A2E, a Fluorophore of RPE Lipofuscin: Can It Cause RPE Degeneration?

Abstract

In atrophic age-related macular degeneration (AMD) and Stargardt disease, the death of retinal pigment epithelial (RPE) cell death leads to photoreceptor cell degeneration and visual impairment. Nevertheless, the cause of RPE atrophy is poorly understood. One factor that may place RPE cells at risk is the accumulation of critical levels of lipofuscin. Indeed, several lines of evidence indicate that the excessive accumulation of lipofuscin by RPE cells is significant in terms of the etiology of AMD. Firstly, histological analyses of human donor eyes (Wing et al., 1978; Weiter et al., 1986), in addition to fundus spectrophotometry (Delori et al., 1995a; Delori et al., 2001), and confocal ophthalmoscopy (von Rückmann et al., 1997), have shown that RPE cells overlying the macula, with the exception of RPE in the cone-rich fovea, exhibit the most pronounced age-related accumulation of fluorescent material. Lipofuscin levels in RPE cells are also topographically correlated with histopathological indicators of AMD (Feeney-Burns et al., 1984; Dorey et al., 1989) and with the loss of photoreceptor cells in aged eyes (Dorey et al., 1989). Interestingly, increased fundus autofluorescence at the borders of geographic atrophy is considered to represent an enhanced accumulation of RPE lipofuscin and to implicate the latter in the disease process (Holz et al., 1999; Holz et al., 2001). While the amassing of lipofuscin by RPE is a feature of aging, excessive accretion also occurs in Stargardt disease, some forms of retinitis pigmentosa and cone-rod dystrophy (Weingeist et al., 1982; Rabb et al., 1986; Lopez et al., 1990; Delori et al., 1995b; Kennedy et al., 1995).