Natural History of Retinal Function and Structure in the Rpe65-/- Murine Model of Leber Congenital Amaurosis

Abstract

Abstract: : Purpose: To characterize the natural history of functional and structural changes in the Rpe65 -/- mouse model of Leber congenital amaurosis. Methods: Full-field ERGs were performed in anesthetized and dark-adapted Rpe65-/- (n=30) and Rpe65+/+ (n=26) mice at ages of 3, 5, 9, 12, and 15 months. Flash stimuli in the range of -4.1 to +3.6 log scot-cd.s.m^-2 were used; b-waves were measured conventionally and leading edges of photoresponses were fit with a model of rod phototransduction activation. A subset of the mice was studied by light microscopy and immunofluorescence. Results: At 3 months of age, ERG b-wave thresholds were elevated by ~3 log units in Rpe65-/- mice compared to normals; b-wave amplitudes to maximal stimulus were 50% of normal; photoresponse amplitude was 30% of normal and there was dramatic reduction of sensitivity. At this age, outer nuclear layer (ONL) counts were similar to those of age-matched controls (10 rows) and outer segments (OS) appeared normal. At 5 months of age, b-wave and photoresponse maximal amplitudes were reduced to 30% and 20% of normal respectively. The ONL was reduced to 7 rows (normal, 10 rows); rod OS became shorter and disorganized. There was anti-rod opsin positive labeling in the OS, cell bodies and synapses. In addition to astrocytes, Muller cells in Rpe65-/- retinas showed anti-GFAP staining throughout their cytoplasm. At >12 months of age, b-wave and photoresponse maximal amplitudes were further reduced to 25% and 10% of normal. The ONL was reduced to 6 rows of nuclei (normal, 8 rows). Conclusions: Structure and function studies indicate a slowly progressive retinal degeneration in Rpe65-/- mice. At all ages studied, photoreceptor nuclear layer changes were relatively mild compared with degree of retinal dysfunction.

Keywords: retinal degenerations: hereditary • electroretinography: non-clinical • animal model