Biology subjects

Remme, C. A.

Publications and source records attributed to Remme, C. A..

3 recordsLinked to original sources

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↗