BBA - Molecular and Cell Biology of Lipids (v.1801, #8)

Lipids and Alzheimer's disease by Brett Garner (747-749).

Three neuropathological features attracted the attention of Alzheimer in his examination of the brain of Auguste Deter: abnormal fibrillary structures, cortical depositions now termed “plaques,” and glial proliferation, whereby he noted remarkable lipid granule accumulation in the glia. These features were also recorded by Perusini and Kraepelin, but by 1930 the lipoid deposits were no longer regarded by neuropathologists with great interest.
Keywords: Alzheimer's disease; Neuropathology; Lipid deposits; History;

Genetic evidence for the involvement of lipid metabolism in Alzheimer's disease by Lesley Jones; Denise Harold; Julie Williams (754-761).
Alzheimer's disease (AD) is the most common cause of dementia in the elderly and presents a great burden to sufferers and to society. The genetics of rare Mendelian forms of AD have been central to our understanding of AD pathogenesis for the past twenty years and now the genetics of the common form of the disease in the elderly is beginning to be unravelled by genome-wide association studies. Four new genes for common AD have been revealed in the past year, CLU, CR1, PICALM and BIN1. Their possible involvement in lipid metabolism and how that relates to AD is discussed here.
Keywords: Alzheimer's disease; Neurodegeneration; Genetics; GWAS; Clusterin; PICALM; BIN1;

Cholesterol-related genes in Alzheimer's disease by M. Axel Wollmer (762-773).
Experimental data show that cholesterol can modulate central processes in the pathogenesis of Alzheimer's disease (AD). The epidemiological link between elevated plasma cholesterol at midlife and increased risk for AD and the possibility that 3-hydroxy-3-methylglutaryl-coenzym A reductase inhibitors (statins) may be protective against AD support a role of cholesterol metabolism in AD and have rendered it a potential therapeutic target in the treatment and prevention of the disease. The strong association of AD and AD endophenotypes with the APOE gene provides a genetic link between AD and cholesterol metabolism, because the apolipoprotein E (ApoE) is the most prevalent cholesterol transport protein in the central nervous system. Against this background several other genes with a role in cholesterol metabolism have been investigated for association with AD. In this review a compilation of genes related to cholesterol based on the information of the AmiGo gene ontology database is matched with the AlzGene database of AD candidate genes. 56 out of 149 (37.6%) genes with a relation to cholesterol metabolism have been investigated for association with AD. Given that only 660 out of about 23,000 (2.9%) genes have been assessed in hypothesis-driven candidate gene studies on AD, the cholesterol metabolic pathway is strongly represented among these genes. Among 34 cholesterol-related genes for which association with AD has been described APOE, CH25H, CLU, LDLR, SORL1 outstand with positive meta-analyses. However, it is unclear, if their association with AD is mediated by cholesterol-related mechanisms or by more specific direct effects of the respective proteins on Aβ metabolism.
Keywords: Genetic; Polymorphism; Beta amyloid; Lipid;

Multi-dimensional mass spectrometry-based shotgun lipidomics (MDMS-SL) is a well-developed technology for global lipid analysis, which identifies and quantifies individual lipid molecular species directly from lipid extracts of biological samples. By using this technology, we have revealed three marked changes of lipids in brain samples of subjects with mild cognitive impairment of Alzheimer's disease including sulfatides, ceramides, and plasmalogens. Further studies using MDMS-SL lead us to the identification of the potential biochemical mechanisms responsible for the altered lipids at the disease state, which are thoroughly discussed in this minireview. Specifically, in studies to identify the causes responsible for sulfatide depletion at the mild cognitive impairment stage of Alzheimer's disease, we have found that apolipoprotein E is associated with sulfatide transport and mediates sulfatide homeostasis in the nervous system through lipoprotein metabolism pathways and that alterations in apolipoprotein E-mediated sulfatide trafficking can lead to sulfatide depletion in the brain. Collectively, the results obtained from lipidomic analyses of brain samples provide important insights into the biochemical mechanisms underlying the pathogenesis of Alzheimer's disease.
Keywords: Alzheimer's disease; Apolipoprotein E; Ceramide; Electrospray ionization-mass spectrometry; Plasmalogen; Shotgun lipidomics; Sulfatide;

Phospholipase A2 and arachidonic acid in Alzheimer's disease by Rene O. Sanchez-Mejia; Lennart Mucke (784-790).
Essential fatty acids (EFA) play a critical role in the brain and regulate many of the processes altered in Alzheimer's disease (AD). Technical advances are allowing for the dissection of complex lipid pathways in normal and diseased states. Arachidonic acid (AA) and specific isoforms of phospholipase A2 (PLA2) appear to be critical mediators in amyloid-β (Aβ)-induced pathogenesis, leading to learning, memory, and behavioral impairments in mouse models of AD. These findings and ongoing research into lipid biology in AD and related disorders promise to reveal new pharmacological targets that may lead to better treatments for these devastating conditions.
Keywords: Amyloid; Excitotoxicity; Fatty acid; Glutamate receptor; Lipid; Neurodegeneration; Phospholipase A2;

Alzheimer's disease (AD) is a major public health concern due to longer life expectancy in the Western countries. Amyloid-beta (Aβ) oligomers are considered the proximate effectors in the early stages of AD. AD-related cognitive impairment, synaptic loss and neurodegeneration result from interactions of Aβ oligomers with the synaptic membrane and subsequent activation of pro-apoptotic signalling pathways. Therefore, membrane structure and lipid status appear determinant in Aβ-induced toxicity. Numerous epidemiological studies have highlighted the beneficial influence of docosahexaenoic acid (DHA, C22:6 n-3) on the preservation of synaptic function and memory capacities in aged individuals or upon Aβ exposure, whereas its deficiency is presented as a risk factor for AD. An elevated number of studies have been reporting the beneficial effects of dietary DHA supplementation on cognition and synaptic integrity in various AD models. In this review, we describe the important potential of DHA to preserve neuronal and brain functions and classified its numerous molecular and cellular effects from impact on membrane lipid content and organisation to activation of signalling pathways sustaining synaptic function and neuronal survival. DHA appears as one of the most valuable diet ingredients whose neuroprotective properties could be crucial for designing nutrition-based strategies able to prevent AD as well as other lipid- and age-related diseases whose prevalence is progressing in elderly populations.
Keywords: Alzheimer's disease; Docosahexaenoic acid; Membrane lipids; Nutrition; Synapse; Neuroprotection; Cognition;

Phospholipase D in brain function and Alzheimer's disease by Tiago Gil Oliveira; Gilbert Di Paolo (799-805).
Alzheimer's disease is the most common neurodegenerative disorder. Although lipids are major constituents of brain, their role in Alzheimer's disease pathogenesis is poorly understood. Much attention has been given to cholesterol, but growing evidence suggests that other lipids, such as phospholipids, might play an important role in this disorder. In this review, we will summarize the evidence linking phospholipase D, a phosphatidic acid-synthesizing enzyme, to multiple aspects of normal brain function and to Alzheimer's disease. The role of phospholipase D in signaling mechanisms downstream of beta-amyloid as well as in the trafficking and processing of amyloid precursor protein will be emphasized.
Keywords: Lipid enzyme; Lipid metabolism; Phospholipid; Neurodegeneration; Neurodegenerative disorder; Neuronal function;

The strongest known genetic risk factor for the development of late-onset Alzheimer disease is inheritance of the apolipoprotein (apo) E4 (ε4 allele) although the mechanisms underlying this connection are still not entirely clear. In this review, we shall discuss the role of apo E in the brain, particularly in relation to Alzheimer disease. Cholesterol transport and homeostasis in the central nervous system (CNS) are separated from that in the peripheral circulation by the blood–brain barrier. However, the brain operates its own lipoprotein transport system that is mediated by high density lipoprotein-sized, apo E-containing lipoproteins that are synthesized and secreted by glial cells (primarily astrocytes). Several ATP-binding cassette (ABC) transporters are expressed in the brain, including ABCA1 and ABCG1 which play important roles in the transfer of phospholipids and cholesterol to apo E. The astrocyte-derived apo E-containing lipoproteins can bind to, and be internalized by, receptors of the low density lipoprotein receptor superfamily that are located on the surface of neurons. In addition to these receptors serving as endocytosis receptors for lipoproteins, several of these receptors also act as signaling receptors in neurons and activate pathways involved in axonal growth, as well as neuronal survival. These beneficial pathways appear to be enhanced to a greater extent by apo E3 than by apo E4. Apo E has also been implicated in the deposition of amyloid plaques since apo E3, more readily than apo E4, forms a complex with Aß peptides, and mediates the degradation of amyloid deposits.
Keywords: Neuron; Astrocyte; Apolipoprotein E; Cholesterol; Amyloid ß peptide; Alzheimer disease;

Proposed mechanism for lipoprotein remodelling in the brain by Chunjiang Yu; Katherine L. Youmans; Mary J. LaDu (819-823).
Lipoprotein remodelling in the periphery has been extensively studied. For example, the processing of nascent apoAI particles to cholesterol-loaded HDL lipoproteins during reverse cholesterol transport involves a series of enzymes, transporters in peripheral tissue, as well as other apolipoproteins and lipoproteins. These extensive modifications and interconversions are well defined. Here, we present the hypothesis that a similar process occurs within the blood brain barrier (BBB) via glia-secreted lipid-poor apoE particles undergoing remodelling to become mature central nervous system (CNS) lipoproteins. We further pose several pressing issues and future directions for the study of lipoproteins in the brain.
Keywords: Lipid transport; ApoE; Lipoprotein; Brain;

The role of ATP-binding cassette transporter A1 in Alzheimer's disease and neurodegeneration by Radosveta Koldamova; Nicholas F. Fitz; Iliya Lefterov (824-830).
ATP-binding cassette transporter A1 — ABCA1, is the most extensively studied transporter in human pathology. ABCA1 became a primary subject of research in many academic and pharmaceutical laboratories immediately after the discovery that mutations at the gene locus cause severe familial High Density Lipoprotein (HDL) deficiency and, in the homozygous form — Tangier disease. The protein is the major regulator of intracellular cholesterol efflux which is the initial and essential step in the biogenesis and formation of nascent HDL particles. The transcriptional regulation of ABCA1 by nuclear Liver X Receptors (LXR) provided a starting point for drug discovery and development of synthetic LXR ligands/ABCA1 activators for treatment of arteriosclerosis. A series of reports that revealed the role of ABCA1 in Aβ deposition and clearance, as well as the possibility for association of some ABCA1 genetic variants with risk for Alzheimer's disease (AD) brought a new dimension to ABCA1 research. The LXR-ABCA1-APOE regulatory axis is now considered a promising therapeutic target in AD, which includes the only proven risk factor for AD – APOE, at two distinct levels – transcriptional regulation by LXR, and ABCA1 controlled lipidation which can influence Aβ aggregation and amyloid clearance. This review will summarize the results of research on ABCA1, particularly related to AD and neurodegeneration.
Keywords: Alzheimer's disease; ABCA1; Liver X Receptor; Cell cholesterol transport; APOE; Animal model; Amyloid deposition; Cognitive impairment;

Increased expression of the lysosomal cholesterol transporter NPC1 in Alzheimer's disease by Katarina Kågedal; Woojin Scott Kim; Hanna Appelqvist; Sharon Chan; Danni Cheng; Lotta Agholme; Kevin Barnham; Heather McCann; Glenda Halliday; Brett Garner (831-838).
The Niemann-Pick type C1 (NPC1) protein mediates the trafficking of cholesterol from lysosomes to other organelles. Mutations in the NPC1 gene lead to the retention of cholesterol and other lipids in the lysosomal compartment, and such defects are the basis of NPC disease. Several parallels exist between NPC disease and Alzheimer's disease (AD), including altered cholesterol homeostasis, changes in the lysosomal system, neurofibrillary tangles, and increased amyloid-beta generation. How the expression of NPC1 in the human brain is affected in AD has not been investigated so far. In the present study, we measured NPC1 mRNA and protein expression in three distinct regions of the human brain, and we revealed that NPC1 expression is upregulated at both mRNA and protein levels in the hippocampus and frontal cortex of AD patients compared to control individuals. In the cerebellum, a brain region that is relatively spared in AD, no difference in NPC1 expression was detected. Similarly, murine NPC1 mRNA levels were increased in the hippocampus of 12-month-old transgenic mice expressing a familial AD form of human amyloid-beta precursor protein (APP) and presenilin-1 (APP/PS1tg) compared to 12-month-old wild type mice, whereas no change in NPC1 was detected in mouse cerebellum. Immunohistochemical analysis of human hippocampus indicated that NPC1 expression was strongest in neurons. However, in vitro studies revealed that NPC1 expression was not induced by transfecting SK-N-SH neurons with human APP or by treating them with oligomeric amyloid-beta peptide. Total cholesterol levels were reduced in hippocampus from AD patients compared to control individuals, and it is therefore possible that the increased expression of NPC1 is linked to perturbed cholesterol homeostasis in AD.
Keywords: Alzheimer's disease; Niemann-Pick; Cholesterol; Lysosome; CA1; Hippocampus; Cerebellum; Frontal cortex;

Cholesterol changes in Alzheimer's disease: methods of analysis and impact on the formation of enlarged endosomes by Jack-Christophe Cossec; Catherine Marquer; Mai Panchal; Adina N. Lazar; Charles Duyckaerts; Marie-Claude Potier (839-845).
An increasing number of results implicating cholesterol metabolism in the pathophysiology of Alzheimer's disease (AD) suggest cholesterol as a target for treatment. Research in genetics, pathology, epidemiology, biochemistry, and cell biology, as well as in animal models, suggests that cholesterol, its transporter in the brain, apolipoprotein E, amyloid precursor protein, and amyloid-β all interact in AD pathogenesis. Surprisingly, key questions remain unanswered due to the lack of sensitive and specific methods for assessing cholesterol levels in the brain at subcellular resolution. The aims of this review are not only to discuss the various methods for measuring cholesterol and its metabolites and to catalog results obtained from AD patients but also to discuss some new data linking high plasma membrane cholesterol with modifications of the endocytic compartments. These studies are particularly relevant to AD pathology, since enlarged endosomes are believed to be the first morphological change observed in AD brains, in both sporadic cases and Down syndrome.
Keywords: Alzheimer's disease; Cholesterol; Down syndrome; Endosome; Methyl-beta-cyclodextrine; Rab5;

Clathrin-dependent APP endocytosis and Aβ secretion are highly sensitive to the level of plasma membrane cholesterol by Jack-Christophe Cossec; Anne Simon; Catherine Marquer; Randal X. Moldrich; Christophe Leterrier; Jean Rossier; Charles Duyckaerts; Zsolt Lenkei; Marie-Claude Potier (846-852).
Several lines of evidence support a strong relationship between cholesterol and Alzheimer's disease pathogenesis. Membrane cholesterol is known to modulate amyloid precursor protein (APP) endocytosis and amyloid-β (Aβ) secretion. Here we show in a human cell line model of endocytosis (HEK293 cells) that cholesterol exerts these effects in a dose-dependent and linear manner, over a wide range of concentrations (-40% to + 40% variations of plasma membrane cholesterol induced by methyl-beta-cyclodextrin (MBCD) and MBCD-cholesterol complex respectively). We found that the gradual effect of cholesterol is inhibited by small interference RNA-mediated downregulation of clathrin. Modulation of clathrin-mediated APP endocytosis by cholesterol was further demonstrated using mutants of proteins involved in the formation of early endosomes (dynamin2, Eps15 and Rab5). Importantly we show that membrane proteins other than APP are not affected by cholesterol to the same extent. Indeed clathrin-dependent endocytosis of transferrin and cannabinoid1 receptors as well as internalization of surface proteins labelled with a biotin derivative (sulfo-NHS-SS-biotin) were not sensitive to variations of plasma membrane cholesterol from -40% to 40%. In conclusion clathrin-dependent APP endocytosis appears to be very sensitive to the levels of membrane cholesterol. These results suggest that cholesterol increase in AD could be responsible for the enhanced internalization of clathrin-, dynamin2-, Eps15- and Rab5-dependent endocytosis of APP and the ensuing overproduction of Aβ.
Keywords: Alzheimer's disease; Cholesterol; Endocytosis; Clathrin; Amyloidβ;

Many preclinical and clinical studies have implied a role for cholesterol in the pathogenesis of Alzheimer's disease (AD). In this review we will discuss the movement of intracellular cholesterol and how normal distribution, transport, and export of cholesterol are vital for regulation of the AD related protein, Aβ. We focus on cholesterol distribution in the plasma membrane, transport through the endosomal/lysosomal system, control of cholesterol intracellular signaling at the endoplasmic reticulum and Golgi, the HMG-CoA reductase pathway and finally export of cholesterol from the cell.
Keywords: Alzheimer's disease; Amyloid; Apolipoprotein E (apoE); APP; Cholesterol; Cholesterol ester; Lipid raft; Sterol regulatory element binding protein (SREBP); SREBP cleavage activating protein (Scap); Niemann–Pick type C disease (NPC);

Membrane rafts in Alzheimer's disease beta-amyloid production by Kulandaivelu S. Vetrivel; Gopal Thinakaran (860-867).
Alzheimer's disease (AD), the most common age-associated dementing disorder, is pathologically manifested by progressive cognitive dysfunction concomitant with the accumulation of senile plaques consisting of amyloid-β (Aβ) peptide aggregates in the brain of affected individuals. Aβ is derived from a type I transmembrane protein, amyloid precursor protein (APP), by the sequential proteolytic events mediated by β-site APP cleaving enzyme 1 (BACE1) and γ-secretase. Multiple lines of evidence have implicated cholesterol and cholesterol-rich membrane microdomains, termed lipid rafts in the amyloidogenic processing of APP. In this review, we summarize the cell biology of APP, β- and γ-secretases and the data on their association with lipid rafts. Then, we will discuss potential raft targeting signals identified in the secretases and their importance on amyloidogenic processing of APP.
Keywords: Alzheimer's disease; Amyloid; Amyloid precursor protein; Cholesterol; Palmitoylation; Lipid rafts;

Aβ polymerization through interaction with membrane gangliosides by Katsumi Matsuzaki; Koichi Kato; Katsuhiko Yanagisawa (868-877).
Clarification of the molecular and cellular mechanisms underlying the assembly of amyloid β-protein (Aβ) into insoluble fibrils in the brain has been one of the biggest challenges in the research on Alzheimer disease (AD). We previously identified a novel Aβ species, which was characterized by its tight binding to GM1 ganglioside (GM1), in the brain showing early pathological changes of AD. The ganglioside-bound Aβ (GAβ) possessed unique characteristics, including its altered immunoreactivity, which suggests its distinct conformation from native Aβ, and its strong potency to accelerate Aβ assembly into fibrils. On the basis of these characteristics, it was hypothesized that Aβ adopts an altered conformation following interaction with GM1, leading to the generation of GAβ, and then GAβ acts as an endogenous seed for Alzheimer amyloid in the brain. To date, various in vitro and in vivo studies on GAβ have revealed how Aβ binds to gangliosides, i.e., what are the favorable physicochemical and neurobiological conditions for generating GAβ, and what is the pathological significance of ganglioside-induced Aβ assembly in the development of AD. Interestingly, GAβ is favorably generated in the unique ganglioside-enriched (clustered), raft-like microdomains; moreover, amyloid fibrils formed in the presence of gangliosides are neurotoxic. Furthermore, the conformational change of Aβ in the presence of ganglioside has been characterized by an NMR study. In this review, we focus on the recent progress of GAβ studies and highlight the possibility that ganglioside binding is the initial and common step in the development of a part of human misfolding-type amyloidoses, including AD.
Keywords: Alzheimer disease; Amyloid β-protein; Ganglioside; Raft;

Roles for dysfunctional sphingolipid metabolism in Alzheimer's disease neuropathogenesis by Norman J. Haughey; Veera V.R. Bandaru; Mihyun Bae; Mark P. Mattson (878-886).
Sphingolipids in the membranes of neurons play important roles in signal transduction, either by modulating the localization and activation of membrane-associated receptors or by acting as precursors of bioactive lipid mediators. Activation of cytokine and neurotrophic factor receptors coupled to sphingomyelinases results in the generation of ceramides and gangliosides, which in turn, modify the structural and functional plasticity of neurons. In aging and neurodegenerative conditions such as Alzheimer's disease (AD), there are increased membrane-associated oxidative stress and excessive production and accumulation of ceramides. Studies of brain tissue samples from human subjects, and of experimental models of the diseases, suggest that perturbed sphingomyelin metabolism is a pivotal event in the dysfunction and degeneration of neurons that occurs in AD and HIV dementia. Dietary and pharmacological interventions that target sphingolipid metabolism should be pursued for the prevention and treatment of neurodegenerative disorders.
Keywords: Alzheimer's disease; Sphingomylein; Ceramide; Sphingosine; Ganglioside; Synapse;

Modulation of amyloid precursor protein processing by synthetic ceramide analogues by Hongyun Li; Woojin S. Kim; Gilles J. Guillemin; Andrew F. Hill; Genevieve Evin; Brett Garner (887-895).
Previous studies suggest that membrane lipids may regulate proteolytic processing of the amyloid precursor protein (APP) to generate amyloid-beta peptide (Abeta). In the present study, we have assessed the capacity for a series of structurally related synthetic ceramide analogues to modulate APP processing in vitro. The compounds tested are established glucosylceramide synthase (GS) inhibitors based on the d-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) structure. PDMP and related compounds PPMP and EtDO-P4 inhibited Abeta secretion from Chinese hamster ovary cells expressing human APP (CHO-APP) with approximate IC50 values of 15, 5, and 1 μM, respectively. A trend for reduced secretion of the APP alpha-secretase product, sAPPalpha, was also observed in PDMP-treated cells but not in PPMP- or ETDO-P4-treated cells, whereas levels of the cellular beta-secretase product APP C-terminal fragment, CTFbeta, were increased by both PDMP and PPMP but unaltered with EtDO-P4 treatment. Our data also revealed that EtDO-P4 inhibits endogenous Abeta production by human neurons. In conclusion, this study provides novel information regarding the regulation of APP processing by synthetic ceramide analogues and reveals that the most potent of these compounds is EtDO-P4.
Keywords: Glycosphingolipid; Sphingolipids; Amyloid precursor protein; Alzheimer's disease; Neurodegeneration; Amyloid-beta peptide;

Isoprenoids, small GTPases and Alzheimer's disease by Gero P. Hooff; W. Gibson Wood; Walter E. Müller; Gunter P. Eckert (896-905).
The mevalonate pathway is a crucial metabolic pathway for most eukaryotic cells. Cholesterol is a highly recognized product of this pathway but growing interest is being given to the synthesis and functions of isoprenoids. Isoprenoids are a complex class of biologically active lipids including for example, dolichol, ubiquinone, farnesylpyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP). Early work had shown that the long-chain isoprenoid dolichol is decreased but that dolichyl phosphate and ubiquinone are elevated in brains of Alzheimer′s disease (AD) patients. Until recently, levels of their biological active precursors FPP and GGPP were unknown. These short-chain isoprenoids are critical in the post-translational modification of certain proteins which function as molecular switches in numerous signaling pathways. The major protein families belong to the superfamily of small GTPases, consisting of roughly 150 members. Recent experimental evidence indicated that members of the small GTPases are involved in AD pathogenesis and stimulated interest in the role of FPP and GGPP in protein prenylation and cell function. A straightforward prediction derived from those studies was that FPP and GGPP levels would be elevated in AD brains as compared with normal neurological controls. For the first time, recent evidence shows significantly elevated levels of FPP and GGPP in human AD brain tissue. Cholesterol levels did not differ between AD and control samples. One obvious conclusion is that homeostasis of FPP and GGPP but not of cholesterol is specifically targeted in AD. Since prenylation of small GTPases by FPP or GGPP is indispensable for their proper function we are proposing that these two isoprenoids are up-regulated in AD resulting in an over abundance of certain prenylated proteins which contributes to neuronal dysfunction.
Keywords: Farnesylpyrophosphate; Geranylgeranylpyrophosphate; Synaptic plasticity; Small GTPases; Rho; Cholesterol;

Lipid mediators in the nucleus: Their potential contribution to Alzheimer's disease by Akhlaq A. Farooqui; Wei-Yi Ong; Tahira Farooqui (906-916).
Degradation of glycerophospholipids, sphingolipids and cholesterol in the nucleus modulates neural cell proliferation and differentiation, inflammation, apoptosis, migration, cell adhesion, and intracellular trafficking. Extracellular signals from agonists (neurotransmitters, cytokines, and growth factors) regulate the activity of a key set of lipid-metabolizing enzymes, such as phospholipases, sphingomyelinases, and cholesterol hydroxylases. These enzymes and their downstream targets constitute a complex lipid signaling network with multiple nodes of interaction and cross-regulation through their lipid mediators, which include eicosanoids, docosanoids, diacylglycerols, platelet activating factor, lysophosphatidic acid, ceramide and ceramide 1-phosphate, sphingosine and sphingosine 1-phosphate, and hydroxycholesterols. Receptors for above lipid mediators are localized at the neural cell nucleus. Stimulation of isolated nuclei with these lipids and agonists results in changes in transcriptional regulation of major genes, including c-fos, cylooxygenase-2, secretory phospholipase A2 and endothelial as well as inducible nitric oxide synthases. Imbalances in signaling network involving above genes may contribute to the pathogenesis of human neurological disorders. In this review, we have attempted to integrate available information on above lipid mediators in the nucleus. In addition, attempts have been made to explain cross-talk among glycerophospholipid-, sphingolipid-, and cholesterol-derived lipid mediators in neural cell death in Alzheimer's disease.
Keywords: Nucleus; Eicosanoid; Docosanoid; Ceramide; Sphingosine; Hydroxycholesterol;

A second class of nuclear receptors for oxysterols: Regulation of RORα and RORγ activity by 24S-hydroxycholesterol (cerebrosterol) by Yongjun Wang; Naresh Kumar; Christine Crumbley; Patrick R. Griffin; Thomas P. Burris (917-923).
The retinoic acid receptor-related orphan receptors α and γ (RORα [NR1F1] and RORγ [NR1F3]) are members of the nuclear hormone receptor superfamily. These 2 receptors regulate many physiological processes including development, metabolism and immunity. We recently found that certain oxysterols, namely the 7-substituted oxysterols, bound to the ligand binding domains (LBDs) of RORα and RORγ with high affinity, altered the LBD conformation and reduced coactivator binding resulting in suppression of the constitutive transcriptional activity of these two receptors. Here, we show that another oxysterol, 24S-hydroxycholesterol (24S-OHC), is also a high affinity ligand for RORα and RORγ (K i ∼ 25 nM). 24S-OHC is also known as cerebrosterol due to its high level in the brain where it plays an essential role as an intermediate in cholesterol elimination from the CNS. 24S-OHC functions as a RORα/γ inverse agonist suppressing the constitutive transcriptional activity of these receptors in cotransfection assays. Additionally, 24S-OHC suppressed the expression of several RORα target genes including BMAL1 and REV-ERBα in a ROR-dependent manner. We also demonstrate that 24S-OHC decreases the ability of RORα to recruit the coactivator SRC-2 when bound to the BMAL1 promoter. We also noted that 24(S), 25-epoxycholesterol selectively suppressed the activity of RORγ. These data indicate that RORα and RORγ may serve as sensors of oxsterols. Thus, RORα and RORγ display an overlapping ligand preference with another class of oxysterol nuclear receptors, the liver X receptors (LXRα [NR1H3] and LXRβ [NR1H2]).
Keywords: Cholesterol; LXR; Lipid; REV-ERB; Circadian; Orphan receptor;

Involvements of the lipid peroxidation product, HNE, in the pathogenesis and progression of Alzheimer's disease by D. Allan Butterfield; Miranda L. Bader Lange; Rukhsana Sultana (924-929).
Alzheimer's disease (AD) is an age-related neurodegenerative disorder. A number of hypotheses have been proposed to explain AD pathogenesis. One such hypothesis proposed to explain AD pathogenesis is the oxidative stress hypothesis. Increased levels of oxidative stress markers including the markers of lipid peroxidation such as acrolein, 4-hydroxy-2-trans-nonenal (HNE), malondialdehyde, etc. are found in brains of AD subjects. In this review, we focus principally on research conducted in the area of HNE in the central nervous system (CNS) of AD and mild cognitive impairment (MCI), and further, we discuss likely consequences of lipid peroxidation with respect to AD pathogenesis and progression. Based on the research conducted so far in the area of lipid peroxidation, it is suggested that lipid accessible antioxidant molecules could be a promising therapeutic approach to treat or slow progression of MCI and AD.
Keywords: Lipid peroxidation; Alzheimer's disease; HNE; Amyloid beta-peptide; Proteomics; Oxidatively modified proteins;

In its sporadic form Alzheimer's disease (AD) results from a combination of genetic and environmental risk factors with abnormal oxidative reactions, which result in free radical mediated injury of the brain. Isoprostanes are oxidized lipids formed by a free radical mediated mechanism, which in recent years have emerged as a reliable and sensitive marker of lipid peroxidation and oxidative stress. Consistent data show that they are increased in the brain of human AD as well as AD animal models. Besides their role as biomarkers, isoprostanes possess important biological effects, functioning as mediators of the cellular response to oxidative stress within the CNS. Recent evidence indicates that these lipid oxidation products, by activating the thromboxane receptor system, mediate the pro-amyloidotic neuronal response to oxidative stress in an experimental model of AD. This novel observation has important clinical implication, since pharmacologic modulation of the TP receptor system by selective antagonists, some of which are already available, could represent a novel therapeutic opportunity for AD as disease-modifying agents.
Keywords: Isoprostane; Oxidative stress; Alzheimer's disease; Amyloid beta; Thromboxane receptor;

Brain cholesterol in normal and pathological aging by Mauricio Martin; Carlos G. Dotti; Maria Dolores Ledesma (934-944).
Correct lipid homeostasis at the plasma membrane is essential for cell survival and performance. These are critically challenged in the aging brain. Changes in the levels of cholesterol, a major membrane component especially enriched in neurons, accompany the brain aging process. They also occur in neurodegenerative diseases. Understanding the causes and consequences of these changes is a crucial step when trying to delay the cognitive decline, which comes with age, or to design strategies to fight neurodegenerative disorders such as Alzheimer's disease. We here review work that has contributed to this understanding.
Keywords: Cholesterol; aging; Alzheimer's disease; CYP46; brain;

Alterations of cholesterol precursor levels in Alzheimer's disease by Heike Kölsch; Reinhard Heun; Frank Jessen; Julius Popp; Frank Hentschel; Wolfgang Maier; Dieter Lütjohann (945-950).
Cerebral and extracerebral cholesterol metabolism are altered in Alzheimer's disease (AD) as indicated by reduced plasma levels of the cholesterol elimination products 24S-hydroxycholesterol, which is of cerebral origin, and of 27-hydroxycholesterol, which is formed extracerebrally. However, it has to be evaluated, if changes of cholesterol metabolism in the whole body or in the CNS are exclusively due to the altered elimination of cholesterol or are also due to altered de novo synthesis in AD. We investigated CSF and plasma levels of cholesterol and of its precursors lanosterol, lathosterol and desmosterol in AD patients and non-demented controls. We found CSF levels of cholesterol (p  = 0.011), absolute levels of all investigated cholesterol precursors (each p  < 0.001) and ratios of cholesterol precursors/cholesterol (each < 0.01) to be lower in AD patients as compared to controls. In plasma, the absolute levels of lanosterol (p  = 0.026) and lathosterol (p  < 0.001) and the ratio of lathosterol/cholesterol (p  = 0.002) but none of the other investigated parameters were reduced in AD patients (p  > 0.1). Furthermore, ratios of desmosterol/lathosterol in CSF (p  = 0.023) and plasma (p  = 0.009) were higher in AD patients as compared to controls. Our data support the hypothesis that cholesterol metabolism is altered in AD and further suggest that especially cholesterol de novo synthesis within the CNS of AD patients might be reduced. These findings raise doubt on a beneficial effect of cholesterol lowering treatment in manifest AD.
Keywords: Alzheimer disease; Cholesterol metabolism; Cholesterol synthesis; Lathosterol; Desmosterol; Lanosterol;

Allopregnanolone levels are reduced in temporal cortex in patients with Alzheimer's disease compared to cognitively intact control subjects by Jennifer C. Naylor; Jason D. Kilts; Christine M. Hulette; David C. Steffens; Dan G. Blazer; John F. Ervin; Jennifer L. Strauss; Trina B. Allen; Mark W. Massing; Victoria M. Payne; Nagy A. Youssef; Lawrence J. Shampine; Christine E. Marx (951-959).
The neurosteroid allopregnanolone has pronounced neuroprotective actions, increases myelination, and enhances neurogenesis. Evidence suggests that allopregnanolone dysregulation may play a role in the pathophysiology of Alzheimer's disease (AD) and other neurodegenerative disorders. Our prior data demonstrate that allopregnanolone is reduced in prefrontal cortex in male patients with AD compared to male cognitively intact control subjects, and inversely correlated with neuropathological disease stage (Braak and Braak). We therefore determined if allopregnanolone levels are also reduced in AD patients compared to control subjects in temporal cortex, utilizing a larger set of samples from both male and female patients. In addition, we investigated if neurosteroids are altered in subjects who are APOE4 allele carriers. Allopregnanolone, dehydroepiandrosterone (DHEA), and pregnenolone levels were determined in temporal cortex postmortem samples by gas chromatography/mass spectrometry, preceded by high performance liquid chromatography (40 subjects with AD/41 cognitively intact control subjects). Allopregnanolone levels are reduced in temporal cortex in patients with AD (median 2.68 ng/g, n  = 40) compared to control subjects (median 5.64 ng/g, n  = 41), Mann–Whitney p  = 0.0002, and inversely correlated with Braak and Braak neuropathological disease stage (Spearman r  = − 0.38, p  = 0.0004). DHEA and pregnenolone are increased in patients with AD compared to control subjects. Patients carrying an APOE4 allele demonstrate reduced allopregnanolone levels in temporal cortex (Mann–Whitney p  = 0.04). In summary, our findings indicate that neurosteroids are altered in temporal cortex in patients with AD and related to neuropathological disease stage. In addition, the APOE4 allele is associated with reduced allopregnanolone levels. Neurosteroids may be relevant to the neurobiology and therapeutics of AD.
Keywords: Alzheimer's disease; temporal cortex; allopregnanolone; DHEA; pregnenolone; neurosteroid; postmortem;

ACAT inhibition and amyloid beta reduction by Raja Bhattacharyya; Dora M. Kovacs (960-965).
Alzheimer's disease (AD) is a devastating neurodegenerative disorder. Accumulation and deposition of the beta-amyloid (Aβ) peptide generated from its larger amyloid precursor protein (APP) is one of the pathophysiological hallmarks of AD. Intracellular cholesterol was shown to regulate Aβ production. Recent genetic and biochemical studies indicate that not only the amount, but also the distribution of intracellular cholesterol is critical to regulate Aβ generation. Acyl-coenzyme A: cholesterol acyl-transferase (ACAT) is a family of enzymes that regulates the cellular distribution of cholesterol by converting membrane cholesterol into hydrophobic cholesteryl esters for cholesterol storage and transport. Using pharmacological inhibitors and transgenic animal models, we and others have identified ACAT1 as a potential therapeutic target to lower Aβ generation and accumulation. Here we discuss data focusing on ACAT inhibition as an effective strategy for the prevention and treatment of AD.
Keywords: Alzheimer's disease; Aβ; ACAT; Cholesterol; Cholesteryl ester; Lipid droplet;

Role of amyloid beta in lipid homeostasis by Sven Grösgen; Marcus O.W. Grimm; Petra Frieß; Tobias Hartmann (966-974).
Alzheimer's disease (AD), the most common neurodegenerative disorder, which affects more than 35 million people worldwide, is characterized by a massive accumulation of tangles and amyloid plaques. Several risk factors linked to lipid homeostasis have been identified. Apolipoprotein E (ApoE), which also has a strong impact in coronary artery disease, is besides aging the most prominent risk factor in sporadic AD. High levels of lipoproteins and cholesterol increase the risk of AD and some cholesterol lowering drugs like statins seem to correlate with a reduced risk for dementia. Moreover, cholesterol increases amyloid β (Aβ) production, which is derived from amyloid precursor protein (APP) by proteolytic processing. Beside cholesterol, other lipids that strongly modulate APP processing could be identified and interestingly the APP cleavage products itself regulate lipid homeostasis resulting in complex regulatory feedback cycles. Here, we review the mechanistic link of cholesterol and sphingolipid homeostasis and APP processing and the consequence of this bidirectional link for and in AD. Although cholesterol is the best studied brain lipid in AD, many other lipids are involved in the Aβ-lipid regulatory system and some of these lipids exceed the cholesterol effect on Aβ production [1–5]. This involvement is bidirectional. On the one hand, lipids control APP processing and, on the other hand, APP processing controls the levels of several key lipids [6, ]. Beside the physiological function of APP processing in lipid homeostasis, under pathological conditions like AD, these regulating (feedback-) cycles are dysfunctional. Additionally, mutual influence of lipids and APP processing raises the question if altered lipid homeostasis is the cause or consequence of AD.
Keywords: Alzheimer's disease; Lipids; Amyloid beta; Sphingolipid; Secretase; Ganglioside; Cholesterol; Raft; Sphingomyelinase; SMase; 3-Hydroxy-3-methylglutaryl CoA; HMGCR;

It is generally believed that cholesterol homoeostasis in the brain is both linked to and impacted by Alzheimer's disease (AD). For example, elevated levels of cholesterol in neuronal plasma and endosome membranes appear to be a pro-amyloidogenic factor. The recent observation that the C-terminal transmembrane domain (C99, also known as the β-C-terminal fragment, or β-CTF) of the amyloid precursor protein (APP) specifically binds cholesterol helps to tie together previously loose ends in the web of our understanding of Alzheimer's–cholesterol relationships. In particular, binding of cholesterol to C99 appears to favor the amyloidogenic pathway in cells by promoting localization of C99 in lipid rafts. In turn, the products of this pathway—amyloid-β and the intracellular domain of the APP (AICD)—may down-regulate ApoE-mediated cholesterol uptake and cholesterol biosynthesis. If confirmed, this negative-feedback loop for membrane cholesterol levels has implications for understanding the function of the APP and for devising anti-amyloidogenic preventive strategies for AD.
Keywords: Alzheimer's disease; Amyloid precursor protein; APP; Cholesterol; NMR; Lipid raft; Membrane; Structure; Trafficking;