Synthesis of sphingosine is required for oxidative stress-induced apoptosis of photoreceptors

ABRAHAN C, MIRANDA, G, POLITI, L AND ROTSTEIN NP

INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE

IOVS Editorial

Año: 2009

0146-0404

AbstractPURPOSE. Oxidative stress is involved in inducing apoptosis of photoreceptors in manyretinal neurodegenerative diseases. We have previously shown that oxidative stress increasesin photoreceptors the synthesis of ceramide, a sphingolipid precursor that then activatesapoptosis. In several cell types ceramide is converted by ceramidases to sphingosine (Sph),another apoptosis mediator; hence, we investigated whether Sph participates in triggeringphotoreceptor apoptosis.METHODS. Rat retina neurons were incubated with [3H]palmitic acid and treated with theoxidant paraquat (PQ) to evaluate Sph synthesis. Sph was added to cultures with or withoutdocosahexaenoic acid (DHA), the major retina polyunsaturated fatty acid and a photoreceptorsurvival factor, to evaluate apoptosis. Synthesis of Sph and sphingosine-1-phosphate (S1P), aprosurvival signal, were inhibited with alkaline ceramidase or sphingosine kinase inhibitors,respectively, before adding PQ, C2-ceramide or Sph. Apoptosis, mitochondrial membranepolarization, cytochrome c localization and reactive oxygen species (ROS) production weredetermined.RESULTS. PQ increased [3H]Sph synthesis in photoreceptors and blocking this synthesis byinhibiting alkaline ceramidase decreased PQ-induced apoptosis. Sph addition inducedphotoreceptor apoptosis, increased ROS production and promoted cytochrome C release frommitochondria. While DHA prevented this apoptosis, inhibiting Sph conversion to S1Pblocked DHA protection.CONCLUSIONS. These results suggest that oxidative stress enhances formation ofceramide and its subsequent breakdown to Sph; ceramide and/or Sph would then triggerphotoreceptor apoptosis. Preventing Sph synthesis or promoting its phosphorylation to S1Prescued photoreceptors, suggesting that Sph is a mediator of their apoptosis and modulationof Sph metabolism might be crucial for promoting photoreceptor survival