DETECTION OF OSTEOPONTIN IN CALCIFIED HUMAN AORTIC VALVES

Cardiac valve calcification often results in obstruction of blood flow , which eventually leads to valve replacement. The molecular mechanism s resulting in valve calcification are unknown. Collagen and specific bone matrix proteins are thought to provide the framework for ectopic tissue calcification. This investigation was performed to determine wh ether the bone matrix protein osteopontin was present in calcified hum an aortic valves. Proteins extracted from human aortic valve tissue we re subjected to polyacrylamide gel electrophoresis followed by Western blotting, using polyclonal antibodies directed against osteopontin. F resh frozen tissue sections were also screened for osteopontin and mac rophages using immunohistochemical techniques. Osteopontin was present in both heavily and minimally calcified aortic valves and absent in n oncalcified purely regurgitant or normal aortic valves by both radioim munoassay (n=16) and immunohistochemical techniques (n=8). Osteopontin colocalized with valvular calcific deposits, and macrophages were ide ntified in the vicinity of osteopontin. These results, in addition to showing that osteopontin is present in calcified human aortic valves, suggest that osteopontin is a regulatory protein in pathological calci fication. Identification of the cells producing osteopontin in abnorma l cardiac valves and of proximate stimuli for its secretion may lead t o novel therapeutic strategies to prevent and/or reverse calcific valv e disease.