Acyl Coenzyme A:Cholesterol Acyltransferase (ACAT) in Macrophage-Derived Foam Cells and Its Distribution in Human Organs.

Acyl coenzyme A:cholesterol acyltransferase(ACAT) is a critical enzyme participating in both intracellular cholesterol homeostasis and systemic sterol metabolism and are classified into two ACAT−isozymes termed ACAT−1 and ACAT−2. In humans, ACAT−1 is expressed ubiquitously in a variety of cells such as macrophages, enterocytes/hepatocytes, and steroid hormone−producing cells. In macrophages, immunoelectron microscopic examination revealed that ACAT−1 is localized in the endoplasmic reticulum(ER). When the cells are exposed to modified low density lipoprotein to induce foam cell transformation, a portion of ACAT−1 is shifted from ER to ER−derived small vesicles. The histological distribution of ACAT−2 in humans is still unclear, but recent data demonstrated that this isozyme is expressed in enterocytes.