title: High glucose concentration leads to differential expression of tight junction proteins in human retinal pigment epithelial cells.
abstract: BACKGROUND
  One of the early features of diabetic retinopathy is the breakdown of the blood-retinal barrier (BRB) due to disruption of the tight junctions. Whereas impairment of the proteins involved in the disruption of the tight junctions of the internal BRB has been extensively studied, there is no information on the direct effect of high glucose concentration on the barrier function of the outer blood-retinal barrier (formed by the retinal pigment epithelium [RPE]). The aim of this study was to explore the effect of high glucose concentration on the expression of tight junction proteins (occludin, zonula occludens-1 [ZO-1] and claudin-1) in a human RPE line under two distinct glucose concentrations.
  
  
  METHODS
  An RPE cell line (ARPE-19) were cultured for 3 weeks in a medium supplemented with 10% fetal calf serum containing 5.5 mmol D-glucose (mimicking physiological conditions) or 25 mmol Dglucose (mimicking the hyperglycemia that occurs in diabetic patients). Occludin, ZO-1 and claudin-1 were studied by real-time polymerase chain reaction and Western blot at 14 and 21 days.
  
  
  RESULTS
  Occludin and ZO-1 mRNA levels and protein content were similar in cultures maintained at 5.5 mmol and 25 mmol of D-glucose. In contrast, high glucose concentration (25 mmol) induced a clear upregulation in claudin-1 mRNA expression and protein content at 21 days (mRNA level: 1.03 vs 2.29; protein content: 0.92 vs 1.14).
  
  
  CONCLUSIONS
  High glucose concentration leads to differential expression of tight junction proteins in ARPE-19 cells. In addition, our results suggest that the upregulation of claudin-1by glucose is involved in the increase of tight junction sealing function. The functional consequences and clinical applicability of these findings require further investigation.
authors.affiliation: Diabetes and Metabolism Research Unit. Institut de Recerca Hospital Vall d'Hebron. Universitat Autònoma de Barcelona (UAB). Barcelona. Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Villarroel
authors.forename: Marta
authors.initials: M
authors.lastname: García-Ramírez
authors.forename: Lidia
authors.initials: L
authors.lastname: Corraliza
authors.forename: Cristina
authors.initials: C
authors.lastname: Hernández
authors.forename: Rafael
authors.initials: R
authors.lastname: Simó
mesh_terms: D001813:Blood-Retinal Barrier / Q000187:drug effects; D002461:Cell Line, Transformed / Q000187:drug effects; D062445:Claudin-1; D003930:Diabetic Retinopathy / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005136:Eye Proteins / Q000096:biosynthesis* / Q000235:genetics; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D008565:Membrane Proteins / Q000096:biosynthesis* / Q000235:genetics; D062793:Occludin; D010750:Phosphoproteins / Q000096:biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D055213:Retinal Pigment Epithelium / Q000187:drug effects* / Q000378:metabolism; D019108:Tight Junctions / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects; D062826:Zonula Occludens-1 Protein
chemical_list: C568108:CLDN1 protein, human; D062445:Claudin-1; D005136:Eye Proteins; D008565:Membrane Proteins; C568985:OCLN protein, human; D062793:Occludin; D010750:Phosphoproteins; D012333:RNA, Messenger; C569042:TJP1 protein, human; D062826:Zonula Occludens-1 Protein; D005947:Glucose