title: Role of cathepsin D in U18666A-induced neuronal cell death: potential implication in Niemann-Pick type C disease pathogenesis.
abstract: Cathepsin D is an aspartyl protease that plays a crucial role in normal cellular functions and in a variety of neurodegenerative disorders, including Niemann-Pick type C (NPC) disease, which is characterized by intracellular accumulation of cholesterol and glycosphingolipids in many tissues, including the brain. There is evidence that the level and activity of cathepsin D increased markedly in vulnerable neurons in NPC pathology, but its involvement in neurodegeneration remains unclear. In the present study, using mouse hippocampal cultured neurons, we evaluated the significance of cathepsin D in toxicity induced by U18666A, a class II amphiphile, which triggers cell death by impairing the trafficking of cholesterol, as observed in NPC pathology. Our results showed that U18666A-mediated toxicity is accompanied by an increase in cathepsin D mRNA and enzyme activity but a decrease in the total peptide content. The cytosolic level of cathepsin D, on the other hand, was increased along with cytochrome c and activated caspase-3 in U18666A-treated neurons. The cathepsin D inhibitor, pepstatin A, partially protected neurons against toxicity by attenuating these signaling mechanisms. Additionally, down-regulation of cathepsin D level prevented, whereas overexpression of the protease increased, vulnerability of cultured N2a cells to U18666A-induced toxicity. We also showed that extracellular cathepsin D from U18666A-treated neurons or application of exogenous enzyme can induce neurotoxicity by activating the autophagic pathway. These results suggest that increased release/activation of cathepsin D can trigger neurodegeneration and possibly development of NPC pathology. Thus, targeting cathepsin D level/activity may provide a new therapeutic opportunity for the treatment of NPC pathology.
authors.affiliation: Department of Psychiatry, Centre for Prions and Protein Folding Diseases, University of Alberta, Edmonton, Alberta T6G 2M8, Canada.
authors.forename: Asha
authors.initials: A
authors.lastname: Amritraj
authors.forename: Yanlin
authors.initials: Y
authors.lastname: Wang
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Revett
authors.forename: David
authors.initials: D
authors.lastname: Vergote
authors.forename: David
authors.initials: D
authors.lastname: Westaway
authors.forename: Satyabrata
authors.initials: S
authors.lastname: Kar
mesh_terms: D000736:Androstenes / Q000633:toxicity*; D000818:Animals; D000071187:Autophagy-Related Protein 5; D015415:Biomarkers / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D002402:Cathepsin D / Q000037:antagonists & inhibitors / Q000378:metabolism*; D016923:Cell Death / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism; D045304:Cytochromes c / Q000378:metabolism; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism; D005347:Fibroblasts / Q000187:drug effects / Q000201:enzymology / Q000473:pathology; D006624:Hippocampus / Q000473:pathology; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000201:enzymology / Q000473:pathology*; D052556:Niemann-Pick Disease, Type C / Q000201:enzymology* / Q000209:etiology / Q000473:pathology*; D011480:Protease Inhibitors / Q000494:pharmacology; D019311:Staurosporine / Q000494:pharmacology
chemical_list: D000736:Androstenes; C495773:Atg5 protein, mouse; D000071187:Autophagy-Related Protein 5; D015415:Biomarkers; D008869:Microtubule-Associated Proteins; D011480:Protease Inhibitors; C006261:3-beta-(2-(diethylamino)ethoxy)androst-5-en-17-one; D045304:Cytochromes c; D002784:Cholesterol; D053148:Caspase 3; D002402:Cathepsin D; D019311:Staurosporine