Expression of transport proteins in the rete mirabile of european silver and yellow eel

Background In physoclist fishes filling of the swimbladder requires acid secretion of gas gland cells to switch on the Root effect and subsequent countercurrent concentration of the initial gas partial pressure increase by back-diffusion of gas molecules in the rete mirabile. It is generally assumed that the rete mirabile functions as a passive exchanger, but a detailed analysis of lactate and water movements in the rete mirabile of the eel revealed that lactate is diffusing back in the rete. In the present study we therefore test the hypothesis that expression of transport proteins in rete capillaries allows for back-diffusion of ions and metabolites, which would support the countercurrent concentrating capacity of the rete mirabile. It is also assumed that in silver eels, the migratory stage of the eel, the expression of transport proteins would be enhanced. Results Analysis of the transcriptome and of the proteome of rete mirabile tissue of the European eel revealed the expression of a large number of membrane ion and metabolite transport proteins, including monocarboxylate and glucose transport proteins. In addition, ion channel proteins, Ca2+-ATPase, Na+/K+-ATPase and also F1F0-ATP synthase were detected. In contrast to our expectation in silver eels the expression of these transport proteins was not elevated as compared to yellow eels. A remarkable number of enzymes degrading reactive oxygen species (ROS) was detected in rete capillaries. Conclusions Our results reveal the expression of a large number of transport proteins in rete capillaries, so that the back diffusion of ions and metabolites, in particular lactate, may significantly enhance the countercurrent concentrating ability of the rete. Metabolic pathways allowing for aerobic generation of ATP supporting secondary active transport mechanisms are established. Rete tissue appears to be equipped with a high ROS defense capacity, preventing damage of the tissue due to the high oxygen partial pressures generated in the countercurrent system.

Modified N-linked glycosylation status predicts trafficking defective human Piezo1 channel mutations

Mechanosensitive channels are integral membrane proteins that sense mechanical stimuli. Like most plasma membrane ion channel proteins they must pass through biosynthetic quality control in the endoplasmic reticulum that results in them reaching their destination at the plasma membrane. Here we show that N-linked glycosylation of two highly conserved asparagine residues in the ‘cap’ region of mechanosensitive Piezo1 channels are necessary for the mature protein to reach the plasma membrane. Both mutation of these asparagines (N2294Q/N2331Q) and treatment with an enzyme that hydrolyses N-linked oligosaccharides (PNGaseF) eliminates the fully glycosylated mature Piezo1 protein. The N-glycans in the cap are a pre-requisite for N-glycosylation in the ‘propeller’ regions, which are present in loops that are essential for mechanotransduction. Importantly, trafficking-defective Piezo1 variants linked to generalized lymphatic dysplasia and bicuspid aortic valve display reduced fully N-glycosylated Piezo1 protein. Thus the N-linked glycosylation status in vitro correlates with efficient membrane trafficking and will aid in determining the functional impact of Piezo1 variants of unknown significance.

Early Predictive Biomarkers for Hypertension Using Human Fetal Astrocytes

Hypertension is a major risk factor for cardiovascular and cerebrovascular diseases, causing high numbers of deaths and /or disabilities worldwide. Previous studies have reported numerous biomolecules, such as, triglycerides and fibrinogen as biomarkers of hypertension (HTN), but none of these biomolecules could be considered as ‘true’ predictive biomarkers as they were produced after the establishment of HTN. Therefore, there is an urgent need for identifying and monitoring molecules that are linked to early pre-HTN stages, that is, prior to the onset of HTN. Astrocytes are the most abundant cells in the nervous system and through their long processes, astrocytes can communicate with both neuronal and non-neuronal cells such as endothelial cells lining blood vessels. Thus, any biochemical changes in astrocytes will affect both blood vessels and neurons. We are using human fetal astrocytes (HFAs) to investigate the molecules which may possibly act as early predictive biomarkers for hypertension. Astrocytic processes are mostly supported by the intermediate filaments, an example is the glial fibrillary acidic protein (GFAP) which is a type III intermediate filament. Elevated GFAP levels are being considered as a marker of astroglial injury, indicating the conversion of non-reactive (A2) into reactive (A1) astrocytes. Our initial immunohistochemistry studies using anti-GFAP antibodies on astrocytes from spontaneous hypertensive rats (SHRs) and their normal counter parts (WKY) rats showed a similar profile to that of reactive (A1) and non-reactive (A2) HFAs, respectively. Numerous studies point to a significant role of calcium ion channel proteins in hypertension, and calcium channel blockers such as Amlodipine (Norvasc) Diltiazem (Cardizem) are commonly used as antihypertensive drugs. By using liquid chromatography–tandem mass spectrometry (LC–MS/MS) we observed that reactive (A1) astrocytes, contain more calcium-activated proteins such as calpain, calpastatin, cathepsin and mitogen activated protein kinase (MAPK) as compare to normal (A2) HFAs, suggesting their possible link to the future onset of HTN. Hence these proteins could be considered as potential early predictive biomarkers of HTN.

Structural biology of coronavirus ion channels

Viral infection compromises specific organelles of the cell and readdresses its functional resources to satisfy the needs of the invading body. Around 70% of the coronavirus positive-sense single-stranded RNA encodes proteins involved in replication, and these viruses essentially take over the biosynthetic and transport mechanisms to ensure the efficient replication of their genome and trafficking of their virions. Some coronaviruses encode genes for ion-channel proteins – the envelope protein E (orf4a), orf3a and orf8 – which they successfully employ to take control of the endoplasmic reticulum–Golgi complex intermediate compartment or ERGIC. The E protein, which is one of the four structural proteins of SARS-CoV-2 and other coronaviruses, assembles its transmembrane protomers into homopentameric channels with mild cationic selectivity. Orf3a forms homodimers and homotetramers. Both carry a PDZ-binding domain, lending them the versatility to interact with more than 400 target proteins in infected host cells. Orf8 is a very short 29-amino-acid single-passage transmembrane peptide that forms cation-selective channels when assembled in lipid bilayers. This review addresses the contribution of biophysical and structural biology approaches that unravel different facets of coronavirus ion channels, their effects on the cellular machinery of infected cells and some structure–functional correlations with ion channels of higher organisms.

Parallel Recordings of Transmembrane hERG Channel Currents Based on Solvent-Free Lipid Bilayer Microarray

The reconstitution of ion-channel proteins in artificially formed bilayer lipid membranes (BLMs) forms a well-defined system for the functional analysis of ion channels and screening of the effects of drugs that act on these proteins. To improve the efficiency of the BLM reconstitution system, we report on a microarray of stable solvent-free BLMs formed in microfabricated silicon (Si) chips, where micro-apertures with well-defined nano- and micro-tapered edges were fabricated. Sixteen micro-wells were manufactured in a chamber made of Teflon®, and the Si chips were individually embedded in the respective wells as a recording site. Typically, 11 to 16 BLMs were simultaneously formed with an average BLM number of 13.1, which corresponded to a formation probability of 82%. Parallel recordings of ion-channel activities from multiple BLMs were successfully demonstrated using the human ether-a-go-go-related gene (hERG) potassium channel, of which the relation to arrhythmic side effects following drug treatment is well recognized.

Multiple mutations in associated with LQTS genes in patients with life-threating ventricular tachyarrhythmias

Синдром удлиненного интервала QT (LQTS) представляет собой генетически детерминированное заболевание, характеризующееся удлинением интервала QT на электрокардиограмме, высоким риском жизнеугрожающих аритмий и внезапной сердечной смерти. Причиной данного синдрома являются мутации в генах, кодирующих белки ионных каналов, а также протеины, опосредованно связанные с ионными каналами. От 4,5 до 8% пациентов с LQTS имеют более одной мутации в генах, связанных с развитием каналопатий. Цель работы: описание двух клинических случаев пациентов с жизнеугрожающими аритмиями, у которых выявлено сочетание редких мутантных аллелей в генах, ассоциированных с LQTS. Клиническое обследование включало ЭКГ в 12 отведениях, ЭхоКГ, МРТ сердца с отсроченным контрастированием и суточное мониторирование ЭКГ (СМ ЭКГ). Генетическое тестирование выполнено методом высокопроизводительного секвенирования (NGS) с использованием набора реагентов «TruSight™ Cardio Sequencing Panel» (Illumina). Оба пациента без отягощенного семейного анамнеза имели злокачественные желудочковые тахиаритмии, которые потребовали имплантации кардиовертера-дефибриллятора. В результате проведенного генотипирования методом NGS у пациента с идиопатической желудочковой тахикардией выявлено сочетание замен в генах ANK2 (c.9161C>G, p.Ala3054Gly, rs139007578) и KCNE1 (c.253G>A, p.Asp85Asn, rs1805128). У пациента с идиопатической фибрилляцией желудочков обнаружен аллельный вариант также в гене ANK2 (c.1397C>T, p.Thr466Met, rs786205722) и дополнительная замена в гене SNTA1 (c.787G>T, (p.Ala263Ser), rs150576530). При наличии у пациентов нескольких генетических дефектов может наблюдаться «кумулятивный эффект» мутаций, фенотипически проявляющийся тяжелым течением заболевания с неблагоприятными исходами. Показано, что при генотипировании пациентов с идиопатическими жизнеугрожающими тахиаритмиями использование панелей с большим количеством генов, ассоциированных с сердечно-сосудистой патологией, является вполне оправданным. Комплексное исследование генов позволяет увеличить диагностическую и прогностическую ценность генетического скрининга. Long QT syndrome (LQTS) is the genetically determined disease characterized by the QT interval elongation at the electrocardiogram, a high risk of life-threatening arrhythmias and sudden cardiac death. This syndrome is determined by mutations in genes encoding ion channel proteins, as well as proteins indirectly associated with ion channels. 4.5-8% of patients with LQTS have more than one mutation in the genes associated with the development of channelopathies. Purpose of work: description of two clinical cases of patients with life-threatening arrhythmia in which a combination of rare mutant alleles in the genes associated with LQTS was detected. The clinical examination included 12-lead ECG, echocardiography, cardiac MRI with delayed contrast, and 24-hour ECG monitoring (SM ECG). Genetic testing was performed by next generation sequencing (NGS) using the TruSight ™ Cardio Sequencing Panel reagent kit (Illumina). Both patients with no burdened family history had malignant ventricular tachyarrhythmias, which required the implantation of a cardioverter defibrillator. The NGS method allowed to detect a combination of substitutions in the genes ANK2 (c.9161C>G, p.Ala3054Gly, rs139007578) and KCNE1 (c.253G>A, p.Asp85Asn, rs1805128) in a patient with idiopathic ventricular tachycardia. In the patient with idiopathic ventricular fibrillation, the allelic variant was also found in the gene ANK2 (c.1397C>T, p.Thr466Met, rs786205722) and an additional substitution in the gene SNTA1 (c.1877>T, (p.Ala263Ser), rs150576530). If patients have several genetic defects, a “cumulative effect” of mutations can be observed, phenotypically manifested by a severe course of the disease with unfavorable outcomes. It has been shown that when genotyping patients with idiopathic life-threatening tachyarrhythmias, the use of panels with a large number of genes associated with cardiovascular pathology is quite justified. A comprehensive study of genes can increase the diagnostic and prognostic value of genetic screening.

AMPA and Kainate Receptors

α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and kainate-type glutamate receptors (AMPARs and KARs) are dynamic ion channel proteins that govern neuronal excitation and signal transduction in the mammalian brain. The four AMPAR and five KAR subunits can heteromerize with other subfamily members to create several combinations of tetrameric channels with unique physiological and pharmacological properties. While both receptor classes are noted for their rapid, millisecond-scale channel gating in response to agonist binding, the intricate structural rearrangements underlying their function have only recently been elucidated. This chapter begins with a review of AMPAR and KAR nomenclature, topology, and rules of assembly. Subsequently, receptor gating properties are outlined for both single-channel and synaptic contexts. The structural biology of AMPAR and KAR proteins is also discussed at length, with particular focus on the ligand-binding domain, where allosteric regulation and alternative splicing work together to dictate gating behavior. Toward the end of the chapter there is an overview of several classes of auxiliary subunits, notably transmembrane AMPAR regulatory proteins and Neto proteins, which enhance native AMPAR and KAR expression and channel gating, respectively. Whether bringing an ion channel novice up to speed with glutamate receptor theory and terminology or providing a refresher for more seasoned biophysicists, there is much to appreciate in this summation of work from the glutamate receptor field.