Ceramide is a key mediator in photoreceptor apoptosis

ROTSTEIN N., GERMAN L., MIRANDA G. AND ABRAHAN C.

Fort Lauderdale, Florida, EEUU

Congreso; Association For Research In Vision and Ophthalmology (ARVO) Annual Meeting; 2005

ARVO

Ceramide is a Key Mediator in the Apoptosis of Retina Photoreceptors Rotstein N., German L., Abrahan C. and Miranda G. Instituto de Investigaciones Bioquimicas, 8000Bahia Blanca, Buenos Aires, Argentina. inrotste@criba.edu.ar Oxidative stress has a critical role in triggering photoreceptor apoptosis. However, the precise molecular mechanisms that induce the death of these cells are still unclear. In this work we demonstrate that ceramide, a sphingolipid that activates apoptosis in response to cellular stress, participates in the induction of photoreceptor apoptosis upon oxidative damage. Treatment of 3-day rat retina neuronal cultures with the cell permeable ceramide analog, acetyl-sphingosine (C2-ceramide) markedly increased apoptosis in photoreceptor and amacrine neurons, decreasing mitochondrial membrane integrity. We had previously shown that oxidative stress, generated by the oxidant paraquat (PQ) induced neuronal apoptosis. Inhibition of sphingolipid synthesis with fumonisin B1 substantially reduced photoreceptor apoptosis upon PQ treatment, preserving mitochondrial membrane integrity. This suggests that an increase in ceramide synthesis triggers photoreceptor apoptosis. Docosahexaenoic fatty acid (DHA), retina major polyunsaturated fatty acid, which protects photoreceptors from apoptosis induced by oxidative stress, completely prevented C2-ceramide-induced photoreceptor death. DHA increased Bcl-2 expression in photoreceptors and precluded mitochondrial depolarization. Inhibition of glucosylceramide synthase, which catalyzes ceramide glucosylation thus diminishing ceramide levels, before C2-ceramide or PQ treatment, blocked DHA protective effect. As a whole these results suggest that oxidative stress increases ceramide synthesis, which in turn triggers photoreceptor apoptosis. DHA prevents oxidative stress and ceramide deleterious effects by enhancing Bcl-2 expression and simultaneously reducing ceramide endogenous levels, by increasing ceramide glucosylation. In summary, this work shows for the first time that ceramide is a key mediator in the activation of photoreceptor apoptosis in mammalian retina. It also suggests that modulating ceramide levels by regulating the enzymes involved in sphingolipid metabolism might offer a therapeutic strategy to prevent photoreceptor death in neurodegenerative diseases.