1. ¹Second Department of Pathology, Kumamoto University School of Medicine, Kumamoto, Japan
2. ²Department of Biochemistry, Kumamoto University School of Medicine, Kumamoto, Japan
3. ³Department of Biochemistry, Showa University School of Medicine, Tokyo, Japan
4. ⁴Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire
5. ⁵Department of Microbiology, Dartmouth Medical School and Veteran's Administration Hospital, White River Junction, Vermont

Correspondence: Dr. Naomi Sakashita, Department of Biochemistry, Dartmouth Medical School, 7200 Vail Building, Room 304, Hanover, New Hampshire 03755. E-mail: Naomi.Sakashita@Dartmouth.edu

Received 11 July 2003.

Abstract

To test the possibility that acyl-coenzyme A:cholesterol acyltransferase 2 (ACAT2) may be expressed in human macrophages under pathologic conditions, we employed specific anti-ACAT2 antibodies and found clear ACAT2 signals in lipid-laden as well as lipid-free macrophages under various disease conditions, including atherosclerosis. However, no ACAT2 signal was detectable in macrophages under normal physiologic conditions. Using cultured human macrophages derived from blood-borne monocytes, immunoblot and RT-PCR analyses demonstrated that immature macrophages expressed only ACAT1, but the fully differentiated macrophages expressed both ACAT1 and ACAT2. Furthermore, RT-PCR clearly revealed the presence of both ACAT1 and ACAT2 mRNAs in human atherosclerotic aorta. Double immunohistochemical staining indicated that in human atherosclerotic aorta, all macrophages expressed ACAT1, while approximately 70% to 80% of macrophages also expressed ACAT2. In congenital hyperlipidemic mice, immunohistochemistry and RT-PCR demonstrated that ACAT2 was also present in lipid-laden cells of the atheromatous plaques. Our results suggest that in atherosclerotic plaque, the ability of macrophage foam cell transformation may be augmented by the dual expressions of ACAT1 and ACAT2. Additional immunoblot and RT-PCR experiments showed that the ACAT2 signal was clearly detectable in thioglycollate-elicited exudate mouse macrophages but not in peritoneal resident macrophages. We conclude that under various pathologic conditions, fully differentiated macrophages express ACAT2 in addition to ACAT1.