Trafficking of neuronal calcium channels

Ca2+ channel and active zone protein abundance intersects with input-specific synapse organization to shape functional synaptic diversity

Synaptic heterogeneity is a hallmark of nervous systems that enables complex and adaptable communication in neural circuits. To understand circuit function, it is thus critical to determine the factors that contribute to the functional diversity of synapses. We investigated the contributions of voltage-gated calcium channel (VGCC) abundance, spatial organization, and subunit composition to synapse diversity among and between synapses formed by two closely related Drosophila glutamatergic motor neurons with distinct neurotransmitter release probabilities (Pr). Surprisingly, VGCC levels are highly predictive of heterogeneous Pr among individual synapses of either low- or high-Pr inputs, but not between inputs. We find that the same number of VGCCs are more densely organized at high-Pr synapses, consistent with tighter VGCC-synaptic vesicle coupling. We generated endogenously tagged lines to investigate VGCC subunits in vivo and found that the α2δ-3 subunit Straightjacket along with the CAST/ELKS active zone (AZ) protein Bruchpilot, both key regulators of VGCCs, are less abundant at high-Pr inputs, yet positively correlate with Pr among synapses formed by either input. Consistently, both Straightjacket and Bruchpilot levels are dynamically increased across AZs of both inputs when neurotransmitter release is potentiated to maintain stable communication following glutamate receptor inhibition. Together, these findings suggest a model in which VGCC and AZ protein abundance intersects with input-specific spatial and molecular organization to shape the functional diversity of synapses.

The role of voltage-gated calcium channels in the pathogenesis of Parkinson's disease

Aim: Voltage-gated calcium (CaV) channels play an essential role in maintaining calcium homeostasis and regulating numerous physiological processes in neurons. Therefore, dysregulation of calcium signaling is relevant in many neurological disorders, including Parkinson's disease (PD). This review aims to introduce the role of CaV channels in PD and discuss some novel aspects of channel regulation and its impact on the molecular pathophysiology of the disease.

Methods: an exhaustive search of the literature in the field was carried out using the PubMed database of The National Center for Biotechnology Information. Systematic searches were performed from the initial date of publication to May 2022.

Results: Although α-synuclein aggregates are the main feature of PD, L-type calcium (CaV1) channels seem to play an essential role in the pathogenesis of PD. Changes in the functional expression of CaV1.3 channels alter Calcium homeostasis and contribute to the degeneration of dopaminergic neurons. Furthermore, recent studies suggest that CaV channel trafficking towards the cell membrane depends on the activity of the ubiquitin-proteasome system (UPS). In PD, there is an increase in the expression of L-type channels associated with a decrease in the expression of Parkin, an E3 enzyme of the UPS. Therefore, a link between Parkin and CaV channels could play a fundamental role in the pathogenesis of PD and, as such, could be a potentially attractive target for therapeutic intervention.

Conclusion: The study of alterations in the functional expression of CaV channels will provide a framework to understand better the neurodegenerative processes that occur in PD and a possible path toward identifying new therapeutic targets to treat this condition.

CaV 2.1 α1 subunit motifs that control presynaptic CaV 2.1 subtype abundance are distinct from CaV 2.1 preference

Presynaptic voltage-gated Ca2+ channel (CaV ) subtype abundance at mammalian synapses regulates synaptic transmission in health and disease. In the mammalian central nervous system (CNS), most presynaptic terminals are CaV 2.1 dominant with a developmental reduction in CaV 2.2 and CaV 2.3 levels, and CaV 2 subtype levels are altered in various diseases. However, the molecular mechanisms controlling presynaptic CaV 2 subtype levels are largely unsolved. Because the CaV 2 α1  subunit cytoplasmic regions contain varying levels of sequence conservation, these regions are proposed to control presynaptic CaV 2 subtype preference and abundance. To investigate the potential role of these regions, we expressed chimeric CaV 2.1 α1  subunits containing swapped motifs with the CaV 2.2 and CaV 2.3 α1  subunit on a CaV 2.1/CaV 2.2 null background at the calyx of Held presynaptic terminals. We found that expression of CaV 2.1 α1  subunit chimeras containing the CaV 2.3 loop II-III region or cytoplasmic C-terminus (CT) resulted in a large reduction of presynaptic Ca2+ currents compared to the CaV 2.1 α1  subunit. However, the Ca2+ current sensitivity to the CaV 2.1 blocker agatoxin-IVA was the same between the chimeras and the CaV 2.1 α1  subunit. Additionally, we found no reduction in presynaptic Ca2+ currents with CaV 2.1/2.2 cytoplasmic CT chimeras. We conclude that the motifs in the CaV 2.1 loop II-III and CT do not individually regulate CaV 2.1 preference, although these motifs control CaV 2.1 levels and the CaV 2.3 CT contains motifs that negatively regulate presynaptic CaV 2.3 levels. We propose that the motifs controlling presynaptic CaV 2.1 preference are distinct from those regulating CaV 2.1 levels and may act synergistically to impact pathways regulating CaV 2.1 preference and abundance. KEY POINTS: Presynaptic CaV 2 subtype abundance regulates neuronal circuit properties, although the mechanisms regulating presynaptic CaV 2 subtype abundance and preference remain enigmatic. The CaV α1  subunit determines subtype and contains multiple motifs implicated in regulating presynaptic subtype abundance and preference. The CaV 2.1 α1  subunit domain II-III loop and cytoplasmic C-terminus are positive regulators of presynaptic CaV 2.1 abundance but do not regulate preference. The CaV 2.3 α1  subunit cytoplasmic C-terminus negatively regulates presynaptic CaV 2 subtype abundance but not preference, whereas the CaV 2.2 α1  subunit cytoplasmic C-terminus is not a key regulator of presynaptic CaV 2 subtype abundance or preference. The CaV 2 α1  subunit motifs determining the presynaptic CaV 2 preference are distinct from abundance.

Stress-related cellular pathophysiology as a crosstalk risk factor for neurocognitive and psychiatric disorders

In this narrative review, we examine biological processes linking psychological stress and cognition, with a focus on how psychological stress can activate multiple neurobiological mechanisms that drive cognitive decline and behavioral change. First, we describe the general neurobiology of the stress response to define neurocognitive stress reactivity. Second, we review aspects of epigenetic regulation, synaptic transmission, sex hormones, photoperiodic plasticity, and psychoneuroimmunological processes that can contribute to cognitive decline and neuropsychiatric conditions. Third, we explain mechanistic processes linking the stress response and neuropathology. Fourth, we discuss molecular nuances such as an interplay between kinases and proteins, as well as differential role of sex hormones, that can increase vulnerability to cognitive and emotional dysregulation following stress. Finally, we explicate several testable hypotheses for stress, neurocognitive, and neuropsychiatric research. Together, this work highlights how stress processes alter neurophysiology on multiple levels to increase individuals' risk for neurocognitive and psychiatric disorders, and points toward novel therapeutic targets for mitigating these effects. The resulting models can thus advance dementia and mental health research, and translational neuroscience, with an eye toward clinical application in cognitive and behavioral neurology, and psychiatry.

CaV2.1 α1 subunit motifs that control presynaptic CaV2.1 subtype abundance are distinct from CaV2.1 preference

Presynaptic voltage-gated Ca2+ channels (CaV) subtype abundance at mammalian synapses regulates synaptic transmission in health and disease. In the mammalian central nervous system, most presynaptic terminals are CaV2.1 dominant with a developmental reduction in CaV2.2 and CaV2.3 levels, and CaV2 subtype levels are altered in various diseases. However, the molecular mechanisms controlling presynaptic CaV2 subtype levels are largely unsolved. Since the CaV2 α1 subunit cytoplasmic regions contain varying levels of sequence conservation, these regions are proposed to control presynaptic CaV2 subtype preference and abundance. To investigate the potential role of these regions, we expressed chimeric CaV2.1 α1subunits containing swapped motifs with the CaV2.2 and CaV2.3 α1 subunit on a CaV2.1/CaV2.2 null background at the calyx of Held presynaptic terminal. We found that expression of CaV2.1 α1 subunit chimeras containing the CaV2.3 loop II-III region or cytoplasmic C-terminus (CT) resulted in a large reduction of presynaptic Ca2+ currents compared to the CaV2.1 α1 subunit. However, the Ca2+ current sensitivity to the CaV2.1 blocker Agatoxin-IVA, was the same between the chimeras and the CaV2.1 α1 subunit. Additionally, we found no reduction in presynaptic Ca2+ currents with CaV2.1/2.2 cytoplasmic CT chimeras. We conclude that the motifs in the CaV2.1 loop II-III and CT do not individually regulate CaV2.1 preference, but these motifs control CaV2.1 levels and the CaV2.3 CT contains motifs that negatively regulate presynaptic CaV2.3 levels. We propose that the motifs controlling presynaptic CaV2.1 preference are distinct from those regulating CaV2.1 levels and may act synergistically to impact pathways regulating CaV2.1 preference and abundance.

Differential Expression of the β3 Subunit of Voltage-Gated Ca2+ Channel in Mesial Temporal Lobe Epilepsy

The purpose of this study was to identify and validate new putative lead drug targets in drug-resistant mesial temporal lobe epilepsy (mTLE) starting from differentially expressed genes (DEGs) previously identified in mTLE in humans by transcriptome analysis. We identified consensus DEGs among two independent mTLE transcriptome datasets and assigned them status as "lead target" if they (1) were involved in neuronal excitability, (2) were new in mTLE, and (3) were druggable. For this, we created a consensus DEG network in STRING and annotated it with information from the DISEASES database and the Target Central Resource Database (TCRD). Next, we attempted to validate lead targets using qPCR, immunohistochemistry, and Western blot on hippocampal and temporal lobe neocortical tissue from mTLE patients and non-epilepsy controls, respectively. Here we created a robust, unbiased list of 113 consensus DEGs starting from two lists of 3040 and 5523 mTLE significant DEGs, respectively, and identified five lead targets. Next, we showed that CACNB3, a voltage-gated Ca2+ channel subunit, was significantly regulated in mTLE at both mRNA and protein level. Considering the key role of Ca2+ currents in regulating neuronal excitability, this suggested a role for CACNB3 in seizure generation. This is the first time changes in CACNB3 expression have been associated with drug-resistant epilepsy in humans, and since efficient therapeutic strategies for the treatment of drug-resistant mTLE are lacking, our finding might represent a step toward designing such new treatment strategies.

Critical Pronociceptive Role of Family 2 Voltage-Gated Calcium Channels in a Novel Mouse Model of HIV-Associated Sensory Neuropathy

Some people living with HIV present painful sensory neuropathy (HIV-SN) that is pharmacoresistant, sex-associated, and a major source of morbidity. Since the specific mechanisms underlying HIV-SN are not well understood, the aim of our study was to characterize a novel model of painful HIV-SN by combining the HIV-1 gp120 protein and the antiretroviral stavudine (d4T) in mice and to investigate the pronociceptive role of the family 2 voltage-gated calcium channel (VGCC) α1 subunit (Cav2.X channels) in such a model. HIV-SN was induced in male and female C57BL/6 mice by administration of gp120 and/or d4T and detected by a battery of behavior tests and by immunohistochemistry. The role of Cav2.X channels was assessed by the treatment with selective blockers and agonists as well as by mRNA detection. Repeated administration with gp120 and/or d4T produced long-lasting touch-evoked painful-like behaviors (starting at 6 days, reaching a maximum on day 13, and lasting up to 28 days after treatment started), with a greater intensity in female mice treated with the combination of gp120 + d4T. Moreover, gp120 + d4T treatment reduced the intraepidermal nerve fibers and well-being of female mice, without altering other behaviors. Mechanistically, gp120 + d4T treatment induced Cav2.1, 2.2, and 2.3 transcriptional increases in the dorsal root ganglion and the Cav2.X agonist-induced nociception. Accordingly, intrathecal selective Cav2.2 blockade presented longer and better efficacy in reversing the hyperalgesia induced by gp120 + d4T treatment compared with Cav2.1 or Cav2.3, but also presented the worst safety (inducing side effects at effective doses). We conclude that the family 2 calcium channels (Cav2.X) exert a critical pronociceptive role in a novel mouse model of HIV-SN.

Regulation of Cardiac Cav1.2 Channels by Calmodulin

Cav1.2 Ca2+ channels, a type of voltage-gated L-type Ca2+ channel, are ubiquitously expressed, and the predominant Ca2+ channel type, in working cardiac myocytes. Cav1.2 channels are regulated by the direct interactions with calmodulin (CaM), a Ca2+-binding protein that causes Ca2+-dependent facilitation (CDF) and inactivation (CDI). Ca2+-free CaM (apoCaM) also contributes to the regulation of Cav1.2 channels. Furthermore, CaM indirectly affects channel activity by activating CaM-dependent enzymes, such as CaM-dependent protein kinase II and calcineurin (a CaM-dependent protein phosphatase). In this article, we review the recent progress in identifying the role of apoCaM in the channel ‘rundown’ phenomena and related repriming of channels, and CDF, as well as the role of Ca2+/CaM in CDI. In addition, the role of CaM in channel clustering is reviewed.

T-type Ca2+ channels and their relationship with pre-neoplastic and neoplastic lesions in the human breast

The expression of T-type voltage-dependent Ca2+ channels (Cav3) has been previously observed in breast cancer, but their expression and subcellular localization were not evaluated in pre-neoplastic lesions. Therefore, this work aimed to evaluate protein expression and subcellular localization of T-type channel isoforms in human breast tissue samples. Protein expressions of CaV3.1, CaV3.2, and CaV3.3 were evaluated by immunohistochemistry in breast without alteration, in proliferative non-neoplastic lesions, and in neoplastic ductal epithelial lesions of the human breast. CaV3.1, CaV3.2, and CaV3.3 nuclear expressions were decreased in advanced stages of neoplastic transformation, whereas CaV3.1 and CaV3.2 cytoplasmic expression increased. Also, the decrease in nuclear expression was correlated with an increase in cytoplasmic expression for CaV3.1 isoform. The change in CaV3 protein expression and subcellular localization are consistent with the neoplastic transformation stages of mammary epithelial cells, evident in early neoplastic lesions, such as ductal carcinomas in situ. These results suggest a possible involvement of CaV3 in the carcinogenic processes and could be considered as a potential pharmacological target in new therapies for breast cancer treatment.

L-type voltage-dependent Ca2+ channels expression involved in pre-neoplastic transformation of breast cancer

Background

Intracellular Ca2+ levels can modulate several cellular functions, including proliferation and other processes found altered in neoplastic cells. Helping to maintain Ca2+ homeostasis, L-type voltage-dependent Ca2+ channels had its expression identified in neoplasias, including breast cancer. Invasive breast carcinoma of no special type, the most common classification of breast cancer, has ductal hyperplasia and ductal carcinoma in situ as its possible non-obligate precursors. This channel’s role in breast cancer development from these precursors has not been investigated. Evaluate protein expression and subcellular localization of CaV1.1, CaV1.2, and CaV1.3 in mammary epithelium without alteration and neoplastic and non-neoplastic ductal proliferative lesions through immunohistochemistry was the aim of this investigation.

Methods

In the present study, CaV1.1, CaV1.2, and CaV1.3 protein expression was evaluated by immunohistochemistry in breast without alteration and in proliferative non-neoplastic and neoplastic ductal epithelial lesions of the human breast.

Results

It was observed that CaV1.3 presented a reduction in nuclear expression at neoplastic lesions, in addition to an increase in cytoplasmic CaV1.1 expression. The analyses of membrane immunostaining showed that CaV1.2 and CaV1.3 had an increase of expression as the lesions progressed in the stages leading to invasive carcinomas.

Conclusions

Changes in protein expression and subcellular localization of these channels during the progression stages indicate that they may be involved in neoplastic transformation.

Glycosylation of CaV3.2 Channels Contributes to the Hyperalgesia in Peripheral Neuropathy of Type 1 Diabetes

Our previous studies implicated glycosylation of the Ca_V3.2 isoform of T-type Ca²⁺ channels (T-channels) in the development of Type 2 painful peripheral diabetic neuropathy (PDN). Here we investigated biophysical mechanisms underlying the modulation of recombinant Ca_V3.2 channel by de-glycosylation enzymes such as neuraminidase (NEU) and PNGase-F (PNG), as well as their behavioral and biochemical effects in painful PDN Type 1. In our in vitro study we used whole-cell recordings of current-voltage relationships to confirm that Ca_V3.2 current densities were decreased ~2-fold after de-glycosylation. Furthermore, de-glycosylation induced a significant depolarizing shift in the steady-state relationships for activation and inactivation while producing little effects on the kinetics of current deactivation and recovery from inactivation. PDN was induced in vivo by injections of streptozotocin (STZ) in adult female C57Bl/6j wild type (WT) mice, adult female Sprague Dawley rats and Ca_V3.2 knock-out (KO mice). Either NEU or vehicle (saline) were locally injected into the right hind paws or intrathecally. We found that injections of NEU, but not vehicle, completely reversed thermal and mechanical hyperalgesia in diabetic WT rats and mice. In contrast, NEU did not alter baseline thermal and mechanical sensitivity in the Ca_V3.2 KO mice which also failed to develop painful PDN. Finally, we used biochemical methods with gel-shift analysis to directly demonstrate that N-terminal fragments of native Ca_V3.2 channels in the dorsal root ganglia (DRG) are glycosylated in both healthy and diabetic animals. Our results demonstrate that in sensory neurons glycosylation-induced alterations in Ca_V3.2 channels in vivo directly enhance diabetic hyperalgesia, and that glycosylation inhibitors can be used to ameliorate painful symptoms in Type 1 diabetes. We expect that our studies may lead to a better understanding of the molecular mechanisms underlying painful PDN in an effort to facilitate the discovery of novel treatments for this intractable disease.

KLHL1 Controls CaV3.2 Expression in DRG Neurons and Mechanical Sensitivity to Pain

Dorsal root ganglion (DRG) neurons process pain signaling through specialized nociceptors located in their peripheral endings. It has long been established low voltage-activated (LVA) CaV3.2 calcium channels control neuronal excitability during sensory perception in these neurons. Silencing CaV3.2 activity with antisense RNA or genetic ablation results in anti-nociceptive, anti-hyperalgesic and anti-allodynic effects. CaV3.2 channels are regulated by many proteins (Weiss and Zamponi, 2017), including KLHL1, a neuronal actin-binding protein that stabilizes channel activity by recycling it back to the plasma membrane through the recycling endosome. We explored whether manipulation of KLHL1 levels and thereby function as a CaV3.2 modifier can modulate DRG excitability and mechanical pain transmission or sensitivity to pain. We first assessed the mechanical sensitivity threshold and DRG properties in the KLHL1 KO mouse model. KO DRG neurons exhibited smaller T-type current density compared to WT without significant changes in voltage dependence, as expected in the absence of its modulator. Western blot analysis confirmed CaV3.2 but not CaV3.1, CaV3.3, CaV2.1, or CaV2.2 protein levels were significantly decreased; and reduced neuron excitability and decreased pain sensitivity were also found in the KLHL1 KO model. Analogously, transient down-regulation of KLHL1 levels in WT mice with viral delivery of anti-KLHL1 shRNA also resulted in decreased pain sensitivity. These two experimental approaches confirm KLHL1 as a physiological modulator of excitability and pain sensitivity, providing a novel target to control peripheral pain.

Role for calcium signaling in manganese neurotoxicity

BACKGROUND

Calcium is an essential macronutrient that is involved in many cellular processes. Homeostatic control of intracellular levels of calcium ions [Ca²⁺] is vital to maintaining cellular structure and function. Several signaling molecules are involved in regulating Ca²⁺ levels in cells and perturbation of calcium signaling processes is implicated in several neurodegenerative and neurologic conditions. Manganese [Mn] is a metal which is essential for basic physiological functions. However, overexposure to Mn from environmental contamination and workplace hazards is a global concern. Mn overexposure leads to its accumulation in several human organs particularly the brain. Mn accumulation in the brain results in a manganism, a Parkinsonian-like syndrome. Additionally, Mn is a risk factor for several neurodegenerative diseases including Parkinson's disease and Alzheimer's disease. Mn neurotoxicity also affects several neurotransmitter systems including dopaminergic, cholinergic and GABAergic. The mechanisms of Mn neurotoxicity are still being elucidated.

AIM

The review will highlight a potential role for calcium signaling molecules in the mechanisms of Mn neurotoxicity.

CONCLUSION

Ca²⁺ regulation influences the neurodegenerative process and there is possible role for perturbed calcium signaling in Mn neurotoxicity. Mechanisms implicated in Mn-induced neurodegeneration include oxidative stress, generation of free radicals, and apoptosis. These are influenced by mitochondrial integrity which can be dependent on intracellular Ca²⁺ homeostasis. Nevertheless, further elucidation of the direct effects of calcium signaling dysfunction and calcium-binding proteins activities in Mn neurotoxicity is required.

Ankyrin B and Ankyrin B variants differentially modulate intracellular and surface Cav2.1 levels

Ankyrin B (AnkB) is an adaptor and scaffold for motor proteins and various ion channels that is ubiquitously expressed, including in the brain. AnkB has been associated with neurological disorders such as epilepsy and autism spectrum disorder, but understanding of the underlying mechanisms is limited. Cav2.1, the pore-forming subunit of P/Q type voltage gated calcium channels, is a known interactor of AnkB and plays a crucial role in neuronal function. Here we report that wildtype AnkB increased overall Cav2.1 levels without impacting surface Cav2.1 levels in HEK293T cells. An AnkB variant, p.S646F, which we recently discovered to be associated with seizures, further increased overall Cav2.1 levels, again with no impact on surface Cav2.1 levels. AnkB p.Q879R, on the other hand, increased surface Cav2.1 levels in the presence of accessory subunits α2δ1 and β4. Additionally, AnkB p.E1458G decreased surface Cav2.1 irrespective of the presence of accessory subunits. In addition, we found that partial deletion of AnkB in cortex resulted in a decrease in overall Cav2.1 levels, with no change to the levels of Cav2.1 detected in synaptosome fractions. Our work suggests that depending on the particular variant, AnkB regulates intracellular and surface Cav2.1. Notably, expression of the AnkB variant associated with seizure (AnkB p.S646F) caused further increase in intracellular Cav2.1 levels above that of even wildtype AnkB. These novel findings have important implications for understanding the role of AnkB and Cav2.1 in the regulation of neuronal function in health and disease.

Identification of a molecular gating determinant within the carboxy terminal region of Cav3.3 T-type channels

The physiological functions controlled by T-type channels are intrinsically dependent on their gating properties, and alteration of T-type channel activity is linked to several human disorders. Therefore, it is essential to develop a clear understanding of the structural determinants responsible for the unique gating features of T-type channels. Here, we have investigated the specific role of the carboxy terminal region by creating a series a deletion constructs expressed in tsA-201 cells and analyzing them by patch clamp electrophysiology. Our data reveal that the proximal region of the carboxy terminus contains a structural determinant essential for shaping several gating aspects of Cav3.3 channels, including voltage-dependence of activation and inactivation, inactivation kinetics, and coupling between the voltage sensing and the pore opening of the channel. Altogether, our data are consistent with a model in which the carboxy terminus stabilizes the channel in a closed state.

Duplex signaling by CaM and Stac3 enhances CaV1.1 function and provides insights into congenital myopathy

CaV1.1 is essential for skeletal muscle excitation-contraction coupling. Its functional expression is tuned by numerous regulatory proteins, yet underlying modulatory mechanisms remain ambiguous as CaV1.1 fails to function in heterologous systems. In this study, by dissecting channel trafficking versus gating, we evaluated the requirements for functional CaV1.1 in heterologous systems. Although coexpression of the auxiliary β subunit is sufficient for surface-membrane localization, this baseline trafficking is weak, and channels elicit a diminished open probability. The regulatory proteins calmodulin and stac3 independently enhance channel trafficking and gating via their interaction with the CaV1.1 carboxy terminus. Myopathic stac3 mutations weaken channel binding and diminish trafficking. Our findings demonstrate that multiple regulatory proteins orchestrate CaV1.1 function via duplex mechanisms. Our work also furnishes insights into the pathophysiology of stac3-associated congenital myopathy and reveals novel avenues for pharmacological intervention.