https://doi.org/10.1007/s00392-025-02625-4
1Heidelberg Univerisity Hospital, Heidelberg Internal Medicine III Heidelberg, Deutschland; 2University Hospital, Heidelberg Internal Medicine III Heidelberg, Deutschland; 3Medical school Hamburg Hamburg, Deutschland; 4Universitätsklinikum Heidelberg Klinik für Innere Med. III, Kardiologie, Angiologie u. Pneumologie Heidelberg, Deutschland; 5Universitätsklinikum Schleswig-Holstein Med. Klinik III / Kardiologie, Angiologie, Intensivmedizin Kiel, Deutschland; 6Universitätsklinikum Schleswig-Holstein Innere Medizin III mit den Schwerpunkten Kardiologie und internistische Intensivmedizin Kiel, Deutschland
Background: Mitochondrial dysfunction is a key contributor to cardiovascular disease, including arrhythmias and heart failure. The high energy demand of the heart underscores the importance of mitochondrial regulators. We identified Letm1 as a novel binding partner of SH3BGR, with a poorly defined role in cardiac health, warranting investigation into its impact on cardiomyocyte function.
Methods: Neonatal rat ventricular cardiomyocytes (NRVCMs) were used to overexpress Letm1. Transcriptomic profiling, immunoblotting, qPCR, Seahorse metabolic assays, patch-clamp measurements, and contractility assays were performed to assess changes in mitochondrial and cellular function.
Results: Our analysis demonstrated that Letm1 expression is significantly altered in human cardiac disease samples, suggesting its potential role in disease pathology. Transcriptomic profiling of cardiomyocytes with Letm1 overexpression revealed a marked downregulation of genes associated with oxidative phosphorylation, highlighting disrupted mitochondrial gene expression. Consistent with these transcriptomic changes, immunoblotting confirmed a reduction in oxidative phosphorylation (OXPHOS) complex protein levels, indicating impaired mitochondrial function. Functional assays further corroborated these findings. Seahorse metabolic analysis revealed a decrease in ATP production and diminished oxidative phosphorylation capacity, reflecting compromised mitochondrial bioenergetics. Electrophysiological characterization of Letm1-overexpressing cardiomyocytes showed a significant reduction in action potential duration at 50% (APD50) and 90% (APD90) repolarization, suggesting alterations in electrical activity and ion channel function. Calcium transient measurements revealed decreased L-type calcium currents, indicative of dysregulated calcium handling—a critical determinant of cardiac excitability and contractility. These electrophysiological disturbances were mirrored by functional deficits in cardiomyocyte contractility, with contractility assays showing significantly impaired mechanical performance. Moreover, elevated levels of cleaved caspase-3, a marker of apoptosis, and decreased cell viability pointed to increased cell death associated with elevated Letm1 expression.
Conclusion: Our study identifies Letm1 as a critical regulator of mitochondrial and cardiomyocyte function. Elevated Letm1 levels impair mitochondrial energy supply, disrupts calcium handling, and promotes apoptosis, potentially contributing to arrhythmias and heart failure. These findings highlight Letm1’s pivotal role in cardiac pathophysiology and underscore its potential as a therapeutic target.