Abstract
Purpose :
Retinal degenerations are a diverse group of diseases, yet photoreceptors often undergo a universal response to stress. One hallmark of this response is the downregulation of rod-specific genes that make up the phototransduction machinery, which are often damaged during degeneration. We have previously shown that the neuroprotective factor STAT3 can directly regulate many of these highly expressed outer segment genes. This study aimed to elucidate a mechanism for how activation of STAT3 causes downregulation of rod genes during photoreceptor stress.
Methods :
For the pSTAT3 chromatin immunoprecipitation (ChIP) microarray, STAT3 was activated in Balb/cJ mice by either intravitreal injection of 2 μg/μl recombinant human leukemia inhibitory factor or by exposing the mice to 600 lux cyclic light for 6 days. ChIP was performed using an antibody against Y705 pSTAT3. Previously published NRL and CRX ChIP-seq datasets were used for meta-analyses. Interval analysis was achieved using BEDTools and all gene target predictions were performed using BETA.
Results :
pSTAT3 ChIP microarray experiments showed that STAT3 targets many rod-specific genes, including those involved in ciliary transport and phototransduction, as well as directly targeting key regulators of these pathways, such as NRL and CRX. STAT3 shares 41.7% (NRL) and 44.1% (CRX) of target genes with these master regulators. Further interval analysis revealed a significant number of STAT3 binding sites in close proximity to NRL and CRX intervals. Moreover, 5.2% of NRL and 21% of CRX binding sites had overlap with a STAT3 site. Of the 396 genes shared between STAT3 and NRL, 103 could be attributed to binding sites with a ≧ 1 base pair overlap, while 238 of the 445 targets shared by STAT3 and CRX existed from overlapping intervals.
Conclusions :
Our data showing that STAT3 binds genes controlled by NRL and CRX suggest that STAT3 could interact with regulators that typically drive high gene expression in rods. The frequent overlap between STAT3 and NRL and CRX binding sites suggest that STAT3 may compete with these factors to bind to similar sites when rods are stressed, reducing gene expression. Further investigation of the relationship of STAT3 as a modifier of NRL and CRX-regulated transcription is ongoing. Overall, this study provides one mechanistic explanation of how STAT3 decreases photoreceptor-specific gene expression as part of the cell’s stress response.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.