Cholesterol Content Of Lipid Rafts Research Articles

Inhibiting the Cholesterol Storage Enzyme ACAT1/SOAT1 in Aging Apolipoprotein E4 Mice Alters Their Brains' Inflammatory Profiles.

Aging and apolipoprotein E4 (APOE4) are the two most significant risk factors for late-onset Alzheimer's disease (LOAD). Compared to APOE3, APOE4 disrupts cholesterol homeostasis, increases cholesteryl esters (CEs), and exacerbates neuroinflammation in brain cells, including microglia. Targeting CEs and neuroinflammation could be a novel strategy to ameliorate APOE4-dependent phenotypes. Toll-like receptor 4 (TLR4) is a key macromolecule in inflammation, and its regulation is associated with the cholesterol content of lipid rafts in cell membranes. We previously demonstrated that in normal microglia expressing APOE3, inhibiting the cholesterol storage enzyme acyl-CoA:cholesterol acyltransferase 1 (ACAT1/SOAT1) reduces CEs, dampened neuroinflammation via modulating the fate of TLR4. We also showed that treating myelin debris-loaded normal microglia with ACAT inhibitor F12511 reduced cellular CEs and activated ABC transporter 1 (ABCA1) for cholesterol efflux. This study found that treating primary microglia expressing APOE4 with F12511 also reduces CEs, activates ABCA1, and dampens LPS-dependent NFκB activation. In vivo, two-week injections of nanoparticle F12511, which consists of DSPE-PEG2000, phosphatidylcholine, and F12511, to aged female APOE4 mice reduced TLR4 protein content and decreased proinflammatory cytokines, including IL-1β in mice brains. Overall, our work suggests nanoparticle F12511 is a novel agent to ameliorate LOAD.

Inhibiting the cholesterol storage enzyme ACAT1/SOAT1 in aging Apolipoprotein E4 mice alter their brains inflammatory profiles.

Aging and Apolipoprotein E4 (APOE4) are the two most significant risk factors for late-onset Alzheimer's disease (LOAD). Compared to APOE3, APOE4 disrupts cholesterol homeostasis, increases cholesteryl esters (CEs), and exacerbates neuroinflammation in brain cells including microglia. Targeting CEs and neuroinflammation could be a novel strategy to ameliorate APOE4 dependent phenotypes. Toll-like receptor 4 (TLR4) is a key player in inflammation, its regulation is associated with cholesterol content of lipid rafts in cell membranes. We previously demonstrated that in normal microglia expressing APOE3, inhibiting the cholesterol storage enzyme acylCoA:cholesterol acyltransferase 1 (ACAT1/SOAT1) reduces CEs, dampened neuroinflammation via modulating the fate of TLR4. We also showed that treating myelin debris-loaded normal microglia with ACAT inhibitor F12511 reduced cellular CEs and activated ABC transporter 1 (ABCA1) for cholesterol efflux. In this study, we found that treating primary microglia expressing APOE4 with F12511 also reduces CEs, activated ABCA1, and dampened LPS dependent NFkB activation. In vivo, a two-week injections of nanoparticle F12511, which consists of DSPE-PEG 2000 , phosphatidylcholine, and F12511, to aged female APOE4 mice reduced TLR4 protein content and decreased proinflammatory cytokines including IL-1β in APOE4 mice brains. Overall, our work suggests nanoparticle F12511 is a novel agent to ameliorate LOAD.

M6A-Mediated Induction of 7-Dehydrocholesterol Reductase Stimulates Cholesterol Synthesis and cAMP Signaling to Promote Bladder Cancer Metastasis.

Dysregulation of cholesterol homeostasis occurs in multiple types of tumors and promotes cancer progression. Investigating the specific processes that induce abnormal cholesterol metabolism could identify therapeutic targets to improve cancer treatment. In this investigation, we observed upregulation of 7-dehydrocholesterol reductase (DHCR7), a vital enzyme involved in the synthesis of cholesterol, within bladder cancer tissues in comparison to normal tissues, which was correlated with increased bladder cancer metastasis. Increased expression of DHCR7 in bladder cancer was attributed to decreased mRNA degradation mediated by YTHDF2. Loss or inhibition of DHCR7 reduced bladder cancer cell invasion in vitro and metastasis in vivo. Mechanistically, DHCR7 promoted bladder cancer metastasis by activating the cAMP/protein kinase A/FAK pathway. Specifically, DHCR7 increased cAMP levels by elevating cholesterol content in lipid rafts, thereby facilitating the transduction of signaling pathways mediated by cAMP receptors. DHCR7 additionally enhanced the cAMP signaling pathway by reducing the concentration of 7-dehydrocholesterol and promoting the transcription of the G protein-coupled receptor, namely gastric inhibitory polypeptide receptor. Overall, these findings demonstrate that DHCR7 plays an important role in bladder cancer invasion and metastasis by modulating cholesterol synthesis and cAMP signaling. Furthermore, inhibition of DHCR7 shows promise as a viable therapeutic strategy for suppressing bladder cancer invasion and metastasis. Significance: Inhibiting DHCR7 induces cholesterol metabolism reprogramming and lipid raft remodeling to inactivate the cAMP/protein kinase A/FAK axis and suppress bladder cancer metastasis, indicating the therapeutic potential of targeting DHCR7.

Hypercapnia increases ACE2 expression and pseudo-SARS-CoV-2 entry in bronchial epithelial cells by augmenting cellular cholesterol.

Patients with chronic lung disease, obesity, and other co-morbid conditions are at increased risk of severe illness and death when infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Hypercapnia, the elevation of CO2 in blood and tissue, commonly occurs in patients with severe acute and chronic lung disease, including those with pulmonary infections, and is also associated with high mortality risk. We previously reported that hypercapnia increases viral replication and mortality of influenza A virus infection in mice. We have also shown that culture in elevated CO2 upregulates expression of cholesterol synthesis genes in primary human bronchial epithelial cells. Interestingly, factors that increase the cholesterol content of lipid rafts and lipid droplets, platforms for viral entry and assembly, enhance SARS-CoV-2 infection. In the current study, we investigated the effects of hypercapnia on ACE2 expression and entry of SARS-CoV-2 pseudovirus (p-SARS-CoV-2) into airway epithelial cells. We found that hypercapnia increased ACE2 expression and p-SARS-CoV-2 uptake by airway epithelium in mice, and in cultured VERO and human bronchial epithelial cells. Hypercapnia also increased total cellular and lipid raft-associated cholesterol in epithelial cells. Moreover, reducing cholesterol synthesis with inhibitors of sterol regulatory element binding protein 2 (SREBP2) or statins, and depletion of cellular cholesterol, each blocked the hypercapnia-induced increases in ACE2 expression and p-SARS-CoV-2 entry into epithelial cells. Cigarette smoke extract (CSE) also increased ACE2 expression, p-SARS-CoV-2 entry and cholesterol accumulation in epithelial cells, an effect not additive to that of hypercapnia, but also inhibited by statins. These findings reveal a mechanism that may account, in part, for poor clinical outcomes of SARS-CoV-2 infection in patients with advanced lung disease and hypercapnia, and in those who smoke cigarettes. Further, our results suggest the possibility that cholesterol-lowering therapies may be of particular benefit in patients with hypercapnia when exposed to or infected with SARS-CoV-2.

Effects of activation and assisted reproduction techniques on the composition, structure, and properties of the sauger (Sander Canadensis) spermatozoa plasma membrane

The sperm plasma membrane is a multifunctional organelle essential to fertilization. However, assisted reproduction techniques often negatively affect this structure, resulting in reduced fertility. These reductions have been attributed to plasma membrane damage in a wide array of species, including fish. Considerable research has been conducted on the fish sperm membrane, but few have examined the effect of cryopreservation and other assisted reproduction techniques (ARTs) on not only membrane composition, but also specific characteristics (e.g., fluidity) and organization (e.g., lipid rafts). Herein, we determined the effects of three ARTs (testicular harvest, strip spawning, and cryopreservation) on the sperm plasma membrane, using Sauger (Sander canadensis) sperm as a model. To this end, a combination of fluorescent dyes (e.g., merocyanine 540, filipin III, cholera toxin subunit β), liquid chromatography – mass spectroscopy (LC-MS) analysis of membrane lipids, and membrane ultracentrifugation coupled with plate assays and immunofluorescence were used to describe and compare sperm fluidity, membrane composition, as well as lipid raft composition and distribution among sperm types. Stripped sperm became more fluid following motility activation (40% increase in highly fluid cells characterized by a 2 × increase in fluorescence) and contained lipid rafts restricted to the midpiece. Testicular harvest yielded sperm with characteristics similar to stripped sperm. By contrast, cryopreservation impacted every aspect of membrane physiology. Two cell populations, one highly fluid and the other rigid, resulted from the freeze-thaw process. Cryopreservation reduced lipid raft cholesterol content by 44% and flotilin-2 (a lipid raft marker) was partially displaced owing to a decrease in buoyancy. Unlike stripped and testicular sperm, LC-MS analysis revealed increases in oxidative damage markers, membrane destabilization, and apoptotic signaling in cryopreserved sperm. Ultrastructural analysis also revealed widespread physical damage to the membrane following freeze-thaw. Sperm motility, however, was unrelated to any measure of membrane physiology used in this study. Our results demonstrate that ARTs have the potential to substantially affect the sperm plasma membrane, but not always detrimentally. These results provide multiple potential biomarkers of sperm quality as well as insight into sources of sub-fertility resulting from use of ARTs.

Mesenchymal stem cell-derived exosomes altered neuron cholesterol metabolism via Wnt5a-LRP1 axis and alleviated cognitive impairment in a progressive Parkinson’s disease model

Parkinson’s disease (PD) is associated with abnormal metabolism of brain cholesterol, and the metabolites of neuronal cholesterol may also affect neurodegenerative progression. In this study, we aim to explore the therapeutic effect of BMSC derived exosomes on motor and cognitive deficits in α-synuclein (α-Syn) A53T transgenic mice, a progressive PD animal model. Results revealed that rotating rod performance of α-Syn A53T TG mice decreased by 45.4 %±8.6 % at the age of 12 months compared with wide-type (WT) mice. Striatum injection of BMSC quiescent exosomes (BMSCquiescent-EXO) and BMSC induced exosomes (BMSCinduced-EXO) rescued the rotation behavior (BMSCquiescent-EXO: 92.3 %±12.5 % P = 0.008; BMSCinduced-EXO: 102.3 %±16.7 %, P = 0.006). Although there was no difference in the escape latency within 5 days of Morris water maze learning between groups in the 12-month old mice. The exploration latency was shorter (p < 0.05) in BMSCquiescent-EXO and BMSCinduced-EXO groups, the number of explorations and novel object recognition index were significantly increased (p < 0.05). More importantly, the total cholesterol level was increased (p < 0.05), while the content of 24S-hydroxycholesterol significantly decreased (p < 0.05) after intrastriatal injection BMSCquiescent-EXO and BMSCinduced-EXO in A53T group. Liquid chromatography-mass spectrometry (LC/MS) was performed to profile phospholipid metabolites in lipid raft of hippocampal neurons, demonstrating that BMSCquiescent-EXO injection caused the decreasing relative percentages of phosphatidylglycerol (PG) and phosphatidylethanolamine (PE) compared to those in A53T mice, while the relative percentages of phosphatidylinositol (PI), phosphatidylserine (PS), and phosphatidylcholine (PC) increased. The cholesterol content of lipid rafts was lower in BMSCquiescent-EXO and BMSCinduced-EXO groups than that in A53T group (P < 0.05). In summary, exosomes isolated during BMSC dopaminergic neuron differentiation can significantly improve the motor, learning and memory ability of the progressive PD mice model, and its mechanism may be related to the change of altered phospholipid composition and cholesterol metabolism in hippocampal neurons.

Targeting CRABP-II overcomes pancreatic cancer drug resistance by reversing lipid raft cholesterol accumulation and AKT survival signaling

BackgroundResistance to standard therapy is a major reason for the poor prognosis of pancreatic ductal adenocarcinoma (PDAC). Developing novel therapy to overcome PDAC drug-resistance is urgently needed. CRABP-II was highly expressed in all PDAC but not expressed in normal pancreatic tissues and chronic pancreatitis. CRABP-II was shown to promote PDAC migration and metastasis while its potential role in promoting PDAC drug-resistance was not known.MethodsA paired cohort of human primary and relapsing PDAC tissues was assessed for CRABP-II expression by immunohistochemistry. CRISPR/cas9 gene editing was used to establish CRABP-II knockout cell lines and MTT assays were performed to assess gemcitabine sensitivity in vitro. Cleaved caspase-3/PARP blots and Annexin V staining were conducted to detect cell apoptosis. Gene expression microarray, Q-PCR, western blots, Co-IP and RNA-IP were used to study the molecular function of CRABP-II. Sucrose gradient ultracentrifugation was applied to isolate lipid rafts and LC–MS-MS was used to assess cholesterol content. Both subcutaneous CDX models and orthotopic PDX models were established to examine the efficacy of SNIPER-11 and the synergistic effect between SNIPER-11 and gemcitabine in vivo.ResultsA higher expression of CRABP-II was found in relapsing PDAC tissue and was associated with poor prognosis. Gemcitabine-resistant cell lines exhibited increased level of CRABP-II, while CRABP-II knockout resensitized PDAC cells to gemcitabine. Mechanistically, aberrant expression of CRABP-II increased the stability of SREBP-1c mRNA through cooperation with HuR and upregulated the downstream genes of SREBP-1c to favor cholesterol uptake and accumulation in lipid rafts. Increased lipid raft cholesterol accumulation facilitated ATK survival signaling and PDAC drug resistance. The small compound SNIPER-11 treatment effectively induced CRABP-II protein degradation, induced apoptosis, and suppressed tumor growth. Combination of SNIPER-11 and gemcitabine significantly reduced the lipid raft cholesterol content in CDX/PDX and profoundly inhibited tumor progression.ConclusionsThese findings identified CRABP-II as a novel regulator of cholesterol metabolism and suggested that CRABP-II is a selective target for overcoming PDAC drug resistance.

Association of lipid rafts cholesterol with clinical profile in fragile X syndrome

Fragile X syndrome (FXS) is the most prevalent monogenic cause of intellectual disability and autism spectrum disorder (ASD). Affected individuals have a high prevalence of hypocholesterolemia, however, the underlying mechanisms and the clinical significance remains unknown. We hypothesized that decrease in the plasma cholesterol levels is associated with an alteration of cholesterol content within the lipid rafts (LRs) which ultimately affects the clinical profile of FXS individuals. The platelets LRs were isolated by ultracentrifugation on sucrose gradient from 27 FXS and 25 healthy controls, followed by measurements of proteins, cholesterol, and gangliosides content. Autistic and adaptive behaviour of affected individuals were respectively assessed by the Social Communication Questionnaire and Adaptive Behavior Assessment System. Our results suggest a decrease in the cholesterol content of LRs in FXS individuals as compared to controls. As opposed to controls, LR cholesterol was significantly associated with plasma total cholesterol (r = 0.47; p = 0.042) in the FXS group. Furthermore, the correlation between LRs cholesterol and the clinical profile showed a significant association with autistic traits (r = − 0.67; p < 0.001) and adaptative behavior (r = 0.70; p < 0.001). These results support the clinical significance of LR cholesterol alterations in FXS. Further studies are warranted to investigate the implication of LRs in FXS pathophysiology and ASD.

Reductions in ApoE and GPx4 highlight the Alzheimer's disease lipid raft vulnerability.

AD is associated with increases in lipid peroxidation and decreased antioxidant defense. Little is known about antioxidant defense of brain lipid rafts which are the site of APP processing. Oxidative damage to lipid rafts increases amyloid production. Lipid hydroperoxidases, glutathione peroxidase 4 (GPx4) and peroxiredoxin 6 (Prdx6) are potential detoxifying enzymes capable of reducing oxidized phospholipids and oxysterols within cellular membranes. We hypothesized that lipid hydroperoxidases would be reduced in ApoE4 carriers, which also have deficient cholesterol transport. To determine this, we investigated the status of the AD lipid raft by ApoE isoform in human frontal cortex. Lipid rafts were isolated (Invent Biotechnologies; LR-039) from postmortem AD (ApoE3,3, ApoE3,4, and ApoE4,4) and age-matched controls (ApoE3,3) and were analyzed by western blot and enzymatic assay. Lipid raft ApoE protein level of AD brains showed large decreases: 43% (Ctl vs AD3,3; p<0.01), 53% (Ctl vs AD3,4; p<0.001) and 70% (Ctl vs AD4,4; p<0.0001). Total cholesterol content of lipid rafts decreased 25% (Ctl vs AD; p<0.01). GPx4 protein of lipid rafts decreased 30% (Ctl vs AD3,3; p<0.01), 45% (Ctl vs AD3,4; p<0.0001) and 57% (Ctl vs AD4,4; p<0.001). AD brains from ApoE4,4 carriers had 36%(p<0.01) lower GPx4 localization than ApoE3,3. Prdx6 localization was not detected in the lipid rafts. Reductions in ApoE, total cholesterol, and GPx4 in the AD lipid raft suggests its vulnerability during AD. Furthermore, many of these decreases were ApoE isoform dependent, suggesting that antioxidant defense may differ by ApoE isoform.

WITHDRAWN: Selenium supplementation inhibits lipopolysaccharide-induced endometritis by decreasing the cholesterol content of lipid rafts

WITHDRAWN: Selenium supplementation inhibits lipopolysaccharide-induced endometritis by decreasing the cholesterol content of lipid rafts

Abstract 365: Inhibiting Hmg Coa Reductase Reduces Palmitate-Induced Inflammation in Adipocytes

Adipose tissue inflammation associates with insulin resistance and increased cardiovascular disease risk. We previously observed that 3T3-L1 adipocytes exposed to palmitate become inflamed and demonstrate increased plasma membrane cholesterol and lipid raft content. It is known that palmitate induces translocation of NAPH oxidase and toll-like receptor 4 into lipid rafts, increasing adipocyte inflammation. However, it is unclear (1) how palmitate alters plasma membrane cholesterol content; and (2) whether increased cholesterol content in the plasma membrane is related to adipocyte inflammation induced by palmitate exposure. We hypothesize that mechanisms involved in increasing plasma membrane cholesterol content after palmitate treatment could be related to cholesterol synthesis and/or ER stress, and that increased cholesterol in lipid rafts is essential for induction of inflammation in adipocytes. To test these hypotheses, differentiated murine 3T3-L1 adipocytes were exposed to palmitate for 24 hours, with and without pre-treatment with HMG-CoA reductase inhibitors (statins) or HDL. RT-PCR was used to evaluate gene expression of inflammation ( Saa3 , Ccl2 ), ER stress ( Bip , Chop ), and HMG-CoA reductase ( Hmgcr ). Cholera toxin subunit β staining and flow cytometry were used to evaluate plasma membrane lipid raft content. In differentiated adipocytes, palmitate-induced inflammation neither increased expression of ER stress genes nor HMG-CoA reductase gene expression. However, treatment with 3 different statins (simvastatin, lovastatin, atorvastatin) significantly reduced palmitate-induced adipocyte inflammation as indicated by decreased gene expression of Saa3 and Ccl2 ( P &lt;0.05). A similar effect was seen with pre-treatment with HDL. Lipid raft content induced by palmitate was decreased by HMG-CoA reductase inhibitors (difference in mean fluorescence intensity P &lt;0.05) and also by pre-treatment with HDL. These findings indicate that ER stress was not involved in increased plasma membrane cholesterol after palmitate-induced inflammation in adipocytes. However, regulating cholesterol content in lipid rafts plays an important role in adipocyte inflammation induced by palmitate.

MicroRNA-33 Controls Adaptive Fibrotic Response in the Remodeling Heart by Preserving Lipid Raft Cholesterol.

Heart failure and atherosclerosis share the underlying mechanisms of chronic inflammation followed by fibrosis. A highly conserved microRNA (miR), miR-33, is considered as a potential therapeutic target for atherosclerosis because it regulates lipid metabolism and inflammation. However, the role of miR-33 in heart failure remains to be elucidated. To clarify the role of miR-33 involved in heart failure. We first investigated the expression levels of miR-33a/b in human cardiac tissue samples with dilated cardiomyopathy. Increased expression of miR-33a was associated with improving hemodynamic parameters. To clarify the role of miR-33 in remodeling hearts, we investigated the responses to pressure overload by transverse aortic constriction in miR-33-deficient (knockout [KO]) mice. When mice were subjected to transverse aortic constriction, miR-33 expression levels were significantly upregulated in wild-type left ventricles. There was no difference in hypertrophic responses between wild-type and miR-33KO hearts, whereas cardiac fibrosis was ameliorated in miR-33KO hearts compared with wild-type hearts. Despite the ameliorated cardiac fibrosis, miR-33KO mice showed impaired systolic function after transverse aortic constriction. We also found that cardiac fibroblasts were mainly responsible for miR-33 expression in the heart. Deficiency of miR-33 impaired cardiac fibroblast proliferation, which was considered to be caused by altered lipid raft cholesterol content. Moreover, cardiac fibroblast-specific miR-33-deficient mice also showed decreased cardiac fibrosis induced by transverse aortic constriction as systemic miR-33KO mice. Our results demonstrate that miR-33 is involved in cardiac remodeling, and it preserves lipid raft cholesterol content in fibroblasts and maintains adaptive fibrotic responses in the remodeling heart.

Lipid-Free Apolipoprotein A-I Reduces Progression of Atherosclerosis by Mobilizing Microdomain Cholesterol and Attenuating the Number of CD131 Expressing Cells: Monitoring Cholesterol Homeostasis Using the Cellular Ester to Total Cholesterol Ratio.

BackgroundAtherosclerosis is a chronic inflammatory disorder whose development is inversely correlated with high‐density lipoprotein concentration. Current therapies involve pharmaceuticals that significantly elevate plasma high‐density lipoprotein cholesterol concentrations. Our studies were conducted to investigate the effects of low‐dose lipid‐free apolipoprotein A‐I (apoA‐I) on chronic inflammation. The aims of these studies were to determine how subcutaneously injected lipid‐free apoA‐I reduces accumulation of lipid and immune cells within the aortic root of hypercholesterolemic mice without sustained elevations in plasma high‐density lipoprotein cholesterol concentrations.Methods and Results Ldlr −/− and Ldlr −/− apoA‐I −/− mice were fed a Western diet for a total of 12 weeks. After 6 weeks, a subset of mice from each group received subcutaneous injections of 200 μg of lipid‐free human apoA‐I 3 times a week, while the other subset received 200 μg of albumin, as a control. Mice treated with lipid‐free apoA‐I showed a decrease in cholesterol deposition and immune cell retention in the aortic root compared with albumin‐treated mice, regardless of genotype. This reduction in atherosclerosis appeared to be directly related to a decrease in the number of CD131 expressing cells and the esterified cholesterol to total cholesterol content in several immune cell compartments. In addition, apoA‐I treatment altered microdomain cholesterol composition that shifted CD131, the common β subunit of the interleukin 3 receptor, from lipid raft to nonraft fractions of the plasma membrane.ConclusionsApoA‐I treatment reduced lipid and immune cell accumulation within the aortic root by systemically reducing microdomain cholesterol content in immune cells. These data suggest that lipid‐free apoA‐I mediates beneficial effects through attenuation of immune cell lipid raft cholesterol content, which affects numerous types of signal transduction pathways that rely on microdomain integrity for assembly and activation.

Abstract 277: Microrna-33 Promotes Cardiac Fibrosis by Maintaining Cellular Lipid Homeostasis

Background: A highly conserved microRNA, miR-33 is considered as a potential therapeutic target for atherosclerosis, because recent reports, including ours, indicated miR-33 has atherogenic effects by reducing HDL-C. However, the functions of miR-33 in heart failure remain to be elucidated. Methods and results: To clarify the functions of miR-33 involved in cardiac hypertrophy and fibrosis in vivo, we investigated the responses to pressure overload by transverse aortic constriction (TAC) in miR-33 deficient (KO) mice. When subjected to TAC, miR-33 expression level was significantly up-regulated in wild-type (WT) left ventricles, whereas miR-33 KO hearts displayed no less hypertrophic responses than WT hearts. However, interestingly, histological and gene expression analyses showed ameliorated cardiac fibrosis in miR-33 KO hearts compared to WT hearts. Furthermore, we generated cardiac fibroblast specific miR-33 deficient mice, which also showed ameliorated cardiac fibrosis when they were subjected to TAC. We also found that cardiac fibroblasts were mainly responsible for miR-33 expression in the heart, because its expression was about 4-folds higher in isolated primary cardiac fibroblasts than cardiomyocytes. Deficiency of miR-33 impaired cell proliferation in primary fibroblasts, which was considered due to altered lipid raft cholesterol content by up-regulated ATP-binding cassette transporter A1/G1. Conclusion: Deficiency of miR-33 impaired fibroblast proliferation in vitro, and ameliorated cardiac fibrosis induced by pressure overload in vivo.

Role of Cholesteryl Ester (CE) Hydrolase Mediated Mobilization of Intracellular CE in Regulating Inflammasome Activation

Cellular cholesterol content and inflammatory pathways are thought to be linked but the underlying mechanisms are not completely defined. Dramatic (>20 fold) reduction in circulating IL-1b in macrophage-specific CE hydrolase (CEH) transgenic (Tg) mice indicates a role of macrophage cholesterol homeostasis in regulating IL-1b production. Cellular priming for inducing transcription via NF-kB (Signal 1) and activation of NLRP3 inflammasome for proteolytic cleavage of pro-IL-1b (Signal 2) are required for IL-1b secretion. While activation of surface TLR4 represents Signal 1, several disparate signals can activate inflammasome and decrease in cellular K+ by increased efflux is an important convergence point. Since membrane cholesterol/lipid-raft levels regulate the function of cell surface receptors and K+ channels, we hypothesized that CEH-mediated reduction in cellular cholesterol attenuates IL-1b secretion by reducing inflammasome activation. Mouse peritoneal macrophages (MPM) from C57BL/6 (WT) or CEHTg mice were used for all the studies. Membrane cholesterol content was reduced by CEH over-expression with significant reduction in lipid-raft cholesterol content (A). Delayed reappearance of TLR4 (MFI, B) following LPS stimulation in CEHTg MPMs indicates attenuation of Signal 1. Efflux of K+ (Signal 2) required for inflammasome activation occurs via K+ channels and single cell patch clamp studies were performed to monitor channel activity. Significantly lower outward K+ currents in CEHTg MPMs were observed in CEHTg MPMs (C). Pharmacological inhibition of CEH increased IL-1b secretion from MPMs (D) confirming the role of CEH-mediated cellular cholesterol homeostasis in regulating inflammasome activation.

PMP22 is critical for actin-mediated cellular functions and for establishing lipid rafts.

Haploinsufficiency of peripheral myelin protein 22 (PMP22) causes hereditary neuropathy with liability to pressure palsies, a peripheral nerve lesion induced by minimal trauma or compression. As PMP22 is localized to cholesterol-enriched membrane domains that are closely linked with the underlying actin network, we asked whether the myelin instability associated with PMP22 deficiency could be mediated by involvement of the protein in actin-dependent cellular functions and/or lipid raft integrity. In peripheral nerves and cells from mice with PMP22 deletion, we assessed the organization of filamentous actin (F-actin), and actin-dependent cellular functions. Using in vitro models, we discovered that, in the absence of PMP22, the migration and adhesion capacity of Schwann cells and fibroblasts are similarly impaired. Furthermore, PMP22-deficient Schwann cells produce shortened myelin internodes, and display compressed axial cell length and collapsed lamellipodia. During early postnatal development, F-actin-enriched Schmidt-Lanterman incisures do not form properly in nerves from PMP22(-/-) mice, and the expression and localization of molecules associated with uncompacted myelin domains and lipid rafts, including flotillin-1, cholesterol, and GM1 ganglioside, are altered. In addition, we identified changes in the levels and distribution of cholesterol and ApoE when PMP22 is absent. Significantly, cholesterol supplementation of the culture medium corrects the elongation and migration deficits of PMP22(-/-) Schwann cells, suggesting that the observed functional impairments are directly linked with cholesterol deficiency of the plasma membrane. Our findings support a novel role for PMP22 in the linkage of the actin cytoskeleton with the plasma membrane, likely through regulating the cholesterol content of lipid rafts.

Utilities of 320-slice computed-tomography for evaluation of tricuspid valve annular diameter before tricuspid-valve-plasty compared with the direct-measurement of tricuspid valve annular diameter during open heart-surgery

cholesterol content in the lipid rafts and as CD14 is usually located in the lipid rafts [6], we investigated whether HDL3, which efficiently modulates cholesterol content in lipid rafts [6], could influence CD14 levels on monocyte cell surface. Incubation of human monocytes with human HDL3 (100 to 500 μg/mL) or reconstituted HDL (mimicking HDL3) (100 to 500 μg/mL) [5] resulted in a reduction of lipid rafts and in a reduction of CD14 levels (Fig. 2C). Overall our data indicate a prevalence of the classical subset but not of the intermediate subset in hypoalphalipoproteinemia which support the observation that the classical subset could be associated with conditions known to increase the risk of cardiovascular events [1] while do not favor a role for the intermediate subset, at least under our experimental conditions. Future studies are warranted to clarify the potential role of HDL in modulating monocyte subset markers and whether influencing HDL levels could affect the distribution of the different subsets in relation to the cardiovascular outcome. References

Haloperidol disrupts lipid rafts and impairs insulin signaling in SH-SY5Y cells

Haloperidol exerts its therapeutic effects basically by acting on dopamine receptors. We previously reported that haloperidol inhibits cholesterol biosynthesis in cultured cells. In the present work we investigated its effects on lipid-raft composition and functionality. In both neuroblastoma SH-SY5Y and promyelocytic HL-60 human cell lines, haloperidol inhibited cholesterol biosynthesis resulting in a decrease of the cell cholesterol content and the accumulation of different sterol intermediates (7-dehydrocholesterol, zymostenol and cholesta-8,14-dien-3β-ol) depending on the dose of the drug. As a consequence, the cholesterol content in lipid rafts was greatly reduced, and several pre-cholesterol sterols, particularly cholesta-8,14-dien-3β-ol, were incorporated into the cell membrane. This was accompanied by the disruption of lipid rafts, with redistribution of flotillin-1 and Fyn and the impairment of insulin-Akt signaling. Supplementing the medium with free cholesterol abrogated the effects of haloperidol on lipid-raft composition and functionality. LDL (low-density lipoprotein), a physiological vehicle of cholesterol in plasma, was much less effective in preventing the effects of haloperidol, which is attributed to the drug's inhibition of intracellular vesicular trafficking. These effects on cellular cholesterol homeostasis that ultimately result in the alteration of lipid-raft-dependent insulin signaling action may underlie some of the metabolic effects of this widely used antipsychotic.

HIV hijacks cholesterol transporter ABCA1 to get access to cellular cholesterol

Cholesterol plays an important role in the HIV life cycle, and cholesterol depletion impairs both production and infectivity of HIV virions. Such dependence on cholesterol suggests that HIV may have evolved mechanisms to ensure access to cellular cholesterol during viral assembly. Recently, we demonstrated that HIV-1, via its protein Nef, inhibits activity of the cellular cholesterol transporter ABCA1 and impairs reverse cholesterol transport (RCT) from infected cells. In this study, we examined interaction between Nef and ABCA1 and investigated the role of ABCA1 in cholesterol delivery to nascent HIV virions. ABCA1 is a 12-transmembrane domain protein, and co-immunoprecipitation analysis using Nef and various fragments of ABCA1 identified multiple sites of interaction. Importantly, Nef was found to interact with the 46-aminoacid carboxyl-terminal domain of ABCA1, which was previously implicated in RCT. Mutation of leucines to alanines in positions 2230, 2233 and 2235 impaired interaction of this C-terminal domain of ABCA1 with Nef. When these mutations were introduced in the full-length ABCA1, such mutant protein was able to support RCT but lost sensitivity to Nef. To further characterize the role of ABCA1 inhibition in HIV biology, we analyzed cholesterol content of lipid rafts and HIV virions produced in cells expressing or not ABCA1. This analysis demonstrated that ABCA1 expression significantly reduced lipid raft cholesterol content, resulting in a corresponding reduction of virus-associated cholesterol and viral infectivity. This result is consistent with ABCA1-mediated redirection of cholesterol from lipid rafts (sites of HIV assembly) to non-raft regions of the plasma membrane (physiological localization of ABCA1). Intriguingly, Nef expression induced re-localization of ABCA1 to lipid rafts, suggesting that HIV hijacks the ABCA1 pathway to deliver cholesterol to the sites of HIV assembly.

High-Density Lipoprotein Reduces the Human Monocyte Inflammatory Response

Whereas the anti-inflammatory effects of high-density lipoprotein (HDL) on endothelial cells are well described, such effects on monocytes are less studied. Human monocytes were isolated from whole blood followed by assessment of CD11b activation/expression and cell adhesion under shear-flow. HDL caused a dose-dependent reduction in the activation of CD11b induced by PMA or receptor-dependent agonists. The constituent of HDL responsible for the antiinflammatory effects on CD11b activation was found to be apolipoprotein A-I (apoA-I). Cyclodextrin, but not cyclodextrin/cholesterol complex, also inhibited PMA-induced CD11b activation implicating cholesterol efflux as the main mechanism. This was further confirmed with the demonstration that cholesterol content of lipid rafts diminished after treatment with the cholesterol acceptors. Blocking ABCA1 with an anti-ABCA1 antibody abolished the effect of apoA-I. Furthermore, monocytes derived from a Tangier disease patient definitively confirmed the requirement of ABCA1 in apoA-I-mediated CD11b inhibition. The antiinflammatory effects of apoA-I were also observed in functional models including cell adhesion to an endothelial cell monolayer, monocytic spreading under shear flow, and transmigration. HDL and apoA-I exhibit an antiinflammatory effect on human monocytes by inhibiting activation of CD11b. ApoA-I acts through ABCA1, whereas HDL may act through several receptors.