Biology subjects

Hatem, S. N.

Publications and source records attributed to Hatem, S. N..

5 recordsLinked to original sources

bioRxiv2024

Depleting trafficking regulator CASK promotes intercalated disc organization and ventricular function

BackgroundThe intercalated disc (ID) electromechanically couples adjacent cardiomyocytes. Alteration of this structure plays a central role in cardiac arrhythmias, notably arrhythmogenic cardiomyopathy (ACM), an inherited genetic disorder of desmosomes. Calcium/Calmodulin-Dependent Serine Protein Kinase (CASK), a costameric component of the lateral membrane, regulates cardiomyocyte protein trafficking. Here, we investigated CASK regulation of the organization of ID components in normal and pathological contexts. Here, we investigated CASK regulation of the organization of ID components in normal and pathological contexts. MethodsWe studied the outcomes of CASK depletion in neonatal rat hearts using a cardiac-specific adeno-associated virus strategy. We used conventional and strain echocardiography, hemodynamics, electrocardiography, histology, and gene and protein expression studies to characterize adult rat hearts. We also studied the effects of CASK depletion in neonatal rat ventricular cardiomyocytes (NRVM), and control and ACM (PKP2+/-) IPS cell-derived CM (hIPS-CM) using proteomics, electron microscopy, high-resolution imaging, mechano-scanning ion conductance microscopy (mechano-SICM), and stress resistance tests. We studied cardiac CASK expression and localization in human ACM and non-transplantable control hearts. ResultsDepletion of CASK in our multiple experimental models revealed that CASK regulates cardiomyocyte IDs. In rats, CASK depletion improved contractile reserve and compliance. In cultured rat cardiomyocytes, CASK knockdown increased localization of connexin 43 (Cx43) and PKP2 at IDs, resulting in increased contact stiffness. In PKP2+/- hIPS-CMs, CASK expression was increased. CASK depletion in these cells promoted PKP2 accumulation at cell contacts, formation of desmosome-like structures, and stress resistance. In the right ventricles of ACM patients, CASK protein level was also increased and CASK abnormally localized at the ID. ConclusionCASK functions as a repressor of ID organization and tissue cohesion, suggesting novel mechanisms for regulating ID structure and function. These observations, along with CASK upregulation and mislocalization in ACM, open up new perspectives on understanding the pathophysiology of ACM and suggest innovative strategies for its treatment.

physiology↗

bioRxiv2024

Inhibition of Atrial Natriuretic Peptide Clearance Reduces Myocardial Fibrosis and Improves Cardiac Function in Diabetic Rats

BackgroundNatriuretic peptides (NP) exert pleotropic effects through the recruitment of cGMP-signaling pathways depending on their bioavailability which is regulated by clearance receptors and peptidases. Here, we tested the hypothesis that increasing myocardial bioavailability of NP has a beneficial effect on heart failure. We studied the effects of a mutated NP, MANP, resistant to neprilysin in a model of diabetic cardiomyopathy characterized by a marked myocardial fibrosis. MethodsNatriuretic peptides as well as sacubritril were delivered via osmotic mini-pumps to high-fat/streptozotocin-induced type-2 diabetic (T2D) rats. Cardiac function was evaluated by echocardiography. Myocardial remodeling was studied by histological approaches, collagen phenotype and measurement of cGMP tissue concentration. Live-cell cGMP biosensing was conducted on cultured rat cardiac fibroblasts to investigate biological effects of NPs. cGMP signaling pathway was studied using various antibody arrays and biochemicals assays in cardiac tissue and cultured fibroblasts. ResultsMANP exhibits superior efficacy than ANP in reducing left ventricular dysfunction and to reduce myocardial fibrosis with less extracellular matrix deposition. In vitro, MANP and ANP similarly generated cGMP and activated PKG signaling pathway in cardiac fibroblasts, attenuating SMAD activation, collagen secretion and cell proliferation. Nevertheless, in vivo, MANP enhanced cardiac cGMP accumulation and was more potent than ANP in activating myocardial cGMP/PKG signaling and inhibiting the profibrotic SMAD pathway. Endopeptidase inhibition using sacubitril also led to cardiac cGMP accumulation and reduced myocardial fibrosis ConclusionsMyocardial bioavailability of ANP is a major determinant of peptide efficacy in reducing cardiac fibrosis and improving pump function during diabetic cardiomyopathy. Clinical PerspectiveO_ST_ABSWhat Is New?C_ST_ABSO_LIMutated atrial natriuretic peptide (MANP) resistant to neprilysin degradation outperforms wild-type ANP in reducing myocardial fibrosis and improving cardiac function in type-2 diabetes (T2D) C_LIO_LIWhile the antifibrotic effect of the two ANP isoforms involves similarly cGMP-dependent PKG signaling and inhibition of fibroblast activation, MANP enhanced cGMP myocardial concentration more importantly than ANP. C_LIO_LISacubitril that inhibits ANP degradation also reduces cardiac fibrosis through myocardial accumulation of cGMP and activation of cGMP-dependent PKG signaling pathway. C_LIO_LICardiac bioavailability of natriuretic peptides is a major determinant of their effects on myocardial fibrosis and cardiac function. C_LI What Are the Clinical Implications?O_LIMyocardial bioavailability of natriuretic peptides is crucial for mitigating cardiac fibrosis and improving cardiac function in diabetic cardiomyopathy and heart failure in general. C_LIO_LIMANP holds the potential as a new treatment modality in the management of heart failure. C_LI

physiology↗

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

HIGH FAT DIET STIMULATES BETA-OXIDATION, ALTERS ELECTRICAL PROPERTIES AND INDUCES ADIPOGENICITY OF ATRIA IN OBESE MICE

Metabolic disorders such as obesity are risk factors of atrial fibrillation, not only by sharing comorbidities but likely through their direct impact on atria, notably its adipogenicity. Here, we submitted mice that lack cardiac adipose tissue to a high fat diet and first studied the atrial metabolomic and lipidomic phenotypes using liquid chromatography-mass spectrometry. We found an increased consumption of free fatty acid by the beta-oxidation and an accumulation of long-chain lipids in atria of obese mice. Free fatty acid was the main substrate of mitochondrial respiration studied in the saponin-permeabilized atrial muscle. Conducted action potential recorded in atrial trabeculae was short, and ATP-sensitive potassium current was increased in perforated patch-clamp atrial myocytes of obese mice. There was histological and phenotypical evidence for an accumulation of adipose tissue in obese mice atria. Thus, an obesogenic diet transforms the energy metabolism, causes fat accumulation and induces electrical remodeling of atria myocardium. HIGHLIGHTS- Untargeted metabolomic and lipidomic analysis revealed that a high fat diet induces profound transformation of atrial energy metabolism with beta-oxidation activation and long-chain lipid accumulation. - Mitochondria respiration studied in atrial myocardial trabecula preferentially used Palmitoyl-CoA as energy substrate in obese mice. - Atria of obese mice become vulnerable to atrial fibrillation and show short action potential due to the activation of K-ATP dependent potassium current. - Adipocytes and fat molecular markers were detected in atria of obese mice together with an inflammatory profile consistence with a myocardial accumulation of fat.

physiology↗

bioRxiv2019

Distinct CASK domains control cardiac sodium channel membrane expression and focal adhesion anchoring

Membrane-associated guanylate kinase (MAGUK) proteins function as adaptor proteins to mediate the recruitment and scaffolding of ion channels in the plasma membrane in various cell types. In the heart, the protein CASK (Calcium/CAlmodulin-dependent Serine protein Kinase) negatively regulates the main cardiac sodium channel, NaV1.5, which carries the sodium current (INa) by preventing its anterograde trafficking. CASK is also a new member of the dystrophin-glycoprotein complex, and like syntrophin, binds to the C-terminal domain of the channel. Here we show that both L27B and GUK domains are required for the negative regulatory effect of CASK on INa and NaV1.5 surface expression and that the HOOK domain is essential for interaction with the cell adhesion dystrophin-glycoprotein complex. Thus, the multi-modular structure of CASK potentially provides the ability to control channel delivery at adhesion points in cardiomyocyte.\n\nSUMMARYSequential functional domain deletion approach identifies three critical domains of CASK in cardiomyocytes. CASK binds the cell adhesion dystrophin-glycoprotein complex through HOOK domain and inhibits NaV1.5 channel membrane expression by impeding trafficking through L27B and GUK domains.

physiology↗