Biology subjects

Verkerk, A. O.

Publications and source records attributed to Verkerk, A. O..

11 recordsLinked to original sources

bioRxiv2025

Adeno-associated virus (AAV)-TBX18 does not generate biological pacemaker activity, unlike AAV-Hcn2

Gene therapy-based biological pacemakers have been proposed as an alternative to their hardware-based counterparts. In this context, short-term ectopic expression of the T-box transcription factor 18 (TBX18) in the ventricle reportedly generated potent short-term pacemaker function in various animal models. Here, we investigated the effect of adeno-associated virus (AAV)-mediated long-term expression of TBX18, and compared the outcome to that of the pacemaker ion channel Hcn2. Our findings revealed that CMV-driven ectopic TBX18 expression in mouse hearts led to severe cardiac fibrosis. At lower, non-fibrogenic levels, TBX18 maintained its transcriptional function but failed to induce pacemaker phenotypes. TBX18-expressing cells showed suppressed expression of key working myocardial genes, but the pacemaker gene program was not induced. Electrophysiological studies showed abnormal automaticity in TBX18-expressing cells, combined with prolonged repolarization and various current changes. However, no hyperpolarization-activated funny current was detected. In a complete AV-block rat model, AAV-mediated Hcn2 expression induced robust ectopic pacemaker activity in the presence of isoproterenol, whereas TBX18 expression neither generated such activities, nor augmented Hcn2-mediated pacing. In conclusion, at functional non-fibrogenic levels, TBX18 is neither sufficient nor necessary to induce pacemaker activity. In contrast, Hcn2 generates reliable pacing, making it a more viable candidate for biological pacemaker development.

physiology↗

bioRxiv2025

AAV6-HCN4t-mediated biological pacing as a potential life-saving therapy for congenital complete heart block

Congenital complete heart block (CCHB) is a life-threatening condition in fetuses due to severe bradycardia. Maternal administration of {beta}-adrenergic agonists is used to increase fetal heart rates, but its effectiveness is limited and lost over time most likely due to insufficient expression of HCN channels in some individuals. We report the development of an injectable gene therapy that produces reliable cardiac pacemaker function in the presence of {beta}-adrenergic stimulation. Intramyocardial injection of adeno-associated viral serotype 6 vectors expressing HCN4t (AAV6-HCN4t) into the left ventricular apex significantly increased ectopic pacing frequency and heart rate in response to isoproterenol in rats with complete heart block, and this effect remained stable throughout the 4 weeks of follow-up. Injection of AAV6-HCN4t showed similar reliable biological pacing in complete heart block pigs. These results suggest that AAV6-HCN4t generates robust biological pacing in the presence of isoproterenol, providing the foundation for a potentially life-saving therapy for in utero CCHB.

physiology↗

bioRxiv2025

Redefining catecholaminergic polymorphic ventricular tachycardia (CPVT) as a neurocardiac condition

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmia syndrome characterised by adrenergic activity-induced sudden cardiac death. It is most often caused by mutations in the RYR2 gene encoding ryanodine receptor 2 (RyR2), which is essential for intracellular calcium handling. Research has traditionally focused on the consequences of mutations at the cardiomyocyte level. However, RyR2 is also expressed in neuronal tissue, and patients often present with clinical signs of autonomic dysfunction. Here, we assessed if there is a neuronal phenotype in this classically cardiac condition. Using the established CPVT mouse model Ryr2-R2474S, we found that RyR2 is abundantly expressed in stellate ganglia neurons (SGNs) - the adrenergic neurons that project directly to the myocardium and modulate heart function. We revealed that in isolated Ryr2-R2474S SGNs there is altered calcium homeostasis suggestive of intracellular calcium leakage, and increased neurite projections when maintained in culture. We furthermore showed that hearts of Ryr2-R2474S mice are sympathetically hyper-innervated, with an increased heterogeneity in innervation within the myocardium. This led to changes in the quantities of neurotransmitters and their metabolites within the heart, indicating increased norepinephrine turnover. CPVT may therefore be redefined as a neurocardiac disorder, with neuronal dysregulation being a prominent component of the disease. In addition to cardiomyocytes, RYR2 mutations also affect stellate ganglia neuron function and cardiac innervation, with potential implications for arrhythmogenesis, risk stratification and therapy. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=98 SRC="FIGDIR/small/635037v1_ufig1.gif" ALT="Figure 1"> View larger version (22K): org.highwire.dtl.DTLVardef@1494446org.highwire.dtl.DTLVardef@1218190org.highwire.dtl.DTLVardef@c11db9org.highwire.dtl.DTLVardef@8674aa_HPS_FORMAT_FIGEXP M_FIG C_FIG In wildtype hearts, activation of sympathetic neurons leads to their release of norepinephrine (NE), which binds to beta adrenergic receptors ({beta}-ARs) on the cardiomyocyte membrane. The resultant initiation of intracellular signalling cascades involving cyclic AMP (cAMP) leads to reduced inhibition of the sarcoendoplasmic reticulum (SR) calcium ATPase (SERCA) pump and consequent calcium overload in the SR. This triggers the opening of ryanodine receptor 2 (RyR2), causing SR calcium to be released into the cytoplasmic space resulting in a calcium wave which triggers contraction. In CPVT hearts, there is increased sympathetic neuron innervation of the ventricular myocardium. When cardiac sympathetic nerves are activated, there is an enhanced release of NE. This excess NE causes increased activation of {beta}-ARs and an augmented intracellular cAMP response, which in turn leads to a greater reduction of the inhibition of SERCA, augmented SR calcium overload, and a heightened propensity for spontaneous calcium leakage to trigger a calcium wave, delayed afterdepolarisations, and arrhythmias. Figure created with BioRender.com.

physiology↗

bioRxiv2025

The Brugada syndrome associated gene WT1 impacts on SCN5A expression and cardiac conduction

Brugada syndrome (BrS) is an inherited cardiac arrhythmic disorder caused by conduction slowing primarily affecting the right ventricular (RV) outflow tract (RVOT). A recent genome-wide association study (GWAS) implicated a genomic region in chromosome 11, overlapping the transcription factor WT1, in BrS susceptibility. Here, we investigated the role of WT1 on cardiac conduction using a heterozygous knockout mouse model (Wt1+/-). Transcriptomic analysis revealed increased Scn5a predominantly in Wt1+/- cardiomyocytes located subepicardially in the RV and RVOT without any changes in electrical properties. To unmask an effect on cardiac conduction, we performed optical mapping in a severely challenged setting offered by Scn5a haploinsufficiency, ageing, and exposure to the sodium channel blocker ajmaline and found that diminished Wt1 improved the observed slowed conduction. Examination of human single-nuclei cardiac datasets indicated a strong negative correlation between WT1 and SCN5A expression. In line with this observation, cardiac samples from patients carrying mutations in SCN5A showed increased WT1 protein abundance in histological sections, suggesting that increased WT1, and not loss, is associated with BrS pathophysiology. By deleting the mouse orthologue of a BrS-associated noncoding region (RE) harboring a candidate regulatory element, we established that this RE controls expression of Wt1 specifically in the (sub)epicardium of the RV. Lastly, transient overexpression of WT1 in hiPSC-derived cardiomyocytes resulted in notably reduced sodium current density. Our study thereby identifies the transcription factor WT1 as a novel contributor to the pathophysiology of BrS, at least in part, through SCN5A.

genetics↗

bioRxiv2024

Electrophysiological comparison of left versus right stellate ganglia neurons

BackgroundThe stellate ganglia of the peripheral autonomic nervous system innervate the heart and continuously fine-tune cardiac function to meet physiological demands. The right stellate ganglion (RSG) predominantly innervates the sinoatrial node and has functional effects on chronotropy/heart rate, whereas the left stellate ganglion (LSG) has predominance in the ventricular myocardium and impacts inotropy/contractility. Whilst the innervation patterns and functional consequences of block and stimulation are well-documented, basic electrophysiological characterisation and single-cell comparison of RSG and LSG neurons has not been performed. In addition, sex differences in stellate ganglion action potential (AP) parameters may exist, but remain as yet unknown. Methods/ResultsHere we characterise the electrical properties of enzymatically isolated mouse stellate ganglia neurons using the patch clamp technique. Using 500 ms depolarising pulses of varying amplitude, we provide detailed characterisation of basic AP properties and their correlations. We reveal that there are two populations of neurons in terms of their AP firing properties (phasic or tonic firing), with the majority (67%) firing with a phasic pattern. When all recordings were pooled, tonic neurons had a significantly larger AP amplitude (85 {+/-} 3.0 vs 76 {+/-} 2.4 mV) and overshoot (28 {+/-} 1.8 vs 19 {+/-} 1.8 mV) compared to phasic neurons (P<0.05). Moreover, phasic neurons did not fire spontaneously, whereas 50% of tonic neurons did, and more often presented with anodal break excitation (P<0.05). When male vs female neurons were compared, males had a more negative minimum diastolic potential (MDP; -55 {+/-} 1.7 vs -47 {+/-} 3.0 mV, P<0.05). When LSG vs RSG neurons were compared, the RSG had a more negative resting membrane potential (Vrest; -60 {+/-} 1.5 vs -54 {+/-} 1.3 mV, P<0.05). All other AP parameters did not differ significantly between these groups. ConclusionsThe RSG and LSG contain a similar proportion of phasic and tonic firing neurons. A significant difference was observed in the Vrest of RSG vs LSG neurons, and in the MDP of male vs female neurons. However, all other AP parameters were similar. This suggests that the LSG and RSG can be combined irrespective of sex when investigating the electrophysiological properties of these distinct anatomical structures in healthy and disease conditions.

physiology↗

bioRxiv2024

TMPRSS6 cleaves KCNE1 and causes arrhythmias in iron overload disease

Iron storage disease is associated with cardiovascular manifestations, including various forms of cardiac arrhythmias of unknown origin. In this study, cardiac arrhythmias associated with iron overload were investigated in human iPSC-derived cardiomyocytes (hiPSC-CM) and hiPSC-derived sinus node-like pacemaker cells. Among other effects, iron overload leads to an increase in the plasma membrane-anchored protease TMPRSS6. TMPRSS6 cleaves the auxiliary subunit KCNE1 N-terminally and thus modulates the function of both the IKs (KCNQ1/KCNE1 current) and the If (HCN4/KCNE1) ion channels. Furthermore, TMPRSS6 induces a reduction of electric field potential (EFP) count and increased duration in hiPSC-derived ventricular-like cells and in hiPSC-derived pacemaker-like cells. In accordance with these in vitro generated results, TMPRSS6-mediated interactions show pro-arrhythmic effects in silico. Therefore, the TMPRSS6 - KCNE1-KCNQ1 and TMPRSS6 - KCNE1-HCN4 cascades may represent new clinically relevant pro-arrhythmic mechanisms in iron overload diseases.

physiology↗

bioRxiv2022

Reclassification of a likely pathogenic Dutch founder variant in KCNH2; implications of reduced penetrance

BackgroundVariants in KCNH2, encoding the hERG channel which is responsible for the rapid component of the cardiac delayed rectifier K+ current (IKr), are causal to Long QT Syndrome type 2 (LQTS2). We identified eight index patients with a new variant of unknown significance (VUS), KCNH2:c.2717C>T:p.(Ser906Leu). We aimed to elucidate the biophysiological effect of this variant, to enable reclassification and consequent clinical decision-making. MethodsA genotype-phenotype overview of the patients and relatives was created. The biophysiological effects were assessed by manual whole-cell patch-clamp using HEK293a cells expressing: (I) wild type (WT) KCNH2, (II) KCNH2-p.S906L alone (homozygous, Hm) or (III) KCNH2-p.S906L in combination with WT (1:1) (heterozygous, Hz). A calibrated automated patch-clamp assay using Flp-In HEK293 was used to follow up on the functional data. ResultsIncomplete penetrance of LQTS2 in KCNH2:p.(Ser906Leu) carriers was observed. In addition, some patients were heterozygous for other VUSs in CACNA1C, PKP2, RYR2, or AKAP9. The phenotype of carriers of KCNH2:p.(Ser906Leu) ranged from asymptomatic to life-threatening arrhythmic events. Manual patch-clamp showed a reduced current density by 69.8%, and 60.4% in KCNH2-p.S906L-Hm and KCNH2-p.S906L-Hz, respectively. The time constant of activation was significantly increased with 80.1% in KCNH2-p.S906L-Hm compared to KCNH2-WT. Assessment of KCNH2-p.S906L-Hz, by calibrated automatic patch-clamp showed a reduction in current density by 35.6%. ConclusionThe reduced current density in the KCNH2-p.S906L-Hz indicates a moderate loss of function. Combined with the reduced penetrance and variable phenotype, we conclude that KCNH2:p.(Ser906Leu) is a low penetrant likely pathogenic variant for LQTS2.

genetics↗

bioRxiv2022

An atrial fibrillation-associated regulatory region modulates cardiac Tbx5 levels and arrhythmia susceptibility

Heart development and rhythm control are highly Tbx5 dosage-sensitive. TBX5 haploinsufficiency causes congenital conduction disorders, whereas increased expression levels of TBX5 in human heart samples has been associated with atrial fibrillation. We deleted the conserved mouse orthologues of two independent AF-associated genomic regions in the Tbx5 locus, one intronic (RE(int)-/-) and one downstream of Tbx5 (RE(down)-/-). In both lines we observed a modest (30%) increase of Tbx5 in the postnatal atria. To gain insight into the effects of slight dosage increase in vivo, we investigated the atrial transcriptional, epigenetic and electrophysiological properties of both lines. We observed induction of genes involved in development, ion transport and conduction, increased action potential duration and increased susceptibility to atrial arrhythmias. We identified an AF-associated variant in the human intronic regulatory region that increases transcriptional activity. Expression of the AF-associated transcription factor Prrx1 was induced in RE(int)-/- cardiomyocytes. We found that some of the transcriptional and functional changes in the atria caused by increased Tbx5 expression were normalized when reducing cardiac Prrx1 expression in RE(int)-/- mice, indicating an interaction between these two AF genes. We conclude that modest increases in expression of dose-dependent transcription factors, caused by common regulatory variants, significantly impact on the cardiac gene regulatory network and disease susceptibility.

molecular biology↗

bioRxiv2021

A single cell transcriptional roadmap for human pacemaker cell differentiation

Each heartbeat is triggered by the sinoatrial node, the natural pacemaker of the heart. Animal models have revealed that pacemaker cells share a common progenitor with the (pro)epicardium, and that the pacemaker cardiomyocytes further diversify into "transitional", "tail" and "head" subtypes. However, the underlying molecular mechanisms are poorly understood. Here, we studied the differentiation of human induced pluripotent stem cells into pacemaker cardiomyocytes. Single cell RNA sequencing identified the presence of myocardial populations resembling subtypes present in the formed sinoatrial node, and in addition revealed a side population of (pro)epicardial cells. Time-course trajectory analysis uncovered a role for WNT signaling in determining myocardial versus proepicardial cell fate. We experimentally demonstrate that presence of WNT signaling prior to the branching point of a common progenitor enhances proepicardial cell differentiation at the expense of myocardial pacemaker cells. Furthermore, we uncover a role for TGF{beta} and WNT signaling in differentiation towards transitional and head pacemaker subtypes, respectively. Our findings provide new biological insights into human pacemaker differentiation, open avenues for complex disease modeling and inform regenerative approaches.

developmental biology↗

bioRxiv2019

Isogenic sets of hiPSC-CMs harboring KCNH2 mutations capture location-related phenotypic differences

AimsLong QT syndrome type 2 (LQT2) is caused by mutations in the gene KCNH2, encoding the hERG ion channel. Clinically, mild and severe phenotypes are associated with this cardiac channelopathy, complicating efforts to predict patient risk. The location of the mutation within KCNH2 contributes to this variable disease manifestation. Here we determined whether such phenotypic differences could be detected in cardiomyocytes derived from isogenic human induced pluripotent stem cells (hiPSCs) genetically edited to harbour a range of KCNH2 mutations. Methods and ResultsThe hiPSC lines heterozygous for missense mutations either within the pore or tail region of the ion channel were generated using CRISPR-Cas9 editing and subsequently differentiated to cardiomyocytes (hiPSC-CMs) for functional assessment. Electrophysiological analysis confirmed the mutations prolonged the action potentials and field potentials of the hiPSC-CMs, with differences detected between the pore and tail region mutations when measured as paced 2D monolayers. This was also reflected in the cytosolic Ca2+ transients and contraction kinetics of the different lines. Pharmacological blocking of the hERG channel in the hiPSC-CMs also revealed that mutations in the pore-loop region conferred a greater susceptibility to arrhythmic events. ConclusionThese findings establish that subtle phenotypic differences related to the location of the KCNH2 mutation in LQT2 patients are reflected in hiPSC-CMs under genetically controlled conditions. Moreover, the results validate hiPSC-CMs as a strong candidate for evaluating the underlying severity of individual KCNH2 mutations in humans which could ultimately facilitate patient risk stratification. Translational perspectiveClinical management of patients diagnosed with cardiac channelopathy diseases such as LQT2 is complicated by the variable disease phenotypes observed among mutation carriers, creating challenges for diagnosis, risk stratification and treatment. The genotype of the patient contributes to this clinical heterogeneity, with the influence of the mutations location within KCNH2 on a patients risk of a cardiac event being an example. Here we demonstrate that under stringently controlled genetic and experimental conditions, hiPSC-CMs are able to reflect these subtle genotype-phenotype differences, thereby providing new opportunities to stratify and potentially lessen sudden cardiac death risk amongst KCNH2 mutation carriers.

cell biology↗

bioRxiv2019

Cryopreservation of human pluripotent stem cell-derived cardiomyocytes is not detrimental to their molecular and functional properties

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have emerged as a powerful platform for in vitro modelling of cardiac diseases, safety pharmacology, and drug screening. All these applications require large quantities of well-characterised and standardised batches of hiPSC-CMs. Cryopreservation of hiPSC-CMs without affecting their biochemical or biophysical phenotype is essential for facilitating this, but ideally requires the cells being unchanged by the freeze-thaw procedure. We therefore compared the in vitro functional and molecular characteristics of fresh and cryopreserved hiPSC-CMs generated from two independent hiPSC lines. While the frozen hiPSC-CMs exhibited poorer replating than their freshly-derived counterparts, there was no difference in the proportion of cardiomyocytes retrieved from the mixed population when this was factored in. Interestingly, cryopreserved hiPSC-CMs from one line exhibited longer action potential durations. These results provide evidence that cryopreservation does not compromise the in vitro molecular, physiological and mechanical properties of hiPSC-CMs, though can lead to an enrichment in ventricular myocytes. It also validates this procedure for storing hiPSC-CMs, thereby allowing the same batch of hiPSC-CMs to be used for multiple applications and evaluations.

cell biology↗