Experimental traumatic brain injury in rats stimulates the expression, production and activity of Alzheimer's disease β-secretase (BACE-1)

Traumatic brain injury (TBI) is a risk factor for the development of Alzheimer's disease (AD). After a traumatic brain injury depositions of amyloid beta (Abeta) in the brain parenchyma were found. In this study we investigated the expression pattern of beta-secretase (BACE-1) in ipsi- or contralateral hippocampus and cortex following controlled cortical TBI in rats. BACE-1 mRNA levels, estimated by real time RT-PCR, were elevated 24 h post injury, and persisting up to 72 h, in the ipsi- and contralateral hippocampus and cerebral cortex as compared to the sham-treated animals (p<0.01). The TBI-induced changes in BACE-1 mRNA are due to enhanced hippocampal and cortical expression of BACE-1 mRNA in neurons and reactive astrocytes as revealed by in situ hybridization. The alterations in hippocampal BACE-1 mRNA levels are accompanied by corresponding increases in BACE-1 protein levels in ipsi- and contralateral hippocampus and ipsilateral cortex as demonstrated by Western blot analysis. In contrast, in the contralateral cortex only a weak increase of traumatically induced BACE-1 protein production was found. The activity of BACE-1 as measured by the formation of the cleavage product of amyloid beta precursor protein, transiently increased up to 48 h after injury, but returned to basal level 7 days post injury. This study demonstrates that the beta-secretase is stimulated following TBI and may suggest a mechanism for the temporal increase of Abeta levels observed in patients with brain trauma.