title: Effects of modified LDL and HDL on retinal pigment epithelial cells: a role in diabetic retinopathy?
abstract: OBJECTIVE
  Blood-retina barrier leakage in diabetes results in extravasation of plasma lipoproteins. Intra-retinal modified LDLs have been implicated in diabetic retinopathy (DR), but their effects on retinal pigment epithelial (RPE) cells and the added effects of extravasated modified HDLs are unknown.
  
  
  METHODS
  In human retinas from individuals with and without diabetes and DR, immunohistochemistry was used to detect ApoB, ApoA1 and endoplasmic reticulum (ER) stress markers. In cell culture, human RPE cells were treated with native LDL (N-LDL) or heavily-oxidised glycated LDL (HOG-LDL) with or without pretreatment with native HDL (N-HDL) or heavily-oxidised glycated HDL (HOG-HDL). Cell viability, oxidative stress, ER stress, apoptosis and autophagy were assessed by Cell Counting Kit-8 assay, dichlorofluorescein assay, western blotting, immunofluorescence and TUNEL assay. In separate experiments, RPE cells were treated with lipid oxidation products, 7-ketocholesterol (7-KC, 5-40 μmol/l) or 4-hydroxynonenal (4-HNE, 5-80 μmol/l), with or without pretreatment with N-HDL or HOG-HDL.
  
  
  RESULTS
  ApoB, ApoA1 staining and RPE ER stress were increased in the presence of DR. HOG-LDL but not N-LDL significantly decreased RPE cell viability and increased reactive oxygen species generation, ER stress, apoptosis and autophagy. Similarly, 4-HNE and 7-KC decreased viability and induced ER stress. Pretreatment with N-HDL mitigated these effects, whereas HOG-HDL was less effective by most, but not all, measures.
  
  
  CONCLUSIONS
  In DR, extravascular modified LDL may promote RPE injury through oxidative stress, ER stress, autophagy and apoptosis. N-HDL has protective effects, but HOG-HDL is less effective. Extravasation and modification of HDL may modulate the injurious effects of extravasated modified LDL on the retinal pigment epithelium.
authors.affiliation: Harold Hamm Diabetes Center and Section of Endocrinology and Diabetes, University of Oklahoma Health Sciences Center, HHDC Suite 2900, Oklahoma City, OK 73104, USA.
authors.forename: M
authors.initials: M
authors.lastname: Du
authors.forename: M
authors.initials: M
authors.lastname: Wu
authors.forename: D
authors.initials: D
authors.lastname: Fu
authors.forename: S
authors.initials: S
authors.lastname: Yang
authors.forename: J
authors.initials: J
authors.lastname: Chen
authors.forename: K
authors.initials: K
authors.lastname: Wilson
authors.forename: T J
authors.initials: TJ
authors.lastname: Lyons
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D001343:Autophagy / Q000187:drug effects; D002478:Cells, Cultured; D003930:Diabetic Retinopathy / Q000188:drug therapy* / Q000378:metabolism*; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects; D017127:Glycation End Products, Advanced; D006801:Humans; D066298:In Vitro Techniques; D008075:Lipoproteins, HDL / Q000627:therapeutic use*; D008077:Lipoproteins, LDL / Q000627:therapeutic use*; D018384:Oxidative Stress / Q000187:drug effects; D012160:Retina / Q000187:drug effects* / Q000378:metabolism*; D000093844:Glycated Proteins
chemical_list: D017127:Glycation End Products, Advanced; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL; C031797:glycated lipoproteins, LDL; D000093844:Glycated Proteins