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Zsolt Ablonczy, Danielle Desjardins, Yueying Liu, Jie Fan, Craig E Crosson; VEGF induced changes in RPE function are dependent on increased HDAC activity.. Invest. Ophthalmol. Vis. Sci. 2016;57(12):No Pagination Specified.
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© ARVO (1962-2015); The Authors (2016-present)
Loss of vision due to the accumulation of fluid within the retina, broadly termed retinal edema, is a common end-point in clinical conditions, including age-related macular degeneration and diabetic retinopathy. Numerous previous studies focused on the contributions of vascular endothelial growth factor (VEGF) in endothelia to the pathogenesis of edema. However, it has been shown that VEGF can also directly impair the function of the retinal pigment epithelium (RPE) to remove fluid. Here, we investigated the role of histone deacetylases (HDACs) in mediating VEGF activity in the RPE.
VEGF administration in monolayer cultures of human RPE cells, intravitreal injections of glycated-albumin (gAlb), and hyperglycemic rats were utilized to simulate conditions of VEGF-release in the retina. In the cells, RPE function was assessed by transepithelial resistance. In the animals, the resorption of subretinal saline blebs was monitored. HDAC activity was determined by commercial assays and was antagonized by trichostatin-A (TSA). VEGF-R2 activity was blocked by ZM323881 or bevacizumab. Acetyl-α-tubulin levels were established from immunoblots.
In all three models, VEGF action resulted in the breakdown of RPE function. The pan-HDAC inhibitor, TSA, had a significant inhibitory effect on the VEGF-response; nevertheless, TSA required co-administration of albumin to be efficacious. In cells, the TSA-response was concentration-dependent, with an IC50 of 1.8 nmol/L and a Hill coefficient of 1, indicating a single inhibitory target. Both gAlb and VEGF induced a significant increase in total HDAC activity (2.7±1.4 fold for VEGF and 2.2±1.2 fold for gAlb), paralleled with a significant decrease in the acetylation level of α-tubulin (24% for VEGF and 34 % for gAlb). The loss of α-tubulin acetylation indicated a specific role of HDAC6 in the process.
These studies provided evidence that an increase in HDAC activity mediated the breakdown of RPE function by VEGF. Moreover, the activity of VEGF was linked to downstream cytoskeletal changes within the tissue. However, further studies will be required to understand the detailed mechanism of HDAC activity. Our results are in agreement with the idea that VEGF modulates the function of the RPE creating conditions that permit the accumulation of edematous fluid in the retina.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
TSA blocks the progressive early breakdown of RPE fluid resorption in hyperglycemic rats.
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