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.     

Is the major Drosophila heat shock protein present in cells that have not been heat shocked?

When eukaryotic cells are exposed to elevated temperatures they respond by vigorously synthesizing a small group of proteins called the heat shock proteins. An essential element in defining the role of these proteins is determining whether they are unique to a stressed state or are also found in healthy, rapidly growing cells at normal temperatures. To date, there have been conflicting reports concerning the major heat-induced protein of Drosophila cells, HSP 70. We report the development of monoclonal antibodies specific for this protein. These antibodies were used to assay HSP 70 in cells incubated under different culture conditions. The protein was detectable in cells maintained at normal temperatures, but only when immunological techniques were pushed to the limits of their sensitivity. To test for the possibility that these cells contain a reservoir of protein in a cryptic antigenic state (i.e., waiting posttranslational modification for use at high temperature), we treated cells with cycloheximide or actinomycin D immediately before heat shock. HSP 70 was not detected in these cells. Finally, we tested for the presence of a reservoir of inactive messages by using a high stringency hybridization of 32P- labeled cloned gene sequences to electrophoretically separated RNAs. Although HSP 70 mRNA was detectable in rapidly growing cells, it was present at less than 1/1,000th the level achieved after induction.     

Biochemical and genetic factors in the heat inactivation of murine β-glucuronidase

The enzymes coded for by two alleles at the glucuronidase structural locus (Gus) were compared in their response to pH, buffering anion, buffer molarity, ionic strength, and temperature. The heat-labile Gus^h gene product responded in a qualitatively similar but quantitatively reduced manner compared to the relatively heat-stable Gus ^b gene product. In all buffers tested, the enzyme was most heat stable at pH 5.0. Ranking of the various buffer anions tested, according to increasing heat stabilization, was water acetate phosphate < citrate. Varying the molarity of the buffers from 0.01 to 0.6 m at pH 5.0 revealed further differences among the buffers. Increasing ionic strength exerted a destabilizing force on the protein. The half-life of the enzyme decreased by as much as a hundredfold between 71 and 75 C. The Gus^h/Gus^h genotype also results in decreased activity levels in all tissues, reportedly because of decreased synthesis. The heat inactivation curves of Gus^b/Gus^h heterozygotes were incompatible with any theoretical curve based on the assumption that the Gus^b and Gus^h chromosomes in the heterozygote behave in a manner similar to that seen in the homozygotes.This research was supported by a Basil O'Connor Starter Research Grant from the National Foundation—March of Dimes (R. J. M.) and by a grant from The Jane Coffin Childs Memorial Fund for Medical Research (K. H.).Fellow of The Jane Coffin Childs Memorial Fund for Medical Research.     

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.

     

The calcium‐dependent protein kinase ZmCDPK7 functions in heat‐stress tolerance in maize

Global warming poses a serious threat to crops. Calcium‐dependent protein kinases (CDPKs)/CPKs play vital roles in plant stress responses, but their exact roles in plant thermotolerance remains elusive. Here, we explored the roles of heat‐induced ZmCDPK7 in thermotolerance in maize. ZmCDPK7‐overexpressing maize plants displayed higher thermotolerance, photosynthetic rates, and antioxidant enzyme activity but lower H₂O₂ and malondialdehyde (MDA) contents than wild‐type plants under heat stress. ZmCDPK7‐knockdown plants displayed the opposite patterns. ZmCDPK7 is attached to the plasma membrane but can translocate to the cytosol under heat stress. ZmCDPK7 interacts with the small heat shock protein sHSP17.4, phosphorylates sHSP17.4 at Ser‐44 and the respiratory burst oxidase homolog RBOHB at Ser‐99, and upregulates their expression. Site‐directed mutagenesis of sHSP17.4 to generate a Ser‐44‐Ala substitution reduced ZmCDPK7's enhancement of catalase activity but enhanced ZmCDPK7's suppression of MDA accumulation in heat‐stressed maize protoplasts. sHSP17.4, ZmCDPK7, and RBOHB were less strongly upregulated in response to heat stress in the abscisic acid‐deficient mutant vp5 versus the wild type. Pretreatment with an RBOH inhibitor suppressed sHSP17.4 and ZmCDPK7 expression. Therefore, abscisic acid‐induced ZmCDPK7 functions both upstream and downstream of RBOH and participates in thermotolerance in maize by mediating the phosphorylation of sHSP17.4, which might be essential for its chaperone function.     

Oral administration of γ-aminobutyric acid affects heat production in a hot environment in resting humans

Background

Central administration of γ-amino butyric acid (GABA) induces lower body temperature in animals in hot ambient air. However, it is still unknown whether oral GABA administration affects temperature regulation at rest in a hot environment in humans. Therefore, in the present study, we specifically hypothesized that systemic administration of GABA in humans would induce hypothermia in a hot environment and that this response would be observed in association with decreased heat production.

Methods

Eight male participants drank a 200-ml sports drink with 1 g of GABA (trial G) or without GABA (trial C), then rested for 30 minutes in a sitting position in a hot environment (ambient air temperature 33°C, relative humidity 50%).

Results

We found that changes in esophageal temperature from before drinking the sports drink were lower in trial G than in trial C (-0.046 ± 0.079°C vs 0.001 ± 0.063°C; P < 0.05), with lower heat production calculated by oxygen consumption (41 ± 5 W/m² vs 47 ± 8 W/m²; P < 0.05).

Conclusions

In this study, we have demonstrated that a single oral administration of GABA induced a larger decrease in body core temperature compared to a control condition during rest in a hot environment and that this response was concomitant with a decrease in total heat production.     

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.     

Changes in body temperature in king penguins at sea: the result of fine adjustments in peripheral heat loss?

To investigate thermoregulatory adjustments at sea, body temperatures (the pectoral muscle and the brood patch) and diving behavior were monitored during a foraging trip of several days at sea in six breeding king penguins Aptenodytes patagonicus. During inactive phases at sea (water temperature: 4-7 degrees C), all tissues measured were maintained at normothermic temperatures. The brood patch temperature was maintained at the same values as those measured when brooding on shore (38 degrees C). This high temperature difference causes a significant loss of heat. We hypothesize that high-energy expenditure associated with elevated peripheral temperature when resting at sea is the thermoregulatory cost that a postabsorptive penguin has to face for the restoration of its subcutaneous body fat. During diving, mean pectoral temperature was 37.6 +/- 1.6 degrees C. While being almost normothermic on average, the temperature of the pectoral muscle was still significantly lower than during inactivity in five out of the six birds and underwent temperature drops of up to 5.5 degrees C. Mean brood patch temperature was 29.6 +/- 2.5 degrees C during diving, and temperature decreases of up to 21.6 degrees C were recorded. Interestingly, we observed episodes of brood patch warming during the descent to depth, suggesting that, in some cases, king penguins may perform active thermolysis using the brood patch. It is hypothesized that functional pectoral temperature may be regulated through peripheral adjustments in blood perfusion. These two paradoxical features, i.e., lower temperature of deep tissues during activity and normothermic peripheral tissues while inactive, may highlight the key to the energetics of this diving endotherm while foraging at sea.     

Small heat shock protein αA-crystallin prevents photoreceptor degeneration in experimental autoimmune uveitis

The small heat shock protein, αA-crystallin null (αA-/-) mice are known to be more prone to retinal degeneration than the wild type mice in Experimental Autoimmune Uveoretinitis (EAU). In this report we demonstrate that intravenous administration of αA preserves retinal architecture and prevents photoreceptor damage in EAU. Interestingly, only αA and not αB-crystallin (αB), a closely related small heat shock protein works, pointing to molecular specificity in the observed retinal protection. The possible involvement of αA in retinal protection through immune modulation is corroborated by adaptive transfer experiments, (employing αA-/- and wild type mice with EAU as donors and Rag2-/- as the recipient mice), which indicate that αA protects against the autoimmune challenge by modulating the systemic B and T cell immunity. We show that αA administration causes marked reduction in Th1 cytokines (TNF-α, IL-12 and IFN-γ), both in the retina and in the spleen; notably, IL-17 was only reduced in the retina suggesting local intervention. Importantly, expression of Toll-like receptors and their associated adaptors is also inhibited suggesting that αA protection, against photoreceptor loss in EAU, is associated with systemic suppression of both the adaptive and innate immune responses.     

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.     

Stat1 mediates an auto-regulation of hsp90β gene in heat shock response

We have reported earlier that a heat shock element in the first intron of human hsp90β gene (iHSE) acts as an intronic enhancer to bind the heat shock factor (HSF1) and activates hsp90β gene under heat shock. Here, we show that, in addition to the HSF1, Stat1 phosphorylation is indispensable in the event. We show that Jak2, a Janus kinase specifically associated with the β subunit of IFNγ receptor, and PKCε? an isoform of the atypical PKC family, are the two dominant kinases responsible for the heat shock induced phosphorylation on Y701 and S727 of Stat1. However, the activation of these kinases under heat shock requires the association of chaperone proteins of the Hsp90 family, in particular, the Hsp90β under heat shock. Furthermore, Brg1, an ATPase subunit of the SWI/SNF chromatin remodeling complex is likely recruited by HSF1 and Stat1 at the iHSE under heat shock. Brg1 further confers an open chromatin conformation at the promoter region that is pivotal to the heat shock induced fully activation of the hsp90β gene in Jurkat cells. This is a novel example of how multiple activation steps occur under heat shock, first on the kinases and then the Stat1 and the SWI/SNF chromatin remodeling complex that follows to conduct an auto-regulation based fully activation of the gene.     

Does 2003 summer heat wave modified prevalence of bovine helminthosis in southwestern France?

The heat wave of 2003 summer had serious consequences on helminths prevalence and epidemiology. Comparison of 1917 cattle epg counts in southwestern France for years before and after showed that prevalence and mean numbers of Fasciola hepatica, paramphistomids, Dicroccelium lanceolatum and gastrointestinal strongyles eggs were significantly reduced. Nevertheless, the next year the epg counts were quickly increasing. Several factors may have induced a more or less long modification: strains of helminths may become adapted, a new spreading of intermediate hosts may occur with a modified ecology and finally moving of hosts and reservoirs may be amongst causes of epidemiological changes. Finally, after a heat wave the anthelmintic pressure may be maintained, as parasites seem quickly become adapted to a novel and modified environment.     

Metal chelatorNNN’ N’-tetrakis-(2-pyridylmethyl)ethylene diamine inhibits the induction of heat shock protein 70 synthesis by heat in cultured keratinocytes

Heat shock protein (HSP) synthesis results from various types of injury, including heat shock (HS) and some oxidants. The intracellular signals leading to HSP synthesis are not yet fully elucidated. We have studied the influence ofNNN’N’-tetrakis(2-pyridylmethyl)ethylene diamine (TPEN), a metal chelator known to induce cellular zinc and copper deprivation, on resistance to heat and on hsp70 synthesis in HaCaT keratinocytes. TPEN was shown to sensitize HaCaT cells to heat shock. The effect of TPEN was neutralized by equimolar Zn²⁺. By the use of sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis and Western blotting characterization of hsp70, it was shown that cultured HaCaT cells constitutively express the inducible form of hsp70. The application of TPEN alone slightly increases the level of hsp70 but inhibits its induction by HS. This inhibitory effect is related to metal deprivation, because it is eliminated when Cu²⁺ or Zn²⁺ ions are supplied together with TPEN. These results suggest that these metals are involved in the expression by keratinocytes of a stress protein which has a protective action against environmental stress.     

Characterization of a heat resistant ß-glucosidase as a new reporter in cells and mice

Background   

Reporter genes are widely used in biology and only a limited number are available. We present a new reporter gene for the localization of mammalian cells and transgenic tissues based on detection of the bglA (SYNbglA) gene of Caldocellum saccharolyticum that encodes a thermophilic β-glucosidase.     

Changes in cell morphology and actin organization during heat shock in Dictyostelium discoideum: does HSP70 play a role in acquired thermotolerance?

In response to heat shock (34°C, 30 min), cell morphology and actin organization in Dictyostelium discoideum are drastically changed. Loss of pseudopodia and disappearance of F-actin-containing structures were observed by using fluorescence microscopy. These changes were paralleled by a rapid decrease of the F-actin content measured by a TRITC-phalloidin binding assay. The effects of heat shock on cell morphology and actin organization are transient: After heat shock (34°C) or during a long-term heat treatment (30°C), cell morphology, F-actin patterns and F-actin content recovered/adapted to a state which is characteristic for untreated cells. Because F-actin may be stabilized by increased amounts of heat shock proteins, their response and interaction with F-actin was analyzed. After a 1 h heat treatment (34°C), the major heat shock protein of D. discoideum (HSP70) showed maximally increased synthesis rates and levels. During recovery from a 34°C shock or during a continuous heat treatment at 30°C, the HSP70 content first increased and then declined slowly toward normal levels. Pre-treatment of cells with a short heat shock of 30 min at 34°C stabilized the F-actin content when the cells were exposed to a second heat shock. Furthermore, a transient colocalization of HSP70 and actin was observed at the beginning of heat treatment (30°C) using immunological detection of HSP70 in the cytoskeletal actin fraction.     

Antibodies against heat shock proteins in environmental stresses and diseases: friend or foe?

Heat shock proteins (Hsps) can be found in two forms, intracellular and extracellular. The intracellular Hsps are induced as a result of stress and have been found to be cytoprotective in many instances due to their chaperone functions in protein folding and in protein degradation. The origin and role of extracellular Hsps is less clear. Although they were suspected originally to be released from damaged cells (necrosis), their presence in most normal individuals rather suggests that they have regulatory functions in circulation. As immunodominant molecules, Hsps can stimulate the immune system, leading to the production of autoantibodies recognizing epitopes shared by microbial and human Hsps. Thus, extracellular Hsps can influence the inflammatory response as evidenced by the production of inflammatory cytokines. Antibodies to Hsps have been found under normal conditions but seem to be increased in certain stresses and diseases. Such antibodies could regulate the inflammatory response positively or negatively. Here, we review the literature on the findings of antibodies to Hsps in situations of environmental or occupational stress and in a number of diseases and discuss their possible significance for the diagnosis, prognosis, or pathogenesis of these diseases.     

Stomatal movement in response to long distance-communicated signals initiated by heat shock in partial roots of Commelina communis L.

It is well known that animals are able to positively respond to environmental stimuli, thereby avoiding or reducing the possible injures or impacts on them, and the base for the rapid and positive responses is long- distance signal transmission mediated b…