Sphingosine Kinase-1 Is Essential for Maintaining External/Outer Limiting Membrane and Associated Adherens Junctions in the Aging Retina
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Sphingosine-1-phosphate (S1P) produced by sphingosine kinases (SPHK1 and SPHK2) is a signaling molecule involved in cell proliferation and formation of cellular junctions. In this study, we characterized the retinas of Sphk1 knockout (KO) mice by electron microscopy and immunocytochemistry. We also tested cultured Müller glia for their response to S1P. We found that S1P plays an important role in retinal and retinal pigment epithelial (RPE) structural integrity in aging mice. Ultrastructural analysis of Sphk1 KO mouse retinas aged to 15 months or raised with moderate light stress revealed a degenerated outer limiting membrane (OLM). This membrane is formed by adherens junctions between neighboring Müller glia and photoreceptor cells. We also show that Sphk1 KO mice have reduced retinal function in mice raised with moderate light stress. In vitro assays revealed that exogenous S1P modulated cytoskeletal rearrangement and increased N-cadherin production in human Müller glia cells. Aged mice also had morphological degeneration of the RPE, as well as increased lipid storage vacuoles and undigested phagosomes reminiscent of RPE in age-related macular degeneration. These findings show that SPHK1 and S1P play a vital role in the structural maintenance of the mammalian retina and retinal pigmented epithelium by supporting the formation of adherens junctions.
KeywordsRetina Outer limiting membrane Sphingosine kinase Sphingosine-1-phosphate Retinal degeneration N-cadherin
We would like to thank the services of the Imaging Core and all the hard work done by the animal facility at the Dean McGee Eye Institute. We also want to thank Ben Fowler and Julie Crane at the Oklahoma Medical Research Foundation for their help with the super-resolution microscopy and use of the Imaging Facility to do our TEM work; Dr. Koushik Mondal from Ophthalmology, UTHSC for his help in animal experiments; Dr. Jeremy Allegood, Operational Director of Lipidomics, Virginia Commonwealth University School of Medicine, Richmond, VA 23298-5048; and VCU Lipidomics/Metabolomics Core, the NIH-NCI Cancer Center Support Grant P30 CA016059 to the VCU Massey Cancer Center, as well as a shared resource grant (S10RR031535) from the National Institutes of Health in all manuscripts of which data generated by the VCU Lipidomics/Metabolomics Core is included as well as maintain NIH compliance for NCBI registration of manuscripts that utilize data derived from the VCU Lipidomics/Metabolomics core.
NAM: NIH grants EY022071, EY025256, and EY021725 (Foundation Fighting Blindness and Research to Prevent Blindness, USA). JLW: T32EY023202 (VCU Lipidomics/Metabolomics Core: NIH grants P30 CA016059 and S10 RR031535).
Compliance with Ethical Standards
Conflict of Interest
The authors declare that they have no conflicts of interest.
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