Aging and Light Stress Result in Overlapping and Unique Gene Expression Changes in Photoreceptors

Abstract

Advanced age is one of the leading risk factors for vision loss and eye disease. Photoreceptors are the primary sensory neurons of the eye. The extended photoreceptor cell lifespan, in addition to its high metabolic needs due to phototransduction, makes it critical for these neurons to continually respond to the stresses associated with aging by mounting an appropriate gene expression response. Here, we sought to untangle the more general neuronal age-dependent transcriptional signature of photoreceptors with that induced by light stress. To do this, we aged flies or exposed them to various durations of blue light, followed by photoreceptor nuclei-specific transcriptome profiling. Using this approach, we identified genes that are both common and uniquely regulated by aging and light induced stress. Whereas both age and blue light induce expression of DNA repair genes and a neuronal-specific signature of death, both conditions result in downregulation of phototransduction. Interestingly, blue light uniquely induced genes that directly counteract the overactivation of the phototransduction signaling cascade. Lastly, unique gene expression changes in aging photoreceptors included the downregulation of genes involved in membrane potential homeostasis and mitochondrial function, as well as the upregulation of immune response genes. We propose that light stress contributes to the aging transcriptome of photoreceptors, but that there are also other environmental or intrinsic factors involved in age-associated photoreceptor gene expression signatures.

Proteome-wide quantitative analysis of redox cysteine availability in the Drosophila melanogaster eye reveals oxidation of phototransduction machinery during blue light exposure and age

“…To do this, we exposed white-eyed w 1118 flies to 8 h of blue light, which significantly decreases redox GSH:GSSG ratios relative to untreated controls ( Fig. 2 C) [ 30 ]. Retinal degeneration occurs progressively after the 8 h blue light exposure, and our previous studies generally assessed retinal degeneration 7–10 days post-exposure using confocal and/or electron microscopy [ 29 , 72 ].…”

“…p-value (* < 0.05) Student's T-test, data reused from Ref. [ 30 ]. (D) Enriched GO process (GOP) categories for significantly oxidized proteins identified in the eye.…”

“…Since we only measured glutathione ratios in the eye under light stress and aging, which is a limitation of our study, it is possible that there could be changes in the levels and/or localization of specific ROS under these two different conditions. In addition, there are both overlapping and distinct gene expression changes in photoreceptors within the eye under blue light versus aging [ 30 ], suggesting that each of these conditions have some unique effects on the eye. For example, aging is associated with chronic inflammation and expression of proteins associated with the innate immune response [ 67 ] whereas blue light stress induces hyperactivation of the phototransduction pathway and perturbs calcium homeostasis in the eye [ 29 ].…”

“…In addition, redox glutathione ratios change in the Drosophila eye under normal diurnal light cycles relative to dark [ 28 ], suggesting that redox signaling may have roles in phototransduction [ 24 ]. However, increases in ROS levels caused by acute blue light stress are damaging, inducing retinal degeneration [ [28] , [29] , [30] ].…”

Transcriptional changes in specific subsets of Drosophila neurons following inhibition of the serotonin transporter

“…Finally, it is possible that sample prep methodology should be further refined for this type of investigation. For example, in future experiments we will consider alternative methods such as flash freezing tissue [92,93], which may result in a faster and cleaner sample prep with fewer artefactual changes.…”