Secretogranin III as a novel disease-associated target for anti-angiogenic therapy of diabetic retinopathy

Abstract

Purpose : Vascular endothelial growth factor (VEGF) inhibitors have been approved for diabetic macular edema (DME) therapy but with limited efficacy. The purpose of this study is to identify unknown vascular permeability factors (VPFs) and develop novel therapies for diabetic retinopathy (DR).

Methods : We applied a new technology of ligandomics to diabetic or control mice for global identification of cell-wide retinal endothelial ligands. Quantitative comparison of the entire ligand profiles for diabetic vs. control retina systematically identified ligands with increased or decreased binding to diabetic endothelia. Identified ligands were independently verified as VPFs by in vitro endothelial permeability assay. Disease-associated angiogenic activity was verified by corneal pocket assay in diabetic or control mice. Monoclonal antibodies (mAb) were generated. Therapeutic agents were intravitreally injected to evaluate their ability to inhibit retinal vascular leakage using Evans blue assay.

Results : Comparative ligandomics systematically identified 353 ligands with increased binding (DR-high) to diabetic retinal endothelia and 105 ligands with decreased binding (DR-low). Secretogranin III (Scg3) was identified as a DR-high ligand with the highest binding activity ratio for diabetic vs. control retina (1,731:0, p<0.0001, c² test). Scg3 was upregulated in the vitreous fluid of diabetic mice only by 1.38-fold (p<0.05). We independently verified Scg3 as a novel VPF. Scg3 was corroborated as a DR-high ligand that selectively stimulated corneal angiogenesis in diabetic but not control mice. In contrast, VEGF induced angiogenesis in both diabetic and control mice. Scg3 induced angiogenesis through a VEGF-independent receptor pathway. Intravitreal injection of Scg3-neutralizing mAb significantly alleviated retinal vascular leakage in two independent mouse models of DR with high efficacy (p<0.01).

Conclusions : Scg3 was previously reported as a protein to regulate secretory granule biogenesis and has not hitherto been described as a cellular ligand. This study discovers Scg3 as a novel and highly disease-associated VPF and angiogenic factor. Scg3-neutralizing mAb ameliorates DR leakage with high efficacy, implicating its potential for DME therapy. These results also demonstrate the validity and utility of the comparative ligandomics for systematic mapping of therapeutic ligands.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.