Odor identification score as an alternative method for early identification of amyloidogenesis in Alzheimer's disease

A simple screening test to identify the early stages of Alzheimer's disease (AD) is urgently needed. We investigated whether odor identification impairment can be used to differentiate between stages of the A/T/N classification (amyloid,  tau, neurodegeneration) in individuals with amnestic mild cognitive impairment or AD and in healthy controls. We collected data from 132 Japanese participants visiting the Toranomon Hospital dementia outpatient clinic. The odor identification scores correlated significantly with major neuropsychological scores, regardless of apolipoprotein E4 status, and with effective cerebrospinal fluid (CSF) biomarkers [amyloid β 42 (Aβ42) and the Aβ42/40 and phosphorylated Tau (p-Tau)/Aβ42 ratios] but not with ineffective biomarkers [Aβ40 and the p-Tau/total Tau ratio]. A weak positive correlation was observed between the corrected odor identification score (adjusted for age, sex, ApoE4 and MMSE), CSF Aβ42, and the Aβ42/40 ratio. The odor identification score demonstrated excellent discriminative power for the amyloidogenesis stage , according to the A/T/N classification, but was unsuitable for differentiating between the p-Tau accumulation and the neurodegeneration stages. After twelve odor species were analyzed, a version of the score comprising only four odors-India ink, wood, curry, and sweaty socks-proved highly effective in identifying AD amyloidogenesis, showing promise for the screening of preclinical AD.

Extracellular vesicle proteome unveils cathepsin B connection to Alzheimer's disease pathogenesis

Extracellular vesicles (EVs) are membrane vesicles that are released extracellularly and considered to be implicated in the pathogenesis of neurodegenerative diseases including Alzheimer's disease. Here, CSF EVs of 16 ATN-classified cases were subjected to quantitative proteome analysis. In these CSF EVs, levels of 11 proteins were significantly altered during the ATN stage transitions (P < 0.05 and fold-change > 2.0). These proteins were thought to be associated with Alzheimer's disease pathogenesis and represent candidate biomarkers for pathogenic stage classification. Enzyme-linked immunosorbent assay analysis of CSF and plasma EVs revealed altered levels of cathepsin B (CatB) during the ATN transition (seven ATN groups in validation set, n = 136). The CSF and plasma EV CatB levels showed a negative correlation with CSF amyloid-β42 concentrations. This proteomic landscape of CSF EVs in ATN classifications can depict the molecular framework of Alzheimer's disease progression, and CatB may be considered a promising candidate biomarker and therapeutic target in Alzheimer's disease amyloid pathology.

Stereochemistry-activity relationship of ceramide-induced exosome production to clear amyloid-β in Alzheimer's disease

Stereochemistry has a substantial impact on the biological activity of various drugs. We investigated the role of stereochemistry of ceramides in inducing the production of exosomes, a type of extracellular vesicle, from neuronal cells, with a potential benefit in improving the clearance of amyloid-β (Aβ), a causal agent of Alzheimer's disease. A stereochemical library of diverse ceramides with different tail lengths was synthesized with the purpose of varying stereochemistry (D-erythro: DE, D-threo: DT, L-erythro: LE, L-threo: LT) and hydrophobic tail length (C6, C16, C18, C24). The exosome levels were quantified using TIM4-based exosome enzyme-linked immunosorbent assay after concentrating the conditioned medium using centrifugal filter devices. The results revealed a pivotal role of stereochemistry in determining the biological activity of ceramide stereoisomers, with the superiority of those based on DE and DT stereochemistry with C16 and C18 tails, which demonstrated significantly higher exosome production, without a significant change in the particle size of the released exosomes. In transwell experiments with Aβ-expressed neuronal and microglial cells, DE- and DT-ceramides with C16 and C18 tails significantly decreased extracellular Aβ levels. The results reported here are promising in the design of non-classic therapies for the treatment of Alzheimer's disease.

Immuno-digital invasive cleavage assay for analyzing Alzheimer's amyloid ß-bound extracellular vesicles

BACKGROUND

The protracted preclinical stage of Alzheimer's disease (AD) provides the opportunity for early intervention to prevent the disease; however, the lack of minimally invasive and easily detectable biomarkers and their measurement technologies remain unresolved. Extracellular vesicles (EVs) are nanosized membrane vesicles released from a variety of cells and play important roles in cell-cell communication. Neuron-derived and ganglioside-enriched EVs capture amyloid-ß protein, a major AD agent, and transport it into glial cells for degradation; this suggests that EVs influence Aß accumulation in the brain. EV heterogeneity, however, requires the use of a highly sensitive technique for measuring specific EVs in biofluid. In this study, immuno-digital invasive cleavage assay (idICA) was developed for quantitating target-intact EVs.

METHODS

EVs were captured onto ganglioside GM1-specific cholera toxin B subunit (CTB)-conjugated magnetic beads and detected with a DNA oligonucleotide-labeled Aß antibody. Fluorescence signals for individual EVs were then counted using an invasive cleavage assay (ICA). This idICA examines the Aß-bound and GM1-containing EVs isolated from the culture supernatant of human APP-overexpressing N2a (APP-N2a) cells and APP transgenic mice sera.

RESULTS

The idICA quantitatively detected Aß-bound and GM1-containing EVs isolated from culture supernatants of APP-N2a cells and sera of AD model mice. The idICA levels of Aß-associated EVs in blood gradually increased from 3- to 12-month-old mice, corresponding to the progression of Aß accumulations in the brain of AD model mice.

CONCLUSIONS

The present findings suggest that peripheral EVs harboring Aß and GM1 reflect Aß burden in mice. The idICA is a valuable tool for easy quantitative detection of EVs as an accessible biomarker for preclinical AD diagnosis.

Evaluation of Plant Ceramide Species-Induced Exosome Release from Neuronal Cells and Exosome Loading Using Deuterium Chemistry

The extracellular accumulation of aggregated amyloid-β (Aβ) in the brain leads to the early pathology of Alzheimer’s disease (AD). The administration of exogenous plant-type ceramides into AD model mice can promote the release of neuronal exosomes, a subtype of extracellular vesicles, that can mediate Aβ clearance. In vitro studies showed that the length of fatty acids in mammalian-type ceramides is crucial for promoting neuronal exosome release. Therefore, investigating the structures of plant ceramides is important for evaluating the potential in releasing exosomes to remove Aβ. In this study, we assessed plant ceramide species with D-erythro-(4E,8Z)-sphingadienine and D-erythro-(8Z)-phytosphingenine as sphingoid bases that differ from mammalian-type species. Some plant ceramides were more effective than mammalian ceramides at stimulating exosome release. In addition, using deuterium chemistry-based lipidomics, most exogenous plant ceramides were confirmed to be derived from exosomes. These results suggest that the ceramide-dependent upregulation of exosome release may promote the release of exogenous ceramides from cells, and plant ceramides with long-chain fatty acids can effectively release neuronal exosomes and prevent AD pathology.

Penta-deuterium-labeled 4E, 8Z-sphingadienine for rapid analysis in sphingolipidomics study

The use of deuterium-incorporated bioactive compounds is an efficient method for tracing their metabolic fate and for quantitative analysis by mass spectrometry without complicated HPLC separation even if their amounts are extremely small. Plant sphingolipids and their metabolites, which have C4, 8-olefins on a common backbone as a sphingoid base, show unique and fascinating bioactivities compared to those of sphingolipids in mammals. However, the functional and metabolic mechanisms of exogenous plant sphingolipids have not been elucidated due to the difficulty in distinguishing exogenous sphingolipids from endogenous sphingolipids having the same polarity and same molecular weight by mass spectrometric analysis. Their roles might be elucidated by the use of deuterated probes with original biological and physicochemical properties. In this study, we designed (2S,3R,4E,8Z)-2-aminooctadeca-4,8-diene-17,17,18,18,18-d₅-1,3-diol (penta-deuterium-labeled 4E, 8Z-sphingadienine) as a tracer for exogenous metabolic studies. In addition, the sphingadienine was confirmed to be metabolized in HEK293 cells and showed distinct peaks in mass spectrometric analysis.

Konjac Ceramide (kCer)-Mediated Signal Transduction of the Sema3A Pathway Promotes HaCaT Keratinocyte Differentiation

Simple Summary

Konjac ceramide (kCer) is a unique molecular species of plant-type ceramide, and is a potential Sema3A-like ligand of Nrp1. kCer suppresses histamine-stimulated cell migration of HaCaT keratinocytes. This effect of kCer is not due to histamine-activated GPCRs, but rather to Sema3A-Nrp1 receptor binding. The present study focused on the ability of kCer to induce cell differentiation, in addition to its anti-migratory effects. We demonstrated that the effects of kCer on cell migration and cell differentiation are perpetuated by a cascade of crosstalk between pathways downstream of Nrp1 and GPCR in HaCaT cells.

Abstract

Histamines suppress epidermal keratinocyte differentiation. Previously, we reported that konjac ceramide (kCer) suppresses histamine-stimulated cell migration of HaCaT keratinocytes. kCer specifically binds to Nrp1 and does not interact with histamine receptors. The signaling mechanism of kCer in HaCaT cells is also controlled by an intracellular signaling cascade activated by the Sema3A-Nrp1 pathway. In the present study, we demonstrated that kCer treatment induced HaCaT keratinocyte differentiation after migration of immature cells. kCer-induced HaCaT cell differentiation was accompanied by some features of keratinocyte differentiation markers. kCer induced activating phosphorylation of p38MAPK and c-Fos, which increased the protein levels of involucrin that was the latter differentiation marker. In addition, we demonstrated that the effects of both kCer and histamines are regulated by an intracellular mechanism of Rac1 activation/RhoA inhibition downstream of the Sema3A/Nrp1 receptor and histamine/GPCR pathways. In summary, the effects of kCer on cell migration and cell differentiation are regulated by cascade crosstalk between downstream Nrp1 and histamine-GPCR pathways in HaCaT cells.

Comprehensive Glycomic Approach Reveals Novel Low-Molecular-Weight Blood Group-Specific Glycans in Serum and Cerebrospinal Fluid

ABO blood antigens on the human red blood cell membrane as well as different cells in various human tissues have been thoroughly studied. Anti-A and -B antibodies of IgM are present in serum/plasma, but blood group-specific glyco-antigens have not been extensively described. In this study, we performed comprehensive and quantitative serum glycomic analyses of various glycoconjugates and free oligosaccharides in all blood groups. Our comprehensive glycomic approach revealed that blood group-specific antigens in serum/plasma are predominantly present on glycosphingolipids on lipoproteins rather than glycoproteins. Expression of the ABO antigens on glycosphingolipids depends not only on blood type but also on secretor status. Blood group-specific glycans in serum/plasma were classified as type I, whereas those on RBCs had different structures including hexose and hexosamine residues. Analysis of free oligosaccharides revealed that low-molecular-weight blood group-specific glycans, commonly containing lacto-N-difucotetraose, were expressed in serum/plasma according to blood group. Furthermore, comprehensive glycomic analysis in human cerebrospinal fluid showed that many kinds of free oligosaccharides were highly expressed, and low-molecular-weight blood group-specific glycans, which existed in plasma from the same individuals, were present. Our findings provide the first evidence for low-molecular-weight blood group-specific glycans in both serum/plasma and cerebrospinal fluid.

Structure-dependent absorption of atypical sphingoid long-chain bases from digestive tract into lymph

BACKGROUND

Dietary sphingolipids have various biofunctions, including skin barrier improvement and anti-inflammatory and anti-carcinoma properties. Long-chain bases (LCBs), the essential backbones of sphingolipids, are expected to be important for these bioactivities, and they vary structurally between species. Given these findings, however, the absorption dynamics of each LCB remain unclear.

METHODS

In this study, five structurally different LCBs were prepared from glucosylceramides (GlcCers) with LCB 18:2(4E,8Z);2OH and LCB 18:2(4E,8E);2OH moieties derived from konjac tuber (Amorphophallus konjac), from GlcCers with an LCB 18(9Me):2(4E,8E);2OH moiety derived from Tamogi mushroom (Pleurotus cornucopiae var. citrinopileatus), and from ceramide 2-aminoethyphosphonate with LCB 18:3(4E,8E,10E);2OH moiety and LCB 18(9Me):3(4E,8E,10E);2OH moiety derived from giant scallop (Mizuhopecten yessoensis), and their absorption percentages and metabolite levels were analyzed using a lymph-duct-cannulated rat model via liquid chromatography tandem mass spectrometry (LC/MS/MS) with a multistage fragmentation method.

RESULTS

The five orally administered LCBs were absorbed and detected in chyle (lipid-containing lymph) as LCBs and several metabolites including ceramides, hexosylceramides, and sphingomyelins. The absorption percentages of LCBs were 0.10-1.17%, depending on their structure. The absorption percentage of LCB 18:2(4E,8Z);2OH was the highest (1.17%), whereas that of LCB 18:3(4E,8E,10E);2OH was the lowest (0.10%). The amount of sphingomyelin with an LCB 18:2(4E,8Z);2OH moiety in chyle was particularly higher than sphingomyelins with other LCB moieties.

CONCLUSIONS

Structural differences among LCBs, particularly geometric isomerism at the C8-C9 position, significantly affected the absorption percentages and ratio of metabolites. This is the first report to elucidate that the absorption and metabolism of sphingolipids are dependent on their LCB structure. These results could be used to develop functional foods that are more readily absorbed.

Mevalonate Pathway-mediated ER Homeostasis Is Required for Haploid Stability in Human Somatic Cells

The somatic haploidy is unstable in diplontic animals, but cellular processes determining haploid stability remain elusive. Here, we found that inhibition of mevalonate pathway by pitavastatin, a widely used cholesterol-lowering drug, drastically destabilized the haploid state in HAP1 cells. Interestingly, cholesterol supplementation did not restore haploid stability in pitavastatin-treated cells, and cholesterol inhibitor U18666A did not phenocopy haploid destabilization. These results ruled out the involvement of cholesterol in haploid stability. Besides cholesterol perturbation, pitavastatin induced endoplasmic reticulum (ER) stress, the suppression of which by a chemical chaperon significantly restored haploid stability in pitavastatin-treated cells. Our data demonstrate the involvement of the mevalonate pathway in the stability of the haploid state in human somatic cells through managing ER stress, highlighting a novel link between ploidy and ER homeostatic control.Key words: haploid, ER stress, Mevalonate pathway.

Blood-brain barrier permeability analysis of plant ceramides

Ceramides, a type of sphingolipid, are cell membrane components and lipid mediators that modulate a variety of cell functions. In plants, ceramides are mostly present in a glucosylated glucosylceramide (GlcCer) form. We previously showed that oral administration of konjac-derived GlcCer to a mouse model of Alzheimer’s disease reduced brain amyloid-β and amyloid plaques. Dietary plant GlcCer compounds are absorbed as ceramides, but it is unclear whether they can cross the blood-brain barrier (BBB). Herein, we evaluated the BBB permeability of synthetic plant-type ceramides (4, 8-sphingadienine, d18:2) using mouse and BBB cell culture models, and found that they could permeate the BBB both in vivo and in vitro. In addition, administrated ceramides were partially metabolized to other sphingolipid species, namely sphingomyelin (SM) and GlcCer, while crossing the BBB. Thus, plant ceramides can cross the BBB, suggesting that ceramides and their metabolites might affect brain functions.

Lysosomal-associated transmembrane protein 4B regulates ceramide-induced exosome release

Exosomes are extracellular vesicles that mediate the transport of intracellular molecules, including neurodegenerative agents. Exogenously administrated ceramides have been implicated in the acceleration of exosome production by neurons; however, the molecular machinery involved in this process is unknown. Here, we found that ceramides, especially those consisting of long fatty acids, were internalized into the endocytic pathway in neuroblastoma SH-SY5Y cells to induce exosome secretion through lysosome-associated protein transmembrane 4B (LAPTM4B). Knockdown of LAPTM4B inhibited the ceramide-mediated increase in exosome release completely. Fluorescence microscopy observations indicated that exogenous ceramides promote the transport of multivesicular bodies to the plasma membranes in a LAPTM4B-dependent manner. Similarly, inhibition of acid ceramidase, which tends to induce intracellular ceramide accumulation, increased exosome production by SH-SY5Y cells in a LAPTM4B-dependent manner. Furthermore, the level of amyloid-ß protein (Aß) was decreased in neuronal cells following treatment with exogenous ceramide or inhibition of acid ceramidase, and this effect was attributed to the LAPTM4B-dependent efflux of Aß-containing exosomes. Overall, these findings reveal the novel machinery involved in exosome secretion regulated by ceramides and LAPTM4B, and may contribute to efforts to ameliorate the cellular accumulation of neurodegenerative agents such as Aß.

Glucocerebrosidases catalyze a transgalactosylation reaction that yields a newly-identified brain sterol metabolite, galactosylated cholesterol

β-Glucocerebrosidase (GBA) hydrolyzes glucosylceramide (GlcCer) to generate ceramide. Previously, we demonstrated that lysosomal GBA1 and nonlysosomal GBA2 possess not only GlcCer hydrolase activity, but also transglucosylation activity to transfer the glucose residue from GlcCer to cholesterol to form β-cholesterylglucoside (β-GlcChol) in vitro β-GlcChol is a member of sterylglycosides present in diverse species. How GBA1 and GBA2 mediate β-GlcChol metabolism in the brain is unknown. Here, we purified and characterized sterylglycosides from rodent and fish brains. Although glucose is thought to be the sole carbohydrate component of sterylglycosides in vertebrates, structural analysis of rat brain sterylglycosides revealed the presence of galactosylated cholesterol (β-GalChol), in addition to β-GlcChol. Analyses of brain tissues from GBA2-deficient mice and GBA1- and/or GBA2-deficient Japanese rice fish (Oryzias latipes) revealed that GBA1 and GBA2 are responsible for β-GlcChol degradation and formation, respectively, and that both GBA1 and GBA2 are responsible for β-GalChol formation. Liquid chromatography-tandem MS revealed that β-GlcChol and β-GalChol are present throughout development from embryo to adult in the mouse brain. We found that β-GalChol expression depends on galactosylceramide (GalCer), and developmental onset of β-GalChol biosynthesis appeared to be during myelination. We also found that β-GlcChol and β-GalChol are secreted from neurons and glial cells in association with exosomes. In vitro enzyme assays confirmed that GBA1 and GBA2 have transgalactosylation activity to transfer the galactose residue from GalCer to cholesterol to form β-GalChol. This is the first report of the existence of β-GalChol in vertebrates and how β-GlcChol and β-GalChol are formed in the brain.

Plant sphingolipids promote extracellular vesicle release and alleviate amyloid-β pathologies in a mouse model of Alzheimer's disease

The accumulation of amyloid-β protein (Aβ) in brain is linked to the early pathogenesis of Alzheimer’s disease (AD). We previously reported that neuron-derived exosomes promote Aβ clearance in the brains of amyloid precursor protein transgenic mice and that exosome production is modulated by ceramide metabolism. Here, we demonstrate that plant ceramides derived from Amorphophallus konjac, as well as animal-derived ceramides, enhanced production of extracellular vesicles (EVs) in neuronal cultures. Oral administration of plant glucosylceramide (GlcCer) to APP overexpressing mice markedly reduced Aβ levels and plaque burdens and improved cognition in a Y-maze learning task. Moreover, there were substantial increases in the neuronal marker NCAM-1, L1CAM, and Aβ in EVs isolated from serum and brain tissues of the GlcCer-treated AD model mice. Our data showing that plant ceramides prevent Aβ accumulation by promoting EVs-dependent Aβ clearance in vitro and in vivo provide evidence for a protective role of plant ceramides in AD. Plant ceramides might thus be used as functional food materials to ameliorate AD pathology.

Malabaricone C as Natural Sphingomyelin Synthase Inhibitor against Diet-Induced Obesity and Its Lipid Metabolism in Mice

The interaction between natural occurring inhibitors and targeted membrane proteins could be an alternative medicinal strategy for the treatment of metabolic syndrome, notably, obesity. In this study, we identified malabaricones A-C and E (1-4) isolated from the fruits of Myristica cinnamomea King as natural inhibitors for sphingomyelin synthase (SMS), a membrane protein responsible for sphingolipid biosynthesis. Having the most promising inhibition, oral administration of compound 3 exhibited multiple efficacies in reducing weight gain, improving glucose tolerance, and reducing hepatic steatosis in high fat diet-induced obesity mice models. Liver lipid analysis revealed a crucial link between the SMS activities of compound 3 and its lipid metabolism in vitro and in vivo. The nontoxic nature of compound 3 makes it a suitable candidate in search of drugs which can be employed in the treatment and prevention of obesity.

Isolation of Sphingoid Bases from Starfish Asterias amurensis Glucosylceramides and Their Effects on Sphingolipid Production in Cultured Keratinocytes

Starfish Asterias amurensis produces sphingoid bases d18:3, 9-methyl-d18:3 (9Me-d18:3), and d22:2, which possess unique structural features. In this study, sphingoid bases prepared from A. amurensis glucosylceramides displayed unexpected elution behaviors from a general octadecyl silyl high-performance liquid chromatography (HPLC) column. For separation and isolation, sphingoid bases were fractionated by octadecyl silyl HPLC after N-acetylation, yielding d18:3, 9Me-d18:3, and two d22:2 isomers. To compare the biological activities of individual sphingoid bases, their effects on sphingolipid production in normal human keratinocytes were evaluated. Treatment with sphingoid bases increased the content of ceramides, glucosylceramides, and sphingomyelins in keratinocytes. Moreover, ceramides, which contain saturated ultra-long-chain fatty acids (C30-34), were significantly increased by treatment with d18:3, but not with other A. amurensis sphingoid bases. The mRNA level of the early differentiation marker keratin 10 was markedly decreased and sphingolipid synthesis-related genes were slightly increased in keratinocytes exposed to A. amurensis-derived d18:3, 9Me-d18:3, and d22:2 isomers. These results suggest that A. amurensis-derived sphingoid bases induce differentiation to varying degrees, sphingolipid production depends on their chemical structures, and d18:3 is the most promising functional sphingoid base.

Konjac Ceramide (kCer) Regulates NGF-Induced Neurite Outgrowth via the Sema3A Signaling Pathway

The tuber of the konjac plant is a source enriched with GlcCer (kGlcCer), and has been used as a dietary supplement to improve the dry skin and itching that are caused by a deficiency of epidermal ceramide. Previously, we showed chemoenzymatically prepared konjac ceramide has a neurite-outgrowth inhibitory effect that is very similar to that of Sema3A and is not seen with animal-type ceramides. While, it has been unclear whether kCer may act on Sema3A or TrkA signaling pathway. In the present study, we showed kCer induces phosphorylation of CRMP2 and microtubules depolymerization via Sema3A signaling pathway not TrkA. It is concluded that kCer may be a potential Sema3A-like agonist that activates Sema3A signaling pathway directly.

Exosomes as Carriers of Alzheimer's Amyloid-ß

The intracerebral level of the aggregation-prone peptide, amyloid-ß (Aß), is constantly maintained by multiple clearance mechanisms, including several degradation enzymes, and brain efflux. Disruption of the clearance machinery and the resultant Aß accumulation gives rise to neurotoxic assemblies, leading to the pathogenesis of Alzheimer's disease (AD). In addition to the classic mechanisms of Aß clearance, the protein may be processed by secreted vesicles, although this possibility has not been extensively investigated. We showed that neuronal exosomes, a subtype of extracellular nanovesicles, enwrap, or trap Aß and transport it into microglia for degradation. Here, we review Aß sequestration and elimination by exosomes, and discuss how this clearance machinery might contribute to AD pathogenesis and how it might be exploited for effective AD therapy.

Physiological and pathological roles of exosomes in the nervous system

Exosomes represent a subtype of extracellular nanovesicles that are generated from the luminal budding of limiting endosomal membranes and subsequent exocytosis. They encapsulate or associate with obsolete molecules to eliminate or to transfer their cargos in intercellular communication. The exosomes are also released and transported between neurons and glia in the nervous system, having a broad impact on nerve development, activation and regeneration. Accumulating evidence suggests that the exosomes are attributed to the pathogenesis of several neurodegenerative diseases such as prion disease, Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, as well as aging, in which the exosomes lack the capacity for cellular self-repair and spread their enclosed pathological agents among neurons. In this article, we review the current proposed functions of exosomes in physiological and pathological processes in the nervous system.

Decreased amyloid-β pathologies by intracerebral loading of glycosphingolipid-enriched exosomes in Alzheimer model mice

Elevated levels of amyloid-β peptide (Aβ) in the human brain are linked to the pathogenesis of Alzheimer disease. Recent in vitro studies have demonstrated that extracellular Aβ can bind to exosomes, which are cell-secreted nanovesicles with lipid membranes that are known to transport their cargos intercellularly. Such findings suggest that the exosomes are involved in Aβ metabolism in brain. Here, we found that neuroblastoma-derived exosomes exogenously injected into mouse brains trapped Aβ and with the associated Aβ were internalized into brain-resident phagocyte microglia. Accordingly, continuous intracerebral administration of the exosomes into amyloid-β precursor protein transgenic mice resulted in marked reductions in Aβ levels, amyloid depositions, and Aβ-mediated synaptotoxicity in the hippocampus. In addition, we determined that glycosphingolipids (GSLs), a group of membrane glycolipids, are highly abundant in the exosomes, and the enriched glycans of the GSLs are essential for Aβ binding and assembly on the exosomes both in vitro and in vivo. Our data demonstrate that intracerebrally administered exosomes can act as potent scavengers for Aβ by carrying it on the exosome surface GSLs and suggest a role of exosomes in Aβ clearance in the central nervous system. Improving Aβ clearance by exosome administration would provide a novel therapeutic intervention for Alzheimer disease.

Cooperative Synthesis of Ultra Long-Chain Fatty Acid and Ceramide during Keratinocyte Differentiation

The lipid lamellae in the stratum corneum is important for the epidermal permeability barrier. The lipid lamellae component ceramide (CER), comprising an ultra long-chain (ULC) fatty acid (FA) of ≥26 carbons (ULC CER), plays an essential role in barrier formation. ULC acyl-CoAs, produced by the FA elongase ELOVL4, are converted to ULC CERs by the CER synthase CERS3. In the presented study, we observed that ELOVL4 and CERS3 mRNAs increased during keratinocyte differentiation in vivo and in vitro. We also determined that peroxisome proliferator-activated receptor β/δ is involved in the up-regulation of the mRNAs. Knockdown of CERS3 caused a reduction in the elongase activities toward ULC acyl-CoAs, suggesting that CERS3 positively regulates ULCFA. Thus, we reveal that the two key players in ULC CER production in epidermis, CERS3 and ELOVL4, are coordinately regulated at both the transcriptional and enzymatic levels.

Involvement of gangliosides in the process of Cbp/PAG phosphorylation by Lyn in developing cerebellar growth cones

The association of gangliosides with specific proteins in the central nervous system was examined by coimmunoprecipitation with an anti-ganglioside antibody. The monoclonal antibody to the ganglioside GD3 (R24) immunoprecipitated the Csk (C-terminal src kinase)-binding protein (Cbp). Sucrose density gradient analysis showed that Cbp of rat cerebellum was detected in detergent-resistant membrane (DRM) raft fractions. R24 treatment of the rat primary cerebellar cultures induced Lyn activation and tyrosine phosphorylation of Cbp. Treatment with anti-ganglioside GD1b antibody also induced tyrosine phosphorylation. Furthermore, over-expressions of Lyn and Cbp in Chinese hamster ovary (CHO) cells resulted in tyrosine 314 phosphorylation of Cbp, which indicates that Cbp is a substrate for Lyn. Immunoblotting analysis showed that the active form of Lyn and the Tyr314-phosphorylated form of Cbp were highly accumulated in the DRM raft fraction prepared from the developing cerebellum compared with the DRM raft fraction of the adult one. In addition, Lyn and the Tyr314-phosphorylated Cbp were highly concentrated in the growth cone fraction prepared from the developing cerebellum. Immunoelectron microscopy showed that Cbp and GAP-43, a growth cone marker, are localized in the same vesicles of the growth cone fraction. These results suggest that Cbp functionally associates with gangliosides on growth cone rafts in developing cerebella.

Sphingolipid-modulated exosome secretion promotes clearance of amyloid-β by microglia

Amyloid β-peptide (Aβ), the pathogenic agent of Alzheimer disease, is a physiological metabolite whose levels are constantly controlled in normal brain. Recent studies have demonstrated that a fraction of extracellular Aβ is associated with exosomes, small membrane vesicles of endosomal origin, although the fate of Aβ in association with exosome is largely unknown. In this study, we identified novel roles for neuron-derived exosomes acting on extracellular Aβ, i.e. exosomes drive conformational changes in Aβ to form nontoxic amyloid fibrils and promote uptake of Aβ by microglia. The Aβ internalized together with exosomes was further transported to lysosomes and degraded. We also found that blockade of phosphatidylserine on the surface of exosomes by annexin V not only prevented exosome uptake but also suppressed Aβ incorporation into microglia. In addition, we demonstrated that secretion of neuron-derived exosomes was modulated by the activities of sphingolipid-metabolizing enzymes, including neutral sphingomyelinase 2 (nSMase2) and sphingomyelin synthase 2 (SMS2). In transwell experiments, up-regulation of exosome secretion from neuronal cells by treatment with SMS2 siRNA enhanced Aβ uptake into microglial cells and significantly decreased extracellular levels of Aβ. Our findings indicate a novel mechanism responsible for clearance of Aβ through its association with exosomes. The modulation of the vesicle release and/or elimination may alter the risk of AD.

Accelerated release of exosome-associated GM1 ganglioside (GM1) by endocytic pathway abnormality: another putative pathway for GM1-induced amyloid fibril formation

Exosomes are extracellularly released small vesicles that are derived from multivesicular bodies formed via the endocytic pathway. We treated pheochromocytoma PC12 cells with chloroquine, an acidotropic agent, which potently perturbs membrane trafficking from endosomes to lysosomes. Chloroquine treatment increased the level of GM1 ganglioside in cell media only when the cells were exposed to KCl for depolarization, which is known to enhance exosome release from neurons. In the sucrose-density-gradient fractionation of cell media, GM1 ganglioside was exclusively recovered with Alix, a specific marker of exosomes, in the fractions with the density corrresponding to that of exosomes. Notably, amyloid-beta assembly was markedly accelerated when incubated with the exosome fraction prepared from the culture media of PC12 cells treated with chloroquine and KCl. Furthermore, amyloid-beta assembly was significantly suppressed by the co-incubation with an antibody specific to GM1-bound amyloid-beta, an endogenous seed for amyloid formation of Alzheimer's disease. Together with our previous finding that chloroquine treatment induces the accumulation of GM1 ganglioside in early endosomes, results of this study suggest that endocytic pathway abnormality accelerates the release of exosome-associated GM1 ganglioside following its accumulation in early endosomes. Furthermore, this study also suggests that extracellular amyloid fibril formation is induced by not only GM1 gangliosides accumulated on the surface of the cells but also those released in association with exosomes.

Translocation of activated heterotrimeric G protein Galpha(o) to ganglioside-enriched detergent-resistant membrane rafts in developing cerebellum

The association of gangliosides with specific proteins in the central nervous system was examined by co-immunoprecipitation with an anti-ganglioside antibody. The monoclonal antibody to the ganglioside GD3 immunoprecipitated phosphoproteins of 40, 53, 56, and 80 kDa from the rat cerebellum. Of these proteins, the 40-kDa protein was identified as the alpha-subunit of a heterotrimeric G protein, G(o) (Galpha(o)). Using sucrose density gradient analysis of cerebellar membranes, Galpha(o), but not Gbetagamma, was observed in detergent-resistant membrane (DRM) raft fractions in which GD3 was abundant after the addition of guanosine 5'-O-(thiotriphosphate) (GTPgammaS), which stabilizes G(o) in its active form. On the other hand, both Galpha(o) and Gbetagamma were excluded from the DRM raft fractions in the presence of guanyl-5'-yl thiophosphate, which stabilizes G(o) in its inactive form. Only Galpha(o) was observed in the DRM fractions from the cerebellum on postnatal day 7, but not from that in adult. After pertussis toxin treatment, Galpha(o) was not observed in the DRM fractions, even from the cerebellum on postnatal day 7. These results indicate the activation-dependent translocation of Galpha(o) into the DRM rafts. Furthermore, Galpha(o) was concentrated in the neuronal growth cones. Treatment with stromal cell-derived factor-1alpha, a physiological ligand for the G protein-coupled receptor, stimulated [(35)S]GTPgammaS binding to Galpha(o) and caused Galpha(o) translocation to the DRM fractions and RhoA translocation to the membrane fraction, leading to the growth cone collapse of cerebellar granule neurons. The collapse was partly prevented by pretreatment with the cholesterol-sequestering and raft-disrupting agent methyl-beta-cyclodextrin. These results demonstrate the involvement of signal-dependent Galpha(o) translocation to the DRM in the growth cone behavior of cerebellar granule neurons.

Chloroquine-induced endocytic pathway abnormalities: Cellular model of GM1 ganglioside-induced Abeta fibrillogenesis in Alzheimer's disease

Endocytic pathway abnormalities were previously observed in brains affected with Alzheimer's disease (AD). To clarify the pathological relevance of these abnormalities to assembly of amyloid beta-protein (Abeta), we treated PC12 cells with chloroquine, which potently perturbs membrane trafficking from endosomes to lysosomes. Chloroquine treatment induced accumulation of GM1 ganglioside (GM1) in Rab5-positive enlarged early endosomes and on the cell surface. Notably, an increase in GM1 level on the cell surface was sufficient to induce Abeta assembly. Our results suggest that endocytic pathway abnormalities in AD brain induce GM1 accumulation on the cell surface, leading to amyloid fibril formation in brain.

Low concentrations of nitric oxide (NO) induced cell death in PC12 cells through activation of p38 mitogen-activated protein kinase (p38 MAPK) but not via extracellular signal-regulated kinases (ERK1/2) or c-Jun N-terminal protein kinase (JNK)

Nitric oxide (NO), a highly reactive gaseous molecule, has been previously reported to induce apoptosis-like cell death even at a low concentration in PC12 cells. In this study, we examined NO-induced activation of members of the mitogen-activated protein kinase (MAPK) family, i.e., p38 MAPK, extracellular signal-regulated kinases (ERK1/2), and c-Jun N-terminal protein kinase (JNK). Following the exposure of PC12 cells to an NO donor, (+)-(E)-4-ethyl-2-[hydroxyimino]-5-nitro-3-hexenamide (NOR3; 100 muM), the phosphorylation level of p38 MAPK increased time dependently from 2 to 6 h, but that of both ERK1/2 and JNK did not. Treatment with a p38 MAPK inhibitor SB203580 partially blocked the NOR3-induced cell death. Neither PD98059, U0126 (inhibitors of ERK1/2) nor SP600125 (a specific inhibitor of JNK) treatments had any significant effect on the NOR3-induced cell death. These findings suggest that the activation of a p38 MAPK pathway, but not that of ERK1/2 or JNK, plays an essential role in the apoptosis-like cell death induced by low concentrations of NO.

Caspase-independent cell death by low concentrations of nitric oxide in PC12 cells: involvement of cytochrome C oxidase inhibition and the production of reactive oxygen species in mitochondria

We reported previously that low levels of nitric oxide (NO) induced cell death with properties of apoptosis, including chromatin fragmentation and condensation in undifferentiated PC12 pheochromocytoma cells. The present study demonstrates that cytotoxicity of low concentrations of NO is mediated by inhibition of mitochondrial cytochrome c oxidase and generation of reactive oxygen species (ROS). An NO donor, (+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide (NOR3) induced cell death even at low concentrations (10-100 microM), whereas peroxynitrite and a peroxynitrite generator, 3-(4-morpholinyl)-sydnonimine (SIN-1), did not have a significant effect on cell viability up to a concentration of 0.5 mM. The NOR3-induced cell death was unaffected by pretreatment with superoxide dismutase (SOD) or its mimetic peroxynitrite scavenger, manganese(III) tetrakis(benzoic acid)porphyrin chloride (Mn-TBAP), or with uric acid. These findings indicate that peroxynitrite does not contribute to this cell death. Furthermore, neither the release of cytochrome c from mitochondrial membranes, the cleavage of poly-ADP ribose polymerase (PARP), nor the activation of caspase-3-like activities was observed. Inhibitors of PARP, benzamide, and aminobenzamide, had no effect on the NOR3-induced cell death. In addition, pretreatment with general or selective caspase inhibitors, benzyloxy-carbonyl-Val-Ala-Asp-fluoromethylketone (Z-VAD-fmk), N-acetyl-Asp-Glu-Val-Asp-aldehyde (Ac-DEVD-CHO), and benzyloxycarbonyl-Asp-2,6-dichlorobenzoyloxymethylketone (Z-Asp-Ch(2)-DCB) did not prevent NOR3-induced cell death. Taken together, these findings suggest that cell death induced by NOR3 occurs by a caspase-independent mechanism. In contrast, we found an early increase in mitochondrial H(2)O(2) production during NOR3 exposure using the fluorescent dye 2',7'-dichlorofluorescin-diacetate (DCFH-DA) and dihydrorohdamine123 (DHR123), and these events were accompanied by strong inhibition of cytochrome c oxidase activity in the cells. Furthermore, we observed that several antioxidants, such as ascorbate, glutathione (GSH), cysteine, tetrahydrobiopterin, and dithiothreitol (DTT), all effectively prevented the NOR3-induced cell death. NOR3 treatment decreased the level of total intracellular GSH, but did not affect the activities of antioxidant enzymes SOD, GSH-peroxidase (GPX), and catalase. These results suggest that cell death induced at physiologically low concentrations of NO is mediated by ROS production in mitochondria, most likely resulting from the inhibition of cytochrome c oxidase, with ROS acting as an initiator of caspase-independent cell death.

Overexpression of V-1 prevents nitric oxide-induced cell death: involvement of enhanced tetrahydrobiopterin biosynthesis

Previously we reported that the synthesis of catecholamines, dopamine, and noradrenaline was enhanced by overexpression of V-1 protein, a neuronal protein active in the initial stage of development of the rat cerebellum, in the neuronal cell line PC12D, a model of dopamine cells (Yamakuni et al. [1998] J. Biol. Chem. 273:27051-27054). To investigate the physiological role of this protein, we examined the effect of V-1 overexpression on cell toxicity induced by nitric oxide (NO) used at low concentrations. Two clones of PC12D cells overexpressing V-1, transfectants termed V1-46 and V1-69, were significantly more resistant to NOR3 (an NO donor) but not to etoposide (an inhibitor of topoisomerase II)-induced apoptotic cell death than the control cells (termed C-7 and C-9) that had been transfected with the vector alone. The addition of L-DOPA, dopamine, or noradrenaline to the medium did not abolish NOR3-induced cell death in PC12D cells. Moreover, pretreatment of V1-46 and V1-69 cells with L-alpha-methyl-p-tyrosine (alpha-MPT), an inhibitor of tyrosine hydroxylase, to inhibit catecholamine biosynthesis did not affect the resistance to NO toxicity. These results indicate that the catecholamine levels increased by V-1 overexpression did not produce the protection against NOR3-induced toxicity. We further showed that overexpression of V-1 enhanced the synthesis of (6R)-L-erythro-5,6,7,8-tetrahydrobiopterin (BH(4)). In addition, pretreatment with BH(4) or with sepiapterin, which is converted to BH(4) intracellularly, significantly protected PC12D cells in a dose-dependent manner. The increased BH(4) synthesis by V-1 overexpression was dose dependently inhibited by pretreatment with diaminohydroxypyrimidine (DAHP), an inhibitor of GTP-cyclohydrolase I, which is the rate-limiting enzyme for the biosynthesis of BH(4), concomitantly with the loss of protective effect afforded by V-1 overexpression. Furthermore, the addition of BH(4) or sepiapterin to DAHP-pretreated V146 and V1-69 cells restored cell viability. Taken together, these results indicate that V1 protein plays an important role in protection against cell death induced by NO at low levels by promoting the synthesis of BH(4). Moreover, these findings suggest the up-regulation of V1 expression as a possible therapeutic target for protection against the insult of NO-induced oxidative stress.

Resistance of PC12 cells against nitric oxide (NO)-induced toxicity in long-term culture: implication of neuronal NO synthase expression

We have previously reported that a nitric oxide (NO)-donor, (+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide (NOR3) induced cell death even at a low concentration in undifferentiated PC12 cells. In the present study, we found that PC12 cells which were cultured long-term for over 80 passages acquired resistance to the NOR3-induced cell toxicity. After 24 h exposure to 10-100 microM NOR3, a concentration-dependent cell death was observed in short-term cultured PC12 cells (8-30 passages), but not in long-term cultured cells (over 80 passages). In the cells cultured short-term, the cell death was accompanied by nuclear condensation and fragmentation. We further examined the alterations in total glutathione (GSH) levels, and activities of antioxidant enzymes, superoxide dismutase (SOD) and catalase in the short- and long-term cultured PC12 cells. SOD activity decreased in the long-term cultured cells, while catalase activity did not change. The GSH content significantly increased in the cells cultured long-term. Furthermore, the long-term but not the short-term cultured cells, expressed neuronal NO synthase (nNOS), but neither endothelial nor inducible NOS. These findings suggest that the PC12 cells acquire resistance to the NO-induced toxicity, accompanied by an increase in the GSH level and the expression of nNOS after long-term culture.

Kinetic characterization of the nitric oxide toxicity for PC12 cells: effect of half-life time of NO release

We investigated the effects of low concentrations of nitric oxide (NO) on cell viability using NO donors, (+/-)-(E)-4-methyl-2-[(E)-hydroxyimino]-5-nitro-6-methoxy-3-hex enamid e (NOR1), (+/-)-(E)-4-methyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide (NOR2), (+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide (NOR3) and (+/-)-N-[(E)-4-ethyl-2-[(Z)-hydroxyimino]-5-nitro-3-hexen-1- yl]-3-pyr idine (NOR4). The half-life times of the NO release from these four NOR analogs, NOR1, NOR2, NOR3 and NOR4, were determined (6.5, 84, 105 and 340 min, respectively) by using 4,5-diaminofluorescein (DAF-2), a newly developed indicator of NO. Exposure of undifferentiated PC12 cells to low concentrations of NO donors, NOR2 or NOR3 (1-100 microM), but not NOR1 nor NOR4, resulted in cell death in a dose- and time-dependent manner, as determined from cell viability assessed by 3-(4,5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2H-tetrazolium (MTT) assay. After 24 h exposure to 50 microM NOR2 or NOR3, more than 90% of PC12 cells had died. Furthermore, while the toxic effect of NOR3 was attenuated by replacing the medium at 20 min, 1 or 2 h after drug addition, it was continued by replacing the medium at 3 h or later after drug addition. The cell death was characterized by DNA degradation, nuclear condensation and fragmentation, suggesting apoptosis-like cell death. Pretreatment with an antioxidant ascorbic acid (0.1-0.5 mM) completely prevented the cell death caused by NOR3, while glutathione (0.1-0.2 mM) and cysteine (0.2-0.4 mM) provided partial protection. These findings suggest that the cell toxicity induced by NO at low concentrations strongly depends upon the duration of expose to NO from NO donors, and these toxic effects are effectively prevented by the antioxidant, ascorbic acid.