HSP70 constitutive expression in rat central nervous system from postnatal development to maturity

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.

Heat Shock Protein 70 as a Sex-Skewed Regulator of α-Synucleinopathy

The role of molecular chaperones, such as heat shock protein 70 (Hsp70), is not typically studied as a function of biological sex, but by addressing this gap we might improve our understanding of proteinopathic disorders that predominate in one sex. Therefore, we exposed male or female primary hippocampal cultures to preformed α-synuclein fibrils in a model of early-stage Lewy pathology. We first discovered that two mechanistically distinct inhibitors of Hsp70 function increased phospho-α-synuclein+ inclusions more robustly in male-derived neurons. Because Hsp70 is released into extracellular compartments and may restrict cell-to-cell transmission/amplification of α-synucleinopathy, we then tested the effects of low-endotoxin, exogenous Hsp70 (eHsp70) in primary hippocampal cultures. eHsp70 was taken up by and reduced α-synuclein+ inclusions in cells of both sexes, but pharmacological suppression of Hsp70 function attenuated the inhibitory effect of eHsp70 on perinuclear inclusions only in male neurons. In 20-month-old male mice infused with α-synuclein fibrils in the olfactory bulb, daily intranasal eHsp70 delivery also reduced inclusion numbers and the time to locate buried food. eHsp70 penetrated the limbic system and spinal cord of male mice within 3 h but was cleared within 72 h. Unexpectedly, no evidence of eHsp70 uptake from nose into brain was observed in females. A trend towards higher expression of inducible Hsp70-but not constitutive Hsp70 or Hsp40-was observed in amygdala tissues from male subjects with Lewy body disorders compared to unaffected male controls, supporting the importance of this chaperone in human disease. Women expressed higher amygdalar Hsp70 levels compared to men, regardless of disease status. Together, these data provide a new link between biological sex and a key chaperone that orchestrates proteostasis.

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.

Mitochondrial HSP70 cognate-mediated differential expression of JNK1/2 in the pollution stressed grey mullets, Mugil cephalus

Cells have evolved different networks of cellular stress responses to adapt during environmental changes and survive combating wide variety of stress. Mitochondrial heat shock protein 70 (mtHSP70) are essential for maintaining cellular homeostasis. c-Jun-N terminal kinase (JNK), a subfamily of MAPK, plays a key role in the transmission of extracellular signal for survival and death. In the present investigation, the differential expression of phosphorylated JNK1/2 with corresponding increases in heat shock transcription factor-1 (HSF-1) under high levels of B-cell lymphoma 2 (Bcl-2), HSP70 transcripts (twofold) and mtHSP70 has been correlated with fish survival in polluted Ennore estuary. This study suggests that in Ennore sample, the amplification in HSP70 transcripts along with corresponding mtHSP70 overexpression might be due to activation of JNK1/2 and HSF-1. This would influence the expression of Bcl-2 protein involved in mitochondrial survival under pollution-stressed condition.

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.

The expression pattern of the 70-kDa heat shock protein Hspa2 in mouse tissues

The highest expression level of a 70-kDa heat shock protein family member Hspa2 is detected specifically in meiotic and post-meiotic male germ cells, which is reflected by original name of this protein, i.e., testis-specific Hsp70. However, this chaperon protein could be also detected in certain somatic tissues. Here, the extra-testicular expression pattern of mouse Hspa2 was analyzed. We found expression of Hspa2 in various epithelial cells including lining of bronchioles and oviduct, columnar epithelium of endometrium, epithelial reticular cells of thymus, transitional epithelium of the urinary bladder, or ependymal cells covering walls of the ventricular system of the brain. Surprisingly, Hspa2 was a putative secretory protein in intestine, endometrial glands and subcommissural organ. Hspa2 was detected in central and peripheral nervous system: in neuron's bodies and fiber tracts, in the subventricular zone of the lateral ventricles, in the dentate gyrus of the hippocampus, in enteric ganglia of the gastrointestinal tract. Hspa2 was also expressed in smooth muscles and at low level in immune system (in germinal centers associated with B-lymphocyte production). In addition to somatic tissues listed above, Hspa2 was detected in oocytes arrested at diplotene of the first meiotic division.

Heat shock protein72 protects hippocampal neurons from apoptosis induced by chronic psychological stress

When exposed to nonlethal heat stress (i.e., heat shock preconditioning), HSP72 expression increased in the mammalian brain. HSP72 enhance the viability of neurons and decrease TUNEL-positive neurons under several kinds of stress (e.g., ischemic). Chronic psychological stress is a kind of stress that could cause hippocampal neuron apoptosis. But whether overexpression of HSP72 can decrease TUNEL-positive hippocampal neurons caused by chronic psychological stress is unclear. To investigate the possible protective role of HSP72 in decreasing chronic psychological stress-induced hippocampal neuron apoptosis, this study analyzed HSP72 expression, apoptotic neurons in the hippocampus of mice. Adult mice were divided into four groups unstressed group; chronic psychological stress group; heat shock stress group; heat shock preconditioning plus psychological stress group; receiving no experimental stress, chronic psychological stress, heat shock stress, heat shock preconditioning plus psychological stress separately. Mice were killed after one month, two months, or three months of stress. A three-way ANOVA (psychological stress x heat shock stress x time) revealed a significant effect of heat shock stress in increasing HSP72 expression, decreasing neuronal apoptosis in hippocampus CA3 region caused by chronic psychological stress, and showed that HSP72 protected hippocampus CA3 neurons from chronic psychological stress.

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.

Persistent borna disease virus infection confers instability of HSP70 mRNA in glial cells during heat stress

Borna disease virus (BDV) is a highly neurotropic RNA virus that causes neurological disorders in many vertebrate species. Although BDV readily establishes lasting persistence, persistently infected cells maintain an apparently normal cell phenotype in terms of morphology, viability, and proliferation. In this study, to understand the regulation of stress responses in BDV infection, we investigated the expression of heat shock proteins (HSPs) in glial cells persistently infected with BDV. Interestingly, we found that BDV persistence did not upregulate HSP70 expression even in cells treated with heat stress. Furthermore, BDV-infected glial cells exhibited rapid rounding and detachment from the culture plate under various stressful conditions. Immunofluorescence analysis demonstrated that heat stress rapidly disrupts the cell cytoskeleton only in persistently infected cells, suggesting a lack of thermotolerance. Intriguingly, we found that although persistently infected glial cells expressed HSP70 mRNA after heat stress, its expression rapidly disappeared during the recovery period. These observations indicated that persistent BDV infection may affect the stability of HSP70 mRNA. Finally, we found that the double-stranded RNA-dependent protein kinase (PKR) is expressed at a constant level in persistently infected cells with or without heat shock. Considering the interrelationship between HSP70 and PKR production, our data suggest that BDV infection disturbs the cellular stress responses to abolish antiviral activities and maintain persistence.