Cardiology and Cardiovascular Medicine, Pharmacology, Toxicology and Pharmaceutics, Cell Biology
84
Scopus Publications
Scopus Publications
Chamber-specific chromatin architecture guides functional interpretation of disease-associated Cis-regulatory elements in human cardiomyocytes S. Haydar, R. Bednarz, P. Laurette, I. Sobitov, N. Díaz i Pedrosa, et al. Nature Communications, 2026 Cis- regulatory elements (CREs) are noncoding DNA regions regulating cell-type-specific gene expression programs by interacting with distal gene promoters. Here, we aim to decode the function and spatial organization of CRE-promoter interactions in human cardiomyocytes. We analyzed the epigenome and chromatin interactions of human male atrial, ventricular, and failing cardiomyocytes. Atrial and ventricular cardiomyocytes harbored chamber-specific CRE-promoter interactions modulating gene expression as confirmed by functional epigenetic silencing. These CRE-promoter interactions explain the distinct contribution of non-coding genetic variants to atrial and ventricular diseases, such as dilated cardiomyopathy and arrhythmias. We dissected the prototypic KCNJ2 locus, encoding a potassium channel associated with ventricular arrhythmia susceptibility. Functional epigenetic silencing confirmed that CREs, harboring QT-duration-associated genetic risk factors, modulate KCNJ2 gene expression levels, alter KCNJ2-dependent channel currents, and affect cardiomyocyte repolarization. The presented human CM-specific chromatin interaction analysis provides key insights into regulatory mechanisms and aids in interpreting genetic risk factors.
Enhancing KLF15 activity in cardiomyocytes: a novel approach to prevent pathological reprogramming and fibrosis via nuclease-deficient dCas9VPR Eric Schoger, Rosa Kim, Federico Bleckwedel, Tomas Peralta, Laura Priesmeier, et al. Signal Transduction and Targeted Therapy, 2026 Transcriptional activity perturbation holds promise for selectively modulating harmful transcriptional networks, but its therapeutic potential remains largely unexplored. We employed a network-based analysis of single-cell heart transcriptomes to identify transcription factor activities linked to pathological cardiomyocytes in vivo. This analysis revealed that transcriptional activity of Krüppel-like factor 15 (KLF15) exhibited the most significant change in pathological cardiomyocytes, characterized by less effective repression of disease-associated genes in stressed hearts, which correlated with reduced KLF15 expression. To restore KLF15 activity, we utilized CRISPR/nuclease-dead (d)Cas9-based transcriptional enhancement (CRISPRa) in cardiomyocytes, which effectively abolished fetal reprogramming by simultaneously suppressing pathological gene expression and restoring metabolic homeostasis under sustained stress conditions. Furthermore, we identified a novel cell-nonautonomous anti-fibrotic effect mediated by cardiomyocyte-fibroblast crosstalk, and revealed the contribution of KLF15-dependent Alpha-2-glycoprotein 1, zinc-binding (AZGP1) regulation in this process. We also elucidated the upstream mechanisms of KLF15 regulation, highlighting its role as a cell-specific downstream target of the broad TGF-β canonical signaling pathway, along with its downstream-dependent mechanisms in human cardiomyocytes. Finally, to enhance the therapeutic potential of this approach, we engineered and validated an adeno-associated viral (AAV) vector with a small CRISPRa system for endogenous regulation in human cardiomyocytes suitable for clinical applications. Overall, we elucidated a regulatory circuit involving TGF-β, KLF15, and AZGP1, which coordinates critical pathological responses through cellular crosstalk between cardiomyocytes and fibroblasts. Importantly, we demonstrated the efficacy of CRISPRa as an epigenetic intervention restoring a critical transcriptional function disrupted in non-genetic heart failure. This approach provides a promising blueprint for future adaptation targeting additional non-hereditary pathologies.
Models of the human heart for biomedical research: Opportunities and challenges Katrin Streckfuss‐Bömeke, Laura C. Zelarayán, Renate B. Schnabel, Nicolle Kränkel, Christoph Maack, et al. Physiological Reports, 2026 Model systems that mimic human cardiac structure and function are essential for the development of novel diagnostics and effective treatments for cardiovascular diseases. While non‐human vertebrate models, from zebrafish to pig, remain vital to cardiovascular research, the translatability of findings to human patients is often limited. Therefore, animal experiments should be supplemented with human model systems, including human induced pluripotent stem cell‐derived cells, 3D engineered constructs, and last but not least, native tissue preparations and isolated primary cardiomyocytes. However, while human myocardium remains the gold standard, human heart tissue – and particularly tissue from control hearts–remains scarce, and its use in research is generally restricted to settings where tissue has been excised from diseased or failing hearts. While it is in principle possible to use tissue from rejected non‐failing donor hearts that cannot be transplanted, legal hurdles (e.g., in Germany) can restrict the use of non‐transplanted donor organs in research. Given the challenges associated with accessing and using human tissue in biomedical research, an integrated strategy towards combining non‐human vertebrate models, in silico models, and human tissue‐derived models is recommended, enhancing the chances of successful research and development, and helping bridge the gap between preclinical and clinical research.
A human-on-human assay for detecting anti-myocardial antibodies in patients with myocardial disease Anne Auer, Johanna Siegel, Stasa Janjatovic, Margarete Heinrichs, Stefan Störk, et al. Frontiers in Immunology, 2026 Adaptive immune responses, particularly the production of anti-myocardial antibodies, have been implicated as critical mediators in myocardial healing and remodeling following myocardial infarction (MI), acute myocarditis (Myo), and heart failure (HF). However, current methods for detecting heart-reactive antibodies in patients are insufficient, as most rely on heart tissue slices from primates or other species. These approaches pose technical, logistical, and ethical challenges, including the risk of false negative results due to lack of inter-species cross-reactivity. To address these limitations, we developed a human cell-based assay to screen for patient-derived serum or plasma reactivity against human cardiomyocytes differentiated from induced pluripotent stem cells (iPSC-CMs). This human-on-human test system can detect cardiomyocyte-specific immunoglobulins present in patient plasma by applying indirect immunofluorescence staining, followed by convenient visualization through either confocal microscopy or standard widefield systems available in clinical laboratories. Overall, this approach provides a physiologically relevant and ethically responsible model for rapid, accurate testing of anti-myocardial antibodies across various clinical settings, thus offering accessible tools to stratify patients with myocardial disease according to their adaptive immune response status.
Impaired Atrial Mitochondrial Calcium Handling in Patients With Atrial Fibrillation Julius Ryan D. Pronto, Fleur E. Mason, Eva A. Rog-Zielinska, Funsho E. Fakuade, Donata Bülow, et al. Circulation Research, 2025 BACKGROUND: Mitochondrial calcium (Ca 2+ ) is a key regulator of cardiac energetics by stimulating the tricarboxylic acid cycle during elevated workload. Atrial fibrillation (AF) is associated with a reduction in cytosolic Ca 2+ transient amplitude, but its effect on mitochondrial Ca 2+ handling and cellular redox state has not been explored. METHODS: Cardiac myocytes isolated from patient-derived right atrial biopsies were subjected to workload transitions using patch-clamp stimulation and β-adrenergic stimulation (isoproterenol). In conjunction, nicotinamide adenine dinucleotide (phosphate)/flavin adenine dinucleotide (NAD[P]H/FAD) autofluorescence, cytosolic and mitochondrial [Ca 2+ ] were monitored using epifluorescence microscopy. Sarcoplasmic reticulum and mitochondria were imaged using electron microscopy and tomography and stimulated emission depletion microscopy. The effects of the mitochondrial Ca 2+ uptake enhancer ezetimibe on proarrhythmic activity in atrial myocytes and on AF burden in patients were investigated. RESULTS: Mitochondrial Ca 2+ accumulation during increased workload was blunted in AF, and was associated with impaired regeneration of nicotinamide adenine dinucleotide and flavin adenine dinucleotide. Nanoscale imaging revealed spatial disorganization of sarcoplasmic reticulum and mitochondria, associated with microtubule destabilization. This was confirmed in human induced pluripotent stem cell–derived cardiac myocytes, where treatment with the microtubule destabilizer nocodazole displaced mitochondria and increased proarrhythmic Ca 2+ sparks, which were rescued by MitoTEMPO. Ezetimibe also reduced the occurrence of arrhythmogenic Ca 2+ release events both in AF myocytes and nocodazole-treated human induced pluripotent stem cell–derived cardiac myocytes. Retrospective patient analysis also revealed a reduced AF burden in patients on ezetimibe treatment. CONCLUSIONS: Mitochondrial Ca 2+ uptake and accumulation are impaired in atrial myocytes from patients with AF. The disturbed spatial association between sarcoplasmic reticulum and mitochondria driven by destabilized microtubules may underlie impaired Ca 2+ transfer in AF. Enhancing mitochondrial Ca 2+ uptake potentially protects against arrhythmogenic events.
Arrhythpy: an automated tool to quantify and classify arrhythmias in Ca2+ transients of iPSC-cardiomyocytes Karim Ajmail, Charlotte Brand, Thomas Borchert, Benjamin Meder, Sabine Rebs, et al. American Journal of Physiology Heart and Circulatory Physiology, 2025 Arrhythmias in calcium transients are easy to detect by human perception. However, quantifying these arrhythmias in a computer-readable manner remains challenging. To address this, we developed Arrhythpy, an automated tool that measures arrhythmias in iPSC-derived cardiomyocytes by analyzing Ca2+ transients. Unlike other tools, Arrhythpy directly evaluates arrhythmia levels. It effectively monitors arrhythmias in healthy and diseased iPSC-CMs, including dilated cardiomyopathy and Takotsubo syndrome. Arrhythpy’s flexible framework suits varied cell types and measurement techniques.