Abstract 10866: Novel Role of Macrophage-derived Matrix Vesicles in Arterial Microcalcification
Microcalcifications located in the thin fibrous cap of atherosclerotic plaques increase the risk of fatal ruptures. Using molecular imaging, we previously demonstrated that chronic renal disease (CRD) accelerates formation of macrophage-rich atherosclerotic plaques and calcification. Although cardiovascular disease is the main cause of death in CRD, the mechanism remains unclear. Here we hypothesized that macrophages release microcalcification-generating matrix vesicles (MV), promoting atherosclerotic intimal calcification under CRD conditions. Macrophage number and calcified area were increased in apoE-/- mice with CRD induced by 5/6 nephrectomy vs. apoE-/- mice (p<0.001 and p<0.01 respectively; n=24). Near-infrared fluorescence microscopy, using hydroxyapatite-binding molecular imaging agent, readily detected microcalcifications, containing vesicular structures. S100A9, a newly suggested promoter of inflammation and calcification, was shown by immunohistochemistry to be increased in calcifying plaques and co-localized with both macrophages and microcalcifications. ApoE-/-S100A9-/- mice contained fewer lesions (p<0.02) and less macrophage accumulation (p<0.003) compared to apoE-/- cohort as detected by histopathology (n=9 per group). ApoE-/-S100A9-/- mice had less MV in plasma (n=5), and reduced calcific potential of peritoneal macrophage-derived MV compared to apoE-/- mice. S100A9 silencing with siRNA reduced the production of MV derived from human primary macrophages (p<0.05). Elevated calcium and phosphate levels, comparable to those observed in CRD patients, increase the calcific potential of human aortic smooth muscle cell-derived MV containing S100A9, in a model of medial calcification. We found that similar calcium phosphate levels increase the calcific potential of macrophage-derived MV (RAW 264.7 cell line; p<0.01; n=3). These conditions did not induce apoptosis and thus this effect is not attributed to apoptotic bodies. This is the first report to our knowledge to demonstrate a direct role of macrophage-derived MV in inflammation-driven calcification, which further suggests the importance of MV in the formation of microcalcifications and the advancement of atherosclerotic calcification in CRD.
- © 2011 by American Heart Association, Inc.