Nuclear calcium signaling controls CREB-mediated gene expression triggered by synaptic activity

Pathogenic Tau Causes a Toxic Depletion of Nuclear Calcium

Synaptic activity-induced calcium (Ca2+) influx and subsequent propagation into the nucleus is a major way in which synapses communicate with the nucleus to regulate transcriptional programs important for activity-dependent survival and memory formation. Nuclear Ca2+ shapes the transcriptome by regulating cyclic AMP (cAMP) response element-binding protein (CREB). Here, we utilize a Drosophila model of tauopathy and induced pluripotent stem cell (iPSC)-derived neurons from humans with Alzheimer's disease to study the effects of pathogenic tau, a pathological hallmark of Alzheimer's disease and related tauopathies, on nuclear Ca2+. We find that pathogenic tau depletes nuclear Ca2+ and CREB to drive neuronal death, that CREB-regulated genes are over-represented among differentially expressed genes in tau transgenic Drosophila, and that activation of big potassium (BK) channels elevates nuclear Ca2+ and suppresses tau-induced neurotoxicity. Our studies identify nuclear Ca2+ depletion as a mechanism contributing to tau-induced neurotoxicity, adding an important dimension to the calcium hypothesis of Alzheimer's disease.

Ca2+ as a therapeutic target in cancer

Ca2+ is a ubiquitous and dynamic second messenger molecule that is induced by many factors including receptor activation, environmental factors, and voltage, leading to pleiotropic effects on cell function including changes in migration, metabolism and transcription. As such, it is not surprising that aberrant regulation of Ca2+ signals can lead to pathological phenotypes, including cancer progression. However, given the highly context-specific nature of Ca2+-dependent changes in cell function, delineation of its role in cancer has been a challenge. Herein, we discuss the distinct roles of Ca2+ signaling within and between each type of cancer, including consideration of the potential of therapeutic strategies targeting these signaling pathways.

Contribution of NAADP to Glutamate-Evoked Changes in Ca2+ Homeostasis in Mouse Hippocampal Neurons

Nicotinic acid adenine dinucleotide phosphate (NAADP) is a second messenger that evokes calcium release from intracellular organelles by the engagement of calcium release channels, including members of the Transient Receptor Potential (TRP) family, such as TRPML1, the (structurally) related Two Pore Channel type 1 (TPC1) and TPC2 channels as well as Ryanodine Receptors type 1 (RYR1; Guse, 2012). NAADP evokes calcium release from acidic calcium stores of many cell types (Guse, 2012), and NAADP-sensitive Ca²⁺ stores have been described in hippocampal neurons of the rat (Bak et al., 1999; McGuinness et al., 2007). Glutamate triggers Ca²⁺-mediated neuronal excitotoxicity in inflammation-induced neurodegenerative pathologies such as Multiple Sclerosis (MS; Friese et al., 2014), and when applied extracellularly to neurons glutamate can elevate NAADP levels in these cells. Accordingly, glutamate-evoked Ca²⁺ signals from intracellular organelles were inhibited by preventing organelle acidification (Pandey et al., 2009). Analysis of reported RNA sequencing experiments of cultured hippocampal neurons revealed the abundance of Mcoln1 (encoding TRPML1), Tpcn1, and Tpcn2 (encoding TPC1 and TPC2, respectively) as potential NAADP target channels in these cells. Transcripts encoding Ryr1 were not found in contrast to Ryr2 and Ryr3. To study the contribution of NAADP signaling to glutamate-evoked calcium transients in murine hippocampal neurons we used the NAADP antagonists Ned-19 (Naylor et al., 2009) and BZ194 (Dammermann et al., 2009). Our results show that both NAADP antagonists significantly reduce glutamate-evoked calcium transients. In addition to extracellular glutamate application, we studied synchronized calcium oscillations in the cells of the neuronal cultures evoked by addition of the GABA_A receptor antagonist bicuculline. Pretreatment with Ned-19 (50 μM) or BZ194 (100 μM) led to an increase in the frequency of bicuculline-induced calcium oscillations at the cost of calcium transient amplitudes. Interestingly, Ned-19 triggered a rise in intracellular calcium concentrations 25 min after bicuculline stimulation, leading to the question whether NAADP acts as a neuroprotective messenger in hippocampal neurons. Taken together, our results are in agreement with the concept that NAADP signaling significantly contributes to glutamate evoked Ca²⁺ rise in hippocampal neurons and to the amplitude and frequency of synchronized Ca²⁺ oscillations triggered by spontaneous glutamate release events.

N-Methyl-D-Aspartate Receptors in Hematopoietic Cells: What Have We Learned?

The N-methyl-D-aspartate receptor (NMDAR) provides a pathway for glutamate-mediated inter-cellular communication, best known for its role in the brain but with multiple examples of functionality in non-neuronal cells. Data previously published by others and us provided ex vivo evidence that NMDARs regulate platelet and red blood cell (RBC) production. Here, we summarize what is known about these hematopoietic roles of the NMDAR. Types of NMDAR subunits expressed in megakaryocytes (platelet precursors) and erythroid cells are more commonly found in the developing rather than adult brain, suggesting trophic functions. Nevertheless, similar to their neuronal counterparts, hematopoietic NMDARs function as ion channels, and are permeable to calcium ions (Ca2+). Inhibitors that block open NMDAR (memantine and MK-801) interfere with megakaryocytic maturation and proplatelet formation in primary culture. The effect on proplatelet formation appears to involve Ca2+ influx-dependent regulation of the cytoskeletal remodeling. In contrast to normal megakaryocytes, NMDAR effects in leukemic Meg-01 cells are diverted away from differentiation to increase proliferation. NMDAR hypofunction triggers differentiation of Meg-01 cells with the bias toward erythropoiesis. The underlying mechanism involves changes in the intracellular Ca2+ homeostasis, cell stress pathways, and hematopoietic transcription factors that upon NMDAR inhibition shift from the predominance of megakaryocytic toward erythroid regulators. This ability of NMDAR to balance both megakaryocytic and erythroid cell fates suggests receptor involvement at the level of a bipotential megakaryocyte-erythroid progenitor. In human erythroid precursors and circulating RBCs, NMDAR regulates intracellular Ca2+ homeostasis. NMDAR activity supports survival of early proerythroblasts, and in mature RBCs NMDARs impact cellular hydration state, hemoglobin oxygen affinity, and nitric oxide synthase activity. Overexcitation of NMDAR in mature RBCs leads to Ca2+ overload, K+ loss, RBC dehydration, and oxidative stress, which may contribute to the pathogenesis of sickle cell disease. In summary, there is growing evidence that glutamate-NMDAR signaling regulates megakaryocytic and erythroid cells at different stages of maturation, with some intriguing differences emerging in NMDAR expression and function between normal and diseased cells. NMDAR signaling may provide new therapeutic opportunities in hematological disease, but in vivo applicability needs to be confirmed.

Transcriptome Analysis of Deafness: Intracellular Signal Transduction Signaling Pathways Regulate Neuroplastic Changes in the Auditory Cortex

HYPOTHESIS AND BACKGROUND

Hearing loss leads to synaptic changes in auditory neurons and their networks, and functions as a consequence of the interplay between genes and proteins. However, cellular and molecular mechanisms leading to deafness-induced plasticity in the auditory cortex (AC) remain unclear. Here, we examined the changes in gene expression and key signaling pathways that regulate differentially expressed genes (DEGs) in the AC following auditory deafferentation using RNA-sequencing (RNA-Seq) analysis.

METHODS

Cochlear ablation-induced bilaterally deafened Sprague-Dawley rats were maintained for 12 weeks and their ACs were harvested. RNA-seq analysis was performed on each sample to identify which genes were expressed. This information was then used for comparative analysis of DEGs between samples. The statistical significance of DEGs was determined by fold change (|FC| > 1.5) and independent t test (p < 0.05).

RESULTS

RNA-seq analysis identified 72 DEGs, of which 19 were upregulated and 53 were down-regulated after bilateral deafening in the ACs. Gene ontology (GO) analysis revealed the potential involvement of mitogen-activated protein kinase, tumor necrosis factor, and cyclic adenosine 3',5'-monophosphate (e.g., Bdnf, Gli1, and c-Fos) signaling pathways in regulating changes in the expression of the genes listed herein. The DEGs of interest-including c-Fos, Arc, Ntf3, and Gli1-from the RNA-seq analysis were consistent with result of quantitative reverse transcriptase polymerase chain reaction.

CONCLUSION

RNA-seq analysis revealed that auditory deprivation in adult rats elicited changes in gene expression, transcription factor levels, and their complex interaction at specific gene promoters in the AC. Particularly, activation of intracellular signal transduction signaling pathways may be key to neuronal plasticity in deafness.

Functional Consequences of Calcium-Dependent Synapse-to-Nucleus Communication: Focus on Transcription-Dependent Metabolic Plasticity

In the nervous system, calcium signals play a major role in the conversion of synaptic stimuli into transcriptional responses. Signal-regulated gene transcription is fundamental for a range of long-lasting adaptive brain functions that include learning and memory, structural plasticity of neurites and synapses, acquired neuroprotection, chronic pain, and addiction. In this review, we summarize the diverse mechanisms governing calcium-dependent transcriptional regulation associated with central nervous system plasticity. We focus on recent advances in the field of synapse-to-nucleus communication that include studies of the signal-regulated transcriptome in human neurons, identification of novel regulatory mechanisms such as activity-induced DNA double-strand breaks, and the identification of novel forms of activity- and transcription-dependent adaptations, in particular, metabolic plasticity. We summarize the reciprocal interactions between different kinds of neuroadaptations and highlight the emerging role of activity-regulated epigenetic modifiers in gating the inducibility of signal-regulated genes.

Deletion of Voltage-Gated Calcium Channels in Astrocytes during Demyelination Reduces Brain Inflammation and Promotes Myelin Regeneration in Mice

To determine whether Cav1.2 voltage-gated Ca²⁺ channels contribute to astrocyte activation, we generated an inducible conditional knock-out mouse in which the Cav1.2 α subunit was deleted in GFAP-positive astrocytes. This astrocytic Cav1.2 knock-out mouse was tested in the cuprizone model of myelin injury and repair which causes astrocyte and microglia activation in the absence of a lymphocytic response. Deletion of Cav1.2 channels in GFAP-positive astrocytes during cuprizone-induced demyelination leads to a significant reduction in the degree of astrocyte and microglia activation and proliferation in mice of either sex. Concomitantly, the production of proinflammatory factors such as TNFα, IL1β and TGFβ1 was significantly decreased in the corpus callosum and cortex of Cav1.2 knock-out mice through demyelination. Furthermore, this mild inflammatory environment promotes oligodendrocyte progenitor cells maturation and myelin regeneration across the remyelination phase of the cuprizone model. Similar results were found in animals treated with nimodipine, a Cav1.2 Ca²⁺ channel inhibitor with high affinity to the CNS. Mice of either sex injected with nimodipine during the demyelination stage of the cuprizone treatment displayed a reduced number of reactive astrocytes and showed a faster and more efficient brain remyelination. Together, these results indicate that Cav1.2 Ca²⁺ channels play a crucial role in the induction and proliferation of reactive astrocytes during demyelination; and that attenuation of astrocytic voltage-gated Ca²⁺ influx may be an effective therapy to reduce brain inflammation and promote myelin recovery in demyelinating diseases.SIGNIFICANCE STATEMENT Reducing voltage-gated Ca²⁺ influx in astrocytes during brain demyelination significantly attenuates brain inflammation and astrocyte reactivity. Furthermore, these changes promote myelin restoration and oligodendrocyte maturation throughout remyelination.

Nanoelectrode-mediated single neuron activation

Elucidating cellular dynamics at the level of a single neuron and its associated role within neuronal circuits is essential for interpreting the complex nature of the brain. To investigate the operation of neural activity within its network, it is necessary to precisely manipulate the activation of each neuron and verify its propagation path via the synaptic connection. In this study, by exploiting the intrinsic physical and electrical advantages of a nanoelectrode, a vertical nanowire multi electrode array (VNMEA) is developed as a neuronal activation platform presenting the spatially confined effect on the intracellular space of individual cells. VNMEA makes a distinct difference between the interior and exterior cell potential and the current density, deriving the superior effects on activating Ca2+ responses compared to extracellular methods under the same conditions, with about 2.9-fold higher amplitude of Ca2+ elevation and a 2.6-fold faster recovery rate. Moreover, the synchronized propagation of evoked activities is shown in connected neurons implying cell-to-cell communications following the intracellular stimulation. The simulation and experimental consequences prove the outstanding property of temporal/spatial confinement of VNMEA-mediated intracellular stimulation to activate a single neuron and show its potential in localizing spiking neurons within neuronal populations, which may be utilized to reveal the connection and activation modalities of neural networks.

Exercise Plus Pharmacological Neuromodulation of Synaptic Inhibition Enhance Motor Function Recovery After Ischemic Stroke

The objective of this study was to examine the interactive effects of exercise and low-level inhibition of GABA_A receptors on the recovery of motor function and BDNF expression in the primary motor cortex (M1) of a stroke rat model. Male Sprague-Dawley rats were divided into five groups: sham (SHAM), control (CON), exercise (EX), bicuculline (BIC), and bicuculline plus exercise (BICEX) groups. All rats, except those in the SHAM group, underwent middle cerebral artery occlusion (MCAO) surgery to induce an ischemic stroke. GABA_A receptor antagonist, bicuculline (0.25 mg/kg, i.p.), was administered to the BIC and BICEX groups. The EX and BICEX groups exercised on a treadmill (11 m/min for 30 min). Each intervention started 3 days after the MCAO surgery and was carried out every day for 2 weeks. Following the intervention, bilateral M1 BDNF mRNA and protein expression levels were assessed using qRT-PCR and ELISA. Marginal recovery was found in the EX and BIC groups, whereas motor function recovery was enhanced with exercise in the presence of BIC administration specifically in the BICEX group. Furthermore, BDNF protein level in the ipsilateral M1 was significantly higher in the BICEX group than in other groups. This study indicated that exercise combined with low-level inhibition of GABA_A receptors after stroke could facilitate the recovery of motor function accompanied by BDNF upregulation in the ipsilateral M1. Therefore, this study provides a novel insight of pharmacological neuromodulation into stroke rehabilitation.

In Vivo Imaging of the Coupling between Neuronal and CREB Activity in the Mouse Brain

Sensory experiences cause long-term modifications of neuronal circuits by modulating activity-dependent transcription programs that are vital for regulation of long-term synaptic plasticity and memory. However, it has not been possible to precisely determine the interaction between neuronal activity patterns and transcription factor activity. Here we present a technique using two-photon fluorescence lifetime imaging (2pFLIM) with new FRET biosensors to chronically image in vivo signaling of CREB, an activity-dependent transcription factor important for synaptic plasticity, at single-cell resolution. Simultaneous imaging of the red-shifted CREB sensor and GCaMP permitted exploration of how experience shapes the interplay between CREB and neuronal activity in the neocortex of awake mice. Dark rearing increased the sensitivity of CREB activity to Ca²⁺ elevations and prolonged the duration of CREB activation to more than 24 h in the visual cortex. This technique will allow researchers to unravel the transcriptional dynamics underlying experience-dependent plasticity in the brain.

The neuronal stimulation-transcription coupling map

Neurons transcribe different genes in response to different extracellular stimuli, and these genes regulate neuronal plasticity. Thus, understanding how different stimuli regulate different stimulus-dependent gene modules would deepen our understanding of plasticity. To systematically dissect the coupling between stimulation and transcription, we propose creating a 'stimulation-transcription coupling map' that describes the transcription response to each possible extracellular stimulus. While we are currently far from having a complete map, recent genomic experiments have begun to facilitate its creation. Here, we describe the current state of the stimulation-transcription coupling map as well as the transcriptional regulation that enables this coupling.

The Mechanosensitive Ion Channel Piezo1 Significantly Mediates In Vitro Ultrasonic Stimulation of Neurons

Ultrasound brain stimulation is a promising modality for probing brain function and treating brain disease non-invasively and with high spatiotemporal resolution. However, the mechanism underlying its effects remains unclear. Here, we examine the role that the mouse piezo-type mechanosensitive ion channel component 1 (Piezo1) plays in mediating the in vitro effects of ultrasound in mouse primary cortical neurons and a neuronal cell line. We show that ultrasound alone could activate heterologous and endogenous Piezo1, initiating calcium influx and increased nuclear c-Fos expression in primary neurons but not when pre-treated with a Piezo1 inhibitor. We also found that ultrasound significantly increased the expression of the important proteins phospho-CaMKII, phospho-CREB, and c-Fos in a neuronal cell line, but Piezo1 knockdown significantly reduced this effect. Our findings demonstrate that the activity of mechanosensitive ion channels such as Piezo1 stimulated by ultrasound is an important contributor to its ability to stimulate cells in vitro.

Roles for the Endoplasmic Reticulum in Regulation of Neuronal Calcium Homeostasis

By influencing Ca²⁺ homeostasis in spatially and architecturally distinct neuronal compartments, the endoplasmic reticulum (ER) illustrates the notion that form and function are intimately related. The contribution of ER to neuronal Ca²⁺ homeostasis is attributed to the organelle being the largest reservoir of intracellular Ca²⁺ and having a high density of Ca²⁺ channels and transporters. As such, ER Ca²⁺ has incontrovertible roles in the regulation of axodendritic growth and morphology, synaptic vesicle release, and neural activity dependent gene expression, synaptic plasticity, and mitochondrial bioenergetics. Not surprisingly, many neurological diseases arise from ER Ca²⁺ dyshomeostasis, either directly due to alterations in ER resident proteins, or indirectly via processes that are coupled to the regulators of ER Ca²⁺ dynamics. In this review, we describe the mechanisms involved in the establishment of ER Ca²⁺ homeostasis in neurons. We elaborate upon how changes in the spatiotemporal dynamics of Ca²⁺ exchange between the ER and other organelles sculpt neuronal function and provide examples that demonstrate the involvement of ER Ca²⁺ dyshomeostasis in a range of neurological and neurodegenerative diseases.

Ginkgo biloba Extract EGb 761 and Its Specific Components Elicit Protective Protein Clearance Through the Autophagy-Lysosomal Pathway in Tau-Transgenic Mice and Cultured Neurons

Alzheimer's disease (AD) is a neurodegenerative disease pathologically characterized by extracellular amyloid-β (Aβ) deposits and intracellular neurofibrillary tangles (NFT) in many brain regions. NFT are primarily composed of hyperphosphorylated tau protein (p-Tau). Aβ and p-Tau are two major pathogenic molecules with tau acting downstream to Aβ to induce neuronal degeneration. In this study, we investigated whether Ginkgo biloba extract EGb 761 reduces cerebral p-Tau level and prevents AD pathogenesis. Human P301S tau mutant-transgenic mice were fed with EGb 761, added to the regular diet for 2 or 5 months. We observed that treatment with EGb 761 for 5 months significantly improved the cognitive function of mice, attenuated the loss of synaptophysin and recovered the phosphorylation of CREB in the mouse brain. Treatment with EGb 761 for 5 but not 2 months also decreased p-Tau protein amount and shifted microglial pro-inflammatory to anti-inflammatory activation in the brain. As potential therapeutic mechanisms, we demonstrated that treatment with EGb 761, especially the components of ginkgolide A, bilobalide, and flavonoids, but not with purified ginkgolide B or C, increased autophagic activity and degradation of p-Tau in lysosomes of neurons. Inhibiting ATG5 function or treating cells with Bafilomycin B1 abolished EGb 761-enhanced degradation of p-Tau in cultured neurons. Additionally, we observed that 5- instead of 2-month-treatment with EGb 761 inhibited the activity of p38-MAPK and GSK-3β. Therefore, long-term treatment with Ginkgo biloba extract EGb 761, a clinically available and well-tolerated herbal medication, ameliorates AD pathology through mechanisms against multiple AD pathogenic processes.

Retinal Characterization of the Thy1-GCaMP3 Transgenic Mouse Line After Optic Nerve Transection

Purpose

GCaMP3 is a genetically encoded calcium indicator for monitoring intracellular calcium dynamics. We characterized the expression pattern and functional properties of GCaMP3 in the Thy1-GCaMP3 transgenic mouse retina.

Methods

To determine the specificity of GCaMP3 expression, Thy1-GCaMP3 (B6; CBA-Tg(Thy1-GCaMP3)6Gfng/J) retinas were processed for immunohistochemistry with anti-green fluorescent protein (anti-GFP, to enhance GCaMP3 fluorescence), anti-RBPMS (retinal ganglion cell [RGC]-specific marker), and antibodies against amacrine cell markers (ChAT, GABA, GAD67, syntaxin). Calcium imaging was used to characterize functional responses of GCaMP3-expressing (GCaMP+) cells by recording calcium transients evoked by superfusion of kainic acid (KA; 10, 50, or 100 μM). In a subset of animals, optic nerve transection (ONT) was performed 3, 5, or 7 days prior to calcium imaging.

Results

GFP immunoreactivity colocalized with RBPMS but not amacrine cell markers in both ONT and non-ONT (control) groups. Calcium transients evoked by KA were reduced after ONT (50 μM KA; ΔF/F0 [SD]; control: 1.00 [0.67], day 3: 0.50 [0.35], day 5: 0.31 [0.28], day 7: 0.35 [0.36]; P < 0.05 versus control). There was also a decrease in the number of GCaMP3+ cells after ONT (cells/mm2 [SD]; control: 2198 [453], day 3: 2224 [643], day 5: 1383 [375], day 7: 913 [178]; P < 0.05). Furthermore, the proportion of GCaMP3+ cells that responded to KA decreased after ONT (50 μM KA, 97%, 54%, 47%, and 58%; control, 3, 5, and 7 days, respectively).

Conclusions

Following ONT, functional RGC responses are lost prior to the loss of RGC somata, suggesting that anatomical markers of RGCs may underestimate the extent of RGC dysfunction.

CNS luteinizing hormone receptor activation rescues ovariectomy-related loss of spatial memory and neuronal plasticity

Ovariectomy (OVX), a menopause model, leads to cognition and neuronal plasticity deficits that are rescued by estrogen administration or downregulation of pituitary luteinizing hormone (LH). LH is present in the brain. However, whether LH levels differ across brain regions, change across reproductive stages, or whether brain-specific LHR signaling play a role in OVX-related cognitive and neuroplasticity losses is completely unknown. To address this, we measured brain LH in cycling and OVX C57Bl/6 across brain regions and determined whether OVX-related functional and plasticity deficits could be rescued by intracerebroventricular administration of the LHR agonist (hCG). Here, we show that while pituitary LH is increased in OVX, brain LH is decreased, primarily in spatial memory and navigation areas. Furthermore, intracerebroventricular hCG delivery after OVX rescued dendritic spine density and spatial memory. In vitro, we show that hCG increased neurite outgrowth in primary hippocampal neurons in a receptor-specific manner. Taken together, our data suggest that loss of brain LH signaling is involved in cognitive and plasticity losses associated with OVX and loss of ovarian hormones.

Granisetron Alleviates Alzheimer's Disease Pathology in TgSwDI Mice Through Calmodulin-Dependent Protein Kinase II/cAMP-Response Element Binding Protein Pathway

Alzheimer's disease (AD) is characterized by a compromised blood-brain barrier (BBB) and disrupted intracellular calcium homeostasis in the brain. Therefore, rectifying the BBB integrity and restoring calcium homeostasis could provide an effective strategy to treat AD. Recently, we developed a high throughput-screening assay to screen for compounds that enhance a cell-based BBB model integrity, which identified multiple hits among which is granisetron, a Food and Drug Administration approved drug. Here, we evaluated the therapeutic potential of granisetron against AD. Granisetron was tested in C57Bl/6J young and aged wild-type mice, and in a transgenic mouse model of AD namely TgSwDI for its effect on BBB intactness and amyloid-β (Aβ)-related pathology. Our study findings showed that granisetron enhanced BBB integrity in both aged and TgSwDI mice. This effect was associated with an overall reduction in Aβ load and neuroinflammation in TgSwDI mice brains. In addition, and supported by proteomics analysis, granisetron significantly reduced Aβ induced calcium influx in vitro, and rectified calcium dyshomeostasis in TgSwDI mice brains by restoring calmodulin-dependent protein kinase II/cAMP-response element binding protein pathway, which was associated with cognitive improvement. These results support granisetron repurposing as a potential drug to hold, slow, and/or treat AD.

Friend and foe: β-cell Ca2+ signaling and the development of diabetes

BACKGROUND

The divalent cation Calcium (Ca²⁺) regulates a wide range of processes in disparate cell types. Within insulin-producing β-cells, increases in cytosolic Ca²⁺ directly stimulate insulin vesicle exocytosis, but also initiate multiple signaling pathways. Mediated through activation of downstream kinases and transcription factors, Ca²⁺-regulated signaling pathways leverage substantial influence on a number of critical cellular processes within the β-cell. Additionally, there is evidence that prolonged activation of these same pathways is detrimental to β-cell health and may contribute to Type 2 Diabetes pathogenesis.

SCOPE OF REVIEW

This review aims to briefly highlight canonical Ca²⁺ signaling pathways in β-cells and how β-cells regulate the movement of Ca²⁺ across numerous organelles and microdomains. As a main focus, this review synthesizes experimental data from in vitro and in vivo models on both the beneficial and detrimental effects of Ca²⁺ signaling pathways for β-cell function and health.

MAJOR CONCLUSIONS

Acute increases in intracellular Ca²⁺ stimulate a number of signaling cascades, resulting in (de-)phosphorylation events and activation of downstream transcription factors. The short-term stimulation of these Ca²⁺ signaling pathways promotes numerous cellular processes critical to β-cell function, including increased viability, replication, and insulin production and secretion. Conversely, chronic stimulation of Ca²⁺ signaling pathways increases β-cell ER stress and results in the loss of β-cell differentiation status. Together, decades of study demonstrate that Ca²⁺ movement is tightly regulated within the β-cell, which is at least partially due to its dual roles as a potent signaling molecule.

X11 and X11-like proteins regulate the level of extrasynaptic glutamate receptors

X11/Mint 1 and X11-like (X11L)/Mint 2 are neuronal adaptor protein to regulate trafficking and/or localization of various membrane proteins. By analyzing the localization of neuronal membrane proteins in X11-, X11L-, and X11/X11L doubly deficient mice with membrane fractionation procedures, we found that deficient of X11 and X11L decreased the level of glutamate receptors in non-PSD fraction. This finding suggests that X11 and X11L regulate the glutamate receptor micro-localization to the extrasynaptic region. In vitro coimmunoprecipitation studies of NMDA receptors lacking various cytoplasmic regions with X11 and X11L proteins harboring domain deletion suggest that extrasynaptic localization of NMDA receptor may be as a result of the multiple interactions of the receptor subunits with X11 and X11L regulated by protein phosphorylation, while that of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunits is not dependent on the binding with X11 and X11L proteins. Because the loss of X11 and X11L tends to impair the exocytosis, but not endocytosis, of glutamate receptors, NMDA receptors are likely to be supplied to the extrasynaptic plasma membrane with a way distinct from the mechanism regulating the localization of NMDA receptors into synaptic membrane region. Reduced localization of NMDA receptor into the extrasynaptic region increased slightly the phosphorylation level of cAMP responsible element binding protein in brain of X11/X11L doubly deficient mice compare to wild-type mice, suggesting a possible role of X11 and X11L in the regulation of signal transduction pathway through extrasynaptic glutamate receptors. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/.

Pathway sensor-based functional genomics screening identifies modulators of neuronal activity

Neuronal signal transduction shapes brain function and malfunction may cause mental disorders. Despite the existence of functional genomics screens for proliferation and toxicity, neuronal signalling has been difficult to address so far. To overcome this limitation, we developed a pooled screening assay which combines barcoded activity reporters with pooled genetic perturbation in a dual-expression adeno-associated virus (AAV) library. With this approach, termed pathScreener, we comprehensively dissect signalling pathways in postmitotic neurons. This overcomes several limitations of lentiviral-based screens. By applying first a barcoded and multiplexed reporter assay, termed cisProfiler, we identified the synaptic-activity responsive element (SARE) as top performance sensor of neuronal activity. Next, we targeted more than 4,400 genes and screened for modulatory effects on SARE activity in primary cortical neurons. We identified with high replicability many known genes involved in glutamatergic synapse-to-nucleus signalling of which a subset was validated in orthogonal assays. Several others have not yet been associated with the regulation of neuronal activity such as the hedgehog signalling members Ptch2 and Ift57. This assay thus enhances the toolbox for analysing regulatory processes during neuronal signalling and may help identifying novel targets for brain disorders.

Excitotoxic superoxide production and neuronal death require both ionotropic and non-ionotropic NMDA receptor signaling

NMDA-type glutamate receptors (NMDAR) trigger superoxide production by neuronal NADPH oxidase-2 (NOX2), which if sustained leads to cell death. This process involves Ca²⁺ influx through NMDAR channels. By contrast, comparable Ca²⁺ influx by other routes does not induce NOX2 activation or cell death. This contrast has been attributed to site-specific effects of Ca²⁺ flux through NMDAR. Here we show instead that it stems from non-ionotropic signaling by NMDAR GluN2B subunits. To evaluate non-ionotropic effects, mouse cortical neurons were treated with NMDA together with 7-chlorokynurenate, L-689,560, or MK-801, which block Ca²⁺ influx through NMDAR channels but not NMDA binding. NMDA-induced superoxide formation was prevented by the channel blockers, restored by concurrent Ca²⁺ influx through ionomycin or voltage-gated calcium channels, and not induced by the Ca²⁺ influx in the absence of NMDAR ligand binding. Neurons expressing either GluN2B subunits or chimeric GluN2A/GluN2B C-terminus subunits exhibited NMDA-induced superoxide production, whereas neurons expressing chimeric GluN2B/GluN2A C-terminus subunits did not. Neuronal NOX2 activation requires phosphoinositide 3-kinase (PI3K), and NMDA binding to NMDAR increased PI3K association with NMDA GluN2B subunits independent of Ca²⁺ influx. These findings identify a non-ionotropic signaling pathway that links NMDAR to NOX2 activation through the C-terminus domain of GluN2B.

A transgenic mouse for imaging activity-dependent dynamics of endogenous Arc mRNA in live neurons

Localized translation plays a crucial role in synaptic plasticity and memory consolidation. However, it has not been possible to follow the dynamics of memory-associated mRNAs in living neurons in response to neuronal activity in real time. We have generated a novel mouse model where the endogenous Arc/Arg3.1 gene is tagged in its 3' untranslated region with stem-loops that bind a bacteriophage PP7 coat protein (PCP), allowing visualization of individual mRNAs in real time. The physiological response of the tagged gene to neuronal activity is identical to endogenous Arc and reports the true dynamics of Arc mRNA from transcription to degradation. The transcription dynamics of Arc in cultured hippocampal neurons revealed two novel results: (i) A robust transcriptional burst with prolonged ON state occurs after stimulation, and (ii) transcription cycles continue even after initial stimulation is removed. The correlation of stimulation with Arc transcription and mRNA transport in individual neurons revealed that stimulus-induced Ca²⁺ activity was necessary but not sufficient for triggering Arc transcription and that blocking neuronal activity did not affect the dendritic transport of newly synthesized Arc mRNAs. This mouse will provide an important reagent to investigate how individual neurons transduce activity into spatiotemporal regulation of gene expression at the synapse.

MICU3 is a tissue-specific enhancer of mitochondrial calcium uptake

The versatility and universality of Ca²⁺ as intracellular messenger is guaranteed by the compartmentalization of changes in [Ca²⁺]. In this context, mitochondrial Ca²⁺ plays a central role, by regulating both specific organelle functions and global cellular events. This versatility is also guaranteed by a cell type-specific Ca²⁺ signaling toolkit controlling specific cellular functions. Accordingly, mitochondrial Ca²⁺ uptake is mediated by a multimolecular structure, the MCU complex, which differs among various tissues. Its activity is indeed controlled by different components that cooperate to modulate specific channeling properties. We here investigate the role of MICU3, an EF-hand containing protein expressed at high levels, especially in brain. We show that MICU3 forms a disulfide bond-mediated dimer with MICU1, but not with MICU2, and it acts as enhancer of MCU-dependent mitochondrial Ca²⁺ uptake. Silencing of MICU3 in primary cortical neurons impairs Ca²⁺ signals elicited by synaptic activity, thus suggesting a specific role in regulating neuronal function.

Synaptic activity-induced glycolysis facilitates membrane lipid provision and neurite outgrowth

The formation of neurites is an important process affecting the cognitive abilities of an organism. Neurite growth requires the addition of new membranes, but the metabolic remodeling necessary to supply lipids for membrane expansion is poorly understood. Here, we show that synaptic activity, one of the most important inducers of neurite growth, transcriptionally regulates the expression of neuronal glucose transporter Glut3 and rate-limiting enzymes of glycolysis, resulting in enhanced glucose uptake and metabolism that is partly used for lipid synthesis. Mechanistically, CREB regulates the expression of Glut3 and Siah2, the latter and LDH activity promoting the normoxic stabilization of HIF-1α that regulates the expression of rate-limiting genes of glycolysis. The expression of dominant-negative HIF-1α or Glut3 knockdown blocks activity-dependent neurite growth in vitro while pharmacological inhibition of the glycolysis and specific ablation of HIF-1α in early postnatal mice impairs the neurite architecture. These results suggest that the manipulation of neuronal glucose metabolism could be used to treat some brain developmental disorders.

Serum calcium levels and neuropsychological performance in depression and matched healthy controls: Reversal of correlation a marker of the aging cognitive clock?

BACKGROUND

Major depressive disorder (MDD) is associated with cognitive impairment, that might be related to disturbed calcium homeostasis. Calcium-related processes have also been implicated in age related cognitive decline. Since serum calcium and brain interstitial fluids maintain long-term equilibrium under normal physiological states, serum calcium levels could affect neuronal and hence cognitive function. High serum calcium has been associated with cognitive decline in geriatric populations, whereas evidence for MDD and healthy populations is less consistent.

METHODS

Differences in neuropsychological (NPS) performance and their relationship with serum calcium (total, ionized, total to ionized ratio) in (partially) remitted MDD patients (n = 59) and healthy controls (HC) (n = 59) individually matched for age, gender and education (age-range 19-60 years) were examined. Modulation of study parameters and their interaction by the factor age was investigated, with subgroups young and old divided at median = 37 years. Participants provided blood samples and completed an extensive NPS test battery.

RESULTS

MDD showed significantly poorer NPS performance compared to HC. Serum calcium associated positively with NPS performance in HC and negatively in MDD for entire age-range samples. While younger MDD and HC showed positive NPS-calcium correlations, older MDD and HC exhibited negative NPS-calcium correlations ('correlation reversal'). Age had a significant effect on cognition and ionized calcium and interacted with illness-status, with an exaggerated influence on cognition in MDD compared to HC.

CONCLUSIONS

The results place calcium 'correlation reversal' to early middle-age time window, which may be accelerated for MDD and highlight the central role of calcium pathways in normal and pathological cognitive aging.

An open source tool for automatic spatiotemporal assessment of calcium transients and local 'signal-close-to-noise' activity in calcium imaging data

Local and spontaneous calcium signals play important roles in neurons and neuronal networks. Spontaneous or cell-autonomous calcium signals may be difficult to assess because they appear in an unpredictable spatiotemporal pattern and in very small neuronal loci of axons or dendrites. We developed an open source bioinformatics tool for an unbiased assessment of calcium signals in x,y-t imaging series. The tool bases its algorithm on a continuous wavelet transform-guided peak detection to identify calcium signal candidates. The highly sensitive calcium event definition is based on identification of peaks in 1D data through analysis of a 2D wavelet transform surface. For spatial analysis, the tool uses a grid to separate the x,y-image field in independently analyzed grid windows. A document containing a graphical summary of the data is automatically created and displays the loci of activity for a wide range of signal intensities. Furthermore, the number of activity events is summed up to create an estimated total activity value, which can be used to compare different experimental situations, such as calcium activity before or after an experimental treatment. All traces and data of active loci become documented. The tool can also compute the signal variance in a sliding window to visualize activity-dependent signal fluctuations. We applied the calcium signal detector to monitor activity states of cultured mouse neurons. Our data show that both the total activity value and the variance area created by a sliding window can distinguish experimental manipulations of neuronal activity states. Notably, the tool is powerful enough to compute local calcium events and ‘signal-close-to-noise’ activity in small loci of distal neurites of neurons, which remain during pharmacological blockade of neuronal activity with inhibitors such as tetrodotoxin, to block action potential firing, or inhibitors of ionotropic glutamate receptors. The tool can also offer information about local homeostatic calcium activity events in neurites.

Calcium imaging has become a standard tool to investigate local, spontaneous, or cell-autonomous calcium signals in neurons. Some of these calcium signals are fast and ‘small’, thus making it difficult to identify real signaling events due to an unavoidable signal noise. Therefore, it is difficult to assess the spatiotemporal activity footprint of individual neurons or a neuronal network. We developed this open source tool to automatically extract, count, and localize calcium signals from the whole x,y-t image series. As demonstrated here, the tool is useful for an unbiased comparison of activity states of neurons, helps to assess local calcium transients, and even visualizes local homeostatic calcium activity. The tool is powerful enough to visualize signal-close-to-noise calcium activity.

Age-related NMDA signaling alterations in SOD2 deficient mice

Oxidative stress affects the survival and function of neurons. Hence, they have a complex and highly regulated machinery to handle oxidative changes. The dysregulation of this antioxidant machinery is associated with a wide range of neurodegenerative conditions. Therefore, we evaluated signaling alterations, synaptic properties and behavioral performance in 2 and 6-month-old heterozygous manganese superoxide dismutase knockout mice (SOD2^+/- mice). We found that their low antioxidant capacity generated direct oxidative damage in proteins, lipids, and DNA. However, only 6-month-old heterozygous knockout mice presented behavioral impairments. On the other hand, synaptic plasticity, synaptic strength and NMDA receptor (NMDAR) dependent postsynaptic potentials were decreased in an age-dependent manner. We also analyzed the phosphorylation state of the NMDAR subunit GluN2B. We found that while the levels of GluN2B phosphorylated on tyrosine 1472 (synaptic form) remain unchanged, we detected increased levels of GluN2B phosphorylated on tyrosine 1336 (extrasynaptic form), establishing alterations in the synaptic/extrasynaptic ratio of GluN2B. Additionally, we found increased levels of two phosphatases associated with dephosphorylation of p-1472: striatal-enriched protein tyrosine phosphatase (STEP) and phosphatase and tensin homolog deleted on chromosome Ten (PTEN). Moreover, we found decreased levels of p-CREB, a master transcription factor activated by synaptic stimulation. In summary, we describe mechanisms by which glutamatergic synapses are altered under oxidative stress conditions. Our results uncovered new putative therapeutic targets for conditions where NMDAR downstream signaling is altered. This work also contributes to our understanding of processes such as synapse formation, learning, and memory in neuropathological conditions.

AD-Related N-Terminal Truncated Tau Is Sufficient to Recapitulate In Vivo the Early Perturbations of Human Neuropathology: Implications for Immunotherapy

The NH₂tau 26-44 aa (i.e., NH₂htau) is the minimal biologically active moiety of longer 20-22-kDa NH₂-truncated form of human tau-a neurotoxic fragment mapping between 26 and 230 amino acids of full-length protein (htau40)-which is detectable in presynaptic terminals and peripheral CSF from patients suffering from AD and other non-AD neurodegenerative diseases. Nevertheless, whether its exogenous administration in healthy nontransgenic mice is able to elicit a neuropathological phenotype resembling human tauopathies has not been yet investigated. We explored the in vivo effects evoked by subchronic intracerebroventricular (i.c.v.) infusion of NH₂htau or its reverse counterpart into two lines of young (2-month-old) wild-type mice (C57BL/6 and B6SJL). Six days after its accumulation into hippocampal parenchyma, significant impairment in memory/learning performance was detected in NH₂htau-treated group in association with reduced synaptic connectivity and neuroinflammatory response. Compromised short-term plasticity in paired-pulse facilitation paradigm (PPF) was detected in the CA3/CA1 synapses from NH₂htau-impaired animals along with downregulation in calcineurin (CaN)-stimulated pCREB/c-Fos pathway(s). Importantly, these behavioral, synaptotoxic, and neuropathological effects were independent from the genetic background, occurred prior to frank neuronal loss, and were specific because no alterations were detected in the control group infused with its reverse counterpart. Finally, a 2.0-kDa peptide which biochemically and immunologically resembles the injected NH₂htau was endogenously detected in vivo, being present in hippocampal synaptosomal preparations from AD subjects. Given that the identification of the neurotoxic tau species is mandatory to develop a more effective tau-based immunological approach, our evidence can have important translational implications for cure of human tauopathies.

Epigenome Interactions with Patterned Neuronal Activity

The temporal coding of action potential activity is fundamental to nervous system function. Here we consider how gene expression in neurons is regulated by specific patterns of action potential firing, with an emphasis on new information on epigenetic regulation of gene expression. Patterned action potential activity activates intracellular signaling networks selectively in accordance with the kinetics of activation and inactivation of second messengers, phosphorylation and dephosphorylation of protein kinases, and cytoplasmic and nuclear calcium dynamics, which differentially activate specific transcription factors. Increasing evidence also implicates activity-dependent regulation of epigenetic mechanisms to alter chromatin architecture. Changes in three-dimensional chromatin structure, including chromatin compaction, looping, double-stranded DNA breaks, histone and DNA modification, are altered by action potential activity to selectively inhibit or promote transcription of specific genes. These mechanisms of activity-dependent regulation of gene expression are important in neural development, plasticity, and in neurological and psychological disorders.

Influence of sevoflurane exposure on mitogen-activated protein kinases and Akt/GSK-3β/CRMP-2 signaling pathways in the developing rat brain

Prolonged exposure to volatile anesthetics causes neurodegeneration in developing animal brains. However, their underlying mechanisms of action remain unclear. The current study investigated the expression of proteins associated with the mitogen-activated protein kinases (MAPK) and protein kinase B (Akt)/glycogen synthase kinase-3β (GSK-3β)/collapsin response mediator protein 2 (CRMP-2) signaling pathways in the cortices of neonatal mice following exposure to sevoflurane. Seven-day-old (P7) neonatal C57BL/6 mice were randomly divided into 2 groups and either exposed to 2.6% sevoflurane or air for 6 h. Terminal deoxyribonucleotide transferase mediated dUTP nick end labeling (TUNEL) staining, as well as the expression of activated caspase-3 and α-fodrin, was used to detect neuronal apoptosis in the cortices of mice. MAPK signaling pathways were investigated by detecting the expression of phosphorylated (p-) extracellular signal-regulated kinase 1/2 (ERK1/2), p-cyclic adenosine monophosphate response element-binding protein (CREB), p-p38, p-nuclear factor (NF-κB) and p-c-Jun N-terminal kinase (p-JNK). Akt/GSK-3β/CRMP-2 signaling pathways were assessed by detecting the expression of p-Akt, p-GSK-3β and p-CRMP-2 in the cortices of P7 mice 2 h following exposure to sevoflurane. The results demonstrated that sevoflurane significantly increased the apoptosis of cells in the retrosplenial cortex (RS), frontal cortex (FC) and parietal association cortex (PtA), increased the expression of cleaved caspase-3 expression and promoted the formation of 145 kDa and 120 kDa fragments from α-fodrin. Sevoflurane inhibited the phosphorylation of ERK1/2 and CREB, stimulated the phosphorylation of p38 and NF-κB, but did not significantly affect the phosphorylation of JNK. Furthermore, sevoflurane inhibited the phosphorylation of Akt, decreased the phosphorylation of GSK-3β at ser9 and increased the phosphorylation of CRMP2 at Thr514. These results suggest that multiple signaling pathways, including ERK1/2, P38 and Akt/GSK-3β/CRMP-2 may be involved in sevoflurane-induced neuroapoptosis in the developing brain.

Lineage divergence of activity-driven transcription and evolution of cognitive ability

Excitation-transcription coupling shapes network formation during brain development and controls neuronal survival, synaptic function and cognitive skills in the adult. New studies have uncovered differences in the transcriptional responses to synaptic activity between humans and mice. These differences are caused both by the emergence of lineage-specific activity-regulated genes and by the acquisition of signal-responsive DNA elements in gene regulatory regions that determine whether a gene can be transcriptionally induced by synaptic activity or alter the extent of its inducibility. Such evolutionary divergence may have contributed to lineage-related advancements in cognitive abilities.

Networks of Cultured iPSC-Derived Neurons Reveal the Human Synaptic Activity-Regulated Adaptive Gene Program

Long-term adaptive responses in the brain, such as learning and memory, require synaptic activity-regulated gene expression, which has been thoroughly investigated in rodents. Using human iPSC-derived neuronal networks, we show that the human and the mouse synaptic activity-induced transcriptional programs share many genes and both require Ca²⁺-regulated synapse-to-nucleus signaling. Species-specific differences include the noncoding RNA genes BRE-AS1 and LINC00473 and the protein-coding gene ZNF331, which are absent in the mouse genome, as well as several human genes whose orthologs are either not induced by activity or are induced with different kinetics in mice. These results indicate that lineage-specific gain of genes and DNA regulatory elements affects the synaptic activity-regulated gene program, providing a mechanism driving the evolution of human cognitive abilities.

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The repertoire of human activity-induced genes is expanded lineage specifically

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Temporal expression profiles of many activity-responsive genes are species specific

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Some human orthologs of mouse genes have gained inducibility by synaptic activity

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The human HIC1 gene promoter has gained an activity-responsive regulatory element

Rubinstein-Taybi Syndrome and Epigenetic Alterations

Rubinstein-Taybi syndrome (RSTS) is a rare genetic disorder in humans characterized by growth and psychomotor delay, abnormal gross anatomy, and mild to severe mental retardation (Rubinstein and Taybi, Am J Dis Child 105:588-608, 1963, Hennekam et al., Am J Med Genet Suppl 6:56-64, 1990). RSTS is caused by de novo mutations in epigenetics-associated genes, including the cAMP response element-binding protein (CREBBP), the gene-encoding protein referred to as CBP, and the EP300 gene, which encodes the p300 protein, a CBP homologue. Recent studies of the epigenetic mechanisms underlying cognitive functions in mice provide direct evidence for the involvement of nuclear factors (e.g., CBP) in the control of higher cognitive functions. In fact, a role for CBP in higher cognitive function is suggested by the finding that RSTS is caused by heterozygous mutations at the CBP locus (Petrij et al., Nature 376:348-351, 1995). CBP was demonstrated to possess an intrinsic histone acetyltransferase activity (Ogryzko et al., Cell 87:953-959, 1996) that is required for CREB-mediated gene expression (Korzus et al., Science 279:703-707, 1998). The intrinsic protein acetyltransferase activity in CBP might directly destabilize promoter-bound nucleosomes, facilitating the activation of transcription. Due to the complexity of developmental abnormalities and the possible genetic compensation associated with this congenital disorder, however, it is difficult to establish a direct role for CBP in cognitive function in the adult brain. Although aspects of the clinical presentation in RSTS cases have been extensively studied, a spectrum of symptoms found in RSTS patients can be accessed only after birth, and, thus, prenatal genetic tests for this extremely rare genetic disorder are seldom considered. Even though there has been intensive research on the genetic and epigenetic function of the CREBBP gene in rodents, the etiology of this devastating congenital human disorder is largely unknown.

The Intellectual Disability and Schizophrenia Associated Transcription Factor TCF4 Is Regulated by Neuronal Activity and Protein Kinase A

Transcription factor 4 (TCF4 also known as ITF2 or E2-2) is a basic helix-loop-helix (bHLH) protein associated with Pitt-Hopkins syndrome, intellectual disability, and schizophrenia (SCZ). Here, we show that TCF4-dependent transcription in cortical neurons cultured from embryonic rats of both sexes is induced by neuronal activity via soluble adenylyl cyclase and protein kinase A (PKA) signaling. PKA phosphorylates TCF4 directly and a PKA phosphorylation site in TCF4 is necessary for its transcriptional activity in cultured neurons and in the developing brain in vivo We also demonstrate that Gadd45g (growth arrest and DNA damage inducible gamma) is a direct target of neuronal-activity-induced, TCF4-dependent transcriptional regulation and that TCF4 missense variations identified in SCZ patients alter the transcriptional activity of TCF4 in neurons. This study identifies a new role for TCF4 as a neuronal-activity-regulated transcription factor, offering a novel perspective on the association of TCF4 with cognitive disorders.SIGNIFICANCE STATEMENT The importance of the basic helix-loop-helix transcription factor transcription factor 4 (TCF4) in the nervous system is underlined by its association with common and rare cognitive disorders. In the current study, we show that TCF4-controlled transcription in primary cortical neurons is induced by neuronal activity and protein kinase A. Our results support the hypotheses that dysregulation of neuronal-activity-dependent signaling plays a significant part in the etiology of neuropsychiatric and neurodevelopmental disorders.

Calcium Dysregulation in Alzheimer's Disease: A Target for New Drug Development

Alzheimer's disease (AD) is a devastating neurodegenerative disorder and the most common cause of dementia among aged people whose population is rapidly increasing. AD not only seriously affects the patient's physical health and quality of life, but also adds a heavy burden to the patient's family and society. It is urgent to understand AD pathogenesis and develop the means of prevention and treatment. AD is a chronic devastating neurodegenerative disease without effective treatment. Current approaches for management focus on helping patients relieve or delay the symptoms of cognitive dysfunction. The calcium ion (Ca²⁺) is an important second messenger in the function and structure of nerve cell circuits in the brain such as neuronal growth, exocytosis, as well as in synaptic and cognitive function. Increasing numbers of studies suggested that disruption of intracellular Ca²⁺ homeostasis, especially the abnormal and excessive Ca²⁺ release from the endoplasmic reticulum (ER) via the ryanodine receptor (RYR), plays important roles in orchestrating the dynamic of the neuropathology of AD and associated memory loss, cognitive dysfunction. Dantrolene, a known antagonist of the RYR and a clinically available drug to treat malignant hyperthermia, can ameliorate the abnormal Ca²+ release from the RYR in AD and the subsequent pathogenesis, such as increased β-secretase and γ-secretase activities, production of Amyloid-β 42 (Aβ 42) and its oligomer, impaired autophagy, synapse dysfunction, and memory loss. However, more studies are needed to confirm the efficacy and safety repurposing dantrolene as a therapeutic drug in AD.

A novel mechanism for Ca2+/calmodulin-dependent protein kinase II targeting to L-type Ca2+ channels that initiates long-range signaling to the nucleus

Neuronal excitation can induce new mRNA transcription, a phenomenon called excitation-transcription (E-T) coupling. Among several pathways implicated in E-T coupling, activation of voltage-gated L-type Ca²⁺ channels (LTCCs) in the plasma membrane can initiate a signaling pathway that ultimately increases nuclear CREB phosphorylation and, in most cases, expression of immediate early genes. Initiation of this long-range pathway has been shown to require recruitment of Ca²⁺-sensitive enzymes to a nanodomain in the immediate vicinity of the LTCC by an unknown mechanism. Here, we show that activated Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) strongly interacts with a novel binding motif in the N-terminal domain of Ca_V1 LTCC α1 subunits that is not conserved in Ca_V2 or Ca_V3 voltage-gated Ca²⁺ channel subunits. Mutations in the Ca_V1.3 α1 subunit N-terminal domain or in the CaMKII catalytic domain that largely prevent the in vitro interaction also disrupt CaMKII association with intact LTCC complexes isolated by immunoprecipitation. Furthermore, these same mutations interfere with E-T coupling in cultured hippocampal neurons. Taken together, our findings define a novel molecular interaction with the neuronal LTCC that is required for the initiation of a long-range signal to the nucleus that is critical for learning and memory.

Zinc mediates the neuronal activity-dependent anti-apoptotic effect

Synaptic activity increases the resistance of neurons to diverse apoptotic insults; however, the underlying mechanisms remain less well understood. Zinc promotes cell survival under varied conditions, but the role of synaptically released zinc in the activity-dependent anti-apoptotic effect is unknown. Using cultured hippocampal slices and primary neurons we show that a typical apoptosis inducer–staurosporine (STP) was able to cause concentration-dependent apoptotic cell death in brain slices; Enhanced synaptic activity by bicuculline (Bic)/4-Aminopyridine (AP) treatment effectively prevented neurons from STP-induced cell apoptosis, as indicated by increased cell survival and suppressed caspase-3 activity. Application of Ca-EDTA, a cell membrane-impermeable zinc chelator which can efficiently capture the synaptically released zinc, completely blocked the neuronal activity-dependent anti-apoptotic effect. Same results were also observed in cultured primary hippocampal neurons. Therefore, our results indicate that synaptic activity improves neuronal resistance to apoptosis via synaptically released zinc.

Predator odor evokes sex-independent stress responses in male and female Wistar rats and reduces phosphorylation of cyclic-adenosine monophosphate response element binding protein in the male, but not the female hippocampus

Post-traumatic stress disorder (PTSD) is characterized by memory disturbances following trauma. Acute predator threat has emerged as an ethological model of PTSD, yet the effects of predator odor on signaling cascades associated with long-term memory remain poorly understood. In this study, we exposed male and female Wistar rats to the synthetic predator odor 2,5-dihydro-2,4,5-trimethylthiazoline (TMT) to assess behavioral and physiological responses as well as rapid modulation of signal transduction cascades associated with learning and memory in the male and female hippocampus. During exposure to TMT in the homecage, both male and female animals displayed robust immobility, avoidance, and altered activity as a function of time. Physiologically, TMT exposure increased circulating corticosterone and blood glucose in both male and female rodents, suggesting that TMT evokes sex-independent behavioral and physiological responses. With respect to signal transduction, TMT exposure rapidly reduced phosphorylation of cyclic-adenosine monophosphate response element binding protein (CREB) in the male, but not the female hippocampus. Furthermore, TMT exposure reduced phosphorylation of extracellular signal-regulated kinase 1/2 and increased nuclear expression of the synapto-nuclear messenger protein Jacob in the male hippocampus, consistent with activation of the CREB shut-off pathway. In a follow-up behavioral experiment, post-training exposure to TMT did not affect spatial water maze performance of male rats. However, male rats re-introduced to the context in which TMT had previously been presented displayed avoidance and hyperactivity, but not freezing behavior or elevated corticosterone responses, suggesting that TMT exposure supports a form of contextual conditioning which is not characterized by immobility. Taken together, our findings suggest that TMT evokes similar behavioral and physiological responses in male and female Wistar rats, but affects distinct signaling cascades in the male and female hippocampus which may contribute to behavioral disruptions associated with predator exposure.

Homeostatic interplay between electrical activity and neuronal apoptosis in the developing neocortex

An intriguing feature of nervous system development in most animal species is that the initial number of generated neurons is higher than the number of neurons incorporated into mature circuits. A substantial portion of neurons is indeed eliminated via apoptosis during a short time window - in rodents the first two postnatal weeks. While it is well established that neurotrophic factors play a central role in controlling neuronal survival and apoptosis in the peripheral nervous system (PNS), the situation is less clear in the central nervous system (CNS). In postnatal rodent neocortex, the peak of apoptosis coincides with the occurrence of spontaneous, synchronous activity patterns. In this article, we review recent results that demonstrate the important role of electrical activity for neuronal survival in the neocortex, describe the role of Ca²⁺ and neurotrophic factors in translating electrical activity into pro-survival signals, and finally discuss the clinical impact of the tight relation between electrical activity and neuronal survival versus apoptosis.

Synaptic activity suppresses expression of neurogenic differentiation factor 2 in an NMDA receptor-dependent manner

Neurogenic differentiation factor 2 (NeuroD2) is a highly expressed transcription factor in the developing central nervous system. In newborn neurons, NeuroD2-mediated gene expression promotes differentiation, maturation, and survival. In addition to these early, cell-intrinsic developmental processes, NeuroD2 in postmitotic neurons also regulates synapse growth and ion channel expression to control excitability. While NeuroD2 transactivation can be induced in an activity-dependent manner, little is known about how expression of NeuroD2 itself is regulated. Using genome-wide, mRNA-based microarray analysis, we found that NeuroD2 is actually one of hundreds of genes whose mRNA levels are suppressed by synaptic activity, in a manner dependent upon N-methyl d-aspartate receptor (NMDAR) activation. We confirmed this observation both in vitro and in vivo and provide evidence that this happens at the level of transcription and not mRNA stability. Our experiments further indicate that suppression of NeuroD2 message by NMDARs likely involves both CaMKII and MAPK but not voltage-gated calcium channels, in contrast to its mechanism of transactivation. We predict from these data that NMDARs may transduce information about the level of synaptic activity a developing neuron receives, to down-regulate NeuroD2 and allow proper maturation of cortical circuits by suppressing expression of neurite and synaptic growth promoting gene products.

Early neurotrophic pharmacotherapy rescues developmental delay and Alzheimer's-like memory deficits in the Ts65Dn mouse model of Down syndrome

Down syndrome (DS), caused by trisomy 21, is the most common genetic cause of intellectual disability and is associated with a greatly increased risk of early-onset Alzheimer’s disease (AD). The Ts65Dn mouse model of DS exhibits several key features of the disease including developmental delay and AD-like cognitive impairment. Accumulating evidence suggests that impairments in early brain development caused by trisomy 21 contribute significantly to memory deficits in adult life in DS. Prenatal genetic testing to diagnose DS in utero, provides the novel opportunity to initiate early pharmacological treatment to target this critical period of brain development. Here, we report that prenatal to early postnatal treatment with a ciliary neurotrophic factor (CNTF) small-molecule peptide mimetic, Peptide 021 (P021), rescued developmental delay in pups and AD-like hippocampus-dependent memory impairments in adult life in Ts65Dn mice. Furthermore, this treatment prevented pre-synaptic protein deficit, decreased glycogen synthase kinase-3beta (GSK3β) activity, and increased levels of synaptic plasticity markers including brain derived neurotrophic factor (BNDF) and phosphorylated CREB, both in young (3-week-old) and adult (~ 7-month-old) Ts65Dn mice. These findings provide novel evidence that providing neurotrophic support during early brain development can prevent developmental delay and AD-like memory impairments in a DS mouse model.

Ultrafast Near-Infrared Light-triggered Intracellular Uncaging to Probe Cell Signaling

The possibility of regulating cell signaling with high spatial and temporal resolution within individual cells and complex cellular networks has important implications in biomedicine. In this report, we demonstrate a general strategy that uses near-infrared tissue-penetrating laser pulses to uncage biomolecules from plasmonic gold-coated liposomes, i.e. plasmonic liposomes, to activate cell signaling in a non-thermal, ultrafast and highly controllable fashion. Near-infrared picosecond laser pulse induces transient nanobubbles around plasmonic liposomes. The mechanical force generated from the collapse of nanobubbles rapidly ejects encapsulated compound within 0.1 ms. We showed that single pulse irradiation triggers the rapid intracellular uncaging of calcein from plasmonic liposomes inside endo-lysosomes. The uncaged calcein then evenly distributes over the entire cytosol and nucleus. Furthermore, we demonstrated the ability to trigger calcium signaling in both an immortalized cell line and primary dorsal root ganglion (DRG) neurons by intracellular uncaging of inositol triphosphate (IP3), an endogenous cell calcium signaling second messenger. Compared with other uncaging techniques, this ultrafast near-infrared light-driven molecular uncaging method is easily adaptable to deliver a wide range of bioactive molecules with an ultrafast optical switch, enabling new possibilities to investigate signaling pathways within individual cells and cellular networks.

Nonreciprocal homeostatic compensation in Drosophila potassium channel mutants

Homeostatic control of intrinsic excitability is important for long-term regulation of neuronal activity. In conjunction with many other forms of plasticity, intrinsic homeostasis helps neurons maintain stable activity regimes in the face of external input variability and destabilizing genetic mutations. In this study, we report a mechanism by which Drosophila melanogaster larval motor neurons stabilize hyperactivity induced by the loss of the delayed rectifying K⁺ channel Shaker cognate B (Shab), by upregulating the Ca²⁺-dependent K⁺ channel encoded by the slowpoke (slo) gene. We also show that loss of SLO does not trigger a reciprocal compensatory upregulation of SHAB, implying that homeostatic signaling pathways utilize compensatory pathways unique to the channel that was mutated. SLO upregulation due to loss of SHAB involves nuclear Ca²⁺ signaling and dCREB, suggesting that the slo homeostatic response is transcriptionally mediated. Examination of the changes in gene expression induced by these mutations suggests that there is not a generic transcriptional response to increased excitability in motor neurons, but that homeostatic compensations are influenced by the identity of the lost conductance.NEW & NOTEWORTHY The idea that activity-dependent homeostatic plasticity is driven solely by firing has wide credence. In this report we show that homeostatic compensation after loss of an ion channel conductance is tailored to identity of the channel lost, not its properties.

One nuclear calcium transient induced by a single burst of action potentials represents the minimum signal strength in activity-dependent transcription in hippocampal neurons

Neurons undergo dramatic changes in their gene expression profiles in response to synaptic stimulation. The coupling of neuronal excitation to gene transcription is well studied and is mediated by signaling pathways activated by cytoplasmic and nuclear calcium transients. Despite this, the minimum synaptic activity required to induce gene expression remains unknown. To address this, we used cultured hippocampal neurons and cellular compartment analysis of temporal activity by fluorescence in situ hybridization (catFISH) that allows detection of nascent transcripts in the cell nucleus. We found that a single burst of action potentials, consisting of 24.4±5.1 action potentials during a 6.7±1.9s depolarization of 19.5±2.0mV causing a 9.3±0.9s somatic calcium transient, is sufficient to activate transcription of the immediate early gene arc (also known as Arg3.1). The total arc mRNA yield produced after a single burst-induced nuclear calcium transient was very small and, compared to unstimulated control neurons, did not lead to a significant increase in arc mRNA levels measured using quantitative reverse transcriptase PCR (qRT-PCR) of cell lysates. Significantly increased arc mRNA levels became detectable in hippocampal neurons that had undergone 5-8 consecutive burst-induced nuclear calcium transients at 0.05-0.15Hz. These results indicate that a single burst-induced nuclear calcium transient can activate gene expression and that transcription is rapidly shut off after synaptic stimulation has ceased.

CREB at the Crossroads of Activity-Dependent Regulation of Nervous System Development and Function

The central nervous system is a highly plastic network of cells that constantly adjusts its functions to environmental stimuli throughout life. Transcription-dependent mechanisms modify neuronal properties to respond to external stimuli regulating numerous developmental functions, such as cell survival and differentiation, and physiological functions such as learning, memory, and circadian rhythmicity. The discovery and cloning of the cyclic adenosine monophosphate (cAMP) responsive element binding protein (CREB) constituted a big step toward deciphering the molecular mechanisms underlying neuronal plasticity. CREB was first discovered in learning and memory studies as a crucial mediator of activity-dependent changes in target gene expression that in turn impose long-lasting modifications of the structure and function of neurons. In this chapter, we review the molecular and signaling mechanisms of neural activity-dependent recruitment of CREB and its cofactors. We discuss the crosstalk between signaling pathways that imprints diverse spatiotemporal patterns of CREB activation allowing for the integration of a wide variety of stimuli.

TRPC Channels and Programmed Cell Death

Neurotrophins, including nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), bind to their high-affinity receptors to promote neuronal survival during brain development. One of the key downstream pathways is the phospholipase C (PLC) pathway, which not only plays a central role in calcium release from internal store but also in activation of TRPC channels coupled with neurotrophin receptors. TRPC channels are required for the neurotrophin-mediated neuronal protective effects. In addition, activation of TRPC channels is able to protect neurons in the absence of neurotrophin. In some circumstances, TRPC channels coupled with metabotropic glutamate receptor may mediate the excitotoxicity by calcium overload. One of the key questions in the field is the channel gating mechanisms; understanding of which would help design compounds to modulate the channel properties. The development and identification of TRPC channel agonists or blockers are promising and may unveil new therapeutic drugs for the treatment of neurodegenerative diseases and epilepsy.

Spontaneous Glutamatergic Synaptic Activity Regulates Constitutive COX-2 Expression in Neurons: OPPOSING ROLES FOR THE TRANSCRIPTION FACTORS CREB (cAMP RESPONSE ELEMENT BINDING) PROTEIN AND Sp1 (STIMULATORY PROTEIN-1)

Burgeoning evidence supports a role for cyclooxygenase metabolites in regulating membrane excitability in various forms of synaptic plasticity. Two cyclooxygenases, COX-1 and COX-2, catalyze the initial step in the metabolism of arachidonic acid to prostaglandins. COX-2 is generally considered inducible, but in glutamatergic neurons in some brain regions, including the cerebral cortex, it is constitutively expressed. However, the transcriptional mechanisms by which this occurs have not been elucidated. Here, we used quantitative PCR and also analyzed reporter gene expression in a mouse line carrying a construct consisting of a portion of the proximal promoter region of the mouse COX-2 gene upstream of luciferase cDNA to characterize COX-2 basal transcriptional regulation in cortical neurons. Extracts from the whole brain and from the cerebral cortex, hippocampus, and olfactory bulbs exhibited high luciferase activity. Moreover, constitutive COX-2 expression and luciferase activity were detected in cortical neurons, but not in cortical astrocytes, cultured from wild-type and transgenic mice, respectively. Constitutive COX-2 expression depended on spontaneous but not evoked excitatory synaptic activity and was shown to be N-methyl-d-aspartate receptor-dependent. Constitutive promoter activity was reduced in neurons transfected with a dominant-negative cAMP response element binding protein (CREB) and was eliminated by mutating the CRE-binding site on the COX-2 promoter. However, mutation of the stimulatory protein-1 (Sp1)-binding site resulted in an N-methyl-d-aspartate receptor-dependent enhancement of COX-2 promoter activity. Basal binding of the transcription factors CREB and Sp1 to the native neuronal COX-2 promoter was confirmed. In toto, our data suggest that spontaneous glutamatergic synaptic activity regulates constitutive neuronal COX-2 expression via Sp1 and CREB protein-dependent transcriptional mechanisms.

Effects of a novel phosphodiesterase 10A inhibitor in non-human primates: A therapeutic approach for schizophrenia with improved side effect profile

Schizophrenia symptoms are associated with alterations in basal ganglia-cortical networks that include the cyclic nucleotides (cAMP/cGMP) signaling pathways. Phosphodiesterase 10A (PDE10A) inhibitors have been considered as therapeutic agents for schizophrenia because the regulation of cAMP and cGMP in the striatum by PDE10A plays an important role in the signaling mechanisms of the striatal-cortical network, and thereby in cognitive function. In the present study we assessed in non-human primates (NHPs) the effects of a novel PDE10A inhibitor (FRM-6308) that has demonstrated high potency and selectivity for human recombinant PDE10A in vitro. The behavioral effects of FRM-6308 in a dose range were determined in rhesus monkeys using a standardized motor disability scale for primates, motor tasks, and the "drug effects on the nervous system" (DENS) scale. The neuronal metabolic effects of FRM-6308 were determined with [(18)F]-fluorodeoxyglucose PET imaging. Results showed that FRM-6308 did not have any specific effects on the motor system at s.c. doses up to 0.32 mg/kg in NHPs, which induced a significant increase in the FDG-SUV in striatum (F 16.069, p < 0.05) and cortical (F 15.181, p < 0.05) regions. Higher doses induced sedation and occasional involuntary movements with clear development of tolerance after repeated exposures. These findings suggest that FRM-6308 has the adequate pharmacological profile to advance testing in clinical trials and demonstrate antipsychotic efficacy of PDE10A inhibition for the treatment of schizophrenia patients.