Semaphorin 3A Promotes Vascular Leakage in Diabetic Retinopathy

Abstract

Purpose: : Diabetic macular edema (DME), the main cause of central vision loss in diabetics, is a manifestation of diabetic retinopathy (DR) caused by the deterioration of the blood-retinal barrier, which leads to thickening of the ischemic retina through increased retinal vascular permeability (VP). Our lab has shown that Semaphorin 3A (Sema3A), a classic neuronal guidance cue that also affects endothelial cell behaviour, participates in vascular degeneration and later blocks physiological revascularization of the ischemic retina. Given the vaso-modulatory role of Sema3A, we set out to determine the ability of Sema3A to promote increased retinal vascular leakage in DR.

Methods: : Human vitreous samples from patients with DR and non-vascular ocular pathology (control) were analyzed by western blot for their levels of Sema3A. Sema3A levels were measured in retinal lysates from 3 different models of Diabetes Mellitus (DM) by RT-qPCR: 1. streptozotocin (STZ) treated mice (T1DM); 2.NOD mice (non-obese diabetic - autoimmune T1DM) and 3. leptin receptor knockout (db/db) mice (T2DM). The ability of Sema3A to induce retinal VP was quantified by Evans Blue permeation assay in mice intravitreally injected with Sema3A.Vascular-Endothelial cadherin phosphorylation was assayed by western blot of endothelial cells treated with rhSema3A.

Results: : Vitreous from DR patients showed a robust increase in Sema3A protein levels when compared to controls. STZ-injected mouse and NOD mouse retinas (non-fasted blood glucose over 300 mg/dL) showed 2-fold increases in Sema3A mRNA, while a similar 2-fold induction in Sema3A mRNA was observed in 6-month old db/db mouse retinas during the onset of retinal disease. In line, retinal permeability was 2.7-fold higher in Sema3A-injected mice relative to saline injected controls. In addition, Sema3A induced a robust increase in VE-cadherin phosphorylation at tyrosine-731 after rhSema treatment in vascular endothelial cells.This post-translational modification is associated with increased VP.

Conclusions: : Sema3A is induced in the retinas of diabetic patients and T1DM and T2DM mouse models. This increase in Sema3A is associated with increased retinal VP. Notably, inhibition of Sema3A may represent an attractive strategy to counter pathologic VP in DR.

Keywords: diabetic retinopathy • edema