Role of voltage-gated L-type Ca2+ channel isoforms for brain function

Selective dopaminergic neurotoxicity modulated by inherent cell-type specific neurobiology

Parkinson's disease (PD) is a debilitating neurodegenerative disease affecting millions of individuals worldwide. Hallmark features of PD pathology are the formation of Lewy bodies in neuromelanin-containing dopaminergic (DAergic) neurons of the substantia nigra pars compacta (SNpc), and the subsequent irreversible death of these neurons. Although genetic risk factors have been identified, around 90 % of PD cases are sporadic and likely caused by environmental exposures and gene-environment interaction. Mechanistic studies have identified a variety of chemical PD risk factors. PD neuropathology occurs throughout the brain and peripheral nervous system, but it is the loss of DAergic neurons in the SNpc that produce many of the cardinal motor symptoms. Toxicology studies have found specifically the DAergic neuron population of the SNpc exhibit heightened sensitivity to highly variable chemical insults (both in terms of chemical structure and mechanism of neurotoxic action). Thus, it has become clear that the inherent neurobiology of nigral DAergic neurons likely underlies much of this neurotoxic response to broad insults. This review focuses on inherent neurobiology of nigral DAergic neurons and how such neurobiology impacts the primary mechanism of neurotoxicity. While interactions with a variety of other cell types are important in disease pathogenesis, understanding how inherent DAergic biology contributes to selective sensitivity and primary mechanisms of neurotoxicity is critical to advancing the field. Specifically, key biological features of DAergic neurons that increase neurotoxicant susceptibility.

Effects of L-Type Voltage-Gated Calcium Channel (LTCC) Inhibition on Hippocampal Neuronal Death after Pilocarpine-Induced Seizure

Epilepsy, marked by abnormal and excessive brain neuronal activity, is linked to the activation of L-type voltage-gated calcium channels (LTCCs) in neuronal membranes. LTCCs facilitate the entry of calcium (Ca2+) and other metal ions, such as zinc (Zn2+) and magnesium (Mg2+), into the cytosol. This Ca2+ influx at the presynaptic terminal triggers the release of Zn2+ and glutamate to the postsynaptic terminal. Zn2+ is then transported to the postsynaptic neuron via LTCCs. The resulting Zn2+ accumulation in neurons significantly increases the expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunits, contributing to reactive oxygen species (ROS) generation and neuronal death. Amlodipine (AML), typically used for hypertension and coronary artery disease, works by inhibiting LTCCs. We explored whether AML could mitigate Zn2+ translocation and accumulation in neurons, potentially offering protection against seizure-induced hippocampal neuronal death. We tested this by establishing a rat epilepsy model with pilocarpine and administering AML (10 mg/kg, orally, daily for 7 days) post-epilepsy onset. We assessed cognitive function through behavioral tests and conducted histological analyses for Zn2+ accumulation, oxidative stress, and neuronal death. Our findings show that AML's LTCC inhibition decreased excessive Zn2+ accumulation, reactive oxygen species (ROS) production, and hippocampal neuronal death following seizures. These results suggest amlodipine's potential as a therapeutic agent in seizure management and mitigating seizures' detrimental effects.

Inhibition of ferroptosis through regulating neuronal calcium homeostasis: An emerging therapeutic target for Alzheimer's disease

Alzheimer's disease (AD), a chronic and progressive neurodegenerative disease, generates a serious threat to the health of the elderly. The AD brain is microscopically characterized by amyloid plaques and neurofibrillary tangles. There are still no effective therapeutic drugs to restrain the progression of AD though much attention has been paid to exploit AD treatments. Ferroptosis, a type of programmed cell death, has been reported to promote the pathological occurrence and development of AD, and inhibition of neuronal ferroptosis can effectively improve the cognitive impairment of AD. Studies have shown that calcium (Ca²⁺) dyshomeostasis is closely related to the pathology of AD, and can drive the occurrence of ferroptosis through several pathways, such as interacting with iron, and regulating the crosstalk between endoplasmic reticulum (ER) and mitochondria. This paper mainly reviews the roles of ferroptosis and Ca²⁺ in the pathology of AD, and highlights that restraining ferroptosis through maintaining the homeostasis of Ca²⁺ may be an innovative target for the treatment of AD.

[Nimodipine in treatment of bipolar disorder]

The purpose of this review is to correlate current data on the molecular mechanisms of action of the drug Nimodipine with its clinical effects and applicability in mental disorders belonging to the spectrum of affective pathology. The article discusses the prospects for using the calcium channel blocker nimodipine as a method of both mono and combination therapy for bipolar disorders with various types of course. Nimodipine is a selective blocker of voltage-dependent calcium channels, a dihydropyridine derivative. By blocking L type calcium channels, it prevents the entry of calcium ions into the cell. Due to its pronounced ability to penetrate the blood-brain barrier, it has a selective effect on brain neurons and has a vasodilating, antihypertensive and normotimic effect. Nimodipine blocks LTCC channels in brain neurons, thereby influencing synaptic plasticity, transmitter release and excitation-transcription coupling, which makes it possible to influence various clinical conditions with pathology in the area of affect, including bipolar disorders with ultra-rapid cycling, and also, in cases with high resistance and intolerance to other mood stabilizers.

The Role of Voltage-Gated Calcium Channels in Basal Ganglia Neurodegenerative Disorders

Calcium (Ca2+) plays a central role in regulating many cellular processes and influences cell survival. Several mechanisms can disrupt Ca2+ homeostasis to trigger cell death, including oxidative stress, mitochondrial damage, excitotoxicity, neuroinflammation, autophagy, and apoptosis. Voltage-gated Ca2+ channels (VGCCs) act as the main source of Ca2+ entry into electrically excitable cells, such as neurons, and they are also expressed in glial cells such as astrocytes and oligodendrocytes. The dysregulation of VGCC activity has been reported in both Parkinson's disease (PD) and Huntington's (HD). PD and HD are progressive neurodegenerative disorders (NDs) of the basal ganglia characterized by motor impairment as well as cognitive and psychiatric dysfunctions. This review will examine the putative role of neuronal VGCCs in the pathogenesis and treatment of central movement disorders, focusing on PD and HD. The link between basal ganglia disorders and VGCC physiology will provide a framework for understanding the neurodegenerative processes that occur in PD and HD, as well as a possible path towards identifying new therapeutic targets for the treatment of these debilitating disorders.

The Role of Striatal Cav1.3 Calcium Channels in Therapeutics for Parkinson's Disease

Parkinson's disease (PD) is a relentlessly progressive neurodegenerative disorder with typical motor symptoms that include rigidity, tremor, and akinesia/bradykinesia, in addition to a host of non-motor symptoms. Motor symptoms are caused by progressive and selective degeneration of dopamine (DA) neurons in the SN pars compacta (SNpc) and the accompanying loss of striatal DA innervation from these neurons. With the exception of monogenic forms of PD, the etiology of idiopathic PD remains unknown. While there are a number of symptomatic treatment options available to individuals with PD, these therapies do not work uniformly well in all patients, and eventually most are plagued with waning efficacy and significant side-effect liability with disease progression. The incidence of PD increases with aging, and as such the expected burden of this disease will continue to escalate as our aging population increases (Dorsey et al. Neurology 68:384-386, 2007). The daunting personal and socioeconomic burden has pressed scientists and clinicians to find improved symptomatic treatment options devoid side-effect liability and meaningful disease-modifying therapies. Federal and private sources have supported clinical investigations over the past two-plus decades; however, no trial has yet been successful in finding an effective therapy to slow progression of PD, and there is currently just one FDA approved drug to treat the antiparkinsonian side-effect known as levodopa-induced dyskinesia (LID) that impacts approximately 90% of all individuals with PD. In this review, we present biological rationale and experimental evidence on the potential therapeutic role of the L-type voltage-gated Cav1.3 calcium (Ca2+) channels in two distinct brain regions, with two distinct mechanisms of action, in impacting the lives of individuals with PD. Our primary emphasis will be on the role of Cav1.3 channels in the striatum and the compelling evidence of their involvement in LID side-effect liability. We also briefly discuss the role of these same Ca2+ channels in the SNpc and the longstanding interest in Cav1.3 in this brain region in halting or delaying progression of PD.

Neuroprotective effects of aripiprazole in stress-induced depressive-like behavior: Possible role of CACNA1C

BACKGROUND

Depression is the most common psychiatric disorder. Recently, aripiprazole, a novel antipsychotic drug, has been approved as the adjunctive therapy for the Treatment-Resistant Depression (TRD). However, the mechanisms underlying the antidepressant effects of aripiprazole are not fully known. Besides the involvement of calcium signaling dysregulations in the pathophysiology of depression, there is some evidence of overexpressed CACNA1C (the gene encoding the Cav1.2 channels) following chronic stress in the brain regions, which involved in emotional and stress responses. Based on the data indicating the aripiprazole's effects on intracellular calcium levels, this study aimed to investigate the mechanisms of therapeutic effects of aripiprazole, by a focus on the modulation of CACNA1C expression, in the rat stress-induced model of depression.

METHODS

Using Chronic Unpredictable Mild Stress (CUMS) model of depression, we examined the effects of aripiprazole on depressive and anxiety-like behaviors (by forced swimming test and elevated plus maze), serum IL-6 (Elisa), and cell survival (Nissl staining). In addition, CACNA1C, BDNF, and TrkB expression in the PFC and hippocampus (RT-qPCR), as well as BDNF and GAP-43 protein levels in the hippocampus (Immunohistofluorescence), have been assayed.

RESULTS

Our data indicated that aripiprazole could improve anxiety and depressive-like behaviors, decrease the serum levels of IL-6 and hippocampal cell death following CUMS. In addition, we showed the significant modulation on overexpressed CACNA1C, as well as downregulated BDNF and GAP-43 expression DISCUSSION: These results demonstrate that aripiprazole may promote synaptic plasticity by improving the expression of BDNF and gap-43. In addition, inflammation reduction and CACNA1C expression downregulation may be some of mechanisms by which aripiprazole alleviates chronic stress-induced hippocampal cell death and play its pivotal antidepressant role.

Cav1.3 calcium channels are full-range linear amplifiers of firing frequencies in lateral DA SN neurons

The low-threshold L-type calcium channel Cav1.3 accelerates the pacemaker rate in the heart, but its functional role for the extended dynamic range of neuronal firing is still unresolved. Here, we show that Cav1.3 calcium channels act as unexpectedly simple, full-range linear amplifiers of firing rates for lateral dopamine substantia nigra (DA SN) neurons in mice. This means that they boost in vitro or in vivo firing frequencies between 2 and 50 hertz by about 30%. Furthermore, we demonstrate that clinically relevant, low nanomolar concentrations of the L-type channel inhibitor isradipine selectively reduce the in vivo firing activity of these nigrostriatal DA SN neurons at therapeutic plasma concentrations. Thus, our study identifies the pacemaker function of neuronal Cav1.3 channels and provides direct evidence that repurposing dihydropyridines such as isradipine is feasible to selectively modulate the in vivo activity of highly vulnerable DA SN subpopulations in Parkinson's disease.

Potential role of IP3/Ca2+ signaling and phosphodiesterases: Relevance to neurodegeneration in Alzheimer's disease and possible therapeutic strategies

Despite large investments by industry and governments, no disease-modifying medications for the treatment of patients with Alzheimer's disease (AD) have been found. The failures of various clinical trials indicate the need for a more in-depth understanding of the pathophysiology of AD and for innovative therapeutic strategies for its treatment. Here, we review the rational for targeting IP3 signaling, cytosolic calcium dysregulation, phosphodiesterases (PDEs), and secondary messengers like cGMP and cAMP, as well as their correlations with the pathophysiology of AD. Various drugs targeting these signaling cascades are still in pre-clinical and clinical trials which support the ideas presented in this article. Further, we describe different molecular mechanisms and medications currently being used in various pre-clinical and clinical trials involving IP3/Ca⁺² signaling. We also highlight various isoforms, as well as the functions and pharmacology of the PDEs broadly expressed in different parts of the brain and attempt to unravel the potential benefits of PDE inhibitors for use as novel medications to alleviate the pathogenesis of AD.

Mechanisms and Physiological Implications of Cooperative Gating of Ion Channels Clusters

Ion channels play a central role in the regulation of nearly every cellular process. Dating back to the classic 1952 Hodgkin-Huxley model of the generation of the action potential, ion channels have always been thought of as independent agents. A myriad of recent experimental findings exploiting advances in electrophysiology, structural biology, and imaging techniques, however, have posed a serious challenge to this long-held axiom as several classes of ion channels appear to open and close in a coordinated, cooperative manner. Ion channel cooperativity ranges from variable-sized oligomeric cooperative gating in voltage-gated, dihydropyridine-sensitive Ca_v1.2 and Ca_v1.3 channels to obligatory dimeric assembly and gating of voltage-gated Na_v1.5 channels. Potassium channels, transient receptor potential channels, hyperpolarization cyclic nucleotide-activated channels, ryanodine receptors (RyRs), and inositol trisphosphate receptors (IP₃Rs) have also been shown to gate cooperatively. The implications of cooperative gating of these ion channels range from fine tuning excitation-contraction coupling in muscle cells to regulating cardiac function and vascular tone, to modulation of action potential and conduction velocity in neurons and cardiac cells, and to control of pace-making activity in the heart. In this review, we discuss the mechanisms leading to cooperative gating of ion channels, their physiological consequences and how alterations in cooperative gating of ion channels may induce a range of clinically significant pathologies.

Ca2+ administration prevents α-synuclein proteotoxicity by stimulating calcineurin-dependent lysosomal proteolysis

The capacity of a cell to maintain proteostasis progressively declines during aging. Virtually all age-associated neurodegenerative disorders associated with aggregation of neurotoxic proteins are linked to defects in the cellular proteostasis network, including insufficient lysosomal hydrolysis. Here, we report that proteotoxicity in yeast and Drosophila models for Parkinson's disease can be prevented by increasing the bioavailability of Ca2+, which adjusts intracellular Ca2+ handling and boosts lysosomal proteolysis. Heterologous expression of human α-synuclein (αSyn), a protein critically linked to Parkinson's disease, selectively increases total cellular Ca2+ content, while the levels of manganese and iron remain unchanged. Disrupted Ca2+ homeostasis results in inhibition of the lysosomal protease cathepsin D and triggers premature cellular and organismal death. External administration of Ca2+ reduces αSyn oligomerization, stimulates cathepsin D activity and in consequence restores survival, which critically depends on the Ca2+/calmodulin-dependent phosphatase calcineurin. In flies, increasing the availability of Ca2+ discloses a neuroprotective role of αSyn upon manganese overload. In sum, we establish a molecular interplay between cathepsin D and calcineurin that can be activated by Ca2+ administration to counteract αSyn proteotoxicity.

Contributions of CaV1.3 Channels to Ca2+ Current and Ca2+-Activated BK Current in the Suprachiasmatic Nucleus

Daily regulation of Ca²⁺– and voltage-activated BK K⁺ channel activity is required for action potential rhythmicity in the suprachiasmatic nucleus (SCN) of the hypothalamus, the brain's circadian clock. In SCN neurons, BK activation is dependent upon multiple types of Ca²⁺ channels in a circadian manner. Daytime BK current predominantly requires Ca²⁺ influx through L-type Ca²⁺ channels (LTCCs), a time when BK channels are closely coupled with their Ca²⁺ source. Here we show that daytime BK current is resistant to the Ca²⁺ chelator BAPTA. However, at night when LTCCs contribute little to BK activation, BK current decreases by a third in BAPTA compared to control EGTA conditions. In phase with this time-of-day specific effect on BK current activation, LTCC current is larger during the day. The specific Ca²⁺ channel subtypes underlying the LTCC current in SCN, as well as the subtypes contributing the Ca²⁺ influx relevant for BK current activation, have not been identified. SCN neurons express two LTCC subtypes, Ca_V1.2 and Ca_V1.3. While a role for Ca_V1.2 channels has been identified during the night, Ca_V1.3 channel modulation has also been suggested to contribute to daytime SCN action potential activity, as well as subthreshold Ca²⁺ oscillations. Here we characterize the role of Ca_V1.3 channels in LTCC and BK current activation in SCN neurons using a global deletion of CACNA1D in mouse (Ca_V1.3 KO). Ca_V1.3 KO SCN neurons had a 50% reduction in the daytime LTCC current, but not total Ca²⁺ current, with no difference in Ca²⁺ current levels at night. During the day, Ca_V1.3 KO neurons exhibited oscillations in membrane potential, and most neurons, although not all, also had BK currents. Changes in BK current activation were only detectable at the highest voltage tested. These data show that while Ca_V1.3 channels contribute to the daytime Ca²⁺ current, this does not translate into a major effect on the daytime BK current. These data suggest that BK current activation does not absolutely require Ca_V1.3 channels and may therefore also depend on other LTCC subtypes, such as Ca_V1.2.

Reflex memory theory of acquired involuntary motor and sensory disorders

Background

Explicit and implicit memories are conserved but flexible biological tools that nature uses to regulate the daily behaviors of human beings. An aberrant form of the implicit memory is presumed to exist and may be contributory to the pathophysiology of disorders such as tardive syndromes, phantom phenomena, flashback, posttraumatic stress disorders (PTSD), and related disorders. These disorders have posed significant clinical problems for both patients and physicians for centuries. All extant pathophysiological theories of these disorders have failed to provide basis for effective treatment.

Objective

The objective of this article is to propose an alternative pathophysiological theory that will hopefully lead to new treatment approaches.

Methods

The author sourced over 60 journal articles that treated topics on memory, and involuntary motor and sensory disorders, from open access journals using Google Scholar, and reviewed them and this helped in the formulation of this theory.

Results

From the reviews, the author thinks physical or chemical insult to the nervous system can cause defective circuit remodeling, leading to generation of a variant of implicit (automatic) memory, herein called “reflex memory” and this is encoded interoceptively to contribute to these phenomena states.

Conclusion

Acquired involuntary motor and sensory disorders are caused by defective circuit remodeling involving multiple neural mechanisms. Dysregulation of excitatory neurotransmitters, calcium overload, homeostatic failure, and neurotoxicity are implicated in the process. Sustained effects of these defective mechanisms are encoded interoceptively as abnormal memory in the neurons and the conscious manifestations are these disorders. Extant theories failed to recognize this possibility.

The Involvement of CaV1.3 Channels in Prolonged Root Reflexes and Its Potential as a Therapeutic Target in Spinal Cord Injury

Spinal cord injury (SCI) results in not only the loss of voluntary muscle control, but also in the presence of involuntary movement or spasms. These spasms post-SCI involve hyperexcitability in the spinal motor system. Hyperactive motor commands post SCI result from enhanced excitatory postsynaptic potentials (EPSPs) and persistent inward currents in voltage-gated L-type calcium channels (LTCCs), which are reflected in evoked root reflexes with different timings. To further understand the contributions of these cellular mechanisms and to explore the involvement of LTCC subtypes in SCI-induced hyperexcitability, we measured root reflexes with ventral root recordings and motoneuron activities with intracellular recordings in an in vitro preparation using a mouse model of chronic SCI (cSCI). Specifically, we explored the effects of 1-(3-chlorophenethyl)-3-cyclopentylpyrimidine-2,4,6-(1H,3H,5H)-trione (CPT), a selective negative allosteric modulator of Ca_V1.3 LTCCs. Our results suggest a hyperexcitability in the spinal motor system in these SCI mice. Bath application of CPT displayed slow onset but dose-dependent inhibition of the root reflexes with the strongest effect on LLRs. However, the inhibitory effect of CPT is less potent in cSCI mice than in acute SCI (aSCI) mice, suggesting changes either in composition of Ca_V1.3 or other cellular mechanisms in cSCI mice. For intracellular recordings, the intrinsic plateau potentials, was observed in more motoneurons in cSCI mice than in aSCI mice. CPT inhibited the plateau potentials and reduced motoneuron firings evoked by intracellular current injection. These results suggest that the LLR is an important target and that CPT has potential in the therapy of SCI-induced muscle spasms.

Zika E Glycan Loop Region and Guillain-Barré Syndrome-Related Proteins: A Possible Molecular Mimicry to Be Taken in Account for Vaccine Development

The neurological complications of infection by the mosquito-borne Zika virus (ZIKV) include Guillain-Barré syndrome (GBS), an acute inflammatory demyelinating polyneuritis. GBS was first associated with recent ZIKV epidemics caused by the emergence of the ZIKV Asian lineage in South Pacific. Here, we hypothesize that ZIKV-associated GBS relates to a molecular mimicry between viral envelope E (E) protein and neural proteins involved in GBS. The analysis of the ZIKV epidemic strains showed that the glycan loop (GL) region of the E protein includes an IVNDT motif which is conserved in voltage-dependent L-type calcium channel subunit alpha-1C (Cav1.2) and Heat Shock 70 kDa protein 12A (HSP70 12A). Both VSCC-alpha 1C and HSP70 12A belong to protein families which have been associated with neurological autoimmune diseases in central nervous system. The purpose of our in silico analysis is to point out that IVNDT motif of ZIKV E-GL region should be taken in consideration for the development of safe and effective anti-Zika vaccines by precluding the possibility of adverse neurologic events including autoimmune diseases such as GBS through a potent mimicry with Heat Shock 70 kDa protein 12A (HSP70 12A).

The molecular basis of the inhibition of CaV1 calcium-dependent inactivation by the distal carboxy tail

Ca2+/calmodulin-dependent inactivation (CDI) of CaV channels is a critical regulatory process that tunes the kinetics of Ca2+ entry for different cell types and physiologic responses. CDI is mediated by calmodulin (CaM), which is bound to the IQ domain of the CaV carboxy tail. This modulatory process is tailored by alternative splicing such that select splice variants of CaV1.3 and CaV1.4 contain a long distal carboxy tail (DCT). The DCT harbors an inhibitor of CDI (ICDI) module that competitively displaces CaM from the IQ domain, thereby diminishing CDI. While this overall mechanism is now well described, the detailed interactions required for ICDI binding to the IQ domain are yet to be elucidated. Here, we perform alanine-scanning mutagenesis of the IQ and ICDI domains and evaluate the contribution of neighboring regions to CDI inhibition. Through FRET binding analysis, we identify functionally relevant residues within the CaV1.3 IQ domain and the CaV1.4 ICDI and nearby A region, which are required for high-affinity IQ/ICDI binding. Importantly, patch-clamp recordings demonstrate that disruption of this interaction commensurately diminishes ICDI function resulting in the re-emergence of CDI in mutant channels. Furthermore, CaV1.2 channels harbor a homologous DCT; however, the ICDI region of this channel does not appear to appreciably modulate CaV1.2 CDI. Yet coexpression of CaV1.2 ICDI with select CaV1.3 splice variants significantly disrupts CDI, implicating a cross-channel modulatory scheme in cells expressing both channel subtypes. In all, these findings provide new insights into a molecular rheostat that fine-tunes Ca2+-entry and supports normal neuronal and cardiac function.

Cerebellar developmental deficits underlie neurodegenerative disorder spinocerebellar ataxia type 23

Spinocerebellar ataxia type 23 (SCA23) is a late‐onset neurodegenerative disorder characterized by slowly progressive gait and limb ataxia, for which there is no therapy available. It is caused by pathogenic variants in PDYN, which encodes prodynorphin (PDYN). PDYN is processed into the opioid peptides α‐neoendorphin and dynorphins (Dyn) A and B; inhibitory neurotransmitters that function in pain signaling, stress‐induced responses and addiction. Variants causing SCA23 mostly affect Dyn A, leading to loss of secondary structure and increased peptide stability. PDYN^R212W mice express human PDYN containing the SCA23 variant p.R212W. These mice show progressive motor deficits from 3 months of age, climbing fiber (CF) deficits from 3 months of age, and Purkinje cell (PC) loss from 12 months of age. A mouse model for SCA1 showed similar CF deficits, and a recent study found additional developmental abnormalities, namely increased GABAergic interneuron connectivity and non‐cell autonomous disruption of PC function. As SCA23 mice show a similar pathology to SCA1 mice in adulthood, we hypothesized that SCA23 may also follow SCA1 pathology during development. Examining PDYN^R212W cerebella during development, we uncovered developmental deficits from 2 weeks of age, namely a reduced number of GABAergic synapses on PC soma, possibly leading to the observed delay in early phase CF elimination between 2 and 3 weeks of age. Furthermore, CFs did not reach terminal height, leaving proximal PC dendrites open to be occupied by parallel fibers (PFs). The observed increase in vGlut1 protein—a marker for PF‐PC synapses—indicates that PFs indeed take over CF territory and have increased connectivity with PCs. Additionally, we detected altered expression of several critical Ca²⁺ channel subunits, potentially contributing to altered Ca²⁺ transients in PDYN^R212W cerebella. These findings indicate that developmental abnormalities contribute to the SCA23 pathology and uncover a developmental role for PDYN in the cerebellum.

A Single Amino Acid Determines the Selectivity and Efficacy of Selective Negative Allosteric Modulators of CaV1.3 L-Type Calcium Channels

Ca²⁺ channels with a Ca_V1.3 pore-forming α₁ subunit have been implicated in both neurodegenerative and neuropsychiatric disorders, motivating the development of selective and potent inhibitors of Ca_V1.3 versus Ca_V1.2 channels, the calcium channels implicated in hypertensive disorders. We have previously identified pyrimidine-2,4,6-triones (PYTs) that preferentially inhibit Ca_V1.3 channels, but the structural determinants of their interaction with the channel have not been identified, impeding their development into drugs. By a combination of biochemical, computational, and molecular biological approaches, it was found that PYTs bind to the dihydropyridine (DHP) binding pocket of the Ca_V1.3 subunit, establishing them as negative allosteric modulators of channel gating. Site-directed mutagenesis, based on homology models of Ca_V1.3 and Ca_V1.2 channels, revealed that a single amino acid residue within the DHP binding pocket (M1078) is responsible for the selectivity of PYTs for Ca_V1.3 over Ca_V1.2. In addition to providing direction for chemical optimization, these results suggest that, like dihydropyridines, PYTs have pharmacological features that could make them of broad clinical utility.

Association of the CACNA2D2 gene with schizophrenia in Chinese Han population

Background

Schizophrenia (SCZ) is a severely complex psychiatric disorder in which ~80% can be explained by genetic factors. Single nucleotide polymorphisms (SNPs) in calcium channel genes are potential genetic risk factors for a spectrum of psychiatric disorders including SCZ. This study evaluated the association between SNPs in the voltage-gated calcium channel auxiliary subunit alpha2delta 2 gene (CACNA2D2) and SCZ in the Han Chinese population of Northeast China.

Methods

A total of 761 SCZ patients and 775 healthy controls were involved in this case-control study. Three SNPs (rs3806706, rs45536634 and rs12496815) of CACNA2D2 were genotyped by the MALDI-TOF-MS technology. Genotype distribution and allele frequency differences between cases and controls were tested by Chi-square (χ²) in males and females respectively using SPSS 24.0 software. Linkage disequilibrium and haplotype analyses were conducted using Haploview4.2. The false discovery rate correction was utilized to control for Type I error by R3.2.3.

Results

There was a significant difference in allele frequencies (χ² = 9.545, P_adj = 0.006) and genotype distributions (χ² = 9.275, P_adj = 0.006) of rs45536634 between female SCZ patients and female healthy controls after adjusting for multiple comparisons. Minor allele A (OR = 1.871, 95% CI [1.251–2.798]) and genotype GA + AA (OR = 1.931, 95% CI [1.259–2.963]) were associated with an increased risk of SCZ. Subjects with haplotype AG consisting of rs45536634 and rs12496815 alleles had a higher risk of SCZ (OR = 1.91, 95% CI [1.26–2.90]) compared those with other haplotypes.

Conclusions

This study provides evidence that CACNA2D2 polymorphisms may influence the susceptibility to SCZ in Han Chinese women.

Influence of magnesium supplementation and L-type calcium channel blocker on haloperidol-induced movement disturbances

Haloperidol (Hal) is an antipsychotic related to movement disorders. Magnesium (Mg) showed benefits on orofacial dyskinesia (OD), suggesting its involvement with N-methyl-D-aspartate receptors (NMDAR) since it acts blocking calcium channels. Comparisons between nifedipine (NIF; a calcium channel blocker) and Mg were performed to establish the Mg mechanism. Male rats concomitantly received Hal and Mg or NIF for 28 days, and OD behaviors were weekly assessed. Both Mg and NIF decreased Hal-induced OD. Hal increased Ca²⁺-ATPase activity in the striatum, and Mg reversed it. In the cortex, both Mg and NIF decreased such activity. Dopaminergic and glutamatergic immunoreactivity were modified by Hal and treatments: i) in the cortex: Hal reduced D1R and D2R, increasing NMDAR immunoreactivity. Mg and NIF reversed this Hal influence on D1R and NMDAR, while only Mg reversed Hal effects on D2R levels; ii) in the striatum: Hal decreased D2R and increased NMDAR while Mg and NIF decreased D1R and reversed the Hal-induced decreasing D2R levels. Only Mg reversed the Hal-induced increasing NMDAR levels; iii) in the substantia nigra (SN): while Hal increased D1R, D2R, and NMDAR, both Mg and NIF reversed this influence on D2R, but only Mg reversed the Hal-influence on D1R levels. Only NIF reversed the Hal effects on NMDAR immunoreactivity. These findings allow us to propose that Mg may be useful to minimize Hal-induced movement disturbances. Mg molecular mechanism seems to be involved with a calcium channel blocker because the NIF group showed less expressive effects than the Mg group.

The voltage-gated calcium channel CaV1.2 promotes adult oligodendrocyte progenitor cell survival in the mouse corpus callosum but not motor cortex

Throughout life, oligodendrocyte progenitor cells (OPCs) proliferate and differentiate into myelinating oligodendrocytes. OPCs express cell surface receptors and channels that allow them to detect and respond to neuronal activity, including voltage‐gated calcium channel (VGCC)s. The major L‐type VGCC expressed by developmental OPCs, CaV1.2, regulates their differentiation. However, it is unclear whether CaV1.2 similarly influences OPC behavior in the healthy adult central nervous system (CNS). To examine the role of CaV1.2 in adulthood, we conditionally deleted this channel from OPCs by administering tamoxifen to P60 Cacna1c^fl/fl (control) and Pdgfrα‐CreER:: Cacna1c^fl/fl (CaV1.2‐deleted) mice. Whole cell patch clamp analysis revealed that CaV1.2 deletion reduced L‐type voltage‐gated calcium entry into adult OPCs by ~60%, confirming that it remains the major L‐type VGCC expressed by OPCs in adulthood. The conditional deletion of CaV1.2 from adult OPCs significantly increased their proliferation but did not affect the number of new oligodendrocytes produced or influence the length or number of internodes they elaborated. Unexpectedly, CaV1.2 deletion resulted in the dramatic loss of OPCs from the corpus callosum, such that 7 days after tamoxifen administration CaV1.2‐deleted mice had an OPC density ~42% that of control mice. OPC density recovered within 2 weeks of CaV1.2 deletion, as the lost OPCs were replaced by surviving CaV1.2‐deleted OPCs. As OPC density was not affected in the motor cortex or spinal cord, we conclude that calcium entry through CaV1.2 is a critical survival signal for a subpopulation of callosal OPCs but not for all OPCs in the mature CNS.

Dementia associated with disorders of the basal ganglia

Dementia is now the leading cause of death in the United Kingdom, accounting for over 12% of all deaths and is the fifth most common cause of death worldwide. As treatments for heart disease and cancers improve and the population ages, the number of sufferers will only increase, with the chance of developing dementia doubling every 5 years after the age of 65. Finding an effective treatment is ever more critical to avert this pandemic health (and economic) crisis. To date, most dementia-related research has focused on the cortex and the hippocampus; however, with dementia becoming more fully recognized as aspects of diseases historically categorized as motor disorders (e.g., Parkinson's and Huntington's diseases), the role of the basal ganglia in dementia is coming to the fore. Conversely, it is highly likely that neuronal pathways in these structures traditionally considered as spared in Alzheimer's disease are also affected, particularly in later stages of the disease. In this review, we examine some of the limited evidence linking the basal ganglia to dementia.

Association of Hydroxylmethyl Glutaryl Coenzyme A Reductase Inhibitors, L-Type Calcium Channel Antagonists, and Biguanides With Rates of Psychiatric Hospitalization and Self-Harm in Individuals With Serious Mental Illness

IMPORTANCE

Drug repurposing is potentially cost-effective, low risk, and necessary in psychiatric drug development. The availability of large, routine data sets provides the opportunity to evaluate the potential for currently used medication to benefit people with serious mental illness (SMI).

OBJECTIVE

To determine whether hydroxylmethyl glutaryl coenzyme A reductase inhibitors (HMG-CoA RIs), L-type calcium channel (LTCC) antagonists, and biguanides are associated with reduced psychiatric hospitalization and self-harm in individuals with SMI.

DESIGN, SETTING, AND PARTICIPANTS

These within-individual cohort studies of patients with SMI compared rates of psychiatric hospitalization and self-harm during periods of exposure and nonexposure to the study drugs, with adjusting for a number of time-varying covariates. Participants included 142 691 individuals from the entire population of Sweden with a diagnosis of bipolar disorder (BPD), schizophrenia, or nonaffective psychosis (NAP) who were 15 years or older and who were treated with psychiatric medication from October 1, 2005, through December 31, 2016. Data were analyzed from April 1 through August 31, 2018.

INTERVENTIONS

Treatment with HMG-CoA RIs, LTCC antagonists, or biguanides.

MAIN OUTCOMES AND MEASURES

Psychiatric hospitalizations and self-harm admissions.

RESULTS

Among the 142 691 eligible participants, the HMG-CoA RI exposure periods were associated with reduced rates of psychiatric hospitalization in BPD (adjusted hazard ratio [aHR], 0.86; 95% CI, 0.83-0.89; P < .001), schizophrenia (aHR, 0.75; 95% CI, 0.71-0.79; P < .001), and NAP (aHR, 0.80; 95% CI, 0.75-0.85; P < .001) and reduced self-harm rates in BPD (aHR, 0.76; 95% CI, 0.66-0.86; P < .001) and schizophrenia (aHR, 0.58; 95% CI, 0.45-0.74; P < .001). Exposure to LTCC antagonists was associated with reduced rates of psychiatric hospitalization and self-harm in subgroups with BPD (aHRs, 0.92 [95% CI, 0.88-0.96; P < .001] and 0.81 [95% CI, 0.68-0.95; P = .01], respectively), schizophrenia (aHRs, 0.80 [95% CI, 0.74-0.85; P < .001] and 0.30 [95% CI, 0.18-0.48; P < .001], respectively), and NAP (aHRs, 0.89 [95% CI, 0.83-0.96; P = .002] and 0.56 [95% CI, 0.42-0.74; P < .001], respectively). During biguanide exposure, psychiatric hospitalization rates were reduced in subgroups with BPD (aHR, 0.80; 95% CI, 0.77-0.84; P < .001), schizophrenia (aHR, 0.73; 95% CI, 0.69-0.77; P < .001), and NAP (aHR, 0.85; 95% CI, 0.79-0.92; P < .001), and self-harm was reduced in BPD (aHR, 0.73; 95% CI, 0.62-0.84; P < .001) and schizophrenia (aHR, 0.64; 95% CI, 0.48-0.85; P < .001).

CONCLUSIONS AND RELEVANCE

This study provides additional evidence that exposure to HMG-CoA RIs, LTCC antagonists, and biguanides might lead to improved outcomes for individuals with SMI. Given the well-known adverse event profiles of these agents, they should be further investigated as repurposed agents for psychiatric symptoms.

CACNA1C risk variant affects microstructural connectivity of the amygdala

Deficits in perception of emotional prosody have been described in patients with affective disorders at behavioral and neural level. In the current study, we use an imaging genetics approach to examine the impact of CACNA1C, one of the most promising genetic risk factors for psychiatric disorders, on prosody processing on a behavioral, functional and microstructural level. Using functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) we examined key areas involved in prosody processing, i.e. the amygdala and voice areas, in a healthy population. We found stronger activation to emotional than neutral prosody in the voice areas and the amygdala, but CACNA1C rs1006737 genotype had no influence on fMRI activity. However, significant microstructural differences (i.e. mean diffusivity) between CACNA1C rs1006737 risk allele carriers and non carriers were found in the amygdala, but not the voice areas. These modifications in brain architecture associated with CACNA1C might reflect a neurobiological marker predisposing to affective disorders and concomitant alterations in emotion perception.

D-cis-Diltiazem Can Produce Oxidative Stress in Healthy Depolarized Rods In Vivo

Purpose

New perspectives are needed to understand decades of contradictory reports on the neuroprotective effects of the Cav1.2 L-type calcium channel blocker d-cis-diltiazem in retinitis pigmentosa (RP) models. Here, we address, in vivo, the following two knowledge gaps regarding d-cis-diltiazem's actions in the murine outer retina: (1) do normal mouse rods contain d-cis-diltiazem-insensitive Cav1.2 L-type calcium channels? (2) Can d-cis-diltiazem modify the normal rod redox environment?

Methods

First, transretinal Cav1.2 L-type calcium channels were noninvasively mapped with manganese-enhanced magnetic resonance imaging (MRI) following agonist Bay K 8644 in C57BL/6 (B6) and in Cav1.2 L-type calcium channel BAY K 8644-insensitive mutant B6 mice. Second, d-cis-diltiazem-treated oxidative stress-vulnerable (B6) or -resistant [129S6 (S6)] mice were examined in vivo (QUEnch-assiSTed [QUEST] MRI) and in whole retina ex vivo (lucigenin). Retinal thickness was measured using MRI.

Results

The following results were observed: (1) manganese uptake patterns in BAY K 8644-treated controls and mutant mice identified in vivo Cav1.2 L-type calcium channels in inner and outer retina; and (2) d-cis-diltiazem induced rod oxidative stress in dark-adapted B6 mice but not in light-adapted B6 mice or dark-adapted S6 mice (QUEST MRI). Oxidative stress in vivo was limited to inferior outer retina in dark-adapted B6 mice approximately 1-hour post d-cis-diltiazem. By approximately 4 hours post, only superior outer retina oxidative stress was observed and whole retinal superoxide production was supernormal. All groups had unremarkable retinal thicknesses.

Conclusions

D-cis-diltiazem's unexpectedly complex spatiotemporal outer retinal oxidative stress pattern in vivo was dependent on genetic background and rod membrane depolarization, but not apparently dependent on Cav1.2 L-type calcium channels, providing a potential rationale for contradictory results in different RP models.

CACNA1C: Association With Psychiatric Disorders, Behavior, and Neurogenesis

Large-scale genome-wide association studies have consistently shown that genetic variation in CACNA1C, a gene that encodes calcium voltage-gated channel subunit alpha1C, increases risk for psychiatric disorders. CACNA1C encodes the Cav1.2 subunit of voltage-gated calcium channels, which themselves have been functionally implicated in a broad spectrum of neuropsychiatric syndromes. Research has concentrated on uncovering the underlying biological mechanisms that could be responsible for this increased risk. This review presents an overview of recent findings regarding Cacna1c variation in animal models, particularly focusing on behavioral phenotypes associated with neurodevelopmental disorders such as cognition, anxiety and depressive phenotypes, and fear conditioning. The impact of reduced gene dosage of Cacna1c on adult hippocampal neurogenesis is also assessed, including new data from a novel Cacna1c+/- rat model.

A Common CACNA1C Gene Risk Variant has Sex-Dependent Effects on Behavioral Traits and Brain Functional Activity

Genome-wide association studies have suggested that allelic variations in the CACNA1C gene confer susceptibility to schizophrenia and bipolar disorder only in women. Here we investigated the sex-specific effects of the CACNA1C variant rs1024582 on psychiatry-related traits, brain activity during tasks and rest, and brain volume in 1207 normal male and female subjects. After correcting for multiple comparisons, there were significant interaction effects between sex and the minor allele of this polymorphism on the hostile behavior subscale scores of the Coronary-Prone Type Scale mediated by higher scores in female carriers of the minor allele. Imaging analyses revealed significant interaction effects between sex and the minor allele on fractional amplitude of low-frequency fluctuations in the right dorsolateral prefrontal cortex and on brain activity during the 2-back task in areas of the right posterior cingulate cortex, right thalamus, and right hippocampus, which were all mediated by reduced activity in female carriers of the minor allele. Our results demonstrated that the rs1024582 risk variant of CACNA1C is associated with reduced activity in the frontolimbic regions at rest and during a working memory task as well as with greater hostility in females in the healthy population.

Micro-RNA-137 Inhibits Tau Hyperphosphorylation in Alzheimer's Disease and Targets the CACNA1C Gene in Transgenic Mice and Human Neuroblastoma SH-SY5Y Cells

Background

Alzheimer’s disease (AD) results in cognitive impairment. The calcium voltage-gated channel subunit alpha-1 C CACNA1C gene encodes an alpha-1 C subunit of L-type calcium channel (LTCC). The aim of this study was to investigate the role of micro-RNA-137 (miR-137) and the CACNA1C gene in APPswe/PS1ΔE9 (APP/PS1) double-transgenic AD mice and in human neuroblastoma SH-SY5Y cells.

Material/Methods

Six-month-old APP/PS1 double-transgenic AD mice (N=6) and age-matched normal C57BL/6 mice (N=6) underwent a Morris water maze (MWM) test, expression levels of amyloid-β (Aβ), LTCC, the CACNA1C gene, and miR-137 were measured in the rat hippocampus and cerebral cortex in both groups of mice. A luciferase assay was used to evaluate the effect of miR-137 on the expression of CACNA1C in SH-SY5Y human neuroblastoma SH-SY5Y cells. Western blotting was used to detect the CACNA1C, phosphorylated-tau (p-tau), and Aβ proteins.

Results

In APP/PS1 transgenic AD mice, spatial learning and memory was significantly reduced, levels of Aβ_1–40 and Aβ_1–42 were increased in the serum, hippocampus, and cerebral cortex, expression levels of miR-137 were reduced, expression of CACNA1C protein was increased in the hippocampus and cerebral cortex, compared with normal control mice. miR-137 regulated the expression of the CACNA1C gene. Increased expression levels of p-tau (Ser202, Ser396, and Ser404) induced by Aβ_1–42 were inhibited by miR-137 mimics in SH-SY5Y human neuroblastoma cells in vitro.

Conclusions

In a transgenic mouse model of AD, miR-137 and expression of the CACNA1C gene inhibited the hyperphosphorylation of tau protein.

A Critical Neurodevelopmental Role for L-Type Voltage-Gated Calcium Channels in Neurite Extension and Radial Migration

Despite many association studies linking gene polymorphisms and mutations of L-type voltage-gated Ca²⁺ channels (VGCCs) in neurodevelopmental disorders such as autism and schizophrenia, the roles of specific L-type VGCC during brain development remain unclear. Calcium signaling has been shown to be essential for neurodevelopmental processes such as sculpting of neurites, functional wiring, and fine tuning of growing networks. To investigate this relationship, we performed submembraneous calcium imaging using a membrane-tethered genetically encoded calcium indicator (GECI) Lck-G-CaMP7. We successfully recorded spontaneous regenerative calcium transients (SRCaTs) in developing mouse excitatory cortical neurons prepared from both sexes before synapse formation. SRCaTs originated locally in immature neurites independently of somatic calcium rises and were significantly more elevated in the axons than in dendrites. SRCaTs were not blocked by tetrodoxin, a Na⁺ channel blocker, but were strongly inhibited by hyperpolarization, suggesting a voltage-dependent source. Pharmacological and genetic manipulations revealed the critical importance of the Ca_v1.2 (CACNA1C) pore-forming subunit of L-type VGCCs, which were indeed expressed in immature mouse brains. Consistently, knocking out Ca_v1.2 resulted in significant alterations of neurite outgrowth. Furthermore, expression of a gain-of-function Ca_v1.2 mutant found in Timothy syndrome, an autosomal dominant multisystem disorder exhibiting syndromic autism, resulted in impaired radial migration of layer 2/3 excitatory neurons, whereas postnatal abrogation of Ca_v1.2 enhancement could rescue cortical malformation. Together, these lines of evidence suggest a critical role for spontaneous opening of L-type VGCCs in neural development and corticogenesis and indicate that L-type VGCCs might constitute a perinatal therapeutic target for neuropsychiatric calciochannelopathies.SIGNIFICANCE STATEMENT Despite many association studies linking gene polymorphisms and mutations of L-type voltage-gated Ca²⁺ channels (VGCCs) in neurodevelopmental disorders such as autism and schizophrenia, the roles of specific L-type VGCCs during brain development remain unclear. We here combined the latest Ca²⁺ indicator technology, quantitative pharmacology, and in utero electroporation and found a hitherto unsuspected role for L-type VGCCs in determining the Ca²⁺ signaling landscape of mouse immature neurons. We found that malfunctional L-type VGCCs in immature neurons before birth might cause errors in neuritic growth and cortical migration. Interestingly, the retarded corticogenesis phenotype was rescued by postnatal correction of L-type VGCC signal aberration. These findings suggest that L-type VGCCs might constitute a perinatal therapeutic target for neurodevelopment-associated psychiatric disorders.

Isradipine attenuates MPTP-induced dopamine neuron degeneration by inhibiting up-regulation of L-type calcium channels and iron accumulation in the substantia nigra of mice

The aim of this study is to investigate the effects of L-type calcium channels (LTCCs) on MPTP-induced dopamine (DA) neuron degeneration and iron accumulation in the substantia nigra (SN) of mice. By real-time PCR and western blots, we first quatified expressions of L-type Cav1.2 and Cav1.3 calcium channel α1 subunits in the SN of experimental mice treated with MPTP. We found that the expressions of Cav1.2 and Cav1.3 calcium channel α1 subunits markedly increased after MPTP treatment for 2 and 3 weeks. Secondly, we observed the effects of isradipine, a LTCC antagonist, on MPTP-induced DA neuron degeneration and iron accumulation in the SN. Our results showed that isradipine treatment prevented against MPTP-induced Cav1.2 and Cav1.3 calcium channel α1 subunits up-regulation in the SN. We also found that isradipine prevented against MPTP-induced DA neuron depletion in the SN and partly restored the DA content in the striatum. Moreover, we found that isradipine inhibited the increase of iron positive cells in the SN of the MPTP-treated mice. Finally, we investigated the effects of isradipine on cellular iron accumulation in the dopaminergic MES23.5 cell line. Our studies showed that MPP⁺ treatment accelerated iron influx in the MES23.5 cells. Treatment with Bayk8644 further aggravated iron accumulation. Treatment with isradipine prevented against MPP⁺-induced iron influx in the MES23.5 cells. These results suggest that up-regulation of LTCCs may be responsible for the DA neuron degeneration in the MPTP-treated mice, The LTCCs may directly contribute to iron influx into DA neurons, and isradipine may suppress cellular iron accumulation and prevents neurodegeneration.

Alternative Splicing of L-type CaV1.2 Calcium Channels: Implications in Cardiovascular Diseases

L-type Ca_V1.2 calcium channels are the major pathway for Ca²⁺ influx to initiate the contraction of smooth and cardiac muscles. Alteration of Ca_V1.2 channel function has been implicated in multiple cardiovascular diseases, such as hypertension and cardiac hypertrophy. Alternative splicing is a post-transcriptional mechanism that expands Ca_V1.2 channel structures to modify function, pharmacological and biophysical property such as calcium/voltage-dependent inactivation (C/VDI), or to influence its post-translational modulation by interacting proteins such as Galectin-1. Alternative splicing has generated functionally diverse Ca_V1.2 isoforms that can be developmentally regulated in the heart, or under pathophysiological conditions such as in heart failure. More importantly, alternative splicing of certain exons of Ca_V1.2 has been reported to be regulated by splicing factors such as RNA-binding Fox-1 homolog 1/2 (Rbfox 1/2), polypyrimidine tract-binding protein (PTBP1) and RNA-binding motif protein 20 (RBM20). Understanding how Ca_V1.2 channel function is remodelled in disease will provide better information to guide the development of more targeted approaches to discover therapeutic agents for cardiovascular diseases.

Type-1 astrocyte-like stem cells harboring Cacna1d gene deletion exhibit reduced proliferation and decreased neuronal fate choice

In the central nervous system, Ca_V 1.2 and Ca_V 1_. 3 constitute the main L-type voltage-gated calcium channels (LTCCs) coupling membrane depolarization to gene transcription. We have previously demonstrated that inducible disruption of Cav1.2 in type-1 astrocyte-like stem cells of the adult dentate gyrus (DG) impairs hippocampal neurogenesis in a cell-autonomous fashion. To address the role of Cav1.3 channels (encoded by the Cacna1d gene), we here generated Tg^{GLAST-CreERT2} /Cacna1d^fl/fl /RCE:loxP mice which facilitate inducible deletion of Cacna1d in tandem with induction of EGFP expression in type-1 cells, allowing tracking of recombined cells and their descendants. Neurosphere cultures derived from fluorescence-activated cell sorting sorted Cacna1d-deficient (Cacna1d^-/- /EGFP) hippocampal neural precursor cells (NPCs) exhibited a significant decrease in proliferative activity. Further, under differentiation conditions, Cacna1d deficiency conferred an increase in astrogenesis at the expense of neurogenesis. In like manner, type-1 cells lacking Cacna1d showed reduced proliferation in the dentate gyrus (DG) in vivo. Moreover, Cacna1d deficiency resulted in a significant decrease in the number of newly born cells adopting a neuronal fate. Finally, massive excitation induced by repeated electroconvulsive seizures rescued the proliferation defect of Cacna1d^-/- /EGFP type-1 cells. Together, the effects of Cacna1d gene deletion closely recapitulate our earlier findings on the role of Cav1.2 channels expressed by type-1 cells. Similar to Cav1.2 channels, Cav1.3 channels on type-1 cells boost type-1 cell proliferation and promote subsequent neuronal fate choice.

L-type VDCCs participate in behavioral-LTP and memory retention

Although L-type voltage-dependent calcium channels (VDCCs) have been reported to display different even contrary actions on cognitive functions and long-term potentiation (LTP) formation, there is little information regarding the role of L-type VDCCs in behavioral LTP, a learning-induced LTP model, in the intact brain of freely behaving animals. Here we investigated the effects of verapamil, a non-selective blocker of L-type VDCCs, on behavioral LTP and cognitive functions. Population spikes (PS) were recorded by using electrophysiological methods to examine the role of verapamil in behavioral LTP in the hippocampal dentate gyrus (DG) region. Y-maze assay was used to evaluate the effects of verapamil on learning and memory. Electron microscope was used to observe the changes on synaptic ultrastructural morphology in hippocampal DG area. We found that intrahippocampal verapamil treatments had no significant changes on the PS amplitude during a 90min recordings period. However, intrahippocampal applications of verapamil, including pre- or post-training, reduced behavioral LTP magnitude and memory retention but did not prevent the induction of behavioral LTP and the acquisition of learning. The saline group with behaving trainings showed obvious increases in the number of smile synapses, the length of active zones and the thickness of postsynaptic density as compared to the baseline group, but verapamil with pre-training treatment almost returned these changes to the baseline levels except for the synaptic interface curvature. In conclusion, our results suggest that L-type VDCCs may only contribute to the magnitude of behavioral LTP and the memory maintenance with an activity-independent relationship. L-type VDCCs may be critical to new information long-term storage rather than acquisition in hippocampus.

Impaired Fear Extinction Due to a Deficit in Ca2+ Influx Through L-Type Voltage-Gated Ca2+ Channels in Mice Deficient for Tenascin-C

Mice deficient in the extracellular matrix glycoprotein tenascin-C (TNC^−/−) express a deficit in specific forms of hippocampal synaptic plasticity, which involve the L-type voltage-gated Ca²⁺ channels (L-VGCCs). The mechanisms underlying this deficit and its functional implications for learning and memory have not been investigated. In line with previous findings, we report on impairment in theta-burst stimulation (TBS)-induced long-term potentiation (LTP) in TNC^−/− mice in the CA1 hippocampal region and its rescue by the L-VGCC activator Bay K-8644. We further found that the overall pattern of L-VGCC expression in the hippocampus in TNC^−/− mice was normal, but Western blot analysis results uncovered upregulated expression of the Ca_v1.2 and Ca_v1.3 α-subunits of L-VGCCs. However, these L-VGCCs were not fully functional in TNC^−/− mice, as demonstrated by Ca²⁺ imaging, which revealed a reduction of nifedipine-sensitive Ca²⁺ transients in CA1 pyramidal neurons. TNC^−/− mice showed normal learning and memory in the contextual fear conditioning paradigm but impaired extinction of conditioned fear responses. Systemic injection of the L-VGCC blockers nifedipine and diltiazem into wild-type mice mimicked the impairment of fear extinction observed in TNC^−/− mice. The deficiency in TNC^−/− mice substantially occluded the effects of these drugs. Our results suggest that TNC-mediated modulation of L-VGCC activity is essential for fear extinction.

Role of CACNA1C gene polymorphisms and protein expressions in the pathogenesis of schizophrenia: a case-control study in a Chinese population

The study aimed to investigate the correlations of CACNA1C genetic polymorphisms and protein expression with the pathogenesis of schizophrenia in a Chinese population. This research included 139 patients diagnosed with schizophrenia (case group) and 141 healthy volunteers (control group). Case and control samples were genotyped using denaturing high-performance liquid chromatography (DHPLC). Haplotypes of rs10848683, rs2238032, and rs2299661 were analyzed using the Shesis software. A mouse model of schizophrenia was established and assigned to test and blank groups. Western blotting was used to detect CACNA1C protein expression. The genotype and allele distribution of rs2238032 and rs2299661 differed between the case and control groups. TT genotype of rs2238032 and G allele of rs2299661 could potentially reduce the risk of schizophrenia. The distribution of rs2238032 genotype has a close connection with cognitive disturbance and the results of the general psychopathology classification exam. The distribution of rs2299661 genotypes was closely related to sensory and perceptual disorders, negative symptom subscales, and the results of the general psychopathology classification exam. CTC haplotype increased and CTG decreased the risk of schizophrenia in healthy people. In the brain tissues of mice with schizophrenia, the CACNA1C protein expression was higher in the test group than in the blank group. Our study demonstrated that CACNA1C gene polymorphisms and CACNA1C protein expression were associated with schizophrenia and its clinical phenotypes.

The role of Ca2+ signaling in Parkinson's disease

Across all kingdoms in the tree of life, calcium (Ca2+) is an essential element used by cells to respond and adapt to constantly changing environments. In multicellular organisms, it plays fundamental roles during fertilization, development and adulthood. The inability of cells to regulate Ca2+ can lead to pathological conditions that ultimately culminate in cell death. One such pathological condition is manifested in Parkinson's disease, the second most common neurological disorder in humans, which is characterized by the aggregation of the protein, α-synuclein. This Review discusses current evidence that implicates Ca2+ in the pathogenesis of Parkinson's disease. Understanding the mechanisms by which Ca2+ signaling contributes to the progression of this disease will be crucial for the development of effective therapies to combat this devastating neurological condition.

Cav1.2, but not Cav1.3, L-type calcium channel subtype mediates nicotine-induced conditioned place preference in mice

Nicotine use is one of the most common forms of drug addiction. Although L-type calcium channels (LTCCs) are involved in nicotine addiction, the contribution of the two primary LTCC subtypes (Ca_v1.2 and 1.3) is unknown. This study aims to determine the contribution of these two LTCC subtypes to nicotine-induced conditioned place preference (CPP) responses by using transgenic mouse models that do not express Ca_v1.3 (Ca_v1.3^-/-) or contain a mutation in the dihydropyridine (DHP) site of the Ca_v1.2 (Ca_v1.2DHP^-/-). We found a hyperbolic dose dependent nicotine (0.1-1mg/kg; 0.5mg/kg optimum) effect on place preference in wild type (WT) mice, that could be prevented by the DHP LTCC blocker nifedipine pretreatment. Similarly, Ca_v1.3^-/- mice showed nicotine-induced place preference which was antagonized by nifedipine. In contrast, nifedipine pretreatment of Ca_v1.2DHP^-/- mice had no effect on nicotine-induced CPP responses, suggesting an involvement of Ca_v1.2 subtype in the nicotine-induced CPP response. Nifedipine alone failed to produce either conditioned place aversion or CPP in WT mice. These results collectively indicate Ca_v1.2, but not Ca_v1.3 LTCC subtype regulates, at least in part, the reinforcing effects of nicotine use.

Calcium signalling through L-type calcium channels: role in pathophysiology of spinal nociceptive transmission

L-type voltage-gated calcium channels are ubiquitous channels in the CNS. L-type calcium channels (LTCs) are mostly post-synaptic channels regulating neuronal firing and gene expression. They play a role in important physio-pathological processes such as learning and memory, Parkinson's disease, autism and, as recognized more recently, in the pathophysiology of pain processes. Classically, the fundamental role of these channels in cardiovascular functions has limited the use of classical molecules to treat LTC-dependent disorders. However, when applied locally in the dorsal horn of the spinal cord, the three families of LTC pharmacological blockers - dihydropyridines (nifedipine), phenylalkylamines (verapamil) and benzothiazepines (diltiazem) - proved effective in altering short-term sensitization to pain, inflammation-induced hyperexcitability and neuropathy-induced allodynia. Two subtypes of LTCs, Ca_v 1.2 and Ca_v 1.3, are expressed in the dorsal horn of the spinal cord, where Ca_v 1.2 channels are localized mostly in the soma and proximal dendritic shafts, and Ca_v 1.3 channels are more distally located in the somato-dendritic compartment. Together with their different kinetics and pharmacological properties, this spatial distribution contributes to their separate roles in shaping short- and long-term sensitization to pain. Ca_v 1.3 channels sustain the expression of plateau potentials, an input/output amplification phenomenon that contributes to short-term sensitization to pain such as prolonged after-discharges, dynamic receptive fields and windup. The Ca_v 1.2 channels support calcium influx that is crucial for the excitation-transcription coupling underlying nerve injury-induced dorsal horn hyperexcitability. These subtype-specific cellular mechanisms may have different consequences in the development and/or the maintenance of pathological pain. Recent progress in developing more specific compounds for each subunit will offer new opportunities to modulate LTCs for the treatment of pathological pain with reduced side-effects.

LINKED ARTICLES

This article is part of a themed section on Recent Advances in Targeting Ion Channels to Treat Chronic Pain. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.12/issuetoc.

A high-throughput fluorimetric microarray with enhanced fluorescence and suppressed "coffee-ring" effects for the detection of calcium ions in blood

A rapid, ultrasensitive, and high-throughput fluorimetric microarray method has been developed using hydrophobic pattern as the microarray substrate and 3-aminopropyltriethoxysilane-coupled carboxylic acid calcium (APS-CCA) as the fluorescent probes for sensing Ca2+ ions in blood. The hydrophobic pattern of the developed Ca2+ analysis microarray could largely suppress the "coffee-ring" effects to facilitate the better distribution density of testing microspots toward the high-throughput detections, and especially prevent the cross-contamination of the multiple samples between adjacent microspots. Moreover, the use of APS matrix could endow the CCA probe the enhanced environmental stability and fluorescence intensity, which is about 2.3-fold higher than that of free CCA. The interactions between APS-CCA and Ca2+ ions were systematically characterized by UV-vis and fluorescence measurements including microscopy imaging. It was demonstrated that the fluorimetric microarray could display the strong capacity of specifically sensing Ca2+ ions with the minimal interferences from blood backgrounds. Such an APS-CCA-based fluorimetric microarray can allow for the analysis of Ca2+ ions down to 0.0050 mM in blood, promising a highly sensitive and selective detection candidate for Ca2+ ions to be applied in the clinical laboratory.

CACNA1C SNP rs1006737 associates with bipolar I disorder independent of the Bcl-2 SNP rs956572 variant and its associated effect on intracellular calcium homeostasis

OBJECTIVES

Intracellular calcium (Ca(2+)) dyshomeostasis (ICDH) has been implicated in bipolar disorder (BD) pathophysiology. We previously showed that SNP rs956572 in the B-cell CLL/lymphoma 2 (Bcl-2) gene associates with elevated B lymphoblast (BLCL) intracellular Ca(2+) concentrations ([Ca(2+)]B) differentially in BD-I. Genome-wide association studies strongly support the association between BD and the SNP rs1006737, located within the L-type voltage-dependent Ca(2+) channel α1C subunit gene (CACNA1C). Here we investigated whether this CACNA1C variant also associates with ICDH and interacts with SNP rs956572 on [Ca(2+)]B in BD-I.

METHODS

CACNA1C SNP rs1006737 was genotyped in 150 BD-I, 65 BD-II, 30 major depressive disorder patients, and 70 healthy subjects with available BLCL [Ca(2+)]B and Bcl-2 SNP rs956572 genotype measures.

RESULTS

SNP rs1006737 was significantly associated with BD-I. The [Ca(2+)]B was significantly higher in BD-I rs1006737 A compared with healthy A allele carriers and also in healthy GG compared with A allele carriers. There was no significant interaction between SNP rs1006737 and SNP rs956572 on [Ca(2+)]B.

CONCLUSIONS

Our study further supports the association of SNP rs1006737 with BD-I and suggests that CACNA1C SNP rs1006737 and Bcl-2 SNP rs956572, or specific causal variants in LD with these proxies, act independently to increase risk and ICDH in BD-I.

Common variants in CACNA1C and MDD susceptibility: A comprehensive meta-analysis

Major depressive disorder (MDD) is one of the most common psychiatric disorders with a relatively high heritability (35-40%). Though rs1006737 in the CACNA1C gene showed significant association with MDD in a British large-scale candidate association study, most of the replication analyses with relatively small sample size reported negative association. Moreover, this locus has never been identified in previous genome-wide association studies (GWAS) for MDD. Here, we conducted a comprehensive meta-analysis of the association between CACNA1C variants and MDD risk by combining all published data. Genetic data from one European GWAS and five individual follow-up studies, which include up to 12,629 patients of MDD and 28,653 controls, that is, the largest sample size on CACNA1C to date, were collected. Rs1006737 showed significant association with MDD in the fixed-effect model (Z = 2.56, P = 0.011, OR = 1.08, 95%CI = 1.04-1.12) and the association remained after reanalyzing the data according to ethnicity. We additionally analyzed other 25 SNPs, genotyped in only one replication study, across the CACNA1C locus, and found that two SNPs, rs4765905 (P = 0.041, OR = 1.05, 95%CI 1.00-1.09) and rs4765937 (P = 0.025, OR = 1.05, 95%CI 1.01-1.09) showed nominal association with MDD, while rs2239073 (P = 0.002, OR = 1.07, 95%CI 1.02-1.11) exhibited significant association with MDD, which survived from multiple corrections. Our study provides support for positive association between CACNA1C and MDD; however, the current data suggest the necessity of replication analyses in a larger-scale sample. © 2016 Wiley Periodicals, Inc.

Calcium and Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease in the world. Its causes are poorly understood and there is no proven therapeutic strategy for slowing disease progression. The core motor symptoms of PD are caused by the death of dopaminergic neurons in the substantia nigra pars compacta (SNc). In these neurons, Ca²⁺entry through plasma membrane Cav1 channels drives a sustained feed-forward stimulation of mitochondrial oxidative phosphorylation. Although this design helps prevent bioenergetic failure when activity needs to be sustained, it leads to basal mitochondrial oxidant stress. Over decades, this basal oxidant stress could compromise mitochondrial function and increase mitophagy, resulting in increased vulnerability to other proteostatic stressors, like elevated alpha synuclein expression. Because this feedforward mechanism is no longer demanded by our lifestyle, it could be dispensed with. Indeed, use of dihydropyridines - negative allosteric modulators of Cav1 Ca²⁺ channels - comes with little or no effect on brain function but is associated with decreased risk and progression of PD. An ongoing, NIH sponsored, Phase 3 clinical trial in North America is testing the ability of one member of the dihydropyridine class (isradipine) to slow PD progression in early stage patients. The review summarizes the rationale for the trial and outlines some unanswered questions.

Regulation and the Mechanism of Estrogen on Cav1.2 Gene in Rat-Cultured Cortical Astrocytes

L-type calcium channel (LTCC) gene Cav1.2 is believed to play an important role in the alteration of Ca(2+) homeostasis in brain astrocytes. Increasing evidence shows that alteration of intracellular Ca(2+) concentration is related to the effect of 17β-estradiol (E2) in a variety of neurophysiological and neuropathological conditions. In this study, we measured immunoreactivity of Cav1.2 protein expression in rat primary cortical astrocytes by using Western blots. We demonstrated that E2 upregulated Cav1.2 expression in a dose- and time-dependent manner and the effect of E2 on Cav1.2 expression were blocked by an estrogen receptor (ER) antagonist, ICI-182,780. The ER subtype-selective ERα agonists propylpyrazole triole (PPT) and ERβ agonist diarylpropionitrile (DPN) both increase the expression of Cav1.2 in a dose-dependent manner. Also, the PPT most closely mimicked the upregulation of Cav1.2 protein expression by E2. Similar experiments of 10 nM E2-treated ERα- or ERβ-knockdown astrocytes have also shown that the E2 regulation of Cav1.2 protein expression is mediated through an ERα-dependent pathway. Furthermore, we established that E2 did not change the level of Cav1.2 mRNA. The induction of E2-mediated Cav1.2 expression was inhibited by cycloheximide (CHX) but not by actinomycin D (Act-D), suggesting that E2 regulation of Cav1.2 expression occurred at a posttranscriptional level. We also found that E2 may increase Cav1.2 levels by decreasing its ubiquitination and degradation rate. These findings provide new information about the effect of E2 on Cav1.2 in astrocytes, particularly necessary for the treatment of neurological disease.

Do Copy Number Changes in CACNA2D2, CACNA2D3, and CACNA1D Constitute a Predisposing Risk Factor for Alzheimer's Disease?

Dysregulation of calcium (Ca²⁺) homeostasis is now being recognized to be a key step in the pathogenesis of Alzheimer’s disease (AD). Data from the literature, in particular the association between AD and polymorphism that interfere with Ca²⁺ homeostasis indicates the presence of genetic factors in this process; further, presenilins mutations, which are known to cause the familial form of AD, are involved in the regulation of intracellular Ca²⁺ stores. Here, we wish to draw attention to rare DNA copy number variations identified in two subjects with late-onset AD that led to partial or full duplication of genes that encode different subunits of the same type of voltage-gated Ca²⁺ channels; these duplications of voltage-gated Ca²⁺ channel genes is consistent with the critical role of calcium signaling in molecular processes underlying memory as has been demonstrated by several studies.

Ca(2+) entry into neurons is facilitated by cooperative gating of clustered CaV1.3 channels

CaV1.3 channels regulate excitability in many neurons. As is the case for all voltage-gated channels, it is widely assumed that individual CaV1.3 channels behave independently with respect to voltage-activation, open probability, and facilitation. Here, we report the results of super-resolution imaging, optogenetic, and electrophysiological measurements that refute this long-held view. We found that the short channel isoform (CaV1.3S), but not the long (CaV1.3L), associates in functional clusters of two or more channels that open cooperatively, facilitating Ca(2+) influx. CaV1.3S channels are coupled via a C-terminus-to-C-terminus interaction that requires binding of the incoming Ca(2+) to calmodulin (CaM) and subsequent binding of CaM to the pre-IQ domain of the channels. Physically-coupled channels facilitate Ca(2+) currents as a consequence of their higher open probabilities, leading to increased firing rates in rat hippocampal neurons. We propose that cooperative gating of CaV1.3S channels represents a mechanism for the regulation of Ca(2+) signaling and electrical activity.

Sleep Spindles as Facilitators of Memory Formation and Learning

Over the past decades important progress has been made in understanding the mechanisms of sleep spindle generation. At the same time a physiological role of sleep spindles is starting to be revealed. Behavioural studies in humans and animals have found significant correlations between the recall performance in different learning tasks and the amount of sleep spindles in the intervening sleep. Concomitant neurophysiological experiments showed a close relationship between sleep spindles and other sleep related EEG rhythms as well as a relationship between sleep spindles and synaptic plasticity. Together, there is growing evidence from several disciplines in neuroscience for a participation of sleep spindles in memory formation and learning.

Converging roles of ion channels, calcium, metabolic stress, and activity pattern of Substantia nigra dopaminergic neurons in health and Parkinson's disease

Dopamine‐releasing neurons within the Substantia nigra (SN DA) are particularly vulnerable to degeneration compared to other dopaminergic neurons. The age‐dependent, progressive loss of these neurons is a pathological hallmark of Parkinson's disease (PD), as the resulting loss of striatal dopamine causes its major movement‐related symptoms. SN DA neurons release dopamine from their axonal terminals within the dorsal striatum, and also from their cell bodies and dendrites within the midbrain in a calcium‐ and activity‐dependent manner. Their intrinsically generated and metabolically challenging activity is created and modulated by the orchestrated function of different ion channels and dopamine D2‐autoreceptors. Here, we review increasing evidence that the mechanisms that control activity patterns and calcium homeostasis of SN DA neurons are not only crucial for their dopamine release within a physiological range but also modulate their mitochondrial and lysosomal activity, their metabolic stress levels, and their vulnerability to degeneration in PD. Indeed, impaired calcium homeostasis, lysosomal and mitochondrial dysfunction, and metabolic stress in SN DA neurons represent central converging trigger factors for idiopathic and familial PD. We summarize double‐edged roles of ion channels, activity patterns, calcium homeostasis, and related feedback/feed‐forward signaling mechanisms in SN DA neurons for maintaining and modulating their physiological function, but also for contributing to their vulnerability in PD‐paradigms. We focus on the emerging roles of maintained neuronal activity and calcium homeostasis within a physiological bandwidth, and its modulation by PD‐triggers, as well as on bidirectional functions of voltage‐gated L‐type calcium channels and metabolically gated ATP‐sensitive potassium (K‐ATP) channels, and their probable interplay in health and PD.

We propose that SN DA neurons possess several feedback and feed‐forward mechanisms to protect and adapt their activity‐pattern and calcium‐homeostasis within a physiological bandwidth, and that PD‐trigger factors can narrow this bandwidth. We summarize roles of ion channels in this view, and findings documenting that both, reduced as well as elevated activity and associated calcium‐levels can trigger SN DA degeneration.

This article is part of a special issue on Parkinson disease.

Genetic analysis of SNPs in CACNA1C and ANK3 gene with schizophrenia: A comprehensive meta-analysis

Recently, genome-wide association studies (GWAS), meta-analyses, and replication studies focusing on bipolar disorder (BD) have implicated the α-1C subunit of the L-type voltage-dependent calcium channel (CACNA1C) and ankyrin 3 (ANK3) genes in BD. Based on the hypothesis that both schizophrenia (SZ) and BD may share some common genetic risk factors, we investigated the association of CACNA1C and ANK3 with SZ using meta-analytic techniques, combining all published data up to April 2015. Nine teams, including four European decent samples and five Asian samples, contributed 14,141 cases and 30,679 controls for the analysis of CACNA1C rs1006737 and SZ. A significant difference was identified between patients and controls for the A-allele of rs1006737 in combined studies (Z = 6.02, P = 1.74E-09), in European studies (Z = 4.08, P = 4.50E-05), and in Asian studies (Z = 4.60, P = 4.22E-06). Meanwhile, for the T-allele of ANK3 rs10761482 (1,794 cases versus 1,395 controls), a significant association was observed in combined samples (Z = 2.06, P = 0.04) and in Asian samples (Z = 3.10, P = 0.002). In summary, our study provides further evidence for the positive association of CACNA1C and ANK3 with SZ. These results support the hypothesis that both SZ and BD share common genetic risk factors. Further research is needed to examine the functions of CACNA1C and ANK3, and their interacting partners in the molecular, developmental, and pathophysiological processes in SZ.