[Show abstract][Hide abstract] ABSTRACT: Glycosphingolipids are key elements of cellular membranes, thereby, controlling a variety of cellular functions. Accumulation of the simple glycosphingolipid glucosylceramide results in life-threatening lipid storage-diseases or in male infertility. How glucosylceramide regulates cellular processes is ill defined. Here, we reveal that glucosylceramide accumulation in GBA2 knockout-mice alters cytoskeletal dynamics due to a more ordered lipid organization in the plasma membrane. In dermal fibroblasts, accumulation of glucosylceramide augments actin polymerization and promotes microtubules persistence, resulting in a higher number of filopodia and lamellipodia and longer microtubules. Similar cytoskeletal defects were observed in male germ and Sertoli cells from GBA2 knockout-mice. In particular, the organization of F-actin structures in the ectoplasmic specialization and microtubules in the sperm manchette is affected. Thus, glucosylceramide regulates cytoskeletal dynamics, providing mechanistic insights into how glucosylceramide controls signaling pathways not only during sperm development, but also in other cell types.
[Show abstract][Hide abstract] ABSTRACT: During endocytosis, membrane components move to intraluminal vesicles of the endolysosomal compartment for digestion. At the late endosomes, cholesterol is sorted out mainly by two sterol-binding proteins, NPC1 and NPC2. To study the NPC2 mediated intervesicular cholesterol transfer we developed a liposomal assay system (Abdul-Hammed et al. 2010 J. Lipid Res. 51: 1747-1760). Anionic lipids stimulate cholesterol transfer between liposomes while sphingomyelin inhibits it, even in the presence of anionic bis(monoacylglycero)phosphate. Preincubation of vesicles containing sphingomyelin with acid sphingomyelinase (sphingomyelin phosphodiesterase EC 220.127.116.11) results in hydrolysis of sphingomyelin to ceramide which enhances cholesterol transfer. Besides sphingomyelin, acid sphingomyelinase also cleaves liposomal phosphatidylcholine. Anionic phospholipids derived from the plasma membrane (phosphatidylglycerol and phosphatidic acid) stimulate sphingomyelin and phosphatidylcholine hydrolysis by acid sphingomyelinase more effectively than bis(monoacylglycero)phosphate, which is generated during endocytosis. Acid sphingomyelinase mediated hydrolysis of liposomal sphingomyelin was also stimulated by incorporation of diacylglycerol, ceramide, and free fatty acids into the liposomal membranes. Conversely, phosphatidylcholine hydrolysis was inhibited by incorporation of cholesterol, ceramide, diacylglycerol, monoacylglycerol, and fatty acids. Our data suggest that sphingomyelin degradation by acid sphingomyelinase is required for physiological secretion of cholesterol from the late endosomal compartment, and is a key regulator of endolysosomal lipid digestion.
The Journal of Lipid Research 10/2014; 55(12). DOI:10.1194/jlr.M054528 · 4.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Within the recent years, ganglioside patterns have been increasingly analyzed by mass spectrometry. However, internals standards for calibration are only available for gangliosides GM1, GM2, and GM3. For this reason, we prepared homologous internal standards bearing non-natural fatty acids of the major mammalian brain gangliosides GM1, GD1a, GD1b, GT1b, and GQ1b, and of the tumor associated gangliosides GM2 and GD2. The fatty acid moieties were incorporated after selective chemical or enzymatic deacylation of bovine brain gangliosides. For modification of the sphingoid bases, we developed a new synthetic method based on olefin cross metathesis. This method was used for the preparation of a lyso-GM1- and a lyso-GM2 standard. The total yield of this method was 8.7 % for the synthesis of d17:1-lyso-GM1 from d20:1/18:0-GM1 in four steps. The title compounds are currently used as calibration substances for MS quantification and are also suitable for functional studies.
The Journal of Lipid Research 10/2014; 55(12). DOI:10.1194/jlr.D054734 · 4.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The transcription factor Nrf2 is a key regulator of the cellular stress response, and pharmacological Nrf2 activation is a promising strategy for skin protection and cancer prevention. We show here that prolonged Nrf2 activation in keratinocytes causes sebaceous gland enlargement and seborrhea in mice due to upregulation of the growth factor epigen, which we identified as a novel Nrf2 target. This was accompanied by thickening and hyperkeratosis of hair follicle infundibula. These abnormalities caused dilatation of infundibula, hair loss, and cyst development upon aging. Upregulation of epigen, secretory leukocyte peptidase inhibitor (Slpi), and small proline-rich protein 2d (Sprr2d) in hair follicles was identified as the likely cause of infundibular acanthosis, hyperkeratosis, and cyst formation. These alterations were highly reminiscent to the phenotype of chloracne/"metabolizing acquired dioxin-induced skin hamartomas" (MADISH) patients. Indeed, SLPI, SPRR2, and epigen were strongly expressed in cysts of MADISH patients and upregulated by dioxin in human keratinocytes in an NRF2-dependent manner. These results identify novel Nrf2 activities in the pilosebaceous unit and point to a role of NRF2 in MADISH pathogenesis.
EMBO Molecular Medicine 04/2014; 6(4). DOI:10.1002/emmm.201303281 · 8.25 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Lysosomes are cellular stomachs. They degrade macromolecules and release their components as nutrients into the cytosol. Digestion of sphingolipids and other membrane lipids occurs at luminal intraendosomal vesicles and IMs (intraendosomal membranes). Sphingolipid and membrane digestion needs catabolic hydrolases with the help of lipid-binding proteins [SAPs (sphingolipid activator proteins)] and anionic lipids such as BMP [bis(monoacylglycero)phosphate]. Inherited defects of hydrolases or SAPs or uptake of cationic amphiphilic drugs cause lipid accumulation, eventually leading to death, especially in inherited sphingolipid storage diseases. IMs are formed during endocytosis and their lipid composition is adjusted for degradation. Their cholesterol content, which stabilizes membranes, decreases and the level of negatively charged BMP, which stimulates sphingolipid degradation, increases. At the level of late endosomes, cholesterol is transported out of the luminal vesicles preferentially by cholesterol-binding proteins, NPC (Niemann-Pick type C)-2 and NPC-1. Their defects lead to an endolysosomal accumulation of cholesterol and sphingolipids in Niemann-Pick type C disease. BMP and ceramide stimulate NPC-2-mediated cholesterol transfer, whereas sphingomyelin inhibits it. Anionic membrane lipids also activate sphingomyelin degradation by ASM (acid sphingomyelinase), facilitating cholesterol export by NPC-2. ASM is a non-specific phospholipase C and degrades more than 23 phospholipids. SAPs are membrane-perturbing proteins which solubilize lipids, facilitating glycolipid digestion by presenting them to soluble catabolic enzymes at acidic pH. High BMP and low cholesterol levels favour lipid extraction and membrane disintegration by saposin A and B. The simultaneous inherited defect of saposins A-D causes a severe membrane and sphingolipid storage disease, also disrupting the water permeability barrier of the skin.
Biochemical Society Transactions 12/2013; 41(6):1562-1568. DOI:10.1042/BST20130083 · 3.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Juvenile neuronal ceroid lipofuscinosis (JNCL) is a fatal childhood-onset neurodegenerative disorder caused by mutations in ceroid lipofuscinosis neuronal-3 (CLN3), a hydrophobic transmembrane protein of unresolved function. Previous studies indicate blood-brain barrier (BBB) defects in JNCL, and our earlier report showed prominent Cln3 expression in mouse brain endothelium. Here we find that CLN3 is necessary for normal trafficking of the microdomain-associated proteins caveolin-1, syntaxin-6, and multidrug resistance protein 1 (MDR1) in brain endothelial cells. Correspondingly, CLN3-null cells have reduced caveolae, and impaired caveolae- and MDR1-related functions including endocytosis, drug efflux, and cell volume regulation. We also detected an abnormal blood-brain barrier response to osmotic stress in vivo. Evaluation of the plasma membrane with fluorescent sphingolipid probes suggests microdomain destabilization and enhanced fluidity in CLN3-null cells. In further work we found that application of the glycosphingolipid lactosylceramide to CLN3-deficient cells rescues protein transport and caveolar endocytosis. Last, we show that CLN3 localizes to the trans-Golgi network (TGN) and partitions with buoyant microdomain fractions. We propose that CLN3 facilitates TGN-to-plasma membrane transport of microdomain-associated proteins. Insult to this pathway may underlie BBB dysfunction and contribute to JNCL pathogenesis.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 11/2013; 33(46):18065-79. DOI:10.1523/JNEUROSCI.0498-13.2013 · 6.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Endocytosed (glyco)sphingolipids are degraded, together with other membrane lipids in a stepwise fashion by endolysosomal enzymes with the help of small lipid binding proteins, the sphingolipid activator proteins (SAPs), at the surface of intraluminal lysosomal vesicles. Inherited defects in a sphingolipid-degrading enzyme or SAP cause the accumulation of the corresponding lipid substrates, including cytotoxic lysosphingolipids, such as galactosylsphingosine and glucosylsphingosine, and lead to a sphingolipidosis. Analysis of patients with prosaposin deficiency revealed the accumulation of intra-endolysosmal vesicles and membrane structures (IM). Feeding of prosaposin reverses the storage, suggesting inner membrane structures as platforms of sphingolipid degradation. Water soluble enzymes can hardly attack sphingolipids embedded in the membrane of inner endolysosomal vesicles. The degradation of sphingolipids with few sugar residues therefore requires the help of the SAPs, and is strongly stimulated by anionic membrane lipids. IMs are rich in anionic bis(monoacylglycero)phosphate (BMP).
[Show abstract][Hide abstract] ABSTRACT: Gaucher disease (GD) is the most common inherited lysosomal storage disorder in humans, caused by mutations in the gene encoding the lysosomal enzyme glucocerebrosidase (GBA1). GD is clinically heterogeneous and although the type of GBA1 mutation plays a role in determining the type of GD, it does not explain the clinical variability seen among patients. Cumulative evidence from recent studies suggests that GBA2 could play a role in the pathogenesis of GD and potentially interacts with GBA1.
We used a framework of functional and genetic approaches in order to further characterize a potential role of GBA2 in GD. Glucosylceramide (GlcCer) levels in spleen, liver and brain of GBA2-deficient mice and mRNA and protein expression of GBA2 in GBA1-deficient murine fibroblasts were analyzed. Furthermore we crossed GBA2-deficient mice with conditional Gba1 knockout mice in order to quantify the interaction between GBA1 and GBA2. Finally, a genetic approach was used to test whether genetic variation in GBA2 is associated with GD and/ or acts as a modifier in Gaucher patients. We tested 22 SNPs in the GBA2 and GBA1 genes in 98 type 1 and 60 type 2/3 Gaucher patients for single- and multi-marker association with GD.
We found a significant accumulation of GlcCer compared to wild-type controls in all three organs studied. In addition, a significant increase of Gba2-protein and Gba2-mRNA levels in GBA1-deficient murine fibroblasts was observed. GlcCer levels in the spleen from Gba1/Gba2 knockout mice were much higher than the sum of the single knockouts, indicating a cross-talk between the two glucosylceramidases and suggesting a partially compensation of the loss of one enzyme by the other. In the genetic approach, no significant association with severity of GD was found for SNPs at the GBA2 locus. However, in the multi-marker analyses a significant result was detected for p.L444P (GBA1) and rs4878628 (GBA2), using a model that does not take marginal effects into account.
All together our observations make GBA2 a likely candidate to be involved in GD etiology. Furthermore, they point to GBA2 as a plausible modifier for GBA1 in patients with GD.
[Show abstract][Hide abstract] ABSTRACT: The epidermal permeability barrier of mammalian skin is localized in the stratum corneum. Corneocytes are embedded in an extracellular, highly ordered lipid matrix of hydrophobic lipids consisting of about 50% ceramides, 25% cholesterol and 15% long and very long chain fatty acids. The most important lipids for the epidermal barrier are ceramides. The scaffold of the lipid matrix is built of acylceramides, containing ω-hydroxylated very long chain fatty acids, acylated at the ω-position with linoleic acid. After glucosylation of the acylceramides at Golgi membranes and secretion, the linoleic acid residues are replaced by glutamate residues originating from proteins exposed on the surface of corneocytes. Removal of their glucosyl residues generates a hydrophobic surface on the corneocytes used as a template for the formation of extracellular lipid layers of the water permeability barrier. Misregulation or defects in the formation of extracellular ceramide structures disturbs barrier function. Important anabolic steps are the synthesis of very long chain fatty acids, their ω-hydroxylation, formation of very long chain ceramides and glucosylceramides. The main probarrier precursor lipids, glucosylceramides and sphingomyelins, are packed in lamellar bodies together with hydrolytic enzymes such as glucosylceramide-β-glucosidase and acid sphingomyelinase and secreted into the intercelullar space between the stratum corneum and stratum granulosum. Inherited defects in the extracellular hydrolytic processing of the probarrier acylglucosylceramides impair epidermal barrier formation and cause fatal diseases: such as prosaposin deficiency resulting in lack of lysosomal lipid binding and transfer proteins, or the symptomatic clinical picture of the "collodion baby" in the absence of glucocerebrosidase. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier.
[Show abstract][Hide abstract] ABSTRACT: Early onset of age-related changes in the brain of cannabinoid 1 receptor knockout (Cnr1(-/-)) mice suggests that cannabinoid 1 (CB1) receptor activity significantly influences the progression of brain aging. In the present study we show that lack of CB1 receptors leads to a significant increase in lipofuscin accumulation and a reduced expression and activity of cathepsin D, lysosomal protease implicated in the degradation of damaged macromolecules, in the hippocampus of 12-month-old mice. The impaired clearance of damaged macromolecules due to the low cathepsin D levels and not enhanced oxidative stress may be responsible for the lipofuscin accumulation because macromolecule oxidation levels were comparable between the genotypes within the same age group. The altered levels of autophagy markers p62 and LC3-II suggest that autophagy is upregulated in CB1 knockout mice. Increased autophagic flux in the absence of CB1 receptors is probably a compensatory mechanism to partially counteract decreased lysosomal degradation capacity. Together, these results suggest that CB1 receptor activity affects lysosomal activity, degradation of damaged macromolecules and thus it may influence the course and onset of brain aging.
Mechanisms of ageing and development 08/2013; 134(9). DOI:10.1016/j.mad.2013.08.001 · 3.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Gangliosides are the main glycolipids of neuronal plasma membranes. Their surface patterns are generated by coordinated processes, involving biosynthetic pathways of the secretory compartments, catabolic steps of the endolysosomal system, and intracellular trafficking. Inherited defects in ganglioside biosynthesis causing fatal neurodegenerative diseases have been described so far almost exclusively in mouse models, whereas inherited defects in ganglioside catabolism causing various clinical forms of GM1- and GM2-gangliosidoses have long been known. For digestion, gangliosides are endocytosed and reach intra-endosomal vesicles. At the level of late endosomes, they are depleted of membrane-stabilizing lipids like cholesterol and enriched with bis(monoacylglycero)phosphate (BMP). Lysosomal catabolism is catalyzed at acidic pH values by cationic sphingolipid activator proteins (SAPs), presenting lipids to their respective hydrolases, electrostatically attracted to the negatively charged surface of the luminal BMP-rich vesicles. Various inherited defects of ganglioside hydrolases, e.g., of β-galactosidase and β-hexosaminidases, and of GM2-activator protein, cause infantile (with tetraparesis, dementia, blindness) and different protracted clinical forms of GM1- and GM2-gangliosidoses. Mutations yielding proteins with small residual catabolic activities in the lysosome give rise to juvenile and adult clinical forms with a wide range of clinical symptomatology. Apart from patients' differences in their genetic background, clinical heterogeneity may be caused by rather diverse substrate specificities and functions of lysosomal hydrolases, multifunctional properties of SAPs, and the strong regulation of ganglioside catabolism by membrane lipids. Currently, there is no treatment available for neuronal ganglioside storage diseases. Therapeutic approaches in mouse models and patients with juvenile forms of gangliosidoses are discussed.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 06/2013; 33(25):10195-208. DOI:10.1523/JNEUROSCI.0822-13.2013 · 6.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Unesterified Cholesterol, together with glycolipids, accumulates in cells leading to Niemann-Pick type C disease, an autosomal recessive neurodegenerative disease . Two types of genes, NPC1 and NPC2 responsible for this neurodegenerative disorder have been identified but their respective precise functions are yet to be fully elucidated. NPC1-NPC2 proteins interplay has been elucidated in such a way that NPC2 binds and transfers cholesterol to a cholesterol binding site of NPC1 for export out of the endosomal system. Until now, the study of Cholesterol has been hampered because the lipid lacks a functional group that can be readily tagged without altering its physical and chemical properties. Transfer studies of fluorescent cholesterol esters or cholesterol analogs are biased because of changes in the physicochemical nature of the lipids and might not correctly reflect the properties of unmodified cholesterol. A simple liposomal assay system which allows probing of the intermembrane transfer of radioactive cholesterol from donor to acceptor vesicles is therefore developed as well as a model to measure the vesicle fusion induced by some proteins. Abilities of the lysosomal lipid binding proteins (such as NPC2 protein) to transfer cholesterol in model membranes which mimic the endosomal/lysosomal compartments and to mediate vesicle fusion as well as the influence of lipid compositions were investigated. Other lysosomal lipid binding proteins investigated are saposins A-D and GM2AP while non-lysosomal proteins such as cytochrome C and bovine serum albumin were used as controls.
[Show abstract][Hide abstract] ABSTRACT: The unraveling of sphingolipid metabolism and function in the last 40 years relied on the extensive study of inherited human disease and specifically-tailored mouse models. However, only few of the achievements made so far would have been possible without chemical biology tools, such as fluorescent and/or radio-labeled and other artificial substrates, (mechanism-based) enzyme inhibitors, cross-linking probes or artificial membrane models. In this review we provide an overview over chemical biology tools that have been used to gain more insight into the molecular basis of sphingolipid-related biology. Many of these tools are still of high relevance for the investigation of current sphingolipid-related questions, others may stimulate the tailoring of novel probes suitable to address recent and future issues in the field. This article is part of a Special Issue entitled Tools to study lipid functions.
Biochimica et Biophysica Acta (BBA) - Molecular and Cell Biology of Lipids 01/2013; 1841(8). DOI:10.1016/j.bbalip.2013.12.011 · 4.50 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Analysis of lipid storage in postmortem brains of patients with amaurotic idiocy led to the recognition of five lysosomal ganglioside storage diseases and identification of their inherited metabolic blocks. Purification of lysosomal acid sphingomyelinase and ceramidase and analysis of their gene structures were the prerequisites for the clarification of Niemann-Pick and Farber disease. For lipid catabolism, intraendosomal vesicles are formed during the endocytotic pathway. They are subjected to lipid sorting processes and were identified as luminal platforms for cellular lipid and membrane degradation. Lipid binding glycoproteins solubilize lipids from these cholesterol poor membranes and present them to water-soluble hydrolases for digestion. Biosynthesis and intracellular trafficking of lysosomal hydrolases (hexosaminidases, acid sphingomyelinase and ceramidase) and lipid binding and transfer proteins (GM2 activator, saposins) were analyzed to identify the molecular and metabolic basis of several sphingolipidoses. Studies on the biosynthesis of glycosphingolipids yielded the scheme of Combinatorial Ganglioside Biosynthesis involving promiscuous glycosyltransferases. Their defects in mutagenized mice impair brain development and function.(Communicated by Kunihiko SUZUKI, M.J.A.).
Proceedings of the Japan Academy Ser B Physical and Biological Sciences 12/2012; 88(10):554-82. DOI:10.2183/pjab.88.554 · 2.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ceramide synthase 1 (CerS1) catalyzes the synthesis of C18 ceramide and is mainly expressed in the brain. Custom-made antibodies to a peptide from the C-terminal region of the mouse CerS1 protein yielded specific immuno-signals in neurons and no other cell types of wild type brain, but did not detect the CerS1 protein in CerS1 deficient mouse brains. To elucidate the biological function of CerS1-derived sphingolipids in the brain, we generated CerS1 deficient mice by introducing a targeted mutation into the coding region of the cers1 gene. General deficiency of CerS1 in mice causes a foliation defect, progressive shrinkage and neuronal apoptosis in the cerebellum. Mass spectrometric analyses reveal up to 60% decreased levels of gangliosides in cerebellum and forebrain. Expression of Myelin Associated Glycoprotein (MAG) is also decreased by about 60% in cerebellum and forebrain, suggesting that interaction and stabilization of oligodendrocytic MAG protein by neuronal gangliosides is due to the C18-acyl membrane anchor of CerS1 derived precursor ceramides. A behavioral analysis of CerS1 deficient mice yielded functional deficits including impaired exploration of novel objects, locomotion and motor coordination. Our results reveal an essential function of CerS1-derived ceramide in regulation of cerebellar development and neurodevelopmentally-regulated behavior.
[Show abstract][Hide abstract] ABSTRACT: The specificity and the strong binding capacity of the biotin-streptavidin complex makes the system to be one of the most widely used affinity pairs in molecular, immunological and cellular (in-vitro) assays. Previously reported regeneration process of the active streptavidin solid support in DNA sequencing using water at temperatures above 70oC, without denaturing the streptavidin tetramer was shown here to be ineffective when the streptavidin-coated magnetic beads was previously used in the lipid transfer assay. Regeneration of the used beads in chloroform inactivated the beads while the use of 10M NaOH destroyed the solid support of the bead. However, regenerating the paramagnetic beads used in lipid transfer assay with 25% aqueous ammonia only and with 25% aqueous ammonia in methanol (9:1) at 25oC are the most effective methods, with the reuse efficiency of about 90% after recovery. This represents about 50 – 67 % research cost savings, especially in this era of economic depression.
2nd General Assembly/ National Conference of the Nigerian Young Academy; 06/2012
[Show abstract][Hide abstract] ABSTRACT: The skin provides an efficient permeability barrier and protects from microbial invasion and oxidative stress. Here, we show that these essential functions are linked through the Nrf2 transcription factor. To test the hypothesis that activation of Nrf2 provides skin protection under stress conditions, we determined the consequences of pharmacological or genetic activation of Nrf2 in keratinocytes. Surprisingly, mice with enhanced Nrf2 activity in keratinocytes developed epidermal thickening, hyperkeratosis and inflammation resembling lamellar ichthyosis. This resulted from upregulation of the cornified envelope proteins small proline-rich proteins (Sprr) 2d and 2h and of secretory leukocyte peptidase inhibitor (Slpi), which we identified as novel Nrf2 targets in keratinocytes. Since Sprrs are potent scavengers of reactive oxygen species and since Slpi has antimicrobial activities, their upregulation contributes to Nrf2's protective function. However, it also caused corneocyte fragility and impaired desquamation, followed by alterations in the epidermal lipid barrier, inflammation and overexpression of mitogens that induced keratinocyte hyperproliferation. These results identify an unexpected role of Nrf2 in epidermal barrier function, which needs to be considered for pharmacological use of Nrf2 activators.
EMBO Molecular Medicine 05/2012; 4(5):364-79. DOI:10.1002/emmm.201200219 · 8.25 Impact Factor