13The measurement of cell activity changes during damage is important to 14 understand the process of cell death and evaluate the effect of medicines. To 15 evaluate cell activity generally, we extended the method of intensity fluctuation in 16 which intensity change in the pixel induced by the movement of organelles was 17 calculated. Cancer, endothelial and iPS cells were damaged by reactive oxygen 18 species (ROS) generated by a fluorescent dye (IR700), hydrogen peroxide, and 19 ultraviolet light. The intensity fluctuation in damaged cells gradually decreased 20 independent of the kind of cell, indicating that the decrease in the fluctuation is a 21 general phenomenon in damaged cells. The rupture of vesicles and 22 mitochondria in the cells were observed upon ROS production. The motility of 23 purified kinesin and dynein which transport vesicles and organelles was inhibited 24 by ROS. These suggest that ROS and cytotoxic molecules spreading from 25 ruptured organelles contribute to the reduction in cell activity which brings about 26 the decrease in the motility and intensity fluctuation of organelles driven by 27 kinesin and dynein.28 Liao et al., 2017). The motility of mitochondria gradually decreased just after the 65 addition of hydrogen peroxide, and the decrease in the motility reached 50% 66 within 10 minutes (Debattisti et al., 2017). These results suggested that the 67 effect on the motility of organelles in damaged cells occurred earlier than the 68 changes in cell morphology and motility. Thus, the method of detecting 69 intracellular motility under a conventional microscope would overcome the 70 disadvantages of previous fluorescence, morphological, and cell motility 71 methods. However, little is understood about the generality and mechanism of 72 motility reduction.
73In this study, various cells were damaged by several methods, including 74 photoactivation of IR700, irradiation with ultraviolet (UV) light and treatment with 75 hydrogen peroxide (H 2 O 2 ), and the change in the motility of organelles was 76 quantitatively evaluated by the developed intensity fluctuation method (IFM). We 77 found that all cells showed a decrease in motility caused by damage. To 78 elucidate the mechanisms of the decrease in motility in damaged cells, we 79 measured the reduction in the motile speeds of single vesicles in cells and in 80 purified kinesin and dynein in vitro assays. These measurements revealed that 81 the decrease detected by IMF resulted in the reduction in the organelle motility 82 driven by motor proteins. Since the transport system commonly exists in animal 83 cells, the decrease in the motility or transport of organelles would be a universal 84 phenomenon in various kinds of cells. 85 5 Results 86 87 1 Decrement of motility of organelles in damaged cells 88 Changes in the motility of organelles in damaged cells were evaluated 89 by the intensity fluctuation method (IFM) in various cell types. Six kinds of cells, 90 four cancer cell lines, one endothelial cell line, and one iPS cell line...