Abstract
Purpose :
Rods and cones secrete IRBP, the major soluble protein component of the interphotoreceptor matrix. In addition to protecting and trafficking visual cycle retinoids, IRBP may have a neuroprotective role as there is an inverse relationship between the level of vitreous IRBP and severity of diabetic retinopathy (DR). The mechanism and location of reduced IRBP expression is not understood. Here, we investigated IRBP expression in-vitro in response to glucose and VEGF. Globes from diabetic patients were used to characterize retinal location of IRBP.
Methods :
1.5 x106 661W and Y79 cells, which express cone and rod-like phenotypes, respectively were treated with 5.5 or 30 mM glucose with or without VEGF (10ng/ml) for 24 hrs. In 661W cells, IRBP and GAPDH mRNAs were quantified by RTPCR, and IRBP in conditioned media by ELISA. Human globes studies were obtained through the NDRI. Death to placement in 10% formalin was <10.5 hrs except in one control. Cases: Diabetes (2 no DR, 4 non-proliferative, 2 proliferative); and normal controls (6 cases). Donors age range was 30-98 yrs. Clinical histories were correlated with gross and histopathology, and serial sagittal sections prepared through the fovea. IHC compared the distribution of IRBP and peanut agglutinin binding matrix domains, with that of the choroidal proteins albumin, and BIGH3.
Results :
High glucose (30 mM) resulted in a 1.44 increased IRBP mRNA in 661W cells (vs 1.34 for cells treated with 5.5 mM glucose). IRBP in the conditioned media in high glucose was ~3 X times greater compared to low glucose (13.1 vs 4.5 pg/ml). VEGF reduced IRBP secretion in cells in high (to 5.0 pg/ml) vs low glucose (0 pg/ml). IRBP in the media of Y79 cells were similar (70 vs 74 pg/ml for high and low glucose, respectively). Only a small decrease of IRBP level was noted in Y79 cells with VEGF treatment (69 vs 68 pg/ml). Ocular Pathology showed: Except when the postmortem interval was > 12 hrs, IRBP was restricted to the IPM; albumin and BIGH3 to the choroid. In DR, IRBP was reduced in the IPM, and albumin was often present.
Conclusions :
Taken together our studies show that hyperglycemia results a reduction of IRBP within the interphotoreceptor matrix. VEGF mediated reduced IRBP expression may contribute to the pathogenesis of DR.
This is a 2021 ARVO Annual Meeting abstract.