Ion Channel Dysregulation Research Articles

Abstract 4137646: Transcriptomic Profiling of Human Myocardium at Sudden Death to Define Vulnerable Substrate for Lethal Arrhythmias

Background: While some chronic pathological substrates for sudden cardiac death (SCD) are well-known (e.g., coronary disease and left ventricular [LV] dysfunction), the vulnerable myocardial state predisposing to fatal arrhythmia remains a critical barrier to near-term SCD prevention. Hypothesis: Myocardium of autopsy-defined SCDs exhibit distinct expression profiles vs. non-cardiac sudden deaths and trauma deaths that reflect its acute vulnerable state in the hours to days before SCD, as expression arrests upon death. Goals/Aims: Define the vulnerable myocardial substrate for lethal arrhythmia by targeted RNA profiling. Methods: We used autopsy to adjudicate arrhythmic from non-arrhythmic causes in 1,265 sudden deaths in San Francisco from 2011-2018. We performed a transcriptomic evaluation of LV sampled at the time of SCD from 245 consented cases using a curated panel of 448 genes with known or hypothesized association with SCD. Results: Comparison between Arrhythmic (n=129) and Non-Arrhythmic (n=116) cohorts revealed 31 differentially upregulated and 36 downregulated genes (p-adj<0.05), related to collagen-containing extracellular matrix (upregulation of FAP , FMOD , LTBP2 ), ion transport (upregulation of KCNA5 and KCNN3 , and downregulation of KCNJ8, KCNK1, KCNJ5 ), and contraction (downregulation of MYH6 ). Fibrosis-related genes showed the highest magnitude increased expression in Arrhythmic vs. Non-arrhythmic deaths and vs. published transcriptomes from end-stage heart failure. After molecular stratification by known markers for mature ( COL1A1, COL1A2, COL3A1) and active ( POSTN , MEOX1 ) fibrosis, cases with highest expression of both had the highest proportion of arrhythmic cause of death (27/36 [75%]) vs. cases with low expression of both (87/181 [38%], p=0.006) or vs. mature only (10/14 [71%]) or active only (5/14 [36%]). Activated fibroblast gene expression was enriched in Arrhythmic female vs. Arrhythmic male cases, among other sex-specific differences in ion channel and myosin (upregulation of SCN4B , SCN8A , KCNAB1 in females, KCNJ4 and MYH7B in males) expression. Conclusions: RNA profiling of myocardium at SCD identifies active fibrosis, undetectable by conventional clinical methods, in the presence of fixed scar and selected ion channel dysregulation (more pronounced among female cases) as an acute vulnerable substrate for fatal arrhythmias, and may identify patients at elevated near-term risk for SCD and novel pathways for intervention.

VTA dopamine neurons are hyperexcitable in 3xTg-AD mice due to casein kinase 2-dependent SK channel dysfunction

Alzheimer’s disease (AD) patients exhibit neuropsychiatric symptoms that extend beyond classical cognitive deficits, suggesting involvement of subcortical areas. Here, we investigated the role of midbrain dopamine (DA) neurons in AD using the amyloid + tau-driven 3xTg-AD mouse model. We found deficits in reward-based operant learning in AD mice, suggesting possible VTA DA neuron dysregulation. Physiological assessment revealed hyperexcitability and disrupted firing in DA neurons caused by reduced activity of small-conductance calcium-activated potassium (SK) channels. RNA sequencing from contents of single patch-clamped DA neurons (Patch-seq) identified up-regulation of the SK channel modulator casein kinase 2 (CK2), which we corroborated by immunohistochemical protein analysis. Pharmacological inhibition of CK2 restored SK channel activity and normal firing patterns in 3xTg-AD mice. These findings identify a mechanism of ion channel dysregulation in VTA DA neurons that could contribute to behavioral abnormalities in AD, paving the way for novel treatment strategies.

Transcriptomic Profiling of Human Myocardium at Sudden Death to DefineVulnerable Substrate for LethalArrhythmias.

While some chronic pathological substrates for sudden cardiac death (SCD) are well known (eg, coronary artery disease and left ventricular [LV] dysfunction), the acute vulnerable myocardial state predisposing to fatal arrhythmia remains a critical barrier to near-term SCD prevention. This study sought to define the distinct myocardial transcriptomic profile of autopsy-defined arrhythmic sudden deaths, compared to nonarrhythmic sudden deaths and trauma deaths, to determine the acute vulnerable state in the hours to days before SCD. We used autopsy to adjudicate arrhythmic from nonarrhythmic causes in 1,265 sudden deaths in San Francisco County from 2011 to 2018. We performed a degradation-tolerant transcriptomic evaluation of LVs sampled at the time of SCD from 245 consented cases using a curated panel of 448 gene probes with known or hypothesized association with SCD. The targeted transcriptome of arrhythmic (n = 129) vs nonarrhythmic (n=90 nonarrhythmic sudden deaths+ 26 trauma deaths) LV samples revealed 31 differentially up-regulated and 36 down-regulated genes (adjusted P< 0.05) related to the collagen-containing extracellular matrix (up-regulation of FAP, FMOD, and LTBP2), regulation of ion transport (up-regulation of KCNA5 and KCNN3 and down-regulation of KCNJ8, KCNK1, and KCNJ5), and contraction (down-regulation of MYH6). Fibrosis-related genes showed the highest magnitude increased expression in arrhythmic vs nonarrhythmic deaths and vs published transcriptomes from end-stage heart failure. After molecular stratification by known markers for mature (COL1A1, COL1A2, COL3A1) and active (POSTN, MEOX1) fibrosis, cases with the highest expression of both had the largest proportion of arrhythmic cause of death (n=27 of 36 [75%]) vs cases with low expression of both markers (n=87 of 181 [38%]) (P = 0.006) or vs mature only (n=10 of 14 [71%]) or active only (n=5 of 14 [36%]). Activated fibroblast gene expression signature was enriched in arrhythmic female vs arrhythmic male cases, among other sex-specific differences in ion-channel and myosin (up-regulation of SCN4B, SCN8A, and KCNAB1 in females and KCNJ4 and MYH7B in males) expression. RNA profiling of the myocardium at SCD identifies active fibrosis, undetectable by conventional clinical methods, in the presence of fixed scar and selected ion-channel dysregulation (more pronounced among female cases) as an acute vulnerable substrate for fatal arrhythmias. These findings may represent novel directions to identify patients at elevated near-term risk for SCD and critical pathways for intervention to reduce acute lethal arrhythmias.

Pathophysiological Roles of Ion Channels in Epidermal Cells, Immune Cells, and Sensory Neurons in Psoriasis.

Psoriasis is a chronic inflammatory skin disease characterized by the rapid abnormal growth of skin cells in the epidermis, driven by an overactive immune system. Consequently, a complex interplay among epidermal cells, immune cells, and sensory neurons contributes to the development and progression of psoriasis. In these cellular contexts, various ion channels, such as acetylcholine receptors, TRP channels, Ca2+ release-activated channels, chloride channels, and potassium channels, each serve specific functions to maintain the homeostasis of the skin. The dysregulation of ion channels plays a major role in the pathophysiology of psoriasis, affecting various aspects of epidermal cells, immune responses, and sensory neuron signaling. Impaired function of ion channels can lead to altered calcium signaling, inflammation, proliferation, and sensory signaling, all of which are central features of psoriasis. This overview summarizes the pathophysiological roles of ion channels in epidermal cells, immune cells, and sensory neurons during early and late psoriatic processes, thereby contributing to a deeper understanding of ion channel involvement in the interplay of psoriasis and making a crucial advance toward more precise and personalized approaches for psoriasis treatment.

Dysregulation of Ion Channels and Transporters and Blood-Brain Barrier Dysfunction in Alzheimer's Disease and Vascular Dementia.

The blood-brain barrier (BBB) plays a critical role in maintaining ion and fluid homeostasis, essential for brain metabolism and neuronal function. Regulation of nutrient, water, and ion transport across the BBB is tightly controlled by specialized ion transporters and channels located within its unique cellular components. These dynamic transport processes not only influence the BBB's structure but also impact vital signaling mechanisms, essential for its optimal function. Disruption in ion, pH, and fluid balance at the BBB is associated with brain pathology and has been implicated in various neurological conditions, including stroke, epilepsy, trauma, and neurodegenerative diseases such as Alzheimer's disease (AD). However, knowledge gaps exist regarding the impact of ion transport dysregulation on BBB function in neurodegenerative dementias. Several factors contribute to this gap: the complex nature of these conditions, historical research focus on neuronal mechanisms and technical challenges in studying the ion transport mechanisms in in vivo models and the lack of efficient in vitro BBB dementia models. This review provides an overview of current research on the roles of ion transporters and channels at the BBB and poses specific research questions: 1) How are the expression and activity of key ion transporters altered in AD and vascular dementia (VaD); 2) Do these changes contribute to BBB dysfunction and disease progression; and 3) Can restoring ion transport function mitigate BBB dysfunction and improve clinical outcomes. Addressing these gaps will provide a greater insight into the vascular pathology of neurodegenerative disorders.

Ion Channel Dysregulation Following Intracerebral Hemorrhage.

Injury to the brain after intracerebral hemorrhage (ICH) results from numerous complex cellular mechanisms. At present, effective therapy for ICH is limited and a better understanding of the mechanisms of brain injury is necessary to improve prognosis. There is increasing evidence that ion channel dysregulation occurs at multiple stages in primary and secondary brain injury following ICH. Ion channels such as TWIK-related K+ channel 1, sulfonylurea 1 transient receptor potential melastatin 4 and glutamate-gated channels affect ion homeostasis in ICH. They in turn participate in the formation of brain edema, disruption of the blood-brain barrier, and the generation of neurotoxicity. In this review, we summarize the interaction between ions and ion channels, the effects of ion channel dysregulation, and we discuss some therapeutics based on ion-channel modulation following ICH.

Shank3 related muscular hypotonia is accompanied by increased intracellular calcium concentrations and ion channel dysregulation in striated muscle tissue.

Phelan-McDermid syndrome (PMS) is a syndromic form of Autism Spectrum Disorders (ASD) classified as a rare genetic neurodevelopmental disorder featuring global developmental delay, absent or delayed speech, ASD-like behaviour and neonatal skeletal muscle hypotonia. PMS is caused by a heterozygous deletion of the distal end of chromosome 22q13.3 or SHANK3 mutations. We analyzed striated muscles of newborn Shank3Δ11(-/-) animals and found a significant enlargement of the sarcoplasmic reticulum as previously seen in adult Shank3Δ11(-/-) mice, indicative of a Shank3-dependent and not compensatory mechanism for this structural alteration. We analyzed transcriptional differences by RNA-sequencing of muscle tissue of neonatal Shank3Δ11(-/-) mice and compared those to Shank3(+/+) controls. We found significant differences in gene expression of ion channels crucial for muscle contraction and for molecules involved in calcium ion regulation. In addition, calcium storage- [i.e., Calsequestrin (CSQ)], calcium secretion- and calcium-related signaling-proteins were found to be affected. By immunostainings and Western blot analyses we could confirm these findings both in Shank3Δ11(-/-) mice and PMS patient muscle tissue. Moreover, alterations could be induced in vitro by the selective downregulation of Shank3 in C2C12 myotubes. Our results emphasize that SHANK3 levels directly or indirectly regulate calcium homeostasis in a cell autonomous manner that might contribute to muscular hypotonia especially seen in the newborn.

From squid giant axon to automated patch-clamp: electrophysiology in venom and antivenom research.

Ion channels play a crucial role in diverse physiological processes, including neurotransmission and muscle contraction. Venomous creatures exploit the vital function of ion channels by producing toxins in their venoms that specifically target these ion channels to facilitate prey capture upon a bite or a sting. Envenoming can therefore lead to ion channel dysregulation, which for humans can result in severe medical complications that often necessitate interventions such as antivenom administration. Conversely, the discovery of highly potent and selective venom toxins with the capability of distinguishing between different isoforms and subtypes of ion channels has led to the development of beneficial therapeutics that are now in the clinic. This review encompasses the historical evolution of electrophysiology methodologies, highlighting their contributions to venom and antivenom research, including venom-based drug discovery and evaluation of antivenom efficacy. By discussing the applications and advancements in patch-clamp techniques, this review underscores the profound impact of electrophysiology in unravelling the intricate interplay between ion channels and venom toxins, ultimately leading to the development of drugs for envenoming and ion channel-related pathologies.

Targeting Ion Channels and Purkinje Neuron Intrinsic Membrane Excitability as a Therapeutic Strategy for Cerebellar Ataxia.

In degenerative neurological disorders such as Parkinson's disease, a convergence of widely varying insults results in a loss of dopaminergic neurons and, thus, the motor symptoms of the disease. Dopamine replacement therapy with agents such as levodopa is a mainstay of therapy. Cerebellar ataxias, a heterogeneous group of currently untreatable conditions, have not been identified to have a shared physiology that is a target of therapy. In this review, we propose that perturbations in cerebellar Purkinje neuron intrinsic membrane excitability, a result of ion channel dysregulation, is a common pathophysiologic mechanism that drives motor impairment and vulnerability to degeneration in cerebellar ataxias of widely differing genetic etiologies. We further propose that treatments aimed at restoring Purkinje neuron intrinsic membrane excitability have the potential to be a shared therapy in cerebellar ataxia akin to levodopa for Parkinson's disease.

Abstract P2-16-07: Overexpression of the alpha subunit of the epithelial sodium channel in MDAMB231 breast cancer cells reduces cell migration and proliferation

Abstract Breast cancer is the most common cancer diagnosed in women worldwide and leads to 600,000+ deaths annually. The vast majority of breast cancer-related deaths are attributed to metastasis from the primary site in the breast to visceral organs or the brain. Therefore, understanding how these cells achieve metastasis is vital. Ion channels, such as the epithelial sodium channel (ENaC), are emerging as new targets for cancer research due to their role in regulating cell functions such as the process that allows cancer cells to undergo phenotypic changes necessary for metastasis. Ion channel dysregulation may be crucial in cancer development due to the ion channels’ potential role in controlling cancer cell characteristics such as migration and proliferation. There is limited research investigating the role ENaC may have in breast cancer. We have shown that more migratory, mesenchymal breast cancer cell lines have reduced mRNA and protein expression of ENaC compared to more epithelial breast cancer cell lines. Importantly, higher expression levels of the pore-forming alpha-ENaC subunit is correlated with an increased breast cancer survival in patients (n=1705) included in the SCAN-B data set. Bioinformatic analysis, using the SCAN-B data set, showed an increase in the expression of alpha-ENaC mRNA correlated with lower expression levels of migration and proliferation markers, suggesting ENaC has a role in breast cancer cell proliferation and migration. Therefore, this research examines the influence of stably overexpressing the pore-forming subunit of ENaC, alpha-ENaC, in breast cancer cells on their cell migration and proliferation ability. We hypothesised that increasing the expression of ENaC will restore the cells to a more epithelial state, thus reducing cell migration and proliferation. MDAMB231 breast cancer cells were engineered via a stable transfection to overexpress alpha-ENaC or to express an empty vector control. Several clones were isolated and expanded and using RTqPCR, alpha-ENaC mRNA overexpression was confirmed to consistently have 200-fold increased mRNA expression compared to control cells (n=9, p=0.0006). An increase in alpha-ENaC protein expression was also confirmed via western blotting. Using an EdU assay the alpha-ENaC overexpressing cells were shown to have a significant reduction in proliferation compared to the control cell line (n=3, p=0.0048). The alpha-ENaC overexpressing cells showed reduced migratory ability when examined in two established migration assays. In scratch wound assays, the alpha-ENaC overexpressing cells had a significant reduction in cell migration at 24 hours post scratch (n=4, p=0.0001). In Boyden chamber assays, the number of alpha-ENaC-overexpressing cells that migrated through the membrane was significantly reduced compared to the control cell line (n=4, p=0.02). Our results suggest that increased sodium entry into the cell through ENaC has a role in preventing the development of metastatic breast cancer cells, and highlights ENaC as a potential target for future breast cancer therapies. Citation Format: Sarah McQueen, Adam Ware, Heather Cunliffe, Fiona McDonald. Overexpression of the alpha subunit of the epithelial sodium channel in MDAMB231 breast cancer cells reduces cell migration and proliferation [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-16-07.

A small molecule inhibitor of SUMO prevents the hypoxia-induced decrease in IK1 current.

The inward rectifying potassium current (IK1) shapes the initial depolarization and the final repolarization phases of the cardiac action potential and is critical for maintaining the resting membrane potential of ventricular cardiomyocytes. Kir2, the inward rectifying potassium channels are the main contributors to the IK1 current, with Kir2.1 dominating. Disruption of IK1 current activity has been implicated in many cardiac arrhythmia phenotypes. Acute hypoxia during coronary occlusion changes the electrophysiological properties of the myocardium and can precipitate disordered conduction and arrhythmias due to ion channel dysregulation. However, the mechanistic basis for the proarrhythmic effects of acute hypoxia on cardiac tissue has remained unclear, limiting the development of novel therapeutics. Using whole-cell patch-clamp recording we show that acute hypoxia inhibits IK1 in rat ventricular cardiomyocytes, as well as in heterologous expression systems. We provide evidence to show that this inhibition is due to the rapid SUMOylation of Kir2.1 at lysine 49. When SUMO binds to the channel it decreases the efficacy and potency of the membrane phospholipid, phosphatidylinositol 4,5-bisphosphate (PIP2) to activate the channel. Finally, we show that a small molecule inhibitor of the SUMO-pathway precludes the hypoxia-mediated decrease in Kir2.1. We confirm that this effect is due to the direct inhibition of Kir2.1 SUMOylation within the cell. These data provide potential insight into investigation of the SUMO pathway as a target for treating the proarrhythmic effects of acute hypoxia.

Proteomic profiling reveals neuronal ion channel dysregulation and cellular responses to DNA damage-induced cell cycle arrest and senescence in human neuroblastoma SH-SY5Y cells exposed to cypermethrin

Cypermethrin (CYP), a synthetic pyrethroid of class II, is widely used as a pesticide worldwide. The primary target of cypermethrin is a voltage-gated sodium channel. The neurotoxicity of CYP has been extensively studied in terms of affecting neuronal development, increasing cellular oxidative stress, and apoptosis. However, little is known about how it affects the expression of channel proteins involved in synaptic transmission, as well as the effects of cypermethrin on DNA damage and cell cycle processes. We found that the ligand and voltage-gated calcium channels and proteins involved in synaptic transmission including NMDA 1 receptor subunit, alpha 1A-voltage-dependent calcium channel, synaptotagmin-17, and synaptojanin-2 were downregulated in CYP-treated cells. After 48 h of CYP exposure, cell viability was reduced with flattened and enlarged morphology. The levels of 23 proteins regulating cell cycle processes were altered in CYP-treated cells, according to a proteomic study. The cell cycle analysis showed elevated G0/G1 cell cycle arrest and DNA fragmentation at the sub-G0 stage after CYP exposure. CYP treatment also increased senescence-associated β-galactosidase positive cells, DNA damage, and apoptotic markers. Taken together, the current study showed that cypermethrin exposure caused DNA damage and hastened cellular senescence and apoptosis via disrupting cell cycle regulation. In addition, despite its primary target sodium channel, CYP might cause synaptic dysfunction via the downregulation of synaptic proteins and dysregulation of synapse-associated ion channels.

Novel Perspective of Cardiovascular Diseases: Volume-Regulatory Anion Channels in the Cell Membrane.

Cardiovascular diseases (CVDs) are the leading cause of morbidity and mortality worldwide. Although there are established mechanisms and preventions for CVDs, they are not totally elucidative and effective. Emerging evidence suggests that the dysregulation of ion channels in the cell membranes underpins the dysfunction of the cardiovascular system. To date, a variety of cation channels have been widely recognized as important targets for the treatment of CVDs. As a critical component of the anion channels, the volume-regulated anion channel (VRAC) is involved in a series of cell functions by the volume regulation and maintenance of membrane homeostasis. It has been confirmed to play crucial roles in cell action potential generation, cell proliferation, differentiation and apoptosis, and the VRAC appears to be a major participant in metabolic processes during CVDs. This review summarizes the current evidence and progress concerning the VRAC, to determine the future directions and challenges for CVDs for both preventive and therapeutic purposes.

Preventing unfolded protein response-induced ion channel dysregulation to treat arrhythmias.

Cardiomyopathies are associated with arrhythmias and cardiac ion channel downregulation. This downregulation is arrhythmogenic. Paradoxically, antiarrhythmic therapies are based on ion channel-blocking drugs that further downregulate these channels and exhibit proarrhythmic risk. Recent studies have shown that inhibition of the protein kinase RNA-like ER kinase (PERK) arm of the unfolded protein response (UPR) prevents select cardiac ion channel downregulation and plays a protective role against arrhythmias. Prevention of ion channel downregulation represents as a novel therapeutic strategy to treat arrhythmias in myocardial infarction and heart failure.

Polyglutamine diseases.

Polyglutamine diseases are a collection of nine CAG trinucleotide expansion disorders, presenting with a spectrum of neurological and clinical phenotypes. Recent human, mouse and cell studies of Huntington's diseasehave highlighted the role of DNA repair genes in somatic expansion of the CAG repeat region, modifying disease pathogenesis. Incomplete splicing of the HTT gene has also been shown to occur in humans, with the resulting exon 1 fragment most probably contributing to the Huntington's disease phenotype. In the spinocerebellar ataxias, studies have converged on transcriptional dysregulation of ion channels as a key disease modifier. In addition, advances have been made in understanding how increased levels of toxic, polyglutamine-expanded proteins can arise in the spinocerebellar ataxias through post-transcriptional and -translational modifications and autophagic mechanisms. Recent studies in spinal and bulbar muscular atrophyimplicate similar pathogenic pathways to the more common polyglutamine diseases, highlighting autophagy stimulation as a potential therapeutic target. Finally, the therapeutic use of antisense oligonucleotides in several polyglutamine diseases has shown preclinical benefits and serves as potential future therapies in humans.

MicroRNA Biophysically Modulates Cardiac Action Potential by Direct Binding to Ion Channel.

MicroRNAs (miRs) play critical roles in regulation of numerous biological events, including cardiac electrophysiology and arrhythmia, through a canonical RNA interference mechanism. It remains unknown whether endogenous miRs modulate physiologic homeostasis of the heart through noncanonical mechanisms. We focused on the predominant miR of the heart (miR1) and investigated whether miR1 could physically bind with ion channels in cardiomyocytes by electrophoretic mobility shift assay, in situ proximity ligation assay, RNA pull down, and RNA immunoprecipitation assays. The functional modulations of cellular electrophysiology were evaluated by inside-out and whole-cell patch clamp. Mutagenesis of miR1 and the ion channel was used to understand the underlying mechanism. The effect on the heart ex vivo was demonstrated through investigating arrhythmia-associated human single nucleotide polymorphisms with miR1-deficient mice. We found that endogenous miR1 could physically bind with cardiac membrane proteins, including an inward-rectifier potassium channel Kir2.1. The miR1-Kir2.1 physical interaction was observed in mouse, guinea pig, canine, and human cardiomyocytes. miR1 quickly and significantly suppressed IK1 at sub-pmol/L concentration, which is close to endogenous miR expression level. Acute presence of miR1 depolarized resting membrane potential and prolonged final repolarization of the action potential in cardiomyocytes. We identified 3 miR1-binding residues on the C-terminus of Kir2.1. Mechanistically, miR1 binds to the pore-facing G-loop of Kir2.1 through the core sequence AAGAAG, which is outside its RNA interference seed region. This biophysical modulation is involved in the dysregulation of gain-of-function Kir2.1-M301K mutation in short QT or atrial fibrillation. We found that an arrhythmia-associated human single nucleotide polymorphism of miR1 (hSNP14A/G) specifically disrupts the biophysical modulation while retaining the RNA interference function. It is remarkable that miR1 but not hSNP14A/G relieved the hyperpolarized resting membrane potential in miR1-deficient cardiomyocytes, improved the conduction velocity, and eliminated the high inducibility of arrhythmia in miR1-deficient hearts ex vivo. Our study reveals a novel evolutionarily conserved biophysical action of endogenous miRs in modulating cardiac electrophysiology. Our discovery of miRs' biophysical modulation provides a more comprehensive understanding of ion channel dysregulation and may provide new insights into the pathogenesis of cardiac arrhythmias.

Diarrheal Mechanisms and the Role of Intestinal Barrier Dysfunction in Campylobacter Infections.

Campylobacter enteritis is the most common cause of foodborne bacterial diarrhea in humans. Although various studies have been performed to clarify the pathomechanism in Campylobacter infection, the mechanism itself and bacterial virulence factors are yet not completely understood. The purpose of this chapter is to (i) give an overview on Campylobacter-induced diarrheal mechanisms, (ii) illustrate underlying barrier defects, (iii) explain the role of the mucosal immune response and (iv) weigh preventive and therapeutic approaches. Our present knowledge of pathogenetic and diarrheal mechanisms of Campylobacter jejuni is explained in the first part of this chapter. In the second part, the molecular basis for the Campylobacter-induced barrier dysfunction is compared with that of other species in the Campylobacter genus. The bacteria are capable of overcoming the intestinal epithelial barrier. The invasion into the intestinal mucosa is the initial step of the infection, followed by a second step, the epithelial barrier impairment. The extent of the impairment depends on various factors, including tight junction dysregulation and epithelial apoptosis. The disturbed intestinal epithelium leads to a loss of water and solutes, the leak flux type of diarrhea, and facilitates the uptake of harmful antigens, the leaky gut phenomenon. The barrier dysfunction is accompanied by increased pro-inflammatory cytokine secretion, which is partially responsible for the dysfunction. Moreover, cytokines also mediate ion channel dysregulation (e.g., epithelial sodium channel, ENaC), leading to another diarrheal mechanism, which is sodium malabsorption. Future perspectives of Campylobacter research are the clarification of molecular pathomechanisms and the characterization of therapeutic and preventive compounds to combat and prevent Campylobacter infections.

Abstract 15963: Microrna Biophysically Modulates Cardiac Physiology via Directly Binding to Ion Channel

Background: Cardiac arrhythmias are a leading cause of morbidity and mortality. MicroRNAs (miRs) regulate the (electro) physiology of the heart and remodeling by canonical RNAi mechanism. Hypothesis: miRs maintain cardiac physiology also through noncanonical mechanisms. Methods: The physical binding between cardiac predominant miR--miR1 and ion channels was explored by EMSA, in situ PLA, RNA pull down and RIP assays. Electrophysiology of cardiomyocytes (CMs) and ex vivo miR1-deficient hearts were studied to reveal the functional outcome and the pathophysiological significance. Results: miR1 physically binds with an inward rectifier K + channel Kir2.1, which exists endogenously in CMs. This miR1-Kir2.1 binding is evolutionarily conserved. Functionally, miR1, at sub-pmol/L concentration, significantly suppresses IK1, depolarizes resting membrane potential, and prolongs final repolarization of action potentials in CMs. Mechanistically, miR1 binds to the pore-facing G-loop of Kir2.1 though the core sequence AAGAAG, which is outside the seed region. This biophysical modulation is involved in the dysregulation of a gain-of-function mutation Kir2.1-M301K in short-QT/AF patients. An AF-associated miR1-hSNP14A/G specifically disrupts the biophysical modulation while maintains miR1’s RNAi function. Significantly, miR1 but not hSNP14A/G eliminates the high inducibility of arrhythmia in miR1-deficient hearts. Conclusion: We reveal a novel function of miRs and develop a ground-breaking concept that endogenous miRs can physically bind with ion channels and rapidly modulate cardiac electrophysiology before its long-term effect of conventional RNAi mechanism. Our study provides more comprehensive understanding of ion-channel dysregulation associated with cardiac arrhythmias.

Carfilzomib-Induced Hypertension Is Mediated By Ion Channel Dysregulation in the Kidneys; The Potent Role of AMP-Activated Kinase α

Introduction: Carfilzomib (Cfz), an irreversible proteasome inhibitor (PI), is an approved agent against relapsed/refractory multiple myeloma (R/R MM). Cfz is associated with high incidence of cardiovascular adverse effects. Hypertension stands as the most frequent cardiovascular complication of Cfz. Even though thrombotic microangiopathy (TMA) is inculpated of Cfz's hypertensive phenotype, its exact pathophysiology is still elusive. In our previous work, we showed that Cfz establishes cardiotoxicity in vivo in a Protein Phosphatase 2A (PP2A)-AMP-activated kinase α (AMPKα)-dependent manner (Efentakis P et al. Blood. 2019;133(7):710-723) but does not lead to a permanent vascular deficit, indicating that hypertension is not vascular derived [Efentakis P et al. IJMS 2020;21(15):E5185]. Taking under consideration that renal homeostasis plays an important role in blood pressure regulation we sought to (i) characterize the dose-dependent manifestation of Cfz-induced hypertension; (ii) investigate the molecular signaling of Cfz in the kidneys by proteomic and immunoblotting analyses and (iii) study the renal ion channels regulation. Methods: Forty C57Bl/6 mice (12-14 weeks of age) were randomly assigned to: (i) Acute Protocol: a. Control [Normal Saline (N/S) 0.9%] and b. Cfz (8mg/kg) for two days and (ii) Sub-acute Protocol: a) Control (N/S 0.9%,) and b) Cfz (8mg/kg) for seven days. Intraperitoneal administration of N/S 0.9% and Cfz was performed at two consecutive and on alternate days for the acute and sub-acute protocols respectively. At baseline and endpoint of the experiments, systolic (SBP) and diastolic blood pressure (DBP) were measured, and subsequently mice were sacrificed for the collection of blood and renal samples. Blood samples were collected in citrate buffer for hematological/coagulation profiling [prothrombin time (PT) and INR estimation] and for cleaved Von Willebrand Factor (cl. VWF) immunoblotting assessment as well as for blood testing of white blood cells (WBCs) and platelets. Renal samples underwent histological proteomic and molecular analyses. Results: SBP and DBP were found to be elevated in Cfz group only in the sub-acute protocol compared to control (SBP: 78.5±2.0 vs 68.2±0.7, p&amp;lt;0.01 and DBP: 104.1±2.3 vs 97.4±2.4, p&amp;lt;0.05, respectively). Neutrophil count in the whole blood was elevated both in the acute and sub-acute protocols, while platelet count was decreased in the acute protocol and restored after sub-acute Cfz administration. Mice presented a thrombotic phenotype characterized by increased PT and INR and decreased cl. VWF after acute Cfz treatment, and a hemorrhagic phenotype with restored cl. VWF after sub-acute Cfz administration. However, the presence of TMA was not confirmed by histological evaluation of the kidneys in any of the protocols. Nonetheless histological evaluation of the kidneys revealed inflammation of the perirenal adipose tissue only in the sub-acute protocol. Proteomic analysis presented that proteasome regulation, metabolism and transport of organic anion processes are affected by Cfz administration. Molecular analysis of the renal tissue showed that Cfz induced an increase in the inducible nitric oxide synthase (iNOS) and microtubule-associated proteins 1A/1B light chain 3B (LC3-B) expression and a decreased AMPKα phosphorylation. Moreover, RT-PCR analysis of the renal samples revealed that collecting duct ion channels epithelial Na+ channel (ENaC), Na+/K+/ATPase and urea transporter 1 (UTA-1) mRNA levels were increased in Cfz group. Conclusion: Sub-acute Cfz treatment establishes a renal-derived hypertensive phenotype and a circulating inflammatory phenotype as indicated by the increased neutrophil and WBCs count in the blood. TMA does not seem to be implicated with the observed phenotype in vivo as investigated molecularly and histologically. Cfz-induced dephosphorylation of AMPKα and the subsequent dysregulation of the collecting duct renal ion channel homeostasis is found to be responsible for the observed effect. Therefore, Cfz seems to induce hypertension by a dysregulation of water-ion re-absorbance leading to increased cardiac preload. The latter comes in agreement with clinical data showing that some Cfz-treated patients present with fluid retention, which can be attributed to the aforementioned renal effects of the drug. Disclosures Efentakis: Amgen: Research Funding. Kastritis:Amgen: Consultancy, Honoraria, Research Funding; Genesis Pharma: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy, Honoraria. Dimopoulos:BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Personal fees; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Personal fees, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Personal fees, Speakers Bureau; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Personal fees, Research Funding, Speakers Bureau; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Personal fees, Research Funding, Speakers Bureau. Andreadou:Amgen: Research Funding. Terpos:Amgen: Honoraria, Research Funding; Genesis pharma SA: Honoraria, Other: travel expenses , Research Funding; Janssen: Honoraria, Research Funding; Takeda: Honoraria, Other: travel expenses , Research Funding; Celgene: Honoraria; Sanofi: Honoraria; BMS: Honoraria.

Tb1, a Neurotoxin from Tityus bahiensis Scorpion Venom, Induces Epileptic Seizures by Increasing Glutamate Release.

Here, we report the neurotoxic effects aroused by the intracerebral injection (in rats) of Tb1, which is a neurotoxin isolated from Tityus bahiensis scorpion venom. Biochemical analyses have demonstrated that this toxin is similar to the gamma toxin from T. serrulatus, which is a β-scorpion toxin that acts on sodium channels, causing the activation process to occur at more hyperpolarized membrane voltages. Male Wistar rats were stereotaxically implanted with intrahippocampal electrodes and cannulas for electroencephalographic recording and the evaluation of amino acid neurotransmitters levels. Treated animals displayed behavioral and electroencephalographic alterations similar to epileptiform activities, such as myoclonus, wet dog shakes, convulsion, strong discharges, neuronal loss, and increased intracerebral levels of glutamate. Scorpion toxins are important pharmacological tools that are widely employed in ion channel dysregulation studies. The current work contributes to the understanding of channelopathies, particularly epilepsy, which may originate, among other events, from dysfunctional sodium channels, which are the main target of the Tb1 toxin.