Lack of causal relationship between clusterin expression and photoreceptorapoptosis in light-induced retinal degeneration

Induction of apoptosis in the retina leads to cellular death by molecular m echanisms that are not well understood. Clusterin expression is increased i n tissues undergoing apoptosis, including retinal neurodegenerative states, but the causal relationships remain to be clarified. To gain insight into clusterin's role in photoreceptor apoptosis, the cellular distribution of c lusterin mRNA was compared with the pattern of apoptotic nuclear labelling in a rat model of light-induced retinal degeneration. In control retinal se ctions, clusterin mRNA was localized to the retinal pigment epithelium cell s, photoreceptor inner segments, inner nuclear layer, and ganglion cell lay er. Clusterin expression decreased in photoreceptors and retinal pigment ep ithelium cells, which progressively degenerated, and increased in preserved inner nuclear layer, in proportion to the duration of light exposure in bo th cyclic light- and dark-reared animals. These results suggest that cluste rin is not causally involved in apoptotic mechanisms of photoreceptor death , but may relate to cytoprotective functions.