Abstract
Mitochondria are known as organelles which are the major source of reactive oxygen species. In interphase cells, mitochondria are fused their membrane together and configured tubular morphology, while they become fragmented in mitotic and pro-apoptotic cells. Mitochondrial fusion is now thought to protect mitochondrial function by sharing materials such as metabolites and mitochondrial DNA. We have hypothesized that ionizing radiation causes mitochondrial fragmentation, which leads to dysfunction of mitochondria. Here, we examine how radiation exposure introduces morphological change and dysfunction of mitochondria in normal human cells exposed to gamma-irradiation.
Immortalized normal human fibroblast cells (BJ-hTERT) were used in this study. Mitochondria were visualized by staining with MitoTracher reagent, and structural change was examined under fluorescence microscope.
While most of the unirradiated cells showed tubular mitochondria, mitochondrial fragmentation was observed in about 50 % cells 3 days after 6 Gy of gamma-irradiation. We found that the amount of Drp1, a protein involved in mitochondrial fission, in the mitochondrial fraction was increased after 6 Gy irradiation. Expression of Drp1 dominant negative mutant (Drp1K38A) suppressed mitochondrial fragmentation after irradiation. Moreover, cells expressing Drp1K38A did not show loss of mitochondrial membrane potential after 6 Gy irradiation, and production of mitochondrial O2- was partially inhibited. These data indicate gamma-irradiation accelerates localization of Drp1 to mitochondria, which leads to mitochondrial fragmentation and dysfunction in normal human cells.
