Article

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

Hospital Clínic i Provincial and Centro de Investigación Biomédica en Red de Enfermedades Hepaticas y Digestivas, Instituto Investigaciones Biomédicas Barcelona, Consejo Superior de Investigaciones Científicas, 08036-Barcelona, Spain.
The Journal of Lipid Research (impact factor: 5.56). 10/2007; 48(9):1924-35. DOI:10.1194/jlr.M700069-JLR200 pp.1924-35
Source: PubMed

ABSTRACT 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.

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Keywords

apoptotic effects
 
bSMase-induced ceramide
 
caspase-3 activation
 
cell growth
 
cellular processes
 
ceramide generation
 
ceramide levels
 
cytochrome c
 
dose-dependent manner
 
exogenous bacterial neutral sphingomyelinase
 
germinal vesicle breakdown indicative
 
human placenta recapitulated
 
increased ceramide levels
 
intracellular site
 
mature stage VI oocytes
 
mitochondrial downstream events
 
neutral Bacillus cereus sphingomyelinase
 
oocyte maturation
 
reactive oxygen species
 
Xenopus laevis oocytes