Disturbed Cholesterol Homeostasis Research Articles

Intracerebroventricular 2-hydroxypropyl-γ-cyclodextrin alleviates hepatic manifestations without distributing to the liver in a murine model of Niemann–Pick disease type C

Niemann–Pick disease type C (NPC) is a lysosomal lipid storage disorder characterized by progressive neurodegeneration and hepatic dysfunction. A cyclic heptasaccharide, 2-hydroxypropyl-β-cyclodextrin (HP-β-CD), is currently under clinical investigation for NPC, but its adverse events remain problematic. We previously identified that a cyclic octasaccharide, 2-hydroxypropyl-γ-cyclodextrin (HP-γ-CD), also ameliorated NPC manifestations with higher biocompatibility than HP-β-CD. However, preclinical studies describing the associations between the biodistribution and pharmacodynamics of these compounds, which are essential for clinical application, are still lacking. Here, we investigated these properties of HP-γ-CD by measuring its organ biodistribution and therapeutic effect after systemic and central administration. The effect of HP-γ-CD on disturbed cholesterol homeostasis appeared within several hours after exposure and persisted for several days in NPC model cells and mice. Tissue distribution indicated that only a small fraction of subcutaneously administered HP-γ-CD rapidly distributed to peripheral organs and contributed to disease amelioration. We found that a subcutaneous dose of HP-γ-CD negligibly ameliorated neurological characteristics because it has limited penetration of the blood–brain barrier; however, an intracerebroventricular microdose unexpectedly attenuated hepatic dysfunction without the detection of HP-γ-CD in the liver. These results demonstrate that central administration of HP-γ-CD can indirectly attenuate peripheral manifestations of NPC.

Evidence for hypoxia-induced dysregulated cholesterol homeostasis in preeclampsia: Insights into the mechanisms from human placental cells and tissues.

Preeclampsia (PE) poses a considerable risk to the long-term cardiovascular health of both mothers and their offspring due to a hypoxic environment in the placenta leading to reduced fetal oxygen supply. Cholesterol is vital for fetal development by influencing placental function. Recent findings suggest an association between hypoxia, disturbed cholesterol homeostasis, and PE. This study investigates the influence of hypoxia on placental cholesterol homeostasis. Using primary human trophoblast cells and placentae from women with PE, various aspects of cholesterol homeostasis were examined under hypoxic and hypoxia/reoxygenation (H/R) conditions. Under hypoxia and H/R, intracellular total and non-esterified cholesterol levels were significantly increased. This coincided with an upregulation of HMG-CoA-reductase and HMG-CoA-synthase (key genes regulating cholesterol biosynthesis), and a decrease in acetyl-CoA-acetyltransferase-1 (ACAT1), which mediates cholesterol esterification. Hypoxia and H/R also increased the intracellular levels of reactive oxygen species and elevated the expression of hypoxia-inducible factor (HIF)-2α and sterol-regulatory-element-binding-protein (SREBP) transcription factors. Additionally, exposure of trophoblasts to hypoxia and H/R resulted in enhanced cholesterol efflux to maternal and fetal serum. This was accompanied by an increased expression of proteins involved in cholesterol transport such as the scavenger receptor class B type I (SR-BI) and the ATP-binding cassette transporter G1 (ABCG1). Despite these metabolic alterations, mitogen-activated-protein-kinase (MAPK) signaling, a key regulator of cholesterol homeostasis, was largely unaffected. Our findings indicate dysregulation of cholesterol homeostasis at multiple metabolic points in both the trophoblast hypoxia model and placentae from women with PE. The increased cholesterol efflux and intracellular accumulation of non-esterified cholesterol may have critical implications for both the mother and the fetus during pregnancy, potentially contributing to an elevated cardiovascular risk later in life.

Metabolic dysfunction-associated gallstone disease: expecting more from critical care manifestations.

About 20% of adults worldwide have gallstones which are solid conglomerates in the biliary tree made of cholesterol monohydrate crystals, mucin, calcium bilirubinate, and protein aggregates. About 20% of gallstone patients will definitively develop gallstone disease, a condition which consists of gallstone-related symptoms and/or complications requiring medical therapy, endoscopic procedures, and/or cholecystectomy. Gallstones represent one of the most prevalent digestive disorders in Western countries and patients with gallstone disease are one of the largest categories admitted to European hospitals. About 80% of gallstones in Western countries are made of cholesterol due to disturbed cholesterol homeostasis which involves the liver, the gallbladder and the intestine on a genetic background. The incidence of cholesterol gallstones is dramatically increasing in parallel with the global epidemic of insulin resistance, type 2 diabetes, expansion of visceral adiposity, obesity, and metabolic syndrome. In this context, gallstones can be largely considered a metabolic dysfunction-associated gallstone disease, a condition prone to specific and systemic preventive measures. In this review we discuss the key pathogenic and clinical aspects of gallstones, as the main clinical consequences of metabolic dysfunction-associated disease.

Inflammation Induced by Lipopolysaccharide and Palmitic Acid Increases Cholesterol Accumulation via Enhancing Myeloid Differentiation Factor 88 Expression in HepG2 Cells.

Recently, multiple studies have shown that chronic inflammation disturbs cholesterol homeostasis and promotes its accumulation in the liver. The underlying molecular mechanism remains to be revealed. The relationship between the toll-like receptor 4 (TLR4) inflammatory signaling pathway and cholesterol accumulation was investigated in HepG2 cells treated with lipopolysaccharide (LPS) or palmitic acid (PA) for different lengths of time. In addition, the effects of pretreatment with 20μmol/L ST2825 (MyD88 inhibitor) were also studied in LPS- or PA-treated HepG2 cells and myeloid differentiation factor 88 (MyD88)-overexpressing HEK293T cells. The intracellular total and free cholesterol levels were measured using a commercial kit and filipin staining, respectively. The expression levels of sterol regulatory element-binding protein-2 (SREBP-2) and components in the TLR4 signaling pathway were determined using Western blotting. The treatments with LPS for 12 h and with PA for 24 h significantly increased the contents of intracellular total and free cholesterol, as well as the expression levels of SREBP-2 and components in the TLR4 signaling pathway. The inhibition of MyD88 by ST2825 significantly decreased the cholesterol content and the expression levels of SREBP-2 and components of the TLR4/MyD88/NF-κB pathway in HepG2 cells, as well as MyD88-overexpressing HEK293T cells. These results indicated that LPS and PA treatments increase SREBP-2-mediated cholesterol accumulation via the activation of the TLR4/MyD88/NF-κB signaling pathway in HepG2 cells.

Combined morphological and proteome profiling reveals target-independent impairment of cholesterol homeostasis

Unbiased profiling approaches are powerful tools for small-molecule target or mode-of-action deconvolution as they generate a holistic view of the bioactivity space. This is particularly important for non-protein targets that are difficult to identify with commonly applied target identification methods. Thereby, unbiased profiling can enable identification of novel bioactivity even for annotated compounds. We report the identification of a large bioactivity cluster comprised of numerous well-characterized drugs with different primary targets using a combination of the morphological Cell Painting Assay and proteome profiling. Cluster members alter cholesterol homeostasis and localization due to their physicochemical properties that lead to protonation and accumulation in lysosomes, an increase in lysosomal pH, and a disturbed cholesterol homeostasis. The identified cluster enables identification of modulators of cholesterol homeostasis and links regulation of genes or proteins involved in cholesterol synthesis or trafficking to physicochemical properties rather than to nominal targets.

Development of Cell Culture Infectious Hepatitis C Virus Genotype 1b Clones and 1b-Induced Angiogenesis and Cholesterol Disorders

Globally, hepatitis C virus (HCV) genotype 1b is most prevalent, and its infection has been found to associate with a higher risk of hepatocellular carcinoma (HCC) than other genotype viruses. However, an efficient infectious HCV genotype 1b culture system is unavailable, which has largely hampered the study of this important genotype virus. In this study, by using a systematic approach combining adaptive mutations and infectious 1a TNcc sequences, we succeeded in culture adaption of two full-length 1b clones for the reference strain Con1 and a clinical isolate A6, and designated as Con1cc and A6cc, respectively. Con1cc and A6cc replicated efficiently in hepatoma Huh7.5.1 cells, released HCV infectivity titers of 104.1 and 103.72 focus forming units per milliliter, respectively, and maintained the engineered mutations after passages. Both viruses responded to sofosbuvir and velpatasvir in a dose-dependent manner. With culture infectious 1b clones, we characterized the transcriptomes of 1b Con1cc-infected cells. Con1cc infection activated angiogenesis and disturbed cholesterol homeostasis compared with uninfected cells. In conclusion, we have developed infectious clones for genotype 1b and shown a novel strategy for culture adaptation of HCV isolates by using a genetically close backbone sequence. Besides, this study provides transcriptional landscape of HCV 1b-infected hepatoma cells facilitating the study of genotype 1b infection. Funding Statement: This work was supported by the National Natural Science Foundation of China (No. 81971938 for Y.-P.L.; 81772923 for Y.Z.), The Innovation Research Team for Basic and Clinical Studies on Chronic Liver Diseases of 2018 High-Level Health Teams of Zhuhai (for Y.-P.L. and F.X.), National Key Basic Research Program of China (No. 2015CB554301 for Y.-P.L.), Entrepreneurial Talent Team Award of Guangdong Province (No. 2016ZT06S252 for Y.-P.L.). Declaration of Interests: The authors declare no conflict of interest. Ethics Approval Statement: The use of patient serum was approved by the Medical Ethics Committee at the Zhongshan School of Medicine, Sun Yat-sen University (No. 2014-072).

Hyperphosphatemia in chronic kidney disease exacerbates atherosclerosis via a mannosidases-mediated complex-type conversion of SCAP N-glycans

Blood phosphate levels are linked to atherosclerotic cardiovascular disease in patients with chronic kidney disease (CKD), but the molecular mechanisms remain unclear. Emerging studies indicate an involvement of hyperphosphatemia in CKD accelerated atherogenesis through disturbed cholesterol homeostasis. Here, we investigated a potential atherogenic role of high phosphate concentrations acting through aberrant activation of sterol regulatory element-binding protein (SREBP) and cleavage-activating protein (SCAP)-SREBP2 signaling in patients with CKD, hyperphosphatemic apolipoprotein E (ApoE) knockout mice, and cultured vascular smooth muscle cells. Hyperphosphatemia correlated positively with increased atherosclerotic cardiovascular disease risk in Chinese patients with CKD and severe atheromatous lesions in the aortas of ApoE knockout mice. Mice arteries had elevated SCAP levels with aberrantly activated SCAP-SREBP2 signaling. Excess phosphate invitro raised the activity of α-mannosidase, resulting in delayed SCAP degradation through promoting complex-type conversion of SCAP N-glycans. The retention of SCAP enhanced transactivation of SREBP2 and expression of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase, boosting intracellular cholesterol synthesis. Elevated α-mannosidase II activity was also observed in the aortas of ApoE knockout mice and the radial arteries of patients with uremia and hyperphosphatemia. High phosphate concentration invitro elevated α-mannosidase II activity in the Golgi, enhanced complex-type conversion of SCAP N-glycans, thereby upregulating intracellular cholesterol synthesis. Thus, our studies explain how hyperphosphatemia independently accelerates atherosclerosis in CKD.

Genetic deletion of Abcc6 disturbs cholesterol homeostasis in mice

Genetic studies link adenosine triphosphate-binding cassette transporter C6 (ABCC6) mutations to pseudoxanthoma elasticum (PXE). ABCC6 sequence variations are correlated with altered HDL cholesterol levels and an elevated risk of coronary artery diseases. However, the role of ABCC6 in cholesterol homeostasis is not widely known. Here, we report reduced serum cholesterol and phytosterol levels in Abcc6-deficient mice, indicating an impaired sterol absorption. Ratios of cholesterol precursors to cholesterol were increased, confirmed by upregulation of hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase (Hmgcr) expression, suggesting activation of cholesterol biosynthesis in Abcc6−/− mice. We found that cholesterol depletion was accompanied by a substantial decrease in HDL cholesterol mediated by lowered ApoA-I and ApoA-II protein levels and not by inhibited lecithin-cholesterol transferase activity. Additionally, higher proprotein convertase subtilisin/kexin type 9 (Pcsk9) serum levels in Abcc6−/− mice and PXE patients and elevated ApoB level in knockout mice were observed, suggesting a potentially altered very low-density lipoprotein synthesis. Our results underline the role of Abcc6 in cholesterol homeostasis and indicate impaired cholesterol metabolism as an important pathomechanism involved in PXE manifestation.

High folic acid intake increases methylation-dependent expression of Lsr and dysregulates hepatic cholesterol homeostasis

Food fortification with folic acid and increased use of vitamin supplements have raised concerns about high folic acid intake. We previously showed that high folic acid intake was associated with hepatic degeneration, decreased levels of methylenetetrahydrofolate reductase (MTHFR), lower methylation potential, and perturbations of lipid metabolism. MTHFR synthesizes the folate derivative for methylation reactions. In this study, we assessed the possibility that high folic acid diets, fed to wild-type and Mthfr+/− mice, could alter DNA methylation and/or deregulate hepatic cholesterol homeostasis. Digital restriction enzyme analysis of methylation in liver revealed DNA hypomethylation of a CpG in the lipolysis-stimulated lipoprotein receptor (Lsr) gene, which is involved in hepatic uptake of cholesterol. Pyrosequencing confirmed this methylation change and identified hypomethylation of several neighboring CpG dinucleotides. Lsr expression was increased and correlated negatively with DNA methylation and plasma cholesterol. A putative binding site for E2F1 was identified. ChIP-qPCR confirmed reduced E2F1 binding when methylation at this site was altered, suggesting that it could be involved in increasing Lsr expression. Expression of genes in cholesterol synthesis, transport or turnover (Abcg5, Abcg8, Abcc2, Cyp46a1, and Hmgcs1) was perturbed by high folic acid intake. We also observed increased hepatic cholesterol and increased expression of genes such as Sirt1, which might be involved in a rescue response to restore cholesterol homeostasis. Our work suggests that high folic acid consumption disturbs cholesterol homeostasis in liver. This finding may have particular relevance for MTHFR-deficient individuals, who represent ~10% of many populations.

Impact of Sex and Age on the Mevalonate Pathway in the Brain: A Focus on Effects Induced by Maternal Exposure to Exogenous Compounds.

The mevalonate pathway produces cholesterol and other compounds crucial for numerous cellular processes. It is well known that age and sex modulate this pathway in the liver. Recently, similar effects were also noted in different brain areas, suggesting that alterations of the mevalonate pathway are at the root of marked sex-specific disparities in some neurodevelopmental disorders related to disturbed cholesterol homeostasis. Here, we show how the mevalonate pathway is modulated in a sex-, age- and region-specific manner, and how maternal exposure to exogenous compounds can disturb the regulation of this pathway in the brain, possibly inducing functional alterations.

ABC Transporters, Cholesterol Efflux, and Implications for Cardiovascular Diseases.

Most types of cells in the body have no or very limited capacity of catabolizing cholesterol, so cholesterol efflux is essential for cholesterol homeostasis. There are multiple mechanisms responsible for cellular cholesterol efflux. Among them, the active efflux pathways are mediated primarily by the ATP-binding cassette (ABC) transporters ABCA1 and ABCG1. ABCA1 is essential for cholesterol and phospholipid efflux to apolipoprotein A-I and high density lipoprotein (HDL) biogenesis. ABCG1 promotes cholesterol efflux primarily to HDL particles. Atherosclerotic cardiovascular disease is a chronic inflammatory disease characterized by marked macrophage foam cell accumulation in atherosclerotic plaques and associated pro-inflammatory responses in lesional cells. Findings from both animal and human studies indicate a critical role of disturbed cholesterol homeostasis in pro-inflammatory responses in these cells, particularly in lesional macrophages. ABCA1 and ABCG1 are highly expressed in macrophages, particularly in response to cholesterol accumulation, and are essential in maintenance of cholesterol homeostasis. Functional deficiency of ABCA1 and ABCG1 in macrophage markedly increases atherogenesis, with exacerbated inflammatory responses. ABCA1 and ABCG1 also play a critical role in control of hematopoietic stem and progenitor cell (HSPC) proliferation and extramedullary hematopoiesis. Hematopoietic ABCA1 and ABCG1 deficiencies cause marked HSPC expansion and extramedullary hematopoiesis, particularly in hypercholesterolemia, and lead to marked monocytosis and neutrophilia with exacerbated pro-inflammatory responses. All these contribute to atherosclerosis. In this chapter, we describe these findings and discuss the current understanding of the underlying mechanisms. We also discuss other ABC transporters such as ABCG4, which also promotes cholesterol efflux to HDL and controls megakaryocyte proliferation and platelet biogenesis. By this pathway, ABCG4 also modulates atherogenesis. Therapeutic approaches targeting the pathways and mechanisms described also are discussed.

UNIVERSAL THEORY OF ATHEROSCLEROSIS PATHOGENESIS

The paper shows that atherosclerosis results from disturbed cholesterol homeostasis in the body, the development of systemic stromal-vascular lipid-protein dystrophy (or lipidosis, or cholesterolosis) complicated by extracellular focal lipid deposits with a predominant cholesterol in the interstitial tissue of the inner arterial and aortic layer. These deposits are foreign to this body tissue. They induce the development of chronic productive granulomatous inflammation in it – granulomatosis around endogenous foreign bodies. Cholesterol deposition is promoted by a positive cholesterol balance in the body; increased permeability of the endothelium in hemodynamically vulnerable parts of the arteries, where blood components, including LP, infiltrate their wall; a lack of hydrolytic enzymes in the cell lysosomes that could destroy the steroid nucleus of the cholesterol molecule. Being essential for each specific organism (for building membranes, the formation of bile acids, the synthesis of steroid hormones, vitamin D3), cholesterol, if exceeded, can increase the probability of developing atherosclerosis. Genetic mechanisms are implicated in the disturbed lipid protein metabolism in the human body. Hyperlipoproteinemias (HLPs) are known to be the most common metabolic disorders. The dystrophy under consideration results from primary HLP types IIa, IIb, III, IV, V, as well as secondary HLPs in patients with various medical conditions associated with an increase in blood LDL and / or VLDL and/or a decrease in HDL. A reduced cholesterol efflux from peripheral tissues due to a decreased HDL content and the development of lipidosis are seen in diabetes, obesity, physical inactivity, stress, puberty, menopause, hypertriglyceridemia, cigarette smoking, uremia, treatment with anabolic steroids, beta-adrenergic blocking agents, gestagens, and the use of contraceptives. The most pronounced manifestations of dystrophy are characteristic of HLP types IIA, IIb, III, but its moderate development complicated by atherosclerosis also occurs in types IV and V, which are accompanied by increased blood VLDL. Mutations of LDL receptor genes, apoprotein genes lead to the development of stromal vascular dystrophy and atherosclerosis. A number of rare genetic disorders of sterol metabolism accompany impaired metabolism of cholesterol and its esters: hepatic lipase deficiency (with accumulation of VLDL and IDLs); a deficiency in lysosomal hydrolase of cholesterol esters with impaired LDL metabolism (Wolman disease); cholesterol ester accumulation disease; cerebrotendinous xanthomatosis; cerebral cholesterolosis; Toichlander and Hand Schüler Christian syndromes. The main factor contributing to the development of inflammation in the inner vascular wall of arteries and aorta in atherosclerosis is the cyclic hydrocarbonic structure of cholesterol, which cannot be cleaved in the lysosomes of MPs. The leading role of the cyclic hydrocarbonic structure of cholesterol, which is insoluble and indestructible by MPs, in the induction of atherosclerosis-related inflammation is confirmed by the fact of the atherogenic action of cholesterol derivatives having its structure. An important factor in inflammatory morphogenesis is the lipoprotein dyscolloidosis occurring in the arterial intima and the physical and chemical metamorphosis of cholesterol. A colloidal solution, solid crystals of free cholesterol and liquid crystals of cholesterol esters have a pronounced phlogogenic and sclerogenic effect on the interstitial tissue of the arterial intima.

The sterol regulatory element-binding protein 2 is dysregulated by tau alterations in Alzheimer disease.

Disturbed neuronal cholesterol homeostasis has been observed in Alzheimer disease (AD) and contributes to the pathogenesis of AD. As the master switch of cholesterol biosynthesis, the sterol regulatory element-binding protein 2 (SREBP-2) translocates to the nucleus after cleavage/activation, but its expression and activation have not been studied in AD which is the focus of the current study. We found both a significant decrease in the nuclear translocation of N-terminal SREBP-2 accompanied by a significant accumulation of C-terminal SREBP-2 in NFT-containing pyramidal neurons in AD. N-terminal- SREBP-2 is also found in dystrophic neurites around plaques in AD brain. Western blot confirmed a significantly reduced nuclear translocation of mature SREBP-2 (mSREBP-2) in AD brain. Interestingly, reduced nuclear mSREBP-2 was only found in animal models of tauopathies such as 3XTg AD mice and P301L Tau Tg mice but not in CRND8 APP transgenic mice, suggesting that tau alterations likely are involved in the changes of mSREBP-2 distribution and activation in AD. Altogether, our study demonstrated disturbed SREBP-2 signaling in AD and related models, and proved for the first time that tau alterations contribute to disturbed cholesterol homeostasis in AD likely through modulation of nuclear mSREBP-2 translocation.

ABCA7 Downregulation Modifies Cellular Cholesterol Homeostasis and Decreases Amyloid-β Peptide Efflux in an in vitro Model of the Blood-Brain Barrier.

The role of ABCA7 in brain homeostasis and Alzheimer's disease (AD) is currently under intense scrutiny, since it has been reported that polymorphisms in the Abca7 gene and a loss of function of the protein are closely linked to excessive accumulation of amyloid peptides and disturbed cholesterol homeostasis. The blood-brain barrier (BBB), which isolates the brain from the blood compartment, is involved in both of these processes. We therefore hypothesized that ABCA7 downregulation might affect cholesterol and amyloid exchanges at the BBB. Using siRNA and primary cultures of mouse endothelial cells purified from brain microvessels and seeded on Transwell ® inserts, we investigated the role of ABCA7 in cholesterol and amyloid exchanges across the BBB. Our results showed that a decrease in ABCA7 expression at the BBB provokes in vitro a reduction in ABCA1 expression and a decrease in APOE secretion. In vitro, these decreases reduce cholesterol exchange across the BBB, particularly for high-density lipoproteins and ApoA-I particles. When ABCA7 was absent, we observed a reduction in Aβ peptide basolateral-to-apical transport in the presence of ApoA-I, with non-significant changes in the expression levels of Rage, Lrp1, Abcb1, Abcc1, and Abcg2. Our study in murine BBB model highlighted a putative new role for ABCA7 in AD via the protein's involvement in cholesterol metabolism and amyloid clearance at the BBB.

Erratum: Effects of disturbed liver growth and oxidative stress of high-fat diet-fed dams on cholesterol metabolism in offspring mice.

[This corrects the article on p. 386 in vol. 10, PMID: 27478544.].

Effects of disturbed liver growth and oxidative stress of high-fat diet-fed dams on cholesterol metabolism in offspring mice.

BACKGROUND/OBJECTIVESChanges in nutritional status during gestation and lactation have detrimental effects on offspring metabolism. Several animal studies have shown that maternal high-fat diet (HFD) can predispose the offspring to development of obesity and metabolic diseases, however the mechanisms underlying these transgenerational effects are poorly understood. Therefore, we examined the effect of maternal HFD consumption on metabolic phenotype and hepatic expression of involved genes in dams to determine whether any of these parameters were associated with the metabolic outcomes in the offspring.MATERIALS/METHODSFemale C57BL/6 mice were fed a low-fat diet (LFD: 10% calories from fat) or a high-fat diet (HFD: 45% calories from fat) for three weeks before mating, and during pregnancy and lactation. Dams and their male offspring were studied at weaning.RESULTSDams fed an HFD had significantly higher body and adipose tissue weights and higher serum triglyceride and cholesterol levels than dams fed an LFD. Hepatic lipid levels and mRNA levels of genes involved in lipid metabolism, including LXRα, SREBP-2, FXR, LDLR, and ABCG8 were significantly changed by maternal HFD intake. Significantly lower total liver DNA and protein contents were observed in dams fed an HFD, implicating the disturbed liver adaptation in the pregnancy-related metabolic demand. HFD feeding also induced significant oxidative stress in serum and liver of dams. Offspring of dams fed an HFD had significantly higher serum cholesterol levels, which were negatively correlated with liver weights of dams and positively correlated with hepatic lipid peroxide levels in dams.CONCLUSIONSMaternal HFD consumption induced metabolic dysfunction, including altered liver growth and oxidative stress in dams, which may contribute to the disturbed cholesterol homeostasis in the early life of male mice offspring.

Pharmacological Activation of LXRs Decreases Amyloid-β Levels in Niemann-Pick Type C Model Cells

Niemann-Pick type C disease (NPC) is an inherited disorder mainly caused by loss-of-function mutations in the NPC1 gene, that lead to intracellular cholesterol accumulation and disturbed cholesterol homeostasis. Similarly to Alzheimer's disease (AD), NPC is associated with progressive neurodegeneration and altered metabolism of amyloid precursor protein (APP). Liver X receptors (LXRs), the key transcriptional regulators of cholesterol homeostasis, were reported to play neuroprotective roles in NPC mice. We investigated the impacts of LXRs on APP metabolism in mutant CHO cells lacking the NPC1 gene (-NPC1 cells). Pharmacological activation of LXRs in -NPC1 cells tended to reduce the ratio of total secreted APP (sAPP) to full length APP (flAPP) levels and sAPPβ levels as well as to increase the ratio of APP Cterminal fragments to flAPP levels, resulting in decreased levels of amyloid β (Aβ) peptides. -NPC1 cells treated with LXR agonist TO901317 (TO90) displayed a modest increase in cholesterol efflux to apolipoprotein A-I (apoA-I) but not to HDL3, or in the absence of extracellular cholesterol acceptors. The observed similar reduction of Aβ levels upon TO90 treatment in the presence or in the absence of extracellular apoA-I indicated a cholesterol-efflux independent effect of TO90 on Aβ levels. Furthermore, TO90 had no effect on the cholesterol synthesis rate in -NPC1 cells, while it reduced the rate of cholesterol esterification. The obtained results indicate that LXR activation may decrease Aβ levels in NPC1- deficient conditions. The underlying mechanism of this action does not appear to be related to effects on cholesterol efflux or synthesis rates.

Crocin Improves Lipid Dysregulation in Subacute Diazinon Exposure through ERK1/2 Pathway in Rat Liver

Diazinon Yis one of the most broadly used organophosphorus insecticides in agriculture. It has been shown that exposure to diazinon may interfere with lipid metabolism. Moreover, the hypolipidemic effect of crocin has been established. Earlier studies revealed the major role of Extracellular signal-regulated kinase (ERK) pathways in low-density lipoprotein receptor (LDLr) expression. The aim of this study was to evaluate changes in the regulation of lipid metabolism, ERK and LDLr expression in the liver of rats exposed to subacute diazinon. Furthermore ameliorating effect of crocin on diazinon induced disturbed cholesterol homeostasis was studied. 24 Rats were divided into 4 groups and received following treatments for 4 weeks; Corn oil (control), diazinon (15mg/kg per day, orally) and crocin (12.5 and 25mg/kg per day, intraperitoneally) in combination with diazinon (15 mg/kg). The levels of cholesterol, triglyceride and LDL in blood of rats were analyzed. Moreover mRNA levels of LDLr and ERK1/2 as well as protein levels of total and activated forms of ERK1/2 in rat liver were evaluated by Western blotting and quantitative real time polymerase chain reaction analysis. Our data showed that subacute exposure to diazinon significantly increased concentrations of cholesterol, triglyceride and LDL. Moreover diazinon decreased ERK1/2 protein phosphorylation and LDLr transcript. Crocin reduced inhibition of ERK activation and diazinon-induced hyperlipemia and increased levels of LDLr transcript. Crocin may be considered as a novel protective agent in diazinon-induced hyperlipemia through modulating of ERK pathway and increase of LDLr expression.

The role of extracerebral cholesterol homeostasis and ApoE e4 in cognitive decline

We examined the associations between extracerebral markers of cholesterol homeostasis and cognitive decline over 6 years of follow-up, and studied the modifying effect of apolipoprotein E (ApoE) e4. Data were collected in the Longitudinal Aging Study Amsterdam (n = 967, with longitudinal data on cognition, ages ≥ 65 years) and analyzed using linear mixed models. General cognition (Mini-Mental State Examination; MMSE), memory (Auditory Verbal Learning Test), and information processing speed (Coding task) were measured. The results show that ApoE e4 was a significant effect modifier. Significant associations were found only in ApoE e4 noncarriers (n = 718). We found a nonlinear negative association between the ratio of lanosterol to cholesterol (≤ 189.96 ng/mg), a marker for cholesterol synthesis, and general cognition. Lower cholesterol absorption, i.e., lower ratios of campesterol and sitosterol to cholesterol, as well as a higher rate of cholesterol synthesis relative to absorption were associated with lower information processing speed. In ApoE e4 carriers, the negative association between the ratio of campesterol to cholesterol and memory reached borderline significance. Future research should focus on the interaction between (disturbed) cholesterol homeostasis and ApoE e4 status with respect to dementia.

Chlamydia pneumoniae disturbs cholesterol homeostasis in human THP-1 macrophages via JNK-PPARγ dependent signal transduction pathways

Chlamydia pneumoniae ( C. pneumoniae) induces macrophage-derived foam cell formation, a hallmark of early atherosclerosis, in the presence of low density lipoprotein (LDL). However, its mechanisms have yet to be elucidated. In this study we examined the effects of live, heat-killed and UV-inactivated C. pneumoniae on cholesterol metabolism in THP-1-derived macrophages and the role of c-Jun NH 2 terminal kinase (JNK), which may participate in the C. pneumoniae-induced disruption of intracellular cholesterol homeostasis. We investigated whether SP600125, a special JNK inhibitor, affects the expression of peroxisome proliferator-activated receptor gamma (PPARγ), and also its downstream target genes Acyl-CoA cholesterol acyltransferase-1 (ACAT1), ATP-binding cassette transporter A1 and G1 (ABCA1/G1) in human THP-1 macrophages infected with C. pneumoniae. In this paper we found that both live and inactivated C. pneumoniae infection induce intracellular cholesterol accumulation and foam cell formation. C. pneumoniae infection increased the expression of ACAT1 and decreased the expression of ABCA1/G1, all of which facilitated cholesterol accumulation and promoted macrophage-derived foam cell formation. However, these responses were attenuated by SP600125 in a dose-dependent manner. These results demonstrate for the first time that both live and inactivated C. pneumoniae infections disturb cholesterol homeostasis in human THP-1 macrophages and C. pneumoniae infection disturbs cholesterol homeostasis via JNK-PPARγ dependent signal transduction pathways.