ORIGINAL ARTICLE Cell Research (2008): 1210-1219 Apaf-1-deficient fog mouse cell apoptosis involves hypo-polarization of the mitochondrial inner membrane, ATP depletion and citrate accumulationIyoko Katoh1, Shingo Sato2, Nahoko Fukunishi3, Hiroki Yoshida4, Takasuke Imai5 and Shun-ichi Kurata3 1Department of Microbiology, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Yamanashi 409-3898, Japan; 2Department of Immunoregulation, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku 113-8510, Japan; 3Redox Response Cell Biology, Medical Research Institute, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku 113-8510, Japan; 4Department of Biomolecular Sciences, Faculty of Medicine, Saga University, Saga 849-8581, Japan; 5Department of Critical Care Medicine, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku 113-8510, Japan
To explore how the intrinsic apoptosis pathway is controlled in the spontaneous fog (forebrain overgrowth) mutant mice with an Apaf1 splicing deficiency, we examined spleen and bone marrow cells from Apaf1+/+ (+/+) and Apaf1fog/fog (fog/fog) mice for initiator caspase-9 activation by cellular stresses. When the mitochondrial inner membrane potential (Δψm) was disrupted by staurosporine, +/+ cells but not fog/fog cells activated caspase-9 to cause apoptosis, indicating the lack of apoptosome (apoptosis protease activating factor 1 (Apaf-1)/cytochrome c/(d)ATP/procaspase-9) function in fog/fog cells. However, when a marginal (~20%) decrease in Δψm was caused by hydrogen peroxide (0.1 mM), peroxynitritedonor 3-morpholinosydnonimine (0.1 mM) and UV-C irradiation (20 J/m2), both +/+ and fog/fog cells triggered procaspase-9 auto-processing and its downstream cascade activation. Supporting our previous results, procaspase-9 pre-existing in the mitochondria induced its auto-processing before the cytosolic caspase activation regardless of the genotypes. Cellular ATP concentration significantly decreased under the hypoactive Δψm condition. Furthermore, we detected accumulation of citrate, a kosmotrope known to facilitate procaspase-9 dimerization, probably due to a feedback control of the Krebs cycle by the electron transfer system. Thus, mitochondrial in situ caspase-9 activation may be caused by the major metabolic reactions in response to physiological stresses, which may represent a mode of Apaf-1-independent apoptosis hypothesized from recent genetic studies. Cell Research (2008) 18:1210-1219. doi: 10.1038/cr.2008.87; published online 29 July 2008 Keywords: apoptosis, Apaf-1, caspase-9, mitochondria, citrate, ATP |
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