Biology subjects

Juhaszova, M.

Publications and source records attributed to Juhaszova, M..

5 recordsLinked to original sources

bioRxiv2024

Structure-Function Relationship of the Ryanodine Receptor Cluster Network in Sinoatrial Node Cells

The rate of spontaneous action potentials (APs) generated by sinoatrial node cells (SANC) is regulated by local Ca2+ release (LCR) from the sarcoplasmic reticulum via Ca2+ release channels (ryanodine receptors, RyRs). LCR events propagate and self-organize within the network of RyR clusters (Ca release units, CRUs) via Ca-induced-Ca-release (CICR) that depends on CRU sizes and locations: while larger CRUs generate stronger release signals, the networks topology governs signal diffusion and propagation. This study used super-resolution structured illumination microscopy to image the 3D network of CRUs in rabbit SANC. The peripheral CRUs formed a spatial mesh, reflecting the cell surface geometry. Two distinct subpopulations of CRUs were identified within each cell, with size distributions conforming to a two component Gamma mixture model. Furthermore, neighboring CRUs exhibited repulsive behavior. Functional properties of the CRU network were further examined in a novel numerical SANC model developed using our experimental data. Model simulations revealed that heterogeneities in both CRU sizes and locations facilitate CICR and increase AP firing rate in a cooperative manner. However, these heterogeneities reduce the effect of {beta}-adrenergic stimulation in terms of its relative change in AP firing rate. The presence of heterogeneities in both sizes and locations allows SANC to reach higher absolute AP firing rates during {beta}-adrenergic stimulation. Thus, the CICR facilitation by heterogeneities in CRU sizes and locations regulates and optimizes cardiac pacemaker cell operation under various physiological conditions. Dysfunction of this optimization could be a key factor in heart rate reserve decline in aging and disease.

biophysics↗

bioRxiv2022

A Remarkable Adaptive Paradigm Of Heart Performance And Protection Emerges In Response To The Constitutive Challenge Of Marked Cardiac-Specific Overexpression Of Adenylyl Cyclase Type 8

Adult mice with cardiac-specific overexpression of adenylyl cyclase (AC) type VIII (TGAC8) adapt to an incessantly increased cAMP-induced cardiac workload ([~]30% increases in heart rate, ejection fraction and cardiac output) for up to a year without signs of heart failure or excessive mortality. Here we show that despite markedly increased cardiac work, classical cardiac hypertrophy markers were absent in TGAC8, total left ventricular (LV) mass was not increased: a reduced LV cavity volume in TGAC8 was encased by thicker LV walls harboring an increased number of small cardiac myocytes and a network of small interstitial non-cardiac myocytes, manifesting increased proliferation markers and compared to WT. Protein synthesis, proteosome activity, autophagy, and Nrf-2, Hsp90, ACC2 protein levels were increased in TGAC8, but LV ATP and phosphocreatine levels in vivo did not differ by genotype. 2,323 transcripts and 2,184 proteins identified in unbiased omics analyses, spanning a wide array of biological processes and molecular functions in numerous cellular compartments differed in TGAC8 vs WT; and over 250 canonical signaling pathways characteristic of adaptive survival circuitry of cancers, including PI3K and growth factor signaling, cytokine and T cell receptor signaling, immune responses, ROS scavenging, proliferation, protection from apoptosis, and nutrient sensing, were activated in TGAC8; and compared to WT there was a shift from fatty acid oxidation to increased aerobic glycolysis in the context of increased utilization of the pentose phosphate shunt and nucleotide synthesis. Thus, the adaptive paradigm, that becomes activated in the LV of TGAC8 in response to severe chronic, intense AC/PKA/Ca2+ signaling embodies many hallmarks of cancer.

physiology↗

bioRxiv2022

The Heart's Pacemaker Mimics Brain Cytoarchitecture and Function: Autonomic innervation, a peripheral glial cell web, and a novel S100B expressing interstitial cell type impart structural and functional complexity to the sinoatrial node

ObjectivesThis study sought to describe the 3D cytoarchitecture of sinoatrial node tissue, including autonomic innervation, peripheral glial cells, and pacemaker cells. BackgroundThe sinoatrial node of the heart produces rhythmic action potentials (AP), generated via calcium signaling within and among pacemaker cells. Our previous work has described the SAN as composed of an HCN4-expressing pacemaker cell meshwork, which merges with a network of CX43+/F-actin+ cells. It is also known that sympathetic and parasympathetic innervation from epicardial ganglia create an autonomic plexus in the sinoatrial node, which modulates heart rate and rhythm. However, the anatomical details of the interaction of this plexus with the pacemaker cell meshwork have yet to be described. Methods3D confocal laser-scanning microscopy of triple immunolabeled SAN whole mount preparations with combinations of antibodies for HCN4, S100B, GFAP, ChAT or VAChT, and TH, and transmission electron microscopy (TEM). ResultsThe SAN exhibited heterogeneous autonomic innervation, which was accompanied by a web of peripheral glial cells (PGCs). Further, we identified a novel S100B+/GFAP- interstitial cell population, with unique morphology and distinct distribution pattern, creating complex interactions with other cell types in the node. TEM images showed a similar population of cells, here identified as telocytes, which appeared to secrete vesicles towards pacemaker cells. Application of S100B protein to SAN preparations induced distinct changes in rhythmogenic calcium signaling. ConclusionsThe autonomic plexus and its associated peripheral glial cell web, a novel network of S100B expressing interstitial cells resembling telocytes, and a meshwork of HCN4+ cells interact to impart structural complexity to the sinoatrial node. Summary Table [Table 1][Table 1]

physiology↗

bioRxiv2020

Synchronized cardiac impulses emerge from multi-scale, heterogeneous local calcium signals within and among cells of heart pacemaker tissue

ABSTRACTBackground The current paradigm of Sinoatrial Node (SAN) impulse generation: (i) is that full-scale action potentials (APs) of a common frequency are initiated at one site and are conducted within the SAN along smooth isochrones; and (ii) does not feature fine details of Ca2+ signalling present in isolated SAN cells, in which small subcellular, subthreshold local Ca2+ releases (LCRs) self-organize to generate cell-wide APs.Objectives To study subcellular Ca2+ signals within and among cells comprising the SAN tissue.Methods We combined immunolabeling with a novel technique to detect the occurrence of LCRs and AP-induced Ca2+ transients (APCTs) in individual pixels (chonopix) across the entire mouse SAN images.Results At high magnification, Ca2+ signals appeared markedly heterogeneous in space, amplitude, frequency, and phase among cells comprising an HCN4+/CX43- cell meshwork. The signalling exhibited several distinguishable patterns of LCR/APCT interactions within and among cells. Apparently conducting rhythmic APCTs of the meshwork were transferred to a truly conducting HCN4-/CX43+ network of straited cells via narrow functional interfaces where different cell types intertwine, i.e. the SAN anatomical/functional unit. At low magnification, the earliest APCT of each cycle occurred within a small area of the HCN4 meshwork and subsequent APCT appearance throughout SAN pixels was discontinuous.Conclusions We have discovered a novel, microscopic Ca2+ signalling paradigm of SAN operation that has escaped detection using low-resolution, macroscopic tissue isochrones employed in prior studies: APs emerge from heterogeneous subcellular subthreshold Ca2+ signals, resembling multiscale complex processes of impulse generation within clusters of neurons in neuronal networks.Condensed abstract By combining immunolabeling with a novel optical technique we detected markedly heterogenous Ca2+signals within and among cell clusters of an HCN4+/CX43- meshwork in mouse sinoatrial node. These Ca2+ signals self-organized and transferred, throughout the node, to projections from an HCN4-/CX43+ network connected to a highly organized, rapidly conducting part of the CX43+ network. Thus, APs emerge from heterogeneous, subthreshold Ca2+ signaling not detected in low-resolution macroscopic isochrones. Our discovery requires a fundamental paradigm shift from concentric impulse propagation initiated within a leading site, to a multiscale/complex process, resembling the emergence of organized signals from heterogeneous local signals within neuronal networks.Competing Interest StatementThe authors have declared no competing interest.Abbreviations listAPaction potentialAPCTAP-induced Ca2+ transientChronopixchrono-pixelCX43Connexin 43 (Gap junction alpha-1 protein)FFTFast Fourier TransformHCN4Hyperpolarization-Activated Cyclic Nucleotide-Gated Channel 4ICaLL-type Ca2+ currentICaTT-type Ca2+ currentIVCInferior Vena CavaLCRLocal Ca2+ ReleaseNCXNa+/Ca2+ exchangerPBSPhosphate-Buffered SalinepreBötCpreBötzinger ComplexROIRegion of InterestSANSinoatrial NodeSVCSuperior Vena CavaView Full Text

physiology↗

bioRxiv2018

ATP synthase K+- and H+-flux drive ATP synthesis and enable mitochondrial K+-uniporter function

ATP synthase (F1Fo) synthesizes daily our bodys weight in ATP, whose production-rate can be transiently increased several-fold. Using purified mammalian F1Fo-reconstituted proteoliposomes and isolated mitochondria, we show that F1Fo utilizes both H+- and K+-transport (because of >106-fold K+ excess vs H+) to drive ATP synthesis with the H+:K+ permeability of ~106:1. F1Fo can be upregulated by endogenous survival-related proteins (Bcl-xL, Mcl-1) and synthetic molecules (diazoxide, pinacidil) to increase its chemo-mechanical efficiency via IF1. Increasing K+- and H+-driven ATP synthesis enables F1Fo to operate as a primary mitochondrial K+-uniporter regulating energy supply-demand matching, and as the recruitable mitochondrial KATP-channel that can limit ischemia-reperfusion injury. Isolated mitochondria in the presence of K+ can sustain ~3.5-fold higher ATP-synthesis-flux (vs K+ absence) driven by a 2.7:1 K+:H+ stoichiometry with unaltered OxPhos coupling. Excellent agreement between F1Fo single-molecule and intact-mitochondria experiments is consistent with K+-transport through ATP synthase driving a major fraction of ATP synthesis.

biophysics↗