Traumatic brain injury induces biphasic upregulation of ApoE and ApoJ protein in rats

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Abstract

Apolipoproteins play an important role in cell repair and have been found to increase shortly after traumatic brain injury (TBI). In addition, apolipoproteins reduce amyloid-β (Aβ) accumulation in models of Alzheimer's disease. Considering that TBI induces progressive neurodegeneration including Aβ accumulation, we explored potential long-term changes in the gene and protein expression of apolipoproteins E and J (ApoE and J) over 6 months after injury. Anesthetized male Sprague-Dawley rats were subjected to parasagittal fluid-percussion brain injury and their brains were evaluated at 2, 4, 7, 14 days, and 1 and 6 months after TBI. In situ hybridization, Western blot, and immunohistochemical analysis demonstrated that although there was a prolonged upregulation in both the gene expression and protein concentration of ApoE and J after injury, these responses were uncoupled. Upregulation of ApoE and J mRNA expression lasted from 4 days to 1 month after injury. In contrast, a biphasic increase in protein concentration and number of immunoreactive cells for ApoE and ApoJ was observed, initially peaking at 2 days (i.e., before increased mRNA expression), returning to baseline by 2 weeks and then gradually increasing through 6 months postinjury. In addition, ApoE and J were found to colocalize with Aβ accumulation in neurons and astrocytes at 1–6 months after injury. Collectively, these data suggest that ApoE and J play a role in the acute sequelae of brain trauma and reemerge long after the initial insult, potentially to modulate progressive neurodegenerative changes. © 2005 Wiley-Liss, Inc.

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