Upregulation of tPA/plasminogen proteolytic system in the periphery of amyloid deposits in the Tg2576 mouse model of Alzheimer's disease

Although the tissue plasminogen activator (tPA)/plasminogen/plasmin proteolytic system is thought to modulate the catabolism of arnyloid-beta (A beta), in vivo evidence remains insufficient. In the brain of human amyloid precursor protein transgenic Tg2576 mice, we found co-accumulation of tPA and plasminogen at the periphery of compact amyloid deposits, mainly A beta 42-cored plaques, as well as in the walls of blood vessels with cerebral amyloid angiopathy (CAA). This tPAlplasminogen system contained high levels of proteolytic activity. High levels of tPA were also found in reactive astrocytes with increased A beta 42 expression, whereas plasminogen was found only in neurons. When the brain sections of Tg2576 mice were treated with both tPA and plasminogen, levels of thioflavin-S fluorescence, congophilicity and birefringence in the compact amyloid plaques were significantly reduced, and the ultrastructure of A beta 42-fibrils was disrupted. These results suggest that the assembled A beta 42 may promote upregulation of the tPA/plasminogen proteolytic system, which can modulate the deposition of amyloid plaques in vivo. (C) 2007 Elsevier Ireland Ltd. All rights reserved.