Abstract
Purpose :
Ocular Nrf2 overexpression using an adeno-associated virus (AAV 2/8) with promoters active in the retinal pigment epithelium (RPE) are sufficient to slow the degeneration of cone photoreceptors and RPE cells and preserve visual acuity in the rd1 mouse model of retinal degneration. Interestingly, rescue of visual acuity occurs whether or not the AAV causes overexpression in photoreceptors and RPE (CMV) or RPE only (Best1). The mechanism by which RPE-only expression of Nrf2 leads to improved visual acuity is of great interest. Here, we used the scanning electron microscope (SEM) to study RPE morphology from rd1 mice with and without Nrf2 overexpression.
Methods :
Rd1 mice received subretinal injections at P0 of either AAV Best1 Nrf2, AAV CMV Nrf2, or AAV hRedO [human red opsin] Nrf2 in one eye and control AAV hRedO GFP virus in the contralateral eye. Eyes from rd1 or wild type mice were enucleated at P30-P35 with retinas carefully dissected from the RPE. The RPE was fixed in 2.5% glutaraldehyde and processed for scanning electron microscopy. A subset of eyes with Best1 hNrf2 were also enucleated at P40-45.
Results :
The RPE from wild type mice showed good preservation of apical processes. RPE from rd1 mouse eyes receiving only control GFP virus showed significant loss of microvilli. On the other hand, contralateral eyes of rd1 mice with overexpression of Nrf2 in the RPE secondary to AAV CMV or Best1 Nrf2 infection showed signiifcant preservation of RPE apical processes at P30-P35. Eyes infected with AAV hRedO Nrf2, which only overexpresses Nrf2 in the photoreceptors, did not show in preservation of these processes. Some rd1 eyes that received Best1 Nrf2 were processed at P40-45, and the protective effects were found to extend to this timepoint.
Conclusions :
Overexpression of hNrf2 in the RPE protects gross RPE morphology slows vision loss in rd1 mice. We now show that the microstructure of the RPE is improved as well. There is preservation of the apical microvilli between P30 and P45 days, a where the RPE begins to become dysmoprhic without Nrf2 overexpression. The Nrf2 must be expressed in the RPE, as overexpression in photoreceptors using AAV hRedO promoter was insufficident to produce this rescue phenotype. Our results suggest that preservation of the interface between the RPE and surviving cones may be important in preserving visual acuity in rd1 mice.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.