AAV-Mediated Gene Therapy in the Rd6 Mouse Model of Retinal Degeneration

Abstract

Purpose: : To evaluate the effect of AAV-mediated gene therapy in the rd6 mouse model of an autosomal recessive retinal degeneration caused by an in-frame deletion of exon 4 in the membrane-type frizzled-related protein (MFRP) gene. In the mouse eye, MFRP displays the highest level of expression in the RPE and ciliary body. Human patients with certain homozygous mutations in the Mfrp gene develop microphthalmos, retinitis pigmentosa and foveoschisis.

Methods: : Subretinal injections of AAV5-CBA-Mfrp were performed on 3-week old rd6 mice in the right eye only. The left eye was not treated and served as a control. Fundoscopic and electroretinographic analyses were carried out periodically following injection. Histological examination of treated and untreated eyes was performed at 4 months post-injection on some animals. Western blot analysis was used to detect the expression of the FLAG-tagged Mfrp protein in mouse whole eyecups.

Results: : Fundoscopic examination revealed significant improvement in the treated rd6 eyes at 4 months post-injection, which appeared almost normal compared to untreated contralateral controls that displayed a high density of distinctive white spots. Although the ERG signals decreased with age in all animals examined, the a-wave amplitude under dark-adapted conditions was slightly larger in the treated eyes. Histologically, the injected eyes contained far fewer aberrant cells in the subretinal space, although all layers of the retina were comparable to those of control eyes, and photoreceptor loss could not be prevented.

Conclusions: : AAV5-mediated gene delivery of the Mfrp gene to the subretinal space of rd6 mice improves some of the characteristic pathological features associated with the disease phenotype in this mouse model of retinal degeneration. Future experiments will determine if the beneficial effects of gene therapy could be enhanced by placing the Mfrp gene under the control of a VMD2 promoter for more selective AAV-mediated targeting to RPE cells.

Keywords: gene transfer/gene therapy • retinal pigment epithelium • retinal degenerations: hereditary