Intrahippocampal grafts containing cholinergic and serotonergic fetal neurons ameliorate spatial reference but not working memory in rats with fimbria-fornix/cingular bundle lesions

Three-month-old Long-Evans female rats sustained aspirative lesions of the dorsal septohippocampal pathways and, 2 weeks later, received intrahippocampal suspension grafts containing cells from the mesencephalic raphe, cells from the medial septum and the diagonal band of Broca, or a mixture of both. Lesion-only and sham-operated rats were used as controls. All rats were tested for locomotor activity 1 week, 3 and 5 months after lesion surgery, for spatial working memory in a radial maze from 5 to 9 months, and for reference and working memory in a water tank during the 9th month after lesioning. Determination of hippocampal concentration of acetylcholine, noradrenaline, and serotonin was made after completion of behavioral testing. Compared to sham-operated rats, all rats with lesions, whether grafted or not, exhibited increased levels of locomotor activity and made more errors in the radial maze. The lesioned rats were also impaired in the probe trial (30 first seconds) of the water-tank test made according to a protocol requiring intact reference memory capabilities. While rats with septal or raphe grafts were also impaired, the rats with co-grafts showed performances not significantly different from those of sham-operated rats. With a protocol requiring intact working memory capabilities, all lesioned rats, whether grafted or not, were impaired in the water-tank test. In the dorsal hippocampus of lesion-only rats, the concentration of acetylcholine and serotonin was significantly reduced. In rats with septal grafts or co-grafts, the concentration of acetylcholine was close to normal, as was that of serotonin in rats with raphe grafts or co-grafts. These results confirm previous findings showing that co-grafts enabled the neurochemical properties of single grafts to be combined. Data from the water-tank test suggest that cholinergic and serotonergic hippocampal reinnervations by fetal cell grafts may induce partial recovery of spatial reference, but not working memory capabilities in rats

Do Cellular Entry Mechanisms of SARS-Cov-2 Affect Myocardial Cells and Contribute to Cardiac Injury in COVID-19 Patients?

International audienceAlthough the main vital organ affected by SARS CoV-2 is the lung, more than 20% of hospitalized patients show heart injury, however, the underlying mechanisms are still actively investigated. Inflammation or myocardial ischemia are now well-established pathogenic factors. Direct cardiac damage by the virus is likely and might account for some aspects of cardiac disease in COVID-19 patients. However, precise knowledge on mechanisms of virus entry and progression in host cells and notably in cardiac cells is necessary in order to define the broad spectrum of pathogenicity of SARS-Cov-2 on myocardium and to identify specific therapeutic targets. This review will focus on the intracellular trafficking machinery, the Achilles heel of host cells, which can be used by the virus to infect cells of the cardiovascular system

Ion Channel Trafficking: Control of Ion Channel Density as a Target for Arrhythmias?

The shape of the cardiac action potential (AP) is determined by the contributions of numerous ion channels. Any dysfunction in the proper function or expression of these ion channels can result in a change in effective refractory period (ERP) and lead to arrhythmia. The processes underlying the correct targeting of ion channels to the plasma membrane are complex, and have not been fully characterized in cardiac myocytes. Emerging evidence highlights ion channel trafficking as a potential causative factor in certain acquired and inherited arrhythmias, and therapies which target trafficking as opposed to pore block are starting to receive attention. In this review we present the current evidence for the mechanisms which underlie precise control of cardiac ion channel trafficking and targeting

Inhibition latérale dans la rétine (Caractérisation électrophysiologique des cellules bipolaires humaines in vitro et des cônes de porc en culture ou purifiés par " lectin-panning ")

Dans la rétine, le traitement de l'information visuelle est réalisé par une transmission verticale excitatrice, des photorécepteurs aux cellules bipolaires puis ganglionnaires, qui est modulée par des inhibitions latérales, principalement GABAergiques et glycinergiques, issues des cellules horizontales, amacrines et interplexiformes. L'objectif de cette thèse était de caractériser d'un point de vue électrophysiologique, moléculaire et cellulaire les substrats de cette inhibition au niveau des photorécepteurs et des cellules bipolaires.Dans les cellules bipolaires humaines en culture, nous avons relevé des réponses au GABA montrant des propriétés physiologiques et pharmacologiques intermédiaires entre celles des récepteurs GABAA et GABAC pouvant suggérer l'existence d'un récepteur hybride. D'autre part, nous avons démontré selon des approches électrophysiologique, immunohistochimique et moléculaire, la présence de récepteurs glycine au niveau d'une sous-population de cônes de porc in vitro mais aussi in situ. Enfin, cette volonté de caractériser les cônes nous a conduit à développer une technique de purification sélective de ces cellules, le "lectin-panning", qui nous a permis de mettre en évidence un effet bénéfique du milieu conditionné de glie sur la survie et la croissance neuritique des cônes de porc in vitro.La présence inattendue de récepteurs glycine dans les cônes et l'expression de récepteurs GABA atypiques dans les cellules bipolaires humaines ouvrent des perspectives nouvelles dans la compréhension des mécanismes d'inhibition latérale au niveau de la rétine externe. Ce travail s'inscrit également dans une perspective thérapeutique puisque le lectin-panning permettra un criblage à haut débit de molécules potentiellement neuroprotectrices mais aussi de caractériser les cônes, au niveau protéomique et génomique, dans des modèles de dégénérescence rétinienne ou après traitement avec des molécules neuroprotectrices.Visual information processing in the retina is achieved through excitatory transmission from photoreceptors to bipolar cells and then from bipolar to ganglion cells. This vertical pathway is modulated by GABAergic and glycinergic lateral inhibitions arising from horizontal, amacrines and interplexiform cells. The aim of our work was to characterize these inhibitory pathways in cone photoreceptors and bipolar cells at electrophysiological, cellular and molecular levels.On one hand, GABA responses recorded in cultured human bipolar cells were found to exhibit mixed physiological and pharmacological properties from both GABAA and GABAC receptors thereby suggesting heteromeric assembly of GABAA and GABAC receptor subunits. On the other hand, one subpopulation of adult pig cone photoreceptors was found to express glycine receptors, both in vitro and in situ, as demonstrated by electrophysiology, immunohistochemistry and single-cell RT-PCR. This characterization of cone photoreceptors led us to develop a new purification procedure named lectin-panning that allowed us to demonstrate the neuroprotective effect of glial cell-conditioned medium on both cone photoreceptors survival and neuritic outgrowth.The unexpected presence of glycine receptors in cone photoreceptors and the expression of uncommon GABA receptors on human bipolar cells provide new insights into the understanding of mechanisms of lateral interactions occurring in the outer retina. This work also offers interesting perspectives for the development of therapeutic strategies since the lectin-panning procedure could allow us to screen for neuroprotective molecules such as pharmaceutical compounds, neurotrophic factors and glia-derived factors. Moreover, purification of cone photoreceptors should open new possibilities to study gene regulation at genomic and proteomic levels either in animal models of retinal degeneration and/or following neuroprotective treatment administration.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Remodeling of Ion Channel Trafficking and Cardiac Arrhythmias

International audienceBoth inherited and acquired cardiac arrhythmias are often associated with the abnormal functional expression of ion channels at the cellular level. The complex machinery that continuously traffics, anchors, organizes, and recycles ion channels at the plasma membrane of a cardiomyocyte appears to be a major source of channel dysfunction during cardiac arrhythmias. This has been well established with the discovery of mutations in the genes encoding several ion channels and ion channel partners during inherited cardiac arrhythmias. Fibrosis, altered myocyte contacts, and post-transcriptional protein changes are common factors that disorganize normal channel trafficking during acquired cardiac arrhythmias. Channel availability, described notably for hERG and KV1.5 channels, could be another potent arrhythmogenic mechanism. From this molecular knowledge on cardiac arrhythmias will emerge novel antiarrhythmic strategies

Early Protective Role of Inflammation in Cardiac Remodeling and Heart Failure: Focus on TNFα and Resident Macrophages

International audienceCardiac hypertrophy, initiated by a variety of physiological or pathological stimuli (hemodynamic or hormonal stimulation or infarction), is a critical early adaptive compensatory response of the heart. The structural basis of the progression from compensated hypertrophy to pathological hypertrophy and heart failure is still largely unknown. In most cases, early activation of an inflammatory program reflects a reparative or protective response to other primary injurious processes. Later on, regardless of the underlying etiology, heart failure is always associated with both local and systemic activation of inflammatory signaling cascades. Cardiac macrophages are nodal regulators of inflammation. Resident macrophages mostly attenuate cardiac injury by secreting cytoprotective factors (cytokines, chemokines, and growth factors), scavenging damaged cells or mitochondrial debris, and regulating cardiac conduction, angiogenesis, lymphangiogenesis, and fibrosis. In contrast, excessive recruitment of monocyte-derived inflammatory macrophages largely contributes to the transition to heart failure. The current review examines the ambivalent role of inflammation (mainly TNFα-related) and cardiac macrophages (Mφ) in pathophysiologies from non-infarction origin, focusing on the protective signaling processes. Our objective is to illustrate how harnessing this knowledge could pave the way for innovative therapeutics in patients with heart failure

Transcriptomic and Lipidomic Mapping of Macrophages in the Hub of Chronic Beta-Adrenergic-Stimulation Unravels Hypertrophy-, Proliferation-, and Lipid Metabolism-Related Genes as Novel Potential Markers of Early Hypertrophy or Heart Failure

International audienceSympathetic nervous system overdrive with chronic release of catecholamines is the most important neurohormonal mechanism activated to maintain cardiac output in response to heart stress. Beta-adrenergic signaling behaves first as a compensatory pathway improving cardiac contractility and maladaptive remodeling but becomes dysfunctional leading to pathological hypertrophy and heart failure (HF). Cardiac remodeling is a complex inflammatory syndrome where macrophages play a determinant role. This study aimed at characterizing the temporal transcriptomic evolution of cardiac macrophages in mice subjected to beta-adrenergic-stimulation using RNA sequencing. Owing to a comprehensive bibliographic analysis and complementary lipidomic experiments, this study deciphers typical gene profiles in early compensated hypertrophy (ECH) versus late dilated remodeling related to HF. We uncover cardiac hypertrophy- and proliferation-related transcription programs typical of ECH or HF macrophages and identify lipid metabolism-associated and Na+ or K+ channel-related genes as markers of ECH and HF macrophages, respectively. In addition, our results substantiate the key time-dependent role of inflammatory, metabolic, and functional gene regulation in macrophages during beta-adrenergic dependent remodeling. This study provides important and novel knowledge to better understand the prevalent key role of resident macrophages in response to chronically activated beta-adrenergic signaling, an effective diagnostic and therapeutic target in failing hearts

Epicardial origin of cardiac arrhythmias: clinical evidences and pathophysiology

International audienceRecent developments in imaging, mapping and ablation techniques have shown that the epicardial region of the heart is a key player in the occurrence of ventricular arrhythmic events in several cardiac diseases such as Brugada syndrome, arrhythmogenic cardiomyopathy or dilated cardiomyopathy. At the atrial level as well, the epicardial region has emerged as an important determinant of the substrate of atrial fibrillation, pointing to common underlying pathophysiological mechanisms. Alteration in the gradient of repolarization between myocardial layers favoring the occurrence of re-entry circuits has largely been described. The fibro-fatty infiltration of the subepicardium is another shared substrate between ventricular and atrial arrhythmias. Recent data have emphasized the role of the epicardial reactivation in the formation of this arrhythmogenic substrate. There are new evidences supporting this structural remodeling process to be regulated by the recruitment of epicardial progenitor cells that can differentiate into adipocytes or fibroblasts under various stimuli. In addition, immune-inflammatory processes can also contribute to fibrosis of the subepicardial layer. A better understanding of such "electrical fragility" of the epicardial area will open perspectives for novel biomarkers and therapeutic strategies. In this review article, a pathophysiological scheme of epicardial-driven arrhythmias will be proposed

cAMP-dependent regulation of IKs single-channel kinetics

International audienceThe delayed potassium rectifier current, IKs, is composed of KCNQ1 and KCNE1 subunits and plays an important role in cardiac action potential repolarization. During β-adrenergic stimulation, 3′-5′-cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) phosphorylates KCNQ1, producing an increase in IKs current and a shortening of the action potential. Here, using cell-attached macropatches and single-channel recordings, we investigate the microscopic mechanisms underlying the cAMP-dependent increase in IKs current. A membrane-permeable cAMP analog, 8-(4-chlorophenylthio)-cAMP (8-CPT-cAMP), causes a marked leftward shift of the conductance–voltage relation in macropatches, with or without an increase in current size. Single channels exhibit fewer silent sweeps, reduced first latency to opening (control, 1.61 ± 0.13 s; cAMP, 1.06 ± 0.11 s), and increased higher-subconductance-level occupancy in the presence of cAMP. The E160R/R237E and S209F KCNQ1 mutants, which show fixed and enhanced voltage sensor activation, respectively, largely abolish the effect of cAMP. The phosphomimetic KCNQ1 mutations, S27D and S27D/S92D, are much less and not at all responsive, respectively, to the effects of PKA phosphorylation (first latency of S27D + KCNE1 channels: control, 1.81 ± 0.1 s; 8-CPT-cAMP, 1.44 ± 0.1 s, P < 0.05; latency of S27D/S92D + KCNE1: control, 1.62 ± 0.1 s; cAMP, 1.43 ± 0.1 s, nonsignificant). Using total internal reflection fluorescence microscopy, we find no overall increase in surface expression of the channel during exposure to 8-CPT-cAMP. Our data suggest that the cAMP-dependent increase in IKs current is caused by an increase in the likelihood of channel opening, combined with faster openings and greater occupancy of higher subconductance levels, and is mediated by enhanced voltage sensor activation