Sterol O-Acyltransferase 1 (SOAT1): A Genetic Modifier of Niemann-Pick Disease, Type C1.

Niemann-Pick disease type C1 (NPC1) is a lysosomal disorder due to impaired intracellular cholesterol transport out of the endolysosomal compartment.. Marked heterogeneity has been observed in individuals with the same NPC1 genotype, thus suggesting a significant effect of modifier genes. Prior work demonstrated that decreased SOAT1 activity decreased disease severity in an NPC1 mouse model. Thus, we hypothesized that a polymorphism associated with decreased SOAT1 expression might influence the NPC1 phenotype. Phenotyping and genomic sequencing of 117 individuals with NPC1 was performed as part of a Natural History trial. Phenotyping included determination of disease severity and disease burden. Significant clinical heterogeneity is present in individuals homozygous for the NPC1I1061T variant and in siblings. Analysis of the SOAT1 polymorphism, rs1044925 (A>C), showed a significant association of the C-allele with earlier age of neurological onset. The C-allele may be associated with a higher Annualized Severity Index Score as well as increased frequency of liver disease and seizures. A polymorphism associated with decreased expression of SOAT1 appears to be a genetic modifier of the NPC1 phenotype. This finding is consistent with prior data showing decreased phenotypic severity in Npc1-/-:Soat1-/- mice and supports efforts to investigate the potential of SOAT1 inhibitors as a potential therapy for NPC1.

Characterization of Stealth Liposome-Based Nanoparticles Encapsulating the ACAT1/SOAT1 Inhibitor F26: Efficacy and Toxicity Studies In Vitro and in Wild-Type Mice.

Cholesterol homeostasis is pivotal for cellular function. Acyl-coenzyme A:cholesterol acyltransferase 1 (ACAT1), also abbreviated as SOAT1, is an enzyme responsible for catalyzing the storage of excess cholesterol to cholesteryl esters. ACAT1 is an emerging target to treat diverse diseases including atherosclerosis, cancer, and neurodegenerative diseases. F12511 is a high-affinity ACAT1 inhibitor. Previously, we developed a stealth liposome-based nanoparticle to encapsulate F12511 to enhance its delivery to the brain and showed its efficacy in treating a mouse model for Alzheimer's disease (AD). In this study, we introduce F26, a close derivative of F12511 metabolite in rats. F26 was encapsulated in the same DSPE-PEG2000/phosphatidylcholine (PC) liposome-based nanoparticle system. We employed various in vitro and in vivo methodologies to assess F26's efficacy and toxicity compared to F12511. The results demonstrate that F26 is more effective and durable than F12511 in inhibiting ACAT1, in both mouse embryonic fibroblasts (MEFs), and in multiple mouse tissues including the brain tissues, without exhibiting any overt systemic or neurotoxic effects. This study demonstrates the superior pharmacokinetic and safety profile of F26 in wild-type mice, and suggests its therapeutic potential against various neurodegenerative diseases including AD.

Acute ACAT1/SOAT1 Blockade Increases MAM Cholesterol and Strengthens ER-Mitochondria Connectivity.

Cholesterol is a key component of all mammalian cell membranes. Disruptions in cholesterol metabolism have been observed in the context of various diseases, including neurodegenerative disorders such as Alzheimer's disease (AD). The genetic and pharmacological blockade of acyl-CoA:cholesterol acyltransferase 1/sterol O-acyltransferase 1 (ACAT1/SOAT1), a cholesterol storage enzyme found on the endoplasmic reticulum (ER) and enriched at the mitochondria-associated ER membrane (MAM), has been shown to reduce amyloid pathology and rescue cognitive deficits in mouse models of AD. Additionally, blocking ACAT1/SOAT1 activity stimulates autophagy and lysosomal biogenesis; however, the exact molecular connection between the ACAT1/SOAT1 blockade and these observed benefits remain unknown. Here, using biochemical fractionation techniques, we observe cholesterol accumulation at the MAM which leads to ACAT1/SOAT1 enrichment in this domain. MAM proteomics data suggests that ACAT1/SOAT1 inhibition strengthens the ER-mitochondria connection. Confocal and electron microscopy confirms that ACAT1/SOAT1 inhibition increases the number of ER-mitochondria contact sites and strengthens this connection by shortening the distance between these two organelles. This work demonstrates how directly manipulating local cholesterol levels at the MAM can alter inter-organellar contact sites and suggests that cholesterol buildup at the MAM is the impetus behind the therapeutic benefits of ACAT1/SOAT1 inhibition.

Stealth Liposomes Encapsulating a Potent ACAT1/SOAT1 Inhibitor F12511: Pharmacokinetic, Biodistribution, and Toxicity Studies in Wild-Type Mice and Efficacy Studies in Triple Transgenic Alzheimer's Disease Mice.

Cholesterol is essential for cellular function and is stored as cholesteryl esters (CEs). CEs biosynthesis is catalyzed by the enzymes acyl-CoA:cholesterol acyltransferase 1 and 2 (ACAT1 and ACAT2), with ACAT1 being the primary isoenzyme in most cells in humans. In Alzheimer's Disease, CEs accumulate in vulnerable brain regions. Therefore, ACATs may be promising targets for treating AD. F12511 is a high-affinity ACAT1 inhibitor that has passed phase 1 safety tests for antiatherosclerosis. Previously, we developed a nanoparticle system to encapsulate a large concentration of F12511 into a stealth liposome (DSPE-PEG2000 with phosphatidylcholine). Here, we injected the nanoparticle encapsulated F12511 (nanoparticle F) intravenously (IV) in wild-type mice and performed an HPLC/MS/MS analysis and ACAT enzyme activity measurement. The results demonstrated that F12511 was present within the mouse brain after a single IV but did not overaccumulate in the brain or other tissues after repeated IVs. A histological examination showed that F12511 did not cause overt neurological or systemic toxicity. We then showed that a 2-week IV delivery of nanoparticle F to aging 3xTg AD mice ameliorated amyloidopathy, reduced hyperphosphorylated tau and nonphosphorylated tau, and reduced neuroinflammation. This work lays the foundation for nanoparticle F to be used as a possible therapy for AD and other neurodegenerative diseases.

PACS-2 deficiency in tubular cells aggravates lipid-related kidney injury in diabetic kidney disease.

BACKGROUND: Lipid accumulation in tubular cells plays a key role in diabetic kidney disease (DKD). Targeting lipid metabolism disorders has clinical value in delaying the progression of DKD, but the precise mechanism by which molecules mediate lipid-related kidney injury remains unclear. Phosphofurin acidic cluster sorting protein 2 (PACS-2) is a multifunctional sorting protein that plays a role in lipid metabolism. This study determined the role of PACS-2 in lipid-related kidney injury in DKD. METHODS: Diabetes was induced by a high-fat diet combined with intraperitoneal injections of streptozotocin (HFD/STZ) in proximal tubule-specific knockout of Pacs-2 mice (PT-Pacs-2-/- mice) and the control mice (Pacs-2fl/fl mice). Transcriptomic analysis was performed between Pacs-2fl/fl mice and PT-Pacs-2-/- mice. RESULTS: Diabetic PT-Pacs-2-/- mice developed more severe tubule injury and proteinuria compared to diabetic Pacs-2fl/fl mice, which accompanied with increasing lipid synthesis, uptake and decreasing cholesterol efflux as well as lipid accumulation in tubules of the kidney. Furthermore, transcriptome analysis showed that the mRNA level of sterol O-acyltransferase 1 (Soat1) was up-regulated in the kidney of control PT-Pacs-2-/- mice. Transfection of HK2 cells with PACS-2 siRNA under high glucose plus palmitic acid (HGPA) condition aggravated lipid deposition and increased the expression of SOAT1 and sterol regulatory element-binding proteins (SREBPs), while the effect was blocked partially in that of co-transfection of SOAT1 siRNA. CONCLUSIONS: PACS-2 has a protective role against lipid-related kidney injury in DKD through SOAT1/SREBPs signaling.

High-affinity SOAT1 ligands remodeled cholesterol metabolism program to inhibit tumor growth.

BACKGROUND: Although cholesterol metabolism is a common pathway for the development of antitumor drugs, there are no specific targets and drugs for clinical use. Here, based on our previous study of sterol O-acyltransferase 1 (SOAT1) in hepatocelluar carcinoma, we sought to screen an effective targeted drug for precise treatment of hepatocelluar carcinoma and, from the perspective of cholesterol metabolism, clarify the relationship between cholesterol regulation and tumorigenesis and development. METHODS: In this study, we developed a virtual screening integrated affinity screening technology for target protein drug screening. A series of in vitro and in vivo experiments were used for drug activity verification. Multi-omics analysis and flow cytometry analysis were used to explore antitumor mechanisms. Comparative analysis of proteome and transcriptome combined with survival follow-up information of patients reveals the clinical therapeutic potential of screened drugs. RESULTS: We screened three compounds, nilotinib, ABT-737, and evacetrapib, that exhibited optimal binding with SOAT1. In particular, nilotinib displayed a high affinity for SOAT1 protein and significantly inhibited tumor activity both in vitro and in vivo. Multi-omics analysis and flow cytometry analysis indicated that SOAT1-targeting compounds reprogrammed the cholesterol metabolism in tumors and enhanced CD8+ T cells and neutrophils to suppress tumor growth. CONCLUSIONS: Taken together, we reported several high-affinity SOAT1 ligands and demonstrated their clinical potential in the precision therapy of liver cancer, and also reveal the potential antitumor mechanism of SOAT1-targeting compounds.

SOAT1: A Suitable Target for Therapy in High-Grade Astrocytic Glioma?

Targeting molecular alterations as an effective treatment for isocitrate dehydrogenase-wildtype glioblastoma (GBM) patients has not yet been established. Sterol-O-Acyl Transferase 1 (SOAT1), a key enzyme in the conversion of endoplasmic reticulum cholesterol to esters for storage in lipid droplets (LD), serves as a target for the orphan drug mitotane to treat adrenocortical carcinoma. Inhibition of SOAT1 also suppresses GBM growth. Here, we refined SOAT1-expression in GBM and IDH-mutant astrocytoma, CNS WHO grade 4 (HGA), and assessed the distribution of LD in these tumors. Twenty-seven GBM and three HGA specimens were evaluated by multiple GFAP, Iba1, IDH1 R132H, and SOAT1 immunofluorescence labeling as well as Oil Red O staining. To a small extent SOAT1 was expressed by tumor cells in both tumor entities. In contrast, strong expression was observed in glioma-associated macrophages. Triple immunofluorescence labeling revealed, for the first time, evidence for SOAT1 colocalization with Iba1 and IDH1 R132H, respectively. Furthermore, a notable difference in the amount of LD between GBM and HGA was observed. Therefore, SOAT1 suppression might be a therapeutic option to target GBM and HGA growth and invasiveness. In addition, the high expression in cells related to neuroinflammation could be beneficial for a concomitant suppression of protumoral microglia/macrophages.

The ER membrane protein complex promotes biogenesis of sterol-related enzymes maintaining cholesterol homeostasis.

The eukaryotic endoplasmic reticulum (ER) membrane contains essential complexes that oversee protein biogenesis and lipid metabolism, impacting nearly all aspects of cell physiology. The ER membrane protein complex (EMC) is a newly described transmembrane domain (TMD) insertase linked with various phenotypes, but whose clients and cellular responsibilities remain incompletely understood. We report that EMC deficiency limits the cellular boundaries defining cholesterol tolerance, reflected by diminished viability with limiting or excessive extracellular cholesterol. Lipidomic and proteomic analyses revealed defective biogenesis and concomitant loss of the TMD-containing ER-resident enzymes sterol-O-acyltransferase 1 (SOAT1) and squalene synthase (SQS, also known as FDFT1), which serve strategic roles in the adaptation of cells to changes in cholesterol availability. Insertion of the weakly hydrophobic tail-anchor (TA) of SQS into the ER membrane by the EMC ensures sufficient flux through the sterol biosynthetic pathway while biogenesis of polytopic SOAT1 promoted by the EMC provides cells with the ability to store free cholesterol as inert cholesteryl esters. By facilitating insertion of TMDs that permit essential mammalian sterol-regulating enzymes to mature accurately, the EMC is an important biogenic determinant of cellular robustness to fluctuations in cholesterol availability.This article has an associated First Person interview with the first author of the paper.

Impacts of the SOAT1 genetic variants and protein expression on HBV-related hepatocellular carcinoma.

BACKGROUND: Hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC) remains a major public health problem and its pathogenesis remains unresolved. A recent proteomics study discovered a lipid enzyme Sterol O-acyltransferase (SOAT1) involvement in the progression of HCC. We aimed to explore the association between SOAT1 genetic variation and HCC. METHODS: We genotyped three exonic SOAT1 variants (rs10753191, V323V; rs3753526, L475L; rs13306731, Q526R) tagging most variations in the gene, in 221 HCC patients and 229 healthy individuals, to assess the impact of SOAT1 gene variation on risk of HCC occurrence. We further conducted immunohistochemistry to compare SOAT1 protein expression levels in 42 paired tumor and adjacent non-tumor tissues. RESULTS: We found that rs10753191 (Odds ratio (OR) = 0.58, P = 0.04) and a haplotype TGA (OR = 0.40, P = 0.01) were associated with reduced HCC risk after adjusting for lipid levels. In the immunohistochemistry experiment, we found that the protein expression of SOAT1 was significantly increased in the tumor compared with adjacent tissue (P < 0.001). CONCLUSION: This study revealed for the first time SOAT1 genetic variation that associates with host susceptibility to HCC occurrence. Our results suggest a role of SOAT1 in the HCC development, which warrants further elucidation.

Knockdown of sterol O-acyltransferase 1 (SOAT1) suppresses SCD1-mediated lipogenesis and cancer procession in prostate cancer.

Prostate cancer (PCa) is one of the most fatal malignant tumors that occurs in the prostate epithelium, especially in older men, the mortality of which ranks sixth among all cancer-related deaths. It has been urgently needed to elucidate the pathogenesis of PCa and provide promising therapeutic targets for PCa treatment. The Sterol O-acyltransferase 1 (SOAT1), cholesterol metabolism enzyme, was widely expressed in various cancer tissues, resulting in cancer progression. SOAT1 has been demonstrated to be highly expressed in prostate cancer tissues, whereas the underlying mechanism has not been elucidated. Herein, we found the expression of SOAT1 was elevated in human PCa tissues, which demonstrated SOAT1 level was correlated with lymph node metastasis (p = 0.006), clinical stage (p = 0.032), grading (p = 0.036), and Gleason score (p = 0.030) of PCa patients. In addition, we revealed that SOAT1 promoted proliferation and liposynthesis of PCa cells by targeting Stearoyl-CoA Desaturase 1 (SCD1). Our data further confirmed that SCD1 overexpression reversed the proliferation and liposynthesis defects caused by SOAT1 depletion in PCa cells, however, SOAT1 depletion inhibited tumor growth of PCa cells in mice. We further found SOAT1 contributed to the progression of PCa via SREBF1 pathway. Taken together, our data revealed the mechanism underlying SOAT1 promoting PCa progression in vitro and in vivo.

Depletion of Cholesteryl Esters Causes Meibomian Gland Dysfunction-Like Symptoms in a Soat1-Null Mouse Model.

Previous studies on ablation of several key genes of meibogenesis related to fatty acid elongation, omega oxidation, and esterification into wax esters have demonstrated that inactivation of any of them led to predicted changes in the meibum lipid profiles and caused severe abnormalities in the ocular surface and Meibomian gland (MG) physiology and morphology. In this study, we evaluated the effects of Soat1 ablation that were expected to cause depletion of the second largest class of Meibomian lipids (ML)-cholesteryl esters (CE)-in a mouse model. ML of the Soat1-null mice were examined using liquid chromatography high-resolution mass spectrometry and compared with those of Soat1+/- and wild-type mice. Complete suppression of CE biosynthesis and simultaneous accumulation of free cholesterol (Chl) were observed in Soat1-null mice, while Soat1+/- mutants had normal Chl and CE profiles. The total arrest of the CE biosynthesis in response to Soat1 ablation transformed Chl into the dominant lipid in meibum accounting for at least 30% of all ML. The Soat1-null mice had clear manifestations of dry eye and MG dysfunction. Enrichment of meibum with Chl and depletion of CE caused plugging of MG orifices, increased meibum rigidity and melting temperature, and led to a massive accumulation of lipid deposits around the eyes of Soat1-null mice. These findings illustrate the role of Soat1/SOAT1 in the lipid homeostasis and pathophysiology of MG.

Enhanced acyl-CoA:cholesterol acyltransferase activity increases cholesterol levels on the lipid droplet surface and impairs adipocyte function.

Cholesterol plays essential structural and signaling roles in mammalian cells, but too much cholesterol can cause cytotoxicity. Acyl-CoA:cholesterol acyltransferases 1 and 2 (ACAT1/2) convert cholesterol into its storage form, cholesteryl esters, regulating a key step in cellular cholesterol homeostasis. Adipose tissue can store >50% of whole-body cholesterol. Interestingly, however, almost no ACAT activity is present in adipose tissue, and most adipose cholesterol is stored in its free form. We therefore hypothesized that increased cholesterol esterification may have detrimental effects on adipose tissue function. Here, using several approaches, including protein overexpression, quantitative RT-PCR, immunofluorescence, and various biochemical assays, we found that ACAT1 expression is significantly increased in the adipose tissue of the ob/ob mice. We further demonstrated that ACAT1/2 overexpression partially inhibited the differentiation of 3T3-L1 preadipocytes. In mature adipocytes, increased ACAT activity reduced the size of lipid droplets (LDs) and inhibited lipolysis and insulin signaling. Paradoxically, the amount of free cholesterol increased on the surface of LDs in ACAT1/2-overexpressing adipocytes, accompanied by increased LD localization of caveolin-1. Moreover, cholesterol depletion in adipocytes by treating the cells with cholesterol-deficient media or ß-cyclodextrins induced changes in cholesterol distribution that were similar to those caused by ACAT1/2 overexpression. Our results suggest that ACAT1/2 overexpression increases the level of free cholesterol on the LD surface, thereby impeding adipocyte function. These findings provide detailed insights into the role of free cholesterol in LD and adipocyte function and suggest that ACAT inhibitors have potential utility for managing disorders associated with extreme obesity.

Myeloid Acat1/Soat1 KO attenuates pro-inflammatory responses in macrophages and protects against atherosclerosis in a model of advanced lesions.

Cholesterol esters are a key ingredient of foamy cells in atherosclerotic lesions; their formation is catalyzed by two enzymes: acyl-CoA:cholesterol acyltransferases (ACATs; also called sterol O-acyltransferases, or SOATs) ACAT1 and ACAT2. ACAT1 is present in all body cells and is the major isoenzyme in macrophages. Whether blocking ACAT1 benefits atherosclerosis has been under debate for more than a decade. Previously, our laboratory developed a myeloid-specific Acat1 knockout (KO) mouse (Acat1-M/-M), devoid of ACAT1 only in macrophages, microglia, and neutrophils. In previous work using the ApoE KO (ApoE-/-) mouse model for early lesions, Acat1-M/-M significantly reduced lesion macrophage content and suppressed atherosclerosis progression. In advanced lesions, cholesterol crystals become a prominent feature. Here we evaluated the effects of Acat1-M/-M in the ApoE KO mouse model for more advanced lesions and found that mice lacking myeloid Acat1 had significantly reduced lesion cholesterol crystal contents. Acat1-M/-M also significantly reduced lesion size and macrophage content without increasing apoptotic cell death. Cell culture studies showed that inhibiting ACAT1 in macrophages caused cells to produce less proinflammatory responses upon cholesterol loading by acetyl low-density lipoprotein. In advanced lesions, Acat1-M/-M reduced but did not eliminate foamy cells. In advanced plaques isolated from ApoE-/- mice, immunostainings showed that both ACAT1 and ACAT2 are present. In cell culture, both enzymes are present in macrophages and smooth muscle cells and contribute to cholesterol ester biosynthesis. Overall, our results support the notion that targeting ACAT1 or targeting both ACAT1 and ACAT2 in macrophages is a novel strategy to treat advanced lesions.

Sterol-O-acyltransferase-1 has a role in kidney disease associated with diabetes and Alport syndrome.

Defective cholesterol metabolism primarily linked to reduced ATP-binding cassette transporter A1 (ABCA1) expression is closely associated with the pathogenesis and progression of kidney diseases, including diabetic kidney disease and Alport Syndrome. However, whether the accumulation of free or esterified cholesterol contributes to progression in kidney disease remains unclear. Here, we demonstrate that inhibition of sterol-O-acyltransferase-1 (SOAT1), the enzyme at the endoplasmic reticulum that converts free cholesterol to cholesterol esters, which are then stored in lipid droplets, effectively reduced cholesterol ester and lipid droplet formation in human podocytes. Furthermore, we found that inhibition of SOAT1 in podocytes reduced lipotoxicity-mediated podocyte injury in diabetic kidney disease and Alport Syndrome in association with increased ABCA1 expression and ABCA1-mediated cholesterol efflux. In vivo, Soat1 deficient mice did not develop albuminuria or mesangial expansion at 10-12 months of age. However, Soat1 deficiency/inhibition in experimental models of diabetic kidney disease and Alport Syndrome reduced cholesterol ester content in kidney cortices and protected from disease progression. Thus, targeting SOAT1-mediated cholesterol metabolism may represent a new therapeutic strategy to treat kidney disease in patients with diabetic kidney disease and Alport Syndrome, like that suggested for Alzheimer's disease and cancer treatments.

A phase 1 study of nevanimibe HCl, a novel adrenal-specific sterol O-acyltransferase 1 (SOAT1) inhibitor, in adrenocortical carcinoma.

Background Adrenocortical carcinoma (ACC) is a rare and aggressive malignancy with very limited treatment options. Nevanimibe HCl (formerly ATR-101), a novel adrenal-specific sterol O-acyltransferase 1 (SOAT1) inhibitor, has been shown in nonclinical studies to decrease adrenal steroidogenesis at lower doses and to cause apoptosis of adrenocortical cells at higher doses. Methods This phase 1, multicenter, open-label study assessed the safety and pharmacokinetics (PK) of nevanimibe in adults with metastatic ACC (NCT01898715). A "3 + 3" dose-escalation design was used. Adverse events (AEs), PK, and tumor response based on Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 were evaluated every 2 months. Results 63 patients with metastatic ACC, all of whom had previously failed systemic chemotherapy and only 2 of whom were mitotane-naïve, were dosed with oral nevanimibe at doses ranging from 1.6 mg/kg/day to 158.5 mg/kg/day. Subjects who did not experience tumor progression or a dose-limiting toxicity (DLT) could continue to receive additional cycles. No patients experienced a complete or partial response; however, 13 of the 48 (27%) patients who underwent imaging at 2 months had stable disease (SD), and 4 of these had SD > 4 months. In addition, drug-related adrenal insufficiency, considered a pharmacologic effect of nevanimibe, was observed in two patients. The most common treatment-emergent AEs were gastrointestinal disorders (76%), including diarrhea (44%) and vomiting (35%). A maximum tolerated dose (MTD) could not be defined, as very few dose-limiting toxicities (DLTs) occurred. Because the large number of tablets required at the highest dose (i.e., ~24 tablets/day) resulted in low-grade gastrointestinal adverse effects, a maximum feasible dose of 128.2 mg/kg/day was established as a dose that could be taken on a long-term basis. Conclusions This study demonstrated the safety of nevanimibe at doses of up to ~6000 mg BID. As the total number of tablets required to achieve an MTD exceeded practical administration limits, a maximum feasible dose was defined. Given that the expected exposure levels necessary for an apoptotic effect could not be achieved, the current formulation of nevanimibe had limited efficacy in patients with advanced ACC.

Nonglucuronidated Ezetimibe Disrupts CD13- and CD64-Coassembly in Membrane Microdomains and Decreases Cellular Cholesterol Content in Human Monocytes/Macrophages.

Ezetimibe (EZE) and glucuronidated EZE (EZE-Glu) differentially target Niemann-Pick C1-like 1 (NPC1L1) and CD13 (aminopeptidase-N) to inhibit intestinal cholesterol absorption and cholesterol processing in other cells, although the precise molecular mechanisms are not fully elucidated. Cellular effects of EZE, EZE-Glu, and the low-absorbable EZE-analogue S6130 were investigated on human monocyte-derived macrophages upon loading with atherogenic lipoproteins. EZE and S6130, but not EZE-Glu disturbed the colocalization of CD13 and its coreceptor CD64 (Fcγ receptor I) in membrane microdomains, and decreased the presence of both receptors in detergent-resistant membrane fractions. Biotinylated cholesterol absorption inhibitor C-5 (i.e., derivative of EZE) was rapidly internalized to perinuclear tubular structures of cells, resembling endoplasmic reticulum (ER), but CD13 was detected on extracellular sites of the plasma membrane and endolysosomal vesicles. Administration of EZE, but not of EZE-Glu or S6130, was associated with decreased cellular cholesteryl ester content, indicating the sterol-O acyltransferase 1 (SOAT1)-inhibition by EZE. Furthermore, EZE decreased the expression of molecules involved in cholesterol uptake and synthesis, in parallel with increased apolipoprotein A-I-mediated cholesterol efflux and upregulation of efflux-effectors. However, NPC1L1 the other claimed molecular target of EZE, was not detected in macrophages, thereby excluding this protein as target for EZE in macrophages. Thus, EZE is very likely a CD13-linked microdomain-disruptor and SOAT1-inhibitor in macrophages leading to in vitro anti-atherosclerotic effects through a decrease of net cellular cholesterol content. © 2019 International Society for Advancement of Cytometry.

SOAT1 methylation is associated with coronary heart disease.

BACKGROUND: This study was designed to investigate whether differential DNA methylationin of cholesterol absorption candidate genes can function as a biomarker for patients with coronary heart disease (CHD). METHODS: DNA methylation levels of the candidate genes FLOT1, FLOT2 and SOAT1 were measured in peripheral blood leukocytes (PBLs) from 99 patients diagnosed with CHD and 89 control subjects without CHD. A total of 110 CPG sites around promoter regions of them were examined. RESULTS: Compared with groups without CHD, patients with CHD had lower methylation levels of SOAT1 (P<0.001). When each candidate genes were divided into different target segments, patients with CHD also had lower methylation levels of SOAT1 than patients without (P = 0.005). After adjustment of other confounders, methylation levels of SOAT1 were still associated with CHD (P = 0.001, OR = 0.290, 95% CI: 0.150-0.561). CONCLUSIONS: SOAT1 methylation may be associated with development of CHD. Patients with lower methylation levels in SOAT1 may have increased risks for CHD. Further studies on the specific mechanisms of this relationship are necessary.

SOAT1 deficiency attenuates atherosclerosis by regulating inflammation and cholesterol transportation via HO-1 pathway.

Sterol O-acyltransferase 1 (SOAT1) is a key enzyme for cholesteryl ester biosynthesis. The objective of the present study is to investigate the role and underlying molecular mechanisms of SOAT1 in atherosclerosis. Our results indicated that SOAT1 was highly expressed in endothelial cells of atherosclerotic lesions in human patients with atherosclerosis and in apolipoprotein E deficient (ApoE-/-) mice fed with high fat diet (HFD). We established a model of atherosclerosis using ApoE and SOAT1 gene double knockout (ApoE-/-SOAT1-/-) mice. SOAT1-/- alleviated HFD-induced and spontaneously developed atherosclerotic lesions in ApoE-/- mice, accompanied with the reduced triglyceride (TG), total cholesterol (TC) and low-density lipoprotein-cholesterol (LDL-C), while the enhanced high-density lipoprotein-cholesterol (HDL-C) in serum of ApoE-/- mice. SOAT1-/- decreased collagen accumulation in the lesions. SOAT1-/- reduced macrophage infiltration and suppressed inflammation in ApoE-/- mice fed with HFD, as evidenced by the decreased expressions of pro-inflammatory cytokines, including interleukin (IL)-1ß, IL-6 and tumor necrosis factor α (TNF-α). Of importance, SOAT1-/--attenuated inflammation was along with the inactivation of ß-catenin and nuclear factor kappa B (NF-κB) ApoE-/- mice. Moreover, oxidative stress observed in ApoE-/- mice was inactivated by SOAT1 double knockout. In addition, expression levels of fatty acid synthase (FAS), stearoyl-CoA desaturase 1 (SCD1), protein convertase subtilisin/kexin type 9 (PCSK 9) and sterol regulatory element-binding protein-1c (SREBP-1c) were decreased in liver, peritoneal macrophages and abdominal aortas of SOAT1-knockout ApoE-/- mice. In contrast, SOAT1-/- displayed improved expressions of peroxisome proliferator-activated receptor-γ (PPAR-γ) and lipoxygenase (LOX)-α in liver, peritoneal macrophages and abdominal aortas of ApoE-/- mice. Of note, the in vitro study, oxidized low-density lipoprotein (ox-LDL) incubation reduced heme oxygenase (HO-1) expressions in human umbilical vein endothelial cells (HUVECs), which was improved by SOAT1 knockdown. Pre-treatment of sn-protoporphyrin (SnPP), an important HO-1 inhibitor, abolished the role of SOAT1 inhibition in suppressing inflammation and abnormal cholesterol transportation. These results indicated that SOAT1 deficiency protected against atherosclerosis progression via inhibiting cholesterol transportation in ApoE-/- mice, which was, at least partly, dependent on HO-1 expressions.

Sterol O-acyltransferase 1 deficiency improves defective insulin signaling in the brains of mice fed a high-fat diet.

Insulin resistance induced by a high-fat diet (HFD) is related to metabolic diseases, and sterol O-acyltransferase 1 (SOAT1) is a key enzyme for the biosynthesis of cholesteryl ester. In the present study, wild-type (WT) mice and SOAT1-knockout (KO) mice with a C57BL6 background fed a HFD were used to explore the role of SOAT1 in the hypothalamus. The results show that the WT mice exhibited a significant increase in body weight as well as hepatic histologic changes; they also had a lower glucose and insulin tolerance than the WT mice fed a normal diet. However, the metabolic syndrome was attenuated in the SOAT1-KO HFD-fed mice. With regard to brain function, the SOAT1-KO HFD-fed mice showed improved cognitive function; they also manifested reduced levels of pro-inflammatory cytokines, including tumor necrosis factor-α (TNF-α), interleukin-1ß (IL-1ß), and IL-6, which would otherwise be raised by a HFD. In addition, the HFD led to the overexpression of GFAP and phosphorylated NF-κB in the hypothalamus, changes that were reversed in the SOAT1-KO HFD-fed mice. Moreover, SOAT1-KO mice improved HFD-caused defective hypothalamic insulin resistance, as evidenced by the upregulation of p-insulin receptor (INSR), p-AKT and p-glycogen synthase kinase (GSK)-3ß, while the downregulation of p-AMP-activated protein kinase (AMPK)-α and p-acetyl-CoA carboxylase (ACC)-α. In addition, similar results were observed in high fructose (HFR)-stimulated astrocytes (ASTs) isolated from WT or KO mice. These results suggest that SOAT1 plays an important role in hypothalamic insulin sensitivity, linked to cognitive impairment, in HFD-fed mice.

Extra-hepatic metabolism of 7-ketocholesterol occurs by esterification to fatty acids via cPLA2α and SOAT1 followed by selective efflux to HDL.

Accumulation of 7-ketocholesterol (7KCh) in tissues has been previously associated with various chronic aging diseases. Orally ingested 7KCh is readily metabolized by the liver and does not pose a toxicity threat. However, 7KCh formed in situ, usually associated with lipoprotein deposits, can adversely affect surrounding tissues by causing inflammation and cytotoxicity. In this study we have investigated various mechanisms for extra-hepatic metabolism of 7KCh (e.g. hydroxylation, sulfation) and found only esterification to fatty acids. The esterification of 7KCh to fatty acids involves the combined action of cytosolic phospholipase A2 alpha (cPLA2α) and sterol O-acyltransferase (SOAT1). Inhibition of either one of these enzymes ablates 7KCh-fatty acid ester (7KFAE) formation. The 7KFAEs are not toxic and do not induce inflammatory responses. However, they can be unstable and re-release 7KCh. The higher the degree of unsaturation, the more unstable the 7KFAE (e.g. 18:0>18:1>18:2>18:3≫20:4). Biochemical inhibition and siRNA knockdown of SOAT1 and cPLA2α ablated the 7KFAE synthesis in cultured ARPE19 cells, but had little effect on the 7KCh-induced inflammatory response. Overexpression of SOAT1 reduced the 7KCh-induced inflammatory response and provided some protection from cell death. This effect is likely due to the increased conversion of 7KCh to 7KFAEs, which reduced the intracellular 7KCh levels. Addition of HDL selectively increased the efflux of 7KFAEs and enhanced the effect of SOAT1 overexpression. Our data suggests an additional function for HDL in aiding extra-hepatic tissues to eliminate 7KCh by returning 7KFAEs to the liver for bile acid formation.