beta-Amyloid disrupts activity-dependent gene transcription required for memory through the CREB coactivator CRTC1

Unlocking the epigenetic symphony: histone acetylation's impact on neurobehavioral change in neurodegenerative disorders

Recent genomics and epigenetic advances have empowered the exploration of DNA/RNA methylation and histone modifications crucial for gene expression in response to stress, aging and disease. Interest in understanding neuronal plasticity's epigenetic mechanisms, influencing brain rewiring amid development, aging and neurodegenerative disorders, continues to grow. Histone acetylation dysregulation, a commonality in diverse brain disorders, has become a therapeutic focus. Histone acetyltransferases and histone deacetylases have emerged as promising targets for neurodegenerative disorder treatment. This review delves into histone acetylation regulation, potential therapies and future perspectives for disorders like Alzheimer's, Parkinson's and Huntington's. Exploring genetic-environmental interplay through models and studies reveals molecular changes, behavioral insights and early intervention possibilities targeting the epigenome in at-risk individuals.

Comorbidity Genes of Alzheimer's Disease and Type 2 Diabetes Associated with Memory and Cognitive Function

Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM) are comorbidities that result from the sharing of common genes. The molecular background of comorbidities can provide clues for the development of treatment and management strategies. Here, the common genes involved in the development of the two diseases and in memory and cognitive function are reviewed. Network clustering based on protein-protein interaction network identified tightly connected gene clusters that have an impact on memory and cognition among the comorbidity genes of AD and T2DM. Genes with functional implications were intensively reviewed and relevant evidence summarized. Gene information will be useful in the discovery of biomarkers and the identification of tentative therapeutic targets for AD and T2DM.

Amyloid-β-induced dendritic spine elimination requires Ca2+-permeable AMPA receptors, AKAP-Calcineurin-NFAT signaling, and the NFAT target gene Mdm2

Alzheimer's Disease (AD) is associated with brain accumulation of synaptotoxic amyloid-β (Aβ) peptides produced by the proteolytic processing of amyloid precursor protein (APP). Cognitive impairments associated with AD correlate with dendritic spine and excitatory synapse loss, particularly within the hippocampus. In rodents, soluble Aβ oligomers impair hippocampus-dependent learning and memory, promote dendritic spine loss, inhibit NMDA-type glutamate receptor (NMDAR)-dependent long-term potentiation (LTP), and promote synaptic depression (LTD), at least in part through activation of the Ca2+-CaM-dependent phosphatase calcineurin (CaN). Yet, questions remain regarding Aβ-dependent postsynaptic CaN signaling specifically at the synapse to mediate its synaptotoxicity. Here, we use pharmacologic and genetic approaches to demonstrate a role for postsynaptic signaling via A kinase-anchoring protein 150 (AKAP150)-scaffolded CaN in mediating Aβ-induced dendritic spine loss in hippocampal neurons from rats and mice of both sexes. In particular, we found that Ca2+-permeable AMPA-type glutamate receptors (CP-AMPARs), which were previously shown to signal through AKAP-anchored CaN to promote both LTD and Aβ-dependent inhibition of LTP, are also required upstream of AKAP-CaN signaling to mediate spine loss via overexpression of APP containing multiple mutations linked to familial, early-onset AD and increased Aβ production. In addition, we found that the CaN-dependent nuclear factor of activated T-cells (NFAT) transcription factors are required downstream to promote Aβ-mediated dendritic spine loss. Finally, we identified the E3-ubiquitin ligase Mdm2, which was previously linked to LTD and developmental synapse elimination, as a downstream NFAT target gene upregulated by Aβ whose enzymatic activity is required for Aβ-mediated spine loss.Significance Statement Impaired hippocampal function and synapse loss are hallmarks of AD linked to Aβ oligomers. Aβ exposure acutely blocks hippocampal LTP and enhances LTD and chronically leads to dendritic spine synapse loss. In particular, Aβ hijacks normal plasticity mechanisms, biasing them toward synapse weakening/elimination, with previous studies broadly linking CaN phosphatase signaling to this synaptic dysfunction. However, we do not understand how Aβ engages signaling specifically at synapses. Here we elucidate a synapse-to-nucleus signaling pathway coordinated by the postsynaptic scaffold protein AKAP150 that is activated by Ca2+ influx through CP-AMPARs and transduced to nucleus by CaN-NFAT signaling to transcriptionally upregulate the E3-ubiquitin ligase Mdm2 that is required for Aβ-mediated spine loss. These findings identify Mdm2 as potential therapeutic target for AD.

CREB: A multifaceted transcriptional regulator of neural and immune function in CNS tumors

Cancers of the central nervous system (CNS) are unique with respect to their tumor microenvironment. Such a status is due to immune-privilege and the cellular behaviors within a highly networked, neural-rich milieu. During tumor development in the CNS, neural, immune and cancer cells establish complex cell-to-cell communication networks which mimic physiological functions, including paracrine signaling and synapse-like formations. This crosstalk regulates diverse pathological functions contributing to tumor progression. In the CNS, regulation of physiological and pathological functions relies on various cell signaling and transcription programs. At the core of these events lies the cyclic adenosine monophosphate (cAMP) response element binding protein (CREB), a master transcriptional regulator in the CNS. CREB is a kinase inducible transcription factor which regulates many CNS functions, including neurogenesis, neuronal survival, neuronal activation and long-term memory. Here, we discuss how CREB-regulated mechanisms operating in diverse cell types, which control development and function of the CNS, are co-opted in CNS tumors.

Nr4a2 blocks oAβ-mediated synaptic plasticity dysfunction and ameliorates spatial memory deficits in the APP Sw,Ind mouse

Alzheimer's disease AD is associated with disruptions in neuronal communication, especially in brain regions crucial for learning and memory, such as the hippocampus. The amyloid hypothesis suggests that the accumulation of amyloid-beta oligomers (oAβ) contributes to synaptic dysfunction by internalisation of synaptic AMPA receptors. Recently, it has been reported that Nr4a2, a member of the Nr4a family of orphan nuclear receptors, plays a role in hippocampal synaptic plasticity by regulating BDNF and synaptic AMPA receptors. Here, we demonstrate that oAβ inhibits activity-dependent Nr4a2 activation in hippocampal neurons, indicating a potential link between oAβ and Nr4a2 down-regulation. Furthermore, we have observed a reduction in Nr4a2 protein levels in postmortem hippocampal tissue samples from early AD stages. Pharmacological activation of Nr4a2 proves effective in preventing oAβ-mediated synaptic depression in the hippocampus. Notably, Nr4a2 overexpression in the hippocampus of AD mouse models ameliorates spatial learning and memory deficits. In conclusion, the findings suggest that oAβ may contribute to early cognitive impairment in AD by blocking Nr4a2 activation, leading to synaptic dysfunction. Thus, our results further support that Nr4a2 activation is a potential therapeutic target to mitigate oAβ-induced synaptic and cognitive impairments in the early stages of Alzheimer's disease.

Sustained CREB phosphorylation by lipid-peptide liquid crystalline nanoassemblies

Cyclic-AMP-response element-binding protein (CREB) is a leucine zipper class transcription factor that is activated through phosphorylation. Ample CREB phosphorylation is required for neurotrophin expression, which is of key importance for preventing and regenerating neurological disorders, including the sequelae of long COVID syndrome. Here we created lipid-peptide nanoassemblies with different liquid crystalline structural organizations (cubosomes, hexosomes, and vesicles) as innovative nanomedicine delivery systems of bioactive PUFA-plasmalogens (vinyl ether phospholipids with polyunsaturated fatty acid chains) and a neurotrophic pituitary adenylate cyclase-activating polypeptide (PACAP). Considering that plasmalogen deficiency is a potentially causative factor for neurodegeneration, we examined the impact of nanoassemblies type and incubation time in an in vitro Parkinson's disease (PD) model as critical parameters for the induction of CREB phosphorylation. The determined kinetic changes in CREB, AKT, and ERK-protein phosphorylation reveal that non-lamellar PUFA-plasmalogen-loaded liquid crystalline lipid nanoparticles significantly prolong CREB activation in the neurodegeneration model, an effect unattainable with free drugs, and this effect can be further enhanced by the cell-penetrating peptide PACAP. Understanding the sustained CREB activation response to neurotrophic nanoassemblies might lead to more efficient use of nanomedicines in neuroregeneration.

Microglia sense and suppress epileptic neuronal hyperexcitability

Microglia are the resident immune cells of the central nervous system, undertaking surveillance role and reacting to brain homeostasis and neurological diseases. Recent studies indicate that microglia modulate epilepsy-induced neuronal activities, however, the mechanisms underlying microglia-neuron communication in epilepsy are still unclear. Here we report that epileptic neuronal hyperexcitability activates microglia and drives microglial ATP/ADP hydrolyzing ectoenzyme CD39 (encoded by Entpd1) expression via recruiting the cAMP responsive element binding protein (CREB)-regulated transcription coactivator-1 (CRTC1) from cytoplasm to the nucleus and binding to CREB. Activated microglia in turn suppress epileptic neuronal hyperexcitability in a CD39 dependent manner. Disrupting microglial CREB/CRTC1 signaling, however, decreases CD39 expression and diminishes the inhibitory effect of microglia on epileptic neuronal hyperexcitability. Overall, our findings reveal CD39-dependent control of epileptic neuronal hyperexcitability by microglia is through an excitation-transcription coupling mechanism.

Mechanisms of NURR1 Regulation: Consequences for Its Biological Activity and Involvement in Pathology

NURR1 (Nuclear receptor-related 1 protein or NR4A2) is a nuclear protein receptor transcription factor with an essential role in the development, regulation, and maintenance of dopaminergic neurons and mediates the response to stressful stimuli during the perinatal period in mammalian brain development. The dysregulation of NURR1 activity may play a role in various diseases, including the onset and progression of neurodegenerative diseases, and several other pathologies. NURR1 is regulated by multiple mechanisms, among which phosphorylation by kinases or SUMOylation are the best characterized. Both post-translational modifications can regulate the activity of NURR1, affecting its stability and transcriptional activity. Other non-post-translational regulatory mechanisms include changes in its subcellular distribution or interaction with other protein partners by heterodimerization, also affecting its transcription activity. Here, we summarize the currently known regulatory mechanisms of NURR1 and provide a brief overview of its participation in pathological alterations.

CRTC1 is a potential target to delay aging-induced cognitive deficit by protecting the integrity of the blood-brain barrier via inhibiting inflammation

Aging can cause attenuation in the functioning of multiple organs, and blood-brain barrier (BBB) breakdown could promote the occurrence of disorders of the central nervous system during aging. Since inflammation is considered to be an important factor underlying BBB injury during aging, vascular endothelial cell senescence serves as a critical pathological basis for the destruction of BBB integrity. In the current review, we have first introduced the concepts related to aging-induced cognitive deficit and BBB integrity damage. Thereafter, we reviewed the potential relationship between disruption of BBB integrity and cognition deficit and the role of inflammation, vascular endothelial cell senescence, and BBB injury. We have also briefly introduced the function of CREB-regulated transcription co-activator 1 (CRTC1) in cognition and aging-induced CRTC1 changes as well as the critical roles of CRTC1/cyclooxygenase-2 (COX-2) in regulating inflammation, endothelial cell senescence, and BBB injury. Finally, the underlying mechanisms have been summarized and we propose that CRTC1 could be a promising target to delay aging-induced cognitive deficit by protecting the integrity of BBB through promoting inhibition of inflammation-mediated endothelial cell senescence.

Activity-Dependent Nr4a2 Induction Modulates Synaptic Expression of AMPA Receptors and Plasticity via a Ca2+/CRTC1/CREB Pathway

Transcription factors have a pivotal role in synaptic plasticity and the associated modification of neuronal networks required for memory formation and consolidation. The nuclear receptors subfamily 4 group A (Nr4a) have emerged as possible modulators of hippocampal synaptic plasticity and cognitive functions. However, the molecular and cellular mechanisms underlying Nr4a2-mediated hippocampal synaptic plasticity are not completely known. Here, we report that neuronal activity enhances Nr4a2 expression and function in cultured mouse hippocampal neurons (both sexes) by an ionotropic glutamate receptor/Ca2+/cAMP response element-binding protein/CREB-regulated transcription factor 1 (iGluR/Ca2+/CREB/CRTC1) pathway. Nr4a2 activation mediates BDNF production and increases expression of iGluRs, thereby affecting LTD at CA3-CA1 synapses in acute mouse hippocampal slices (both sexes). Together, our results indicate that the iGluR/Ca2+/CREB/CRTC1 pathway mediates activity-dependent expression of Nr4a2, which is involved in glutamatergic synaptic plasticity by increasing BDNF and synaptic GluA1-AMPARs. Therefore, Nr4a2 activation could be a therapeutic approach for brain disorders associated with dysregulated synaptic plasticity.SIGNIFICANCE STATEMENT A major factor that regulates fast excitatory synaptic transmission and plasticity is the modulation of synaptic AMPARs. However, despite decades of research, the underlying mechanisms of this modulation remain poorly understood. Our study identified a molecular pathway that links neuronal activity with AMPAR modulation and hippocampal synaptic plasticity through the activation of Nr4a2, a member of the nuclear receptor subfamily 4. Since several compounds have been described to activate Nr4a2, our study not only provides mechanistic insights into the molecular pathways related to hippocampal synaptic plasticity and learning, but also identifies Nr4a2 as a potential therapeutic target for pathologic conditions associated with dysregulation of glutamatergic synaptic function.

Protein transport from pre- and postsynapse to the nucleus: Mechanisms and functional implications

The extreme length of neuronal processes poses a challenge for synapse-to-nucleus communication. In response to this challenge several different mechanisms have evolved in neurons to couple synaptic activity to the regulation of gene expression. One of these mechanisms concerns the long-distance transport of proteins from pre- and postsynaptic sites to the nucleus. In this review we summarize current evidence on mechanisms of transport and consequences of nuclear import of these proteins for gene transcription. In addition, we discuss how information from pre- and postsynaptic sites might be relayed to the nucleus by this type of long-distance signaling. When applicable, we highlight how long-distance protein transport from synapse-to-nucleus can provide insight into the pathophysiology of disease or reveal new opportunities for therapeutic intervention.

Natural essential oils derived from herbal medicines: A promising therapy strategy for treating cognitive impairment

Cognitive impairment (CI), mainly Alzheimer’s disease (AD), continues to increase in prevalence and is emerging as one of the major health problems in society. However, until now, there are no first-line therapeutic agents for the allopathic treatment or reversal of the disease course. Therefore, the development of therapeutic modalities or drugs that are effective, easy to use, and suitable for long-term administration is important for the treatment of CI such as AD. Essential oils (EOs) extracted from natural herbs have a wide range of pharmacological components, low toxicity, and wide sources, In this review, we list the history of using volatile oils against cognitive disorders in several countries, summarize EOs and monomeric components with cognitive improvement effects, and find that they mainly act by attenuating the neurotoxicity of amyloid beta, anti-oxidative stress, modulating the central cholinergic system, and improving microglia-mediated neuroinflammation. And combined with aromatherapy, the unique advantages and potential of natural EOs in the treatment of AD and other disorders were discussed. This review hopes to provide scientific basis and new ideas for the development and application of natural medicine EOs in the treatment of CI.

Jacob-induced transcriptional inactivation of CREB promotes Aβ-induced synapse loss in Alzheimer's disease

Synaptic dysfunction caused by soluble β-amyloid peptide (Aβ) is a hallmark of early-stage Alzheimer's disease (AD), and is tightly linked to cognitive decline. By yet unknown mechanisms, Aβ suppresses the transcriptional activity of cAMP-responsive element-binding protein (CREB), a master regulator of cell survival and plasticity-related gene expression. Here, we report that Aβ elicits nucleocytoplasmic trafficking of Jacob, a protein that connects a NMDA-receptor-derived signalosome to CREB, in AD patient brains and mouse hippocampal neurons. Aβ-regulated trafficking of Jacob induces transcriptional inactivation of CREB leading to impairment and loss of synapses in mouse models of AD. The small chemical compound Nitarsone selectively hinders the assembly of a Jacob/LIM-only 4 (LMO4)/ Protein phosphatase 1 (PP1) signalosome and thereby restores CREB transcriptional activity. Nitarsone prevents impairment of synaptic plasticity as well as cognitive decline in mouse models of AD. Collectively, the data suggest targeting Jacob protein-induced CREB shutoff as a therapeutic avenue against early synaptic dysfunction in AD.

Breakdown of the central synapses in C9orf72-linked ALS/FTD

Amyotrophic lateral sclerosis (ALS) is a progressive, fatal neurodegenerative disease that leads to the death of motor and cortical neurons. The clinical manifestations of ALS are heterogenous, and efficacious treatments to significantly slow the progression of the disease are lacking. Cortical hyper-excitability is observed pre-symptomatically across disease-causative genetic variants, as well as in the early stages of sporadic ALS, and typically precedes motor neuron involvement and overt neurodegeneration. The causes of cortical hyper-excitability are not yet fully understood but is mainly agreed to be an early event. The identification of the nucleotide repeat expansion (GGGGCC)_n in the C9ORF72 gene has provided evidence that ALS and another neurodegenerative disease, frontotemporal dementia (FTD), are part of a disease spectrum with common genetic origins. ALS and FTD are diseases in which synaptic dysfunction is reported throughout disease onset and stages of progression. It has become apparent that ALS/FTD-causative genes, such as C9ORF72, may have roles in maintaining the normal physiology of the synapse, as mutations in these genes often manifest in synaptic dysfunction. Here we review the dysfunctions of the central nervous system synapses associated with the nucleotide repeat expansion in C9ORF72 observed in patients, organismal, and cellular models of ALS and FTD.

Mild membrane depolarization in neurons induces immediate early gene transcription and acutely subdues responses to successive stimulus

Immediate early genes (IEGs) are transcribed in response to neuronal activity from sensory stimulation during multiple adaptive processes in the brain. The transcriptional profile of IEGs is indicative of the duration of neuronal activity, but its sensitivity to the strength of depolarization remains unknown. Also unknown is whether activity history of graded potential changes influence future neuronal activity. In this work with dissociated rat cortical neurons, we found that mild depolarization—mediated by elevated extracellular potassium (K⁺)—induces a wide array of rapid IEGs and transiently depresses transcriptional and signaling responses to a successive stimulus. This latter effect was independent of de novo transcription, translation, and signaling via calcineurin or mitogen-activated protein kinase. Furthermore, as measured by multiple electrode arrays and calcium imaging, mild depolarization acutely subdues subsequent spontaneous and bicuculline-evoked activity via calcium- and N-methyl-d-aspartate receptor–dependent mechanisms. Collectively, this work suggests that a recent history of graded potential changes acutely depress neuronal intrinsic properties and subsequent responses. Such effects may have several potential downstream implications, including reducing signal-to-noise ratio during synaptic plasticity processes.

Medicinal Chemistry and Chemical Biology of Nurr1 Modulators: An Emerging Strategy in Neurodegeneration

Nuclear receptor related 1 (Nurr1) is a transcription factor with neuroprotective and antineuroinflammatory properties. Observations from genetic studies and human patients support potential of Nurr1 as a therapeutic target in neurodegeneration, but due to a lack of high-quality chemical tools for pharmacological control of Nurr1, its target validation is pending. Nevertheless, considerable progress has recently been made in elucidating structural and functional characteristics of Nurr1, and several ligand scaffolds have been discovered. Here, we analyze Nurr1's structure and mechanisms compared to other nuclear receptors, summarize the known small molecule Nurr1 ligands, and discuss the available evidence for the therapeutic potential of Nurr1 in neurodegeneration.

New Insights Into the Pivotal Role of CREB-Regulated Transcription Coactivator 1 in Depression and Comorbid Obesity

Depression and obesity are major public health concerns, and there is mounting evidence that they share etiopathophysiological mechanisms. The neurobiological pathways involved in both mood and energy balance regulation are complex, multifactorial and still incompletely understood. As a coactivator of the pleiotropic transcription factor cAMP response element-binding protein (CREB), CREB-regulated transcription coactivator 1 (CRTC1) has recently emerged as a novel regulator of neuronal plasticity and brain functions, while CRTC1 dysfunction has been associated with neurodegenerative and psychiatric diseases. This review focuses on recent evidence emphasizing the critical role of CRTC1 in the neurobiology of depression and comorbid obesity. We discuss the role of CRTC1 downregulation in mediating chronic stress-induced depressive-like behaviors, and antidepressant response in the light of the previously characterized Crtc1 knockout mouse model of depression. The putative role of CRTC1 in the alteration of brain energy homeostasis observed in depression is also discussed. Finally, we highlight rodent and human studies supporting the critical involvement of CRTC1 in depression-associated obesity.

Scaffold hopping from amodiaquine to novel Nurr1 agonist chemotypes via microscale analogue libraries

Several lines of evidence suggest the ligand‐sensing transcription factor Nurr1 as a promising target to treat neurodegenerative diseases. Nurr1 modulators to validate and exploit this therapeutic potential are rare, however. To identify novel Nurr1 agonist chemotypes, we have employed the Nurr1 activator amodiaquine as template for microscale analogue library synthesis. The first set of analogues was based on the 7‐chloroquiolin‐4‐amine core fragment of amodiaquine and revealed superior N‐substituents compared to diethylaminomethylphenol contained in the template. A second library of analogues was subsequently prepared to replace the chloroquinolineamine scaffold. The two sets of analogues enabled a full scaffold hop from amodiaquine to a novel Nurr1 agonist sharing no structural features with the lead but comprising superior potency on Nurr1. Additionally, pharmacophore modeling based on the entire set of active and inactive analogues suggested key features for Nurr1 agonists.

Nr4a2 Transcription Factor in Hippocampal Synaptic Plasticity, Memory and Cognitive Dysfunction: A Perspective Review

Long-lasting changes of synaptic efficacy are largely mediated by activity-induced gene transcription and are essential for neuronal plasticity and memory. In this scenario, transcription factors have emerged as pivotal players underlying synaptic plasticity and the modification of neural networks required for memory formation and consolidation. Hippocampal synaptic dysfunction is widely accepted to underlie the cognitive decline observed in some neurodegenerative disorders including Alzheimer’s disease. Therefore, understanding the molecular pathways regulating gene expression profiles may help to identify new synaptic therapeutic targets. The nuclear receptor 4A subfamily (Nr4a) of transcription factors has been involved in a variety of physiological processes within the hippocampus, ranging from inflammation to neuroprotection. Recent studies have also pointed out a role for the activity-dependent nuclear receptor subfamily 4, group A, member 2 (Nr4a2/Nurr1) in hippocampal synaptic plasticity and cognitive functions, although the underlying molecular mechanisms are still poorly understood. In this review, we highlight the specific effects of Nr4a2 in hippocampal synaptic plasticity and memory formation and we discuss whether the dysregulation of this transcription factor could contribute to hippocampal synaptic dysfunction, altogether suggesting the possibility that Nr4a2 may emerge as a novel synaptic therapeutic target in brain pathologies associated to cognitive dysfunctions.

MiRNA-132/212 regulates tight junction stabilization in blood-brain barrier after stroke

MicroRNA-132/212 has been supposed as a critical gene related to the blood–brain barrier (BBB) protection after stroke, but its regulation pathway including the upstream regulator and downstream targets is still unclear. Herein, we demonstrated the cAMP response element-binding protein (CREB)-regulated transcription coactivator-1 (CRTC1) to be the upstream regulator of miRNA-132/212 using CRTC1 knockout and wild-type mice. CRTC1 deletion led to the reduction of miRNA-132/212 expression in mice brain after ischemic stroke, significantly increased infarct volume, and aggravated BBB permeability with worsening neurological deficits. Furthermore, we identified that miRNA-132 repressed Claudin-1, tight junction-associated protein-1 (TJAP-1), and RNA-binding Fox-1 (RBFox-1) by directly binding to their respective 3′-untranslated regions, which alleviated the ischemic damage by enhancing neuronal survival and BBB integrity. Moreover, the co-culture of endothelial cells with CRTC1-deficient neurons aggravated the cell vulnerability to hypoxia, also supporting the idea that miRNA-132/212 cluster is regulated by CRTC1 and acts as a crucial role in the mitigation of ischemic damage. This work is a step forward for understanding the role of miRNA-132/212 in neurovascular interaction and may be helpful for potential gene therapy of ischemic stroke.

Aminothioneine, a product derived from golden oyster mushrooms (Pleurotus cornucopiae var. citrinopileatus), activates Ca2+ signal-mediated brain-derived neurotrophic factor expression in cultured cortical neurons

Ameliorating reduced brain-derived neurotrophic factor (BDNF) expression or maintaining high BDNF levels in the brain has been suggested to improve brain function in neurological diseases and prevent aging-related brain dysfunction. In this study, we found that a food-derived product, Aminothioneine® (AT), which is prepared from the extract of golden oyster mushrooms (Pleurotus cornucopiae var. citrinopileatus), increased Bdnf mRNA expression levels in primary rat cortical neuron cultures. Ergothioneine (ET) comprises more than 1% in AT and is an active constituent of AT, and ET has been reported to increase neurotrophin-4/5, but not BDNF, expression levels in neural stem cells. ET also did not affect Bdnf mRNA expression in cultured cortical neurons, suggesting that AT contains other active constituents that induce Bdnf mRNA expression in neurons. AT-induced Bdnf mRNA expression was completely blocked by d-(−)-2-Amino-5-phosphonopentanoic acid but partially blocked by nicardipine, U0126, and FK506. This result suggested that N-methyl-d-aspartate receptor-derived Ca²⁺ signals, including those mediated by extracellular signal-regulated kinase/mitogen-activated protein kinase and calcineurin, are the main contributors to Bdnf mRNA induction. In addition, AT increased cAMP-response element-binding protein (CREB) phosphorylation and the nuclear localization of CREB-regulated transcriptional coactivator 1 in neurons. Thus, AT can increase Bdnf mRNA expression via Ca²⁺ signal-induced CREB-dependent transcription in neurons. Because AT is a food-derived product, increasing and/or maintaining BDNF levels in the brain by daily intake of the product could be possible, which may be beneficial for neurological and aging-related disorders.

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Aminothioneine® (AT) induced Bdnf mRNA expression in cultured rat cortical neurons.

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Ergothioneine tended to induce Nt-4/5 but did not affect Bdnf mRNA expression.

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AT activated MAPK and calcineurin-regulated CREB-dependent transcription.

Brain transcriptome analysis of a CLN2 mouse model as a function of disease progression

Background

Neuronal ceroid lipofuscinoses, (NCLs or Batten disease) are a group of inherited, early onset, fatal neurodegenerative diseases associated with mutations in 13 genes. All forms of the disease are characterized by lysosomal accumulation of fluorescent storage material, as well as profound neurodegeneration, but the relationship of the various genes’ function to a single biological process is not obvious. In this study, we used a well-characterized mouse model of classical late infantile NCL (cLINCL) in which the tripeptidyl peptidase 1 (Tpp1) gene is disrupted by gene targeting, resulting in loss of detectable TPP1 activity and leading to progressive neurological phenotypes including ataxia, increased motor deficiency, and early death.

Methods

In order to identify genes and pathways that may contribute to progression of the neurodegenerative process, we analyzed forebrain/midbrain and cerebellar transcriptional differences at 1, 2, 3 and 4 months of age in control and TPP1-deficient mice by global RNA-sequencing.

Results

Progressive neurodegenerative inflammatory responses involving microglia, astrocytes and endothelial cells were observed, accompanied by activation of leukocyte extravasation signals and upregulation of nitric oxide production and reactive oxygen species. Several astrocytic (i.e., Gfap, C4b, Osmr, Serpina3n) and microglial (i.e., Ctss, Itgb2, Itgax, Lyz2) genes were identified as strong markers for assessing disease progression as they showed increased levels of expression in vivo over time. Furthermore, transient increased expression of choroid plexus genes was observed at 2 months in the lateral and fourth ventricle, highlighting an early role for the choroid plexus and cerebrospinal fluid in the disease pathology. Based on these gene expression changes, we concluded that neuroinflammation starts, for the most part, after 2 months in the Tpp1^−/− brain and that activation of microglia and astrocytes occur more rapidly in cerebellum than in the rest of the brain; confirming increased severity of inflammation in this region.

Conclusions

These findings have led to a better understanding of cLINCL pathological onset and progression, which may aid in development of future therapeutic treatments for this disease.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02302-z.

Dopamine, sleep, and neuronal excitability modulate amyloid-β-mediated forgetting in Drosophila

Alzheimer disease (AD) is one of the main causes of age-related dementia and neurodegeneration. However, the onset of the disease and the mechanisms causing cognitive defects are not well understood. Aggregation of amyloidogenic peptides is a pathological hallmark of AD and is assumed to be a central component of the molecular disease pathways. Pan-neuronal expression of Aβ42Arctic peptides in Drosophila melanogaster results in learning and memory defects. Surprisingly, targeted expression to the mushroom bodies, a center for olfactory memories in the fly brain, does not interfere with learning but accelerates forgetting. We show here that reducing neuronal excitability either by feeding Levetiracetam or silencing of neurons in the involved circuitry ameliorates the phenotype. Furthermore, inhibition of the Rac-regulated forgetting pathway could rescue the Aβ42Arctic-mediated accelerated forgetting phenotype. Similar effects are achieved by increasing sleep, a critical regulator of neuronal homeostasis. Our results provide a functional framework connecting forgetting signaling and sleep, which are critical for regulating neuronal excitability and homeostasis and are therefore a promising mechanism to modulate forgetting caused by toxic Aβ peptides.

Dysregulated CRTC1-BDNF signaling pathway in the hippocampus contributes to Aβ oligomer-induced long-term synaptic plasticity and memory impairment

Expression of CREB-regulated transcription coactivator 1 (CRTC1) in the hippocampus is impaired in Alzheimer's disease (AD). However, CRTC1 related mechanisms associated with long-term synaptic plasticity impairment and cognitive decline in the onset of AD are unknown. In this study, electrophysiological recordings indicated that lentivirus-mediated CRTC1 overexpression effectively ameliorates suppression of late-phase long-term potentiation (L-LTP) in rat hippocampal slices treated with oligomeric amyloid β(1-42) peptides (oAβ42) (200 nM). In addition, application of oAβ42 and genetic knockdown of CRTC1 by lentivirus-mediated CRTC1-shRNA inhibit L-LTP, whereas their combination does not further impair L-LTP. Brain-derived neurotrophic factor (BDNF), an important downstream protein confers protection of CRTC1 overexpression against oAβ42-induced L-LTP impairment as shown by administration of K252a (200 nM) and TrkB-FC (20 μg/ml). Furthermore, behavioral and western blotting analyses showed that CRTC1 overexpression reverses oAβ42-induced hippocampal-dependent cognitive deficits, downregulation of CRTC1 and BDNF expression. Notably, CRTC1-shRNA directly elicits cognitive deficits. In summary, these findings show that hippocampal CRTC1 signaling is affected by soluble oAβ, and CRTC1-BDNF pathway is involved in hippocampal L-LTP impairment and memory deficits induced by oAβ42.

PAK4 suppresses motor neuron degeneration in hSOD1G93A -linked amyotrophic lateral sclerosis cell and rat models

OBJECTIVES

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the progressive loss of motor neurons (MN). CREB pathway-mediated inhibition of apoptosis contributes to neuron protection, and PAK4 activates CREB signalling in diverse cell types. This study aimed to investigate PAK4's effect and mechanism of action in ALS.

METHODS

We analysed RNA levels by qRT-PCR, protein levels by immunofluorescence and Western blotting, and apoptosis by flow cytometry and TUNEL staining. Cell transfection was performed for in vitro experiment. Mice were injected intraspinally to evaluate PAK4 function in vivo experiment. Rotarod test was performed to measure motor function.

RESULTS

The expression and activation of PAK4 significantly decreased in the cell and mouse models of ALS as the disease progressed, which was caused by the negative regulation of miR-9-5p. Silencing of PAK4 increased the apoptosis of MN by inhibiting CREB-mediated neuroprotection, whereas overexpression of PAK4 protected MN from hSOD1^G93A -induced degeneration by activating CREB signalling. The neuroprotective effect of PAK4 was markedly inhibited by CREB inhibitor. In ALS models, the PAK4/CREB pathway was inhibited, and cell apoptosis increased. In vivo experiments revealed that PAK4 overexpression in the spinal neurons of hSOD1^G93A mice suppressed MN degeneration, prolonged survival and promoted the CREB pathway.

CONCLUSIONS

PAK4 protects MN from degeneration by activating the anti-apoptotic effects of CREB signalling, suggesting it may be a therapeutic target in ALS.

CREB Coactivator CRTC2 Plays a Crucial Role in Endothelial Function

The cAMP pathway is known to stabilize endothelial barrier function and maintain vascular physiology. The family of cAMP-response element binding (CREB)-regulated transcription coactivators (CRTC)1-3 activate transcription by targeting the basic leucine zipper domain of CREB. CRTC2 is a master regulator of glucose metabolism in liver and adipose tissue. However, the role of CRTC2 in endothelium remains unknown. The aim of this study was to evaluate the effect of CRTC2 on endothelial function. We focused the effect of CRTC2 in endothelial cells and its relationship with p190RhoGAP-A. We examined the effect of CRTC2 on endothelial function using a mouse aorta ring assay ex vivo and with photothrombotic stroke in endothelial cell-specific CRTC2-knock-out male mice in vivo CRTC2 was highly expressed in endothelial cells and related to angiogenesis. Among CRTC1-3, only CRTC2 was activated under ischemic conditions at endothelial cells, and CRTC2 maintained endothelial barrier function through p190RhoGAP-A expression. Ser¹⁷¹ was a pivotal regulatory site for CRTC2 intracellular localization, and Ser³⁰⁷ functioned as a crucial phosphorylation site. Endothelial cell-specific CRTC2-knock-out mice showed reduced angiogenesis ex vivo, exacerbated stroke via endothelial dysfunction, and impaired neurologic recovery via reduced vascular beds in vivo These findings suggest that CRTC2 plays a crucial protective role in vascular integrity of the endothelium via p190RhoGAP-A under ischemic conditions.SIGNIFICANCE STATEMENT Previously, the role of CRTC2 in endothelial cells was unknown. In this study, we firstly clarified that CRTC2 was expressed in endothelial cells and among CRTC1-3, only CRTC2 was related to endothelial function. Most importantly, only CRTC2 was activated under ischemic conditions at endothelial cells and maintained endothelial barrier function through p190RhoGAP-A expression. Ser³⁰⁷ in CRTC2 functioned as a crucial phosphorylation site. Endothelial cell-specific CRTC2-knock-out mice showed reduced angiogenesis ex vivo, exacerbated stroke via endothelial dysfunction, and impaired neurologic recovery via reduced vascular beds in vivo These results suggested that CRTC2 maybe a potential therapeutic target for reducing blood-brain barrier (BBB) damage and improving recovery.

Signalling Pathways Implicated in Alzheimer's Disease Neurodegeneration in Individuals with and without Down Syndrome

Down syndrome (DS), the most common cause of intellectual disability of genetic origin, is characterized by alterations in central nervous system morphology and function that appear from early prenatal stages. However, by the fourth decade of life, all individuals with DS develop neuropathology identical to that found in sporadic Alzheimer's disease (AD), including the development of amyloid plaques and neurofibrillary tangles due to hyperphosphorylation of tau protein, loss of neurons and synapses, reduced neurogenesis, enhanced oxidative stress, and mitochondrial dysfunction and neuroinflammation. It has been proposed that DS could be a useful model for studying the etiopathology of AD and to search for therapeutic targets. There is increasing evidence that the neuropathological events associated with AD are interrelated and that many of them not only are implicated in the onset of this pathology but are also a consequence of other alterations. Thus, a feedback mechanism exists between them. In this review, we summarize the signalling pathways implicated in each of the main neuropathological aspects of AD in individuals with and without DS as well as the interrelation of these pathways.

RP1, a RAGE antagonist peptide, can improve memory impairment and reduce Aβ plaque load in the APP/PS1 mouse model of Alzheimer's disease

Amyloid-β (Aβ) accumulation is a pathological hallmark of Alzheimer's disease (AD). The receptor for advanced glycation end products (RAGE) is involved in the production and accumulation of Aβ. RP1, a peptide antagonist of RAGE, was screened by phage display technology in our previous studies, and its neuroprotective effects on an AD cell model have been confirmed. However, its efficacy in vivo remains unclear. Here, the intranasal delivery of RP1 to APPSwe/PS1dE9 (APP/PS1) mice significantly improved memory impairment and relieved the Aβ burden by decreasing the expression of amyloid precursor protein and β-secretase. RNA-sequencing (RNA-seq) was utilized to identify differentially expressed genes (DEGs) in APP/PS1 mice after RP1 administration. Several DEGs in RAGE downstream signalling pathways were downregulated. Some transcription factors (such as Fos) and the pathways enriched in the remarkable modules may also be related to the efficacy of RP1. In conclusion, RP1 significantly improves the AD symptoms of APP/PS1 mice, and the RNA-seq results provide new ideas for elucidating the possible mechanisms of RP1 treatment.

The role of CREB and BDNF in neurobiology and treatment of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia worldwide. β-amyloid peptide (Aβ) is currently assumed to be the main cause of synaptic dysfunction and cognitive impairments in AD, but the molecular signaling pathways underlying its neurotoxic consequences have not yet been completely explored. Additional investigations regarding these pathways will contribute to development of new therapeutic targets. In context, developing evidence suggest that Aβ decreases brain-derived neurotrophic factor (BDNF) mostly by lowering phosphorylated cyclic adenosine monophosphate (cAMP) response element binding protein (CREB) protein. In fact, it has been observed that brain or serum levels of BDNF appear to be beneficial markers for cognitive condition. In addition, the participation of transcription mediated by CREB has been widely analyzed in the memory process and AD development. Designing pharmacologic or genetic therapeutic approaches based on the targeting of CREB-BDNF signaling could be a promising treatment potential for AD. In this review, we summarize data demonstrating the role of CREB-BDNF signaling pathway in cognitive status and mediation of Aβ toxicity in AD. Finally, we also focus on the developing intervention methods for improvement of cognitive decline in AD based on targeting of CREB-BDNF pathway.

The Critical Role of Nurr1 as a Mediator and Therapeutic Target in Alzheimer's Disease-related Pathogenesis

Several studies have revealed that the transcription factor nuclear receptor related 1 (Nurr1) plays several roles not only in the regulation of gene expression related to dopamine synthesis, but also in alternative splicing, and miRNA targeting. Moreover, it regulates cognitive functions and protects against inflammation-induced neuronal death. In particular, the role of Nurr1 in the pathogenesis of Parkinson’s disease (PD) has been well investigated; for example, it has been shown that it restores behavioral and histological impairments in PD models. Although many studies have evaluated the connection between Nurr1 and PD pathogenesis, the role of Nurr1 in Alzheimer’s disease (AD) remain to be studied. There have been several studies describing Nurr1 protein expression in the AD brain. However, only a few studies have examined the role of Nurr1 in the context of AD. Therefore, in this review, we highlight the overall effects of Nurr1 under the neuropathologic conditions related to AD. Furthermore, we suggest the possibility of using Nurr1 as a therapeutic target for AD or other neurodegenerative disorders.

Alzheimer's Disease: The Link Between Amyloid-β and Neurovascular Dysfunction

While prevailing evidence supports that the amyloid cascade hypothesis is a key component of Alzheimer's disease (AD) pathology, many recent studies indicate that the vascular system is also a major contributor to disease progression. Vascular dysfunction and reduced cerebral blood flow (CBF) occur prior to the accumulation and aggregation of amyloid-β (Aβ) plaques and hyperphosphorylated tau tangles. Although research has predominantly focused on the cellular processes involved with Aβ-mediated neurodegeneration, effects of Aβ on CBF and neurovascular coupling are becoming more evident. This review will describe AD vascular disturbances as they relate to Aβ, including chronic cerebral hypoperfusion, hypertension, altered neurovascular coupling, and deterioration of the blood-brain barrier. In addition, we will describe recent findings about the relationship between these vascular defects and Aβ accumulation with emphasis on in vivo studies utilizing rodent AD models.

Merits and Limitations of Studying Neuronal Depolarization-Dependent Processes Using Elevated External Potassium

Elevated extracellular potassium chloride is widely used to achieve membrane depolarization of cultured neurons. This technique has illuminated mechanisms of calcium influx through L-type voltage sensitive calcium channels, activity-regulated signaling, downstream transcriptional events, and many other intracellular responses to depolarization. However, there is enormous variability in these treatments, including durations from seconds to days and concentrations from 3mM to 150 mM KCl. Differential effects of these variable protocols on neuronal activity and transcriptional programs are underexplored. Furthermore, potassium chloride treatments in vitro are criticized for being poor representatives of in vivo phenomena and are questioned for their effects on cell viability. In this review, we discuss the intracellular consequences of elevated extracellular potassium chloride treatment in vitro, the variability of such treatments in the literature, the strengths and limitations of this tool, and relevance of these studies to brain functions and dysfunctions.

Mathematical Models to Shed Light on Amyloid-Beta and Tau Protein Dependent Pathologies in Alzheimer's Disease

The number of patients suffering from dementia due to Alzheimer's disease (AD) is constantly rising worldwide. This has accordingly resulted in huge burdens on the health systems and involved families. Lack of profound understanding of neural networking in normal brain and their interruption in AD makes the treatment of this neurodegenerative multifaceted disease a challenging issue. In recent years, mathematical and computational methods have paved the way towards a better understanding of the brain functional connectivity. Thus, much attention has been paid to this matter from both basic science researchers and clinicians with an interdisciplinary approach to determine what is not functioning properly in AD patients and how this malfunctioning can be addressed. In this review, a number of AD-related articles and well-studied pathophysiologic topics (e.g., amyloid-beta, neurofibrillary tangles, Ca²⁺ dysregulation, and synaptic plasticity alterations) has been literally surveyed from a computational and systems biology point of view. The neural networks were discussed from biological and mathematical point of views and their alterations in recent findings were further highlighted. Application of the graph theoretical analysis in the brain imaging was reviewed, depicting the relations between brain structure and function, without diving into mathematical details. Moreover, differential rate equations were briefly articulated, emphasizing the potential use of these equations in simplifying complex processes in relevance to pathologies of AD. Comprehensive insights were given into the AD progression from neural networks perspective, which may lead us towards potential strategies for early diagnosis and effective treatment of AD.

Presenilin/γ-secretase-dependent EphA3 processing mediates axon elongation through non-muscle myosin IIA

EphA/ephrin signaling regulates axon growth and guidance of neurons, but whether this process occurs also independently of ephrins is unclear. We show that presenilin-1 (PS1)/γ-secretase is required for axon growth in the developing mouse brain. PS1/γ-secretase mediates axon growth by inhibiting RhoA signaling and cleaving EphA3 independently of ligand to generate an intracellular domain (ICD) fragment that reverses axon defects in PS1/γ-secretase- and EphA3-deficient hippocampal neurons. Proteomic analysis revealed that EphA3 ICD binds to non-muscle myosin IIA (NMIIA) and increases its phosphorylation (Ser1943), which promotes NMIIA filament disassembly and cytoskeleton rearrangement. PS1/γ-secretase-deficient neurons show decreased phosphorylated NMIIA and NMIIA/actin colocalization. Moreover, pharmacological NMII inhibition reverses axon retraction in PS-deficient neurons suggesting that NMIIA mediates PS/EphA3-dependent axon elongation. In conclusion, PS/γ-secretase-dependent EphA3 cleavage mediates axon growth by regulating filament assembly through RhoA signaling and NMIIA, suggesting opposite roles of EphA3 on inhibiting (ligand-dependent) and promoting (receptor processing) axon growth in developing neurons.

Synapse-to-Nucleus Signaling in Neurodegenerative and Neuropsychiatric Disorders

Synapse-to-nucleus signaling is critical for converting signals received at synapses into transcriptional programs essential for cognition, memory, and emotion. This neuronal mechanism usually involves activity-dependent translocation of synaptonuclear factors from synapses to the nucleus resulting in regulation of transcriptional programs underlying synaptic plasticity. Acting as synapse-to-nucleus messengers, amyloid precursor protein intracellular domain associated-1 protein, cAMP response element binding protein (CREB)-regulated transcription coactivator-1, Jacob, nuclear factor kappa-light-chain-enhancer of activated B cells, RING finger protein 10, and SH3 and multiple ankyrin repeat domains 3 play essential roles in synapse remodeling and plasticity, which are considered the cellular basis of memory. Other synaptic proteins, such as extracellular signal-regulated kinase, calcium/calmodulin-dependent protein kinase II gamma, and CREB2, translocate from dendrites or cytosol to the nucleus upon synaptic activity, suggesting that they could contribute to synapse-to-nucleus signaling. Notably, some synaptonuclear factors converge on the transcription factor CREB, indicating that CREB signaling is a key hub mediating integration of synaptic signals into transcriptional programs required for neuronal function and plasticity. Although major efforts have been focused on identification and regulatory mechanisms of synaptonuclear factors, the relevance of synapse-to-nucleus communication in brain physiology and pathology is still unclear. Recent evidence, however, indicates that synaptonuclear factors are implicated in neuropsychiatric, neurodevelopmental, and neurodegenerative disorders, suggesting that uncoupling synaptic activity from nuclear signaling may prompt synapse pathology, contributing to a broad spectrum of brain disorders. This review summarizes current knowledge of synapse-to-nucleus signaling in neuron survival, synaptic function and plasticity, and memory. Finally, we discuss how altered synapse-to-nucleus signaling may lead to memory and emotional disturbances, which is relevant for clinical and therapeutic strategies in neurodegenerative and neuropsychiatric diseases.

Inhibition of Reactive Astrocytes with Fluorocitrate Ameliorates Learning and Memory Impairment Through Upregulating CRTC1 and Synaptophysin in Ischemic Stroke Rats

Ischemic stroke often causes motor and cognitive deficits. Deregulated glia gap junction communication, which is reflected by increased protein levels of glial fibrillary acidic protein (GFAP) and connexin 43 (Cx43), has been observed in ischemic hippocampus and has been associated with cognitive impairment in animal stroke models. Here, we tested the hypothesis that reactive astrocytes-mediated loss of synaptophysin (SYP) and CREB-regulated transcription coactivator 1 (CRTC1) contribute to dysfunction in glia gap junction communication and memory impairment after ischemic stroke. Male Sprague-Dawley rats were subjected to a 90-min middle cerebral artery occlusion (MCAO) with 7-day reperfusion. Fluorocitrate (1 nmol), the reversible inhibitor of the astrocytic tricarboxylic acid cycle, was injected into the right lateral ventricle of MCAO rats once every 2 days starting immediately before reperfusion. The Morris water maze was used to assess memory in conjunction with western blotting and immunostaining to detect protein expression and distribution in the hippocampus. Our results showed that ischemic stroke caused significant memory impairment accompanied by increased protein levels of GFAP and Cx43 in hippocampal tissue. In addition, the levels of several key memory-related important proteins including SYP, CRTC1, myelin basic protein and high-mobility group-box-1 were significantly reduced in the hippocampal tissue. Of note, inhibition of reactive astrocytes with fluorocitrate was shown to significantly reverse the above noted changes induced by ischemic stroke. Taken together, our findings demonstrate that inhibiting reactive astrocytes with fluorocitrate immediately before reperfusion may protect against ischemic stroke-induced memory impairment through the upregulation of CRTC1 and SYP.

CREB signals as PBMC-based biomarkers of cognitive dysfunction: A novel perspective of the brain-immune axis

To date, there is no reliable biomarker for the assessment or determination of cognitive dysfunction in Alzheimer's disease and related dementia. Such a biomarker would not only aid in diagnostics, but could also serve as a measure of therapeutic efficacy. It is widely acknowledged that the hallmarks of Alzheimer's disease, namely, amyloid deposits and neurofibrillary tangles, as well as their precursors and metabolites, are poorly correlated with cognitive function and disease stage and thus have low diagnostic or prognostic value. A lack of biomarkers is one of the major roadblocks in diagnosing the disease and in assessing the efficacy of potential therapies. The phosphorylation of cAMP Response Element Binding protein (pCREB) plays a major role in memory acquisition and consolidation. In the brain, CREB activation by phosphorylation at Ser133 and the recruitment of transcription cofactors such as CREB binding protein (CBP) is a critical step for the formation of memory. This set of processes is a prerequisite for the transcription of genes thought to be important for synaptic plasticity, such as Egr-1. Interestingly, recent work suggests that the expression of pCREB in peripheral blood mononuclear cells (PBMC) positively correlates with pCREB expression in the postmortem brain of Alzheimer's patients, suggesting not only that pCREB expression in PBMC might serve as a biomarker of cognitive dysfunction, but also that the dysfunction of CREB signaling may not be limited to the brain in AD, and that a link may exist between the regulation of CREB in the blood and in the brain. In this review we consider the evidence suggesting a correlation between the level of CREB signals in the brain and blood, the current knowledge about CREB in PBMC and its association with CREB in the brain, and the implications and mechanisms for a neuro-immune cross talk that may underlie this communication. This Review will discuss the possibility that peripheral dysregulation of CREB is an early event in AD pathogenesis, perhaps as a facet of immune system dysfunction, and that this impairment in peripheral CREB signaling modifies CREB signaling in the brain, thus exacerbating cognitive decline in AD. A more thorough understanding of systemic dysregulation of CREB in AD will facilitate the search for a biomarker of cognitive function in AD, and also aid in the understanding of the mechanisms underlying cognitive decline in AD.

Ca2+ homeostasis dysregulation in Alzheimer's disease: a focus on plasma membrane and cell organelles

Emerging evidence indicates that Ca²⁺ is a vital factor in modulating the pathogenesis of Alzheimer's disease (AD). In healthy neurons, Ca²⁺ concentration is balanced to maintain a lower level in the cytosol than in the extracellular space or certain intracellular compartments such as endoplasmic reticulum (ER) and the lysosome, whereas this homeostasis is broken in AD. On the plasma membrane, the AD hallmarks amyloid-β (Aβ) and tau interact with ligand-gated or voltage-gated Ca²⁺-influx channels and inhibit the Ca²⁺-efflux ATPase or exchangers, leading to an elevated intracellular Ca²⁺ level and disrupted Ca²⁺ signal. In the ER, the disabled presenilin "Ca²⁺ leak" function and the direct implications of Aβ and presenilin mutants contribute to Ca²⁺-signal disorder. The enhanced ryanodine receptor (RyR)-mediated and inositol 1,4,5-trisphosphate receptor (IP₃R)-mediated Ca²⁺ release from the ER aggravates cytosolic Ca²⁺ disorder and triggers apoptosis; the down-regulated ER Ca²⁺ sensor, stromal interaction molecule (STIM), alleviates store-operated Ca²⁺ entry in plasma membrane, leading to spine loss. The increased transfer of Ca²⁺ from ER to mitochondria through mitochondria-associated ER membrane (MAM) causes Ca²⁺ overload in the mitochondrial matrix and consequently opens the cellular damage-related channel, mitochondrial permeability transition pore (mPTP). In this review, we discuss the effects of Aβ, tau and presenilin on neuronal Ca²⁺ signal, focusing on the receptors and regulators in plasma membrane and ER; we briefly introduce the involvement of MAM-mediated Ca²⁺ transfer and mPTP opening in AD pathogenesis.-Wang, X., Zheng, W. Ca²⁺ homeostasis dysregulation in Alzheimer's disease: a focus on plasma membrane and cell organelles.

Nurr1 (NR4A2) regulates Alzheimer's disease-related pathogenesis and cognitive function in the 5XFAD mouse model

The orphan nuclear receptor Nurr1 (also known as NR4A2) is critical for the development and maintenance of midbrain dopaminergic neurons, and is associated with Parkinson's disease. However, an association between Nurr1 and Alzheimer's disease (AD)‐related pathology has not previously been reported. Here, we provide evidence that Nurr1 is expressed in a neuron‐specific manner in AD‐related brain regions; specifically, it is selectively expressed in glutamatergic neurons in the subiculum and the cortex of both normal and AD brains. Based on Nurr1’s expression patterns, we investigated potential functional roles of Nurr1 in AD pathology. Nurr1 expression was examined in the hippocampus and cortex of AD mouse model and postmortem human AD subjects. In addition, we performed both gain‐of‐function and loss‐of‐function studies of Nurr1 and its pharmacological activation in 5XFAD mice. We found that knockdown of Nurr1 significantly aggravated AD pathology while its overexpression alleviated it, including effects on Aβ accumulation, neuroinflammation, and neurodegeneration. Importantly, 5XFAD mice treated with amodiaquine, a highly selective synthetic Nurr1 agonist, showed robust reduction in typical AD features including deposition of Aβ plaques, neuronal loss, microgliosis, and impairment of adult hippocampal neurogenesis, leading to significant improvement of cognitive impairment. These in vivo and in vitro findings suggest that Nurr1 critically regulates AD‐related pathophysiology and identify Nurr1 as a novel AD therapeutic target.

Sex Differences in Neuropathology and Cognitive Behavior in APP/PS1/tau Triple-Transgenic Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia among the elderly, characterized by amyloid plaques, neurofibrillary tangles, and neuroinflammation in the brain, as well as impaired cognitive behaviors. A sex difference in the prevalence of AD has been noted, while sex differences in the cerebral pathology and relevant molecular mechanisms are not well clarified. In the present study, we systematically investigated the sex differences in pathological characteristics and cognitive behavior in 12-month-old male and female APP/PS1/tau triple-transgenic AD mice (3×Tg-AD mice) and examined the molecular mechanisms. We found that female 3×Tg-AD mice displayed more prominent amyloid plaques, neurofibrillary tangles, neuroinflammation, and spatial cognitive deficits than male 3×Tg-AD mice. Furthermore, the expression levels of hippocampal protein kinase A-cAMP response element-binding protein (PKA-CREB) and p38-mitogen-activated protein kinases (MAPK) also showed sex difference in the AD mice, with a significant increase in the levels of p-PKA/p-CREB and a decrease in the p-p38 in female, but not male, 3×Tg-AD mice. We suggest that an estrogen deficiency-induced PKA-CREB-MAPK signaling disorder in 12-month-old female 3×Tg-AD mice might be involved in the serious pathological and cognitive damage in these mice. Therefore, sex differences should be taken into account in investigating AD biomarkers and related target molecules, and estrogen supplementation or PKA-CREB-MAPK stabilization could be beneficial in relieving the pathological damage in AD and improving the cognitive behavior of reproductively-senescent females.

Molecular and functional interaction between GPR18 and cannabinoid CB2 G-protein-coupled receptors. Relevance in neurodegenerative diseases

GPR18, still considered an orphan receptor, may respond to endocannabinoids, whose canonical receptors are CB₁ and CB₂. GPR18 and CB₂ receptors share a role in peripheral immune response regulation and are co-expressed in microglia, which are immunocompetent cells in the central nervous system (CNS). We aimed at identifying heteroreceptor complexes formed by GPR18 and CB₁R or CB₂R in resting and activated microglia. Receptor-receptor interaction was assessed using energy-transfer approaches, and receptor function by determining cAMP levels and ERK1/2 phosphorylation in heterologous cells and primary cultures of microglia. Heteroreceptor identification in primary cultures of microglia was achieved by in situ proximity ligation assays. Energy transfer results showed interaction of GPR18 with CB₂R but not with CB₁R. CB₂-GPR18 heteroreceptor complexes displayed particular functional properties (heteromer prints) often consisting of negative cross-talk (activation of one receptor reduces signaling arising from the partner receptor) and cross-antagonism (the response of one of the receptors is blocked by a selective antagonist of the partner receptor). Activated microglia showed the heteromer print (negative cross-talk and bidirectional cross-antagonism) and increased expression of CB₂R and GPR18. Due to the important role of CB₂R in neuroprotection, we further investigated heteroreceptor occurrence in primary cultures of microglia from transgenic mice overexpressing human APP_Sw,Ind, an Alzheimer's disease model. Microglial cells from transgenic mice showed the heteromer print and functional interactions that were similar to those found in cells from wild-type animals that were activated by treatment with lipopolysaccharide and interferon-γ. Our results suggest that GPR18 and its heteromers may play important roles in neurodegenerative processes.

ΔFosB Regulates Gene Expression and Cognitive Dysfunction in a Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is characterized by cognitive decline and 5- to 10-fold increased seizure incidence. How seizures contribute to cognitive decline in AD or other disorders is unclear. We show that spontaneous seizures increase expression of ΔFosB, a highly stable Fos-family transcription factor, in the hippocampus of an AD mouse model. ΔFosB suppressed expression of the immediate early gene c-Fos, which is critical for plasticity and cognition, by binding its promoter and triggering histone deacetylation. Acute histone deacetylase (HDAC) inhibition or inhibition of ΔFosB activity restored c-Fos induction and improved cognition in AD mice. Administration of seizure-inducing agents to nontransgenic mice also resulted in ΔFosB-mediated suppression of c-Fos, suggesting that this mechanism is not confined to AD mice. These results explain observations that c-Fos expression increases after acute neuronal activity but decreases with chronic activity. Moreover, these results indicate a general mechanism by which seizures contribute to persistent cognitive deficits, even during seizure-free periods.

Intraneuronal Amyloid Beta Accumulation Disrupts Hippocampal CRTC1-Dependent Gene Expression and Cognitive Function in a Rat Model of Alzheimer Disease

In Alzheimer disease (AD), the accumulation of amyloid beta (Aβ) begins decades before cognitive symptoms and progresses from intraneuronal material to extracellular plaques. To date, however, the precise mechanism by which the early buildup of Aβ peptides leads to cognitive dysfunction remains unknown. Here, we investigate the impact of the early Aβ accumulation on temporal and frontal lobe dysfunction. We compared the performance of McGill-R-Thy1-APP transgenic AD rats with wild-type littermate controls on a visual discrimination task using a touchscreen operant platform. Subsequently, we conducted studies to establish the biochemical and molecular basis for the behavioral alterations. It was found that the presence of intraneuronal Aβ caused a severe associative learning deficit in the AD rats. This coincided with reduced nuclear translocation and genomic occupancy of the CREB co-activator, CRTC1, and decreased production of synaptic plasticity-associated transcripts Arc, c-fos, Egr1, and Bdnf. Thus, blockade of CRTC1-dependent gene expression in the early, preplaque phase of AD-like pathology provides a molecular basis for the cognitive deficits that figure so prominently in early AD.

Long-term Treatment with Low-Dose Caffeine Worsens BPSD-Like Profile in 3xTg-AD Mice Model of Alzheimer's Disease and Affects Mice with Normal Aging

Coffee or caffeine has recently been suggested as prophylaxis for dementia. Although memory problems are hallmarks of Alzheimer's disease, this dementia is also characterized by neuropsychiatric symptoms called Behavioral and Psychological Symptoms of Dementia (BPSD). The impact of preventive/therapeutic strategies on both cognitive and non-cognitive symptoms can be addressed in the 3xTg-AD mice, since they exhibit cognitive but also BPSD-like profiles. Here, we studied the long-term effects of a low dose of caffeine in male 3xTg-AD mice and as compared to age-matched non-transgenic (NTg) counterparts with normal aging. Animals were treated (water or caffeine in drinking water) from adulthood (6 months of age) until middle-aged (13 months of age), that in 3xTg-AD mice correspond to onset of cognitive impairment and advanced stages, respectively. The low caffeine dosing used (0.3 mg/ml) was previously found to give a plasma concentration profile in mice roughly equivalent to that of a human coffee drinker. There were significant effects of caffeine on most behavioral variables, especially those related to neophobia and other anxiety-like behaviors, emotionality, and cognitive flexibility. The 3xTg-AD and NTg mice were differently influenced by caffeine. Overall, the increase of neophobia and other anxiety-related behaviors resulted in an exacerbation of BPSD-like profile in 3xTg-AD mice. Learning and memory, strongly influenced by anxiety in 3xTg-AD mice, got little benefit from caffeine, only shown after a detailed analysis of navigation strategies. The worsened pattern in NTg mice and the use of search strategies in 3xTg-AD mice make both groups more similar. Circadian motor activity showed genotype differences, which were found to be enhanced by caffeine. Selective effects of caffeine on NTg were found in the modulation of behaviors related to emotional profile and risk assessment. Caffeine normalized splenomegaly of 3xTg-AD mice, a physical indicator of their impaired peripheral immune system, and trended to increase their corticosterone levels. Our observations of adverse caffeine effects in an Alzheimer's disease model together with previous clinical observations suggest that an exacerbation of BPSD-like symptoms may partly interfere with the beneficial cognitive effects of caffeine. These results are relevant when coffee-derived new potential treatments for dementia are to be devised and tested.

Nigral dopaminergic PAK4 prevents neurodegeneration in rat models of Parkinson's disease

Parkinson's disease (PD) is characterized by progressive loss of dopaminergic (DA) neurons in the substantia nigra. No neuroprotective treatments have successfully prevented the progression of this disease. We report that p21-activated kinase 4 (PAK4) is a key survival factor for DA neurons. We observed PAK4 immunoreactivity in rat and human DA neurons in brain tissue, but not in microglia or astrocytes. PAK4 activity was markedly decreased in postmortem brain tissue from PD patients and in rodent models of PD. Expression of constitutively active PAK4^S445N/S474E (caPAK4) protected DA neurons in both the 6-hydroxydopamine and α-synuclein rat models of PD and preserved motor function. This neuroprotective effect of caPAK4 was mediated by phosphorylation of CRTC1 [CREB (adenosine 3',5'-monophosphate response element-binding protein)-regulated transcription coactivator] at S215. The nonphosphorylated form of CRTC1^S215A compromised the ability of caPAK4 to induce the expression of the CREB target proteins Bcl-2, BDNF, and PGC-1α. Our results support a neuroprotective role for the PAK4-CRTC1^S215-CREB signaling pathway and suggest that this pathway may be a useful therapeutic target in PD.

CRTC1 mediates preferential transcription at neuronal activity-regulated CRE/TATA promoters

Gene expression mediated by the transcription factor cAMP-responsive element-binding protein (CREB) is essential for a wide range of brain processes. The transcriptional coactivartor CREB-regulated transcription coactivator-1 (CRTC1) is required for efficient induction of CREB target genes during neuronal activity. However, the mechanisms regulating induction of specific CREB/CRTC1-dependent genes during neuronal activity remain largely unclear. Here, we investigated the molecular mechanisms regulating activity-dependent gene transcription upon activation of the CREB/CRTC1 signaling pathway in neurons. Depolarization and cAMP signals induce preferential transcription of activity-dependent genes containing promoters with proximal CRE/TATA sequences, such as c-fos, Dusp1, Nr4a1, Nr4a2 and Ptgs2, but not genes with proximal CRE/TATA-less promoters (e.g. Nr4a3, Presenilin-1 and Presenilin-2). Notably, biochemical and chromatin immunoprecipitation analyses reveal constitutive binding of CREB to target gene promoters in the absence of neuronal activity, whereas recruitment of CRTC1 to proximal CRE/TATA promoters depends on neuronal activity. Neuronal activity induces rapid CRTC1 dephosphorylation, nuclear translocation and binding to endogenous CREB. These results indicate that neuronal activity induces a preferential binding of CRTC1 to the transcriptional complex in CRE/TATA-containing promoters to engage activity-dependent transcription in neurons.

Emerging Roles of CREB-Regulated Transcription Coactivators in Brain Physiology and Pathology

The brain has the ability to sense, coordinate, and respond to environmental changes through biological processes involving activity-dependent gene expression. cAMP-response element binding protein (CREB)-regulated transcription coactivators (CRTCs) have recently emerged as novel transcriptional regulators of essential biological functions, while their deregulation is linked to age-related human diseases. In the brain, CRTCs are unique signaling factors that act as sensors and integrators of hormonal, metabolic, and neural signals contributing to brain plasticity and brain-body communication. In this review, we focus on the regulatory mechanisms and functions of CRTCs in brain metabolism, lifespan, circadian rhythm, and synaptic mechanisms underlying memory and emotion. We also discuss how CRTCs deregulation in cognitive and emotional disorders may provide the basis for potential clinical and therapeutic applications in neurodegenerative and psychiatric diseases.

Effects of Aluminium on Long-Term Memory in Rats and on SIRT1 Mediating the Transcription of CREB-Dependent Gene in Hippocampus

Epidemiological investigations have shown that aluminium (Al) is an important neurotoxicant which can be absorbed by organisms via various routes. Previous studies have confirmed that exposure to Al could cause neurodegenerative diseases, decline CREB phosphorylation and then down-regulate the transcription and protein expression of its target genes including BDNF. However, recent studies revealed that CREB activation alone was far from enough to activate the expression of long-term memory (LTM)-related genes; there might be other regulatory factors involved in this process. Several studies showed that TORC1 might be involved in regulating the transcription of downstream target genes as well. Also, TORC1 could be mediated by SIRT1 during the formation of LTM. However, the role of CREB regulating system in Al-induced LTM impairment was still not utterly elucidated till now. This study was designed to establish the rat model of subchronic Al exposure to observe the neuroethology, regulatory factor levels and molecular biological alterations in hippocampal cells. The results showed that, with the increasing AlCl3 dose, blood Al content increased gradually; morphology of the hippocampus and neuronal ultrastructure were aberrant; in the Morris water maze test, the escape latency and distance travelled became longer, swimming traces turned more complicated in the place navigation test; intracellular Ca2+ , cAMP levels declined significantly in AlCl3 -treated rats, followed by abated nuclear translocation of TORC1 and decreased SIRT1, TORC1 and pCREB levels. These results indicate that SIRT1 and TORC1 might play an important mediating role in Al-induced LTM impairment.