Delayed, but marked, expression of apolipoprotein E is involved in tissue clearance after cerebral infarction

Clearance of infarct tissue would be an important process for tissue repair after a stroke. Delayed clearance may hamper reconstitution of the blood-b rain barrier and glial boundary formation. Recent growing evidence has indi cated that apolipoprotein E (APOE), a major apoprotein, plays an important role in lipid transport and homeostasis in the brain. The tissue in the inf arction contains abundant lipids must be removed for tissue clearance. In t he current study, the authors investigated APOE expression after focal isch emia and the functional role of APOE in tissue clearance using APOE-knockou t mice. Expression of APOE was delayed, but marked, in immunohistochemistry and immunoblotting 7 days after permanent focal ischemia. Macrophages were found to express APOE in the infarct center. Infarct size was similar afte r focal ischemia between wild-type and APOE-knockout mice, although there w as no APOE protein expression in knockout mice. However, clearance of infar ct tissue 2 weeks after ischemia was significantly delayed in APOE-knockout mice compared with wild-type mice. The current study supports current thin king that APOE is a key molecule for tissue remodeling in the brain. Cleara nce of damaged tissue may be one of the important functions of APOE in the brain.