Overexpression of PrPC by Adenovirus-Mediated Gene Targeting Reduces Ischemic Injury in a Stroke Rat Model

摘要

Prion diseases are induced by pathologically misfolded prion protein (PrP^Sc), which recruit normal sialoglycoprotein PrP^C by a template-directed process. In this study, we investigated the expression of PrP^C in a rat model of cerebral ischemia to more fully understand its physiological role. Immunohistochemical analysis demonstrated that PrP^C-immunoreactive cells increased significantly in the penumbra of ischemic rat brain compared with the untreated brain. Western blot analysis showed that PrP^C protein expression increased in ischemic brain tissue in a time-dependent manner. In addition, PrP^C protein expression was seen to colocalize with neuron, glial, and vascular endothelial cells in the penumbric region of the ischemic brain. Overexpression of PrP^C by injection of rAd (replication-defective recombinant adenoviral)-PGK (phosphoglycerate kinase)-PrP^C-Flag into ischemic rat brain improved neurological behavior and reduced the volume of cerebral infarction, which is supportive of a role for PrP^C in the neuroprotective adaptive cellular response to ischemic lesions. Concomitant upregulation of PrP^C and activated extracellular signal-regulated kinase (ERK1/2) under hypoxia–reoxygenation in primary cortical cultures was shown to be dependent on ERK1/2 phosphorylation. During hypoxia–reoxygenation, mouse neuroblastoma cell line N18 cells transfected with luciferase rat PrP^C promoter reporter constructs, containing the heat shock element (HSE), expressed higher luciferase activities (3- to 10-fold) than those cells transfected with constructs not containing HSE. We propose that HSTF-1 (hypoxia-activated transcription factor), phosphorylated by ERK1/2, may in turn interact with HSE in the promoter of PrP^C resulting in gene expression of the prion gene. In summary, we conclude that upregulation of PrP^C expression after cerebral ischemia and hypoxia exerts a neuroprotective effect on injured neural tissue. This study suggests that PrP^C has physiological relevance to cerebral ischemic injury and could be useful as a therapeutic target for the treatment of cerebral ischemia.