Time course of osteopontin, osteocalcin, and osteonectin accumulation and calcification after acute vessel wall injury

Although mineral deposits have long been described to be a prominent featur e of atherosclerosis, the mechanisms of arterial calcification are not well understood. However, accumulation of the non-collagenous matrix bone-assoc iated proteins, osteopontin, osteocalcin, and osteonectin, has been demonst rated in atheromatous plaques. The aim of this study was to evaluate the ro le of these proteins in arterial calcification and, more precisely, during the initiation of this process. A model of rapid aortic calcification was d eveloped in rabbits by an oversized balloon angioplasty. Calcification was followed using von Kossa staining and osteopontin, osteocalcin, and osteone ctin were identified using immunohistochemistry. The aortic injury was rapi dly followed by calcified deposits that appeared in the media as soon as 2 days after injury and then accumulated in zipper-like structures. Osteonect in was not detected in calcified deposits at any time after injury. In cont rast, osteopontin and osteocalcin were detected in 8- and 14-day calcified structures, respectively, but not in the very early 2-day mineral deposits. These results suggest that these matrix proteins, osteopontin, osteocalcin , and osteonectin, are not involved in the initiation step of the aortic ca lcification process and that the former two might play a role in the regula tion of arterial calcification.