Inhibiting the Cholesterol Storage Enzyme ACAT1/SOAT1 in Myelin Debris-Treated Microglial Cell Lines Activates the
Thao N Huynh1, Matthew C Havrda2, George J Zanazzi3
1Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755, USA.
Abstract:
Aging is the major risk factor for Alzheimer's disease (AD). In the aged brain, myelin debris accumulates and is cleared by microglia. Phagocytosed myelin debris increases neutral lipid droplet content in microglia. Neutral lipids include cholesteryl esters (CE) and triacylglycerol (TAG). To examine the effects of myelin debris on neutral lipid content in microglia, we added myelin debris to human HMC3 and mouse N9 cells. The results obtained when using 3H-oleate as a precursor in intact cells reveal that myelin debris significantly increases the biosynthesis of CE but not TAG. Mass analyses have shown that myelin debris increases both CE and TAG. The increase in CE biosynthesis was abolished using inhibitors of the cholesterol storage enzyme acyl-CoA:cholesterol acyltransferase 1 (ACAT1/SOAT1). ACAT1 inhibitors are promising drug candidates for AD treatment. In myelin debris-loaded microglia, treatment with two different ACAT1 inhibitors, K604 and F12511, increased the mRNA and protein content of ATP-binding cassette subfamily A1 (ABCA1), a protein that is located at the plasma membrane and which controls cellular cholesterol disposal. The effect of the ACAT1 inhibitor on ABCA1 was abolished by preincubating cells with the liver X receptor (LXR) antagonist GSK2033. We conclude that ACAT1 inhibitors prevent the accumulation of cholesterol and CE in myelin debris-treated microglia by activating ABCA1 gene expression via the LXR pathway.
Insights
Myelin debris in aging brains increases harmful cholesterol esters in microglia. Inhibiting acyl-CoA:cholesterol acyltransferase 1 (ACAT1) reduces this buildup, offering a potential Alzheimer
Area of Science:
- Neuroscience
- Cell Biology
- Biochemistry
Background:
- Aging is a primary risk factor for Alzheimer's disease (AD).
- Microglia clear myelin debris in the aged brain, leading to increased neutral lipids like cholesteryl esters (CE) and triacylglycerol (TAG) within these cells.
- Accumulation of these lipids in microglia is implicated in AD pathogenesis.
Purpose of the Study:
- To investigate the impact of myelin debris on neutral lipid metabolism in microglia.
- To explore the potential of acyl-CoA:cholesterol acyltransferase 1 (ACAT1) inhibitors as a therapeutic strategy for AD by modulating lipid accumulation.
Main Methods:
- Human HMC3 and mouse N9 microglial cells were treated with myelin debris.
- Lipid biosynthesis was assessed using 3H-oleate precursor and mass analysis.
- ACAT1 inhibitors (K604, F12511) and an LXR antagonist (GSK2033) were used to study molecular mechanisms.
- Gene and protein expression of ATP-binding cassette subfamily A1 (ABCA1) was quantified.
Main Results:
- Myelin debris significantly increased cholesteryl ester (CE) biosynthesis and overall CE and triacylglycerol (TAG) content in microglia.
- Inhibition of ACAT1 abolished the increase in CE biosynthesis.
- ACAT1 inhibitors upregulated both mRNA and protein levels of ABCA1, a cholesterol efflux transporter.
- The ACAT1 inhibitor's effect on ABCA1 was dependent on the liver X receptor (LXR) pathway.
Conclusions:
- ACAT1 inhibitors effectively reduce cholesterol and CE accumulation in myelin debris-laden microglia.
- These inhibitors activate ABCA1 expression through the LXR pathway, promoting cholesterol disposal.
- Targeting ACAT1 represents a promising therapeutic avenue for Alzheimer's disease by mitigating microglial lipid dysregulation.
