Activation of heat shock factor 1 in rat brain during cerebral ischemia or after heat shock

RiboTag RNA Sequencing Identifies Local Translation of HSP70 in Astrocyte Endfeet After Cerebral Ischemia

Brain ischemia causes disruption in cerebral blood flow and blood-brain barrier integrity, which are normally maintained by astrocyte endfeet. Emerging evidence points to dysregulation of the astrocyte translatome during ischemia, but its effects on the endfoot translatome are unknown. In this study, we aimed to investigate the early effects of ischemia on the astrocyte endfoot translatome in a rodent cerebral ischemia and reperfusion model of stroke. To do so, we immunoprecipitated astrocyte-specific tagged ribosomes (RiboTag IP) from mechanically isolated brain microvessels. In mice subjected to middle cerebral artery occlusion and reperfusion and contralateral controls, we sequenced ribosome-bound RNAs from perivascular astrocyte endfeet and identified 205 genes that were differentially expressed in the endfoot translatome after ischemia. The main biological processes associated with these differentially expressed genes included proteostasis, inflammation, cell cycle/death, and metabolism. Transcription factors whose targets were enriched amongst upregulated translating genes included HSF1, the master regulator of the heat shock response. The most highly upregulated genes in the translatome were HSF1-dependent Hspa1a and Hspa1b, which encode the inducible HSP70. Using qPCR, Western blot, and immunohistochemistry, we confirmed that HSP70 is upregulated in astrocyte endfeet after ischemia. This coincided with an increase in ubiquitination across the proteome that suggests that ischemia induces a disruption in proteostasis in astrocyte endfeet. These findings suggest a robust proteostasis response to proteotoxic stress in the endfoot translatome after ischemia. Modulating proteostasis in endfeet may be a strategy to preserve endfoot function and BBB integrity after ischemic stroke.

HSP90 Family Members, Their Regulators and Ischemic Stroke Risk: A Comprehensive Molecular-Genetics and Bioinformatics Analysis

BACKGROUND

Disruptions in proteostasis are recognized as key drivers in cerebro- and cardiovascular disease progression. Heat shock proteins (HSPs), essential for maintaining protein stability and cellular homeostasis, are pivotal in neuroperotection. Consequently, deepening the understanding the role of HSPs in ischemic stroke (IS) risk is crucial for identifying novel therapeutic targets and advancing neuroprotective strategies.

AIM

Our objective was to examine the potential correlation between single nucleotide polymorphisms (SNPs) in genes that encode members of the Heat shock protein 90 (HSP90), small heat shock proteins (HSPB), and heat shock factors (HSF) families, and the risk and clinical characteristics of IS.

METHODS

953 IS patients and 1265 controls from Central Russia were genotyped for nine SNPs in genes encoding HSP90AA1, HSFs, and HSPBs using the MassArray-4 system and probe-based polymerase chain reaction (PCR).

RESULTS

In smokers, SNP rs1133026 HSPB8 increased the risk of IS (risk allele A, odds ratio (OR) = 1.43, 95% Confidence Interval (CI) 1.02-2.02, p = 0.035), and rs556439 HSF2 increased the brain infarct size (risk allele A, p = 0.02). In non-smokers, SNPs rs4279640 HSF1 (protective allele T, OR = 0.58, 95% CI 0.37-0.92, p = 0.02) and rs4264324 HSP90AA1 (protective allele C, OR = 0.11, 95% CI 0.01-0.78, p = 0.001) lowered the risk of recurrent stroke; SNP rs7303637 HSPB8 increased the age of onset of IS (protective allele T, p = 0.04). In patients with body mass index (BMI) ≥25, SNPs rs556439 HSF2 (risk allele A, OR = 1.33, 95% CI 1.04-1.69, p = 0.02) and rs549302 HSF2 (risk allele G, OR = 1.34, 95% CI 1.02-1.75, p = 0.03) were linked to a higher risk of IS.

CONCLUSIONS

The primary molecular mechanisms through which the studied SNPs contribute to IS pathogenesis were found to be the regulation of cell death, inflammatory and oxidative stress responses.

Heat shock factor HSF1 regulates BDNF gene promoters upon acute stress in the hippocampus, together with pCREB

Heat shock factor 1 (HSF1) is a master stress-responsive transcriptional factor, protecting cells from death. However, its gene regulation in vivo in the brain in response to neuronal stimuli remains elusive. Here, we investigated its direct regulation of the brain-derived neurotrophic factor (BDNF) gene (Bdnf) in response to acute neuronal stress stimuli in the brain. The results of immunohistochemistry and chromatin immunoprecipitation quantitative PCR (ChIP-qPCR) showed that administration of kainic acid (a glutamate receptor agonist inducing excitotoxity) to young adult mice induced HSF1 nuclear translocation and its binding to multiple Bdnf promoters in the hippocampus. Footshock, a physical stressor used for learning, also induced HSF1 binding to selected Bdnf promoters I and IV. This is, to our knowledge, the first demonstration of HSF1 gene regulation in response to neuronal stimuli in the hippocampus in vivo. HSF1 binding sites (HSEs) in Bdnf promoters I and IV were also detected when immunoprecipitated by an antibody of phosphorylated (p)CREB (cAMP-responsive element-binding protein), suggesting their possible interplay in acute stress-induced Bdnf transcription. Interestingly, their promoter binding patterns differed by KA and footshock, suggesting that HSF1 and pCREB orchestrate to render fine-tuned promoter control depending on the types of stress. Further, HSF1 overexpression increased Bdnf promoter activity in a luciferase assay, while virus infection of constitutively active-form HSF1 increased levels of BDNF mRNA and protein in vitro in primary cultured neurons. These results indicated that HSF1 activation of Bdnf promoter was sufficient to induce BDNF expression. Taken together, these results suggest that HSF1 promoter-specific control of Bdnf gene regulation plays an important role in neuronal protection and plasticity in the hippocampus in response to acute stress, possibly interplaying with pCREB.

Bone Marrow Stromal Cell Transplantation Drives Molecular Switch from Autophagy to the Ubiquitin-Proteasome System in Ischemic Stroke Mice

BACKGROUND

Bone marrow stromal cell (BMSC) transplantation is a promising therapeutic approach for cerebral ischemia, as it elicits multiple neuroprotective effects. However, it remains unclear how BMSC transplantation modulates the ubiquitin-proteasome system (UPS) and autophagy under cerebral ischemia.

METHODS

In the present study, an intermediate level of cerebral ischemia (30 minutes) was chosen to examine the effect of BMSC transplantation on the molecular switch regulating UPS and autophagy. BMSC or vehicle was stereotactically injected into the penumbra 15 minutes after sham operation or transient middle cerebral artery occlusion (tMCAO).

RESULTS

Thirty minutes of tMCAO artery occlusion significantly increased TUNEL-, ubiquitin-, and p62-positive cells (which peaked at 72 hours, 2 hours, and 2 hours after reperfusion, respectively) and ratios of both BAG3/BAG1 and LC3-II/LC3-I at 24 hours after reperfusion. However, intracerebral injection of BMSCs significantly reduced infarct volume and numbers of TUNEL- and p62-positive cells, and improved BAG3/BAG1 and LC3-II/LC3-I ratios. In addition, observed increases in ubiquitin-positive cells 2 hours after reperfusion were slightly suppressed by BMSC transplantation.

CONCLUSIONS

These data suggest a protective role of BMSC transplantation, which drove the molecular switch from autophagy to UPS in a murine model of ischemic stroke.

Tailoring of Proteostasis Networks with Heat Shock Factors

Heat shock factors (HSFs) are the main transcriptional regulators of the heat shock response and indispensable for maintaining cellular proteostasis. HSFs mediate their protective functions through diverse genetic programs, which are composed of genes encoding molecular chaperones and other genes crucial for cell survival. The mechanisms that are used to tailor HSF-driven proteostasis networks are not yet completely understood, but they likely comprise from distinct combinations of both genetic and proteomic determinants. In this review, we highlight the versatile HSF-mediated cellular functions that extend from cellular stress responses to various physiological and pathological processes, and we underline the key advancements that have been achieved in the field of HSF research during the last decade.

Surface wetting strategy prevents acute heat exposure-induced alterations of hypothalamic stress- and metabolic-related genes in broiler chickens

Heat stress (HS) is devastating to poultry production worldwide, yet its biology and molecular responses are not well defined. Although advances in management strategy have partially alleviated the negative impact of HS, productivity still continues to decline when the ambient temperature rises. Therefore, identifying mechanism-based approaches to decrease HS susceptibility while improving production traits is critical. Recently, we made a breakthrough by applying a surface wetting strategy and showing that it improves growth performance compared with the current conventional cooling system. In the present study, we aimed to further define molecular mechanisms associated with surface wetting in ameliorating HS productivity loss in broilers. Five-week-old broiler chickens were exposed to acute HS (35°C for 2 h) alone or in combination with surface wetting. A control group was maintained at thermoneutral conditions (25°C). Core body temperature (BT) and feed intake were recorded. Blood was collected and hypothalamic tissues (main site involved in the regulation of energy homeostasis) were harvested to determine the expression profile of stress- and metabolic-related genes. Surface wetting prevents HS from increasing BT and plasma corticosterone levels ( < 0.05) and improves feeding and drinking behaviors. At molecular levels, surface wetting blocks the activation of hypothalamic heat shock protein and adenosine monophosphate-activated protein-induced by HS and significantly modulates the expression of feeding-related hypothalamic neuropeptides (agouti-related protein, proopiomelanocortin, orexin, orexin receptor, and leptin receptor). Taken together, our data represent the first evidence that surface wetting alleviates systemic and intracellular stress induced by HS and preserves the intracellular energy status, which, in turn, may result in improved broiler well-being and growth performance.

HSF1 is essential for the resistance of zebrafish eye and brain tissues to hypoxia/reperfusion injury

Ischemia and subsequent reperfusion (IR) produces injury to brain, eye and other tissues, contributing to the progression of important clinical pathologies. The response of cells to IR involves activation of several signaling pathways including those activating hypoxia and heat shock responsive transcription factors. However, specific roles of these responses in limiting cell damage and preventing cell death after IR have not been fully elucidated. Here, we have examined the role of heat shock factor 1 (HSF1) in the response of zebrafish embryos to hypoxia and subsequent return to normoxic conditions (HR) as a model for IR. Heat shock preconditioning elevated heat shock protein expression and protected zebrafish embryo eye and brain tissues against HR-induced apoptosis. These effects were inhibited by translational suppression of HSF1 expression. Reduced expression of HSF1 also increased cell death in brain and eye tissues of embryos subjected to hypoxia and reperfusion without prior heat shock. Surprisingly, reduced expression of HSF1 had only a modest effect on hypoxia-induced expression of Hsp70 and no effect on hypoxia-induced expression of Hsp27. These results establish the zebrafish embryo as a model for the study of ischemic injury in the brain and eye and reveal a critical role for HSF1 in the response of these tissues to HR. Our results also uncouple the role of HSF1 expression from that of Hsp27, a well characterized heat shock protein considered essential for cell survival after hypoxia. Alternative roles for HSF1 are considered.

Cerebral ischemia/stroke and small ubiquitin-like modifier (SUMO) conjugation--a new target for therapeutic intervention?

Transient cerebral ischemia/stroke activates various post-translational protein modifications such as phosphorylation and ubiquitin conjugation that are believed to play a major role in the pathological process triggered by an interruption of blood supply and culminating in cell death. A new system of post-translational protein modification has been identified, termed as small ubiquitin-like modifier (SUMO) conjugation. Like ubiquitin, SUMO is conjugated to the lysine residue of target proteins in a complex process. This review summarizes observations from recent experiments focusing on the effect of cerebral ischemia on SUMO conjugation. Transient global and focal cerebral ischemia both induced a rapid, dramatic and long-lasting rise in levels of SUMO2/3 conjugation. After transient focal cerebral ischemia, SUMO conjugation was particularly prominent in neurons located at the border of the ischemic territory where SUMO-conjugated proteins translocated to the nucleus. Many SUMO conjugation target proteins are transcription factors and sumoylation has been shown to have a major impact on the activity, stability, and cellular localization of target proteins. The rise in levels of SUMO-conjugated proteins is therefore likely to have a major effect on the fate of post-ischemic neurons. The sumoylation process could provide an exciting new target for therapeutic intervention.

Greater stress protein expression enhanced by combined prostaglandin A1 and lithium in a rat model of focal ischemia

AIM

To investigate the effects of lithium (Li) and prostaglandin A1 (PGA1) on the expression of heat shock factor 1 (HSF-1), heat shock proteins (HSP), and apoptosis protease activating factor-1 (Apaf-1) induced by permanent focal ischemia in rats.

METHODS

The rats were pretreated with a subcutaneous (sc) injection of Li for 2 d or a single intracerebral ventricle (icv) administration of PGA1 for 15 min before ischemic insult, or a combination of Li (sc, 1 mEq/kg, 2 d) and PGA1 (icv, 15 min prior to ischemic insult). Brain ischemia was induced by the permanent middle cerebral artery occlusion (pMCAO). Twenty-four hours after the occlusion, the expression of HSF-1, HSP, and Apaf-1 in the ischemic striatum were examined with Western blot analysis.

RESULTS

The expression of HSF-1, heme oxygenase-1 (HO-1), HSP90alpha, and Apaf-1 were significantly increased, but the expression of HSP90beta was significantly decreased 24 h after the pMCAO. PGA1 and Li and their combination significantly enhanced the ischemia-induced elevation in the levels of HSF-1, HO-1, and HSP90alpha, and recovered HSP90beta expression, but decreased Apaf-1 levels in the ischemic striatum.

CONCLUSION

The present study demonstrates that PGA1 and Li have synergistic effects on the enhancement of the expression of HSP, suggesting that the synergistic effects of PGA1 and Li in the rat model of permanent focal cerebral ischemia may be mediated by the enhancement expression of HSP expression and the downregulation of Apaf-1. Our studies suggest that combined PGA1 and Li may have potential clinical value for the treatment of stroke.

Hsp27 inhibits 6-hydroxydopamine-induced cytochrome c release and apoptosis in PC12 cells

Cellular stress may stimulate cell survival pathways or cell death depending on its severity. 6-Hydroxydopamine (6-OHDA) is a neurotoxin that targets dopaminergic neurons that is often used to induce neuronal cell death in models of Parkinson's disease. Here we present evidence that 6-OHDA induces apoptosis in rat PC12 cells that involves release of cytochrome c and Smac/Diablo from mitochondria, caspase-3 activation, cleavage of PARP, and nuclear condensation. 6-OHDA also induced the heat shock response, leading to increased levels of Hsp25 and Hsp70. Increased Hsp25 expression was associated with cell survival. Prior heat shock or overexpression of Hsp27 (human homologue of Hsp25) delayed cytochrome c release, caspase activation, and reduced the level of apoptosis caused by 6-OHDA. We conclude that 6-OHDA induces a variety of responses in cultured PC12 cells ranging from cell survival to apoptosis, and that induction of stress proteins such as Hsp25 may protect cells from undergoing 6-OHDA-induced apoptosis.

Selective neuronal vulnerability and inadequate stress response in superoxide dismutase mutant mice

To understand the role of oxidative stress and mitochondrial defects in the development of neurodegeneration, we examined the age-related pathological changes and corresponding gene expression profiles in homozygous mutant mice deficient in the mitochondrial form of superoxide dismutase (MnSOD, SOD2). These Sod2-/- mice, generated on a B6D2F1 background, developed ataxia at Postnatal Day (P) 11 and progressively deteriorated with frequent seizures by P14. Histopathological examination revealed neurodegenerative changes consistent with the neurological signs. Vacuolar degeneration was observed in neurons and neuropil throughout the brainstem and rostral cortex. The motor trigeminal nucleus in brainstem and the deeper layers of the motor cortex were the earliest regions to degenerate, with the thalamus and hippocampus affected at later stages. Oligonucleotide microarrays were used to compare gene expression profiles in the brainstem and thalamus of Sod2+/+ and -/- mice from birth to P18. Notably, a large set of heat-shock protein genes was transcriptionally down regulated, and this was most likely due to a reduction in the heat-shock transcription factor 1 (HSF1). Other major classes of differentially expressed genes include lipid biosynthesis and ROS metabolism.

In vivo heat-shock response in the brain: signalling pathway and transcription factor activation

We analysed the expression of the hsp70 gene, the phosphorylation status of different members of the mitogen-activated protein kinase (MAPK) family, the behaviour of the Akt-GSK3 pathway, as well as the DNA-binding activity of several transcription factors, potential targets of these kinases, in the brain of rats exposed to a fever-like increase in body temperature. Two different brain regions, the cerebellum and the hippocampus, were studied. Hyperthermia caused HSF activation and the induction of hsp70 mRNA and protein to a greater extent in the cerebellum than in the hippocampus. In the cerebellum, ERK1/2 and p38 MAPK phosphorylation were increased by hyperthermia and returned to basal levels during the recovery from heat stress, whereas JNK3 phosphorylation decreased and recovered to above control levels within 60 min of recovery. JNK1 phosphorylation was never modified. In the hippocampus, ERK phosphorylation did not increase but rather decreased, whereas the behaviour of p38 MAPK and JNK was similar to that observed in the cerebellum. Akt phosphorylation increased after hyperthermia and was accompanied by an increased phosphorylation of two substrates, GSK3 and FKHRL1, in both brain areas, with a major effect in the cerebellum. DNA-binding activities of AP-1, NF-kappaB, and MEF2 were activated by heat shock in the cerebellum, whereas only MEF2 was activated in the hippocampus. Our data indicate that a physiologically relevant increase in body temperature induces brain injury and survival response to it as demonstrated by induction of hsp70 gene expression and activation of specific signalling pathways. Reprogramming of gene expression, by the specific transcription factors activated, probably plays a central role in cell adaptation and survival to heat stress. The hippocampus shows less responsiveness to hyperthermia than the cerebellum.

Postinsult treatment with lithium reduces brain damage and facilitates neurological recovery in a rat ischemia/reperfusion model

Lithium has long been a primary drug used to treat bipolar mood disorder, even though the drug's therapeutic mechanisms remain obscure. Recent studies demonstrate that lithium has neuroprotective effects against glutamate-induced excitotoxicity in cultured neurons and in vivo. The present study was undertaken to examine whether postinsult treatment with lithium reduces brain damage induced by cerebral ischemia. We found that s.c. injection of lithium dose dependently (0.5-3 mEq/kg) reduced infarct volume in the rat model of middle cerebral artery occlusionreperfusion. Infarct volume was reduced at a therapeutic dose of 1 mEq/kg even when administered up to 3 h after the onset of ischemia. Neurological deficits induced by ischemia were also reduced by daily administration of lithium over 1 week. Moreover, lithium treatment decreased the number of neurons showing DNA damage in the ischemic brain. These neuroprotective effects were associated with an up-regulation of cytoprotective heat shock protein 70 (HSP70) in the ischemic brain hemisphere as determined by immunohistochemistry and Western blotting analysis. Lithium-induced HSP70 up-regulation in the ischemic hemisphere was preceded by an increase in the DNA binding activity of heat shock factor 1, which regulates the transcription of HSP70. Physical variables and cerebral blood flow were unchanged by lithium treatment. Our results suggest that postinsult lithium treatment reduces both ischemia-induced brain damage and associated neurological deficits. Moreover, the heat shock response is likely to be involved in lithium's neuroprotective actions. Additionally, our studies indicate that lithium may have clinical utility for the treatment of patients with acute stroke.

Expression and localization of heat shock factor (Hsf) 1 in the rodent cochlea

Activation of heat shock factors (Hsfs) is one of the potential mechanisms for regulating the transcription of the heat shock proteins (Hsps) and certain other stress-responsive genes. Reverse transcription polymerase chain reaction (RT-PCR), Western blot and immunocytochemistry were used to examine the expression and localization of Hsf1, the stress-responsive member of the Hsf family, in the rat and mouse cochlea. Cerebellum was used as a positive control. Semi-quantitative RT-PCR of cochlear RNA revealed that Hsf1 was more highly expressed in a subfraction containing sensorineural epithelium and lateral wall than in a subfraction containing modiolus, with the alpha splice form predominant over the beta in both subfractions. Immunocytochemistry showed selective staining in the rodent cochlea. Hsf1 immunostaining was found in the nuclei of inner and outer hair cells in the organ of Corti, spiral ganglion cells in the modiolus, and cells in the marginal and intermediate layers of the stria vascularis. This is largely consistent with where Hsp70 induction is reported. Hsf1 activation following heat shock was examined by Western blot. Hyperthermia resulted in stress-induced Hsf1 hyperphosphorylation in cochlea as well as cerebellum. This hyperphosphorylation as well as the correlation of its localization with Hsp70 induction supports a role for Hsf1 in the cochlear stress response.

Nuclear transcription factors in the hippocampus

In the mammalian hippocampus, there is a trisynaptic loop that has been often referred to in studies on learning and memory mechanisms and their physiological correlate, the long-term potentiation (LTP). The three sets of synapses are formed by the fibers of perforant pathway terminating on granule cells and by the mossy fibers and Schaeffer collaterals making connections with the pyramidal cells. Each of the three types of synapses can develop LTP. LTP is accompanied by changes in gene expression and it is the nuclear transcription, involving specific transcription factors, that is the starting point for the series of biological amplifications and consolidations both necessary for such sustained changes. The transcription factors are proteins that control gene expression, development and functional formation in every eukaryotic cell. Two categories of transcription factors have been defined to date: general factors that comprise at least 20 proteins to form multiple preinitiation complex at the TATA box (TATA rich sequence) or regulatory factors that bind to promoter or enhancer regions at specific sites on the DNA close to, or distant from, the TATA box. Transcription factors have been divided into five different major classes according to unique protein motifs. These include basic domain, zinc-finger, helix-turn-helix, beta-Scaffold factors with minor groove contacts and other transcription factors not specifically classified. Much evidence has been accumulating in favor of the participation of several transcription factors in the consolidation of memory in the mammalian hippocampus following a spatial memory task. It is, therefore, of great importance that the involvement of transcription factors in de novo protein synthesis relevant to the synaptic mechanisms that mediate the formation of long-term memory should be summarized and discussed. No specific correlation between transduction of extracellular signals and expression of nuclear transcription factors, however, has been demonstrated to date.

Phosphorylation of cAMP response element-binding protein in hippocampal neurons as a protective response after exposure to glutamate in vitro and ischemia in vivo

Although accumulating evidence indicates that cAMP response element-binding protein (CREB) phosphorylation mediates not only synaptic plasticity but also survival of certain neurons, it remains uncertain whether CREB phosphorylation induced after metabolic insult leads to CRE-mediated gene transcription and is involved in cell survival or not. In the present study, we clarified that (1) CREB phosphorylation and ischemic tolerance induced after preconditioning ischemia in the hippocampal neurons was abolished by MK801 administration in gerbil global ischemia model, (2) CREB phosphorylation induced after exposure to glutamate in cultured neurons was inhibited by removal of extracellular calcium, by MK801 and by an inhibitor of calcium-calmodulin-dependent protein kinase (CaMK) II and IV, (3) inhibitor of CaMK II-IV or CRE-decoy oligonucleotide suppressed upregulation of BCL-2 expression and accelerated neuronal damage after exposure to glutamate, and (4) CREB phosphorylation induced in the hippocampal neurons after ischemia and in cultured neurons after exposure to glutamate was followed by CRE-mediated gene transcription in transgenic mice with a CRE-LacZ reporter. Our results suggest that CREB phosphorylation in neurons after ischemia and exposure to glutamate is induced by NMDA receptor-gated calcium influx and subsequent activation of CaMK II-IV and that CREB phosphorylation after metabolic stress might show a neuroprotective response through CRE-mediated gene induction.

Synergistic induction of HSP40 and HSC70 in the mouse hippocampal neurons after cerebral ischemia and ischemic tolerance in gerbil hippocampus

An ischemia-induced gene was screened using a differential display technique in mouse transient forebrain ischemia. One of the ischemia-responsive clones was found to encode mouse hsp40. HSP40 has a critical regulatory function in the HSC70 ATPase activity. Expression of hsp40 mRNA was low in the nonischemic mouse hippocampus, but it was significantly upregulated 4 hr after ischemia by Northern blot analysis. In situ hybridization analysis revealed hsp40 mRNA induction in the neuron. HSP40 protein expression was also enhanced in the pyramidal and dentate granular neurons from 2 to 4 days after ischemia. The temporal expression and distribution profile of HSC70 protein was similar to that of HSP40, and both proteins were colocalized in ischemic hippocampal neurons. In the gerbil transient forebrain ischemia model, both HSP40 and HSC70 proteins were expressed strongly in ischemia-resistant CA3 neurons and dentate granule cells 1 day after 5 min ischemia, but were not expressed in vulnerable CA1 neurons. However, both proteins were in parallel expressed in the tolerance-acquired CA1 neurons. Based on the current observation that both HSP40 and HSC70 proteins were synergistically expressed in the ischemia-resistant and tolerance-acquired neurons, cochaperone HSP40 may play a significant role against postischemic neuronal response and lead to cell survival through interaction with simultaneously induced HSC70.

Heat shock transcription factors and the hsp70 induction response in brain and kidney of the hyperthermic rat during postnatal development

Heat shock transcription factor (HSF) 1 levels increase in brain regions and decline in kidney during postnatal rat development. In both neonatal and adult rats, levels of HSF1 protein in brain and kidney are proportional to the levels of HSF DNA-binding activity and the magnitude of heat shock protein hsp70 induction after thermal stress. There appears to be more HSF1 protein in adult brain than is needed for induction of hsp70 after thermal stress, suggesting that HSF1 may have other functions in addition to its role as a stress-inducible activator of heat shock genes. HSF2 protein levels decline during postnatal rat development in brain regions and kidney. Gel mobility shift analysis shows that HSF2 is not in a DNA-binding form in the neonatal brain and kidney, suggesting that HSF2 may not be involved in the constitutive expression of hsps in early postnatal development. There is no apparent relationship between levels of HSF2 protein and basal levels of hsp90, hsp70, heat shock cognate protein hsc70, and hsp60.

Effects of geranyl-geranyl-acetone administration before heat shock preconditioning for conferring tolerance against ischemia-reperfusion injury in rat livers

The effect of geranyl-geranyl-acetone (GGA) administration before heat shock preconditioning on heat shock protein (HSP) 72 induction and on the acquisition of tolerance against ischemia-reperfusion Injury was studied in rat livers. Male Wistar rats were divided into four groups: a control group (group C); a GGA group (group G); a simple heat shock group (group VH); and a heat shock with GGA premedication group (group GH). Five-, 10-, and 15-minute periods of heat shock preconditioning at 42 degrees C were performed in groups VH and GH. Subgroups were determined according to the period of heat shock exposure. After a 48-hour recovery, rats in groups C, VH5, VH15, and GH5 received a 30-minute period of hepatic ischemia. Induction of HSP72, survival rates, and changes in biochemical and histologic parameters were compared among the groups. Five-minute heat shock preconditioning was not enough to Induce HSP72. However, livers in group GH5 expressed approximately the same amount of HSP72 as those in group VH15. The expression of HSP72 in group GH15 was stronger than that found in group VH15. The degree and location of HSP72 expression were not different between groups GH5 and VH15. Seven-day survival was significantly better in groups GH5 (16/16) and VH15 (15/16) than in group C (8/16) or VH5 (9/16). The recovery of adenosine triphosphate in liver tissue was faster, and the release of liver-related enzymes during reperfusion was lower in groups GH5 and VH15 than in group C or VH5. Administration of GGA before heat shock preconditioning augmented the induction of HSP72 by decreasing the threshold for triggering the stress response.

The augmentative effect of repeated heat shock preconditioning on the production of heat shock protein 72 and on ischemic tolerance in rat liver tissue

OBJECTIVE

Heat shock pretreatment induces heat shock protein (HSP)72 strongly in rat livers and provides the tolerance against subsequent ischemia-reperfusion injury. In this study, the effects of repeated heat shock pretreatment on the production of HSP72 in rat livers and on subsequent ischemic tolerance were investigated.

METHODS

Rats pretreated with repeated heat shock were compared with those that received a single heat shock pretreatment. The production of HSP72 was analysed using Western-blotting and densitometer. At 48 h after heat shock pretreatment, all rats were subjected to warm liver ischemia for 30 or 45 min and then reperfused. Survival rate of the animals and liver functions during reperfusion were analysed.

RESULTS

The production of HSP72 increased in the repeated heat shock group more than in the single heat shock group. Although there were no significant differences in animal survival or in liver functions after a 30-min ischemia between the single heat shock group and the repeated heat shock group, animal survival and liver functions after a 45-min ischemia were significantly better in the repeated heat shock group.

CONCLUSION

In rats, repetition of heat shock pretreatment augmented the production of HSP72 in liver tissue and protected the liver from ischemia-reperfusion injury.

HSP70 induction in the brain following ethanol administration in the rat: regulation by glutathione redox state

Changes in glutathione (GSH) and glutathione disulfide (GSSG) levels and/or redox status have been suggested to mediate the induction of heat shock proteins (HSPs) that follows exposure to oxidizing agents such as ethanol. Here we report the effects of ethanol administration to rats at intracellular levels of GSH, GSSG, HSP70, and protein carbonyls in brain and liver. Following 7 days of ethanol administration, there was a significant decrease in GSH, a significant induction of HSP70, and a significant increase in protein carbonyls in all brain regions studied and in liver. In cortex, striatum, and hippocampus there was a significant correlation between (a) the decrease in GSH, (b) the increase in GSSG, and (c) the decrease in GSH/GSSG ratio and HSP70 levels induced in response to ethanol. These data support the hypothesis that a redox mechanism may be involved in the heat-shock signal pathway responsible for HSP70 induction in the brain.

Cell-specific expression of heat shock transcription factors 1 and 2 in unstressed rat spinal cord

We investigated the intracellular distribution of heat shock factors 1 and 2 (HSF1, HSF2) in rat spinal cord by immunoblotting and immunohistochemistry using selective policlonal antibodies. Our results showed that both HSF1 and HSF2 were expressed in spinal cord cells (both neurons and glia) but at different intensity and cell localization. HSF1 was unusually distributed in the perinuclear compartment of selected neurons of the gray matter while astrocytes, oligodendrocytes and ependymal cells were predominantly stained in the nucleus. HSF2 was expressed at lower levels than HSF1 and was scattered in both nucleus and cytoplasm of the motoneurons of the ventral horns while glial cells again showed a nuclear positivity. This study suggested that the different ability of neurons vs. glial cells to react against adverse conditions might well be correlated with the different constitutive localization of HSFs.

Upregulation of MAP1B and MAP2 in the rat brain after middle cerebral artery occlusion: effect of age

Although stroke in humans usually afflicts the elderly, most experimental studies on the nature of cerebral ischemia have used young animals. This is especially important when studying restorative processes that are age dependent. To explore the potential of older animals to initiate regenerative processes after cerebral ischemia, the authors studied the expression of the juvenile-specific cytoskeletal protein, microtubule-associated protein (MAP) 1B, and the adult-specific protein, MAP2, in male Sprague-Dawley rats at 3 months and 20 months of age. The levels of MAP1B and MAP2 transcripts and the corresponding proteins declined with increasing age in the hippocampus. In the cortex, the levels of the transcripts did not change significantly with age, but the morphologic features of immunostained fibers were clearly affected by age; that is, cortical MAP1B fibers became thicker, and MAP2 fibers, more diffuse, in aged rats. Focal cerebral ischemia, produced by reversible occlusion of the right middle cerebral artery, resulted in a large decrease in the expression of both MAP1B and MAP2 in the infarct core at the messenger ribonucleic acid and protein levels. However, at 1 week after the stroke, there was vigorous expression of MAP1B and its messenger ribonucleic acid, as well as MAP2 protein, in the border zone adjacent to the infarct of 3-month-old and 20 month-old male Sprague-Dawley rats. The upregulation of these key cytologic elements generally was diminished in aged rats compared with young animals, although the morphologic features of fibers in the infarct border zone were similar in both age groups. These results suggest that the regenerative potential of the aged rat brain appears to be competent, although attenuated, at least with respect to MAP1B and MAP2 expression up to 20 months of age.

Molecular cloning of a novel member of the HSP110 family of genes, ischemia-responsive protein 94 kDa (irp94), expressed in rat brain after transient forebrain ischemia

To identify genes induced by transient forebrain ischemia, we used the mRNA differential display technique in the four-vessel occlusion model in rats. Some genes were identified as candidates that encode ischemia-responsive protein, and one of them was cloned as ischemia-responsive protein 94 kDa (irp94) from the rat hippocampal cDNA library. Sequence analysis suggested that rat irp94 was a transcriptional variant or a homologue of mouse apg-2 and human heat shock protein (hsp) 70RY and a member of the HSP110 family, because IRP94 was >90% identical to APG-2 and HSP70RY and approximately 60% identical to the other members of the HSP110 family. Although irp94 mRNA was constitutively expressed in the normal hippocampus, it was clearly enhanced 4-24 h after ischemia for 10 (1.9-fold increase) and 15 min (3.4-fold increase). These changes mainly occurred in neuronal cells, as judged by the localization of irp94 mRNA using in situ hybridization histochemistry. On the other hand, hyperthermic stress did not enhance irp94 mRNA expression, suggesting that irp94 expression was enhanced under ischemic stress and not related to the heat shock signaling mechanism. Our study suggested that irp94, a novel member of the HSP110 family, might play an important role in the environment altering neuronal functions, especially after transient forebrain ischemia.

Reactive oxygen species play an important role in the activation of heat shock factor 1 in ischemic-reperfused heart

BACKGROUND

The myocardial protective role of heat shock protein (HSP) has been demonstrated. Recently, we reported that ischemia/reperfusion induced a significant activation of heat shock factor (HSF) 1 and an accumulation of mRNA for HSP70 and HSP90. We examined the role of reactive oxygen species (ROSs) in the induction of stress response in the ischemic-reperfused heart.

METHODS AND RESULTS

Rat hearts were isolated and perfused with Krebs-Henseleit buffer by the Langendorff method. Whole-cell extracts were prepared for gel mobility shift assay using oligonucleotides containing the heat shock element. Induction of mRNA for HSP70 and HSP90 was examined by Northern blot analysis. Repetitive ischemia/reperfusion, which causes recurrent bursts of free radical generation, resulted in burst activation of HSF1, and this burst activation was significantly reduced with either allopurinol 1 mmol/L (an inhibitor of xanthine oxidase) or catalase 2x10(5) U/L (a scavenger of H2O2). Significant activation of HSF1 was observed on perfusion with buffer containing H2O2 150 micromol/L or xanthine 1 mmol/L plus xanthine oxidase 5 U/L. The accumulation of mRNA for HSP70 or HSP90 after repetitive ischemia/reperfusion was reduced with either allopurinol or catalase.

CONCLUSIONS

Our findings demonstrate that ROSs play an important role in the activation of HSF1 and the accumulation of mRNA for HSP70 and HSP90 in the ischemic-reperfused heart.

The heat shock stress response after brain lesions: induction of 72 kDa heat shock protein (cell types involved, axonal transport, transcriptional regulation) and protein synthesis inhibition

The cerebral stress response is examined following a variety of pathological conditions such as focal and global ischemia, administration of excitotoxins, and hyperthermia. Expression of 72 kDa heat shock protein (Hsp70) and hsp70 mRNA, the mechanism underlying induction of hsp70 mRNA involving activation of heat shock factor 1, and inhibition of cerebral protein synthesis are different aspects of the stress response considered here. The results are compared with those in the literature on induction, transcriptional regulation, expression, and cellular location of Hsp70, with a view to getting more insight into the function of the stress response in the injured brain. The present results illustrate that Hsp70 can be expressed in cells affected at various degrees following an insult that will either survive or dic as the brain lesion develops, depending on the severity of cell injury. This indicates that, under certain circumstances, synthesized Hsp70 might be necessary but not sufficient to ensure cell survival. Other situations involve uncoupling between synthesis of hsp70 mRNA and protein, probably due to very strict protein synthesis blockade, and often result in cell loss. Cells eventually will die if protein synthesis rates do not go back to normal after a period of protein synthesis inhibition. The stress response is a dynamic event that is switched on in neural cells sensitive to a brain insult. The stress response is, however, tricky, as affected cells seem to need it, have to deal transiently with it, but eventually be able to get rid of it, in order to survive. Putative therapeutic treatments can act either selectively, potentiating the synthesis of Hsp70 protein and recovery of protein synthesis, or preventing the stress response by deadening the insult severity.

Reperfusion causes significant activation of heat shock transcription factor 1 in ischemic rat heart

BACKGROUND

The myocardial protective role of heat shock protein (HSP) has been demonstrated, and there has been increasing interest in stress response in the heart. We examined the DNA-binding activity of heat shock transcription factor (HSF), by which the transcription of heat shock genes is mainly regulated, during heat shock or ischemia/reperfusion in isolated rat heart.

METHODS AND RESULTS

Rat hearts were isolated and perfused with Krebs-Henseleit buffer by the Langendorff method. Whole-cell extracts were prepared for gel mobility shift assay using oligonucleotides containing the heat shock element, which is present upstream of all heat shock genes. Induction of mRNAs for HSP70, HSP90, and GRP78 (glucose-regulated protein) was examined by Northern blot analysis. Although the activation of HSF during global ischemia was weak and rapidly attenuated, postischemic reperfusion induced a significant activation of HSF. In addition, although HSP70 mRNA was hardly induced during ischemia, its burst induction was detected during postischemic reperfusion. Supershift assays using specific antisera for HSF1 and HSF2 revealed that ischemia/reperfusion as well as heat shock induced the activation of HSF1 in hearts. Although the expression of HSP70 mRNA during heat shock was more vigorous than the expression during ischemia/reperfusion, the induction of HSP90 mRNA in postischemic reperfusion was significantly greater than that in heat shock.

CONCLUSIONS

Our findings demonstrated that reperfusion causes a significant activation of HSF1 in ischemia-reperfused heart. The striking contrast between the induction of HSP70 mRNA and that of HSP90 mRNA suggests the presence of regulatory mechanisms other than HSF.

Regulation of thermotolerance and ischemic tolerance

Thermotolerance and ischemic tolerance are two major biological aspects where heat shock (stress) proteins exert essential roles for survival in cells as well as in various tissues. Bioflavonoids prevent the cells from acquiring thermotolerance after stresses through specific inhibition in the induction of heat shock proteins. The mechanism of this inhibition is revealed to be due to the prevention of the activation of heat shock factor 1 after heat shock. The induction of stress proteins during the ischemic stress is then described in global as well as focal cerebral ischemic model in rats. The activation of heat shock factor 1 after ischemia is first shown to induce various stress proteins in the central nervous system.