Protective gene expression changes elicited by an inherited defect in photoreceptor structure.

To investigate pathogenic mechanisms in such instances, we have characterized rod photoreceptor and retinal gene expression changes in response to a defined insult to photoreceptor structure, using the retinal degeneration slow (rds) mouse model. Global gene expression profiling was performed on flow-sorted rds and wild-type rod photoreceptors immediately prior and subsequent to times at which OSs are normally elaborated. Dysregulated genes were identified via microarray hybridization, and selected candidates were validated using quantitative PCR analyses. We identified a single key gene, Egr1, that was dysregulated in a sustained fashion in rds rod photoreceptors and in the retina. Egr1 upregulation was associated with microglial activation and migration, into the outer retina at times subsequent to the major peak of photoreceptor cell death. Interestingly, this response was accompanied by neurotrophic factor upregulation. We hypothesize that activation of Egr1 and neurotrophic factors represents a protective immune mechanism, contributing to the characteristically slow retinal degeneration of the rds mouse model.

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