[Lambert-Eaton Myasthenic Syndrome].

Lambert-Eaton myasthenic syndrome (LEMS), an autoimmune disorder that affects the neuromuscular junction, is characterized by proximal muscle weakness, reduction of tendon reflexes, and autonomic dysfunction. LEMS shows a prevalence of approximately 0.25-0.27 per 100,000 population. The characteristic muscle weakness observed in patients with LEMS is attributed to the role of pathogenic autoantibodies directed against voltage-gated calcium channels (VGCC) present on the presynaptic nerve terminal. Notably, 50-60% of patients with LEMS have an associated tumor, small-cell lung carcinoma (SCLC), which also expresses functional voltage-gated calcium channels (VGCC). The Japanese LEMS diagnostic criteria 2022 recommend documentation of typical electrophysiological abnormalities combined with myasthenic symptoms for accurate diagnosis. P/Q-type VGCC antibody positivity strongly supports the diagnosis. Treatment options are categorized as oncological treatment, immunotherapy, and symptomatic treatments. Effective treatment of the tumor can improve LEMS in patients with SCLC. Most patients benefit from 3,4-diaminopyridine administration for symptomatic treatment. A treatment algorithm is established by the clinical practice guidelines 2022.

A wheat resistosome defines common principles of immune receptor channels.

Plant intracellular nucleotide-binding leucine-rich repeat receptors (NLRs) detect pathogen effectors to trigger immune responses1. Indirect recognition of a pathogen effector by the dicotyledonous Arabidopsis thaliana coiled-coil domain containing NLR (CNL) ZAR1 induces the formation of a large hetero-oligomeric protein complex, termed the ZAR1 resistosome, which functions as a calcium channel required for ZAR1-mediated immunity2-4. Whether the resistosome and channel activities are conserved among plant CNLs remains unknown. Here we report the cryo-electron microscopy structure of the wheat CNL Sr355 in complex with the effector AvrSr356 of the wheat stem rust pathogen. Direct effector binding to the leucine-rich repeats of Sr35 results in the formation of a pentameric Sr35-AvrSr35 complex, which we term the Sr35 resistosome. Wheat Sr35 and Arabidopsis ZAR1 resistosomes bear striking structural similarities, including an arginine cluster in the leucine-rich repeats domain not previously recognized as conserved, which co-occurs and forms intramolecular interactions with the 'EDVID' motif in the coiled-coil domain. Electrophysiological measurements show that the Sr35 resistosome exhibits non-selective cation channel activity. These structural insights allowed us to generate new variants of closely related wheat and barley orphan NLRs that recognize AvrSr35. Our data support the evolutionary conservation of CNL resistosomes in plants and demonstrate proof of principle for structure-based engineering of NLRs for crop improvement.

NAADP: From Discovery to Mechanism.

Nicotinic acid adenine dinucleotide 2'-phosphate (NAADP) is a naturally occurring nucleotide that has been shown to be involved in the release of Ca2+ from intracellular stores in a wide variety of cell types, tissues and organisms. Current evidence suggests that NAADP may function as a trigger to initiate a Ca2+ signal that is then amplified by other Ca2+ release mechanisms. A fundamental question that remains unanswered is the identity of the NAADP receptor. Our recent studies have identified HN1L/JPT2 as a high affinity NAADP binding protein that is essential for the modulation of Ca2+ channels.

RIPK3 Activates MLKL-mediated Necroptosis and Inflammasome Signaling during Streptococcus Infection.

Community-acquired pneumonia is the most common type of pneumonia and remains a leading cause of morbidity and mortality worldwide. Although many different pathogens can contribute to pneumonia, Streptococcus pneumoniae is one of the common bacterial pathogens that underlie community-acquired pneumonia. RIPK3 (receptor-interacting protein kinase 3) is widely recognized as a key modulator of inflammation and cell death. To elucidate a potential role of RIPK3 in pneumonia, we examined plasma from healthy control subjects and patients positive for streptococcal pneumonia. In human studies, RIPK3 protein concentrations were significantly elevated and were identified as a potential plasma marker of pneumococcal pneumonia. To expand these findings, we used an in vivo murine model of pneumococcal pneumonia to demonstrate that RIPK3 deficiency leads to reduced bacterial clearance, severe pathological damage, and high mortality. Our results illustrated that RIPK3 forms a complex with RIPK1, MLKL (mixed-lineage kinase domain-like protein), and MCU (mitochondrial calcium uniporter) to induce mitochondrial calcium uptake and mitochondrial reactive oxygen species(mROS) production during S. pneumoniae infection. In macrophages, RIPK3 initiated necroptosis via the mROS-mediated mitochondrial permeability transition pore opening and NLRP3 inflammasome activation via the mROS-AKT pathway to protect against S. pneumoniae. In conclusion, our study demonstrated a mechanism by which RIPK3-initiated necroptosis is essential for host defense against S. pneumoniae.

Arachidonic acid-regulated calcium signaling in T cells from patients with rheumatoid arthritis promotes synovial inflammation.

Rheumatoid arthritis (RA) and psoriatic arthritis (PsA) are two distinct autoimmune diseases that manifest with chronic synovial inflammation. Here, we show that CD4+ T cells from patients with RA and PsA have increased expression of the pore-forming calcium channel component ORAI3, thereby increasing the activity of the arachidonic acid-regulated calcium-selective (ARC) channel and making T cells sensitive to arachidonic acid. A similar increase does not occur in T cells from patients with systemic lupus erythematosus. Increased ORAI3 transcription in RA and PsA T cells is caused by reduced IKAROS expression, a transcriptional repressor of the ORAI3 promoter. Stimulation of the ARC channel with arachidonic acid induces not only a calcium influx, but also the phosphorylation of components of the T cell receptor signaling cascade. In a human synovium chimeric mouse model, silencing ORAI3 expression in adoptively transferred T cells from patients with RA attenuates tissue inflammation, while adoptive transfer of T cells from healthy individuals with reduced expression of IKAROS induces synovitis. We propose that increased ARC activity due to reduced IKAROS expression makes T cells more responsive and contributes to chronic inflammation in RA and PsA.

CaV α2δ Autoimmune Encephalitis: A Novel Antibody and its Characteristics.

OBJECTIVE: Discovery of a novel antibody would enable diagnosis and early treatment of autoimmune encephalitis. The aim was to discover a novel antibody targeting a synaptic receptor and characterize the pathogenic mechanism. METHOD: We screened for unknown antibodies in serum and cerebrospinal fluid samples from autoimmune encephalitis patients. Samples with reactivity to rat brain sections and no reactivity to conventional antibody tests underwent further processing for antibody discovery, using immunoprecipitation to primary neuronal cells, mass-spectrometry analysis, an antigen-binding assay on an antigen-overexpressing cell line, and an electrophysiological assay with cultured hippocampal neurons. RESULTS: Two patients had a novel antibody against CaV α2δ (voltage-gated calcium channel alpha-2/delta subunit). The patient samples stained neuropils of the hippocampus, basal ganglia, and cortex in rat brain sections and bound to a CaV α2δ-overexpressing cell line. Knockdown of CaV α2δ expression in cultured neurons turned off the immunoreactivity of the antibody from the patients to the neurons. The patients were associated with preceding meningitis or neuroendocrine carcinoma and responded to immunotherapy. In cultured neurons, the antibody reduced neurotransmitter release from presynaptic nerve terminals by interfering with tight coupling of calcium channels and exocytosis. INTERPRETATION: Here, we discovered a novel autoimmune encephalitis associated with anti-CaV α2δ antibody. Further analysis of the antibody in autoimmune encephalitis might promote early diagnosis and treatment. ANN NEUROL 2021;89:740-752.

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.

The Function of Mitochondrial Calcium Uniporter at the Whole-Cell and Single Mitochondrion Levels in WT, MICU1 KO, and MICU2 KO Cells.

Mitochondrial Ca2+ ([Ca2+]M) uptake through its Ca2+ uniporter (MCU) is central to many cell functions such as bioenergetics, spatiotemporal organization of Ca2+ signals, and apoptosis. MCU activity is regulated by several intrinsic proteins including MICU1, MICU2, and EMRE. While significant details about the role of MICU1, MICU2, and EMRE in MCU function have emerged recently, a key challenge for the future experiments is to investigate how these regulatory proteins modulate mitochondrial Ca2+ influx through MCU in intact cells under pathophysiological conditions. This is further complicated by the fact that several variables affecting MCU function change dynamically as cell functions. To overcome this void, we develop a data-driven model that closely replicates the behavior of MCU under a wide range of cytosolic Ca2+ ([Ca2+]C), [Ca2+]M, and mitochondrial membrane potential values in WT, MICU1 knockout (KO), and MICU2 KO cells at the single mitochondrion and whole-cell levels. The model is extended to investigate how MICU1 or MICU2 KO affect mitochondrial function. Moreover, we show how Ca2+ buffering proteins, the separation between mitochondrion and Ca2+-releasing stores, and the duration of opening of Ca2+-releasing channels affect mitochondrial function under different conditions. Finally, we demonstrate an easy extension of the model to single channel function of MCU.

Antibody-induced internalisation of retroviral envelope glycoproteins is a signal initiation event.

As obligate parasites, viruses highjack, modify and repurpose the cellular machinery for their own replication. Viral proteins have, therefore, evolved biological functions, such as signalling potential, that alter host cell physiology in ways that are still incompletely understood. Retroviral envelope glycoproteins interact with several host proteins, extracellularly with their cellular receptor and anti-envelope antibodies, and intracellularly with proteins of the cytoskeleton or sorting, endocytosis and recirculation pathways. Here, we examined the impact of endogenous retroviral envelope glycoprotein expression and interaction with host proteins, particularly antibodies, on the cell, independently of retroviral infection. We found that in the commonly used C57BL/6 substrains of mice, where murine leukaemia virus (MLV) envelope glycoproteins are expressed by several endogenous MLV proviruses, the highest expressed MLV envelope glycoprotein is under the control of an immune-responsive cellular promoter, thus linking MLV envelope glycoprotein expression with immune activation. We further showed that antibody ligation induces extensive internalisation from the plasma membrane into endocytic compartments of MLV envelope glycoproteins, which are not normally subject to constitutive endocytosis. Importantly, antibody binding and internalisation of MLV envelope glycoproteins initiates signalling cascades in envelope-expressing murine lymphocytic cell lines, leading to cellular activation. Similar effects were observed by MLV envelope glycoprotein ligation by its cellular receptor mCAT-1, and by overexpression in human lymphocytic cells, where it required an intact tyrosine-based YXXΦ motif in the envelope glycoprotein cytoplasmic tail. Together, these results suggest that signalling potential is a general property of retroviral envelope glycoproteins and, therefore, a target for intervention.

Case report: Headache and neurological deficits with CSF lymphocytosis (HaNDL) associated with P/Q type voltage-gated calcium channel antibodies (CACNA1A).

BACKGROUND: Headache and Neurological Deficits with cerebrospinal fluid (CSF) Lymphocytosis (HaNDL) is an increasingly recognised syndrome but the aetiology remains unclear. HaNDL has striking clinical features similar to Familial Hemiplegic Migraine (FHM), commonly related to gene mutations encoding the P/Q-type voltage-gated calcium channel (VGCC). CASE REPORT: We report a case of HaNDL associated with high P/Q-type voltage-gated calcium channel antibodies. Extensive investigations excluded alternative diagnoses and CSF lymphocytosis resolved within 3 months. The case was complicated by raised intracranial pressure resulting in an enlarged blind spot, papilloedema and bilateral lateral rectus palsies. CONCLUSION: This novel association of P/Q-type voltage-gated calcium channel antibodies with HaNDL has implications for the pathology of HaNDL and spectrum of voltage-gated calcium channel-antibody disorders. We compare the clinical features of FHM and HaNDL and the potential pathological role of these antibodies. This case also highlights that raised intracranial pressure is a common feature of HaNDL, rarely resulting in serious complications.

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.

Calcium Ion Channels: Roles in Infection and Sepsis Mechanisms of Calcium Channel Blocker Benefits in Immunocompromised Patients at Risk for Infection.

Immunosuppression may occur for a number of reasons related to an individual's frailty, debility, disease or from therapeutic iatrogenic intervention or misadventure. A large percentage of morbidity and mortality in immunodeficient populations is related to an inadequate response to infectious agents with slow response to antibiotics, enhancements of antibiotic resistance in populations, and markedly increased prevalence of acute inflammatory response, septic and infection related death. Given known relationships between intracellular calcium ion concentrations and cytotoxicity and cellular death, we looked at currently available data linking blockade of calcium ion channels and potential decrease in expression of sepsis among immunosuppressed patients. Notable are relationships between calcium, calcium channel, vitamin D mechanisms associated with sepsis and demonstration of antibiotic-resistant pathogens that may utilize channels sensitive to calcium channel blocker. We note that sepsis shock syndrome represents loss of regulation of inflammatory response to infection and that vitamin D, parathyroid hormone, fibroblast growth factor, and klotho interact with sepsis defense mechanisms in which movement of calcium and phosphorus are part of the process. Given these observations we consider that further investigation of the effect of relatively inexpensive calcium channel blockade agents of infections in immunosuppressed populations might be worthwhile.

Low specificity of voltage-gated calcium channel antibodies in Lambert-Eaton myasthenic syndrome: a call for caution.

As testing for neuronal antibodies become more readily available, the spectrum of conditions potentially associated with these autoantibodies has been widening. Voltage-gated calcium channel antibodies (VGCC-Ab) are no exception to this trend. The significance of an elevated VGCC-Ab titer beyond its original clinicopathological correlate, Lambert-Eaton myasthenic syndrome (LEMS) remains undetermined. We sought to determine the diagnostic significance of an elevated serum VGCC-Ab titer in a large single-center cohort of 100 patients. The majority of patients (58%) with elevated VGCC-Ab levels lacked an inflammatory or autoimmune etiology of their neurologic diagnosis. Only six cases (6%) of LEMS and two cases (2%) of SCLC (without LEMS) were identified. No significant differences in antibody titers were seen between the autoimmune and non-autoimmune groups. These findings support the notions that: (a) elevated VGCC-Ab titers without clinical correlation must be interpreted with caution, and (b) the clinical and electrodiagnostic criteria for LEMS should remain the mainstay in the diagnosis of LEMS.

Paraneoplastic Lambert-Eaton syndrome in a patient with disseminated metastatic cancer. / Síndrome paraneoplásico de Lambert-Eaton en paciente con cáncer metastásico diseminado

Background: Neurological paraneoplastic syndromes are rare, occur in 0.01% of all cancer patients; like part of them, the Lambert-Eaton syndrome is an autoimmune presynaptic disorder of neuromuscular transmission characterized by muscle weakness and neurovegetative dysfunction, and often associated with small cell lung cancer. Case report: A 72 years old female with a family history of lung cancer and leukemia, with 7 months of dry cough and 3 months with waist and pelvic muscle weakness, oropharyngeal dysphagia, dry mouth, chronic constipation and weight loss of 10 kg. Physical examination: patient prostrated; clinical muscle examination: pelvic muscles waist -3/5 and -4/5 the rest; diminished reflexes. Laboratory normal parathormone and hypercalcemia. With electrophysiological study and positive anti-voltage-gated calcium channel antibodies, confirming Lambert-Eaton syndrome and imaging studies with neoplastic condition in brain, liver and kidney, with unspecified primary origin.

Antecedentes: Los síndromes paraneoplásicos neurológicos son poco frecuentes; se presentan en el 0.01% de todos los pacientes con cáncer. Uno de ellos es el síndrome de Lambert-Eaton, correspondiendo a un trastorno presináptico autoinmunitario de transmisión neuromuscular caracterizado por debilidad muscular y disfunción neurovegetativa, y asociado con frecuencia al carcinoma microcítico de pulmón. Caso clínico: Mujer de 72 años, con antecedentes heredofamiliares de cáncer de pulmón y leucemia, con tos seca de 7 meses, 3 meses con debilidad de los músculos de cintura pélvica, disfagia al inicio de la deglución, xerostomía, estreñimiento crónico y pérdida de peso de 10 kg. A la exploración física: paciente postrada; examen clínico muscular: músculos de cintura pélvica en −3/5, resto en −4/5; reflejos disminuidos. Pruebas de laboratorio indicando hipercalcemia y paratohormona normal. Estudio electrofisiológico y anticuerpos anticanales de calcio positivos, demostrando síndrome de Lamber-Eaton, y estudios de imagen con afectación neoplásica en cerebro, hígado y riñón, sin lograr especificar el origen primario.

Paraneoplastic Lambert-Eaton Myasthenic Syndrome With Limbic Encephalitis: Clinical Correlation With the Coexistence of Anti-VGCC and Anti-GABAB Receptor Antibodies.

OBJECTIVE: To characterize Lambert-Eaton myasthenic syndrome and limbic encephalitis with coexistent voltage-gated calcium channel (VGCC) antibody and γ-aminobutyric acid (GABA) B receptor antibody. METHODS: Case study. RESULTS: A 57-year-old man presented with 6 months of weakness, unsteadiness, and vision difficulties. Examination revealed proximal weakness and diminished reflexes. Electrodiagnostic study revealed low-amplitude motor potentials and facilitation on high-frequency stimulation. Laboratory evaluation identified P/Q-type VGCC antibody. Positron emission tomography identified a mediastinal lesion, confirmed as small-cell lung carcinoma. The patient developed confusion and seizures. Cerebrospinal fluid analysis identified antibodies to GABAB receptor. CONCLUSIONS: This case describes a patient with Lambert-Eaton myasthenic syndrome, limbic encephalitis, and autoantibodies to VGCC and GABAB receptor. Atypical presentation of paraneoplastic neurological syndromes could indicate the presence of a second antibody that may have significant impact on therapy.

A Rare Case of Cerebellar Ataxia Due to Voltage-Gated Calcium Channel and Glutamic Acid Decarboxylase Autoantibodies.

BACKGROUND Autoimmune cerebellar ataxia can be paraneoplastic in nature or can occasionally present without evidence of an ongoing malignancy. The detection of specific autoantibodies has been statistically linked to different etiologies. CASE REPORT A 55-year-old African-American woman with hypertension and a past history of morbid obesity and uncontrolled diabetes status post gastric bypass four years prior to the visit (with significantly improved body mass index and hemoglobin A1c controlled at the time of the clinical encounter) presented to the office complaining of gradual onset of unsteadiness and recurrent falls for the past three years, as well as difficulties coordinating routine daily activities. The neurologic exam showed moderate dysarthria and ataxic gait with bilateral dysmetria and positive Romberg test. Routine laboratory test results were only remarkable for a mild elevation of erythrocyte sedimentation rate, and most laboratory and imaging tests for common causes of ataxia failed to demonstrate an etiology. Upon further workup, evidence of anti-voltage-gated calcium channel and anti-glutamic acid decarboxylase antibody was demonstrated. She was then treated with intravenous immunoglobulins with remarkable clinical improvement. CONCLUSIONS We present a case of antibody-mediated ataxia not associated with malignancy. While ataxia is rarely related to autoantibodies, in such cases it is critical to understand the etiology of this disabling condition in order to treat it correctly. Clinicians should be aware of the possible association with specific autoantibodies and the necessity to rule out an occult malignancy in such cases.

Store-Operated Ca2+ Entry Controls Clonal Expansion of T Cells through Metabolic Reprogramming.

Store-operated Ca2+ entry (SOCE) is the main Ca2+ influx pathway in lymphocytes and is essential for T cell function and adaptive immunity. SOCE is mediated by Ca2+ release-activated Ca2+ (CRAC) channels that are activated by stromal interaction molecule (STIM) 1 and STIM2. SOCE regulates many Ca2+-dependent signaling molecules, including calcineurin, and inhibition of SOCE or calcineurin impairs antigen-dependent T cell proliferation. We here report that SOCE and calcineurin regulate cell cycle entry of quiescent T cells by controlling glycolysis and oxidative phosphorylation. SOCE directs the metabolic reprogramming of naive T cells by regulating the expression of glucose transporters, glycolytic enzymes, and metabolic regulators through the activation of nuclear factor of activated T cells (NFAT) and the PI3K-AKT kinase-mTOR nutrient-sensing pathway. We propose that SOCE controls a critical "metabolic checkpoint" at which T cells assess adequate nutrient supply to support clonal expansion and adaptive immune responses.

Membrane translocation of transient receptor potential ankyrin 1 induced by inflammatory cytokines in lung cancer cells.

Transient receptor potential ankyrin 1 (TRPA1) is known as one of the nociceptors expressed in sensory neurons. It also plays a role in non-neural cells in inflammatory sites. However, the regulatory mechanisms for the reactivity of TRPA1 in these cells under inflammatory conditions are not clear. To clarify these mechanisms, we examined the effects of inflammatory cytokines (interleukin [IL]-1α, IL-1ß and tumor necrosis factor α [TNFα]) on TRPA1 reactivity and expression in the endogenously TRPA1-expressing lung tumor cell line A549. Treatment with IL-1α, but not IL-1ß or TNFα, increased the number of cells responding to allyl isothiocyanate, a TRPA1 agonist, in a dose- and time-dependent manner. The IL-1α-induced increase of TRPA1 responsiveness was inhibited by an extracellular-regulated kinase (Erk) inhibitor (PD98059) but not by inhibitors of c-Jun kinase, p38 mitogen-activated protein kinase or phosphatidylinositol-3 kinase. Phosphorylation of Erk gradually increased at 24 h after its transient induction in cells treated with IL-1α. IL-1α increased the TRPA1 levels on biotinylated cell surface proteins. These results suggest that IL-1α enhances the translocation of TRPA1 to the plasma membrane via the activation of Erk in A549. TRPA1 may have a pathophysiological role in non-neural lung cells under inflammatory conditions.