Intracellular signaling mechanisms responsive to laser-induced photochemical and thermal stress

The cells of the retinal pigment epithelium (RPE) are subject to photo-oxidative stress arising from the interaction of incident light with lipofuscin, melanin, and other pigment granules in the RPE cytoplasm. Specific genotypic responses to these stressors are controlled by transcription factors, such as NF-κB (RelA/p50 dimer). The effects of CW laser exposures on NF-κB nuclear translocation have been studied in a line of human-derived RPE cells (hTERT-RPE) that develop melanin pigmentation in culture. The cells were exposed to the CW emission of an Argon-ion laser for 10 m at 0.5 W/cm2, a range previously shown to produce oxidation of cellular proteins, DNA, and antioxidants. NF-κB dimer was measured in nuclear extracts by an electrophoretic mobility shift assay. NF-κB nuclear translocation exhibited a modest, early peak at 1 h, and a larger, late peak at 24 h. NF-κB activation could be reduced only by some antioxidants; for example, 20 mM N-acetyl-L-cysteine or 100 μM pyrrolidine dithiocarbamate were ineffective, while 500 μM ascorbic acid was highly effective. These results indicate that interaction of the laser with the RPE melanin granules is a likely source of oxidative reactions, and that the induction of photoxidative stress activates NF-κB, but it remains to be determined if NF-κB is pro- or anti-apoptotic in the RPE cell.