title: PEDF improves mitochondrial function in RPE cells during oxidative stress.
abstract: OBJECTIVE
  Oxidative stress plays an important role in health and aging. We have shown that oxidative stress impairs mitochondrial function and promotes RPE cell death in an age-dependent manner. This study investigates the role of pigment epithelium-derived factor (PEDF) in limiting oxidative stress-induced damage to RPE cells through mitochondrial pathways.
  
  
  METHODS
  Three groups of early-passaged RPE cells from donors 50 to 55, 60 to 65, and 70 to 75 years old (yo) were either preconditioned with PEDF followed by exposure to sublethal doses of hydrogen peroxide (H2O2) or post-treated with PEDF after H2O2 treatment. Effects of PEDF on mitochondrial function and cell viability were examined.
  
  
  RESULTS
  Oxidative stress induced an age-dependent increase in LDH release, reactive oxygen species (ROS) levels, and cell death and a decrease in adenosine triphosphate (ATP) production and mitochondrial membrane potential (ΔΨm) in human RPE cells. Preconditioning or poststressed treatment with PEDF resulted in increased cell viability, inhibition of cytochrome c release and caspase 3 cleavage, and improved mitochondria function denoted by a decrease in ROS generation and increases in ATP production and ΔΨm. Oxidative stress also disrupted the reticular network, trafficking, and distribution of the mitochondria and blocked activation of phosphatidylinositol 3 kinase (PI3K), Akt, and Erk signaling in the cells. These effects were more pronounced in RPE cells from individuals>60 yo compared to the 50 to 55 yo age group. Pigment epithelium-derived factor mitigated negative effects of oxidative stress on mitochondrial remodeling and cellular distribution and unblocked its control of PI3K/Akt and mitogen-activated protein kinase (MAPK) signaling. Although PEDF potentiated both PI3K/Akt and MAPK signaling in the cells, stabilization of mitochondrial networks and function was dependent on its activation of PI3K/Akt. Specificity of PEDF's activity was confirmed using the pharmacological inhibitors LY294002, SH6, and U0126. We also show that in the absence of oxidative stress, pharmacological inhibition of the PI3K/Akt pathway alone was sufficient to disrupt mitochondrial structure and function. In addition, PEDF blocked effects of oxidative stress on expression of cyclophilin D and UCP2, genes controlling mitochondrial function, and the apoptotic genes caspase 3, Bax, and Bcl2. Control of ROS levels by PEDF was specifically linked to UCP2 regulation since PEDF-induced expression of this gene in UCP2-deficient cells was associated with a decrease in ROS production.
  
  
  CONCLUSIONS
  We provide evidence that PEDF promotes resilience of aging RPE cells to oxidative stress by stabilizing mitochondrial networks and function and that mitochondrial dynamics in human RPE cells are controlled, in part, through the PI3K/Akt pathway.
authors.affiliation: Department of Neural and Behavioral Sciences, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States Department of Ophthalmology, The Second Affiliated Hospital of Xi'an College of Medicine, Xi'an, China.
authors.forename: Yuan
authors.initials: Y
authors.lastname: He
authors.affiliation: Division of Life Science, The Hong Kong University of Science and Technology, Hong Kong.
authors.forename: Kar Wah
authors.initials: KW
authors.lastname: Leung
authors.affiliation: Department of Ophthalmology, The Second Affiliated Hospital of Xi'an College of Medicine, Xi'an, China.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Ren
authors.affiliation: Department of Ophthalmology, The Second Affiliated Hospital of Xi'an College of Medicine, Xi'an, China.
authors.forename: Jinzhi
authors.initials: J
authors.lastname: Pei
authors.affiliation: State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China.
authors.forename: Jian
authors.initials: J
authors.lastname: Ge
authors.affiliation: Department of Neural and Behavioral Sciences, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States Department of Ophthalmology, The Second Affiliated Hospital of Xi'an College of Medicine, Xi'an, China State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China Department of Ophthalmology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States.
authors.forename: Joyce
authors.initials: J
authors.lastname: Tombran-Tink
mesh_terms: D000368:Aged; D000375:Aging / Q000502:physiology*; D017209:Apoptosis; D015153:Blotting, Western; D002478:Cells, Cultured; D005136:Eye Proteins / Q000494:pharmacology*; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D007473:Ion Channels / Q000096:biosynthesis / Q000235:genetics; D008297:Male; D008875:Middle Aged; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology*; D024101:Mitochondrial Proteins / Q000096:biosynthesis / Q000235:genetics; D009414:Nerve Growth Factors / Q000494:pharmacology*; D018384:Oxidative Stress; D011480:Protease Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D012164:Retinal Diseases / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D055213:Retinal Pigment Epithelium / Q000378:metabolism* / Q000473:pathology; D015843:Serpins / Q000494:pharmacology*; D015398:Signal Transduction; D000071246:Uncoupling Protein 2; D000099174:Pigment Epithelium-Derived Factor
chemical_list: D005136:Eye Proteins; D007473:Ion Channels; D024101:Mitochondrial Proteins; D009414:Nerve Growth Factors; D011480:Protease Inhibitors; D012333:RNA, Messenger; D015843:Serpins; D000071246:Uncoupling Protein 2; D000099174:Pigment Epithelium-Derived Factor; C000604389:UCP2 protein, human
keywords: ATP; MAPK; PEDF; PI3K/Akt; ROS; RPE; UCP2; aging; apoptosis; caspase 3; cyclophilin D; mitochondria; mitochondria structure; mitochondrial membrane potential; oxidative stress