La concentration des semences par ml et le nombre total de spermatozoïdes furent réduits de façon significative (p < 0,05). L'inverse du temps de réduction au bleu de Méthylène, le taux et le nombre total de spermatozoïdes mobiles dans l'éjaculat furent également réduits de façon significative (p < 0,01). Le taux des spermatozoïdes présentant des abnormités morphologiques primaires et secondaires fut plus élevé de façon significative (p < 0,01). Les plus grandes différences entre les individus d'une même paire furent relevées du 28ème au 32ème jour après le traitement. Au 64ème jour, toute différence avait disparu.

     

Phase separation—a strategy to resist autophagic degradation under heat stress

<正>Stress spans our whole lives. When exposed to stressful conditions, every life, from a worm to a human, adjusts its internal properties to adapt to new environments. This principle applies to adults, and is also essential during development in animals. Dr. Zhang and coworkers from Institute of Biophysics, Chinese Academy of Sciences made a remarkable discovery showing that heat-stress-triggered accumulation of PGL granules is an adaptive response to maintain embryonic viability (Figure 1). Their work was published in the September 6th issue of Cell, entitled"mTOR regulates phase separation of PGL granules to modulate their autophagic degradation"(Zhang et al., 2018).     

Evaporative heat loss in Bos taurus: Do different cattle breeds cope with heat stress in the same way?

The aim of this study was to compare two Portuguese (Alentejana and Mertolenga) and two exotic (Frisian and Limousine) cattle breeds in terms of the relationship between the increase in ambient temperature and the responses of the evaporative heat loss pathways and the effects on homeothermy. In the experiment, six heifers of the Alentejana, Frisian, and Mertolenga breeds and four heifers of the Limousine breed were used. The animals were placed in four temperature levels, the first one under thermoneutral conditions and the other ones with increase levels of thermal stress. When submitted to severe heat stress, the Frisian developed high thermal tachypnea (125 mov/min) and moderate sweating rates (117 g m⁻² h⁻¹), which did not prevent an increase in the rectal temperature (from 38.4 °C to 40.0 °C). Moderate increases in rectal temperature were observed in the Alentejana (from 38.8 °C to 39.4 °C) and Limousine (from 38.6 °C to 39.4 °C), especially in the period of highest heat stress. The Limousine showed moderate levels of tachypnea (101 mov/min) while showing the lowest sweating rates. The Alentejana showed significant increases in sweating rate (156 g m⁻² h⁻¹) that played a major role in homeothermy. The Mertolenga showed a superior stability of body temperature, even in the period of highest heat stress (from 38.5 °C to 39.1 °C). Uncommonly, the maintenance of homeothermy during moderate heat stress was achieved primarily by intense tachypnea (122 mov/min). The sweating rate remained abnormally low under conditions of moderate heat stress, rising significantly (110 g m⁻² h⁻¹) without evidence of stabilization, only when tendency for heat storage occurred. This unusual response of the evaporative heat loss pathways infers a different thermoregulatory strategy, suggesting a different adaptation to semi-arid environment and strong association with water metabolism.     

Does heat shock enhance oxidative stress? Studies with ferrous and ferric iron

Chinese hamster ovary cells were exposed to FeSO4 or FeCl3 during a 43 degrees C heat shock. Concentrations of iron, which were not toxic when cells were incubated at 37 degrees C, became toxic in a dose-dependent fashion during hyperthermia treatment. The iron chelator EDTA, which supports oxidation/reduction reactions, promoted hyperthermia-induced iron cytotoxicity while the iron chelator desferrioxamine, which has been shown to inhibit iron redox cycling, inhibited cytotoxicity. The presence of exogenous superoxide dismutase, catalase, or mannitol during hyperthermia treatment did not inhibit iron toxicity. Depletion of intracellular glutathione by diethylmaleate increased hyperthermia-induced iron toxicity by 76%. These data are interpreted to mean that heat shock promotes intracellular oxidative damage and intracellular glutathione is necessary for protection.     

Firefighter feedback during active cooling: A useful tool for heat stress management?

Monitoring an individual's thermic state in the workplace requires reliable feedback of their core temperature. However, core temperature measurement technology is expensive, invasive and often impractical in operational environments, warranting investigation of surrogate measures which could be used to predict core temperature. This study examines an alternative measure of an individual's thermic state, thermal sensation, which presents a more manageable and practical solution for Australian firefighters operating on the fireground. Across three environmental conditions (cold, warm, hot & humid), 49 Australian volunteer firefighters performed a 20-min fire suppression activity, immediately followed by 20 min of active cooling using hand and forearm immersion techniques. Core temperature (T_c) and thermal sensation (TS) were measured across the rehabilitation period at five minute intervals. Despite the decline in T_c and TS throughout the rehabilitation period, there was little similarity in the magnitude or rate of decline between each measure in any of the ambient conditions. Moderate to strong correlations existed between T_c and TS in the cool (0.41, p<0.05) and hot & humid (0.57, p<0.05) conditions, however this was resultant in strong correlation during the earlier stages of rehabilitation (first five minutes), which were not evident in the latter stages. Linear regression revealed TS to be a poor predictor of T_c in all conditions (SEE=0.45–0.54 °C) with a strong trend for TS to over-predict T_c (77–80% of the time). There is minimal evidence to suggest that ratings of thermal sensation, which represent a psychophysical assessment of an individual's thermal comfort, are an accurate reflection of the response of an individual's core temperature. Ratings of thermal sensation can be highly variable amongst individuals, likely moderated by local skin temperature. In account of these findings, fire managers require a more reliable source of information to guide decisions of heat stress management.     

Biochemical analysis of ‘kerosene tree’ Hymenaea courbaril L. under heat stress

Hymenaea courbaril or jatoba is a tropical tree known for its medically important secondary metabolites production. Considering climate change, the goal of this study was to investigate differential expression of proteins and lipids produced by this tree under heat stress conditions. Total lipid was extracted from heat stressed plant leaves and various sesquiterpenes produced by the tree under heat stress were identified. Gas chromatographic and mass spectrometric analysis were used to study lipid and volatile compounds produced by the plant. Several volatiles, isoprene, 2-methyl butanenitrile, β ocimene and a numbers of sesquiterpenes differentially produced by the plant under heat stress were identified. We propose these compounds were produced by the tree to cope up with heat stress. A protein gel electrophoresis (2-D DIGE) was performed to study differential expression of proteins in heat stressed plants. Several proteins were found to be expressed many folds different in heat stressed plants compared to the control. These proteins included heat shock proteins, histone proteins, oxygen evolving complex, and photosynthetic proteins, which, we believe, played key roles in imparting thermotolerance in Hymenaea tree. To the best of our knowledge, this is the first report of extensive molecular physiological study of Hymenaea trees under heat stress. This work will open avenues of further research on effects of heat stress in Hymenaea and the findings can be applied to understand how global warming can affect physiology of other plants.     

Plastic and evolutionary responses to heat stress in a temperate dung fly: negative correlation between basal and induced heat tolerance?

Extreme weather events such as heat waves are becoming more frequent and intense. Populations can cope with elevated heat stress by evolving higher basal heat tolerance (evolutionary response) and/or stronger induced heat tolerance (plastic response). However, there is ongoing debate about whether basal and induced heat tolerance are negatively correlated and whether adaptive potential in heat tolerance is sufficient under ongoing climate warming. To evaluate the evolutionary potential of basal and induced heat tolerance, we performed experimental evolution on a temperate source population of the dung fly Sepsis punctum. Offspring of flies adapted to three thermal selection regimes (Hot, Cold and Reference) were subjected to acute heat stress after having been exposed to either a hot‐acclimation or non‐acclimation pretreatment. As different traits may respond differently to temperature stress, several physiological and life history traits were assessed. Condition dependence of the response was evaluated by exposing juveniles to different levels of developmental (food restriction/rearing density) stress. Heat knockdown times were highest, whereas acclimation effects were lowest in the Hot selection regime, indicating a negative association between basal and induced heat tolerance. However, survival, adult longevity, fecundity and fertility did not show such a pattern. Acclimation had positive effects in heat‐shocked flies, but in the absence of heat stress hot‐acclimated flies had reduced life spans relative to non‐acclimated ones, thereby revealing a potential cost of acclimation. Moreover, body size positively affected heat tolerance and unstressed individuals were less prone to heat stress than stressed flies, offering support for energetic costs associated with heat tolerance. Overall, our results indicate that heat tolerance of temperate insects can evolve under rising temperatures, but this response could be limited by a negative relationship between basal and induced thermotolerance, and may involve some but not other fitness‐related traits.     

Effect of acute heat stress on rat adrenal cortex — a morphological and ultrastructural study

The stereological structure of rat adrenal gland was analysed by light and electron microscopy after an acute (60 min) exposure to high ambient temperature (38°C). Under these conditions a significant increase in plasma corticotrophin (ACTH), serum corticosterone and aldosterone levels were observed. Histological and stereological investigation at light microscopy showed significant decrease in volume density of capsule and zona glomerulosa, increase in volume of fasciculata cells, and decrease of numerical density of zona fasciculata cells and mean diameter of blood vessels. At the ultrastructural level, volume density of nuclei and mitochondria of zona glomerulosa cells were significantly increased and that of lipid droplets decreased. Volume density of mitochondria of fasciculata cells was significantly increased, while number of lipid droplets per μm² of cell was reduced. In the cells of zona reticularis significant increase in the number of lipid droplets was found. The response of zona glomerulosa may be interpreted as immediate reaction to dehydration, while alterations detected in zona fasciculata, which were less extensive, were related to purely stressogenic effects of high ambiental temperature.     

Constitutive heat shock protein 70 interacts with α-enolase and protects cardiomyocytes against oxidative stress

Constitutive heat shock protein 70 (Hsc70) is a molecular chaperone that has been shown to protect cardiomyocytes against oxidative stress. However, the molecular mechanism responsible for this protection remains uncertain. To understand the mechanism associated with the myocardial protective role of Hsc70, we have embarked upon a systematic search for Hsc70-interacting proteins. Using adenosine diphosphate (ADP) affinity chromatography and mass spectrometry, we have identified α-enolase, a rate-limiting enzyme in glycolysis, as a novel Hsc70-interacting protein in the myocardium of both sham and myocardial ischemia-reperfused Sprague-Dawley rat hearts. This interaction was confirmed by co-immunoprecipitation (IP) assays in the myocardial tissues and H9c2 cardiomyocytes and protein overlay assay (POA). It was further shown that Hsc70-overexpression alleviated the H(2)O(2)-induced decrease of α-enolase activity and cell damage, and Hsc70 deficiency aggravated the decrease of α-enolase activity and cell damage in H(2)O(2) treated H9c2 cells. Our research suggests that the protective effect of Hsc70 on the cardiomyocytes against oxidative stress is partly associated with its interaction with α-enolase.     

Water-stress-induced heat tolerance in geranium leaf tissues: A possible linkage through stress proteins?

Evidence is accumulating in favor of a linkage at the cellular level between various abiotic stresses. We conducted a study to evaluate the effect of water stress on the heat tolerance of zonal geraniums, Pelargonium × hortorum cv. Evening Glow. Water stress was imposed by withholding irrigation until pots reached 30% (by weight) of well‐watered controls, and by maintaining the pot weight by additions of water for another 7 days. Leaf xylem water potential (XWP, MPa), relative water content (RWC. %), and heat‐stress tolerance (HST; LT₅₀, defined as the temperature causing half‐maximal % injury based on electrolyte leakage) were measured in control, stressed, and recovered plants. Proteins were extracted from the leaves following the above treatments, and SDS‐PAGE and immunoblotting were performed by using standard procedures. Immunoblots were probed with antibodies to dehydrin and 70‐kDa heat shock cognate (HSC70) proteins. Data indicate that XWP and RWC, respectively, were −0.378 MPa and 92.3% for control plants and −0.804 MPa and 78.6% for stressed plants. Water‐stressed plants exhibited a significant increase in HST compared to control (LT₅₀ of 55°C vs 51°C). Water‐stress‐induced HST was not due to heat acclimation (leaf warming in stressed plants). Data also indicate that water‐stress treatment did not increase freezing tolerance of geranium leaves. Increased HST was associated with the accumulation of several heat‐stable, dehydrin proteins (25–60 kDa), and both cytosolic and ER luminal (BiP) HSC70 proteins. Leaf XWP, RWC, and HST reversed to control levels concomitant with the disappearance/reduction of dehydrins and HSC70 proteins in water‐stress‐relieved plants. The possibility of a cellular linkage between water stress and heat‐stress tolerance is discussed.     

Constitutive heat shock protein 70 interacts with α-enolase and protects cardiomyocytes against oxidative stress

Abstract

Constitutive heat shock protein 70 (Hsc70) is a molecular chaperone that has been shown to protect cardiomyocytes against oxidative stress. However, the molecular mechanism responsible for this protection remains uncertain. To understand the mechanism associated with the myocardial protective role of Hsc70, we have embarked upon a systematic search for Hsc70-interacting proteins. Using adenosine diphosphate (ADP) affinity chromatography and mass spectrometry, we have identified α-enolase, a rate-limiting enzyme in glycolysis, as a novel Hsc70-interacting protein in the myocardium of both sham and myocardial ischemia-reperfused Sprague–Dawley rat hearts. This interaction was confirmed by co-immunoprecipitation (IP) assays in the myocardial tissues and H9c2 cardiomyocytes and protein overlay assay (POA). It was further shown that Hsc70-overexpression alleviated the H₂O₂-induced decrease of α-enolase activity and cell damage, and Hsc70 deficiency aggravated the decrease of α-enolase activity and cell damage in H₂O₂ treated H9c2 cells. Our research suggests that the protective effect of Hsc70 on the cardiomyocytes against oxidative stress is partly associated with its interaction with α-enolase.     

Effect of acute heat stress on rat adrenal medulla — a morphological and ultrastructural study

Isolated rat adrenal medulla was analyzed by light and electron microscope after an acute (60 min) exposure to high ambient temperature (38°C). Under these conditions there was a significant rise in plasma adrenaline and noradrenaline. Stereological investigation by light microscopy showed a significant decrease in volume density of cells and an increase in the interstitium. At the ultrastructural level, the profile area of cells, nuclei and cytoplasm of adrenaline cells were significantly decreased. After the heat stress numbers of resting granules in adre naline and noradrenaline cells were significantly reduced, while the numbers of altered granules and empty containers in both types of adrenomedullar cells were significantly increased.     

Trehalose: Protector of antioxidant enzymes or reactive oxygen species scavenger under heat stress?

Trehalose is known to protect membranes and macromolecules. Its accumulation has been implicated in allowing plants to tolerate stress, including heat-shock. However, under heat-shock, it is not clear whether trehalose eliminates reactive oxygen species (ROS) directly or indirectly by protecting antioxidant enzymes. In this study, we initially examined the effects of trehalose on the activities of key antioxidant enzymes, including superoxide dismutases (SODs), ascorbate catalases (CATs), and ascorbate peroxidases (APX) from wheat (Triticum aestivum L.), and then measured the ability of trehalose to scavenge hydrogen peroxide (H₂O₂) and superoxide anions (O₂⁻). Our results indicated that trehalose protected SOD activity slightly. However, it inhibited CAT and APX activities under heat stress, with a little protection of CAT activity (only about 7% promotion) at 22 °C. Moreover, trehalose scavenged H₂O₂ and O₂⁻ greatly in a concentration-dependent manner, reaching the maximal scavenging H₂O₂ rate of 95% and O₂⁻ rate of 78%, respectively, at 50 mM trehalose. These results suggest that trehalose plays a direct role in eliminating H₂O₂ and O₂⁻ in wheat under heat stress.