Aberrant calcium/calmodulin-dependent protein kinase II (CaMKII) activity is associated with abnormal dendritic spine morphology in the ATRX mutant mouse brain

Rac1 promotes the lipopolysaccharide-induced inflammatory response and contraction-associated proteins (CAPs) expression in mouse uterine smooth muscle cells

Activation of the maternal immune system leads to a downstream cascade of proinflammatory events that culminate in the activation of spontaneous uterine contractions, which is associated with preterm birth. Ras-related C3 botulinum toxin substrate 1 (Rac1) is a crucial protein related to cell contraction and inflammation. The main purpose of this study was to explore the role and function of Rac1's regulation of inflammation through in- vivo and in-vitro experiments. Rac1 inhibitor was used in animal model of preterm birth and cells isolated from the uterine tissues of pregnant mice on gestational day 16 were transfected with adenovirus to knockdown or overexpress Rac1 and treated with the Calcium-calmodulin-dependent protein kinase II (CaMKII) inhibitor KN93. The expression of Rac1, uterine contraction-associated proteins (CAPs) (COX-2 and Connexin43), and inflammatory cytokines, were assessed by Western blotting and RTPCR. LPS upregulated Rac1, COX-2 and Connexin43 expression in uterine smooth muscle cells (USMCs). The expression of inflammatory cytokines, COX-2, and Connexin43 was significantly decreased in shRac1-transfected cells compared with cells stimulated with LPS only. Rac1 overexpression led to an increase in the expression of inflammatory cytokines, COX-2, and Connexin43. Furthermore, after Rac1 overexpression, KN93 reduced the expression of uterine contraction-associated proteins and inflammatory cytokines. It is thought that the effect of Rac1 on inflammatory cytokine and contraction-associated protein expression in USMCs is mediated by CaMKII. Rac1 can modulate the expression of contraction-associated proteins and inflammatory cytokines through the CaMKII pathway. Rac1 could be an effective therapeutic target for improving the outcome of preterm birth.

A new mouse model of ATR-X syndrome carrying a common patient mutation exhibits neurological and morphological defects

ATRX is a chromatin remodelling ATPase that is involved in transcriptional regulation, DNA damage repair and heterochromatin maintenance. It has been widely studied for its role in ALT-positive cancers, but its role in neurological function remains elusive. Hypomorphic mutations in the X-linked ATRX gene cause a rare form of intellectual disability combined with alpha-thalassemia called ATR-X syndrome in hemizygous males. Clinical features also include facial dysmorphism, microcephaly, short stature, musculoskeletal defects and genital abnormalities. As complete deletion of ATRX in mice results in early embryonic lethality, the field has largely relied on conditional knockout models to assess the role of ATRX in multiple tissues. Given that null alleles are not found in patients, a more patient-relevant model was needed. Here, we have produced and characterized the first patient mutation knock-in model of ATR-X syndrome, carrying the most common causative mutation, R246C. This is one of a cluster of missense mutations located in the chromatin-binding domain and disrupts its function. The knock-in mice recapitulate several aspects of the patient disorder, including craniofacial defects, microcephaly, reduced body size and impaired neurological function. They provide a powerful model for understanding the molecular mechanisms underlying ATR-X syndrome and testing potential therapeutic strategies.

ATRX, a guardian of chromatin

ATRX (alpha-thalassemia mental retardation X-linked) is one of the most frequently mutated tumor suppressor genes in human cancers, especially in glioma, and recent findings indicate roles for ATRX in key molecular pathways, such as the regulation of chromatin state, gene expression, and DNA damage repair, placing ATRX as a central player in the maintenance of genome stability and function. This has led to new perspectives about the functional role of ATRX and its relationship with cancer. Here, we provide an overview of ATRX interactions and molecular functions and discuss the consequences of its impairment, including alternative lengthening of telomeres and therapeutic vulnerabilities that may be exploited in cancer cells.

The regulatory role of endoplasmic reticulum chaperone proteins in neurodevelopment

The endoplasmic reticulum (ER) is the largest tubular reticular organelle spanning the cell. As the main site of protein synthesis, Ca2+ homeostasis maintenance and lipid metabolism, the ER plays a variety of essential roles in eukaryotic cells, with ER molecular chaperones participate in all these processes. In recent years, it has been reported that the abnormal expression of ER chaperones often leads to a variety of neurodevelopmental disorders (NDDs), including abnormal neuronal migration, neuronal morphogenesis, and synaptic function. Neuronal development is a complex and precisely regulated process. Currently, the mechanism by which neural development is regulated at the ER level remains under investigation. Therefore, in this work, we reviewed the recent advances in the roles of ER chaperones in neural development and developmental disorders caused by the deficiency of these molecular chaperones.

Comparison of Golgi-Cox and Intracellular Loading of Lucifer Yellow for Dendritic Spine Density and Morphology Analysis in the Mouse Brain

Dendritic spines are small protrusions on dendrites that serve as the postsynaptic site of the majority of excitatory synapses. These structures are important for normal synaptic transmission, and alterations in their density and morphology have been documented in various disease states. Over 130 years ago, Ramón y Cajal used Golgi-stained tissue sections to study dendritic morphology. Despite the array of technological advances, including iontophoretic microinjection of Lucifer yellow (LY) fluorescent dye, Golgi staining continues to be one of the most popular approaches to visualize dendritic spines. Here, we compared dendritic spine density and morphology among pyramidal neurons in layers 2/3 of the mouse medial prefrontal cortex (mPFC) and pyramidal neurons in hippocampal CA1 using three-dimensional digital reconstructions of (1) brightfield microscopy z-stacks of Golgi-impregnated dendrites and (2) confocal microscopy z-stacks of LY-filled dendrites. Analysis of spine density revealed that the LY microinjection approach enabled detection of approximately three times as many spines as the Golgi staining approach in both brain regions. Spine volume measurements were larger using Golgi staining compared to LY microinjection in both mPFC and CA1. Spine length was mostly comparable between techniques in both regions. In the mPFC, head diameter was similar for Golgi staining and LY microinjection. However, in CA1, head diameter was approximately 50% smaller on LY-filled dendrites compared to Golgi staining. These results indicate that Golgi staining and LY microinjection yield different spine density and morphology measurements, with Golgi staining failing to detect dendritic spines and overestimating spine size.

Epigenetic genes and epilepsy - emerging mechanisms and clinical applications

An increasing number of epilepsies are being attributed to variants in genes with epigenetic functions. The products of these genes include factors that regulate the structure and function of chromatin and the placing, reading and removal of epigenetic marks, as well as other epigenetic processes. In this Review, we provide an overview of the various epigenetic processes, structuring our discussion around five function-based categories: DNA methylation, histone modifications, histone-DNA crosstalk, non-coding RNAs and chromatin remodelling. We provide background information on each category, describing the general mechanism by which each process leads to altered gene expression. We also highlight key clinical and mechanistic aspects, providing examples of genes that strongly associate with epilepsy within each class. We consider the practical applications of these findings, including tissue-based and biofluid-based diagnostics and precision medicine-based treatments. We conclude that variants in epigenetic genes are increasingly found to be causally involved in the epilepsies, with implications for disease mechanisms, treatments and diagnostics.

[The cellular functions of G-quadruplex in neurological diseases]

G-quadruplex (G4) is a unique nucleic acid structure that formed when a four-stranded structure is produced within a single-stranded guanine-rich sequence. Four guanine molecules form a square planar arrangement, termed G-quartet, which are stacked on top of each other to form the G4 structure in DNA (G4DNA) and in RNA (G4RNA). Recent studies have revealed that G4DNA and G4RNA are folded in cells, which suggested their biological and pharmacological significance in DNA replication, transcription, epigenetic modification, and RNA metabolism. So far, we have reported the following; 1) G4 is a target of cognitive function therapy for ATR-X intellectual disability syndrome, in which mutations are found in a G4 binding protein ATRX. 2) G4 is formed in heterochromatin depending on neuronal development. 3) G4 promotes prionoids in a CGG triplet repeat disease, Fragile X-associated tremor/ataxia syndrome (FXTAS). 4) 5-aminolevulinic acid is a potential candidate drug for treating some neurological diseases through the G4 binding ability. In this review, we summarized the significant roles of G4 in neurological diseases.

Atrx Deletion in Neurons Leads to Sexually Dimorphic Dysregulation of miR-137 and Spatial Learning and Memory Deficits

ATRX gene mutations have been identified in syndromic and non-syndromic intellectual disabilities in humans. ATRX is known to maintain genomic stability in neuroprogenitor cells, but its function in differentiated neurons and memory processes remains largely unresolved. Here, we show that the deletion of neuronal Atrx in mice leads to distinct hippocampal structural defects, fewer presynaptic vesicles, and an enlarged postsynaptic area at CA1 apical dendrite-axon junctions. We identify male-specific impairments in long-term contextual memory and in synaptic gene expression, linked to altered miR-137 levels. We show that ATRX directly binds to the miR-137 locus and that the enrichment of the suppressive histone mark H3K27me3 is significantly reduced upon the loss of ATRX. We conclude that the ablation of ATRX in excitatory forebrain neurons leads to sexually dimorphic effects on miR-137 expression and on spatial memory, identifying a potential therapeutic target for neurological defects caused by ATRX dysfunction.

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Loss of ATRX in neurons has sexually dimorphic effects on long-term spatial memory

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Targeted deletion of neuronal ATRX in mice causes ultrastructural synaptic defects

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ATRX null neurons show sex-specific changes in miR-137 and target synaptic transcripts

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ATRX directly binds and suppresses miR-137 in males via enrichment of H3K27me3

Modulation of dendritic spines by protein phosphatase-1

Protein phosphatase-1 (PP-1), a highly conserved multifunctional serine/threonine phosphatase, is enriched in dendritic spines where it plays a major role in modulating excitatory synaptic activity. In addition to established functions in spine maturation and development, multi-subunit holoenzyme forms of PP-1 modulate higher-order cognitive functions such learning and memory. Mechanisms involved in regulating PP-1 activity and localization in spines include interactions with neurabin and spinophilin, structurally related synaptic scaffolding proteins associated with the actin cytoskeleton. Since PP-1 is a critical element in synaptic development, signaling, and plasticity, alterations in PP-1 signaling in dendritic spines are implicated in various neurological and psychiatric disorders. The effects of PP-1 depend on its isoform-specific association with regulatory proteins and activation of downstream signaling pathways. Here we review the role of PP-1 and its binding proteins neurabin and spinophilin in both developing and established dendritic spines, as well as some of the disorders that result from its dysregulation.

TRP Channels Regulation of Rho GTPases in Brain Context and Diseases

Neurological and neuropsychiatric disorders are mediated by several pathophysiological mechanisms, including developmental and degenerative abnormalities caused primarily by disturbances in cell migration, structural plasticity of the synapse, and blood-vessel barrier function. In this context, critical pathways involved in the pathogenesis of these diseases are related to structural, scaffolding, and enzymatic activity-bearing proteins, which participate in Ca²⁺- and Ras Homologs (Rho) GTPases-mediated signaling. Rho GTPases are GDP/GTP binding proteins that regulate the cytoskeletal structure, cellular protrusion, and migration. These proteins cycle between GTP-bound (active) and GDP-bound (inactive) states due to their intrinsic GTPase activity and their dynamic regulation by GEFs, GAPs, and GDIs. One of the most important upstream inputs that modulate Rho GTPases activity is Ca²⁺ signaling, positioning ion channels as pivotal molecular entities for Rho GTPases regulation. Multiple non-selective cationic channels belonging to the Transient Receptor Potential (TRP) family participate in cytoskeletal-dependent processes through Ca²⁺-mediated modulation of Rho GTPases. Moreover, these ion channels have a role in several neuropathological events such as neuronal cell death, brain tumor progression and strokes. Although Rho GTPases-dependent pathways have been extensively studied, how they converge with TRP channels in the development or progression of neuropathologies is poorly understood. Herein, we review recent evidence and insights that link TRP channels activity to downstream Rho GTPase signaling or modulation. Moreover, using the TRIP database, we establish associations between possible mediators of Rho GTPase signaling with TRP ion channels. As such, we propose mechanisms that might explain the TRP-dependent modulation of Rho GTPases as possible pathways participating in the emergence or maintenance of neuropathological conditions.

Neurodevelopmental Disorders Caused by Defective Chromatin Remodeling: Phenotypic Complexity Is Highlighted by a Review of ATRX Function

The ability to determine the genetic etiology of intellectual disability (ID) and neurodevelopmental disorders (NDD) has improved immensely over the last decade. One prevailing metric from these studies is the large percentage of genes encoding epigenetic regulators, including many members of the ATP-dependent chromatin remodeling enzyme family. Chromatin remodeling proteins can be subdivided into five classes that include SWI/SNF, ISWI, CHD, INO80, and ATRX. These proteins utilize the energy from ATP hydrolysis to alter nucleosome positioning and are implicated in many cellular processes. As such, defining their precise roles and contributions to brain development and disease pathogenesis has proven to be complex. In this review, we illustrate that complexity by reviewing the roles of ATRX on genome stability, replication, and transcriptional regulation and how these mechanisms provide key insight into the phenotype of ATR-X patients.

SAK3 Administration Improves Spine Abnormalities and Cognitive Deficits in AppNL-G-F/NL-G-F Knock-in Mice by Increasing Proteasome Activity through CaMKII/Rpt6 Signaling

Alzheimer's disease (AD) is the most common form of dementia and is characterized by neuropathological hallmarks consisting of accumulation of extracellular amyloid-β (Aβ) plaques and intracellular neurofibrillary tangles (NFT). Recently, we have identified a new AD therapeutic candidate, ethyl-8'-methyl-2',4-dioxo-2-(piperidin-1-yl)-2'H-spiro[cyclopentane-1,3'-imidazo [1,2-a] pyridin]-2-ene-3-carboxylate (SAK3), which ameliorates the AD-like pathology in AppNL-F/NL-F knock-in mice. However, the detailed mechanism underlying the therapeutic effects of SAK3 remains unclear. In this study, we found that SAK3 administration improved the reduced proteasome activity through the activation of CaMKII/Rpt6 signaling in AppNL-F/NL-F knock-in (NL-G-F) mice. Moreover, spine abnormalities observed in NL-G-F mice were significantly reversed by SAK3 administration. Along with this, cognitive impairments found in NL-G-F mice were markedly ameliorated by SAK3. In summary, our data suggest that SAK3 administration increases the activity of the proteasome via activation of the CaMKII/Rpt6 signaling pathway, contributing to improvements in spine abnormalities and cognitive deficits in NL-G-F mice. Overall, our findings suggest that SAK3 might be a new attractive drug candidate, representing a new mechanism for the treatment of AD pathology.

Oral glutathione administration inhibits the oxidative stress and the inflammatory responses in AppNL-G-F/NL-G-F knock-in mice

Alzheimer's disease (AD) is the most common neurodegenerative disease characterized by the presence of extracellular amyloid-β (Aβ) plaques and intracellular neurofibrillary tangles. Reduced antioxidants and increased oxidative stress and inflammation are responsible for the pathological features characteristic of an AD brain. We observed decreased levels of the reduced form of glutathione (GSH), the most abundant brain antioxidant, and decreased GSH/glutathione disulfide (GSSG) ratios in App^{NL-G-F/NL-G-F} knock-in (NL-G-F) mouse brains. Repeated oral GSH administration for 3 weeks dose-dependently increased GSH levels and restored the GSH/GSSH ratio. Consistent with the restoration of GSH levels, the levels of 4-hydroxy-2-nonenal (4-HNE), a marker of oxidative stress, were significantly decreased in the hippocampus of NL-G-F mice. Additionally, inflammatory responses, such as microgliosis and increased mRNA expression of inflammatory cytokines, were also inhibited. Moreover, behavioral deficits including cognitive decline, depressive-like behaviors, and anxiety-related behaviors observed in NL-G-F mice were significantly improved by oral and chronic GSH administration. Taken together, our data suggest that oral GSH administration is an attractive therapeutic strategy to reduce the excessive oxidative stress and inflammatory responses in the AD brain.

[The potential of G-quadruplexes as a therapeutic target for neurological diseases]

The most common form of DNA is a right-handed helix, the B-form DNA. DNA can also adopt a variety of alternative conformations, termed non-B-form DNA secondary structures, including the G-quadruplex (G4). Furthermore, non-canonical RNA G4 secondary structures are also observed. Recent bioinformatics analysis revealed genomic positions of G4. In addition, G4 formation may be associated with various biological functions, including DNA replication, transcription, epigenetic modification, and RNA metabolism. In this review, we focus on G4 structures in neuronal functions, which may have important roles reveal mechanisms underlying neurological disorders. In addition, we discuss the potential of G4s as a therapeutic target for neurological diseases.

Perspectives for Applying G-Quadruplex Structures in Neurobiology and Neuropharmacology

The most common form of DNA is a right-handed helix or the B-form DNA. DNA can also adopt a variety of alternative conformations, non-B-form DNA secondary structures, including the DNA G-quadruplex (DNA-G4). Furthermore, besides stem-loops that yield A-form double-stranded RNA, non-canonical RNA G-quadruplex (RNA-G4) secondary structures are also observed. Recent bioinformatics analysis of the whole-genome and transcriptome obtained using G-quadruplex–specific antibodies and ligands, revealed genomic positions of G-quadruplexes. In addition, accumulating evidence pointed to the existence of these structures under physiologically- and pathologically-relevant conditions, with functional roles in vivo. In this review, we focused on DNA-G4 and RNA-G4, which may have important roles in neuronal function, and reveal mechanisms underlying neurological disorders related to synaptic dysfunction. In addition, we mention the potential of G-quadruplexes as therapeutic targets for neurological diseases.

Glial ensheathment of the somatodendritic compartment regulates sensory neuron structure and activity

Sensory neurons perceive environmental cues and are important of organismal survival. Peripheral sensory neurons interact intimately with glial cells. While the function of axonal ensheathment by glia is well studied, less is known about the functional significance of glial interaction with the somatodendritic compartment of neurons. Herein, we show that three distinct glia cell types differentially wrap around the axonal and somatodendritic surface of the polymodal dendritic arborization (da) neuron of the Drosophila peripheral nervous system for detection of thermal, mechanical, and light stimuli. We find that glial cell-specific loss of the chromatin modifier gene dATRX in the subperineurial glial layer leads to selective elimination of somatodendritic glial ensheathment, thus allowing us to investigate the function of such ensheathment. We find that somatodendritic glial ensheathment regulates the morphology of the dendritic arbor, as well as the activity of the sensory neuron, in response to sensory stimuli. Additionally, glial ensheathment of the neuronal soma influences dendritic regeneration after injury.

m6A facilitates hippocampus-dependent learning and memory through YTHDF1

N6-methyladenosine (m6A), the most prevalent internal RNA modification on mammalian messenger RNAs, regulates the fates and functions of modified transcripts through m6A-specific binding proteins1-5. In the nervous system, m6A is abundant and modulates various neural functions6-11. Whereas m6A marks groups of mRNAs for coordinated degradation in various physiological processes12-15, the relevance of m6A for mRNA translation in vivo remains largely unknown. Here we show that, through its binding protein YTHDF1, m6A promotes protein translation of target transcripts in response to neuronal stimuli in the adult mouse hippocampus, thereby facilitating learning and memory. Mice with genetic deletion of Ythdf1 show learning and memory defects as well as impaired hippocampal synaptic transmission and long-term potentiation. Re-expression of YTHDF1 in the hippocampus of adult Ythdf1-knockout mice rescues the behavioural and synaptic defects, whereas hippocampus-specific acute knockdown of Ythdf1 or Mettl3, which encodes the catalytic component of the m6A methyltransferase complex, recapitulates the hippocampal deficiency. Transcriptome-wide mapping of YTHDF1-binding sites and m6A sites on hippocampal mRNAs identified key neuronal genes. Nascent protein labelling and tether reporter assays in hippocampal neurons showed that YTHDF1 enhances protein synthesis in a neuronal-stimulus-dependent manner. In summary, YTHDF1 facilitates translation of m6A-methylated neuronal mRNAs in response to neuronal stimulation, and this process contributes to learning and memory.

SA4503, A Potent Sigma-1 Receptor Ligand, Ameliorates Synaptic Abnormalities and Cognitive Dysfunction in a Mouse Model of ATR-X Syndrome

α-thalassemia X-linked intellectual disability (ATR-X) syndrome is caused by mutations in ATRX. An ATR-X model mouse lacking Atrx exon 2 displays phenotypes that resemble symptoms in the human intellectual disability: cognitive defects and abnormal dendritic spine formation. We herein target activation of sigma-1 receptor (Sig-1R) that can induce potent neuroprotective and neuroregenerative effects by promoting the activity of neurotrophic factors, such as brain-derived neurotrophic factor (BDNF). We demonstrated that treatment with SA4503, a potent activator of Sig-1R, reverses axonal development and dendritic spine abnormalities in cultured cortical neurons from ATR-X model mice. Moreover, the SA4503 treatment rescued cognitive deficits exhibited by the ATR-X model mice. We further found that significant decreases in the BDNF-protein level in the medial prefrontal cortex of ATR-X model mice were recovered with treatment of SA4503. These results indicate that the rescue of dendritic spine abnormalities through the activation of Sig-1R has a potential for post-diagnostic therapy in ATR-X syndrome.

The Disease-modifying Drug Candidate, SAK3 Improves Cognitive Impairment and Inhibits Amyloid beta Deposition in App Knock-in Mice

Alzheimer's disease (AD) is a progressive neurodegenerative disease and the most common form of elderly dementia in the world. At present, acetylcholine inhibitors, such as donepezil, galantamine and rivastigmine, are used for AD therapy, but the therapeutic efficacy is limited. We recently proposed T-type voltage-gated Ca²⁺ channels' (T-VGCCs) enhancer as a new therapeutic candidate for AD. In the current study, we confirmed the pharmacokinetics of SAK3 in the plasma and brain of mice using ultra performance liquid chromatography-tandem mass spectrometry. We also investigated the effects of SAK3 on the major symptoms of AD, such as cognitive dysfunction and amyloid beta (Aβ) accumulation, in App^NL-F knock-in (NL-F) mice, which have been established as an AD model. Chronic SAK3 (0.5 mg/kg/day) oral administration for 3 months from 9 months of age improved cognitive function and inhibited Aβ deposition in 12-month-old NL-F mice. Using microarray and real-time PCR analysis, we discovered serum- and glucocorticoid-induced protein kinase 1 (SGK1) as one of possible genes involved in the inhibition of Aβ deposition and improvement of cognitive function by SAK3. These results support the idea that T-VGCC enhancer, SAK3 could be a novel candidate for disease-modifying therapeutics for AD.

Reduced expression of Na+/Ca2+ exchangers is associated with cognitive deficits seen in Alzheimer's disease model mice

Na⁺/Ca²⁺ exchangers (NCXs) are expressed primarily in the plasma membrane of most cell types, where they mediate electrogenic exchange of one Ca²⁺ for three Na⁺ ions, depending on Ca²⁺ and Na⁺ electrochemical gradients across the membrane. Three mammalian NCX isoforms (NCX1, NCX2, and NCX3) are each encoded by a distinct gene. Here, we report that NCX2 and NCX3 protein and mRNA levels are relatively reduced in hippocampal CA1 of APP23 and APP-KI mice. Likewise, NCX2^+/- or NCX3^+/- mice exhibited impaired hippocampal LTP and memory-related behaviors. Moreover, relative to controls, calcium/calmodulin-dependent protein kinase II (CaMKII) autophosphorylation significantly decreased in NCX2^+/- mouse hippocampus but increased in hippocampus of NCX3^+/- mice. NCX2 or NCX3 heterozygotes displayed impaired maintenance of hippocampal LTP, a phenotype that in NCX2^+/- mice was correlated with elevated calcineurin activity and rescued by treatment with the calcineurin (CaN) inhibitor FK506. Likewise, FK506 treatment significantly restored impaired hippocampal LTP in APP-KI mice. Moreover, Ca²⁺ clearance after depolarization following high frequency stimulation was slightly delayed in hippocampal CA1 regions of NCX2^+/- mice. Electron microscopy revealed relatively decreased synaptic density in CA1 of NCX2^+/- mice, while the number of spines with perforated synapses in CA1 significantly increased in NCX3^+/- mice. We conclude that memory impairment seen in NCX2^+/- and NCX3^+/- mice reflect dysregulated hippocampal CaMKII activity, which alters dendritic spine morphology, findings with implications for memory deficits seen in Alzheimer's disease model mice.

Physiological and Pathological Roles of CaMKII-PP1 Signaling in the Brain

Ca²⁺/calmodulin (CaM)-dependent protein kinase II (CaMKII), a multifunctional serine (Ser)/threonine (Thr) protein kinase, regulates diverse activities related to Ca²⁺-mediated neuronal plasticity in the brain, including synaptic activity and gene expression. Among its regulators, protein phosphatase-1 (PP1), a Ser/Thr phosphatase, appears to be critical in controlling CaMKII-dependent neuronal signaling. In postsynaptic densities (PSDs), CaMKII is required for hippocampal long-term potentiation (LTP), a cellular process correlated with learning and memory. In response to Ca²⁺ elevation during hippocampal LTP induction, CaMKIIα, an isoform that translocates from the cytosol to PSDs, is activated through autophosphorylation at Thr286, generating autonomous kinase activity and a prolonged Ca²⁺/CaM-bound state. Moreover, PP1 inhibition enhances Thr286 autophosphorylation of CaMKIIα during LTP induction. By contrast, CaMKII nuclear import is regulated by Ser332 phosphorylation state. CaMKIIδ3, a nuclear isoform, is dephosphorylated at Ser332 by PP1, promoting its nuclear translocation, where it regulates transcription. In this review, we summarize physio-pathological roles of CaMKII/PP1 signaling in neurons. CaMKII and PP1 crosstalk and regulation of gene expression is important for neuronal plasticity as well as survival and/or differentiation.

Ketamine Self-Administration Elevates αCaMKII Autophosphorylation in Mood and Reward-Related Brain Regions in Rats

Modulation of αCaMKII expression and phosphorylation is a feature shared by drugs of abuse with different mechanisms of action. Accordingly, we investigated whether αCaMKII expression and activation could be altered by self-administration of ketamine, a non-competitive antagonist of the NMDA glutamate receptor, with antidepressant and psychotomimetic as well as reinforcing properties. Rats self-administered ketamine at a sub-anesthetic dose for 43 days and were sacrificed 24 h after the last drug exposure; reward-related brain regions, such as medial prefrontal cortex (PFC), ventral striatum (vS), and hippocampus (Hip), were used for the measurement of αCaMKII-mediated signaling. αCaMKII phosphorylation was increased in these brain regions suggesting that ketamine, similarly to other reinforcers, activates this kinase. We next measured the two main targets of αCaMKII, i.e., GluN2B (S1303) and GluA1 (S831), and found increased activation of GluN2B (S1303) together with reduced phosphorylation of GluA1 (S831). Since GluN2B, via inhibition of ERK, regulates the membrane expression of GluA1, we measured ERK2 phosphorylation in the crude synaptosomal fraction of these brain regions, which was significantly reduced suggesting that ketamine-induced phosphorylation of αCaMKII promotes GluN2B (S1303) phosphorylation that, in turn, inhibits ERK 2 signaling, an effect that results in reduced membrane expression and phosphorylation of GluA1. Taken together, our findings point to αCaMKII autophosphorylation as a critical signature of ketamine self-administration providing an intracellular mechanism to explain the different effects caused by αCaMKII autophosphorylation on the post-synaptic GluN2B- and GluA1-mediated functions. These data add ketamine to the list of drugs of abuse converging on αCaMKII to sustain their addictive properties.

Endocytosis following dopamine D2 receptor activation is critical for neuronal activity and dendritic spine formation via Rabex-5/PDGFRβ signaling in striatopallidal medium spiny neurons

Aberrant dopamine D₂ receptor (D₂R) activity is associated with neuropsychiatric disorders, making those receptors targets for antipsychotic drugs. Here, we report that novel signaling through the intracellularly localized D₂R long isoform (D_2LR) elicits extracellular signal-regulated kinase (ERK) activation and dendritic spine formation through Rabex-5/platelet-derived growth factor receptor-β (PDGFRβ)-mediated endocytosis in mouse striatum. We found that D_2LR directly binds to and activates Rabex-5, promoting early-endosome formation. Endosomes containing D_2LR and PDGFRβ are then transported to the Golgi apparatus, where those complexes trigger Gαi3-mediated ERK signaling. Loss of intracellular D_2LR-mediated ERK activation decreased neuronal activity and dendritic spine density in striatopallidal medium spiny neurons (MSNs). In addition, dendritic spine density in striatopallidal MSNs significantly increased following treatment of striatal slices from wild-type mice with quinpirole, a D₂R agonist, but those changes were lacking in D_2LR knockout mice. Moreover, intracellular D_2LR signaling mediated effects of a typical antipsychotic drug, haloperidol, in inducing catalepsy behavior. Taken together, intracellular D_2LR signaling through Rabex-5/PDGFRβ is critical for ERK activation, dendritic spine formation and neuronal activity in striatopallidal MSNs of mice.

Retinal interneuron survival requires non-cell-autonomous Atrx activity

ATRX is a chromatin remodeling protein that is mutated in several intellectual disability disorders including alpha-thalassemia/mental retardation, X-linked (ATR-X) syndrome. We previously reported the prevalence of ophthalmological defects in ATR-X syndrome patients, and accordingly we find morphological and functional visual abnormalities in a mouse model harboring a mutation occurring in ATR-X patients. The visual system abnormalities observed in these mice parallels the Atrx-null retinal phenotype characterized by interneuron defects and selective loss of amacrine and horizontal cells. The mechanisms that underlie selective neuronal vulnerability and neurodegeneration in the central nervous system upon Atrx mutation or deletion are unknown. To interrogate the cellular specificity of Atrx for its retinal neuroprotective functions, we employed a combination of temporal and lineage-restricted conditional ablation strategies to generate five different conditional knockout mouse models, and subsequently identified a non-cell-autonomous requirement for Atrx in bipolar cells for inhibitory interneuron survival in the retina. Atrx-deficient retinal bipolar cells exhibit functional, structural and molecular alterations consistent with impairments in neuronal activity and connectivity. Gene expression changes in the Atrx-null retina indicate defective synaptic structure and neuronal circuitry, suggest excitotoxic mechanisms of neurodegeneration, and demonstrate that common targets of ATRX in the forebrain and retina may contribute to similar neuropathological processes underlying cognitive impairment and visual dysfunction in ATR-X syndrome.

Corticosteroids Mediate Heart Failure-Induced Depression through Reduced σ1-Receptor Expression

Cardiovascular diseases are risk factors for depression in humans. We recently proposed that σ1 receptor (σ1R) stimulation rescued cardiac hypertrophy and heart failure induced by transverse aortic constriction (TAC) in mice. Importantly, σ1R stimulation reportedly ameliorates depression-like behaviors in rodents. Thus, we hypothesized that impaired σ1R activity in brain triggers depression-like behaviors in animals with cardiovascular disease. Indeed, here we found that cardiac hypertrophy and heart failure induced by TAC were associated with depression-like behaviors concomitant with downregulation of σ1R expression in brain 6 weeks after surgery. σ1R levels significantly decreased in astrocytes in both the hippocampal CA1 region and dentate gyrus. Oral administration of the specific σ1R agonist SA4503 (0.3-1.0mg/kg) significantly improved TAC-induced depression-like behaviors concomitant with rescued astrocytic σ1R expression in CA1 and the dentate gyrus. Plasma corticosterone levels significantly increased 6 weeks after TAC, and chronic treatment of mice with corticosterone for 3 weeks elicited depression-like behaviors concomitant with reduced astrocytic σ1R expression in hippocampus. Furthermore, the glucocorticoid receptor antagonist mifepristone antagonized depressive-like behaviors and ameliorated decreased hippocampal σ1R expression in TAC mice. We conclude that elevated corticosterone levels trigger hippocampal σ1R downregulation and that σ1R stimulation with SA4503 is an attractive therapy to improve not only cardiac dysfunction but depression-like behaviors associated with heart failure.

Caloric restriction improves diabetes-induced cognitive deficits by attenuating neurogranin-associated calcium signaling in high-fat diet-fed mice

Diabetes-induced cognitive decline has been recognized in human patients of type 2 diabetes mellitus and mouse model of obesity, but the underlying mechanisms or therapeutic targets are not clearly identified. We investigated the effect of caloric restriction on diabetes-induced memory deficits and searched a molecular mechanism of caloric restriction-mediated neuroprotection. C57BL/6 mice were fed a high-fat diet for 40 weeks and RNA-seq analysis was performed in the hippocampus of high-fat diet-fed mice. To investigate caloric restriction effect on differential expression of genes, mice were fed high-fat diet for 20 weeks and continued on high-fat diet or subjected to caloric restriction (2 g/day) for 12 weeks. High-fat diet-fed mice exhibited insulin resistance, glial activation, blood-brain barrier leakage, and memory deficits, in that we identified neurogranin, a down-regulated gene in high-fat diet-fed mice using RNA-seq analysis; neurogranin regulates Ca(2+)/calmodulin-dependent synaptic function. Caloric restriction increased insulin sensitivity, reduced high-fat diet-induced blood-brain barrier leakage and glial activation, and improved memory deficit. Furthermore, caloric restriction reversed high-fat diet-induced expression of neurogranin and the activation of Ca(2+)/calmodulin-dependent protein kinase II and calpain as well as the downstream effectors. Our results suggest that neurogranin is an important factor of high-fat diet-induced memory deficits on which caloric restriction has a therapeutic effect by regulating neurogranin-associated calcium signaling.

Wip1 phosphatase modulates both long-term potentiation and long-term depression through the dephosphorylation of CaMKII

Synaptic plasticity is an important mechanism that underlies learning and cognition. Protein phosphorylation by kinases and dephosphorylation by phosphatases play critical roles in the activity-dependent alteration of synaptic plasticity. In this study, we report that Wip1, a protein phosphatase, is essential for long-term potentiation (LTP) and long-term depression (LTD) processes. Wip1-deletion suppresses LTP and enhances LTD in the hippocampus CA1 area. Wip1 deficiency-induced aberrant elevation of CaMKII T286/287 and T305 phosphorylation underlies these dysfunctions. Moreover, we showed that Wip1 modulates CaMKII dephosphorylation. Wip1(-/-) mice exhibit abnormal GluR1 membrane expression, which could be reversed by the application of a CaMKII inhibitor, indicating that Wip1/CaMKII signaling is crucial for synaptic plasticity. Together, our results demonstrate that Wip1 phosphatase plays a vital role in regulating hippocampal synaptic plasticity by modulating the phosphorylation of CaMKII.

Kalirin is required for BDNF-TrkB stimulated neurite outgrowth and branching

Exogenous brain-derived neurotrophic factor (BDNF), acting through TrkB, is known to promote neurite formation and branching. This response to BDNF was eliminated by inhibition of TrkB kinase and by specific inhibition of the GEF1 domain of Kalirin, which activates Rac1. Neurons from Kalrn knockout mice were unable to activate Rac1 in response to BDNF. BDNF-triggered neurite outgrowth was abolished when Kalrn expression was reduced using shRNA that targets all of the major Kalrn isoforms, and reduced in neurons from Kalrn knockout mice. The Kalrn isoforms expressed early in development also include a GEF2 domain that activates RhoA. However, BDNF-stimulated neurite outgrowth in Kalrn knockout neurons was rescued by expression of Kalirin-7, which includes only the GEF1 domain but lacks the GEF2 domain. Dendritic morphogenesis, which requires spatially restricted, coordinated changes in the actin cytoskeleton and in the organization of microtubules, involves essential contributions from multiple Rho GEFs. Since Tiam1, another Rho GEF, is also required for BDNF-stimulated neurite outgrowth, an inhibitory fragment of Tiam1 (PHn-CC-EX) was tested and found to interfere with both Kalirin and Tiam1 GEF activity. The prolonged TrkB activation observed in response to BDNF in Kalrn knockout neurons and the altered time course and extent of ERK, CREB and Akt activation observed in the absence of Kalrn would be expected to alter the response of these neurons to other regulatory factors.

Alterations in dendrite and spine morphology of cortical pyramidal neurons in DISC1-binding zinc finger protein (DBZ) knockout mice

Dendrite and dendritic spine formation are crucial for proper brain function. DISC1-binding zinc finger protein (DBZ) was first identified as a Disrupted-In-Schizophrenia1 (DISC1) binding partner. DBZ is highly expressed in the cerebral cortex of developing and adult rodents and is involved in neurite formation, cell positioning, and the development of interneurons and oligodendrocytes. The functional roles of DBZ in postnatal brain remain unknown; thus we investigated cortical pyramidal neuron morphology in DBZ knockout (KO) mice. Morphological analyses by Golgi staining alone in DBZ KO mice revealed decreased dendritic arborization, increased spine density. A morphological analysis of the spines revealed markedly increased numbers of thin spines. To investigate whole spine structure in detail, electron tomographic analysis using ultra-high voltage electron microscopy (UHVEM) combined with Golgi staining was performed. Tomograms and three-dimensional models of spines revealed that the spines of DBZ KO mice exhibited two types of characteristic morphology, filopodia-like spines and abnormal thin-necked spines having an extremely thin spine neck. Moreover, conventional electron microscopy revealed significantly decreased number of postsynaptic densities (PSDs) in spines of DBZ KO mice. In conclusion, DBZ deficiency impairs the morphogenesis of dendrites and spines in cortical pyramidal neurons.

Aberrant Rho GTPases signaling and cognitive dysfunction: in vivo evidence for a compelling molecular relationship

Rho GTPases are key intracellular signaling molecules that coordinate dynamic changes in the actin cytoskeleton, thereby stimulating a variety of processes, including morphogenesis, migration, neuronal development, cell division and adhesion. Deviations from normal Rho GTPases activation state have been proposed to disrupt cognition and synaptic plasticity. This review focuses on the functional consequences of genetic ablation of upstream and downstream Rho GTPases molecules on cognitive function and neuronal morphology and connectivity. Available information on this issue is described and compared to that gained from mice carrying mutations in the most studied Rho GTPases and from pharmacological in vivo studies in which brain Rho GTPases signaling was modulated. Results from reviewed literature provide definitive evidence of a compelling link between Rho GTPases signaling and cognitive function, thus supporting the notion that Rho GTPases and their downstream effectors may represent important therapeutic targets for disorders associated with cognitive dysfunction.

Snf2h-mediated chromatin organization and histone H1 dynamics govern cerebellar morphogenesis and neural maturation

Chromatin compaction mediates progenitor to post-mitotic cell transitions and modulates gene expression programs, yet the mechanisms are poorly defined. Snf2h and Snf2l are ATP-dependent chromatin remodelling proteins that assemble, reposition and space nucleosomes, and are robustly expressed in the brain. Here we show that mice conditionally inactivated for Snf2h in neural progenitors have reduced levels of histone H1 and H2A variants that compromise chromatin fluidity and transcriptional programs within the developing cerebellum. Disorganized chromatin limits Purkinje and granule neuron progenitor expansion, resulting in abnormal post-natal foliation, while deregulated transcriptional programs contribute to altered neural maturation, motor dysfunction and death. However, mice survive to young adulthood, in part from Snf2l compensation that restores Engrailed-1 expression. Similarly, Purkinje-specific Snf2h ablation affects chromatin ultrastructure and dendritic arborization, but alters cognitive skills rather than motor control. Our studies reveal that Snf2h controls chromatin organization and histone H1 dynamics for the establishment of gene expression programs underlying cerebellar morphogenesis and neural maturation.

CaMKII: claiming center stage in postsynaptic function and organization

While CaMKII has long been known to be essential for synaptic plasticity and learning, recent work points to new dimensions of CaMKII function in the nervous system, revealing that CaMKII also plays an important role in synaptic organization. Ca(2+)-triggered autophosphorylation of CaMKII not only provides molecular memory by prolonging CaMKII activity during long-term plasticity (LTP) and learning but also represents a mechanism for autoactivation of CaMKII's multifaceted protein-docking functions. New details are also emerging about the distinct roles of CaMKIIα and CaMKIIβ in synaptic homeostasis, further illustrating the multilayered and complex nature of CaMKII's involvement in synaptic regulation. Here, I review novel molecular and functional insight into how CaMKII supports synaptic function.

Neuroblastoma and MYCN

Neuroblastoma, the most common extracranial solid tumor of childhood, is thought to originate from undifferentiated neural crest cells. Amplification of the MYC family member, MYCN, is found in ∼25% of cases and correlates with high-risk disease and poor prognosis. Currently, amplification of MYCN remains the best-characterized genetic marker of risk in neuroblastoma. This article reviews roles for MYCN in neuroblastoma and highlights recent identification of other driver mutations. Strategies to target MYCN at the level of protein stability and transcription are also reviewed.

The epigenetics of stroke recovery and rehabilitation: from polycomb to histone deacetylases

Classical de-afferentation studies, as well as experience-dependent visual plasticity paradigms, have confirmed that both the developing and adult nervous system are capable of unexpected levels of plasticity. This capacity is underscored by the significant spontaneous recovery that can occur in patients with mild-to-moderate impairment following stroke. An evolving model is that an interaction of biological and environmental factors during all epochs post-stroke influences the extent and quality of this plasticity. Here, we discuss data that have implicated specific epigenetic proteins as integrators of environmental influences in 3 aspects of stroke recovery: spontaneous impairment reduction in humans; peri-infarct rewiring in animals as a paradigm for developing therapeutically-driven impairment reduction beyond natural spontaneous recovery; and, finally, classical hippocampal learning and memory paradigms that are theoretically important in skill acquisition for both impairment reduction and compensatory strategies in the rehabilitation setting. Our discussion focuses primarily on B lymphoma Mo-MLV1 insertion region proteins of the polycomb repressive complex, alpha thalassemia/mental retardation syndrome X-linked chromatin remodeling factors, and the best known and most dynamic gene repressors, histone deacetylases. We will highlight exciting current data associated with these proteins and provide promising speculation about how they can be manipulated by drugs, biologics, or noninvasive stimulation for stroke recovery.

Histone regulation in the CNS: basic principles of epigenetic plasticity

Postmitotic neurons are subject to a vast array of environmental influences that require the nuclear integration of intracellular signaling events to promote a wide variety of neuroplastic states associated with synaptic function, circuit formation, and behavioral memory. Over the last decade, much attention has been paid to the roles of transcription and chromatin regulation in guiding fundamental aspects of neuronal function. A great deal of this work has centered on neurodevelopmental and adulthood plasticity, with increased focus in the areas of neuropharmacology and molecular psychiatry. Here, we attempt to provide a broad overview of chromatin regulation, as it relates to central nervous system (CNS) function, with specific emphasis on the modes of histone posttranslational modifications, chromatin remodeling, and histone variant exchange. Understanding the functions of chromatin in the context of the CNS will aid in the future development of pharmacological therapeutics aimed at alleviating devastating neurological disorders.

Activity-dependent modulation of the interaction between CaMKIIα and Abi1 and its involvement in spine maturation

Remodeling of dendritic spines through regulation of actin dynamics is a key event in activity-dependent structural plasticity. However, the molecular mechanism underlying this process is poorly understood. Here, we show that activity-dependent modulation of Abl interactor 1-Ca(2+)/calmodulin-dependent kinase IIα (Abi1-CaMKIIα) interaction, and thereby their activity, is important for regulation of spine morphology in cultured rat hippocampal neurons. Abi1 interacts with CaMKIIα at resting conditions through Abi1's tSNARE (target membrane-associated SNARE), which harbors striking homology with CaMKIIα regulatory domain. The interaction of the two proteins, Abi1 and CaMKIIα, results in their simultaneous inhibition, inhibition of CaMKIIα activity, and also inhibition of Abi1-dependent Rac activation. Their functional impediment is released when they dissociate from each other by calmodulin binding through glutamate receptor activation. Before dissociation, Abi1 is phosphorylated by CaMKIIα at serine 88, which may involve in regulation of Rac activation and spine maturation. Our results suggest that modulation of the interaction between Abi1 and CaMKIIα, through the glutamate receptor pathway, may be a molecular mechanism underlying activity-regulated structural plasticity in rat hippocamapal neurons.

Epigenetic mechanisms in neurological disease

The exploration of brain epigenomes, which consist of various types of DNA methylation and covalent histone modifications, is providing new and unprecedented insights into the mechanisms of neural development, neurological disease and aging. Traditionally, chromatin defects in the brain were considered static lesions of early development that occurred in the context of rare genetic syndromes, but it is now clear that mutations and maladaptations of the epigenetic machinery cover a much wider continuum that includes adult-onset neurodegenerative disease. Here, we describe how recent advances in neuroepigenetics have contributed to an improved mechanistic understanding of developmental and degenerative brain disorders, and we discuss how they could influence the development of future therapies for these conditions.

Expression of a truncated form of the endoplasmic reticulum chaperone protein, σ1 receptor, promotes mitochondrial energy depletion and apoptosis

The σ1 receptor (σ(1)R) regulates endoplasmic reticulum (ER)/mitochondrial interorganellar Ca(2+) mobilization through the inositol 1,4,5-trisphosphate receptor (IP(3)R). Here, we observed that expression of a novel splice variant of σ(1)R, termed short form σ(1)R (σ(1)SR), has a detrimental effect on mitochondrial energy production and cell survival. σ(1)SR mRNA lacks 47 ribonucleotides encoding exon 2, resulting in a frameshift and formation of a truncated receptor. σ(1)SR localizes primarily in the ER at perinuclear regions and forms a complex with σ(1)R but not with IP(3)R in the mitochondrion-associated ER membrane. Overexpression of both σ(1)R and the truncated isoform promotes mitochondrial elongation with increased ER mitochondrial contact surface. σ(1)R overexpression increases the efficiency of mitochondrial Ca(2+) uptake in response to IP(3)R-driven stimuli, whereas σ(1)SR overexpression reduces it. Most importantly, σ(1)R promotes ATP production via increased mitochondrial Ca(2+) uptake, promoting cell survival in the presence of ER stress. By contrast, σ(1)SR suppresses ATP production following ER stress, enhancing cell death. Taken together, the newly identified σ(1)SR isoform interferes with σ(1)R function relevant to mitochondrial energy production under ER stress conditions, promoting cellular apoptosis.

Sequencing of neuroblastoma identifies chromothripsis and defects in neuritogenesis genes

Neuroblastoma is a childhood tumour of the peripheral sympathetic nervous system. The pathogenesis has for a long time been quite enigmatic, as only very few gene defects were identified in this often lethal tumour. Frequently detected gene alterations are limited to MYCN amplification (20%) and ALK activations (7%). Here we present a whole-genome sequence analysis of 87 neuroblastoma of all stages. Few recurrent amino-acid-changing mutations were found. In contrast, analysis of structural defects identified a local shredding of chromosomes, known as chromothripsis, in 18% of high-stage neuroblastoma. These tumours are associated with a poor outcome. Structural alterations recurrently affected ODZ3, PTPRD and CSMD1, which are involved in neuronal growth cone stabilization. In addition, ATRX, TIAM1 and a series of regulators of the Rac/Rho pathway were mutated, further implicating defects in neuritogenesis in neuroblastoma. Most tumours with defects in these genes were aggressive high-stage neuroblastomas, but did not carry MYCN amplifications. The genomic landscape of neuroblastoma therefore reveals two novel molecular defects, chromothripsis and neuritogenesis gene alterations, which frequently occur in high-risk tumours.

Age-dependent targeting of protein phosphatase 1 to Ca2+/calmodulin-dependent protein kinase II by spinophilin in mouse striatum

Mechanisms underlying age-dependent changes of dendritic spines on striatal medium spiny neurons are poorly understood. Spinophilin is an F-actin- and protein phosphatase 1 (PP1)-binding protein that targets PP1 to multiple downstream effectors to modulate dendritic spine morphology and function. We found that calcium/calmodulin-dependent protein kinase II (CaMKII) directly and indirectly associates with N- and C-terminal domains of spinophilin, but F-actin can displace CaMKII from the N-terminal domain. Spinophilin co-localizes PP1 with CaMKII on the F-actin cytoskeleton in heterologous cells, and spinophilin co-localizes with synaptic CaMKII in neuronal cultures. Thr286 autophosphorylation enhances the binding of CaMKII to spinophilin in vitro and in vivo. Although there is no change in total levels of Thr286 autophosphorylation, maturation from postnatal day 21 into adulthood robustly enhances the levels of CaMKII that co-immunoprecipitate with spinophilin from mouse striatal extracts. Moreover, N- and C-terminal domain fragments of spinophilin bind more CaMKII from adult vs. postnatal day 21 striatal lysates. Total levels of other proteins that interact with C-terminal domains of spinophilin decrease during maturation, perhaps reducing competition for CaMKII binding to the C-terminal domain. In contrast, total levels of α-internexin and binding of α-internexin to the spinophilin N-terminal domain increases with maturation, perhaps bridging an indirect interaction with CaMKII. Moreover, there is an increase in the levels of myosin Va, α-internexin, spinophilin, and PP1 in striatal CaMKII immune complexes isolated from adult and aged mice compared to those from postnatal day 21. These changes in spinophilin/CaMKII interactomes may contribute to changes in striatal dendritic spine density, morphology, and function during normal postnatal maturation and aging.