Expression of annexin II in experimental abdominal aortic aneurysms.

Annexin II is a receptor of tissue-type plasminogen activator (t-PA). We have previously identified annexin II by immunolocalization in human atherosclerotic abdominal aortic aneurysms (AAAs). To investigate possible interactions between annexin II and AAA development, we examined annexin II mRNA and protein expression in a rat model of experimental AAA. AAAs were induced in rats by transient aortic infusion of elastase. The rats were divided into three groups: a saline-treated control group, a group with 15-min elastase infusion, and a group with 30-min elastase infusion. The 15-min elastase-infused group had smaller aneurysms and more preserved media than the 30-min elastase-infused group. Immunohistochemistry showed that annexin II expression was increased in the thickened intima and media of AAA rats as compared with the media of control rats. Furthermore, annexin II was colocalized with macrophages and smooth muscle cells. Quantitative real-time polymerase chain reaction showed that annexin II mRNA levels were up-regulated only in the smaller aneurysm group compared with the control group. In contrast, t-PA mRNA levels were increased in both the 15- and 30-min elastase-infused groups as compared with the control group. These results demonstrate various levels of annexin II expression within the aortic wall of rats with experimental AAAs. It has been suggested that alteration of fibrinolytic activity regulated by annexin II within the aortic wall may be associated with aneurysm formation.