title: Ubiquitin proteasome system in Parkinson's disease: a keeper or a witness?
abstract: OBJECTIVE
  The aim of this work was to evaluate the role of ubiquitin-proteasome system (UPS) on mitochondrial-driven alpha-synuclein (aSN) clearance in in vitro, ex vivo and in vivo Parkinson's disease (PD) cellular models.
  
  
  METHODS
  We used SH-SY5Y ndufa2 knock-down (KD) cells, PD cybrids and peripheral blood mononuclear cells (PBMC) from patients meeting the diagnostic criteria for PD. We quantified aSN aggregation, proteasome activity and protein ubiquitination levels. In PBMC of PD patient population we evaluated the aSN levels in the plasma and the influence of several demographic characteristics in the above mentioned determinations.
  
  
  RESULTS
  We found that ubiquitin-independent proteasome activity was up-regulated in SH-SY5Y ndufa2 KD cells while a downregulation was observed in PD cybrids and PBMC. Moreover, we observed an increase in protein ubiquitination that correlates with a decrease in ubiquitin-dependent proteasome activity. Accordingly, proteasome inhibition prevented ubiquitin-dependent aSN clearance. Ubiquitin-independent proteasome activity was positively correlated with ubiquitination in PBMC. We also report a negative correlation of chymotrypsin-like activity with age in control and late-onset PD groups. Total ubiquitin content is positively correlated with aSN oligomer levels, which leads to an age-dependent increase of aSN ubiquitination in LOPD. Moreover, aSN levels are increased in the plasma of PD patients.
  
  
  CONCLUSIONS
  aSN oligomers are ubiquitinated and we identified a ubiquitin-dependent clearance insufficiency with the accumulation of both aSN and ubiquitin. However, SH-SY5Y ndufa2 KD cells showed a significant up-regulation of ubiquitin-independent proteasomal enzymatic activity that could mean a cell rescue attempt. Moreover, we identified that UPS function is age-dependent in PBMC.
authors.affiliation: CNC-Center for Neuroscience and Cell Biology, University of Coimbra, Portugal.
authors.forename: Diogo
authors.initials: D
authors.lastname: Martins-Branco
authors.forename: Ana R
authors.initials: AR
authors.lastname: Esteves
authors.forename: Daniel
authors.initials: D
authors.lastname: Santos
authors.forename: Daniela M
authors.initials: DM
authors.lastname: Arduino
authors.forename: Russell H
authors.initials: RH
authors.lastname: Swerdlow
authors.forename: Catarina R
authors.initials: CR
authors.lastname: Oliveira
authors.forename: Cristina
authors.initials: C
authors.lastname: Januario
authors.forename: Sandra M
authors.initials: SM
authors.lastname: Cardoso
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D016022:Case-Control Studies; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002918:Chymotrypsin / Q000378:metabolism; D002950:Citrate (si)-Synthase / Q000378:metabolism; D042967:Electron Transport Complex I; D005260:Female; D049452:Green Fluorescent Proteins / Q000235:genetics; D006801:Humans; D047468:Immunoprecipitation; D019344:Lactic Acid / Q000494:pharmacology; D007963:Leukocytes, Mononuclear / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism; D009447:Neuroblastoma / Q000473:pathology; D010300:Parkinson Disease / Q000097:blood / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D010949:Plasma / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D013223:Statistics as Topic; D013778:Tetrazolium Salts; D013844:Thiazoles; D014162:Transfection; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination / Q000187:drug effects / Q000235:genetics; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics
chemical_list: D034741:RNA, Small Interfering; D013778:Tetrazolium Salts; D013844:Thiazoles; D025801:Ubiquitin; D049452:Green Fluorescent Proteins; D019344:Lactic Acid; D002950:Citrate (si)-Synthase; D002918:Chymotrypsin; D046988:Proteasome Endopeptidase Complex; D042967:Electron Transport Complex I; C022616:thiazolyl blue