Biology subjects

Akerman, E.

Publications and source records attributed to Akerman, E..

6 recordsLinked to original sources

bioRxiv2026

Molecular and Structural Basis of Cardiac Remodelling in Niemann-Pick Type C

Key Point SummaryNiemann-Pick disease type C (NPC) patients showed a high prevalence of ECG abnormalities, with additional echocardiographic evidence of altered left-ventricular structure and function. Npc1-/- mouse hearts exhibited age-associated glycosphingolipid accumulation accompanied by marked myocardial fibrosis and increased collagen deposition. Ex vivo electrophysiology revealed QT prolongation and atrioventricular conduction defects in Npc1-/- hearts, particularly under {beta}-adrenergic stress. Transcriptomic profiling identified inflammatory and fibrotic pathway activation consistent with the structural and electrophysiological abnormalities observed. Together, these findings demonstrate previously unrecognised cardiac involvement in NPC and support routine cardiac screening to improve clinical management. Niemann-Pick disease type C (NPC) is a rare autosomal recessive neurodegenerative lysosomal storage disease caused by pathogenic variants in NPC1 or NPC2. Sudden death can occur due to seizures, but cardiac involvement has not been well defined. We performed 12-lead electrocardiograms (ECG) in 14 adult NPC patients (8 male, 6 female). Cardiac structure and function were examined in Npc1-/- adult mouse hearts, alongside wild-type controls. Glycosphingolipid accumulation was quantified by high-performance liquid chromatography, fibrosis and collagen deposition were quantified using Massons Trichrome (M&T) and Picrosirius Red (PR) staining. Whole-heart morphology, including chamber size and wall thickness, was assessed. Ex vivo ECG recordings assessed conduction abnormalities and arrhythmias. RNA-seq transcriptomics characterised molecular pathways altered in Npc1-/- hearts. 8/14 patients showed ECG abnormalities including abnormal QRS transitions (N=8), increased QRS amplitude (N=4), fascicular block (N=2), and abnormal T wave inversion (N=1). 13 patients also had transthoracic echocardiograms identifying mildly impaired LV systolic function (N=2) and increased wall thickness/LV mass (N=4). In Npc1-/- mice, age-related glycosphingolipid accumulation was associated with pronounced ventricular fibrotic remodelling. There was a significant increase in stained connective tissue area and connective tissue to cardiac tissue ratio in both M&T and PR staining. ECG from Langendorff-perfused Npc1-/- hearts showed QT prolongation and atrioventricular conduction abnormalities under isoprenaline stress. Transcriptomics revealed major changes in Npc1-/- hearts, consistent with histological fibrosis and linking NPC to inflammation-driven remodelling and arrhythmogenesis. These findings support routine cardiac screening in NPC patients and highlight the need for further studies to improve management and treatment.

physiology↗

bioRxiv2026

Lysosomal abundance in young and aged mouse hearts assessed by In Vivo Imaging Systems (IVIS) Lysotracker imaging and autophagy-related gene expression

Lysosomal function is essential for cardiac proteostasis and cellular health, yet its regulation during ageing remains poorly defined. We hypothesised that ageing alters both the abundance of acidic organelles and the machinery supporting their acidification. Using fluorescence-based In Vivo Imaging Systems (IVIS) with Lysotracker Red in young (2-4 months) and aged (18 months) mouse hearts, we quantified whole-heart acidic-vesicle signals and assessed expression of lysosomal and autophagy-related genes (Lamp2, Atp6v1a, Sqstm1, Cd63, Atg12, Nfe2l2, M6pr) by RT-qPCR. Whole-heart labelled Lysotracker fluorescence did not differ significantly between age groups, indicating preservation of the total acidic-vesicle pool. No changes in Atp6v1a and Lamp2 expression suggest acidification capacity and structural stability are maintained, whereas the minor, upregulation of Sqstm1 might indicate increased autophagic demand and altered vesicle trafficking, which warrants further investigation. No statistical significant changes in M6pr, Atg12, or Nfe2l2 were detected, suggesting transcriptional stability in enzyme trafficking, core autophagy, and oxidative stress pathways. Regionally, atria showed higher Lysotracker signal than ventricles, consistent with known enrichment of acidic vesicular stores in atrial physiology. These findings highlight the utility of IVIS imaging of Lysotracker-labelled hearts, providing rapid whole-organ assessment of acidic vesicle distribution, albeit with limited depth resolution. Complementary techniques such as RT-qPCR analysis is essential to interpret IVIS findings, enabling insight into underlying molecular changes in lysosomal and autophagy pathways during cardiac ageing.

physiology↗

bioRxiv2024

Lysosomal calcium signalling contributes to the acute α-adrenergic response via calcium-stimulated adenylyl cyclase 1 and 8

Inositol trisphosphate (IP3), a calcium (Ca2+)-mobilizing second messenger, releases Ca2+ from the sarcoplasmic reticulum (SR) via IP3 receptors and modulates adenylyl cyclase (AC) activity in atrial myocytes. Lysosomes participate in Ca2+ homeostasis by mobilising Ca2+ in response to Nicotinic Acid Adenine Dinucleotide Phosphate (NAADP). We postulate that both downstream activation of Ca2+ sensitive AC (AC1 and AC8) and lysosomal Ca2+ signalling in response to IP3R activation contribute to atrial myocyte function and pacemaking. Ectopic application of phenylephrine (PE) increased chronotropy and inotropy and this response was reduced in the presence of NAADP pathway inhibitors (BZ-194 and SAN4825) and Bafilomycin A1. PE increased cyclic adenosine 3-5 monophosphate (cAMP) activity in neonatal rat atrial myocytes (NRAMs) and this was inhibited by NAADP pathway inhibitors. This inhibition was not observed in neonatal rat ventricular myocytes (NRVMs), revealing specificity of this response to NRAMs. We investigated expression of AC1 and AC8 as a possible explanation to these observations. Genetic perturbation of AC1 and AC8 by double-knockout of Adcy1 and Adcy8 in a mouse model showed a decrease in positive chronotropic and inotropic response upon cumulative dose of PE in atrial tissue, reduced PE stimulated amplitude of Ca2+ transient in isolated atrial myocytes and presented decreased cytosolic cAMP levels in response to PE in neonatal atrial myocytes that was not inhibited by NAADP pathway inhibitors. Our data identifies a link between NAADP and -adrenergic signalling pathways in atrial myocytes, highlighting that lysosomal Ca2+ is an important component of -adrenergic stimulation in the cardiac atria and warrants further investigation.

physiology↗

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↗

bioRxiv2022

Cross-talk between cAMP and Ca2+ signalling in cardiac pacemaker cells involves IP3-evoked Ca2+ release and stimulation of adenylyl cyclase 1

Atrial arrhythmias, such as atrial fibrillation (AF), are a major mortality risk and a leading cause of stroke. The IP3 signalling pathway has been proposed as an atrial specific target for AF therapy, and atrial IP3 signalling has been linked to the activation of calcium sensitive adenylyl cyclases AC1 and AC8. Here we investigated the involvement of AC1 in the response of intact mouse atrial tissue and isolated guinea pig atrial and sinoatrial node (SAN) cells to the -adrenoceptor agonist phenylephrine (PE) using the selective AC1 inhibitor ST034307. The maximum rate change of spontaneously beating mouse right atrial tissue exposed to PE was reduced from 14.46 % to 8.17% (P = 0.005) in the presence of 1 M ST034307, whereas the increase in tension generated in paced left atrial tissue in the presence of PE was not inhibited by ST034307 (Control = 14.20 %, ST034307 = 16.32 %; P > 0.05). Experiments were performed using isolated guinea pig atrial and SAN cells loaded with Fluo-5F-AM to record changes in calcium transient amplitude (CaT) generated by 10M PE in the presence and absence of 1M ST034307. ST034307 significantly reduced the beating rate of SAN cells (0.34-fold decrease; P = 0.004), but did not result in an inhibition of CaT amplitude increase in response to PE in atrial cells. The results presented here demonstrate the involvement of AC1 in the downstream response of atrial pacemaker activity to -adrenoreceptor stimulation and IP3R calcium release.

pharmacology and toxicology↗