Monitoring mitochondrial biogenesis as the early event for prediction of radiation-induced apoptosis

Mitochondrial biogenesis is a cell response to external stimuli which is generally believed to be negatively correlated with apoptosis. However, in the process of apoptosis, whether mitochondrial biogenesis occurs in the early period of the apoptotic cells exposed to the external stimuli such as radiation remains unclear. To address this question, we constructed the COX8-EGFP-ACTIN-mCherry HeLa cells with recombinant fluorescent proteins respectively tagged on the nucleus and mitochondria, and monitored the mitochondrial changes in living cells exposed to the gamma-ray radiation. Besides the in situ and real-time detection of mitochondrial fluorescence changes, we also examined the cell viability, nuclear DNA damage, mitochondrial DNA copy number and the expression of transcription genes of mitochondrial biogenesis and apoptosis marker proteins. As such, we confirmed that mitochondrial biogenesis is taking place preceding apoptosis, and enhancement of mitochondrial biogenesis at at early time is actually positively correlated with the apoptotic cells at late stage.