title: Retinal microglial activation and inflammation induced by amadori-glycated albumin in a rat model of diabetes.
abstract: OBJECTIVE
  During diabetes, retinal microglial cells are activated to release inflammatory cytokines that initiate neuronal loss and blood-retinal barrier breakdown seen in diabetic retinopathy (DR). The mechanism by which diabetes activates microglia to release those inflammatory mediators is unclear and was therefore elucidated.
  
  
  METHODS
  Microglia activation was characterized in streptozocin-injected rats and in isolated microglial cells using immunofluorescence, enzyme-linked immunosorbent assay, RT-PCR, and Western blot analyses.
  
  
  RESULTS
  In 8-week diabetic retina, phospho-extracellular signal-related kinase (ERK) and P38 mitogen-activated protein kinases were localized in microglia, but not in Mueller cells or astrocytes. At the same time, Amadori-glycated albumin (AGA)-like epitopes were featured in the regions of microglia distribution, implicating a pathogenic effect on microglial activation. To test this, diabetic rats were treated intravitreally with A717, a specific AGA-neutralizing antibody, or murine IgG. Relative to nondiabetic rats, diabetic rats (IgG-treated) manifested 3.9- and 7.9-fold increases in Iba-1 and tumor necrosis factor (TNF)-α mRNAs, respectively. Treatment of diabetic rats with A717 significantly attenuated overexpression of these mRNAs. Intravitreal injection of AGA per se in normal rats resulted in increases of Iba-1 expression and TNF-α release. Guided by these results, a cultured retinal microglia model was developed to study microglial response after AGA treatment and the mechanistic basis behind this response. The results showed that formation of reactive oxygen species and subsequent activation of ERK and P38, but not Jun NH2-terminal kinase, are molecular events underpinning retinal microglial TNF-α release during AGA treatment.
  
  
  CONCLUSIONS
  These results provide new insights in understanding the pathogenesis of early DR, showing that the accumulated AGA within the diabetic retina elicits the microglial activation and secretion of TNF-α. Thus, intervention trials with agents that neutralize AGA effects may emerge as a new therapeutic approach to modulate early pathologic pathways long before the occurrence of vision loss among patients with diabetes.
authors.affiliation: epartment of Ophthalmology, Medical College of Georgia, Augusta, Georgia, USA.
authors.forename: Ahmed S
authors.initials: AS
authors.lastname: Ibrahim
authors.forename: Azza B
authors.initials: AB
authors.lastname: El-Remessy
authors.forename: Suraporn
authors.initials: S
authors.lastname: Matragoon
authors.forename: Wenbo
authors.initials: W
authors.lastname: Zhang
authors.forename: Yogin
authors.initials: Y
authors.lastname: Patel
authors.forename: Sohail
authors.initials: S
authors.lastname: Khan
authors.forename: Mohammed M
authors.initials: MM
authors.lastname: Al-Gayyar
authors.forename: Mamdouh M
authors.initials: MM
authors.lastname: El-Shishtawy
authors.forename: Gregory I
authors.initials: GI
authors.lastname: Liou
mesh_terms: D000818:Animals; D002135:Calcium-Binding Proteins / Q000235:genetics; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D003930:Diabetic Retinopathy / Q000378:metabolism* / Q000473:pathology*; D004797:Enzyme-Linked Immunosorbent Assay; D017127:Glycation End Products, Advanced; D008840:Microfilament Proteins; D017628:Microglia / Q000187:drug effects* / Q000378:metabolism*; D051381:Rats; D012160:Retina / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012709:Serum Albumin / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics; D000093423:Glycated Serum Albumin
chemical_list: C100745:Aif1 protein, rat; D002135:Calcium-Binding Proteins; D017127:Glycation End Products, Advanced; D008840:Microfilament Proteins; D012709:Serum Albumin; D014409:Tumor Necrosis Factor-alpha; D000093423:Glycated Serum Albumin