Abstract
Purpose :
Sphingosine 1-phosphate (S1P) is a potent lipid mediator that modulates inflammation and angiogenesis. We previously demonstrated that S1P induced inflammatory and angiogenic response in the retinal pigment epithelial (RPE) cells suggesting the relationship between S1P and the pathology of age-related macular degeneration. In this study we investigated whether S1P is involved in the pathology of light-induced retinal degeneration in vivo and vitro.
Methods :
Photoreceptor cell line 661W cells and RPE cell line ARPE-19 cells were used for the experiments. Cells were exposed to approximately 8000 lux of visible light emitted by a light emitting diode (LED) lamp. The concentration of intracellular S1P was measured with liquid chromatography mass spectrometry. The sphingosine kinase activity was evaluated with the Sphingosine Kinase (SphK) Activity Assay. In vivo experiments, mice were adapted to dark conditions 24 hours prior to the light exposure. Then mice were exposed to approximately 8000 lux of LED light. After the light exposure, mice were sacrificed and enucleated. Immunochemistry for SphK1 and SphK2 was performed on frozen sections of murine retina. The retinal structure was analyzed using optical coherence tomography to evaluate the effect of SKI-2 (SphK1/2 inhibitor) on light-induced retinal degeneration.
Results :
The concentration of S1P in photoreceptor cells significantly increased after 1 hour of beginning the LED light exposure. SphK activity significantly increased 15 minutes after starting the treatment. Intracellular S1P also significantly increased in RPE cells by LED light. In vivo, immunohistochemical analysis of retinal sections found that the light exposure enhanced the expression of SphK1 and SphK2 in the outer segment of photoreceptor cells and retinal glial cells. In addition, intravitreal injection of SKI-2 signifincantly reduced the thinning in the outer nuclear layer compared to the control.
Conclusions :
These findings suggested that light-damage induced the increment of synthesis of S1P in retinal cells, indicating the cause of retinal degeneration. Inhibition of these enhancement may be the therapeutic target of AMD.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.