Interphotoreceptor retinoid-binding protein (IRBP) is downregulated at early stages of diabetic retinopathy.
OBJECTIVE
Interphotoreceptor retinoid-binding protein (IRBP) plays a major role in the visual cycle and is essential to the maintenance of photoreceptors. The aim of this study was to determine whether a decrease in IRBP production exists in the early stages of diabetic retinopathy.


METHODS
Vitreous samples from diabetic patients with proliferative and non-proliferative diabetic retinopathy (PDR, NPDR), and from non-diabetic patients with macular hole (control group) were selected for IRBP quantitative assessment by proteomic analysis (fluorescence-based difference gel electrophoresis) and western blot. Human post mortem eyes (n = 16) from diabetic donors without clinically detectable retinopathy and from non-diabetic donors (n = 16) were used to determine IRBP (also known as RBP3) mRNA levels (RT-PCR) and protein content (western blot and confocal microscopy). Retinal neurodegeneration was assessed by measuring glial fibrillar acidic protein (GFAP) and the apoptotic rate. Y79 human retinoblastoma cells were used to test the effects of glucose, TNF-alpha and IL-1beta on IRBP expression and IRBP levels.


RESULTS
Intravitreous IRBP concentration was significantly lower in PDR < NPDR < control in proteomic and western blot analysis. IRBP mRNA levels and IRBP protein content were significantly lower in the retinas from diabetic donors than in those from non-diabetic donors. Increased GFAP and a higher degree of apoptosis were observed in diabetic retinas compared with non-diabetic retinas. A dose-dependent downregulation of IRBP mRNA expression and IRBP content was detected with glucose, TNF-alpha and IL-1beta in cultures of Y79 human retinoblastoma cells.


CONCLUSIONS
Underproduction of IRBP is an early event in the human diabetic retina and is associated with retinal neurodegeneration. The mechanisms leading to this deficit deserve further investigation.
Garcia-Ramírez
M
M
CIBER for Diabetes and Associated Metabolic Diseases (CIBERDEM), Diabetes and Metabolism Research Unit, Institut de Recerca Hospital Universitari Vall d'Hebron, Universitat Autònoma de Barcelona Pg. Vall d'Hebron 119-129, 08035, Barcelona, Spain.
Hernández
C
C
Villarroel
M
M
Canals
F
F
Alonso
M A
MA
Fortuny
R
R
Masmiquel
L
L
Navarro
A
A
García-Arumí
J
J
Simó
R
R
D017668:Age of Onset; D000368:Aged; D017209:Apoptosis; D003930:Diabetic Retinopathy / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D015536:Down-Regulation; D005136:Eye Proteins / Q000235:genetics* / Q000378:metabolism; D005260:Female; D005784:Gene Amplification; D016161:Genes, Retinoblastoma / Q000235:genetics; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D006801:Humans; D008297:Male; D018613:Microscopy, Confocal / Q000379:methods; D008875:Middle Aged; D020419:Photoreceptor Cells, Vertebrate / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D019572:Retinal Neoplasms / Q000235:genetics / Q000473:pathology; D012167:Retinal Perforations / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D012175:Retinoblastoma / Q000235:genetics / Q000473:pathology; D012177:Retinol-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014822:Vitreous Body / Q000378:metabolism; D000099214:Retinol-Binding Proteins, Interstitial
D005136:Eye Proteins; D005904:Glial Fibrillary Acidic Protein; D012333:RNA, Messenger; D012177:Retinol-Binding Proteins; D000099214:Retinol-Binding Proteins, Interstitial