Heat shock is lethal to fibroblasts microinjected with antibodies against hsp70

Sequence of neuronal responses assessed by immunohistochemistry in the newborn rat brain after hypoxia-ischemia

OBJECTIVE

Our purpose was to study the neuronal responses of heat shock protein-72 (a stress-inducible protein) and microtubule-associated protein-2 (a constitutive protein of the neuronal cytoskeleton) after hypoxia-ischemia and their relationship with permanent damage in the newborn rat brain.

STUDY DESIGN

Seven-day-old rats were exposed to unilateral carotid artery ligation followed by 2 hours of hypoxia (8% oxygen/92% nitrogen) and then killed at time points ranging from 1 to 72 hours after injury. Brains were removed for immunohistochemical and routine staining.

RESULTS

Heat shock protein-72 appearance and microtubule-associated protein-2 disappearance occurred from 1 hour after injury, mainly in the dentate gyrus of the hippocampal formation and the cerebral cortex. Such alterations reached maximal levels at 24 hours for both proteins. Microtubule-associated protein-2 staining recovered in almost all parts of the brain. However, the hippocampal CA3 showed a delay in the responses for both proteins, and microtubule-associated protein-2 did not recover the response to immunostaining. Histologic evaluation at 72 hours after hypoxia by routine methods showed predominant damage in the hippocampal CA3.

CONCLUSION

Our results show that delayed responses of heat shock protein-72 and microtubule-associated protein-2 are related to a high incidence of neuronal cell loss in the hippocampal CA3 region.

Ontogeny of temperature-regulated heat shock protein 70 synthesis in preimplantation bovine embryos

Development of the preimplantation embryo is very susceptible to disruption by heat shock. As embryos proceed through development, they acquire resistance to heat shock, perhaps because they become transcriptionally active and can respond to environmental changes by undergoing transcriptionally-regulated cellular adaptation. Objectives were to determine the ontogeny of heat shock protein 70 (HSP70) synthesis in preimplantation bovine embryos and to ascertain whether heat-induced increases in HSP70 in embryos are caused by environmental alterations in gene expression. Exposure of bovine embryos to heat shock induced synthesis of a 68 kDa form of HSP70 called HSP68 as early as the two-cell stage of development. Induction of HSP68 was alpha-amanitin independent at the two-cell stage but was blocked by alpha-amanitin as early as the early four-cell stage. Therefore, heat-induced synthesis of HSP68 is regulated at the level of transcription at a time before the major round of embryonic genome activation is considered to occur. Two other constitutive HSP70 molecules were identified called heat shock cognates (HSC) 71 and 70; both proteins were synthesized during all stages of development from the two-cell to hatched blastocyst stages. However, heat-induced synthesis of HSC71 and HSC70 was not evident until the expanded blastocyst stage. In conclusion, environmental signals can activate gene expression before the major round of embryonic genome activation occurs in bovine embryos. Moreover, differences in thermal sensitivity of early embryos to heat shock is not caused by an inability to synthesize HSP70, suggesting that other mechanisms are involved in developmental acquisition of thermotolerance.

HSP 70 induction and thermotolerance following interstitial hyperthermia in the dunning R3327 tumor in vivo

We investigated the use of an interstitial temperature self-regulating implant for fractionated hyperthermia delivery for treatment of prostatic disease. Nonuniform heating, lower temperatures between the implants, and lingering thermotolerance for additional hyperthermia treatments are concerns associated with the technique. Thermotolerance of the Dunning R3327 prostate adenocarcinoma to a 1 hour interstitial heating of 42-43°C has been estimated using inducible heat shock protein (HSP) 72 as an assay. The duration of thermotolerance in a nonuniformly heated tumor is necessary for optimization of multiple-treatment planning. HSP 72 expression is increased between 8 and 16 hours posttreatment. Growth curves for conditioned (treated once at 42-43°C minimum) tumors retreated at a minimum temperature of 45°C after 10 hours recovery (where elevated HSP 72 expression is evident) were compared with those retreated after 48 hours recovery (with normal HSP 72 expression) and with conditioned controls; both retreatment groups differed from controls (p < 0.0001). Growth curves for tumors with elevated HSP 72 expression after 10 hours differed from those retreated after 48 hours (p ≤ 0.0202). The results indicate that in vivo measurement of HSP 72 expression in the Dunning tumor is an adequate indicator of thermotolerance for optimal sequencing of hyperthermia fractions and that sufficiently high thermal doses are effective against thermotolerant cell populations.

Identification and characterization of a constitutive HSP75 in sea urchin embryos

An antiserum against a hsp of the 70-kDa family was prepared, by means of a fusion protein, which was able to detect a constitutive 75-kDa hsc in the sea urchin P. lividus. This hsc was present both during oogenesis and at all developmental stages. A two-dimensional electrophoresis has revealed four isolectric forms of this 75-kDa hsc. The amino acid sequence of the fragment used to prepare the anti-hsp70 antibodies revealed a 43% identity with the corresponding part of sea urchin sperm receptor, and in mature eggs a brighter immunofluorescence was seen all around the cell cortex where the receptor for sea urchin sperm is localized. In oocytes the hsp75 was localized in the cytoplasms but not in the nuclei. In the embryos a higher hsp75 concentration was found in the portion facing the lumen of the cells which invaginate at gastrulation.

Differential induction of heat shock mRNA in oligodendrocytes, microglia, and astrocytes following hyperthermia

A time course analysis of hsp70 mRNA induction in response to a physiologically relevant increase in body temperature of 2.6 degrees C was performed in the rabbit forebrain. A protocol that combined in situ hybridization and cytochemistry on the same tissue section was employed to identify reactive glial cell types. Cytochemical markers for astrocytes, microglia, and oligodendrocytes were utilized in combination with a DIG-labelled hsp70 riboprobe, which permitted mRNA localization at high resolution. Four glial cell body-enriched regions of the rabbit forebrain were examined, namely, cortical layer 1, hippocampal fissure, corpus callosum, and fimbria. Maximal hsp70 mRNA induction was observed in 2 and 3 h hyperthermic animals. The colocalization analysis demonstrated that hsp70 mRNA was induced in oligodendrocytes and microglia, but not in forebrain GFAP positive astrocytes. In addition, cell counts were performed which showed that almost all oligodendrocytes induced hsp70 mRNA while a subpopulation of microglial cells responded. These data are consistent with the notion that oligodendrocytes, microglia, and astrocytes exhibit distinct thresholds for activation of the heat shock response following a physiologically relevant increase in body temperature.

Modulation of a cardiogenic shock inducible RNA by chemical stress: adapt73/PigHep3

BACKGROUND

Understanding how mammalian cells respond to stress is important in the study, detection, and therapy of stress-related disorders. We have been studying cellular stress response in hamster HA-1 cells by using an adaptive response model. HA-1 cells respond to a minimally toxic "pretreatment" dose of hydrogen peroxide by synthesizing RNAs and proteins that protect them against subsequent exposure to a higher cytotoxic concentration of peroxide. The purpose of our studies is to identify and partially characterize any mRNA whose steady state level is significantly modulated during adaptation.

METHODS

HA-1 cells were exposed to a pretreatment dose of hydrogen peroxide and RNA extracted. The differential display technique was used to identify modulated mRNAs. The effects of calcium ionophore A23187 and cis (II)-platinum on the modulation of mRNA from HA-1 cells and A23187 on the modulation of mRNAs from human IMR-90 cells were also determined.

RESULTS

One of the RNAs induced by a pretreatment concentration of hydrogen peroxide was designated adapt73. The size of the induced adapt73 RNA was determined to be 2.1 kb. Induction of adapt73 was maximal 5 hours after peroxide treatment, but elevated levels were still obvious at 10 hours. This induction was not specific to oxidative stress, because other stress agents including as (II)-platinum and especially calcium ionophore A23187 also induced adapt73 mRNA levels. Partial sequencing of adapt73 and a subsequent GenBank homology search revealed extensive homology to a novel RNA from pig, designated PigHep3, that was identified as a cardiogenic shock response gene from liver in pigs that were undergoing resuscitation after circulatory shock. Homology to a completely sequenced but uncharacterized human homolog was also found. Using a partially sequenced expressed sequence tag (EST) human clone to adapt73, we probed Northern blots containing RNA from IMR-90 human fibroblasts treated with A23187. A strongly induced human adapt73 mRNA homolog was observed, almost identical in size to its hamster homolog. In vitro transcription and translation of the human EST clone revealed a translatable Adapt73 protein product.

CONCLUSIONS

These data indicate that adapt73/PigHep3 RNA can be induced by multiple chemical stress, that these inductions occur under protective or adaptive response conditions, that there is an inducible human homolog to adapt73, and suggest that adapt73 may be an important physiologic mediator of organ and cellular shock response in mammals.

Blocking the endogenous increase in HSP 72 increases susceptibility to hypoxia and reoxygenation in isolated adult feline cardiocytes

BACKGROUND

Heat shock protein (HSP) 72 is a ubiquitous protein that is rapidly induced in response to stress and is thought to constitute an endogenous protective response. Previously, work has focused on the effect of overexpression of HSP 72 in various cell types. We were interested in testing the hypothesis that blocking the increase in HSP 72 that occurs in response to hypoxia or ischemia would be deleterious, thus showing that the endogenous response in cells, particularly cardiac cells, is an important line of defense against cell injury.

METHODS AND RESULTS

Isolated adult feline cardiocytes were treated with a 14-mer phosphorothioate antisense (AS) to HSP 72 and then exposed to mild (8 hours) or severe (12 hours) hypoxia. With mild hypoxia, an increase in LDH release, a decrease in MTT uptake, and a decrease in live-to-dead ratios were seen in AS-treated cells compared with control cells and cells treated with the complementary sense sequence or with AS to major histocompatibility complex I. AS treatment converted mild hypoxic injury to a pattern of cell injury seen with severe injury. After severe hypoxia, all treatment groups showed an increase in LDH, a decrease in MTT uptake, and a decrease in live-to-dead ratios; AS-treated cells had the greatest increase in cell injury. AS treatment produced a 40% decrease in HSP 72 levels after hypoxia compared with control cells treated with hypoxia. A dose-response study showed inhibition of the increase in HSP 72 with as little as 5 micrograms (1.24 mumol/L) of AS.

CONCLUSIONS

(1) Blocking an increase in HSP 72 with AS increases the susceptibility of adult cardiac myocytes to hypoxic injury. (2) HSP 72 is an important part of the normal cell response to stress and is important in protecting cardiac myocytes from hypoxia and reoxygenation.

Identification and characterization of a novel hsc70-like gene in the human lung tumor cell line HS24

We determined the cDNA sequence and analyzed the genomic structure of a novel human gene designated HS24/p52, which shows significant similarity to the ATP-binding domain of stress-70 proteins in the human lung tumor cell line HS24. The 2,203-nucleotide-long cDNA sequence is divided into an incomplete 10-nucleotide 5' nontranslated region, a 1,425-nucleotide open reading frame which codes for 474 amino acids and a 768-nucleotide 3' nontranslated region. The first 404 of the deduced 474 amino acids resemble the amino-terminal regions of Hsp70 proteins from different species. Furthermore, single amino acid and short amino acid stretches, which are thought to be essential for the ATPase mechanism and ATP-binding activity in Hsp70 proteins, are conserved in this sequence, too. The carboxy-terminal 70 amino acids exhibit no significant similarity to hsp70 nor to any other known protein sequences. The HS24/p52 gene contains at least five introns, which differ significantly from hsc70 genes with regard to their size and location within the coding sequences. The total size of this gene is more than 15 kbp. Polymerase chain reaction (PCR) experiments showed that this gene is expressed in different human cell lines and tissues and it also seems to be highly conserved between human and mouse.

Activation signals regulate heat shock transcription factor 1 in human B lymphocytes

We previously showed that the ability of human B lymphocytes to elicit a cytoprotective heat shock response when confronted by heat or other stresses was dependent upon the state of cell activation. This was unexpected, considering the highly conserved nature of the heat shock response and the widely held belief that all nonmutated mature cells were capable of eliciting a heat shock response when stressed. To elucidate the mechanism by which activation primes B cells to respond to stresses, we examined heat shock transcription factor 1 (hHSF1) in B cells since this factor appears to be solely responsible for stress-induced transcription of heat shock genes in human cells. In the current report, we show that hHSF1-DNA binding complexes are undetectable in extracts of unactivated B cells. In fact, hHSF1 protein is not constitutively expressed in unactivated B cells, nor is its synthesis stress-inducible. However, following activation, hHSF1 can be found in either a transcriptionally active or an inactive state, depending upon whether the cell has been stressed or not. Thus, activation pathways play an important role in enabling B cells to survive and function properly in the context of physiologic stresses by regulating hHSF1.

Induction of Hsp72 and transient nuclear localization of Hsp73 and Hsp72 correlate with the acquisition and loss of thermotolerance in postimplantation rat embryos

A number of cell culture studies have indicated that there is a positive correlation between the induction and decay of thermotolerance and the kinetics of Hsp72 expression. In this study, we have demonstrated that, in gestational day 10 embryos, induction and decay of thermotolerance occur over an 8 hr period. To test the hypothesis that there is a correlation between loss of thermotolerance and the decline of Hsp72 or Hsp73 gene products over time, expression levels of both Hsp72 and constitutively expressed Hsp73 mRNAs and proteins were examined at several time points following exposure to a thermotolerance-inducing exposure of 42 degrees C. Our results indicated that Hsp72 mRNA was strongly induced 1 hr after exposure but no longer detectable by 8 hr. Although our Western blot results indicated that Hsp72 protein was present beyond 8 hr after exposure, Northern blot analysis showed that Hsp72 mRNA was no longer present 5 hr after exposure to 42 degrees C. The latter finding indicates that no new Hsp72 can be synthesized at this time point and beyond. Although there was very little or no induction of Hsp73, immunohistochemical analysis revealed a dramatic, transient shift in intracellular localization of Hsp73 protein, as well as Hsp72. Under non-stress conditions, Hsp73 was cytoplasmically localized but localization was largely nuclear 1 hr after exposure, when thermotolerance was demonstrable. Hsp73 and Hsp72 proteins were no longer localized in the nucleus by 8 hr, when thermotolerance was no longer detectable. Thus, the induction of Hsp72 and the transient nuclear localization of both Hsp72 and Hsp73 correlate with the kinetics of thermotolerance in the postimplantation rat embryo.

Tissue-specific differences in heat shock protein hsc70 and hsp70 in the control and hyperthermic rabbit

The ability to resolve protein members of the hsp70 multigene family by two-dimensional Western blotting permitted the characterization of antibodies which were specific in discriminating constitutively expressed hsc70 isoforms from stress-inducible hsp70 isoforms. This antibody characterization demonstrated that basal levels of hsp70 isoforms were present in the cerebellum of the control rabbit and that these were elevated following hyperthermia, whereas levels of hsc70 were similar in control and hyperthermic tissue. Multiple isoforms of hsp70 were detected but tissue-specific differences were not apparent in various organs of the rabbit. However, species differences were observed as fewer hsp70 isoforms were noted in rat and mouse. In the control rabbit, higher levels of hsc70 protein were present in neural tissues compared to non-neural tissues. Following physiologically relevant hyperthermia, induction of hsp70 was greatest in non-neural tissues such as liver, heart, muscle, spleen, and kidney compared to regions of the nervous system. These studies suggest that the amount of preexisting constitutive hsc70 protein may influence the level of induction of hsp70 in the stress response. Given this observation, caution is required in the employment of hsp70 induction as an index of cellular stress since endogenous levels of hsc70, and perhaps hsp70, may modulate the level of induction.

Differential responses of bovine oocytes and preimplantation embryos to heat shock

The authors sought to determine whether developmental differences in the magnitude of embryonic mortality caused by heat stress in vivo are caused by changes in resistance of embryos to elevated temperature. In this regard, responses of oocytes, two-cell embryos, four-to eight-cell embryos, and compacted morulae to heat shock were compared. An additional goal was to define further the role of cumulus cells and glutathione in thermoprotection of oocytes. In experiment 1, heat shock (41 degrees C for 12 hr) decreased the number of embryos developing to the blastocyst stage for two-cell (26% vs. 0%) and four- to eight-cell (25% vs. 10%) embryos but did not affect morulae (37% vs. 42%). In experiment 2, exposure of two-cell embryos to 41 degrees C for 12 hr reduced the number of four- to eight-cell embryos present 24 hr after the end of heat shock (88% vs. 62%). In experiment 3, heat shock reduced the number of two-cell embryos developing to blastocyst (49% vs. 8%) but did not affect subsequent development of oocytes when heat shock occurred during the first 12 hr of maturation (46% vs. 41% development to blastocyst); membrane integrity was not altered. In experiment 4, oocytes were cultured with an inhibitor of glutathione synthesis, DL-buthionine-[S,R]-sulfoximine (BSO), for 24 hr and exposed to 41 degrees C for the first 12 hr of maturation. Percentages of blastocysts were 35% (39 degrees C), 18% (41 degrees C), 17% (39 degrees C + BSO), and 11% (41 degrees C + BSO). For experiment 5, oocytes were either denuded or left with cumulus intact and were then radiolabeled with [35S]methionine and [35S]cysteine at 39 degrees C or 41 degrees C for 12 hr. Exposure of oocytes to 41 degrees C for 12 hr reduced overall synthesis of 35S-labeled TCA-precipitable intracellular proteins (18,160 vs. 14,594 dpm/oocyte), whereas presence of cumulus increased synthesis (9,509 vs. 23,246). Analysis by two-dimensional SDS PAGE and fluorography revealed that heat shock protein 68 (HSP68) and two other putative heat shock proteins, P71 and P70, were synthesized by all oocytes regardless of treatment. Heat shock did not alter the synthesis of HSP68 or P71 but decreased amounts of newly synthesized P70. Cumulus cells increased synthesis of P71 and P70. Results indicate there is a biphasic change in resistance to elevations in temperature as oocytes mature, become fertilized, and develop. Resistance declines from the oocyte to the two-cell stage and then increases. Evidence suggests a role for cumulus cells in increasing HSP70 molecules and protein synthesis. Data also indicate a role for glutathione in oocyte function.

Cellular immunity: the final paradigm?

Cytotoxic T lymphocyte activation and most probably tolerance induction, is dependent on antigen presentation by a specialized group of cells, APC, including macrophages, dendritic cells and B cells. Since T lymphocytes are, at least, the majority of the time MHC molecule class-specific, CD8+ T cells require antigen presented by MHC class I molecules. MHC class I molecules are, however, restricted to presenting endogenously produced antigenic peptides. Most threats to the organism are of exogenous origin and do not uniformly affect all or even most of the cells of an organism. This precludes the likelihood that any number of APC would be involved in every threatening situation, which raises the important question of how T lymphocytes are indeed activated, especially CD8+ T cells (MHC class I restricted).

Characterization of human proximal tubular cells after hypoxic preconditioning: constitutive and hypoxia-induced expression of heat shock proteins HSP70 (A, B, and C), HSC70, and HSP90

In animal models of cardiac or cerebral ischemic preconditioning, induction of heat shock proteins (HSPs), especially HSP70, correlates with protection from subsequent injury. The extent of HSP70 induction after stress correlates inversely with initial HSP70 levels. Primate cells, unlike nonprimate cells, express high basal levels of HSP70; thus, primate cells may respond differently to preconditioning than nonprimate cells. We have demonstrated that exposing cultured human proximal tubular epithelial cells (PTEC) to 12 h of hypoxia followed by a 24-h recovery period (hypoxic preconditioning) induces resistance to subsequent hypoxic injury. Herein, we characterize the expression of HSP70, HSP90, and heat shock cognate-70 (HSC70) in PTEC under basal conditions and after hypoxic preconditioning. By Northern blot analysis, we demonstrate that hypoxic preconditioning of PTEC increases mRNA for HSP70 > HSP90 > HSC70. With reverse transcription and polymerase chain reaction, mRNA transcripts from three different HSP70 genes (HSP70 A, B, and C) were detected in unstressed PTEC. Transcripts from these genes were also detected in freshly isolated human renal cortex, indicating that all three genes are expressed in vivo. By Western blot analysis, we demonstrate that PTEC express high basal levels of HSP70, HSC70, and HSP90. Hypoxic preconditioning did not lead to a significant increase in protein content of any of these HSPs, despite increased mRNA levels. This suggests that HSP accumulation cannot account for the development of cytoresistance after hypoxic preconditioning in PTEC. However, high basal expression of HSP70 in human PTEC may contribute to their innate resistance for hypoxia.

Preliminary studies on the relationship between autoantibodies to heat stress proteins and heat injury of pilots during acute heat stress

Comparison in the heart rate, oral temperature and lymphocyte DNA damage during heat stress was made in pilots with negative antibodies to heat stress proteins (HSPs) and those with positive antibodies in the man-made climate room with Western blot and comet assay. Our results showed that the increase in oral temperature, heart rate and lymphocyte DNA damage in pilots with the positive antibodies to HSPs were higher than those in pilots with the negative antibodies during heat stress. These results indicated that the presence of autoantibodies in plasma of pilots might reflect heat damage and high sensitivity to heat.

Is post-hypoxic-ischemic cell damage associated with excessive ATP consumption rather than a failure of ATP production?

Secondary cell damage after ATP depletion due to hypoxia or ischemia is clinically important because it correlates with residual effects; post-hypoxic-ischemic fits can be associated with later cerebral palsy. The mechanisms involved in delayed secondary cell damage are not clear, possibly because extensive relevant evidence is often fragmented. However, a sequence of changes can be suggested; this cross-linked sequence is tentatively outlined in this review. The outline suggests explanations for otherwise ill-understood clinical disturbances such as the loss of inhibitory control in damaged cells and the well documented reduction of cellular ATP. Loss of control may be due to reduced synthesis of control proteins and the reduced ATP concentration may be due to increased energy consumption.

Induction of heat shock protein 70 (HSP70) by zinc bis (DL-hydrogen aspartate) reduces ischemic small-bowel tissue damage in rats

The aim of the study was to determine whether the induction of HSP70 by Zn2+ is able to protect the small bowel of rats against ischemia. Twenty-four male Wistar rats (weight 200-300 g) were divided into four groups: (1) saline treatment for 24 h (n = 4); (2) Zn2+ treatment for 24 h (n = 4); (3) Saline pretreatment for 24 h and ischemia (n = 8); (4) Zn2+ pretreatment for 24 h and ischemia (n = 8). Pretreatment with Zn2+ was carried out by intraperitoneal administration of 50 mg/kg zinc bis (DL-hydrogen aspartate) = 10 mg/kg Zn2+. Ischemia in a defined segment of the small bowel was produced by ligation of the mesenteric vein and artery and ligation of both ends of the segment. Tissue samples were collected before and 2, 4 and 6 h after ligation and investigated by histology, immunohistochemistry and Western blotting. Twenty-four h after i.p. Zn2+ injection, the small bowel expressed increased HSP70 tissue levels. Histology with subsequent grading of ischemic tissue injury showed significantly decreased tissue necrosis after Zn2+ pretreatment and HSP70 induction compared with saline pretreated controls. In conclusion, this study proves that Zn2+ is inducing HSP70 in the small bowel in vivo and hereby able to protect the small bowel against ischemia.

HSP70 is essential to the neuroprotective effect of heat-shock

Many kinds of injuries induce 72 kDa heat-shock protein (HSP70) in the central nervous system. We investigated the role of HSP70 in promoting the survival of rat hippocampal neurons in primary culture. Heat-shock (42 degrees C for 30 min) significantly increased the number of surviving neurons independently of the initial density of plated cells, suggesting a direct effect on the neurons. Immunohistochemical detection revealed that HSP70 was expressed in virtually all cells six hours after the heat-shock and the immunostaining became stronger during the observation period of 72 h. HSP70 immunoreactivity was localized in the nucleus at 24 h after the heat-shock, but was diffused throughout the cytoplasm at 72 h. Addition of an antisense oligonucleotide to the medium significantly suppressed the neuroprotective effect of the heat-shock to control level, while a sense oligonucleotide had no effect. HSP70 immunoreactivity was completely abolished in the presence of the antisense oligonucleotide. These results indicate that HSP70 is essential for neuroprotection by heat-shock.

Cell Signaling and Heat Shock Protein Expression

Exposure of cells and organs to heat shock is associated with numerous changes in various cellular metabolic parameters and overexpression of proteins collectively known as heat shock proteins (HSP). In this communication we review the cell-signaling events that are altered in response to heat shock as they relate to the subsequent induction of HSP 70 kd (HSP-70) expression. We also review the mechanisms by which HSP-70 is involved in conferring cytoprotective effects. The possibility of altering HSP expression through manipulations of the cell-signal process has clinical importance. Copyright 1996 S. Karger AG, Basel

Therapeutic hyperthermia

Those diseases that medicines do not cure, are cured by the knife, and those diseases that the knife cannot cure are cured by fire. And those diseases that fire does not cure are to be reckoned wholly incurable.

Cytotoxicity, zinc protection, and stress protein induction in rat proximal tubule cells exposed to cadmium chloride in primary cell culture

Primary cell culture was utilized to study the relationships between stress protein induction by zinc in vivo and cadmium toxicity in vitro. Effects of cadmium on cell viability were evaluated by the alamar blue assay, in conjunction with the ultrastructural morphology of cells by transmission electron microscopy. The expression of stress protein gene products was evaluated by 35S two-dimensional gel electrophoresis. The results showed cytotoxicity of CdCl2 at and above 129 microM (14.55 micrograms cadmium/mL medium) following 4 h of exposure. Prior zinc administration (20 mg zinc/kg, s.c., two daily doses) in vivo significantly protected the cells in vitro as demonstrated by improved cell viability. The 35S labeling of proteins induced by CdCl2 exposure clearly demonstrated for the first time that gene product of the 70-kDa family was induced in cultured rat proximal tubule cells which are the target cells for cadmium toxicity in vivo. Zinc in vivo pretreatment of animals induced proteins in the 90-, 70-, and 38-kDa families, which may act together with metallothionein to protect cells against cadmium toxicity. The results also indicate that the protective effect of zinc remains after the cells have been put in culture and thus provides a system in which we can study the changes that occur as a result of zinc exposure that decreases cadmium toxicity.

Influence of heat shock protein 70 and metallothionein induction by zinc-bis-(DL-hydrogenaspartate) on the release of inflammatory mediators in a porcine model of recurrent endotoxemia

The manipulation of stress gene expression by heavy metals provides protection against the lethal effects of endotoxemia in murine models of septic shock. Recent in vitro studies with alveolar macrophages or monocytes show that induction of the stress response in these cells is followed by a decreased liberation of major cytokines [tumor necrosis factor-alpha (TNF alpha) and interleukin-1 (IL-1)] after endotoxin challenge. These findings suggest that the increased resistance to endotoxin in vivo after stress protein induction could be explained by an altered pattern of inflammatory mediator release. Therefore, we measured the time course of thromboxane-B2 (TxB2), 6-keto-PGF1 alpha, platelet activating factor (PAF), TNF alpha, interleukin-1 beta (IL-1 beta), and interleukin-6 (IL-6) formation with and without induction of the stress response in an established porcine model of recurrent endotoxemia (Klosterhalfen et al., Biochem Pharmacol 43: 2103-2109, 1992). Induction of the stress response was done by a pretreatment with Zn2+ (25 mg/kg zinc-bis-(DL-hydrogenasparate = 5 mg/kg Zn2+). Pretreatment with Zn2+ prior to lipopolysaccharide (LPS) infusion induced an increased heat shock protein 70 and metallothionein expression in the lungs, liver, and kidneys and increased plasma levels of TNF alpha, IL-1 beta, IL-6, and TxB2 as opposed to untreated controls. After LPS infusion, however, pretreated animals showed significantly decreased peak plasma levels of all mediators as opposed to the untreated group. The time course of mediator release was identical with the decreasing and increasing three peak profiles described previously. Hemodynamic data presented significantly decreased peak pulmonary artery pressures and significantly altered hypodynamic/hyperdynamic cardiac output levels in the pretreated group. In conclusion, the data show that the induction of stress proteins by Zn2+ could be a practicable strategy to prevent sepsis.

Acclimatization, preconditioning and heat shock proteins

During prior acclimatization, mineworkers acquire tolerance against the adverse effects of working in a warm environment. In this article, the possible involvement of heat shock proteins as mediators of acclimatization is proposed. Acclimatization is compared with preconditioning. Preconditioning of isolated cells or organs by prior exposure to a temperature higher than normal or exposure to an ischaemic insult endow tolerance on them when later confronted with a severe ischaemic stress. This tolerance is possibly mediated by heat shock proteins induced by the heating or ischaemic preconditioning episode. Functioning of the induced heat shock proteins may therefore underlie the protective mechanisms in both acclimatization and preconditioning.

Ischemic preconditioning of the liver in rats: implications of heat shock protein induction to increase tolerance of ischemia-reperfusion injury

It has been reported that ischemic preconditioning of the heart or brain has a possible relevance to heat shock protein (HSP). It is still unknown, however, whether HSP induced by means of ischemic preconditioning of the liver is a direct factor in the acquisition of tolerance to succeeding ischemia-reperfusion injury. In the present study we used ischemic preconditioning of the liver to verify the effects of induced HSP72 in the liver on the subsequent longer warm ischemia and reperfusion. Rats preconditioned with short-term (15-minute) ischemia were compared with rats preconditioned by heat exposure or with control rats. After a 48-hour recovery from the sublethal stress for preconditioning, all rats were exposed to longer (30-minute) warm ischemia and reperfusion. Forty-eight hours after ischemic preconditioning, HSP72 was clearly induced in the liver, as well as in the liver preconditioned with heat shock, but not in the kidney or heart. This ischemic preconditioning also attenuated the liver damage in the subsequent ischemia-reperfusion injury, improving the restoration of hepatic function during reperfusion and resulting in higher postischemic rat survival. According to the proposed model of tolerance acquisition for ischemia-reperfusion injury by stress preconditioning, these observations support the speculation that the induced HSP72 plays some beneficial role in this protection mechanism.

Modulation of thermal induction of hsp70 expression by Ku autoantigen or its individual subunits

Previously, we proposed a dual control mechanism for the regulation of the heat shock response in mammalian cells: a positive control mediated by the heat shock transcription factor HSF1 and a negative control mediated by the constitutive heat shock element-binding factor (CHBF). To study the physiological role of CHBF in the regulation of heat shock response, we purified CHBF to apparent homogeneity and showed it to be identical to the Ku autoantigen, a heterodimer consisting of 70-kDa (Ku-70) and 86-kDa (Ku-80) polypeptides. To study further the functional significance of Ku/CHBF in the cellular response to heat shock, we established rodent cell lines that stably and constitutively overexpressed one or both subunits of the human Ku protein, and examined the thermal induction of hsp70 and other heat shock proteins in these Ku-overexpressing ing cells. We show that expression of the human Ku-70 and Ku-80 subunits jointly or of the Ku-70 subunit alone specifically inhibits heat-induced hsp70 expression. Conversely, expression of human Ku-80 alone does not have this effect. Thermal induction of other heat shock proteins in all of the Ku-overexpressing cell lines appears not to be significantly affected, nor is the state of phosphorylation or the DNA-binding ability of HSF1 affected. These findings support a model in which hsp70 expression is controlled by a second regulatory factor in addition to the positive activation of HSF1. The Ku protein, specifically the Ku-70 subunit, is involved in the regulation of hsp70 gene expression.

Mitochondria are selective targets for the protective effects of heat shock against oxidative injury

Heat shock (HS) proteins (HSPs) induce protection against a number of stresses distinct from HS, including reactive oxygen species. In the human premonocytic line U937, we investigated in whole cells the effects of preexposure to HS and exposure to hydrogen peroxide (H2O2) on mitochondrial membrane potential, mass, and ultrastructure. HS prevented H2O2-induced alterations in mitochondrial membrane potential and cristae formation while increasing expression of HSPs and the protein product of bcl-2. Protection correlated best with the expression of the 70-kDa HSP, hsp70. We propose that mitochondria represent a selective target for HS-mediated protection against oxidative injury.

Astrocyte survival and HSP70 heat shock protein induction following heat shock and acidosis

Although severe acidosis is an important mediator of brain infarction, recent evidence suggests that mild acidosis may protect ischemic cells. The HSP70 heat shock protein is induced by acidosis in cultured cells and in ischemic brain and protects cells against many types of injury. Therefore, this study determined whether induction of heat shock proteins protects cultured astrocytes against acidosis. Brief exposure of cultured cortical astrocytes to acid (pH 5.2 for 40 min) or heat shock (45 degrees C for 40 min) markedly induced hsp70 mRNA and HSP70 protein. HSP70 protein was detected with the C92 monoclonal antibody (Welch and Suhan: J Cell Biol 103:2035, 1986), which has been shown to recognize the protein product of the full-length rat hsp70 cDNA (Longo et al: J Neurosci Res 36:325, 1993). Heat shock of the cultured cortical astrocytes completely protected the astrocytes from an otherwise lethal heat exposure 24 h later (45 degrees C for 4 h). In contrast, heat pretreatment sensitized the astrocytes to injury from acidosis 24 h later. Acid pretreatment, which markedly induced the HSP70 protein without producing astrocytic cell death, similarly sensitized the cells to injury from acidosis 24 h later (60% survival following pH 5.2 for 3 h versus 90% survival in controls; P < 0.0001). Surprisingly, heat shock pretreatment protected astrocytes against exposure to acid 48 h later (P < 0.05, 1.5-3 h), whereas acid pretreatment had no effect on astrocyte survival 48 h later. Since heat shock did not protect against acidosis at 24 h when HSP70 induction was maximal but did protect at 48 h when HSP70 was markedly diminished, the protective effect of heat shock at 48 h may be related to stress proteins present at 48 h. It is concluded that induction of HSP70 and other heat shock proteins by heat shock protects astrocytes against subsequent lethal heat shock. However, heat shock and acid treatment increase the vulnerability of astrocytes to acidosis 24 h later in spite of the induction of HSP70 heat shock proteins. The finding that heat shock protected astrocytes against acidosis 2 days later may suggest that delayed induction of stress proteins partially protects the astrocytes against damage produced by high concentrations of hydrogen ions.

Caloric restriction increases the expression of heat shock protein in the gut

OBJECTIVE

The authors determined whether caloric restriction (CR) either acutely or chronically, alters heat shock protein 70 (hsp70) gene expression in the gut.

SUMMARY BACKGROUND DATA

Caloric restriction prolongs the life span and delays age-related disease (e.g., cancer) in mammals; the mechanisms responsible for these effects are not known. Heat shock proteins are a group of stress-responsive genes of which the most prominent member is hsp70.

METHODS

In the first experiment, adult (4-month-old) rats (n = 3/group) were killed after a 48-hour fast or 6 and 24 hours after refeeding. In addition, three rats (controls) were killed without fasting or refeeding. The stomach was removed and RNA was extracted for hsp70 gene expression. In the second experiment, aged (22- to 26-month-old) rats were fed ad libitum (AL) or a CR diet (60% caloric intake of AL diet). Rats were killed, the stomach and duodenum were removed, and RNA was extracted for determination of hsp70 gene expression.

RESULTS

In the first experiment, hsp70 mRNA levels were increased approximately threefold in the stomach of rats fasted for 48 hours; levels decreased to control values by 6 and 24 hours after refeeding. In the second experiment, hsp70 mRNA levels were increased significantly in both the stomach and duodenum of aged CR rats compared with AL controls.

CONCLUSIONS

The authors have demonstrated that hsp70 mRNA levels are increased in the proximal gut of young and old rats, either acutely (with fasting) or with CR. Increased expression of the cytoprotective hsp70 gene in the gut may provide a possible cellular mechanism for the beneficial effects noted with CR.

Stable expression of a human HSP70 gene in a rat myogenic cell line confers protection against endotoxin

Recent reports show that a pre-heat shock has a protective effect against endotoxin "in vivo" in rodents. It has remains unclear what actually confers the protection against endotoxin. One candidate for this protective effect is the heat shock protein of 70 kDa (HSP70). We found that a mild heat shock pretreatment is the rat myogenic cell line, H9c2(2-1), confers resistance to a subsequent exposure to endotoxin. A myogenic rat cell line stably transfected with the human inducible HSP70 exhibits an increased survival rate compared with cells stably transfected solely with the selectable neomycin marker gene or the parental cell line H9c2(2-1) when exposed to endotoxin. The mechanism of endotoxin-induced cell injury is postulated to be through the generation of nitric oxide in these myogenic cells during exposure to endotoxin. We conclude that HSP70, regardless of the particular mechanism of cytotoxicity, plays a role in protecting the cell against the deleterious effects of endotoxin.

Effect of heat stress on development in vitro and in vivo and on synthesis of heat shock proteins in porcine embryos

The present study was conducted (1) to examine the effect of an acute increase in ambient temperature on the development of porcine day 6 embryos in culture and after transfer to recipient gilts, and (2) to analyze intracellular production of heat shock proteins (hsps). The viability of porcine day 6 embryos following a temporary acute elevation in ambient temperature (at 42 degrees-45.5 degrees C and for 10-180 min) was examined. Synthesis of 70 kDa hsp (hsp70) and 90 kDa hsp (hsp90) was determined by SDS-PAGE and Western blot analysis in porcine day 6 embryos subjected to heat stresses. Nonheat-stressed embryos were considered as control. Significantly higher numbers of viable nuclei were observed in treatment groups of 42 degrees C-10 min (236.6 +/- 71.4; P < 0.05) and 43 degrees C-30 min (276.8 +/- 89.4; P < 0.005) compared to control (173.9 +/- 53.9). The 42 degrees C-180 min group (158.0 +/- 27.1 microns) had a greater increase in diameter after 24 hr in culture following heat stress compared to control (82.5 +/- 47.3 microns), while heat stress with 43 degrees C for > or = 60 min, 44 degrees-44.5 degrees C for > or = 30 min, or 45 degrees-45.5 degrees C for > or = 10 min impaired their survival, as assessed by differences in number of viable nuclei. The embryos subjected to heat stresses under the conditions of 42 degrees C-180 min, 43 degrees C-10 min, 43 degrees C-30 min, 44 degrees C-10 min, or 45 degrees C-10 min developed to normal piglets after transfer to recipient gilts. Overall pregnancy rate was 75% (6/8), and farrowing rate 62.5% (5/8). Of heat-stressed embryos transferred, 59% (36/61) developed to normal piglets. Heat-stress conditions of 42 degrees C for 180 min, 43 degrees C for 30 min, 44 degrees C for 10 min, and 45 degrees C for 10 min were determined as critical with respect to the in vitro and in vivo survival of porcine embryos. Porcine day 6 embryos constitutively synthesized hsp70 even without heat stress, while hsp90 was detected only at trace level. Neither hsp70 nor hsp90 levels increased in the embryos subjected to heat stresses. In conclusion, porcine day 6 embryos could continue to develop in vivo or during in vitro culture after exposure to acute and temporary rise in temperature. However, no increase of hsp70 and hsp90 was observed in the heat-stressed porcine embryos, while hsp70 was detected in the nonheat-stressed porcine embryos. The precise mechanism of the thermotolerance was unclear.

Molecular chaperones and disease

Molecular chaperones are intracellular protein-folding proteins which form part of an ancient cellular response to stress called the heat shock response. They have been the focus for attention during the last decade because of the discovery of their vital role in cell functioning. In very recent years additional roles for these 'topologically-active' proteins in the process of tissue pathology and its treatment have been indicated and are reviewed.

Cardioprotective effects of 70-kDa heat shock protein in transgenic mice

Heat shock proteins are proposed to limit injury resulting from diverse environmental stresses, but direct metabolic evidence for such a cytoprotective function in vertebrates has been largely limited to studies of cultured cells. We generated lines of transgenic mice to express human 70-kDa heat shock protein constitutively in the myocardium. Hearts isolated from these animals demonstrated enhanced recovery of high energy phosphate stores and correction of metabolic acidosis following brief periods of global ischemia sufficient to induce sustained abnormalities of these variables in hearts from nontransgenic littermates. These data demonstrate a direct cardioprotective effect of 70-kDa heat shock protein to enhance postischemic recovery of the intact heart.

Evidence for different mechanisms of induction of HSP70i: a comparison of cultured rat cortical neurons with astrocytes

This study is a follow-up of previous work which demonstrated that cultured cortical neurons did not synthesize HSP70i immediately after heat stress when compared with cultured cortical astrocytes. We have extended the period of observation for HSP70i induction of cultured cortical neurons and astrocytes up to 24 h after heat stress. Cultured rat cortical neurons derived from 16-day-old fetal rats respond differently to heat stress than cultured rat astrocytes derived from newborn rats. They showed a delayed HSP70i induction in the majority of cultured neurons and the response was heterogeneous and was absent in most smaller neurons. The delayed neuronal induction was accompanied by a prolonged activation of heat-shock transcription factor 1 (HSF-1) and prolonged transcription of HSP70i mRNA. In comparison astrocytes showed a marked early induction of HSP70i mRNA and protein. In addition the induction of HSP70i in astrocytes was followed by translocation of the protein into the nucleus, a finding which we failed to demonstrate in neurons. Immunostaining for HSP70i was more uniform in astrocytes than neurons. Many neurons did not stain for up to 24 h after heat shock in this study. Immunocytochemical staining of HSF-1 and 2 showed major differences between neurons and astrocytes. Astrocytes showed localization of HSF-1 to the nucleus before and after heat stress, while neurons showed HSF-1 localization to the cytoplasm and nucleus before and after heat stress. Finally HSF-2 was undetectable in neurons when compared with astrocytes by Western immunoblot analysis. However, astrocytes and neurons revealed weak immunostaining of HSF-2 in the cytoplasm and nucleus. The staining in the neurons was likely secondary to cross-reactivity to an unidentified protein. We conclude that HSP70i expression after heat shock is delayed in rat cortical neurons when compared with rat cortical astrocytes. In addition most small neurons did not synthesize HSP70i after heat shock. This difference in induction of HSP70i may be secondary to localization and activation of HSF-1 but not HSF-2. Neuronal susceptibility to injury may be related to the delayed induction of HSP70i and also the possible failure of newly synthesized HSP70i to translocate into the nucleus.

The potential role of HSP70 as an indicator of response to radiation and hyperthermia treatments for recurrent breast cancer

Twenty-three patients with recurrent breast cancer participating in a Phase III trial evaluating radiotherapy (XRT) with or without hyperthermia (HT) were included in a parallel study of heat shock protein (hsp) expression. The patients had core biopsies and/or fine needle aspirates (FNA) performed on their tumours, before and after treatment. These were analysed for hsp content using immunohistochemical staining with a monoclonal antibody to the inducible form of hsp 70. The proportion of samples containing identifiable cancer cells was greater for the core biopsy specimens (80%) than with FNA (60%). Staining intensity was analysed using either the majority score, i.e. the staining intensity (on a relative scale from 0 to 3) for the largest proportion of tumour cells, or the arithmetic score, which is the sum of the product of percentage of tumour cells and their staining intensity. The staining intensity for hsp's after treatment correlated inversely with the probability of attaining a complete response (CR). Specifically, the median and maximum scores for the biopsy specimens were significantly inversely related to the probability of attaining CR. The results suggest that this technique may be useful in predicting for thermotolerance development, though more data is needed to confirm the utility of the technique. Results from this study corroborate data from other clinical studies which suggest that tumours with elevated hsp levels may demonstrate resistant biologic behaviour.

Heat shock proteins HSP25, HSP60, HSP72, HSP73 in isoosmotic cortex and hyperosmotic medulla of rat kidney

The distribution of heat shock proteins (HSP) HSP60, HSP73, HSP72 and HSP25 in the isoosmotic cortex and the hyperosmotic medulla of the rat kidney was investigated using Western blot analysis and immunohistochemistry. HSP73 was homogeneously distributed throughout the whole kidney. The level of HSP60 was high in the renal cortex and low in the medulla. HSP25 and HSP72 were present in large amounts in the medulla. Only low levels of HSP25 and almost undetectable amounts of HSP72 were found in the cortex. HSP25 exists in one nonphosphorylated and several phosphorylated isoforms. Western blot analysis preceded by isoelectric focussing showed that HSP25 predominates in its nonphosphorylated form in the outer medulla but in its phosphorylated form in cortex and inner medulla. Although this intrarenal distribution pattern was not changed during prolonged anaesthesia (thiobutabarbital sodium), a shift from the nonphosphorylated to the phosphorylated isoforms of HSP25 occurred in the medulla. The characteristic intrarenal distribution of the constitutively expressed HSPs (HSP73, HSP60, HSP25) may reflect different states of metabolic activity in the isoosmotic (cortex) and hyperosmotic (medulla) zones of the kidney. The high content of inducible HSP72 in the medulla most likely is a consequence of the osmotic stress imposed upon the cells by the high urea and salt concentrations in the hyperosmotic medullary environment.

Thermotolerance and heat shock proteins: possible involvement of Ku autoantigen in regulating Hsp70 expression

Here we characterize and compare the phenomenon of thermotolerance and permanent heat resistance in mammalian cells. The biochemical and molecular mechanisms underlying the induction of thermotolerance, and the role that heat shock proteins play in its development and decay are discussed. Finally, we describe a novel constitutive HSE-binding factor (CHBF/Ku) that appears to be involved in the regulation of the heat shock response.

HSP27 and HSP70 increase the survival of WEHI-S cells exposed to hyperthermia

Exposure of cells to hyperthermia and various other stress conditions induces synthesis of a small group of proteins, the heat shock proteins (HSPs). Synthesis of HSPs correlates with the development of thermotolerance, but little is known about the role of individual HSPs in this phenomenon. Using stably transfected WEHI-S murine fibrosarcoma cells we show that overexpression of either HSP27 or HSP70 clearly protects these cells from the toxic effect of elevated temperatures. Moreover, a clone expressing HSP70 mRNA in antisense orientation, and thereby reduced levels of endogenous HSP70 protein, is more thermosensitive than transfection control cells. Using indirect immunofluorescence we show that following heat treatment exogeneous HSP27 and HSP70 are relocated from the cytoplasm to the nucleus and nucleoli respectively. A similar pattern of localization was seen for the endogenous HSPs. Taken together, these results indicate that both HSP27 and HSP70 protect cells from heat mediated killing.

Effect of caloric restriction on the expression of heat shock protein 70 and the activation of heat shock transcription factor 1

The regulation of heat shock protein 70 (hsp70) expression is an excellent example of a cellular mechanism that has evolved to protect all living organisms from various types of physiological stresses; therefore, the reported age-related alterations in the ability of cells to express hsp70 in response to stress could seriously compromise the ability of a senescent organism in respond to changes in its environment. Because caloric restriction (CR) is the only experimental manipulation known to retard aging and increase the survival of rodents, it was of interest to analyze the effect of CR on the age-related alteration in the induction of hsp70 expression in rat hepatocytes. The effect of CR on the nuclear transcription of hsp70 gene in rat hepatocytes in response to various levels of heat shock was determined, and it was found that the age-related decline in the transcription of hsp70 at all temperatures studied was reversed by CR. Because the heat shock transcription factor (HSF) mediates the heat-induced transcription of hsp70, the effect of CR on the induction of HSF binding activity by heat shock was studied and found to arise from HSF1, which has been shown to be involved in the induction of HSF binding activity in other cell types. The age-related decrease in the induction of HSF1 binding activity in rat hepatocytes was reversed by CR, and did not appear to be due to an accumulation of inhibitory molecules with age. Interestingly, the level of HSF1 protein was significantly higher in hepatocytes isolated from old rats fed ad libitum compared to hepatocytes obtained from rats fed the CR diet even though the levels of HSF1 binding activity were lower for hepatocytes isolated from the old rats fed ad libitum. The levels of the mRNA transcript for HSF1 was not significantly altered by age or CR. Thus, the changes in HSF1 binding activity with age and CR do not arise from changes in the level of HSF1 protein available for activation.

Deficient heat shock protein expression: a potential mechanism for the sudden infant death syndrome

Induction of heat shock proteins follows a metabolic stress and protects from subsequent stresses. Stressors proposed for the sudden infant death syndrome include infection, environmentally-induced hyperthermia and hypoxia. Failure to express heat shock proteins to such stressful conditions may lead to reduced tolerance, and enhance inappropriate physiologic responses and vulnerability which ultimately may lead to infant death.

Induction of the 72-kD heat shock protein in human skin melanoma and squamous cell carcinoma cell lines

Heat shock proteins (HSPs) or stress proteins comprise a characteristic group of proteins synthesized in cells exposed to heat or other environmental stimuli. Of the many HSPs, the 72-kD heat shock protein (HSP72) is the most stress-inducible one. In the present study, we examined the effects of heat, chemicals (azetidine and sodium arsenite), ultraviolet (UV) light, and gamma-ray irradiation on the induction of HSP72 in cultured human skin melanoma cell lines (P-39 and G-361), a human skin squamous cell carcinoma cell line (HSC-1), and an SV40-transformed human lung fibroblast cell line (WI38VA13) as a control. In these cell lines, heat treatment induced HSP72 more rapidly and intensely than did chemical exposure. Compared with the SCC cell line, the two melanoma cell lines produced less HSP72 with heat treatment. UVC irradiation (20 J/m2) induced HSP72 only in the WI38VA13 cells. After gamma-ray irradiation, no HSP72 induction was detected in any of the cell lines examined. These observations suggest that, in cultured cells, inducibility of HSP72 depends not only on the inducer but also on the origin of each cell line.

The effect of hypothermia on induction of heat shock protein (HSP)-72 in ischemic brain

Intra-ischemic hypothermia has been demonstrated to be protective against ischemic neuronal injury. The present study examined the effect of moderate hypothermia on the expression of heat shock protein (HSP)-72 following transient forebrain ischemia in gerbils by immunohistochemistry. Global forebrain ischemia with concurrent moderate hypothermia (30 degrees C) was induced in gerbils by 10-minute bilateral carotid artery occlusion followed by recirculation periods of 1 hour (h), 6h, 24h, and 48h. Normothermic forebrain ischemic animals with similar recirculation periods were utilized for comparison of the HSP expression. Sham-operated normothermic and hypothermic animals were also included. 72-kDa heat shock protein immunoreactivity was demonstrated in the hippocampus and neocortex of the normothermic ischemic animals following 24h and 48h recirculation similar to that reported previously. However, the immunoreactivity was absent in the brains of the animals subjected to hypothermic ischemia or sham-operation. Only the ependymal cells were immunopositive in all hypothermic brains as was the case with all normothermic brains. The hypothermic ischemic brains showed no significant necrosis in the hippocampus. These findings suggest that the protection of ischemic neuronal necrosis conferred by intra-ischemic hypothermia is not associated with induction of HSP-72 protein and that mechanisms other then HSP-72 protein induction are likely to be responsible for this neuroprotective effect.

Inhibition mechanism of HSP70 induction in murine FM3A cells maintained at low culture temperature

We have shown previously that induction of HSP70 synthesis in murine FM3A and its mutant ts85 cells by heat shock is somehow modulated by culture temperature. In this study, we further examined activation of heat shock transcription factor (HSF) and induction kinetics of HSP70 synthesis and HSP70 mRNA in FM3A and ts85 cells maintained at 37 degrees C (37 degrees C-cells) and 33 degrees C (33 degrees C-cells). Upon exposure to heat shock, HSF was activated to a high level in 37 degrees C-FM3A cells, whereas HSF was activated only to a low level in the 33 degrees C-cells. The induction of HSP70 mRNA and HSP70 synthesis occurred successively in the 37 degrees C-cells but not in the 33 degrees C-cells. On the other hand, in both 37 and 33 degrees C-ts85 cells, activation of HSF, induction of HSP70 mRNA, and HSP70 synthesis occurred successively. Characteristically, protein synthesis in both 33 degrees C-FM3A and ts85 cells was significantly lower than in the respective 37 degrees C-cells, but constitutive HSP73 levels were similar among both the 37 and 33 degrees C-cells. Furthermore, inhibition of protein synthesis of FM3A cells did not influence the activation of HSF, but accelerated inactivation of the activated HSF. We discuss the possible inhibition mechanisms of activation of HSF in 33 degrees C-FM3A cells, regarding the function of HSP70 in both protein synthesis and repression of HSF.

The combined effects of high temperature and carbon monoxide on heat stress response

In this study, we have examined the effects of exposure to high temperature, carbon monoxide or a combination of both conditions in a model system, the rat and in industrial workers. In the rat liver, HSP70 mRNA and HSP70 synthesis were measured by dot hybridization and western blot. The results showed that after a heat stress HSP70 mRNA and its product, HSP70 increased significantly and there was a synergism in the combined effects of high temperature and carbon monoxide exposure on the induction of HSP70 mRNA and HSP70 synthesis. Heat played a major role in this induction. The presence of antibodies to human HSP27, HSP60, HSP70, HSC73, HSP89 alpha and beta in workers exposed to heat, carbon monoxide was also measured by western blot using purified HSPs as antigens. Plasma free amino acids were measured in the same group of workers. The incidence of antibodies to HSP27 and HSP70 was significantly higher in the workers working in an environment with extreme heat, and high carbon monoxide emission than in a control group. The carbon monoxide exposed group showed the highest incidence of antibodies to HSPs. Although our previous results indicated that workers had an insufficient protein intake, plasma free amino acids tended to increase, especially in methionine and tryptophan two kinds of amino acids which are absent from the main stress protein, HSP70. These results suggest that the major problems that these workers may face are how to facilitate the use of plasma free amino acids and reduce the inhibition of synthesis of normal proteins when they are exposed to occupational harmful factors. These results also add new information on the measurement of HSPs as a potential biomonitor to assess whether organisms are experiencing metabolic stress within their environment.