Ceramide-1-phosphate: a new mediator of survival and development in retina photoreceptors

Abstract

Purpose. Simple sphingolipids control crucial cellular processes in several cell types. We demonstrated that sphingolipids such as ceramide, sphingosine and sphingosine-1-phosphate are key mediators in the regulation of survival, differentiation and proliferation of retina photoreceptors. Ceramide-1-phosphate (C1P) regulates growth and survival in several cell types; however, little is known concerning its functions in the retina. We here explored whether C1P also participated in controlling photoreceptor development. Methods. Rat retina neuronal cultures were supplemented with 1-10 µM C1P. Proliferation was determined by evaluating 5-bromo-2-deoxyuridine (BrdU) uptake and number of mitotic figures and differentiation by establishing opsin and peripherin expression by immunocytochemistry and Western blot. Apoptosis was inhibited with the caspase pan-inhibitor ZVADFMK and evaluated by TUNEL assay, propidium iodide/annexin V and DAPI labeling. Preservation of mitochondrial membrane potential was evaluated. Results. C1P enhanced BrdU uptake and increased mitosis in retinal progenitors. C1P addition advanced photoreceptor differentiation, enhancing opsin and peripherin expression and stimulating development of apical processes, in which these proteins were concentrated. In the absence of their trophic factors, photoreceptors degenerate after 4 days in vitro and at day 6 almost 50% of photoreceptors were apoptotic; C1P decreased photoreceptor apoptosis, reducing this percentage by half. Inhibiting caspase activity reduced photoreceptor apoptosis in controls but did not increase opsin expression, implying C1P has separate effects on differentiation and survival. Conclusions. These results suggest for the first time that C1P is a novel mediator that plays multiple functions in photoreceptors, initially regulating their proliferation and then promoting their survival and differentiation.