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RATIONALECardiac rhythm, conduction and synchronization of electrical activity require the coordinated action of different types of ion channels that differ according to transmural and regional specificities. Classical pharmacology affects these ion channels in a non-regionalized way which explains why treating arrhythmias, that often occur in specific foci, has often limited efficacy in addition to negative side-effects on non-targeted organs. Photopharmacology is an emergent technology that has the potential to counteract all the negative aspects of classical pharmacology by restricting drug activity in a spatio-temporal manner.OBJECTIVEWe tested the potential of photopharmacology in specifically regulating heart activity by using a caged derivative of a natural peptide inhibitor of the ERG channel, BeKm1. The peptide was uncaged and activity monitoredin vitroon a cell line expressing the hERG channel, on human cardiomyocytes derived from iPS cells, andex vivoandin vivoon zebrafish larvae and rat hearts.METHODS AND RESULTSCaged BeKm-1 is inactive and fully active upon uncaging. Uncaging of the peptide on human iPS-derived cardiomyocytes enlarges the action potential duration and triggers arrhythmias. Uncaging also triggers bradycardia and disturbs cardiac conduction within the atria in perfused rat hearts upon illumination. The potency of photopharmacology for cardiac electrical modulation was further validated in zebrafish larvae where illumination of the caged compound induces bradycardia and atrio-ventricular desynchrony. Finally, in anesthetized rats, illumination of the caged peptide in the right atria, containing the sino-atrial node, leads to bradycardia without arrhythmia.CONCLUSIONSThis report demonstrates that photopharmacology, using the caged peptide strategy, can be used for dynamically regulating cardiac electrical activityin vivoand that spatial illumination restriction can dissociate the bradycardic effect from the arrhythmic one. The technology is applicable to all kinds of cardiac ion channels and regions of interest to create arrhythmogenic models or investigate new clinical applications.

Introduction. Septic shock is a systemic inflammatory response syndrome associated with organ failures. Earlier clinical diagnosis would be of benefit to a decrease in the mortality rate. However, there is currently a lack of predictive biomarkers. The secretome is the set of proteins secreted by a cell, tissue, or organism at a given time and under certain conditions. The plasma secretome is easily accessible from biological fluids and represents a good opportunity to discover new biomarkers that can be studied with nontargeted “omic” strategies. Aims. To identify relevant deregulated proteins (DEP) in the secretome of a rat endotoxemic shock model. Methods. Endotoxemic shock was induced in rats by intravenous injection of lipopolysaccharides (LPS, S. enterica typhi, 0.5 mg/kg) and compared to controls (Ringer Lactate, iv). Under isoflurane anesthesia, carotid cannulation allowed mean arterial blood pressure (MAP) and heart rate (HR) monitoring and blood sampling at different time points (T0 and T50 or T0 and T90, with EDTA and protease inhibitor). Samples were prepared for large-scale tandem mass spectrometry (MS-MS) based on a label-free quantification to allow identification of the proteins deregulated upon endotoxemic conditions. A Gene Ontology (GO) analysis defined several clusters of biological processes (BP) in which the DEP are involved. Results. Ninety minutes after shock induction, the LPS group presents a reduction in MAP (-45%, p < 0.05 ) and increased lactate levels (+27.5%, p < 0.05 ) compared to the control group. Proteomic analyses revealed 10 and 33 DEP in the LPS group, respectively, at 50 and 90 minutes after LPS injection. At these time points, GO-BP showed alterations in pathways involved in oxidative stress response and coagulation. Conclusion. This study proposes an approach to identify relevant DEP in septic shock and brings new insights into the understanding of the secretome adaptations upon sepsis.

Background and purpose Protoxin II (ProTx II) is a high affinity gating modifier that is thought to selectively block the Nav 1.7 voltage-dependent Na+ channel, a major therapeutic target for the control of pain. We aimed at producing ProTx II analogues entitled with novel functionalities for cell distribution studies and biochemical characterization of its Nav channel targets. Experimental approach We took advantage of the high affinity properties of the peptide, combined to its slow off rate, to design a number of new tagged analogues useful for imaging and biochemistry purposes. We used high-throughput automated patch-clamp to identify the analogues best matching the native properties of ProTx II and validated them on various Nav -expressing cells in pull-down and cell distribution studies. Key results Two of the produced ProTx II analogues, Biot-ProTx II and ATTO488-ProTx II, best recapitulate the pharmacological properties of unlabelled ProTx II, while other analogues remain high affinity blockers of Nav 1.7. The biotinylated version of ProTx II efficiently works for the pull-down of several Nav isoforms tested in a concentration-dependent manner, while the fluorescent ATTO488-ProTx II specifically labels the Nav 1.7 channel over other Nav isoforms tested in various experimental conditions. Conclusions and implications The properties of these ProTx II analogues as tools for Nav channel purification and cell distribution studies pave the way for a better understanding of ProTx II channel receptors in pain and their pathophysiological implications in sensory neuronal processing. The new fluorescent ProTx II should also reveal itself useful for the design of new drug screening strategies.

Aims Coronavirus disease of 2019 (COVID-19) has rapidly become a worldwide pandemic. Many clinical trials have been initiated to fight the disease. Among those, hydroxychloroquine and azithromycin had initially been suggested to improve clinical outcomes. Despite any demonstrated beneficial effects, they are still in use in some countries but have been reported to prolong the QT interval and induce life-threatening arrhythmia. Since a significant proportion of the world population may be treated with such COVID-19 therapies, evaluation of the arrhythmogenic risk of any candidate drug is needed. Methods and results Using the O'Hara-Rudy computer model of human ventricular wedge, we evaluate the arrhythmogenic potential of clinical factors that can further alter repolarization in COVID-19 patients in addition to hydroxychloroquine (HCQ) and azithromycin (AZM) such as tachycardia, hypokalaemia, and subclinical to mild long QT syndrome. Hydroxychloroquine and AZM drugs have little impact on QT duration and do not induce any substrate prone to arrhythmia in COVID-19 patients with normal cardiac repolarization reserve. Nevertheless, in every tested condition in which this reserve is reduced, the model predicts larger electrocardiogram impairments, as with dofetilide. In subclinical conditions, the model suggests that mexiletine limits the deleterious effects of AZM and HCQ. Conclusion By studying the HCQ and AZM co-administration case, we show that the easy-to-use O'Hara-Rudy model can be applied to assess the QT-prolongation potential of off-label drugs, beyond HCQ and AZM, in different conditions representative of COVID-19 patients and to evaluate the potential impact of additional drug used to limit the arrhythmogenic risk.

In neocortical layer-5 pyramidal neurons, the action potential (AP) is generated in the axon initial segment (AIS) when the membrane potential (Vm) reaches the threshold for activation of two diverse voltage-gated Na+ channels, that differ in spatial distribution and biophysical properties. Yet, the understanding of specific functional differences between these two channels remains elusive. Here, using ultrafast Na+, Vm and Ca2+ imaging in combination with partial block of Nav1.2 by a recent peptide, we demonstrate an exclusive role of Nav1.2 in shaping the generating AP. Precisely, Ca2+ influx via Nav1.2 activates BK Ca2+-activated K+ channels determining the amplitude and the early phase of repolarisation of the AP in the AIS. We mimicked this result with a NEURON model where the role of the different ion channels tested reproduced the experimental evidence. The exclusive role of Nav1.2 reported here is important for understanding the physiology and pathology of neuronal excitability.

Thanks to the crosstalk between Na+ and Ca2+ channels, Na+ and Ca2+ homeostasis interplay in so-called excitable cells enables the generation of action potential in response to electrical stimulation. Here, we investigated the impact of persistent activation of voltage-gated Na+ (NaV) channels by neurotoxins, such as veratridine (VTD), on intracellular Ca2+ concentration ([Ca2+]i) in a model of excitable cells, the rat pituitary GH3b6 cells, in order to identify the molecular actors involved in Na+-Ca2+ homeostasis crosstalk. By combining RT-qPCR, immunoblotting, immunocytochemistry, and patch-clamp techniques, we showed that GH3b6 cells predominantly express the NaV1.3 channel subtype, which likely endorses their voltage-activated Na+ currents. Notably, these Na+ currents were blocked by ICA-121431 and activated by the β-scorpion toxin Tf2, two selective NaV1.3 channel ligands. Using Fura-2, we showed that VTD induced a [Ca2+]i increase. This effect was suppressed by the selective NaV channel blocker tetrodotoxin, as well by the selective L-type CaV channel (LTCC) blocker nifedipine. We also evidenced that crobenetine, a NaV channel blocker, abolished VTD-induced [Ca2+]i elevation, while it had no effects on LTCC. Altogether, our findings highlight a crosstalk between NaV and LTCC in GH3b6 cells, providing a new insight into the mode of action of neurotoxins.

Background and aims Mutations in KCNH2 cause long or short QT syndromes (LQTS or SQTS) predisposing to life‐threatening arrhythmias. Over 1000 hERG variants have been described by clinicians, but most remain to be characterised. The objective is to standardise and accelerate the phenotyping process to contribute to clinician diagnosis and patient counselling. In silico evaluation was also included to characterise the structural impact of the variants. Methods We selected 11 variants from known LQTS patients and two variants for which diagnosis was problematic. Using the Gibson assembly strategy, we efficiently introduced mutations in hERG cDNA despite GC‐rich sequences. A pH‐sensitive fluorescent tag was fused to hERG for efficient evaluation of channel trafficking. An optimised 35‐s patch‐clamp protocol was developed to evaluate hERG channel activity in transfected cells. R software was used to speed up analyses. Results In the present work, we observed a good correlation between cell surface expression, assessed by the pH‐sensitive tag, and current densities. Also, we showed that the new biophysical protocol allows a significant gain of time in recording ion channel properties and provides extensive information on WT and variant channel biophysical parameters, that can all be recapitulated in a single parameter defined herein as the repolarisation power. The impacts of the variants on channel structure were also reported where structural information was available. These three readouts (trafficking, repolarisation power and structural impact) define three pathogenicity indexes that may help clinical diagnosis. Conclusions Fast‐track characterisation of KCNH2 genetic variants shows its relevance to discriminate mutants that affect hERG channel activity from variants with undetectable effects. It also helped the diagnosis of two new variants. This information is meant to fill a patient database, as a basis for personalised medicine. The next steps will be to further accelerate the process using an automated patch‐clamp system., We developed a method for rapid analysis of the properties of new hERG channel variants that is helpful for clinicians to diagnose an arrhythmia and help counseling the patient. This method is rapid enough to provide a complete set of channel properties and will set the stage for a more extensive characterization in the future.

Background: Plakophilin-2 (PKP2) is classically defined as a desmosomal protein. Mutations in PKP2 associate with most cases of gene-positive arrhythmogenic right ventricular cardiomyopathy. A better understanding of PKP2 cardiac biology can help elucidate the mechanisms underlying arrhythmic and cardiomyopathic events consequent to PKP2 deficiency. Here, we sought to capture early molecular/cellular events that can act as nascent arrhythmic/cardiomyopathic substrates. Methods: We used multiple imaging, biochemical and high-resolution mass spectrometry methods to study functional/structural properties of cells/tissues derived from cardiomyocyte-specific, tamoxifen-activated, PKP2 knockout mice (PKP2cKO) 14 days post-tamoxifen injection, a time point preceding overt electrical or structural phenotypes. Myocytes from right or left ventricular free wall were studied separately. Results: Most properties of PKP2cKO left ventricular myocytes were not different from control; in contrast, PKP2cKO right ventricular (RV) myocytes showed increased amplitude and duration of Ca 2+ transients, increased Ca 2+ in the cytoplasm and sarcoplasmic reticulum, increased frequency of spontaneous Ca 2+ release events (sparks) even at comparable sarcoplasmic reticulum load, and dynamic Ca 2+ accumulation in mitochondria. We also observed early- and delayed-after transients in RV myocytes and heightened susceptibility to arrhythmias in Langendorff-perfused hearts. In addition, ryanodine receptor 2 in PKP2cKO-RV cells presented enhanced Ca 2+ sensitivity and preferential phosphorylation in a domain known to modulate Ca 2+ gating. RNAseq at 14 days post-tamoxifen showed no relevant difference in transcript abundance between RV and left ventricle, neither in control nor in PKP2cKO cells. Instead, we found an RV-predominant increase in membrane permeability that can permit Ca 2+ entry into the cell. Connexin 43 ablation mitigated the membrane permeability increase, accumulation of cytoplasmic Ca 2+ , increased frequency of sparks and early stages of RV dysfunction. Connexin 43 hemichannel block with GAP19 normalized [Ca 2+ ] i homeostasis. Similarly, protein kinase C inhibition normalized spark frequency at comparable sarcoplasmic reticulum load levels. Conclusions: Loss of PKP2 creates an RV-predominant arrhythmogenic substrate (Ca 2+ dysregulation) that precedes the cardiomyopathy; this is, at least in part, mediated by a Connexin 43-dependent membrane conduit and repressed by protein kinase C inhibitors. Given that asymmetric Ca 2+ dysregulation precedes the cardiomyopathic stage, we speculate that abnormal Ca 2+ handling in RV myocytes can be a trigger for gross structural changes observed at a later stage.

Sepsis in the young population, which is particularly at risk, is rarely studied. O-GlcNAcylation is a post-translational modification involved in cell survival, stress response and metabolic regulation. O-GlcNAc stimulation is beneficial in adult septic rats. This modification is physiologically higher in the young rat, potentially limiting the therapeutic potential of O-GlcNAc stimulation in young septic rats. The aim is to evaluate whether O-GlcNAc stimulation can improve sepsis outcome in young rats. Endotoxemic challenge was induced in 28-day-old rats by lipopolysaccharide injection (E. Coli O111:B4, 20 mg·kg−1) and compared to control rats (NaCl 0.9%). One hour after lipopolysaccharide injection, rats were randomly assigned to no therapy, fluidotherapy (NaCl 0.9%, 10 mL·kg−1) ± NButGT (10 mg·kg−1) to increase O-GlcNAcylation levels. Physiological parameters and plasmatic markers were evaluated 2h later. Finally, untargeted mass spectrometry was performed to map cardiac O-GlcNAcylated proteins. Lipopolysaccharide injection induced shock with a decrease in mean arterial pressure and alteration of biological parameters (p &lt, 0.05). NButGT, contrary to fluidotherapy, was associated with an improvement of arterial pressure (p &lt, 0.05). ATP citrate lyase was identified among the O-GlcNAcylated proteins. In conclusion, O-GlcNAc stimulation improves outcomes in young septic rats. Interestingly, identified O-GlcNAcylated proteins are mainly involved in cellular metabolism.

Background: O -GlcNAcylation ( O -GlcNAc) is a post-translational modification involved in the stress response. A single pair of enzymes, O -GlcNAc transferase (OGT) and O -GlcNAcase (OGA) controls the O -GlcNAcylation. Due to the contribution of energy-linked metabolites (e.g. glucose, glutamine, etc.) to produce UDP-GlcNAc, the substrate used by OGT, O -GlcNAc is considered as a nutrient sensor. Metabolic sources vary from carbohydrates in utero , to fatty acids after birth then a mix once adult. Yet the link between diet composition and O -GlcNAc has never been explored. Purpose: Evaluate changes in O -GlcNAc levels and regulatory mechanisms throughout development. Methods: Organs were harvested from Wistar rats (n=6-8 for each group) before and after birth (D-1 and D0), in suckling animals (D12), after weaning with a standard (D28) or a carbohydrate free diet (D28F), and adult (D84). O -GlcNAc levels and regulatory enzymes were evaluated by Western blots. Mass spectrometry (MS) was performed to quantify known regulators of O -GlcNAc (n=6-8) and identify cardiac O -GlcNAcylated proteins at D0 and D28 (n=2). Results: O -GlcNAc levels fell after birth in the heart, brain and liver (2.5, 1.5 and 1.3-fold, respectively). Interestingly, while O -GlcNAc levels decrease progressively from D0 to D84 (5.75-fold pO -GlcNAc changes are opposite and of much smaller magnitude in liver and brain. Regulatory mechanisms appear to be in accordance in heart with a decrease in OGT (4.5-fold; pO -GlcNAc levels in brain and liver. O -GlcNAc levels are unaffected by weaning diet in any tissues. MS analyses identified changes in cardiac levels of specific O -GlcNAcylated proteins, namely those involved in the energy metabolism, such as ACAT1, which is only O -GlcNAcylated at D0. Conclusion: We demonstrate that O -GlcNAc levels are not linked to dietary intake and are regulated in a time and tissue-specific manner during postnatal development. We have identified by MS proteins with a particular O -GlcNAc signature across the development process suggesting specific role for those proteins.

The patch-clamp technique and more recently the high throughput patch-clamp technique have contributed to major advances in the characterization of ion channels. However, the whole-cell voltage-clamp technique presents certain limits that need to be considered for robust data generation. One major caveat is that increasing current amplitude profoundly impacts the accuracy of the biophysical analyses of macroscopic ion currents under study. Using mathematical kinetic models of a cardiac voltage-gated sodium channel and a cardiac voltage-gated potassium channel, we demonstrated how large current amplitude and series resistance artefacts induce an undetected alteration in the actual membrane potential and affect the characterization of voltage-dependent activation and inactivation processes. We also computed how dose–response curves are hindered by high current amplitudes. This is of high interest since stable cell lines frequently demonstrating high current amplitudes are used for safety pharmacology using the high throughput patch-clamp technique. It is therefore critical to set experimental limits for current amplitude recordings to prevent inaccuracy in the characterization of channel properties or drug activity, such limits being different from one channel type to another. Based on the predictions generated by the kinetic models, we draw simple guidelines for good practice of whole-cell voltage-clamp recordings.

IKr current, a major component of cardiac repolarization, is mediated by human Ether-&agrave, go-go-Related Gene (hERG, Kv11.1) potassium channels. The blockage of these channels by pharmacological compounds is associated to drug-induced long QT syndrome (LQTS), which is a life-threatening disorder characterized by ventricular arrhythmias and defects in cardiac repolarization that can be illustrated using cardiomyocytes derived from human-induced pluripotent stem cells (hiPS-CMs). This study was meant to assess the modification in hiPS-CMs excitability and contractile properties by BeKm-1, a natural scorpion venom peptide that selectively interacts with the extracellular face of hERG, by opposition to reference compounds that act onto the intracellular face. Using an automated patch-clamp system, we compared the affinity of BeKm-1 for hERG channels with some reference compounds. We fully assessed its effects on the electrophysiological, calcium handling, and beating properties of hiPS-CMs. By delaying cardiomyocyte repolarization, the peptide induces early afterdepolarizations and reduces spontaneous action potentials, calcium transients, and contraction frequencies, therefore recapitulating several of the critical phenotype features associated with arrhythmic risk in drug-induced LQTS. BeKm-1 exemplifies an interesting reference compound in the integrated hiPS-CMs cell model for all drugs that may block the hERG channel from the outer face. Being a peptide that is easily modifiable, it will serve as an ideal molecular platform for the design of new hERG modulators displaying additional functionalities.

Aim Deletion of QKP1507-1509 amino-acids in SCN5A gene product, the voltage-gated Na+ channel Nav1.5, has been associated with a large phenotypic spectrum of type 3 long QT syndrome, conduction disorder, dilated cardiomyopathy and high incidence of sudden death. The aim of this study was to develop and characterize a novel model of type 3 long QT syndrome to study the consequences of the QKP1507–1509 deletion. Methods and results We generated a knock-in mouse presenting the delQKP1510–1512 mutation (Scn5a+/ΔQKP) equivalent to human deletion. Scn5a+/ΔQKP mice showed prolonged QT interval, conduction defects and ventricular arrhythmias at the age of 2 weeks, and, subsequently, structural defects and premature mortality. The mutation increased Na+ window current and generated a late Na+ current. Ventricular action potentials from Scn5a+/ΔQKP mice were prolonged. At the age of 4 weeks, Scn5a+/ΔQKP mice exhibited a remodeling leading to [Ca2+]i transients with higher amplitude and slower kinetics, combined with enhanced SR Ca2+ load. SERCA2 expression was not altered. However, total phospholamban expression was higher whereas the amount of Ca2+-calmodulin-dependent kinase II (CaMKII)-dependent T17-phosphorylated form was lower, in hearts from 4-week-old mice only. This was associated with a lower activity of CaMKII and lower calmodulin expression. In addition, Scn5a+/ΔQKP cardiomyocytes showed larger Ca2+ waves, correlated with the presence of afterdepolarizations during action potential recording. Ranolazine partially prevented action potential and QT interval prolongation in 4-week-old Scn5a+/ΔQKP mice and suppressed arrhythmias. Conclusion The Scn5a+/ΔQKP mouse model recapitulates the clinical phenotype of mutation carriers and provides new and unexpected insights into the pathological development of the disease in patients carrying the QKP1507–1509 deletion.

Introduction Mutations in KCNH2 (coding for hERG) cause long or short QT syndromes (LQTS or SQTS), predisposing to life-threatening arrhythmias. More than 1000 variations in hERG sequences have been described, most of them are to be characterized. Objective The objective is to standardize and accelerate the entire process necessary to phenotype hERG variants. An in silico evaluation was also included to characterize the structural impact of the variants. Methods We selected 12 variants from patients with LQTS, and 1 with SQTS. We optimized the protocol to efficiently introduce mutations in hERG cDNA despite GC-rich sequences, using the Gibson assembly strategy. A pH-sensitive fluorescent tag was fused to hERG for fast-track evaluation of hERG cell trafficking. An optimized patch-clamp protocol of 35 sec was developed to evaluate hERG channel activity in transfected cells. R software was used to speed up analyses. Results In the present work, we observed a good correlation between cell surface expression, assessed by the pH-sensitive tag, and current densities. Also, we showed that the new biophysical protocol allows a significant gain of time in recording ion channel properties and provides extensive information on WT and variant channel biophycical parameters, that can all be recapitulated in a single parameter defined herein as the repolarization power. The impact of the variants on channel structure were also reported where structural information was available. These three readouts (trafficking, repolarization power and structural impact) define 3 pathogenicity indexes that may help clinical diagnosis. Conclusion Fast track characterization of KCNH2 genetic variants shows its relevance to discriminate mutants that affect hERG channel activity from variants with undetectable effects. This information is meant to fill a patient database, as a basis for personalized medicine. The next steps will be to further accelerate the process using an automated patch-clamp system.

Plakophilin-2 (PKP2) is a component of the desmosome and known for its role in cell–cell adhesion. Mutations in human PKP2 associate with a life-threatening arrhythmogenic cardiomyopathy, often of right ventricular predominance. Here, we use a range of state-of-the-art methods and a cardiomyocyte-specific, tamoxifen-activated, PKP2 knockout mouse to demonstrate that in addition to its role in cell adhesion, PKP2 is necessary to maintain transcription of genes that control intracellular calcium cycling. Lack of PKP2 reduces expression of Ryr2 (coding for Ryanodine Receptor 2), Ank2 (coding for Ankyrin-B), Cacna1c (coding for CaV1.2) and Trdn (coding for triadin), and protein levels of calsequestrin-2 (Casq2). These factors combined lead to disruption of intracellular calcium homeostasis and isoproterenol-induced arrhythmias that are prevented by flecainide treatment. We propose a previously unrecognized arrhythmogenic mechanism related to PKP2 expression and suggest that mutations in PKP2 in humans may cause life-threatening arrhythmias even in the absence of structural disease., It is believed that mutations in desmosomal adhesion complex protein plakophilin 2 (PKP2) cause arrhythmia due to loss of cell-cell communication. Here the authors show that PKP2 controls the expression of proteins involved in calcium cycling in adult mouse hearts, and that lack of PKP2 can cause arrhythmia in a structurally normal heart.

Introduction The secretome is a set of proteins secreted by a cell at a given time and under certain conditions. The secretome, easily accessible from plasma and analyzable by a proteomic approach, represents a good opportunity to identify biomarkers in septic shock. This pathology corresponds to a systemic inflammatory response syndrome related to an infection and associated with cardiocirculatory failure leading to organ dysfunction with a mortality rate of 40%. The identification of diagnostic/prognostic biomarkers is crucial to improve patient outcome. Objective Study the secretome of a rat model of endotoxemic shock to identify relevant deregulated proteins (DEP). Methods Endotoxemic shock was induced by lipopolysaccharides injection (LPS, S. enterica typhi, 0.5 mg/kg, iv) and compared to controls (Ringer lactate, iv). Under isoflurane anesthesia, carotid cannulation allowed evaluation of mean arterial blood pressure (MAP), heart rate and blood sampling (T0, and T50 or T90 min on EDTA and protease inhibitor). Plasma was analyzed with tandem MS based on a label free quantification. Gene ontology (GO) analyses defined several groups of biological process (BP) in which the DEP were involved. Results Ninety minutes after shock induction, the LPS group present a reduction in MAP (−45%, P Conclusion This study proposes an approach to identify DEP in septic shock. DEP need to be tested in cellular models in order to understand their role in the physiopathology of shock and to improve understanding of adaptations of the secretome during sepsis. The link between our results and patient prognosis will need to be studied for clinical use.

Introduction The young population, particularly at risk of septic shock, is rarely studied. The O-GlcNAcylation is a post-translational modification involved in cell survival, metabolism and stress response. We have shown that O-GlcNAc stimulation at the early phase of septic shock is beneficial in adult rats. Considering that O-GlcNAc levels are higher in the young, the impact of O-GlcNAc stimulation on sepsis in the young should be tested. Objective Evaluate if O-GlcNAc stimulation could improve sepsis outcomes in young. Method Endotoxemic shock was induced in 28 days old rats by injection of LPS (O111 :B4, 20 mg.kg−1–LPS) and compared to control rats (injection of saline–CTRL). One hour after LPS injection rats were randomly assigned to no therapy (LPS), fluidotherapy (saline, 10 mL.kg−1–LPS + R) ± NButGT (10 mg.kg−1–NButGT) to increase O-GlcNAc levels (n = 11 per group). Physiological functions and plasmatic markers were evaluated 2 hours later. Impact of treatment was evaluated with an adapted Pediatric RISk of Mortality score (PRISM score) and mortality was evaluated over 36 hours (n = 16 per group). Untargeted mass spectrometry was performed to identify cardiac O-GlcNAcylated proteins. Results LPS induced a shock (mean arterial pressure (MAP): CTRL: 67.2 ± 1.9; LPS: 50.7 ± 2.1 mmHg; P Conclusion O-GlcNAc stimulation acutely improves outcome in young septic shock rat. The impact of O-GlcNAcylation on ACLY is a potential issue to decipher the role of this protein during sepsis.

Introduction Kv11.1 channel (hERG) and the corresponding IKr current is a major component of cardiac repolarization and sinoatrial pacemaking. Dysfunctions in hERG channels are associated with cardiac arrhythmias and remains a driving force to study the structure, biophysics and pharmacology of this channel. Several compounds that block hERG channels have been developed. In this study, we focused on BeKm-1, a toxin which is highly selective for the hERG channel. Objective To study hERG channels at high temporal and spatial resolution, we developed a photo-protected analog of BeKm-1 that enables control of hERG using light. Method We developed a photo-protected BeKm-1 analog (BeKm-1-Lys18Nvoc) which is cleaved by UV-light at 365 nm. Using a hERG stable cell line and high-throughput automated patch-clamp (Syncropatch 384, Nanion) we validated several properties of the BeKm-1 analog blockage. To demonstrate spatial control of cardiomyocyte function, hiPS-derived cardiomyocytes were plated on CardioExcyte96 to record extrafield potentials. Results We first validated physico-chemical properties of BeKm-1-Nvoc compared to BeKm-1 using HPLC analyses. Patch-clamp experiments displayed no inhibition of hERG current by BeKm-1-Nvoc at concentrations for which wild-type Bekm-1 is maximally inhibiting. Illumination of BeKm-1-Nvoc (100 nM) at 365 nm allows cleavage of the protecting group and strong inhibition of hERG current. The block of hERG is reversible after washes. Illumination of BeKm-1-Nvoc on hiPS-derived cardiomyocytes induces prolongation of extrafied potential which reflects an increase in repolarization time. Study of effects of photoactivation of BeKm-1 on mouse and zebrafish heart rates are ongoing. Conclusion We developed for the first time a photo-sensitive blocker of endogenous hERG channel which allows control of its activity with the spatiotemporal precision of light. Studies of implication of hERG on arrhythmias using this compound are ongoing.

Introduction hERG potassium channels are essential for normal cardiac electrical activity. Mutations in the hERG gene (KCNH2) cause long QT syndrome, a disorder that predisposes individuals to life-threatening arrhythmias. More than 1000 mutations in hERG sequence are described in databases and most of them remains to be characterized. Objective The objective of the work is to determine the consequences of the variants identified in LQT2 patients on the expression and function of the hERG channel. Methods An optimized sequence hERG fused to pHluorin tag was synthesized. By amplifying mutated overlapping fragments, and using the Gibson assembly strategy, we constructed hERG-pHluorin plasmids with missense variations. CHO cells were transfected by electroporation with the Maxcyte system or Fugene method, and studied after 40 hours. Confocal images and flow cytometry analysis were used to evaluate the percentage of transfected cells and to quantify the membrane channel expression, through pH sensitive pHluorin tag. Conventional or automated patch clamp were used to evaluate the hERG activity. Results In the present work, we constructed hERG plasmids carrying 48 variations identified in patients in France. Higher efficiency of transfection was observed with electroporation as compared to the Fugene method. The activity of hERG-pHluorin was validated in manual patch-clamp, the pHluorin tag does not interfere with channel activity. Characterization of several mutations in conventional patch clamp showed difference in current amplitude. Automated patch-clamp data was compared to manual patch-clamp, as an initial validation for high throughput screening of all constructed mutations. Conclusion High-throughput characterization of KCNH2 genetic variants is relevant to discriminate mutants that affect hERG channel activity from variants with undetectable effects. This information will be indicated in a patient database, as a basis of personalized medicine.

Introduction Septic shock is a systemic inflammatory response syndrome associated with circulation failure leading to organ failure with a mortality rate of 40%. Early diagnosis and prognosis of septic shock are necessary for timely and specific treatment but no predictive biomarkers are available. The plasma proteome is easily accessible and may contain biomarkers that can be studied with non-targeted “omic” strategies. Aims We aim to decipher a relevant proteome signature through a non-targeted mass spectrometry (MS) analysis in a rat septic shock model. Methods In 10-week-old Wistar rats (n = 11/group), 30 min post-buprenorphine (0.05 mg/kg, s) endotoxemic shock was induced by lipopolysaccharides injection (LPS, S. enterica typhi, 0.5 mg/kg, iv) and compared to controls (NaCl 0.9%, iv). Under isoflurane anesthesia, carotid cannulation allowed mean arterial blood pressure (MAP), heart rate (HR) monitoring and blood sampling (T0, 50 and 150 min-EDTA with protease inhibitor). Each plasma was prepared for RPHPLC/MS by performing Proteominer, dialysis and trypsin digestion. RPHPLC-MS analysis was performed on a ESI-Q-Exactive mass spectrometer (ThermoFisher) according to a non-targeted label-free MS analysis. Data were analyzed with PEAKS and R software. Results LPS group present circulation failure (−40% MAP, +20% of HR vs Ctrl, P Conclusion This preliminary study revealed propose a new approach to identify relevant deregulated proteins in septic shock. The investigation of the link between our results and patients’ clinical features is in progress.

Aims Previous studies in murine hearts and in cell systems have shown that modifications in the expression or sequence integrity of the desmosomal molecule plakophilin-2 (PKP2) can alter the downstream expression of transcripts necessary for the electrical and mechanical function of the heart. These findings have provided support to mechanistic hypotheses that seek to explain arrhythmogenic right ventricular cardiomyopathy (ARVC) in humans. However, the relation between PKP2 expression and the transcriptome of the human heart remains poorly explored. Furthermore, while a number of studies have documented the clinical similarity between familial ARVC in humans and inheritable ARVC in boxer dogs, there is a puzzling lack of convergence as to the possible genetic causes of disease in one species vs. the other. Methods and results We implemented bioinformatics analysis tools to explore the relation between the PKP2-dependent murine and human transcriptomes. Our data suggest that genes involved in intracellular calcium regulation, and others involved in intercellular adhesion, form part of a co-ordinated gene network. We further identify PROX1 and PPARA (coding for the proteins Prox1 and PPAR-alpha, respectively) as transcription factors within the same network. Conclusion On the basis our analysis, we hypothesize that the molecular cascades initiated by the seemingly unrelated genetic mutations in humans and in boxers actually converge downstream into a common pathway. This can explain the similarities in the clinical manifestation of ARVC in humans and in the boxer dogs.

Deletion of QKP1507-1509 amino-acids in SCN5A gene product, the voltage-gated NaWe generated a knock-in mouse presenting the delQKP1510-1512 mutation (Scn5aThe Scn5a

International audience; Aims: Loss-of-function mutations in SCN5A, the gene encoding NaV1.5 channel, have been associated with inherited progressive cardiac conduction disease (PCCD). We have proposed that Scn5a heterozygous knock-out (Scn5a+/-) mice, which are characterized by ventricular fibrotic remodelling with ageing, represent a model for PCCD. Our objectives were to identify the molecular pathway involved in fibrosis development and prevent its activation. Methods and results: Our study shows that myocardial interstitial fibrosis occurred in Scn5a+/- mice only after 45 weeks of age. Fibrosis was triggered by transforming growth factor β (TGF-β) pathway activation. Younger Scn5a+/- mice were characterized by a higher connexin 43 expression than wild-type (WT) mice. After the age of 45 weeks, connexin 43 expression decreased in both WT and Scn5a+/- mice, although the decrease was larger in Scn5a+/- mice. Chronic inhibition of cardiac sodium current with flecainide (50 mg/kg/day p.o) in WT mice from the age of 6 weeks to the age of 60 weeks did not lead to TGF-β pathway activation and fibrosis. Chronic inhibition of TGF-β receptors with GW788388 (5 mg/kg/day p.o.) in Scn5a+/- mice from the age of 45 weeks to the age of 60 weeks prevented the occurrence of fibrosis. However, current data could not detect reduction in QRS duration with GW788388. Conclusion: Myocardial fibrosis secondary to a loss of NaV1.5 is triggered by TGF-β signalling pathway. Those events are more likely secondary to the decreased NaV1.5 sarcolemmal expression rather than the decreased Na+ current per se. TGF-β receptor inhibition prevents age-dependent development of ventricular fibrosis in Scn5a+/- mouse.

Background Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited cardiac disease exposing afflicted patients to sudden cardiac death. Most CPVT cases have been linked to mutations of the gene encoding ryanodine receptor type 2 (RYR2). RyR2 is a calcium channel located in the membrane of the sarcoplasmic reticulum (SR). It mediates release of calcium stocks from the SR to the cytosol, playing a major role in excitation-contraction coupling. Although several studies have investigated mechanisms underlying CPVT in mice or in vitro models, little has been done concerning functional assessment of CPVT physiopathology in human cardiomyocytes. Objective We aimed at characterizing, at cellular level, CPVT phenotype of patients carrying two new RyR2 mutations. Method Human induced pluripotent stem cells (hiPSCs) were derived from three CPVT patients. Two patients belonging to the same family carry the R4959Q RyR2 pore mutation. The third patient harbors the Y2476D mutation located in the cytosolic domain of the protein. hiPSCs were differentiated into cardiomyocytes for functional studies. Action potentials were recorded using patch-clamp technique. Calcium handling and contractility were investigated using Ionoptix and CardioExcyte technologies. Results hiPS-derived cardiomyocytes (hiPS-CMs) from CPVT patients displayed impaired beating properties. Calcium handling properties were also disrupted with changes in calcium transients, accompanied with increased diastolic calcium leak. At last, CPVT hiPS-CMs showed characteristics changes in action potential and arrhythmic events. Coherently with the patients’ phenotype, arrhythmic events were more frequent under beta-adrenergic stress. Conclusion This work enabled us to characterize two novel CPVT mutations, providing more insight into functional mechanisms involved in this pathology, and further validating the use of human pluripotent stem cells for investigating complex cardiac rhythm disorders.

Background Ryanodine receptors type 2 (RyR2) the intracellular channels that control excitation-contraction (EC) coupling in cardiomyocytes represent an important target for treatment of arrhythmias accompanying cardiac pathologies. Maurocalcine (MCa), a peptide isolated from scorpion venom, has been described as a high affinity activator of RyR in skeletal muscle. Phosphorylation of MCa has been shown to induce a complete remodelling of its effect on RyR, making it a negative allosteric modulator of RyR. Objective The purpose of this study is to characterize the effects of MCa and different analogues on EC coupling in isolated adult ventricular cardiomyocytes and hiPS-derived cardiomyocytes (hiPS-CMs). Methods Adult ventricular myocytes were isolated from 3–6 months-old Sprague Dawley rats with conventional collagenase type II and protease type XIV mix, and hiPS-CMs were obtained from urine cells of healthy volunteers. Changes of cytoplasmic calcium concentration were measured using Fura-2 and IonOptix software. hiPS-CMs contractions and extrafield potentials were recorded with CardioExcyte system (Nanion). Results We first confirmed binding between MCa and RyR2. Next, we showed that MCa (500nM) induces asynchronous calcium release and contractions of isolated adult rat cardiomyocytes under electrical stimulation at 1Hz. Similar results were observed on hiPS-CMs in the presence of MCa. Effects of native MCa and analogues on isoprenaline-mediated stimulation of RyR2 are under investigation. Conclusion Our results demonstrate that MCa penetrates adult cardiomyocytes as well as human iPS derived cardiomyocytes and modulates RyR2 activity. MCa analogues exhibit different effects on RyR2, from positive to negative allosteric modulation. These results provide promising evidence that MCa could be used as an in cellulo modulator of RyR2 to control abnormal RyR activity in pathological situations.

International audience; Phosphatidylinositol-4,5-bisphosphate (PIP(2)) is a phospholipid that has been shown to modulate several ion channels, including some voltage-gated channels like Kv11.1 (hERG). From a biophysical perspective, the mechanisms underlying this regulation are not well characterized. From a physiological perspective, it is critical to establish whether the PIP(2) effect is within the physiological concentration range. Using the giant-patch configuration of the patch-clamp technique on COS-7 cells expressing hERG, we confirmed the activating effect of PIP(2). PIP(2) increased the hERG maximal current and concomitantly slowed deactivation. Regarding the molecular mechanism, these increased amplitude and slowed deactivation suggest that PIP(2) stabilizes the channel open state, as it does in KCNE1-KCNQ1. We used kinetic models of hERG to simulate the effects of the phosphoinositide. Simulations strengthened the hypothesis that PIP(2) is more likely stabilizing the channel open state than affecting the voltage sensors. From the physiological aspect, we established that the sensitivity of hERG to PIP(2) comes close to that of KCNE1-KCNQ1 channels, which lies in the range of physiological PIP(2) variations.

Deletion of QKP1507-1509 amino-acids in SCN5A gene product, the main cardiac Na+ channel Nav1.5, is associated with a large phenotypic spectrum of long QT syndrome (LQT3), dilated cardiomyopathy (DCM) and high incidence of youth sudden death. This mutation does not affect the peak Na+ current (INa) but rather increases the late/persistent Na+ current (INaL). In order to investigate the mechanisms implicated in the phenotype observed on the mutation carriers, a knock-in mouse model presenting the equivalent QKP1510-1512 mutation has been generated (Scn5a+/ΔQKP). Mouse ECGs were recorded weekly from the age of 3 weeks. Na+ current was recorded with the whole cell patch-clamp technique in ventricular myocytes isolated from 4-week-old mice. Histological analysis was performed in paraffin sections of hearts of 4-week-old mice. At the age of 3 weeks, mice were treated with acute administration of ranolazine (30mg/kg i.p.) or β- blocker propranolol (0.3-1-3mg/kg i.p.) to suppress arrhythmias. Scn5a+/ΔQKP mice in sinus rhythm displayed a prolonged QT interval (QTc = 64±2ms vs. 42±1ms in controls) with a high incidence of spontaneous ventricular extrasystoles and/or non-sustained tachycardia, leading to early mortality. Structural analysis showed right ventricular DCM. Voltage-dependent activation and inactivation properties were significantly altered in Scn5a+/ΔQKP mice, leading to an increase in the arrhythmogenic Na+ window current. INaL was enhanced by more than 2-fold in myocytes from Scn5a+/ΔQKP mice compared to control mice. At 3 weeks, ranolazine significantly decreased QTc and suppressed arrhythmias whereas propranolol alone had no beneficial effects. Scn5a+/ΔQKP mice recapitulate a large part of the diverse clinical phenotype of patients carrying the equivalent mutation. Our results show that the mutation induces a late Na+ current involved in the arrhythmogenic process. Ranolazine, rather than β-blockers, could be a good candidate for pharmacological treatment.