Early mitochondrial fragmentation is a potential in vitro biomarker of environmental stress

Mitochondria are essential dynamic organelles that ordinarily balance between fragmentation and fusion. Under stress conditions, a shift toward fragmentation or hyper-fusion is observed as a pro-survival reaction. Fragmentation of mitochondria occurs within minutes or hours after the beginning of the stress and occurs in response to a large number of stress stimuli, including those triggered by environmental contaminants. In this study, we tested whether the change in the mitochondrial phenotype, from tubular to fragmented, could be used as a potential environmental stress biomarker in cells and compared this response with the standard MTT-based viability assay. Firstly, we show that mitochondrial fragmentation induced by selected stressors not only increases with concentrations, but also correlates positively with the cytotoxicity. Secondly, we found that the mitochondrial fragmentation that occurs in the first hour of stress correlated with the viability measured after a 24-h stress, allowing the establishment of a linear relation between mitochondrial fragmentation at 1 h and the predictable associated cytotoxicity of environmental contaminants alone or in mixture. In conclusion, we have succeeded in developing a model of predictable 24 h-cytotoxicity given mitochondrial fragmentation at 1 h with a set of chemicals. This model has been successful applied to three environmental toxicants and to a set of two chemical mixtures. We thus propose that mitochondrial fragmentation is a response that could be used as an early in vitro biomarker of environmental stress for toxicants alone or in mixture.