4812 - A0028 Gangliosides in the retina: a comparative inventory with brain and other ocular structures

Purpose: Gangliosides (GG) make an extremely diverse family of glycosphingolipids particularly abundant in the brain and neural tissues. While it is known that alterations in GG metabolism are associated with visual defects, the precise biological roles of these compounds in the retina are still largely unknown. In this context, we performed an exhaustive inventory and thorough characterization of the human eye GG aiming to reveal specificities and common features of the retina compared to other ocular tissues and brain. Methods: Retina, RPE/Choroid, ciliary body, optic nerve and brain samples were collected from deceased human donors (N=7). GG were extracted and analysed by a comprehensive approach relying on various techniques. First, GG content and class composition were assessed by high-performance thin layer chromatography followed by colorimetric revelation. Second, identification and relative quantification of the different ceramide types represented in each GG class were achieved using liquid chromatography coupled to mass spectrometry. Finally, high-resolution mass spectrometry allowed for the identification of original GG classes and structural characterization of the ceramide moieties (sphingoid base and fatty acid). Results: Retina contained the highest amount of GG among the ocular tissues tested, although much less than brain. It also presented with a wide diversity of GG classes. As other types of nervous tissues, the retina contained high levels of tetraosylGG but the prominence of GD3, GT3 and acetylated GT3 appeared as a specificity of this tissue. Retina also exhibited the largest diversity of ceramide types sharing common features with brain. They both had especially high proportions of monounsaturated ceramides and consecutively low proportions of polyunsaturated ceramides, as well as low proportions of ceramides shorter than 36 carbons or longer than 41 carbons. Moreover, GG of the retina contained 4 different types of sphingoid bases: mostly d18:1 as every other tissues but also significant levels of d20:1 as the brain and optic nerve and in minor proportions d16:1 and d18:2 also found in ciliary body.