title: Lack of enzyme activity in GBA2 mutants associated with hereditary spastic paraplegia/cerebellar ataxia (SPG46).
abstract: Glucosylceramide is a membrane glycolipid made up of the sphingolipid ceramide and glucose, and has a wide intracellular distribution. Glucosylceramide is degraded to ceramide and glucose by distinct, non-homologous enzymes, including glucocerebrosidase (GBA), localized in the endolysosomal pathway, and β-glucosidase 2 (GBA2), which is associated with the plasma membrane and/or the endoplasmic reticulum. It is well established that mutations in the GBA gene result in endolysosomal glucosylceramide accumulation, which triggers Gaucher disease. In contrast, the biological significance of GBA2 is less well understood. GBA2-deficient mice present with male infertility, but humans carrying mutations in the GBA2 gene are affected with a combination of cerebellar ataxia and spastic paraplegia, as well as with thin corpus callosum and cognitive impairment (SPastic Gait locus #46, SPG46). To improve our understanding of the biochemical consequences of the GBA2 mutations, we have evaluated five nonsense and five missense GBA2 mutants for their enzyme activity. In transfected cells, the mutant forms of GBA2 were present in widely different amounts, ranging from overabundant to very minor, compared to the wild type enzyme. Nevertheless, none of the GBA2 mutant cDNAs raised the enzyme activity in transfected cells, in contrast to the wild-type enzyme. These results suggest that SPG46 patients have a severe deficit in GBA2 activity, because the GBA2 mutants are intrinsically inactive and/or reduced in amount. This assessment of the expression levels and enzyme activities of mutant forms of GBA2 offers a first insight in the biochemical basis of the complex pathologies seen in SPG46.
authors.affiliation: Atlantic Research Centre, Department of Pediatrics, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada; Atlantic Research Centre, Department of Biochemistry & Molecular Biology, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada.
authors.forename: Saki
authors.initials: S
authors.lastname: Sultana
authors.affiliation: Centre for Neurology and Hertie Institute for Clinical Brain Research, Eberhard-Karls-University, G-72074, Tübingen, Germany; German Centre of Neurodegenerative Diseases (DZNE), Eberhard-Karls-University, G-72074, Tübingen, Germany.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Reichbauer
authors.affiliation: Centre for Neurology and Hertie Institute for Clinical Brain Research, Eberhard-Karls-University, G-72074, Tübingen, Germany; German Centre of Neurodegenerative Diseases (DZNE), Eberhard-Karls-University, G-72074, Tübingen, Germany; Dr John T. Macdonald Foundation Department of Human Genetics, John P. Hussman Institute for Human Genomics, University of Miami Miller School of Medicine, Miami, FL 33136, USA.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Schüle
authors.affiliation: INSERM U 1127, CNRS UMR 7225, Sorbonne Universités, UPMC Univ Paris 06, fUMRS_1127, Institut du Cerveau et de la Moelle épinière, F-75013, Paris, France; APHP, Hôpital de la Pitié-Salpêtrière, Département de Génétique, F-75013, Paris, France; University Pierre and Marie Curie, Neurometabolic Clinical Research Group, F-75013, Paris, France.
authors.forename: Fanny
authors.initials: F
authors.lastname: Mochel
authors.affiliation: Centre for Neurology and Hertie Institute for Clinical Brain Research, Eberhard-Karls-University, G-72074, Tübingen, Germany; German Centre of Neurodegenerative Diseases (DZNE), Eberhard-Karls-University, G-72074, Tübingen, Germany.
authors.forename: Matthis
authors.initials: M
authors.lastname: Synofzik
authors.affiliation: Atlantic Research Centre, Department of Pediatrics, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada; Atlantic Research Centre, Department of Biochemistry & Molecular Biology, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada. Electronic address: SpoelA@Dal.Ca.
authors.forename: Aarnoud C
authors.initials: AC
authors.lastname: van der Spoel
mesh_terms: D000818:Animals; D019556:COS Cells; D045744:Cell Line, Tumor; D002524:Cerebellar Ataxia / Q000201:enzymology / Q000235:genetics* / Q000473:pathology; D004721:Endoplasmic Reticulum / Q000201:enzymology / Q000473:pathology; D057075:Enzyme Assays; D005786:Gene Expression Regulation; D005962:Glucosylceramidase; D006367:HeLa Cells; D006801:Humans; D008247:Lysosomes / Q000201:enzymology / Q000473:pathology; D009154:Mutation; D009474:Neurons / Q000201:enzymology / Q000473:pathology; D010957:Plasmids / Q000737:chemistry / Q000378:metabolism; D015398:Signal Transduction; D015419:Spastic Paraplegia, Hereditary / Q000201:enzymology / Q000235:genetics* / Q000473:pathology; D014162:Transfection; D019076:Transgenes; D001617:beta-Glucosidase / Q000172:deficiency / Q000235:genetics*
chemical_list: D001617:beta-Glucosidase; C517537:GBA2 protein, human; D005962:Glucosylceramidase
keywords: Cerebellar ataxia; Enzyme activity; GBA2; Glucosylceramide; Miglustat; SPG46; Spastic paraplegia