Mitochondria are selectively eliminated from eukaryotic cells after blockade of caspases during apoptosis

Abstract

Pan caspase inhibitors are potentially powerful cell-protective agents that block apoptosis in response to a wide variety of insults that cause tissue degeneration. In many conditions, however, the blockade of apoptosis by caspase inhibitors does not permit long-term cell survival, but the reasons are not entirely clear. Here we show that the blockade of apoptosis by Boc.Aspartyl(O-methyl)CH2F can result in the highly selective elimination of the entire cohort of mitochondria, including mitochondrial DNA, from both neurons and HeLa cells, irrespective of the stimulus used to trigger apoptosis. In cells that lose their mitochondria, the nuclear DNA, Golgi apparatus, endoplasmic reticulum, centrioles, and plasma membrane remain undamaged. The capacity to remove mitochondria is both specific and regulated since mitochondrial loss in neurons is completely prevented by the expression of the antiapoptotic protein Bcl-2 and partially suppressed by the autolysosomal inhibitor bafilomycin. Cells without mitochondria are more tolerant to an anaerobic environment but are essentially irreversibly committed to death. Prevention of mitochondrial loss may be crucial for the long-term regeneration of tissues emerging from an apoptotic episode in which death was prevented by caspase blockade.

Impairing the bioenergetic status and the biogenesis of mitochondria triggers mitophagy in yeast

“…During apoptosis, mitochondria are acknowledged as a central element; recently, some reports have suggested the involvement of mitochondria in autophagy also. [16][17][18][19] Here, we report for the first time, the occurrence of autophagy as a consequence of a physiological mitochondrial dysfunction in yeast, resulting from either anaerobic and heat stress growth of a FMC1 null mutant or anaerobic growth of a strain carrying a point mutation in the ATP2 gene. This mitochondrial dysfunction results in the collapse of the electrical potential across the mitochondrial inner membrane (DC), while not decreasing the cellular ATP concentration.…”

Mitochondrial factors with dual roles in death and survival

“…Mitochondrial fragmentation and/or other morphological changes may cause or result from damage to mitochondria that subsequently leads to malfunction and degradation of mitochondria. The degradation of mitochondria was suggested to represent the commitment point in the cell death pathway in some cell types (Xue et al, 2001;Tolkovsky et al, 2002;Fannjiang et al, 2004).…”

Redundant cell death mechanisms as relics and backups

“…22 Caspase inhibition has also been shown to lead to a switch from apoptosis to necrosis in, for example, thymocytes responding to DNA damage 23 or from apoptosis to autophagic cell death in, for example, growth factor-deprived neurons. 24 Furthermore, conditions that normally induce apoptosis through cellular stress (e.g. DNA damage or inhibition of protein kinases with staurosporine) induce necrosis when ATP supply is limited.…”

“…59 One of the few diseases in which caspase inhibitors may yield convincing preclinical effects is septic shock, 60 which involves the contribution of caspases, not only as cellular demolition enzymes but also for the biosynthesis of proinflammatory cytokines. Thus, although caspase inhibition can successfully prevent the phenotypic manifestation of apoptosis, it often does not prevent cell death, which is likely to be executed through different mechanisms (including apoptosis-like cell death, autophagy and necrosis) 5,23,24,34,61 and perhaps through phagocytic recognition and destruction. 62,63 As mentioned above, it is possible that different cell types present in the same organism differ in their potential to execute cell death through distinct mechanisms.…”

“…Serial unmasking is conceivable, whereby a cell usually dying from apoptosis might shift to autophagic death when caspases are inhibited and to necrosis when, in addition, Atg genes are inhibited. Caspase inhibition must either be combined with additional inhibitors (for instance of autophagy) to rescue cells from death 22,24 or cell rescue must be attempted by targeting upstream events, perhaps in particular mitochondrial events. Thus, gene therapies and pharmacological agents capable of suppressing the cell death-associated mitochondrial membrane permeabilization have been shown to have a broad cytoprotective effect, in preclinical 68 as well as clinical studies.…”