Regulation of Gene Expression in Aging Rod Photoreceptors

Abstract

Purpose: : Aging is a major risk factor for age-related macular degeneration--the leading cause of blindness in the developed world--and exacerbates the clinical manifestations of other sight-debilitating retinopathies. Rod photoreceptors are especially vulnerable to the adverse effects of aging. We recently reported aging-associated changes in rod gene expression in cellular processes including oxidative phosphorylation, lipid metabolism, angiogenesis, transcriptional regulation, and inflammation. By refining and extending the time course of the study and taking advantage of more comprehensive exon microarrays, we aim to further elucidate major age-related pathways in rod photoreceptors and examine the role of microRNAs as regulators.

Methods: : In order to construct gene expression profiles specific to rod photoreceptors in an aging mouse model, rods were purified from Nrlp-eGFP mice--expressing GFP exclusively in the rod photoreceptors--at 1, 3, 6, 12, and 18 months of age using flow cytometry. RNA was then extracted and hybridized to Affymetrix GeneChip mouse Exon 1.0 ST arrays. Quality control, data analysis, and miRNA predictions were performed using Partek Genomics Suite software.

Results: : We identified 1400 annotated genes that are differentially expressed in rod photoreceptors--1.5 fold change and uncorrected p-value < .05--in at least one time interval between 1 and 18 months of age. From this gene list, miRNA predictions were made using the TargetScan 5.1 database and the expression levels of their target mRNAs assessed. Amongst the most highly enriched miRNAs in the aging photoreceptor dataset were miR-30a--known for its role in autophagy--and miR-124 and miR-9--both expressed in the retina and known for their roles in neuronal development.

Conclusions: : We are in the process of validating our miRNA predictions and their target genes by qRT-PCR and establishing their localization within rod photoreceptors by in situ hybridization. Since each miRNA is expected to regulate multiple mRNAs of shared or similar functions, targeting of miRNA regulators of aging or disease processes in rod photoreceptors promises to be a potentially powerful vision-restoring therapeutic approach.

Keywords: photoreceptors • aging • gene microarray