DISTINCT ALTERATIONS IN MITOCHONDRIAL MASS AND FUNCTION CHARACTERIZE DIFFERENT MODELS OF APOPTOSIS

Recent studies have shown that reduction in mitochondrial membrane pot ential (Delta Psi(m)) and generation of reactive oxygen species are ea rly events in apoptosis, In this study, we present two different model s of apoptotic cell death, Chinese hamster ovary (CHO) cells treated w ith aphidicolin and dexamethasone-treated 2B4 T-cell hybridoma cells, which display opposing mitochondrial changes. CHO cells arrested at G1 /S with aphidicolin have a progressive increase in mitochondria mass a nd number, assessed by how cytometry and fluorescent microscopy with m itochondria-specific probes, The increase in mitochondrial mass was no t accompanied by a gain in net cellular mitochondrial membrane potenti al, consistent with an accumulation of relatively depolarized mitochon dria. Fluorescent microscopy demonstrated an increased content of low Delta Psi(m) mitochondria in aphidicolin-treated CHO cells, but high D elta Psi(m) mitochondria were also present and remained stable in numb er, Mitochondrial mass correlated with decreased clonogenicity of aphi dicolin-treated CHO cells, Cycloheximide prevented both the proliferat ion of mitochondria and subsequent cell death, In contrast, dexamethas one treatment of 2B4 T-cell hybridoma cells caused a decrease in Delta Psi(m) without mitochondrial proliferation, Cycloheximide and Bcl-2 o verexpression inhibited the loss of Delta Psi(m), as well as apoptosis . In both models, cell death was associated with a decrease in mitocho ndrial potential relative to mitochondrial mass, suggesting that an ac cumulation of damaged or dysfunctional mitochondria had occurred. (C) 1998 Academic Press.