TMAO-Triggered Endothelial–Mesenchymal Transition and Microvesicle Release as Mediators of Vascular Smooth Muscle Cell Osteogenic Differentiation and Vascular Calcification

<b>Background:</b> Cardiovascular diseases (CVDs) are the leading global cause of mortality, with vascular calcification (VC) as a major predictor of adverse outcomes. Although vascular smooth muscle cells (VSMCs) are established contributors, the role of endothelial cells (ECs), particularly via the endothelial-mesenchymal transition (EndMT) and exosome signaling, remains less defined. <b>Objective:</b> This study investigated whether the gut microbiota-derived metabolite Trimethylamine-N-oxide (TMAO) induces EndMT in ECs and whether exosomes from TMAO-treated ECs regulate the VSMC phenotype and calcification. <b>Methods:</b> Human umbilical vein endothelial cells (HUVECs) were exposed to TMAO at physiological and pathological levels (10-50 µM). EndMT markers were analyzed by Western blotting and qPCR. Exosomes were isolated, characterized, and applied to HAVSMCs in graded doses. Osteogenic and contractile markers, β-catenin signaling, and calcification were quantified. Exosomal miR-30 and miR-222 were studied. <b>Results:</b> TMAO triggered dose-dependent EndMT, decreasing CD31/VE-cadherin and increasing α-SMA, N-cadherin, and vimentin. Exosomes from TMAO-treated ECs reprogrammed VSMCs, downregulating contractile proteins and upregulating RUNX2, OPN, TNAP, and β-catenin, causing calcium accumulation. These exosomes displayed elevated miR-222 and reduced miR-30, changes that activated β-catenin signaling and promoted the osteogenic reprogramming of VSMCs. <b>Conclusions:</b> Pathophysiological TMAO levels induce EndMT and mediate the formation of exosomes, which drive the osteogenic reprogramming and calcification of VSMCs.