The use of adenovirus-mediated gene transfer to develop a rat model for photoreceptor degeneration

PURPOSE. To investigate the effects of recombinant adenovirus-mediated down regulation of cathepsin S (CatS) on the retinal pigment epithelium and/or n eural retina in vivo. METHODS. The expression of green fluorescent protein (gfp) after subretinal injection of a recombinant adenovirus, Ad.gfp, into rat eyes was first est ablished by in vivo fundus fluorescence photography and fluorescence micros copy. The autofluorescent debris accumulation id Ad.CatSAS (recombinant ade novirus carrying the antisense CatS gene)-injected rat eyes was monitored b y fluorescence microscopy, and the antisense CatS RNA expression was demons trated by in situ hybridization. Changes in the retinal morphology were ass essed by light microscopy. RESULTS. The gfp expression was present in 30% to 90% of the injection area at 3 days and was absent 9 days after Ad.gfp injection. In Ad.CatSAS-injec ted eyes, the expression of antisense CatS RNA was demonstrated by in situ hybridization. Autofluorescent debris accumulation was significantly higher in AD.CatSAS-injected eyes than in control eyes. The shortening of photore ceptor outer segments in Ad.CatSAS-injected eyes coincided with intense aut ofluorescent debris accumulation. The number of layers of photoreceptor cel ls decreased with time and were 11, 9, and 8 at 7, 14, and 28 days after Ad .CatSAS injection, respectively. In control eyes, the number of layers of p hotoreceptor cells (14) remained unchanged. CONCLUSIONS. These results demonstrate that recombinant adenovirus-mediated transient modulation of gene expression in retinal pigment epithelial (RPE ) cells could induce changes in the retina, and, in spite of low expression of endogenous CatS in RPE cells, this enzyme plays an important role in ma intenance of normal retinal function.