The CaV1.4 Calcium Channel Is a Critical Regulator of T Cell Receptor Signaling and Naive T Cell Homeostasis

Conclusive demonstration of iatrogenic Alzheimer's disease transmission in a model of stem cell transplantation

The risk of iatrogenic disease is often underestimated as a concern in contemporary medical procedures, encompassing tissue and organ transplantation, stem cell therapies, blood transfusions, and the administration of blood-derived products. In this context, despite the prevailing belief that Alzheimer's disease (AD) manifests primarily in familial and sporadic forms, our investigation reveals an unexpected transplantable variant of AD in a preclinical context, potentially indicating iatrogenic transmission in AD patients. Through adoptive transplantation of donor bone marrow stem cells carrying a mutant human amyloid precursor protein (APP) transgene into either APP-deficient knockout or normal recipient animals, we observed rapid development of AD pathological hallmarks. These pathological features were significantly accelerated and emerged within 6-9 months post transplantation and included compromised blood-brain barrier integrity, heightened cerebral vascular neoangiogenesis, elevated brain-associated β-amyloid levels, and cognitive impairment. Furthermore, our findings underscore the contribution of β-amyloid burden originating outside of the central nervous system to AD pathogenesis within the brain. We conclude that stem cell transplantation from donors harboring a pathogenic mutant allele can effectively transfer central nervous system diseases to healthy recipients, mirroring the pathogenesis observed in the donor. Consequently, our observations advocate for genomic sequencing of donor specimens prior to tissue, organ, or stem cell transplantation therapies, as well as blood transfusions and blood-derived product administration, to mitigate the risk of iatrogenic diseases.

The link between intracellular calcium signaling and exosomal PD-L1 in cancer progression and immunotherapy

Exosomes are small membrane vesicles containing microRNA, RNA, DNA fragments, and proteins that are transferred from donor cells to recipient cells. Tumor cells release exosomes to reprogram the factors associated with the tumor microenvironment (TME) causing tumor metastasis and immune escape. Emerging evidence revealed that cancer cell-derived exosomes carry immune inhibitory molecule program death ligand 1 (PD-L1) that binds with receptor program death protein 1 (PD-1) and promote tumor progression by escaping immune response. Currently, some FDA-approved monoclonal antibodies are clinically used for cancer treatment by blocking PD-1/PD-L1 interaction. Despite notable treatment outcomes, some patients show poor drug response. Exosomal PD-L1 plays a vital role in lowering the treatment response, showing resistance to PD-1/PD-L1 blockage therapy through recapitulating the effect of cell surface PD-L1. To enhance therapeutic response, inhibition of exosomal PD-L1 is required. Calcium signaling is the central regulator of tumorigenesis and can regulate exosome biogenesis and secretion by modulating Rab GTPase family and membrane fusion factors. Immune checkpoints are also connected with calcium signaling and calcium channel blockers like amlodipine, nifedipine, lercanidipine, diltiazem, and verapamil were also reported to suppress cellular PD-L1 expression. Therefore, to enhance the PD-1/PD-L1 blockage therapy response, the reduction of exosomal PD-L1 secretion from cancer cells is in our therapeutic consideration. In this review, we proposed a therapeutic strategy by targeting calcium signaling to inhibit the expression of PD-L1-containing exosome levels that could reduce the anti-PD-1/PD-L1 therapy resistance and increase the patient's drug response rate.

RNA profiling of sEV (small extracellular vesicles)/exosomes reveals biomarkers and vascular endothelial dysplasia with moyamoya disease

The association of exosomal RNA profiling and pathogenesis of moyamoya disease (MMD) and intracranial Atherosclerotic disease (ICAD) is unknown. In this study, we investigated the RNA profiles of sEV (small extracellular vesicles)/exosomes in patients with MMD and ICAD. Whole blood samples were collected from 30 individuals, including 10 patients with MMD, 10 patients with ICAD, and 10 healthy individuals. Whole transcriptome analysis was performed using the GeneChip WT Pico Reagent kit. Transcriptional correlation was verified using quantitative reverse transcription-polymerase chain reaction (qRT-PCR). The association between functional dysregulation and candidate RNAs was studied in vitro. In total, 1,486 downregulated and 2,405 upregulated RNAs differed significantly between patients with MMD and healthy controls. Differential expression of six circRNAs was detected using qPCR. Among these significantly differentially expressed RNAs, IPO11 and PRMT1 circRNAs were upregulated, whereas CACNA1F circRNA was downregulated. This is the first study showing that the differential expression of exosomal RNAs associated with MMD pathogenesis, such as overexpression of IPO11 and PRMT1 circRNAs, may be related to angiogenesis in MMD. The downregulation of CACNA1F circRNA may be related to vascular occlusion. These results propose the utility of exosomal RNAs as biological markers in MMD.

Concomitant Calcium Channelopathies Involving CACNA1A and CACNA1F: A Case Report and Review of the Literature

Calcium channels are an integral component in maintaining cellular function. Alterations may lead to channelopathies, primarily manifested in the central nervous system. This study describes the clinical and genetic features of a unique 12-year-old boy harboring two congenital calcium channelopathies, involving the CACNA1A and CACNA1F genes, and provides an unadulterated view of the natural history of sporadic hemiplegic migraine type 1 (SHM1) due to the patient's inability to tolerate any preventative medication. The patient presents with episodes of vomiting, hemiplegia, cerebral edema, seizure, fever, transient blindness, and encephalopathy. He is nonverbal, nonambulatory, and forced to have a very limited diet due to abnormal immune responses. The SHM1 manifestations apparent in the subject are consistent with the phenotype described in the 48 patients identified as part of a systematic literature review. The ocular symptoms of CACNA1F align with the family history of the subject. The presence of multiple pathogenic variants make it difficult to identify a clear phenotype-genotype correlation in the present case. Moreover, the detailed case description and natural history along with the comprehensive review of the literature contribute to the understanding of this complex disorder and point to the need for comprehensive clinical assessments of SHM1.

TPC Functions in the Immune System

Two-pore channels (TPCs) are novel intracellular cation channels, which play a key role in numerous (patho-)physiological and immunological processes. In this chapter, we focus on their function in immune cells and immune reactions. Therefore, we first give an overview of the cellular immune response and the partaking immune cells. Second, we concentrate on ion channels which in the past have been shown to play an important role in the regulation of immune cells. The main focus is then directed to TPCs, which are primarily located in the membranes of acidic organelles, such as lysosomes or endolysosomes but also certain other vesicles. They regulate Ca²⁺ homeostasis and thus Ca²⁺ signaling in immune cells. Due to this important functional role, TPCs are enjoying increasing attention within the field of immunology in the last few decades but are also becoming more pertinent as pharmacological targets for the treatment of pro-inflammatory diseases such as allergic hypersensitivity. However, to uncover the precise molecular mechanism of TPCs in immune cell responses, further molecular, genetic, and ultrastructural investigations on TPCs are necessary, which then may pave the way to develop novel therapeutic strategies to treat diseases such as anaphylaxis more specifically.

Whole Exome Sequencing in Multi-Incident Families Identifies Novel Candidate Genes for Multiple Sclerosis

Multiple sclerosis (MS) is a degenerative disease of the central nervous system in which auto-immunity-induced demyelination occurs. MS is thought to be caused by a complex interplay of environmental and genetic risk factors. While most genetic studies have focused on identifying common genetic variants for MS through genome-wide association studies, the objective of the present study was to identify rare genetic variants contributing to MS susceptibility. We used whole exome sequencing (WES) followed by co-segregation analyses in nine multi-incident families with two to four affected individuals. WES was performed in 31 family members with and without MS. After applying a suite of selection criteria, co-segregation analyses for a number of rare variants selected from the WES results were performed, adding 24 family members. This approach resulted in 12 exonic rare variants that showed acceptable co-segregation with MS within the nine families, implicating the genes MBP, PLK1, MECP2, MTMR7, TOX3, CPT1A, SORCS1, TRIM66, ITPR3, TTC28, CACNA1F, and PRAM1. Of these, three genes (MBP, MECP2, and CPT1A) have been previously reported as carrying MS-related rare variants. Six additional genes (MTMR7, TOX3, SORCS1, ITPR3, TTC28, and PRAM1) have also been implicated in MS through common genetic variants. The proteins encoded by all twelve genes containing rare variants interact in a molecular framework that points to biological processes involved in (de-/re-)myelination and auto-immunity. Our approach provides clues to possible molecular mechanisms underlying MS that should be studied further in cellular and/or animal models.

Impact of FOXP3 gene polymorphisms and gene-environment interactions in asthma and atopy in a Brazilian population

BACKGROUND

Polymorphisms in genes related to the activation and development of regulatory T cells (Tregs), such as FOXP3, may be associated with asthma and atopy development. Additionally, environmental factors such as exposure to infections can modify the effect of these associations. This study evaluated the impact of polymorphisms in the FOXP3 on the risk of asthma and atopy as also gene-environment interactions in these outcomes.

METHODS

This study included 1,246 children from the SCAALA program, between 4 and 11 years of age. DNA was extracted from peripheral blood and eight SNPs (rs2280883, rs11465476, rs11465472, rs2232368, rs3761549, rs3761548, rs2232365 and rs2294021) were genotyped using the 2.5 HumanOmni Beadchip from Illumina (San Diego, California, USA) or TaqMan qRT-PCR.

RESULTS

The rs2232368 (Allele T) was positively associated with asthma symptoms (OR=1.95, CI=1.04 to 3.66, p = 0.040) and skin prick test (SPT) reactivity to aeroallergens (OR=2.31, CI=1.16 to 4.59, p = 0.017). The rs3761549 (Allele T) was positively associated with SPT reactivity (OR=1.44, CI=1.03 to 2.02, p = 0.034). The rs2280883 (Allele C) was negatively associated with specific IgE to aeroallergens (OR=0.83, CI=0.70 to 0.99, p = 0.040). Furthermore, the rs2280883 played a protective role in the development of atopy only in individuals seropositive to Epstein-Barr virus (EBV) infection (OR=0.74, CI=0.60 to 0.92, p = 0.003 and OR=0.74; 95% CI=0.61-0.91, p = 0.007 for SPT and slgE respectively), but not in individuals without EBV infection.

CONCLUSION

Polymorphisms in the FOXP3 gene were associated with the risk of atopy and asthma development in our population. In addition, EBV infection had an effect modifier of the observed association for rs2280883 variant.

Distinct Gene Expression Patterns of Calcium Channels and Related Signaling Pathways Discovered in Lymphomas

Cell surface calcium (Ca2+) channels permit Ca2+ ion influx, with Ca2+ taking part in cellular functions such as proliferation, survival, and activation. The expression of voltage-dependent Ca2+ (CaV) channels may modulate the growth of hematologic cancers. Profile analysis of Ca2+ channels, with a focus on the Ca2+ release-activated Ca2+ (CRAC) and L-type CaV channels, was performed on RNA sequencing data from lymphoma cell lines and samples derived from patients with diffuse large B cell lymphoma (DLBCL). CaV1.2 expression was found to be elevated in classical Hodgkin lymphoma (CHL) cell lines when compared to other B cell lymphoma cell lines. In contrast, CHL exhibited reduced expression of ORAI2 and STIM2. In our differential expression analysis comparing activated B cell-like DLBCL (ABC-DLBCL) and germinal centre B cell-like DLBCL (GCB-DLBCL) patient samples, ABC-DLBCL revealed stronger expression of CaV1.3, whereas CaV1.1, CaV1.2, and CaV1.4 showed greater expression levels in GCB-DLBCL. Interestingly, no differences in ORAI/STIM expression were noted in the patient samples. As Ca2+ is known to bind to calmodulin, leading to calcineurin activation and the passage of nuclear factor of activated T cells (NFAT) to the cell nucleus, pathways for calcineurin, calmodulin, NFAT, and Ca2+ signaling were also analyzed by gene set enrichment analysis. The NFAT and Ca2+ signaling pathways were found to be upregulated in the CHL cell lines relative to other B cell lymphoma cell lines. Furthermore, the calmodulin and Ca2+ signaling pathways were shown to be downregulated in the ABC-DLBCL patient samples. The findings of this study suggest that L-type CaV channels and Ca2+-related pathways could serve as differentiating components for biologic therapies in targeted lymphoma treatments.

Cavβ1 regulates T cell expansion and apoptosis independently of voltage-gated Ca2+ channel function

TCR stimulation triggers Ca2+ signals that are critical for T cell function and immunity. Several pore-forming α and auxiliary β subunits of voltage-gated Ca2+ channels (VGCC) were reported in T cells, but their mechanism of activation remains elusive and their contribution to Ca2+ signaling in T cells is controversial. We here identify CaVβ1, encoded by Cacnb1, as a regulator of T cell function. Cacnb1 deletion enhances apoptosis and impairs the clonal expansion of T cells after lymphocytic choriomeningitis virus (LCMV) infection. By contrast, Cacnb1 is dispensable for T cell proliferation, cytokine production and Ca2+ signaling. Using patch clamp electrophysiology and Ca2+ recordings, we are unable to detect voltage-gated Ca2+ currents or Ca2+ influx in human and mouse T cells upon depolarization with or without prior TCR stimulation. mRNAs of several VGCC α1 subunits are detectable in human (CaV3.3, CaV3.2) and mouse (CaV2.1) T cells, but they lack transcription of many 5' exons, likely resulting in N-terminally truncated and non-functional proteins. Our findings demonstrate that although CaVβ1 regulates T cell function, these effects are independent of VGCC channel activity.

Separation of the CaV 1.2-CaV 1.3 calcium channel duo prevents type 2 allergic airway inflammation

BACKGROUND

Voltage-gated calcium (Ca_v 1) channels contribute to T-lymphocyte activation. Ca_v 1.2 and Ca_v 1.3 channels are expressed in Th2 cells but their respective roles are unknown, which is investigated herein.

METHODS

We generated mice deleted for Ca_v 1.2 in T cells or Ca_v 1.3 and analyzed TCR-driven signaling. In this line, we developed original fast calcium imaging to measure early elementary calcium events (ECE). We also tested the impact of Ca_v 1.2 or Ca_v 1.3 deletion in models of type 2 airway inflammation. Finally, we checked whether the expression of both Ca_v 1.2 and Ca_v 1.3 in T cells from asthmatic children correlates with Th2-cytokine expression.

RESULTS

We demonstrated non-redundant and synergistic functions of Ca_v 1.2 and Ca_v 1.3 in Th2 cells. Indeed, the deficiency of only one channel in Th2 cells triggers TCR-driven hyporesponsiveness with weakened tyrosine phosphorylation profile, a strong decrease in initial ECE and subsequent reduction in the global calcium response. Moreover, Ca_v 1.3 has a particular role in calcium homeostasis. In accordance with the singular roles of Ca_v 1.2 and Ca_v 1.3 in Th2 cells, deficiency in either one of these channels was sufficient to inhibit cardinal features of type 2 airway inflammation. Furthermore, Ca_v 1.2 and Ca_v 1.3 must be co-expressed within the same CD4⁺ T cell to trigger allergic airway inflammation. Accordingly with the concerted roles of Ca_v 1.2 and Ca_v 1.3, the expression of both channels by activated CD4⁺ T cells from asthmatic children was associated with increased Th2-cytokine transcription.

CONCLUSIONS

Thus, Ca_v 1.2 and Ca_v 1.3 act as a duo, and targeting only one of these channels would be efficient in allergy treatment.

Insight of the role of mitochondrial calcium homeostasis in hepatic insulin resistance

Due to the rapid rise in the prevalence of chronic metabolic disease, more and more clinicians and basic medical researchers focus their eyesight on insulin resistance (IR), an early and central event of metabolic diseases. The occurrence and development of IR are primarily caused by excessive energy intake and reduced energy consumption. Liver is the central organ that controls glucose homeostasis, playing a considerable role in systemic IR. Decreased capacity of oxidative metabolism and mitochondrial dysfunction are being blamed as the direct reason for the development of IR. Mitochondrial Ca²⁺ plays a fundamental role in maintaining proper mitochondrial function and redox stability. The maintaining of mitochondrial Ca²⁺ homeostasis requires the cooperation of ion channels in the inner and outer membrane of mitochondria, such as mitochondrial calcium uniporter complex (MCUC) and voltage-dependent anion channels (VDACs). In addition, the crosstalk between the endoplasmic reticulum (ER), lysosome and plasma membrane with mitochondria is also significant for mitochondrial calcium homeostasis, which is responsible for an efficient network of cellular Ca²⁺ signaling. Here, we review the recent progression in the research about the regulation factors for mitochondrial Ca²⁺ and how the dysregulation of mitochondrial Ca²⁺ homeostasis is involved in the pathogenesis of hepatic IR, providing a new perspective for further exploring the role of ion in the onset and development of IR.

The Calcium Channel Inhibitor Nimodipine Shapes the Uveitogenic T Cells and Protects Mice from Experimental Autoimmune Uveitis through the p38-MAPK Signaling Pathway

Autoimmune uveitis (AU) is a sight-threatening ocular inflammatory disorder, characterized by massive retinal vascular leakage and inflamed lesions with infiltration of the uveitogenic T cells in the retina and disorders of the T cell-related immune response in the system. Stimulation of TCRs can trigger calcium release and influx via Ca²⁺ channels and then transmit signals from the surface to the nucleus, which are important for energy metabolism, proliferation, activation, and differentiation. Inhibition of Ca²⁺ influx by pharmacological modulation of Ca²⁺ channels may suppress T cell function, representing a novel anti-inflammatory strategy in the treatment of AU. This study investigated the effects of the l-type voltage-gated calcium channel blocker nimodipine in experimental AU (EAU). Nimodipine was found to not only decrease the clinical and histopathological inflammation score of EAU (C57BL/6J mice) but also dwindle the infiltration of uveitogenic CD4⁺ T cells into the retina. Moreover, nimodipine decreased the effector T cells and increased the regulatory T cells in the immune system. In vitro, nimodipine reduced the effector T cell differentiation of the IRBP_1-20-specific CD4⁺ T cells of EAU mice and LPS-stimulated PBMCs of uveitis patients. Meanwhile, nimodipine suppressed the energy metabolism, proliferation, activation, and Th1 cell differentiation of T cells. Further studies on RNA sequencing and molecular mechanisms have established that nimodipine alleviates EAU by regulating T cells response through the p38-MAPK pathway signaling. Taken together, our data reveal a novel therapeutic potential of the l-type Ca²⁺ channels antagonist nimodipine in AU by regulating the balance of T cell subsets.

Cav1.4 calcium channels control cytokine production by human peripheral TH17 cells and psoriatic skin-infiltrating T cells

BACKGROUND

Type-17 inflammation characterizes psoriasis, a chronic skin disease. Because several inflammatory cytokines contribute to psoriasis pathogenesis, inhibiting the simultaneous production of these cytokines in T_H17 cells may be beneficial in psoriasis. We found that Ca_v1.4, encoded by CACNA1F, was the only Ca_v1 calcium channel expressed in T_H17 cells.

OBJECTIVE

We sought to investigate the role of Ca_v1.4 expression in early T_H17-activation events and effector functions, as well as its association with T_H17 signature genes in lesional psoriatic (LP) skins.

METHODS

Transcriptional gene signatures associated with CACNA1F expression were examined in LP skins by RT-PCR and in situ hybridization. Ca_v1 inhibitor and/or shRNA lentivectors were used to assess the contribution of Ca_v1.4 in T_H17 activation and effector functions in a 3-dimensional skin reconstruction model.

RESULTS

CACNA1F expression correlated with inflammatory cytokine expression that characterizes LP skins and was preferentially associated with RORC expression in CD4⁺ and CD4^- cells from LP biopsies. Nicardipine, a Ca_v1 channel antagonist, markedly reduced inflammatory cytokine production by T_H17 cells from blood or LP skin. This was associated with decreased TCR-induced early calcium events at cell membrane and proximal signaling events. The knockdown of Ca_v1.4 in T_H17 cells impaired cytokine production. Finally, Ca_v1 inhibition reduced the expression of the keratinocyte genes characteristic of T_H17-mediated psoriasis inflammation in human skin equivalents.

CONCLUSIONS

Ca_v1.4 channels promote T_H17-cell functions both at the periphery and in inflammatory psoriatic skin.

Modulation of Adaptive Immunity and Viral Infections by Ion Channels

Most cellular functions require of ion homeostasis and ion movement. Among others, ion channels play a crucial role in controlling the homeostasis of anions and cations concentration between the extracellular and intracellular compartments. Calcium (Ca2+) is one of the most relevant ions involved in regulating critical functions of immune cells, allowing the appropriate development of immune cell responses against pathogens and tumor cells. Due to the importance of Ca2+ in inducing the immune response, some viruses have evolved mechanisms to modulate intracellular Ca2+ concentrations and the mobilization of this cation through Ca2+ channels to increase their infectivity and to evade the immune system using different mechanisms. For instance, some viral infections require the influx of Ca2+ through ionic channels as a first step to enter the cell, as well as their replication and budding. Moreover, through the expression of viral proteins on the surface of infected cells, Ca2+ channels function can be altered, enhancing the pathogen evasion of the adaptive immune response. In this article, we review those ion channels and ion transporters that are essential for the function of immune cells. Specifically, cation channels and Ca2+ channels in the context of viral infections and their contribution to the modulation of adaptive immune responses.

GABAergic signaling by cells of the immune system: more the rule than the exception

Gamma-aminobutyric acid (GABA) is best known as an essential neurotransmitter in the evolved central nervous system (CNS) of vertebrates. However, GABA antedates the development of the CNS as a bioactive molecule in metabolism and stress-coupled responses of prokaryotes, invertebrates and plants. Here, we focus on the emerging findings of GABA signaling in the mammalian immune system. Recent reports show that mononuclear phagocytes and lymphocytes, for instance dendritic cells, microglia, T cells and NK cells, express a GABAergic signaling machinery. Mounting evidence shows that GABA receptor signaling impacts central immune functions, such as cell migration, cytokine secretion, immune cell activation and cytotoxic responses. Furthermore, the GABAergic signaling machinery of leukocytes is implicated in responses to microbial infection and is co-opted by protozoan parasites for colonization of the host. Peripheral GABA signaling is also implicated in inflammatory conditions and diseases, such as type 1 diabetes, rheumatoid arthritis and cancer cell metastasis. Adding to its role in neurotransmission, growing evidence shows that the non-proteinogenic amino acid GABA acts as an intercellular signaling molecule in the immune system and, as an interspecies signaling molecule in host–microbe interactions. Altogether, the data raise the assumption of conserved GABA signaling in a broad range of mammalian cells and diversification of function in the immune system.

Metabolic barriers to cancer immunotherapy

Several non-redundant features of the tumour microenvironment facilitate immunosuppression and limit anticancer immune responses. These include physical barriers to immune infiltration, the recruitment of suppressive immune cells and the upregulation of ligands on tumour cells that bind to inhibitory receptors on immune cells. Recent insights into the importance of the metabolic restrictions imposed by the tumour microenvironment on antitumour T cells have begun to inform immunotherapeutic anticancer strategies. Therapeutics that target metabolic restrictions, such as low glucose levels, a low pH, hypoxia and the generation of suppressive metabolites, have shown promise as combination therapies for different types of cancer. In this Review, we discuss the metabolic aspects of the antitumour T cell response in the context of immune checkpoint blockade, adoptive cell therapy and treatment with oncolytic viruses, and discuss emerging combination strategies.

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

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

Voltage-Gated Calcium Channels in Nonexcitable Tissues

The identification of a gain-of-function mutation in CACNA1C as the cause of Timothy syndrome, a rare disorder characterized by cardiac arrhythmias and syndactyly, highlighted roles for the L-type voltage-gated Ca2+ channel CaV1.2 in nonexcitable cells. Previous studies in cells and animal models had suggested that several voltage-gated Ca2+ channels (VGCCs) regulated critical signaling events in various cell types that are not expected to support action potentials, but definitive data were lacking. VGCCs occupy a special position among ion channels, uniquely able to translate membrane excitability into the cytoplasmic Ca2+ changes that underlie the cellular responses to electrical activity. Yet how these channels function in cells not firing action potentials and what the consequences of their actions are in nonexcitable cells remain critical questions. The development of new animal and cellular models and the emergence of large data sets and unbiased genome screens have added to our understanding of the unanticipated roles for VGCCs in nonexcitable cells. Here, we review current knowledge of VGCC regulation and function in nonexcitable tissues and cells, with the goal of providing a platform for continued investigation.

Altered Ca2+ Homeostasis in Immune Cells during Aging: Role of Ion Channels

Aging is an unstoppable process and begins shortly after birth. Each cell of the organism is affected by the irreversible process, not only with equal density but also at varying ages and with different speed. Therefore, aging can also be understood as an adaptation to a continually changing cellular environment. One of these very prominent changes in age affects Ca²⁺ signaling. Especially immune cells highly rely on Ca²⁺-dependent processes and a strictly regulated Ca²⁺ homeostasis. The intricate patterns of impaired immune cell function may represent a deficit or compensatory mechanisms. Besides, altered immune function through Ca²⁺ signaling can profoundly affect the development of age-related disease. This review attempts to summarize changes in Ca²⁺ signaling due to channels and receptors in T cells and beyond in the context of aging.

CRAC Channels and Calcium Signaling in T Cell-Mediated Immunity

Calcium (Ca²⁺) signals play fundamental roles in immune cell function. The main sources of Ca²⁺ influx in mammalian lymphocytes following antigen receptor stimulation are Ca²⁺ release-activated Ca²⁺ (CRAC) channels. These are formed by ORAI proteins in the plasma membrane and are activated by stromal interaction molecules (STIM) located in the endoplasmic reticulum (ER). Human loss-of-function (LOF) mutations in ORAI1 and STIM1 that abolish Ca²⁺ influx cause a unique disease syndrome called CRAC channelopathy that is characterized by immunodeficiency autoimmunity and non-immunological symptoms. Studies in mice lacking Stim and Orai genes have illuminated many cellular and molecular mechanisms by which these molecules control lymphocyte function. CRAC channels are required for the differentiation and function of several T lymphocyte subsets that provide immunity to infection, mediate inflammation and prevent autoimmunity. This review examines new insights into how CRAC channels control T cell-mediated immunity.

iCa2+ Flux, ROS and IL-10 Determines Cytotoxic, and Suppressor T Cell Functions in Chronic Human Viral Infections

Exhaustion of CD8⁺ T cells and increased IL-10 production is well-known in chronic viral infections but mechanisms leading to loss of their cytotoxic capabilities and consequent exhaustion remain unclear. Exhausted CD8⁺T cells also called T suppressors are highly immune suppressive with altered T cell receptor signaling characteristics that mark it exclusively from their cytotoxic counterparts. Our study found that iCa²⁺ flux is reduced following T cell receptor activation in T suppressor cells when compared to their effector counterpart. Importantly chronic activation of murine cytotoxic CD8⁺ T cells lead to reduced iCa²⁺ influx, decreased IFN-γ and enhanced IL-10 production and this profile is mimicked in Tc1 cells upon reduction of iCa²⁺ flux by extracellular calcium channel inhibitors. Further reduced iCa²⁺ flux induced ROS which lead to IFN-γ reduction and increased IL-10 producing T suppressors through the STAT3—STAT5 axis. The above findings were substantiated by our human data where reduced iCa²⁺ flux in chronic Hepatitis infections displayed CD8⁺ T cells with low IFN-γ and increased IL-10 production. Importantly treatment with an antioxidant led to increased IFN-γ and reduced IL-10 production in human chronic Hep-B/C samples suggesting overall a proximal regulatory role for iCa²⁺ influx, ROS, and IL-10 in determining the effector/ suppressive axis of CD8⁺ T cells.

Calcium signalling in T cells

Calcium (Ca²⁺) signalling is of paramount importance to immunity. Regulated increases in cytosolic and organellar Ca²⁺ concentrations in lymphocytes control complex and crucial effector functions such as metabolism, proliferation, differentiation, antibody and cytokine secretion and cytotoxicity. Altered Ca²⁺ regulation in lymphocytes leads to various autoimmune, inflammatory and immunodeficiency syndromes. Several types of plasma membrane and organellar Ca²⁺-permeable channels are functional in T cells. They contribute highly localized spatial and temporal Ca²⁺ microdomains that are required for achieving functional specificity. While the mechanistic details of these Ca²⁺ microdomains are only beginning to emerge, it is evident that through crosstalk, synergy and feedback mechanisms, they fine-tune T cell signalling to match complex immune responses. In this article, we review the expression and function of various Ca²⁺-permeable channels in the plasma membrane, endoplasmic reticulum, mitochondria and endolysosomes of T cells and their role in shaping immunity and the pathogenesis of immune-mediated diseases.

Mutation of an L-Type Calcium Channel Gene Leads to T Lymphocyte Dysfunction

Calcium (Ca²⁺) is a vital secondary messenger in T lymphocytes regulating a vast array of important events including maturation, homeostasis, activation, and apoptosis and can enter the cell through CRAC, TRP, and Ca_V channels. Here we describe a mutation in the L-type Ca²⁺ channel Ca_V1.4 leading to T lymphocyte dysfunction, including several hallmarks of immunological exhaustion. Ca_V1.4-deficient mice exhibited an expansion of central and effector memory T lymphocytes, and an upregulation of inhibitory receptors on several T cell subsets. Moreover, the sustained elevated levels of activation markers on B lymphocytes suggest that they are in a chronic state of activation. Functionally, T lymphocytes exhibited a reduced store-operated Ca²⁺ flux compared to wild-type controls. Finally, modifying environmental conditions by herpes virus infection exacerbated the dysfunctional immune phenotype of the Ca_V1.4-deficient mice. This is the first example where the mutation of a Ca_V channel leads to T lymphocyte dysfunction, including the upregulation of several inhibitory receptors, hallmarks of T cell exhaustion, and establishes the physiological importance of Ca_V channel signaling in maintaining a nimble immune system.

What's Bred in the Bone: Calcium Channels in Lymphocytes

Calcium (Ca²⁺) is an important second messenger in lymphocytes and is essential in regulating various intracellular pathways that control critical cell functions. Ca²⁺ channels are located in the plasma membrane and intracellular membranes, facilitating Ca²⁺ entry into the cytoplasm. Upon Ag receptor stimulation, Ca²⁺ can enter the lymphocyte via the Ca²⁺ release-activated Ca²⁺ channel found in the plasma membrane. The increase of cytosolic Ca²⁺ modulates signaling pathways, resulting in the transcription of target genes implicated in differentiation, activation, proliferation, survival, and apoptosis of lymphocytes. Along with Ca²⁺ release-activated Ca²⁺ channels, several other channels have been found in the membranes of T and B lymphocytes contributing to key cellular events. Among them are the transient receptor potential channels, the P2X receptors, voltage-dependent Ca²⁺ channels, and the inositol 1,4,5-trisphosphate receptor as well as the N-methyl-d-aspartate receptors. In this article, we review the contributions of these channels to mediating Ca²⁺ currents that drive specific lymphocyte functions.

Calling in the CaValry-Toxoplasma gondii Hijacks GABAergic Signaling and Voltage-Dependent Calcium Channel Signaling for Trojan horse-Mediated Dissemination

Dendritic cells (DCs) are regarded as the gatekeepers of the immune system but can also mediate systemic dissemination of the obligate intracellular parasite Toxoplasma gondii. Here, we review the current knowledge on how T. gondii hijacks the migratory machinery of DCs and microglia. Shortly after active invasion by the parasite, infected cells synthesize and secrete the neurotransmitter γ-aminobutyric acid (GABA) and activate GABA-A receptors, which sets on a hypermigratory phenotype in parasitized DCs in vitro and in vivo. The signaling molecule calcium plays a central role for this migratory activation as signal transduction following GABAergic activation is mediated via the L-type voltage-dependent calcium channel (L-VDCC) subtype Cav1.3. These studies have revealed that DCs possess a GABA/L-VDCC/Cav1.3 motogenic signaling axis that triggers migratory activation upon T. gondii infection. Moreover, GABAergic migration can cooperate with chemotactic responses. Additionally, the parasite-derived protein Tg14-3-3 has been associated with hypermigration of DCs and microglia. We discuss the interference of T. gondii infection with host cell signaling pathways that regulate migration. Altogether, T. gondii hijacks non-canonical signaling pathways in infected immune cells to modulate their migratory properties, and thereby promote its own dissemination.

Photoreceptor degeneration in a new Cacna1f mutant mouse model

The Cacna1f gene encodes the α1F subunit of an L-type voltage-gated calcium channel, Cav1.4. In photoreceptor synaptic terminals, Cav1.4 channels mediate glutamate release and postsynaptic responses associated with visual signal transmission. We have discovered a new Cacna1f mutation in nob9 mice, which display more severe phenotypes than do nob2 mice. To characterize the nob9 phenotype at different ages, we examined the murine fundus, applied retinal optical coherence tomography, measured flash electroretinograms (ERGs) in vivo, and analyzed the retinal histology in vitro. After identifying the X-linked recessive inheritance trait, we sequenced Cacna1f as the candidate gene. Mutations in this gene were detected by polymerase chain reaction (PCR) and confirmed by restriction fragment length polymorphism. Morphologically, an early-onset of retinal disorder was detected, and the degeneration of the outer plexiform layers progressed rapidly. Moreover, the mutant mice showed drastically reduced scotopic ERGs with increasing age. In 14-month-old nob9 retinas, immunostaining of cone opsins demonstrated a reduction in the number of short-wavelength opsins (S-opsins) to 54% of wild-type levels, and almost no middle-wavelength opsins (M-opsins) were observed. No cone ERGs could be detected from residual cones, in which S-opsins abnormally migrated to inner segments of the photoreceptors. The mutations of the Cacna1f gene in nob9 mice involved both a single nucleotide G to A transition and a 10-nucleotide insertion, the latter resulting in a frame-shift mutation in exon 14.

TRPM2 mediates mitochondria-dependent apoptosis of melanocytes under oxidative stress

Abnormal mitochondrial calcium accumulation plays a critical role in oxidative stress-induced apoptosis of melanocytes. Transient receptor potential cation channel subfamily M member 2 (TRPM2) is a calcium channel sensitive to oxidative stress. However, whether TRPM2 participates in melanocyte apoptosis under oxidative stress was unknown before. In the present study, we initially found that hydrogen peroxide (H₂O₂) induced the demethylation of the promoter region in TRPM2 gene and increased the expression of TRPM2 in normal human melanocytes (NHMs). Meanwhile, TRPM2 was overexpressed in lesional melanocytes of vitiligo that is a skin disease caused by melanocyte loss under oxidative stress. Furthermore, either TRPM2 inhibitors or TRPM2 shRNA could ameliorate H₂O₂-induced apoptosis, mitochondrial reactive oxygen species (ROS) accumulation and mitochondrial membrane potential (MMP) loss in NHMs, which was similar to the effects of an anti-oxidant. More importantly, TRPM2 mediated the calcium influx into the cytoplasm and the mitochondria of NHMs exposed to H₂O₂, and a specific mitochondrial Ca²⁺ uptake inhibitor Ruthenium 360 (Ru360) could also protect NHMs from apoptosis and mitochondrial damages caused by H₂O₂. Taken together, our findings demonstrate that oxidative stress promotes the expression of TRPM2 and thus facilitates mitochondria-dependent apoptosis of melanocytes by increasing calcium influx. Our study indicates that TRPM2 is a potential target for protecting melanocytes against oxidative damages in vitiligo.

Ion channelopathies of the immune system

Ion channels and transporters move ions across membrane barriers and are essential for a host of cell functions in many organs. They conduct K+, Na+ and Cl-, which are essential for regulating the membrane potential, H+ to control intracellular and extracellular pH and divalent cations such as Ca2+, Mg2+ and Zn2+, which function as second messengers and cofactors for many proteins. Inherited channelopathies due to mutations in ion channels or their accessory proteins cause a variety of diseases in the nervous, cardiovascular and other tissues, but channelopathies that affect immune function are not as well studied. Mutations in ORAI1 and STIM1 genes that encode the Ca2+ release-activated Ca2+ (CRAC) channel in immune cells, the Mg2+ transporter MAGT1 and the Cl- channel LRRC8A all cause immunodeficiency with increased susceptibility to infection. Mutations in the Zn2+ transporters SLC39A4 (ZIP4) and SLC30A2 (ZnT2) result in nutritional Zn2+ deficiency and immune dysfunction. These channels, however, only represent a fraction of ion channels that regulate immunity as demonstrated by immune dysregulation in channel knockout mice. The immune system itself can cause acquired channelopathies that are associated with a variety of diseases of nervous, cardiovascular and endocrine systems resulting from autoantibodies binding to ion channels. These autoantibodies highlight the therapeutic potential of functional anti-ion channel antibodies that are being developed for the treatment of autoimmune, inflammatory and other diseases.

Channeling Vision: CaV1.4-A Critical Link in Retinal Signal Transmission

Voltage-gated calcium channels (VGCC) are key to many biological functions. Entry of Ca2+ into cells is essential for initiating or modulating important processes such as secretion, cell motility, and gene transcription. In the retina and other neural tissues, one of the major roles of Ca2+-entry is to stimulate or regulate exocytosis of synaptic vesicles, without which synaptic transmission is impaired. This review will address the special properties of one L-type VGCC, CaV1.4, with particular emphasis on its role in transmission of visual signals from rod and cone photoreceptors (hereafter called "photoreceptors," to the exclusion of intrinsically photoreceptive retinal ganglion cells) to the second-order retinal neurons, and the pathological effects of mutations in the CACNA1F gene which codes for the pore-forming α1F subunit of CaV1.4.

Involvement of ion channels in allergy

Allergic asthma is a complex disease, often characterized by an inappropriate Th2 response to normally harmless allergens. Epithelial cells damaged or activated by the allergen produce IL-33, TSLP and IL-25, activating ILC2 and dendritic cells. The latter migrate into lymph nodes where they induce Th2-cell commitment. Th2 and other type 2 innate inflammatory cells trigger inflammation and airway hyper-reactivity. The toolbox consisting of the ion channels varies from one cellular type to another and depends on its activation state, offering the possibility to design novel drugs in the field of allergy. We will discuss about some channels as calcium, nonselective cation, potassium and chloride channels that appear as good candidates in allergy.

Staphylococcal Superantigens Use LAMA2 as a Coreceptor To Activate T Cells

Canonical Ag-dependent TCR signaling relies on activation of the src-family tyrosine kinase LCK. However, staphylococcal superantigens can trigger TCR signaling by activating an alternative pathway that is independent of LCK and utilizes a Gα11-containing G protein-coupled receptor (GPCR) leading to PLCβ activation. The molecules linking the superantigen to GPCR signaling are unknown. Using the ligand-receptor capture technology LRC-TriCEPS, we identified LAMA2, the α2 subunit of the extracellular matrix protein laminin, as the coreceptor for staphylococcal superantigens. Complementary binding assays (ELISA, pull-downs, and surface plasmon resonance) provided direct evidence of the interaction between staphylococcal enterotoxin E and LAMA2. Through its G4 domain, LAMA2 mediated the LCK-independent T cell activation by these toxins. Such a coreceptor role of LAMA2 involved a GPCR of the calcium-sensing receptor type because the selective antagonist NPS 2143 inhibited superantigen-induced T cell activation in vitro and delayed the effects of toxic shock syndrome in vivo. Collectively, our data identify LAMA2 as a target of antagonists of staphylococcal superantigens to treat toxic shock syndrome.

Anti-apolipoprotein A-1 autoantibodies are associated with immunodeficiency and systemic inflammation in HIV patients

OBJECTIVES

To determine the existence of autoantibodies against apolipoprotein A-1 (anti-apoA-1 IgG) in HIV patients and explore their association with biological features of HIV infection and different inflammatory biomarkers. We also evaluated their impact on CD4⁺ lymphocytes survival.

METHODS

Anti-apoA-1 IgG plasma levels were assessed by ELISA in 237 HIV positive patients from a national prospective cohort with no current lipid-lowering therapy.

RESULTS

58% of patients were found positive for anti-apoA-1 IgG and were associated with lower CD4⁺ counts, but higher viremia and systemic inflammation. Logistic regression analyses indicated that high anti-apoA-1 IgG levels were associated with a 16-fold increased risk of displaying low CD4⁺ levels, independent of HIV RNA levels and treatment (adjusted Odds ratio [OR]:16.1, 95% Confidence Interval [95%CI]:1.80-143.6; p = 0.01), and a 6-fold increased risk of having a detectable viremia, independent of antiretroviral treatment (OR:5.47; 95% CI:1.63-18.36; p = 0.006). In vitro, anti-apoA-1 IgG induced dose and time-dependent CD4⁺ apoptosis that was increased by exposure to HIV RNA.

CONCLUSIONS

In HIV patients, anti-apoA-1 IgG levels are associated with low CD4+ counts, high viremia and a pro-inflammatory systemic profile. Anti-apoA-1 IgG can promote CD4+ lymphocyte apoptosis via undefined pathways.

The β and α2δ auxiliary subunits of voltage-gated calcium channel 1 (Cav1) are required for TH2 lymphocyte function and acute allergic airway inflammation

BACKGROUND

T lymphocytes express not only cell membrane ORAI calcium release-activated calcium modulator 1 but also voltage-gated calcium channel (Ca_v) 1 channels. In excitable cells these channels are composed of the ion-forming pore α1 and auxiliary subunits (β and α2δ) needed for proper trafficking and activation of the channel. Previously, we disclosed the role of Ca_v1.2 α1 in mouse and human T_H2 but not T_H1 cell functions and showed that knocking down Ca_v1 α1 prevents experimental asthma.

OBJECTIVE

We investigated the role of β and α2δ auxiliary subunits on Ca_v1 α1 function in T_H2 lymphocytes and on the development of acute allergic airway inflammation.

METHODS

We used Ca_vβ antisense oligonucleotides to knock down Ca_vβ and gabapentin, a drug that binds to and inhibits α2δ1 and α2δ2, to test their effects on T_H2 functions and their capacity to reduce allergic airway inflammation.

RESULTS

Mouse and human T_H2 cells express mainly Ca_vβ1, β3, and α2δ2 subunits. Ca_vβ antisense reduces T-cell receptor-driven calcium responses and cytokine production by mouse and human T_H2 cells with no effect on T_H1 cells. Ca_vβ is mainly involved in restraining Ca_v1.2 α1 degradation through the proteasome because a proteasome inhibitor partially restores the α1 protein level. Gabapentin impairs the T-cell receptor-driven calcium response and cytokine production associated with the loss of α2δ2 protein in T_H2 cells.

CONCLUSIONS

These results stress the role of Ca_vβ and α2δ2 auxiliary subunits in the stability and activation of Ca_v1.2 channels in T_H2 lymphocytes both in vitro and in vivo, as demonstrated by the beneficial effect of Ca_vβ antisense and gabapentin in allergic airway inflammation.

The cooling compound icilin attenuates autoimmune neuroinflammation through modulation of the T-cell response

The synthetic supercooling drug, icilin, and its primary receptor target, the cation channel transient receptor potential (TRP) melastatin-8 (TRPM8), have been described as potent negative regulators of inflammation in the colon. The aim of this study was to determine whether the anti-inflammatory action of icilin could potentially be used to treat autoimmune neuroinflammatory disorders, such as multiple sclerosis (MS). During experimental autoimmune encephalomyelitis (EAE)-a CD4⁺ T cell-driven murine model of MS-we found that both wild-type (WT) and TRPM8-deficient EAE mice were protected from disease progression during icilin treatment, as evidenced by delays in clinical onset and reductions in neuroinflammation. In vitro, icilin potently inhibited the proliferation of murine and human CD4⁺ T cells, with the peripheral expansion of autoantigen-restricted T cells similarly diminished by the administration of icilin in mice. Attenuation of both TRPM8^-/- and TRP ankyrin-1^-/- T-cell proliferation by icilin was consistent with the WT phenotype, which suggests a mechanism that is independent of these channels. In addition, icilin treatment altered the expressional profile of activated CD4⁺ T cells to one that was indicative of restricted effector function and limited neuroinflammatory potential. These findings identify a potent anti-inflammatory role for icilin in lymphocyte-mediated neuroinflammation and highlight clear pleiotropic effects of the compound beyond classic TRP channel activation.-Ewanchuk, B. W., Allan, E. R. O., Warren, A. L., Ramachandran, R., Yates, R. M. The cooling compound icilin attenuates autoimmune neuroinflammation through modulation of the T-cell response.

Relevance of tissue specific subunit expression in channelopathies

Channelopathies are a diverse group of human disorders that are caused by mutations in genes coding for ion channels or channel-regulating proteins. Several dozen channelopathies have been identified that involve both non-excitable cells as well as electrically active tissues like brain, skeletal and smooth muscle or the heart. In this review, we start out from the general question which ion channel genes are expressed tissue-selectively. We mined the human gene expression database Human Protein Atlas (HPA) for tissue-enriched ion channel genes and found 85 genes belonging to the ion channel families. Most of these genes were enriched in brain, testis and muscle and a complete list of the enriched ion channel genes is provided. We further focused on the tissue distribution of voltage-gated calcium channel (VGCC) genes including different brain areas and the retina based on the human gene expression from the FANTOM5 dataset. The expression data is complemented by an overview of the tissue-dependent aspects of L-type calcium channel (LTCC) function, dysfunction and pharmacology, as well as of their splice variants. Finally, we focus on the pathology of tissue-restricted LTCC channelopathies and their treatment options. This article is part of the Special Issue entitled 'Channelopathies.'

Cooperative and acute inhibition by multiple C-terminal motifs of L-type Ca2+ channels

Inhibitions and antagonists of L-type Ca²⁺ channels are important to both research and therapeutics. Here, we report C-terminus mediated inhibition (CMI) for Ca_V1.3 that multiple motifs coordinate to tune down Ca²⁺ current and Ca²⁺ influx toward the lower limits determined by end-stage CDI (Ca²⁺-dependent inactivation). Among IQ_V (preIQ₃-IQ domain), PCRD and DCRD (proximal or distal C-terminal regulatory domain), spatial closeness of any two modules, e.g., by constitutive fusion, facilitates the trio to form the complex, compete against calmodulin, and alter the gating. Acute CMI by rapamycin-inducible heterodimerization helps reconcile the concurrent activation/inactivation attenuations to ensure Ca²⁺ influx is reduced, in that Ca²⁺ current activated by depolarization is potently (~65%) inhibited at the peak (full activation), but not later on (end-stage inactivation, ~300 ms). Meanwhile, CMI provides a new paradigm to develop Ca_V1 inhibitors, the therapeutic potential of which is implied by computational modeling of Ca_V1.3 dysregulations related to Parkinson’s disease.

DOI:http://dx.doi.org/10.7554/eLife.21989.001

All cells need calcium ions to stay healthy, but having too many calcium ions can interfere with important processes in the cell and cause severe problems. Proteins known as calcium channels on the cell surface allow calcium ions to flow into the cell from the surrounding environment. Cells carefully control the opening and closing of these channels to prevent too many calcium ions entering the cell at once. Ca_V1.3 channels are a type of calcium channel that are important for the heart and brain to work properly. Defects in Ca_V1.3 channels can lead to irregular heart rhythms and neurodegenerative diseases such as Parkinson’s disease.

Studies have shown that part of the Ca_V1.3 channel that sits inside the cell – known as the “tail” – responds to increases in the levels of calcium ions inside the cell by closing the channel. The tail region of Ca_V1.3 contains three modules, but how these modules work together to regulate channel activity is not clear.

Liu, Yang et al. investigated whether the three modules need to be physically connected to each other in the channel protein. For the experiments, several versions of the protein were constructed with different combinations of tail modules being directly linked as part of the same molecule or present as separate molecules. When any two modules were directly linked, the third module could bind to them and this was enough to close the Ca_V1.3 channel. However, the channel did not close if the modules were totally isolated from each other as three separate molecules.

Certain types of neurons in the brain produce electrical signals in a rhythmic fashion that depends on Ca_V1.3 channels. In Parkinson’s disease, increased movement of calcium ions into these neurons via Ca_V1.3 channels interferes with the rhythms of the signals and can cause these cells to die. Liu, Yang et al. performed computer simulations to analyse the effects of closing Ca_V1.3 channels in these neurons. The results suggest that this can restore normal rhythms of electrical activity and prevent these cells from dying.

The next step is to understand the molecular details of how the tail region closes Ca_V1.3 channels and its role in healthy and diseased cells. This may lead to new ways to block Ca_V1.3 channels in different types of diseases.

DOI:http://dx.doi.org/10.7554/eLife.21989.002

Immunological Disorders: Regulation of Ca2+ Signaling in T Lymphocytes

Engagement of T cell receptors (TCRs) with cognate antigens triggers cascades of signaling pathways in helper T cells. TCR signaling is essential for the effector function of helper T cells including proliferation, differentiation, and cytokine production. It also modulates effector T cell fate by inducing cell death, anergy (nonresponsiveness), exhaustion, and generation of regulatory T cells. One of the main axes of TCR signaling is the Ca²⁺-calcineurin-nuclear factor of activated T cells (NFAT) signaling pathway. Stimulation of TCRs triggers depletion of intracellular Ca²⁺ store and, in turn, activates store-operated Ca²⁺ entry (SOCE) to raise the intracellular Ca²⁺ concentration. SOCE in T cells is mediated by the Ca²⁺ release-activated Ca²⁺ (CRAC) channels, which have been very well characterized in terms of their electrophysiological properties. Identification of STIM1 as a sensor to detect depletion of the endoplasmic reticulum (ER) Ca²⁺ store and Orai1 as the pore subunit of CRAC channels has dramatically advanced our understanding of the regulatory mechanism of Ca²⁺ signaling in T cells. In this review, we discuss our current understanding of Ca²⁺ signaling in T cells with specific focus on the mechanism of CRAC channel activation and regulation via protein interactions. In addition, we will discuss the role of CRAC channels in effector T cells, based on the analyses of genetically modified animal models.

Evaluating frequency and quality of pathogen-specific T cells

It is generally accepted that enumeration and characterization of antigen-specific T cells provide essential information about potency of the immune response. Here, we report a new technique to determine the frequency and potency of antigen-specific CD8 T cells. The assay measures changes of intracellular Ca²⁺ in real time by fluorescent microscopy in individual CD8 T cells responding to cognate peptides. The T cells form continuous monolayer, enabling the cells to present the peptides to each other. This approach allows us to evaluate the kinetics of intracellular Ca²⁺ signalling that characterizes the quality of T cell response. We demonstrate the usefulness of the assay examining the frequency and quality of cytomegalovirus-specific CD8 T cells from healthy donor and patient after haploidentical stem cell transplantation. The new assay has a potential to provide essential information determining the status of the immune system, disease morbidity, potency of therapeutic intervention and vaccine efficacy.

Characterization of T cell antigen specificity human blood is challenging due to the low clonal frequencies. Here the authors develop a fluorescent microscopy-based method to detect antigen-specific CD8 T cell activation, and apply it to characterize the anti-CMV repertoire.

Ionic immune suppression within the tumour microenvironment limits T cell effector function

Tumours progress despite being infiltrated by tumour-specific effector T cells. Tumours contain areas of cellular necrosis, which are associated with poor survival in a variety of cancers. Here, we show that necrosis releases intracellular potassium ions into the extracellular fluid of mouse and human tumours, causing profound suppression of T cell effector function. Elevation of the extracellular potassium concentration ([K+]e) impairs T cell receptor (TCR)-driven Akt-mTOR phosphorylation and effector programmes. Potassium-mediated suppression of Akt-mTOR signalling and T cell function is dependent upon the activity of the serine/threonine phosphatase PP2A. Although the suppressive effect mediated by elevated [K+]e is independent of changes in plasma membrane potential (Vm), it requires an increase in intracellular potassium ([K+]i). Accordingly, augmenting potassium efflux in tumour-specific T cells by overexpressing the potassium channel Kv1.3 lowers [K+]i and improves effector functions in vitro and in vivo and enhances tumour clearance and survival in melanoma-bearing mice. These results uncover an ionic checkpoint that blocks T cell function in tumours and identify potential new strategies for cancer immunotherapy.

L-type voltage-operated calcium channels contribute to astrocyte activation In vitro

We have found a significant upregulation of L-type voltage-operated Ca(++) channels (VOCCs) in reactive astrocytes. To test if VOCCs are centrally involved in triggering astrocyte reactivity, we used in vitro models of astrocyte activation in combination with pharmacological inhibitors, siRNAs and the Cre/lox system to reduce the activity of L-type VOCCs in primary cortical astrocytes. The endotoxin lipopolysaccharide (LPS) as well as high extracellular K(+) , glutamate, and ATP promote astrogliosis in vitro. L-type VOCC inhibitors drastically reduce the number of reactive cells, astrocyte hypertrophy, and cell proliferation after these treatments. Astrocytes transfected with siRNAs for the Cav1.2 subunit that conducts L-type Ca(++) currents as well as Cav1.2 knockout astrocytes showed reduce Ca(++) influx by ∼80% after plasma membrane depolarization. Importantly, Cav1.2 knock-down/out prevents astrocyte activation and proliferation induced by LPS. Similar results were found using the scratch wound assay. After injuring the astrocyte monolayer, cells extend processes toward the cell-free scratch region and subsequently migrate and populate the scratch. We found a significant increase in the activity of L-type VOCCs in reactive astrocytes located in the growing line in comparison to quiescent astrocytes situated away from the scratch. Moreover, the migration of astrocytes from the scratching line as well as the number of proliferating astrocytes was reduced in Cav1.2 knock-down/out cultures. In summary, our results suggest that Cav1.2 L-type VOCCs play a fundamental role in the induction and/or proliferation of reactive astrocytes, and indicate that the inhibition of these Ca(++) channels may be an effective way to prevent astrocyte activation. GLIA 2016. GLIA 2016;64:1396-1415.

Low-Voltage-Activated CaV3.1 Calcium Channels Shape T Helper Cell Cytokine Profiles

Activation of T cells is mediated by the engagement of T cell receptors (TCRs) followed by calcium entry via store-operated calcium channels. Here we have shown an additional route for calcium entry into T cells-through the low-voltage-activated T-type CaV3.1 calcium channel. CaV3.1 mediated a substantial current at resting membrane potentials, and its deficiency had no effect on TCR-initiated calcium entry. Mice deficient for CaV3.1 were resistant to the induction of experimental autoimmune encephalomyelitis and had reduced productions of the granulocyte-macrophage colony-stimulating factor (GM-CSF) by central nervous system (CNS)-infiltrating T helper 1 (Th1) and Th17 cells. CaV3.1 deficiency led to decreased secretion of GM-CSF from in vitro polarized Th1 and Th17 cells. Nuclear translocation of the nuclear factor of activated T cell (NFAT) was also reduced in CaV3.1-deficient T cells. These data provide evidence for T-type channels in immune cells and their potential role in shaping the autoimmune response.

T Cell Receptor Mediated Calcium Entry Requires Alternatively Spliced Cav1.1 Channels

The process of calcium entry in T cells is a multichannel and multi-step process. We have studied the requirement for L-type calcium channels (Ca_v1.1) α1S subunits during calcium entry after TCR stimulation. High expression levels of Ca_v1.1 channels were detected in activated T cells. Sequencing and cloning of Ca_v1.1 channel cDNA from T cells revealed that a single splice variant is expressed. This variant lacks exon 29, which encodes the linker region adjacent to the voltage sensor, but contains five new N-terminal exons that substitute for exons 1 and 2, which are found in the Ca_v1.1 muscle counterpart. Overexpression studies using cloned T cell Ca_v1.1 in 293HEK cells (that lack TCR) suggest that the gating of these channels was altered. Knockdown of Ca_v1.1 channels in T cells abrogated calcium entry after TCR stimulation, suggesting that Ca_v1.1 channels are controlled by TCR signaling.

Harnessing the Flow of Excitation: TRP, Voltage-Gated Na(+), and Voltage-Gated Ca(2+) Channels in Contemporary Medicine

Cellular signaling in both excitable and nonexcitable cells involves several classes of ion channels. Some of them are of minor importance, with very specialized roles in physiology, but here we concentrate on three major channel classes: TRP (transient receptor potential channels), voltage-gated sodium channels (Nav), and voltage-gated calcium channels (Cav). Here, we first propose a conceptual framework binding together all three classes of ion channels, a "flow-of-excitation model" that takes into account the inputs mediated by TRP and other similar channels, the outputs invariably provided by Cav channels, and the regenerative transmission of signals in the neural networks, for which Nav channels are responsible. We use this framework to examine the function, structure, and pharmacology of these channel classes both at cellular and also at whole-body physiological level. Building on that basis we go through the pathologies arising from the direct or indirect malfunction of the channels, utilizing ion channel defects, the channelopathies. The pharmacological interventions affecting these channels are numerous. Part of those are well-established treatments, like treatment of hypertension or some forms of epilepsy, but many other are deeply problematic due to poor drug specificity, ion channel diversity, and widespread expression of the channels in tissues other than those actually targeted.

Bioinformatics Analysis of Proteome Changes in Calu-3 Cell Infected by Influenza A Virus (H5N1)

<b><i>Aim:</i></b> This paper aimed to identify the differentially expressed proteins (DEPs) in Calu-3 cells infected by influenza A virus (IAV) subtype H5N1. <b><i>Methods:</i></b> We downloaded proteome data (BTO: 0000762) from the Proteomics Identifications database and identified the DEPs in the IAV-infected Calu-3 cells. Then we constructed a protein-protein interaction network and a transcriptional regulatory network of the proteins. Finally, we performed gene ontology (GO) analysis to study the IAV infection at a functional level. <b><i>Results:</i></b> A total of 4 protein groups between the normal cells and the Calu-3 cells infected by IAV, severe acute respiratory syndrome or swine influenza were identified. In the networks, we found 5 significant proteins including FAN, CPSF2, AGO1, AGO2 and PAX5. In addition, we demonstrated those proteins were associated with GO terms such as phosphate metabolic process, calcium ion transport, cell division and regulation of cell motion. STAT1, NS2, CD5, NCKX6 and PDGFB were significant DEPs in these GO terms. <b><i>Conclusions:</i></b> By referring to the previous studies, we suggest that proteins including FAN, CPSF2, AGO1, AGO2, PAX5, STAT1 and PDGFB can be used as therapeutic targets of IAV infection.

Signature Channels of Excitability no More: L-Type Channels in Immune Cells

Although the concept of Ca(2+) as a universal messenger is well established, it was assumed that the regulatory mechanisms of Ca(2+)-signaling were divided along the line of electric excitability. Recent advances in molecular biology and genomics have, however, provided evidence that non-excitable cells such as immunocytes also express a wide and diverse pool of ion channels that does not differ as significantly from that of excitable cells as originally assumed. Ion channels and transporters are involved in virtually all aspects of immune response regulation, from cell differentiation and development to activation, and effector functions such as migration, antibody-secretion, phagosomal maturation, or vesicular delivery of bactericidal agents. This comprises TRP channel family members, voltage- and Ca(2+)-gated K(+)- and Na(+)-channels, as well as unexpectedly, components of the CaV1-subfamily of voltage-gated L-type Ca(2+)-channels, originally thought to be signature molecules of excitability. This article provides an overview of recent observations made in the field of CaV1 L-type channel function in the immune context, as well as presents results we obtained studying these channels in B-lymphocytes.

Tweeters, Woofers and Horns: The Complex Orchestration of Calcium Currents in T Lymphocytes

Elevation of intracellular calcium ion (Ca²⁺) levels is a vital event that regulates T lymphocyte homeostasis, activation, proliferation, differentiation, and apoptosis. The mechanisms that regulate intracellular Ca²⁺ signaling in lymphocytes involve tightly controlled concinnity of multiple ion channels, membrane receptors, and signaling molecules. T cell receptor (TCR) engagement results in depletion of endoplasmic reticulum (ER) Ca²⁺ stores and subsequent sustained influx of extracellular Ca²⁺ through Ca²⁺ release-activated Ca²⁺ (CRAC) channels in the plasma membrane. This process termed store-operated Ca²⁺ entry (SOCE) involves the ER Ca²⁺ sensing molecule, STIM1, and a pore-forming plasma membrane protein, ORAI1. However, several other important Ca²⁺ channels that are instrumental in T cell function also exist. In this review, we discuss the role of additional Ca²⁺ channel families expressed on the plasma membrane of T cells that likely contribute to Ca²⁺ influx following TCR engagement, which include the TRP channels, the NMDA receptors, the P2X receptors, and the IP₃ receptors, with a focus on the voltage-dependent Ca²⁺ (Ca_V) channels.

Placing ion channels into a signaling network of T cells: from maturing thymocytes to healthy T lymphocytes or leukemic T lymphoblasts

T leukemogenesis is a multistep process, where the genetic errors during T cell maturation cause the healthy progenitor to convert into the leukemic precursor that lost its ability to differentiate but possesses high potential for proliferation, self-renewal, and migration. A new misdirecting "leukemogenic" signaling network appears, composed by three types of participants which are encoded by (1) genes implicated in determined stages of T cell development but deregulated by translocations or mutations, (2) genes which normally do not participate in T cell development but are upregulated, and (3) nondifferentially expressed genes which become highly interconnected with genes expressed differentially. It appears that each of three groups may contain genes coding ion channels. In T cells, ion channels are implicated in regulation of cell cycle progression, differentiation, activation, migration, and cell death. In the present review we are going to reveal a relationship between different genetic defects, which drive the T cell neoplasias, with calcium signaling and ion channels. We suggest that changes in regulation of various ion channels in different types of the T leukemias may provide the intracellular ion microenvironment favorable to maintain self-renewal capacity, arrest differentiation, induce proliferation, and enhance motility.