Association of osteopontin with ischemic axonal death in periventricular leukomalacia

Osteopontin (OPN) is a bone matrix protein expressed my macrophages and rel ated to the process of tissue calcification, and is also known to protect i schemic cells. To understand how OPN is involved in the process of ischemic axonal death in periventricular leukomalacia (PVL), we examined the immuno reactivity of OPN and ionized calcium binding adaptor molecule 1 (Iba1; mic roglia/macrophage marker) at various stages of PVL. OPN immunoreactivity pa ralleled the number of Iba1-positive foam cells; a finding which suggests t he production of OPN protein by foam cells. OPN immunoreactivity was not fo und in either normal white matter or acute PVL lesions, but was detected at the subacute and chronic stages in swollen and calcified axons bordering t he ischemic zone. These findings suggest that OPN is closely associated wit h death of swollen axons at the periphery of the ischemic zone, regulating the presence or absence of calcification.