Localization of the heat-shock protein Hsp70 to the synapse following hyperthermic stress in the brain

Localized molecular chaperone synthesis maintains neuronal dendrite proteostasis

Proteostasis is maintained through regulated protein synthesis and degradation and chaperone-assisted protein folding. However, this is challenging in neuronal projections because of their polarized morphology and constant synaptic proteome remodeling. Using high-resolution fluorescence microscopy, we discovered that hippocampal and spinal cord motor neurons of mouse and human origin localize a subset of chaperone mRNAs to their dendrites and use microtubule-based transport to increase this asymmetric localization following proteotoxic stress. The most abundant dendritic chaperone mRNA encodes a constitutive heat shock protein 70 family member (HSPA8). Proteotoxic stress also enhanced HSPA8 mRNA translation efficiency in dendrites. Stress-mediated HSPA8 mRNA localization to the dendrites was impaired by depleting fused in sarcoma-an amyotrophic lateral sclerosis-related protein-in cultured spinal cord mouse motor neurons or by expressing a pathogenic variant of heterogenous nuclear ribonucleoprotein A2/B1 in neurons derived from human induced pluripotent stem cells. These results reveal a crucial and unexpected neuronal stress response in which RNA-binding proteins increase the dendritic localization of HSPA8 mRNA to maintain proteostasis and prevent neurodegeneration.

Cell-Permeable HSP70 Protects Neurons and Astrocytes Against Cell Death in the Rotenone-Induced and Familial Models of Parkinson's Disease

Heat shock protein 70 (HSP70) is activated under stress response. Its involvement in cell protection, including energy metabolism and quality control makes it a promising pharmacological target. A strategy to increase HSP70 levels inside the cells is the application of recombinant HSP70. However, cell permeability and functionality of these exogenously applied proteins inside the cells is still disputable. Here, using fluorescence- labeled HSP70, we have studied permeability and distribution of HSP70 inside primary neurons and astrocytes, and how exogenous HSP70 changes mitochondrial metabolism and mitophagy. We have found that exogenous recombinant HSP70 can penetrate the neurons and astrocytes and distributes in mitochondria, lysosomes and in lesser degree in the endoplasmic reticulum. HSP70 increases mitochondrial membrane potential in control neurons and astrocytes, and in fibroblasts of patients with familial Parkinson´s disease (PD) with PINK1 and LRRK2 mutations. Increased mitochondrial membrane potential was associated with higher mitochondrial ROS production and activation of mitophagy. Importantly, preincubation of the cells with HSP70 protected neurons and astrocytes against cell death in a toxic model of PD induced by rotenone, and in the PINK1 and LRRK2 PD human fibroblasts. Thus, exogenous recombinant HSP70 is cell permeable, and acts as endogenous HSP70 protecting cells in the case of toxic model and familial forms of Parkinson's Disease.

Induction of Heat Shock Proteins 27, 60, 70, and 90 in the Cerebellum of Rats After Hyperthermia During Postnatal Development

Heat shock proteins (HSPs) are induced in response to stressful stimuli and play an important role in cell repair and protection. This study, using immunohistochemistry, aimed to determine whether HSPs are induced in the cerebellum of rats subjected to hyperthermia during postnatal development (PND). The results showed that unlike HSP27 and HSP70, HSP60 and HSP90 were constitutively expressed in the cerebellum of rats. However, hyperthermia induced HSP27 in the white matter (WM) and HSP70 in the Bergmann glial cells, the internal granule layer (IGL), and the WM. In the WM, HSP27 induction was only observed on days PND20, PND25, and PND30, and HSP27 expression was higher on day PND30 compared with days PND20 and PND25 (p < 0.001). In the Bergmann glial cells, HSP70 induction was only observed on days PND5, PND10, and PND20, and HSP70 expression was greater on days PND5 and PND10 compared with day PND20 (p < 0.001). In the IGL and the WM, HSP70 expression was higher on days PND20, PND25, and PND30 compared with days PND5 and PND10 (p < 0.001). These findings indicate that unlike HSP60 and HSP90, HSP27 and HSP70 have different expression patterns in the cerebellum of rats after hyperthermia during PND.

Impact of histone deacetylase inhibition and arimoclomol on heat shock protein expression and disease biomarkers in primary culture models of familial ALS

Protein misfolding and mislocalization are common themes in neurodegenerative disorders, including motor neuron disease, and amyotrophic lateral sclerosis (ALS). Maintaining proteostasis is a crosscutting therapeutic target, including the upregulation of heat shock proteins (HSP) to increase chaperoning capacity. Motor neurons have a high threshold for upregulating stress-inducible HSPA1A, but constitutively express high levels of HSPA8. This study compared the expression of these HSPs in cultured motor neurons expressing three variants linked to familial ALS: TAR DNA binding protein 43 kDa (TDP-43)G348C, fused in sarcoma (FUS)R521G, or superoxide dismutase I (SOD1)G93A. All variants were poor inducers of Hspa1a, and reduced levels of Hspa8 mRNA and protein, indicating multiple compromises in chaperoning capacity. To promote HSP expression, cultures were treated with the putative HSP coinducer, arimoclomol, and class I histone deacetylase inhibitors, to promote active chromatin for transcription, and with the combination. Treatments had variable, often different effects on the expression of Hspa1a and Hspa8, depending on the ALS variant expressed, mRNA distribution (somata and dendrites), and biomarker of toxicity measured (histone acetylation, maintaining nuclear TDP-43 and the neuronal Brm/Brg-associated factor chromatin remodeling complex component Brg1, mitochondrial transport, FUS aggregation). Overall, histone deacetylase inhibition alone was effective on more measures than arimoclomol. As in the FUS model, arimoclomol failed to induce HSPA1A or preserve Hspa8 mRNA in the TDP-43 model, despite preserving nuclear TDP-43 and Brg1, indicating neuroprotective properties other than HSP induction. The data speak to the complexity of drug mechanisms against multiple biomarkers of ALS pathogenesis, as well as to the importance of HSPA8 for neuronal proteostasis in both somata and dendrites.

Localized molecular chaperone synthesis maintains neuronal dendrite proteostasis

Proteostasis is maintained through regulated protein synthesis and degradation and chaperone-assisted protein folding. However, this is challenging in neuronal projections because of their polarized morphology and constant synaptic proteome remodeling. Using high-resolution fluorescence microscopy, we discovered that neurons localize a subset of chaperone mRNAs to their dendrites and use microtubule-based transport to increase this asymmetric localization following proteotoxic stress. The most abundant dendritic chaperone mRNA encodes a constitutive heat shock protein 70 family member (HSPA8). Proteotoxic stress also enhanced HSPA8 mRNA translation efficiency in dendrites. Stress-mediated HSPA8 mRNA localization to the dendrites was impaired by depleting fused in sarcoma-an amyotrophic lateral sclerosis-related protein-in cultured mouse motor neurons and expressing a pathogenic variant of heterogenous nuclear ribonucleoprotein A2/B1 in neurons derived from human induced pluripotent stem cells. These results reveal a crucial and unexpected neuronal stress response in which RNA-binding proteins increase the dendritic localization of HSPA8 mRNA to maintain proteostasis and prevent neurodegeneration.

Heat exposure intervention, anxiety level, and multi-omic profiles: A randomized crossover study

BACKGROUND

Climate change has led to the frequent occurrence of high-temperature weather, which has various adverse effects on health, ranging from blood metabolism to systemic organ function. In particular, the sequelae of heat stress injury in most people are related to the nervous system. However, the mechanisms between heat stress and mental health conditions, especially heat stress and anxiety, remain unclear.

OBJECTIVE

We attempted to elucidate the effect of heat exposure intervention on anxiety levels in the population and its mechanism.

METHODS

We first carried out a randomized controlled trial in 20 college students in Beijing, China, to observe the results of the effects of heat exposure intervention on human anxiety. Then, we collected blood samples before and after heat exposure experiment and used metabolomic and transcriptomic approaches to quantify serum metabolites and ELISA measurements to explore the underlying mechanisms.

RESULTS

We found that even 1.5-hour heat exposure intervention significantly increased anxiety levels. Heat stress-induced anxiety was mediated by the activation of the HPA axis, inflammation, oxidative stress, and subsequently unbalanced neurotransmitters. Metabolites such as BDNF, GABA, and glucocorticoids released by the adrenal glands are biomarkers of heat stress-induced anxiety.

CONCLUSIONS

We have demonstrated a causal link between heat stress and anxiety, explored possible biological pathway between heat stress and anxiety. Heat stress can cause the activation of the HPA axis and lead to changes in the body's metabolism, resulting in a series of changes such as inflammation and oxidative stress, leading to anxiety. This study reveals hidden health cost of climate change that has been underexplored, and also reminds us the importance of immediate climate actions.

Temperature-dependent structural plasticity of hippocampal synapses

The function of the central nervous system (CNS) is strongly affected by temperature. However, the underlying processes remain poorly understood. Here, we show that hypothermia and hyperthermia trigger bidirectional re-organization of presynaptic architecture in hippocampal neurons, resulting in synaptic strengthening, and weakening, respectively. Furthermore, hypothermia remodels inhibitory postsynaptic scaffold into enlarged, sparse synapses enriched in GABAA receptors. This process does not require protein translation, and instead is regulated by actin dynamics. Induction of hypothermia in vivo enhances inhibitory synapses in the hippocampus, but not in the cortex. This is confirmed by the proteomic analysis of cortical synapses, which reveals few temperature-dependent changes in synaptic content. Our results reveal a region-specific form of environmental synaptic plasticity with a mechanism distinct from the classic temperature shock response, which may underlie functional response of CNS to temperature.

Proteomics on the role of muscone in the "consciousness-restoring resuscitation" effect of musk on ischemic stroke

ETHNOPHARMACOLOGICAL RELEVANCE

Musk is a representative drug of aroma-relieving traditional Chinese medicine, and it is a commonly used traditional Chinese medicine for the treatment of ischemic stroke. Muscone is the core medicinal component of musk.

AIM OF THE STUDY

We sought to identify the target of muscone in the treatment of ischemic stroke using network pharmacology, an animal model of ischemic stroke, and differential proteomics.

MATERIALS AND METHODS

The drug targets of muscone in the treatment of ischemic stroke were predicted and analyzed using information derived from sources such as the Traditional Chinese Medicine Systems Pharmacology database and Swiss Target Prediction tool. The animal model of focal cerebral ischemia was established by suture-based occlusion of the middle cerebral artery of rats. The rats were divided into six groups: sham-operated control, model, musk, muscone1, muscone2, and muscone3. Neurological deficit scores were calculated after intragastric administration of musk or muscone. The microcirculation blood flow of the pia mater was detected using a laser speckle blood flow meter. The cerebral infarction rate was detected by 2,3,5-triphenyltetrazolium chloride staining. The necrosis rate of the cerebral cortex and the hippocampal neurons was detected by hematoxylin and eosin staining. Blood-brain barrier damage was detected by the Evans blue method. Quantitative proteomics analysis in the sham-operated control, model, and muscone groups was performed using tandem-mass-tags. Considering fold changes exceeding 1.2 as differential protein expression, the quantitative values were compared among groups by analysis of variance. Furthermore, a protein-protein interaction network was constructed, and differentially expressed proteins were analyzed by gene ontology (GO), and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis.

RESULTS

Network pharmacology identified 339 targets for the intersection of 17 components of musk and cerebral ischemia-reperfusion injury. The GO and KEGG enrichment items mainly identified regulation of neuronal synaptic structure and transfer function, synaptic neurotransmitters, and receptor activity. Zoopery showed that the model group had a higher behavioral score, cerebral infarction rate, cortical and hippocampal neuron death rate, Evans blue exudation in the brain, and bilateral pia mater microcirculation blood flow differences than the sham-operated control group (P <0.01). Compared with the model group, the behavioral score, infarction rate, hippocampal neuronal mortality, and Evans blue content decreased significantly in the musk, muscone2, and muscone3 groups (P <0.05). Proteomic analysis showed that 160 genes were differentially expressed among the sham-operated control, model, and muscone groups. GO items with high enrichment included neuronal synapses, postsynaptic signal transduction, etc. KEGG items with high enrichment included cholinergic synapses, calcium signaling pathway, dopaminergic synapses, etc. Protein interaction analysis revealed that the top three protein pairs were Ndufa10/Ndufa6, Kcna2/Kcnab2, and Gsk3b/Traf6.

CONCLUSIONS

Muscone can reduce neuronal necrosis, protect the blood-brain barrier, and improve the neurological damage caused by cerebral ischemia via molecular mechanisms mainly involving the regulation of neuronal synaptic connections. Muscone is an important active component responsible for the "consciousness-restoring resuscitation" effect of musk on ischemic stroke.

Transcriptomic and Proteomic Analysis of CRISPR/Cas9-Mediated ARC-Knockout HEK293 Cells

Arc/Arg3.1 (activity-regulated cytoskeletal-associated protein (ARC)) is a critical regulator of long-term synaptic plasticity and is involved in the pathophysiology of schizophrenia. The functions and mechanisms of human ARC action are poorly understood and worthy of further investigation. To investigate the function of the ARC gene in vitro, we generated an ARC-knockout (KO) HEK293 cell line via CRISPR/Cas9-mediated gene editing and conducted RNA sequencing and label-free LC-MS/MS analysis to identify the differentially expressed genes and proteins in isogenic ARC-KO HEK293 cells. Furthermore, we used bioluminescence resonance energy transfer (BRET) assays to detect interactions between the ARC protein and differentially expressed proteins. Genetic deletion of ARC disturbed multiple genes involved in the extracellular matrix and synaptic membrane. Seven proteins (HSPA1A, ENO1, VCP, HMGCS1, ALDH1B1, FSCN1, and HINT2) were found to be differentially expressed between ARC-KO cells and ARC wild-type cells. BRET assay results showed that ARC interacted with PSD95 and HSPA1A. Overall, we found that ARC regulates the differential expression of genes involved in the extracellular matrix, synaptic membrane, and heat shock protein family. The transcriptomic and proteomic profiles of ARC-KO HEK293 cells presented here provide new evidence for the mechanisms underlying the effects of ARC and molecular pathways involved in schizophrenia pathophysiology.

Involvement of molecular chaperone in protein-misfolding brain diseases

Protein misfolding causes aggregation and build-up in a variety of brain diseases. There are numeral molecules that are linked with the protein homeostasis mechanism. Molecular chaperones are one of such molecules that are responsible for protection against protein misfolded and aggregation-induced neurotoxicity. Many studies have explored the participation of molecular chaperones in Parkinson's disease, Alzheimer's disease, Amyotrophic lateral sclerosis, and Huntington's diseases. In this review, we highlighted the constructive role of molecular chaperones in neurological diseases characterized by protein misfolding and aggregation and their capability to control aberrant protein interactions at an early stage thus successfully suppressing pathogenic cascades. A comprehensive understanding of the protein misfolding associated with brain diseases and the molecular basis of involvement of chaperone against aggregation-induced cellular stress might lead to the progress of new therapeutic intrusion-related to protein misfolding and aggregation.

An association study of the HSPA8 gene polymorphisms with schizophrenia in a Polish population

Heat shock cognate 70 (HSC70/HSPA8) is considered to be a promising candidate gene for schizophrenia (SCZ) due to its many essential functions and potential neuroprotective properties in the CNS (e.g., HSC70 is involved in the turnover of the synaptic proteins, synaptic vesicle recycling, and neurotransmitter homeostasis). An alteration in the expression of HSPA8 in SCZ has been reported. This implies that the genetic variants of HSPA8 might contribute to schizophrenia pathogenesis. The present study attempted to determine whether HSPA8 polymorphisms are associated with a susceptibility to schizophrenia or whether they have an impact on the clinical parameters of the disease in a Polish population. A total of 1066 participants (406 patients and 660 controls) were recruited for the study. Five SNPs of the HSPA8 gene (rs2236659, rs1136141, rs10892958, rs1461496, and rs4936770) were genotyped using TaqMan assays. There were no differences in the allele or genotype distribution in any of the SNPs in the entire sample. We also did not find any HSPA8 haplotype-specific associations with SCZ. A gender stratification analysis revealed that an increasing risk of schizophrenia was associated with the rs1461496 genotype in females (OR: 1.68, p < 0.05) in the recessive model. In addition, we found novel associations between HSPA8 SNPs (rs1136141, rs1461496, and rs10892958) and the severity of the psychiatric symptoms as measured by the PANSS. Further studies with larger samples from various ethnic groups are necessary to confirm our findings. Furthermore, studies that explore the functional contribution of the HSPA8 variants to schizophrenia pathogenesis are also needed.

Acute Ethanol Exposure during Synaptogenesis Rapidly Alters Medium Spiny Neuron Morphology and Synaptic Protein Expression in the Dorsal Striatum

Fetal alcohol spectrum disorders are caused by the disruption of normal brain development in utero. The severity and range of symptoms is dictated by both the dosage and timing of ethanol administration, and the resulting developmental processes that are impacted. In order to investigate the effects of an acute, high-dose intoxication event on the development of medium spiny neurons (MSNs) in the striatum, mice were injected with ethanol on P6, and neuronal morphology was assessed after 24 h, or at 1 month or 5 months of age. Data indicate an immediate increase in MSN dendritic length and branching, a rapid decrease in spine number, and increased levels of the synaptic protein PSD-95 as a consequence of this neonatal exposure to ethanol, but these differences do not persist into adulthood. These results demonstrate a rapid neuronal response to ethanol exposure and characterize the dynamic nature of neuronal architecture in the MSNs. Although differences in neuronal branching and spine density induced by ethanol resolve with time, early changes in the caudate/putamen region have a potential impact on the execution of complex motor skills, as well as aspects of long-term learning and addictive behavior.

Heat Shock Factor 1 Directly Regulates Postsynaptic Scaffolding PSD-95 in Aging and Huntington's Disease and Influences Striatal Synaptic Density

PSD-95 (Dlg4) is an ionotropic glutamate receptor scaffolding protein essential in synapse stability and neurotransmission. PSD-95 levels are reduced during aging and in neurodegenerative diseases like Huntington's disease (HD), and it is believed to contribute to synaptic dysfunction and behavioral deficits. However, the mechanism responsible for PSD-95 dysregulation under these conditions is unknown. The Heat Shock transcription Factor 1 (HSF1), canonically known for its role in protein homeostasis, is also depleted in both aging and HD. Synaptic protein levels, including PSD-95, are influenced by alterations in HSF1 levels and activity, but the direct regulatory relationship between PSD-95 and HSF1 has yet to be determined. Here, we showed that HSF1 chronic or acute reduction in cell lines and mice decreased PSD-95 expression. Furthermore, Hsf1(+/-) mice had reduced PSD-95 synaptic puncta that paralleled a loss in thalamo-striatal excitatory synapses, an important circuit disrupted early in HD. We demonstrated that HSF1 binds to regulatory elements present in the PSD-95 gene and directly regulates PSD-95 expression. HSF1 DNA-binding on the PSD-95 gene was disrupted in an age-dependent manner in WT mice and worsened in HD cells and mice, leading to reduced PSD-95 levels. These results demonstrate a direct role of HSF1 in synaptic gene regulation that has important implications in synapse maintenance in basal and pathological conditions.

Sericin Alleviates Thermal Stress Induced Anxiety-Like Behavior and Cognitive Impairment Through Regulation of Oxidative Stress, Apoptosis, and Heat-Shock Protein-70 in the Hippocampus

Exposure to heat stress (HS) has adverse effects on brain function, leading to anxiety-like behavior and memory impairment. Sericin is a silk derived protein with various neurobiological activities. The present study has investigated the effects of sericin on anxiety and cognitive impairments, in HS-received mice. The adult male mice were exposed to HS (43 ºC, 15 min once a day for 14 days) and simultaneously treated with 100, 150, and 200 mg/kg/day of sericin through oral gavage. Elevated plus-maze and Lashley III Maze tests were used to evaluate anxiety and learning and memory, respectively. The hippocampal BAX, BCL-2, caspase3, caspase9 and heat-shock protein-70 (HSP-70) were evaluated by western blotting and oxidative stress markers including malondialdehyde (MDA), total antioxidant capacity (TAC), super oxide dismutase (SOD) as well as glutathione peroxidase (GPx) were evaluated by spectroscopy method. The serum was collected for the analysis of the corticosterone levels. Treatment with sericin in higher doses reversed anxiety-like behavior and cognitive deficit induced by HS. Moreover, heat exposure increased serum corticosterone, hippocampal MDA, apoptotic proteins and HSP-70 levels. Sericin administration decreased serum corticosterone and enhanced hippocampal antioxidant defense and attenuated apoptosis and HSP-70 levels. The results show that the protective effects of sericin against HS-mediated cognitive dysfunction and anxiety-like behavior is possibly through suppressing HSP-70, oxidative stress and apoptosis.

Role of a Heat Shock Transcription Factor and the Major Heat Shock Protein Hsp70 in Memory Formation and Neuroprotection

Heat shock proteins (Hsps) represent the most evolutionarily ancient, conserved, and universal system for protecting cells and the whole body from various types of stress. Among Hsps, the group of proteins with a molecular weight of 70 kDa (Hsp70) plays a particularly important role. These proteins are molecular chaperones that restore the native conformation of partially denatured proteins after exposure to proteotoxic forms of stress and are critical for the folding and intracellular trafficking of de novo synthesized proteins under normal conditions. Hsp70s are expressed at high levels in the central nervous system (CNS) of various animals and protect neurons from various types of stress, including heat shock, hypoxia, and toxins. Numerous molecular and behavioral studies have indicated that Hsp70s expressed in the CNS are important for memory formation. These proteins contribute to the folding and transport of synaptic proteins, modulate signaling cascades associated with synaptic activation, and participate in mechanisms of neurotransmitter release. In addition, HSF1, a transcription factor that is activated under stress conditions and mediates Hsps transcription, is also involved in the transcription of genes encoding many synaptic proteins, whose levels are increased in neurons under stress and during memory formation. Thus, stress activates the molecular mechanisms of memory formation, thereby allowing animals to better remember and later avoid potentially dangerous stimuli. Finally, Hsp70 has significant protective potential in neurodegenerative diseases. Increasing the level of endogenous Hsp70 synthesis or injecting exogenous Hsp70 reduces neurodegeneration, stimulates neurogenesis, and restores memory in animal models of ischemia and Alzheimer’s disease. These findings allow us to consider recombinant Hsp70 and/or Hsp70 pharmacological inducers as potential drugs for use in the treatment of ischemic injury and neurodegenerative disorders.

Association of HSPA1B Polymorphisms with Paranoid Schizophrenia in a Polish Population

This study aimed to find the potential association between HSPA1B polymorphisms and risk of paranoid schizophrenia, clinical variables of the disease, and suicidal behavior. A total of 901 unrelated Polish subjects of Caucasian origin (377 schizophrenia patients and 524 controls) were recruited. Four single-nucleotide polymorphisms (SNP) were genotyped using PCR–RFLP (rs539689, rs9281590) and TaqMan assays (rs263979, rs6547452). A strong tendency towards statistical significance (p = 0.051) was observed in rs539689 allele distribution between patients and controls in overall study subjects. After stratification according to gender, we found that rs539689 was significantly associated with schizophrenia in males, but not in females. The minor allele C had a protective effect in males [OR 0.73 (95% CI 0.61–0.88, p < 0.05)]. In addition, two SNPs (rs539689, rs9281590) were significantly associated with PANSS scores. Another important finding was a strong significant association between the HSPA1B rs539689 polymorphism and attempted suicide in schizophrenic patients. The C/C genotype and C allele were protective against suicidal behavior in entire sample (p < 0.001), in males (p < 001), and in females (p < 0.05), although associations were weaker than in males. Our findings support that HSPA1B gene may be involved in susceptibility to schizophrenia and clinical presentation of the disease in a sex-dependent manner, and may play a role in suicidal behavior in the Polish population of schizophrenic patients. Further independent analyses in different populations should be performed to clarify the role of HSPA1B in the pathogenesis of schizophrenia.

Rosa canina L. methanolic extract prevents heat stress-induced memory dysfunction in rats

NEW FINDINGS

What is the central question of this study? Heat stress has harmful effects on the brain structure and synaptic density via induction of oxidative stress and neuroinflammation, which result in neuronal damage in the hippocampus and thereby cognitive impairments. In this study, we investigate the effect of Rosa canina treatment on cognitive function in heat stress-exposed rats and its underlying mechanisms. What is the main finding and its importance? We show that R. canina improves cognitive deficits induced by heat stress by attenuation of oxidative stress and neuroinflammation and by upregulation of synaptic proteins in the hippocampus.

ABSTRACT

The aim of the study was to evaluate the effects of aqueous methanolic extract of Rosa canina (RC) dried fruits on oxidative stress, inflammation, synaptic degeneration and memory dysfunction induced by heat stress (HS) in rats. Sixty adult male Wistar rats were randomly divided into five groups as follows: the control group received normal saline (NS); the HS group was exposed to heat stress (43°C) for 15 min once a day for 2 weeks; and HS+R groups were exposed to heat stress and received one of three doses (250, 500 or 1000 mg kg^-1 ) of RC methanolic extract for 2 weeks. A passive avoidance test and a Y-maze test were performed to assess learning and memory. The levels of reactive oxygen species were assessed. The serum cortisol concentration and hippocampal total antioxidant capacity, superoxide dismutase and glutathione peroxidase were also detected using spectrophotometry. The protein expressions of c-Fos, heat-shock protein-70, tumour necrosis factor-α, growth-associated protein 43, post-synaptic density-95 and synaptophysin were evaluated in the hippocampal tissue. The results showed that RC significantly improved cognitive dysfunction induced by HS, which was accompanied by downregulation of tumour necrosis factor-α and upregulation of growth-associated protein 43 and synaptophysin proteins in the hippocampus of HS-exposed rats. Furthermore, RC significantly attenuated serum cortisol concentrations and upregulated heat shock protein-70 and c-Fos in the hippocampus. In addition, the administration of RC attenuated reactive oxygen species levels and enhanced antioxidant defense in the hippocampus. These findings indicate that RC attenuated the deleterious effect of HS on cognition through its antioxidant properties and by enhancing synaptic function and plasticity.

Association Studies of HSPA1A and HSPA1L Gene Polymorphisms With Schizophrenia

BACKGROUND

Schizophrenia is a severe psychiatric disorder with a strong genetic component. The HSP70 chaperones are particularly interesting in terms of schizophrenia, especially with regard to neurodevelopmental hypothesis, because they are critical regulators in normal neural physiological function as well as in cell stress responses.

AIM OF THE STUDY

The present study aimed to determine whether genetic variants in the HSPA1A (rs1008438, rs562047) and HSPA1L (rs2075800) genes are associated with the risk of paranoid schizophrenia and the clinical presentation of the disease.

METHODS

A total of 1080 unrelated Polish subjects of Caucasian origin (401 schizophrenia cases and 679 healthy controls) were recruited. Three single nucleotide polymorphisms (SNP) were genotyped using PCR-RFLP (rs562047) or TaqMan (rs1008438, rs2075800) assays. All analyses were conducted for the full sample and within subgroups stratified by gender.

RESULTS

There were no statistically significant differences in genotype or allele distributions of all polymorphisms tested between the schizophrenia and control groups. We also failed to find any schizophrenia predisposing haplotype in the whole group. A sex-stratified analysis revealed haplotypic association with paranoid schizophrenia in men, albeit the risk effect was contributed only by a rare haplotypes. More importantly, rs562047 variant was significantly associated with PANSS total and PANSS negative scores in schizophrenia.

CONCLUSIONS

Our results support previously reported associations between HSPA1A and HSPA1B SNPs and schizophrenia symptomatology. Further population-based prospective studies with larger sample sizes from different ethnic groups should be performed to clarify the role of different HSP70 genes in the pathogenesis of schizophrenia.

Spinal motor neuron protein supersaturation patterns are associated with inclusion body formation in ALS

Amyotrophic lateral sclerosis (ALS) is a heterogeneous degenerative motor neuron disease linked to numerous genetic mutations in apparently unrelated proteins. These proteins, including SOD1, TDP-43, and FUS, are highly aggregation-prone and form a variety of intracellular inclusion bodies that are characteristic of different neuropathological subtypes of the disease. Contained within these inclusions are a variety of proteins that do not share obvious characteristics other than coaggregation. However, recent evidence from other neurodegenerative disorders suggests that disease-affected biochemical pathways can be characterized by the presence of proteins that are supersaturated, with cellular concentrations significantly greater than their solubilities. Here, we show that the proteins that form inclusions of mutant SOD1, TDP-43, and FUS are not merely a subset of the native interaction partners of these three proteins, which are themselves supersaturated. To explain the presence of coaggregating proteins in inclusions in the brain and spinal cord, we observe that they have an average supersaturation even greater than the average supersaturation of the native interaction partners in motor neurons, but not when scores are generated from an average of other human tissues. These results suggest that inclusion bodies in various forms of ALS result from a set of proteins that are metastable in motor neurons, and thus prone to aggregation upon a disease-related progressive collapse of protein homeostasis in this specific setting.

Targeting therapy-resistant cancer stem cells by hyperthermia

Eradication of all malignant cells is the ultimate but challenging goal of anti-cancer treatment; most traditional clinically-available approaches fail because there are cells in a tumour that either escape therapy or become therapy-resistant. A subpopulation of cancer cells, the cancer stem cells (CSCs), is considered to be of particular significance for tumour initiation, progression and metastasis. CSCs are considered in particular to be therapy-resistant and may drive disease recurrence, which positions CSCs in the focus of anti-cancer research, but successful CSC-targeting therapies are limited. Here, we argue that hyperthermia - a therapeutic approach based on local heating of a tumour - is potentially beneficial for targeting CSCs in solid tumours. First, hyperthermia has been described to target cells in hypoxic and nutrient-deprived tumour areas where CSCs reside and ionising radiation and chemotherapy are least effective. Second, hyperthermia can modify factors that are essential for tumour survival and growth, such as the microenvironment, immune responses, vascularisation and oxygen supply. Third, hyperthermia targets multiple DNA repair pathways, which are generally upregulated in CSCs and protect them from DNA-damaging agents. Addition of hyperthermia to the therapeutic armamentarium of oncologists may thus be a promising strategy to eliminate therapy-escaping and -resistant CSCs.

Induction of heat shock proteins in differentiated human neuronal cells following co-application of celastrol and arimoclomol

Few effective therapies exist for the treatment of neurodegenerative diseases that have been characterized as protein misfolding disorders. Upregulation of heat shock proteins (Hsps) mitigates against the accumulation of misfolded, aggregation-prone proteins and synaptic dysfunction, which is recognized as an early event in neurodegenerative diseases. Enhanced induction of a set of Hsps in differentiated human SH-SY5Y neuronal cells was observed following co-application of celastrol and arimoclomol, compared to their individual application. The dosages employed did not affect cell viability or neuronal process morphology. The induced Hsps included the little studied HSPA6 (Hsp70B'), a potentially neuroprotective protein that is present in the human genome but not in rat and mouse and hence is missing in current animal models of neurodegenerative disease. Enhanced induction of HSPA1A (Hsp70-1), DNAJB1 (Hsp40), HO-1 (Hsp32), and HSPB1 (Hsp27) was also observed. Celastrol activates heat shock transcription factor 1 (HSF1), the master regulator of Hsp gene transcription, and also exhibits potent anti-inflammatory and anti-oxidant activities. Arimoclomol is a co-activator that prolongs the binding of activated HSF1 to heat shock elements (HSEs) in the promoter regions of inducible Hsp genes. Elevated Hsp levels peaked at 10 to 12 h for HSPA6, HSPA1A, DNAJB1, and HO-1 and at 24 h for HSPB1. Co-application of celastrol and arimoclomol induced higher Hsp levels compared to heat shock paired with arimoclomol. The co-application strategy of celastrol and arimoclomol targets multiple neurodegenerative disease-associated pathologies including protein misfolding and protein aggregation, inflammatory and oxidative stress, and synaptic dysfunction.

Focused cerebellar laser light induced hyperthermia improves symptoms and pathology of polyglutamine disease SCA1 in a mouse model

Spinocerebellar ataxia 1 (SCA1) results from pathologic glutamine expansion in the ataxin-1 protein (ATXN1). This misfolded ATXN1 causes severe Purkinje cell (PC) loss and cerebellar ataxia in both humans and mice with the SCA1 disease. The molecular chaperone heat-shock proteins (HSPs) are known to modulate polyglutamine protein aggregation and are neuroprotective. Since HSPs are induced under stress, we explored the effects of focused laser light induced hyperthermia (HT) on HSP-mediated protection against ATXN1 toxicity. We first tested the effects of HT in a cell culture model and found that HT induced Hsp70 and increased its localization to nuclear inclusions in HeLa cells expressing GFP-ATXN1[82Q]. HT treatment decreased ATXN1 aggregation by making GFP-ATXN1[82Q] inclusions smaller and more numerous compared to non-treated cells. Further, we tested our HT approach in vivo using a transgenic (Tg) mouse model of SCA1. We found that our laser method increased cerebellar temperature from 38 to 40 °C without causing any neuronal damage or inflammatory response. Interestingly, mild cerebellar HT stimulated the production of Hsp70 to a significant level. Furthermore, multiple exposure of focused cerebellar laser light induced HT to heterozygous SCA1 transgenic (Tg) mice significantly suppressed the SCA1 phenotype as compared to sham-treated control animals. Moreover, in treated SCA1 Tg mice, the levels of PC calcium signaling/buffering protein calbindin-D28k markedly increased followed by a reduction in PC neurodegenerative morphology. Taken together, our data suggest that laser light induced HT is a novel non-invasive approach to treat SCA1 and maybe other polyglutamine disorders.

Heat shock response and homeostatic plasticity

Heat shock response and homeostatic plasticity are mechanisms that afford functional stability to cells in the face of stress. Each mechanism has been investigated independently, but the link between the two has not been extensively explored. We explore this link. The heat shock response enables cells to adapt to stresses such as high temperature, metabolic stress and reduced oxygen levels. This mechanism results from the production of heat shock proteins (HSPs) which maintain normal cellular functions by counteracting the misfolding of cellular proteins. Homeostatic plasticity enables neurons and their target cells to maintain their activity levels around their respective set points in the face of stress or disturbances. This mechanism results from the recruitment of adaptations at synaptic inputs, or at voltage-gated ion channels. In this perspective, we argue that heat shock triggers homeostatic plasticity through the production of HSPs. We also suggest that homeostatic plasticity is a form of neuroprotection.

Localization of heat shock proteins in cerebral cortical cultures following induction by celastrol

Hsp70, Hsp32, and Hsp27 were induced by celastrol in rat cerebral cortical cultures at dosages that did not affect cell viability. Pronounced differences were observed in the cellular localization of these heat shock proteins in cell types of cerebral cortical cultures. Celastrol-induced Hsp70 localized to the cell body and cellular processes of neurons that were identified by neuron-specific βIII-tubulin. Hsp70 was not detected in adjacent GFAP-positive glial cells that demonstrated a strong signal for Hsp27 and Hsp32 in both glial cell bodies and cellular processes. Cells in the cerebral cortex region of the brain are selectively impacted during the progression of Alzheimer's disease which is a "protein misfolding disorder." Heat shock proteins provide a line of defense against misfolded, aggregation-prone proteins. Celastrol is a potential agent to counter this neurodegenerative disorder as recent evidence indicates that in vivo administration of celastrol in a transgenic model of Alzheimer's reduces an important neuropathological hallmark of this disease, namely, amyloid beta pathology that involves protein aggregation.

Heat shock protein 70 gene polymorphisms are associated with paranoid schizophrenia in the Polish population

HSP70 genes have been considered as promising schizophrenia candidate genes based on their protective role in the central nervous system under stress conditions. In this study, we analyzed the potential implication of HSPA1A +190G/C, HSPA1B +1267A/G, and HSPA1L +2437T/C polymorphisms in the susceptibility to paranoid schizophrenia in a homogenous Caucasian Polish population. In addition, we investigated the association of the polymorphisms with the clinical variables of the disease. Two hundred and three patients with paranoid schizophrenia and 243 healthy controls were enrolled in the study. Polymorphisms of HSPA1A, -1B, and -1L genes were genotyped using the PCR-RFLP technique. Analyses were conducted in entire groups and in subgroups that were stratified according to gender. There were significant differences in the genotype and allele frequencies of HSPA1A polymorphism between the patients and controls. The +190CC genotype and +190C allele were over-represented in the patients and significantly increased the risk for developing schizophrenia (OR = 3.45 and OR = 1.61, respectively). Interestingly, such a risk was higher for females with the +190CC genotype than for males with the +190CC genotype (OR = 5.78 vs. OR = 2.76). We also identified the CGT haplotype as a risk haplotype for schizophrenia and demonstrated the effects of HSPA1A and HSPA1B genotypes on the psychopathology and age of onset. Our study provided the first evidence that the HSPA1A polymorphism may potentially increase the risk of developing paranoid schizophrenia. Further independent analyses in different populations to evaluate the role of gender are needed to replicate these results.

Amyloid-β(25-35) induces a permanent phosphorylation of HSF-1, but a transitory and inflammation-independent overexpression of Hsp-70 in C6 astrocytoma cells

Two hallmarks of Alzheimer diseases are the continuous inflammatory process, and the brain deposit of Amyloid b (Aβ), a cytotoxic protein. The intracellular accumulation of Aβ(25-35) fractions, in the absence of Heat Shock proteins (Hsṕs), could be responsible for its cytotoxic activity. As, pro-inflammatory mediators and nitric oxide control the expression of Hsṕs, our aim was to investigate the effect of Aβ(25-35) on the concentration of IL-1β, TNF-α and nitrite levels, and their relation to pHSF-1, Hsp-60, -70 and -90 expressions, in the rat C6 astrocyte cells. Interleukin-specific ELISA kits, immunohistochemistry with monoclonal anti-Hsp and anti pHSF-1 antibodies, and histochemistry techniques, were used. Our results showed that Aβ25-35 treatment of C6 cells increased, significantly and consistently the concentration of IL-1β, TNF-α and nitrite 3 days after initiating treatment. The immunoreactivity of C6 cells to Hsp-70 reached its peak after 3 days of treatment followed by an abrupt decrease, as opposed to Hsp-60 and -90 expressions that showed an initial and progressive increase after 3 days of Aβ(25-35) treatment. pHSF-1 was identified throughout the experimental period. Nevertheless, progressive and sustained cell death was observed during all the treatment times and it was not caspase-3 dependent. Our results suggest that Hsp-70 temporary expression serves as a trigger to inhibit casapase-3 pathway and allow the expression of Hsp-60 and -90 in C6 astrocytoma cells stimulated with Aβ(25-35).

Interpreting Stress Responses during Routine Toxicity Studies

Stress often occurs during toxicity studies. The perception of sensory stimuli as stressful primarily results in catecholamine release and activation of the hypothalamic–pituitary–adrenal (HPA) axis to increase serum glucocorticoid concentrations. Downstream effects of these neuroendocrine signals may include decreased total body weights or body weight gain; food consumption and activity; altered organ weights (e.g., thymus, spleen, adrenal); lymphocyte depletion in thymus and spleen; altered circulating leukocyte counts (e.g., increased neutrophils with decreased lymphocytes and eosinophils); and altered reproductive functions. Typically, only some of these findings occur in a given study. Stress responses should be interpreted as secondary (indirect) rather than primary (direct) test article–related findings. Determining whether effects are the result of stress requires a weight-of-evidence approach. The evaluation and interpretation of routinely collected data (standard in-life, clinical pathology, and anatomic pathology endpoints) are appropriate and generally sufficient to assess whether or not changes are secondary to stress. The impact of possible stress-induced effects on data interpretation can partially be mitigated by toxicity study designs that use appropriate control groups (e.g., cohorts treated with vehicle and subjected to the same procedures as those dosed with test article), housing that minimizes isolation and offers environmental enrichment, and experimental procedures that minimize stress and sampling and analytical bias.

This article is a comprehensive overview of the biological aspects of the stress response, beginning with a Summary (Section 1) and an Introduction (Section 2) that describes the historical and conventional methods used to characterize acute and chronic stress responses. These sections are followed by reviews of the primary systems and parameters that regulate and/or are influenced by stress, with an emphasis on parameters evaluated in toxicity studies: In-life Procedures (Section 3), Nervous System (Section 4), Endocrine System (Section 5), Reproductive System (Section 6), Clinical Pathology (Section 7), and Immune System (Section 8). The paper concludes (Section 9) with a brief discussion on Minimizing Stress-Related Effects (9.1.), and a final section explaining why Parameters routinely measured are appropriate for assessing the role of stress in toxicology studies (9.2.).

Aestivation and hypoxia-related events share common silent neuron trafficking processes

Background

The availability of oxygen is a limiting factor for neuronal survival since low levels account not only for the impairment of physiological activities such as sleep-wake cycle, but above all for ischemic-like neurodegenerative disorders. In an attempt to improve our knowledge concerning the type of molecular mechanisms operating during stressful states like those of hypoxic conditions, attention was focused on eventual transcriptional alterations of some key AMPAergic silent neuronal receptor subtypes (GluR1 and GluR2) along with HSPs and HIF-1α during either a normoxic or a hypoxic aestivation of a typical aquatic aestivator, i.e. the lungfish (Protopterus annectens).

Results

The identification of partial nucleotide fragments codifying for both AMPA receptor subtypes in Protopterus annectens displayed a putative high degree of similarity to that of not only fish but also to those of amphibians, birds and mammals. qPCR and in situ hybridization supplied a very high (p < 0.001) reduction of GluR1 mRNA expression in diencephalic areas after 6 months of aerial normoxic aestivation (6mAE). Concomitantly, high (p < 0.01) levels of HSP70 mRNAs in hypothalamic, mesencephalic and cerebellar areas of both 6mAE and after 6 months of mud hypoxic aestivation (6mMUD) were detected together with evident apoptotic signals. Surprisingly, very high levels of GluR2 mRNAs were instead detected in thalamic along with mesencephalic areas after 6 days of normoxic (6dAE) and hypoxic (6dMUD) aestivation. Moreover, even short- and long-term hypoxic states featured high levels of HIF-1α and HSP27 transcripts in the different brain regions of the lungfish.

Conclusions

The distinct transcriptional variations of silent neurons expressing GluR1/2 and HSPs tend to corroborate these factors as determining elements for the physiological success of normoxic and hypoxic aestivation. A distinct switching among these AMPA receptor subtypes during aestivation highlights new potential adaptive strategies operating in key brain regions of the lungfish in relation to oxygen availability. This functional relationship might have therapeutic bearings for hypoxia-related dysfunctions, above all in view of recently identified silent neuron-dependent motor activity ameliorations in mammals.

Protein expression following heat shock in the nervous system of Locusta migratoria

There is a thermal range for the operation of neural circuits beyond which nervous system function is compromised. Locusta migratoria is native to the semiarid regions of the world and provides an excellent model for studying neural phenomena. In this organism previous exposure to sublethal high temperatures (heat shock, HS) can protect neuronal function against future hyperthermia but, unlike many organisms, the profound physiological adaptations are not accompanied by a robust increase of Hsp70 transcript or protein in the nervous system. We compared Hsp70 increase following HS in the tissues of isolated and gregarious locusts to investigate the effect of population density. We also localized Hsp70 in the metathoracic ganglion (MTG) of gregarious locusts to determine if HS affects Hsp70 in specific cell types that could be masked in whole ganglion assays. Our study indicated no evidence of a consistent change in Hsp70 level in the MTG of isolated locusts following HS. Also, Hsp70 was mainly localized in perineurium, neural membranes and glia and prior HS had no effect on its density or distribution. Finally, we applied 2-D gels to study the proteomic profile of MTG in gregarious locusts following HS; although these experiments showed some changes in the level of ATP-synthase β isoforms, the overall amount of this protein was found unchanged following HS. We conclude that the constitutive level of Hsps in the tissues of locusts is high. Also the thermoprotective effect of HS on the nervous system might be mediated by post-translational modifications or protein trafficking.

Brain temperature: heat production, elimination and clinical relevance

Neurological insults are a leading cause of morbidity and mortality, both in adults and especially in children. Among possible therapeutic strategies to limit clinical cerebral damage and improve outcomes, hypothermia remains a promising and beneficial approach. However, its advantages are still debated after decades of use. Studies in adults have generated conflicting results, whereas in children recent data even suggest that hypothermia may be detrimental. Is it because brain temperature physiology is not well understood and/or not applied properly, that hypothermia fails to convince clinicians of its potential benefits? Or is it because hypothermia is not, as believed, the optimal strategy to improve outcome in patients affected with an acute neurological insult? This review article should help to explain the fundamental physiological principles of brain heat production, distribution and elimination under normal conditions and discuss why hypothermia cannot yet be recommended routinely in the management of children affected with various neurological insults.

Heat shock cognate protein 70 regulates gephyrin clustering

Formation and stabilization of postsynaptic glycine receptor (GlyR) clusters result from their association with the polymerized scaffold protein gephyrin. At the cell surface, lateral diffusion and local trapping of GlyR by synaptic gephyrin clusters is one of the main factors controlling their number. However, the mechanisms regulating gephyrin/GlyR cluster sizes are not fully understood. To identify molecular binding partners able to control gephyrin cluster stability, we performed pull-down assays with full-length or truncated gephyrin forms incubated in a rat spinal cord extract, combined with mass spectrometric analysis. We found that heat shock cognate protein 70 (Hsc70), a constitutive member of the heat shock protein 70 (Hsp70) family, selectively binds to the gephyrin G-domain. Immunoelectron microscopy of mouse spinal cord sections showed that Hsc70 could be colocalized with gephyrin at inhibitory synapses. Furthermore, ternary Hsc70-gephyrin-GlyR coclusters were formed following transfection of COS-7 cells. Upon overexpression of Hsc70 in mouse spinal cord neurons, synaptic accumulation of gephyrin was significantly decreased, but GlyR amounts were unaffected. In the same way, Hsc70 inhibition increased gephyrin accumulation at inhibitory synapses without modifying GlyR clustering. Single particle tracking experiments revealed that the increase of gephyrin molecules reduced GlyR diffusion rates without altering GlyR residency at synapses. Our findings demonstrate that Hsc70 regulates gephyrin polymerization independently of its interaction with GlyR. Therefore, gephyrin polymerization and synaptic clustering of GlyR are uncoupled events.

Expression of heat shock protein (HSP 72 kDa) during acute methamphetamine intoxication depends on brain hyperthermia: neurotoxicity or neuroprotection?

In the present study, light and electron microscopy were used to examine heat shock protein (HSP 72 kD) expression during acute methamphetamine (METH) intoxication in rats and evaluate its relationships with brain temperature and alterations in a number of other histochemical and morphological parameters. Freely moving rats received METH at the same dose (9 mg/kg, sc) but at different ambient temperatures (23 and 29°C), showing a wide range of brain temperature elevations (37.6-42.5°C); brains were taken for histochemical and morphological evaluations at peak of brain temperature increase. We found that acute METH intoxication induces massive and wide-spread HSP expression in neural and glial cells examined in detail in the cortex, hippocampus, thalamus, and hypothalamus. In each of these structures, the number of HSP-positive cells tightly correlated with brain temperature elevation. The changes in HSP immunoreactivity were also tightly related to alterations in permeability of the blood-brain barrier, acute glial activation, and brain edema assessed by albumin and GFAP immunoreactivity and measuring tissue water content, respectively. While robust and generalized HSP production normally appears to be the part of an adaptive brain response associated with METH-induced metabolic activation, activation of this protective mechanism has its natural limits and could not counteract the damaging effects of oxidative stress, high temperature, and edema--the leading factors of METH-induced neurotoxicity.

NeuroD6 genomic signature bridging neuronal differentiation to survival via the molecular chaperone network

During neurogenesis, expression of the basic helix-loop-helix NeuroD6/Nex1/MATH-2 transcription factor parallels neuronal differentiation and is maintained in differentiated neurons in the adult brain. To dissect NeuroD6 differentiation properties further, we previously generated a NeuroD6-overexpressing stable PC12 cell line, PC12-ND6, which displays a neuronal phenotype characterized by spontaneous neuritogenesis, accelerated NGF-induced differentiation, and increased regenerative capacity. Furthermore, we reported that NeuroD6 promotes long-term neuronal survival upon serum deprivation. In this study, we identified the NeuroD6-mediated transcriptional regulatory pathways linking neuronal differentiation to survival, by conducting a genome-wide microarray analysis using PC12-ND6 cells and serum deprivation as a stress paradigm. Through a series of filtering steps and a gene-ontology analysis, we found that NeuroD6 promotes distinct but overlapping gene networks, consistent with the differentiation, regeneration, and survival properties of PC12-ND6 cells. By using a gene-set-enrichment analysis, we provide the first evidence of a compelling link between NeuroD6 and a set of heat shock proteins in the absence of stress, which may be instrumental in conferring stress tolerance on PC12-ND6 cells. Immunocytochemistry results showed that HSP27 and HSP70 interact with cytoskeletal elements, consistent with their roles in neuritogenesis and preserving cellular integrity. HSP70 also colocalizes with mitochondria located in the soma, growing neurites, and growth cones of PC12-ND6 cells prior to and upon stress stimulus, consistent with its neuroprotective functions. Collectively, our findings support the notion that NeuroD6 links neuronal differentiation to survival via the network of molecular chaperones and endows the cells with increased stress tolerance.

Hsp40 couples with the CSPalpha chaperone complex upon induction of the heat shock response

In response to a conditioning stress, the expression of a set of molecular chaperones called heat shock proteins is increased. In neurons, stress-induced and constitutively expressed molecular chaperones protect against damage induced by ischemia and neurodegenerative diseases, however the molecular basis of this protection is not known. Here we have investigated the crosstalk between stress-induced chaperones and cysteine string protein (CSPα). CSPα is a constitutively expressed synaptic vesicle protein bearing a J domain and a cysteine rich “string” region that has been implicated in the long term functional integrity of synaptic transmission and the defense against neurodegeneration. We have shown previously that the CSPα chaperone complex increases isoproterenol-mediated signaling by stimulating GDP/GTP exchange of Gα_s. In this report we demonstrate that in response to heat shock or treatment with the Hsp90 inhibitor geldanamycin, the J protein Hsp40 becomes a major component of the CSPα complex. Association of Hsp40 with CSPα decreases CSPα-CSPα dimerization and enhances the CSPα-induced increase in steady state GTP hydrolysis of Gα_s. This newly identified CSPα-Hsp40 association reveals a previously undescribed coupling of J proteins. In view of the crucial importance of stress-induced chaperones in the protection against cell death, our data attribute a role for Hsp40 crosstalk with CSPα in neuroprotection.

Analysis of FK506-mediated protection in an organotypic model of spinal cord damage: heat shock protein 70 levels are modulated in microglial cells

Functional loss after spinal cord injuries is originated by primary and secondary injury phases whose underlying mechanisms include massive release of excitatory amino acids to cytotoxic levels that contribute to neural death. Attenuation of this excitotoxicity is a key point for improving the functional outcome after injury. One of the drugs with potential neuroprotective actions is FK506, a molecule widely used as an immunosuppressant. FK506 may exert neuroprotection via inhibition of calcineurin by binding the FKBP12, or by binding other immunophilins such as FKBP52, leading to modulation of heat shock proteins (Hsp) 90 and 70. In the present study, we used an in vitro model of organotypic culture of rat spinal cord slices to assess whether FK506 is able to protect them against glutamate excitotoxicity. The results showed that FK506 promoted a significant protective effect on the spinal cord tissue at concentrations of 50 and 100 nM. Hsp70 induction was restricted to microglial cells in spinal cord slices treated with either glutamate or FK506. In contrast, the combination of both agents led to a transient reduction in Hsp70 levels in parallel to a marked reduction in IL-1beta precursor production by glial cells. The use of geldanamycin, which promotes persistent induction of Hsp70 in these cells as well as in motoneurons, did not produce tissue neuroprotection. These observations suggest that FK506 might protect spinal cord tissue by targeting on microglial cells and that transient downregulation of Hsp70 on these cells after excitotoxicity is a relevant mechanism of action of FK506.

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.

Heat shock proteins and protection of the nervous system

Manipulation of the cellular stress response offers strategies to protect brain cells from damage induced by ischemia and neurodegenerative diseases. Overexpression of Hsp70 reduced ischemic injury in the mammalian brain. Investigation of the domains within Hsp70 that confers ischemic neuroprotection revealed the importance of the carboxyl-terminal domain. Arimoclomol, a coinducer of heat shock proteins, delayed progression of amyotrophic lateral sclerosis (ALS) in a mouse model in which motor neurons in the spinal cord and motor cortex degenerate. Celastrol, a promising candidate as an agent to counter neurodegenerative diseases, induced expression of a set of Hsps in differentiated neurons grown in tissue culture. Heat shock "preconditioning" protected the nervous system at the functional level of the synapse and selective overexpression of Hsp70 enhanced the level of synaptic protection. Following hyperthermia, constitutively expressed Hsc70 increased in synapse-rich areas of the brain where it associates with Hsp40 to form a complex that can refold denatured proteins. Stress tolerance in neurons is not solely dependent on their own Hsps but can be supplemented by Hsps from adjacent glial cells. Hence, application of exogenous Hsps at neural injury sites is an effective strategy to maintain neuronal viability.

Early embryonic exposure to polychlorinated biphenyls disrupts heat-shock protein 70 cognate expression in zebrafish

Polychlorinated biphenyls (PCBs) are persistent environmental contaminants that have documented neurological effects in children exposed in utero. To better define neuronally linked molecular targets during early development, zebrafish embryos were exposed to Aroclor 1254, a mixture of PCB congeners that are common environmental contaminants. Microarray analysis of the zebrafish genome revealed consistent significant changes in 38 genes. Of these genes, 55% (21) are neuronally related. One gene that showed a consistent 50% reduction in expression in PCB-treated embryos was heat-shock protein 70 cognate (Hsc70). The reduction in Hsc70 expression was confirmed by real-time polymerase chain reaction (PCR), revealing a consistent 30% reduction in expression in PCB-treated embryos. Early embryonic exposure to PCBs also induced structural changes in the ventro-rostral cluster as detected by immunocytochemistry. In addition, there was a significant reduction in dorso-rostral neurite outgrowth emanating from the RoL1 cell cluster following PCB exposure. The serotonergic neurons in the developing diencephalon showed a 34% reduction in fluorescence when labeled with a serotonin antibody following PCB exposure, corresponding to a reduction in serotonin concentration in the neurons. The total size of the labeled neurons was not significantly different between treated and control embryos, indicating that the development of the neurons was not affected, only the production of serotonin within the neurons. The structural and biochemical changes in the developing central nervous system following early embryonic exposure to Aroclor 1254 may lead to alterations in the function of the affected regions.

Exogenous androgen treatment delays the stress response following hamster facial nerve injury

Following injury or stress of any type, cells undergo a stress response, involving the cessation of general protein synthesis and the up-regulation of heat shock proteins (HSP), which have been implicated in promoting cell survival and repair. In a variety of neuronal injury models, including the hamster facial motoneurone (FMN) model, steroid hormones augment regeneration and are neuroprotective. We have previously shown that facial nerve axotomy induces expression of HSP70 (HSP70) and/or up-regulates constitutively expressed HSP70 (HSC70) mRNA in axotomised hamster FMN and that testosterone propionate (TP) treatment reduces this response. These previous studies were unable to differentiate between HSC70 mRNA and HSP70 mRNA. Therefore, an objective of the present study was to determine which HSP (HSC70 or HSP70) was being up-regulated by axotomy and reduced by TP. Axotomy increased HSC70 protein in axotomised and non-axotomised FMN, relative to untreated baseline hamsters. Interestingly, TP transiently delayed the stress-induced up-regulation of HSC70 protein in axotomised FMN compared to axotomised FMN from non-TP treated controls. A potential explanation for this delay may involve the TP-induced liberation of HSP from the androgen receptor, which would provide the injured cell with an immediately available pool of protective HSP. An hypothesis is presented suggesting that this TP-induced delay of stress-induced HSC70 up-regulation might allow for the diversion of cellular energy away from HSP synthesis and towards the synthesis of proteins required for regeneration and survival.

Polysialylation of NCAM is upregulated by hyperthermia and participates in heat shock preconditioning-induced neuroprotection

"Brain tolerance"--a phenomenon in which a subtoxic challenge confers resistance to subsequent brain injuries--provides an ideal opportunity for investigating endogenous neuroprotective mechanisms. We investigated the potential role of the polysialylated (PSA) form of neural cell adhesion molecule (NCAM), which is thought to play a key role in plasticity. In a model where prior exposure to heat shock protects against kainate-induced cell damage in the hippocampus, we show that hyperthermia upregulates PSA-NCAM expression for at least 1 week, without affecting neurogenesis. Pharmacological manipulation of heat shock protein (HSP) expression demonstrates a tight positive link between HSP70 and PSA-NCAM. Finally, the presence of PSA was functionally linked to brain tolerance, as protection against kainate-induced cell death by heat shock pre-exposure was abolished in the absence of NCAM polysialylation. The upregulation of PSA-NCAM by hyperthermia may have a significant impact on hippocampal plasticity, permitting induction of the complex molecular cascade responsible for neuroprotection.

Cerebral neurons and glial cell types inducing heat shock protein Hsp70 following heat stress in the rat

In this chapter, the distribution of Hsp70 in brain cell types following whole body hyperthermia is reviewed. The prevalence of Hsp70 expression in oligodendrocytes, microglia, and vascular cells in this type of stress contrasts with scarcity of Hsp70 induction in astrocytes and most neurons of the hyperthermic brain. However, a similarity between hyperthermic- and arsenite-induced brain patterns of Hsp70 expression supports the view that denaturation of specific proteins plays a major role in the selectivity of glial/vascular expression also during hyperthermia in vivo. The mechanism of neuronal Hsp70 non-responsiveness in heat stress despite their ability to use Hsc70 in a partial heat stress response remains to be elucidated.

Manipulation of protein kinases reveals different mechanisms for upregulation of heat shock proteins in motor neurons and non-neuronal cells

Motor neurons have a high threshold for induction of heat shock proteins (Hsps) in response to stress, a property associated with impaired ability to activate heat shock transcription factor 1 (Hsf1). Hyperphosphorylation of Hsf1 has been established as a requirement for transactivation of heat shock genes. This study demonstrated that the impaired heat shock response in motor neurons is not due to altered phosphorylation of Hsf1 by kinases previously shown to affect activation of Hsf1 in other cells (PKC, GSK3beta, ERK1, CaMKIIalpha). However, a constitutively active form of CaMKIV induced robust expression of Hsp70, as well as transcription of a GFP reporter gene driven by the human inducible Hsp70 promoter in unstressed motor neurons, but not in mouse embryonic fibroblasts. The results point to novel mechanisms of activation of heat shock genes in motor neurons that have relevance to exploitation of endogenous stress responses therapeutically.

The CSPα/G protein complex in PC12 cells

Cysteine string proteinalpha (CSPalpha) is a regulated vesicle protein and molecular chaperone that has been found to be critical for continuous synaptic transmission and is implicated in the defense against neurodegeneration. Previous work has revealed links between CSPalpha and heterotrimeric GTP binding protein (G protein) signal transduction pathways. We have shown that CSPalpha is a guanine nucleotide exchange factor (GEF) for Galphas. In vitro Hsc70 (70 kDa heat shock cognate protein) and SGT (small glutamine-rich tetratricopeptide repeat domain protein) switch CSPalpha from an inactive GEF to an active GEF. Here we have examined the cellular distribution of the CSPalpha system in the PC12 neuroendocrine cell line. CSPalpha, an established secretory vesicle protein, was found to concentrate in the processes of NGF-differentiated PC12 cells as expected. Gbeta subunits co-localized and Galphas subunits partially co-localized with CSPalpha. However, under the conditions examined, the GEF activity of CSPalpha is expected to be inactive, in that Hsc70 was not found in PC12 processes. These results indicate that CSPalpha activity is subject to regulation by factors that alter Hsc70 distribution and translocation within the cell.

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.