Extracellular calcium controls background current and neuronal excitability via an UNC79-UNC80-NALCN cation channel complex

Congenital Ataxia with Progressive Cerebellar Atrophy, Camptodactyly, and Hypertrichosis: A Novel Recognizable Phenotype for NALCN Heterozygous Variants

BACKGROUND

 Non-selective sodium leak channel (NALCN) protein encoded by the NALCN gene is of key importance for neuronal cell excitability. Previous reports showed that biallelic NALCN pathogenic variants cause infantile hypotonia with psychomotor retardation and characteristic facies 1 (IHPRF1) while monoallelic variants lead to congenital contractures of the limbs and face, hypotonia, and developmental delay (CLIFAHDD). In our work, we aimed to expand the heterozygous NALCN-related clinical spectrum, presenting two affected individuals and a literature review.

METHODS

 We describe two new unrelated subjects harboring monoallelic NALCN pathogenic variants identified through clinical exome sequencing and review the current literature of other heterozygous NALCN patients.

RESULTS

 The c.3542G > A (p.Arg1181Gln) and the novel c.3423C > A (p.Phe1141Leu) heterozygous missense variants were disclosed in two subjects manifesting a similar phenotype characterized by congenital ataxia with progressive cerebellar atrophy, camptodactyly, and hypertrichosis of the arms (CAPCACH). Other NALCN subjects with overlapping features have already been reported. A combination of these clinical and neuroimaging findings suggests the definition of the new CAPCACH phenotype.

CONCLUSION

 We expand the heterozygous NALCN-related clinical spectrum from the more severe CLIFFAHDD to the milder CAPCACH phenotype. These conditions should be considered in the differential diagnosis of syndromic congenital ataxias, and the presence of camptodactyly and/or hypertrichosis may represent peculiar diagnostic clues.

Cadherin-16 regulates acoustic sensory gating in zebrafish through endocrine signaling

Sensory thresholds enable animals to regulate their behavioral responses to environmental threats. Despite the importance of sensory thresholds for animal behavior and human health, we do not yet have a full appreciation of the underlying molecular-genetic and circuit mechanisms. The larval zebrafish acoustic startle response provides a powerful system to identify molecular mechanisms underlying establishment of sensory thresholds and plasticity of thresholds through mechanisms like habituation. Using this system, we identify Cadherin-16 as a previously undescribed regulator of sensory gating. We demonstrate that Cadherin-16 regulates sensory thresholds via an endocrine organ, the corpuscle of Stannius (CS), which is essential in zebrafish for regulating Ca2+ homeostasis. We further show that Cadherin-16 regulates whole-body calcium and ultimately behavior through the hormone Stanniocalcin 1l (Stc1l), and the IGF-regulatory metalloprotease, Papp-aa. Finally, we demonstrate the importance of the CS through ablation experiments that reveal its role in promoting normal acoustic sensory gating. Together, our results uncover a previously undescribed brain non-autonomous pathway for the regulation of behavior and underscore Ca2+ homeostasis as a critical process underlying sensory gating in vivo.

The sodium leak channel NALCN is regulated by neuronal SNARE complex proteins

NALCN (sodium leak channel, nonselective) is vital for regulating electrical activity in neurons and other excitable cells, and mutations in the channel or its auxiliary proteins lead to severe neurodevelopmental disorders. Here, we show that the neuronal SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) complex proteins syntaxin and SNAP25 (synaptosome-associated protein 25), which enable synaptic transmission in the nervous system, inhibit the activity of the NALCN channel complex in both heterologous systems and primary neurons. The existence of this interaction suggests that the neurotransmitter release machinery can regulate electrical signaling directly and therefore modulate the threshold for its own activity. We further find that reduction of NALCN currents is sufficient to promote cell survival in syntaxin-depleted cells. This suggests that disinhibited NALCN may cause the puzzling phenomenon of rapid neuronal cell death in the absence of syntaxin. This interaction could offer opportunities for future drug development against genetic diseases linked to both NALCN- and SNARE protein-containing complexes.

The Biphasic Effect of Lipopolysaccharide on Membrane Potential

Lipopolysaccharide (LPS) from certain strains of Gram-negative bacteria can induce a rapid (<1 s) hyperpolarization of membrane potential, followed by a gradual depolarization exceeding the initial resting membrane potential. Through overexpression of a Drosophila ORK1 two-pore-domain K+ channel (K2P) in larval muscles and altering the external concentrations of K+ and Na+ ions, it is clear that the hyperpolarization is due to activating K2P channels and the depolarization is due to promoting an inward Na+ leak. When the external Na+ concentration is negligible, the LPS-delayed depolarization is dampened. The hyperpolarization induced by LPS can exceed -100 mV when external K+ and Na+ concentrations are lowered. These results indicate direct action by LPS on ion channels independently of immune responses. Such direct actions may need to be considered when developing clinical treatments for certain forms of bacterial septicemia.

The background sodium leak channel NALCN is a major controlling factor in pituitary cell excitability

The pituitary gland produces and secretes a variety of hormones that are essential to life, such as for the regulation of growth and development, metabolism, reproduction, and the stress response. This is achieved through an intricate signalling interplay between the brain and peripheral feedback signals that shape pituitary cell excitability by regulating the ion channel properties of these cells. In addition, endocrine anterior pituitary cells spontaneously fire action potentials to regulate the intracellular calcium ([Ca2+]i) level, an essential signalling conduit for hormonal secretion. To this end, pituitary cells must regulate their resting membrane potential (RMP) close to the firing threshold, but the molecular identity of the ionic mechanisms responsible for this remains largely unknown. Here, we revealed that the sodium leak channel NALCN, known to modulate neuronal excitability elsewhere in the brain, regulates excitability in the mouse anterior endocrine pituitary cells. Using viral transduction combined with powerful electrophysiology methods and calcium imaging, we show that NALCN forms the major Na+ leak conductance in these cells, appropriately tuning cellular RMP for sustaining spontaneous firing activity. Genetic depletion of NALCN channel activity drastically hyperpolarised these cells, suppressing their firing and [Ca2+]i oscillations. Remarkably, despite this profound function of NALCN conductance in controlling pituitary cell excitability, it represents a very small fraction of the total cell conductance. Because NALCN responds to hypothalamic hormones, our results also provide a plausible mechanism through which hormonal feedback signals from the brain and body could powerfully affect pituitary activity to influence hormonal function. KEY POINTS: Pituitary hormones are essential to life as they regulate important physiological processes, such as growth and development, metabolism, reproduction and the stress response. Pituitary hormonal secretion relies on the spontaneous electrical activity of pituitary cells and co-ordinated inputs from the brain and periphery. This appropriately regulates intracellular calcium signals in pituitary cells to trigger hormonal release. Using viral transduction in combination with electrophysiology and calcium imaging, we show that the activity of the background leak channel NALCN is a major controlling factor in eliciting spontaneous electrical activity and intracellular calcium signalling in pituitary cells. Remarkably, our results revealed that a minute change in NALCN activity could have a major influence on pituitary cell excitability. Our study provides a plausible mechanism through which the brain and body could intricately control pituitary activity to influence hormonal function.

Evaluation of mechanisms involved in regulation of intrinsic excitability by extracellular calcium in CA1 pyramidal neurons of rat

It is well recognized that changes in the extracellular concentration of calcium ions influence the excitability of neurons, yet what mechanism(s) mediate these effects is still a matter of debate. Using patch-clamp recordings from rat hippocampal CA1 pyramidal neurons, we examined the contribution of G-proteins and intracellular calcium-dependent signaling mechanisms to changes in intrinsic excitability evoked by altering the extracellular calcium concentration from physiological (1.2 mM) to a commonly used experimental (2 mM) level. We find that the inhibitory effect on intrinsic excitability of calcium ions is mainly expressed as an increased threshold for action potential firing (with no significant effect on resting membrane potential) that is not blocked by either the G-protein inhibitor GDPβS or the calcium chelator BAPTA. Our results therefore argue that in the concentration range studied, G-protein coupled calcium-sensing receptors, non-selective cation conductances, and intracellular calcium signaling pathways are not involved in mediating the effect of extracellular calcium ions on intrinsic excitability. Analysis of the derivative of the action potential, dV/dt versus membrane potential, indicates a current shift towards more depolarized membrane potentials at the higher calcium concentration. Our results are thus consistent with a mechanism in which extracellular calcium ions act directly on the voltage-gated sodium channels by neutralizing negative charges on the extracellular surface of these channels to modulate the threshold for action potential activation.

The cation channel mechanisms of subthreshold inward depolarizing currents in the mice VTA dopaminergic neurons and their roles in the chronic-stress-induced depression-like behavior

The slow-intrinsic-pacemaker dopaminergic (DA) neurons originating in the ventral tegmental area (VTA) are implicated in various mood- and emotion-related disorders, such as anxiety, fear, stress and depression. Abnormal activity of projection-specific VTA DA neurons is the key factor in the development of these disorders. Here, we describe the crucial role of the NALCN and TRPC6, non-selective cation channels in mediating the subthreshold inward depolarizing current and driving the firing of action potentials of VTA DA neurons in physiological conditions. Furthermore, we demonstrate that down-regulation of TRPC6 protein expression in the VTA DA neurons likely contributes to the reduced activity of projection-specific VTA DA neurons in chronic mild unpredictable stress (CMUS) depressive mice. In consistent with these, selective knockdown of TRPC6 channels in the VTA DA neurons conferred mice with depression-like behavior. This current study suggests down-regulation of TRPC6 expression/function is involved in reduced VTA DA neuron firing and chronic stress-induced depression-like behavior of mice.

Systematized Serendipity: Fishing Expeditions for Anesthetic Drugs and Targets

Most of science involves making observations, forming hypotheses, and testing those hypotheses, to form valid conclusions. However, a distinct, longstanding, and very productive scientific approach does not follow this paradigm; rather, it begins with a screen through a random collection of drugs or genetic variations for a particular effect or phenotype. Subsequently, the identity of the drug or gene is determined, and only then are hypotheses formed and the more standard scientific method employed. This alternative approach is called forward screening and includes methods such as genetic mutant screens, small molecule screens, metabolomics, proteomics, and transcriptomics. This review explains the rational for forward screening approaches and uses examples of screens for mutants with altered anesthetic sensitivities and for novel anesthetics to illustrate the methods and impact of the approach. Forward screening approaches are becoming even more powerful with advances in bioinformatics aided by artificial intelligence.

Cadherin 16 promotes sensory gating via the endocrine corpuscles of Stannius

Sensory thresholds enable animals to regulate their behavioral responses to environmental threats. Despite the importance of sensory thresholds for animal behavior and human health, we do not yet have a full appreciation of the underlying molecular-genetic and circuit mechanisms. The larval zebrafish acoustic startle response provides a powerful system to identify molecular mechanisms underlying establishment of sensory thresholds and plasticity of thresholds through mechanisms like habituation. Using this system, we identify Cadherin 16 as a previously undescribed regulator of sensory gating. We demonstrate that Cadherin 16 regulates sensory thresholds via an endocrine organ, the corpuscle of Stannius (CS), which is essential in zebrafish for regulating Ca2+ homeostasis. We further show that Cadherin 16 regulates whole-body calcium and ultimately behavior through the hormone Stanniocalcin 1L, and the IGF-regulatory metalloprotease, Papp-aa. Finally, we demonstrate the importance of the CS through ablation experiments that reveal its role in promoting normal acoustic sensory gating. Together, our results uncover a previously undescribed brain non-autonomous pathway for the regulation of behavior and establish Ca2+ homeostasis as a critical process underlying sensory gating in vivo.

Astrocyte Ca2+ in the dorsal striatum suppresses neuronal activity to oppose cue-induced reinstatement of cocaine seeking

Recent literature supports a prominent role for astrocytes in regulation of drug-seeking behaviors. The dorsal striatum, specifically, is known to play a role in reward processing with neuronal activity that can be influenced by astrocyte Ca2+. However, the manner in which Ca2+ in dorsal striatum astrocytes impacts neuronal signaling after exposure to self-administered cocaine remains unclear. We addressed this question following over-expression of the Ca2+ extrusion pump, hPMCA2w/b, in dorsal striatum astrocytes and the Ca2+ indicator, GCaMP6f, in dorsal striatum neurons of rats that were trained to self-administer cocaine. Following extinction of cocaine-seeking behavior, the rats over-expressing hMPCA2w/b showed a significant increase in cue-induced reinstatement of cocaine seeking. Suppression of astrocyte Ca2+ increased the amplitude of neuronal Ca2+ transients in brain slices, but only after cocaine self-administration. This was accompanied by decreased duration of neuronal Ca2+ events in the cocaine group and no changes in Ca2+ event frequency. Acute administration of cocaine to brain slices decreased amplitude of neuronal Ca2+ in both the control and cocaine self-administration groups regardless of hPMCA2w/b expression. These results indicated that astrocyte Ca2+ control over neuronal Ca2+ transients was enhanced by cocaine self-administration experience, although sensitivity to acutely applied cocaine remained comparable across all groups. To explore this further, we found that neither the hMPCA2w/b expression nor the cocaine self-administration experience altered regulation of neuronal Ca2+ events by NPS-2143, a Ca2+ sensing receptor (CaSR) antagonist, suggesting that plasticity of neuronal signaling after hPMCA2w/b over-expression was unlikely to result from elevated extracellular Ca2+. We conclude that astrocyte Ca2+ in the dorsal striatum impacts neurons via cell-intrinsic mechanisms (e.g., gliotransmission, metabolic coupling, etc.) and impacts long-term neuronal plasticity after cocaine self-administration differently from neuronal response to acute cocaine. Overall, astrocyte Ca2+ influences neuronal output in the dorsal striatum to promote resistance to cue-induced reinstatement of cocaine seeking.

Imbalance in Unc80 RNA Editing Disrupts Dynamic Neuronal Activity and Olfactory Perception

A-to-I RNA editing, catalyzed by the ADAR protein family, significantly contributes to the diversity and adaptability of mammalian RNA signatures, aligning with developmental and physiological needs. Yet, the functions of many editing sites are still to be defined. The Unc80 gene stands out in this context due to its brain-specific expression and the evolutionary conservation of its codon-altering editing event. The precise biological functions of Unc80 and its editing, however, are still largely undefined. In this study, we first demonstrated that Unc80 editing occurs in an ADAR2-dependent manner and is exclusive to the brain. By employing the CRISPR/Cas9 system to generate Unc80 knock-in mouse models that replicate the natural editing variations, our findings revealed that mice with the "gain-of-editing" variant (Unc80G/G) exhibit heightened basal neuronal activity in critical olfactory regions, compared to the "loss-of-editing" (Unc80S/S) counterparts. Moreover, an increase in glutamate levels was observed in the olfactory bulbs of Unc80G/G mice, indicating altered neurotransmitter dynamics. Behavioral analysis of odor detection revealed distinctive responses to novel odors-both Unc80 deficient (Unc80+/-) and Unc80S/S mice demonstrated prolonged exploration times and heightened dishabituation responses. Further elucidating the olfactory connection of Unc80 editing, transcriptomic analysis of the olfactory bulb identified significant alterations in gene expression that corroborate the behavioral and physiological findings. Collectively, our research advances the understanding of Unc80's neurophysiological functions and the impact of its editing on the olfactory sensory system, shedding light on the intricate molecular underpinnings of olfactory perception and neuronal activity.

In Silico and In Vitro Evaluation of the Molecular Mimicry of the SARS-CoV-2 Spike Protein by Common Short Constituent Sequences (cSCSs) in the Human Proteome: Toward Safer Epitope Design for Vaccine Development

Spike protein sequences in SARS-CoV-2 have been employed for vaccine epitopes, but many short constituent sequences (SCSs) in the spike protein are present in the human proteome, suggesting that some anti-spike antibodies induced by infection or vaccination may be autoantibodies against human proteins. To evaluate this possibility of "molecular mimicry" in silico and in vitro, we exhaustively identified common SCSs (cSCSs) found both in spike and human proteins bioinformatically. The commonality of SCSs between the two systems seemed to be coincidental, and only some cSCSs were likely to be relevant to potential self-epitopes based on three-dimensional information. Among three antibodies raised against cSCS-containing spike peptides, only the antibody against EPLDVL showed high affinity for the spike protein and reacted with an EPLDVL-containing peptide from the human unc-80 homolog protein. Western blot analysis revealed that this antibody also reacted with several human proteins expressed mainly in the small intestine, ovary, and stomach. Taken together, these results showed that most cSCSs are likely incapable of inducing autoantibodies but that at least EPLDVL functions as a self-epitope, suggesting a serious possibility of infection-induced or vaccine-induced autoantibodies in humans. High-risk cSCSs, including EPLDVL, should be excluded from vaccine epitopes to prevent potential autoimmune disorders.

Effects of 4 Testing Arena Sizes and 11 Types of Embryo Media on Sensorimotor Behaviors in Wild-Type and chd7 Mutant Zebrafish Larvae

The larval zebrafish is a highly versatile model across research disciplines, and the expanding use of behavioral analysis has contributed to many advances in neuropsychiatric, developmental, and toxicological studies, often through large-scale chemical and genetic screens. In the absence of standardized approaches to larval zebrafish behavior analysis, however, it is critical to understand the impact on behavior of experimental variables such as the size of testing arenas and the choice of embryo medium. Using a custom-built, modular high-throughput testing system, we examined the effects of 4 testing arena sizes and 11 types of embryo media on conserved sensorimotor behaviors in zebrafish larvae. Our data show that testing arena size impacts acoustic startle sensitivity and kinematics, as well as spontaneous locomotion and thigmotaxis, with fish tested in larger arenas displaying reduced startle sensitivity and increased locomotion. We also find that embryo media can dramatically affect startle sensitivity, kinematics, habituation, and prepulse inhibition, as well as spontaneous swimming, turning, and overall activity. Common medium components such as methylene blue and high calcium concentration consistently reduced startle sensitivity and locomotion. To further address how the choice of embryo medium can impact phenotype expression in zebrafish models of disease, we reared chd7 mutant larvae, a model of CHARGE syndrome with previously characterized morphological and behavioral phenotypes, in five different types of media and observed impacts on all phenotypes. By defining the effects of these key extrinsic factors on larval zebrafish behavior, these data can help researchers select the most appropriate conditions for their specific research questions, particularly for genetic and chemical screens.

The Na+ leak channel NALCN controls spontaneous activity and mediates synaptic modulation by α2-adrenergic receptors in auditory neurons

Cartwheel interneurons of the dorsal cochlear nucleus (DCN) potently suppress multisensory signals that converge with primary auditory afferent input, and thus regulate auditory processing. Noradrenergic fibers from locus coeruleus project to the DCN, and α2-adrenergic receptors inhibit spontaneous spike activity but simultaneously enhance synaptic strength in cartwheel cells, a dual effect leading to enhanced signal-to-noise for inhibition. However, the ionic mechanism of this striking modulation is unknown. We generated a glycinergic neuron-specific knockout of the Na+ leak channel NALCN in mice and found that its presence was required for spontaneous firing in cartwheel cells. Activation of α2-adrenergic receptors inhibited both NALCN and spike generation, and this modulation was absent in the NALCN knockout. Moreover, α2-dependent enhancement of synaptic strength was also absent in the knockout. GABAB receptors mediated inhibition through NALCN as well, acting on the same population of channels as α2 receptors, suggesting close apposition of both receptor subtypes with NALCN. Thus, multiple neuromodulatory systems determine the impact of synaptic inhibition by suppressing the excitatory leak channel, NALCN.

New insights into the physiology and pathophysiology of the atypical sodium leak channel NALCN

Cell excitability and its modulation by hormones and neurotransmitters involve the concerted action of a large repertoire of membrane proteins, especially ion channels. Unique complements of coexpressed ion channels are exquisitely balanced against each other in different excitable cell types, establishing distinct electrical properties that are tailored for diverse physiological contributions, and dysfunction of any component may induce a disease state. A crucial parameter controlling cell excitability is the resting membrane potential (RMP) set by extra- and intracellular concentrations of ions, mainly Na+, K+, and Cl-, and their passive permeation across the cell membrane through leak ion channels. Indeed, dysregulation of RMP causes significant effects on cellular excitability. This review describes the molecular and physiological properties of the Na+ leak channel NALCN, which associates with its accessory subunits UNC-79, UNC-80, and NLF-1/FAM155 to conduct depolarizing background Na+ currents in various excitable cell types, especially neurons. Studies of animal models clearly demonstrate that NALCN contributes to fundamental physiological processes in the nervous system including the control of respiratory rhythm, circadian rhythm, sleep, and locomotor behavior. Furthermore, dysfunction of NALCN and its subunits is associated with severe pathological states in humans. The critical involvement of NALCN in physiology is now well established, but its study has been hampered by the lack of specific drugs that can block or agonize NALCN currents in vitro and in vivo. Molecular tools and animal models are now available to accelerate our understanding of how NALCN contributes to key physiological functions and the development of novel therapies for NALCN channelopathies.

Nitric oxide modulates NMDA receptor through a negative feedback mechanism and regulates the dynamical behavior of neuronal postsynaptic components

Nitric oxide (NO) is known to be an important regulator of neurological processes in the central nervous system which acts directly on the presynaptic neuron and enhances the release of neurotransmitters like glutamate into the synaptic cleft. Calcium influx activates a cascade of biochemical reactions to influence the production of nitric oxide in the postsynaptic neuron. This has been modeled in the present work as a system of ordinary differential equations, to explore the dynamics of the interacting components and predict the dynamical behavior of the postsynaptic neuron. It has been hypothesized that nitric oxide modulates the NMDA receptor via a feedback mechanism and regulates the dynamic behavior of postsynaptic components. Results obtained by numerical analyses indicate that the biochemical system is stimulus-dependent and shows oscillations of calcium and other components within a limited range of concentration. Some of the parameters such as stimulus strength, extracellular calcium concentration, and rate of nitric oxide feedback are crucial for the dynamics of the components in the postsynaptic neuron.

High calcium concentrations reduce cellular excitability of mouse MNTB neurons

Calcium, a universal intracellular signaling molecule, plays essential roles in neural functions. Historically, in most in vitro brain slice electrophysiology studies, the extracellular calcium concentration ([Ca2+]e) in artificial cerebrospinal fluid is of a wide range and typically higher than the physiological value. At high [Ca2+]e, synaptic transmission is generally enhanced. However, the effects and the underlying mechanisms of calcium on intrinsic neuronal properties are diverse. Using whole-cell patch clamp in acute brainstem slices obtained from mice of either sex, we investigated the effects and the underlying mechanisms of high [Ca2+]e on intrinsic neuronal properties of neurons in the medial nucleus of the trapezoid body (MNTB), an auditory brainstem component in the sound localization circuitry. Compared to the physiological [Ca2+]e (1.2 mM), high [Ca2+]e at 1.8 and 2.4 mM significantly reduced the cellular excitability of MNTB neurons, resulting in decreased spike firing rate, depolarized spike threshold, and decreased the ability to follow high frequency inputs. High extracellular magnesium concentrations at 1.8 and 2.4 mM produced similar but less robust effects, due to surface charge screening. Upon high calcium application, voltage-gated sodium channel currents remained largely unchanged. Calcium-sensing receptors were detected in MNTB neurons, but blocking these receptors did not eliminate the effects of high calcium on spontaneous spiking. We attribute the lack of significant effects in these last two experiments to the moderate changes in calcium we tested. Our results call for the use of physiological [Ca2+]e in brain slice experiments.

Activity-dependent ectopic action potentials in regular-spiking neurons of the neocortex

Introduction

Action potentials usually travel orthodromically along a neuron's axon, from the axon initial segment (AIS) toward the presynaptic terminals. Under some circumstances action potentials also travel in the opposite direction, antidromically, after being initiated at a distal location. Given their initiation at an atypical site, we refer to these events as "ectopic action potentials." Ectopic action potentials (EAPs) were initially observed in pathological conditions including seizures and nerve injury. Several studies have described regular-spiking (RS) pyramidal neurons firing EAPs in seizure models. Under nonpathological conditions, EAPs were reported in a few populations of neurons, and our group has found that EAPs can be induced in a large proportion of parvalbumin-expressing interneurons in the neocortex. Nevertheless, to our knowledge there have been no prior reports of ectopic firing in the largest population of neurons in the neocortex, pyramidal neurons, under nonpathological conditions.

Methods

We performed in vitro recordings utilizing the whole-cell patch clamp technique. To elicit EAPs, we triggered orthodromic action potentialswith either long, progressively increasing current steps, or with trains of brief pulses at 30, 60, or 100 Hz delivered in 3 different ways, varying in stimulus and resting period duration.

Results

We found that a large proportion (72.7%) of neocortical RS cells from mice can fire EAPs after a specific stimulus in vitro, and that most RS cells (56.1%) are capable of firing EAPs across a broad range of stimulus conditions. Of the 37 RS neurons in which we were able to elicit EAPs, it took an average of 863.8 orthodromic action potentials delivered over the course of an average of ~81.4 s before the first EAP was seen. We observed that some cells responded to specific stimulus frequencies while less selective, suggesting frequency tuning in a subset of the cells.

Discussion

Our findings suggest that pyramidal cells can integrate information over long time-scales before briefly entering a mode of self-generated firing that originates in distal axons. The surprising ubiquity of EAP generation in RS cells raises interesting questions about the potential roles of ectopic spiking in information processing, cortical oscillations, and seizure susceptibility.

The Na+ leak channel NALCN controls spontaneous activity and mediates synaptic modulation by α2-adrenergic receptors in auditory neurons

Cartwheel interneurons of the dorsal cochlear nucleus (DCN) potently suppress multisensory signals that converge with primary auditory afferent input, and thus regulate auditory processing. Noradrenergic fibers from locus coeruleus project to the DCN, and α2-adrenergic receptors inhibit spontaneous spike activity but simultaneously enhance synaptic strength in cartwheel cells, a dual effect leading to enhanced signal-to-noise for inhibition. However, the ionic mechanism of this striking modulation is unknown. We generated a glycinergic neuron-specific knockout of the Na+ leak channel NALCN, and found that its presence was required for spontaneous firing in cartwheel cells. Activation of α2-adrenergic receptors inhibited both NALCN and spike generation, and this modulation was absent in the NALCN knockout. Moreover, α2-dependent enhancement of synaptic strength was also absent in the knockout. GABAB receptors mediated inhibition through NALCN as well, acting on the same population of channels as α2 receptors, suggesting close apposition of both receptor subtypes with NALCN. Thus, multiple neuromodulatory systems determine the impact of synaptic inhibition by suppressing the excitatory leak channel, NALCN.

Neurovirulent cytokines increase neuronal excitability in a model of coronavirus-induced neuroinflammation

BACKGROUND

Neurological manifestations of severe coronavirus infections, including SARS-CoV-2, are wide-ranging and may persist following virus clearance. Detailed understanding of the underlying changes in brain function may facilitate the identification of therapeutic targets. We directly tested how neocortical function is impacted by the specific panel of cytokines that occur in coronavirus brain infection. Using the whole-cell patch-clamp technique, we determined how the five cytokines (TNFα, IL-1β, IL-6, IL-12p40 and IL-15 for 22-28-h) at concentrations matched to those elicited by MHV-A59 coronavirus brain infection, affected neuronal function in cultured primary mouse neocortical neurons.

RESULTS

We evaluated how acute cytokine exposure affected neuronal excitability (propensity to fire action potentials), membrane properties, and action potential characteristics, as well as sensitivity to changes in extracellular calcium and magnesium (divalent) concentration. Neurovirulent cytokines increased spontaneous excitability and response to low divalent concentration by depolarizing the resting membrane potential and hyperpolarizing the action potential threshold. Evoked excitability was also enhanced by neurovirulent cytokines at physiological divalent concentrations. At low divalent concentrations, the change in evoked excitability was attenuated. One hour after cytokine removal, spontaneous excitability and hyperpolarization of the action potential threshold normalized but membrane depolarization and attenuated divalent-dependent excitability persisted.

CONCLUSIONS

Coronavirus-associated cytokine exposure increases spontaneous excitability in neocortical neurons, and some of the changes persist after cytokine removal.

Contributions of the Sodium Leak Channel NALCN to Pacemaking of Medial Ventral Tegmental Area and Substantia Nigra Dopaminergic Neurons

We tested the role of the sodium leak channel, NALCN, in pacemaking of dopaminergic neuron (DAN) subpopulations from adult male and female mice. In situ hybridization revealed NALCN RNA in all DANs, with lower abundance in medial ventral tegmental area (VTA) relative to substantia nigra pars compacta (SNc). Despite lower relative abundance of NALCN, we found that acute pharmacological blockade of NALCN in medial VTA DANs slowed pacemaking by 49.08%. We also examined the electrophysiological properties of projection-defined VTA DAN subpopulations identified by retrograde labeling. Inhibition of NALCN reduced pacemaking in DANs projecting to medial nucleus accumbens (NAc) and others projecting to lateral NAc by 70.74% and 31.98%, respectively, suggesting that NALCN is a primary driver of pacemaking in VTA DANs. In SNc DANs, potentiating NALCN by lowering extracellular calcium concentration speeded pacemaking in wildtype but not NALCN conditional knockout mice, demonstrating functional presence of NALCN. In contrast to VTA DANs, however, pacemaking in SNc DANs was unaffected by inhibition of NALCN. Instead, we found that inhibition of NALCN increased the gain of frequency-current plots at firing frequencies slower than spontaneous firing. Similarly, inhibition of the hyperpolarization-activated cyclic nucleotide-gated (HCN) conductance increased gain but had little effect on pacemaking. Interestingly, simultaneous inhibition of NALCN and HCN resulted in significant reduction in pacemaker rate. Thus, we found NALCN makes substantial contributions to driving pacemaking in VTA DAN subpopulations. In SNc DANs, NALCN is not critical for pacemaking but inhibition of NALCN makes cells more sensitive to hyperpolarizing stimuli.SIGNIFICANCE STATEMENT Pacemaking in midbrain dopaminergic neurons (DAN) relies on multiple subthreshold conductances, including a sodium leak. Whether the sodium leak channel, NALCN, contributes to pacemaking in DANs located in the VTA and the SNc has not yet been determined. Using electrophysiology and pharmacology, we show that NALCN plays a prominent role in driving pacemaking in projection-defined VTA DAN subpopulations. By contrast, pacemaking in SNc neurons does not rely on NALCN. Instead, the presence of NALCN regulates the excitability of SNc DANs by reducing the gain of the neuron's response to inhibitory stimuli. Together, these findings will inform future efforts to obtain DAN subpopulation-specific treatments for use in neuropsychiatric disorders.

Modification of the synaptic cleft under excitatory conditions

The synaptic cleft is the extracellular part of the synapse, bridging the pre- and postsynaptic membranes. The geometry and molecular organization of the cleft is gaining increased attention as an important determinant of synaptic efficacy. The present study by electron microscopy focuses on short-term morphological changes at the synaptic cleft under excitatory conditions. Depolarization of cultured hippocampal neurons with high K+ results in an increased frequency of synaptic profiles with clefts widened at the periphery (open clefts), typically exhibiting patches of membranes lined by postsynaptic density, but lacking associated presynaptic membranes (18.0% open clefts in high K+ compared to 1.8% in controls). Similarly, higher frequencies of open clefts were observed in adult brain upon a delay of perfusion fixation to promote excitatory/ischemic conditions. Inhibition of basal activity in cultured neurons through the application of TTX results in the disappearance of open clefts whereas application of NMDA increases their frequency (19.0% in NMDA vs. 5.3% in control and 2.6% in APV). Depletion of extracellular Ca2+ with EGTA also promotes an increase in the frequency of open clefts (16.6% in EGTA vs. 4.0% in controls), comparable to that by depolarization or NMDA, implicating dissociation of Ca2+-dependent trans-synaptic bridges. Dissociation of transsynaptic bridges under excitatory conditions may allow perisynaptic mobile elements, such as AMPA receptors to enter the cleft. In addition, peripheral opening of the cleft would facilitate neurotransmitter clearance and thus may have a homeostatic and/or protective function.

A new neurodevelopmental disorder linked to heterozygous variants in UNC79

PURPOSE

The "NALCN channelosome" is an ion channel complex that consists of multiple proteins, including NALCN, UNC79, UNC80, and FAM155A. Only a small number of individuals with a neurodevelopmental syndrome have been reported with disease causing variants in NALCN and UNC80. However, no pathogenic UNC79 variants have been reported, and in vivo function of UNC79 in humans is largely unknown.

METHODS

We used international gene-matching efforts to identify patients harboring ultrarare heterozygous loss-of-function UNC79 variants and no other putative responsible genes. We used genetic manipulations in Drosophila and mice to test potential causal relationships between UNC79 variants and the pathology.

RESULTS

We found 6 unrelated and affected patients with UNC79 variants. Five patients presented with overlapping neurodevelopmental features, including mild to moderate intellectual disability and a mild developmental delay, whereas a single patient reportedly had normal cognitive and motor development but was diagnosed with epilepsy and autistic features. All displayed behavioral issues and 4 patients had epilepsy. Drosophila with UNC79 knocked down displayed induced seizure-like phenotype. Mice with a heterozygous loss-of-function variant have a developmental delay in body weight compared with wild type. In addition, they have impaired ability in learning and memory.

CONCLUSION

Our results demonstrate that heterozygous loss-of-function UNC79 variants are associated with neurologic pathologies.

Effects of 4 testing arena sizes and 11 types of embryo media on sensorimotor behaviors in wild-type and chd7 mutant zebrafish larvae: Media and arena size impact zebrafish behavior

The larval zebrafish is a highly versatile model across research disciplines, and the expanding use of behavioral analysis has contributed to many advances in neuro-psychiatric, developmental, and toxicological studies, often through large-scale chemical and genetic screens. In the absence of standardized approaches to larval zebrafish behavior analysis, however, it is critical to understand the impact on behavior of experimental variables such as the size of testing arenas and the choice of embryo medium. Using a custom-built, modular high-throughput testing system, we examined the effects of 4 testing arena sizes and 11 types of embryo media on conserved sensorimotor behaviors in zebrafish larvae. Our data show that testing arena size impacts acoustic startle sensitivity and kinematics as well as spontaneous locomotion and thigmotaxis, with fish tested in larger arenas displaying reduced startle sensitivity and increased locomotion. We also find that embryo media can dramatically affect startle sensitivity, kinematics, habituation, and pre-pulse inhibition, as well as spontaneous swimming, turning, and overall activity. Common media components such as methylene blue and high calcium concentration consistently reduced startle sensitivity and locomotion. To further address how the choice of embryo medium can impact phenotype expression in zebrafish models of disease, we reared chd7 mutant larvae, a model of CHARGE syndrome with previously characterized morphological and behavioral phenotypes, in 5 different types of media and observed impacts on all phenotypes. By defining the effects of these key extrinsic factors on larval zebrafish behavior, these data can help researchers select the most appropriate conditions for their specific research questions, particularly for genetic and chemical screens.

NALCN-mediated sodium influx confers metastatic prostate cancer cell invasiveness

There is growing evidence that ion channels are critically involved in cancer cell invasiveness and metastasis. However, the molecular mechanisms of ion signaling promoting cancer behavior are poorly understood and the complexity of the underlying remodeling during metastasis remains to be explored. Here, using a variety of in vitro and in vivo techniques, we show that metastatic prostate cancer cells acquire a specific Na+ /Ca2+ signature required for persistent invasion. We identify the Na+ leak channel, NALCN, which is overexpressed in metastatic prostate cancer, as a major initiator and regulator of Ca2+ oscillations required for invadopodia formation. Indeed, NALCN-mediated Na+ influx into cancer cells maintains intracellular Ca2+ oscillations via a specific chain of ion transport proteins including plasmalemmal and mitochondrial Na+ /Ca2+ exchangers, SERCA and store-operated channels. This signaling cascade promotes activity of the NACLN-colocalized proto-oncogene Src kinase, actin remodeling and secretion of proteolytic enzymes, thus increasing cancer cell invasive potential and metastatic lesions in vivo. Overall, our findings provide new insights into an ion signaling pathway specific for metastatic cells where NALCN acts as persistent invasion controller.

Potentiation of neuronal activity by tonic GluD1 current in brain slices

Ion channel function of native delta glutamate receptors (GluD_R ) is incompletely understood. Previously, we and others have shown that activation of Gαq protein-coupled receptors (GqPCR) produces a slow inward current carried by GluD1_R . GluD1_R also carries a tonic cation current of unknown cause. Here, using voltage-clamp electrophysiological recordings from adult mouse brain slices containing the dorsal raphe nucleus, we find no role of ongoing G-protein-coupled receptor activity in generating or sustaining tonic GluD1_R currents. Neither augmentation nor disruption of G protein activity affects tonic GluD1_R currents, suggesting that ongoing G-protein-coupled receptor activity does not give rise to tonic GluD1_R currents. Further, the tonic GluD1_R current is unaffected by the addition of external glycine or D-serine, which influences GluD2_R current at millimolar concentrations. Instead, GqPCR-stimulated and tonic GluD1_R currents are regulated by physiological levels of external calcium. In current-clamp recordings, block of GluD1_R channels hyperpolarizes the membrane by ~7 mV at subthreshold potentials, reducing excitability. Thus, GluD1_R carries a G-protein-independent tonic current that contributes to subthreshold neuronal excitation in the dorsal raphe nucleus.

Circadian regulation of dentate gyrus excitability mediated by G-protein signaling

The central circadian regulator within the suprachiasmatic nucleus transmits time of day information by a diurnal spiking rhythm driven by molecular clock genes controlling membrane excitability. Most brain regions, including the hippocampus, harbor similar intrinsic circadian transcriptional machinery, but whether these molecular programs generate oscillations of membrane properties is unclear. Here, we show that intrinsic excitability of mouse dentate granule neurons exhibits a 24-h oscillation that controls spiking probability. Diurnal changes in excitability are mediated by antiphase G-protein regulation of potassium and sodium currents that reduce excitability during the Light phase. Disruption of the circadian transcriptional machinery by conditional deletion of Bmal1 enhances excitability selectively during the Light phase by removing G-protein regulation. These results reveal that circadian transcriptional machinery regulates intrinsic excitability by coordinated regulation of ion channels by G-protein signaling, highlighting a potential novel mechanism of cell-autonomous oscillations.

Loss of sodium leak channel (NALCN) in the ventral dentate gyrus impairs neuronal activity of the glutamatergic neurons for inflammation-induced depression in male mice

BACKGROUND

The dentate gyrus (DG) has been implicated in the pathophysiology of depression. Many studies have revealed the cellular types, neural circuits, and morphological changes of the DG involved in the development of depression. However, the molecular regulating its intrinsic activity in depression is unknown.

METHODS

Utilizing the mode of depression induced by lipopolysaccharide (LPS), we investigate the involvement of the sodium leak channel (NALCN) in inflammation-induced depressive-like behaviors of male mice. The expression of NALCN was detected by immunohistochemistry and real-time polymerase chain reaction. DG microinjection of the adeno-associated virus or lentivirus was carried out using a stereotaxic instrument and followed by behavioral tests. Neuronal excitability and NALCN conductance were recorded by whole-cell patch-clamp techniques.

RESULTS

The expression and function of NALCN were reduced in both the dorsal and ventral DG in LPS-treated mice; whereas, only knocking down NALCN in the ventral pole produced depressive-like behaviors and this effect of NALCN was specific to ventral glutamatergic neurons. The excitability of ventral glutamatergic neurons was impaired by both the knockdown of NALCN and/or the treatment of LPS. Then, the overexpression of NALCN in the ventral glutamatergic neurons decreased the susceptibility of mice to inflammation-induced depression, and the intracranial injection of substance P (non-selective NALCN activator) into the ventral DG rapidly ameliorated inflammation-induced depression-like behaviors in an NALCN-dependent manner.

CONCLUSIONS

NALCN, which drives the neuronal activity of the ventral DG glutamatergic neurons, uniquely regulates depressive-like behaviors and susceptibility to depression. Therefore, the NALCN of glutamatergic neurons in the ventral DG may present a molecular target for rapid antidepressant drugs.

Activity-Dependent Fluctuations in Interstitial [K+]: Investigations Using Ion-Sensitive Microelectrodes

In the course of action potential firing, all axons and neurons release K⁺ from the intra- cellular compartment into the interstitial space to counteract the depolarizing effect of Na⁺ influx, which restores the resting membrane potential. This efflux of K⁺ from axons results in K⁺ accumulation in the interstitial space, causing depolarization of the K⁺ reversal potential (E_K), which can prevent subsequent action potentials. To ensure optimal neuronal function, the K⁺ is buffered by astrocytes, an energy-dependent process, which acts as a sink for interstitial K⁺, absorbing it at regions of high concentration and distributing it through the syncytium for release in distant regions. Pathological processes in which energy production is compromised, such as anoxia, ischemia, epilepsy and spreading depression, can lead to excessive interstitial K⁺ accumulation, disrupting sensitive trans-membrane ion gradients and attenuating neuronal activity. The changes that occur in interstitial [K⁺] resulting from both physiological and pathological processes can be monitored accurately in real time using K⁺-sensitive microelectrodes, an invaluable tool in electrophysiological studies.

The calcium-sensing receptor (CaSR) regulates zebrafish sensorimotor decision making via a genetically defined cluster of hindbrain neurons

Decision making is a fundamental nervous system function that ranges widely in complexity and speed of execution. We previously established larval zebrafish as a model for sensorimotor decision making and identified the G-protein-coupled calcium-sensing receptor (CaSR) to be critical for this process. Here, we report that CaSR functions in neurons to dynamically regulate the bias between two behavioral outcomes: escapes and reorientations. By employing a computational guided transgenic strategy, we identify a genetically defined neuronal cluster in the hindbrain as a key candidate site for CaSR function. Finally, we demonstrate that transgenic CaSR expression targeting this cluster consisting of a few hundred neurons shifts behavioral bias in wild-type animals and restores decision making deficits in CaSR mutants. Combined, our data provide a rare example of a G-protein-coupled receptor that biases vertebrate sensorimotor decision making via a defined neuronal cluster.

The Na+/K+ pump dominates control of glycolysis in hippocampal dentate granule cells

Cellular ATP that is consumed to perform energetically expensive tasks must be replenished by new ATP through the activation of metabolism. Neuronal stimulation, an energetically demanding process, transiently activates aerobic glycolysis, but the precise mechanism underlying this glycolysis activation has not been determined. We previously showed that neuronal glycolysis is correlated with Ca2+ influx, but is not activated by feedforward Ca2+ signaling (Díaz-García et al., 2021a). Since ATP-powered Na+ and Ca2+ pumping activities are increased following stimulation to restore ion gradients and are estimated to consume most neuronal ATP, we aimed to determine if they are coupled to neuronal glycolysis activation. By using two-photon imaging of fluorescent biosensors and dyes in dentate granule cell somas of acute mouse hippocampal slices, we observed that production of cytoplasmic NADH, a byproduct of glycolysis, is strongly coupled to changes in intracellular Na+, while intracellular Ca2+ could only increase NADH production if both forward Na+/Ca2+ exchange and Na+/K+ pump activity were intact. Additionally, antidromic stimulation-induced intracellular [Na+] increases were reduced >50% by blocking Ca2+ entry. These results indicate that neuronal glycolysis activation is predominantly a response to an increase in activity of the Na+/K+ pump, which is strongly potentiated by Na+ influx through the Na+/Ca2+ exchanger during extrusion of Ca2+ following stimulation.

Activating SIRT-1 Signalling with the Mitochondrial-CoQ10 Activator Solanesol Improves Neurobehavioral and Neurochemical Defects in Ouabain-Induced Experimental Model of Bipolar Disorder

Bipolar disorder (BD) is a chronic mental illness characterized by mood fluctuations that range from depressive lows to manic highs. Several studies have linked the downregulation of SIRT-1 (silent mating type information regulation-2 homologs) signaling to the onset of BD and other neurological dysfunctions. This research aimed to look into the neuroprotective potential of Solanesol (SNL) in rats given ICV-Ouabain injections, focusing on its effect on SIRT-1 signaling activation in the brain. Ouabain, found in hypothalamic and medullary neurons, is an endogenous inhibitor of brain Na⁺/K⁺ ATPase. The inhibition of brain Na⁺/K⁺ ATPase by Ouabain may also result in changes in neurotransmission within the central nervous system. SNL is a Solanaceae family active phytoconstituent produced from the plant Nicotiana tabacum. SNL is used as a precursor for the production of CoQ10 (Coenzyme Q10), a powerful antioxidant and neuroprotective compound. In the current study, lithium (Li), an important mood stabilizer drug, was used as a control. This study looked at the neuroprotective potential of SNL at dosages of 40 and 80 mg/kg in ICV-OUA injections that caused BD-like neurobehavioral and neurochemical defects in Wistar rats. Wistar rats were placed into eight groups (n = 6) and administered 1 mM/0.5 µL ICV-OUA injections for three days. Neurochemical assessments were done in rat brain homogenates, CSF, and blood plasma samples at the end of the experiment protocol schedule. Long-term SNL and lithium administration have been shown to decrease the number of rearing and crossings and reduce time spent in the center, locomotor activities, and immobility time. Solansesol treatment gradually raises the amount of Na⁺/K⁺ ATPase, limiting the severity of behavioural symptoms. These findings also revealed that SNL increases the levels of SIRT-1 in CSF, blood plasma, and brain homogenate samples. Moreover, in rat brain homogenates and blood plasma samples, SNL modulates apoptotic markers such as Caspase-3, Bax (pro-apoptotic), and Bcl-2 (anti-apoptotic). Mitochondrial-ETC complex enzymes, including complex-I, II, IV, V, and CoQ10, were also restored following long-term SNL treatment. Furthermore, SNL lowered inflammatory cytokines (TNF-α, IL-1β) levels while restoring neurotransmitter levels (serotonin, dopamine, glutamate, and acetylcholine) and decreasing oxidative stress markers. Histological examinations also validated Solanesol’s protective effect. As a result, our findings suggest that SNL, as a SIRT-1 signalling activator, may be a promising therapeutic approach for BD-like neurological dysfunctions.

Structure and mechanism of NALCN-FAM155A-UNC79-UNC80 channel complex

NALCN channel mediates sodium leak currents and is important for maintaining proper resting membrane potential. NALCN and FAM155A form the core complex of the channel, the activity of which essentially depends on the presence of both UNC79 and UNC80, two auxiliary proteins. NALCN, FAM155A, UNC79, and UNC80 co-assemble into a large hetero-tetrameric channel complex. Genetic mutations of NALCN channel components lead to neurodevelopmental diseases. However, the structure and mechanism of the intact channel complex remain elusive. Here, we present the cryo-EM structure of the mammalian NALCN-FAM155A-UNC79-UNC80 quaternary complex. The structure shows that UNC79-UNC80 form a large piler-shaped heterodimer which was tethered to the intracellular side of the NALCN channel through tripartite interactions with the cytoplasmic loops of NALCN. Two interactions are essential for proper cell surface localization of NALCN. The other interaction relieves the self-inhibition of NALCN by pulling the auto-inhibitory CTD Interacting Helix (CIH) out of its binding site. Our work defines the structural mechanism of NALCN modulation by UNC79 and UNC80.

Differential modulation of C. elegans motor behavior by NALCN and two-pore domain potassium channels

Two-pore domain potassium channels (K2P) are a large family of “background” channels that allow outward “leak” of potassium ions. The NALCN/UNC80/UNC79 complex is a non-selective channel that allows inward flow of sodium and other cations. It is unclear how K2Ps and NALCN differentially modulate animal behavior. Here, we found that loss of function (lf) in the K2P gene twk-40 suppressed the reduced body curvatures of C. elegans NALCN(lf) mutants. twk-40(lf) caused a deep body curvature and extended backward locomotion, and these phenotypes appeared to be associated with neuron-specific expression of twk-40 and distinct twk-40 transcript isoforms. To survey the functions of other less studied K2P channels, we examined loss-of-function mutants of 13 additional twk genes expressed in the motor circuit and detected defective body curvature and/or locomotion in mutants of twk-2, twk-17, twk-30, twk-48, unc-58, and the previously reported twk-7. We generated presumptive gain-of-function (gf) mutations in twk-40, twk-2, twk-7, and unc-58 and found that they caused paralysis. Further analyses detected variable genetic interactions between twk-40 and other twk genes, an interdependence between twk-40 and twk-2, and opposite behavioral effects between NALCN and twk-2, twk-7, or unc-58. Finally, we found that the hydrophobicity/hydrophilicity property of TWK-40 residue 159 could affect the channel activity. Together, our study identified twk-40 as a novel modulator of the motor behavior, uncovered potential behavioral effects of five other K2P genes and suggests that NALCN and some K2Ps can oppositely affect C. elegans behavior.

Architecture of the human NALCN channelosome

NALCN regulates the resting membrane potential by mediating the Na⁺ leak current in neurons, and it functions as a channelosome in complex with FAM155A, UNC79, and UNC80. Dysfunction of the NALCN channelosome causes a broad range of neurological and developmental diseases called NALCN channelopathies in humans. How the auxiliary subunits, especially the two large components UNC79 and UNC80, assemble with NALCN and regulate its function remains unclear. Here we report an overall architecture of the human NALCN channelosome. UNC79 and UNC80 each adopt an S-shape super-helical structure consisting of HEAT and armadillo repeats, forming a super-coiled heterodimeric assembly in the cytoplasmic side, which may provide a scaffold for the binding of other potential modulators of the channelosome. The UNC79-UNC80 assembly specifically associates with the NALCN-FAM155A subcomplex through the intracellular II-III linker of NALCN. Disruptions of the interaction interfaces between UNC79 and UNC80, and between the II-III linker of NALCN and the UNC79-UNC80 assembly, significantly reduce the NALCN-mediated currents in HEK293T system, suggesting the importance of the UNC79-UNC80 assembly in regulating channelosome function. Cross-linking mass spectrometry analysis identified an additional calmodulin (CaM) bound in the carboxyl-terminal domain of NALCN. Our study thus provides a structural basis for understanding the unique assembly mechanism and functional regulation of the NALCN channelosome, and also provides an opportunity for the interpretation of many disease-related mutations in UNC80.

Structural architecture of the human NALCN channelosome

Depolarizing sodium (Na⁺) leak currents carried by the NALCN channel regulate the resting membrane potential of many neurons to modulate respiration, circadian rhythm, locomotion and pain sensitivity^1-8. NALCN requires FAM155A, UNC79 and UNC80 to function, but the role of these auxiliary subunits is not understood^3,7,9-12. NALCN, UNC79 and UNC80 are essential in rodents^2,9,13, and mutations in human NALCN and UNC80 cause severe developmental and neurological disease^14,15. Here we determined the structure of the NALCN channelosome, an approximately 1-MDa complex, as fundamental aspects about the composition, assembly and gating of this channelosome remain obscure. UNC79 and UNC80 are massive HEAT-repeat proteins that form an intertwined anti-parallel superhelical assembly, which docks intracellularly onto the NALCN-FAM155A pore-forming subcomplex. Calmodulin copurifies bound to the carboxy-terminal domain of NALCN, identifying this region as a putative modulatory hub. Single-channel analyses uncovered a low open probability for the wild-type complex, highlighting the tightly closed S6 gate in the structure, and providing a basis to interpret the altered gating properties of disease-causing variants. Key constraints between the UNC79-UNC80 subcomplex and the NALCN DI-DII and DII-DIII linkers were identified, leading to a model of channelosome gating. Our results provide a structural blueprint to understand the physiology of the NALCN channelosome and a template for drug discovery to modulate the resting membrane potential.

Differential gene expression analysis following olfactory learning in honeybee (Apis mellifera L.)

Insects change their stimulus-response through the perception of associating these stimuli with important survival events such as rewards, threats, and mates. Insects develop strong associations and relate them to their experiences through several behavioral procedures. Among the insects, Apis species, Apis mellifera ligustica are known for their outstanding ability to learn with tremendous economic importance. Apis mellifera ligustica has a strong cognitive ability and promising model species for investigating the neurobiological basis of remarkable olfactory learning abilities. Here we evaluated the olfactory learning ability of A. mellifera by using the proboscis extension reflex (PER) protocol. The brains of the learner and failed-learner bees were examined for comparative transcriptome analysis by RNA-Seq to explain the difference in the learning capacity. In this study, we used an appetitive olfactory learning paradigm in the same age of A. mellifera bees to examine the differential gene expression in the brain of the learner and failed-learner. Bees that respond in 2nd and 3rd trials or only responded to 3rd trials were defined as learned bees, failed-learner individuals were those bees that did not respond in all learning trials The results indicate that the learning ability of learner bees was significantly higher than failed-learner bees for 12 days. We obtained approximately 46.7 and 46.4 million clean reads from the learner bees failed-learner bees, respectively. Gene expression profile between learners' bees and failed-learners bees identified 74 differentially expressed genes, 57 genes up-regulated in the brains of learners and 17 genes were down-regulated in the brains of the bees that fail to learn. The qRT-PCR validated the differently expressed genes. Transcriptome analyses revealed that specific genes in learner and failed-learner bees either down-regulated or up-regulated play a crucial role in brain development and learning behavior. Our finding suggests that down-regulated genes of the brain involved in the integumentary system, storage proteins, brain development, sensory processing, and neurodegenerative disorder may result in reduced olfactory discrimination and olfactory sensitivity in failed-learner bees. This study aims to contribute to a better understanding of the olfactory learning behavior and gene expression information, which opens the door for understanding of the molecular mechanism of olfactory learning behavior in honeybees.

Case Report: Complete Maternal Uniparental Disomy of Chromosome 2 With a Novel UNC80 Splicing Variant c.5609-4G> A in a Chinese Patient With Infantile Hypotonia With Psychomotor Retardation and Characteristic Facies 2

Background: Infantile hypotonia with psychomotor retardation and characteristic facies 2 (IHPRF2) is a rare autosomal recessive neurodevelopmental disorder caused by mutations in the UNC80 gene. It is characterized by severe global developmental delay, poor or absent speech and absent or limited walking abilities. The current study explored a case of a Chinese patient with IHPRF2 caused by a novel splicing variant of UNC80.

Case Report: The proband is a 8-year-old Chinese male manifested with global developmental delay, severe truncal hypotonia, absent speech and intellectual disability. SNP array analysis revealed a uniparental isodisomy of the entire chromosome 2 [UPD(2)] in the proband. Whole exome sequencing (WES) subsequently identified a novel mutation c.5609-4G>A in the UNC80 gene, which was inherited from his mother and was confirmed by Sanger sequencing, indicating that UPD(2) was of maternal origin.

Conclusion: A novel UNC80 homozygous splicing variant c.5609-4G>A associated with maternal UPD(2) was identified. These findings indicate that UPD poses a high risk of autosomal recessive diseases, and provides information on the variant spectrum for UNC80. Our findings elucidate on understanding of the genotype-phenotype associations that occur in IHPRF2 patients.

Sodium background currents in endocrine/neuroendocrine cells: Towards unraveling channel identity and contribution in hormone secretion

In endocrine/neuroendocrine tissues, excitability of secretory cells is patterned by the repertoire of ion channels and there is clear evidence that extracellular sodium (Na⁺) ions contribute to hormone secretion. While voltage-gated channels involved in action potential generation are well-described, the background 'leak' channels operating near the resting membrane potential are much less known, and in particular the channels supporting a background entry of Na⁺ ions. These background Na⁺ currents (called here 'I_Nab') have the ability to modulate the resting membrane potential and subsequently affect action potential firing. Here we compile and analyze the data collected from three endocrine/neuroendocrine tissues: the anterior pituitary gland, the adrenal medulla and the endocrine pancreas. We also model how I_Nab can be functionally involved in cellular excitability. Finally, towards deciphering the physiological role of I_Nab in endocrine/neuroendocrine cells, its implication in hormone release is also discussed.

Maternal opioid use disorder: Placental transcriptome analysis for neonatal opioid withdrawal syndrome

Excessive prenatal opioid exposure may lead to the development of Neonatal Opioid Withdrawal Syndrome (NOWS). RNA-seq was done on 64 formalin-fixed paraffin-embedded placental tissue samples from 32 mothers with opioid use disorder, with newborns with NOWS that required treatment, and 32 prenatally unexposed controls. We identified 93 differentially expressed genes in the placentas of infants with NOWS compared to unexposed controls. There were 4 up- and 89 downregulated genes. Among these, 7 genes CYP1A1, APOB, RPH3A, NRXN1, LINC01206, AL157396.1, UNC80 achieved an FDR p-value of <0.01. The remaining 87 genes were significant with FDR p-value <0.05. The 4 upregulated, CYP1A1, FP671120.3, RAD1, RN7SL856P, and the 10 most significantly downregulated genes were RNA5SP364, GRIN2A, UNC5D, DMBT1P1, MIR3976HG, LINC02199, LINC02822, PANTR1, AC012178.1, CTNNA2. Ingenuity Pathway Analysis identified the 7 most likely to play an important role in the etiology of NOWS. Our study expands insights into the genetic mechanisms of NOWS development.

The sodium leak channel NALCN regulates cell excitability of pituitary endocrine cells

Anterior pituitary endocrine cells that release hormones such as growth hormone and prolactin are excitable and fire action potentials. In these cells, several studies previously showed that extracellular sodium (Na⁺ ) removal resulted in a negative shift of the resting membrane potential (RMP) and a subsequent inhibition of the spontaneous firing of action potentials, suggesting the contribution of a Na⁺ background conductance. Here, we show that the Na⁺ leak channel NALCN conducts a Ca²⁺ - Gd³⁺ -sensitive and TTX-resistant Na⁺ background conductance in the GH₃ cell line, a cell model of pituitary endocrine cells. NALCN knockdown hyperpolarized the RMP, altered GH₃ cell electrical properties and inhibited prolactin secretion. Conversely, the overexpression of NALCN depolarized the RMP, also reshaping the electrical properties of GH₃ cells. Overall, our results indicate that NALCN is functional in GH₃ cells and involved in endocrine cell excitability as well as in hormone secretion. Indeed, the GH₃ cell line suitably models native pituitary cells that display a similar Na⁺ background conductance and appears as a proper cellular model to study the role of NALCN in cellular excitability.

The gating pore blocker 1-(2,4-xylyl)guanidinium selectively inhibits pacemaking of midbrain dopaminergic neurons

Although several ionic mechanisms are known to control rate and regularity of the slow pacemaker in dopamine (DA) neurons, the core mechanism of pacing is controversial. Here we tested the hypothesis that pacemaking of SNc DA neurons is enabled by an unconventional conductance. We found that 1-(2,4-xylyl)guanidinium (XG), an established blocker of gating pore currents, selectively inhibits pacemaking of DA neurons. The compound inhibited all slow pacemaking DA neurons that were tested, both in the substantia nigra pars compacta, and in the ventral tegmental area. Interestingly, bursting behavior was not affected by XG. Furthermore, the drug did not affect fast pacemaking of GABAergic neurons from substantia nigra pars reticulata neurons or slow pacemaking of noradrenergic neurons. In DA neurons, current-clamp analysis revealed that XG did not appear to affect ion channels involved in the action potential. Its inhibitory effect persisted during blockade of all ion channels previously suggested to contribute to pacemaking. RNA sequencing and voltage-clamp recordings yielded no evidence for a gating pore current to underlie the conductance. However, we could isolate a small subthreshold XG-sensitive current, which was carried by both Na⁺ and Cl^- ions. Although the molecular target of XG remains to be defined, these observations represent a step towards understanding pacemaking in DA neurons.

Human CALHM5: Insight in large pore lipid gating ATP channel and associated neurological pathologies

Recently calcium homeostasis modulators (CALHMs) are identified as ATP release channels play crucial role in functioning of neurons including gustatory signaling and neuronal excitability. Pathologies of Alzheimer's disease and depression have been associated with the dysfunction of CALHMs. Recently, CALHMs has been emerged as an important therapeutic research particularly in neurobiological studies. CALHM1 is most extensively studied among CALHMs and is an ATP and ion channel that is activated by membrane depolarization or removal of extracellular Ca²⁺. Despite the emerged role of CALHM5 shown by an recently assembled data; however, the neuronal function remains obscure until the first Cryo-EM structure of CALHM5 was recently solved by various research group which acts as a template to study the hidden functional properties of the CALHM5 protein based on structure function mechanism. It provides insight in some of the different pathophysiological roles. CALHM5 structure showed an abnormally large pore channel structure assembled as an undecamer with four transmembrane helices (TM1-TM4), an N-terminal helix (NTH), an extracellular loop region and an intracellular C-terminal domain (CTD) that consists of three α-helices CH1-3. The TM1 and NTH were always poorly defined among all CALHMs; however, these regions were well defined in CALHM5 channel structure. In this context, this review will provide insight in structure, function and mechanism to understand its significant role in pathological diseases particularly in Alzheimer's disease. Moreover, it focuses on CALHM5 structure and recent associated properties based on Cryo-EM research.

Enhanced excitability of cortical neurons in low-divalent solutions is primarily mediated by altered voltage-dependence of voltage-gated sodium channels

Increasing extracellular [Ca2+] ([Ca2+]o) strongly decreases intrinsic excitability in neurons but the mechanism is unclear. By one hypothesis, [Ca2+]o screens surface charge, reducing voltage-gated sodium channel (VGSC) activation and by another [Ca2+]o activates Calcium-sensing receptor (CaSR) closing the sodium-leak channel (NALCN). Here we report that neocortical neurons from CaSR-deficient (Casr-/-) mice had more negative resting potentials and did not fire spontaneously in reduced divalent-containing solution (T0.2) in contrast with wild-type (WT). However, after setting membrane potential to −70 mV, T0.2 application similarly depolarized and increased action potential firing in Casr-/- and WT neurons. Enhanced activation of VGSCs was the dominant contributor to the depolarization and increase in excitability by T0.2 and occurred due to hyperpolarizing shifts in VGSC window currents. CaSR deletion depolarized VGSC window currents but did not affect NALCN activation. Regulation of VGSC gating by external divalents is the key mechanism mediating divalent-dependent changes in neocortical neuron excitability.

Recovery of Depleted miR-146a in ALS Cortical Astrocytes Reverts Cell Aberrancies and Prevents Paracrine Pathogenicity on Microglia and Motor Neurons

Reactive astrocytes in Amyotrophic Lateral Sclerosis (ALS) change their molecular expression pattern and release toxic factors that contribute to neurodegeneration and microglial activation. We and others identified a dysregulated inflammatory miRNA profile in ALS patients and in mice models suggesting that they represent potential targets for therapeutic intervention. Such cellular miRNAs are known to be released into the secretome and to be carried by small extracellular vesicles (sEVs), which may be harmful to recipient cells. Thus, ALS astrocyte secretome may disrupt cell homeostasis and impact on ALS pathogenesis. Previously, we identified a specific aberrant signature in the cortical brain of symptomatic SOD1-G93A (mSOD1) mice, as well as in astrocytes isolated from the same region of 7-day-old mSOD1 mice, with upregulated S100B/HMGB1/Cx43/vimentin and downregulated GFAP. The presence of downregulated miR-146a on both cases suggests that it can be a promising target for modulation in ALS. Here, we upregulated miR-146a with pre-miR-146a, and tested glycoursodeoxycholic acid (GUDCA) and dipeptidyl vinyl sulfone (VS) for their immunoregulatory properties. VS was more effective in restoring astrocytic miR-146a, GFAP, S100B, HMGB1, Cx43, and vimentin levels than GUDCA, which only recovered Cx43 and vimentin mRNA. The miR-146a inhibitor generated typical ALS aberrancies in wild type astrocytes that were abolished by VS. Similarly, pre-miR-146a transfection into the mSOD1 astrocytes abrogated aberrant markers and intracellular Ca²⁺ overload. Such treatment counteracted miR-146a depletion in sEVs and led to secretome-mediated miR-146a enhancement in NSC-34-motor neurons (MNs) and N9-microglia. Secretome from mSOD1 astrocytes increased early/late apoptosis and FGFR3 mRNA in MNs and microglia, but not when derived from pre-miR-146a or VS-treated cells. These last strategies prevented the impairment of axonal transport and synaptic dynamics by the pathological secretome, while also averted microglia activation through either secretome, or their isolated sEVs. Proteomic analysis of the target cells indicated that pre-miR-146a regulates mitochondria and inflammation via paracrine signaling. We demonstrate that replenishment of miR-146a in mSOD1 cortical astrocytes with pre-miR-146a or by VS abrogates their phenotypic aberrancies and paracrine deleterious consequences to MNs and microglia. These results propose miR-146a as a new causal and emerging therapeutic target for astrocyte pathogenic processes in ALS.

Anti-Aβ-scFv-loaded polymeric nano-micelles with enhanced plasma stability

OBJECTIVES

Immunotherapy using recombinant monoclonal antibodies specifically Anti-amyloid-beta (Anti-Aβ) scFv is envisaged as an appropriate therapeutic for Alzheimer through reduction of amyloid-beta aggregation. The solubilization of therapeutics using polymeric micelles facilitates an improved bioavailability and extended blood half-life. In this study, the optimum production condition for Anti-amyloid-beta (Anti-Aβ) scFv was obtained. To increase the stability of plasma, Anti-Aβ-loaded polymeric micelles were synthesized.

METHODS

Escherichia coli SHuffle expression strain was used and purified by Ni-NTA. Pluronics P85 and F127 micelles were used for the Anti-Aβ delivery and were characterized in terms of morphology, drug loading and drug release in phosphate buffer and artificial cerebrospinal fluid. The stability profile was quantified at 4°C over a 30 days storage period. The stability in human plasma was also evaluated.

KEY FINDINGS

Proteins expressed in SHuffle resulted in increased levels of protein expression and solubility. Low critical micelle concentration value and high micelle encapsulation efficiency (<200 nm) achieved via direct dissolution method. Anti-Aβ-loaded micelles were around 2.2-fold more stable than Anti-Aβ in plasma solution. A sustained in-vitro release of Anti-Aβ from micelles was observed.

CONCLUSIONS

Results confirmed that Pluronic-micelles pose benefits as a nano-carrier to increase the stability of Anti-Aβ scFvin in the plasma.

A growth-factor-activated lysosomal K+ channel regulates Parkinson's pathology

Lysosomes have fundamental physiological roles and have previously been implicated in Parkinson's disease^1-5. However, how extracellular growth factors communicate with intracellular organelles to control lysosomal function is not well understood. Here we report a lysosomal K⁺ channel complex that is activated by growth factors and gated by protein kinase B (AKT) that we term lysoK_GF. LysoK_GF consists of a pore-forming protein TMEM175 and AKT: TMEM175 is opened by conformational changes in, but not the catalytic activity of, AKT. The minor allele at rs34311866, a common variant in TMEM175, is associated with an increased risk of developing Parkinson's disease and reduces channel currents. Reduction in lysoK_GF function predisposes neurons to stress-induced damage and accelerates the accumulation of pathological α-synuclein. By contrast, the minor allele at rs3488217-another common variant of TMEM175, which is associated with a decreased risk of developing Parkinson's disease-produces a gain-of-function in lysoK_GF during cell starvation, and enables neuronal resistance to damage. Deficiency in TMEM175 leads to a loss of dopaminergic neurons and impairment in motor function in mice, and a TMEM175 loss-of-function variant is nominally associated with accelerated rates of cognitive and motor decline in humans with Parkinson's disease. Together, our studies uncover a pathway by which extracellular growth factors regulate intracellular organelle function, and establish a targetable mechanism by which common variants of TMEM175 confer risk for Parkinson's disease.

Structure of the human sodium leak channel NALCN in complex with FAM155A

NALCN, a sodium leak channel expressed mainly in the central nervous system, is responsible for the resting Na+ permeability that controls neuronal excitability. Dysfunctions of the NALCN channelosome, NALCN with several auxiliary subunits, are associated with a variety of human diseases. Here, we report the cryo-EM structure of human NALCN in complex with FAM155A at an overall resolution of 3.1 angstroms. FAM155A forms extensive interactions with the extracellular loops of NALCN that may help stabilize NALCN in the membrane. A Na+ ion-binding site, reminiscent of a Ca2+ binding site in Cav channels, is identified in the unique EEKE selectivity filter. Despite its 'leaky' nature, the channel is closed and the intracellular gate is sealed by S6I, II-III linker and III-IV linker. Our study establishes the molecular basis of Na+ permeation and voltage sensitivity, and provides important clues to the mechanistic understanding of NALCN regulation and NALCN channelosome-related diseases.

A Homozygous Truncating Mutation in NALCN Causing IHPRF1: Detailed Clinical Manifestations and a Review of Literature

Infantile hypotonia, with psychomotor retardation and characteristic facies 1 (IHPRF1), is a rare disorder characterized by global developmental delay and dysmorphic features. This syndrome is caused by genetic anomalies within the NALCN gene. The current report examines a 9-year-old female IHPRF1 patient. Our objective was to contribute to the delineation of the underlying factors influencing this rare condition. Whole exome sequencing (WES) was utilized to identify the disease-causing mutation in the affected individual. Subsequently, Sanger sequencing was performed for the patient, her parents, and two close relatives in order to confirm the detected mutation. Moreover, detailed clinical examinations including EEG, echocardiography, and biochemical/physical tests were carried out to elucidate the effects of the mutation. WES identified a homozygous nonsense mutation in the NALCN gene (c.2563C>T p.R855X). This mutation was confirmed by Sanger sequencing in the patient and her family members and segregated with the autosomal recessive inheritance pattern of IHPRF1. Moreover, genotype-phenotype correlation analysis confirmed the disease-causing nature of this mutation. The current report provides the first detailed description of a patient with this homozygous nonsense mutation (c.2563C>T p.R855X) and expands the clinical spectrum of IHPRF1 disease. Possible influences of sex and other factors on this disease are discussed and a review of the literature is also provided.