Competitive inhibition of hsp70 gene expression causes thermosensitivity

Heat shock response in the central nervous system

The heat shock response is induced in nervous tissue in a variety of clinically significant experimental models including ischemic brain injury (stroke), trauma, thermal stress and status epilepticus. Excessive excitatory neurotransmission or the inability to metabolically support normal levels of excitatory neurotransmission may contribute to neuronal death in the nervous system in many of the same pathophysiologic circumstances. We demonstrated that in vitro glutamate-neurotransmitter induced excitotoxicity is attenuated by the prior induction of the heat shock response. A short thermal stress induced a pattern of protein synthesis characteristic of the highly conserved heat shock response and increased the expression of heat shock protein (HSP) mRNA. Protein synthesis was necessary for the neuroprotective effect. The study of the mechanisms of heat shock mediated protection may lead to important clues as to the basic mechanisms underlying the molecular actions of the HSP and the factors important for excitotoxic neuronal injury. The clinical relevance of these findings in vitro is suggested by experiments performed by others in vivo demonstrating that pretreatment of animals with a submaximal thermal or ischemic stress confers protection from a subsequent ischemic insult.

Hsp70 in myocardial ischaemia

Numerous reports suggest that stress protein accumulation confers protection in various mammalian tissues against differing stresses. The purpose of this article is to review the evidence that stress proteins, in particular hsp70, are able to alter the resistance of the heart to subsequent ischaemic and non-ischaemic injury and to discuss the possible physiological basis for this apparent protection. The possible, though unlikely involvement of heat stress proteins in classical ischaemic preconditioning is addressed as is the possibility of their involvement in a delayed second window of protection.

Hsp70 and aging

An alteration in the ability of cells to express heat shock proteins could be physiologically important in aging because all living organisms show a reduced ability to respond to stress with increasing age. Using hepatocytes freshly isolated from young adult and old rats, we have shown that the induction of hsp70 expression by heat shock is reduced approximately 50% with age. The decrease in hsp70 expression occurs at the level of transcription and appears to arise from a defect in the heat shock transcription factor. Other investigators have also shown that the induction of hsp70 expression by heat shock as well as other stresses declines significantly with age in a variety of tissues from rats as well as mononuclear cells from human subjects. In addition, a decrease in the inducibility of hsp70 is observed with cell senescence in cultured cells. Therefore, it appears that a reduced ability to express hsp70 in response to stress may be a common phenomenon underlying the aging process.

Small subclass of rat olfactory neurons with specific bulbar projections is reactive with monoclonal antibodies to the HSP70 heat shock protein

As part of a study of turnover of rat olfactory receptor neurons we have been examining immunohistochemical expression of members of the 70 kD heat shock protein (HSP70) family in the olfactory epithelium. Expression of HSP70 family members is up-regulated in many cells following exposure to physiologically stressing conditions. Because dying neurons are likely to undergo some sort of physiological stress before the onset of frank degeneration, we hoped that anti-HSP70 monoclonal antibodies would prove to be useful markers for early stages of olfactory neuron cell death. Two anti-human HSP70 monoclonal antibodies were used, Mabs 2A4 and 3a3. Two-dimensional gel electrophoresis/western blot analysis indicates that these Mabs are reactive with the HSC70 and HSP70 members of the rat HSP70 family. Immunohistological observations show that both Mabs are strongly reactive with a widely dispersed subpopulation of olfactory receptor neurons. Morphological, immunohistological, and autoradiographic birthdating analyses demonstrate that reactive cells are fully mature receptor neurons. Their reactivity, however, does not appear to be stress-related. More significantly, axons of reactive neurons show intense anti-2A4 reactivity. This has allowed us to trace these axons to their target glomeruli in the olfactory bulb, demonstrating that the reactive neurons project to just one to two glomeruli on either side of each bulb via consistent and predictable pathways. This is the first subpopulation of olfactory receptor neurons to be traced to such a small number of glomeruli. Given this extremely small number, it seems likely that the reactive receptor cell subpopulation serves some specific olfactory function. In addition, axonal 2A4 reactivity should also prove useful in defining the relative roles of receptor neurons and glomeruli in the establishment of epithelial-glomerular connections.

cAMP modulates stress protein synthesis in human monocytes-macrophages

The synthesis of heat-shock proteins (HSPs) and other stress proteins, including heme oxygenase (HO) and ferritin, is differentially induced by heat and oxidizing agents. In order to determine what role cAMP plays in those inductions in human monocytes-macrophages (m phi), we used cAMP activators or analogues alone or in combination with various stressful conditions. A stimulation in cAMP production did not per se affect stress proteins synthesis in m phi but modulated their induction in a differential way according to the stimulus. cAMP increased the synthesis of HSPs after heat shock. During erythrophagocytosis, whereas cAMP depressed the phagocytic process and the associated generation of superoxide anions, it enhanced the synthesis of HSPs, while inhibiting that of HO and ferritin. These results indicate that cAMP has a direct enhancing effect on the expression of stress proteins controlled by a classic heat-shock promoter, while decreasing their expression when induced by oxidative stress.

Acquired thermotolerance and heat shock proteins in thermophiles from the three phylogenetic domains

Thermophilic organisms from each of the three phylogenetic domains (Bacteria, Archaea, and Eucarya) acquired thermotolerance after heat shock. Bacillus caldolyticus grown at 60 degrees C and heat shocked at 69 degrees C for 10 min showed thermotolerance at 74 degrees C, Sulfolobus shibatae grown at 70 degrees C and heat shocked at 88 degrees C for 60 min showed thermotolerance at 95 degrees C, and Thermomyces lanuginosus grown at 50 degrees C and heat shocked at 55 degrees C for 60 min showed thermotolerance at 58 degrees C. Determinations of protein synthesis during heat shock revealed differences in the dominant heat shock proteins for each species. For B. caldolyticus, a 70-kDa protein dominated while for S. shibatae, a 55-kDa protein dominated and for T. lanuginosus, 31- to 33-kDa proteins dominated. Reagents that disrupted normal protein synthesis during heat shock prevented the enhanced thermotolerance.

Heat shock modulates UVB-induced cell death in human epidermal keratinocytes: evidence for a hyperthermia-inducible protective response

The ability of heat shock to induce functional protection against ultraviolet B (UVB) light was examined in keratinocytes cultured from human skin. Cell death, measured with fluorescent vital dyes, increased in a UVB dose-dependent manner (LD50 approximately 20-60 mJ/cm2). However, a 60-min heat shock at 40 degrees C or 42 degrees C, administered several hours before UVB irradiation, reduced cell death by 2.0-2.5 times. Inducible protection took time to develop, with an optimal interval of approximately 6 h between heat and UVB exposures. Heat-inducible protection was completely blocked if either cordycepin (3'-deoxyadenosine), to inhibit mRNA synthesis, or cycloheximide, to inhibit protein synthesis, were present during the heating period. To determine whether apoptosis might be involved in UVB-induced keratinocyte death in this system, evidence for endonuclease activity was sought via in situ enzymatic labeling with terminal deoxynucleotidyl transferase and biotinylated-dUTP. Labeled nuclei were detected in UVB-irradiated cultures, and heat pretreatment at 6 h prior to UVB exposure (< 60 mJ/cm2) resulted in a 50% reduction in labeled nuclei. Overall, the data show that UVB-induced cell death in human keratinocyte cultures is attenuated by a heat-inducible mechanism that requires ongoing synthesis of mRNA and protein.

HSP-72 synthesis is promoted by increase in [Ca2+]i or activation of G proteins but not pHi or cAMP

The family of 70-kDa heat-shock proteins (HSP-70) is evolutionarily highly conserved and has been shown to enhance cell survival from thermal injury. This study characterized HSP-72 induction in human epidermoid A-431 cells exposed to 45 degrees C for 10 min and determined the relationship between HSP-72, intracellular pH (pHi), adenosine 3',5'-cyclic monophosphate (cAMP), G proteins, and intracellular cytosolic free Ca2+ concentration ([Ca2+]i). Heat shock induced HSP-72 production, which was dependent on both temperature and the duration of heating. This HSP-72 induction was confirmed by Western blot analysis. HSP-72 levels in cells that had been heated then returned to 37 degrees C were elevated at 2 h (1.5 +/- 0.1 x control), reached a maximum at 8 h (2.7 +/- 0.1 x control), and remained above baseline for up to 4 days. Levels of HSP-72 mRNA, determined by dot-blot analysis, reached a maximum at 2 h and returned to baseline within 8 h. Both actinomycin D and cycloheximide blocked HSP-72 induction. Because heating causes intracellular acidification and increases in cAMP and [Ca2+]i, we studied the effect of pHi, cellular cAMP, and [Ca2+]i on HSP-72 induction. The reduction of pHi to 6.9 by acid loading did not affect the basal level of HSP-72 in unheated cells. Treatment with pertussis toxin, cholera toxin, or forskolin, but not 8-bromo-cAMP, 3-isobutyl-1-methylxanthine, or N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide potentiated heat-induced HSP-72 production. Inhibition of the heat-induced increase in [Ca2+]i attenuated, but failed to completely block, heat-induced HSP-72 production, mRNA synthesis, and the heat-shock transcriptional factor-heat-shock element binding complex formation, which suggests there are Ca(2+)-dependent and -independent processes involved in HSP-72 synthesis. Our results show that an increase in [Ca2+]i or activation of G proteins, but not pHi and cAMP, enhances HSP-72 induction.

Shifts in type I fiber proportion in rat hindlimb muscle are accompanied by changes in HSP72 content

Heat-shock protein 72 (HSP72), the inducible isoform of the HSP70 family, is constitutively expressed in rat hindlimb muscles in proportion to the content of type I muscle fibers. To determine whether this relationship was maintained after fiber transformation, male Sprague-Dawley rats were treated with 3,5,3'-triiodo-DL-thyronine (T3) for 40 days or underwent surgical removal of the left gastrocnemius muscle, after which the left plantaris muscle was allowed to hypertrophy for 30 days. Hypertrophied plantaris muscles exhibited an increased number of type I fibers, type I myosin heavy-chain (MHC) protein, and HSP72 content compared with contralateral muscles. Soleus muscles from rats administered T3 exhibited an increased number of type II fibers, citrate synthase activity, and decreased HSP72 content compared with soleus muscles from controls. These results indicate that the relationship between HSP72 content and type I muscle fiber-MHC composition is maintained when muscles undergo fiber transformation and substantiate that HSP72 content in rat skeletal muscle is not directly linked to a muscle's oxidative capacity.

Heat stress induces hsc70/nuclear topoisomerase I complex formation in vivo: evidence for hsc70-mediated, ATP-independent reactivation in vitro

We previously demonstrated that in murine T cells thermotolerance correlated with heat shock protein 70 (hsp70) synthesis and protection of nuclear type I topoisomerase (topo I). Topo I activity returned to normal levels following heat stress even in cells not rendered thermotolerant by a prior heat shock. Recovery of topo I activity was not dependent on de novo protein synthesis, suggesting that the cell possesses a pathway(s) for refolding this nuclear protein. In this report we demonstrate that topo I and hsc70, the constitutively produced member of the hsp70 family, associated in vivo during heat stress. That this association may play a physiologically important role in protecting topo I activity from heat stress was suggested by the observation that hsc70 protected topo I from heat inactivation in vitro. hsc70 but not actin also reactivated previously heat-denatured topo I in a dose-dependent fashion. However, refolding of heat-denatured topo I by purified hsc70 was inefficient relative to a hsc70-containing cell lysate. Protection from heat inactivation as well as reactivation by hsc70 did not require exogenous ATP. Similarly, reactivation by the cell lysate was not inhibited by ADP or a nonhydrolyzable analogue of ATP. Thus, our studies suggest that nuclear topo I complexes with hsc70 during heat stress, which may explain, at least in part, why hsp70 proteins accumulate in the nucleus, particularly the nucleolus. This interaction may limit heat-induced protein damage and/or accelerate restoration of protein function in an ATP-independent reaction.

Increased expression of mRNA encoding calbindin-D28K, the glucose-regulated proteins, or the 72 kDa heat-shock protein in three models of acute CNS injury

Changes at the level of gene expression are becoming an increasingly recognized component of the neuronal response to injury. We used Northern analysis and three in vivo models of central nervous system (CNS) injury in the rat to determine whether injury alters the expression of certain gene products related to cellular homeostasis. The three models included kainate (KA)-induced seizures, global ischemia, and lateral fluid percussion injury to the cerebral cortex. Animals were sacrificed at various times after injury, and total RNA was isolated from specific brain regions. Northern blots were hybridized with probes for calbindin-D28K, the 78 and 94 kDa glucose-regulated proteins (grp78, grp94), the inducible 72 kDa heat-shock protein (hsp72), and a control probe for the 18S ribosomal subunit. Results showed that mRNA for calbindin-D28K, grp78, and hsp72 increased in the hippocampus following seizures. Peak expression occurred 6-12 h after administration of KA, and returned towards baseline in most cases by 24 h. Changes in all four transcripts were seen in the hippocampus or cortex following global ischemia, although the return to baseline tended to exceed 24 h for the grps. In the trauma model, mRNA for hsp72 was increased in the cortex ipsilateral to the impact 12 h after injury. These results expand the repertoire of known changes in mRNA expression following CNS injury. The increases in hsp72 and grps indicate the occurrence of a generalized stress response. Furthermore, given the evidence that grp78 and grp94 are induced by calcium ionophores in vitro, and the potential role of calbindin-D28K in buffering cytoplasmic calcium, the changes observed in this study may represent a cellular response to perturbed calcium homeostasis that is known to occur in acute CNS injury.

Expression of inducible stress protein 70 in rat heart myogenic cells confers protection against simulated ischemia-induced injury

Myocardial ischemia markedly increases the expression of several members of the stress/heat shock protein (HSP) family, especially the inducible HSP70 isoforms. Increased expression of HSP70 has been shown to exert a protective effect against a lethal heat shock. We have examined the possibility of using this resistance to a lethal heat shock as a protective effect against an ischemic-like stress in vitro using a rat embryonic heart-derived cell line H9c2 (2-1). Myogenic cells in which the heat shock proteins have been induced by a previous heat shock are found to become resistant to a subsequent simulated ischemic stress. In addition, to address the question of how much does the presence of the HSP70 contribute to this protective effect, we have generated stably transfected cell lines overexpressing the human-inducible HSP70. Embryonal rat heart-derived H9c2(2-1) cells were used for this purpose. This stably transfected cell line was found to be significantly more resistant to an ischemic-like stress than control myogenic cells only expressing the selectable marker (neomycin) or the parental cell line H9c2(2-1). This finding implicates the inducible HSP70 protein as playing a major role in protecting cardiac cells against ischemic injury.

Induction of 27-kDa heat shock protein following cerebral ischemia in a rat model of ischemic tolerance

Preconditioning the brain with sublethal cerebral ischemia induces tolerance to subsequent lethal periods of ischemia (ischemic tolerance). The purpose of this study is to investigate the role of low-molecular weight stress proteins, 27-kDa heat shock protein (HSP27) and alpha B crystallin, in ischemic tolerance. We measured the content of these proteins with enzyme immunoassay in the rat hippocampus and cerebral cortex following 6 min of ischemia with and without preconditioning with 3 min of ischemia and 3 days of reperfusion. We also visualized the localization of HSP27 immunohistochemically in comparison with that of HSP70. A 3-min period of ischemia caused a 2.4-fold increase in HSP27 content in the hippocampus after 3 days. Immunohistochemical localization of HSP27 was found in glial cells in all subregions of the hippocampus, whereas HSP70 immunostaining was seen only in CA1 pyramidal neurons. HSP27 content in the hippocampus decreased 2 h after 6 min of ischemia. HSP27 content progressively increased in the unpreconditioned hippocampus after 1 and 3 days, but returned to preischemic levels in the preconditioned hippocampus. HSP27 and HSP70 immunostaining was seen in CA1 pyramidal neurons after 1 day both with and without preconditioning. After 3 and 7 days, an intense HSP27 staining was observed in reactive glial cells in the CA1 without preconditioning, whereas the staining decreased in the preconditioned hippocampus. HSP70 staining was seen only in neurons at these time points. We observed no significant changes in HSP27 content in the cerebral cortex although neurons in the third and fifth layers were immunostained after 1 and 3 days. We observed no alterations in alpha B crystallin content after ischemia both in the hippocampus and the cortex. The present study demonstrated that cerebral ischemia induces HSP27 expression but not alpha B crystallin. Both HSP27 and HSP70 induction had a good temporal correlation with the induction of ischemic tolerance. However, different sites of action were suggested because the localization and cell types of HSP27 induction were quite different from those of HSP70 induction. The result suggests that it is unlikely that HSP27 is directly involved in the protection afforded by ischemic preconditioning.

The heat shock/stress response in focal cerebral ischemia

Focal ischemia results in striking changes in gene expression. Induction of hsp72, a member of the family of 70 kDa heat shock/stress proteins is a widely studied component of the generalized cellular response to injury known as the 'stress response' that is detected in brain after ischemia and other insults. This overview summarizes observations on hsp72 expression in models of focal cerebral ischemia, considering its cellular distribution, factors affecting its transcriptional and translational expression, and its potential relevance to post-ischemic pathophysiology. Hsp72 expression is essentially limited to regions in which cerebral blood flow falls below 50% of control levels, provided that residual perfusion allows synthesis of the induced mRNA and protein. The cellular distribution of hsp72 depends on the nature of the ischemic insult, with preferential vascular expression in severely ischemic territory that is destined to necrose, pronounced neuronal expression throughout the ischemic 'penumbra', and limited glial involvement in a narrow zone immediately surrounding the infarct. Together with results in other injury models, these observations indicate that hsp72 induction identifies discrete populations of surviving cells that are metabolically compromised, but not irreversibly damaged after focal ischemia. Available evidence suggests that the stress response is an important component of cellular defense mechanisms, and that successful accumulation of hsp72 is critical to survival following ischemia. Its expression may also contribute to mechanisms of induced ischemic tolerance. Future studies may be expected to more fully characterize the range of altered gene expression in response to focal ischemic injury and to establish specific roles for hsp72 and other induced proteins in the progression of injury and recovery following such insults.

HSP72 induction by heat stress is not universal in mammalian neural cell lines

Heat-induced expression of 72-kDa heat shock protein (HSP72) was investigated in a panel of neuronal and non-neuronal cell lines by immunoblotting and immunocytochemistry using monoclonal antibodies directed to HSP72. By immunoblotting, HSP72 expression was observed in most cell lines of mouse (SN6.1b, CL8c4.7, NSC34.6, B2A, C2C12), rat (PC12, C-6, L3), and human (NB-1, GOTO, IMR-32, HeLa) origin under the heat-stressed condition. The mouse neuroblastoma cell line N18TG2, however, did not express HSP72 under the heat-stressed condition. By immunocytochemistry, HSP72 was undetectable in the heat-stressed N18TG2 cells, while it was identified in the heat-stressed SN6.1b cells, a clonal hybrid neuron between N18TG2 and mouse septal cholinergic neuron. By exposure to a priming sublethal heat shock, SN6.1b cells but not N18TG2 cells acquired a significant level of tolerance to a subsequent lethal heat shock. These results suggest that heat-induced expression of HSP72 may contribute to acquisition of the thermotolerant state in SN6.1b cells.

Neuronal survival is associated with 72-kDa heat shock protein expression after transient middle cerebral artery occlusion in the rat

Induction of the 72-kDa heat shock protein expression is thought to protect neurons against the subsequent effects of ischemia. However, it is not clear whether the induction of 72-kDa heat shock protein expression by an ischemic event improves neuronal survival. To address this question, we outlined the temporal profile of neuronal induction and expression of the 72-kDa heat shock protein in a model of transient focal ischemia in the rat. Fifty two adult Wistar rats were subjected to middle cerebral artery occlusion of 2 h duration. At 0.5, 3, 6, 9, 12, 24, 48, 96 and 168 h after reopening the artery, coronal brain sections were analyzed using both immunohistochemical methods and hematoxylin and eosin staining to determine the topographic and cellular distribution of the 72-kDa heat shock protein, as well as the extent of neuronal damage. Immunoreactivity to the 72-kDa heat shock protein was not detected in neurons that were destined to become necrotic, and were located in the ischemic core of the brain lesions. However, 72-kDa heat shock protein expression was evident in morphologically intact neurons located in the peripheral zone. The earliest neuronal expression of 72-kDa heat shock protein was detected in animals in which the 2 h occlusion of the middle cerebral artery was followed by 6 h recirculation; the intensity of the 72-kDa heat shock protein immunoreactivity peaked at 48 h, and progressively disappeared 7 days after the ischemic reperfusion event.(ABSTRACT TRUNCATED AT 250 WORDS)

Transfection-mediated expression of human Hsp70i protects rat dorsal root ganglian neurones and glia from severe heat stress

Considerable evidence suggests that the expression of heat shock proteins prior to a toxic insult (e.g. ischaemia, excitoxins, heat) can confer protection to neurones and glia. It is not certain which hsp(s) are involved in conveying these neuroprotective effects. Here we show that calcium phosphate-mediated transfection of dorsal root ganglia with an EF-1 alpha promoter-hsp70i expression vector significantly increased the survival of neurones and glia exposed to a severe heat stress. These data suggest that overexpression of hsp70i plays an important role in protecting neurones and glia from the denaturing effects of severe thermal stress. Inducing the expression of specific hsps may lead to the development of novel treatment strategies for CNS diseases.

Regulation of hsp70 induction in thermotolerant HeLa cells

Upon exposure to heat shock, non-thermotolerant (NT) HeLa cells transiently synthesize a large amount of 70-kDa heat-shock protein (hsp70), whereas thermotolerant (TT) cells synthesize a small amount of hsp70. When the hsp70 mRNA of HeLa cells was analyzed, it became apparent that hsp70 mRNA in TT cells did not increase following heat shock, whereas hsp70 mRNA in NT cells did increase dramatically. A further analysis of the activation of the heat-shock transcription factor (HSF) showed that significant activation of HSF was observed immediately after heat shock in both NT and TT cells. However, activated HSF was rapidly repressed in the TT cells, but not in the NT cells. Thus, the decreased induction of hsp70 synthesis observed in the TT HeLa cells may be due to the immediate repression of activated cellular HSF, which probably results in the reduced induction of hsp70 mRNA. The hsp70 content in the TT cells was usually higher than in the NT cells. However, after heat-shock treatment, the hsp70 content of the NT cells increased to nearly the level of the TT cells concomitant with the repression of hsp70 synthesis. The association of activated HSF with hsp70 was observed in both NT and TT cells, and the amount of HSF-hsp70 complex within the cell increased in proportion to the increase in hsp70 in the cells. These findings strongly suggest that the activity of HSF is negatively regulated by the intracellular content of hsp70 in these cells. Furthermore, in vitro experiments on the activation of HSF suggest that HSFs of NT and TT cells may have different properties, or an unknown factor may exist which regulates HSF activation in these cells.

Temporal and spatial distribution of heat shock mRNA and protein (hsp70) in the rabbit cerebellum in response to hyperthermia

We have previously investigated the expression of hsp70 genes in the hyperthermic rabbit brain at the mRNA level by Northern blot and in situ hybridization procedures. Our studies have now been extended to the protein level utilizing Western blot and immunocytochemistry. Using an antibody which is specific to inducible hsp70, a prominent induction of hsp70 protein in glial cells of hyperthermic animals was noted. In particular, Bergmann glial cells in the cerebellum are strongly immunoreactive while adjacent Purkinje neurons are immunonegative. Extension of our in situ hybridization studies to a time course analysis revealed that the initial glial induction events were followed by a delayed accumulation of inducible hsp70 mRNA in Purkinje neurons at 10 hr post-heat shock. In control animals, high levels of constitutively expressed hsc70 mRNA and protein were observed in Purkinje neurons. Similar hsc70 and hsp70 mRNA observations were also made in neurons of the deep cerebellar nuclei and in motor neurons of the spinal cord. Our results suggest that these neuronal cell types accumulate hsp70 mRNA in response to hyperthermic treatment; however, the response is delayed when compared to the rapid response seen in glial cells. The high constitutive levels of hsc70 in certain neuronal cell types may play a role in the initial dampening of the hsp70 induction response in these cells.

Extracellular matrix components affect the pattern of protein synthesis of endothelial cells responding to hyperthermia

The biosynthetic profile of endothelial cells responding to hyperthermia is altered by extracellular matrix components. The extracellular matrix components influence the quantitative expression of members of the HSP70 family and HSP90. The expression of several HSP70 mRNA species, which are strictly stress inducible, are modulated by extracellular matrix components. Both laminin and collagen type IV decrease the amount of HSP70 protein and mRNA expressed by endothelial cells exposed to hyperthermia relative to control cultures attached to virgin plastic. In contrast, both laminin and collagen type IV increased the amount of HSP90 mRNA constitutively expressed by endothelial cells at 37 degrees C. When endothelial cells were exposed to elevated temperatures, these two extracellular matrix proteins decrease the amount of HSP90 mRNA relative to control cultures attached to virgin plastic. Our observations are consistent with the proposal that the extracellular matrix components regulate gene expression and cell behavior in regard to thermotolerance.

Gene expression under temperature stress

In this review, changes in plant gene expression in response to environmental stresses are discussed using the examples of high and low temperature treatments. While some changes may contribute to acclimatory processes which improve plant survival or performance under stress, others may be 'shock' responses indicative of sensitivity. The heat-shock response, which is almost ubiquitous among eukaryotic organisms, is characterized by repression of normal cellular protein synthesis mediated at both the transcriptional and the translational level, and induction of heat-shock protein (HSP) synthesis. There is a correlation between HSP synthesis and induced thermotolerance in plants, but the evidence for a causal relationship is not conclusive. The possible biochemical functions of some of the HSPs are now becoming apparent; they are believed to play an important role in preventing accumulation of damaged proteins in the cell during heat shock. Although no other environmental stress elicits the full heat-shock response, certain treatments do induce synthesis of subsets of the HSPs, and the reasons for this are considered. Alterations in gene expression in response to low temperatures are more diverse and usually less dramatic than the heat-shock response, with which they share little, if any, homology. Biochemical adjustments during cold treatment are discussed, with particular reference to those which contribute to acclimation. Several genes whose expression is induced by cold have been cloned and characterized, and in some cases it is possible to attribute in vivo functions to them; they include enzymes of lipid, carbohydrate and protein metabolism, structural proteins and putative cryoprotectants. The use of transgenic plants is further facilitating an investigation of the biochemical factors which are important in cold acclimation. Drought, osmotic stress and abscisic acid induce expression of many of the same genes as does cold treatment; it seems likely that some of the products of these genes contribute to increased freezing tolerance by protecting against intracellular dehydration. Contents Summary 1 I. Introduction 1 II. High temperature stress 3 III. Low temperature stress 10 IV. Concluding remarks 20 Acknowledgements 21 References 21.

Acceleration of HSP70 and HSC70 heat shock gene expression following transient ischemia in the preconditioned gerbil hippocampus

To evaluate the mechanism of tolerance to ischemia, inductions of heat shock protein (HSP) 70 and heat shock cognate protein (HSC) 70 mRNAs in gerbil hippocampus were compared with in situ hybridization between cases of a single 3.5-min period of forebrain ischemia and a 3.5-min period of ischemia 2 days after 2-min pretreatment with ischemia. Immunohistochemistry for HSP70 protein and morphological studies were also performed in the same brains up to 7 days after the reperfusion. Following a single 3.5-min period of ischemia, HSP70 and HSC70 mRNAs were induced in all hippocampal cells. However, the hippocampal CA1 cells produced only a minimum of HSP70 protein, and the cells were almost lost by 7 days. Following 3.5 min of ischemia after 2-min pretreatment, large populations of the CA1 cells survived at 7 days. The peak time of the HSP70 and HSC70 mRNA induction shifted to an earlier period of reperfusion in all hippocampal cells as compared with the case of a single episode of ischemia. The peak of HSP70 and HSC70 mRNA induction shifted from 1 day to 3 h in the CA1 cells. The CA1 cells produced strongly immunoreactive HSP70 from 3 hr to 2 days. These results suggest that pretreatment with an initial period of ischemia (for 2 min) accelerated HSP70 and HSC70 gene expression at the transcriptional level, ameliorated the translational disturbance of HSP70 mRNA to protein, and saved the CA1 cells from subsequent lethal ischemia (for 3.5 min). These changes of heat shock gene expression might play important roles in the acquisition of ischemic tolerance of hippocampal CA1 neurons.

Human keratinocytes in vivo and in vitro constitutively express the 72-kD heat shock protein

Exposure of cells to elevated temperatures induces a physiologic response characterized by the synthesis of a specific set of proteins (heat shock or stress proteins, HSPs) mediating repair mechanisms and protection from cellular damage. In the present study upon immunohistochemistry using a specific monoclonal antibody, the constitutive and heat-induced expression of the 72-kD HSP (HSP72) in normal human skin and in human epidermal cell lines (KB, A431) was investigated. Normal (unstressed) epidermis and adnexal structures of normal human skin were found to constitutively express HSP72. In contrast, a substantial HSP72 expression could not be observed in the dermal cellular compartment. In vitro heat treatment of punch biopsies from normal skin (42 degrees C, 4 h) resulted in a further increase of epidermal HSP72 expression. In addition, dermal cells were found to be induced to express HSP72. To further evaluate the spontaneous HSP72 expression of epidermal cells two epidermoid carcinoma cell lines (A431, KB) were investigated. Upon immunohistochemistry and Western blot analysis a significant HSP72 expression could be detected in unstressed KB and A431 cells. In contrast, a human fibrosarcoma cell line (HT1080) was negative for HSP72 at 37 degrees C but upon heat treatment a strong induction was observed. Furthermore, Northern blot analysis using a cDNA probe specific for human HSP72 revealed a constitutive expression of HSP72 mRNA in both epidermal cell lines. These findings demonstrate a significant expression of the stress-inducible HSP72 in unstressed human skin as well as in epidermal cell lines, suggesting that HSP72 may inherently be involved in the protective function of normal human skin.

Ischemic tolerance due to the induction of HSP70 in a rat ischemic recirculation model

Various studies have demonstrated an increase in heat shock protein 70 (HSP70) synthesis in the brain following transiently induced ischemia, suggesting a protective role for HSP70 against ischemic insult. In this study, we determined the time course of HSP70 mRNA and protein induction in rat hippocampus following ischemia using Pulsinelli's four-vessel occlusion model, and suggested a protective role for HSP70 induction in limiting ischemic damage to neurons and delayed neuronal death. In Northern blotting analysis using human HSP70 DNA as a probe, the accumulation of HSP70 mRNA after 5 min ischemia became evident at 4 h, and continued until 16 h, while after 30 min ischemia, HSP70 mRNA appeared at 2 h, and continued above control level until 24 h after treatment. In immunoblot analysis using anti-HSP70 antibody, induction of HSP70 protein appeared 24 h and reached a maximum 48 h after 5 min ischemia. In immunohistochemical analysis using anti-HSP70 antibody, staining was not detected in CA1 neurons until 16 h after 5 min ischemia, but staining in CA1 gradually increased 1 day after ischemia and reached a maximum level 2 days after ischemia. Similar time profiles in the staining pattern of HSP70 protein were observed in CA3 and CA4 neuronal cells following 30 min ischemia. When rats pretreated with 5 min ischemia (non-lethal for CA1 pyramidal neurons) were exposed to a 30 min, lethal period of ischemia, 2 days after pretreatment, considerable staining of HSP70 was observed. Pretreated rats had much less neuronal damage in the CA1 sector than did rats subjected to lethal, 30 min ischemia alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Cloning of the mouse hsp25 gene and an extremely conserved hsp25 pseudogene

A genomic clone of the murine gene encoding the small heat-shock protein, Hsp25, was isolated. The coding region is interrupted by two introns of 128 bp and approximately 600 bp at identical positions as the human hsp27 gene. The 5' flanking regions of the mouse and human genes are very strongly conserved and contain several sequence motives for the transcription factors, HSF and Sp1. In the same screen we also isolated a hsp25 pseudogene. The sequence conservation between this pseudogene and hsp25 cDNA is very high (99%) indicating that this pseudogene emerged very recently.

The preconditioned hippocampus accelerates HSP70 heat shock gene expression following transient ischemia in the gerbil

To evaluate the mechanism of tolerance for ischemia, inductions of heat shock protein (HSP) 70 mRNA and immunoreactive HSP70 protein were studied in the preconditioned gerbil hippocampus. Following the single 3.5-min ischemia, HSP70 mRNA was induced in all hippocampal cells. However, the hippocampal CA1 cells produced only a minimum HSP70 protein, and the cells were almost lost by 7 days. Following the 3.5-min ischemia after 2-min pretreatment, the CA1 cells produced a strong immunoreactive HSP70 signal and large populations of the CA1 cells survived at 7 days. The peak time of the HSP70 mRNA induction shifted to earlier period of reperfusion in the CA1 cells as compared to the case with single ischemia. This accelerated change of HSP70 expression could play an important role for the acquisition of ischemic tolerance of the hippocampal CA1 neurons.

Expression of heat shock protein 70 is altered by age and diet at the level of transcription

Because heat shock proteins have been shown to play a critical role in protecting cells from hyperthermia and other types of physiological stresses, it was of interest to determine what effect age and caloric restriction have on the ability of cells to regulate the expression of heat shock protein 70 (hsp70), the most prominent and most evolutionarily conserved of the heat shock proteins. Caloric restriction is the only experimental manipulation known to retard aging and increase survival of mammals. The ability of hepatocytes isolated from young/adult (4- to 7-month-old) and old (22- to 28-month-old) male Fischer F344 rats fed ad libitum or a caloric restriction diet (60% of the content of the ad libitum diet) to express hsp70 was determined after a mild heat shock (42.5 degrees C for 30 min). We found that the induction of hsp70 synthesis and mRNA levels by heat shock was 40 to 50% lower in hepatocytes isolated from old rats than in hepatocytes isolated from young rats. Using in situ hybridization, we found that essentially all hepatocytes from the young/adult and old rats expressed hsp70 in response to heat shock; therefore, the age-related decrease in the induction of hsp70 expression was not due to an age-related accumulation of cells that do not respond to heat shock. Measurements of hsp70 mRNA stability and hsp70 transcription demonstrated that the age-related decline in hsp70 expression arose from a decline in hsp70 transcription. Interestingly, the age-related decline in the induction of hsp70 expression was reversed by caloric restriction; e.g., the induction of hsp70 synthesis, mRNA levels, and nuclear transcription were significantly higher in hepatocytes isolated from old rats fed the caloric restricted diet than in hepatocytes isolated from old rats fed ad libitum. The levels of the heat shock transcription factor in nuclear extracts isolated from heat-shocked hepatocytes were measured in a gel shift assay. Binding of the heat shock transcription factor to the heat shock element decreased with age and was significantly higher in hepatocyte extracts isolated from old rats fed the caloric restriction diet than in those from old rats fed ad libitum. Thus, our study demonstrates that the ability of hepatocytes to respond to hyperthermia and express hsp70 decreases significantly with age and that this decrease occurs at the transcriptional level. In addition, caloric restriction, which retards aging, reversed the age-related decline in the induction of hsp70 transcription in hepatocytes.

Expression of heat shock protein 70 is altered by age and diet at the level of transcription

Because heat shock proteins have been shown to play a critical role in protecting cells from hyperthermia and other types of physiological stresses, it was of interest to determine what effect age and caloric restriction have on the ability of cells to regulate the expression of heat shock protein 70 (hsp70), the most prominent and most evolutionarily conserved of the heat shock proteins. Caloric restriction is the only experimental manipulation known to retard aging and increase survival of mammals. The ability of hepatocytes isolated from young/adult (4- to 7-month-old) and old (22- to 28-month-old) male Fischer F344 rats fed ad libitum or a caloric restriction diet (60% of the content of the ad libitum diet) to express hsp70 was determined after a mild heat shock (42.5 degrees C for 30 min). We found that the induction of hsp70 synthesis and mRNA levels by heat shock was 40 to 50% lower in hepatocytes isolated from old rats than in hepatocytes isolated from young rats. Using in situ hybridization, we found that essentially all hepatocytes from the young/adult and old rats expressed hsp70 in response to heat shock; therefore, the age-related decrease in the induction of hsp70 expression was not due to an age-related accumulation of cells that do not respond to heat shock. Measurements of hsp70 mRNA stability and hsp70 transcription demonstrated that the age-related decline in hsp70 expression arose from a decline in hsp70 transcription. Interestingly, the age-related decline in the induction of hsp70 expression was reversed by caloric restriction; e.g., the induction of hsp70 synthesis, mRNA levels, and nuclear transcription were significantly higher in hepatocytes isolated from old rats fed the caloric restricted diet than in hepatocytes isolated from old rats fed ad libitum. The levels of the heat shock transcription factor in nuclear extracts isolated from heat-shocked hepatocytes were measured in a gel shift assay. Binding of the heat shock transcription factor to the heat shock element decreased with age and was significantly higher in hepatocyte extracts isolated from old rats fed the caloric restriction diet than in those from old rats fed ad libitum. Thus, our study demonstrates that the ability of hepatocytes to respond to hyperthermia and express hsp70 decreases significantly with age and that this decrease occurs at the transcriptional level. In addition, caloric restriction, which retards aging, reversed the age-related decline in the induction of hsp70 transcription in hepatocytes.

Alpha B-crystallin expression in mouse NIH 3T3 fibroblasts: glucocorticoid responsiveness and involvement in thermal protection

alpha B-crystallin, a major soluble protein of vertebrate eye lenses, is a small heat shock protein which transiently accumulates in response to heat shock and other kinds of stress in mouse NIH 3T3 fibroblasts. Ectopic expression of an alpha B-crystallin cDNA clone renders NIH 3T3 cells thermoresistant. alpha B-crystallin accumulates in response to the synthetic glucocorticoid hormone dexamethasone. Dexamethasone-treated NIH 3T3 cells become thermoresistant to the same extent as they accumulate alpha B-crystallin. A cell clone in which alpha B-crystallin is superinduced upon heat shock acquires augmented thermotolerance. Expression of the ras oncogene causes a rapid but transient accumulation of alpha B-crystallin within 1 day. Later, sustained ras oncogene expression suppresses the dexamethasone-mediated alpha B-crystallin accumulation. Thus, oncogenic transformation triggered by the ras oncogene interferes with hormone-mediated accumulation of alpha B-crystallin and concomitant acquisition of thermoresistance. Other known heat shock proteins do not accumulate in response to ectopic alpha B-crystallin expression or to dexamethasone treatment. These results indicate that alpha B-crystallin can protect NIH 3T3 fibroblasts from thermal shock.

Phagocytosis of Staphylococcus aureus induces a selective stress response in human monocytes-macrophages (M phi): modulation by M phi differentiation and by iron

Phagocytosis of microorganisms represents a stress not only for the phagocytosed agent but also for the host cell. We have investigated the stress response induced in human monocytes-macrophages (M phi) phagocytosing inactivated Staphylococcus aureus. Exposure of human M phi to S. aureus induced in these cells (i) a threefold increase in superoxide dismutase activity, (ii) a selective and differentiation-dependent induction of host heat shock protein synthesis (HSP70 but not HSP65), and (iii) de novo synthesis of heme oxygenase, but only when exogenous iron was added to the cultures. The coordinate upregulation of two scavenging enzymes and of HSP70 suggests that all three are part of cellular protective mechanisms against phagocytosis-related oxidative injury to host cells.

Alpha B-crystallin expression in mouse NIH 3T3 fibroblasts: glucocorticoid responsiveness and involvement in thermal protection

alpha B-crystallin, a major soluble protein of vertebrate eye lenses, is a small heat shock protein which transiently accumulates in response to heat shock and other kinds of stress in mouse NIH 3T3 fibroblasts. Ectopic expression of an alpha B-crystallin cDNA clone renders NIH 3T3 cells thermoresistant. alpha B-crystallin accumulates in response to the synthetic glucocorticoid hormone dexamethasone. Dexamethasone-treated NIH 3T3 cells become thermoresistant to the same extent as they accumulate alpha B-crystallin. A cell clone in which alpha B-crystallin is superinduced upon heat shock acquires augmented thermotolerance. Expression of the ras oncogene causes a rapid but transient accumulation of alpha B-crystallin within 1 day. Later, sustained ras oncogene expression suppresses the dexamethasone-mediated alpha B-crystallin accumulation. Thus, oncogenic transformation triggered by the ras oncogene interferes with hormone-mediated accumulation of alpha B-crystallin and concomitant acquisition of thermoresistance. Other known heat shock proteins do not accumulate in response to ectopic alpha B-crystallin expression or to dexamethasone treatment. These results indicate that alpha B-crystallin can protect NIH 3T3 fibroblasts from thermal shock.

Stress protein synthesis and accumulation after traumatic injury of crayfish CNS

By several days after a crush injury of crayfish CNS, the wound site heals. Changes in protein synthesis and accumulation occur at the lesion site and nearby. During the first few hours, synthesis of 35, 70, 90, and 150 kDa proteins is induced in the injured tissue. By one day, the relative amounts of 70-90 kDa proteins increase dramatically, particularly at the crush site and adjacent to it. The 70 kDa proteins, which are related to mammalian stress proteins (SPs), remain elevated for at least one month in the traumatized region or nearby. The crushed tissue contains an SP70 isoform not present in its uncrushed counterpart. These biochemical changes may reflect the cellular changes that accompany wound healing and/or a cellular stress response to compensate for the lesion. Since similar adaptations occur in the mammalian CNS, they may represent a phylogenetically conserved attempt to retard or repair CNS tissue deterioration.

Vascular heat shock protein expression in response to stress. Endocrine and autonomic regulation of this age-dependent response

Adaptation to stress requires coordinated interactions between the vascular and endocrine systems. Previously we demonstrated that restraint stress induces the expression of the major heat shock protein, HSP70, in the adrenal cortex of the rat. Here we demonstrate that restraint also induces expression of HSP70 in the vasculature. We further demonstrate that the adrenal and vascular responses are differentially regulated: the adrenal response is adrenocorticotropin dependent, whereas the vascular response is under adrenergic control. In addition, the adrenal response is restricted to members of the HSP70 gene family, whereas in vascular tissue the low molecular weight HSP, HSP27, is also induced by restraint. Further characterization of the vascular response revealed that HSP70 induction occurred in both the thoracic and abdominal aortas as well as in the vena cava. However, no HSP70 induction was apparent in the heart or in a wide variety of other tissues examined. In situ hybridization showed that the vascular expression was localized to the aortic smooth muscle cells with minimal expression in the endothelium. Induction of HSP70 mRNA in both the adrenal cortex and aorta was followed by an elevation in HSP70 protein. Maximum HSP70 protein levels were seen within 3-12 h after restraint, but declined thereafter. Stress induced HSP70 expression was dramatically reduced with age, which may explain, in part, the diminished tolerance to stress seen in elderly individuals.

Expression of the murine small heat shock proteins hsp 25 and alpha B crystallin in the absence of stress

Stress induces the synthesis of several large and small heat shock proteins (hsp's). Two related small hsp's, hsp25 and alpha B crystallin exist in mice. alpha B crystallin is an abundant protein in several tissues even in the absence of stress. Particularly high amounts accumulate in the eye lens. Here we show that hsp25 is likewise constitutively expressed in many normal adult tissues. In the absence of stress the protein is most abundant in the eye lens, heart, stomach, colon, lung, and bladder. The stress-independent expression pattern of the two small hsp's is distinct. In several tissues the amount of hsp25 exceeds that accumulating in NIH 3T3 fibroblasts in response to heat stress. hsp25, like alpha B crystallin, exists in a highly aggregated form in the eye lens. The expression of hsp25 and alpha B crystallin in normal tissues suggests an essential, but distinct function of the two related proteins under standard physiological conditions.

Temporal profile of the induction of heat shock protein 70 and heat shock cognate protein 70 mRNAs after transient ischemia in gerbil brain

Distributions of heat shock protein (HSP) 70 and heat shock cognate protein (HSC) 70 mRNAs after 2, 5 and 15 min of transient global ischemia in gerbil forebrain were investigated by in situ hybridization using cloned cDNA probes selective for each mRNA species. Morphological studies were also performed at the dorsal hippocampal level of coronal sections from the identical brains until 7 days after the reperfusion. Following 2 min of ischemia, HSP70 and HSC70 mRNAs were induced together in hippocampal dentate granule cells at 1 and 3 h of the reperfusion. No histological change was observed in brain cells. Following 5 min of ischemia, HSP70 and HSC70 mRNAs were induced in all hippocampal cells. The induction of HSP70 mRNA in hippocampal CA1 cells sustained until 2 days, while that of HSC70 mRNA declined gradually. Only CA1 cells were lost at 7 days of the reperfusion. Following 15 min of ischemia, the mRNAs were induced in more extensive brain regions including neocortex and thalamic nuclei. In hippocampal CA1 cells, inductions of HSP70 and HSC70 mRNAs diminished by 2 days corresponding with the neuronal damage. HSC70 mRNA induction was not so much as HSP70 mRNA induction especially in hippocampal CA1 and thalamic cells. Our results showed that HSP70 and HSC70 mRNAs were generally induced together after transient ischemia, but that the inductions were spatially and chronologically different after different periods of ischemia. The dissociation of the induction was also found in cells severely injured after 5 and 15 min of ischemia.

Changes in heat shock protein synthesis and heat sensitivity during mouse thymocyte development

Heat shock protein synthesis was examined in mouse thymocytes at three stages of development: early embryonic thymocytes, which are CD4-CD8-, adult thymocytes, which are primarily CD4+CD8+, and mature spleen T cells, which are CD4+CD8- or CD4-CD8+. After either a 41 degrees C or 42 degrees C heat shock, the synthesis of the major heat-inducible protein (hsp68) was elevated during the first hour of recovery but then decreased abruptly in thymocytes from adult mice. In contrast, the synthesis of hsp68 continued for up to 4 h after heating embryonic mouse thymocytes or mature spleen T cells. The more rapid termination of the heat shock response in the adult thymocytes was not the result of either less heat damage or more rapid repair since the recovery of general protein synthesis was more severely delayed in these cells. As well, the double positive CD4+CD8+ cells were more sensitive to hyperthermia than either the double negative CD4-CD8- or single positive CD4+CD8- or CD4-CD8+ cells. Exposure of fetal thymus organ cultures to elevated temperature revealed that the double negative thymocytes were able to survive and differentiate normally following a heat shock treatment that was lethal for the double positive thymocytes. Exposure of thymocytes from adult mice to elevated temperatures induced apoptotic cell death. This was evident by the cleavage of DNA into oligonucleosome-sized fragments. Quantitation of the extent of DNA fragmentation and the number of apoptotic cells by flow cytometry demonstrated that the extent of apoptotic cell death was related to the severity of the heat stress. Double positive (CD4+CD8+) thymocytes are selected on the basis of their T-cell antigen receptor (TCR). Most of these cells are negatively selected and die within the thymus by an active process of cell deletion known as apoptosis. Restricting hsp synthesis in response to stress might be essential during developmental processes in which cell maturation is likely to result in death rather than functional differentiation.

Lack of concordance between heat shock proteins and the development of tolerance to teratogen-induced neural tube defects

The present study was undertaken to examine the role of heat shock response in the development of tolerance and cross-tolerance in an in vivo murine model of teratogen-induced neural tube defects. The experimental paradigm designed to address this question was to utilize inbred mouse strains that differed in their sensitivity to hyperthermia and valproic acid induced neural tube defects, subjecting the dams to subteratogenic pretreatments with either heat or valproic acid at two different timepoints during development prior to the administration of the teratogenic insult. A statistically significant reduction in the frequency of neural tube defects and/or embryolethality following a pretreatment in dams subsequently exposed to a teratogenic treatment was considered evidence for the induction of tolerance. This was observed in the SWV embryos exposed to the 38 degrees C pretreatment at 8:06 and to embryos exposed to either pretreatment temperature at 8:10 prior to a teratogenic heat shock at 8:12. In the LM/Bc embryos, only the 41 degrees C pretreatment at 8:06 induced thermotolerance. There was no evidence of tolerance induced in either mouse strain using valproic acid. On the other hand, cross-tolerance was clearly demonstrated in this study, with a low temperature (41 degrees C) pretreatment successfully protecting SWV fetuses from a subsequent teratogenic treatment with valproic acid, while valproic acid (200 mg/kg) was effective in reducing the risk of hyperthermia-induced neural tube defects in the LM/Bc fetuses. In all instances, tolerance was induced in the absence of significant induction of hsp synthesis. The lack of concordance between hsps and thermotolerance suggests that some other factor(s) is involved in conferring thermotolerance on developing murine embryos.

Induction of heat stress proteins is associated with decreased mortality in an animal model of acute lung injury

This study examined the hypothesis that transient, whole-body hyperthermia would reduce lung damage and/or mortality in a previously described animal model of acute lung injury. Normal, adult Sprague-Dawley rats were randomly assigned either to a heated (n = 40) or to a sham-heated (n = 49) group. Heated animals were warmed to 41 to 42 degrees C 18 h before intratracheal instillation of phospholipase A2. Forty-eight hours after phospholipase A2 exposure, the two groups were compared in a blinded fashion for mortality rate, PaO2, AaPO2, lung wet/dry weight ratio, alveolar inflammatory cell number, and lung histopathology. Heated, injured animals exhibited a reduced mortality rate and less lung damage than did unheated animals: mortality (zero versus 27%, p < 0.001); AaPO2 (22 +/- 3 versus 36 +/- 15 mm Hg, p < 0.002); lung lavage cell counts (5.3 +/- 3 versus 16.9 +/- 7 x 10(6)/ml, p < 0.05); lung wet/dry weight ratio (4.1 +/- 0.6 versus 5.1 +/- 0.7, p < 0.025); parenchymal lung injury fraction (0.10 versus 0.51, p < 0.001). Transcription and translation of heat shock proteins (HSP70) were examined by Northern and Western analysis. Pulmonary tissue HSP70 mRNA was elevated 1 h after heating. HSP72 protein levels were increased over baseline levels between 12 and 72 h after whole-body hyperthermia, but they were unchanged in sham-heated animals. These data indicate that thermal pretreatment associated with the induction of HSP72 protein synthesis, attenuates tissue damage and mortality in experimental lung injury.

Induction of 70-kDa heat shock protein and hsp70 mRNA following transient focal cerebral ischemia in the rat

Induction of the 70-kDa heat shock protein (HSP70) was demonstrated immunocytochemically in adult rats 4 h to 7 days following temporary middle cerebral artery (MCA) occlusions lasting 30, 60, or 90 min. Maximal HSP70 induction occurred approximately 24 h following ischemia. Thirty minutes of ischemia induced HSP70 in neurons throughout the cortex in the MCA distribution, whereas 90 min of ischemia induced HSP70 in neurons in the penumbra. HSP70 protein was induced in endothelial cells in infarcted neocortex following 60-90 min of MCA occlusion, and HSP70 was induced in endothelial cells in infarcted regions of lateral striatum following 30-90 min of MCA occlusion. hsp70 mRNA was induced in the MCA distribution in cortex and to a lesser extent in striatum at 2 h to 3 days following 60 min of ischemia. It is proposed that brief ischemia induces hsp70 mRNA and HSP70 protein in the cells most vulnerable to ischemia--the neurons. HSP70 protein is not induced in most neurons and glia following 60-90 min of ischemia in areas destined to infarct, whereas it is induced in vascular endothelial cells.

The induction of pyruvate kinase synthesis by heat shock in Xenopus laevis embryos

Heat-shocked Xenopus embryos have an unusually complex heat shock response. The dominant heat shock protein (Hsp) has a relative molecular mass (M(r)) of 62,000 D (Hsp62). Affinity-purified IgGs against the glycolytic enzyme pyruvate kinase (PK; EC 2.7.1.40) specifically immunoprecipitated Hsp62 from extracts of embryos that had been heat-shocked at 37 degrees C for 30 min. Thus, Hsp62 and pyruvate kinase are immunologically cross-reacting. Electrophoretic separation of PK isoforms suggests that heat-shocked Xenopus embryos increase synthesis of an isoform of PK. Thermal denaturation studies suggest that this isoform has enhanced thermal stability. The identification of PK as an Hsp is discussed within the context of a physiological requirement for elevated levels of anaerobic glycolysis in heat-stressed cells as a vital component of the acquisition of thermotolerance.

Thermotolerance in mammalian cells. Protein denaturation and aggregation, and stress proteins

Cells that have been pre-exposed to thermal stress can acquire a transient resistance against the killing effect of a subsequent thermal stress. The cause for this phenomenon, called thermotolerance, seems to be an enhanced resistance of proteins against thermal denaturation and aggregation. This resistance can be expressed as an attenuation of damage formation (less initial damage) or as a better repair of the protein damage (facilitated recovery). Heat Shock (or better, Stress) Proteins (HSPs) may play a role in and even be required for thermal resistance. However, rather than stress-induced enhanced synthesis and elevated total levels of HSPs per se, the concentration of, both constitutive and inducible, HSPs at and/or (re)distributed to specific subcellular sites may be the most important factor for the acquisition of thermotolerance. Specific HSPs may be involved either in damage protection or in damage repair.

Influence of oxidative stress on induced tolerance to ischemia in gerbil hippocampal neurons

We investigated whether reversible oxidative stress induced by the administration of the superoxide dismutase inhibitor, diethyldithiocarbamate, could induce tolerance to subsequent cerebral ischemia in gerbil hippocampal neurons. Mature male gerbils received intraperitoneal injections of diethyldithiocarbamate (1.0 g/kg), which led to reduced superoxide dismutase activity and increases in thiobarbituric acid-reactive substance in the brain. Cerebral ischemia was produced by occluding the bilateral common carotid arteries for 5 min, either 2 or 4 days after diethyldithiocarbamate injection. One week after ischemia, samples from each brain were stained with hematoxylin-eosin to evaluate ischemic neuronal damage in the hippocampal CA1 sector. Diethyldithiocarbamate treatment 4 days before ischemia had significant protective effects against cerebral ischemia, while diethyldithiocarbamate 2-day pretreatment and vehicle treatment failed to show neuroprotection. Biochemical examinations showed a clear induction of heat shock protein 72 and a significant increase in manganese-containing superoxide dismutase in the hippocampus in animals treated with diethyldithiocarbamate 4 days prior to ischemia. These results suggested that the oxidative stress caused by diethyldithiocarbamate could induced tolerance to ischemia in the gerbil brain, and that the increase in the biosynthesis of manganese-containing superoxide dismutase and heat shock protein 72 could provide a biochemical explanation of the tolerance induced under these conditions.

Hsp70 mRNA induction is reduced in neurons of aged rat hippocampus after thermal stress

Levels of heat-shock 70 mRNAs, relative to those of 18S rRNA, were quantitated in specific cell types of hippocampus of adult and aged rats subjected to identical heat shock regimens. Body temperature changes in response to the heat stress were no different in adult and aged rats. In control rats, as well as 3 h after initiation of heat shock in both adult and aged rats, relative levels of the constitutively synthesized heat-shock cognate 70 (hsc70) mRNA were highest in hippocampal neurons and much lower in glia. No heat-shock protein 70 (hsp70) mRNAs were present in any cell type of control adult or aged rats. In heat-shocked adult rats, the relative levels of the heat-shock-inducible hsp70 mRNAs were highest in a subpopulation of glia, intermediate in granule cells of the dentate gyrus, and lowest in pyramidal cells of Ammon's horn. Relative levels of hsp70 mRNA were several-fold lower in the dentate gyrus granule cells of aged rats compared to relative levels in controls and were also reduced in many pyramidal cells of the hippocampus but not in hippocampal glia. These findings suggest that some neuronal populations in the hippocampus may be at increased risk for stress-related injury in the aged animal.

Quercetin, an inhibitor of heat shock protein synthesis, inhibits the acquisition of thermotolerance in a human colon carcinoma cell line

Here, we describe the effects of quercetin on the induction of thermotolerance as examined by colony forming assay in a cell line derived from human colon carcinoma (COLO320 DM). Cells became resistant to heat treatment at 45 degrees C when they were preheated at 42 degrees C for 1.5 h or at 45 degrees C for 10 min. This induction of thermotolerance was almost completely inhibited by continuous treatment with 100 microM quercetin during the first and second heating sessions, and the interval between. This effect of quercetin was demonstrated to be dose-dependent over a concentration range of 50-200 microM. Quercetin did not increase the thermosensitivity of non-tolerant cells. The presence of quercetin during the first conditioning heating was more effective in inhibiting thermotolerance than its presence during the second heating. Quercetin was also found to inhibit the acquisition of thermotolerance induced by sodium arsenite. Cycloheximide, a nonspecific inhibitor of protein synthesis, did not affect the acquisition of thermotolerance by the same cell line. Quercetin specifically inhibits the synthesis of all heat shock proteins so far reported previously, and this leads to inhibition of the induction of thermotolerance. Such inhibition of thermotolerance by quercetin may improve the efficacy of clinical fractionated hyperthermia.