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Apoptosis_Physiology_and_Pathology.pdf
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THOMAS D. MULLEN, RUSSELL W. JENKINS, LINA M. OBEID, AND YUSUF A. HANNUN

ceramide is only one module. On the basis of current understanding, one might speculate that those events that specifically require membrane involvement (e.g., receptor signaling, lysosomal permeabilization, mitochondrial outer membrane permeabilization) are more likely to depend on ceramide signaling. This final question will only be answered when all of the previous questions are answered and the pieces of the conceptual puzzle are amassed and assembled.

6. SUMMARY

Lipid signaling is an essential component of multiple cell signaling processes. In the context of programmed cell death, the sphingolipid ceramide is generated by multiple mechanisms to promote cell death.

Sphingolipid metabolism is a complex and highly regulated process with ceramide being a crossroads for the generation and breakdown of multiple sphingolipid species.

Cellular levels of ceramide and its metabolites are regulated by enzymes of sphingolipid metabolism through multiple enzymatic pathways, including de novo synthesis, sphingomyelinase-mediated sphingomyelin hydrolysis, and re-acylation of free sphingosine via the salvage pathway.

Ceramide accumulates in cells and tissues undergoing apoptosis in response to a wide variety of stimuli.

An increase in ceramide, whether endogenously or exogenously, induces cell death or sensitizes cells to death.

Elimination of ceramide accumulation prevents programmed cell death in a variety of cell death models.

aSMase-mediated ceramide production via SM hydrolysis at the plasma membrane and/or the endolysosomal system is relatively acute after stimulation and modulates receptor-mediated and non–receptor- mediated pathways.

An increase in the de novo generation of ceramide, due to SPT and/or CerS activation, occurs after several hours of proapoptotic stimulation and may be regulated by p53 and Bcl-2 family members.

SUGGESTED READINGS

Introduction to Bioactive Lipids

Hannun, Y.A. and L.M. Obeid. Principles of bioactive lipid signalling: lessons from sphingolipids. Nat Rev Mol Cell Biol, 2008. 9(2): pp. 139–50. A comprehensive discussion of basic properties of sphingolipids as bioactive molecules.

van Meer, G., D.R. Voelker, and G.W. Feigenson. Membrane lipids: where they are and how they behave. Nat Rev Mol Cell Biol, 2008. 9(2): pp. 112–24. An excellent review covering basic principles of lipids in the cell, including the importance of localization.

Wymann, M.P. and R. Schneiter. Lipid signalling in disease. Nat Rev Mol Cell Biol, 2008. 9(2): pp. 162–76. Highlights the crucial roles of various lipids, including ceramide, in common diseases.

Sphingolipid Metabolism:

Members of the Sphingolipid Family

Goni, F.M. and A. Alonso. Sphingomyelinases: enzymology and membrane activity. FEBS Lett, 2002. 531(1): pp. 38–46.

Pewzner-Jung, Y., S. Ben-Dor, and A.H. Futerman. When do Lasses (longevity assurance genes) become CerS (ceramide synthases)? Insights into the regulation of ceramide synthesis. J Biol Chem, 2006. 281(35): pp. 25001–5. Provides a concise review about ceramide synthases.

Zheng, W., et al. Ceramides and other bioactive sphingolipid backbones in health and disease: lipidomic analysis, metabolism and roles in membrane structure, dynamics, signaling and autophagy. Biochim Biophys Acta, 2006. 1758(12): pp. 1864–84. Excellent overview of sphingolipid metabolism.

Sphingolipid as Mediators of Apoptotic Signaling

Kolesnick, R. and Z. Fuks. Radiation and ceramide-induced apoptosis. Oncogene, 2003. 22(37): pp. 5897–906. An excellent review of the role of SMase and de novo ceramide pathways in radiation-induced death.

Obeid, L.M., et al. Programmed cell death induced by ceramide.

Science, 1993. 259(5102): pp. 1769–71. The first report that exogenous ceramide induces cell death.

Smith, E.L. and E.H. Schuchman. The unexpected role of acid sphingomyelinase in cell death and the pathophysiology of common diseases. FASEB J, 2008. 22(10): pp. 3419–31. A comprehensive review of the role of aSMase in cell death with an emphasis on human diseases.

van Blitterswijk, W.J., et al. Ceramide: second messenger or modulator of membrane structure and dynamics? Biochem J, 2003. 369(Pt 2): pp. 199–211. A fascinating review discussing the controversial role of ceramide as a putative second messenger and as a modulator of membrane structure and function.

Ceramide mediates apoptotic cell death: role of particular enzyme systems

aSMase/ceramide pathway

Bezombes, C., et al. Lysosomal sphingomyelinase is not solicited for apoptosis signaling. FASEB J, 2001. 15(2): pp. 297–9.

Garcia-Barros, M., et al. Tumor response to radiotherapy regulated by endothelial cell apoptosis. Science, 2003. 300(5622): pp. 1155–9.

CERAMIDE AND LIPID MEDIATORS IN APOPTOSIS

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Haimovitz-Friedman, A., et al. Lipopolysaccharide induces disseminated endothelial apoptosis requiring ceramide generation. J Exp Med, 1997. 186(11): pp. 1831–41.

Lang, P.A., et al. Liver cell death and anemia in Wilson disease involve acid sphingomyelinase and ceramide. Nat Med, 2007. 13(2): pp. 164–70.

Lin, T., et al. Role of acidic sphingomyelinase in Fas/CD95mediated cell death. J Biol Chem, 2000. 275(12): pp. 8657–63.

Lozano, J., et al. Cell autonomous apoptosis defects in acid sphingomyelinase knockout fibroblasts. J Biol Chem, 2001. 276(1): pp: 442–8.

Nix, M. and Stoffel, W. Perturbation of membrane microdomains reduces mitogenic signaling and increases susceptibility to apoptosis after T cell receptor stimulation. Cell Death Differ, 2000. 7(5): pp. 413–24.

Osawa, Y., et al. Roles for C16-ceramide and sphingosine 1- phosphate in regulating hepatocyte apoptosis in response to tumor necrosis factor-alpha. J Biol Chem, 2005. 280(30): pp. 27879–87.

Santana, P., et al. Acid sphingomyelinase-deficient human lymphoblasts and mice are defective in radiation-induced apoptosis. Cell, 1996. 86(2): pp. 189–99.

De novo/salvage ceramide pathway

Bose, R., et al. Ceramide synthase mediates daunorubicininduced apoptosis: an alternative mechanism for generating death signals. Cell, 1995. 82(3): pp. 405–14. First description of de novo ceramide-mediated cell death.

Carracedo, A., et al. The stress-regulated protein p8 mediates cannabinoid-induced apoptosis of tumor cells. Cancer Cell, 2006. 9(4): pp. 301–12.

Ch’ang, H.J., et al. ATM regulates target switching to escalating doses of radiation in the intestines. Nat Med, 2005. 11(5): pp. 484–90. Provides evidence for aSMaseand CerS-mediated cell death in the same experimental model.

Dbaibo, G.S., et al. p53-dependent ceramide response to genotoxic stress. J Clin Invest, 1998. 102(2): pp. 329–39.

Kitatani, K., J. Idkowiak-Baldys, and Y.A. Hannun. The sphingolipid salvage pathway in ceramide metabolism and signaling. Cell Signal, 2008. 20(6): pp. 1010–8.

Petrache, I., et al. Ceramide upregulation causes pulmonary cell apoptosis and emphysema-like disease in mice. Nat Med, 2005,11(5): pp. 491–498.

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