Abstract 15888: Scamc-1 is a Novel Extracellular Vesicle Protein Linked to Vascular Calcification
Introduction: Calcification is an excellent predictor of cardiovascular morbidity and mortality. Microcalcifications in thin fibrous caps of atherosclerotic plaques create biomechanical instability, leading to plaque rupture and subsequent myocardial infarction and stroke. We previously showed that cellular-derived extracellular vesicles (EVs) play a role in the microcalcification nucleation; however, the mechanisms remain unknown. We hypothesize that the aggregation of specialized EVs with a unique proteomic fingerprint serve as nucleating foci for microcalcifications.
Methods and Results: Transmission electron microscopy of atherosclerotic plaques indicated aggregation of EVs within regions of disrupted collagen. Using super-resolution confocal microscopy and a near-infrared calcium tracer we observed EVs derived from human coronary artery smooth muscle cells (SMCs) cultured in osteogenic media (OM) aggregating to form microcalcifications within collagen hydrogels, a 3D model of fibrous cap. After 21 days in OM, SMCs produced an endogenous collagen matrix with entrapped microcalcifications. We collected the conditioned media from SMCs cultured in OM or control media for 21 days (enriched in non-calcifying EVs) and a collagenase digestion was performed to obtain the trapped calcifying EVs. Mass spectrometry with tandem mass tagging was used to assess the proteome of each EV population. Cluster analyses of the 621 identified proteins (> 2 unique peptides) revealed 131 proteins that increased in OM and trapped within the collagen matrix. SCaMC-1 was 3.2 fold increased in EVs from SMCs cultured in OM. A protein with homology to SCaMC-1 was recently shown to induce calcium mineralization in the Japanese pearl oyster and calcium phosphate deposition in the mitochondria of cancer cells, suggesting its role in biomineralization. We further performed immunostaining of calcified human carotid arteries that revealed a colocalization of SCaMC-1 expression and microcalcifications, while SCaMC-1 was not detected in non-calcified regions of the tissue.
Conclusions: Here, we identify SCaMC-1, a calcium-dependent ATP transporter previously unreported in vascular calcification, that is associated with EV mineralization.
Author Disclosures: J.D. Hutcheson: None. C. Goettsch: None. N. Maldonado: None. P. Ricchiuto: None. S.A. Singh: None. E. Aikawa: None.
- © 2014 by American Heart Association, Inc.