Author ORCID Identifier

Date of Award

Spring 3-7-2023

Document Type

Thesis (Ph.D.)

Department or Program

Biochemistry and Cell Biology

First Advisor

Ta Yuan Chang


Cholesterol is an important component of all mammalian cell membranes. It governs the membrane’s physical properties and creates the membrane order and heterogeneity required for complex membrane-related processes. Tight regulation of cholesterol levels and distribution are necessary for maintaining proper cell health. Likewise, disruptions in cholesterol homeostasis have been implicated in a variety of diseases, including Alzheimer’s disease (AD). Our lab, and others, have demonstrated the benefits of blocking acyl-CoA:cholesterol acyltransferase1/sterol O:acyltransferase 1 (ACAT1/SOAT1) in AD models by genetic ablation or pharmacological inhibition. We understand that blocking ACAT1/SOAT1 activity reduces amyloid and tau pathology, and that this is, at least in part, due to an upregulation of autophagy and lysosomal biogenesis, however, the exact molecular events linking ACAT1/SOAT1 inhibition with disease rescue remain unknown.

Here, we report the initial molecular and cellular events that occur immediately downstream of acute ACAT1/SOAT1 inhibition with small molecule inhibitors K-604 and F12511. ACAT1/SOAT1 inhibition leads to cholesterol accumulation in the metabolically important subdomain of the endoplasmic reticulum (ER) known as the mitochondria-associated ER membrane (MAM). This cholesterol accumulation coincides with selective enrichment of ACAT1/SOAT1 in the MAM domain and ultimately results in the strengthening of the ER-mitochondria contact site.

We also report that ACAT1/SOAT1 activity has a broad impact on lipid metabolism. ACAT1/SOAT1 inhibition with small-molecule inhibitor K-604, but not small-molecule inhibitor F12511, leads to broad upregulation of glycerolipid synthesis. The K-604 upregulation of glycerolipid synthesis depends on the presence of ACAT1/SOAT1 while F12511 appears to have an off-target effect. Additionally, ACAT1/SOAT1 knockout replicates the glycerolypid synthesis response seen with K-604 treatment. The ACAT1/SOAT1 blockade-dependent upregulation of glycerolipid synthesis is likely explained by GPAT sensitivity to local cholesterol levels.

These results indicate that cholesterol accumulation at the MAM is the first downstream response to ACAT1/SOAT1 inhibition and serves as the impetus behind the previously reported beneficial responses to ACAT1/SOAT1 blockade.

Original Citation

Harned, T.C.; Stan, R.V.; Cao, Z.; Chakrabarti, R.; Higgs, H.N.; Chang, C.C.Y.; Chang, T.Y. Acute ACAT1/SOAT1 Blockade Increases MAM Cholesterol and Strengthens ER-Mitochondria Connectivity. Int. J. Mol. Sci. 2023, 24, 5525.

Available for download on Saturday, March 15, 2025