Biology subjects

Essers, M. C.

Publications and source records attributed to Essers, M. C..

4 recordsLinked to original sources

bioRxiv2022

Knockdown of the TRPM4 channel alters cardiac electrophysiology and hemodynamics in a sex- and age-dependent manner in mice

BackgroundTRPM4 is a calcium-activated, voltage-modulated, non-selective ion channel widely expressed in various types of cells and tissues. TRPM4 regulates the influx of sodium ions, thus playing a role in regulating the membrane potential. In the heart, TRPM4 is expressed in both cardiomyocytes and cells of the conductive pathways. Clinical studies have linked TRPM4 mutations to several cardiac disorders. While data from experimental studies have demonstrated TRPM4s functional significance in cardiac physiology, its exact roles in the heart remain unclear. AimTo investigate the role of TRPM4 in cardiac physiology in a newly generated knockdown Trpm4 mouse model. Methods and resultsMale and female Trpm4 knockdown (Trpm4 -/-) and wild-type mice 5- to 12-weeks-old (young) or 24-week-old or more (adult) were characterized using a multimodal approach, encompassing surface electrocardiograms (ECG), echocardiography recordings, pseudo and intracardiac ECGs, western blots, and mRNA quantifications. The assessment of cardiac electrophysiology by surface ECGs revealed no significant differences between wild type and Trpm4 -/- 5- to 12-weeks-old mice of either sex. Above 24 weeks of age, adult male Trpm4 -/- mice showed significantly reduced heart rate and increased heart rate variability. Echocardiography reveals that only adult male Trpm4 -/- mice exhibited slight left ventricular hypertrophic alterations with an alteration of the mitral valve pressure half time, the mitral valve E/A ratio, the isovolumetric relaxation time, and the mitral valve deceleration. In addition, an assessment of the right ventricular systolic function by scanning the pulmonary valve highlighted an alteration in pulmonary valve peak velocity and pressure in male Trpm4 -/- adult mice. Finally, intracardiac ECG recordings showed that the application of 5 {micro}M NBA triggered a third-degree atrioventricular block on 40% of wild-type hearts only. ConclusionsThese results confirm the important role of TRPM4 in the proper structure and electrical function of the heart. It also reveals significant differences between male and female animals that have never been reported before. In addition, the investigation of the effects of NBA on heart function highlights the role of TRPM4 in atrioventricular conduction and provides the first evidence showing the efficacy of this compound on native cardiac tissues.

physiology↗

bioRxiv2020

Deletion of Trpm4 alters the function and expression of NaV1.5 channel in murine cardiac myocytes

Transient receptor potential melastatin member 4 (TRPM4) encodes a Ca+ -activated non-selective cation channel that is functionally expressed in several tissues including the heart. Pathogenic mutants in TRPM4 have been reported in patients with inherited cardiac diseases including conduction block and Brugada syndrome. Heterologous expression of mutant channels in cell lines indicates that these mutations can lead to an increase or decrease in TRPM4 expression and function at the cell surface. While the expression and clinical variant studies further stress the importance of TRPM4 in cardiac function, the cardiac electrophysiological phenotypes in Trpm4 knockdown mouse models remain incompletely characterized. To study the functional consequences of Trpm4 deletion on cardiac electrical activity in mice, we performed perforated-patch clamp and immunohistochemistry studies on isolated atrial and ventricular cardiac myocytes and surface, pseudo and intracardiac ECGs either in vivo or on Langendorff-perfused explanted mouse hearts. We observed that Trpm4 is expressed in atrial and ventricular cardiac myocytes and that deletion of Trpm4 unexpectedly reduces the peak Na+ currents in the myocytes. Hearts from Trpm4-/- mice presented increased sensitivity towards mexiletine, a Na+ channel blocker, and slower intraventricular conduction, consistent with the reduction of peak Na+ current observed in the isolated cardiac myocytes. This reduction in Na+ current is explained by the observed decrease in protein expression of NaV1.5 in Trpm4-/- mice. This study suggests that Trpm4 expression impacts Na+ current in murine cardiac myocytes and points towards a novel function of Trpm4 regulating the NaV1.5 expression in murine cardiac myocytes.

physiology↗

bioRxiv2019

A distinct pool of Nav1.5 channels at the lateral membrane of murine ventricular cardiomyocytes

BackgroundIn cardiac ventricular muscle cells, the presence of voltage-gated sodium channels Nav1.5 at the lateral membrane depends in part on the interaction between the dystrophin-syntrophin complex and the Nav1.5 C-terminal PDZ-domain-binding sequence Ser-Ile-Val (SIV motif). 1-Syntrophin, a PDZ-domain adaptor protein, mediates the interaction between Nav1.5 and dystrophin at the lateral membrane of cardiac cells. Using the cell-attached patch-clamp approach on cardiomyocytes expressing Nav1.5 in which the SIV motif is deleted ({Delta}SIV), sodium current (INa) recordings from the lateral membrane revealed an SIV-motif-independent INa. Since immunostainings have suggested that Nav1.5 is expressed in transverse (T-) tubules, this remaining INa might be conducted by channels in the T-tubules. Of note, a recent study using heterologous expression systems showed that 1-syntrophin also interacts with the Nav1.5 N-terminus, which may explain the SIV-motif independent INa at the lateral membrane of cardiomyocytes.\n\nAimTo address the role of 1-syntrophin in regulating the INa at the lateral membrane of cardiac cells.\n\nMethods and resultsPatch-clamp experiments in cell-attached configuration were performed on the lateral membranes of wild-type, 1-syntrophin knock-down, and {Delta}SIV ventricular mouse cardiomyocytes. Compared to wild-type, a reduction of the lateral INa was observed in myocytes from 1-syntrophin knockdown hearts. However, similar to {Delta}SIV myocytes, a remaining INa was still recorded. In addition, cell-attached INa recordings from lateral membrane did not differ significantly between non-detubulated and detubulated {Delta}SIV cardiomyocytes. Lastly, we obtained evidence suggesting that cell-attached patch-clamp experiments on the lateral membrane cannot record currents conducted by channels in T-tubules such as calcium channels.\n\nConclusionAltogether, these results suggest the presence of a sub-pool of sodium channels at the lateral membrane of cardiomyocytes that is independent of 1-syntrophin and the PDZ-binding motif of Na 1.5, located in membrane domains outside of T-tubules. The question of a T-tubular pool of Nav1.5 channels however remains open.

physiology↗

bioRxiv2019

Dystrophin and calcium current are decreased in cardiomyocytes expressing Cre enzyme driven by αMHC but not TNT promoter

BackgroundThe Cre/lox system is a potent technology to control gene expression in mouse tissues. However, cardiac alterations following cardiac-specific Cre enzyme expression in non-loxP-flanked genome heart have been reported. Recently, many loxP like sites have been identified in the wild-type mouse genome. Interestingly one of them is localized in the Dmd gene encoding the dystrophin protein known to be crucial for stabilization of cardiac voltage-gated ion channels Nav1.5 and Cav1.2. AimHere, we studied the potential alteration of dystrophin expression in adult alpha-myosin heavy chain (MHC)-Cre mice, which are extensively used for cardiac-specific recombination, and investigated Troponin T (TNT)-Cre mice as a potential alternative. MethodsCardiac-specific MHC-Cre and TNT-Cre mouse lines expressing Cre recombinase under the control of the cardiac-specific alpha-myosin-heavy chain, and rat cardiac troponin T2 promoter respectively were used. Western blots, quantitative RT-PCR, immunostainings, and patch-clamp experiments were performed to characterize MHC-Cre and TNT-Cre mouse hearts and cardiomyocytes. ResultsDystrophin protein level was decreased in hearts from 12-week-old MHC-Cre+ mice compared to MHC-Cre-. Reduction of dystrophin was more pronounced with age. No significant difference was observed between 8-week-old MHC-Cre+ mice and MHC-Cre-. Immunostainings performed on cardiac sections showed reduced dystrophin signal at the lateral membrane of MHC-Cre+ cardiomyocytes. Quantitative RT-PCR showed decreased mRNA levels of Dmd gene encoding dystrophin. Finally, patch-clamp experiments showed a significant decrease in calcium current (ICaL) in adult MHC-Cre+ cardiomyocytes compared to MHC-Cre-. Neither dystrophin nor ICaL was reduced in adult TNT-Cre+ mouse hearts compared to TNT-Cre-. ConclusionIn contrary to TNT-Cre+ mice, the sole expression of Cre recombinase can alter the cardiac phenotype of MHC-Cre+ mice. Thus, researchers should include the "Cre-only" condition as control condition when designing experiments with Cre mouse strains.

physiology↗