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 suppress apoptosis. However, during the process of apoptosis, whether mitochondrial biogenesis occurs in the early stage of the apoptotic cells 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 gamma-ray radiation. Besides in situ detection of mitochondrial fluorescence changes, we also examined the cell viability, nuclear DNA damage, reactive oxygen species (ROS), Mitochondrial superoxide, citrate synthase activity, ATP, cytoplasmic and mitochondrial calcium, mitochondrial DNA copy number and expression of transcription genes related to mitochondrial biogenesis as well as the apoptosis biomarkers. As a result, we confirmed that significant mitochondrial biogenesis took place preceding the radiation-induced apoptosis, and the change of mitochondrial biogenesis at early time was closely correlated with the apoptotic cells at late stage. The involved mechanism was also discussed. HighlightsO_LIA dual fluorescence reporter system was successfully constructed for in-situ observation of mitochondrial biogenesis in living cells. C_LIO_LIThe whole process of radiation-induced mitochondrial biogenesis and apoptosis was scrutinized. C_LIO_LIThe conception of the relationship between mitochondrial biogenesis and apoptosis was revised. C_LIO_LIAssessment of the early event of mitochondrial biogenesis is critical for prediction of the late fate of cells. C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=130 SRC="FIGDIR/small/263152v3_ufig1.gif" ALT="Figure 1"> View larger version (37K): org.highwire.dtl.DTLVardef@122afb8org.highwire.dtl.DTLVardef@3e87c6org.highwire.dtl.DTLVardef@143fa24org.highwire.dtl.DTLVardef@1db5d6a_HPS_FORMAT_FIGEXP M_FIG C_FIG