Novel role and mechanism of protein inhibitor of activated STAT1 in spatial learning

Influenza virus infection exacerbates gene expression related to neurocognitive dysfunction in brains of old mice

BACKGROUND

Age > 65 years is a key risk factor for poor outcomes after human influenza infection. Specifically, in addition to respiratory disease, non-neurotropic influenza A virus (IAV) causes neuro-cognitive complications, e.g. new onset depression and increases the risk of dementia after hospitalization. This study aimed to identify potential mechanisms of these effects by determining differences between young and old mice in brain gene expression in a mouse model of non-neurotropic IAV infection.

METHODS

Young (12 weeks) and old (70 weeks) C57Bl/6J mice were inoculated intranasally with 200 PFU H1N1 A/PR/34/8 (PR8) or sterile PBS (mock). Gene expression in lung and brain was measured by qRT-PCR and normalized to β-actin. Findings were confirmed using the nCounter Mouse Neuroinflammation Array (NanoString) and analyzed with nSolver 4.0 and Ingenuity Pathway Analysis (IPA, Qiagen).

RESULTS

IAV PR8 did not invade the central nervous system. Young and old mice differed significantly in brain gene expression at baseline and during non-neurotropic IAV infection. Expression of brain Ifnl, Irf7, and Tnf mRNAs was upregulated over baseline control at 3 days post-infection (p.i.) only in young mice, but old mice expressed more Ifnl than young mice 7 days p.i. Gene arrays showed down-regulation of the Epigenetic Regulation, Insulin Signaling, and Neurons and Neurotransmission pathways in old mice 3 days p.i. while young mice demonstrated no change or induction of these pathways at the same time point. IPA revealed marked baseline differences between old and young mice. Gene expression related to Cognitive Impairment, Memory Deficits and Learning worsened in old mice relative to young mice during IAV infection. Aged mice demonstrate more severe changes in gene expression related to memory loss and cognitive dysfunction by IPA.

CONCLUSIONS

These data suggest the genes and pathways related to learning and cognitive performance that were worse at baseline in old mice were further worsened by IAV infection, similar to old patients. Early events in the brain triggered by IAV infection portend downstream neurocognitive pathology in old adults.

Novel role of NCoR1 in impairing spatial memory through the mediation of a novel interacting protein DEC2

Long-term memory formation requires de novo RNA and protein synthesis. Using differential display PCR, we found that the NCoR1 cDNA fragment is differentially expressed between fast learners and slow learners, with fast learners showing a lower expression level than slow learners in the water maze learning task. Fast learners also show lower NCoR1 mRNA and protein expression levels. In addition, spatial training decreases both NCoR1 mRNA and protein expression, whereas NCoR1 conditional knockout (cKO) mice show enhanced spatial memory. In studying the molecular mechanism, we found that spatial training decreases the association between NCoR1 and DEC2. Both NCoR1 and DEC2 suppress the expression of BDNF, integrin α3 and SGK1 through C/EBPα binding to their DNA promoters, but overexpression of DEC2 in NCoR1 cKO mice rescues the decreased expression of these proteins compared with NCoR1 loxP mice overexpressing DEC2. Further, spatial training decreases DEC2 expression. Spatial training also enhances C/EBPα binding to Bdnf, Itga3 and Sgk1 promoters, an effect also observed in fast learners, and both NCoR1 and DEC2 control C/EBPα activity. Whereas knockdown of BDNF, integrin α3 or SGK1 expression impairs spatial learning and memory, it does not affect Y-maze performance, suggesting that BDNF, integrin α3 and SGK1 are involved in long-term memory formation, but not short-term memory formation. Moreover, NCoR1 expression is regulated by the JNK/c-Jun signaling pathway. Collectively, our findings identify DEC2 as a novel interacting protein of NCoR1 and elucidate the novel roles and mechanisms of NCoR1 and DEC2 in negative regulation of spatial memory formation.

STAT3 ameliorates truncated tau-induced cognitive deficits

Proteolytic cleavage of tau by asparagine endopeptidase (AEP) creates tau-N368 fragments, which may drive the pathophysiology associated with synaptic dysfunction and memory deterioration in the brain of Alzheimer's disease patients. Nonetheless, the molecular mechanisms of truncated tau-induced cognitive deficits remain unclear. Evidence suggests that signal transduction and activator of transcription-3 (STAT3) is associated with modulating synaptic plasticity, cell apoptosis, and cognitive function. Using luciferase reporter assays, electrophoretic mobility shift assays, western blotting, and immunofluorescence, we found that human tau-N368 accumulation inhibited STAT3 activity by suppressing STAT3 translocation into the nucleus. Overexpression of STAT3 improved tau-N368-induced synaptic deficits and reduced neuronal loss, thereby improving the cognitive deficits in tau-N368 mice. Moreover, in tau-N368 mice, activation of STAT3 increased N-methyl-D-aspartic acid receptor levels, decreased Bcl-2 levels, reversed synaptic damage and neuronal loss, and thereby alleviated cognitive deficits caused by tau-N368. Taken together, STAT3 plays a critical role in truncated tau-related neuropathological changes. This indicates a new mechanism behind the effect of tau-N368 on synapses and memory deficits. STAT3 can be used as a new molecular target to treat tau-N368-induced protein pathology.

The Role of Protein Methyltransferases in Immunity

The immune system protects our body from bacteria, viruses, and toxins and removes malignant cells. Activation of immune cells requires the onset of a network of important signaling proteins. Methylation of these proteins affects their structure and biological function. Under stimulation, T cells, B cells, and other immune cells undergo activation, development, proliferation, differentiation, and manufacture of cytokines and antibodies. Methyltransferases alter the above processes and lead to diverse outcomes depending on the degree and type of methylation. In the previous two decades, methyltransferases have been reported to mediate a great variety of immune stages. Elucidating the roles of methylation in immunity not only contributes to understanding the immune mechanism but is helpful in the development of new immunotherapeutic strategies. Hence, we review herein the studies on methylation in immunity, aiming to provide ideas for new approaches.

Unique aspects of IFN-γ/STAT1 signaling in neurons

The IFN-γ/STAT1 immune signaling pathway impacts many homeostatic and pathological aspects of neurons, beyond its canonical role in controlling intracellular pathogens. Well known for its potent pro-inflammatory and anti-viral functions in the periphery, the IFN-γ/STAT1 pathway is rapidly activated then deactivated to prevent excessive inflammation; however, neurons utilize unique IFN-γ/STAT1 activation patterns, which may contribute to the non-canonical neuron-specific downstream effects. Though it is now well-established that the immune system interacts and supports the CNS in health and disease, many aspects regarding IFN-γ production in the CNS and how neurons respond to IFN-γ are unclear. Additionally, it is not well understood how the diversity of the IFN-γ/STAT1 pathway is regulated in neurons to control homeostatic functions, support immune surveillance, and prevent pathologies. In this review, we discuss the neuron-specific mechanisms and kinetics of IFN-γ/STAT1 activation, the potential sources and entry sites of IFN-γ in the CNS, and the diverse set of homeostatic and pathological effects IFN-γ/STAT1 signaling in neurons has on CNS health and disease. We will also highlight the different contexts and conditions under which IFN-γ-induced STAT1 activation has been studied in neurons, and how various factors might contribute to the vast array of downstream effects observed.

Concerted type I interferon signaling in microglia and neural cells promotes memory impairment associated with amyloid β plaques

The principal signals that drive memory and cognitive impairment in Alzheimer's disease (AD) remain elusive. Here, we revealed brain-wide cellular reactions to type I interferon (IFN-I), an innate immune cytokine aberrantly elicited by amyloid β plaques, and examined their role in cognition and neuropathology relevant to AD in a murine amyloidosis model. Using a fate-mapping reporter system to track cellular responses to IFN-I, we detected robust, Aβ-pathology-dependent IFN-I activation in microglia and other cell types. Long-term blockade of IFN-I receptor (IFNAR) rescued both memory and synaptic deficits and resulted in reduced microgliosis, inflammation, and neuritic pathology. Microglia-specific Ifnar1 deletion attenuated the loss of post-synaptic terminals by selective engulfment, whereas neural Ifnar1 deletion restored pre-synaptic terminals and decreased plaque accumulation. Overall, IFN-I signaling represents a critical module within the neuroinflammatory network of AD and prompts concerted cellular states that are detrimental to memory and cognition.

Selenium Restores Synaptic Deficits by Modulating NMDA Receptors and Selenoprotein K in an Alzheimer's Disease Model

Aims: Strong evidence has implicated synaptic failure as a direct contributor to cognitive decline in Alzheimer's disease (AD), and selenium (Se) supplementation has demonstrated potential for AD treatment. However, the exact roles of Se and related selenoproteins in mitigating synaptic deficits remain unclear. Results: Our data show that selenomethionine (Se-Met), as the major organic form of Se in vivo, structurally restored synapses, dendrites, and spines, leading to improved synaptic plasticity and cognitive function in triple transgenic AD (3 × Tg-AD) mice. Furthermore, we found that Se-Met ameliorated synaptic deficits by inhibiting extrasynaptic N-methyl-d-aspartate acid receptors (NMDARs) and stimulating synaptic NMDARs, thereby modulating calcium ion (Ca²⁺) influx. We observed that a decrease in selenoprotein K (SELENOK) levels was closely related to AD, and a similar disequilibrium was found between synaptic and extrasynaptic NMDARs in SELENOK knockout mice and AD mice. Se-Met treatment upregulated SELENOK levels and restored the balance between synaptic and extrasynaptic NMDAR expression in AD mice. Innovation: These findings establish a key signaling pathway linking SELENOK and NMDARs with synaptic plasticity regulated by Se-Met, and thereby provide insight into mechanisms by which Se compounds mediate synaptic deficits in AD. Conclusion: Our study demonstrates that Se-Met restores synaptic deficits through modulating Ca²⁺ influx mediated by synaptic and extrasynaptic NMDARs in 3 × Tg-AD mice, and suggests a potentially functional interaction between SELENOK and NMDARs. Antioxid. Redox Signal. 35, 863-884.

Super-resolution study of PIAS SUMO E3-ligases in hippocampal and cortical neurons

The SUMOylation machinery is a regulator of neuronal activity and synaptic plasticity. It is composed of SUMO isoforms and specialized enzymes named E1, E2 and E3 SUMO ligases. Recent studies have highlighted how SUMO isoforms and E2 enzymes localize with synaptic markers to support previous functional studies but less information is available on E3 ligases. PIAS proteins - belonging to the protein inhibitor of activated STAT (PIAS) SUMO E3-ligase family - are the best-characterized SUMO E3-ligases and have been linked to the formation of spatial memory in rodents. Whether however they exert their function co-localizing with synaptic markers is still unclear. In this study, we applied for the first time structured illumination microscopy (SIM) to PIAS ligases to investigate the co-localization of PIAS1 and PIAS3 with synaptic markers in hippocampal and cortical murine neurons. The results indicate partial co-localization of PIAS1 and PIAS3 with synaptic markers in hippocampal neurons and much rarer occurrence in cortical neurons. This is in line with previous super-resolution reports describing the co-localization with synaptic markers of other components of the SUMOylation machinery.

Neuronal activity-induced SUMOylation of Akt1 by PIAS3 is required for long-term potentiation of synaptic transmission

Neuronal activity regulates spatial distribution of the SUMOylation system in cytosolic and dendritic sites, which has been implicated in learning, memory, and underlying synaptic structural and functional remodeling in the hippocampus. However, the functional target proteins for activated small ubiquitin-like modifiers (SUMOs) and downstream molecular consequences behind long-term potentiation (LTP) of synaptic plasticity remain to be elucidated. In this study, we showed that N-methyl-D-aspartate receptor-mediated neuronal activity induced the covalent modification of cytosolic Akt1 by small ubiquitin-like modifier 1 (SUMO1) in rat cortical and hippocampal CA1 neurons. Protein inhibitor of activated STAT3 (PIAS3) was involved in the activity-induced Akt1 SUMO1-ylation, and K64 and K276 residues were major SUMOylated sites. Importantly, Akt1 SUMOylation at K64 and K276 enhanced its enzymatic activity and facilitated T308 phosphorylation. Furthermore, the N-terminal SAP domain of PIAS3 bound Akt1 directly. The disruption of Akt1-PIAS3 interaction by Tat-SAP, a synthetic Tat-fused cell-permeable peptide containing PIAS3 SAP domain, inhibited neuronal activity-induced Akt1 SUMOylation and impaired LTP expression and late phase LTP maintenance in the hippocampus. Correlatedly, Tat-SAP not only blocked the LTP-related extracellular signal-regulated kinase (ERK)1/2-Elk-1-brain-derived neurotrophic factor (BDNF)/Arc signaling, but also disrupted mammalian target of rapamycin (mTOR)-eIF4E-binding protein 1 (4E-BP1) pathway. These findings reveal an activity-induced Akt1 SUMOylation by PIAS3 that contributes to ERK1/2-BDNF/Arc and mTOR-4E-BP1 cascades, and in turn, long-lasting excitatory synaptic responses.

STAT3 ameliorates cognitive deficits via regulation of NMDAR expression in an Alzheimer's disease animal model

Background: Abnormal tau accumulation in the brain has a positively correlation with neurodegeneration and memory deterioration, but the mechanism underlying tau-associated synaptic and cognitive impairments remains unclear. Our previous work has found that human full length tau (hTau) accumulation activated signal transducer and activator of transcription-1 (STAT1) to suppress N-methyl-D-aspartate receptors (NMDARs) expression, followed by memory deficits. STAT3 also belongs to STAT protein family and is reported to involve in regulation of synaptic plasticity and cognition. Here, we investigated the role of STAT3 in the cognitive deficits induced by hTau accumulation. Methods: In vitro studies HEK293 cells were used. EMSA, Luciferase reporter assay, and Immunoprecipitation were applied to detect STAT3 activity. In vivo studies, AAV virus were injected into the hippocampal CA3 region of C57 mice. Western blotting, quantitative real-time polymerase chain reaction, and immunofluorescence were applied to examine the level of synaptic proteins. Electrophysiological analysis, behavioral testing and Golgi impregnation were used to determine synaptic plasticity and memory ability recovery after overexpressing STAT3 or non-acetylated STAT1. Results: Our results showed that hTau accumulation acetylated STAT1 to retain STAT3 in the cytoplasm by increasing the binding of STAT1 with STAT3, and thus inactivated STAT3. Overexpressing STAT3 or non-acetylated STAT1 ameliorated hTau-induced synaptic loss and memory deficits by increasing the expression of NMDARs. Conclusions: Taken together, our study indicates that hTau accumulation impaired synaptic plasticity through STAT3 inactivation induced suppression of NMDARs expression, revealing a novel mechanism for hTau-associated synapse and memory deficits.

STAT3 ameliorates cognitive deficits by positively regulating the expression of NMDARs in a mouse model of FTDP-17

In tauopathies, memory impairment positively strongly correlates with the amount of abnormal tau aggregates; however, how tau accumulation induces synapse impairment is unclear. Recently, we found that human tau accumulation activated Signal Transduction and Activator of Transcription-1 (STAT1) to inhibit the transcription of synaptic N-methyl-D-aspartate receptors (NMDARs). Here, overexpressing human P301L mutant tau (P301L-hTau) increased the phosphorylated level of Signal Transduction and Activator of Transcription-3 (STAT3) at Tyr705 by JAK2, which would promote STAT3 translocate into the nucleus and activate STAT3. However, STAT3 was found mainly located in the cytoplasm. Further study found that P301L-htau acetylated STAT1 to bind with STAT3 in the cytoplasm, and thus inhibited the nuclear translocation and inactivation of STAT3. Knockdown of STAT3 in STAT3^flox/flox mice mimicked P301L-hTau-induced suppression of NMDARs expression, synaptic and memory impairments. Overexpressing STAT3 rescued P301L-hTau-induced synaptic and cognitive deficits by increasing NMDARs expression. Further study proved that STAT3 positively regulated NMDARs transcription through direct binding to the specific GAS element of NMDARs promoters. These findings indicate that accumulated P301L-hTau inactivating STAT3 to suppress NMDARs expression, revealed a novel mechanism for tau-associated synapse and cognition deficits, and STAT3 will hopefully serve as a potential pharmacological target for tauopathies treatment.

SUMO E3 ligase PIAS1 is a potential biomarker indicating stress susceptibility

Prior studies suggest that individual differences in stress responses contribute to the pathogenesis of neuropsychiatric disorders. In the present study, we investigated the role of small ubiquitin-like modifier (SUMO) E3 ligase protein inhibitor of activated STAT1 (PIAS1) in mediating stress responses to chronic social defeat stress (CSDS). We found that mRNA and protein levels of PIAS 1 were decreased in the hippocampus of high-susceptibility (HS) mice but not in low-susceptibility (LS) mice after CSDS. Local overexpression of PIAS1 in the hippocampus followed by CSDS exposure promoted stress resilience by attenuating social avoidance and improving anxiety-like behaviors. Viral-mediated gene transfer to generate a conditional knockdown of PIAS1 in the hippocampus promoted social avoidance and stress vulnerability after subthreshold microdefeat. HS mice displayed decreased levels of glucocorticoid receptor (GR) expression, and GR SUMOylation in the hippocampus was associated with stress vulnerability. Furthermore, cytokine/chemokine levels were changed predominantly in the hippocampus of HS mice. These results suggest that hippocampal PIAS1 plays a role in the regulation of stress susceptibility by post-translational modification of GRs.

Small ubiquitin-like modifier 2 (SUMO2) is critical for memory processes in mice

Small ubiquitin-like modifier (SUMO1-3) conjugation (SUMOylation), a posttranslational modification, modulates almost all major cellular processes. Mounting evidence indicates that SUMOylation plays a crucial role in maintaining and regulating neural function, and importantly its dysfunction is implicated in cognitive impairment in humans. We have previously shown that simultaneously silencing SUMO1-3 expression in neurons negatively affects cognitive function. However, the roles of the individual SUMOs in modulating cognition and the mechanisms that link SUMOylation to cognitive processes remain unknown. To address these questions, in this study, we have focused on SUMO2 and generated a new conditional Sumo2 knockout mouse line. We found that conditional deletion of Sumo2 predominantly in forebrain neurons resulted in marked impairments in various cognitive tests, including episodic and fear memory. Our data further suggest that these abnormalities are attributable neither to constitutive changes in gene expression nor to alterations in neuronal morphology, but they involve impairment in dynamic SUMOylation processes associated with synaptic plasticity. Finally, we provide evidence that dysfunction on hippocampal-based cognitive tasks was associated with a significant deficit in the maintenance of hippocampal long-term potentiation in Sumo2 knockout mice. Collectively, these data demonstrate that protein conjugation by SUMO2 is critically involved in cognitive processes.

Melatonin Induction of APP Intracellular Domain 50 SUMOylation Alleviates AD through Enhanced Transcriptional Activation and Aβ Degradation

The amyloid precursor protein (APP) intracellular domain (AICD) is implicated in the pathogenesis of Alzheimer’s disease (AD), but post-translational modification of AICD has rarely been studied and its role in AD is unknown. In this study, we examined the role and molecular mechanism of AICD SUMOylation in the pathogenesis of AD. We found that AICD is SUMO-modified by the SUMO E3 ligase protein inhibitor of activated STAT1 (PIAS1) in the hippocampus at Lys-43 predominantly, and that knockdown of PIAS1 decreases endogenous AICD SUMOylation. AICD SUMOylation increases AICD association with its binding protein Fe65 and increases AICD nuclear translocation. Furthermore, AICD SUMOylation increases AICD association with cyclic AMP-responsive element binding protein (CREB) and p65 and their DNA binding for transcriptional activation of neprilysin (NEP) and transthyretin (TTR), two major Aβ-degrading enzymes, respectively. Consequently, AICD SUMOylation decreases the Aβ level, Aβ oligomerization, and amyloid plaque deposits. It also rescues spatial memory deficits in APP/PS1 mice. Conversely, blockade of AICD SUMOylation at Lys-43 produces the opposite effects. Melatonin is identified as an endogenous stimulus that induces AICD SUMOylation. It also decreases the Aβ level and rescues reduction of PIAS1, NEP, and TTR expression in APP/PS1 mice. In this study, we demonstrate that AICD SUMOylation functions as a novel endogenous defense mechanism to combat AD.

Activity-Induced SUMOylation of Neuronal Nitric Oxide Synthase Is Associated with Plasticity of Synaptic Transmission and Extracellular Signal-Regulated Kinase 1/2 Signaling

Aims: Neuronal nitric oxide synthase (nNOS) and nitric oxide (NO) signaling have been implicated in learning, memory, and underlying long-lasting synaptic plasticity. In this study, we aimed at detecting whether nNOS is a target protein of SUMOylation in the hippocampus and its contributions to hippocampal long-term potentiation (LTP) of synaptic transmission. Results: We showed that N-methyl-d-aspartate receptor-dependent neuronal activity enhancement induced the attachment of small ubiquitin-like modifier 1 (SUMO1) to nNOS. Protein inhibitor of activated STAT3 (PIAS3) promoted SUMO1 conjugation at K725 and K739 on nNOS, which upregulated NO production and nNOS S1412 phosphorylation (activation). In addition, the N-terminus (amino acids 43-86) of PIAS3 bound nNOS directly. Tat-tagged PIAS3 segment representing amino acids 43-86, a cell-permeable peptide containing PIAS3 residues 43-86, suppressed activity-induced nNOS SUMOylation by disrupting PIAS3-nNOS association. It also decreased LTP-related expression of Arc and brain-derived neurotrophic factor and blocked signaling via extracellular signal-regulated kinase (ERK) 1/2 and Elk-1 in the hippocampus. More importantly, PIAS3-mediated nNOS SUMOylation was required for activity-regulated ERK1/2 activation in nNOS-positive neurons and hippocampal LTP induction. Innovation and Conclusion: These findings indicated that network activity-regulated nNOS SUMOylation underlies excitatory synaptic LTP by facilitating nNOS-NO-ERK1/2 signal cascades.

Galectin-3 promotes Aβ oligomerization and Aβ toxicity in a mouse model of Alzheimer's disease

Amyloid-β (Aβ) oligomers largely initiate the cascade underlying the pathology of Alzheimer's disease (AD). Galectin-3 (Gal-3), which is a member of the galectin protein family, promotes inflammatory responses and enhances the homotypic aggregation of cancer cells. Here, we examined the role and action mechanism of Gal-3 in Aβ oligomerization and Aβ toxicities. Wild-type (WT) and Gal-3-knockout (KO) mice, APP/PS1;WT mice, APP/PS1;Gal-3^+/- mice and brain tissues from normal subjects and AD patients were used. We found that Aβ oligomerization is reduced in Gal-3 KO mice injected with Aβ, whereas overexpression of Gal-3 enhances Aβ oligomerization in the hippocampi of Aβ-injected mice. Gal-3 expression shows an age-dependent increase that parallels endogenous Aβ oligomerization in APP/PS1 mice. Moreover, Aβ oligomerization, Iba1 expression, GFAP expression and amyloid plaque accumulation are reduced in APP/PS1;Gal-3^+/- mice compared with APP/PS1;WT mice. APP/PS1;Gal-3^+/- mice also show better acquisition and retention performance compared to APP/PS1;WT mice. In studying the mechanism underlying Gal-3-promoted Aβ oligomerization, we found that Gal-3 primarily co-localizes with Iba1, and that microglia-secreted Gal-3 directly interacts with Aβ. Gal-3 also interacts with triggering receptor expressed on myeloid cells-2, which then mediates the ability of Gal-3 to activate microglia for further Gal-3 expression. Immunohistochemical analyses show that the distribution of Gal-3 overlaps with that of endogenous Aβ in APP/PS1 mice and partially overlaps with that of amyloid plaque. Moreover, the expression of the Aβ-degrading enzyme, neprilysin, is increased in Gal-3 KO mice and this is associated with enhanced integrin-mediated signaling. Consistently, Gal-3 expression is also increased in the frontal lobe of AD patients, in parallel with Aβ oligomerization. Because Gal-3 expression is dramatically increased as early as 3 months of age in APP/PS1 mice and anti-Aβ oligomerization is believed to protect against Aβ toxicity, Gal-3 could be considered a novel therapeutic target in efforts to combat AD.

Tau accumulation triggers STAT1-dependent memory deficits by suppressing NMDA receptor expression

Intracellular tau accumulation forming neurofibrillary tangles is hallmark pathology of Alzheimer's disease (AD), but how tau accumulation induces synapse impairment is elusive. By overexpressing human full-length wild-type tau (termed hTau) to mimic tau abnormality as seen in the brain of sporadic AD patients, we find that hTau accumulation activates JAK2 to phosphorylate STAT1 (signal transducer and activator of transcription 1) at Tyr701 leading to STAT1 dimerization, nuclear translocation, and its activation. STAT1 activation suppresses expression of N-methyl-D-aspartate receptors (NMDARs) through direct binding to the specific GAS element of GluN1, GluN2A, and GluN2B promoters, while knockdown of STAT1 by AAV-Cre in STAT1^flox/flox mice or expressing dominant negative Y701F-STAT1 efficiently rescues hTau-induced suppression of NMDAR expression with amelioration of synaptic functions and memory performance. These findings indicate that hTau accumulation impairs synaptic plasticity through JAK2/STAT1-induced suppression of NMDAR expression, revealing a novel mechanism for hTau-associated synapse and memory deficits.

Protein inhibitor of activated STAT1 Ser503 phosphorylation-mediated Elk-1 SUMOylation promotes neuronal survival in APP/PS1 mice

BACKGROUND AND PURPOSE

Protein inhibitor of activated STAT1 (PIAS1) is phosphorylated by IKKα at Ser⁹⁰ in a PIAS1 E3 ligase activity-dependent manner. Whether PIAS1 is also phosphorylated at other residues and the functional significance of these additional phosphorylation events are not known. The transcription factor Elk-1 remains SUMOylated under basal conditions, but the role of Elk-1 SUMOylation in brain is unknown. Here, we examined the functional significance of PIAS1-mediated Elk-1 SUMOylation in Alzheimer's disease (AD) using the APP/PS1 mouse model of AD and amyloid β (Aβ) microinjections in vivo.

EXPERIMENTAL APPROACH

Novel phosphorylation site(s) on PIAS1 were identified by LC-MS/MS, and MAPK/ERK-mediated phosphorylation of Elk-1 demonstrated using in vitro kinase assays. Elk-1 SUMOylation by PIAS1 in brain was determined using in vitro SUMOylation assays. Apoptosis in hippocampus was assessed by measuring GADD45α expression by western blotting, and apoptosis of hippocampal neurons in APP/PS1 mice was assessed by TUNEL assay.

KEY RESULTS

Using LC-MS/MS, we identified a novel MAPK/ERK-mediated phosphorylation site on PIAS1 at Ser⁵⁰³ and showed this phosphorylation determines PIAS1 E3 ligase activity. In rat brain, Elk-1 was SUMOylated by PIAS1, which decreased Elk-1 phosphorylation and down-regulated GADD45α expression. Moreover, lentiviral-mediated transduction of Elk-1-SUMO1 reduced the number of hippocampal apoptotic neurons in APP/PS1 mice.

CONCLUSIONS AND IMPLICATIONS

MAPK/ERK-mediated phosphorylation of PIAS1 at Ser⁵⁰³ determines PIAS1 E3 ligase activity. Moreover, PIAS1 mediates SUMOylation of Elk-1, which functions as an endogenous defence mechanism against Aβ toxicity in vivo. Targeting Elk-1 SUMOylation could be considered a novel therapeutic strategy against AD.

In ovo Sound Stimulation Mediated Regulation of BDNF in the Auditory Cortex and Hippocampus of Neonatal Chicks

Brain-derived neurotrophic factor (BDNF) is known to mediate activity-dependent changes in the developing auditory system. Its expression in the brainstem auditory nuclei, auditory cortex and hippocampus of neonatal chicks (Gallus gallus domesticus) in response to in ovo high intensity sound exposure at 110 dB (arrhythmic sound: recorded traffic noise, 30-3000 Hz with peak at 2700 Hz, rhythmic sound: sitar music, 100-4000 Hz) was examined to understand the previously reported altered volume and neuronal number in these regions. In the brainstem auditory nuclei, no mature BDNF, but proBDNF at the protein level was detected, and no change in its levels was observed after in ovo sound stimulation (music and noise). Increased ProBDNF protein levels were found in the auditory cortex in response to arrhythmic sound, along with decreased levels of one of the BDNF mRNA transcripts, in response to both rhythmic and arrhythmic sound stimulation. In the hippocampus, increased levels of mature BDNF were found in response to music. Expression microarray analysis was performed to understand changes in gene expression in the hippocampus in response to music and noise, followed by gene ontology analysis showing enrichment of probable signaling pathways. Differentially expressed genes like CAMK1 and STAT1 were found to be involved in downstream signaling on comparing music versus noise-exposed chicks. In conclusion, we report that BDNF is differentially regulated in the auditory cortex at the transcriptional and post-translational level, and in the hippocampus at the post-translational level in response to in ovo sound stimulation.

Smad4 SUMOylation is essential for memory formation through upregulation of the skeletal myopathy gene TPM2

Background

Smad4 is a critical effector of TGF-β signaling that regulates a variety of cellular functions. However, its role in the brain has rarely been studied. Here, we examined the molecular mechanisms underlying the post-translational regulation of Smad4 function by SUMOylation, and its role in spatial memory formation.

Results

In the hippocampus, Smad4 is SUMOylated by the E3 ligase PIAS1 at Lys-113 and Lys-159. Both spatial training and NMDA injection enhanced Smad4 SUMOylation. Inhibition of Smad4 SUMOylation impaired spatial learning and memory in rats by downregulating TPM2, a gene associated with skeletal myopathies. Similarly, knockdown of TPM2 expression impaired spatial learning and memory, while TPM2 mRNA and protein expression increased after spatial training. Among the TPM2 mutations associated with skeletal myopathies, the TPM2E122K mutation was found to reduce TPM2 expression and impair spatial learning and memory in rats.

Conclusions

We have identified a novel role of Smad4 SUMOylation and TPM2 in learning and memory formation. These results suggest that patients with skeletal myopathies who carry the TPM2E122K mutation may also have deficits in learning and memory functions.

Electronic supplementary material

The online version of this article (doi:10.1186/s12915-017-0452-9) contains supplementary material, which is available to authorized users.

Galectin-3 Negatively Regulates Hippocampus-Dependent Memory Formation through Inhibition of Integrin Signaling and Galectin-3 Phosphorylation

Galectin-3, a member of the galectin protein family, has been found to regulate cell proliferation, inhibit apoptosis and promote inflammatory responses. Galectin-3 is also expressed in the adult rat hippocampus, but its role in learning and memory function is not known. Here, we found that contextual fear-conditioning training, spatial training or injection of NMDA into the rat CA1 area each dramatically decreased the level of endogenous galectin-3 expression. Overexpression of galectin-3 impaired fear memory, whereas galectin-3 knockout (KO) enhanced fear retention, spatial memory and hippocampal long-term potentiation. Galectin-3 was further found to associate with integrin α3, an association that was decreased after fear-conditioning training. Transfection of the rat CA1 area with small interfering RNA against galectin-3 facilitated fear memory and increased phosphorylated focal adhesion kinase (FAK) levels, effects that were blocked by co-transfection of the FAK phosphorylation-defective mutant Flag-FAKY397F. Notably, levels of serine-phosphorylated galectin-3 were decreased by fear conditioning training. In addition, blockade of galectin-3 phosphorylation at Ser-6 facilitated fear memory, whereas constitutive activation of galectin-3 at Ser-6 impaired fear memory. Interestingly galectin-1 plays a role in fear-memory formation similar to that of galectin-3. Collectively, our data provide the first demonstration that galectin-3 is a novel negative regulator of memory formation that exerts its effects through both extracellular and intracellular mechanisms.

The Role of PIAS SUMO E3-Ligases in Cancer

SUMOylation modifies the interactome, localization, activity, and lifespan of its target proteins. This process regulates several cellular machineries, including transcription, DNA damage repair, cell-cycle progression, and apoptosis. Accordingly, SUMOylation is critical in maintaining cellular homeostasis, and its deregulation leads to the corruption of a plethora of cellular processes that contribute to disease states. Among the proteins involved in SUMOylation, the protein inhibitor of activated STAT (PIAS) E3-ligases were initially described as transcriptional coregulators. Recent findings also indicate that they have a role in regulating protein stability and signaling transduction pathways. PIAS proteins interact with up to 60 cellular partners affecting several cellular processes, most notably immune regulation and DNA repair, but also cellular proliferation and survival. Here, we summarize the current knowledge about their role in tumorigenesis and cancer-related processes. Cancer Res; 77(7); 1542-7. ©2017 AACR.

Epigenetic regulation of HDAC1 SUMOylation as an endogenous neuroprotection against Aβ toxicity in a mouse model of Alzheimer's disease

Amyloid-β (Aβ) produces neurotoxicity in the brain and causes neuronal death, but the endogenous defense mechanism that is activated on Aβ insult is less well known. Here we found that acute Aβ increases the expression of PIAS1 and Mcl-1 via activation of MAPK/ERK, and Aβ induction of PIAS1 enhances HDAC1 SUMOylation in rat hippocampus. Knockdown of PIAS1 decreases endogenous HDAC1 SUMOylation and blocks Aβ induction of Mcl-1. Sumoylated HDAC1 reduces it association with CREB, increases CREB binding to the Mcl-1 promoter and mediates Aβ induction of Mcl-1 expression. Transduction of SUMO-modified lenti-HDAC1 vector to the hippocampus of APP/PS1 mice rescues spatial learning and memory deficit and long-term potentiation impairment in APP/PS1 mice. It also reduces the amount of amyloid plaque and the number of apoptotic cells in CA1 area of APP/PS1 mice. Meanwhile, HDAC1 SUMOylation decreases HDAC1 binding to the neprilysin promoter. These results together reveal an important role of HDAC1 SUMOylation as a naturally occurring defense mechanism protecting against Aβ toxicity and provide an alternative therapeutic strategy against AD.

PIAS1 binds p300 and behaves as a coactivator or corepressor of the transcription factor c-Myb dependent on SUMO-status

The PIAS proteins (Protein Inhibitor of Activated STATs) constitute a family of multifunctional nuclear proteins operating as SUMO E3 ligases and being involved in a multitude of interactions. They participate in a range of biological processes, also beyond their well-established role in the immune system and cytokine signalling. They act both as transcriptional corepressors and coactivators depending on the context. In the present work, we investigated mechanisms by which PIAS1 causes activation or repression of c-Myb dependent target genes. Analysis of global expression data shows that c-Myb and PIAS1 knockdowns affect a subset of common targets, but with a dual outcome consistent with a role of PIAS1 as either a corepressor or coactivator. Our mechanistic studies show that PIAS1 engages in a novel interaction with the acetyltransferase and coactivator p300. Interaction and ChIP analysis suggest a bridging function where PIAS1 enhances p300 recruitment to c-Myb-bound sites through interaction with both proteins. In addition, the E3 activity of PIAS1 enhances further its coactivation. Remarkably, the SUMO status of c-Myb had a decisive role, indicating a SUMO-dependent switch in the way PIAS1 affects c-Myb, either as a coactivator or corepressor. Removal of the two major SUMO-conjugation sites in c-Myb (2KR mutant), which enhances its activity significantly, turned PIAS1 into a corepressor. Also, p300 was less efficiently recruited to chromatin by c-Myb-2KR. We propose that PIAS1 acts as a "protein inhibitor of activated c-Myb" in the absence of SUMOylation while, in its presence, PIAS behaves as a "protein activator of repressed c-Myb".

MeCP2 SUMOylation rescues Mecp2-mutant-induced behavioural deficits in a mouse model of Rett syndrome

The methyl-CpG-binding protein 2 (MeCP2) gene, MECP2, is an X-linked gene encoding the MeCP2 protein, and mutations of MECP2 cause Rett syndrome (RTT). However, the molecular mechanism of MECP2-mutation-caused RTT is less known. Here we find that MeCP2 could be SUMO-modified by the E3 ligase PIAS1 at Lys-412. MeCP2 phosphorylation (at Ser-421 and Thr-308) facilitates MeCP2 SUMOylation, and MeCP2 SUMOylation is induced by NMDA, IGF-1 and CRF in the rat brain. MeCP2 SUMOylation releases CREB from the repressor complex and enhances Bdnf mRNA expression. Several MECP2 mutations identified in RTT patients show decreased MeCP2 SUMOylation. Re-expression of wild-type MeCP2 or SUMO-modified MeCP2 in Mecp2-null neurons rescues the deficits of social interaction, fear memory and LTP observed in Mecp2 conditional knockout (cKO) mice. These results together reveal an important role of MeCP2 SUMOylation in social interaction, memory and synaptic plasticity, and that abnormal MeCP2 SUMOylation is implicated in RTT.

Post-translational modifications of methyl-CpG-binding protein 2 (MeCP2) are important for its function and dysfunction in Rett syndrome. Here, Tai et al. show a functional interaction between MeCP2 SUMOylation and phosphorylation in rodent behavior and synaptic plasticity.

Immune mediators in the brain and peripheral tissues in autism spectrum disorder

Increasing evidence points to a central role for immune dysregulation in autism spectrum disorder (ASD). Several ASD risk genes encode components of the immune system and many maternal immune system-related risk factors--including autoimmunity, infection and fetal reactive antibodies--are associated with ASD. In addition, there is evidence of ongoing immune dysregulation in individuals with ASD and in animal models of this disorder. Recently, several molecular signalling pathways--including pathways downstream of cytokines, the receptor MET, major histocompatibility complex class I molecules, microglia and complement factors--have been identified that link immune activation to ASD phenotypes. Together, these findings indicate that the immune system is a point of convergence for multiple ASD-related genetic and environmental risk factors.

SUMO modification of Akt regulates global SUMOylation and substrate SUMOylation specificity through Akt phosphorylation of Ubc9 and SUMO1

SUMOylation is an important post-translational modification, and Akt SUMOylation was found to regulate cell proliferation, tumorigenesis and cell cycle, but the molecular mechanism of Akt SUMOylation is less well known. Here, we show both endogenous and ectopic Akt SUMOylation and Lys276 is the major SUMO acceptor on Akt. Further, Akt SUMOylation is Akt phosphorylation dependent and Akt SUMOylation increases Akt kinase activity without affecting the phosphorylation level of Akt. Moreover, endogenous Akt SUMOylation is enhanced by insulin treatment and this is Akt activity dependent. Heat-shock stimulus also increases Akt SUMOylation and it is also Akt activity dependent. Endogenous Akt SUMOylation is also found in the rat brain and it is enhanced by insulin-like growth factor-1 stimulation. In addition, Akt directly phosphorylates Ubc9 at Thr35 and phosphorylates SUMO1 at Thr76. Ubc9 phosphorylation at Thr35 promotes Ubc9 thioester bond formation and SUMO1 phosphorylation at Thr76 stabilizes the SUMO1 protein. Through these distinct mechanisms, Akt SUMOylation regulates global SUMOylation, including Akt and Ubc9 SUMOylation, and substrate SUMOylation specificity, including STAT1 and CREB SUMOylation, in different manners. Akt SUMOylation also enhances phosphatase and tensin homolog (PTEN) SUMOylation through Akt phosphorylation of Ubc9 and SUMO1, which serves as an endogenous mechanism to stop the positive feedback loop resulted from Akt activation. Further, Akt SUMOylation increases cyclin D1 expression and cell proliferation, and these effects are also mediated through Ubc9 phosphorylation at Thr35 and SUMO1 phosphorylation at Thr76. Here, we have identified a novel mechanism for SUMOylation regulation. Because of the important role Akt plays in tumorigenesis, this mechanism may also be involved in Akt-regulated tumorigenesis.

STAT1 regulates the homeostatic component of visual cortical plasticity via an AMPA receptor-mediated mechanism

Accumulating evidence points to a role for Janus kinase/signal transducers and activators of transcription (STAT) immune signaling in neuronal function; however, its role in experience-dependent plasticity is unknown. Here we show that one of its components, STAT1, negatively regulates the homeostatic component of ocular dominance plasticity in visual cortex. After brief monocular deprivation (MD), STAT1 knock-out (KO) mice show an accelerated increase of open-eye responses, to a level comparable with open-eye responses after a longer duration of MD in wild-type (WT) mice. Therefore, this component of plasticity is abnormally enhanced in KO mice. Conversely, increasing STAT1 signaling by IFNγ treatment in WT mice reduces the homeostatic component of plasticity by impairing open-eye responses. Enhanced plasticity in KO mice is accompanied by sustained surface levels of GluA1 AMPA receptors and increased amplitude and frequency of AMPA receptor-mediated mEPSCs, which resemble changes in WT mice after a longer duration of MD. These results demonstrate a unique role for STAT1 during visual cortical plasticity in vivo through a mechanism that includes AMPA receptors.

CREB SUMOylation by the E3 ligase PIAS1 enhances spatial memory

cAMP-responsive element binding protein (CREB) phosphorylation and signaling plays an important role in long-term memory formation, but other posttranslational modifications of CREB are less known. Here, we found that CREB1Δ, the short isoform of CREB, could be sumoylated by the small ubiquitin-like modifier (SUMO) E3 ligase protein inhibitor of activated STAT1 (PIAS1) at Lys271 and Lys290 and PIAS1 SUMOylation of CREB1Δ increased the expression level of CREB1Δ. CREB1Δ could also be sumoylated by other PIAS family proteins, but not by the E3 ligases RanBP2 and Pc2 or by the E2 ligase Ubc9. Furthermore, water maze training increased the level of endogenous CREB SUMOylation in rat CA1 neurons determined by in vitro SUMOylation assay, but this effect was not observed in other brain areas. Moreover, transduction of Lenti-CREBWT to rat CA1 area facilitated, whereas transduction of Lenti-CREB double sumo-mutant (CREBK271RK290R) impaired, spatial learning and memory performance. Transduction of Lenti-CREBWT-SUMO1 fusion vector to rat CA1 area showed a more significant effect in enhancing spatial learning and memory and CREB SUMOylation. Lenti-CREBWT transduction increased, whereas Lenti-CREBK271RK290R transduction decreased, CREB DNA binding to the brain-derived neurotrophic factor (bdnf) promoter and decreased bdnf mRNA expression. Knock-down of PIAS1 expression in CA1 area by PIAS1 siRNA transfection impaired spatial learning and memory and decreased endogenous CREB SUMOylation. In addition, CREB SUMOylation was CREB phosphorylation dependent and lasted longer. Therefore, CREB phosphorylation may be responsible for signal transduction during the early phase of long-term memory formation, whereas CREB SUMOylation sustains long-term memory.

Hes-1 SUMOylation by protein inhibitor of activated STAT1 enhances the suppressing effect of Hes-1 on GADD45α expression to increase cell survival

Background

Hairy and Enhancer of split 1 (Hes-1) is a transcriptional repressor that plays an important role in neuronal differentiation and development, but post-translational modifications of Hes-1 are much less known. In the present study, we aimed to investigate whether Hes-1 could be SUMO-modified and identify the candidate SUMO acceptors on Hes-1. We also wished to examine the role of the SUMO E3 ligase protein inhibitor of activated STAT1 (PIAS1) in SUMOylation of Hes-1 and the molecular mechanism of Hes-1 SUMOylation. Further, we aimed to identify the molecular target of Hes-1 and examine how Hes-1 SUMOylation affects its molecular target to affect cell survival.

Results

In this study, by using HEK293T cells, we have found that Hes-1 could be SUMO-modified and Hes-1 SUMOylation was greatly enhanced by the SUMO E3 ligase PIAS1 at Lys8, Lys27 and Lys39. Furthermore, Hes-1 SUMOylation stabilized the Hes-1 protein and increased the transcriptional suppressing activity of Hes-1 on growth arrest and DNA damage-inducible protein alpha (GADD45α) expression. Overexpression of GADD45α increased, whereas knockdown of GADD45αα expression decreased cell apoptosis. In addition, H₂O₂ treatment increased the association between PIAS1 and Hes-1 and enhanced the SUMOylation of Hes-1 for endogenous protection. Overexpression of Hes-1 decreased H₂O₂-induced cell death, but this effect was blocked by transfection of the Hes-1 triple sumo-mutant (Hes-1 3KR). Overexpression of PIAS1 further facilitated the anti-apoptotic effect of Hes-1. Moreover, Hes-1 SUMOylation was independent of Hes-1 phosphorylation and vice versa.

Conclusions

The present results revealed, for the first time, that Hes-1 could be SUMO-modified by PIAS1 and GADD45α is a novel target of Hes-1. Further, Hes-1 SUMOylation mediates cell survival through enhanced suppression of GADD45α expression. These results revealed a novel role of Hes-1 in addition to its involvement in Notch signaling. They also implicate that SUMOylation could be an important posttranslational modification that regulates cell survival.

STAT1 negatively regulates spatial memory formation and mediates the memory-impairing effect of Aβ

Signal transducer and activator of transcription-1 (STAT1) has an important role in inflammation and the innate immune response, but its role in the central nervous system is less well understood. Here, we examined the role of STAT1 in spatial learning and memory, and assessed the involvement of STAT1 in mediating the memory-impairing effect of amyloid-beta (Aβ). We found that water maze training downregulated STAT1 expression in the rat hippocampal CA1 area, and spatial learning and memory function was enhanced in Stat1-knockout mice. Conversely, overexpression of STAT1 impaired water maze performance. STAT1 strongly upregulated the expression of the extracellular matrix protein laminin β1 (LB1), which also impaired water maze performance in rats. Furthermore, Aβ impaired spatial learning and memory in association with a dose-dependent increase in STAT1 and LB1 expression, but knockdown of STAT1 and LB1 both reversed this effect of Aβ. This Aβ-induced increase in STAT1 and LB1 expression was also associated with a decrease in the expression of the N-methyl-D-aspartate receptor (NMDAR) subunits, NR1, and NR2B. Overexpression of NR1 or NR2B or exogenous application of NMDA reversed Aβ-induced learning and memory deficits as well as Aβ-induced STAT1 and LB1 expression. Our results demonstrate that STAT1 negatively regulates spatial learning and memory through transcriptional regulation of LB1 expression. We also identified a novel mechanism for Aβ pathogenesis through STAT1 induction. Notably, impairment of spatial learning and memory by this STAT1-mediated mechanism is independent of cAMP responsive element-binding protein signaling.

NMDA receptor signaling mediates the expression of protein inhibitor of activated STAT1 (PIAS1) in rat hippocampus

Protein inhibitor of activated STAT1 (PIAS1) was shown to play an important role in inflammation and innate immune response, but how PIAS1 is regulated is not known. We have recently demonstrated that PIAS1 enhances spatial learning and memory performance in rats. In this study, we examined the signaling pathway and neural mechanism that regulate PIAS1 expression in the brain by using pharmacological and molecular approaches. Our results revealed that pias1 gene expression is rapidly induced upon NMDA receptor activation in rat hippocampus, but this effect is blocked by transfection of sub-threshold concentrations of ERK1 siRNA/ERK2 siRNA or CREB siRNA. Pias1 gene expression is similarly induced by overexpression of the ERK1/ERK2 plasmids in rat hippocampus, and this effect is also blocked by sub-threshold concentration of CREB siRNA transfection. On the other hand, transfection of ERK1 siRNA/ERK2 siRNA or CREB siRNA at a higher concentration is sufficient to down-regulate PIAS1 expression. Inhibition of PI-3 kinase signaling and CaMKII signaling, which both result in CREB inactivation, similarly decreases PIAS1 expression. But NMDA and MK-801 do not affect the expression of IL-6 and TNFα. NMDA also did not affect the expression of PIAS2, PIAS3 and PIAS4. Further, pias1 mRNA has a similar degradation rate to that of the zif268 gene. These results together suggest that pias1 may function as an immediate early gene in an activity-dependent manner and PIAS1 expression is regulated by the NMDA-MAPK/ERK-CREB signaling pathway implicated in neuronal plasticity.

SUMOylation of the kainate receptor subunit GluK2 contributes to the activation of the MLK3-JNK3 pathway following kainate stimulation

Protein SUMOylation has been implicated in the pathogenesis of ischemic stroke. However, the underlying mechanisms remain unclear. Here, we found that global brain ischemia evokes a sustained elevation of GluK2 SUMOylation in the rat hippocampal CA1 region. Over-expression of wild-type GluK2, but not SUMOylation-deficient mutant, significantly increased the activity of MLK3 and JNK3 after kainate stimulation. SUMOylation deficiency attenuated the kainate-stimulated interaction between MLK3 and GluK2. In addition, inhibition of kainate-evoked GluK2 endocytosis decreased the activation of MLK3-JNK3 signaling and the binding of MLK3-GluK2 in cultured cortical neurons. These results suggest that the internalization of GluK2 following SUMO modification promotes its binding with MLK3, thereby activating the MLK3-JNK3 pathway, which may be responsible for ischemic neuronal cell death.

JNK1 inhibits GluR1 expression and GluR1-mediated calcium influx through phosphorylation and stabilization of Hes-1

The GluR1 subunit of the AMPA receptor plays an important role in excitatory synaptic transmission and synaptic plasticity in the brain, but the regulation mechanism for GluR1 expression is largely unknown. Hairy and enhancer of split 1 (Hes-1) is a mammalian transcription repressor that regulates neuronal differentiation and development, but the role of Hes-1 in differentiated neurons is also less known. Here, we examined the molecular mechanism in regulation of GluR1 expression in rat cultured cortical neurons. We found that Hes-1 suppressed GluR1 promoter activity and decreased GluR1 expression through direct binding to the N-box and through preventing Mash1/E47 from binding to the E-box of GluR1 promoter. We also found that Hes-1 could be regulated by c-Jun N-terminal kinase (JNK1). JNK1 directly phosphorylates Hes-1 at Ser-263. Furthermore, JNK1 phosphorylation of Hes-1 stabilized the Hes-1 protein and enhanced the suppressing effect of Hes-1 on GluR1 expression. These effects were demonstrated both in the soma and at the synapse. Moreover, this JNK1-mediated signaling pathway was found to inhibit AMPA-evoked calcium influx in cortical neurons and this regulation mechanism is Notch independent. Here, we provided the first evidence that Hes-1 plays an important role in synaptic function in differentiated neurons. We also identified a novel JNK1-Hes-1 signaling pathway that regulates GluR1 expression involved in synaptic function in rat cortical neurons.

Laminin-β1 impairs spatial learning through inhibition of ERK/MAPK and SGK1 signaling

Laminin is a major structural element of the basal lamina consisting of an α-chain, a β-chain, and a γ-chain arranged in a cross-like structure, with their C-terminal inter-coiled. Laminin is abundantly expressed in the hippocampus of mature brain and is implicated in several psychiatric disorders, but its possible role involved in learning and memory function is not known. This issue was examined here. Our results revealed that water maze training significantly decreased laminin-β1 (LB1) expression in the rat hippocampal CA1 area. Transfection of LB1 WT plasmid to hippocampal CA1 neurons impaired water maze performance in rats. Meanwhile, it decreased the phosphorylation level of ERK/MAPK and protein kinase serum- and glucocorticoid-inducible kinase-1 (SGK1). By contrast, knockdown of endogenous LB1 expression using RNA interference (LB1 siRNA) enhanced water maze performance. Meanwhile, it increased the phosphorylation level of ERK/MAPK and SGK1. The enhancing effect of LB1 siRNA on spatial learning and on the phosphorylation of ERK/MAPK and SGK1 was blocked by co-treatment with the MEK inhibitor U0126 at a concentration that did not apparently affect spatial learning and ERK/MAPK phosphorylation alone. Further, the enhancing effect of LB1 siRNA on spatial learning and SGK1 phosphorylation was similarly blocked by co-transfection with SGK1 siRNA at a concentration that did not markedly affect spatial learning and SGK1 expression alone. These results together indicate that LB1 negatively regulates spatial learning in rats. In addition, LB1 impairs spatial learning through decreased activation of the ERK/MAPK-SGK1 signaling pathway in the rat hippocampus.