Lack of ceramide synthase 5 protects retinal ganglion cells from ocular hypertensive injury.

Ceramides with varying acyl-chain lengths can have unique biological actions and hence, cellular responses to ceramides may depend not on their overall concentration but on that of individual ceramide species. The purpose of this study was to determine individual ceramide species impacting retinal ganglion cell (RGC) loss under the ocular hypertensive condition. Induced pluripotent stem cell (iPSC)-derived RGCs and primary cultures of human astrocytes were used to determine the effect of individual ceramide species on both RGC viability and astrocyte secretion of inflammatory cytokines in vitro. In in vivo experiments with wild-type (WT) and ceramide synthase 5 (CerS5) knockout mice, intraocular pressure was unilaterally elevated with microbead injection. Retinal function and morphology were evaluated using pattern electroretinography (pERG) and immunofluorescence, respectively. Ceramide levels were determined by LC-MS/MS analysis. Exposure to C16:0-, C18:0-, C18:1-, C20:0- and C24:0-ceramides significantly reduces RGC viability in vitro, with the very long chain C24:0-ceramide being the most neurotoxic; treatment with C18:0-, C18:1- and C24:0-ceramides stimulates an increase of TNF-α secretion by astrocytes. The retinas of CerS5 KO mice have significantly reduced levels of C16:0- and C18:1-ceramides compared to WT; ocular hypertensive eyes of these mice maintain higher pERG amplitudes and RGC numbers compared to WT. Individual ceramides with different chain lengths have different effects on RGCs and astrocytes. Our results demonstrate that suppressing C16:0- and C18:1-ceramide species effectively protects RGCs against ocular hypertensive injury. These results provide a basis for targeting specific ceramide species in the treatment of glaucoma.
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