cytochrome-c-t and Niemann-Pick-Diseases

An elevated level of cholesterol in mitochondrial membranes of Niemann-Pick disease type C1 (NPC1) mouse brains and neural cells has been found to cause mitochondrial dysfunction. In this study, we demonstrate that inhibition of intracellular cholesterol trafficking in primary neurons by class 2 amphiphiles, which mimics the major biochemical and cellular feature of NPC1, led to not only impaired mitochondrial function but also activation of the mitochondrial apoptosis pathway. In activation of this pathway both cytochrome c and Smac/Diablo were released but apoptosis-inducing factor (AIF) was not involved. Treatment of the neurons with taurine, a caspase 9-specific inhibitor, could prevent the amphiphile-induced apoptotic cell death, suggesting that formation of apoptosome, followed by caspase 9 and caspase 3 activation, might play a critical role in the neuronal death pathway. Taken together, the mitochondria-dependent death cascade induced by blocking intracellular cholesterol trafficking was caspase dependent. The findings provide clues for both understanding the molecular basis of neurodegeneration in NPC1 disease and developing therapeutic strategies for treatment of this disorder.

Topics: Animals; Apoptosis; Apoptosis Regulatory Proteins; Carrier Proteins; Caspase 3; Caspase 9; Caspase Inhibitors; Caspases; Cells, Cultured; Cerebral Cortex; Cholesterol; Cytochromes c; Enzyme Activation; Mice; Mitochondria; Mitochondrial Proteins; Nerve Degeneration; Neurons; Niemann-Pick Diseases; Protein Transport; Signal Transduction; Surface-Active Agents

Ultraviolet light-induced apoptosis can be caused by DNA damage but also involves immediate-early cell death cascades characteristic of death receptor signaling. Here we show that the UV light-induced apoptotic signaling pathway is unique, targeting Bax activation at the mitochondrial membrane independent of caspase-8 or cathepsin D activity. Cells deficient in acid sphingomyelinase (ASMase) do not show UV light-induced Bax activation, cytochrome c release, or apoptosis. In ASMase-deficient cells, the apoptotic UV light response is restored by stable or transient expression of human ASMase. Bax conformational change in ASMase(-/-) cells is also caused by synthetic C(16)-ceramide acting on intact cells or isolated mitochondria. The results suggest that UV light-triggered ASMase activation is essentially required for Bax conformational change leading to mitochondrial release of pro-apoptotic factors like cytochrome c and Smac.

Topics: Apoptosis; bcl-2-Associated X Protein; Caspase 3; Caspase 8; Caspases; Cathepsin D; Cell Membrane; Cell-Free System; Ceramides; Cytochromes c; Fluorescent Antibody Technique; Gene Expression; Green Fluorescent Proteins; HeLa Cells; Humans; Mitochondria; Niemann-Pick Diseases; Protein Conformation; Proto-Oncogene Proteins c-bcl-2; RNA, Small Interfering; Signal Transduction; Sphingomyelin Phosphodiesterase; Ultraviolet Rays