Independent functions of hsp90 in neurotransmitter release and in the continuous synaptic cycling of AMPA receptors

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 discover 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 enhances HSPA8 mRNA translation efficiency in dendrites. Stress-mediated HSPA8 mRNA localization to the dendrites is 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 neuronal stress response in which RNA-binding proteins increase the dendritic localization of HSPA8 mRNA to maintain proteostasis and prevent neurodegeneration.

Localized synthesis of molecular chaperones sustains neuronal proteostasis

Neurons are challenged to maintain proteostasis in neuronal projections, particularly with the physiological stress at synapses to support intercellular communication underlying important functions such as memory and movement control. Proteostasis is maintained through regulated protein synthesis and degradation and chaperone-assisted protein folding. Using high-resolution fluorescent microscopy, we discovered that neurons localize a subset of chaperone mRNAs to their dendrites, particularly more proximal regions, and increase this asymmetric localization following proteotoxic stress through microtubule-based transport from the soma. The most abundant chaperone mRNA in dendrites encodes the constitutive heat shock protein 70, HSPA8. Proteotoxic stress in cultured neurons, induced by inhibiting proteasome activity or inducing oxidative stress, enhanced transport of Hspa8 mRNAs to dendrites and the percentage of mRNAs engaged in translation on mono and polyribosomes. Knocking down the ALS-related protein Fused in Sarcoma (FUS) and a dominant mutation in the heterogenous nuclear ribonucleoprotein A2/B1 (HNRNPA2B1) impaired stress-mediated localization of Hspa8 mRNA to dendrites in cultured murine motor neurons and human iPSC-derived neurons, respectively, revealing the importance of these RNA-binding proteins in maintaining proteostasis. These results reveal the increased dendritic localization and translation of the constitutive HSP70 Hspa8 mRNA as a crucial neuronal stress response to uphold proteostasis and prevent neurodegeneration.

Elevated Expression of HSP72 in the Prefrontal Cortex and Hippocampus of Rats Subjected to Chronic Mild Stress and Treated with Imipramine

The HSP70 and HSP90 family members belong to molecular chaperones that exhibit protective functions during the cellular response to stressful agents. We investigated whether the exposure of rats to chronic mild stress (CMS), a validated model of depression, affects the expression of HSP70 and HSP90 in the prefrontal cortex (PFC), hippocampus (HIP) and thalamus (Thal). Male Wistar rats were exposed to CMS for 3 or 8 weeks. The antidepressant imipramine (IMI, 10 mg/kg, i.p., daily) was introduced in the last five weeks of the long-term CMS procedure. Depressive-like behavior was verified by the sucrose consumption test. The expression of mRNA and protein was quantified by real-time PCR and Western blot, respectively. In the 8-week CMS model, stress alone elevated HSP72 and HSP90B mRNA expression in the HIP. HSP72 mRNA was increased in the PFC and HIP of rats not responding to IMI treatment vs. IMI responders. The CMS exposure increased HSP72 protein expression in the cytosolic fraction of the PFC and HIP, and this effect was diminished by IMI treatment. Our results suggest that elevated levels of HSP72 may serve as an important indicator of neuronal stress reactions accompanying depression pathology and could be a potential target for antidepressant strategy.

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.

Chicken pituitary transcriptomic responses to acute heat stress

BACKGROUND

Poultry production is vulnerable to increasing temperatures in terms of animal welfare and in economic losses. With the predicted increase in global temperature and the number and severity of heat waves, it is important to understand how chickens raised for food respond to heat stress. This knowledge can be used to determine how to select chickens that are adapted to thermal challenge. As neuroendocrine organs, the hypothalamus and pituitary provide systemic regulation of the heat stress response.

METHODS AND RESULTS

Here we report a transcriptome analysis of the pituitary response to acute heat stress. Chickens were stressed for 2 h at 35 °C (HS) and transcriptomes compared with birds maintained in thermoneutral temperatures (25 °C).

CONCLUSIONS

The observations were evaluated in the context of ontology terms and pathways to describe the pituitary response to heat stress. The pituitaries of heat stressed birds exhibited responses to hyperthermia through altered expression of genes coding for chaperones, cell cycle regulators, cholesterol synthesis, transcription factors, along with the secreted peptide hormones, prolactin, and proopiomelanocortin.

An Electrophysiological and Proteomic Analysis of the Effects of the Superoxide Dismutase Mimetic, MnTMPyP, on Synaptic Signalling Post-Ischemia in Isolated Rat Hippocampal Slices

Metabolic stress and the increased production of reactive oxygen species (ROS) are two main contributors to neuronal damage and synaptic plasticity in acute ischemic stroke. The superoxide scavenger MnTMPyP has been previously reported to have a neuroprotective effect in organotypic hippocampal slices and to modulate synaptic transmission after in vitro hypoxia and oxygen-glucose deprivation (OGD). However, the mechanisms involved in the effect of this scavenger remain elusive. In this study, two concentrations of MnTMPyP were evaluated on synaptic transmission during ischemia and post-ischemic synaptic potentiation. The complex molecular changes supporting cellular adaptation to metabolic stress, and how these are modulated by MnTMPyP, were also investigated. Electrophysiological data showed that MnTMPyP causes a decrease in baseline synaptic transmission and impairment of synaptic potentiation. Proteomic analysis performed on MnTMPyP and hypoxia-treated tissue indicated an impairment in vesicular trafficking mechanisms, including reduced expression of Hsp90 and actin signalling. Alterations of vesicular trafficking may lead to reduced probability of neurotransmitter release and AMPA receptor activity, resulting in the observed modulatory effect of MnTMPyP. In OGD, protein enrichment analysis highlighted impairments in cell proliferation and differentiation, such as TGFβ1 and CDKN1B signalling, in addition to downregulation of mitochondrial dysfunction and an increased expression of CAMKII. Taken together, our results may indicate modulation of neuronal sensitivity to the ischemic insult, and a complex role for MnTMPyP in synaptic transmission and plasticity, potentially providing molecular insights into the mechanisms mediating the effects of MnTMPyP during ischemia.

Dose-dependent manner of luteolin in the modulation of spatial memory with respect to the hippocampal level of HSP70 and HSP90 in sleep-deprived rats

Sleep deprivation (SD) induces a variety of deleterious effects on different cognitive functions such as memory. Elevated neuroinflammation, oxidative stress, and apoptosis, and decreased synaptic plasticity and antioxidant capacity are involved in the deleterious effects of SD on memory. On the other hand, luteolin (a flavonoid compound) has antioxidant, neuroprotective, and anti-inflammatory properties. Also, Heat shock protein 70 (HSP70) and Heat shock protein 90 (HSP90) can be involved in modulating memory. In this study, we aimed to assess the effects of SD and luteolin on spatial learning and memory using Morris Water Maze apparatus in rats, with respect to the level of HSP70 and HSP90 in the hippocampus. Luteolin was injected intracerebroventricular (i.c.v.) at the doses of 0.5, 1, and 2 µg/rat. The results showed that SD impaired spatial memory, while luteolin dose-dependently restored SD-induced spatial memory impairment. SD increased the expression level of HSP90 in the hippocampus, whereas luteolin dose-dependently reversed the effect of SD. Furthermore, SD decreased the expression level of HSP70 protein in the hippocampus, while luteolin dose-dependently reversed the effect of SD. In conclusion, HSP70 and HSP90 may be involved in the deleterious effect of SD on memory, and in the improvement effect of luteolin on memory. This is a novel study reporting novel data and we suggest further detailed studies to better understand the interactions between SD, luteolin, and Heat shock proteins.

Organismal Roles of Hsp90

Heat shock protein 90 (Hsp90) is a highly conserved molecular chaperone that assists in the maturation of many client proteins involved in cellular signal transduction. As a regulator of cellular signaling processes, it is vital for the maintenance of cellular proteostasis and adaptation to environmental stresses. Emerging research shows that Hsp90 function in an organism goes well beyond intracellular proteostasis. In metazoans, Hsp90, as an environmentally responsive chaperone, is involved in inter-tissue stress signaling responses that coordinate and safeguard cell nonautonomous proteostasis and organismal health. In this way, Hsp90 has the capacity to influence evolution and aging, and effect behavioral responses to facilitate tissue-defense systems that ensure organismal survival. In this review, I summarize the literature on the organismal roles of Hsp90 uncovered in multicellular organisms, from plants to invertebrates and mammals.

Antioxidants Prevent the Effects of Physical Exercise on Visual Cortical Plasticity

BACKGROUND

Physical activity has been recently shown to enhance adult visual cortical plasticity, both in human subjects and animal models. While physical activity activates mitochondrial oxidative metabolism leading to a transient production of reactive oxygen species, it remains unknown whether this process is involved in the plasticizing effects elicited at the visual cortical level.

RESULTS

Here, we investigated whether counteracting oxidative stress through a dietary intervention with antioxidants (vitamins E and C) interferes with the impact of physical exercise on visual cortex plasticity in adult rats. Antioxidant supplementation beyond the closure of the critical period blocked ocular dominance plasticity in response to eye deprivation induced by physical activity in adult rats.

CONCLUSIONS

Antioxidants exerted their action through a mithormetic effect that involved dampening of oxidative stress and insulin-like growth factor 1 (IGF-1) signaling in the brain.

Regulation of Protein Transport Pathways by the Cytosolic Hsp90s

The highly conserved molecular chaperone heat shock protein 90 (Hsp90) is well-known for maintaining metastable proteins and mediating various aspects of intracellular protein dynamics. Intriguingly, high-throughput interactome studies suggest that Hsp90 is associated with a variety of other pathways. Here, we will highlight the potential impact of Hsp90 in protein transport. Currently, a limited number of studies have defined a few mechanistic contributions of Hsp90 to protein transport, yet the relevance of hundreds of additional connections between Hsp90 and factors known to aide this process remains unresolved. These interactors broadly support transport pathways including endocytic and exocytic vesicular transport, the transfer of polypeptides across membranes, or unconventional protein secretion. In resolving how Hsp90 contributes to the protein transport process, new therapeutic targets will likely be obtained for the treatment of numerous human health issues, including bacterial infection, cancer metastasis, and neurodegeneration.

Orthosiphon stamineus Proteins Alleviate Hydrogen Peroxide Stress in SH-SY5Y Cells

The neuroprotective potential of Orthosiphon stamineus leaf proteins (OSLPs) has never been evaluated in SH-SY5Y cells challenged by hydrogen peroxide (H₂O₂). This work thus aims to elucidate OSLP neuroprotective potential in alleviating H₂O₂ stress. OSLPs at varying concentrations were evaluated for cytotoxicity (24 and 48 h) and neuroprotective potential in H₂O₂-induced SH-SY5Y cells (24 h). The protective mechanism of H₂O₂-induced SH-SY5Y cells was also explored via mass-spectrometry-based label-free quantitative proteomics (LFQ) and bioinformatics. OSLPs (25, 50, 125, 250, 500, and 1000 µg/mL; 24 and 48 h) were found to be safe. Pre-treatments with OSLP doses (250, 500, and 1000 µg/mL, 24 h) significantly increased the survival of SH-SY5Y cells in a concentration-dependent manner and improved cell architecture—pyramidal-shaped cells, reduced clumping and shrinkage, with apparent neurite formations. OSLP pre-treatment (1000 µg/mL, 24 h) lowered the expressions of two major heat shock proteins, HSPA8 (heat shock protein family A (Hsp70) member 8) and HSP90AA1 (heat shock protein 90), which promote cellular stress signaling under stress conditions. OSLP is, therefore, suggested to be anti-inflammatory by modulating the “signaling of interleukin-4 and interleukin-13” pathway as the predominant mechanism in addition to regulating the “attenuation phase” and “HSP90 chaperone cycle for steroid hormone receptors” pathways to counteract heat shock protein (HSP)-induced damage under stress conditions.

Genomic Variation, Evolvability, and the Paradox of Mental Illness

Twentieth-century genetics was hard put to explain the irregular behavior of neuropsychiatric disorders. Autism and schizophrenia defy a principle of natural selection; they are highly heritable but associated with low reproductive success. Nevertheless, they persist. The genetic origins of such conditions are confounded by the problem of variable expression, that is, when a given genetic aberration can lead to any one of several distinct disorders. Also, autism and schizophrenia occur on a spectrum of severity, from mild and subclinical cases to the overt and disabling. Such irregularities reflect the problem of missing heritability; although hundreds of genes may be associated with autism or schizophrenia, together they account for only a small proportion of cases. Techniques for higher resolution, genomewide analysis have begun to illuminate the irregular and unpredictable behavior of the human genome. Thus, the origins of neuropsychiatric disorders in particular and complex disease in general have been illuminated. The human genome is characterized by a high degree of structural and behavioral variability: DNA content variation, epistasis, stochasticity in gene expression, and epigenetic changes. These elements have grown more complex as evolution scaled the phylogenetic tree. They are especially pertinent to brain development and function. Genomic variability is a window on the origins of complex disease, neuropsychiatric disorders, and neurodevelopmental disorders in particular. Genomic variability, as it happens, is also the fuel of evolvability. The genomic events that presided over the evolution of the primate and hominid lineages are over-represented in patients with autism and schizophrenia, as well as intellectual disability and epilepsy. That the special qualities of the human genome that drove evolution might, in some way, contribute to neuropsychiatric disorders is a matter of no little interest.

Sleep-wake cycles drive daily dynamics of synaptic phosphorylation

The circadian clock drives daily changes of physiology, including sleep-wake cycles, through regulation of transcription, protein abundance, and function. Circadian phosphorylation controls cellular processes in peripheral organs, but little is known about its role in brain function and synaptic activity. We applied advanced quantitative phosphoproteomics to mouse forebrain synaptoneurosomes isolated across 24 hours, accurately quantifying almost 8000 phosphopeptides. Half of the synaptic phosphoproteins, including numerous kinases, had large-amplitude rhythms peaking at rest-activity and activity-rest transitions. Bioinformatic analyses revealed global temporal control of synaptic function through phosphorylation, including synaptic transmission, cytoskeleton reorganization, and excitatory/inhibitory balance. Sleep deprivation abolished 98% of all phosphorylation cycles in synaptoneurosomes, indicating that sleep-wake cycles rather than circadian signals are main drivers of synaptic phosphorylation, responding to both sleep and wake pressures.

The Disease-Associated Chaperone FKBP51 Impairs Cognitive Function by Accelerating AMPA Receptor Recycling

Increased expression of the FK506-binding protein 5 (FKBP5) gene has been associated with a number of diseases, but most prominently in connection to psychiatric illnesses. Many of these psychiatric disorders present with dementia and other cognitive deficits, but a direct connection between these issues and alterations in FKBP5 remains unclear. We generated a novel transgenic mouse to selectively overexpress FKBP5, which encodes the FKBP51 protein, in the corticolimbic system, which had no overt effects on gross body weight, motor ability, or general anxiety. Instead, we found that overexpression of FKBP51 impaired long-term depression (LTD) as well as spatial reversal learning and memory, suggesting a role in glutamate receptor regulation. Indeed, FKBP51 altered the association of heat-shock protein 90 (Hsp90) with AMPA receptors, which was accompanied by an accelerated rate of AMPA recycling. In this way, the chaperone system is critical in triage decisions for AMPA receptor trafficking. Imbalance in the chaperone system may manifest in impairments in both inhibitory learning and cognitive function. These findings uncover an unexpected and essential mechanism for learning and memory that is controlled by the psychiatric risk factor FKBP5.

What do DNA methylation studies tell us about depression? A systematic review

There has been a limited number of systematic reviews conducted to summarize the overview of the relationship between DNA methylation and depression, and to critically appraise the roles of major study characteristics in the accuracy of study findings. This systematic review aims to critically appraise the impact of study characteristics on the association between DNA methylation and depression, and summarize the overview of this association. Electronic databases and gray literatures until December 2017 were searched for English-language studies with standard diagnostic criteria of depression. A total of 67 studies were included in this review along with a summary of their study characteristics. We grouped the findings into etiological and treatment studies. Majority of these selected studies were recently published and from developed countries. Whole blood samples were the most studied common tissues. Bisulfite conversion, along with pyrosequencing, was widely used to test the DNA methylation level across all the studies. High heterogeneity existed among the studies in terms of experimental and statistical methodologies and study designs. As recommended by the Cochrane guideline, a systematic review without meta-analysis should be undertaken. This review has, in general, found that DNA methylation modifications were associated with depression. Subgroup analyses showed that most studies found BDNF and SLC6A4 hypermethylations to be associated with MDD or depression in general. In contrast, studies on NR3C1, OXTR, and other genes, which were tested by only few studies, reported mixed findings. More longitudinal studies using standardized experimental and laboratory methodologies are needed in future studies to enable more systematical comparisons and quantitative synthesis.

HSP90 is a chaperone for DLK and is required for axon injury signaling

Peripheral nerve injury induces a robust proregenerative program that drives axon regeneration. While many regeneration-associated genes are known, the mechanisms by which injury activates them are less well-understood. To identify such mechanisms, we performed a loss-of-function pharmacological screen in cultured adult mouse sensory neurons for proteins required to activate this program. Well-characterized inhibitors were present as injury signaling was induced but were removed before axon outgrowth to identify molecules that block induction of the program. Of 480 compounds, 35 prevented injury-induced neurite regrowth. The top hits were inhibitors to heat shock protein 90 (HSP90), a chaperone with no known role in axon injury. HSP90 inhibition blocks injury-induced activation of the proregenerative transcription factor cJun and several regeneration-associated genes. These phenotypes mimic loss of the proregenerative kinase, dual leucine zipper kinase (DLK), a critical neuronal stress sensor that drives axon degeneration, axon regeneration, and cell death. HSP90 is an atypical chaperone that promotes the stability of signaling molecules. HSP90 and DLK show two hallmarks of HSP90-client relationships: (i) HSP90 binds DLK, and (ii) HSP90 inhibition leads to rapid degradation of existing DLK protein. Moreover, HSP90 is required for DLK stability in vivo, where HSP90 inhibitor reduces DLK protein in the sciatic nerve. This phenomenon is evolutionarily conserved in Drosophila Genetic knockdown of Drosophila HSP90, Hsp83, decreases levels of Drosophila DLK, Wallenda, and blocks Wallenda-dependent synaptic terminal overgrowth and injury signaling. Our findings support the hypothesis that HSP90 chaperones DLK and is required for DLK functions, including proregenerative axon injury signaling.

Stress-Induced Synaptic Dysfunction and Neurotransmitter Release in Alzheimer's Disease: Can Neurotransmitters and Neuromodulators be Potential Therapeutic Targets?

The communication between neurons at synaptic junctions is an intriguing process that monitors the transmission of various electro-chemical signals in the central nervous system. Albeit any aberration in the mechanisms associated with transmission of these signals leads to loss of synaptic contacts in both the neocortex and hippocampus thereby causing insidious cognitive decline and memory dysfunction. Compelling evidence suggests that soluble amyloid-β (Aβ) and hyperphosphorylated tau serve as toxins in the dysfunction of synaptic plasticity and aberrant neurotransmitter (NT) release at synapses consequently causing a cognitive decline in Alzheimer's disease (AD). Further, an imbalance between excitatory and inhibitory neurotransmission systems induced by impaired redox signaling and altered mitochondrial integrity is also amenable for such abnormalities. Defective NT release at the synaptic junction causes several detrimental effects associated with altered activity of synaptic proteins, transcription factors, Ca2+ homeostasis, and other molecules critical for neuronal plasticity. These detrimental effects further disrupt the normal homeostasis of neuronal cells and thereby causing synaptic loss. Moreover, the precise mechanistic role played by impaired NTs and neuromodulators (NMs) and altered redox signaling in synaptic dysfunction remains mysterious, and their possible interlink still needs to be investigated. Therefore, this review elucidates the intricate role played by both defective NTs/NMs and altered redox signaling in synaptopathy. Further, the involvement of numerous pharmacological approaches to compensate neurotransmission imbalance has also been discussed, which may be considered as a potential therapeutic approach in synaptopathy associated with AD.

A CNS-permeable Hsp90 inhibitor rescues synaptic dysfunction and memory loss in APP-overexpressing Alzheimer's mouse model via an HSF1-mediated mechanism

Induction of neuroprotective heat-shock proteins via pharmacological Hsp90 inhibitors is currently being investigated as a potential treatment for neurodegenerative diseases. Two major hurdles for therapeutic use of Hsp90 inhibitors are systemic toxicity and limited central nervous system permeability. We demonstrate here that chronic treatment with a proprietary Hsp90 inhibitor compound (OS47720) not only elicits a heat-shock-like response but also offers synaptic protection in symptomatic Tg2576 mice, a model of Alzheimer's disease, without noticeable systemic toxicity. Despite a short half-life of OS47720 in mouse brain, a single intraperitoneal injection induces rapid and long-lasting (>3 days) nuclear activation of the heat-shock factor, HSF1. Mechanistic study indicates that the remedial effects of OS47720 depend upon HSF1 activation and the subsequent HSF1-mediated transcriptional events on synaptic genes. Taken together, this work reveals a novel role of HSF1 in synaptic function and memory, which likely occurs through modulation of the synaptic transcriptome.

The mechanism of acetylcholine receptor in binding MuSK in myasthenia gravis and the role of HSP90 molecular chaperone

As an autoimmune disease, myasthenia gravis is caused by the dysfunction of neural transmission. Acetylcholine is known to exert its function after entering into synaptic cleft through binding onto postsynaptic membrane. The role of acetylcholine in binding MuSK in myasthenia gravis, however, remains unknown. A total of 38 myasthenia gravis patients and 27 healthy controls were included in this study for the detection of the expression of MuSK using immunofluorescent method. Expression of both MuSK and interleukin-6 (IL-6) were measured by Western blot, followed by the correlation analysis between heat shock protein 90 (HSP90) and IL-6 which were measured by enzyme-linked immunosorbent assay (ELISA). In myasthenia gravis patients, MuSK was co-localized with acetylcholine at the postsynaptic membrane. Such accumulation of MuSK, however, did not occur in normal people. Meanwhile we also observed elevated expression of IL-6 in myasthenia gravis patients (p<0.05). ELISA assay showed higher expression of HSP90 in patients. Further signaling pathway screening revealed the activation of IL-6-mediated pathways including STAT3 and SPH2. In conclusion, MuSK was co-localized with acetylcholine in myasthenia gravis patients, with elevated expression. HSP90 in disease people can activate IL-6 mediated signaling pathways.

Bidirectional regulation of synaptic transmission by BRAG1/IQSEC2 and its requirement in long-term depression

Dysfunction of the proteins regulating synaptic function can cause synaptic plasticity imbalance that underlies neurological disorders such as intellectual disability. A study found that four distinct mutations within BRAG1, an Arf-GEF synaptic protein, each led to X-chromosome-linked intellectual disability (XLID). Although the physiological functions of BRAG1 are poorly understood, each of these mutations reduces BRAG1's Arf-GEF activity. Here we show that BRAG1 is required for the activity-dependent removal of AMPA receptors in rat hippocampal pyramidal neurons. Moreover, we show that BRAG1 bidirectionally regulates synaptic transmission. On one hand, BRAG1 is required for the maintenance of synaptic transmission. On the other hand, BRAG1 expression enhances synaptic transmission, independently of BRAG1 Arf-GEF activity or neuronal activity, but dependently on its C-terminus interactions. This study demonstrates a dual role of BRAG1 in synaptic function and highlights the functional relevance of reduced BRAG1 Arf-GEF activity as seen in the XLID-associated human mutations.

Enhancement of stress resilience through histone deacetylase 6-mediated regulation of glucocorticoid receptor chaperone dynamics

BACKGROUND

Acetylation of heat shock protein 90 (Hsp90) regulates downstream hormone signaling via the glucocorticoid receptor (GR), but the role of this molecular mechanism in stress homeostasis is poorly understood. We tested whether acetylation of Hsp90 in the brain predicts and modulates the behavioral sequelae of a mouse model of social stress.

METHODS

Mice subjected to chronic social defeat stress were stratified into resilient and vulnerable subpopulations. Hypothalamic-pituitary-adrenal axis function was probed using a dexamethasone/corticotropin-releasing factor test. Measurements of Hsp90 acetylation, Hsp90-GR interactions, and GR translocation were performed in the dorsal raphe nucleus. To manipulate Hsp90 acetylation, we pharmacologically inhibited histone deacetylase 6, a known deacetylase of Hsp90, or overexpressed a point mutant that mimics the hyperacetylated state of Hsp90 at lysine K294.

RESULTS

Lower acetylated Hsp90, higher GR-Hsp90 association, and enhanced GR translocation were observed in dorsal raphe nucleus of vulnerable mice after chronic social defeat stress. Administration of ACY-738, a histone deacetylase 6-selective inhibitor, led to Hsp90 hyperacetylation in brain and in neuronal culture. In cell-based assays, ACY-738 increased the relative association of Hsp90 with FK506 binding protein 51 versus FK506 binding protein 52 and inhibited hormone-induced GR translocation. This effect was replicated by overexpressing the acetylation-mimic point mutant of Hsp90. In vivo, ACY-738 promoted resilience to chronic social defeat stress, and serotonin-selective viral overexpression of the acetylation-mimic mutant of Hsp90 in raphe neurons reproduced the behavioral effect of ACY-738.

CONCLUSIONS

Hyperacetylation of Hsp90 is a predictor and causal molecular determinant of stress resilience in mice. Brain-penetrant histone deacetylase 6 inhibitors increase Hsp90 acetylation and modulate GR chaperone dynamics offering a promising strategy to curtail deleterious socioaffective effects of stress and glucocorticoids.

Antenatal prediction of postpartum depression with blood DNA methylation biomarkers

Postpartum depression (PPD) affects ∼10-18% of women in the general population and results in serious consequences to both the mother and offspring. We hypothesized that predisposition to PPD risk is due to an altered sensitivity to estrogen-mediated epigenetic changes that act in a cell autonomous manner detectable in the blood. We investigated estrogen-mediated epigenetic reprogramming events in the hippocampus and risk to PPD using a cross-species translational design. DNA methylation profiles were generated using methylation microarrays in a prospective sample of the blood from the antenatal period of pregnant mood disorder patients who would and would not develop depression postpartum. These profiles were cross-referenced with syntenic locations exhibiting hippocampal DNA methylation changes in the mouse responsive to long-term treatment with 17β-estradiol (E2). DNA methylation associated with PPD risk correlated significantly with E2-induced DNA methylation change, suggesting an enhanced sensitivity to estrogen-based DNA methylation reprogramming exists in those at risk for PPD. Using the combined mouse and human data, we identified two biomarker loci at the HP1BP3 and TTC9B genes that predicted PPD with an area under the receiver operator characteristic (ROC) curve (area under the curve (AUC)) of 0.87 in antenatally euthymic women and 0.12 in a replication sample of antenatally depressed women. Incorporation of blood count data into the model accounted for the discrepancy and produced an AUC of 0.96 across both prepartum depressed and euthymic women. Pathway analyses demonstrated that DNA methylation patterns related to hippocampal synaptic plasticity may be of etiological importance to PPD.

Hsp90 chaperone inhibitor 17-AAG attenuates Aβ-induced synaptic toxicity and memory impairment

The excessive accumulation of soluble amyloid peptides (Aβ) plays a crucial role in the pathogenesis of Alzheimer's disease (AD), particularly in synaptic dysfunction. The role of the two major chaperone proteins, Hsp70 and Hsp90, in clearing misfolded protein aggregates has been established. Despite their abundant presence in synapses, the role of these chaperones in synapses remains elusive. Here, we report that Hsp90 inhibition by 17-AAG elicited not only a heat shock-like response but also upregulated presynaptic and postsynaptic proteins, such as synapsin I, synaptophysin, and PSD95 in neurons. 17-AAG treatment enhanced high-frequency stimulation-evoked LTP and protected neurons from synaptic damage induced by soluble Aβ. In AD transgenic mice, the daily administration of 17-AAG over 7 d resulted in a marked increase in PSD95 expression in hippocampi. 17-AAG treatments in wild-type C57BL/6 mice challenged by soluble Aβ significantly improved contextual fear memory. Further, we demonstrate that 17-AAG activated synaptic protein expression via transcriptional mechanisms through the heat shock transcription factor HSF1. Together, our findings identify a novel function of Hsp90 inhibition in regulating synaptic plasticity, in addition to the known neuroprotective effects of the chaperones against Aβ and tau toxicity, thus further supporting the potential of Hsp90 inhibitors in treating neurodegenerative diseases.

Identification of Heat Shock Protein 60 as a Regulator of Neutral Sphingomyelinase 2 and Its Role in Dopamine Uptake

Activation of sphingomyelinase (SMase) by extracellular stimuli is the major pathway for cellular production of ceramide, a bioactive lipid mediator acting through sphingomyelin (SM) hydrolysis. Previously, we reported the existence of six forms of neutral pH–optimum and Mg²⁺-dependent SMase (N-SMase) in the membrane fractions of bovine brain. Here, we focus on N-SMase ε from salt-extracted membranes. After extensive purification by 12,780-fold with a yield of 1.3%, this enzyme was eventually characterized as N-SMase2. The major single band of 60-kDa molecular mass in the active fractions of the final purification step was identified as heat shock protein 60 (Hsp60) by matrix-assisted laser desorption/ionization time-of-flight mass spectrometric analysis. Proximity ligation assay and immunoprecipitation study showed that Hsp60 interacted with N-SMase2, prompting us to examine the effect of Hsp60 on N-SMase2 and ceramide production. Interestingly, Hsp60 siRNA treatment significantly increased the protein level of N-SMase2 in N-SMase2-overexpressed HEK293 cells. Furthermore, transfection of Hsp60 siRNA into PC12 cells effectively increased both N-SMase activity and ceramide production and increased dopamine re-uptake with paralleled increase. Taken together, these results show that Hsp60 may serve as a negative regulator in N-SMase2-induced dopamine re-uptake by decreasing the protein level of N-SMase2.

Differentially expressed genes in Hirudo medicinalis ganglia after acetyl-L-carnitine treatment

Acetyl-L-carnitine (ALC) is a naturally occurring substance that, when administered at supra-physiological concentration, is neuroprotective. It is involved in membrane stabilization and in enhancement of mitochondrial functions. It is a molecule of considerable interest for its clinical application in various neural disorders, including Alzheimer's disease and painful neuropathies. ALC is known to improve the cognitive capability of aged animals chronically treated with the drug and, recently, it has been reported that it impairs forms of non-associative learning in the leech. In the present study the effects of ALC on gene expression have been analyzed in the leech Hirudo medicinalis. The suppression subtractive hybridisation methodology was used for the generation of subtracted cDNA libraries and the subsequent identification of differentially expressed transcripts in the leech nervous system after ALC treatment. The method detects differentially but also little expressed transcripts of genes whose sequence or identity is still unknown. We report that a single administration of ALC is able to modulate positively the expression of genes coding for functions that reveal a lasting effect of ALC on the invertebrate, and confirm the neuroprotective and neuromodulative role of the substance. In addition an important finding is the modulation of genes of vegetal origin. This might be considered an instance of ectosymbiotic mutualism.

A protein cross-linking assay for measuring cell surface expression of glutamate receptor subunits in the rodent brain after in vivo treatments

Trafficking of neurotransmitter receptors between intracellular and cell surface compartments is important for regulating neurotransmission. We developed a method for determining if an in vivo treatment has altered receptor distribution in a particular region of rodent brain. After the treatment, brain slices are rapidly prepared from the region of interest. Then, cell surface-expressed proteins are covalently cross-linked using the membrane-impermeable, bifunctional cross-linker bis(sulfosuccinimidyl)suberate (BS(3)). This increases the apparent molecular weight of surface receptors, while intracellular receptors are not modified. Thus, surface and intracellular receptor pools can be separated and quantified using SDS-PAGE and immunoblotting. This method is particularly useful for analyzing AMPA receptor subunits, offering advantages in accuracy, efficiency, and cost compared to biotinylation. A disadvantage is that some antibodies no longer recognize their target protein after cross-linking. We have used this method to quantify changes in receptor distribution after acute and chronic exposure to psychomotor stimulants.

Loss of survivin in neural precursor cells results in impaired long-term potentiation in the dentate gyrus and CA1-region

In adult mammals, newborn neural precursor cells (NPCs) derived from either the subventricular zone (SVZ) or the subgranular zone (SGZ) migrate into the olfactory bulb and the dentate gyrus (DG), respectively, where some of them mature into excitatory and inhibitory neurons. There is increasing evidence that this neurogenesis process is important for some types of learning and synaptic plasticity and vice versa. Survivin, a member of the inhibitor-of-apoptosis protein (IAP) family, has been suggested to have a central role in the regulation of neurogenesis. The protein is abundantly expressed in nervous tissue during embryonic development while being restricted postnatally to proliferating and migrating NPCs in SVZ and SGZ. Here we examined adult Survivin(Camcre) mice with a conditional deletion of the survivin gene in embryonic neurogenic regions. Although the deletion of survivin had no effect on basic excitability in DG and CA1-region, there was a marked impairment of long-term potentiation (LTP) in these areas. Our data support a function of survivin in hippocampal synaptic plasticity and learning and underline the importance of adult brain neurogenesis for proper operation of the hippocampal tri-synaptic circuit and the physiological functions that depend on it.

A detailed modular analysis of heat-shock protein dynamics under acute and chronic stress and its implication in anxiety disorders

Physiological and psychological stresses cause anxiety disorders such as depression and post-traumatic stress disorder (PTSD) and induce drastic changes at a molecular level in the brain. To counteract this stress, the heat-shock protein (HSP) network plays a vital role in restoring the homeostasis of the system. To study the stress-induced dynamics of heat-shock network, we analyzed three modules of the HSP90 network—namely trimerization reactions, phosphorylation–dephosphorylation reactions, and the conversion of HSP90 from an open to a closed conformation—and constructed a corresponding nonlinear differential equation model based on mass action kinetics laws. The kinetic parameters of the model were obtained through global optimization, and sensitivity analyses revealed that the most sensitive parameters are the kinase and phosphatase that drive the phosphorylation–dephosphorylation reactions. Bifurcation analysis carried out with the estimated kinetic parameters of the model with stress as bifurcation parameter revealed the occurrence of “mushroom”, a type of complex dynamics in which S-shaped and Z-shaped hysteretic bistable forms are present together. We mapped the molecular events responsible for generating the mushroom dynamics under stress and interpreted the occurrence of the S-shaped hysteresis to a normal level of stress, and the Z-shaped hysteresis to the HSP90 variations under acute and chronic stress in the fear conditioned system, and further, we hypothesized that this can be extended to stress-related disorders such as depression and PTSD in humans. Finally, we studied the effect of parameter variations on the mushroom dynamics to get insight about the role of phosphorylation–dephosphorylation parameters in HSP90 network in bringing about complex dynamics such as isolas, where the stable steady states in a bistable system are isolated and separated from each other and not connected by an unstable steady state.

Neurogranin targets calmodulin and lowers the threshold for the induction of long-term potentiation

Calcium entry and the subsequent activation of CaMKII trigger synaptic plasticity in many brain regions. The induction of long-term potentiation (LTP) in the CA1 region of the hippocampus requires a relatively high amount of calcium-calmodulin. This requirement is usually explained, based on in vitro and theoretical studies, by the low affinity of CaMKII for calmodulin. An untested hypothesis, however, is that calmodulin is not randomly distributed within the spine and its targeting within the spine regulates LTP. We have previously shown that overexpression of neurogranin enhances synaptic strength in a calmodulin-dependent manner. Here, using post-embedding immunogold labeling, we show that calmodulin is not randomly distributed, but spatially organized in the spine. Moreover, neurogranin regulates calmodulin distribution such that its overexpression concentrates calmodulin closer to the plasma membrane, where a high level of CaMKII immunogold labeling is also found. Interestingly, the targeting of calmodulin by neurogranin results in lowering the threshold for LTP induction. These findings highlight the significance of calmodulin targeting within the spine in synaptic plasticity.

Chronic morphine alters the presynaptic protein profile: identification of novel molecular targets using proteomics and network analysis

Opiates produce significant and persistent changes in synaptic transmission; knowledge of the proteins involved in these changes may help to understand the molecular mechanisms underlying opiate dependence. Using an integrated quantitative proteomics and systems biology approach, we explored changes in the presynaptic protein profile following a paradigm of chronic morphine administration that leads to the development of dependence. For this, we isolated presynaptic fractions from the striata of rats treated with saline or escalating doses of morphine, and analyzed the proteins in these fractions using differential isotopic labeling. We identified 30 proteins that were significantly altered by morphine and integrated them into a protein-protein interaction (PPI) network representing potential morphine-regulated protein complexes. Graph theory-based analysis of this network revealed clusters of densely connected and functionally related morphine-regulated clusters of proteins. One of the clusters contained molecular chaperones thought to be involved in regulation of neurotransmission. Within this cluster, cysteine-string protein (CSP) and the heat shock protein Hsc70 were downregulated by morphine. Interestingly, Hsp90, a heat shock protein that normally interacts with CSP and Hsc70, was upregulated by morphine. Moreover, treatment with the selective Hsp90 inhibitor, geldanamycin, decreased the somatic signs of naloxone-precipitated morphine withdrawal, suggesting that Hsp90 upregulation at the presynapse plays a role in the expression of morphine dependence. Thus, integration of proteomics, network analysis, and behavioral studies has provided a greater understanding of morphine-induced alterations in synaptic composition, and identified a potential novel therapeutic target for opiate dependence.

Proteomics of rat hypothalamus, hippocampus and pre-frontal/frontal cortex after central administration of the neuropeptide PACAP

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide that exerts pleiotropic functions, acting as a hypophysiotropic factor, a neurotrophic and a neuroprotective agent. The molecular pathways activated by PACAP to exert its physiological roles in brain are incompletely understood. In this study, adrenocorticotropic hormone (ACTH), prolactin, luteinising hormone (LH), follicle-stimulating hormone (FSH), thyroid-stimulating hormone (TSH), brain-derived neurotrophic factor and corticosterone blood levels were determined before and 20, 40, 60, and 120 min after PACAP intracerebroventricular administration. PACAP treatment increased ACTH, corticosterone, LH and FSH blood concentrations, while it decreased TSH levels. A proteomics investigation was carried out in hypothalamus, hippocampus and pre-frontal/frontal cortex (P/FC) using 2-dimensional gel electrophoresis at 120 min, the end-point suggested by studies on PACAP hypophysiotropic activities. Spots showing statistically significant alterations after PACAP treatment were identified by Matrix-assisted laser desorption/ionization-Time of flight mass spectrometry. Identified proteins were consistent with PACAP involvement in different molecular processes in brain. Altered expression levels were observed for proteins involved in cytoskeleton modulation and synaptic plasticity: actin in the hypothalamus; stathmin, dynamin, profilin and cofilin in hippocampus; synapsin in P/FC. Proteins involved in cellular differentiation were also modulated: glutathione-S-transferase α and peroxiredoxin in hippocampus; nucleoside diphosphate kinase in P/FC. Alterations were detected in proteins involved in neuroprotection, neurodegeneration and apoptosis: ubiquitin carboxyl-terminal hydrolase isozyme L1 and heat shock protein 90-β in hypothalamus; α-synuclein in hippocampus; glyceraldehyde-3-phosphate dehydrogenase and prohibitin in P/FC. This proteomics study identified new proteins involved in molecular mechanisms mediating PACAP functions in the central nervous system.

Alterations of GABA(A) and glutamate receptor subunits and heat shock protein in rat hippocampus following traumatic brain injury and in posttraumatic epilepsy

Traumatic brain injury (TBI) can result in the development of posttraumatic epilepsy (PTE). Recently, we reported differential alterations in tonic and phasic GABA(A) receptor (GABA(A)R) currents in hippocampal dentate granule cells 90 days after controlled cortical impact (CCI) (Mtchedlishvili et al., 2010). In the present study, we investigated long-term changes in the protein expression of GABA(A)R α1, α4, γ2, and δ subunits, NMDA (NR2B) and AMPA (GluR1) receptor subunits, and heat shock proteins (HSP70 and HSP90) in the hippocampus of Sprague-Dawley rats evaluated by Western blotting in controls, CCI-injured animals without PTE (CCI group), and CCI-injured animals with PTE (PTE group). No differences were found among all three groups for α1 and α4 subunits. Significant reduction of γ2 protein was observed in the PTE group compared to control. CCI caused a 194% and 127% increase of δ protein in the CCI group compared to control (p<0.0001), and PTE (p<0.0001) groups, respectively. NR2B protein was increased in CCI and PTE groups compared to control (p=0.0001, and p=0.011, respectively). GluR1 protein was significantly decreased in CCI and PTE groups compared to control (p=0.003, and p=0.001, respectively), and in the PTE group compared to the CCI group (p=0.036). HSP70 was increased in CCI and PTE groups compared to control (p=0.014, and p=0.005, respectively); no changes were found in HSP90 expression. These results provide for the first time evidence of long-term alterations of GABA(A) and glutamate receptor subunits and a HSP following CCI.

Molecular chaperones in Parkinson's disease--present and future

Parkinson's disease, like many other neurodegenerative disorders, is characterized by the progressive accumulation of pathogenic protein species and the formation of intracellular inclusion bodies. The cascade by which the small synaptic protein α-synuclein misfolds to form distinctive protein aggregates, termed Lewy bodies and Lewy neurites, has been the subject of intensive research for more than a decade. Genetic and pathological studies in Parkinson's disease patients as well as experimental studies in disease models have clearly established altered protein metabolism as a key element in the pathogenesis of Parkinson's disease. Alterations in protein metabolism include misfolding and aggregation, post-translational modification and dysfunctional degradation of cytotoxic protein species. Protein folding and re-folding are both mediated by a highly conserved network of molecules, called molecular chaperones and co-chaperones. In addition to the regulatory role in protein folding, molecular chaperone function is intimately associated with pathways of protein degradation, such as the ubiquitin-proteasome system and the autophagy-lysosomal pathway, to effectively remove irreversibly misfolded proteins. Because of the central role of molecular chaperones in maintaining protein homeostasis, we herein review our current knowledge on the involvement of molecular chaperones and co-chaperones in Parkinson's disease. We further discuss the capacity of molecular chaperones to prevent or modulate neurodegeneration, an important concept for future neuroprotective strategies and summarize the current progress in preclinical studies in models of Parkinson's disease and other neurodegenerative disorders. Finally we include a discussion on the future potential of using molecular chaperones as a disease modifying therapy.

Heat stress preconditioning improves cognitive outcome after diffuse axonal injury in rats

This study investigates the influence of heat stress preconditioning on cognitive outcome for rats with diffuse axonal injury (DAI), and attempts to examine the underlying mechanisms. Wistar rats were divided into four groups: rats subjected to heat stress preconditioning 24 h before induction of DAI (n = 10; HSDAI group), a DAI alone group (n = 10), a heat stress alone group (n = 10), and a sham-injury group (n = 10). From day 14 post-injury, the rats' learning abilities and memory were tested using the Morris water maze (MWM) task, followed by long-term potentiation (LTP) recording of the hippocampus. In addition, hematoxylin and eosin staining (H&E) and immunohistochemical staining (IHC) were conducted to determine the presence of brain lesions and expression of heat shock protein 70 (HSP70) at 24 h, and on days 14 and 20 post-injury. The rats in the DAI group displayed impaired MWM performance and attenuated LTP compared to the sham group (p < 0.05); the rats in the HSDAI and HS groups showed significant improvement in both MWM and LTP compared with the DAI group (p < 0.05), and no significant differences with the sham group (p > 0.05). Following injury, retraction balls, shrunken neurons, and HSP70 expression were visible in the brains of rats from the DAI and HSDAI groups; recovery was expedited in the rats belonging to the HSDAI group, as these pathological changes were alleviated, coincident with higher expression of HSP70. The rats' abilities for learning and memory were impaired following DAI; this may be due to the disconnection of brain regions, damage to neurons in the hippocampus, and a decrease in synaptic plasticity. Heat stress preconditioning is able to significantly attenuate this cognitive impairment, possibly mediated by the neuroprotective effect of HSP70.

Age matters

The age of an experimental animal can be a critical variable, yet age matters are often overlooked within neuroscience. Many studies make use of young animals, without considering possible differences between immature and mature subjects. This is especially problematic when attempting to model traits or diseases that do not emerge until adulthood. In this commentary we discuss the reasons for this apparent bias in age of experimental animals, and illustrate the problem with a systematic review of published articles on long-term potentiation. Additionally, we review the developmental stages of a rat and discuss the difficulty of using the weight of an animal as a predictor of its age. Finally, we provide original data from our laboratory and review published data to emphasize that development is an ongoing process that does not end with puberty. Developmental changes can be quantitative in nature, involving gradual changes, rapid switches, or inverted U-shaped curves. Changes can also be qualitative. Thus, phenomena that appear to be unitary may be governed by different mechanisms at different ages. We conclude that selection of the age of the animals may be critically important in the design and interpretation of neurobiological studies.

Signaling pathway adaptations and novel protein kinase A substrates related to behavioral sensitization to cocaine

Behavioral sensitization is an animal model for aspects of cocaine addiction. Cocaine-sensitized rats exhibit increased AMPA receptor (AMPAR) surface expression in the nucleus accumbens (NAc) which may in turn enhance drug seeking. To identify signaling pathways contributing to AMPAR up-regulation, we measured AMPAR surface expression and signaling pathway activation in the NAc of cocaine-sensitized rats, cocaine-exposed rats that failed to sensitize and saline controls on withdrawal days (WD) 1, 7, and 21. We focused on calcium/calmodulin-dependent protein kinase II (CaMKII), extracellular signal-regulated protein kinase (ERK), and protein kinase A (PKA). In sensitized rats, AMPAR surface expression was elevated on WD7 and WD21 but not WD1. ERK2 activation followed a parallel time-course, suggesting a role in AMPAR up-regulation. Both sensitized and non-sensitized rats exhibited CaMKII activation on WD7, suggesting that CaMKII activation is not sufficient for AMPAR up-regulation. PKA phosphorylation, measured using an antibody recognizing phosphorylated PKA substrates, increased gradually over withdrawal in sensitized rats, from below control levels on WD1 to significantly greater than controls on WD21. Using proteomics, novel sensitization-related PKA substrates were identified, including two structural proteins (CRMP-2 and alpha-tubulin) that we speculate may link PKA signaling to previously reported dendritic remodeling in NAc neurons of cocaine-sensitized rats.

Extinction of morphine-dependent conditioned behavior is associated with increased phosphorylation of the GluR1 subunit of AMPA receptors at hippocampal synapses

In abstinent opiate addicts, relapse can be triggered by exposure to environmental cues associated with drug use; thus, the disruption of these learned associations may be an effective approach for reducing relapse. Interestingly, glutamatergic systems are thought to be involved in opiate-induced behavioral plasticity. In this study, changes in expression and phosphorylation levels of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptor subunits (GluR1, GluR2) in the hippocampus were investigated in rats showing a conditioned response (CR) to an opiate-paired environment as well as in animals in which this conditioned behavior was extinguished. Additionally, another set of animals went through a drug-unpaired paradigm (without conditioning) in order to examine the effects of the pharmacology of the drug itself. Subcellular fractionation techniques were used to analyse the local distribution of AMPA glutamate subunits within the synapse, especially at the postsynaptic density (PSD). Results showed that morphine-dependent CRs did not alter expression or redistribution of GluR1 or GluR2; however, the unpaired administration of morphine resulted in an increase in the phosphorylation of the GluR1 subunit at extrasynaptic sites. Interestingly, the extinction of the CR significantly increased phosphorylation of the GluR1 subunit at the PSD. Therefore we propose that, within the synapse, the phosphorylation of the GluR1 subunit at the PSD may be a key mechanism in the extinction of opiate-associated CRs.

HSP90 beta regulates rapsyn turnover and subsequent AChR cluster formation and maintenance

Rapsyn, an acetylcholine receptor (AChR)-interacting protein, is essential for synapse formation at the neuromuscular junction (NMJ). Like many synaptic proteins, rapsyn turns over rapidly at synapses. However, little is known about molecular mechanisms that govern rapsyn stability. Using a differential mass-spectrometry approach, we identified heat-shock protein 90beta (HSP90beta) as a component in surface AChR clusters. The HSP90beta-AChR interaction required rapsyn and was stimulated by agrin. Inhibition of HSP90beta activity or expression, or disruption of its interaction with rapsyn attenuated agrin-induced formation of AChR clusters in vitro and impaired the development and maintenance of the NMJ in vivo. Finally, we showed that HSP90beta was necessary for rapsyn stabilization and regulated its proteasome-dependent degradation. Together, these results indicate a role of HSP90beta in NMJ development by regulating rapsyn turnover and subsequent AChR cluster formation and maintenance.

Formation of accumbens GluR2-lacking AMPA receptors mediates incubation of cocaine craving

Relapse to cocaine use after prolonged abstinence is an important clinical problem. This relapse is often induced by exposure to cues associated with cocaine use. To account for the persistent propensity for relapse, it has been suggested that cue-induced cocaine craving increases over the first several weeks of abstinence and remains high for extended periods. We and others identified an analogous phenomenon in rats that was termed 'incubation of cocaine craving': time-dependent increases in cue-induced cocaine-seeking over the first months after withdrawal from self-administered cocaine. Cocaine-seeking requires the activation of glutamate projections that excite receptors for alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) in the nucleus accumbens. Here we show that the number of synaptic AMPA receptors in the accumbens is increased after prolonged withdrawal from cocaine self-administration by the addition of new AMPA receptors lacking glutamate receptor 2 (GluR2). Furthermore, we show that these new receptors mediate the incubation of cocaine craving. Our results indicate that GluR2-lacking AMPA receptors could be a new target for drug development for the treatment of cocaine addiction. We propose that after prolonged withdrawal from cocaine, increased numbers of synaptic AMPA receptors combined with the higher conductance of GluR2-lacking AMPA receptors causes increased reactivity of accumbens neurons to cocaine-related cues, leading to an intensification of drug craving and relapse.

Proteomics- and transcriptomics-based screening of differentially expressed proteins and genes in brain of Wig rat: a model for attention deficit hyperactivity disorder (ADHD) research

Two global omics approaches were applied to develop an inventory of differentially expressed proteins and genes in Wig rat, a promising animal model of attention-deficit hyperactivity disorder (ADHD). The frontal cortex, striatum, and midbrain of Wig rat at 4 weeks of age were dissected for proteomics and transcriptomics analyses. Two-dimensional gel electrophoresis detected 13, 1, and 16 differentially expressed silver nitrate-stained spots in the frontal cortex, striatum, and midbrain, respectively. Peptide mass fingerprinting/tandem mass spectrometry identified 19 nonredundant proteins, belonging to 7 functional categories, namely, signal transduction, energy metabolism, cellular transport, protein with binding function, protein synthesis, cytoskeleton, and cell rescue. Interestingly, 10 proteins that were indentified in the present study were also previously reported in studies involving neurodegenerative diseases and psychiatric disorders, such as Alzheimer's disease (AD), Parkinson's disease, and Schizophrenia. Moreover, some of the proteins identified in the midbrain were involved in synaptic vesicular transport, suggesting abnormality in neurotransmitter release in this region. On the other hand, transcriptomics analysis of combined frontal cortex, striatum, and midbrain by rat whole genome 44K DNA oligo microarray revealed highly up-regulated (28) and down-regulated (33) genes. Functional categorization of these genes showed cellular transport, metabolism, protein fate, signal transduction, and transcription as the major categories, with 26% genes of unknown function. Some of the identified genes were related to AD, fragile X syndrome, and ADHD. This is a first comprehensive study providing insight into molecular components in Wig rat brain, and will help to elucidate the roles of identified proteins and genes in Wig rat brain, hopefully leading to uncovering the pathogenesis of ADHD.

Intracellular machinery for the transport of AMPA receptors

AMPA-type glutamate receptors are one of the most dynamic components of excitatory synapses. Their regulated addition and removal from synapses leads to long-lasting forms of synaptic plasticity, known as long-term potentiation (LTP) and long-term depression (LTD). In addition, AMPA receptors reach their synaptic targets after a complicated journey involving multiple transport steps through different membrane compartments. This review summarizes our current knowledge of the trafficking pathways of AMPARs and their relation to synaptic function and plasticity.

Functional compartmentalization of endosomal trafficking for the synaptic delivery of AMPA receptors during long-term potentiation

Endosomal membrane trafficking in dendritic spines is important for proper synaptic function and plasticity. However, little is known about the molecular identity and functional compartmentalization of the membrane trafficking machinery operating at the postsynaptic terminal. Here we report that the transport of AMPA-type glutamate receptors into synapses occurs in two discrete steps, and we identify the specific endosomal functions that control this process during long-term potentiation. We found that Rab11-dependent endosomes translocate AMPA receptors from the dendritic shaft into spines. Subsequently, an additional endosomal trafficking step, controlled by Rab8, drives receptor insertion into the synaptic membrane. Separate from this receptor delivery route, we show that Rab4 mediates a constitutive endosomal recycling within the spine. This Rab4-dependent cycling is critical for maintaining spine size but does not influence receptor transport. Therefore, our data reveal a highly compartmentalized endosomal network within the spine and identify the molecular components and functional organization of the membrane organelles that mediate AMPA receptor synaptic delivery during plasticity.