ACAT1 regulates the dynamics of free cholesterols in plasma membrane which leads to the APP-α-processing alteration

Abstract

Acyl-CoA:cholesterol acyltransferase 1 (ACAT1) is a key enzyme exclusively using free cholesterols as the substrates in cell and is involved in the cellular cholesterol homeostasis. In this study, we used human neuroblastoma cell line SK-N-SH as a model and first observed that inhibiting ACAT1 can decrease the amyloid precursor protein (APP)-α-processing. Meanwhile, the transfection experiments using the small interfering RNA and expression plasmid of ACAT1 indicated that ACAT1 can dependently affect the APP-α-processing. Furthermore, inhibiting ACAT1 was found to increase the free cholesterols in plasma membrane (PM-FC), and the increased PM-FC caused by inhibiting ACAT1 can lead to the decrease of the APP-α-processing, indicating that ACAT1 regulates the dynamics of PM-FC, which leads to the alteration of the APP-α-processing. More importantly, further results showed that under the ACAT1 inhibition, the alterations of the PM-FC and the subsequent APP-α-processing are not dependent on the cellular total cholesterol level, confirming that ACAT1 regulates the dynamics of PM-FC. Finally, we revealed that even when the Niemann-Pick-Type C-dependent pathway is blocked, the ACAT1 inhibition still obviously results in the PM-FC increase, suggesting that the ACAT1-dependent pathway is responsible for the shuttling of PM-FC to the intracellular pool. Our data provide a novel insight that ACAT1 which enzymatically regulates the dynamics of PM-FC may play important roles in the human neuronal cells.

Intracellular Cholesterol Trafficking and Impact in Neurodegeneration

“…Indeed, this outcome of increased lipid droplets is consistent with the presence of higher activity of ACAT1, a MAM-resident protein, in both PSEN1-mutant cells and in cells from AD-patients compared with controls, correlating with increased lipid droplets (Area-Gomez et al, 2012 ). These findings are also consistent with the observation that ACAT1 activity is necessary for the production of Aβ (Puglielli et al, 2004 ; Murphy et al, 2013 ; Zhu et al, 2015 ). For instance, both human fibroblasts and explanted mouse neurons treated with astrocyte-conditioned medium containing ApoE4 show a significant increase of MAM activity measured by both MAM-mediated phospholipid transport and ACAT1-mediated cholesteryl ester synthesis and lipid droplet formation (Tambini et al, 2016 ), suggesting a link between upregulation in MAM function and ApoE4 as a risk factor of AD (Figure 4 ).…”

27-Hydroxycholesterol Promotes the Transfer of Astrocyte-Derived Cholesterol to Neurons in Co-cultured SH-SY5Y Cells and C6 Cells

“…This might explain, from one aspect, the neurotoxic effect of elevated 27-OHC levels on AD-related pathological changes such as Aβ deposition, hyperphosphorylated tau tangles, and cell apoptosis in the brain (Huang et al, 2016;Panahi et al, 2016;Chang et al, 2017). Meanwhile, cholesterol esterifying activity was enhanced in neurons after 27-OHC treatment through the up-regulated protein expression of ACAT1, also called SOAT1 (Zhu et al, 2015), a rate-limiting enzyme responsible for the esterification process of cholesterol mainly expressed in neurons.…”

Cellular cholesterol homeostasis and Alzheimer's disease

“…Thus, it has been proposed by several investigators that the toxicity of A may be produced, in part, by disturbing the lipid raft domains present in various membrane organelles. While A can affect the structure and function of raft domains, the converse is also true: the enzymes involved in the APP processing pathway [i.e., the , , and  secretases (176)(177)(178)(179), as well as APP itself (180)] have all been reported to be affected by the composition of the lipid raft domains in which they reside [Reviewed in (191)]. The fate of APP itself is a complicated matter; in addition to its cleavages by the secretases, a significant fraction of APP and its C-terminal fragments can also be degraded by lysosomal hydrolases (181,182).…”