Increased Severity of Hemorrhage in Transgenic Mice Expressing Cerebral Protease Nexin-2/Amyloid β-Protein Precursor

BACKGROUND AND PURPOSE: Secreted isoforms of amyloid beta-protein precursor (AbetaPP) that contain the Kunitz proteinase inhibitor domain, also known as protease nexin-2 (PN2), are enriched in brain. Although little is known of its physiological function, the potent inhibition of certain prothrombotic proteinases by PN2/AbetaPP suggests that it may function to regulate cerebral thrombosis during vascular injury events. METHODS: To examine the antithrombotic function of cerebral PN2/AbetaPP in vivo, we performed measurements of carotid artery thrombosis and experimental intracerebral hemorrhage in transgenic mice with specific and modest overexpression of PN2/AbetaPP in brain. Comparisons were made with wild-type mice and Tg-rPF4/APP mice, a model that possesses specific and modest overexpression of PN2/AbetaPP in platelets and exhibits reduced thrombosis in vivo. RESULTS: Modest overexpression of PN2/AbetaPP in transgenic mouse brain had no effect on intraluminal carotid arterial thrombosis but resulted in larger hematoma volumes and hemoglobin levels (23.1+/-2.7 mm(3) [n=6; P<0.01] and 1411+/-202 microg/hemisphere [n=12; P<0.01], respectively), compared with wild-type mice (15.9+/-2.2 mm(3) [n=6] and 935+/-418 microg/hemisphere [n=12], respectively). CONCLUSIONS: These findings indicate that cerebral PN2/AbetaPP plays a significant role in regulating thrombosis in brain and that modest age-related increases in the cerebral levels of this protein could markedly enhance the extent of cerebral hemorrhage.