APOE and Alzheimer disease: Lipid metabolism has been a focus in AD research, with previous study7 showing that astrocytes use 3‐Hydroxy‐3‐Methylglutaryl‐CoA Reductase (HMGCR) to produce cholesterol from acetyl coenzyme A. Cholesterol, phospholipids, Apolipoprotein E (APOE), and Clusterin (CLU) combine to form high‐density lipoprotein complex, which is secreted out of astrocytes by ATP‐binding cassette transporter A1/7 (ABCA1, ABCA7).