How do reactive oxygen species and calcium trigger mitochondrial membrane permeabilisation?

BACKGROUND: Mitochondrial membrane permeabilisation (MMP) is classically considered as a point of no return in several forms of cell death and is involved in numerous diseases such as cancer, neurodegenerative disorders or ischemia/reperfusion injuries. Many studies established that reactive oxygen species (ROS) and Ca(2+) were the prominent inducers of MMP. However, the mechanisms connecting ROS and Ca(2+) to the players of MMP are still a matter of debate. SCOPE OF REVIEW: The aim of this review is to summarise the various studies related to the mechanisms of ROS- and Ca(2+)-induced MMP. Several lines of evidence suggest that ROS and Ca(2+) cooperate to induce MMP but the molecular details of the ROS-Ca(2+)-MMP network remain controversial. We then discuss recent data depicting this topic. MAJOR
CONCLUSIONS: Cytotoxic stimuli may be transduced within the cell by ROS and Ca(2+) increases. In most models, Ca(2+) and ROS can cooperate to induce MMP. Moreover, several data suggest that MMP increases mitochondrial Ca(2+) and ROS which therefore amplify the cytotoxic signal. Intriguingly, many reports have identified players of MMP as direct ROS targets. On the contrary, direct targets of Ca(2+) remain elusive. At the same time, the mechanisms by which mitochondrial Ca(2+) overload induces ROS generation are well documented. Upon these observations, we hypothesise that Ca(2+) cannot directly induce MMP and requires ROS production as a mandatory step. GENERAL SIGNIFICANCE: Given the importance of Ca(2+)- and ROS-induced MMP in diseases, we expect that a better understanding of this process will lead to the development of novel therapies.