Activation of de novo synthesis of ceramide induces photoreceptor apoptosis

MIRANDA GE, ABRAHAN CE, GERMAN OL AND ROTSTEIN NP.

Pinamar, Bs. As., Argentina

Congreso; Reunión conjunta de la Panamerican Association for Biochemistry and Molecular Biology (PABMB), SAIB y SAN; 2005

PABMB, SAIB, SAN

ACTIVATION OF DE NOVO SYNTHESIS OF CERAMIDE  INDUCES PHOTORECEPTOR APOPTOSIS Miranda, Gisela; Abrahan, Carolina; German, Lorena and Rotstein Nora. INIBIBB, UNS-CONICET, Bahía Blanca, Argentina. E-mail: gmiranda@criba.edu.ar  The precise mechanisms leading to photoreceptor death in the retina are still unknow. We investigated whether an increase in  ceramide, a sphingolipid known to trigger apoptosis upon cell stress, activates apoptosis in rat retina photoreceptors in culture. Paraquat (PQ)-induced oxidative stress led to the accumulation of newly synthesized [3H]ceramide in photoreceptors, which almost doubled the amount found in controls after 2 and 4 hs of PQ addition, but did not affect the amount of [3H]sphingomyelin. Ceramide increase was paralel to the onset of photoreceptor apoptosis, evaluated by cyto-chemistry.  We previously showed that inhibiting ceramide synthesis with fumonisin B1 (FB) prevented photoreceptor apoptosis upon PQ addition. We here demonstrate that cycloserine, which blocks the first step in ceramide synthesis synthesis, added 30 min before PQ treatment, completely blocked PQ-induced photoreceptor apoptosis. FB addition at day 0 partially diminished photoreceptor apoptosis by day 6 in vitro, which otherwise occurred in the absence of photoreceptor trophic factors. These results suggest that an increase in ceramide levels triggers photoreceptor apoptosis in different situations of cell stress, and that this increase arises in the stimulation of de novo synthesis of ceramide.