Biology subjects

Bronk, P.

Publications and source records attributed to Bronk, P..

4 recordsLinked to original sources

bioRxiv2025

Non-canonical Sodium Channel Isoforms Underlie Chamber Specific Cardiac Excitability

Voltage-gated sodium (NaV) channels drive cardiac excitability. While NaV1.5 is the primary cardiac isoform, the composition and functional contributions of non-NaV1.5 isoforms in the heart remain unclear. Here, we developed a chemical-genetic mouse model (NaV1.5-GX) in which NaV1.5 can be selectively and reversibly inhibited by acyl- and aryl-sulfonamide compounds (GX drugs). NaV1.5-GX mice exhibited normal cardiac function at baseline, but acute GX drug administration caused profound conduction defects and arrhythmias. Whole-heart optical mapping revealed dose-dependent chamber-specific sensitivity to NaV1.5 inhibition, with the right ventricle (RV) being the most sensitive, followed by the left ventricle (LV), left atrium (LA), and right atrium (RA). Patch-clamp recordings of isolated cardiomyocytes with application of NaV isoform-selective inhibitors showed that NaV1.5 contributed 93% of sodium current in the LV, 81% in the RV and 78% in the LA. Non-NaV1.5 isoforms were differentially enriched across chambers: NaV1.8 in the LV, NaV1.1/1.3 in the RV, and NaV1.2/1.6/1.7 in the atria. These results reveal a surprising chamber-specific isoform landscape of cardiac sodium currents which may underlie the right ventricular predominant phenotype of Brugada syndrome and highlight non-NaV1.5 isoforms as potential mediators of chamber-specific cardiac pathologies and as pharmacological targets.

physiology↗

bioRxiv2024

Loss of developmentally derived Irf8+ macrophages promotes hyperinnervation and arrhythmia in the adult zebrafish heart

Recent developments in cardiac macrophage biology have broadened our understanding of the critical functions of macrophages in the heart. As a result, there is further interest in understanding the independent contributions of distinct subsets of macrophage to cardiac development and function. Here, we demonstrate that genetic loss of interferon regulatory factor 8 (Irf8)-positive embryonic-derived macrophages significantly disrupts cardiac conduction, chamber function, and innervation in adult zebrafish. At 4 months post-fertilization (mpf), homozygous irf8st96/st96 mutants have significantly shortened atrial action potential duration and significant differential expression of genes involved in cardiac contraction. Functional in vivo assessments via electro- and echocardiograms at 12 mpf reveal that irf8 mutants are arrhythmogenic and exhibit diastolic dysfunction and ventricular stiffening. To identify the molecular drivers of the functional disturbances in irf8 null zebrafish, we perform single cell RNA sequencing and immunohistochemistry, which reveal increased leukocyte infiltration, epicardial activation, mesenchymal gene expression, and fibrosis. Irf8 null hearts are also hyperinnervated and have aberrant axonal patterning, a phenotype not previously assessed in the context of cardiac macrophage loss. Gene ontology analysis supports a novel role for activated epicardial-derived cells (EPDCs) in promoting neurogenesis and neuronal remodeling in vivo. Together, these data uncover significant cardiac abnormalities following embryonic macrophage loss and expand our knowledge of critical macrophage functions in heart physiology and governing homeostatic heart health.

systems biology↗

bioRxiv2021

Myofibroblast Senescence Promotes Arrhythmogenic Remodeling in the Aged Infarcted Rabbit Heart

Progressive tissue remodeling after myocardial infarction (MI) promotes cardiac arrhythmias. This process is well studied in young animals, but little is known about pro-arrhythmic changes in aged animals. Senescent cells accumulate with age and accelerate age-associated diseases. Senescent cells interfere with cardiac function and outcome post-MI with age, but studies have not been performed in large animals, and the mechanisms are unknown. Here, we investigated the role of senescence in regulating inflammation, fibrosis, and arrhythmogenesis in young and aged infarcted rabbits. Aged rabbits exhibited increased peri-procedural mortality and arrhythmogenic electrophysiological remodeling at the infarct border zone (IBZ) compared to young rabbits. Studies of the aged infarct zone revealed persistent myofibroblast senescence and increased inflammatory signaling over a twelve-week timecourse. Senescent IBZ myofibroblasts in aged rabbits appear to be coupled to myocytes, and our computational modeling showed that senescent myofibroblast- cardiomyocyte coupling prolongs action potential duration (APD) and facilitates conduction block permissive of arrhythmias. Aged infarcted human ventricles show levels of senescence consistent with aged rabbits, and senescent myofibroblasts also couple to IBZ myocytes. Our findings suggest that senolytic drugs may mitigate arrhythmias post-MI.

cell biology↗

bioRxiv2017

Regulation of Eag by calcium/calmodulin controls presynaptic excitability in Drosophila

Drosophila ether-a-go-go (eag) is the founding member of a large family of voltage-gated K+ channels, the KCNH family, which includes Kv10, 11 and 12, (Ganetzky et al. 1999). Concurrent binding of calcium/calmodulin (Ca2+/CaM) to N-and C-terminal sites inhibits mammalian EAG1 channels at sub-micromolar Ca2+ concentrations (Schonherr et al. 2000), likely by causing pore constriction (Whicher and MacKinnon 2016). Although the Drosophila EAG channel was believed to be Ca2+-insensitive (Schonherr et al. 2000), both the N-and C-terminal sites are conserved. Here we show that Drosophila EAG is inhibited by high Ca2+ concentrations that are only present at plasma membrane Ca2+ channel microdomains. To test the role of this regulation in vivo, we engineered mutations that block CaM-binding to the major C-terminal site of the endogenous eag locus, disrupting Ca2+-dependent inhibition. eag CaMBD mutants have reduced evoked release from larval motor neuron presynaptic terminals and show decreased Ca2+ influx in stimulated adult projection neuron presynaptic terminals, consistent with an increase in K+ conductance. These results are predicted by a conductance-based multi-compartment model of the presynaptic terminal in which some fraction of EAG is localized to the Ca2+ channel microdomains that control neurotransmitter release. The reduction of release in the larval neuromuscular junction drives a compensatory increase in motor neuron somatic excitability. This misregulation of synaptic and somatic excitability has consequences for systems-level processes and leads to defects in associative memory formation in adults.\n\nNew and NoteworthyRegulation of excitability is critical to tuning the nervous system for complex behaviors. We demonstrate here that the EAG family of voltage-gated K+ channels exhibit conserved gating by Ca2+/CaM. Disruption of this inhibition in Drosophila results in decreased evoked neurotransmitter release due to truncated Ca2+ influx in presynaptic terminals. In adults, disrupted Ca2+ dynamics cripples memory formation. These data demonstrate that the biophysical details of channels have important implications for cell function and behavior.

neuroscience↗