Biology subjects

Verheule, S.

Publications and source records attributed to Verheule, S..

3 recordsLinked to original sources

bioRxiv2024

Atrial Granules in Atrial Cardiomyocytes as Acidic Calcium Stores

Acidic calcium stores significantly influence basal calcium transient amplitude and {beta}-adrenergic responses in cardiomyocytes. Atrial myocytes express a small acidic organelle called atrial granules (AG), which store and excrete atrial natriuretic peptide and are not expressed by healthy ventricular myocytes. AG are known to be acidic with a high calcium content. The number and position of these calcium-rich organelles relative to other signaling sites has not been investigated. Staining of acidic organelles in adult guinea pig cardiomyocytes showed the presence of fluorescent acidic puncta throughout the cytosol. Atrial myocytes exhibited an increased concentration of acidic organelles at the nuclear poles. Live cell fluorescent studies using PBA to inhibit peptidylglycine -amidating monooxygenase, a crucial component of AG membranes, effectively eliminated staining at the nuclear poles and most acidic puncta in atrial cells. The application of PBA to ventricular myocytes did not affect LysoTracker staining. Electron microscopy studies on goat atrial fibrillation (AF) and sham control tissue, allowed visualization of AGs. Quantitative analysis revealed AGs to be in close apposition to the sarcoplasmic reticulum and mitochondria. AGs were significantly increased in AF goat samples when compared to sinus rhythm from 3D electron tomography images. Our imaging studies suggest that AGs make up a large percentage of atrial acidic stores, with AG associated with the sarcoplasmic reticulum and their number increasing during AF. We raise the question whether the positioning of AGs are strategic to communicate with other calcium organelles. Further studies to investigate whether AGs contribute to physiological calcium signalling are required.

physiology↗

bioRxiv2024

Lysosomal signalling pathways influence heart rhythm, and regulate atrial function

In the heart, endogenous nicotinic acid adenine dinucleotide phosphate (NAADP) triggers lysosomal calcium (Ca2+) release to augment sarcoplasmic reticulum (SR) Ca2+ sequestration, producing larger Ca2+ transients. However, the role of lysosomal Ca2+ signals in pacemaker activity, a distinct Ca2+-operated function of the sinoatrial node (SAN), or in the atrial myocardium has not been investigated. Pharmacological or genetic ablation of the NAADP pathway inhibits the spontaneous beating rate response to beta-adrenergic stimulation in intact SAN. We found intracellular signaling microdomains between lysosomes and neighboring SR or mitochondria in mouse, and goat tissue. The spatial relationship between lysosomes and other Ca2+-handling organelles are altered in goat atrial fibrillation. Furthermore, we demonstrate atrial myocytes produce cAMP in response to lysosomal signaling, adding a novel trigger for cyclic nucleotide signaling. Our findings support the hypothesis that lysosomal Ca2+ signaling contributes to regulation of cardiomyocyte cAMP levels and pacemaker activity.

physiology↗

bioRxiv2023

Compartmentalisation proteomics revealed endolysosomal protein network changes in a goat model of atrial fibrillation

Endolysosomes (EL) are known for their role in regulating both intracellular trafficking and proteostasis. EL help facilitate elimination of damaged membrane and cytosolic proteins, protein aggregates, membranous organelles and also play an important role in calcium signalling. Despite the importance of EL, their specific role in cardiovascular disease is not well understood. In particular, its unclear how EL contribute to atrial pathology over longer time frames. To shed light on this question, we conducted a comprehensive analysis that involved proteomics, transcriptomics, integrated analysis, electron tomography, western blotting, and enzyme assays. To identify the role of EL in atrial fibrillation (AF), we applied a recently published organelle protein isolation method. We used this method to study biopsies from AF goat model and analyse the EL-specific proteins and pathways involved in this condition. Our results revealed the upregulation of the AMPK pathway and the expression of EL-specific proteins that were not found in whole tissue lysates (TL), including GAA, DYNLRB1, CLTB, SIRT3, CCT2, and muscle-specific HSPB2. We also observed structural anomalies, such as autophago-vacuole formation, irregularly shaped mitochondria, and glycogen deposition, which provide insights into the ELs contribution to AF and related pathways and molecular mechanisms. Overall, our findings suggest that EL play an important role in the development of AF over longer time frames, and provide a more detailed understanding of the underlying molecular processes involved.

molecular biology↗