title: Hyperglycemia decreases mitochondrial function: the regulatory role of mitochondrial biogenesis.
abstract: Increased generation of reactive oxygen species (ROS) is implicated in "glucose toxicity" in diabetes. However, little is known about the action of glucose on the expression of transcription factors in hepatocytes, especially those involved in mitochondrial DNA (mtDNA) replication and transcription. Since mitochondrial functional capacity is dynamically regulated, we hypothesized that stressful conditions of hyperglycemia induce adaptations in the transcriptional control of cellular energy metabolism, including inhibition of mitochondrial biogenesis and oxidative metabolism. Cell viability, mitochondrial respiration, ROS generation and oxidized proteins were determined in HepG2 cells cultured in the presence of either 5.5 mM (control) or 30 mM glucose (high glucose) for 48 h, 96 h and 7 days. Additionally, mtDNA abundance, plasminogen activator inhibitor-1 (PAI-1), mitochondrial transcription factor A (TFAM) and nuclear respiratory factor-1 (NRF-1) transcripts were evaluated by real time PCR. High glucose induced a progressive increase in ROS generation and accumulation of oxidized proteins, with no changes in cell viability. Increased expression of PAI-1 was observed as early as 96 h of exposure to high glucose. After 7 days in hyperglycemia, HepG2 cells exhibited inhibited uncoupled respiration and decreased MitoTracker Red fluorescence associated with a 25% decrease in mtDNA and 16% decrease in TFAM transcripts. These results indicate that glucose may regulate mtDNA copy number by modulating the transcriptional activity of TFAM in response to hyperglycemia-induced ROS production. The decrease of mtDNA content and inhibition of mitochondrial function may be pathogenic hallmarks in the altered metabolic status associated with diabetes.
authors.affiliation: Center for Neurosciences and Cell Biology of Coimbra, Department of Zoology, University of Coimbra, 3004-517 Coimbra, Portugal. palmeira@ci.uc.pt
authors.forename: Carlos M
authors.initials: CM
authors.lastname: Palmeira
authors.forename: Anabela P
authors.initials: AP
authors.lastname: Rolo
authors.forename: Jessica
authors.initials: J
authors.lastname: Berthiaume
authors.forename: James A
authors.initials: JA
authors.lastname: Bjork
authors.forename: Kendall B
authors.initials: KB
authors.lastname: Wallace
mesh_terms: D006528:Carcinoma, Hepatocellular / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D002470:Cell Survival; D004272:DNA, Mitochondrial / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D003920:Diabetes Mellitus / Q000503:physiopathology*; D005786:Gene Expression Regulation; D006801:Humans; D006943:Hyperglycemia / Q000503:physiopathology*; D024101:Mitochondrial Proteins / Q000378:metabolism; D051266:Nuclear Respiratory Factor 1 / Q000378:metabolism; D009930:Organic Chemicals; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D017395:Plasminogen Activator Inhibitor 1 / Q000378:metabolism; D016133:Polymerase Chain Reaction; D017382:Reactive Oxygen Species / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic / Q000502:physiology*
chemical_list: D004272:DNA, Mitochondrial; D004268:DNA-Binding Proteins; D024101:Mitochondrial Proteins; D051266:Nuclear Respiratory Factor 1; D009930:Organic Chemicals; D017395:Plasminogen Activator Inhibitor 1; D017382:Reactive Oxygen Species; D014157:Transcription Factors; C422562:mitochondrial transcription factor A; C107472:red dye CMXRos