Biology subjects

Ravens, U.

Publications and source records attributed to Ravens, U..

6 recordsLinked to original sources

bioRxiv2023

Piezo1 stretch-activated channel activity differs between bone marrow-derived and cardiac tissue-resident macrophages

Macrophages (M{Phi}) play pivotal roles in tissue homeostasis and repair. Their mechanical environment recently emerged as a key modulator of various cell functions, and M{Phi} mechanosensitivity is likely to be critical for cellular activity in particular in a rhythmically contracting organ such as the heart. M{Phi}, in-vitro-differentiated from bone marrow (M{Phi}BM), form a popular cell model for research. This study explores the activity of stretch-activated ion channels (SAC) in murine M{Phi}BM and compares it to SAC activity in cardiac tissue-resident M{Phi} (M{Phi}TR). Our main findings are: i) M{Phi}BM and M{Phi}TR have stretch-induced currents, indicating expression of functional SAC at their plasma membrane; ii) the current profiles in M{Phi}BM and in M{Phi}TR show characteristics of cation non-selective SAC; iii) unlike in M{Phi}BM, Piezo1 ion channel activity at the plasma membrane of M{Phi}TR is not detectable, neither by assessing electrophysiological activity using the patch clamp technique, nor by measuring cytosolic calcium concentration upon perfusion with Yoda1, a Piezo1 channel agonist. In mature scars after ventricular cryoablation, stretch-induced current characteristics of M{Phi}TR are not significantly different compared to non-injured control tissue, even though scars are expected to contain a mix of pre-existing and circulation-recruited M{Phi}. This suggests that M{Phi} invading injured cardiac tissue either phenoconvert their mechanosensitivity from M{Phi}BM to M{Phi}TR, or that the in vitro differentiation protocols used to obtain M{Phi}BM generate cells that differ from M{Phi} recruited from the circulation during tissue repair in vivo. Further investigations will explore SAC identity in lineage-traced M{Phi} in scar tissue, and compare mechanosensitivity of circulating monocytes with that of M{Phi}BM. Key pointsO_LIM{Phi}BM and M{Phi}TR have stretch-induced currents, indicating expression of functional SAC at their plasma membrane; C_LIO_LIThe current profiles in M{Phi}BM and in M{Phi}TR show characteristics of cation non-selective SAC; C_LIO_LIUnlike in M{Phi}BM, Piezo1 ion channel activity at the plasma membrane of M{Phi}TR is not detectable C_LI

biophysics↗

bioRxiv2023

Age-related structural and functional changes of the intracardiac nervous system

BackgroundAlthough aging is known to be associated with an increased incidence of both atrial and ventricular arrhythmias, there is limited knowledge about how Schwann cells (SC) and the intracardiac nervous system (iCNS) remodel with age. Here we investigate the differences in cardiac SC, parasympathetic nerve fibers, and muscarinic acetylcholine receptor M2 (M2R) expression in young and old mice. Additionally, we examine age-related changes in cardiac responses to sympathomimetic and parasympathomimetic drugs. Methods and ResultsLower SC density, lower SC proliferation and fewer parasympathetic nerve fibers were observed in cardiac and, as a control sciatic nerves from old (20-24 months) compared to young mice (2-3 months). In old mice, CSPG4 was increased in sciatic but not cardiac nerves. Expression of M2R was lower in ventricular myocardium and ventricular conduction system from old mice compared to young mice, while no significant difference was seen in M2R expression in sino-atrial or atrio-ventricular node pacemaker tissue. Heart rate was slower and PQ intervals were longer in Langendorff-perfused hearts from old mice. Ventricular tachycardia and fibrillation were more frequently observed in response to carbachol administration in hearts from old mice versus those from young mice. ConclusionsOn the background of reduced presence of SC and parasympathetic nerve fibers, and of lower M2R expression in ventricular cardiomyocytes and conduction system of aged hearts, the propensity of ventricular arrhythmogenesis upon parasympathomimetic drug application is increased. Whether this is caused by an increase in heterogeneity of iCNS structure and function remains to be elucidated. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=192 HEIGHT=200 SRC="FIGDIR/small/568538v1_ufig1.gif" ALT="Figure 1"> View larger version (53K): org.highwire.dtl.DTLVardef@11dbccdorg.highwire.dtl.DTLVardef@1563d75org.highwire.dtl.DTLVardef@dcda58org.highwire.dtl.DTLVardef@182e598_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗

bioRxiv2022

TREK-1 knock-down in human atrial fibroblasts leads to a myofibroblastic phenotype: a role in phenoconversion and overview of mechano-sensitive channel mRNA expression in cardiac diseases.

Cardiac cell mechanical environment changes on a beat-by-beat basis and also in the course of various cardiac diseases. Cells sense and adapt to such mechanical cues via specialized mechano-sensors mediating adaptive signaling cascades. Here, we report TREK-1 mRNA expression and activity in human atrial fibroblasts and reveal a cross talk between TREK-1 and fibroblast phenoconversion. With the aim to reveal additional candidates underlying mechano-transduction relevant to cardiac diseases, we investigated mechano-sensitive ion channels (MSC) mRNA expression in diseased and non-diseased human hearts. Our results showed higher TREK-1 expression and activity in fibroblasts compared to myofibroblasts and we found that TREK-1 down-regulation leads a more myofibroblastic phenotype suggesting a role for this mechano-sensor in phenoconversion. In addition, TREK-1 is preferentially expressed in the left atrium compared to the right one and its expression is not significantly changed when fibroblasts from patients in sinus rhythm vs. sustained atrial fibrillation are compared. At the whole-heart level, numerous MSC were differentially expressed between atrial and ventricular or between non-diseased and diseased tissue samples. Thus, we identify atrial fibroblast-specific TREK-1 expression and activity and reveal a role of TREK-1 in atrial fibroblast pheno-conversion. We also provide a comprehensive overview of cardiac MSC mRNA expression in atrial and ventricular tissue from diseased and non-diseased patients, identifying potential novel candidates underlying mechanotransduction in cardiac diseases.

cell biology↗

bioRxiv2021

Piezo1 and BKCa channels in human atrial fibroblasts: interplay and remodelling in atrial fibrillation

AimsAtrial Fibrillation (AF) is an arrhythmia of increasing prevalence in the aging population of developed countries. One of the important indicators of AF is sustained atrial dilatation, highlighting the importance of mechanical overload in the pathophysiology of AF. The mechanisms by which atrial cells, including fibroblasts, sense and react to changing mechanical forces, are not fully elucidated. Here, we characterise stretch-activated ion channels (SAC) in human atrial fibroblasts and changes in SAC-presence and -activity associated with AF. Methods and ResultsUsing primary cultures of human atrial fibroblasts, isolated from patients in sinus rhythm or sustained AF, we combine electrophysiological, molecular and pharmacological tools to identify SAC. Two electrophysiological SAC-signatures were detected, indicative of cation-nonselective and potassium-selective channels. Using siRNA-mediated knockdown, we identified the nonselective SAC as Piezo1. Biophysical properties of the potassium-selective channel, its sensitivity to calcium, paxilline and iberiotoxin (blockers), and NS11021 (activator), indicated presence of calcium-dependent big potassium channels, BKCa. In cells from AF patients, Piezo1 activity and mRNA expression levels were higher than in cells from sinus rhythm patients, while BKCa activity (but not expression) was downregulated. Both Piezo1-knockdown and removal of extracellular calcium from the patch pipette resulted in a significant reduction of BKCa current during stretch. No co-immunoprecipitation of Piezo1 and BKCa was detected. ConclusionsHuman atrial fibroblasts contain at least two types of ion channels that are activated during stretch: Piezo1 and BKCa. While Piezo1 is directly stretch-activated, the increase in BKCa activity during mechanical stimulation appears to be mainly secondary to calcium influx via SAC such as Piezo1. During sustained AF, Piezo1 is increased, while BKCa activity is reduced, highlighting differential regulation of both channels. Our data support the presence and interplay of Piezo1 and BKCa in human atrial fibroblasts in the absence of physical interactions between the two channel proteins.

molecular biology↗

bioRxiv2020

Physiological and pathological changes in the enteric nervous system of rotenone-exposed mice as potential early biomarkers for Parkinson's disease

Parkinsons disease (PD) is known to involve the peripheral nervous system (PNS) and the enteric nervous system (ENS). Functional changes in PNS and ENS appear early in the course of the disease and are responsible for some of the non-motor symptoms observed in PD patients like constipation, that can precede the appearance of motor symptoms by years. We have shown that environmental toxins can trigger the disease by acting on the ENS and on the autonomic nervous system. Oral exposure to the pesticide rotenone, a mitochondrial Complex I inhibitor, leads to decreased stool depositions in mice. Here we analyzed the effect of rotenone on the function and structure of the ENS by measuring intestinal contractility in a tissue bath and by analyzing related protein expression. Our results show that rotenone changes the normal physiological response of the intestine to carbachol, dopamine and electric field stimulation. The magnitude and direction of these alterations varies between intestinal regions and exposure times and is associated with an early up-regulation of dopaminergic, cholinergic and adrenergic receptors and an irregular reduction in the amount of enteric neurons in rotenone-exposed mice. The early appearance of these alterations makes them ideal candidates to be used as biomarkers for the detection of Parkinsons disease in its early stages.

neuroscience↗

bioRxiv2018

Hypoxia-induced epigenetic silencing of polo-like kinase 2 promotes fibrosis in atrial fibrillation

Fibrosis and inflammation promote atrial fibrillation (AF) and worsen its clinical outcome. The underlying molecular mechanisms, that are relevant for effective antifibrotic drug development, are still under debate. This study deciphers a novel mechanistic interplay between polo-like kinase 2 (PLK2) and the pro-inflammatory cytokine osteopontin (OPN) in the pathogenesis of atrial fibrosis. Compared to sinus rhythm (SR) controls, right atrial appendages and isolated right atrial fibroblasts from AF patients showed downregulation of PLK2 mRNA and protein levels, which were accompanied by remarkable hypoxia-sensitive DNA-methylation of the PLK2 promotor. In an experimental setting, both, genetic deletion and pharmacological inhibition of PLK2 induced myofibroblast differentiation and reduced fibroblast proliferation. Notably, proteomics from PLK2-deleted fibroblasts revealed de novo secretion of OPN. Accordingly, we observed higher OPN plasma levels in AF patients with atrial fibrosis compared to non-fibrosis AF patients. Hence, we provide evidence for PLK2 reactivation and/or OPN inhibition as potential novel targets to prevent fibrosis progression in AF.

pharmacology and toxicology↗