Abstract Body (Do not enter title and authors here): Introduction: Myocardial infarction (MI) is a leading cause of death worldwide, and endothelial cells (ECs) are central to the repair process by coordinating angiogenesis, immune cell recruitment, and endothelial-to-mesenchymal transition (EndMT). ADAM17, a membrane-bound protease elevated in cardiovascular disease, regulates multiple cellular processes through ectodomain shedding of different molecules. However, the causal role of endothelial ADAM17 in post-MI recovery remains poorly defined.

Methods: Male and female mice with inducible endothelial-specific ADAM17 knockdown (Adam17^f/f/Cdhr5Cre^ERT; Adam17^EC-KD) and control cohorts (Adam17^f/f, Cdhr5Cre^ERT, WT) underwent left anterior descending coronary artery ligation to induce experimental MI. Cardiac structure and function were evaluated (echocardiography), histological analyses (Trichrome staining), molecular analyses (immunofluorescent staining (IF), western blotting, and single-nucleus RNA sequencing (snRNA-seq)) at various post-MI time points.

Results: Adam17^EC-KD mice exhibited reduced post-MI survival (increased LV rupture), increased left ventricular rupture, and progressive decline in cardiac function with reduced ejection fraction. Adam17^EC-KD mice exhibited increased neutrophil infiltration, NETosis, and cytotoxic T cell accumulation at 1 day post-MI; however, depletion of any of these immune cells further exacerbated the post-MI mortality (due to LV rupture), highlighting their potential protective contribution. Loss of endothelial ADAM17 resulted in decreased coronary density in the infarct myocardium (CD31 IF; 3-D micro-CT imaging), with reduced pVEGFR2 signaling, suggesting impaired angiogenesis. In addition, SnRNA-seq confirmed the suppressed pro-angiogenic pathways, and identified an endothelial cell subpopulation enriched for necroptotic markers, displaying increased ligand-receptor interactions with inflammatory macrophages. Mechanistically, endothelial ADAM17 deficiency enhanced necroptotic cell death via activation of the TNFR1-RIP3K-RIP1K-MLKL axis. Adam17^EC-KD hearts also showed impaired collagen crosslinking and reduced activation of the SMAD pathway (pSMAD2/3), lysyl oxidase, and Fibronectin expression, indicating defective EndMT, supported by reduced EndMT gene signatures in snRNA-seq.

Conclusion: Endothelial ADAM17 is essential for effective post-MI cardiac repair by regulating endothelial survival, angiogenesis, immune cell infiltration, and infarct formation.