title: Pioglitazone restores IGFBP-3 levels through DNA PK in retinal endothelial cells cultured in hyperglycemic conditions.
abstract: OBJECTIVE
  Previously, we reported that pioglitazone prevented insulin resistance and cell death in type 2 diabetic retina by reducing TNFα and suppressor of cytokine signaling 3 (SOCS3) levels. Numerous reports suggest prominent vasoprotective effects of insulin growth factor binding protein-3 (IGFBP-3) in diabetic retinopathy. We hypothesized that pioglitazone protects against retinal cell apoptosis by regulating IGFBP-3 levels, in addition to reducing TNFα. The current study explored potential IGFBP-3 regulatory pathways by pioglitazone in retinal endothelial cells cultured in high glucose.
  
  
  METHODS
  Primary human retinal endothelial cells (REC) were grown in normal (5 mM) and high glucose (25 mM) and treated with pioglitazone for 24 hours. Cell lysates were processed for Western blotting and ELISA analysis to evaluate IGFBP-3, TNFα, and cleaved caspase 3 protein levels.
  
  
  RESULTS
  Our results show that treatment with pioglitazone restored the high glucose-induced decrease in IGFBP-3 levels. This regulation was independent of TNFα actions, as reducing TNFα levels with siRNA did not prevent pioglitazone from increasing IGFBP-3 levels. Pioglitazone required protein kinase A (PKA) and DNA-dependent protein kinase (DNA PK) activity to regulate IGFBP-3, as specific inhibitors for each protein prevented pioglitazone-mediated normalization of IGFBP-3 in high glucose. Insulin growth factor binding protein-3 activity was increased and apoptosis decreased by pioglitazone, which was eliminated when serine site 156 of IGFBP-3 was mutated suggesting a key role of this phosphorylation site in pioglitazone actions.
  
  
  CONCLUSIONS
  Our findings suggest that pioglitazone mediates regulation of IGFBP-3 via activation of PKA/DNA PK pathway in hyperglycemic retinal endothelial cells.
authors.affiliation: Department of Ophthalmology, University of Tennessee Health Science Center, Memphis, Tennessee, United States.
authors.forename: Shalini
authors.initials: S
authors.lastname: Thakran
authors.affiliation: Department of Ophthalmology, University of Tennessee Health Science Center, Memphis, Tennessee, United States.
authors.forename: Qiuhua
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: Department of Ophthalmology, University of Tennessee Health Science Center, Memphis, Tennessee, United States Department of Microbiology, Immunology, and Biochemistry, University of Tennessee Health Science Center, Memphis, Tennessee, United States.
authors.forename: Vanessa
authors.initials: V
authors.lastname: Morales-Tirado
authors.affiliation: Department of Ophthalmology, University of Tennessee Health Science Center, Memphis, Tennessee, United States Department of Anatomy & Neurobiology, University of Tennessee Health Science Center, Memphis, Tennessee, United States Department of Pharmaceutical Sciences, University of Tennessee Health Science Center, Memphis, Tennessee, United States.
authors.forename: Jena J
authors.initials: JJ
authors.lastname: Steinle
mesh_terms: D017209:Apoptosis; D015153:Blotting, Western; D002478:Cells, Cultured; D003470:Culture Media / Q000494:pharmacology; D004247:DNA / Q000235:genetics; D051747:DNA-Activated Protein Kinase / Q000378:metabolism*; D003930:Diabetic Retinopathy / Q000378:metabolism; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D005786:Gene Expression Regulation; D005947:Glucose / Q000494:pharmacology; D006801:Humans; D006943:Hyperglycemia / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology*; D007004:Hypoglycemic Agents / Q000494:pharmacology; D047468:Immunoprecipitation; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000096:biosynthesis / Q000187:drug effects / Q000235:genetics*; D000077205:Pioglitazone; D012160:Retina / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D015398:Signal Transduction; D045162:Thiazolidinediones / Q000494:pharmacology*
chemical_list: D003470:Culture Media; D007004:Hypoglycemic Agents; D018972:Insulin-Like Growth Factor Binding Protein 3; D045162:Thiazolidinediones; D004247:DNA; D051747:DNA-Activated Protein Kinase; D005947:Glucose; D000077205:Pioglitazone
keywords: DNA PK; IGFBP-3; pioglitazone; retinal endothelial cells