title: Cathepsin D expression level affects alpha-synuclein processing, aggregation, and toxicity in vivo.
abstract: BACKGROUND
  Elevated SNCA gene expression and intracellular accumulation of the encoded alpha-synuclein (aSyn) protein are associated with the development of Parkinson disease (PD). To date, few enzymes have been examined for their ability to degrade aSyn. Here, we explore the effects of CTSD gene expression, which encodes the lysosomal protease cathepsin D (CathD), on aSyn processing.
  
  
  RESULTS
  Over-expression of human CTSD cDNA in dopaminergic MES23.5 cell cultures induced the marked proteolysis of exogenously expressed aSyn proteins in a dose-dependent manner. Unexpectedly, brain extractions, Western blotting and ELISA quantification revealed evidence for reduced levels of soluble endogenous aSyn in ctsd knock-out mice. However, these CathD-deficient mice also contained elevated levels of insoluble, oligomeric aSyn species, as detected by formic acid extraction. In accordance, immunohistochemical studies of ctsd-mutant brain from mice, sheep and humans revealed selective synucleinopathy-like changes that varied slightly among the three species. These changes included intracellular aSyn accumulation and formation of ubiquitin-positive inclusions. Furthermore, using an established Drosophila model of human synucleinopathy, we observed markedly enhanced retinal toxicity in ctsd-null flies.
  
  
  CONCLUSIONS
  We conclude from these complementary investigations that: one, CathD can effectively degrade excess aSyn in dopaminergic cells; two, ctsd gene mutations result in a lysosomal storage disorder that includes microscopic and biochemical evidence of aSyn misprocessing; and three, CathD deficiency facilitates aSyn toxicity. We therefore postulate that CathD promotes 'synucleinase' activity, and that enhancing its function may lower aSyn concentrations in vivo.
authors.affiliation: Center for Neurologic Diseases, Department of Neurology, Brigham & Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA. valerie_cullen@hotmail.com
authors.forename: Valerie
authors.initials: V
authors.lastname: Cullen
authors.forename: Maria
authors.initials: M
authors.lastname: Lindfors
authors.forename: Juliana
authors.initials: J
authors.lastname: Ng
authors.forename: Anders
authors.initials: A
authors.lastname: Paetau
authors.forename: Erika
authors.initials: E
authors.lastname: Swinton
authors.forename: Piotr
authors.initials: P
authors.lastname: Kolodziej
authors.forename: Heather
authors.initials: H
authors.lastname: Boston
authors.forename: Paul
authors.initials: P
authors.lastname: Saftig
authors.forename: John
authors.initials: J
authors.lastname: Woulfe
authors.forename: Mel B
authors.initials: MB
authors.lastname: Feany
authors.forename: Liisa
authors.initials: L
authors.lastname: Myllykangas
authors.forename: Michael G
authors.initials: MG
authors.lastname: Schlossmacher
authors.forename: Jaana
authors.initials: J
authors.lastname: Tyynelä
mesh_terms: D000818:Animals; D001921:Brain / Q000187:drug effects / Q000201:enzymology / Q000473:pathology; D002402:Cathepsin D / Q000172:deficiency / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism; D004331:Drosophila melanogaster / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D007231:Infant, Newborn; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D008970:Molecular Weight; D050505:Mutant Proteins / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000187:drug effects*; D020836:Protein Structure, Quaternary; D012756:Sheep; D012995:Solubility / Q000187:drug effects; D014020:Tissue Extracts; D051844:alpha-Synuclein / Q000737:chemistry / Q000378:metabolism* / Q000633:toxicity*
chemical_list: D050505:Mutant Proteins; D014020:Tissue Extracts; D051844:alpha-Synuclein; D002402:Cathepsin D; D004298:Dopamine