Inhibiting ACAT1/SOAT1 in Microglia Stimulates Autophagy-Mediated Lysosomal Proteolysis and Increases Aβ1–42 Clearance

Abstract

Acyl-CoA:cholesterol acyltransferase 1 (ACAT1) is a resident endoplasmic reticulum enzyme that prevents the buildup of cholesterol in membranes by converting it to cholesterol esters. Blocking ACAT1 pharmacologically or by Acat1 gene knock-out (KO) decreases amyloidopathy in mouse models for Alzheimer's disease. However, the beneficial actions of ACAT1 blockage to treat Alzheimer's disease remained not well understood. Microglia play essential roles in the proteolytic clearance of amyloid ␤ (A␤) peptides. Here we show that Acat1 gene KO in mouse increases phagocytic uptake of oligomeric A␤1-42 and stimulates lysosomal A␤1-42 degradation in cultured microglia and in vivo. Additional results show that Acat1 gene KO or a specific ACAT1 inhibitor K604 stimulates autophagosome formation and transcription factor EB-mediated lysosomal proteolysis. Surprisingly, the effect of ACAT1 blockage does not alter mTOR signaling or endoplasmic reticulum stress response but can be modulated by agents that disrupt cholesterol biosynthesis. To our knowledge, our current study provides the first example that a small molecule (K604) can promote autophagy in an mTOR-independent manner to activate the coordinated lysosomal expression and regulation network. Autophagy is needed to degrade misfolded proteins/ peptides. Our results implicate that blocking ACAT1 may provide a new way to benefit multiple neurodegenerative diseases.

ACAT1/SOAT1 as a Therapeutic Target for Alzheimer's Disease

“…We found that in cultured mouse microglia, Acat1 KO or an ACAT1 inhibitor K604 ( Figure 1A) [81] upregulated lysosome biogenesis and enhanced degradation of oligomeric Aβ1-42 [99]. We also showed that Acat1 KO in microglia stimulated oligomeric Aβ1-42 clearance in the mouse brain in vivo [99]. These results suggest that in addition to reducing Aβ production, blocking ACAT1 may benefit AD by stimulating Aβ clearance in microglia.…”

“…Recently Shibuya et al in this laboratory investigated whether ACAT1 blockage enhanced oligomeric Aβ1-42 clearance in microglia. We found that in cultured mouse microglia, Acat1 KO or an ACAT1 inhibitor K604 ( Figure 1A) [81] upregulated lysosome biogenesis and enhanced degradation of oligomeric Aβ1-42 [99]. We also showed that Acat1 KO in microglia stimulated oligomeric Aβ1-42 clearance in the mouse brain in vivo [99].…”

“…Shibuya et al in this laboratory found that blocking ACAT1 in cultured microglia by gene KO or by the ACAT1-specific inhibitor K604 increased autophagy as well as TFEB-mediated lysosome biogenesis [99]. Acat1 KO microglia freshly isolated from adult mouse brains were also found to have increased mRNA levels of several genes in the coordinated lysosomal expression and regulation network [99]. Interestingly, ACAT1 blockage caused increases in autophagy and in TFEB-mediated lysosome biogenesis in an mTORindependent manner; in fact, we found that blocking both ACAT1 and mTOR signaling in microglia showed additive effects in autophagy and in lysosome biogenesis [99].…”

“…Acat1 KO microglia freshly isolated from adult mouse brains were also found to have increased mRNA levels of several genes in the coordinated lysosomal expression and regulation network [99]. Interestingly, ACAT1 blockage caused increases in autophagy and in TFEB-mediated lysosome biogenesis in an mTORindependent manner; in fact, we found that blocking both ACAT1 and mTOR signaling in microglia showed additive effects in autophagy and in lysosome biogenesis [99]. Previous studies have shown that in mouse models of AD, inhibiting mTOR by rapamycin administration increases autophagy in the brain, reduces Aβ1-42 levels possibly by enhancing Aβ1-42 clearance and rescues cognitive deficits [109,110].…”

“…Inhibition of mTOR signaling activates TFEB pathway to promote both auto phagosome formation and lysosome biogenesis [106][107][108]. Shibuya et al in this laboratory found that blocking ACAT1 in cultured microglia by gene KO or by the ACAT1-specific inhibitor K604 increased autophagy as well as TFEB-mediated lysosome biogenesis [99]. Acat1 KO microglia freshly isolated from adult mouse brains were also found to have increased mRNA levels of several genes in the coordinated lysosomal expression and regulation network [99].…”