Ceramide is a mediator of apoptosis in retina photoreceptors

Invest Ophthalmol Vis Sci. 2006 Apr;47(4):1658-68. doi: 10.1167/iovs.05-1310.

Abstract

Purpose: The precise mechanisms involved in photoreceptor apoptosis are still unclear. In the present study, the role of ceramide, a sphingolipid precursor that induces apoptosis on cellular stress, was investigated in relation to the activation of cell death in photoreceptors.

Methods: Rat retina neuronal cultures, with or without docosahexaenoic acid (DHA), were treated with the ceramide analogue acetylsphingosine (C2-ceramide), and with a glucosylceramide synthase inhibitor. Ceramide synthesis in cultures treated with the oxidant paraquat was evaluated with [3H]palmitate. The effect of inhibitors of ceramide de novo synthesis, fumonisin B1 and cycloserine, on photoreceptor apoptosis was investigated. Apoptosis, mitochondrial membrane potential, and Bcl-2 expression were determined.

Results: Addition of C2-ceramide induced photoreceptor apoptosis. Paraquat increased formation of [3H]ceramide in photoreceptors, compared with the control, whereas inhibition of ceramide synthesis, immediately before paraquat treatment, prevented paraquat-induced photoreceptor apoptosis. Fumonisin also reduced photoreceptor apoptosis during early development in vitro. DHA, the retina major polyunsaturated fatty acid, which protects photoreceptors from oxidative stress-induced apoptosis, completely blocked C2-ceramide-induced photoreceptor death, simultaneously increasing Bcl-2 expression. Inhibiting glucosylceramide synthase, which catalyzes ceramide glucosylation, before ceramide or paraquat treatment blocked DHA's protective effect.

Conclusions: The results suggest that oxidative stress stimulated an increase in ceramide levels that induced photoreceptor apoptosis. DHA prevented oxidative stress and ceramide damage by upregulating Bcl-2 expression and glucosylating ceramide, thus decreasing its intracellular concentration. This shows for the first time that ceramide is a critical mediator for triggering photoreceptor apoptosis in mammalian retina and suggests that modulating ceramide levels may provide a therapeutic tool for preventing photoreceptor death in neurodegenerative diseases.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis / drug effects*
  • Ceramides / metabolism
  • Cycloserine / pharmacology
  • Docosahexaenoic Acids / pharmacology
  • Enzyme Inhibitors / pharmacology*
  • Fumonisins / pharmacology
  • Glucosyltransferases / antagonists & inhibitors
  • Glucosyltransferases / metabolism
  • Immunohistochemistry
  • Membrane Potentials / drug effects
  • Mitochondria / drug effects
  • Oxidative Stress
  • Paraquat / pharmacology
  • Photoreceptor Cells, Vertebrate / metabolism
  • Photoreceptor Cells, Vertebrate / pathology*
  • Proto-Oncogene Proteins c-bcl-2 / metabolism
  • Rats
  • Rats, Wistar
  • Sphingosine / analogs & derivatives*
  • Sphingosine / pharmacology

Substances

  • Ceramides
  • Enzyme Inhibitors
  • Fumonisins
  • N-acetylsphingosine
  • Proto-Oncogene Proteins c-bcl-2
  • Docosahexaenoic Acids
  • fumonisin B1
  • Cycloserine
  • Glucosyltransferases
  • ceramide glucosyltransferase
  • Sphingosine
  • Paraquat