Abstract
Purpose :
Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid that acts through G protein-coupled S1P receptors (S1PR1-5) to participate in a variety of signaling pathways, but its role in the neural retina has not been studied extensively. We previously showed that S1PR2 is expressed in mouse and rat retinas, primarily in photoreceptors and bipolar cells, and expression is altered by conditions of retinal stress. In this study, we developed S1PR2 knockout (KO) mice on an albino background and performed structural and functional characterizations of their retinas under normal conditions and after intense light-induced retinal degeneration (LIRD) treatment.
Methods :
Albino S1PR2 KO and wild-type (WT) littermate mice were raised under similar conditions and underwent retinal assessments at various matched age-points between 3 and 6 months. Retinal function was assessed by electroretinography (ERG), and structural differences by electron microscopy (EM) and optical coherence tomography (OCT). Immunohistochemical (IHC) labeling was used to visualize differences in neuronal and synaptic markers in light- and dark-adapted mice. Mice underwent similar assessments after LIRD (1500 lux for 6 hours) to evaluate their sensitivity to retinal stress.
Results :
We found significantly elevated A- and B-wave responses at ERG flash intensities between 4-2000 cd.s/m2 in S1PR2 KO mice compared to WT at baseline (n = 12 and n = 8, respectively) and after LIRD (n = 10 and n = 11; P < 0.05). OCT further showed that KO mice (n = 8) had significantly increased retinal nerve fiber layer (RNFL) (14.8 ± 0.3µm vs 13.3 ± 0.5µm) and outer plexiform layer (OPL) (12.5 ± 0.4µm vs 11.6 ± 0.2µm) thickness compared to WT (n = 10; mean ± SE; P < 0.05). EM likewise showed differences in inner neuronal layers and OPL, and reduced synapses between rod terminal and bipolar cells in KO mice. IHC also showed differential labeling of synaptic markers and dendritic arborization of secondary neurons in KO mice compared to WT.
Conclusions :
Our findings show that S1PR2 knockout alters murine retinal structural and functional characteristics, suggesting an important role of S1PR2 in the mammalian retina.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.