Expression of heparanase in nestin-positive reactive astrocytes in ischemic lesions of rat brain after transient middle cerebral artery occlusion

Heparanase is an enzyme that cleaves heparan sulfate proteoglycans, an important component of the extracellular matrix to generate heparan sulfate fragments, leading to the remodeling of the extracellular matrix and the basement membrane particularly during cancer metastasis. A growing body of evidence suggests that heparanase serves multiple functions in normal tissues including the central nervous system. In this study, we showed that heparanase is expressed in reactive astrocytes in the peri-infarct lesion of a rat brain whose middle cerebral artery was transiently occluded for 90 min. RT-PCR and Western blot analyses revealed that heparanase expression was markedly upregulated during the subacute phase of ischemia (from 3 to 7 days post-reperfusion (dpr)). As revealed by immunohistochemical study, heparanase was localized in astrocytes located in the peri-infarct region. Heparanase+ astrocytes expressed nestin that is known as a marker of reactive astrocytes. Infiltrated neutrophils were weakly heparanase+. After 7 dpr, the expression level of heparanase+ astrocytes considerably decreased. Therefore, the maximum expression of heparanase by astrocytes may correlate with the time of migration of reactive astrocytes toward the ischemic core, which may result in astrogliosis. These findings suggest a novel role of heparanase in the pathophysiology of brain ischemia.