[Show abstract][Hide abstract] ABSTRACT: Impaired function of NPC1 or NPC2 lysosomal proteins leads to the intracellular accumulation of unesterified cholesterol, the primary defect underlying Niemann-Pick type C (NPC) disease. In addition, glycosphingolipids (GSLs) accumulate in lysosomes as well. Intralysosomal lipid accumulation triggers the activation of a set of genes, including potential biomarkers. Transcript levels of Gpnmb have been shown to be elevated in various tissues of an NPC mouse model. We speculated that Gpnmb could serve as a marker for visceral lipid accumulation in NPC disease. We report that Gpnmb expression is increased at protein level in macrophages in the viscera of Npc1nih/nih mice. Interestingly, soluble Gpnmb was also found to be increased in murine and NPC patient plasma. Exposure of RAW264.7 macrophages to the NPC-phenotype-inducing drug U18666A also upregulated Gpnmb expression. Inhibition of GSL synthesis with the glucosylceramide synthase (GCS) inhibitor N-butyl-1-deoxynojirimycin prevented U18666A-induced Gpnmb induction and secretion. In summary, we show that Gpnmb is upregulated in NPC mice and patients, most likely due to GSL accumulation.
[Show abstract][Hide abstract] ABSTRACT: In lysosomal glycosphingolipid storage disorders, marked elevations in corresponding glycosphingoid bases (lyso-glycosphingolipids) have been reported, such as galactosylsphingosine in Krabbe disease, glucosylsphingosine in Gaucher disease and globotriaosylsphingosine in Fabry disease. Using LC–MS/MS, we comparatively investigated the occurrence of abnormal lyso-glycosphingolipids in tissues and plasma of mice with deficiencies in lysosomal α-galactosidase A, glucocerebrosidase and galactocerebrosidase. The nature and specificity of lyso-glycosphingolipid abnormalities are reported and compared to that in correspondingly more abundant N-acylated glycosphingolipids. Specific elevations in tissue and plasma globotriaosylsphingosine were detected in α-galactosidase A-deficient mice; glucosylsphingosine in glucocerebrosidase-deficient mice and galactosylsphingosine in galactocerebrosidase-deficient animals. A similar investigation was conducted for two mouse models of Niemann Pick type C (Npc1nih and Npc1nmf164), revealing significant tissue elevation of several neutral glycosphingolipids and concomitant increased plasma glucosylsphingosine. This latter finding was recapitulated by analysis of plasma of NPC patients. The value of plasma glucosylsphingosine in biochemical confirmation of the diagnosis of NPC is discussed.
No preview · Article · Jan 2016 · Molecular Genetics and Metabolism
[Show abstract][Hide abstract] ABSTRACT: The membrane lipid glucosylceramide (GlcCer) is continuously formed and degraded. Cells express two GlcCer-degrading β-glucosidases, GBA and GBA2, located in and outside the lysosome, respectively. Here we demonstrate that through transglucosylation both GBA and GBA2 are able to catalyze in vitro the transfer of glucosyl-moieties from GlcCer to cholesterol, and vice versa. Furthermore, the natural occurrence of 1-O-cholesteryl-β-D-glucopyranoside (GlcChol) in mouse tissues and human plasma is demonstrated using LC-MS/MS and 13C6-labelled GlcChol as internal standard. In cells the inhibition of GBA increases GlcChol, whereas inhibition of GBA2 decreases glucosylated sterol. Similarly, in GBA2-deficient mice GlcChol is reduced. Depletion of GlcCer by inhibition of GlcCer synthase decreases GlcChol in cells and likewise in plasma of inhibitor-treated Gaucher disease patients. In tissues of mice with Niemann-Pick type C, a condition characterized by intralysosomal accumulation of cholesterol, marked elevations in GlcChol occur as well. When lysosomal accumulation of cholesterol is induced in cultured cells, GlcChol is formed via lysosomal GBA. This illustrates that reversible transglucosylation reactions are highly dependent on local availability of suitable acceptors. In conclusion, mammalian tissues contain GlcChol formed by transglucosylation through β-glucosidases using GlcCer as donor. Our findings reveal a novel metabolic function for GlcCer.
Full-text · Article · Jan 2016 · The Journal of Lipid Research
[Show abstract][Hide abstract] ABSTRACT: Obesity goes hand in hand with low grade inflammation, which is an essential contributor to insulin resistance. This inflammation is orchestrated by a variety of cell types and their released soluble factors. A typical feature observed in obese adipose tissue is the formation of socalled crown like structures, which consist of recruited inflammatory macrophages surrounding non viable adipocytes. Glycoprotein non-metastatic melanoma protein B (GPNMB) is a transmembrane glycoprotein expressed by several cell types including macrophages.
[Show abstract][Hide abstract] ABSTRACT: Iminosugars are carbohydrate analogues currently used as therapeutic agents in the treatment of diabetes mellitus type 2 and Gaucher disease. The lypophilic iminosugar AMP-DMN (adamantine methyloxypentyl-deoxynojirimycin) has been proven to be the most efficient in correcting the hyperglycemia and the metabolic syndrome present in obesity and diabetes type 2 animal models, as compared to other iminosugar compounds.
[Show abstract][Hide abstract] ABSTRACT: It has been extensively described that low-grade inflammatory condition plays a crucial role in the genesis and development of diseases in metabolic syndrome. Furthermore, macrophage infiltration in the adipose compartment increases the local level of inflammatory cytokines that cause insulin resistance and inhibition of adipocyte differentiation.
[Show abstract][Hide abstract] ABSTRACT: Gaucher disease is characterized by lysosomal accumulation of glucosylceramide due to deficient activity of lysosomal glucocerebrosidase (GBA). In cells, glucosylceramide is also degraded outside lysosomes by the enzyme glucosylceramidase 2 (GBA2) of which inherited deficiency is associated with ataxias. The interest in GBA and glucosylceramide metabolism in the brain has grown following the notion that mutations in the GBA gene impose a risk factor for motor disorders such as α-synucleinopathies. We earlier developed a β-glucopyranosyl-configured cyclophellitol-epoxide type activity based probe (ABP) allowing in vivo and in vitro visualization of active molecules of GBA with high spatial resolution. Labeling occurs through covalent linkage of the ABP to the catalytic nucleophile residue in the enzyme pocket. Here, we describe a method to visualize active GBA molecules in rat brain slices using in vivo labeling. Brain areas related to motor control, like the basal ganglia and motor related structures in the brainstem, show a high content of active GBA. We also developed a β-glucopyranosyl cyclophellitol-aziridine ABP allowing in situ labeling of GBA2. Labeled GBA2 in brain areas can be identified and quantified upon gel electrophoresis. The distribution of active GBA2 markedly differs from that of GBA, being highest in the cerebellar cortex. The histological findings with ABP labeling were confirmed by biochemical analysis of isolated brain areas. In conclusion , ABPs offer sensitive tools to visualize active GBA and to study the distribution of GBA2 in the brain and thus may find application to establish the role of these enzymes in neurodegenerative disease conditions such as α-synucleinopathies and cerebellar ataxia.
[Show abstract][Hide abstract] ABSTRACT: Glucosylceramide metabolism and the enzymes involved have attracted significant interest in medicinal chemistry, because aberrations in the levels of glycolipids that are derived from glucosylceramide are causative in a range of human diseases including lysosomal storage disorders, type 2 diabetes, and neurodegenerative diseases. Selective modulation of one of the glycoprocessing enzymes involved in glucosylceramide metabolism-glucosylceramide synthase (GCS), acid glucosylceramidase (GBA1), or neutral glucosylceramidase (GBA2)-is therefore an attractive research objective. In this study we took two established GCS inhibitors, one based on deoxynojirimycin and the other a ceramide analogue, and merged characteristic features to obtain hybrid compounds. The resulting 39-compound library does not contain new GCS inhibitors; however, a potent (200 nM) GBA1 inhibitor was identified that has little activity toward GBA2 and might therefore serve as a lead for further biomedical development as a selective GBA1 modulator.
[Show abstract][Hide abstract] ABSTRACT: Background:
Quantitative proteomic analysis with mass spectrometry holds great promise for simultaneously quantifying proteins in various biosamples, such as human plasma. Thus far, studies addressing the reproducible measurement of endogenous protein concentrations in human plasma have focussed on targeted analyses employing isotopically labelled standards. Non-targeted proteomics, on the other hand, has been less employed to this end, even though it has been instrumental in discovery proteomics, generating large datasets in multiple fields of research.
Using a non-targeted mass spectrometric assay (LCMSE), we quantified abundant plasma proteins (43 mg/mL-40 ug/mL range) in human blood plasma specimens from 30 healthy volunteers and one blood serum sample (ProteomeXchange: PXD000347). Quantitative results were obtained by label-free mass spectrometry using a single internal standard to estimate protein concentrations. This approach resulted in quantitative results for 59 proteins (cut off ≥11 samples quantified) of which 41 proteins were quantified in all 31 samples and 23 of these with an inter-assay variability of ≤ 20%. Results for 7 apolipoproteins were compared with those obtained using isotope-labelled standards, while 12 proteins were compared to routine immunoassays. Comparison of quantitative data obtained by LCMSE and immunoassays showed good to excellent correlations in relative protein abundance (r = 0.72-0.96) and comparable median concentrations for 8 out of 12 proteins tested. Plasma concentrations of 56 proteins determined by LCMSE were of similar accuracy as those reported by targeted studies and 7 apolipoproteins quantified by isotope-labelled standards, when compared to reference concentrations from literature.
This study shows that LCMSE offers good quantification of relative abundance as well as reasonable estimations of concentrations of abundant plasma proteins.
[Show abstract][Hide abstract] ABSTRACT: The enzyme glucocerebrosidase (GBA) hydrolyses glucosylceramide (GlcCer) in lyso-somes. Markedly reduced GBA activity is associated with severe manifestations of Gaucher disease including neurological involvement. Mutations in the GBA gene have recently also been identified as major genetic risk factor for Parkinsonism. Disturbed metabolism of GlcCer may therefore play a role in neuropathology. Besides lysosomal GBA, cells also contain a non-lysosomal glucosylceramidase (GBA2). Given that the two β-glucosidases share substrates, we speculated that over-activity of GBA2 during severe GBA impairment might influence neuropathology. This hypothesis was studied in Niemann-Pick type C (Npc1-/-) mice showing secondary deficiency in GBA in various tissues. Here we report that GBA2 activity is indeed increased in the brain of Npc1-/-mice. We found that GBA2 is particularly abundant in Purkinje cells (PCs), one of the most affected neuronal populations in NPC disease. Inhibiting GBA2 in Npc1-/-mice with a brain-permeable low nanomolar inhibi-tor significantly improved motor coordination and extended lifespan in the absence of correction in cholesterol and ganglioside abnormalities. This trend was recapitulated, although not to full extent, by introducing a genetic loss of GBA2 in Npc1-/-mice. Our findings point to GBA2 activity as therapeutic target in NPC.
[Show abstract][Hide abstract] ABSTRACT: N-alkyl-deoxynojirimycins (DNMs) are an important class of glycoprocessing enzyme inhibitors. Our work on DNMs focuses on identifying potent and selective inhibitors of the human enzymes, glucosylceramide synthase (GCS), lysosomal glucosylceramidase (GBA) and neutral glucosylceramidase (GBA2). We have previously reported on N-alkylated DNM derivatives bearing various hydrophobic head groups (aliphatic, aromatic, branched, cyclic). In this study we report effective procedures for the synthesis of ortho-carborane-modified DNMs and establish the inhibitory potency of six new DNM derivatives 3-8 against GCS, GBA and GBA2. The synthesis of a series of ortho-carborane-containing deoxynojirimycin (DNM) derivatives is described. The resulting compounds are potent inhibitors of human glucosylceramidases and glucosylceramide synthase, with inhibitory profiles comparable to those of the corresponding adamantyl-DNM derivatives.
No preview · Article · Jul 2015 · European Journal of Organic Chemistry
[Show abstract][Hide abstract] ABSTRACT: (Chemical Equation Presented) In this paper, a new synthetic route toward 6-hydroxysphingosine and α-hydroxy ceramide is described. The synthesis employs a cross-metathesis to unite a sphingosine head allylic alcohol with a long-chain fatty acid alkene that also bears an allylic alcohol group. To allow for a productive CM coupling, the sphingosine head allylic alcohol was protected with a cyclic carbonate moiety and a reactive CM catalyst system, consisting of Grubbs II catalyst and CuI, was employed.
No preview · Article · Jun 2015 · The Journal of Organic Chemistry
[Show abstract][Hide abstract] ABSTRACT: The synthesis of a focussed library of sphingolipids differing in the number and position of 13C labels is described. The synthesised sphingolipids differ in substitution at both the sphingosine amine (either palmitoylated or unmodified) and the sphingosine primary hydroxyl (unmodified or glycosylated). Moreover, 13C atoms are incorporated into either the sphingosine or the palmitate moiety, or both. This set of compounds is intended for use in relative quantitative lipidomics studies to gain insight into sphingolipid metabolism in healthy and diseased (lysosomal storage disorders) patients and animal models.
No preview · Article · Apr 2015 · European Journal of Organic Chemistry
[Show abstract][Hide abstract] ABSTRACT: Gaucher disease is caused by an inherited deficiency of the enzyme glucosylceramidase. Due to the lack of a fully functional enzyme there is progressive build-up of the lipid component glucosylceramide. Insufficient glucosylceramidase activity results in hepatosplenomegaly, cytopenias and bone disease in patients. Gene therapy represents a future therapeutic option for patients unresponsive to enzyme replacement therapy and lacking a suitable bone marrow donor. By proof-of-principle experiments we have previously demonstrated a reversal of symptoms in a murine disease model of type 1 Gaucher disease, using gammaretroviral vectors harboring strong viral promoters to drive glucosidase beta acid (GBA) gene expression. To investigate whether safer vectors can correct the enzyme deficiency, we utilized self-inactivating lentiviral vectors (SIN LVs) with the GBA gene under the control of human phosphoglycerate kinase (PGK) and CD68 promoter, respectively. Here we report prevention of, as well as reversal of, manifest disease symptoms after lentiviral gene transfer. Glucosylceramidase activity above levels required for clearance of glucosylceramide from tissues resulted in reversal of splenomegaly, reduced Gaucher cell infiltration and a restoration of hematological parameters. These findings support the use of SIN-LVs with cellular promoters in future clinical gene therapy protocols for type 1 Gaucher disease.Molecular Therapy (2015); doi:10.1038/mt.2015.16.
No preview · Article · Feb 2015 · Molecular Therapy
[Show abstract][Hide abstract] ABSTRACT: GH29 α-L-fucosidases catalyze the hydrolysis of α-L-fucosidic linkages. Deficiency in human lysosomal α-L-fucosidase (FUCA1) leads to the recessively inherited disorder, fucosidosis. Herein we describe the development of fucopyranose-configured cyclophellitol aziridines as activity-based probes (ABPs) for selective in vitro and in vivo labeling of GH29 α-L-fucosidases from bacteria, mice and man. Crystallographic analysis on bacterial α-L-fucosidase confirms that the ABPs act by covalent modification of the active site nucleophile. Competitive activity-based protein profiling identified L-fuconojirimycin as the single GH29 α-L-fucosidase inhibitor from eight configurational isomers.
[Show abstract][Hide abstract] ABSTRACT: Unlabelled:
There is a clinical need for plasma tests for real-time detection of beta cell destruction, as surrogate endpoint in islet transplantation and immunoprevention trials in type 1 diabetes. This study reports on the use of label-free LC-MS/MS proteomics for bottom-up selection of candidate biomarkers. Ubiquitin COOH-terminal hydrolase 1 (UCHL1) was identified as abundant protein in rat and human beta cells, showing promising beta cell-selectivity, and was selected for further validation in standardized toxicity models. In vitro, H2O2-induced necrosis of INS-1 cells and human islets resulted in intracellular UCHL1 depletion and its extracellular discharge. In vivo, streptozotocin progressively depleted UCHL1 from islet cores and in 50% of animals, an associated plasma UCHL1 surge was detected preceding the GAD65 peak. UCHL1 was cleared with a half-life of 20min. Whole-body dynamic planar imaging of (99m)-Technetium-labeled UCHL1 indicated a rapid UCHL1 uptake in the liver and spleen, followed by urinary excretion of mainly proteolytic UCHL1 fragments. We conclude that LC-MS/MS proteomics is a useful tool to prioritize biomarkers for beta cell injury with promising molar abundance. Despite its consistent UCHL1 discharge by damaged beta cells in vitro, its in vivo use might be restrained by its rapid elimination from plasma.
Our bottom-up LC-MS/MS proteomics represents a pragmatic approach to identify protein-type biomarkers of pancreatic beta cell injury. UCHL1 successfully passed sequential validation steps of beta cell-selectivity, antigenicity and toxic discharge in vitro. Whole-body dynamic planar imaging of radiolabeled recombinant UCHL1 indicated rapid clearance through the liver, spleen and urinary excretion of proteolytic fragments, likely explaining non-consistent detection in vivo. Integration of kinetic biomarker clearance studies in the a priori selection criteria is recommended before engaging in resource-intensive custom development of sensitive immunoassays for clinical translation.
Full-text · Article · Jan 2015 · Journal of Proteomics