Visible Light Triggered The Death Pathway In RGC-5Cells

Purpose: The present study was designed to determine visible light mightdirectly trigger the death pathway by damaging nuclear DNA.Methods: RGC-5cells were exposed to various intensities and durationsof visible light exposure. Cell viability and death were monitored with the3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay andpropidium iodide staining. Nuclear DNA damage caused by light wasdetermined with the plasmid assay, genome DNA assay, and in situ terminaldeoxynucleotidyl transferase dUTP nick end labeling. The subsequentactivation of nuclear enzyme poly(ADP-ribose) polymerase-1(PARP-1) wasmeasured with western blot, and PARP-1’s role in the death pathway wasassessed by using specific inhibitors. Poly (ADP-ribose) glycohydrolase andapoptosis-inducing factor (AIF) inhibitors were used to show their influence onlight-induced cell death. Calcium influx was examined with the fura-2assayand calcium channel blocker.Results: We found that visible light induced RGC-5cell death in a time-and intensity-dependent manner. After the light intensity was increased to2,600lx, activation of the death pathway in RGC-5cells was clearly observed bydetecting double-strand DNA breaks and nuclear DNA damage in vitro.Nuclear enzyme PARP-1was promptly activated after exposure to2,600lx oflight for2days, and specific inhibitors of PARP-1had significant neuro-protective effects. The poly(ADP-ribose) glycohydrolase inhibitor tannic acidand AIF inhibitor N-phenylmaleimide partially protected RGC-5cells fromlight injury. A massive calcium influx was detected after2days of lightexposure, and a calcium channel blocker partially protected cells against lightinjury. Conclusions: These results suggest that visible light exposure maydirectly cause nuclear DNA damage, which consequently activates PARP-1.In addition, RGC-5cells damaged by2,600lx of light exposure can be used asan appropriate cell death model for screening neuroprotective drugs, since thistreatment induced remarkable cell death within2days. Moreover, these resultsshow that2,600lx of light exposure provides a more apparent activation of thedeath pathway than1,300lx of light exposure, which was used in a previousstudy.