Hyperthermic induction of the 27-kDa heat shock protein (Hsp27) in neuroglia and neurons of the rat central nervous system

Regional Differences in Heat Shock Protein 25 Expression in Brain and Spinal Cord Astrocytes of Wild-Type and SOD1 G93A Mice

Heterogeneity of glia in different CNS regions may contribute to the selective vulnerability of neuronal populations in neurodegenerative conditions such as amyotrophic lateral sclerosis (ALS). Here, we explored regional variations in the expression of heat shock protein 25 in glia under conditions of acute and chronic stress. Hsp27 (Hsp27; murine orthologue: Hsp25) fulfils a number of cytoprotective functions and may therefore be a possible therapeutic target in ALS. We identified a subpopulation of astrocytes in primary murine mixed glial cultures that expressed Hsp25. Under basal conditions, the proportion of Hsp25-positive astrocytes was twice as high in spinal cord cultures than in cortical cultures. To explore the physiological role of the elevated Hsp25 expression in spinal cord astrocytes, we exposed cortical and spinal cord glia to acute stress, using heat stress and pro-inflammatory stimuli. Surprisingly, we observed no stress-induced increase in Hsp25 expression in either cortical or spinal cord astrocytes. Similarly, exposure to endogenous stress, as modelled in glial cultures from SOD1 G93A-ALS mice, did not increase Hsp25 expression above that observed in astrocytes from wild-type mice. In vivo, Hsp25 expression was greater under conditions of chronic stress present in the spinal cord of SOD1 G93A mice than in wild-type mice, although this increase in expression is likely to be due to the extensive gliosis that occurs in this model. Together, these results show that there are differences in the expression of Hsp25 in astrocytes in different regions of the central nervous system, but Hsp25 expression is not upregulated under acute or chronic stress conditions.

Heat Shock Protein 27 Injection Leads to Caspase Activation in the Visual Pathway and Retinal T-Cell Response

Heat shock protein 27 (HSP27) is one of the small molecular chaperones and is involved in many cell mechanisms. Besides the known protective and helpful functions of intracellular HSP27, very little is known about the mode of action of extracellular HSP27. In a previous study, we showed that intravitreal injection of HSP27 led to neuronal damage in the retina and optic nerve after 21 days. However, it was not clear which degenerative signaling pathways were induced by the injection. For this reason, the pathological mechanisms of intravitreal HSP27 injection after 14 days were investigated. Histological and RT-qPCR analyses revealed an increase in endogenous HSP27 in the retina and an activation of components of the intrinsic and extrinsic apoptosis pathway. In addition, an increase in nucleus factor-kappa-light-chain-enhancer of activated B cells (NFκB), as well as of microglia/macrophages and T-cells could be observed. In the optic nerve, however, only an increased apoptosis rate was detectable. Therefore, the activation of caspases and the induction of an incipient immune response seem to be the main triggers for retinal degeneration in this intravitreal HSP27 model.

Potential of Glial Cell Modulators in the Management of Substance Use Disorders

The pervasive and devastating nature of substance use disorders underlies the need for the continued development of novel pharmacotherapies. We now know that glia play a much greater role in neuronal processes than once believed.  The various types of glial cells (e.g., astrocytes, microglial, oligodendrocytes) participate in numerous functions that are crucial to healthy central nervous system function. Drugs of abuse have been shown to interact with glia in ways that directly contribute to the pharmacodynamic effects responsible for their abuse potential. Through their effect upon glia, drugs of abuse also alter brain function resulting in behavioral changes associated with substance use disorders. Therefore, drug-induced changes in glia and inflammation within the central nervous system (neuroinflammation) have been investigated to treat various aspects of drug abuse and dependence. This article presents a brief overview of the effects of each of the major classes of addictive drugs on glia. Next, the paper reviews the pre-clinical and clinical studies assessing the effects that glial modulators have on abuse-related behavioral effects, such as pleasure, withdrawal, and motivation. There is a strong body of pre-clinical literature demonstrating the general effectiveness of several glia-modulating drugs in models of reward and relapse. Clinical studies have also yielded promising results, though not as robust. There is still much to disentangle regarding the integration between addictive drugs and glial cells. Improved understanding of the relationship between glia and the pathophysiology of drug abuse should allow for more precise exploration in the development and testing of glial-directed treatments for substance use disorders.

MiR-214 sensitizes human colon cancer cells to 5-FU by targeting Hsp27

Overcoming chemorestistance to 5-fluorouracil (5-FU) could offer a new treatment option for highly malignant colon cancer. In our study, differential microRNA expression profiling revealed that miR-214 is downregulated in 5-FU-resistant colon cancer cells compared to normal cells. In vitro, miR-214 could sensitize non-resistant colon cancer cells and 5-FU-resistant colon cancer cellsto 5-FU. Functionally, miR-214 inhibited cell clone formation and cell growth and enhanced 5-FU-inducing cell apoptosis and caspase-3 levels. MiR-214 targeted heat shock protein 27 (Hsp27), as confirmed via dual luciferase reporter assays and western blots. Hsp27 also sensitized HT-29 and LoVo to 5-FU by enhancing cell apoptosis. Overexpression of Hsp27 could block miR-214 with an effect on the sensitivity of colon cancer cells to 5-FU. In conclusion, miR-214 sensitizes colon cancer cells to 5-FU by targeting Hsp27, indicating a significant role for this miRNA in colon cancer chemotherapy.

Elevation of serum heat-shock protein levels in amyotrophic lateral sclerosis

Heat-shock proteins (HSPs) have been implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS). In this study, we aimed to examine whether the serum levels of HSPs (HSP27, HSP70, and HSP90) are altered in patients with ALS. We included 58 patients diagnosed with ALS and 85 control individuals. Serum HSP levels of patients and controls were determined using enzyme-linked immunosorbent assay. The serum levels of HSP70 and HSP90 were significantly higher in patients than in controls. In contrast, serum levels of HSP27 did not differ significantly between the patient and control groups. Moreover, serum levels of HSP70 and HSP90 in patients remained high throughout the duration of the disease. Taken together, our findings suggest that HSPs might have a role in ALS progression throughout the course of the disease. Further studies are needed to clarify the role of HSPs in the pathogenesis of ALS.

Is brain gliosis a characteristic of chronic methamphetamine use in the human?

Animal data show that high doses of the stimulant drug methamphetamine can damage brain dopamine neurones; however, it is still uncertain whether methamphetamine, at any dose, is neurotoxic to human brain. Since gliosis is typically associated with brain damage and is observed in animal models of methamphetamine exposure, we measured protein levels (intact protein and fragments, if any) of markers of microgliosis (glucose transporter-5, human leukocyte antigens HLA-DRα [TAL.1B5] and HLA-DR/DQ/DPβ [CR3/43]) and astrogliosis (glial fibrillary acidic protein, vimentin, and heat shock protein-27) in homogenates of autopsied brain of chronic methamphetamine users (n=20) and matched controls (n=23). Intact protein levels of all markers were, as expected, elevated (+28%-1270%, P<0.05) in putamen of patients with the neurodegenerative disorder multiple system atrophy (as a positive control) as were concentrations of fragments of glial fibrillary acidic protein, vimentin and heat shock protein-27 (+170%-4700%, P<0.005). In contrast, intact protein concentrations of the markers were normal in dopamine-rich striatum (caudate, putamen) and in the frontal cortex of the drug users. However, striatal levels of cleaved vimentin and heat shock protein-27 were increased (by 98%-211%, P<0.05), with positive correlations (r=0.41-0.60) observed between concentrations of truncated heat shock protein-27 and extent of dopamine loss (P=0.006) and levels of lipid peroxidation products 4-hydroxynonenal (P=0.046) and malondialdehyde (P=0.11). Our failure to detect increased intact protein levels of commonly used markers of microgliosis and astrogliosis could be explained by exposure to methamphetamine insufficient to cause a toxic process associated with overt gliosis; however, about half of the subjects had died of drug intoxication suggesting that "high" drug doses might have been used. Alternatively, drug tolerance to toxic effects might have occurred in the subjects, who were all chronic methamphetamine users. Nevertheless, the finding of above-normal levels of striatal vimentin and heat shock protein-27 fragments (which constituted 10-28% of the intact protein), for which changes in the latter correlated with those of several markers possibly suggestive of damage, does suggest that some astrocytic "disturbance" had occurred, which might in principle be related to methamphetamine neurotoxicity or to a neuroplastic remodeling process. Taken together, our neurochemical findings do not provide strong evidence for either marked microgliosis or astrogliosis in at least a subgroup of human recreational methamphetamine users who used the drug chronically and shortly before death. However, a logistically more difficult quantitative histopathological study is needed to confirm whether glial changes occur or do not occur in brain of human methamphetamine (and amphetamine) users.

Stress-induced stimulation of choline transport in cultured choroid plexus epithelium exposed to low concentrations of cadmium

The choroid plexus epithelium forms the blood-cerebrospinal fluid barrier and accumulates essential minerals and heavy metals. Choroid plexus is cited as being a "sink" for heavy metals and excess minerals, serving to minimize accumulation of these potentially toxic agents in the brain. An understanding of how low doses of contaminant metals might alter transport of other solutes in the choroid plexus is limited. Using primary cultures of epithelial cells isolated from neonatal rat choroid plexus, our objective was to characterize modulation of apical uptake of the model organic cation choline elicited by low concentrations of the contaminant metal cadmium (CdCl₂). At 50-1,000 nM, cadmium did not directly decrease or increase 30-min apical uptake of 10 μM [(3)H]choline. However, extended exposure to 250-500 nM cadmium increased [(3)H]choline uptake by as much as 75% without marked cytotoxicity. In addition, cadmium induced heat shock protein 70 and heme oxygenase-1 protein expression and markedly induced metallothionein gene expression. The antioxidant N-acetylcysteine attenuated stimulation of choline uptake and induction of stress proteins. Conversely, an inhibitor of glutathione synthesis l-buthionine-sulfoximine (BSO) enhanced stimulation of choline uptake and induction of stress proteins. Cadmium also activated ERK1/2 MAP kinase. The MEK1 inhibitor PD98059 diminished ERK1/2 activation and attenuated stimulation of choline uptake. Furthermore, inhibition of ERK1/2 activation abated stimulation of choline uptake in cells exposed to cadmium with BSO. These data indicate that in the choroid plexus, exposure to low concentrations of cadmium may induce oxidative stress and consequently stimulate apical choline transport through activation of ERK1/2 MAP kinase.

Reaction of small heat-shock proteins to different kinds of cellular stress in cultured rat hippocampal neurons

Upregulation of small heat-shock proteins (sHsps) in response to cellular stress is one mechanism to increase cell viability.We previously described that cultured rat hippocampal neurons express five of the 11 family members but only upregulate two of them (HspB1 and HspB5) at the protein level after heat stress. Since neurons have to cope with many other pathological conditions, we investigated in this study the expression of all five expressed sHsps on mRNA and protein level after sublethal sodium arsenite and oxidative and hyperosmotic stress. Under all three conditions, HspB1, HspB5, HspB6, and HspB8 but not HspB11 were consistently upregulated but showed differences in the time course of upregulation. The increase of sHsps always occurred earlier on mRNA level compared with protein levels. We conclude from our data that these four upregulated sHsps (HspB1, HspB5, HspB6, HspB8) act together in different proportions in the protection of neurons from various stress conditions.

Stem cell-like dog placenta cells afford neuroprotection against ischemic stroke model via heat shock protein upregulation

In this study, we investigated the dog placenta as a viable source of stem cells for stroke therapy. Immunocytochemical evaluation of phenotypic markers of dog placenta cells (DPCs) cultured in proliferation and differentiation medium revealed that DPCs expressed both stem cell and neural cell markers, respectively. Co-culture with DPCs afforded neuroprotection of rat primary neural cells in a dose-dependent manner against oxygen-glucose deprivation. Subsequent in vivo experiments showed that transplantation of DPCs, in particular intravenous and intracerebral cell delivery, produced significant behavioral recovery and reduced histological deficits in ischemic stroke animals compared to those that received intra-arterial delivery of DPCs or control stroke animals. Furthermore, both in vitro and in vivo studies implicated elevated expression of heat shock protein 27 (Hsp27) as a potential mechanism of action underlying the observed therapeutic benefits of DPCs in stroke. This study supports the use of stem cells for stroke therapy and implicates a key role of Hsp27 signaling pathway in neuroprotection.

Rat vagus nerve stimulation model of seizure suppression: nNOS and ΔFos B changes in the brainstem

Vagus nerve stimulation (VNS) is a moderately effective treatment for intractable epilepsy. However, the mechanism of action is poorly understood. The effect of left VNS in amygdala kindled rats was investigated by studying changes in nNOS and ΔFos B expression in primary and secondary vagus nerve projection nuclei: the nucleus of the solitary tract (NTS), dorsal motor nucleus of the vagus nerve (DMV), parabrachial nucleus (PBN) and locus coeruleus (LC). Rats were fully kindled by stimulation of the amygdala. Subsequently, when the fully kindled state was reached and then maintained for ten days, rats received a single 3-min train of VNS starting 1min prior to the kindling stimulus and lasting for 2min afterwards. In control animals the vagus nerve was not stimulated. Animals were sacrificed 48h later. The brainstems were stained for neuronal nitric oxide synthase (nNOS) and ΔFos B. VNS decreased seizure duration with more than 25% in 21% of rats. No VNS associated changes in nNOS immunoreactivity were observed in the NTS and no changes in ΔFos B were observed in the NTS, PBN, or LC. High nNOS immunopositive cell densities of >300cells/mm(2) were significantly more frequent in the left DMV than in the right (χ(2)(1)=26.2, p<0.01), independent of whether the vagus nerve was stimulated. We conclude that the observed nNOS immunoreactivity in the DMV suggests surgery-induced axonal damage. A 3-min train of VNS in fully kindled rats does not affect ΔFos B expression in primary and secondary projection nuclei of the vagus nerve.

Exploiting the diversity of the heat-shock protein family for primary and secondary tauopathy therapeutics

The heat shock protein (Hsp) family is an evolutionarily conserved system that is charged with preventing unfolded or misfolded proteins in the cell from aggregating. In Alzheimer’s disease, extracellular accumulation of the amyloid β peptide (Aβ) and intracellular aggregation of the microtubule associated protein tau may result from mechanisms involving chaperone proteins like the Hsps. Due to the ability of Hsps to regulate aberrantly accumulating proteins like Aβ and tau, therapeutic strategies are emerging that target this family of chaperones to modulate their pathobiology. This article focuses on the use of Hsp-based therapeutics for treating primary and secondary tauopathies like Alzheimer’s disease. It will particularly focus on the pharmacological targeting of the Hsp70/90 system and the value of manipulating Hsp27 for treating Alzheimer’s disease.

Transcriptional regulation of small HSP-HSF1 and beyond

The members of the small heat shock protein (sHSP) family are molecular chaperones that play major roles in development, stress responses, and diseases, and have been envisioned as targets for therapy, particularly in cancer. The molecular mechanisms that regulate their transcription, in normal, stress, or pathological conditions, are characterized by extreme complexity and subtlety. Although historically linked to the heat shock transcription factors (HSFs), the stress-induced or developmental expression of the diverse members, including HSPB1/Hsp27/Hsp25, αA-crystallin/HSPB4, and αB-crystallin/HSPB5, relies on the combinatory effects of many transcription factors. Coupled with remarkably different cis-element architectures in the sHsp regulatory regions, they confer to each member its developmental expression or stress-inducibility. For example, multiple regulatory pathways coordinate the spatio-temporal expression of mouse αA-, αB-crystallin, and Hsp25 genes during lens development, through the action of master genes, like the large Maf family proteins and Pax6, but also HSF4. The inducibility of Hsp27 and αB-crystallin transcription by various stresses is exerted by HSF-dependent mechanisms, by which concomitant induction of Hsp27 and αB-crystallin expression is observed. In contrast, HSF-independent pathways can lead to αB-crystallin expression, but not to Hsp27 induction. Not surprisingly, deregulation of the expression of sHSP is associated with various pathologies, including cancer, neurodegenerative, or cardiac diseases. However, many questions remain to be addressed, and further elucidation of the developmental mechanisms of sHsp gene transcription might help to unravel the tissue- and stage-specific functions of this fascinating class of proteins, which might prove to be crucial for future therapeutic strategies. This article is part of a Directed Issue entitled: Small HSPs in physiology and pathology.

Low ambient temperature reveals distinct mechanisms for MDMA-induced serotonergic toxicity and astroglial Hsp27 heat shock response in rat brain

3,4-Methylenedioxymethamphetamine (MDMA, 'ecstasy') is a widely used recreational drug known to cause selective long-term serotonergic damage. In our recent paper we described region-specific, dose-dependent increase in the protein expression of astroglial Hsp27 and neuronal Hsp72 molecular chaperones after MDMA administration of rats. Here, we examined the possible interaction of elevated Hsp27 protein level to hyperthermic responses after MDMA administration and its separation from drug-induced serotonergic neurotoxicity. For this, 7-8 week old male Dark Agouti rats were treated with 15 mg/kg i.p. MDMA. Treatment at an ambient temperature of 22 ± 1°C caused a significant elevation of the rectal temperature, an increase of Hsp27 immunoreactive protoplasmic astrocytes in the hippocampus, the parietal and cingulate cortices, and a significant decrease in the density of tryptophan hydroxylase immunoreactive fibers in the same brain regions, 8h as well as 24h after drug administrations. In addition, serotonergic axons exhibited numerous swollen varicosities and fragmented morphology. MDMA treatment at low ambient temperature (10 ± 2°C) almost completely abolished the elevation of body temperature and the increased astroglial Hsp27 expression but failed to alter - or just slightly attenuated - the depletion in the density of tryptophan hydroxylase immunoreactive fibers. These results suggest that the increased astroglial Hsp27 protein expression is rather related to the hyperthermic response after the drug administration and it could be separated from the serotonergic neurotoxicity caused by MDMA. In addition, the induction of Hsp27 per se is uneffective to protect serotonergic fibers after MDMA administration. Our results also suggest that Tph immunohistochemistry is an early and sensitive method to demonstrate MDMA-caused vulnerability.

Cellular and molecular insights into neuropathy-induced pain hypersensitivity for mechanism-based treatment approaches

Neuropathic pain is currently being treated by a range of therapeutic interventions that above all act to lower neuronal activity in the somatosensory system (e.g. using local anesthetics, calcium channel blockers, and opioids). The present review highlights novel and often still largely experimental treatment approaches based on insights into pathological mechanisms, which impact on the spinal nociceptive network, thereby opening the 'gate' to higher brain centers involved in the perception of pain. Cellular and molecular mechanisms such as ectopia, sensitization of nociceptors, phenotypic switching, structural plasticity, disinhibition, and neuroinflammation are discussed in relation to their involvement in pain hypersensitivity following either peripheral neuropathies or spinal cord injury. A mechanism-based treatment approach may prove to be successful in effective treatment of neuropathic pain, but requires more detailed insights into the persistence of cellular and molecular pain mechanisms which renders neuropathic pain unremitting. Subsequently, identification of the therapeutic window-of-opportunities for each specific intervention in the particular peripheral and/or central neuropathy is essential for successful clinical trials. Most of the cellular and molecular pain mechanisms described in the present review suggest pharmacological interference for neuropathic pain management. However, also more invasive treatment approaches belong to current and/or future options such as neuromodulatory interventions (including spinal cord stimulation) and cell or gene therapies, respectively.

HSP27: mechanisms of cellular protection against neuronal injury

The heat shock protein (HSP) family has long been associated with a generalized cellular stress response, particularly in terms of recognizing and chaperoning misfolded proteins. While HSPs in general appear to be protective, HSP27 has recently emerged as a particularly potent neuroprotectant in a number of diverse neurological disorders, ranging from ALS to stroke. Although its robust protective effect on a number of insults has been recognized, the mechanisms and regulation of HSP27's protective actions are still undergoing intense investigation. On the basis of recent studies, HSP27 appears to have a dynamic and diverse range of function in cellular survival. This review provides a forum to compare and contrast recent literature exploring the protective mechanism and regulation of HSP27, focusing on neurological disorders in particular, as they represent a range from protein aggregate-associated diseases to acute stress.

Exercise can increase small heat shock proteins (sHSP) and pre- and post-synaptic proteins in the hippocampus

The molecular events mediating the complex interaction between exercise and cognition are not well-understood. Although many aspects of the signal transduction pathways mediate exercise induced improvement in cognition are elucidated, little is known about the molecular events interrelating physiological stress with synaptic proteins, following physical exercise. Small heat shock proteins (sHSP), HSP27 and alpha-B-crystallin are co-localized to synapses and astrocytes, but their role in the brain is not well-understood. We investigated whether their levels in the hippocampus were modulated by exercise, using a well characterized voluntary exercise paradigm. Since sHSP are known to be regulated by many intracellular signaling molecules in other cells types outside the brain, we investigated whether similar regulation may serve a role in the brain by measuring protein kinase B (PKB/Akt), pGSK3 and the mitogen activated protein (MAP) kinases, p38, phospho-extracellular signal-regulated kinase (pERK) and phospho-c-Jun kinase (pJNK). Results demonstrated exercise-dependent increases in HSP27 and alpha-B-crystallin levels. We observed that increases in sHSP coincided with robust elevations in the presynaptic protein, SNAP25 and the post-synaptic proteins NR2b and PSD95. Exercise had a differential impact on kinases, significantly reducing pAkt and pERK, while increasing p38 MAPK. In conclusion, we demonstrate four early novel hippocampal responses to exercise that have not been identified previously: the induction of (1) sHSPs (2) the synaptic proteins SNAP-25, NR2b, and PSD-95, (3) the MAP kinase p38 and (4) the immediate early gene product MKP1. We speculate that sHSP may play a role in synaptic plasticity in response to exercise.

Pituitary adenylate cyclase-activating polypeptide 38-mediated Rin activation requires Src and contributes to the regulation of HSP27 signaling during neuronal differentiation

Pituitary adenylate cyclase-activating polypeptide 38 (PACAP38) is a potent neuropeptide that acts through G-protein-coupled receptors. While it is well established that PACAP mediates both neurotrophic and neurodevelopmental effects, the signaling cascades that underlie these diverse actions remain incompletely characterized. Here we show that the Ras-related Rin GTP-binding protein, a GTPase that is expressed predominantly in neurons, is regulated by PACAP38 signaling, and loss-of-function analysis demonstrates that Rin makes an essential contribution to PACAP38-mediated pheochromocytoma cell differentiation. Rin is activated following stimulation of both Gsalpha and Gialpha cascades but does not rely upon cyclic AMP (cAMP)-, Ca(2+)-, or Epac-dependent signaling pathways. Instead, Rin is activated in a Src kinase-dependent manner. Surprisingly, Rin knockdown significantly inhibits PACAP38-mediated neurite outgrowth, without affecting mitogen-activated protein kinase signaling cascades. Instead, Rin loss attenuates PACAP38-mediated HSP27 activation by disrupting a cAMP-protein kinase A cascade. RNA interference-mediated HSP27 silencing suppresses both PACAP38- and Rin-mediated neurite outgrowth, while expression of a constitutively active Rin mutant increases both HSP27 protein and phospho-HSP27 levels, supporting a role for Rin-HSP27 signaling in neuronal differentiation. Together, these observations identify an unsuspected role for Rin in neuronal PACAP signaling and establish a novel Galpha-Src-Rin-HSP27 signal transduction pathway as a critical element in PACAP38-mediated neuronal differentiation signaling.

Global profiling of influence of intra-ischemic brain temperature on gene expression in rat brain

Mild to moderate differences in brain temperature are known to greatly affect the outcome of cerebral ischemia. The impact of brain temperature on ischemic disorders has been mainly evaluated through pathological analysis. However, no comprehensive analyses have been conducted at the gene expression level. Using a high-density oligonucleotide microarray, we screened 24000 genes in the hippocampus under hypothermic (32 degrees C), normothermic (37 degrees C), and hyperthermic (39 degrees C) conditions in a rat ischemia-reperfusion model. When the ischemic group at each intra-ischemic brain temperature was compared to a sham-operated control group, genes whose expression levels changed more than three-fold with statistical significance could be detected. In our screening condition, thirty-three genes (some of them novel) were obtained after screening, and extensive functional surveys and literature reviews were subsequently performed. In the hypothermic condition, many neuroprotective factor genes were obtained, whereas cell death- and cell damage-associated genes were detected as the brain temperature increased. At all intra-ischemic brain temperatures, multiple molecular chaperone genes were obtained. The finding that intra-ischemic brain temperature affects the expression level of many genes related to neuroprotection or neurotoxicity coincides with the different pathological outcomes at different brain temperatures, demonstrating the utility of the genetic approach.

Trimethylamine oxide suppresses stress-induced alteration of organic anion transport in choroid plexus

The effect of physicochemical stress on organic anion transport across the vertebrate blood–cerebrospinal fluid (CSF) barrier in the presence and absence of an endogenous cytoprotectant, trimethylamine oxide (TMAO), was investigated in isolated IVth choroid plexus (CP) of spiny dogfish shark(Squalus acanthias), an animal with naturally high levels of TMAO(∼70 mmol l–1). Active transepithelial absorption of the organic anion, 2,4-dichlorophenoxyacetic acid (2,4-D), by IVth CP mounted in Ussing chambers was measured after in vitro stress, and a marker for the cellular stress response, inducible heat shock protein 70 (Hsp70), was assayed by immunoblot analysis. Transient heat stress (a shift from the normal 13.5°C to 23.5°C for 1 h) decreased 2,4-D transport by ∼66%;however, the same stress minus TMAO (isosmotic replacement with urea) had no effect on transport rate. In the absence of TMAO, stress-induced Hsp70 accumulation was more than double that seen in the presence of TMAO. Likewise,exposure to 50 μmol l–1 Zn for 6 h induced a twofold greater Hsp70 accumulation in the absence of TMAO than in its presence, and the higher Hsp70 level was associated with a higher 2,4-D transport rate. Heat stress and 50 μmol l–1 Zn also induced more pronounced increases in Hsp70 mRNA in the absence of TMAO. Thus, the cellular stress response can significantly alter CP organic anion transport capacity, and an endogenous osmolyte can suppress that response.

HSPBAP1 is found extensively in the anterior temporal neocortex of patients with intractable epilepsy

Heat Shock Protein BAP1 (heat shock 27-kDa-associated protein 1, HSPBAP1) inhibits the function of heat shock protein 27, which has a neuroprotective effect during experimentally induced epileptic neuropathology. In our study, fluorescence quantitative polymerase chain reaction, immunohistochemistry, immunofluorescence, western blot were used to test the levels of HSPBAP1 mRNA and protein in surgical samples of the anterior temporal neocortex of patients with intractable epilepsy (IE) and normal controls samples. HSPBAP1 mRNA was abnormally expressed in the anterior temporal neocortex of patients with IE. Moreover, HSPBAP1 was found extensively in the cytoplasm of neurons and glial cells in all epilepsy specimens. Western blot showed a clear immunoreactive band of HSPBAP1 in IE specimens whereas it was absent in control specimens. The expression of HSPBAP1 mRNA and protein in the anterior temporal neocortex from patients with IE may play a role in the development of epileptic seizures in patients with cell loss in this brain region. Additional studies will be required to elucidate the mechanism by which HSPBAP1 affects brain function in IE.

Heat shock protein expression in brain: a protective role spanning intrinsic thermal resistance and defense against neurotropic viruses

Heat shock proteins (HSPs) play an important role in the maintenance of cellular homeostasis, particularly in response to stressful conditions that adversely affect normal cellular structure and function, such as hyperthermia. A remarkable intrinsic resistance of brain to hyperthermia reflects protection mediated by constitutive and induced expression of HSPs in both neurons and glia. Induced expression underlies the phenomenon of hyperthermic pre-reconditioning, where transient, low-intensity heating induces HSPs that protect brain from subsequent insult, reflecting the prolonged half-life of HSPs. The expression and activity of HSPs that is characteristic of nervous tissue plays a role not just in the maintenance and defense of cellular viability, but also in the preservation of neuron-specific luxury functions, particularly those that support synaptic activity. In response to hyperthermia, HSPs mediate preservation or rapid recovery of synaptic function up to the point where damage in other organ systems becomes evident and life threatening. Given the ability of HSPs to enhance gene expression by neurotropic viruses, the constitutive and inducible HSP expression profiles would seem to place nervous tissues at risk. However, we present evidence that the virus-HSP relationship can promote viral clearance in animals capable of mounting effective virus-specific cell-mediated immune responses, potentially reflecting HSP-dependent increases in viral antigenic burden, immune adjuvant effects and cross-presentation of viral antigen. Thus, the protective functions of HSPs span the well-characterized intracellular roles as chaperones to those that may directly or indirectly promote immune function.

Protective role of heat shock and heat shock protein 70 in lactacystin-induced cell death both in the rat substantia nigra and PC12 cells

Proteasomal dysfunction plays an important role in the pathogenesis of Parkinson disease (PD). Although clinical and experimental evidence continues to accumulate indicating heat shock protein 70 (HSP70) is significant in the pathogenesis of PD, few studies have been made to investigate the role of HSP70 under the condition of proteasome dysfunction. In in vivo study, we infused lactacystin into the unilateral substantia nigra (SN) of Sprague-Dawley rats with or without preceding whole body hyperthermia (WBH). Immunohistochemical studies showed the death of dopaminergic neurons and activated microglia in the SN. Lactacystin with prior WBH increased the expression of HSP70 more than did lactacystin alone and decreased lactacystin-induced dopaminergic neuronal death in the SN. In PC12 cells, heat shock pretreatment decreased lactacystin-induced cell death. Although additional treatment of nocodazole, ammonium chloride, and 3-methyladenine augmented cell death by lactacystin, heat shock pretreated to these drugs offsets their additional toxicity. These results indicate that heat shock proteins, especially HSP70, could play an important role under the condition of proteasome dysfunction in part by fostering aggresome formation and lysosome-mediated autophagy.

Brief heat shock affects the permeability and thermotolerance of an in vitro blood-brain barrier model of porcine brain microvascular endothelial cells

Heat shock was imposed on an in vitro model of the blood-brain barrier (BBB) by submersion into prewarmed growth medium. Transendothelial electrical resistance (TEER) was used to assess the functional integrity of the endothelial barrier. Consequences of the heat shock were highly dependent upon the temperature and duration of exposure. Temperatures below 47 degrees C required more than 30 s of exposure to significantly impair barrier function, but full recovery occurred within 1 h. When the temperature was 50-54 degrees C, an exposure of only 10 s significantly diminished barrier function. Ten seconds of 51 degrees C or 54 degrees C caused a significant loss of barrier function (45% and 80%, respectively). Full recovery from the 51 degrees C shock occurred within 5 min, while recovery from the 54 degrees C shock required more than 10 h. When the temperature was 57 degrees C or greater, a 3-s duration diminished barrier function by 80%. In response to heat shock, the brain microvascular endothelial cells developed thermotolerance and over-compensated in their ability to form a physiological barrier. The BBB models lost more than 60% of barrier function when initially exposed to 53 degrees C for 5 s but lost only 30% of function when exposed to the same treatment 24 h later. The BBB models over-compensated to produce a reinforced barrier with double the original TEER following repeated application of heat treatment (57 degrees C for 3 s). In vivo experiments will require exquisite manipulation of the temperature and duration in order to achieve the desired opening of the BBB in therapeutic applications.

Damage of serotonergic axons and immunolocalization of Hsp27, Hsp72, and Hsp90 molecular chaperones after a single dose of MDMA administration in Dark Agouti rat: Temporal, spatial, and cellular patterns

3,4-Methylenedioxymethamphetamine (MDMA, "ecstasy") causes long-term disturbance of the serotonergic system. We examined the temporal, spatial, and cellular distribution of three molecular chaperones, Hsp27, Hsp72, and Hsp90, 3 and 7 days after treatment with 7.5, 15, and 30 mg/kg single intraperitoneal (i.p.) doses of MDMA in Dark Agouti rat brains. Furthermore, we compared the immunostaining patterns of molecular chaperones with serotonergic axonal-vulnerability evaluated by tryptophan-hydroxylase (TryOH) immunoreactivity and with astroglial-activation detected by GFAP-immunostaining. There was a marked reduction in TryOH-immunoreactive axon density after MDMA treatment in all examined areas at both time points. Three days after treatment, a significant dose-dependent increase in Hsp27-immunoreactive protoplasmic astrocytes was found in the cingulate, frontal, occipital, and pyriform cortex, and in the hippocampus CA1. However, there was no increase in astroglial Hsp27-immunoreactivity in the caudate putamen, lateral septal nucleus, or anterior hypothalamus. A significant increase in the GFAP immunostaining density of protoplasmic astrocytes was found only in the hippocampus CA1. In addition, numerous strong Hsp72-immunopositive neurons were found in some brain areas only 3 days after treatment with 30 mg/kg MDMA. Increased Hsp27-immunoreactivity exclusively in the examined cortical areas reveals that Hsp27 is a sensitive marker of astroglial response to the effects of MDMA in these regions of Dark Agouti rat brain and suggests differential responses in astroglial Hsp27-expression between distinct brain areas. The co-occurrence of Hsp27 and GFAP response exclusively in the hippocampus CA1 may suggest the particular vulnerability of this region. The presence of strong Hsp72-immunopositive neurons in certain brain areas may reflect additional effects of MDMA on nonserotonergic neurons.

Bilateral, vascular and perivascular glial upregulation of heat shock protein-27 after repeated epileptic seizures

Heat shock protein-27 (HSP-27) is an inducible stress response protein. It inhibits apoptotic cell death and is a reliable marker for oxidative stress. We studied the induction of HSP-27 in rat brains on days 1, 4 and 14 after repeated, pentylenetetrazole (PTZ)-induced seizures using immunohistochemisty. Saline treated control rats showed no induction of HSP-27. HSP-27 reactive astrocytes were rarely seen 1 or 4 days after PTZ injection. When present, single astrocytes were located in the cortex and/or the hippocampus. After 14 days PTZ treatment, a bilateral distribution of HSP-27 immunoreactive glia was present in piriform and entorhinal cortices and in the dentate gyrus of most brains. Rats with most intense HSP-27 upregulation showed HSP-27 in amygdala and thalamic nuclei. Astrocytes associated with blood vessels presented strongest HSP-27 staining, but did not show upregulation of gial fibrillary acidic protein and none responded with HSP-47 expression. Additionally, HSP-27 immunoreactivity increased in the endothelial cells of blood vessels in the affected brain regions, although no neuronal induction occurred. Contrastingly, a subconvulsive dose of the glutamine synthetase inhibitor L-methionine sulfoxime, which acts directly on astrocytes, resulted in a rapid, homogeneous astrocyte-specific HSP-27 upregulation within 24 h. Thus, repeated PTZ-induced seizure activity elicits a focal "heat shock" response in endothelial cells and astrocytes of selected cerebral regions indicating that expression of HSP-27 occurred in a seizure-dependent manner within the affected cerebral circuitries. Therefore, this PTZ-model of repeated seizure activity exhibited a cortical pattern of HSP-27 expression which is most comparable to that known from patients with epilepsy.

Expression of Hsp72 in lymphocytes in patients with febrile convulsion

The pathophysiology of febrile convulsion, the most common childhood neurologic disease, remains unclear. In this study, we investigated what role a heat shock protein plays in this disease. We enrolled eight boys and two girls with febrile convulsion and 10 age-matched healthy controls. We did a biosynthetic evaluation of both groups by separating lymphocytes and measuring the expression of heat shock protein 72 before and after heat shock treatment. Before the treatment, both groups were found to have small amounts of constitutive heat shock protein 72. Afterwards, its expression increased in both groups, and no statistical difference was found between the increases in the two groups. In addition, there was no obvious difference in the susceptibility to produce heat shock proteins. However, the febrile convulsion group was found to have a significant decrease in phosphorylation of heat shock protein 72. These results suggest the possible involvement of post-translational modification of heat shock proteins, most likely phosphorylation, in the pathogenesis of febrile convulsion.

Heat shock treatment protects against angiotensin II-induced hypertension and inflammation in aorta

Angiotensin II (Ang II) is a potent vasoconstrictor and induces inflammation and end-organ injury through its activation of the proinflammatory transcription factor, nuclear factor-kappaB (NF-kappaB). Heat shock (HS) treatment with subsequent expression of heat shock proteins (Hsps) is an effective strategy for tissue protection against oxidative injuries. Recently, HS and Hsps have been shown to interact with NF-kappaB in tissue injury. In this study, we investigated whether HS could protect against Ang II-induced hypertension and inflammation by inhibiting NF-kappaB. Sprague-Dawley rats were divided into control and HS groups. Control and 24-hour post-heat shocked rats were treated with Ang II. At days 1, 3, 5, 7, 11, and 14 after Ang II administration, systolic blood pressures were measured by tail-cuff plethysmography, and aorta tissues were collected. Aorta NF-kappaB deoxyribonucleic acid-binding activity was measured by electrophoretic mobility shift assay, and NF-kappaB p65 subunit, Hsp70, Hsp27, and interleukin-6 (IL-6) expressions were measured by Western analysis. HS treatment significantly decreased Ang II-induced hypertension. The activation of NF-kappaB in aorta by Ang II was suppressed by HS treatment. The elevated expression of IL-6 induced by Ang II treatment was also decreased by HS treatment. Although Ang II treatment induced an increase in Hsp70 and Hsp27, HS treatment induced a greater elevation of Hsp70 and Hsp27 expression. HS treatment protects against Ang II-induced hypertension and inflammation. This protection may relate to the interaction of Hsps and the NF-kappaB pathway.

Heat Shock Protein-27 Is Upregulated in the Temporal Cortex of Patients with Epilepsy

PURPOSE

Heat shock protein-27 (HSP-27) belongs to the group of small heat shock proteins that become induced in response to various pathologic conditions. HSP-27 has been shown to protect cells and subcellular structures, particularly mitochondria, and serves as a carrier for estradiol. It is a reliable marker for tissues affected by oxidative stress. Oxidative stress and related cellular defence mechanisms are currently thought to play a major role during experimentally induced epileptic neuropathology. We addressed the question whether HSP-27 becomes induced in the neocortex resected from patients with pharmacoresistant epilepsy.

METHODS

Human epileptic temporal neocortex was obtained during neurosurgery, and control tissue was obtained at autopsy from subjects without known neurologic diseases. The tissues were either frozen for Western blot analysis or fixed in Zamboni's fixative for the topographic detection of HSP-27 at the cellular level by means of immunohistochemistry.

RESULTS

HSP-27 was highly expressed in all epilepsy specimens and in the cortex of a patient who died in the final stage of multiple sclerosis (positive control), whereas only low amounts of HSP-27 were detectable in control brains. In epilepsy patients, HSP-27 was present in astrocytes and in the walls of blood vessels. The intracortical distribution patterns varied strongly among the epilepsy specimens.

CONCLUSIONS

These results demonstrate that HSP-27 becomes induced in response to epileptic pathology. Although the functional aspects of HSP-27 induction during human epilepsy have yet to be elucidated, it can be concluded that HSP-27 is a marker for cortical regions in which a stress response has been caused by seizures.

Heat shock treatment suppresses angiotensin II-induced activation of NF-κB pathway and heart inflammation: a role for IKK depletion by heat shock?

Heat shock (HS) proteins (Hsps) function in tissue protection through their chaperone activity and by interacting with cell signaling pathways to suppress apoptosis. Here, we investigated the effect of HS treatment on the nuclear factor (NF)-κB signaling pathway in the angiotensin II (ANG II) model of inflammation. Male Sprague-Dawley rats were divided into sham and HS-, ANG II-, and HS + ANG II-treated groups. HS treatment was administered 24 h before the initiation of ANG II infusion. HS treatment (42°C for 15 min) decreased 7-day ANG II-induced hypertension from 191 ± 4 to 147 ± 3 mmHg ( P < 0.01). Histological staining of hearts showed that HS treatment reduced ANG II-induced leukocyte infiltration, perivascular and interstitial inflammation, and fibrosis. Heart NF-κB nuclear translocation and activity, examined by Western blot analysis and electrophoretic mobility shift assay, was suppressed by HS treatment. HS treatment depleted IκB kinase-α (IKK-α) and phosphorylated IKK-α and suppressed the depletion of IκB-α and the accumulation of phosphorylated IκB-α. HS treatment blocked ANG II induced expression of IL-6 and ICAM-1 in the heart. ANG II and HS treatment induced high-level expression of Hsp27 and Hsp70 and their phosphorylation. Phosphorylated isoforms of Hsp27 and Hsp70 may play an important role in protecting the heart against ANG II-induced inflammation.

Similar effects of cocaine and immobilization stress on the levels of heat-shock proteins and stress-activated protein kinases in the rat hippocampus, and on swimming behaviors: the contribution of dopamine and benzodiazepine receptors

Cocaine (COC) has been reported to cause effects similar to physiological stressors in the brain neuroendocrinal system, including heat-shock protein (HSP) expression, although these effects have not been elucidated in detail. In the present study, we examined the effects of repeated (4 days) treatments with cocaine hydrochloride (35 mg/kg, i.p.) and 10 min immobilization stress (IM) on the distribution of HSP (HSP27, HSP60, HSP70, HSC70) and stress-activated protein kinase (SAPK) (SAPKalpha, SAPKbeta, SAPKgamma) immunoreactive nerve cells (positive cells) in the rat hippocampus. The swimming behaviors of the rats in the forced swimming test were also examined. In both COC and IM groups, an early enhancement (5 h time point) of hippocampal HSP (HSP27, HSP60, HSP70, HSC70) and SAPK (SAPKbeta, SAPKgamma) positive cells was observed, whereas a recovery (SAPKs) or attenuation (HSP60 and HSC70) was observed at the 24 h time point. In both groups, a depression of the swimming behaviors (attenuation in the activity counts and time until immobility) below the control level was observed at the 5 h point, but a recovery was observed at the 24 h time point. At the 48 h time point, all parameters returned to the control level. These alterations in the levels of HSPs and SAPKs, and the swimming behaviors were similar to those observed in the stress (IM) group, and were characteristic in that all of these alterations were attenuated by the benzodiazepine inverse agonist, Ro 15-4513 (5 mg/kg, i.p.), and the dopamine D1 receptor antagonist, SCH23390 (0.5 mg/kg, i.p.), which was not observed in the groups treated with another stressor-like drug (bicuculline).

Expression of Hsp27 in retinal ganglion cells of the rat during postnatal development

The small heat shock protein Hsp27 has been shown to protect neurons from apoptosis. We have recently shown the expression of Hsp27 in a subset of injured adult retinal ganglion cells (RGCs), a response that is muted by the administration of brain-derived neurotrophic factor. This work has suggested a role for Hsp27 in the long-term survival of RGCs following injury. The purpose of this study was to investigate the expression of Hsp27 during postnatal retinal development, based on Hsp27's role as a neuronal survival factor and on its up-regulation in the adult injured retina. Expression of Hsp27 in the developing retina was examined at various times postnatally (between P0 and P24) by using immunohistochemical techniques. We report that Hsp27 expression peaks in the ganglion cell layer between P6 and P12 and is not detected at earlier (P0-P3) or later (P15-P24) times. Double labeling of the Hsp27-positive cells with Fluorogold applied to the superior colliculus confirmed that Hsp27-positive cells in the ganglion cell layer are RGCs. We have shown developmentally regulated expression of Hsp27 in RGCs of the postnatal rat. The retinal expression of Hsp27 correlates temporally with innervation of the tectum by late-born RGCs and with onset of spontaneous retinotectal activity. We propose that the expression of Hsp27 may play an important role in retinal development during a critical period of RGC functional connectivity with the superior colliculus.

Induction of Hsp27 and Hsp32 stress proteins and vimentin in glial cells of the rat hippocampus following hyperthermia

In response to stressful stimuli, cells respond by inducing a set of heat shock (stress) proteins (hsps) that play important roles in repair and protective mechanisms. The present study investigates the expression patterns of Hsp27 and Hsp32 in the adult rat hippocampus following whole body hyperthermia. A pronounced induction of these low-molecular-weight stress proteins was apparent in populations of glial cells such as astrocytes and microglia that were identified using cell-specific markers (GFAP for astrocytes and the lectin GSA I-B4 for microglia). Hyperthermia also resulted in a robust induction of the intermediate filament protein, vimentin, in glial cells in the adult rat hippocampus. Interestingly, a rapid induction of both Hsp27 and vimentin was observed in the microvasculature, suggesting that hyperthermic stress may compromise the blood-brain barrier.

Administration of brain-derived neurotrophic factor suppresses the expression of heat shock protein 27 in rat retinal ganglion cells following axotomy

Optic nerve transection results in the apoptotic cell death of the majority of retinal ganglion cells by 14 days. The neurotrophin brain-derived neurotrophic factor (BDNF) enhances survival of retinal ganglion cells. In addition, the small heat shock protein Hsp27, with its anti-apoptotic effects, may be important for neuron survival following axotomy or trophic factor withdrawal. We recently reported the induction and expression of Hsp27 in a subset of retinal ganglion cells following axotomy. Here we have examined the effect of BDNF administration on the expression of Hsp27 in axotomized adult rodent retinal ganglion cells. Retinal ganglion cells were pre-labeled with Fluorogold prior to optic nerve transection and concomitant intraocular injection of BDNF or vehicle. Hsp27 immunofluorescence was examined in retinal sections from 4 to 28 days following injury. Consistent with previous survival studies, the number of Fluorogold-labeled retinal ganglion cells declined from 100% at 4 days to approximately 15% by 14 days following axotomy and vehicle injection. In contrast, with BDNF administration, retinal ganglion cell survival was maintained at 100% to 7 days following axotomy. We report that the number of Hsp27-positive injured retinal ganglion cells, as detected by immunohistochemical staining, was decreased by 50% in BDNF-treated retinas, when compared with vehicle-treated controls. This decreased expression of Hsp27 in response to BDNF treatment was seen both at early (4 days) and delayed (14 days) times. BDNF following optic nerve transection significantly reduced the expression of Hsp27 in retinal ganglion cells. These results indicate that BDNF may down-regulate alternate cell survival pathways, including the stress-induced expression of Hsp27, and may help to explain the failure of chronic neurotrophin treatment to maintain long-term retinal ganglion cell survival.

A review of heat shock protein induction following cerebellar injury

Exposure of cells to stressful environments such as heat shock, ischemia, trauma and disease, induces the cellular expression of heat shock proteins (Hsps). Since the discovery of heat shock proteins in the early 1960s, efforts to understand their function in both stressed and non-stressed cells have remained the focus of a vast collection of researchers. Post-injury heat shock protein induction is believed to identify regions of reversible cell injury as well as contribute to repair and protective mechanisms following stress. With the role of cerebellum expanding to include a number of cognitive processes in addition to contributing to motor coordination, research contributions that further our understanding of cerebellar repair strategies following injury are significant. Following cellular stress, heat shock protein expression was observed in both neuronal and glial cell populations in the injured cerebellum. Specifically, Hsp27 expression was localized primarily in Purkinje cells and glial cells within the injured cerebellum, whereas Hsp72 induction was more prominent in the granule cell layer of the cerebellum. Thus, there appears to be a preferential expression of different families of heat shock proteins in different cell populations in the injured cerebellum. There are also distinct post-injury time frames of induction for each family of heat shock protein, emphasizing differences in cellular functional requirements for each family of heat shock protein. Hsp27 was expressed immediately following injury and continued up to 20 days post-injury whereas Hsp72 was expressed immediately following injury and disappeared by 4 days post-injury, suggesting the latter contributes to processes involved in the initial repair of injured cells. This review discusses heat shock protein induction patterns in both in vivo and in vitro cerebellar injury models and provides suggestions as to the functional role of heat shock proteins in the injured cerebellum.

Injury to retinal ganglion cells induces expression of the small heat shock protein Hsp27 in the rat visual system

Optic nerve transection results in apoptotic cell death of most adult rat retinal ganglion cells that begins at 4 days and leaves few surviving neurons at 14 days post-injury [Berkelaar et al. (1994) J. Neurosci. 14, 4368-4374]. The small heat shock protein Hsp27 has recently been shown to play a role in sensory neuron survival following peripheral nerve axotomy [Lewis et al. (1999) J. Neurosci. 19, 8945-8953]. To investigate the role of Hsp27 in injured CNS sensory neurons, we have studied the induction and cell-specific expression of Hsp27 in rat retinal ganglion cells 1-28 days after optic nerve transection. Immunohistochemical results indicate that Hsp27 is not present at detectable levels in the ganglion cell layer of control (uninjured) or sham-operated control rats. In contrast, Hsp27 is detected in retinal ganglion cells from 4 to 28 days following axotomy. Furthermore, the percentage of surviving retinal ganglion cells that are Hsp27-positive increased over the same time period. Hsp27 is also detected in glial fibrillary acidic protein-positive astrocytes in the optic layer of the superior colliculus from 4 to 28 days after optic nerve transection. These experiments demonstrate that transection of the optic nerve results in the expression of Hsp27 in three distinct regions of the rat visual system: sensory retinal ganglion cells in the eye, glial cells of the optic tract, and astrocytes in the optic layer of the superior colliculus. Hsp27 may be associated with enhanced survival of a subset of retinal ganglion cells, providing evidence of a protective role for Hsp27 in CNS neuronal injury.

Effects of global cerebral ischemia and preconditioning on heat shock protein 27 immunocontent and phosphorylation in rat hippocampus

Global cerebral ischemia, with or without preconditioning, leads to an increase in heat shock protein 27 (HSP27) immunocontent and alterations in HSP27 phosphorylation in CA1 and dentate gyrus areas of the hippocampus. We studied different times of reperfusion (1, 4, 7, 14, 21 and 30 days) using 2 min, 10 min or 2+10 min of ischemia. The results showed an increase in HSP27 immunocontent of about 300% after 10 min of ischemia in CA1 and dentate gyrus. CA1, a hippocampal vulnerable area, showed an increase in HSP27 phosphorylation, parallel with immunocontent. In dentate gyrus, a resistant area, the increase in HSP phosphorylation was lower than immunocontent. After preconditioned ischemia (2+10 min), when CA1 neurons are protected to a lethal, 10 min insult, we observed an increase in HSP immunocontent and a decrease in phosphorylation in both regions of the hippocampus, suggesting that, when there is no neuronal death, HSP27 in a vulnerable area responds similarly to the resistant area.When dephosphorylated, HSP27 acts as a chaperone, protecting other proteins from denaturation. As it is markedly expressed in astrocytes, we suggest that HSP27 could be protecting hippocampal astrocytes, which could then be helping neurons to resist to the insult, maintaining tissue normal homeostasis.

Heat shock protein 27 shows a distinctive widespread spatial and temporal pattern of induction in CNS glial and neuronal cells compared to heat shock protein 70 and caspase 3 following kainate administration

Kainate-induced status epilepticus is associated with both apoptotic and necrotic cell death and induction of heat shock proteins (HSPs) in hippocampal and cortical regions of the rodent brain. In the present study we have examined the temporal, spatial and cellular expression patterns of mRNAs for the highly inducible HSPs, HSP70 and HSP27, together with the apoptotic marker, caspase 3 (CPP32) in rat brain after systemic administration of kainate. HSP70 mRNA was transiently induced in the forebrain by kainate, principally in the CA1, CA3 and hilar cells of the hippocampal formation, in piriform cortex and discrete thalamic nuclei. Maximal expression was seen at 8 h after kainate which then declined to background levels by 7 days. Labelling was predominantly neuronal. In contrast, HSP27 mRNA expression was more widespread. Intense labelling was observed in CA1, CA3 and the hilar region at 8 h after kainate but the expression profile for HSP27 mRNA expanded considerably with intense signals seen in corpus callosum, cortex and thalamus at 24 h post kainate. Emulsion autoradiographs indicated a predominantly glial localisation for HSP27 mRNA. In the hilus, a distinct subpopulation of interneurones were found to express HSP27 mRNA. CPP32 mRNA was upregulated in CA1, CA3 and hilus of the hippocampal formation and in piriform cortex. CPP32 mRNA expression was more restricted and similar in distribution to HSP70 mRNA being localised to neurones. The present study demonstrates the unique early expression of HSP27 mRNA by glial cells and distinct populations of neurones which extends beyond those in which HSP70 and CPP32 induction occurs with subsequent cell loss.