AAV-mediated expression of human VEGF-A as a novel rat model of diabetic retinopathy

Abstract

Purpose : Diabetic retinopathy (DR) is a complex disease displaying a complex angiogenic pathology, including upregulation of vascular endothelial growth factor A (VEGF), vascular leakage and neovascularization, ultimately leading to visual impairment. However, animal models accurately reflecting vascular pathologies of DR are lacking. In this study, we evaluated the efficacy of adeno-associated virus (AAV)-mediated long-term expression of VEGF to establish angiogenic DR-related phenotypes in Brown Norway rats.

Methods : Brown Norway rats received an intravitreal (IVT) injection of either low (1×10¹⁰ vg/eye) or high (5×10¹⁰ vg/eye) dose of AAV-hVEGF165.V5 on Day 0. AAV-stuffer (a non-coding DNA packaged into the same viral capsid) was used as negative control (1×10¹⁰ vg/eye). Pathology was evaluated weekly by spectral domain-optical coherence tomography (SD-OCT) and fluorescein angiography (FA) for 6 weeks after AAV administration. Retinal leakage was evaluated using vitreous fluorophotometry (VFP) at week 3; visual function was assessed by flash electroretinography (fERG) 6 weeks after IVT.

Results : AAV-mediated VEGF expression resulted in ocular vascular pathology, manifesting as vascular tortuosity, dilated or constricted vessels (20%of eyes), microaneurysms (30%), and increased vascular leakage and neovascularization (50%) at weeks 3 and 4. Inner retinal thickness increased at week 4 in low (64.89±1.32μm, p<0.01) and high (64.48±1.4μm, p<0.01) dose groups compared with control (58.75±0.25μm), suggestive of retinal edema. By week 6, inner retinal thickness decreased significantly in high-dose injected rats (53.21±1.12μm, p<0.05) compared with control (56.82±0.53µm). Outer nuclear layer thickness decreased in low (48.97±1.11μm, p<0.01) and high (48.83±0.66μm, p<0.01) dose groups by week 6 compared with control (53.37±0.33μm). The retinal-to-midvitreal slope of VFP responses were significantly decreased at week 3 in high dose group (-9.64) vs. control (-37.98, p<0.05), indicating retinal leakage. fERG a-wave amplitudes were significantly reduced in high-dose group (308.1±37.48µV) compared with control (342.1±20.10µV) at week 6.

Conclusions : AAV-mediated expression of human VEGF-A resulted in DR-like vascular pathology in rats, offering an attractive approach to gain valuable insights into the underlying molecular mechanisms of VEGF-mediated pathologies, including DR and for testing novel anti-angiogenic therapies.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.