Purpose: To investigate the effects of recombinant adenovirus-mediated downregulation of cathepsin S (CatS) on the retinal pigment epithelium and/or neural 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 established by in vivo fundus fluorescence photography and fluorescence microscopy. The autofluorescent debris accumulation in Ad.CatSAS (recombinant adenovirus carrying the antisense CatS gene)injected rat eyes was monitored by fluorescence microscopy, and the antisense CatS RNA expression was demonstrated by in situ hybridization. Changes in the retinal morphology were assessed 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-injected 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 photoreceptor outer segments in Ad.CatSAS-injected eyes coincided with intense autofluorescent debris accumulation. The number of layers of photoreceptor cells 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 photoreceptor 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 the low expression of endogenous CatS in RPE cells, this enzyme plays an important role in maintenance of normal retinal function.