Biology subjects

Dobrev, D.

Publications and source records attributed to Dobrev, D..

8 recordsLinked to original sources

bioRxiv2026

Predicting Sex-Specific Antiarrhythmic Strategies for Atrial Fibrillation through a Regression-Guided Computational Modeling Pipeline

Atrial fibrillation (AF), the most common sustained cardiac arrhythmia, is a major contributor to stroke, heart failure, and mortality worldwide. Although AF affects both men and women at a similar rate, accumulating experimental and clinical evidence indicates that its underlying mechanisms, disease progression, and treatment responses differ by sex. However, current antiarrhythmic drug development and clinical management of AF remains largely sex neutral, likely contributing to limited efficacy and increased adverse effects. To address this gap, we developed a computational drug-screening pipeline based on experimentally constrained, sex-specific human atrial cardiomyocyte models to predict and evaluate sex-specific pharmacological strategies for AF. The pipeline integrates multivariable regression with mechanistic modeling to systematically test multi-target combinations of ion channel inhibitors and Ca2+ handling modulators and identify interventions that reduce arrhythmia vulnerability by restoring sex-specific electrophysiological and Ca2+ handling properties toward normal sinus rhythm (nSR). Application of this approach revealed a greater number of successful inhibitory drug combinations in males than in females. In males, optimal recovery to nSR primarily required inhibition of Na+ and K+ channels to prolong repolarization and refractoriness, increase Ca2+ transient amplitude (CaTAmp), and reduce susceptibility to action potential duration (APD) alternans. In females, modulation of Ca2+-related pathways was additionally required to suppress delayed afterdepolarizations (DADs). Forward single-cell simulations confirmed the predictions of the drug-analysis pipeline, demonstrating recovery of APD, CaTAmp, and arrhythmia vulnerability indices without introducing instabilities. Importantly, extension of these interventions to two-dimensional atrial tissue simulations demonstrated that sex-specific drug strategies reduce vulnerability to triggered activity, while suppression of reentry was most effective when combined with partial recovery of cell-cell coupling. Our results establish a multiscale computational pipeline for identifying sex-informed, multi-target antiarrhythmic therapies, amenable to experimental validation and translation to the clinic. Clinical PerspectiveO_ST_ABSWhat is KnownC_ST_ABSO_LIAtrial fibrillation arises from multiple interacting multiscale mechanisms, which limit the effectiveness of single-target therapies. C_LIO_LICurrent single-target antiarrhythmic drugs for atrial fibrillation show more limited efficacy and higher adverse event rates in women than in men C_LI What the Study AddsO_LIThis study demonstrates that effective pharmacologic strategies require different combinations of ion channel and calcium handling modulation in males versus females with persistent (chronic) atrial fibrillation. C_LIO_LIIn males, coordinated Na+ and K+ channel inhibition most effectively improves electrical stability, whereas in females additional targeting of Ca2+ handling is required to suppress triggered activity. C_LIO_LISex-specific multi-target drug strategies including partial recovery of intercellular coupling suppress triggered activity and reentry in atrial tissue while preserving conduction. C_LI

pharmacology and toxicology↗

bioRxiv2025

Mechanistic Insights into Sex Differences in Atrial Electrophysiology and Arrhythmia Vulnerability through Sex-specific Computational Models.

Atrial fibrillation (AF), the most common cardiac arrhythmia, is characterized by notable sex differences in clinical presentation, treatment response, and outcomes. Although prevalence is similar between sexes, women often experience more severe symptoms, higher rates of adverse drug effects, and reduced treatment efficacy. To investigate the underlying sex-specific AF mechanisms, we developed and validated male and female human atrial cardiomyocyte models that integrate known sex-based differences in electrophysiology and calcium (Ca2+) handling under normal sinus rhythm (nSR) and chronic AF (cAF) conditions. While the model parameterizations were based on limited human data, and the assumptions may not capture the full spectrum of clinical variability, the models reproduced key reported sex-dependent differences in human atrial cardiomyocyte action potential (AP) and Ca2+ transient (CaT) dynamics. Simulations revealed that both sexes exhibited shortened effective refractory periods and wavelengths in cAF vs. nSR. However, females were more prone to delayed afterdepolarizations (DADs), while males were more susceptible to AP duration (APD) and CaT amplitude (CaTAmp) alternans. Population-based modeling identified distinct parameter associations with arrhythmia mechanisms, whereby DAD vulnerability was associated with enhanced ryanodine receptor sensitivity to Ca2+ (in females), and alternans in males correlated with reduced L-type Ca2+ current maximal conductance. Pharmacological simulations revealed sex-specific responses to antiarrhythmic therapies. In males, multiple drug combinations proved effective in restoring APD at 90% repolarization (APD90), CaTAmp, and reducing alternans susceptibility, whereas females responded to only one combination improving APD90 and CaTAmp but with minimal impact on DAD risk. These findings underscore the need for sex-specific therapeutic strategies and support the use of computational modeling in guiding precision medicine approaches against AF. Key pointsO_LIAtrial fibrillation (AF) is a common heart rhythm disorder that presents differently in males and females, but how the underlying mechanisms differ in males and females is not fully understood. C_LIO_LIWe developed and validated computer models of male and female human atrial cardiomyocytes that incorporate known sex differences in ion channels and calcium handling under normal sinus rhythm and AF conditions. C_LIO_LIUnder normal rhythm, males and females showed distinct electrical activity, which became less pronounced in AF. In AF, both sexes showed reduced effective refractory period and wavelength and depressed calcium transients. Males were more susceptible to electrical alternans, while females showed a greater tendency for calcium-driven delayed afterdepolarizations. C_LIO_LISimulated drug treatments showed greater benefit in male models, particularly with combinations targeting multiple potassium channels, while female models showed limited response. These results highlight the need for sex-specific approaches to treating AF and may help guide future drug development. C_LI

physiology↗

bioRxiv2025

Time-dependent Mitochondrial Remodeling in Experimental Atrial Fibrillation and Potential Therapeutic Relevance

BACKGROUNDChanges in mitochondria have been implicated in atrial fibrillation (AF), but their manifestations and significance are poorly understood. Here, we studied changes in mitochondrial morphology and function during AF and assessed the effect of a mitochondrial-targeted intervention in a large animal model. METHODS AND RESULTSAtrial cardiomyocytes (ACMs) were isolated from dogs in electrically-driven AF for periods of 24 hours to 3 weeks and from humans with/without longstanding persistent AF. Mitochondrial Ca2+-concentration ([Ca2+]Mito), reactive oxygen species (mtROS) production, membrane potential ({Delta}{Psi}m), permeability transition-pore (mPTP) opening and flavin adenine dinucleotide (FAD) were measured via confocal microscopy; nicotine adenine dinucleotide (NADH) under ultraviolet light. mtROS-production increased within 24 hours and superoxide-dismutase type-2 was significantly reduced from 3-day AF. [Ca2+]Mito and mPTP-opening frequency/duration increased progressively during AF. Mitochondrial depolarization was detectable 24 hours after AF-onset. NADH increased by 15% at 24-hour AF, concomitant with increased pyruvate-dehydrogenase expression, then gradually decreased. Mitochondria enlarged and elongated at 24-hour and 3-day AF, followed by progressive fragmentation, rupture and shrinkage. Mitochondrial fusion protein-1 (MFN1) was reduced from 3-day to 3-week AF and phosphorylated dynamin-related protein-1 (p-DRP1ser-616) increased after 1 week of canine AF and in human AF. Addition of the mitochondrial antioxidant MitoTempo attenuated action-potential shortening and L-type Ca2+-current (ICaL)-downregulation in canine and human AF ACMs in vitro. Administration of the orally-active mitochondrial-targeted ubiquinone mitoquinone to dogs during 3-week AF prevented mitochondrial Ca2+-overload, mtROS-overproduction, structural damage and abnormalities in {Delta}{Psi}m and respiration. Functionally, mitoquinone reduced AF-induced Ca2+-current downregulation, action-potential abbreviation, contractile dysfunction and fibrosis, preventing AF-substrate development and AF-sustainability. CONCLUSIONSMitochondria show a series of changes during AF, with early hyperfunction and enhanced ROS-generation, followed by progressive damage and dysfunction. Mitochondrial-targeted therapy prevents mitochondrial dysfunction and attenuates adverse AF-related remodeling, positioning mitochondrial protection as a potential novel therapeutic target in AF.

pathology↗

bioRxiv2024

Enhanced Ca2+-Driven Arrhythmias in Female Patients with Atrial Fibrillation: Insights from Computational Modeling

Background and AimsSubstantial sex-based differences have been reported in atrial fibrillation (AF), with female patients experiencing worse symptoms, increased complications from drug side effects or ablation, and elevated risk of AF-related stroke and mortality. Recent studies revealed sex-specific alterations in AF-associated Ca2+ dysregulation, whereby female cardiomyocytes more frequently exhibit potentially proarrhythmic Ca2+-driven instabilities compared to male cardiomyocytes. In this study, we aim to gain a mechanistic understanding of the Ca2+-handling disturbances and Ca2+-driven arrhythmogenic events in males vs females and establish their responses to Ca2+-targeted interventions. Methods and ResultsWe incorporated known sex differences and AF-associated changes in the expression and phosphorylation of key Ca2+-handling proteins and in ultrastructural properties and dimensions of atrial cardiomyocytes into our recently developed 3D atrial cardiomyocyte model that couples electrophysiology with spatially detailed Ca2+-handling processes. Our simulations of quiescent cardiomyocytes show increased incidence of Ca2+ sparks in female vs male myocytes in AF, in agreement with previous experimental reports. Additionally, our female model exhibited elevated propensity to develop pacing-induced spontaneous Ca2+ releases (SCRs) and augmented beat-to-beat variability in action potential (AP)-elicited Ca2+ transients compared with the male model. Parameter sensitivity analysis uncovered precise arrhythmogenic contributions of each component that was implicated in sex and/or AF alterations. Specifically, increased ryanodine receptor phosphorylation in female AF cardiomyocytes emerged as the major SCR contributor, while reduced L-type Ca2+ current was protective against SCRs for male AF cardiomyocytes. Furthermore, simulations of tentative Ca2+-targeted interventions identified potential strategies to attenuate Ca2+-driven arrhythmogenic events in female atria (e.g., t-tubule restoration, and inhibition of ryanodine receptor and sarcoplasmic/endoplasmic reticulum Ca{superscript 2}-ATPase), and revealed enhanced efficacy when applied in combination. ConclusionsOur sex-specific computational models of human atrial cardiomyocytes uncover increased propensity to Ca2+-driven arrhythmogenic events in female compared to male atrial cardiomyocytes in AF, and point to combined Ca2+-targeted interventions as promising approaches to treat AF in female patients. Our study establishes that AF treatment may benefit from sex-dependent strategies informed by sex-specific mechanisms. Translational perspectiveAccumulating evidence demonstrates substantial sex-related differences in atrial fibrillation (AF), which is the most common arrhythmia, with female patients faring worse with the condition. By integrating known sex-differential components into our computational atrial cardiomyocyte model we found that female atrial cardiomyocytes in AF exhibit greater propensity to develop Ca2+-driven arrhythmia than male cardiomyocytes. Model analyses provided novel mechanistic insights and suggested strategies such as t-tubule restoration, correction of Ca2+-handling disturbances, and the combination of both, as promising approaches to treat AF in female patients. Our study uncovers and validate sex-specific AF mechanisms and inform the development of targeted anti-AF strategies. O_FIG O_LINKSMALLFIG WIDTH=184 HEIGHT=200 SRC="FIGDIR/small/583217v2_figa1.gif" ALT="Figure 1"> View larger version (45K): org.highwire.dtl.DTLVardef@d3ec3borg.highwire.dtl.DTLVardef@13a2c7borg.highwire.dtl.DTLVardef@3e4605org.highwire.dtl.DTLVardef@6726b4_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical abstract:C_FLOATNO Sex-specific 3D spatiotemporal models of human atrial cardiomyocyte Ca2+ signaling reveal a greater propensity to develop Ca2+-driven arrhythmic events in female vs male atrial cardiomyocytes in AF. Model analysis links sex-specific AF remodeling to arrhythmogenic mechanisms. AF, atrial fibrillation; SCR, spontaneous Ca2+ release; CaT, cytosolic Ca2+ transient; RyR2-P, phosphorylated ryanodine receptor type 2 (RyR2); CSQ, calsequestrin; LTCC, L-type Ca2+ channel; PLB, phospholamban; SERCA, sarcoendoplasmic reticulum Ca2+ ATPase; SR, sarcoplasmic reticulum. C_FIG

physiology↗

bioRxiv2023

Dual effects of the small-conductance Ca2+-activated K+ current on human atrial electrophysiology and Ca2+-driven arrhythmogenesis: an in silico study

By sensing changes in intracellular Ca2+, small-conductance Ca2+-activated K+ (SK) channels dynamically regulate the dynamics of the cardiac action potential (AP) on a beat-to-beat basis. Given their predominance in atria vs. ventricles, SK channels are considered a promising atrial-selective pharmacological target against atrial fibrillation (AF), the most common cardiac arrhythmia. However, the precise contribution of SK current (ISK) to atrial arrhythmogenesis is poorly understood, and may potentially involve different mechanisms that depend on species, heart rates, and degree of AF-induced atrial remodeling. Both reduced and enhanced ISK have been linked to AF. Similarly, both SK channel up- and downregulation have been reported in chronic AF (cAF) vs. normal sinus rhythm (nSR) patient samples. Here, we use our multi-scale modeling framework to obtain mechanistic insights into the contribution of ISK in human atrial myocyte electrophysiology. We simulate several protocols to quantify how ISK modulation affects the regulation of AP duration (APD), Ca2+ transient, refractoriness, and occurrence of alternans and delayed afterdepolarizations (DADs). Our simulations show that ISK activation shortens the APD and atrial effective refractory period, limits Ca2+ cycling, and slightly increases the propensity for alternans in both nSR and cAF conditions. We also show that increasing ISK counteracts DAD development by reducing the coupling between transmembrane potential and intracellular Ca2+. Taken together, our results suggest that increasing ISK in human atrial myocytes could promote reentry, while protecting against triggered activity. Depending on the leading arrhythmogenic mechanism, ISK inhibition may thus be a beneficial or detrimental anti-AF strategy.

physiology↗

bioRxiv2023

Myosin Light Chain Dephosphorylation by PPP1R12C Promotes Atrial Hypocontractility in Atrial Fibrillation

BackgroundAtrial fibrillation (AF), the most common sustained cardiac arrhythmia, increases thromboembolic stroke risk five-fold. Although atrial hypocontractility contributes to stroke risk in AF, the molecular mechanisms reducing myofilament contractile function remain unknown. We tested the hypothesis that increased expression of PPP1R12C, the PP1 regulatory subunit targeting atrial myosin light chain 2 (MLC2a), causes hypophosphorylation of MLC2a and results in atrial hypocontractility. MethodsRight atrial appendage tissues were isolated from human AF patients versus sinus rhythm (SR) controls. Western blots, co-immunoprecipitation, and phosphorylation studies were performed to examine how the PP1c-PPP1R12C interaction causes MLC2a de-phosphorylation. In vitro studies of pharmacologic MRCK inhibitor (BDP5290) in atrial HL-1 cells were performed to evaluate PP1 holoenzyme activity on MLC2a. Cardiac-specific lentiviral PPP1R12C overexpression was performed in mice to evaluate atrial remodeling with atrial cell shortening assays, echocardiography, and AF inducibility with EP studies. ResultsIn human patients with AF, PPP1R12C expression was increased two-fold versus SR controls (P=2.0x10-2, n=12,12 in each group) with > 40% reduction in MLC2a phosphorylation (P=1.4x10-6, n=12,12 in each group). PPP1R12C-PP1c binding and PPP1R12C-MLC2a binding were significantly increased in AF (P=2.9x10-2 and 6.7x10-3 respectively, n=8,8 in each group). In vitro studies utilizing drug BDP5290, which inhibits T560-PPP1R12C phosphorylation, demonstrated increased PPP1R12C binding with both PP1c and MLC2a, and dephosphorylation of MLC2a. Lenti-12C mice demonstrated a 150% increase in LA size versus controls (P=5.0x10-6, n=12,8,12), with reduced atrial strain and atrial ejection fraction. Pacing-induced AF in Lenti-12C mice was significantly higher than controls (P=1.8x10-2 and 4.1x10-2 respectively, n= 6,6,5). ConclusionsAF patients exhibit increased levels of PPP1R12C protein compared to controls. PPP1R12C overexpression in mice increases PP1c targeting to MLC2a and causes MLC2a dephosphorylation, which reduces atrial contractility and increases AF inducibility. These findings suggest that PP1 regulation of sarcomere function at MLC2a is a key determinant of atrial contractility in AF.

molecular biology↗

bioRxiv2022

Integrative human atrial modeling unravels interactive PKA and CaMKII signaling as key determinant of atrial arrhythmogenesis

Atrial fibrillation (AF), the most prevalent clinical arrhythmia, is associated with atrial remodeling manifesting as acute and chronic alterations in expression, function, and regulation of atrial electrophysiological and Ca2+-handling processes. These AF-induced modifications crosstalk and propagate across spatial scales creating a complex pathophysiological network, which renders AF resistant to existing pharmacotherapies that predominantly target transmembrane ion channels. Developing innovative therapeutic strategies requires a systems approach to disentangle quantitatively the proarrhythmic contributions of individual AF-induced alterations. Here, we built a novel computational framework for simulating electrophysiology and Ca2+-handling in human atrial cardiomyocytes and tissues, and their regulation by key upstream signaling pathways (i.e., protein kinase A, PKA, and Ca2+/calmodulin-dependent protein kinase II, CaMKII) involved in AF-pathogenesis. Populations of atrial cardiomyocyte models were constructed to determine the influence of subcellular ionic processes, signaling components, and regulatory networks on atrial arrhythmogenesis. Our results reveal a novel synergistic crosstalk between PKA and CaMKII that promotes atrial cardiomyocyte electrical instability and arrhythmogenic triggered activity. Simulations of heterogeneous tissue demonstrate that this cellular triggered activity is further amplified by CaMKII-dependent alterations of tissue properties, further exacerbating atrial arrhythmogenesis. Our analysis positions CaMKII as a key nodal master switch of the adaptive changes and the maladaptive proarrhythmic triggers at the cellular and tissue levels and establishes CaMKII inhibition as potential anti-AF strategy. Collectively, our integrative approach is powerful and instrumental to assemble and reconcile existing knowledge into a systems network for identifying novel anti-AF targets and innovative approaches moving beyond the traditional ion channel-based strategy. Significance statementDespite significant advancement in our understanding of pathological mechanisms and alterations underlying atrial fibrillation (AF), a highly prevalent clinical arrhythmia causing substantial health and socioeconomic burden, development of effective pharmacological therapeutics for AF remains an urgent unmet clinical need. We built a systems framework integrating key processes and their regulatory upstream signaling pathways that are involved in atrial electrophysiology and modified by AF. By simulating populations of single atrial cardiomyocyte models and heterogeneous tissues, our analysis demonstrated synergistic interactions between upstream signaling pathways that promote atrial arrhythmogenesis across spatial scales, added new insight into complex atrial arrhythmia mechanisms, and revealed adaptive and maladaptive alterations caused by AF, thus providing a powerful new tool for identifying innovative therapeutic approaches against AF.

physiology↗

bioRxiv2020

Major threats to a migratory raptor vary geographically along the eastern Mediterranean flyway

Millions of large soaring birds migrate from the Palaearctic to Africa every year, and follow distinct flyways around the Mediterranean Sea. While there is conservation concern for many long-distance migratory bird populations, the magnitude and geographic range of threats affecting birds along flyways are poorly known, which complicates efficient mitigation. We used an endangered soaring migrant, the Egyptian Vulture Neophron percnopterus, as an example species to assess important threats in 13 countries along the eastern Mediterranean flyway. We tracked 71 birds using satellite telemetry to quantify mortalities, surveyed 4198 km of powerlines to detect dead birds, conducted 910 interviews to quantify the prevalence of poison use, and assessed the magnitude of direct persecution by surveying markets and hunters. We lost 44 birds (50% in Europe and the Mediterranean Sea, 16% in the Middle East, and 34% in Africa), and mortality causes varied geographically. Inadvertent poisoning resulting from rural stakeholders targeting predators occurred along most of the flyway. On the breeding grounds in eastern Europe, poisoning and collision and electrocution continue to be major threats. Electrocution on small and poorly designed electricity pylons was most severe in Turkey, Ethiopia and Saudi Arabia, while direct persecution to meet market demands for belief-based use of vulture products appears to be the largest threat in Nigeria and Niger. Illegal direct persecution for leisure is a major threat in the Middle East and Egypt. Although our work cannot quantitatively estimate which of the identified threats has the greatest demographic impact on Egyptian Vultures, none of threats are species-specific and are therefore relevant for many other migratory birds. Our assessment highlights the key threats per country that range states need to address to meet their obligations under the Convention of Migratory Species to protect migratory birds.

zoology↗