Acyl-coenzyme A:cholesterol acyltransferase-2 (ACAT-2) is responsible for elevated intestinal ACAT activity in diabetic rats.

OBJECTIVE: Diabetes-induced dyslipidemia is seen in streptozotocin-induced diabetic rats. This is caused, in part, by elevated intestinal acyl-coenzyme A:cholesterol acyltransferase (ACAT) activity. Because two ACAT isozymes (ACAT-1 and ACAT-2) were identified, in the present study we determined which ACAT isozyme was involved in the elevated intestinal ACAT activity in diabetic rats. METHODS AND RESULTS: We cloned a full-length cDNA of rat ACAT-2. Its overexpression in ACAT-deficient AC29 cells demonstrated that the ACAT activity is derived from the cloned cDNA, and a 45-kDa protein of rat ACAT-2 cross-reacts with an anti-human ACAT-2 antibody. The tissue distribution of rat ACAT-2 mRNA revealed its restricted expression to liver and small intestine. Immunohistochemical analyses using an anti-human ACAT-2 antibody demonstrated that ACAT-2 is localized in villus-crypt axis of rat small intestine. The intestinal ACAT activity in diabetic rats was significantly immunodepleted by an anti-ACAT-2 antibody but not by an anti-ACAT-1 antibody. Finally, intestinal ACAT-2 in diabetic rats significantly increased at both protein and mRNA levels as compared with that in control rats. CONCLUSIONS: Our data demonstrate that ACAT-2 isozyme is responsible for the increased intestinal ACAT activity of diabetic rats, suggesting an important role of ACAT-2 for dyslipidemia in diabetic patients. Diabetic rats exhibit dyslipidemia caused, in part, by elevated intestinal acyl-coenzyme A:cholesterol acyltransferase (ACAT) activity. We determined which ACAT isozyme (ACAT-1 or ACAT-2) was involved in the elevated intestinal ACAT activity in diabetic rats. We demonstrated an important role of ACAT-2, implicating its involvement in dyslipidemia in diabetic patients.

Up-regulation of acyl-coenzyme A:cholesterol acyltransferase-1 by transforming growth factor-beta1 during differentiation of human monocytes into macrophages.

Expression of acyl-coenzyme A:cholesterol acyltransferase-1 (ACAT-1) increases during differentiation of human monocytes into macrophages. To further elucidate the mechanism for ACAT-1 regulation in macrophages, we examined the effects of five cytokines including transforming growth factor-beta1 (TGF- beta1) on ACAT-1 expression in cultured human monocyte-macrophages. Immunoblot analyses showed that TGF-beta1 increased ACAT-1 protein expression by two- to threefold when added during differentiation of human monocytes into macrophages. ACAT activity increased in parallel by 1.8-fold. Northern blot analyses revealed that among the three ACAT-1 mRNA transcripts detected (2.8-, 3.6-, and 4.3-kb), the 2.8- and 3.6-kb transcripts were selectively increased by TGF-beta1. When TGF-beta1 was added after differentiation, ACAT-1 expression was not altered. Since TGF-beta1 is expressed in human atherosclerotic lesions, the current results suggest that ACAT-1 expression in monocytes infiltrating from the circulation to vascular walls may be enhanced by pre-existing TGF-beta1.

Acyl-coenzyme A:cholesterol acyltransferase 2 (ACAT2) is induced in monocyte-derived macrophages: in vivo and in vitro studies.

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.