The effect of insulin and glucose levels on retinal glial cell activation and pigment epithelium-derived fibroblast growth factor-2.
OBJECTIVE
The diabetic retina exhibits decreases in endogenous nonangiogenic neurotrophins. This study hypothesized that deficiencies in systemic and retinal pigment epithelium-derived (RPE) neurotrophic factors also influence retinal changes in diabetes.


METHODS
Diabetes was established in Listar hooded rats with streptozotocin. Reverse transcriptase coupled polymerase chain reaction (RT-PCR) and immunoblotting were used to determine the expression of fibroblast growth factor-2 (FGF-2) in the retina and RPE, and glial fibrillary acid protein (GFAP) in the retina. In addition, primary human RPE cultures and a transformed Müller cell line were used to determine the effect of insulin, glucose, and insulin-like growth factor (IGF) on the expression of these substances.


RESULTS
FGF-2 and GFAP were increased in retina, but FGF-2 was decreased in the RPE of diabetic animals. Retinal GFAP correlated with RPE FGF-2 expression in these animals. Insulin produced a dose-dependent increase in FGF-2 in RPE cells and decrease in GFAP in Müller cells grown in 15 mM glucose. In 5 mM glucose, insulin had no effect on expression of either protein. Physiological levels of insulin inhibited changes induced by 15 mM glucose. The effect of 9 nM insulin on each culture was mimicked by 1 nM IGF, and blocked with an IGFR-1 inhibitor.


CONCLUSIONS
It is suggested that decreased systemic insulin and high glucose levels contribute to decreased FGF-2 production in the RPE and increased glial cell activation in the diabetic retina. Addition of insulin and IGF act to reverse this effect through the IGFR-1. These mechanisms may contribute to the development of diabetic retinopathy.
Layton
Christopher J
CJ
Nuffield Laboratory of Ophthalmology, Oxford, UK. cjlayton@bigpond.com
Becker
Simone
S
Osborne
Neville N
NN
D000818:Animals; D002478:Cells, Cultured; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism / Q000503:physiopathology*; D004305:Dose-Response Relationship, Drug; D016222:Fibroblast Growth Factor 2 / Q000378:metabolism*; D005904:Glial Fibrillary Acidic Protein / Q000037:antagonists & inhibitors / Q000378:metabolism; D005947:Glucose / Q000008:administration & dosage / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D007328:Insulin / Q000008:administration & dosage / Q000378:metabolism* / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D008297:Male; D009457:Neuroglia; D010857:Pigment Epithelium of Eye / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D017526:Receptor, IGF Type 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D012160:Retina / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*
D005904:Glial Fibrillary Acidic Protein; D007328:Insulin; D016222:Fibroblast Growth Factor 2; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1; D005947:Glucose