title: Succination of Protein Disulfide Isomerase Links Mitochondrial Stress and Endoplasmic Reticulum Stress in the Adipocyte During Diabetes.
abstract: OBJECTIVE
  Protein succination by fumarate increases in the adipose tissue of diabetic mice and in adipocytes matured in high glucose as a result of glucotoxicity-driven mitochondrial stress. The endoplasmic reticulum (ER) oxidoreductase protein disulfide isomerase (PDI) is succinated in adipocytes that are matured in high glucose, and in this study we investigated whether succination would alter PDI oxidoreductase activity, directly linking mitochondrial stress and ER stress.
  
  
  RESULTS
  Protein succination and the ER stress marker C/EBP homologous protein (CHOP) were diminished after pharmaceutical targeting of mitochondrial stress with the chemical uncoupler niclosamide in adipocytes matured in high-glucose concentrations. PDI was succinated by fumarate on both CXXC-containing active sites, contributing to reduced enzymatic activity. Succinated PDI decreased reductase activity in adipocytes matured in high glucose, and in db/db epididymal adipose tissue, in association with increased levels of CHOP. PDI succination was increased in fumarase knockdown adipocytes, leading to reduced PDI oxidoreductase activity, increased CHOP levels, and pro-inflammatory cytokine secretion, confirming the specific role of elevated fumarate levels in contributing to ER stress. In addition, PDI succination and ER stress were decreased, and PDI reductase activity was restored when exposure to chronic high glucose was limited, highlighting the importance of calorie restriction in the improvement of adipocyte metabolic function.
  
  
  METHODS
  These experiments identify PDI succination as a novel biochemical mechanism linking altered mitochondrial metabolism to ER stress in the adipocyte during diabetes.
  
  
  CONCLUSIONS
  The current study demonstrates that early biochemical changes in mitochondrial metabolism have important implications for the development of adipocyte stress. Antioxid. Redox Signal. 27, 1281-1296.
authors.affiliation: 1 Department of Pharmacology, Physiology and Neuroscience, School of Medicine, University of South Carolina , Columbia, South Carolina.
authors.forename: Allison M
authors.initials: AM
authors.lastname: Manuel
authors.affiliation: 2 Mass Spectrometry Center, Department of Chemistry and Biochemistry, University of South Carolina , Columbia, South Carolina.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Walla
authors.affiliation: 3 Department of Chemistry and Biochemistry, University of Windsor , Windsor, Canada .
authors.forename: Adam
authors.initials: A
authors.lastname: Faccenda
authors.affiliation: 1 Department of Pharmacology, Physiology and Neuroscience, School of Medicine, University of South Carolina , Columbia, South Carolina.
authors.forename: Stephanie L
authors.initials: SL
authors.lastname: Martin
authors.affiliation: 1 Department of Pharmacology, Physiology and Neuroscience, School of Medicine, University of South Carolina , Columbia, South Carolina.
authors.forename: Ross M
authors.initials: RM
authors.lastname: Tanis
authors.affiliation: 1 Department of Pharmacology, Physiology and Neuroscience, School of Medicine, University of South Carolina , Columbia, South Carolina.
authors.forename: Gerardo G
authors.initials: GG
authors.lastname: Piroli
authors.affiliation: 4 Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford , Oxford, United Kingdom .
authors.forename: Julie
authors.initials: J
authors.lastname: Adam
authors.affiliation: 5 Viral Vector Core, Department of Pharmacology, Physiology and Neuroscience, School of Medicine, University of South Carolina , Columbia, South Carolina.
authors.forename: Boris
authors.initials: B
authors.lastname: Kantor
authors.affiliation: 3 Department of Chemistry and Biochemistry, University of Windsor , Windsor, Canada .
authors.forename: Bulent
authors.initials: B
authors.lastname: Mutus
authors.affiliation: 6 Department of Pharmaceutical and Biomedical Sciences, Medical University of South Carolina , Charleston, South Carolina.
authors.forename: Danyelle M
authors.initials: DM
authors.lastname: Townsend
authors.affiliation: 1 Department of Pharmacology, Physiology and Neuroscience, School of Medicine, University of South Carolina , Columbia, South Carolina.
authors.forename: Norma
authors.initials: N
authors.lastname: Frizzell
mesh_terms: D041721:3T3-L1 Cells; D017667:Adipocytes / Q000378:metabolism*; D000818:Animals; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D059865:Endoplasmic Reticulum Stress; D005650:Fumarates / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D051379:Mice; D008928:Mitochondria / Q000378:metabolism*; D009534:Niclosamide / Q000494:pharmacology; D018384:Oxidative Stress; D019704:Protein Disulfide-Isomerases / Q000737:chemistry / Q000378:metabolism*; D051742:Transcription Factor CHOP / Q000378:metabolism
chemical_list: C497250:Ddit3 protein, mouse; D005650:Fumarates; D051742:Transcription Factor CHOP; D009534:Niclosamide; D019704:Protein Disulfide-Isomerases; D005947:Glucose
keywords: adipocytes; adipose cell metabolism; endoplasmic reticulum; glucotoxicity; metabolism; protein modification