DREAM is a Ca2+-regulated transcriptional repressor

Excitation-transcription coupling, neuronal gene expression and synaptic plasticity

Excitation-transcription coupling (E-TC) links synaptic and cellular activity to nuclear gene transcription. It is generally accepted that E-TC makes a crucial contribution to learning and memory through its role in underpinning long-lasting synaptic enhancement in late-phase long-term potentiation and has more recently been linked to late-phase long-term depression: both processes require de novo gene transcription, mRNA translation and protein synthesis. E-TC begins with the activation of glutamate-gated N-methyl-D-aspartate-type receptors and voltage-gated L-type Ca2+ channels at the membrane and culminates in the activation of transcription factors in the nucleus. These receptors and ion channels mediate E-TC through mechanisms that include long-range signalling from the synapse to the nucleus and local interactions within dendritic spines, among other possibilities. Growing experimental evidence links these E-TC mechanisms to late-phase long-term potentiation and learning and memory. These advances in our understanding of the molecular mechanisms of E-TC mean that future efforts can focus on understanding its mesoscale functions and how it regulates neuronal network activity and behaviour in physiological and pathological conditions.

Repaglinide Induces ATF6 Processing and Neuroprotection in Transgenic SOD1G93A Mice

The interaction of the activating transcription factor 6 (ATF6), a key effector of the unfolded protein response (UPR) in the endoplasmic reticulum, with the neuronal calcium sensor Downstream Regulatory Element Antagonist Modulator (DREAM) is a potential therapeutic target in neurodegeneration. Modulation of the ATF6-DREAM interaction with repaglinide (RP) induced neuroprotection in a model of Huntington's disease. Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder with no cure, characterized by the progressive loss of motoneurons resulting in muscle denervation, atrophy, paralysis, and death. The aim of this work was to investigate the potential therapeutic significance of DREAM as a target for intervention in ALS. We found that the expression of the DREAM protein was reduced in the spinal cord of SOD1G93A mice compared to wild-type littermates. RP treatment improved motor strength and reduced the expression of the ALS progression marker collagen type XIXα1 (Col19α1 mRNA) in the quadriceps muscle in SOD1G93A mice. Moreover, treated SOD1G93A mice showed reduced motoneuron loss and glial activation and increased ATF6 processing in the spinal cord. These results indicate that the modulation of the DREAM-ATF6 interaction ameliorates ALS symptoms in SOD1G93A mice.

KV Channel-Interacting Proteins in the Neurological and Cardiovascular Systems: An Updated Review

K_V channel-interacting proteins (KChIP1-4) belong to a family of Ca²⁺-binding EF-hand proteins that are able to bind to the N-terminus of the K_V4 channel α-subunits. KChIPs are predominantly expressed in the brain and heart, where they contribute to the maintenance of the excitability of neurons and cardiomyocytes by modulating the fast inactivating-K_V4 currents. As the auxiliary subunit, KChIPs are critically involved in regulating the surface protein expression and gating properties of K_V4 channels. Mechanistically, KChIP1, KChIP2, and KChIP3 promote the translocation of K_V4 channels to the cell membrane, accelerate voltage-dependent activation, and slow the recovery rate of inactivation, which increases K_V4 currents. By contrast, KChIP4 suppresses K_V4 trafficking and eliminates the fast inactivation of K_V4 currents. In the heart, I_Ks, I_Ca,L, and I_Na can also be regulated by KChIPs. I_Ca,L and I_Na are positively regulated by KChIP2, whereas I_Ks is negatively regulated by KChIP2. Interestingly, KChIP3 is also known as downstream regulatory element antagonist modulator (DREAM) because it can bind directly to the downstream regulatory element (DRE) on the promoters of target genes that are implicated in the regulation of pain, memory, endocrine, immune, and inflammatory reactions. In addition, all the KChIPs can act as transcription factors to repress the expression of genes involved in circadian regulation. Altered expression of KChIPs has been implicated in the pathogenesis of several neurological and cardiovascular diseases. For example, KChIP2 is decreased in failing hearts, while loss of KChIP2 leads to increased susceptibility to arrhythmias. KChIP3 is increased in Alzheimer's disease and amyotrophic lateral sclerosis, but decreased in epilepsy and Huntington's disease. In the present review, we summarize the progress of recent studies regarding the structural properties, physiological functions, and pathological roles of KChIPs in both health and disease. We also summarize the small-molecule compounds that regulate the function of KChIPs. This review will provide an overview and update of the regulatory mechanism of the KChIP family and the progress of targeted drug research as a reference for researchers in related fields.

Eupatilin Improves Cilia Defects in Human CEP290 Ciliopathy Models

The photoreceptor outer segment is a highly specialized primary cilium that is essential for phototransduction and vision. Biallelic pathogenic variants in the cilia-associated gene CEP290 cause non-syndromic Leber congenital amaurosis 10 (LCA10) and syndromic diseases, where the retina is also affected. While RNA antisense oligonucleotides and gene editing are potential treatment options for the common deep intronic variant c.2991+1655A>G in CEP290, there is a need for variant-independent approaches that could be applied to a broader spectrum of ciliopathies. Here, we generated several distinct human models of CEP290-related retinal disease and investigated the effects of the flavonoid eupatilin as a potential treatment. Eupatilin improved cilium formation and length in CEP290 LCA10 patient-derived fibroblasts, in gene-edited CEP290 knockout (CEP290 KO) RPE1 cells, and in both CEP290 LCA10 and CEP290 KO iPSCs-derived retinal organoids. Furthermore, eupatilin reduced rhodopsin retention in the outer nuclear layer of CEP290 LCA10 retinal organoids. Eupatilin altered gene transcription in retinal organoids by modulating the expression of rhodopsin and by targeting cilia and synaptic plasticity pathways. This work sheds light on the mechanism of action of eupatilin and supports its potential as a variant-independent approach for CEP290-associated ciliopathies.

Emerging Role of DREAM in Healthy Brain and Neurological Diseases

The downstream regulatory element antagonist modulator (DREAM) is a multifunctional Ca²⁺-sensitive protein exerting a dual mechanism of action to regulate several Ca²⁺-dependent processes. Upon sumoylation, DREAM enters in nucleus where it downregulates the expression of several genes provided with a consensus sequence named dream regulatory element (DRE). On the other hand, DREAM could also directly modulate the activity or the localization of several cytosolic and plasma membrane proteins. In this review, we summarize recent advances in the knowledge of DREAM dysregulation and DREAM-dependent epigenetic remodeling as a central mechanism in the progression of several diseases affecting central nervous system, including stroke, Alzheimer's and Huntington's diseases, amyotrophic lateral sclerosis, and neuropathic pain. Interestingly, DREAM seems to exert a common detrimental role in these diseases by inhibiting the transcription of several neuroprotective genes, including the sodium/calcium exchanger isoform 3 (NCX3), brain-derived neurotrophic factor (BDNF), pro-dynorphin, and c-fos. These findings lead to the concept that DREAM might represent a pharmacological target to ameliorate symptoms and reduce neurodegenerative processes in several pathological conditions affecting central nervous system.

Eupatilin improves cilia defects in human CEP290 ciliopathy models

The photoreceptor outer segment is a highly specialized primary cilium essential for phototransduction and vision. Biallelic pathogenic variants in the cilia-associated gene CEP290 cause non-syndromic Leber congenital amaurosis 10 (LCA10) and syndromic diseases, where the retina is also affected. While RNA antisense oligonucleotides and gene editing are potential treatment options for the common deep intronic variant c.2991+1655A>G in CEP290 , there is a need for variant-independent approaches that could be applied to a broader spectrum of ciliopathies. Here, we generated several distinct human models of CEP290 -related retinal disease and investigated the effects of the flavonoid eupatilin as a potential treatment. Eupatilin improved cilium formation and length in CEP290 LCA10 patient-derived fibroblasts, in gene-edited CEP290 knockout (CEP290 KO) RPE1 cells, and in both CEP290 LCA10 and CEP290 KO iPSCs-derived retinal organoids. Furthermore, eupatilin reduced rhodopsin retention in the outer nuclear layer of CEP290 LCA10 retinal organoids. Eupatilin altered gene transcription in retinal organoids, by modulating the expression of rhodopsin, and by targeting cilia and synaptic plasticity pathways. This work sheds light into the mechanism of action of eupatilin, and supports its potential as a variant-independent approach for CEP290 -associated ciliopathies.

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Calcineurin Signalling in Astrocytes: From Pathology to Physiology and Control of Neuronal Functions

Calcineurin (CaN), a Ca²⁺/calmodulin-activated serine/threonine phosphatase, acts as a Ca²⁺-sensitive switch regulating cellular functions through protein dephosphorylation and activation of gene transcription. In astrocytes, the principal homeostatic cells in the CNS, over-activation of CaN is known to drive pathological transcriptional remodelling, associated with neuroinflammation in diseases such as Alzheimer's disease, epilepsy and brain trauma. Recent reports suggest that, in physiological conditions, the activity of CaN in astrocytes is transcription-independent and is required for maintenance of basal protein synthesis rate and activation of astrocytic Na⁺/K⁺ pump thereby contributing to neuronal functions such as neuronal excitability and memory formation. In this contribution we overview the role of Ca²⁺ and CaN signalling in astroglial pathophysiology focusing on the emerging physiological role of CaN in astrocytes. We propose a model for the context-dependent switch of CaN activity from the post-transcriptional regulation of cell proteostasis in healthy astrocytes to the CaN-dependent transcriptional activation in neuroinflammation-associated diseases.

Cellular plasticity and myeloid inflammation in the adult brain are independent of the transcriptional modulator DREAM

The downstream regulatory element antagonist modulator (DREAM) modulates ion channel function and gene transcription. Functionally, DREAM is implicated in physiological and pathological processes including cell proliferation, inflammation, and nociception. Despite its multiple functions and robust expression in forebrain tissue, neurons and glial cells, the role of DREAM in regard to cellular plasticity and tumor necrosis factor (TNF)-mediated inflammation is largely unexplored. Here, we demonstrate that adult hippocampal neurogenesis as well as the density and plasticity of glial cells in the hippocampus and thalamus are independent of the presence of DREAM. Further, DREAM deletion does not alter the regional myeloid response and inflammatory gene expression induced by chronic peripheral inflammation in mice overexpressing human TNF. Our data suggest that despite their highly dynamic regulation, neural cell plasticity and adult neurogenesis in the hippocampus do not depend on the multifunctional protein DREAM. Furthermore, TNF-mediated myeloid inflammation in the brain persists in the absence of DREAM.

Repaglinide Elicits a Neuroprotective Effect in Rotenone-Induced Parkinson's Disease in Rats: Emphasis on Targeting the DREAM-ER Stress BiP/ATF6/CHOP Trajectory and Activation of Mitophagy

Repaglinide, a meglitinide insulinotropic antidiabetic, was unraveled as a promising therapeutic agent for Huntington's disease by targeting the neuronal calcium sensor downstream regulatory element antagonist modulator (DREAM). However, its mechanistic profile in Parkinson's disease (PD) especially its impact on endoplasmic reticulum (ER) stress, mitophagy, and their interconnections is poorly elucidated. This study is the first to examine the neuroprotective potential of repaglinide in rotenone-induced PD in rats by exploring its effects on DREAM, BiP/ATF6/CHOP ER stress pathway, apoptosis, mitophagy/autophagy, oxidative stress, astrogliosis/microgliosis, and neuroinflammation. Male Wistar rats were randomly assigned to four groups: groups 1 and 2 received the vehicle or repaglinide (0.5 mg/kg/day p.o). Groups 3 and 4 received rotenone (1.5 mg/kg/48 h s.c) for 21 days; meanwhile, group 4 additionally received repaglinide (0.5 mg/kg/day p.o) for 15 days starting from day 11. Interestingly, repaglinide lessened striatal ER stress and apoptosis as evidenced by reduced BiP/ATF6/CHOP and caspase-3 levels; however, it augmented striatal DREAM mRNA expression. Repaglinide triggered the expression of the mitophagy marker PINK1 and the autophagy protein beclin1 and alleviated striatal oxidative stress through escalating catalase activity. In addition, repaglinide halted astrocyte/microglial activation and neuroinflammation in the striatum as expressed by reducing glial fibrillary acidic protein (GFAP) and ionized calcium-binding adaptor protein 1 (Iba1) immunostaining and decreasing interleukin (IL)-6 and IL-1β levels. Repaglinide restored striatum morphological alterations, intact neuron count, and neurobehavioral motor performance in rats examined by an open field, grip strength, and footprint gait analysis. Conclusively, repaglinide modulates the DREAM-ER stress BiP/ATF6/CHOP cascade, increases mitophagy/autophagy, inhibits apoptosis, and lessens oxidative stress, astrocyte/microglial activation, and neuroinflammation in PD.

IQM-PC332, a Novel DREAM Ligand with Antinociceptive Effect on Peripheral Nerve Injury-Induced Pain

Neuropathic pain is a form of chronic pain arising from damage of the neural cells that sense, transmit or process sensory information. Given its growing prevalence and common refractoriness to conventional analgesics, the development of new drugs with pain relief effects constitutes a prominent clinical need. In this respect, drugs that reduce activity of sensory neurons by modulating ion channels hold the promise to become effective analgesics. Here, we evaluated the mechanical antinociceptive effect of IQM-PC332, a novel ligand of the multifunctional protein downstream regulatory element antagonist modulator (DREAM) in rats subjected to chronic constriction injury of the sciatic nerve as a model of neuropathic pain. IQM-PC332 administered by intraplantar (0.01–10 µg) or intraperitoneal (0.02–1 µg/kg) injection reduced mechanical sensitivity by ≈100% of the maximum possible effect, with ED₅₀ of 0.27 ± 0.05 µg and 0.09 ± 0.01 µg/kg, respectively. Perforated-patch whole-cell recordings in isolated dorsal root ganglion (DRG) neurons showed that IQM-PC332 (1 and 10 µM) reduced ionic currents through voltage-gated K⁺ channels responsible for A-type potassium currents, low, T-type, and high voltage-activated Ca²⁺ channels, and transient receptor potential vanilloid-1 (TRPV1) channels. Furthermore, IQM-PC332 (1 µM) reduced electrically evoked action potentials in DRG neurons from neuropathic animals. It is suggested that by modulating multiple DREAM–ion channel signaling complexes, IQM-PC332 may serve a lead compound of novel multimodal analgesics.

Mass Spectrometry-Based Structural Proteomics for Metal Ion/Protein Binding Studies

Metal ions are critical for the biological and physiological functions of many proteins. Mass spectrometry (MS)-based structural proteomics is an ever-growing field that has been adopted to study protein and metal ion interactions. Native MS offers information on metal binding and its stoichiometry. Footprinting approaches coupled with MS, including hydrogen/deuterium exchange (HDX), "fast photochemical oxidation of proteins" (FPOP) and targeted amino-acid labeling, identify binding sites and regions undergoing conformational changes. MS-based titration methods, including "protein-ligand interactions by mass spectrometry, titration and HD exchange" (PLIMSTEX) and "ligand titration, fast photochemical oxidation of proteins and mass spectrometry" (LITPOMS), afford binding stoichiometry, binding affinity, and binding order. These MS-based structural proteomics approaches, their applications to answer questions regarding metal ion protein interactions, their limitations, and recent and potential improvements are discussed here. This review serves as a demonstration of the capabilities of these tools and as an introduction to wider applications to solve other questions.

Pathophysiological Ionotropic Glutamate Signalling in Neuroinflammatory Disease as a Therapeutic Target

Glutamate signalling is an essential aspect of neuronal communication involving many different glutamate receptors, and underlies the processes of memory, learning and synaptic plasticity. Despite neuroinflammatory diseases covering a range of maladies with very different biological causes and pathophysiologies, a central role for dysfunctional glutamate signalling is becoming apparent. This is not just restricted to the well-described role of glutamate in mediating neurodegeneration, but also includes a myriad of other influences that glutamate can exert on the vasculature, as well as immune cell and glial regulation, reflecting the ability of neurons to communicate with these compartments in order to couple their activity with neuronal requirements. Here, we discuss the role of pathophysiological glutamate signalling in neuroinflammatory disease, using both multiple sclerosis and Alzheimer's disease as examples, and how current steps are being made to harness our growing understanding of these processes in the development of neuroprotective strategies. This review focuses in particular on N-methyl-D-aspartate (NMDA) and 2-amino-3-(3-hydroxy-5-methylisooxazol-4-yl) propionate (AMPA) type ionotropic glutamate receptors, although metabotropic, G-protein-coupled glutamate receptors may also contribute to neuroinflammatory processes. Given the indispensable roles of glutamate-gated ion channels in synaptic communication, means of pharmacologically distinguishing between physiological and pathophysiological actions of glutamate will be discussed that allow deleterious signalling to be inhibited whilst minimising the disturbance of essential neuronal function.

Parkinson Disease: Translating Insights from Molecular Mechanisms to Neuroprotection

Parkinson disease (PD) used to be considered a nongenetic condition. However, the identification of several autosomal dominant and recessive mutations linked to monogenic PD has changed this view. Clinically manifest PD is then thought to occur through a complex interplay between genetic mutations, many of which have incomplete penetrance, and environmental factors, both neuroprotective and increasing susceptibility, which variably interact to reach a threshold over which PD becomes clinically manifested. Functional studies of PD gene products have identified many cellular and molecular pathways, providing crucial insights into the nature and causes of PD. PD originates from multiple causes and a range of pathogenic processes at play, ultimately culminating in nigral dopaminergic loss and motor dysfunction. An in-depth understanding of these complex and possibly convergent pathways will pave the way for therapeutic approaches to alleviate the disease symptoms and neuroprotective strategies to prevent disease manifestations. This review is aimed at providing a comprehensive understanding of advances made in PD research based on leveraging genetic insights into the pathogenesis of PD. It further discusses novel perspectives to facilitate identification of critical molecular pathways that are central to neurodegeneration that hold the potential to develop neuroprotective and/or neurorestorative therapeutic strategies for PD. SIGNIFICANCE STATEMENT: A comprehensive review of PD pathophysiology is provided on the complex interplay of genetic and environmental factors and biologic processes that contribute to PD pathogenesis. This knowledge identifies new targets that could be leveraged into disease-modifying therapies to prevent or slow neurodegeneration in PD.

Calmodulin7: recent insights into emerging roles in plant development and stress

Analyses of the function of Arabidopsis Calmodulin7 (CAM7) in concert with multiple regulatory proteins involved in various signal transduction processes. Calmodulin (CaM) plays various regulatory roles in multiple signaling pathways in eukaryotes. Arabidopsis CALMODULIN 7 (CAM7) is a unique member of the CAM family that works as a transcription factor in light signaling pathways. CAM7 works in concert with CONSTITUTIVE PHOTOMORPHOGENIC 1 and ELONGATED HYPOCOTYL 5, and plays an important role in seedling development. Further, it is involved in the regulation of the activity of various Ca²⁺-gated channels such as cyclic nucleotide gated channel 6 (CNGC6), CNGC14 and auto-inhibited Ca²⁺ ATPase 8. Recent studies further indicate that CAM7 is also an integral part of multiple signaling pathways including hormone, immunity and stress. Here, we review the recent advances in understanding the multifaceted role of CAM7. We highlight the open-ended questions, and also discuss the diverse aspects of CAM7 characterization that need to be addressed for comprehensive understanding of its cellular functions.

CLN3, at the crossroads of endocytic trafficking

The CLN3 gene was identified over two decades ago, but the primary function of the CLN3 protein remains unknown. Recessive inheritance of loss of function mutations in CLN3 are responsible for juvenile neuronal ceroid lipofuscinosis (Batten disease, or CLN3 disease), a fatal childhood onset neurodegenerative disease causing vision loss, seizures, progressive dementia, motor function loss and premature death. CLN3 is a multipass transmembrane protein that primarily localizes to endosomes and lysosomes. Defects in endocytosis, autophagy, and lysosomal function are common findings in CLN3-deficiency model systems. However, the molecular mechanisms underlying these defects have not yet been fully elucidated. In this mini-review, we will summarize the current understanding of the CLN3 protein interaction network and discuss how this knowledge is starting to delineate the molecular pathogenesis of CLN3 disease. Accumulating evidence strongly points towards CLN3 playing a role in regulation of the cytoskeleton and cytoskeletal associated proteins to tether cellular membranes, regulation of membrane complexes such as channels/transporters, and modulating the function of small GTPases to effectively mediate vesicular movement and membrane dynamics.

Epigenetic and Transcriptional Control of the Opioid Prodynorphine Gene: In-Depth Analysis in the Human Brain

Neuropeptides serve as neurohormones and local paracrine regulators that control neural networks regulating behavior, endocrine system and sensorimotor functions. Their expression is characterized by exceptionally restricted profiles. Circuit-specific and adaptive expression of neuropeptide genes may be defined by transcriptional and epigenetic mechanisms controlled by cell type and subtype sequence-specific transcription factors, insulators and silencers. The opioid peptide dynorphins play a critical role in neurological and psychiatric disorders, pain processing and stress, while their mutations cause profound neurodegeneration in the human brain. In this review, we focus on the prodynorphin gene as a model for the in-depth epigenetic and transcriptional analysis of expression of the neuropeptide genes. Prodynorphin studies may provide a framework for analysis of mechanisms relevant for regulation of neuropeptide genes in normal and pathological human brain.

Behavioural effects of cage systems on the G93A Superoxide Dismutase 1 transgenic mouse model for amyotrophic lateral sclerosis

Environmental factors inherent to animal facilities can impact on the neuro-behavioural phenotype of laboratory mice and genetic mouse models for human diseases. Many facilities have upgraded from traditional 'open filter top' cages (FT) to individually ventilated cage (IVC) systems, which have been shown to modify various behavioural responses of laboratory mice. Importantly, the impact of IVC housing on the G93A superoxide dismutase 1 mouse model of amyotrophic lateral sclerosis (ALS) is currently unknown. Male and female wild type-like (WT) and heterozygous SOD1^G93A mice were group-housed in FT or IVC systems from PND 30 ± 5 onwards. Body weight and motor function were assessed weekly from 15 weeks onward. Mice were also tested for cognitive abilities (i.e., fear conditioning and social recognition memory) and sensorimotor gating (i.e., prepulse inhibition: PPI). SOD1^G93A mice lost body weight, and their motor function degenerated over time compared with control littermates. Motor impairments developed faster when SOD1^G93A females were housed in IVCs. Context and cue freezing were increased in SOD1^G93A females compared with controls, whereas all SOD1^G93A mice exhibited lower acoustic startle and PPI than WT mice. IVC housing led to an increase in cue freezing in males and reduced the severity of PPI deficits in SOD1^G93A females. Overall, IVC housing impacted moderately on the SOD1^G93A phenotype but central behavioural deficits were still evident across housing conditions. Nonetheless, our findings indicate the importance of assessing the effect of cage system in genetic mouse models as these systems can modulate the magnitude and onset of genotypic differences.

The role of nuclear Ca2+ in maintaining neuronal homeostasis and brain health

Nuclear Ca2+ has emerged as one of the most potent mediators of the dialogue between neuronal synapses and the nucleus that regulates heterochromatin states, transcription factor activity, nuclear morphology and neuronal gene expression induced by synaptic activity. Recent studies underline the importance of nuclear Ca2+ signaling in long-lasting, activity-induced adaptation and maintenance of proper brain function. Diverse forms of neuroadaptation require transient nuclear Ca2+ signaling and cyclic AMP-responsive element-binding protein (CREB1, referred to here as CREB) as its prime target, which works as a tunable switch to drive and modulate specific gene expression profiles associated with memory, pain, addiction and neuroprotection. Furthermore, a reduction of nuclear Ca2+ levels has been shown to be neurotoxic and a causal factor driving the progression of neurodegenerative disorders, as well as affecting neuronal autophagy. Because of its central role in the brain, deficits in nuclear Ca2+ signaling may underlie a continuous loss of neuroprotection in the aging brain, contributing to the pathophysiology of Alzheimer's disease. In this Review, we discuss the principles of the 'nuclear calcium hypothesis' in the context of human brain function and its role in controlling diverse forms of neuroadaptation and neuroprotection. Furthermore, we present the most relevant and promising perspectives for future studies.

Plant Defense Responses to Biotic Stress and Its Interplay With Fluctuating Dark/Light Conditions

Plants are subjected to a plethora of environmental cues that cause extreme losses to crop productivity. Due to fluctuating environmental conditions, plants encounter difficulties in attaining full genetic potential for growth and reproduction. One such environmental condition is the recurrent attack on plants by herbivores and microbial pathogens. To surmount such attacks, plants have developed a complex array of defense mechanisms. The defense mechanism can be either preformed, where toxic secondary metabolites are stored; or can be inducible, where defense is activated upon detection of an attack. Plants sense biotic stress conditions, activate the regulatory or transcriptional machinery, and eventually generate an appropriate response. Plant defense against pathogen attack is well understood, but the interplay and impact of different signals to generate defense responses against biotic stress still remain elusive. The impact of light and dark signals on biotic stress response is one such area to comprehend. Light and dark alterations not only regulate defense mechanisms impacting plant development and biochemistry but also bestow resistance against invading pathogens. The interaction between plant defense and dark/light environment activates a signaling cascade. This signaling cascade acts as a connecting link between perception of biotic stress, dark/light environment, and generation of an appropriate physiological or biochemical response. The present review highlights molecular responses arising from dark/light fluctuations vis-à-vis elicitation of defense mechanisms in plants.

Cav1 channels is also a story of non excitable cells: Application to calcium signalling in two different non related models

Calcium is a second messenger essential, in all cells, for most cell functions. The spatio-temporal control of changes in intracellular calcium concentration is partly due to the activation of calcium channels. Voltage-operated calcium channels are present in excitable and non-excitable cells. If the mechanism of voltage-operated calcium channels is well known in excitable cells the Ca²⁺ toolkit used in non-excitable cells to activate the calcium channels is less described. Herein we discuss about very similar pathways involving voltage activated Ca_v1 channels in two unrelated non-excitable cells; ectoderm cells undergoing neural development and effector Th2 lymphocytes responsible for parasite elimination and also allergic diseases. We will examine the way by which these channels operate and are regulated, as well as the consequences in terms of gene transcription. Finally, we will consider the questions that remain unsolved and how they might be a challenge for the future.

Pharmacological Approaches for the Modulation of the Potassium Channel KV4.x and KChIPs

Ion channels are macromolecular complexes present in the plasma membrane and intracellular organelles of cells. Dysfunction of ion channels results in a group of disorders named channelopathies, which represent an extraordinary challenge for study and treatment. In this review, we will focus on voltage-gated potassium channels (K_V), specifically on the K_V4-family. The activation of these channels generates outward currents operating at subthreshold membrane potentials as recorded from myocardial cells (I_TO, transient outward current) and from the somata of hippocampal neurons (I_SA). In the heart, K_V4 dysfunctions are related to Brugada syndrome, atrial fibrillation, hypertrophy, and heart failure. In hippocampus, K_V4.x channelopathies are linked to schizophrenia, epilepsy, and Alzheimer's disease. K_V4.x channels need to assemble with other accessory subunits (β) to fully reproduce the I_TO and I_SA currents. β Subunits affect channel gating and/or the traffic to the plasma membrane, and their dysfunctions may influence channel pharmacology. Among K_V4 regulatory subunits, this review aims to analyze the K_V4/KChIPs interaction and the effect of small molecule KChIP ligands in the A-type currents generated by the modulation of the K_V4/KChIP channel complex. Knowledge gained from structural and functional studies using activators or inhibitors of the potassium current mediated by K_V4/KChIPs will better help understand the underlying mechanism involving K_V4-mediated-channelopathies, establishing the foundations for drug discovery, and hence their treatments.

Molecular mechanisms of trigeminal neuralgia: A systematic review

OBJECTIVE

To conduct a systematic review of the available literature for primary research articles identifying potential gene mutations, polymorphisms and other molecular regulatory mechanisms related to trigeminal neuralgia in order to identify the genetic and molecular models of primary trigeminal neuralgia currently being investigated.

METHODS

PubMed and Web of Science were systematically searched to identify primary research articles discussing genetic predictors of trigeminal neuralgia and neuropathic pain that were published prior to July 2020. This review was conducted according to PRISMA guidelines.

RESULTS

Out of the 333 articles originally identified, a total of 14 papers were selected for study inclusion. These articles included 5 human studies, 6 mouse studies and 3 rat studies. Four articles investigated sodium channels, 1 investigated a sodium channel and nerve growth factor receptor, 2 investigated potassium channels, 1 investigated calcium channels, 1 investigated the downstream regulatory element antagonist modulator protein, 1 investigated the dynorphin-kappa opioid receptor system, 1 investigated TRPA1, 1 investigated the Nrg1/ErbB3/ErbB2 signaling complex, 1 investigated a serotonin transporter and 1 investigated potassium channels, sodium channels, calcium channels, chloride channels, TRP channels and gap junctions.

CONCLUSION

Researchers have identified multiple genetic and molecular targets involved with potential pathophysiologies that have a relationship to the creation of trigeminal neuralgia. At this time, there does not seem to be clear causal frontrunner, demonstrating the possibility that genetic predisposition to trigeminal neuralgia may involve multiple genes and/or downstream products, such as ion channels.

Ca2+/Calmodulin Complex Triggers CAMTA Transcriptional Machinery Under Stress in Plants: Signaling Cascade and Molecular Regulation

Calcium (Ca2+) ion is a critical ubiquitous intracellular second messenger, acting as a lead currency for several distinct signal transduction pathways. Transient perturbations in free cytosolic Ca2+ ([Ca2+]cyt) concentrations are indispensable for the translation of signals into adaptive biological responses. The transient increase in [Ca2+]cyt levels is sensed by an array of Ca2+ sensor relay proteins such as calmodulin (CaM), eventually leading to conformational changes and activation of CaM. CaM, in a Ca2+-dependent manner, regulates several transcription factors (TFs) that are implicated in various molecular, physiological, and biochemical functions in cells. CAMTA (calmodulin-binding transcription activator) is one such member of the Ca2+-loaded CaM-dependent family of TFs. The present review focuses on Ca2+ as a second messenger, its interaction with CaM, and Ca2+/CaM-mediated CAMTA transcriptional regulation in plants. The review recapitulates the molecular and physiological functions of CAMTA in model plants and various crops, confirming its probable involvement in stress signaling pathways and overall plant development. Studying Ca2+/CaM-mediated CAMTA TF will help in answering key questions concerning signaling cascades and molecular regulation under stress conditions and plant growth, thus improving our knowledge for crop improvement.

Toll-like receptors in sepsis-associated cytokine storm and their endogenous negative regulators as future immunomodulatory targets

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Sepsis infects more than 48.9 million people world-wide, with 19.7 million deaths.

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Cytokine storm plays a significant role in sepsis, along with severe COVID-19.

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TLR signaling pathways plays a crucial role in generating the cytokine storm.

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Endogenous negative regulators of TLR signaling are crucial to regulate cytokine storm.

Cytokine storm generates during various systemic acute infections, including sepsis and current pandemic called COVID-19 (severe) causing devastating inflammatory conditions, which include multi-organ failure or multi-organ dysfunction syndrome (MODS) and death of the patient. Toll-like receptors (TLRs) are one of the major pattern recognition receptors (PRRs) expressed by immune cells as well as non-immune cells, including neurons, which play a crucial role in generating cytokine storm. They recognize microbial-associated molecular patterns (MAMPs, expressed by pathogens) and damage or death-associate molecular patterns (DAMPs; released and/expressed by damaged/killed host cells). Upon recognition of MAMPs and DAMPs, TLRs activate downstream signaling pathways releasing several pro-inflammatory mediators [cytokines, chemokines, interferons, and reactive oxygen and nitrogen species (ROS or RNS)], which cause acute inflammation meant to control the pathogen and repair the damage. Induction of an exaggerated response due to genetic makeup of the host and/or persistence of the pathogen due to its evasion mechanisms may lead to severe systemic inflammatory condition called sepsis in response to the generation of cytokine storm and organ dysfunction. The activation of TLR-induced inflammatory response is hardwired to the induction of several negative feedback mechanisms that come into play to conclude the response and maintain immune homeostasis. This state-of-the-art review describes the importance of TLR signaling in the onset of the sepsis-associated cytokine storm and discusses various host-derived endogenous negative regulators of TLR signaling pathways. The subject is very important as there is a vast array of genes and processes implicated in these negative feedback mechanisms. These molecules and mechanisms can be targeted for developing novel therapeutic drugs for cytokine storm-associated diseases, including sepsis, severe COVID-19, and other inflammatory diseases, where TLR-signaling plays a significant role.

The intracellular renin-angiotensin system: Friend or foe. Some light from the dopaminergic neurons

The renin-angiotensin system (RAS) is one of the oldest hormone systems in vertebrate phylogeny. RAS was initially related to regulation of blood pressure and sodium and water homeostasis. However, local or paracrine RAS were later identified in many tissues, including brain, and play a major role in their physiology and pathophysiology. In addition, a major component, ACE2, is the entry receptor for SARS-CoV-2. Overactivation of tissue RAS leads several oxidative stress and inflammatory processes involved in aging-related degenerative changes. In addition, a third level of RAS, the intracellular or intracrine RAS (iRAS), with still unclear functions, has been observed. The possible interaction between the intracellular and extracellular RAS, and particularly the possible deleterious or beneficial effects of the iRAS activation are controversial. The dopaminergic system is particularly interesting to investigate the RAS as important functional interactions between dopamine and RAS have been observed in the brain and several peripheral tissues. Our recent observations in mitochondria and nucleus of dopaminergic neurons may clarify the role of the iRAS. This may be important for the developing of new therapeutic strategies, since the effects on both extracellular and intracellular RAS must be taken into account, and perhaps better understanding of COVID-19 cell mechanisms.

EF-hands in Neuronal Calcium Sensor Downstream Regulatory Element Antagonist Modulator Demonstrate Submillimolar Affinity for Li+: A New Prospect for Li+ Therapy

Lithium has been used for the treatment of mood disorders for decades though the molecular mechanism of its therapeutic action and intracellular targets remain furtive. We report that neurotropic agent Li⁺ binds to the neuronal calcium sensor, Downstream Regulatory Element Antagonist Modulator (DREAM), with an equilibrium dissociation constant of 34 ± 4 μM and impacts DREAM structural and dynamic properties in a similar manner as observed for its physiological ligand, Ca²⁺. Results of fluorescence spectroscopy and molecular dynamics are consistent with Li⁺ binding at EF-hands. In the Li⁺ bound form, DREAM association to peptides mimicking DREAM binding sites in a voltage-gated potassium channel is enhanced compared to the apoprotein, whereas DREAM affinity for the presenilin binding site, helix-9, is impeded. These results suggest that DREAM and possibly other members of the neuronal calcium sensor family belong to Li⁺ intracellular targets and interactions between Li⁺ and NCS provide a molecular basis for Li⁺ neuroprotective action.

The Circadian Hormone Melatonin Inhibits Morphine-Induced Tolerance and Inflammation via the Activation of Antioxidative Enzymes

Opioids are commonly prescribed for clinical pain management; however, dose-escalation, tolerance, dependence, and addiction limit their usability for long-term chronic pain. The associated poor sleep pattern alters the circadian neurobiology, and further compromises the pain management. Here, we aim to determine the correlation between constant light exposure and morphine tolerance and explore the potential of melatonin as an adjuvant of morphine for neuropathic pain treatment. Methods: Wistar rats were preconditioned under constant light (LL) or a regular light/dark (LD) cycle before neuropathic pain induction by chronic constriction injury. An intrathecal (i.t.) osmotic pump was used for continued drug delivery to induce morphine tolerance. Pain assessments, including the plantar test, static weight-bearing symmetry, and tail-flick latency, were used to determine the impact of the light disruption or exogenous melatonin on the morphine tolerance progression. Results: constant light exposure significantly aggravates morphine tolerance in neuropathic rats. Continued infusion of low-dose melatonin (3 μg/h) attenuated morphine tolerance in both neuropathic and naïve rats. This protective effect was independent of melatonin receptors, as shown by the neutral effect of melatonin receptors inhibitors. The transcriptional profiling demonstrated a significant enhancement of proinflammatory and pain-related receptor genes in morphine-tolerant rats. In contrast, this transcriptional pattern was abolished by melatonin coinfusion along with the upregulation of the Kcnip3 gene. Moreover, melatonin increased the antioxidative enzymes SOD2, HO-1, and GPx1 in the spinal cord of morphine-tolerant rats. Conclusion: Dysregulated circadian light exposure significantly compromises the efficacy of morphine’s antinociceptive effect, while the cotreatment with melatonin attenuates morphine tolerance/hyperalgesia development. Our results suggest the potential of melatonin as an adjuvant of morphine in clinical pain management, particularly in patients who need long-term opioid treatment.

Modulation of Kv4.2/KChIP3 interaction by the ceroid lipofuscinosis neuronal 3 protein CLN3

Voltage-gated potassium (Kv) channels of the Kv4 subfamily associate with Kv channel-interacting proteins (KChIPs), which leads to enhanced surface expression and shapes the inactivation gating of these channels. KChIP3 has been reported to also interact with the late endosomal/lysosomal membrane glycoprotein CLN3 (ceroid lipofuscinosis neuronal 3), which is modified because of gene mutation in juvenile neuronal ceroid lipofuscinosis (JNCL). The present study was undertaken to find out whether and how CLN3, by its interaction with KChIP3, may indirectly modulate Kv4.2 channel expression and function. To this end, we expressed KChIP3 and CLN3, either individually or simultaneously, together with Kv4.2 in HEK 293 cells. We performed co-immunoprecipitation experiments and found a lower amount of KChIP3 bound to Kv4.2 in the presence of CLN3. In whole-cell patch-clamp experiments, we examined the effects of CLN3 co-expression on the KChIP3-mediated modulation of Kv4.2 channels. Simultaneous co-expression of CLN3 and KChIP3 with Kv4.2 resulted in a suppression of the typical KChIP3-mediated modulation; i.e. we observed less increase in current density, less slowing of macroscopic current decay, less acceleration of recovery from inactivation, and a less positively shifted voltage dependence of steady-state inactivation. The suppression of the KChIP3-mediated modulation of Kv4.2 channels was weaker for the JNCL-related missense mutant CLN3R334C and for a JNCL-related C-terminal deletion mutant (CLN3ΔC). Our data support the notion that CLN3 is involved in Kv4.2/KChIP3 somatodendritic A-type channel formation, trafficking, and function, a feature that may be lost in JNCL.

FTO is a transcriptional repressor to auto-regulate its own gene and potentially associated with homeostasis of body weight

Fat mass and obesity-associated (FTO) protein is a ferrous ion (Fe2+)/2-oxoglutarate (2-OG)-dependent demethylase preferentially catalyzing m6A sites in RNA. The FTO gene is highly expressed in the hypothalamus with fluctuation in response to various nutritional conditions, which is believed to be involved in the control of whole body metabolism. However, the underlying mechanism in response to different nutritional cues remains poorly understood. Here we show that ketogenic diet-derived ketone body β-hydroxybutyrate (BHB) transiently increases FTO expression in both mouse hypothalamus and cultured cells. Interestingly, the FTO protein represses Fto promoter activity, which can be offset by BHB. We then demonstrate that FTO binds to its own gene promoter, and Fe2+, but not 2-OG, impedes this binding and increases FTO expression. The BHB-induced occupancy of the promoter by FTO influences the assembly of the basal transcriptional machinery. Importantly, a loss-of-function FTO mutant (I367F), which induces a lean phenotype in FTOI367F mice, exhibits augmented binding and elevated potency to repress the promoter. Furthermore, FTO fails to bind to its own promoter that promotes FTO expression in the hypothalamus of high-fat diet-induced obese and 48-h fasting mice, suggesting a disruption of the stable expression of this gene. Taken together, this study uncovers a new function of FTO as a Fe2+-sensitive transcriptional repressor dictating its own gene switch to form an auto-regulatory loop that may link with the hypothalamic control of body weight.

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.

Expressions of spinal microglia activation, BDNF, and DREAM proteins correlated with formalin-induced nociceptive responses in painful and painless diabetic neuropathy rats

The complications of diabetic polyneuropathy (DN) determines its level of severity. It may occur with distinctive clinical symptoms (painful DN) or appears undetected (painless DN). This study aimed to investigate microglia activation and signalling molecules brain-derived neurotrophic factor (BDNF) and downstream regulatory element antagonist modulator (DREAM) proteins in spinal cord of streptozotocin-induced diabetic neuropathy rats. Thirty male Sprague-Dawley rats (200-230 g) were randomly assigned into three groups: (1) control, (2) painful DN and (3) painless DN. The rats were induced with diabetes by single intraperitoneal injection of streptozotocin (60 mg/kg) whilst control rats received citrate buffer as a vehicle. Four weeks post-diabetic induction, the rats were induced with chronic inflammatory pain by intraplantar injection of 5% formalin and pain behaviour responses were recorded and assessed. Three days later, the rats were sacrificed and lumbar enlargement region of spinal cord was collected. The tissue was immunoreacted against OX-42 (microglia), BDNF and DREAM proteins, which was also quantified by western blotting. The results demonstrated that painful DN rats exhibited increased pain behaviour score peripherally and centrally with marked increase of spinal activated microglia, BDNF and DREAM proteins expressions compared to control group. In contrast, painless DN group demonstrated a significant reduction of pain behaviour score peripherally and centrally with significant reduction of spinal activated microglia, BDNF and DREAM proteins expressions. In conclusions, the spinal microglia activation, BDNF and DREAM proteins correlate with the pain behaviour responses between the variants of DN.

NCS-1 Deficiency Affects mRNA Levels of Genes Involved in Regulation of ATP Synthesis and Mitochondrial Stress in Highly Vulnerable Substantia nigra Dopaminergic Neurons

Neuronal Ca²⁺ sensor proteins (NCS) transduce changes in Ca²⁺ homeostasis into altered signaling and neuronal function. NCS-1 activity has emerged as important for neuronal viability and pathophysiology. The progressive degeneration of dopaminergic (DA) neurons, particularly within the Substantia nigra (SN), is the hallmark of Parkinson's disease (PD), causing its motor symptoms. The activity-related Ca²⁺ homeostasis of SN DA neurons, mitochondrial dysfunction, and metabolic stress promote neurodegeneration and PD. In contrast, NCS-1 in general has neuroprotective effects. The underlying mechanisms are unclear. We analyzed transcriptional changes in SN DA neurons upon NCS-1 loss by combining UV-laser microdissection and RT-qPCR-approaches to compare expression levels of a panel of PD and/or Ca²⁺-stress related genes from wildtype and NCS-1 KO mice. In NCS-1 KO, we detected significantly lower mRNA levels of mitochondrially coded ND1, a subunit of the respiratory chain, and of the neuron-specific enolase ENO2, a glycolytic enzyme. We also detected lower levels of the mitochondrial uncoupling proteins UCP4 and UCP5, the PARK7 gene product DJ-1, and the voltage-gated Ca²⁺ channel Cav2.3 in SN DA neurons from NCS-1 KO. Transcripts of other analyzed uncoupling proteins (UCPs), mitochondrial Ca²⁺ transporters, PARK genes, and ion channels were not altered. As Cav channels are linked to regulation of gene expression, metabolic stress and degeneration of SN DA neurons in PD, we analyzed Cav2.3 KO mice, to address if the transcriptional changes in NCS-1 KO were also present in Cav.2.3 KO, and thus probably correlated with lower Cav2.3 transcripts. However, in SN DA neurons from Cav2.3 KO mice, ND1 mRNA as well as genomic DNA levels were elevated, while ENO2, UCP4, UCP5, and DJ-1 transcript levels were not altered. In conclusion, our data indicate a possible novel function of NCS-1 in regulating gene transcription or stabilization of mRNAs in SN DA neurons. Although we do not provide functional data, our findings at the transcript level could point to impaired ATP production (lower ND1 and ENO2) and elevated metabolic stress (lower UCP4, UCP5, and DJ-1 levels) in SN DA neurons from NCS-1 KO mice. We speculate that NCS-1 is involved in stimulating ATP synthesis, while at the same time controlling mitochondrial metabolic stress, and in this way could protect SN DA neurons from degeneration.

Neuronal Expression of Opioid Gene is Controlled by Dual Epigenetic and Transcriptional Mechanism in Human Brain

Molecular mechanisms that define patterns of neuropeptide expression are essential for the formation and rewiring of neural circuits. The prodynorphin gene (PDYN) gives rise to dynorphin opioid peptides mediating depression and substance dependence. We here demonstrated that PDYN is expressed in neurons in human dorsolateral prefrontal cortex (dlPFC), and identified neuronal differentially methylated region in PDYN locus framed by CCCTC-binding factor binding sites. A short, nucleosome size human-specific promoter CpG island (CGI), a core of this region may serve as a regulatory module, which is hypomethylated in neurons, enriched in 5-hydroxymethylcytosine, and targeted by USF2, a methylation-sensitive E-box transcription factor (TF). USF2 activates PDYN transcription in model systems, and binds to nonmethylated CGI in dlPFC. USF2 and PDYN expression is correlated, and USF2 and PDYN proteins are co-localized in dlPFC. Segregation of activatory TF and repressive CGI methylation may ensure contrasting PDYN expression in neurons and glia in human brain.

iTRAQ-based proteomic analysis discovers potential biomarkers of diffuse axonal injury in rats

Diffuse axonal injury (DAI) is one of the most common and severe pathological consequences of traumatic brain injury (TBI). The molecular mechanism of DAI is highly complicated and still elusive, yet a clear understanding is crucial for the diagnosis, treatment, and prognosis of DAI. In our study, we used rats to establish a DAI model and applied isobaric tags for relative and absolute quantitation (iTRAQ) coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis to identify differentially expressed proteins (DEPs) in the corpus callosum. As a result, a total of 514 proteins showed differential expression between the injury groups and the control. Among these DEPs, 14 common DEPs were present at all seven time points postinjury (1, 3, 6, 12, 24, 48, and 72 h). Next, bioinformatic analysis was performed to elucidate the pathogenesis of DAI, which was found to possibly involve calcium ion-regulatory proteins (e.g., calsenilin and ryanodine receptor 2), cytoskeleton organization (e.g., peripherin, NFL, NFM, and NFH), apoptotic processes (e.g., calsenilin and protein kinase C delta type), and inflammatory response proteins (e.g., complement C3 and C-reactive protein). Moreover, peripherin and calsenilin were successfully confirmed by western blotting to be significantly upregulated during DAI, and immunohistochemical (IHC) analysis revealed that their expression increased and could be observed in axons after injury, thus indicating their potential as DAI biomarkers. Our experiments not only provide insight into the molecular mechanisms of axonal injury in rats during DAI but also give clinicians and pathologists important reference data for the diagnosis of DAI. Our findings may expand the list of DAI biomarkers and improve the postmortem diagnostic rate of DAI.

Wilm's tumor 1 promotes memory flexibility

Under physiological conditions, strength and persistence of memory must be regulated in order to produce behavioral flexibility. In fact, impairments in memory flexibility are associated with pathologies such as post-traumatic stress disorder or autism; however, the underlying mechanisms that enable memory flexibility are still poorly understood. Here, we identify transcriptional repressor Wilm's Tumor 1 (WT1) as a critical synaptic plasticity regulator that decreases memory strength, promoting memory flexibility. WT1 is activated in the hippocampus following induction of long-term potentiation (LTP) or learning. WT1 knockdown enhances CA1 neuronal excitability, LTP and long-term memory whereas its overexpression weakens memory retention. Moreover, forebrain WT1-deficient mice show deficits in both reversal, sequential learning tasks and contextual fear extinction, exhibiting impaired memory flexibility. We conclude that WT1 limits memory strength or promotes memory weakening, thus enabling memory flexibility, a process that is critical for learning from new experiences.

Kv channel-interacting proteins as neuronal and non-neuronal calcium sensors

Kv channel-interacting proteins (KChIPs) belong to the neuronal calcium sensor (NCS) family of Ca²⁺-binding EF-hand proteins. KChIPs constitute a group of specific auxiliary β-subunits for Kv4 channels, the molecular substrate of transient potassium currents in both neuronal and non-neuronal tissues. Moreover, KChIPs can interact with presenilins to control ER calcium signaling and apoptosis, and with DNA to control gene transcription. Ca²⁺ binding via their EF-hands, with the consequence of conformational changes, is well documented for KChIPs. Moreover, the Ca²⁺ dependence of the presenilin/KChIP complex may be related to Alzheimer’s disease and the Ca²⁺ dependence of the DNA/KChIP complex to pain sensing. However, only in few cases could the Ca²⁺ binding to KChIPs be directly linked to the control of excitability in nerve and muscle cells known to express Kv4/KChIP channel complexes. This review summarizes current knowledge about the Ca²⁺ binding properties of KChIPs and the Ca²⁺ dependencies of macromolecular complexes containing KChIPs, including those with presenilins, DNA and especially Kv4 channels. The respective physiological or pathophysiolgical roles of Ca²⁺ binding to KChIPs are discussed.

Emerging roles for multifunctional ion channel auxiliary subunits in cancer

Several superfamilies of plasma membrane channels which regulate transmembrane ion flux have also been shown to regulate a multitude of cellular processes, including proliferation and migration. Ion channels are typically multimeric complexes consisting of conducting subunits and auxiliary, non-conducting subunits. Auxiliary subunits modulate the function of conducting subunits and have putative non-conducting roles, further expanding the repertoire of cellular processes governed by ion channel complexes to processes such as transcellular adhesion and gene transcription. Given this expansive influence of ion channels on cellular behaviour it is perhaps no surprise that aberrant ion channel expression is a common occurrence in cancer. This review will focus on the conducting and non-conducting roles of the auxiliary subunits of various Ca2+, K+, Na+ and Cl- channels and the burgeoning evidence linking such auxiliary subunits to cancer. Several subunits are upregulated (e.g. Cavβ, Cavγ) and downregulated (e.g. Kvβ) in cancer, while other subunits have been functionally implicated as oncogenes (e.g. Navβ1, Cavα2δ1) and tumour suppressor genes (e.g. CLCA2, KCNE2, BKγ1) based on in vivo studies. The strengthening link between ion channel auxiliary subunits and cancer has exposed these subunits as potential biomarkers and therapeutic targets. However further mechanistic understanding is required into how these subunits contribute to tumour progression before their therapeutic potential can be fully realised.

Minocycline attenuates the development of diabetic neuropathy by modulating DREAM and BDNF protein expression in rat spinal cord

Aim

This study investigates the effects of minocycline (an inhibitor of microglial activation) administration on the expression level of spinal BDNF and DREAM proteins in diabetic neuropathic pain (DNP) rats.

Methods

The rats were divided into four groups (n = 16): non-diabetic control, diabetic control and diabetic rats receiving minocycline (80 μg/day or 160 μg/day). The diabetic rat model was induced by intraperitoneal injection of streptozotocin (60 mg/kg STZ). Tactile allodynia was assessed on day-0 (baseline), day-14 (pre-intervention) and day-22 (post-intervention). Minocycline at doses of 80 μg and 160 μg were given intrathecally from day-15 until day-21. On day-23, formalin test was conducted to assess  nociceptive behaviour response. The spinal expression of OX-42 and level of BDNF and DREAM proteins were detected by immunohistochemistry and western blot analyses.

Results

Diabetes rats showed significant tactile allodynia and nociceptive behaviour. These were accompanied by augmented expression of spinal OX-42, BDNF and DREAM protein levels. Both doses of minocycline attenuated tactile allodynia and nociceptive behaviour and also suppressed the diabetic-induced increase in spinal expressions of OX-42, BDNF and DREAM proteins.

Conclusion

This study revealed that minocycline could attenuate DNP by modulating spinal BDNF and DREAM protein expressions.

Targeting the neuronal calcium sensor DREAM with small-molecules for Huntington's disease treatment

DREAM, a neuronal calcium sensor protein, has multiple cellular roles including the regulation of Ca²⁺ and protein homeostasis. We recently showed that reduced DREAM expression or blockade of DREAM activity by repaglinide is neuroprotective in Huntington’s disease (HD). Here we used structure-based drug design to guide the identification of IQM-PC330, which was more potent and had longer lasting effects than repaglinide to inhibit DREAM in cellular and in vivo HD models. We disclosed and validated an unexplored ligand binding site, showing Tyr118 and Tyr130 as critical residues for binding and modulation of DREAM activity. IQM-PC330 binding de-repressed c-fos gene expression, silenced the DREAM effect on K_V4.3 channel gating and blocked the ATF6/DREAM interaction. Our results validate DREAM as a valuable target and propose more effective molecules for HD treatment.

Calcium Sensors in Neuronal Function and Dysfunction

Calcium signaling in neurons as in other cell types can lead to varied changes in cellular function. Neuronal Ca²⁺ signaling processes have also become adapted to modulate the function of specific pathways over a wide variety of time domains and these can have effects on, for example, axon outgrowth, neuronal survival, and changes in synaptic strength. Ca²⁺ also plays a key role in synapses as the trigger for fast neurotransmitter release. Given its physiological importance, abnormalities in neuronal Ca²⁺ signaling potentially underlie many different neurological and neurodegenerative diseases. The mechanisms by which changes in intracellular Ca²⁺ concentration in neurons can bring about diverse responses is underpinned by the roles of ubiquitous or specialized neuronal Ca²⁺ sensors. It has been established that synaptotagmins have key functions in neurotransmitter release, and, in addition to calmodulin, other families of EF-hand-containing neuronal Ca²⁺ sensors, including the neuronal calcium sensor (NCS) and the calcium-binding protein (CaBP) families, play important physiological roles in neuronal Ca²⁺ signaling. It has become increasingly apparent that these various Ca²⁺ sensors may also be crucial for aspects of neuronal dysfunction and disease either indirectly or directly as a direct consequence of genetic variation or mutations. An understanding of the molecular basis for the regulation of the targets of the Ca²⁺ sensors and the physiological roles of each protein in identified neurons may contribute to future approaches to the development of treatments for a variety of human neuronal disorders.

Veiled Potential of Secretagogin in Diabetes: Correlation or Coincidence?

Secretagogin (SCGN) is a calcium sensor protein enriched in neuroendocrine cells in general and pancreatic β-cells in particular. SCGN regulates insulin secretion through several Ca²⁺-dependent interactions. Recent studies implicate SCGN in the β-cell physiology and extracellular insulin function, making it an intriguing candidate in diabetes research. Here, we propose a conjoining theme of diversified SCGN function in diabetes pathology. In our opinion, SCGN is an attractive therapeutic candidate ascribed by its role in β-cell maintenance and neuronal functions and in the efficacy of insulin. To scrutinize the therapeutic prospects of SCGN, we abridge putative diabetes-related properties of SCGN and put forth strategies to determine the precise role of SCGN in the pathogenesis/preclusion of diabetes.

Pb2+ Binds to Downstream Regulatory Element Antagonist Modulator (DREAM) and Modulates Its Interactions with Binding Partners: A Link between Neuronal Calcium Sensors and Pb2+ Neurotoxicity

Pb²⁺ exposure leads to diverse neurological disorders; however, the mechanism of Pb²⁺-induced neurotoxicity is not clearly understood. Here we demonstrate that Pb²⁺ binds to EF-hands in apo-DREAM (downstream regulatory element antagonist modulator) with a lower equilibrium dissociation constant ( K_d = 20 ± 2 nM) than Ca²⁺ ( K_d = 1 μM). Based on the Trp169 emission and CD spectra, we report that Pb²⁺ association triggers changes in the protein secondary and tertiary structures that are analogous to those previously observed for Ca²⁺-bound protein. The hydrophobic cavity in the C-terminal domain of DREAM is solvent exposed in the presence of Pb²⁺ as determined using a hydrophobic probe, 1-anilinonaphthalene-8-sulfonic acid (1,8-ANS). Pb²⁺ association with DREAM also modulates interactions between DREAM and its intracellular partners as evident from the fact that Pb²⁺-bound DREAM associates with peptide-based model systems, presenilin-1 helix-9 "PS1HL9" K_V4.3(70-90) "site-2" and K_V4.3(2-22) "site 1". Namely, dissociation constants for Pb²⁺-bound DREAM interaction with PS1HL9 ( K_d = 2.4 ± 0.1 μM), site-2 ( K_d = 11.0 ± 0.5 μM) and site 1 ( K_d = 5.0 ± 0.6 μM) are nearly identical to those observed for Ca²⁺ bound DREAM. Isothermal titration calorimetry data reveal that Pb²⁺ binds to two high-affinity sites in Ca²⁺ bound DREAM with the overall apparent constant of 4.81 ± 0.06 μM and its binding to Ca²⁺ bound DREAM is entropy-driven. Taking into account the structural and sequence similarity between DREAM and other neuronal calcium sensor (NCS) proteins, these results strongly indicate that DREAM and possibly other NCS proteins bind Pb²⁺ with a higher affinity than that for Ca²⁺ and Pb²⁺ interactions with NCS proteins can contribute to Pb²⁺-induced neurotoxicity.

ARNT2 Tunes Activity-Dependent Gene Expression through NCoR2-Mediated Repression and NPAS4-Mediated Activation

Neuronal activity-dependent transcription is tuned to ensure precise gene induction during periods of heightened synaptic activity, allowing for appropriate responses of activated neurons within neural circuits. The consequences of aberrant induction of activity-dependent genes on neuronal physiology are not yet clear. Here, we demonstrate that, in the absence of synaptic excitation, the basic-helix-loop-helix (bHLH)-PAS family transcription factor ARNT2 recruits the NCoR2 co-repressor complex to suppress neuronal activity-dependent regulatory elements and maintain low basal levels of inducible genes. This restricts inhibition of excitatory neurons, maintaining them in a state that is receptive to future sensory stimuli. By contrast, in response to heightened neuronal activity, ARNT2 recruits the neuronal-specific bHLH-PAS factor NPAS4 to activity-dependent regulatory elements to induce transcription and thereby increase somatic inhibitory input. Thus, the interplay of bHLH-PAS complexes at activity-dependent regulatory elements maintains temporal control of activity-dependent gene expression and scales somatic inhibition with circuit activity.

Identification of IQM-266, a Novel DREAM Ligand That Modulates KV4 Currents

Downstream Regulatory Element Antagonist Modulator (DREAM)/KChIP3/calsenilin is a neuronal calcium sensor (NCS) with multiple functions, including the regulation of A-type outward potassium currents (I _A). This effect is mediated by the interaction between DREAM and K_V4 potassium channels and it has been shown that small molecules that bind to DREAM modify channel function. A-type outward potassium current (I _A) is responsible of the fast repolarization of neuron action potentials and frequency of firing. Using surface plasmon resonance (SPR) assays and electrophysiological recordings of K_V4.3/DREAM channels, we have identified IQM-266 as a DREAM ligand. IQM-266 inhibited the K_V4.3/DREAM current in a concentration-, voltage-, and time-dependent-manner. By decreasing the peak current and slowing the inactivation kinetics, IQM-266 led to an increase in the transmembrane charge ( Q K V 4.3 / DREAM ) at a certain range of concentrations. The slowing of the recovery process and the increase of the inactivation from the closed-state inactivation degree are consistent with a preferential binding of IQM-266 to a pre-activated closed state of K_V4.3/DREAM channels. Finally, in rat dorsal root ganglion neurons, IQM-266 inhibited the peak amplitude and slowed the inactivation of I _A. Overall, the results presented here identify IQM-266 as a new chemical tool that might allow a better understanding of DREAM physiological role as well as modulation of neuronal I _A in pathological processes.

Global Gene Knockout of Kcnip3 Enhances Pain Sensitivity and Exacerbates Negative Emotions in Rats

The Ca²⁺-binding protein Kv channel interacting protein 3 (KChIP3) or downstream regulatory element antagonist modulator (DREAM), a member of the neuronal calcium sensor (NCS) family, shows remarkable multifunctional properties. It acts as a transcriptional repressor in the nucleus and a modulator of ion channels or receptors, such as Kv4, NMDA receptors and TRPV1 channels on the cytomembrane. Previous studies of Kcnip3^-/- mice have indicated that KChIP3 facilitates pain hypersensitivity by repressing Pdyn expression in the spinal cord. Conversely, studies from transgenic daDREAM (dominant active DREAM) mice indicated that KChIP3 contributes to analgesia by repressing Bdnf expression and attenuating the development of central sensitization. To further determine the role of KChIP3 in pain transmission and its possible involvement in emotional processing, we assessed the pain sensitivity and negative emotional behaviors of Kcnip3^-/- rats. The knockout rats showed higher pain sensitivity compared to the wild-type rats both in the acute nociceptive pain model and in the late phase (i.e., 2, 4 and 6 days post complete Freund’s adjuvant injection) of the chronic inflammatory pain model. Importantly, Kcnip3^-/- rats displayed stronger aversion to the pain-associated compartment, higher anxiety level and aggravated depression-like behavior. Furthermore, RNA-Seq transcriptional profiling of the forebrain cortex were compared between wild-type and Kcnip3^-/- rats. Among the 68 upregulated genes, 19 genes (including Nr4a2, Ret, Cplx3, Rgs9, and Itgad) are associated with neural development or synaptic transmission, particularly dopamine neurotransmission. Among the 79 downregulated genes, 16 genes (including Col3a1, Itm2a, Pcdhb3, Pcdhb22, Pcdhb20, Ddc, and Sncaip) are associated with neural development or dopaminergic transmission. Transcriptional upregulation of Nr4a2, Ret, Cplx3 and Rgs9, and downregulation of Col3a1, Itm2a, Pcdhb3 and Ddc, were validated by qPCR analysis. In summary, our studies showed that Kcnip3^-/- rats displayed higher pain sensitivity and stronger negative emotions, suggesting an involvement of KChIP3 in negative emotions and possible role in central nociceptive processing.

Cadmium association with DREAM promotes DREAM interactions with intracellular partners in a similar manner to its physiological ligand, calcium

Cd²⁺exposure has been associated with neurodegenerative diseases and other pathologies, but the underlying mechanism through which it exerts toxic effects remain unresolved.

Ca2+-Dependent Transcriptional Repressors KCNIP and Regulation of Prognosis Genes in Glioblastoma

Glioblastomas (GBMs) are the most aggressive and lethal primary astrocytic tumors in adults, with very poor prognosis. Recurrence in GBM is attributed to glioblastoma stem-like cells (GSLCs). The behavior of the tumor, including proliferation, progression, invasion, and significant resistance to therapies, is a consequence of the self-renewing properties of the GSLCs, and their high resistance to chemotherapies have been attributed to their capacity to enter quiescence. Thus, targeting GSLCs may constitute one of the possible therapeutic challenges to significantly improve anti-cancer treatment regimens for GBM. Ca²⁺ signaling is an important regulator of tumorigenesis in GBM, and the transition from proliferation to quiescence involves the modification of the kinetics of Ca²⁺ influx through store-operated channels due to an increased capacity of the mitochondria of quiescent GSLC to capture Ca²⁺. Therefore, the identification of new therapeutic targets requires the analysis of the calcium-regulated elements at transcriptional levels. In this review, we focus onto the direct regulation of gene expression by KCNIP proteins (KCNIP1–4). These proteins constitute the class E of Ca²⁺ sensor family with four EF-hand Ca²⁺-binding motifs and control gene transcription directly by binding, via a Ca²⁺-dependent mechanism, to specific DNA sites on target genes, called downstream regulatory element (DRE). The presence of putative DRE sites on genes associated with unfavorable outcome for GBM patients suggests that KCNIP proteins may contribute to the alteration of the expression of these prognosis genes. Indeed, in GBM, KCNIP2 expression appears to be significantly linked to the overall survival of patients. In this review, we summarize the current knowledge regarding the quiescent GSLCs with respect to Ca²⁺ signaling and discuss how Ca²⁺via KCNIP proteins may affect prognosis genes expression in GBM. This original mechanism may constitute the basis of the development of new therapeutic strategies.

Regulators of A20 (TNFAIP3): new drug-able targets in inflammation

Persistent activation of the transcription factor Nuclear factor-κB (NF-κB) is central to the pathogenesis of many inflammatory disorders, including those of the lung such as cystic fibrosis (CF), asthma, and chronic obstructive pulmonary disease (COPD). Despite recent advances in treatment, management of the inflammatory component of these diseases still remains suboptimal. A20 is an endogenous negative regulator of NF-κB signaling, which has been widely described in several autoimmune and inflammatory disorders and more recently in terms of chronic lung disorders. However, the underlying mechanism for the apparent lack of A20 in CF, COPD, and asthma has not been investigated. Transcriptional regulation of A20 is complex and requires coordination of different transcription factors. In this review we examine the existing body of research evidence on the regulation of A20, concentrating on pulmonary inflammation. Special focus is given to the repressor downstream regulatory element antagonist modulator (DREAM) and its nuclear and cytosolic action to regulate inflammation. We provide evidence that would suggest the A20-DREAM axis to be an important player in (airway) inflammatory responses and point to DREAM as a potential future therapeutic target for the modification of phenotypic changes in airway inflammatory disorders. A schematic summary describing the role of DREAM in inflammation with a focus on chronic lung diseases as well as the possible consequences of altered DREAM expression on immune responses is provided.

Inhibition of the Neuronal Calcium Sensor DREAM Modulates Presenilin-2 Endoproteolysis

Deregulated intracellular Ca²⁺ and protein homeostasis underlie synaptic dysfunction and are common features in neurodegenerative diseases. DREAM, also known as calsenilin or KChIP-3, is a multifunctional Ca²⁺ binding protein of the neuronal calcium sensor superfamily with specific functions through protein-DNA and protein-protein interactions. Small-molecules able to bind DREAM, like the anti-diabetic drug repaglinide, disrupt some of the interactions with other proteins and modulate DREAM activity on Kv4 channels or on the processing of activating transcription factor 6 (ATF6). Here, we show the interaction of endogenous DREAM and presenilin-2 (PS2) in mouse brain and, using DREAM deficient mice or transgenic mice overexpressing a dominant active DREAM (daDREAM) mutant in the brain, we provide genetic evidence of the role of DREAM in the endoproteolysis of endogenous PS2. We show that repaglinide disrupts the interaction between DREAM and the C-terminal PS2 fragment (Ct-PS2) by coimmunoprecipitation assays. Exposure to sub-micromolar concentrations of repaglinide reduces the levels of Ct-PS2 fragment in N2a neuroblastoma cells. These results suggest that the interaction between DREAM and PS2 may represent a new target for modulation of PS2 processing, which could have therapeutic potential in Alzheimer’s disease (AD) treatment.

Resveratrol treatment reduces the vulnerability of SH-SY5Y cells and cortical neurons overexpressing SOD1-G93A to Thimerosal toxicity through SIRT1/DREAM/PDYN pathway

In humans, mutation of glycine 93 to alanine of Cu⁺⁺/Zn⁺⁺ superoxide dismutase type-1 (SOD1-G93 A) has been associated to some familial cases of Amyotrophic Lateral Sclerosis (ALS). Several evidence proposed the involvement of environmental pollutants that like mercury could accelerate ALS symptoms. SH-SY5Y cells stably transfected with SOD1 and G93 A mutant of SOD1 constructs were exposed to non-toxic concentrations (0.01 μM) of ethylmercury thiosalicylate (thimerosal) for 24 h. Interestingly, we found that thimerosal, in SOD1-G93 A cells, but not in SOD1 cells, reduced cell survival. Furthermore, thimerosal-induced cell death occurred in a concentration dependent-manner and was prevented by the Sirtuin 1 (SIRT1) activator Resveratrol (RSV). Moreover, thimerosal decreased the protein expression of transcription factor Downstream Regulatory Element Antagonist Modulator (DREAM), but not DREAM gene. Interestingly, DREAM reduction was blocked by co-treatment with RSV, suggesting the participation of SIRT1 in determining this effect. Immunoprecipitation experiments in SOD1-G93 A cells exposed to thimerosal demonstrated that RSV increased DREAM deacetylation and reduced its polyubiquitination. In addition, RSV counteracted thimerosal-enhanced prodynorphin (PDYN) mRNA, a DREAM target gene. Furthermore, cortical neurons transiently transfected with SOD1-G93 A construct and exposed to thimerosal (0.5 μM/24 h) showed a reduction of DREAM and an up-regulation of the prodynorphin gene. Importantly, both the treatment with RSV or the transfection of siRNA against prodynorphin significantly reduced thimerosal-induced neurotoxicity, while DREAM knocking-down potentiated thimerosal-reduced cell survival. These results demonstrate the particular vulnerability of SOD1-G93 A neuronal cells to thimerosal and that RSV via SIRT1 counteracts the neurodetrimental effect of this toxicant by preventing DREAM reduction and prodynorphin up-regulation.