PATALUCH, N. | Search bioRxiv

bioRxiv2025

Sequential mitochondrial remodeling in cardiomyocytes drives diastolic dysfunction and transition to HFrEF in anthracycline-induced cardiotoxicity

Aims. Anthracycline-induced cardiotoxicity is a leading cause of heart failure (HF) in cancer survivors and is usually detected only once systolic dysfunction is established, when myocardial injury may already be advanced. Diastolic dysfunction may occur earlier, but its onset and cellular basis are unknown. We investigated the temporal emergence of diastolic dysfunction during doxorubicin (DOX) exposure and its link to the selective vulnerability of crest/subsarcolemmal mitochondria (SSM) at the cardiomyocyte (CM) surface. Methods and results. Using a clinically relevant chronic DOX protocol in adult mice, we performed longitudinal cardiac assessment from the first exposure, combining conventional echocardiography, tissue Doppler, and global longitudinal strain (GLS). Structural and molecular correlates were characterized by atomic force microscopy, transmission electron microscopy, and 3D-quantitative imaging of native cardiac tissue, spatially resolving the CM surface (SSM) from the interior (interfibrillar mitochondria, IFM) compartment. DOX impaired active myocardial relaxation from the first dose with prolonged isovolumic relaxation time and reduced mitral annular e', whereas passive filling (transmitral filling, left atrial size) was preserved. Ejection fraction remained normal, with an early reduction in GLS. This early relaxation defect coincided with selective remodeling of the surface crest/SSM architecture, evident as crest flattening and progressive SSM loss and with depletion of the crest/SSM determinants Ephrin-B1 and Claudin-5, whereas IFM were affected only later, upon cumulative exposure. Surface SSM injury was accompanied by early, spatially ordered PINK1/Parkin activation, engaging SSM before IFM, and by loss of the sarcolemmal Na+;/Ca2+; exchanger NCX1, likely impairing diastolic Ca2+ removal. In CM-specific Ephrin-B1-deficient mice, which lack mature crest/SSM, DOX precipitated an accelerated transition to HF with reduced ejection fraction. Conclusions. Impaired active relaxation is the earliest functional hallmark of anthracycline cardiotoxicity, underpinned by selective injury of the surface crest/SSM compartment and its Na+;/Ca2+; exchanger NCX1, while IFM and passive filling are initially spared. Diastolic assessment from the first anthracycline cycles may improve early detection and prevention of HF progression.

pathology↗

bioRxiv2024

Unveiling the native architecture of adult cardiac tissue using the 3D-NaissI method

AbstractAccurately imaging adult cardiac tissue in its native state is essential for regenerative medicine and understanding heart disease. Current fluorescence methods encounter challenges with tissue fixation. Here, we introduce the 3D-NaissI (3D-Native Tissue Imaging) method, enabling rapid, cost-effective imaging of fresh cardiac tissue samples in their closest native state, that we also extended to other tissues. We validated 3D-NaissIs efficacy in preserving cardiac tissue integrity using small biopsies under hypothermic conditions in phosphate-buffered saline, offering unparalleled resolution in confocal microscopy for imaging fluorescent-small molecules/-antibodies. Compared to conventional histology, 3D-NaissI preserves cardiac tissue architecture and native protein epitopes, facilitating the use of a wide range of commercial antibodies without unmasking strategies. We successfully identified specific cardiac protein expression patterns in cardiomyocytes (CMs) from rodents and humans, including for the first time ACE2 localization in the lateral membrane/T-Tubules and SGTL2 in the sarcoplasmic reticulum. These findings shed light on COVID-19-related cardiac complications and suggest novel explanations for iSGLT2 therapeutic benefits in HFpEF patients. Additionally, we challenge the notion of "connexin-43 lateralization" in heart pathology, suggesting it may be an artifact of cardiac fixation, as 3D-NaissI clearly revealed native connexin-43 expression at the lateral membrane of healthy CMs. We also discovered previously undocumented periodic ring-like 3D structures formed by pericytes covering CMs lateral surfaces. These structures, positive for laminin-2, delineate a specific spatial architecture of laminin-2 receptors at the CM surface, highlighting the pivotal role of pericytes in CM function. Lastly, 3D-NaissI facilitates mapping native human protein expression in fresh cardiac autopsies, providing insights into both pathological and non-pathological contexts. Hence, 3D-NaissI offers unparalleled insights into native cardiac tissue biology and promises to advance our understanding of physiology and pathophysiology, surpassing standard histology in resolution and accuracy.

cell biology↗