Dynamics of endogenous Hsp70 synthesis in the brain of olfactory bulbectomized mice

Regulation of translation elongation and integrated stress response in heat-shocked neurons

Neurons deviate from a canonical heat shock response (HSR). Here, we revealed that neuronal adaptation to heat shock accompanies a brake on mRNA translation, slowed elongating ribosomes, phosphorylation of eukaryotic elongation factor-2 (p-eEF2), and suppressed the integrated stress response (ISR). Returning neurons to control temperature within 1 h of starting heat shock was necessary for survival and allowed for restored translation following dephosphorylation of eEF2. Subsequent to recovery, neurons briefly activated the ISR and were sensitive to the ISR inhibitor ISRIB, which enhanced protein synthesis and survival. Ribosome profiling and RNA sequencing (RNA-seq) identified newly synthesized and existing transcripts associated with ribosomes during heat shock. Preservation of these transcripts for translation during recovery was in part mediated by p-eEF2 and slowed ribosomes. Our work supports a neuronal heat shock model of a partially suspended state of translation poised for rapid reversal if recovery becomes an option and provides insight into regulation between the HSR and the ISR.

A Mouse Model of Sporadic Alzheimer's Disease with Elements of Major Depression

After olfactory bulbectomy, animals are often used as a model of major depression or sporadic Alzheimer's disease and, hence, the status of this model is still disputable. To elucidate the nature of alterations in the expression of the genome after the operation, we analyzed transcriptomes of the cortex, hippocampus, and cerebellum of the olfactory bulbectomized (OBX) mice. Analysis of the functional significance of genes in the brain of OBX mice indicates that the balance of the GABA/glutamatergic systems is disturbed with hyperactivation of the latter in the hippocampus, leading to the development of excitotoxicity and induction of apoptosis in the background of severe mitochondrial dysfunction and astrogliosis. On top of this, the synthesis of neurotrophic factors decreases leading to the disruption of the cytoskeleton of neurons, an increase in the level of intracellular calcium, and the activation of tau protein hyperphosphorylation. Moreover, the acetylcholinergic system is deficient in the background of the hyperactivation of acetylcholinesterase. Importantly, the activity of the dopaminergic, endorphin, and opiate systems in OBX mice decreases, leading to hormonal dysfunction. On the other hand, genes responsible for the regulation of circadian rhythms, cell migration, and innate immunity are activated in OBX animals. All this takes place in the background of a drastic downregulation of ribosomal protein genes in the brain. The obtained results indicate that OBX mice represent a model of Alzheimer's disease with elements of major depression.

Factors Affecting Pathological Amyloid Protein Transformation: From Post-Translational Modifications to Chaperones

The review discusses the influence of various factors (e.g., post-translational modifications and chaperones) on the pathological transformation of amyloidogenic proteins involved in the onset and development of neurodegenerative diseases (Alzheimer's and Parkinson's diseases) and spongiform encephalopathies of various origin with special focus on the role of α-synuclein, prion protein, and, to a lesser extent, beta-amyloid peptide. The factors investigated by the authors of this review are discussed in more detail, including posttranslational modifications (glycation and S-nitrosylation), cinnamic acid derivatives and dendrimers, and chaperonins (eukaryotic, bacterial, and phage). A special section is devoted to the role of the gastrointestinal microbiota in the pathogenesis of amyloid neurodegenerative diseases, in particular, its involvement in the transformation of infectious prions and possibly other proteins capable of prion-like transmission of amyloidogenic diseases.

Heat shock proteins: Biological functions, pathological roles, and therapeutic opportunities

The heat shock proteins (HSPs) are ubiquitous and conserved protein families in both prokaryotic and eukaryotic organisms, and they maintain cellular proteostasis and protect cells from stresses. HSP protein families are classified based on their molecular weights, mainly including large HSPs, HSP90, HSP70, HSP60, HSP40, and small HSPs. They function as molecular chaperons in cells and work as an integrated network, participating in the folding of newly synthesized polypeptides, refolding metastable proteins, protein complex assembly, dissociating protein aggregate dissociation, and the degradation of misfolded proteins. In addition to their chaperone functions, they also play important roles in cell signaling transduction, cell cycle, and apoptosis regulation. Therefore, malfunction of HSPs is related with many diseases, including cancers, neurodegeneration, and other diseases. In this review, we describe the current understandings about the molecular mechanisms of the major HSP families including HSP90/HSP70/HSP60/HSP110 and small HSPs, how the HSPs keep the protein proteostasis and response to stresses, and we also discuss their roles in diseases and the recent exploration of HSP related therapy and diagnosis to modulate diseases. These research advances offer new prospects of HSPs as potential targets for therapeutic intervention.

Impact of Heat Shock Proteins in Neurodegeneration: Possible Therapeutical Targets

Human neurodegenerative diseases occur as a result of various factors. Regardless of the variety in the etiology of development, many of these diseases are characterized by the accumulation of pathological, misfolded proteins; hence, such diseases are considered as proteinopathies. While plenty of research study has been conducted in order to identify the pathophysiology of these proteinopathies, there is still a lack of understanding in terms of potential therapeutic targets. Molecular chaperones present the main workforce for cellular protection and stress response. Therefore, considering these functions, molecular chaperones present a promising target for research within the field of conformational diseases that arise from proteinopathies. Since the association between neurodegenerative disorders and their long-term consequences is well documented, the need for the development of new therapeutic strategies becomes even more critical. In this review, we summarized the molecular function of heat shock proteins and recent progress on their role, involvement, and other mechanisms related to neurodegeneration caused by different etiological factors. Based on the relevant scientific data, we will highlight the functional classification of heat shock proteins, regulatin, and their therapeutic potential for neurodegenerative disorders.

Mesenchymal stem cells as a potential therapeutic tool to cure cognitive impairment caused by neuroinflammation

An established contribution of neuroinflammation to multiple brain pathologies has raised the requirement for therapeutic strategies to overcome it in order to prevent age- and disease-dependent cognitive decline. Mesenchymal stem cells (MSCs) produce multiple growth and neurotrophic factors and seem to evade immune rejection due to low expression of major histocompatibility complex class I molecules. Therefore, MSCs are widely used in experiments and clinical trials of regenerative medicine. This review summarizes recent data concerning the optimization of MSC use for therapeutic purposes with the emphasis on the achievements of the last 2 years. Specific attention is paid to extracellular vesicles secreted by MSCs and to the role of α7 nicotinic acetylcholine receptors. The reviewed data demonstrate that MSCs have a significant therapeutic potential in treating neuroinflammation-related cognitive disfunctions including age-related neurodegenerative diseases. The novel data demonstrate that maximal therapeutic effect is being achieved when MSCs penetrate the brain and produce their stimulating factors in situ. Consequently, therapeutic application using MSCs should include measures to facilitate their homing to the brain, support the survival in the brain microenvironment, and stimulate the production of neurotrophic and anti-inflammatory factors. These measures include but are not limited to genetic modification of MSCs and pre-conditioning before transplantation.

Heat stress aggravates oxidative stress, apoptosis, and endoplasmic reticulum stress in the cerebellum of male C57 mice

BACKGROUND

The current study was set to assess the effect of heat stress exposure on oxidative stress, apoptosis, and endoplasmic reticulum stress markers in the cerebellum of male mice.

METHODS

Fifty male C57BL/6 mice were assigned to five groups of (I) control, (II) heat stress (HS)7, (III) HS14, (IV) HS21, and (V) HS42 groups. Animals in the control group were not exposed to HS. Mice in the II-V groups were exposed to HS once a day over 7, 14, 21, and 42 days, respectively. Cerebellar reactive oxygen species (ROS) levels, expression of heat shock protein (HSP)70 and caspase 3 as well as endoplasmic reticulum stress-related proteins (PERK, p-PERK, CHOP, and Full-length ATF-6) expression were determined on the 7th, 14th, 21st, and 42nd days.

RESULTS

ROS levels and HSP70 expression increased following HS on the 14th, 21st, and 42nd days and the 7th, and 14th days with a peak level of expression on the 14th day following HS. HSP70 levels decreased afterward on the 21st and 42nd days compared with the control group. Besides, exposure to HS for 14, 21, and 42 days resulted in a significant increase in the CHOP and p-PERK levels in the cerebellum compared with the control group. Heat exposure also increased protein expression of cleaved caspase 3 and active ATF-6/Full-length ATF-6 on the 21st and 42nd days in the cerebellum compared with the control animals.

CONCLUSION

These findings indicated that chronic HS augmented oxidative stress, endoplasmic reticulum stress, and apoptosis pathways in the cerebellum of mice.

Ocimum sanctum Linn. Extract Improves Cognitive Deficits in Olfactory Bulbectomized Mice via the Enhancement of Central Cholinergic Systems and VEGF Expression

This study aimed to clarify the antidementia effects of ethanolic extract of Ocimum sanctum Linn. (OS) and its underlying mechanisms using olfactory bulbectomized (OBX) mice. OBX mice were treated daily with OS or a reference drug, donepezil (DNP). Spatial and nonspatial working memory performance was measured using a modified Y maze test and a novel object recognition test, respectively. Brain tissues of the animals were subjected to histochemical and neurochemical analysis. OS treatment attenuated OBX-induced impairment of spatial and nonspatial working memories. OBX induced degeneration of septal cholinergic neurons, enlargement of the lateral ventricles, and suppression of hippocampal neurogenesis. OS and DNP treatment also depressed these histological damages. OS administration reduced ex vivo activity of acetylcholinesterase in the brain. OBX diminished the expression levels of genes coding vascular endothelial growth factor (VEGF) and VEGF receptor type 2 (VEGFR2). Treatment with OS and DNP reversed OBX-induced decrease in VEGF gene and protein expression levels without affecting the expression of the VEGFR2 gene. These results demonstrate that the administration of OS can lessen the cognitive deficits and neurohistological damages of OBX and that these actions are, at least in part, mediated by the enhancement of central cholinergic systems and VEGF expression.

Heat shock proteins: a history of study in Russia

This review describes a brief history of the discovery and studies in Russia and associated countries of the main stress protein (Hsp70) that plays important roles both in the normal function of the cell and body as well as under various stressful stimuli. Research on this protein at the Institute of Molecular Biology (Moscow) began with the elucidation of its adaptive functions at the cellular level and at the level of the whole organism. These studies examined the function of Hsp70 under normal and extreme conditions using a wide range of model and non-model animal species, from Leishmania and Drosophila to camels and humans. These analyses made it possible to elucidate the primary regulations in the evolution and function of heat shock (HS) genes in the studied organisms. Next, we studied the structure and characteristic features of heat shock genes and proteins in species with contrasting habitat temperatures. The systems of Hsp70 expression and isolation we developed using various research objects allowed us to proceed to study the protective properties of human recombinant Hsp70 in normal-aging animal models as well as animal models experiencing sepsis, Alzheimer's disease, and stroke. The results obtained open the prospects of using recombinant Hsp70 for the treatment of various neuropathologies in humans. This review describes the logic and history of investigation of Hsp70 performed by one group of scientists from Engelhardt Institute of Molecular Biology, Russian Academy of Sciences. It was not the goal of this paper to give a comprehensive general picture of other similar studies carried out in Russia during this period.

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.

Ablation of olfactory bulb glutamatergic neurons induces depressive-like behaviors and sleep disturbances in mice

RATIONALE

Major depression is a serious, but common, psychological disorder, which consists of a long-lasting depressive mood, feelings of helplessness, anhedonia, and sleep disturbances. It has been reported that rats with bilateral olfactory bulbectomies (OBXs) exhibit depressive-like behaviors which indicates that the olfactory bulb (OB) plays an important role in the formation of depression. However, which type of OB neurons plays an important role in the formation of depression remains unclear.

OBJECTIVE

To determine the role of OB neuronal types in depression and related sleep-wake dysfunction.

METHODS

Firstly, we established and evaluated a conventional physical bilateral OBX depression model. Secondly, we used chemical methods to ablate OB neurons, while maintaining the original shape, and evaluated depressive-like behaviors. Thirdly, we utilized AAV-flex-taCasp3-TEVp and transgenetic mice to specifically ablate the OB GABAergic or glutamatergic neurons, then evaluated depressive-like behaviors.

RESULTS

Compared with measured parameters in sham mice, mice with OBXs or ibotenic acid-induced OB lesions exhibited depressive-like behaviors and sleep disturbances, as demonstrated by results of depressive-like behavior tests and sleep recordings. Selective lesioning of OB glutamatergic neurons, but not GABAergic neurons induced depressive-like behaviors and increased rapid eye movement sleep during the light phase of the circadian cycle.

CONCLUSIONS

These results indicate that OB glutamatergic neurons play a key role in olfactory-related depression and sleep disturbance.

Extracellular heat shock proteins in neurodegenerative diseases: New perspectives

One pathological hallmark of neurodegenerative diseases and CNS trauma is accumulation of insoluble, hydrophobic molecules and protein aggregations found both within and outside cells. These may be the consequences of an inadequate or overburdened cellular response to stresses resulting from potentially toxic changes in extra- and intracellular environments. The upregulated expression of heat shock proteins (HSPs) is one example of a highly conserved cellular response to both internal and external stress. Intracellularly these proteins act as chaperones, playing vital roles in the folding of nascent polypeptides, the translocation of proteins between subcellular locations, and the disaggregation of misfolded or aggregated proteins in an attempt to maintain cellular proteostasis during both homeostatic and stressful conditions. While the predominant study of the HSPs has focused on their intracellular chaperone functions, it remains unclear if all neuronal populations can mount a complete stress response. Alternately, it is now well established that some members of this family of proteins can be secreted by nearby, non-neuronal cells to act in the extracellular environment. This review addresses the current literature detailing the use of exogenous and extracellular HSPs in the treatment of cellular and animal models of neurodegenerative disease. These findings offer a new measure of therapeutic potential to the HSPs, but obstacles must be overcome before they can be efficiently used in a clinical setting.

Molecular Mechanisms Underlying Neuroprotective Effect of Intranasal Administration of Human Hsp70 in Mouse Model of Alzheimer's Disease

Heat shock protein 70, encoded by the HSPA1A gene in humans, is a key component of the machinery that protects neuronal cells from various stress conditions and whose production significantly declines during the course of aging and as a result of several neurodegenerative diseases. Herein, we investigated whether sub-chronic intranasal administration of exogenous Hsp70 (eHsp70) exerts a neuroprotective effect on the temporal cortex and areas of the hippocampus in transgenic 5XFAD mice, a model of Alzheimer's disease. The quantitative analysis of neuronal pathologies in the compared groups, transgenic (Tg) versus non-transgenic (nTg), revealed high level of abnormalities in the brains of transgenic mice. Treatment with human recombinant Hsp70 had profound rejuvenation effect on both neuronal morphology and functional state in the temporal cortex and hippocampal regions in transgenic mice. Hsp70 administration had a smaller, but still significant, effect on the functional state of neurons in non-transgenic mice as well. Using deep sequencing, we identified multiple differentially expressed genes (DEGs) in the hippocampus of transgenic and non-transgenic mice. Furthermore, this analysis demonstrated that eHsp70 administration strongly modulates the spectrum of DEGs in transgenic animals, reverting to a pattern similar to that observed in non-transgenic age-matched mice, which included upregulation of genes responsible for amine transport, transmission of nerve impulses and other pathways that are impaired in 5XFAD mice. Overall, our data indicate that Hsp70 treatment may be an effective therapeutic against old age diseases of the Alzheimer's type.

Immunization Against Specific Fragments of Neurotrophin p75 Receptor Protects Forebrain Cholinergic Neurons in the Olfactory Bulbectomized Mice

Alzheimer’s disease (AD) is characterized by progressive cognitive impairment associated with marked cholinergic neuron loss and amyloid-β (Aβ) peptide accumulation in the brain. The cytotoxicity in AD is mediated, at least in part, by Aβ binding with the extracellular domain of the p75 neurotrophin receptor (p75NTR), localized predominantly in the membranes of acetylcholine-producing neurons in the basal forebrain. Hypothesizing that an open unstructured loop of p75NTR might be the effective site for Aβ binding, we have immunized both olfactory bulbectomized (OBX) and sham-operated (SO) mice (n = 82 and 49, respectively) with synthetic peptides, structurally similar to different parts of the loops, aiming to block them by specific antibodies. OBX-mice have been shown in previous studies, and confirmed in the present one, to be characterized by typical behavioral, morphological, and biochemical AD hallmarks, including cholinergic deficits in forebrain neurons. Immunization of OBX- or SO-mice with KLH conjugated fragments of p75NTR induced high titers of specific serum antibodies for each of nine chosen fragments. However, maximal protective effects on spatial memory, evaluated in a Morris water maze, and on activity of choline acetyltransferase in forebrain neurons, detected by immunoreactivity to specific antibodies, were revealed only for peptides with amino acid residue sequences of 155–164 and 167–176. We conclude that the approach based on immunological blockade of specific p75NTR sites, linked with the cytotoxicity, is a useful and effective tool for study of AD-associated mechanisms and for development of highly selective therapy of cholinergic malfunctioning in AD patients.

The Y-Box Binding Protein 1 Suppresses Alzheimer's Disease Progression in Two Animal Models

The Y-box binding protein 1 (YB-1) is a member of the family of DNA- and RNA binding proteins. It is involved in a wide variety of DNA/RNA-dependent events including cell proliferation and differentiation, stress response, and malignant cell transformation. Previously, YB-1 was detected in neurons of the neocortex and hippocampus, but its precise role in the brain remains undefined. Here we show that subchronic intranasal injections of recombinant YB-1, as well as its fragment YB-1₁₋₂₁₉, suppress impairment of spatial memory in olfactory bulbectomized (OBX) mice with Alzheimer’s type degeneration and improve learning in transgenic 5XFAD mice used as a model of cerebral amyloidosis. YB-1-treated OBX and 5XFAD mice showed a decreased level of brain β-amyloid. In OBX animals, an improved morphological state of neurons was revealed in the neocortex and hippocampus; in 5XFAD mice, a delay in amyloid plaque progression was observed. Intranasally administered YB-1 penetrated into the brain and could enter neurons. In vitro co-incubation of YB-1 with monomeric β-amyloid (1–42) inhibited formation of β-amyloid fibrils, as confirmed by electron microscopy. This suggests that YB-1 interaction with β-amyloid prevents formation of filaments that are responsible for neurotoxicity and neuronal death. Our data are the first evidence for a potential therapeutic benefit of YB-1 for treatment of Alzheimer’s disease.

Olfactory Deprivation Hastens Alzheimer-Like Pathologies in a Human Tau-Overexpressed Mouse Model via Activation of cdk5

Olfactory dysfunction is a recognized risk factor for the pathogenesis of Alzheimer's disease (AD), while the mechanisms are still not clear. Here, we applied bilateral olfactory bulbectomy (OBX), an olfactory deprivation surgery to cause permanent anosmia, in human tau-overexpressed mice (htau mice) to investigate changes of AD-like pathologies including aggregation of abnormally phosphorylated tau and cholinergic neuron loss. We found that tau phosphorylation in hippocampus was increased at Thr-205, Ser-214, Thr-231, and Ser-396 after OBX. OBX also increased the level of sarkosyl-insoluble Tau at those epitopes and accelerated accumulation of somatodendritic tau. Moreover, OBX resulted in the elevation of calpain activity accompanied by an increased expression of the cyclin-dependent kinase 5 (cdk5) neuronal activators, p35 and p25, in hippocampus. Furthermore, OBX induces the loss of the cholinergic neurons in medial septal. Administration of cdk5 pharmacological inhibitor roscovitine into lateral ventricles suppressed tau hyperphosphorylation and mislocalization and restored the cholinergic neuron loss. These findings suggest that olfactory deprivation by OBX hastens tau pathology and cholinergic system impairment in htau mice possibly via activation of cdk5.

Therapeutic effect of mesenchymal multipotent stromal cells on memory in animals with Alzheimer-type neurodegeneration

Transplantation of human mesenchymal multipotent stromal cells improved spatial memory in bulbectomized mice with Alzheimer-type neurodegeneration. The positive effect was observed in 1 month after intracerebral transplantation and in 3 months after systemic injection of mesenchymal multipotent stromal cells. No cases of malignant transformation were noted. These findings indicate prospects of using mesenchymal multipotent stromal cells for the therapy of Alzheimer disease and the possibility of their systemic administration for attaining the therapeutic effect.

The importance of the cellular stress response in the pathogenesis and treatment of type 2 diabetes

Organisms have evolved to survive rigorous environments and are not prepared to thrive in a world of caloric excess and sedentary behavior. A realization that physical exercise (or lack of it) plays a pivotal role in both the pathogenesis and therapy of type 2 diabetes mellitus (t2DM) has led to the provocative concept of therapeutic exercise mimetics. A decade ago, we attempted to simulate the beneficial effects of exercise by treating t2DM patients with 3 weeks of daily hyperthermia, induced by hot tub immersion. The short-term intervention had remarkable success, with a 1 % drop in HbA1, a trend toward weight loss, and improvement in diabetic neuropathic symptoms. An explanation for the beneficial effects of exercise and hyperthermia centers upon their ability to induce the cellular stress response (the heat shock response) and restore cellular homeostasis. Impaired stress response precedes major metabolic defects associated with t2DM and may be a near seminal event in the pathogenesis of the disease, tipping the balance from health into disease. Heat shock protein inducers share metabolic pathways associated with exercise with activation of AMPK, PGC1-a, and sirtuins. Diabetic therapies that induce the stress response, whether via heat, bioactive compounds, or genetic manipulation, improve or prevent all of the morbidities and comorbidities associated with the disease. The agents reduce insulin resistance, inflammatory cytokines, visceral adiposity, and body weight while increasing mitochondrial activity, normalizing membrane structure and lipid composition, and preserving organ function. Therapies restoring the stress response can re-tip the balance from disease into health and address the multifaceted defects associated with the disease.