The yeast Saccharomyces cerevisiae undergoes a mitochondrial-dependent programmed cell death in response to different stimuli, such as acetic acid, with features similar to those of mammalian apoptosis. However, the upstream signaling events in this process, including those leading to mitochondrial membrane permeabilization, are still poorly characterized. Changes in sphingolipid metabolism have been linked to modulation of apoptosis in both yeast and mammalian cells, and ceramides have been detected in mitochondria upon apoptotic stimuli. In this study, we aimed to characterize the contribution of enzymes involved in ceramide metabolism to apoptotic cell death induced by acetic acid. We show that isc1Δ and lag1Δ mutants, lacking inositol phosphosphingolipid phospholipase C and ceramide synthase, respectively, exhibited a higher resistance to acetic acid that was associated with lower levels of some phytoceramide species. Consistently, these mutant cells displayed lower levels of ROS production and reduced mitochondrial alterations, such as mitochondrial fragmentation and degradation, and decreased translocation of cytochrome c into the cytosol in response to acetic acid. These results suggest that ceramide production contributes to cell death induced by acetic acid, especially through hydrolysis of complex sphingolipids catalyzed by Isc1p and de novo synthesis catalyzed by Lag1p, and provide the first in vivo indication of its involvement in mitochondrial outer membrane permeabilization in yeast.
It has been established that sphingolipids are engaged in the regulation of apoptosis both as direct executors and as signalling molecules. However, the peculiarities of this class of bioactive lipids, namely the interconnectivity of their metabolic pathways, the specific subcellular localization where they are generated and the transport mechanisms involved, introduce a considerably high level of complexity in deciphering their role in the signalling and regulation of programmed cell death. Although yeast is undeniably a simple model, the conservation of the sphingolipid metabolism and of the core machinery engaged in regulated cell death has already provided valuable clues to the understanding of metabolic pathways involved in distinct cellular processes, including apoptosis. It can be anticipated that studies using this model system will further unravel mechanisms underlying the regulation of apoptosis by sphingolipids and contribute to novel therapeutic strategies against serious human diseases associated with dysfunction of sphingolipid-dependent cell death programmes.
a b s t r a c tWe have previously shown that the yeast Cathepsin D (CatD) Pep4p translocates from the vacuole to the cytosol during acetic acid-induced apoptosis and is required for efficient mitochondrial degradation, though its specific role in this process is still elusive. Here, we show that the protective role of Pep4p in acetic acid-induced apoptosis depends on its catalytic activity and is independent of the yeast voltage-dependent anion channel Por1p (which has no role on mitochondrial degradation) but dependent on AAC proteins, the yeast adenine nucleotide translocator. Our results demonstrate a differential interplay between yeast vacuolar CatD and mitochondrial proteins involved in apoptosis regulation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.