Abstract
Purpose: :
Upregulation of IL-1β in the diabetic retina has been implicated in the pathogenesis of retinopathy. The aims of this study were to evaluate the temporal pattern of IL-1β overexpression in the retina of diabetic rats and to identify the cellular source of IL-1β induction in response to high glucose.
Methods: :
Expression of IL-1β and of markers of glial reactivity were studied in the retina of streptozotocin-diabetic rats with diabetes duration from 1.5 to 6 months. IL-1β mRNA and protein were quantified by RealTime RT-PCR and ELISA. Protein levels of glial fibrillar acidic protein (GFAP), 2-macroglobulin (2M), ceruloplasmin (Cp), and IL-1 type I receptor (IL-1RI) were evaluated by immunoblotting. The effects of high glucose and IL-1β on IL-1β synthesis was investigated in bovine retinal endothelial cells (BREC), rat Müller cells, and rat brain astrocytes and microglial cells. IL-1β mRNA was quantified by RealTime RT-PCR.
Results: :
Diabetes led to a time-dependent increase of IL-1β in the retina. IL-1β mRNA levels began to increase at 10 weeks of diabetes (1.5 fold vs control, P < 0.02) and continue to increase exponentially over time (10 fold vs control at 6 months, P < 0.002). Upregulation of IL-1β was associated with increased expression of GFAP, 2M and Cp, while the expression of IL-1RI was not affected. Under basal culture conditions (5 mM glucose) all four cell types examined expressed IL-1β with the highest levels detected in microglia (>10 times higher than BREC, Müller, and astrocytes). High glucose concentrations (30mM) led to upregulation of IL-1β in BREC (1.8 fold vs 5mM glucose, P < 0.0001) but not in Müller cells, astrocytes, and microglia. IL-1β induced its own synthesis in Müller cells and astrocytes, but not in BREC and microglia.
Conclusions: :
The temporal pattern of IL-1β upregulation coincides with that of GFAP, 2M, and Cp suggesting a mechanistic role of IL-1β in the development of glial reactivity in the diabetic retina. The glucose-mediated increase of IL-1β in retinal endothelial cells might lead to further increase of IL-1β in the diabetic retina via self-amplification of gene expression in macroglial cells.
Keywords: cytokines/chemokines • diabetic retinopathy • inflammation