Aponecrosis: Morphological and biochemical exploration of a syncretic process of cell death sharing apoptosis and necrosis

A rat fibroblastic cell line (rat-1/myc-ER(TM)) was treated with different concentration of Antimycin A, a metabolic poison that affects mitochondrial respiratory chain complex III. The modes of cell death were analyzed by ti me-lapse videomicroscopy, in situ end-labeling (ISEL) technique, and ultras tructural analysis. Intracellular ATP levels were also measured in order to detect whether the energetic stores were determinant for the type of cell death. It was found that while apoptosis was the prevalent cell death in th e fibroblasts treated with low doses, 100 or 200 mu M Antimycin A, a new ty pe of cell demise that shared dynamic, molecular, and morphological feature s with both apoptosis and necrosis represents the most common cell death wh en the cells were exposed to high doses, 300 or 400 mu M, of the hypoxic st imulus. This new type of cell death has been chimerically termed aponecrosi s. The inhibition of caspase 3, an enzyme critical for the apoptotic DNA de gradation, caused a clear shift from aponecrosis to necrosis in the cell cu lture, suggesting that this new type of cell death could account for an inc omplete execution of the apoptotic program and the following degeneration i n necrosis. After being treated with higher doses, i.e., 1000 mu M Antimyci n A, almost all of the cells died by true necrosis. The analysis of the cel lular energetic stores showed that the levels of ATP were a primary determi nant in directing toward active cell death (apoptosis), aponecrosis, or nec rosis. We conclude that chemically induced hypoxia produces different types of cell death depending on the intensity of the insult and on the ATP avai lability of the cell, and that the classic apoptosis and necrosis may repre sent only two extremes of a continuum of intermediate forms of cell demise. J. Cell. Physiol. 182:41-49, 2000. (C) 2000 Wiley-Liss, Inc.