Loss of synaptic Zn2+ transporter function increases risk of febrile seizures

Structures, Mechanisms, and Physiological Functions of Zinc Transporters in Different Biological Kingdoms

Zinc transporters take up/release zinc ions (Zn2+) across biological membranes and maintain intracellular and intra-organellar Zn2+ homeostasis. Since this process requires a series of conformational changes in the transporters, detailed information about the structures of different reaction intermediates is required for a comprehensive understanding of their Zn2+ transport mechanisms. Recently, various Zn2+ transport systems have been identified in bacteria, yeasts, plants, and humans. Based on structural analyses of human ZnT7, human ZnT8, and bacterial YiiP, we propose updated models explaining their mechanisms of action to ensure efficient Zn2+ transport. We place particular focus on the mechanistic roles of the histidine-rich loop shared by several zinc transporters, which facilitates Zn2+ recruitment to the transmembrane Zn2+-binding site. This review provides an extensive overview of the structures, mechanisms, and physiological functions of zinc transporters in different biological kingdoms.

Antiviral activity of zinc against hepatitis viruses: current status and future prospects

Viral hepatitis is a major public health concern globally. World health organization aims at eliminating viral hepatitis as a public health threat by 2030. Among the hepatitis causing viruses, hepatitis B and C are primarily transmitted via contaminated blood. Hepatitis A and E, which gets transmitted primarily via the feco-oral route, are the leading cause of acute viral hepatitis. Although vaccines are available against some of these viruses, new cases continue to be reported. There is an urgent need to devise a potent yet economical antiviral strategy against the hepatitis-causing viruses (denoted as hepatitis viruses) for achieving global elimination of viral hepatitis. Although zinc was known to mankind for a long time (since before Christ era), it was identified as an element in 1746 and its importance for human health was discovered in 1963 by the pioneering work of Dr. Ananda S. Prasad. A series of follow up studies involving zinc supplementation as a therapy demonstrated zinc as an essential element for humans, leading to establishment of a recommended dietary allowance (RDA) of 15 milligram zinc [United States RDA for zinc]. Being an essential component of many cellular enzymes and transcription factors, zinc is vital for growth and homeostasis of most living organisms, including human. Importantly, several studies indicate potent antiviral activity of zinc. Multiple studies have demonstrated antiviral activity of zinc against viruses that cause hepatitis. This article provides a comprehensive overview of the findings on antiviral activity of zinc against hepatitis viruses, discusses the mechanisms underlying the antiviral properties of zinc and summarizes the prospects of harnessing the therapeutic benefit of zinc supplementation therapy in reducing the disease burden due to viral hepatitis.

Comparison of Serum Selenium, Homocysteine, Zinc, and Vitamin D Levels in Febrile Children with and without Febrile Seizures: A Prospective Single-Center Study

OBJECTIVE

Febrile seizure is a complication that makes physicians and families uneasy when detected in children with a high fevers. This study aimed to compare children with febrile seizures and children without seizures in blood selenium, zinc, homocysteine, vitamin D, vitamin B12, and magnesium levels.

MATERIALS AND METHODS

The study group included sixty-one children between the ages of 1-5 who came to the pediatric emergency department with febrile seizure. The control group had 61 children with fever without seizure, who were compatible with the study group in age, sex, and elapsed time since the onset of fever. Blood samples were taken from the patients during their admission. Selenium, zinc, vitamin D, homocysteine, vitamin B12, and magnesium levels were measured, and the data of the two groups were compared. Additionally, patients in the study group had two subgroups, simple and complex febrile seizures, and their parameters were compared.

RESULTS

Selenium, zinc, vitamin D, and vitamin B12 levels were significantly lower in the study group than in the control group (p < 0.001), and there was no significant difference in homocysteine (p = 0.990) and magnesium levels (p = 0.787) between the two groups. Moreover, no significant difference was found between those with simple and complex febrile seizures in selenium, vitamin D, homocysteine, vitamin B12, and magnesium levels.

CONCLUSIONS

Elevated levels of selenium, zinc, vitamin D, and vitamin B12 in the blood of children with fevers help to prevent febrile seizures.

Serum Levels of Growth-Associated Protein-43 and Neurotrophin-3 in Childhood Epilepsy and Their Relation to Zinc Levels

BACKGROUND

Epilepsy is one of the most common neurological disorders, and it places a significant economic strain on the healthcare system around the world. Although the exact mechanism of epilepsy has yet to be illustrated, various pathogenic cascades involving neurotransmitters and trace elements have been reported. We aimed to investigate the serum levels of growth-associated protein-43 (GAP-43) and neurotrophin-3 (NT-3) among cohort of Egyptian children with epilepsy and correlate these biomarkers with their zinc levels.

METHODS

This case-control study included 50 pediatric patients with epilepsy who were comparable with 50 controls. Neurological assessment and electroencephalogram (EEG) were done to all included children. Biochemical measurements of serum GAP-43 and NT-3 using enzyme linked immunosorbent assays (ELISA), and total antioxidant capacity (TAC) and zinc using colorimetric assays, were performed to all participants.

RESULTS

There was significantly frequent positive parental consanguinity among cases with significantly frequent generalized onset seizures (94%) than simple partial seizure (6%). There were significantly lower serum GAP-43 and zinc levels with significantly higher TAC among cases vs. the controls, p˂0.05 for all. There was no significant difference in the serum levels of NT-3 among epileptic children vs. the controls, p = 0.269. Serum Zn was positively correlated with GAP-43 level among epileptic children (r = 0.381, p = 0.006). Serum GAP-43 in diagnosing childhood epilepsy at cut-off point ≤ 0.6 ng/mL showed 78% sensitivity, 62% specificity, positive predictive value (PPV) = 50.6%, negative predictive value (NPP) = 84.9% with AUC = 0.574.

CONCLUSION

GAP-43 can be considered a sensitive good negative biomarker in childhood epilepsy which correlated positively with the zinc status.

Genome-wide association study of febrile seizures implicates fever response and neuronal excitability genes

Febrile seizures represent the most common type of pathological brain activity in young children and are influenced by genetic, environmental and developmental factors. In a minority of cases, febrile seizures precede later development of epilepsy.

We conducted a genome-wide association study of febrile seizures in 7635 cases and 83 966 controls identifying and replicating seven new loci, all with P < 5 × 10⁻¹⁰.

Variants at two loci were functionally related to altered expression of the fever response genes PTGER3 and IL10, and four other loci harboured genes (BSN, ERC2, GABRG2, HERC1) influencing neuronal excitability by regulating neurotransmitter release and binding, vesicular transport or membrane trafficking at the synapse. Four previously reported loci (SCN1A, SCN2A, ANO3 and 12q21.33) were all confirmed. Collectively, the seven novel and four previously reported loci explained 2.8% of the variance in liability to febrile seizures, and the single nucleotide polymorphism heritability based on all common autosomal single nucleotide polymorphisms was 10.8%. GABRG2, SCN1A and SCN2A are well-established epilepsy genes and, overall, we found positive genetic correlations with epilepsies (r_g = 0.39, P = 1.68 × 10⁻⁴). Further, we found that higher polygenic risk scores for febrile seizures were associated with epilepsy and with history of hospital admission for febrile seizures. Finally, we found that polygenic risk of febrile seizures was lower in febrile seizure patients with neuropsychiatric disease compared to febrile seizure patients in a general population sample.

In conclusion, this largest genetic investigation of febrile seizures to date implicates central fever response genes as well as genes affecting neuronal excitability, including several known epilepsy genes. Further functional and genetic studies based on these findings will provide important insights into the complex pathophysiological processes of seizures with and without fever.

Synthesis and Discovery of Schiff Base Bearing Furopyrimidinone for Selective Recognition of Zn2+ and its Applications in Cell Imaging and Detection of Cu2

A simplefuro [2,3-d]pyrimidinone-based Schiff base FPS was synthesized via aza-Wittig reaction and structure elucidation was carried out by spectroscopic studies FT-IR, 1H NMR, and 13C NMR and mass spectrometry. FPS showed weak fluorescence emission in methanol and the selectivity of FPS to different metal ions (Mn²⁺, Ca²⁺, Fe²⁺, Fe³⁺, Mg²⁺, Al³⁺, Ba²⁺, Ag⁺, Co²⁺, Na⁺, K⁺, Cu²⁺, Zn²⁺, Pb²⁺, Bi³⁺) were studied by absorption and fluorescence titration. The results show that FPS has selective fluorescence sensing behavior for Zn²⁺ ions and the limit of detection (LOD) was calculated to be 1.19 × 10^–8 mol/L. Moreover, FPS-Zn²⁺ acts as a metal based highly selective and sensitive new chemosensor for Cu²⁺ ions and the LOD was calculated to be 2.25 × 10^–7 mol/L. In accordance with the results and theoretical calculations, we suspected that the binding mechanisms of FPS to Zn²⁺ and Cu²⁺ were assigned to be the cooperative interaction of Zn²⁺(Cu²⁺)-N.

Role of GPR39 in Neurovascular Homeostasis and Disease

GPR39, a member of the ghrelin family of G protein-coupled receptors, is zinc-responsive and contributes to the regulation of diverse neurovascular and neurologic functions. Accumulating evidence suggests a role as a homeostatic regulator of neuronal excitability, vascular tone, and the immune response. We review GPR39 structure, function, and signaling, including constitutive activity and biased signaling, and summarize its expression pattern in the central nervous system. We further discuss its recognized role in neurovascular, neurological, and neuropsychiatric disorders.

Metal transport mechanism of the cation diffusion facilitator (CDF) protein family - a structural perspective on human CDF (ZnT)-related diseases

Divalent d-block metal cations (DDMCs) participate in many cellular functions; however, their accumulation in cells can be cytotoxic. The cation diffusion facilitator (CDF) family is a ubiquitous family of transmembrane DDMC exporters that ensures their homeostasis. Severe diseases, such as type II diabetes, Parkinson's and Alzheimer's disease, were linked to dysfunctional human CDF proteins, ZnT-1-10 (SLC30A1-10). Each member of the CDF family reduces the cytosolic concentration of a specific DDMC by transporting it from the cytoplasm to the extracellular environment or into intracellular compartments. This process is usually achieved by utilizing the proton motive force. In addition to their activity as DDMC transporters, CDFs also have other cellular functions such as the regulation of ion channels and enzymatic activity. The combination of structural and biophysical studies of different bacterial and eukaryotic CDF proteins led to significant progress in the understanding of the mutual interaction among CDFs and DDMCs, their involvement in ion binding and selectivity, conformational changes and the consequent transporting mechanisms. Here, we review these studies, provide our mechanistic interpretation of CDF proteins based on the current literature and relate the above to known human CDF-related diseases. Our analysis provides a common structure-function relationship to this important protein family and closes the gap between eukaryote and prokaryote CDFs.

Climate change and epilepsy: Insights from clinical and basic science studies

Climate change is with us. As professionals who place value on evidence-based practice, climate change is something we cannot ignore. The current pandemic of the novel coronavirus, SARS-CoV-2, has demonstrated how global crises can arise suddenly and have a significant impact on public health. Global warming, a chronic process punctuated by acute episodes of extreme weather events, is an insidious global health crisis needing at least as much attention. Many neurological diseases are complex chronic conditions influenced at many levels by changes in the environment. This review aimed to collate and evaluate reports from clinical and basic science about the relationship between climate change and epilepsy. The keywords climate change, seasonal variation, temperature, humidity, thermoregulation, biorhythm, gene, circadian rhythm, heat, and weather were used to search the published evidence. A number of climatic variables are associated with increased seizure frequency in people with epilepsy. Climate change-induced increase in seizure precipitants such as fevers, stress, and sleep deprivation (e.g. as a result of more frequent extreme weather events) or vector-borne infections may trigger or exacerbate seizures, lead to deterioration of seizure control, and affect neurological, cerebrovascular, or cardiovascular comorbidities and risk of sudden unexpected death in epilepsy. Risks are likely to be modified by many factors, ranging from individual genetic variation and temperature-dependent channel function, to housing quality and global supply chains. According to the results of the limited number of experimental studies with animal models of seizures or epilepsy, different seizure types appear to have distinct susceptibility to seasonal influences. Increased body temperature, whether in the context of fever or not, has a critical role in seizure threshold and seizure-related brain damage. Links between climate change and epilepsy are likely to be multifactorial, complex, and often indirect, which makes predictions difficult. We need more data on possible climate-driven altered risks for seizures, epilepsy, and epileptogenesis, to identify underlying mechanisms at systems, cellular, and molecular levels for better understanding of the impact of climate change on epilepsy. Further focussed data would help us to develop evidence for mitigation methods to do more to protect people with epilepsy from the effects of climate change.

Augmented seizure susceptibility and hippocampal epileptogenesis in a translational mouse model of febrile status epilepticus

OBJECTIVE

Prolonged fever-induced seizures (febrile status epilepticus [FSE]) during early childhood increase the risk for later epilepsy, but the underlying mechanisms are incompletely understood. Experimental FSE (eFSE) in rats successfully models human FSE, recapitulating the resulting epileptogenesis in a subset of affected individuals. However, the powerful viral and genetic tools that may enhance mechanistic insights into epileptogenesis and associated comorbidities, are better-developed for mice. Therefore, we aimed to determine if eFSE could be generated in mice and if it provoked enduring changes in hippocampal-network excitability and the development of spontaneous seizures.

METHODS

We employed C57BL/6J male mice, the strain used most commonly in transgenic manipulations, and examined if early life eFSE could be sustained and if it led to hyperexcitability of hippocampal networks and to epilepsy. Outcome measures included vulnerability to the subsequent administration of the limbic convulsant kainic acid (KA) and the development of spontaneous seizures. In the first mouse cohort, adult naive and eFSE-experiencing mice were exposed to KA. A second cohort of control and eFSE-experiencing young adult mice was implanted with bilateral hippocampal electrodes and recorded using continuous video-electroencephalography (EEG) for 2 to 3 months to examine for spontaneous seizures (epileptogenesis).

RESULTS

Induction of eFSE was feasible and eFSE increased the susceptibility of adult C57BL/6J mice to KA, thereby reducing latency to seizure onset and increasing seizure severity. Of 24 chronically recorded eFSE mice, 4 (16.5%) developed hippocampal epilepsy with a latent period of ~3 months, significantly different from the expectation by chance (P = .04). The limbic epilepsy that followed eFSE was progressive.

SIGNIFICANCE

eFSE promotes pro-epileptogenic network changes in a majority of C57BL/6J male mice and frank "temporal lobe-like" epilepsy in one sixth of the cohort. Mouse eFSE may thus provide a useful tool for investigating molecular, cellular, and circuit changes during the development of temporal lobe epilepsy and its comorbidities.

The changes of serum zinc, copper, and selenium levels in epileptic patients: a systematic review and meta-analysis

INTRODUCTION

It is widely accepted that trace elements have been implicated in various metabolic processes. Valproic acid (VPA) is a remarkably safe and effective antiepileptic drug. There is no consensus option regarding the fluctuations in serum zinc (Zn), copper (Cu), and selenium (Se) in epileptic patients treated with VPA. We applied a meta-analysis to systematically assess the effects of VPA on serum ions in these patients.

AREAS COVERED

In this study, we performed a meta-analysis of the changes in serum Zn, Cu, and Se levels in human samples of healthy controls, epileptic patients, and patients treated with VPA. Twenty-two published analyzable studies were selected by searching the databases of PubMed, China National Knowledge Infrastructure (CNKI), Google Scholar, Web of Science, EMBASE, WAN FANG and Vip.

EXPERT OPINION

Serum Se levels in epileptic patients were decreased compared to healthy controls. Serum Zn levels in patients with VPA treatment were significantly lower than those in epileptic patients. The results of this meta-analysis are instructive for the intake of trace elements such as Zn, Cu, and Se in the diet balance of patients with epilepsy treated with VPA. Meanwhile, this study provides a theoretical basis for the combined use of other drugs that affect the intake and absorption of trace elements and VPA.

Zinc Status and Febrile Seizures: Results from a Cross-sectional Study

Objective  To estimate the serum zinc levels in children under the age of 5 years with febrile seizures and febrile children without seizures Materials and Methods  In this cross-sectional study from 2017 to 2018, 40 children with febrile seizures (simple and complex) were taken as cases. Forty age- and sex-matched febrile children without convulsions were recruited as controls. Serum zinc estimates were analyzed using a spectrophotometer (Biolis 50i-Autoanalyzer). Statistical Analysis  The demographic variables and serum zinc estimates were analyzed using the Mann-Whitney test. The odds ratio was used to calculate the association of zinc deficiency in febrile seizures; 5% level of significance was considered. Results  The mean serum concentrations of zinc in the cases and controls were 83.8 ± 33.1 μg/dL and 116.3 ± 30.3 μg/dL, respectively ( p = 0.002). Hypozincemia defined by "a serum zinc level of less than 63 μg/dL" was found in 12 (30%) cases and 2(5%) controls with an odds ratio of 8:1. Conclusion  Children with febrile seizures had significantly reduced concentrations of zinc in the serum.

Why and how to investigate the role of protein phosphorylation in ZIP and ZnT zinc transporter activity and regulation

Zinc is required for the regulation of proliferation, metabolism, and cell signaling. It is an intracellular second messenger, and the cellular level of ionic, mobile zinc is strictly controlled by zinc transporters. In mammals, zinc homeostasis is primarily regulated by ZIP and ZnT zinc transporters. The importance of these transporters is underscored by the list of diseases resulting from changes in transporter expression and activity. However, despite numerous structural studies of the transporters revealing both zinc binding sites and motifs important for transporter function, the exact molecular mechanisms regulating ZIP and ZnT activities are still not clear. For example, protein phosphorylation was found to regulate ZIP7 activity resulting in the release of Zn2+ from intracellular stores leading to phosphorylation of tyrosine kinases and activation of signaling pathways. In addition, sequence analyses predict all 24 human zinc transporters to be phosphorylated suggesting that protein phosphorylation is important for regulation of transporter function. This review describes how zinc transporters are implicated in a number of important human diseases. It summarizes the current knowledge regarding ZIP and ZnT transporter structures and points to how protein phosphorylation seems to be important for the regulation of zinc transporter activity. The review addresses the need to investigate the role of protein phosphorylation in zinc transporter function and regulation, and argues for a pressing need to introduce quantitative phosphoproteomics to specifically target zinc transporters and proteins involved in zinc signaling. Finally, different quantitative phosphoproteomic strategies are suggested.

Serum zinc and copper levels in a sample of Egyptian epileptic children

Background

Epilepsy is among the most common disabling neurological disorders among children. Altered serum levels of zinc and copper may facilitate seizure occurrence and repetition, and antiepileptic drugs may disturb their serum levels affecting disease control and outcome.

Objective

To investigate the association between serum levels of zinc and copper and epilepsy and antiepileptic treatment in a group of Egyptian epileptic children.

Methods

Case-control study on 100 epileptic patients, aged from 2 to 16 years, from neurology outpatient clinic and 50 apparently healthy children with matched age and sex. Venous samples were withdrawn from patients and controls then serum levels of zinc and copper were measured with graphite furnace atomic absorption spectrometer-A Analyst 800.

Results

Serum zinc level of patients’ group was significantly lower than that of controls with a mean of 59.1 μ/dL ± 22.7 and 85 μ/dL ± 22.2, respectively (P < 0.01). Serum zinc level of patients with history of febrile seizures was significantly decreased compared to patients without history of febrile seizures with a mean of 41.5 μ/dL ± 20.1 and 67.9 μ/dL ± 19.3, respectively (P < 0.01). Patient on carbamazepine intake showed significantly lower zinc serum level than patients without carbamazepine intake, with a mean of 49.0 μ/dL ± 17 and 61.8 μ/dL ± 23.4, respectively (P < 0.01). A significant negative correlation was noted between the duration of illness of epilepsy and the mean copper serum level (P < 0.05).

Conclusion

Zinc and copper altered homeostasis have mounting evidence about their role in the pathogenesis of epilepsy. Designing treatment plans that selectively restore zinc and copper normal levels may be a beneficial strategy in the future.

Aberrant expression of PAR bZIP transcription factors is associated with epileptogenesis, focus on hepatic leukemia factor

Epilepsy is a widespread neurological disease characterized by abnormal neuronal activity resulting in recurrent seizures. There is mounting evidence that a circadian system disruption, involving clock genes and their downstream transcriptional regulators, is associated with epilepsy. In this study, we characterized the hippocampal expression of clock genes and PAR bZIP transcription factors (TFs) in a mouse model of temporal lobe epilepsy induced by intrahippocampal injection of kainic acid (KA). The expression of PAR bZIP TFs was significantly altered following KA injection as well as in other rodent models of acquired epilepsy. Although the PAR bZIP TFs are regulated by proinflammatory cytokines in peripheral tissues, we discovered that the regulation of their expression is inflammation-independent in hippocampal tissue and rather mediated by clock genes and hyperexcitability. Furthermore, we report that hepatic leukemia factor (Hlf), a member of PAR bZIP TFs family, is invariably downregulated in animal models of acquired epilepsy, regulates neuronal activity in vitro and its overexpression in dentate gyrus neurons in vivo leads to altered expression of genes associated with seizures and epilepsy. Overall, our study provides further evidence of PAR bZIP TFs involvement in epileptogenesis and points to Hlf as the key player.

Maintenance of Intestinal Epithelial Homeostasis by Zinc Transporters

Zinc is an essential micronutrient for normal organ function, and dysregulation of zinc metabolism has been implicated in a wide range of diseases. Emerging evidence has revealed that zinc transporters play diverse roles in cellular homeostasis and function by regulating zinc trafficking via organelles or the plasma membrane. In the gastrointestinal tract, zinc deficiency leads to diarrhea and dysfunction of intestinal epithelial cells. Studies also showed that zinc transporters are very important in intestinal epithelial homeostasis. In this review, we describe the physiological roles of zinc transporters in intestinal epithelial functions and relevance of zinc transporters in gastrointestinal diseases.

Intracellular Zn2+ transients modulate global gene expression in dissociated rat hippocampal neurons

Zinc (Zn²⁺) is an integral component of many proteins and has been shown to act in a regulatory capacity in different mammalian systems, including as a neurotransmitter in neurons throughout the brain. While Zn²⁺ plays an important role in modulating neuronal potentiation and synaptic plasticity, little is known about the signaling mechanisms of this regulation. In dissociated rat hippocampal neuron cultures, we used fluorescent Zn²⁺ sensors to rigorously define resting Zn²⁺ levels and stimulation-dependent intracellular Zn²⁺ dynamics, and we performed RNA-Seq to characterize Zn²⁺-dependent transcriptional effects upon stimulation. We found that relatively small changes in cytosolic Zn²⁺ during stimulation altered expression levels of 931 genes, and these Zn²⁺ dynamics induced transcription of many genes implicated in neurite expansion and synaptic growth. Additionally, while we were unable to verify the presence of synaptic Zn²⁺ in these cultures, we did detect the synaptic vesicle Zn²⁺ transporter ZnT3 and found it to be substantially upregulated by cytosolic Zn²⁺ increases. These results provide the first global sequencing-based examination of Zn²⁺-dependent changes in transcription and identify genes that may mediate Zn²⁺-dependent processes and functions.

How cellular Zn2+ signaling drives physiological functions

Zinc is an essential micronutrient affecting many aspects of human health. Cellular Zn²⁺ homeostasis is critical for cell function and survival. Zn²⁺, acting as a first or second messenger, triggers signaling pathways that mediate the physiological roles of Zn²⁺. Transient changes in Zn²⁺ concentrations within the cell or in the extracellular region occur following its release from Zn²⁺ binding metallothioneins, its transport across membranes by the ZnT or ZIP transporters, or release of vesicular Zn²⁺. These transients activate a distinct Zn²⁺ sensing receptor, ZnR/GPR39, or modulate numerous proteins and signaling pathways. Importantly, Zn²⁺ signaling regulates cellular physiological functions such as: proliferation, differentiation, ion transport and secretion. Indeed, novel therapeutic approaches aimed to maintain Zn²⁺ homeostasis and signaling are evolving. This review focuses on recent findings describing roles of Zn²⁺ and its transporters in regulating physiological or pathological processes.

Canonical Transient Receptor Potential Channel 3 Contributes to Febrile Seizure Inducing Neuronal Cell Death and Neuroinflammation

Febrile seizure (FS) counts as the most common seizures symptom in children undergoing recurrent seizures, posing a high risk to developing subsequent temporal lobe epilepsy. Canonical transient receptor potential channel (TRPC) members are identified as the FS-related genes in hyperthermia prone rats. However, the role of TRPC3 in hyperthermia-induced FS rats remains unclear. In the present study, we investigated whether TRPC3 functionally contributes to the development of FSs. Elevated TRPC3 mRNA and protein levels was detected in hyperthermia-induced FS rats and rat hippocampal neuron cells. The specific inhibitor of TRPC3, Pyr3, remarkably attenuated the susceptibility and severity of seizures, neuronal cell death, and neuroinflammation in FS rats. Conversely, NCX3 activation was apparently suppressed in rats subjected to recurrent FS and rat hippocampal neuron cells. The expression of NCX3 was up-regulated after TRPC3 inhibition in vivo and in vitro. Furthermore, an interaction between TRPC3 and NCX3 was detected by co-immunoprecipitation. Inhibition of TRPC3 suppressed intracellular Ca²⁺ levels in hyperthermia-treated hippocampal neuronal cells. In conclusion, our findings supported that TRPC3 functions as a critical regulator of seizure susceptibility and targeting TRPC3 may be a new therapeutic strategy for FS.

The Zinc Sensing Receptor, ZnR/GPR39, in Health and Disease

A distinct G-protein coupled receptor that senses changes in extracellular Zn²⁺, ZnR/GPR39, was found in cells from tissues in which Zn²⁺ plays a physiological role. Most prominently, ZnR/GPR39 activity was described in prostate cancer, skin keratinocytes, and colon epithelial cells, where zinc is essential for cell growth, wound closure, and barrier formation. ZnR/GPR39 activity was also described in neurons that are postsynaptic to vesicular Zn²⁺ release. Activation of ZnR/GPR39 triggers Gαq-dependent signaling and subsequent cellular pathways associated with cell growth and survival. Furthermore, ZnR/GPR39 was shown to regulate the activity of ion transport mechanisms that are essential for the physiological function of epithelial and neuronal cells. Thus, ZnR/GPR39 provides a unique target for therapeutically modifying the actions of zinc in a specific and selective manner.

Physiological roles of zinc transporters: molecular and genetic importance in zinc homeostasis

Zinc (Zn) is an essential trace mineral that regulates the expression and activation of biological molecules such as transcription factors, enzymes, adapters, channels, and growth factors, along with their receptors. Zn deficiency or excessive Zn absorption disrupts Zn homeostasis and affects growth, morphogenesis, and immune response, as well as neurosensory and endocrine functions. Zn levels must be adjusted properly to maintain the cellular processes and biological responses necessary for life. Zn transporters regulate Zn levels by controlling Zn influx and efflux between extracellular and intracellular compartments, thus, modulating the Zn concentration and distribution. Although the physiological functions of the Zn transporters remain to be clarified, there is growing evidence that Zn transporters are related to human diseases, and that Zn transporter-mediated Zn ion acts as a signaling factor, called "Zinc signal". Here we describe critical roles of Zn transporters in the body and their contribution at the molecular, biochemical, and genetic levels, and review recently reported disease-related mutations in the Zn transporter genes.

Comprehensive analysis of the numbers, lengths and amino acid compositions of transmembrane helices in prokaryotic, eukaryotic and viral integral membrane proteins of high-resolution structure

We report a comprehensive analysis of the numbers, lengths and amino acid compositions of transmembrane helices in 235 high-resolution structures of integral membrane proteins. The properties of 1551 transmembrane helices in the structures were compared with those obtained by analysis of the same amino acid sequences using topology prediction tools. Explanations for the 81 (5.2%) missing or additional transmembrane helices in the prediction results were identified. Main reasons for missing transmembrane helices were mis-identification of N-terminal signal peptides, breaks in α-helix conformation or charged residues in the middle of transmembrane helices and transmembrane helices with unusual amino acid composition. The main reason for additional transmembrane helices was mis-identification of amphipathic helices, extramembrane helices or hairpin re-entrant loops. Transmembrane helix length had an overall median of 24 residues and an average of 24.9 ± 7.0 residues and the most common length was 23 residues. The overall content of residues in transmembrane helices as a percentage of the full proteins had a median of 56.8% and an average of 55.7 ± 16.0%. Amino acid composition was analysed for the full proteins, transmembrane helices and extramembrane regions. Individual proteins or types of proteins with transmembrane helices containing extremes in contents of individual amino acids or combinations of amino acids with similar physicochemical properties were identified and linked to structure and/or function. In addition to overall median and average values, all results were analysed for proteins originating from different types of organism (prokaryotic, eukaryotic, viral) and for subgroups of receptors, channels, transporters and others.

Synaptic Zn2+ and febrile seizure susceptibility

Zn²⁺ , the second most prevalent trace element in the body, is essential for supporting a wide range of biological functions. While the majority of Zn²⁺ in the brain is protein-bound, a significant proportion of free Zn²⁺ is found co-localized with glutamate in synaptic vesicles and is released in an activity-dependent manner. Clinical studies have shown Zn²⁺ levels are significantly lower in blood and cerebrospinal fluid of children that suffer febrile seizures. Likewise, investigations in multiple animal models demonstrate that low levels of brain Zn²⁺ increase seizure susceptibility. Recent work provides human genetic evidence that disruption of brain Zn²⁺ homeostasis at the level of the synapse is associated with increased seizure susceptibility. In this review, we have explored the clinical, functional and genetic data supporting the view that low synaptic Zn²⁺ increases cellular excitability and febrile seizure susceptibility. Finally, the review focuses on the potential of therapeutic Zn²⁺ supplementation for at risk patients.

Altered zinc sensitivity of NMDA receptors harboring clinically-relevant mutations

Recent human genetic studies have identified a surprisingly high number of alterations in genes encoding NMDA receptor (NMDAR) subunits in several common brain diseases. Among NMDAR subunits, the widely-expressed GluN2A subunit appears particularly affected, with tens of de novo or inherited mutations associated with neurodevelopmental conditions including childhood epilepsies and cognitive deficits. Despite the increasing identification of NMDAR mutations of clinical interest, there is still little information about the effects of the mutations on receptor and network function. Here we analyze the impact on receptor expression and function of nine GluN2A missense (i.e. single-point) mutations targeting the N-terminal domain, a large regulatory region involved in subunit assembly and allosteric signaling. While several mutations produced no or little apparent effect on receptor expression, gating and pharmacology, two showed a drastic expression phenotype and two resulted in marked alterations in the sensitivity to zinc, a potent allosteric inhibitor of GluN1/GluN2A receptors and modulator of excitatory synaptic transmission. Surprisingly, both increase (GluN2A-R370W) and decrease (GluN2A-P79R) of zinc sensitivity were observed on receptors containing either one or two copies of the mutated subunits. Overexpression of the mutant subunits in cultured rat neurons confirmed the results from heterologous expression. These results, together with previously published data, indicate that disease-causing mutations in NMDARs produce a wide spectrum of receptor alterations, at least in vitro. They also point to a critical role of the zinc-NMDAR interaction in neuronal function and human health.

The Functions of Metallothionein and ZIP and ZnT Transporters: An Overview and Perspective

Around 3000 proteins are thought to bind zinc in vivo, which corresponds to ~10% of the human proteome. Zinc plays a pivotal role as a structural, catalytic, and signaling component that functions in numerous physiological processes. It is more widely used as a structural element in proteins than any other transition metal ion, is a catalytic component of many enzymes, and acts as a cellular signaling mediator. Thus, it is expected that zinc metabolism and homeostasis have sophisticated regulation, and elucidating the underlying molecular basis of this is essential to understanding zinc functions in cellular physiology and pathogenesis. In recent decades, an increasing amount of evidence has uncovered critical roles of a number of proteins in zinc metabolism and homeostasis through influxing, chelating, sequestrating, coordinating, releasing, and effluxing zinc. Metallothioneins (MT) and Zrt- and Irt-like proteins (ZIP) and Zn transporters (ZnT) are the proteins primarily involved in these processes, and their malfunction has been implicated in a number of inherited diseases such as acrodermatitis enteropathica. The present review updates our current understanding of the biological functions of MTs and ZIP and ZnT transporters from several new perspectives.