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Journal of Lipid Research, Vol. 48, 1924-1935, September 2007
Copyright © 2007 by American Society for Biochemistry and Molecular Biology

Neutral sphingomyelinase-induced ceramide triggers germinal vesicle breakdown and oxidant-dependent apoptosis in Xenopus laevis oocytes

Olga Coll, Albert Morales, José C. Fernández-Checa^1,2 and Carmen Garcia-Ruiz^1,2

Liver Unit and Centro de Investigaciones Biomédicas Esther Koplowitz, Institut de Malalties Digestives i Metaboliques, Hospital Clínic i Provincial and Centro de Investigación Biomédica en Red de Enfermedades Hepaticas y Digestivas, Instituto Investigaciones Biomédicas August Pi i Sunyer and Department of Cell Death and Proliferation, Instituto Investigaciones Biomédicas Barcelona, Consejo Superior de Investigaciones Científicas, 08036-Barcelona, Spain

Published, JLR Papers in Press, June 7, 2007.

¹ J. C. Fernández-Checa and C. Garcia-Ruiz contributed equally to this study.

² To whom correspondence should be addressed. e-mail: checa229{at}yahoo.com. (J.C.F-C.); cgrbam{at}iibb.csic.es (C.G-R.)

Ceramide regulates many cellular processes, including cell growth, differentiation, and apoptosis. Although the effects of exogenous bacterial neutral sphingomyelinase (SMase) in Xenopus laevis oocytes have been investigated, its microinjection into oocytes has not been reported previously. Thus, we compared the incubation versus microinjection of the neutral Bacillus cereus sphingomyelinase (bSMase) to examine whether the topology of ceramide generation determines its effects on the fate of oocytes. In agreement with previous findings, incubation of mature stage VI oocytes with bSMase increased ceramide levels in oocyte extracts over time, causing the germinal vesicle breakdown indicative of maturation, without evidence of cytotoxicity. In contrast, bSMase microinjection, which increased ceramide levels in a time- and dose-dependent manner, resulted in oocyte apoptosis characterized by reactive oxygen species (ROS) generation, reduced glutathione (GSH) depletion in cytosol and mitochondria, release of cytochrome c and Smac/Diablo from mitochondria, and caspase-3 activation. Microinjection of acidic SMase from human placenta recapitulated the apoptotic effects of bSMase microinjection. Preincubation of oocytes with GSH-ethyl ester before bSMase microinjection prevented ROS generation and mitochondrial downstream events, thus protecting oocytes from bSMase-induced death. These findings show a divergent action of bSMase-induced ceramide on oocyte maturation or apoptosis depending on the intracellular site where ceramide is generated.

Supplementary key words mitochondria • reactive oxygen species • cell death • reduced glutathione

Abbreviations: Ac-DEVD-AMC, Ac-Asp-Glu-Val-Asp-7-amino-4-trifluoremethyl coumarin; bSMase, Bacillus cereus sphingomyelinase; GCS, glucosylceramide synthase; GSH, reduced glutathione; GVBD, germinal vesicle breakdown; hSMase, human placenta sphingomyelinase; NSMase, neutral sphingomyelinase; PDMP, 1-phenyl-2-decanoylamino-3-morpholino-1-propanol; ROS, reactive oxygen species; SMase, sphingomyelinase; TNF, tumor necrosis factor

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