Overexpression of β-Secretase 1 (BACE1) by AAV-mediated Gene Delivery Provides Protection in a Mouse Model of AMD

Abstract

Purpose : β-site amyloid precursor protein cleaving enzyme (β-secretase or BACE) is strongly implicated in both Alzheimer’s disease (AD) and Age-related Macular Degeneration (AMD). We have previously reported that β-secretase knockdown in mice resulted in significant retinal abnormalities and that was linked to increased levels of oxidative stress. In this study we investigate if overexpression of BACE1 can prevent/slow the progression of retinal changes in a mouse model of AMD.

Methods : We delivered an AAV1 vector containing a BACE1 gene driven by the small CBA promoter via subretinal injection in control mice and an AMD-like mouse model induced by AAV1-ribozyme knockdown of mitochondrial superoxide dismutase (SOD2) for 2 weeks prior to injection of AAV1-BACE1. AAV1-BACE1 expression was followed by an enhanced GFP report gene (eGFP). The effects of overexpressing BACE1 with two AAV dosages (2E+9 vg/ul = low; 4E+10 vg/ul = high;) were assessed at 2 weeks, 1, 3 and 6 months post the injection by fundus angiography, ERG, OCT, histopathology and immunocytochemistry.

Results : We observed eGFP positive RPE cells as early as 2 weeks and persistent for 6 months after AAV delivery indicating that AAV was expressing BACE1 gene. This was further confirmed by co-staining with a specific antibody against BACE1. In normal mice, fundus angiography, electroretinography and OCT suggested no adverse effects due to increased expression of BACE1 at the low dose. However, we observed retina vascular and RPEs pathology at the high dose overexpression of BACE1 . In the AMD mouse model the disease progression was significantly reduced at both doses of BACE1 and the ERG response was greatly improved compared to control animals receiving AAV1-RzSOD2 knockdown without BACE1 treatment. BACE1 overexpression also resulted in improved retinal morphology, decreased vascular leakage, reduced oxidative stress (4HNE expression) and restoration of the integrity of the RPE blood-retinal barrier (ZO-1 staining) compared to RzSOD2 animals.

Conclusions : Our data demonstrate that BACE1 plays a key role in maintaining normal retina/RPEs physiologic homeostasis and that overexpression of BACE1 reduces oxidative stress and improves RPEs integrity associated with AMD. Supplement of BACE1 provided protections against retinal degeneration and loss of visual function may be further explored as a rescue strategy in AMD model.

This is a 2020 ARVO Annual Meeting abstract.