The crosstalk between extracellular matrix proteins and Tau

Alzheimer's disease is progressive neurodegenerative disease characterize by the presence of extracellular accumulation of amyloid-β plaques and intracellular deposits of neurofibrillary tangles of Tau. Apart from axonal depositions pathological aggregated Tau protein is known to secrete into extracellular spaces and propagate through seeding mechanism. Microglia, the immune cells of the brain display modest ability to internalize the extracellular Tau and degrade it through endolysosomal pathway. However, the excessive burden of pathoproteins weakens the phagocytic ability of microglia. Extracellular supplementation of omega-3 fatty acids (n-3) may regulate the phagocytosis of microglia as they mediate the anti-inflammatory polarization of microglia through membrane lipid compositions changes. The internalization of extracellular Tau in the microglia is regulated by cortical membrane-associated actin remodeling driven by interplay of actin-binding proteins. On the other hand, Tau display capability bind and interact with various actin-binding protein owing to the presence of proline-rich domain in the structure and regulate their activation. In this study, we hypothesize that internalization of Tau in the presence of omega-3 fatty acids would propagate the Tau-mediated activation of actin-binding proteins as well as extracellular matrix and in turn modulate cortical actin remodeling for phagocytosis.

Phospholipidomics in Clinical Trials for Brain Disorders: Advancing our Understanding and Therapeutic Potentials

Phospholipidomics is a specialized branch of lipidomics that focuses on the characterization and quantification of phospholipids. By using sensitive analytical techniques, phospholipidomics enables researchers to better understand the metabolism and activities of phospholipids in brain disorders such as Alzheimer's and Parkinson's diseases. In the brain, identifying specific phospholipid biomarkers can offer valuable insights into the underlying molecular features and biochemistry of these diseases through a variety of sensitive analytical techniques. Phospholipidomics has emerged as a promising tool in clinical studies, with immense potential to advance our knowledge of neurological diseases and enhance diagnosis and treatment options for patients. In the present review paper, we discussed numerous applications of phospholipidomics tools in clinical studies, with a particular focus on the neurological field. By exploring phospholipids' functions in neurological diseases and the potential of phospholipidomics in clinical research, we provided valuable insights that could aid researchers and clinicians in harnessing the full prospective of this innovative practice and improve patient outcomes by providing more potent treatments for neurological diseases.

Towards a Unitary Hypothesis of Alzheimer's Disease Pathogenesis

The "amyloid cascade" hypothesis of Alzheimer's disease (AD) pathogenesis invokes the accumulation in the brain of plaques (containing the amyloid-β protein precursor [AβPP] cleavage product amyloid-β [Aβ]) and tangles (containing hyperphosphorylated tau) as drivers of pathogenesis. However, the poor track record of clinical trials based on this hypothesis suggests that the accumulation of these peptides is not the only cause of AD. Here, an alternative hypothesis is proposed in which the AβPP cleavage product C99, not Aβ, is the main culprit, via its role as a regulator of cholesterol metabolism. C99, which is a cholesterol sensor, promotes the formation of mitochondria-associated endoplasmic reticulum (ER) membranes (MAM), a cholesterol-rich lipid raft-like subdomain of the ER that communicates, both physically and biochemically, with mitochondria. We propose that in early-onset AD (EOAD), MAM-localized C99 is elevated above normal levels, resulting in increased transport of cholesterol from the plasma membrane to membranes of intracellular organelles, such as ER/endosomes, thereby upregulating MAM function and driving pathology. By the same token, late-onset AD (LOAD) is triggered by any genetic variant that increases the accumulation of intracellular cholesterol that, in turn, boosts the levels of C99 and again upregulates MAM function. Thus, the functional cause of AD is upregulated MAM function that, in turn, causes the hallmark disease phenotypes, including the plaques and tangles. Accordingly, the MAM hypothesis invokes two key interrelated elements, C99 and cholesterol, that converge at the MAM to drive AD pathogenesis. From this perspective, AD is, at bottom, a lipid disorder.

Lipidome Profiling in Childhood Obesity Compared to Adults: A Pilot Study

The objective is to assess the circulating lipidome of children with obesity before and after lifestyle intervention and to compare the data to the circulating lipidome of adults with obesity before and after bariatric surgery. Ten pediatric (PE) and thirty adult (AD) patients with obesity were prospectively recruited at a referral single center. The PE cohort received lifestyle recommendations. The AD cohort underwent bariatric surgery. Clinical parameters and lipidome were analyzed in serum before and after six months of metabolic intervention. The abundance of phosphatidylinositols in the PE cohort and phosphatidylcholines in the AD significantly increased, while O-phosphatidylserines in the PE cohort and diacyl/triacylglycerols in the AD decreased. Fifteen lipid species were coincident in both groups after lifestyle intervention and bariatric surgery. Five species of phosphatidylinositols, sphingomyelins, and cholesteryl esters were upregulated. Eight species of diacylglycerols, glycerophosphoglycerols, glycerophosphoethanolamines, and phosphatidylcholines were downregulated. Most matching species were regulated in the same direction except for two phosphatidylinositols: PI(O-36:2) and PI(O-34:0). A specific set of lipid species regulated after bariatric surgery in adult individuals was also modulated in children undergoing lifestyle intervention, suggesting they may constitute a core circulating lipid profile signature indicative of early development of obesity and improvement after clinical interventions regardless of individual age.

Inhibition of ACAT as a Therapeutic Target for Alzheimer's Disease Is Independent of ApoE4 Lipidation

APOE4, encoding apolipoprotein E4 (apoE4), is the greatest genetic risk factor for Alzheimer's disease (AD), compared to the common APOE3. While the mechanism(s) underlying APOE4-induced AD risk remains unclear, increasing the lipidation of apoE4 is an important therapeutic target as apoE4-lipoproteins are poorly lipidated compared to apoE3-lipoproteins. ACAT (acyl-CoA: cholesterol-acyltransferase) catalyzes the formation of intracellular cholesteryl-ester droplets, reducing the intracellular free cholesterol (FC) pool. Thus, inhibiting ACAT increases the FC pool and facilitates lipid secretion to extracellular apoE-containing lipoproteins. Previous studies using commercial ACAT inhibitors, including avasimibe (AVAS), as well as ACAT-knock out (KO) mice, exhibit reduced AD-like pathology and amyloid precursor protein (APP) processing in familial AD (FAD)-transgenic (Tg) mice. However, the effects of AVAS with human apoE4 remain unknown. In vitro, AVAS induced apoE efflux at concentrations of AVAS measured in the brains of treated mice. AVAS treatment of male E4FAD-Tg mice (5xFAD+/-APOE4+/+) at 6-8 months had no effect on plasma cholesterol levels or distribution, the original mechanism for AVAS treatment of CVD. In the CNS, AVAS reduced intracellular lipid droplets, indirectly demonstrating target engagement. Surrogate efficacy was demonstrated by an increase in Morris water maze measures of memory and postsynaptic protein levels. Amyloid-beta peptide (Aβ) solubility/deposition and neuroinflammation were reduced, critical components of APOE4-modulated pathology. However, there was no increase in apoE4 levels or apoE4 lipidation, while amyloidogenic and non-amyloidogenic processing of APP were significantly reduced. This suggests that the AVAS-induced reduction in Aβ via reduced APP processing was sufficient to reduce AD pathology, as apoE4-lipoproteins remained poorly lipidated.

Progress of potential drugs targeted in lipid metabolism research

Lipids are a class of complex hydrophobic molecules derived from fatty acids that not only form the structural basis of biological membranes but also regulate metabolism and maintain energy balance. The role of lipids in obesity and other metabolic diseases has recently received much attention, making lipid metabolism one of the attractive research areas. Several metabolic diseases are linked to lipid metabolism, including diabetes, obesity, and atherosclerosis. Additionally, lipid metabolism contributes to the rapid growth of cancer cells as abnormal lipid synthesis or uptake enhances the growth of cancer cells. This review introduces the potential drug targets in lipid metabolism and summarizes the important potential drug targets with recent research progress on the corresponding small molecule inhibitor drugs. The significance of this review is to provide a reference for the clinical treatment of metabolic diseases related to lipid metabolism and the treatment of tumors, hoping to deepen the understanding of lipid metabolism and health.

Autophagy inhibition and reactive oxygen species elimination by acetyl-CoA acetyltransferase 1 through fused in sarcoma protein to promote prostate cancer

BACKGROUND

Prostate cancer is a major health issue affecting the male population worldwide, and its etiology remains relatively unknown. As presented on the Gene Expression Profiling Interactive Analysis database, acetyl-CoA acetyltransferase 1 (ACAT1) acts as a prostate cancer-promoting factor. ACAT1 expression in prostate cancer tissues is considerably higher than that in normal tissues, leading to a poor prognosis in patients with prostate cancer. Here, we aimed to study the role of the ACAT1-fused in sarcoma (FUS) complex in prostate cancer and identify new targets for the diagnosis and treatment of the disease.

METHODS

We conducted immunohistochemical analysis of 57 clinical samples and in vitro and in vivo experiments using a mouse model and plasmid constructs to determine the expression of ACAT1 in prostate cancer.

RESULTS

The relationship between the expression of ACAT1 and the Gleason score was significant. The expression of ACAT1 was higher in tissues with a Gleason score of > 7 than in tissues with a Gleason score of ≤7 (P = 0.0011). In addition, we revealed that ACAT1 can interact with the FUS protein.

CONCLUSIONS

In prostate cancer, ACAT1 promotes the expression of P62 and Nrf2 through FUS and affects reactive oxygen species scavenging. These effects are due to the inhibition of autophagy by ACAT1. That is, ACAT1 promotes prostate cancer by inhibiting autophagy and eliminating active oxygen species. The expression of ACAT1 is related to prostate cancer. Studying the underlying mechanism may provide a new perspective on the treatment of prostate cancer.

Brain lipidomics: From functional landscape to clinical significance

Lipids are crucial components of cellular function owing to their role in membrane formation, intercellular signaling, energy storage, and homeostasis maintenance. In the brain, lipid dysregulations have been associated with the etiology and progression of neurodegeneration and other neurological pathologies. Hence, brain lipids are emerging as important potential targets for the early diagnosis and prognosis of neurological diseases. This review aims to highlight the significance and usefulness of lipidomics in diagnosing and treating brain diseases. We explored lipid alterations associated with brain diseases, paying attention to organ-specific characteristics and the functions of brain lipids. As the recent advances in brain lipidomics would have been impossible without advances in analytical techniques, we provide up-to-date information on mass spectrometric approaches and integrative analysis with other omic approaches. Last, we present the potential applications of lipidomics combined with artificial intelligence techniques and interdisciplinary collaborative research for treating brain diseases with clinical heterogeneities.

ACAT-1-Regulated Cholesteryl Ester Accumulation Modulates Gemcitabine Resistance in Biliary Tract Cancer

BACKGROUND

Biliary tract cancer (BTC) has few choices of chemotherapy, including gemcitabine, therefore exploring the mechanisms of gemcitabine resistance is important. We focused on lipid metabolism because biliary tract epithelial cells are essential in cholesterol and bile acid metabolism and the messenger RNA (mRNA) microarray analysis showed high acyl coenzyme A: cholesterol acyltransferase 1 (ACAT-1) expression in BTC gemcitabine-resistant (GR) cell lines. We hypothesized that aberrant accumulation of cholesteryl ester (CE) regulated by ACAT-1 could modulate GR in BTC.

METHODS

CE accumulations were measured in human BTC cell lines, and the relationships between CE levels, ACAT-1 expressions, and gemcitabine sensitivity were analyzed. We performed a small-interfering RNA (siRNA)-mediated knockdown and biochemical inhibition of ACAT-1 in BTC cell lines and alterations of gemcitabine sensitivity were evaluated. To evaluate the clinical significance of ACAT-1 in regard to GR, immunohistochemistry was performed and ACAT-1 expressions were analyzed in resected BTC specimens.

RESULTS

CE levels were correlated with ACAT-1 expressions and GR in four human BTC cell lines. siRNA-mediated knockdown of ACAT-1 in two independent GR cell clones as well as ACAT-1 inhibitor treatment significantly increased gemcitabine sensitivity; knockdown of ACAT-1: 5.63- and 8.02-fold; ACAT-1 inhibitor: 8.75- and 9.13-fold, respectively. ACAT-1 expression in resected BTC specimens revealed that the disease-free survival of the ACAT-1 low-intensity group (median 2.3 years) had a significantly better outcome than that of the ACAT-1 high-intensity group (median 1.1 years) under gemcitabine treatment after surgery (*p < 0.05).

CONCLUSIONS

Our findings suggest that CE and ACAT-1 might be a novel therapeutic target for GR in BTC.

G, Zhou X, Zhang Y, Nagai A. Time-Dependent Analysis of Plasmalogens in the Hippocampus of an Alzheimer's Disease Mouse Model: A Role of Ethanolamine Plasmalogen

Plasmalogens are alkenyl-acyl glycerophospholipids and decreased in post-mortem Alzheimer's disease (AD) brains. The aim of this study is to investigate the time-dependent changes of plasmalogens in the hippocampus of an AD model mouse (J20). Plasmalogen levels at 3, 6, 9, 12 and 15 months were analyzed by liquid-chromatography-targeted-multiplexed-selected-reaction-monitoring-tandem-mass-spectrometry (LC-SRM/MS). Reactive oxygen species (ROS) levels were evaluated using dichlorofluorescein diacetate (DCF-DA). Plasmalogen synthesizing enzyme glycerone-phosphate O-acyltransferase (GNPAT) and late endosome marker Rab7 levels were quantified by Western blotting. GNPAT localization, changes of neuronal and glial cell numbers were evaluated by immunostaining. Compared to wild-type mice (WT), total plasmalogen-ethanolamine, but not plasmalogen-choline levels, were increased at 9 months and subsequently decreased at 15 months in J20 mice. A principal component analysis of plasmalogen-ethanolamine species could separate WT and J20 mice both at 9 and 15 months. Both GNPAT and Rab7 protein were increased in J20 mice at 9 months, whereas GNPAT was decreased at 15 months. ROS levels were increased in J20 mice except for 9 months. Our results suggest that increased plasmalogen-ethanolamine could counteract ROS levels and contribute to the phagocytosis process in J20 mice at 9 months. Such results might indicate a transient protective response of plasmalogen-ethanolamine in AD conditions.

Identifying active xenobiotics in humans by use of a suspect screening technique coupled with lipidomic analysis

Lipidomic analysis has been proven to be a powerful technique to explore the underlying associations between xenobiotics and health status of organisms. Here, we established a strategy that combined the lipidomic analysis with high-throughput suspect contaminant screening technique with an aim to efficiently identify active xenobiotics in humans. Firstly, in the light of single liquid phase equilibrium of chloroform-methanol-water (15:14:2, v/v/v), we developed an efficient method that was able to simultaneously extract both polar and nonpolar lipids in serum samples. By use of this method, targeted and non-targeted lipid analyses were conducted for n = 120 serum samples collected from Wuxi city, China. Secondly, we established a suspect database containing 1450 contaminants that have been previously reported in human samples, and contaminants in this database were screened in the same batch of serum samples by use of high-resolution mass spectrometry (HR-MS). Thirdly, the underlying associations between suspect contaminants and lipids were explored and discussed, and we observed that levels of some lipids were statistically correlated with concentrations of numerous contaminants. Among these active contaminants, 23 ones were identified on the basis of HR MS¹ and MS² characteristics, and these contaminants belonged to the classes of phthalates, phenols, parabens, or perfluorinated compounds (PFCs). Three active xenobiotics were fully validated by comparison with authentic standards, and they were perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), and diethyl phthalate (DEP). There were statistically significant changes in levels of triglyceride (TG), lysophosphocholine (LPC), and sphingomyelin (SM) as peak areas of xenobiotics increase. We also observed that, among target lipid molecules, 18:0 lysophosphatidylethanolamine (LPE(18:0)) was very sensitive, and this lipid responded to exposure of various contaminants. Our present study provides novel knowledge on potential alteration of lipid metabolism in humans following exposure to xenobiotics, and provides an efficient strategy for efficiently identifying active xenobiotics in humans.

Dimensional Changes in Lipid Rafts from Human Brain Cortex Associated to Development of Alzheimer's Disease. Predictions from an Agent-Based Mathematical Model

Alzheimer’s disease (AD) is a neurodegenerative disease caused by abnormal functioning of critical physiological processes in nerve cells and aberrant accumulation of protein aggregates in the brain. The initial cause remains elusive—the only unquestionable risk factor for the most frequent variant of the disease is age. Lipid rafts are microdomains present in nerve cell membranes and they are known to play a significant role in the generation of hallmark proteinopathies associated to AD, namely senile plaques, formed by aggregates of amyloid β peptides. Recent studies have demonstrated that human brain cortex lipid rafts are altered during early neuropathological phases of AD as defined by Braak and Braak staging. The lipid composition and physical properties of these domains appear altered even before clinical symptoms are detected. Here, we use a coarse grain molecular dynamics mathematical model to predict the dimensional evolution of these domains using the experimental data reported by our group in human frontal cortex. The model predicts significant size and frequency changes which are detectable at the earliest neuropathological stage (ADI/II) of Alzheimer’s disease. Simulations reveal a lower number and a larger size in lipid rafts from ADV/VI, the most advanced stage of AD. Paralleling these changes, the predictions also indicate that non-rafts domains undergo simultaneous alterations in membrane peroxidability, which support a link between oxidative stress and AD progression. These synergistic changes in lipid rafts dimensions and non-rafts peroxidability are likely to become part of a positive feedback loop linked to an irreversible amyloid burden and neuronal death during the evolution of AD neuropathology.

Shotgun lipidomics of liver and brain tissue of Alzheimer's disease model mice treated with acitretin

Alzheimer’s disease (AD) is a very frequent neurodegenerative disorder characterized by an accumulation of amyloid-β (Aβ). Acitretin, a retinoid-derivative and approved treatment for Psoriasis vulgaris, increases non-amyloidogenic Amyloid-Precursor-Protein-(APP)-processing, prevents Aβ-production and elicits cognitive improvement in AD mouse models. As an unintended side effect, acitretin could result in hyperlipidemia. Here, we analyzed the impact of acitretin on the lipidome in brain and liver tissue in the 5xFAD mouse-model. In line with literature, triglycerides were increased in liver accompanied by increased PCaa, plasmalogens and acyl-carnitines, whereas SM-species were decreased. In brain, these effects were partially enhanced or similar but also inverted. While for SM and plasmalogens similar effects were found, PCaa, TAG and acyl-carnitines showed an inverse effect in both tissues. Our findings emphasize, that potential pharmaceuticals to treat AD should be carefully monitored with respect to lipid-homeostasis because APP-processing itself modulates lipid-metabolism and medication might result in further and unexpected changes. Moreover, deducing effects of brain lipid-homeostasis from results obtained for other tissues should be considered cautiously. With respect to acitretin, the increase in brain plasmalogens might display a further positive probability in AD-treatment, while other results, such as decreased SM, indicate the need of medical surveillance for treated patients.

Serum concentrations of neonicotinoids, and their associations with lipid molecules of the general residents in Wuxi City, Eastern China

Exposure to neonicotinoid insecticides (NNIs) was proven to be harmful to organisms, however, there is a dearth of information regarding their occurrence and adverse effects on the general residents. Here, n = 120 human serum samples were collected from the same area of Wuxi city, Eastern China, and these serum samples were further analyzed for nine NNIs and nine target lipid molecules by use of ultrahigh performance liquid chromatography-quadrupole orbitrap high-resolution mass spectrometer. We observed that four out of nine NNIs exhibited relatively high detection frequencies (DF), and these NNIs were imidacloprid (IMI; DF = 28.3%), clothianidin (CLO; 16.7%), thiacloprid (THI; 14.2%), and acetamiprid (ACE; 12.5%), respectively, with 95th concentrations ranging from 32.0 to 427 pg/mL. Median concentrations of imidacloprid-equivalent total neonicotinoids (IMI_eq) and ∑₇NNI were 46.6 pg/mL and 26 pg/mL, respectively. Five out of nine lipid molecules exhibited higher levels, that were docosahexaenoic acid [FA(22:6)], 18:0 phosphocholine [LysoPC(18:0)], 18:0 phosphoethanolamine [LysoPE(18:0)], D18:1-18:0 sphingomyelin [SM(d18:1/18:0)], and 18:1-18:1 diglycerol [DG(18:1/18:1)], respectively. More interestingly, we observed statistically significant correlations (student's t-test, one-way ANOVA, or Mann-Whitney test; p < 0.05) between NNI levels and population characteristics (i.e. age, smoking, and health status). Beyond that, we also observed statistically significant correlations between levels of selected NNIs (CLO, ACE, or THI) and lipid molecules [LysoPE(18:0), SM(d18:1/18:0), and DG(18:1/18:1)]. Collectively, for the first time, we provided the information on contamination levels of NNIs in serum samples of general residents in China and demonstrated the associations between concentrations of NNIs and levels of lipid molecular species.

Enhanced amyloid-β generation by γ-secretase complex in DRM microdomains with reduced cholesterol levels

A neuropathologic hallmark of Alzheimer's disease (AD) is the presence of senile plaques that contain neurotoxic amyloid-β protein (Aβ) species, which are generated by the cleavage of amyloid β-protein precursor by secretases such as the γ-secretase complex, preferentially located in detergent-resistant membrane (DRM) regions and comprising endoproteolysed amino- and carboxy-terminal fragments of presenilin, nicastrin, anterior pharynx defective 1 and presenilin enhancer 2. Whereas some of familial AD patients harbor causative PSEN mutations that lead to more generation of neurotoxic Aβ42, the contribution of Aβ generation to sporadic/late-onset AD remains unclear. We found that the carboxy-terminal fragment of presenilin 1 was redistributed from DRM regions to detergent-soluble membrane (non-DRM) regions in brain tissue samples from individuals with sporadic AD. DRM fractions from AD brain sample had the ability to generate significantly more Aβ and had a lower cholesterol content than DRM fractions from non-demented control subjects. We further demonstrated that lowering the cholesterol content of DRM regions from cultured cells contributed to the redistribution of γ-secretase components and Aβ production. Taken together, the present analyses suggest that the lowered cholesterol content in DRM regions may be a cause of sporadic/late-onset AD by enhancing overall Aβ generation.

Metabolic disorder in Alzheimer's disease

Alzheimer's disease (AD), a well known aging-induced neurodegenerative disease is related to amyloid proteinopathy. This proteinopathy occurs due to abnormalities in protein folding, structure and thereby its function in cells. The root cause of such kind of proteinopathy and its related neurodegeneration is a disorder in metabolism, rather metabolomics of the major as well as minor nutrients. Metabolomics is the most relevant "omics" platform that offers a great potential for the diagnosis and prognosis of neurodegenerative diseases as an individual's metabolome. In recent years, the research on such kinds of neurodegenerative diseases, especially aging-related disorders is broadened its scope towards metabolic function. Different neurotransmitter metabolisms are also involved with AD and its associated neurodegeneration. The genetic and epigenetic backgrounds are also noteworthy. In this review, the physiological changes of AD in relation to its corresponding biochemical, genetic and epigenetic involvements including its (AD) therapeutic aspects are discussed.

Cerebrospinal Fluid C18 Ceramide Associates with Markers of Alzheimer's Disease and Inflammation at the Pre- and Early Stages of Dementia

Background:

Understanding how dysregulation in lipid metabolism relates to the severity of Alzheimer‘s disease (AD) pathology might be critical in developing effective treatments.

Objective:

To identify lipid species in cerebrospinal fluid (CSF) associated with signature AD pathology and to explore their relationships with measures reflecting AD-related processes (neurodegeneration, inflammation, deficits in verbal episodic memory) among subjects at the pre- and early symptomatic stages of dementia.

Methods:

A total of 60 subjects that had been referred to an Icelandic memory clinic cohort were classified as having CSF AD (n = 34) or non-AD (n = 26) pathology profiles. Untargeted CSF lipidomic analysis was performed using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS) for the detection of mass-to-charge ratio (m/z) features. CSF proteins reflecting neurodegeneration (neurofilament light [NFL]) and inflammation (chitinase-3-like protein 1 [YKL-40], S100 calcium-binding protein B [S100B], glial fibrillary acidic protein [GFAP]) were also measured. Rey Auditory Verbal Learning (RAVLT) and Story tests were used for the assessment of verbal episodic memory.

Results:

Eight out of 1008 features were identified as best distinguishing between the CSF profile groups. Of those, only the annotation of the m/z feature assigned to lipid species C18 ceramide was confirmed with a high confidence. Multiple regression analyses, adjusted for age, gender, and education, demonstrated significant associations of CSF core AD markers (Aβ₄₂: st.β= –0.36, p = 0.007; T-tau: st.β= 0.41, p = 0.005) and inflammatory marker S100B (st.β= 0.51, p = 0.001) with C18 ceramide levels.

Conclusion:

Higher levels of C18 ceramide associated with increased AD pathology and inflammation, suggesting its potential value as a therapeutic target.

LPS and palmitic acid Co-upregulate microglia activation and neuroinflammatory response

Growing evidence indicates that disturbances in the inflammatory response system can have deleterious effects on neuronal function and mental health. While the correlation between elevated peripheral inflammatory markers and psychiatric disorders are well documented, the exact molecular and neuronal mechanism underlying the connection between activated inflammation and neuropsychiatric behaviour remain elusive. Microglia activation is the key interface between neuro-inflammation and manifestation of psychiatric symptoms. Microglia are immunocompetent cells in the central nervous system (CNS) which are primarily involved in the response to inflammatory stimulation and are widely used to study neuroinflammation and test anti-inflammatory chemicals. In the brain, activated microglia play very important roles during neuroinflammation and neurodegeneration. Both stress-related disorders such as Depression and PTSD, and medical conditions such as metabolic syndrome (Mets) and type 2 diabetes (TD2) are associated with increased levels of both saturated fatty acids (SFAs) and lipopolysaccharide (LPS) in circulation. This work was aimed at determining whether SFA interacts with LPS to activate microglia, thus up-regulating neuroinflammatory processes and, if so which pathways were involved in this process. Our results showed that low-dose LPS and palmitic acid (PA) robustly stimulated the expression of proinflammatory cytokines, and the combination of PA and LPS further upregulated proinflammatory cytokines through MAPK, NFκB and AP-1 signaling pathways in the HMC3-human microglial cell line. In addition, PA stimulated ceramide production via de novo synthesis and sphingomyelin hydrolysis, and the combination of LPS and PA further increased ceramide production. HMC3 co-cultured with macrophage and lymphocyte enhanced LPS and PA induced-inflammatory response more than that in HMC3 alone. These results indicate that LPS interacts with PA to activated microglia; induced neuroinflammatory responses, upregulate proinflammatory cytokine expression via MAPK, NFκB, and AP-1 signaling pathways, and induced sphingolipid metabolism in HMC3. These observations suggest that inhibiting microglia activation and reducing LPS and PA-induced inflammatory response may be useful in the treatment of neuronal inflammatory diseases.

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Microglial activation plays critical role in the pathology of various psychiatric conditions.

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PA interacts with LPS to active microglia induce proinflammatory cytokine and gene expression.

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PA and LPS stimulate the MAPK and NFκB signaling pathway regulated IL-6 secretion in microglia.

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U937 and lymphocyte enhance IL-6 secretion in microglia.

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PA and LPS plus PA increase ceramide and decrease sphingomyelin productions.

Sphingolipids metabolism alteration in the central nervous system: Amyotrophic lateral sclerosis (ALS) and other neurodegenerative diseases

Sphingolipids are complex lipids. They play a structural role in neurons, but are also involved in regulating cellular communication, and neuronal differentiation and maturation. There is increasing evidence to suggest that dysregulated metabolism of sphingolipids is linked to neurodegenerative processes in amyotrophic lateral sclerosis (ALS), Parkinson's disease and Gaucher's disease. In this review, we provide an overview of the role of sphingolipids in the development and maintenance of the nervous system. We describe the implications of altered metabolism of sphingolipids in the pathophysiology of certain neurodegenerative diseases, with a primary focus on ALS. Finally, we provide an update of potential treatments that could be used to target the metabolism of sphingolipids in neurodegenerative diseases.

Spatially resolved mass spectrometry analysis of amyloid plaque-associated lipids

Over the last 10 years, considerable technical advances in mass spectrometry (MS)-based bioanalysis have enabled the investigation of lipid signatures in neuropathological structures. In Alzheimer´s Disease (AD) research, it is now well accepted that lipid dysregulation plays a key role in AD pathogenesis and progression. This review summarizes current MS-based strategies, notably MALDI and ToF-SIMS imaging as well as laser capture microdissection combined with LC-ESI-MS. It also presents recent advances to assess lipid alterations associated with Amyloid-β plaques, one of the hallmarks of AD. Collectively, these methodologies offer new opportunities for the study of lipids, thus pushing forward our understanding of their role in such a complex and still untreatable disease as AD.

Statin Use and Risk of Cognitive Decline in the ADNI Cohort

OBJECTIVE

To investigate associations between statin use and cognitive change, as well as diagnostic conversion, in individuals with cognitively normal (CN) status, mild cognitive impairment (MCI), and dementia due to Alzheimer disease (AD-dementia).

METHODS

A multicenter cohort study with 1629 adults 48 to 91 years old with CN status, early MCI (EMCI), late MCI (LMCI), or AD-dementia at baseline followed prospectively for 24 months. Statin use was assessed at baseline, and cognition was measured over time with a composite memory score, a composite executive function score, and a global cognition score (Alzheimer's Disease Assessment Scale). Conversion to a more impaired diagnostic category was determined by clinician assessment. Repeated measures linear mixed-effects models were used to evaluate associations between statin use and change in cognition over time. Cox proportional hazards models were used to evaluate associations between statin use and time to diagnostic conversion. All models were stratified by baseline diagnostic group.

RESULTS

Statin use was not associated with change in cognitive measures for CN, LMCI, or AD-dementia participants. Among EMCI participants, statin use was associated with a significantly slower rate of decline on the memory composite, but no other cognitive measure. Statin use was not associated with time to conversion for any diagnostic group.

CONCLUSIONS

This study did not support an association between statin use and diagnostic conversion but suggested a possible association between statin use and cognitive change in EMCI. Additional randomized clinical trials of statins may be warranted in the prodromal EMCI stage of AD.

Lipid rafts and neurodegeneration: structural and functional roles in physiologic aging and neurodegenerative diseases

Lipid rafts are small, dynamic membrane areas characterized by the clustering of selected membrane lipids as the result of the spontaneous separation of glycolipids, sphingolipids, and cholesterol in a liquid-ordered phase. The exact dynamics underlying phase separation of membrane lipids in the complex biological membranes are still not fully understood. Nevertheless, alterations in the membrane lipid composition affect the lateral organization of molecules belonging to lipid rafts. Neural lipid rafts are found in brain cells, including neurons, astrocytes, and microglia, and are characterized by a high enrichment of specific lipids depending on the cell type. These lipid rafts seem to organize and determine the function of multiprotein complexes involved in several aspects of signal transduction, thus regulating the homeostasis of the brain. The progressive decline of brain performance along with physiological aging is at least in part associated with alterations in the composition and structure of neural lipid rafts. In addition, neurodegenerative conditions, such as lysosomal storage disorders, multiple sclerosis, and Parkinson's, Huntington's, and Alzheimer's diseases, are frequently characterized by dysregulated lipid metabolism, which in turn affects the structure of lipid rafts. Several events underlying the pathogenesis of these diseases appear to depend on the altered composition of lipid rafts. Thus, the structure and function of lipid rafts play a central role in the pathogenesis of many common neurodegenerative diseases.jlr;61/5/636/F1F1f1.

Role of dietary fatty acids in microglial polarization in Alzheimer's disease

Microglial polarization is an utmost important phenomenon in Alzheimer’s disease that influences the brain environment. Polarization depends upon the types of responses that cells undergo, and it is characterized by receptors present on the cell surface and the secreted cytokines to the most. The expression of receptors on the surface is majorly influenced by internal and external factors such as dietary lipids. Types of fatty acids consumed through diet influence the brain environment and glial cell phenotype and types of receptors on microglia. Reports suggest that dietary habits influence microglial polarization and the switching of microglial phenotype is very important in neurodegenerative diseases. Omega-3 fatty acids have more influence on the brain, and they are found to regulate the inflammatory stage of microglia by fine-tuning the number of receptors expressed on microglia cells. In Alzheimer’s disease, one of the pathological proteins involved is Tau protein, and microtubule-associated protein upon abnormal phosphorylation detaches from the microtubule and forms insoluble aggregates. Aggregated proteins have a tendency to propagate within the neurons and also become one of the causes of neuroinflammation. We hypothesize that tuning microglia towards anti-inflammatory phenotype would reduce the propagation of Tau in Alzheimer’s disease.

Potential therapeutic target for aging and age-related neurodegenerative diseases: the role of acid sphingomyelinase

Aging, which is associated with age-related changes in physiological processes, is the most significant risk factor for the development and progression of neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease. Accumulating evidence has indicated that sphingolipids are significant regulators that are associated with pathogenesis in aging and several age-related neurodegenerative diseases. In particular, abnormal levels of acid sphingomyelinase (ASM), one of the significant sphingolipid-metabolizing enzymes, have been found in the blood and some tissues under various neuropathological conditions. Moreover, recent studies have reported the importance of ASM as a critical mediator that contributes to pathologies in aging and age-related neurodegenerative diseases. In this review, we describe the pathophysiological processes that are regulated by ASM, focusing on the age-related neurodegenerative environment. Furthermore, we discuss novel insights into how new therapeutics targeting ASM may potentially lead to effective strategies to combat aging and age-related neurodegenerative diseases.

The Apolipoprotein E ε4 Allele-Dependent Relationship Between Serum Lipid Levels and Cognitive Function: A Population-Based Cross-sectional Study

Objectives: Till now, the effect of serum lipid levels on cognitive function is still controversial. The apolipoprotein E (APOE) ε4 allele is the most critical genetic risk factor for Alzheimer’s disease (AD) and cognitive impairment. Additionally, APOE ε4 allele has a major impact on lipid metabolism. The aim of this study was to investigate the APOE genotype-dependent relationship between peripheral serum lipid levels and cognitive impairment.

Methods: A total of 1,273 subjects aged 40–86 years participated in this cross-sectional study. Serum lipid levels and the APOE genotype were detected. Mini-Mental State Examination was used to diagnose the cognitive impairment or not. Univariate and multivariate analyses were used to analyze the relationships between APOE genotype, serum lipid levels, and cognition function.

Results: After controlling for all possible covariates, a significant interaction between low serum high-density lipoprotein and the APOE ε4 allele on cognitive impairment (Wald’s χ² = 4.269, df = 1, OR = 20.094, p = 0.039) was found in the total participants. In APOE ε4 carriers, low serum high-density lipoprotein was positively associated with cognitive impairment (Wald’s χ² = 8.200, df = 1, OR = 60.335, p = 0.004) and serum high-density lipoprotein levels were positively correlated with Mini-Mental State Examination score (r = 0.217, df = 176, p = 0.004). There was no significant correlation between serum total cholesterol (TC), low-density lipoprotein, triglycerides (TG) levels, and cognitive impairment in either the total participants or APOE ε4 carriers/non-carriers.

Conclusions: APOE ε4 carriers, but not non-carriers, with lower serum high-density lipoprotein had a higher prevalence of cognitive impairment and a lower Mini-Mental State Examination score. These results suggest that the APOE ε4 allele may affect the relationship between serum lipid levels and cognitive impairment. However, the specific mechanism needs to be further elucidated.

Spatial Lipidomics Reveals Region and Long Chain Base Specific Accumulations of Monosialogangliosides in Amyloid Plaques in Familial Alzheimer's Disease Mice (5xFAD) Brain

Ganglioside metabolism is significantly altered in Alzheimer's disease (AD), which is a progressive neurodegenerative disease prominently characterized by one of its pathological hallmarks, amyloid deposits or "senile plaques". While the plaques mainly consist of aggregated variants of amyloid-β protein (Aβ), recent studies have revealed a number of lipid species including gangliosides in amyloid plaques along with Aβ peptides. It has been widely suggested that long chain (sphingosine) base (LCBs), C18:1-LCB and C20:1-LCB, containing gangliosides might play different roles in neuronal function in vivo. In order to elucidate region-specific aspects of amyloid-plaque associated C18:1-LCB and C20:1-LCB ganglioside accumulations, high spatial resolution (10 μm per pixel) matrix assisted laser desorption ionization imaging mass spectrometry (MALDI-IMS) of gangliosides in amyloid plaques was performed in hippocampal and adjacent cortical regions of 12 month old 5xFAD mouse coronal brain sections from two different stereotaxic coordinates (bregma points, -2.2 and -2.7 mm). MALDI-IMS uncovered brain-region (2 and 3D) and/or LCB specific accumulations of monosialogangliosides (GMs): GM1, GM2, and GM3 in the hippocampal and cortical amyloid plaques. The results reveal monosialogangliosides to be an important component of amyloid plaques and the accumulation of different gangliosides is region and LCB specific in 12 month old 5xFAD mouse brain. This is discussed in relation to amyloid-associated AD pathogenesis such as lipid related immune changes in amyloid plaques, AD specific ganglioside metabolism, and, notably, AD-associated impaired neurogenesis in the subgranular zone.

Lipid Assemblies at the Crossroads of Aging, Proteostasis, and Neurodegeneration

The proteostasis network (PN) is a nexus of mechanisms that act in concert to maintain the integrity of the proteome. Efficiency of the PN declines with age, resulting in the accumulation of misfolded proteins, and in some cases in the development of neurodegenerative disorders. Thus, maintaining an active and efficient PN through the late stages of life could delay or prevent neurodegeneration. Indeed, altering the activity of aging-regulating pathways protects model organisms from neurodegeneration-linked toxic protein aggregation. Here, we delineate evidence that the formation and integrity of lipid assemblies are affected by aging-regulating pathways, and describe the roles of these structures in proteostasis maintenance. We also highlight future research directions and discuss the possibility that compounds which modulate lipid assemblies could be used for the treatment of neurodegenerative disorders.

Structure and dynamics of γ-secretase with presenilin 2 compared to presenilin 1

Severe early-onset familial Alzheimer's disease (FAD) is caused by more than 200 different mutations in the genes coding for presenilin, the catalytic subunit of the 4-subunit protease complex γ-secretase, which cleaves the C99 fragment of the amyloid precursor protein (APP) to produce Aβ peptides. γ-Secretase exists with either of two homologues, PS1 and PS2. All cryo-electron microscopic structures and computational work has so far focused on γ-secretase with PS1, yet PS2 mutations also cause FAD. A central question is thus whether there are structural and dynamic differences between PS1 and PS2. To address this question, we use the cryo-electron microscopic data for PS1 to develop the first structural and dynamic model of PS2-γ-secretase in the catalytically relevant mature membrane-bound state at ambient temperature, equilibrated by three independent 500 ns molecular dynamics simulations. We find that the characteristic nicastrin extra-cellular domain breathing mode and major movements in the cytosolic loop between TM6 and TM7 occur in both PS2- and PS1-γ-secretase. The overall structures and conformational states are similar, suggesting similar catalytic activities. However, at the sequence level, charge-controlled membrane-anchoring is extracellular for PS1 and intracellular for PS2, which suggests different subcellular locations. The tilt angles of the TM2, TM6, TM7 and TM9 helices differ in the two forms of γ-secretase, suggesting that the two proteins have somewhat different substrate processing and channel sizes. Our MD simulations consistently indicated that PS2 retains several water molecules near the catalytic site at the bilayer, as required for catalysis. The possible reasons for the differences of PS1 and PS2 are discussed in relation to their location and function.

Plasmalogens and Alzheimer's disease: a review

Growing evidence suggests that ethanolamine plasmalogens (PlsEtns), a subtype of phospholipids, have a close association with Alzheimer’s disease (AD). Decreased levels of PlsEtns have been commonly found in AD patients, and were correlated with cognition deficit and severity of disease. Limited studies showed positive therapeutic outcomes with plasmalogens interventions in AD subjects and in rodents. The potential mechanisms underlying the beneficial effects of PlsEtns on AD may be related to the reduction of γ–secretase activity, an enzyme that catalyzes the synthesis of β-amyloid (Aβ), a hallmark of AD. Emerging in vitro evidence also showed that PlsEtns prevented neuronal cell death by enhancing phosphorylation of AKT and ERK signaling through the activation of orphan G-protein coupled receptor (GPCR) proteins. In addition, PlsEtns have been found to suppress the death of primary mouse hippocampal neuronal cells through the inhibition of caspase-9 and caspase-3 cleavages. Further in-depth investigations are required to determine the signature molecular species of PlsEtns associated with AD, hence their potential role as biomarkers. Clinical intervention with plasmalogens is still in its infancy but may have the potential to be explored for a novel therapeutic approach to correct AD pathology and neural function.

Current and Emerging Pharmacological Targets for the Treatment of Alzheimer's Disease

No cure or disease-modifying therapy for Alzheimer's disease (AD) has yet been realized. However, a multitude of pharmacological targets have been identified for possible engagement to enable drug discovery efforts for AD. Herein, we review these targets comprised around three main therapeutic strategies. First is an approach that targets the main pathological hallmarks of AD: amyloid-β (Aβ) oligomers and hyperphosphorylated tau tangles which primarily focuses on reducing formation and aggregation, and/or inducing their clearance. Second is a strategy that modulates neurotransmitter signaling. Comprising this strategy are the cholinesterase inhibitors and N-methyl-D-aspartate receptor blockade treatments that are clinically approved for the symptomatic treatment of AD. Additional targets that aim to stabilize neuron signaling through modulation of neurotransmitters and their receptors are also discussed. Finally, the third approach comprises a collection of 'sensitive targets' that indirectly influence Aβ or tau accumulation. These targets are proteins that upon Aβ accumulation in the brain or direct Aβ-target interaction, a modification in the target's function is induced. The process occurs early in disease progression, ultimately causing neuronal dysfunction. This strategy aims to restore normal target function to alleviate Aβ-induced toxicity in neurons. Overall, we generally limit our analysis to targets that have emerged in the last decade and targets that have been validated using small molecules in in vitro and/or in vivo models. This review is not an exhaustive list of all possible targets for AD but serves to highlight the most promising and critical targets suitable for small molecule drug intervention.

Influence of membrane lipid composition on the structure and activity of γ-secretase

γ-Secretase (GS) is a multi-subunit membrane-embedded aspartyl protease that cleaves more than 80 integral membrane proteins, including the amyloid precursor protein (APP) to produce the amyloid-β (Aβ) peptide. Oligomerization and aggregation of the 42-amino acid length Aβ isoform in the brain has been associated with the development and progression of Alzheimer's disease (AD). Based on recent experimental structural studies and using multiscale computational modeling approaches, the conformational states and protein-membrane interactions of the GS complex embedded in six homogeneous and six heterogeneous lipid bilayers were characterized. In order to identify potential lipid and cholesterol binding sites, GS regions with high lipid/cholesterol occupancy values were analyzed using atomistic and coarse-grained simulations. Long lipid residence times were observed to be correlated with a large number of hydrogen bonds between the charged headgroups and key GS amino acids. This observation provides a plausible explanation for the inhibition of GS by charged lipids observed in previous experimental studies. Computed lateral pressure profiles suggest that higher transmembrane pressures favor active state conformations of the catalytic subunit. A probable mechanism for the regulation of the local stress response in cholesterol-rich multicomponent lipid bilayers is identified. Finally, it is demonstrated that interactions between the nicastrin extracellular domain and lipid headgroups leads to a compact structural conformation of the GS complex. Overall, this study provides valuable insight into the effect of bilayer lipid composition on the GS structural ensemble and its function.

Aging and Alzheimer's disease: Comparison and associations from molecular to system level

Alzheimer's disease is the most prevalent cause of dementia, which is defined by the combined presence of amyloid and tau, but researchers are gradually moving away from the simple assumption of linear causality proposed by the original amyloid hypothesis. Aging is the main risk factor for Alzheimer's disease that cannot be explained by amyloid hypothesis. To evaluate how aging and Alzheimer's disease are intrinsically interwoven with each other, we review and summarize evidence from molecular, cellular, and system level. In particular, we focus on study designs, treatments, or interventions in Alzheimer's disease that could also be insightful in aging and vice versa.

Bexarotene Binds to the Amyloid Precursor Protein Transmembrane Domain, Alters Its α-Helical Conformation, and Inhibits γ-Secretase Nonselectively in Liposomes

Bexarotene is a pleiotropic molecule that has been proposed as an amyloid-β (Aβ)-lowering drug for the treatment of Alzheimer's disease (AD). It acts by upregulation of an apolipoprotein E (apoE)-mediated Aβ clearance mechanism. However, whether bexarotene induces removal of Aβ plaques in mouse models of AD has been controversial. Here, we show by NMR and CD spectroscopy that bexarotene directly interacts with and stabilizes the transmembrane domain α-helix of the amyloid precursor protein (APP) in a region where cholesterol binds. This effect is not mediated by changes in membrane lipid packing, as bexarotene does not share with cholesterol the property of inducing phospholipid condensation. Bexarotene inhibited the intramembrane cleavage by γ-secretase of the APP C-terminal fragment C99 to release Aβ in cell-free assays of the reconstituted enzyme in liposomes, but not in cells, and only at very high micromolar concentrations. Surprisingly, in vitro, bexarotene also inhibited the cleavage of Notch1, another major γ-secretase substrate, demonstrating that its inhibition of γ-secretase is not substrate specific and not mediated by acting via the cholesterol binding site of C99. Our data suggest that bexarotene is a pleiotropic molecule that interfere with Aβ metabolism through multiple mechanisms.

Gangliosides in Membrane Organization

Since the structure of GM1 was elucidated 55years ago, researchers have been attracted by the sialylated glycans of gangliosides. Gangliosides head groups, protruding toward the extracellular space, significantly contribute to the cell glycocalyx; and in certain cells, such as neurons, are major determinants of the features of the cell surface. Expression of glycosyltransferases involved in the de novo biosynthesis of gangliosides is tightly regulated along cell differentiation and activation, and is regarded as the main metabolic mechanism responsible for the acquisition of cell-specific ganglioside patterns. The resulting sialooligosaccharides are characterized by a high degree of geometrical complexity and by highly dynamic properties, which seem to be functional for complex interactions with other molecules sitting on the same cellular membrane (cis-interactions) or soluble molecules present in the extracellular environment, or molecules associated with the surface of other cells (trans-interactions). There is no doubt that the multifaceted biological functions of gangliosides are largely dependent on oligosaccharide-mediated molecular interactions. However, gangliosides are amphipathic membrane lipids, and their chemicophysical, aggregational, and, consequently, biological properties are dictated by the properties of the monomers as a whole, which are not merely dependent on the structures of their polar head groups. In this chapter, we would like to focus on the peculiar chemicophysical features of gangliosides (in particular, those of the nervous system), that represent an important driving force determining the organization and properties of cellular membranes, and to emphasize the causal connections between altered ganglioside-dependent membrane organization and relevant pathological conditions.

Combined measurement of plasma cystatin C and low-density lipoprotein cholesterol: A valuable tool for evaluating progressive supranuclear palsy

INTRODUCTION

Progressive supranuclear palsy (PSP) was previously thought as a cause of atypical Parkinsonism. Although Cystatin C (Cys C) and low-density cholesterol lipoprotein-C (LDL-C) are known to play critical roles in Parkinsonism, it is unknown whether they can be used as markers to distinguish PSP patients from healthy subjects and to determine disease severity.

METHODS

We conducted a cross-sectional study to determine plasma Cys C/HDL/LDL-C levels of 40 patients with PSP and 40 healthy age-matched controls. An extended battery of motor and neuropsychological tests, including the PSP-Rating Scale (PSPRS), the Non-Motor Symptoms Scale (NMSS), Geriatric Depression Scale (GDS) and Mini-Mental State Examination (MMSE), was used to evaluate the disease severity. Receiver operating characteristic (ROC) curves were adopted to assess the prognostic accuracy of Cys C/LDL-C levels in distinguishing PSP from healthy subjects.

RESULTS

Patients with PSP exhibited significantly higher plasma levels of Cys C and lower LDL-C. The levels of plasma Cys C were positively and inversely correlated with the PSPRS/NMSS and MMSE scores, respectively. The LDL-C/HDL-C ratio was positively associated with PSPRS/NMSS and GDS scores. The ROC curve for the combination of Cys C and LDL-C yielded a better accuracy for distinguishing PSP from healthy subjects than the separate curves for each parameter.

CONCLUSIONS

Plasma Cys C and LDL-C may be valuable screening tools for differentiating PSP from healthy subjects; while they could be useful for the PSP intensifies and severity evaluation. A better understanding of Cys C and LDL-C may yield insights into the pathogenesis of PSP.

Structural Characterization of the Amyloid Precursor Protein Transmembrane Domain and Its γ-Cleavage Site

Alzheimer's disease is the most common form of dementia that affects about 50 million of sufferers worldwide. A major role for the initiation and progression of Alzheimer's disease has been associated with the amyloid β-peptide (Aβ), which is a protease cleavage product of the amyloid precursor protein. The amyloid precursor protein is an integral membrane protein with a single transmembrane domain. Here, we assessed the structural integrity of the transmembrane domain within oriented phosphatidylcholine lipid bilayers and determined the tilt angle distribution and dynamics of various subdomains using solid-state NMR and attenuated total reflectance Fourier transform infrared spectroscopies. Although the overall secondary structure of the transmembrane domain is α-helical, pronounced conformational and topological heterogeneities were observed for the γ- and, to a lesser extent, the ζ-cleavage site, with pronounced implications for the production of Aβ and related peptides, the development of the disease, and pharmaceutical innovation.

Imaging mass spectrometry (IMS) of cortical lipids from preclinical to severe stages of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease affecting millions of patients worldwide. Previous studies have demonstrated alterations in the lipid composition of lipid extracts from plasma and brain samples of AD patients. However, there is no consensus regarding the qualitative and quantitative changes of lipids in brains from AD patients. In addition, the recent developments in imaging mass spectrometry methods are leading to a new stage in the in situ analysis of lipid species in brain tissue slices from human postmortem samples. The present study uses the matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS), permitting the direct anatomical analysis of lipids in postmortem brain sections from AD patients, which are compared with the intensity of the lipid signal in samples from matched subjects with no neurological diseases. The frontal cortex samples from AD patients were classified in three groups based on Braak's histochemical criteria, ranging from non-cognitively impaired patients to those severely affected. The main results indicate a depletion of different sulfatide lipid species from the earliest stages of the disease in both white and gray matter areas of the frontal cortex. Therefore, the decrease in sulfatides in cortical areas could be considered as a marker of the disease, but may also indicate neurochemical modifications related to the pathogenesis of the disease. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.

Metabolomic-guided discovery of Alzheimer's disease biomarkers from body fluid

The rapid increase in the older population has made age-related diseases like Alzheimer's disease (AD) a global concern. Given that there is still no cure for this neurodegenerative disease, the drastic growth in the number of susceptible individuals represents a major emerging threat to public health. The poor understanding of the mechanisms underlying AD is deemed the greatest stumbling block against progress in definitive diagnosis and management of this disease. There is a dire need for biomarkers that can facilitate early diagnosis, classification, prognosis, and treatment response. Efforts have been directed toward discovery of reliable and distinctive AD biomarkers but with very little success. With the recent emergence of high-throughput technology that is able to collect and catalogue vast datasets of small metabolites, metabolomics offers hope for a better understanding of AD and subsequent identification of biomarkers. This review article highlights the potential of using multiple metabolomics platforms as useful means in uncovering AD biomarkers from body fluids. © 2017 Wiley Periodicals, Inc.

Reduction of Ether-Type Glycerophospholipids, Plasmalogens, by NF-κB Signal Leading to Microglial Activation

Neuroinflammation characterized by activation of glial cells is observed in various neurodegenerative diseases including Alzheimer's disease (AD). Although the reduction of ether-type glycerophospholipids, plasmalogens (Pls), in the brain is reported in AD patients, the mechanism of the reduction and its impact on neuroinflammation remained elusive. In the present study, we found for the first time that various inflammatory stimuli reduced Pls levels in murine glial cells via NF-κB activation, which then downregulated a Pls-synthesizing enzyme, glycerone phosphate O-acyltransferase (Gnpat) through increased c-Myc recruitment onto the Gnpat promoter. We also found that systemic injection of lipopolysaccharide, aging, and chronic restraint stress reduced brain Pls contents that were associated with glial NF-κB activation, an increase in c-Myc expression, and downregulation of Gnpat in the mouse cortex and hippocampus. More interestingly, the reduction of Pls contents in the murine cortex itself could increase the activated phenotype of microglial cells and the expression of proinflammatory cytokines, suggesting further acceleration of neuroinflammation by reduction of brain Pls. A similar mechanism of Gnpat reduction was also found in human cell lines, triple-transgenic AD mouse brain, and postmortem human AD brain tissues. These findings suggest a novel mechanism of neuroinflammation that may explain prolonged progression of AD and help us to explore preventive and therapeutic strategies to treat neurodegenerative diseases.SIGNIFICANCE STATEMENT Ether-type glycerophospholipids, plasmalogens (Pls), are reduced in the brain of Alzheimer disease (AD) patients. We found that inflammatory stimuli reduced Pls contents by downregulation of the Pls-synthesizing enzyme glycerone phosphate O-acyltransferase (Gnpat) through NF-κB-mediated recruitment of c-Myc onto the Gnpat promoter in both murine and human cell lines. Murine brains after systemic lipopolysaccharide, chronic stress, and aging, as well as triple-transgenic AD mice and postmortem human AD brain tissues all showed increased c-Myc and reduced Gnpat expression. Interestingly, knockdown of Gnpat itself activated NF-κB in glial cell lines and microglia in mouse cortex. Our findings provide a new insight into the mechanism of neuroinflammation and may help to develop a novel therapeutic approach for neurodegenerative diseases such as AD.

Lipid profiling of parkin-mutant human skin fibroblasts

Parkin mutations are a major cause of early-onset Parkinson's disease (PD). The impairment of protein quality control system together with defects in mitochondria and autophagy process are consequences of the lack of parkin, which leads to neurodegeneration. Little is known about the role of lipids in these alterations of cell functions. In the present study, parkin-mutant human skin primary fibroblasts have been considered as cellular model of PD to investigate on possible lipid alterations associated with the lack of parkin protein. Dermal fibroblasts were obtained from two unrelated PD patients with different parkin mutations and their lipid compositions were compared with that of two control fibroblasts. The lipid extracts of fibroblasts have been analyzed by combined matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF/MS) and thin-layer chromatography (TLC). In parallel, we have performed direct MALDI-TOF/MS lipid analyses of intact fibroblasts by skipping lipid extraction steps. Results show that the proportions of some phospholipids and glycosphingolipids were altered in the lipid profiles of parkin-mutant fibroblasts. The detected higher level of gangliosides, phosphatidylinositol, and phosphatidylserine could be linked to dysfunction of autophagy and mitochondrial turnover; in addition, the lysophosphatidylcholine increase could represent the marker of neuroinflammatory state, a well-known component of PD.

The Impact of Vitamin E and Other Fat-Soluble Vitamins on Alzheimer´s Disease

Alzheimer’s disease (AD) is the most common cause of dementia in the elderly population, currently affecting 46 million people worldwide. Histopathologically, the disease is characterized by the occurrence of extracellular amyloid plaques composed of aggregated amyloid-β (Aβ) peptides and intracellular neurofibrillary tangles containing the microtubule-associated protein tau. Aβ peptides are derived from the sequential processing of the amyloid precursor protein (APP) by enzymes called secretases, which are strongly influenced by the lipid environment. Several vitamins have been reported to be reduced in the plasma/serum of AD-affected individuals indicating they have an impact on AD pathogenesis. In this review we focus on vitamin E and the other lipophilic vitamins A, D, and K, and summarize the current knowledge about their status in AD patients, their impact on cognitive functions and AD risk, as well as their influence on the molecular mechanisms of AD. The vitamins might affect the generation and clearance of Aβ both by direct effects and indirectly by altering the cellular lipid homeostasis. Additionally, vitamins A, D, E, and K are reported to influence further mechanisms discussed to be involved in AD pathogenesis, e.g., Aβ-aggregation, Aβ-induced neurotoxicity, oxidative stress, and inflammatory processes, as summarized in this article.

Hippocampal lipid differences in Alzheimer's disease: a human brain study using matrix-assisted laser desorption/ionization-imaging mass spectrometry

INTRODUCTION

Alzheimer's disease (AD), the leading cause of dementia, is pathologically characterized by β-amyloid plaques and tau tangles. However, there is also evidence of lipid dyshomeostasis-mediated AD pathology. Given the structural diversity of lipids, mass spectrometry is a useful tool for studying lipid changes in AD. Although there have been a few studies investigating lipid changes in the human hippocampus in particular, there are few reports on how lipids change in each hippocampal subfield (e.g., Cornu Ammonis [CA] 1-4, dentate gyrus [DG] etc.). Since each subfield has its own function, we postulated that there could be lipid changes that are unique to each.

METHODS

We used matrix-assisted laser desorption/ionization-imaging mass spectrometry to investigate specific lipid changes in each subfield in AD. Data from the hippocampus region of six age- and gender-matched normal and AD pairs were analyzed with SCiLS lab 2015b software (SCiLS GmbH, Germany; RRID:SCR_014426), using an analysis workflow developed in-house. Hematoxylin, eosin, and luxol fast blue staining were used to precisely delineate each anatomical hippocampal subfield. Putative lipid identities, which were consistent with published data, were assigned using MS/MS.

RESULTS

Both positively and negatively charged lipid ion species were abundantly detected in normal and AD tissue. While the distribution pattern of lipids did not change in AD, the abundance of some lipids changed, consistent with trends that have been previously reported. However, our results indicated that the majority of these lipid changes specifically occur in the CA1 region. Additionally, there were many lipid changes that were specific to the DG.

CONCLUSIONS

Matrix-assisted laser desorption/ionization-imaging mass spectrometry and our analysis workflow provide a novel method to investigate specific lipid changes in hippocampal subfields. Future work will focus on elucidating the role that specific lipid differences in each subfield play in AD pathogenesis.

Food-induced changes of lipids in rat neuronal tissue visualized by ToF-SIMS imaging

Time of flight secondary ion mass spectrometry (ToF-SIMS) was used to image the lipid localization in brain tissue sections from rats fed specially processed cereals (SPC). An IonTof 5 instrument equipped with a Bi cluster ion gun was used to analyze the tissue sections. Data from 15 brain samples from control and cereal-fed rats were recorded and exported to principal components analysis (PCA). The data clearly show changes of certain lipids in the brain following cereal feeding. PCA score plots show a good separation in lipid distribution between the control and the SPC-fed group. The loadings plot reveal that the groups separated mainly due to changes in cholesterol, vitamin E and c18:2, c16:0 fatty acid distribution as well as some short chain monocarboxylic fatty acid compositions. These insights relate to the working mechanism of SPC as a dietary supplement. SPC is thought to activate antisecretory factor (AF), an endogenous protein with regulatory function for inflammation and fluid secretion. These data provide insights into lipid content in brain following SPC feeding and suggest a relation to activating AF.

Intact lipid imaging of mouse brain samples: MALDI, nanoparticle-laser desorption ionization, and 40 keV argon cluster secondary ion mass spectrometry

We have investigated the capability of nanoparticle-assisted laser desorption ionization mass spectrometry (NP-LDI MS), matrix-assisted laser desorption ionization (MALDI) MS, and gas cluster ion beam secondary ion mass spectrometry (GCIB SIMS) to provide maximum information available in lipid analysis and imaging of mouse brain tissue. The use of Au nanoparticles deposited as a matrix for NP-LDI MS is compared to MALDI and SIMS analysis of mouse brain tissue and allows selective detection and imaging of groups of lipid molecular ion species localizing in the white matter differently from those observed using conventional MALDI with improved imaging potential. We demonstrate that high-energy (40 keV) GCIB SIMS can act as a semi-soft ionization method to extend the useful mass range of SIMS imaging to analyze and image intact lipids in biological samples, closing the gap between conventional SIMS and MALDI techniques. The GCIB SIMS allowed the detection of more intact lipid compounds in the mouse brain compared to MALDI with regular organic matrices. The 40 keV GCIB SIMS also produced peaks observed in the NP-LDI analysis, and these peaks were strongly enhanced in intensity by exposure of the sample to trifluororacetic acid (TFA) vapor prior to analysis. These MS techniques for imaging of different types of lipids create a potential overlap and cross point that can enhance the information for imaging lipids in biological tissue sections.

Graphical abstract