Abstract
Cholesterol is a major and essential component of the mammalian cell plasma membrane (PM), and the loss of cholesterol homeostasis leads to various pathologies. Cellular cholesterol uptake and synthesis are regulated by a cholesterol sensor in the endoplasmic reticulum (ER). However, it remains unclear how changes in the cholesterol level of the PM are recognized. Here, we show that the sensing of cholesterol in the PM depends on ABCA1 and the cholesterol transfer protein Aster-A, which cooperatively maintain the asymmetric transbilayer cholesterol distribution in the PM. We demonstrate that ABCA1 translocates (flops) cholesterol from the inner leaflet of the PM to the outer leaflet of the PM to maintain a low inner leaflet cholesterol level. We also found that when inner cholesterol levels were increased, Aster-A was recruited to the PM-ER contact site to transfer cholesterol to the ER. These results suggest that ABCA1 could promote an asymmetric cholesterol distribution to suppress Aster-A recruitment to the PM-ER contact site to maintain intracellular cholesterol homeostasis.