Abstract
Purpose :
Retinoid x receptors (RXR) belong to the family of nuclear receptors comprising RXR α, β and γ isoforms which are well expressed in the brain, however minimal data exists regarding their expression and distribution in the retina. The exact physiological role of RXRs has yet to been fully elucidated but they are believed to play important role in regulating transcriptional signaling and apoptosis. The purpose of this study was to investigate the presence and distribution of RXRs in the rodent retina. In addition, RXR activation was evaluated by treating neuronal cells with an RXR agonist.
Methods :
Immunofluorescence (IF) staining using specific antibodies and DAPI was used to determine the expression of each of the RXR α, β and γ isoforms in various layers of the C57BL/6 mice retinas (n=3). A combination of western blotting (WB) and IF techniques was also used to establish expression of various RXRs in the SH-SY5Y neuronal cell line. The biological effects of activation of RXRs on cell viability was determined by treating cells with RXR agonist bexarotene (12 hrs) in a concentration range of 0.001 µM to 10 µM.
Results :
Differential immuno-reactivity against RXR α, β and γ isoforms was observed in the normal mouse retina. RXRα was observed to localise mainly to the ganglion cell layer (GCL) and the inner nuclear layer (INL) while γ immuno-reactivity was primarily detected in the GCL. We observed only a weak expression of RXR β isoform in the retina. Expression of each of the various RXRs was established in the SH-SY5Y neuronal cells using WB and IF, mainly perinuclear in location. Densitimetric quantification using WB revealed that bexarotene treatment (0.1-1.00 µM range) resulted in increased expression of the α, β, γ receptors compared to controls (p<0.05) (5 replications). Treatment with higher agonist concentrations (5-10 µM range) resulted in significantly reduced neuronal cell viability (p<0.05).
Conclusions :
Our initial findings reveal the expression of RXRs within SH-SY5Y cells and in the laminar structure of mouse retina. Bexarotene treatment suggests that RXRs can be targeted and upregulated by using this specific agonist. Experiments are underway to further localize these receptors to specific cell types within the retina and determine their role and potential use in neuroprotective strategies.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.