Control of ACAT2 Liver Expression by HNF4α Lesson From MODY1 Patients

Objective-ACAT2 is thought to be responsible for cholesteryl ester production in chylomicron and VLDL assembly. Recently, we identified HNF1 alpha as an important regulator of the human ACAT2 promoter. Thus, we hypothesized that MODY3 (HNF1 alpha gene mutations) and possibly MODY1 (HNF4 alpha, upstream regulator of HNF1 alpha, gene mutations) subjects may have lower VLDL esterified cholesterol. Methods and Results-Serum analysis and lipoprotein separation using size-exclusion chromatography were performed in controls and MODY1 and MODY3 subjects. In vitro analyses included mutagenesis and cotransfections in HuH7 cells. Finally, the relevance in vivo of these findings was tested by ChIP assays in human liver. Whereas patients with MODY3 had normal lipoprotein composition, those with MODY1 had lower levels of VLDL and LDL esterified cholesterol, as well as of VLDL triglyceride. Mutagenesis revealed one important HNF4 binding site in the human ACAT2 promoter. ChIP assays and protein-to-protein interaction studies showed that HNF4 alpha, directly or indirectly (via HNF1 alpha), can bind to the ACAT2 promoter. Conclusions-We identified HNF4 alpha as an important regulator of the hepatocyte-specific expression of the human ACAT2 promoter. Our results suggest that the lower levels of esterified cholesterol in VLDL- and LDL-particles in patients with MODY1 may-at least in part-be attributable to lower ACAT2 activity in these patients. (Arterioscler Thromb Vasc Biol. 2009; 29: 1235-1241.)