OSTEOPONTIN EXPRESSION IS INCREASED IN THE HERITABLE CARDIOMYOPATHY OF SYRIAN-HAMSTERS

Background Osteopontin, a noncollagenous matrix protein, is transientl y expressed in the heart after experimental cardiac injury, but its ex pression in states of continuing cardiac remodeling is unknown. We eva luated osteopontin expression in the heritable cardiomyopathy of the S yrian hamster. Methods and Results Hamster hearts were obtained for RN A isolation and analysis and in situ hybridization from two groups: no rmal control animals (n=4) and untreated cardiomyopathic hamsters (n=5 ). Osteopontin mRNA was 12-fold greater in cardiomyopathic hearts comp ared with normal controls (1.76+/-0.31 versus 0.14+/-0.04 arbitrary un its normalized to GAPDH, mean+/-SEM, P<.05). In situ hybridization was used to define the origin of osteopontin in the heart. Osteopontin mR NA above background levels was not detected in sections from noncardio myopathic hamster hearts but was readily detected in sections from car diomyopathic hamsters, in which it originated in cells morphologically consistent with tissue macrophages. Conclusions In the hamster, osteo pontin is expressed in heritably cardiomyopathic hearts under conditio ns of chronic injury and repair, and the source of osteopontin message appears to be tissue macrophage-like cells in foci of inflammation. T his model could be used to evaluate the biological role of osteopontin in myocardial inflammation and remodeling.