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M. Zareba, J. M. Burke; Sub-Lethal Photic Stress Impairs Organelle Translocation in RPE Cells. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5930. doi: https://doi.org/.
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RPE melanosomes, phagosomes and other membrane-bound organelles translocate along scaffolds of actin microfilaments or microtubules. Actin and tubulin are sensitive to modification by oxidative stress, which raises the possibility that stress could impair organelle movement. In this investigation we analyzed the motility of melanosomes within RPE cells subjected to oxidative stress induced by irradiation with visible light. Photic damage to the RPE by visible light, especially blue light, is believed to contribute to age-related degenerations of the adjacent photoreceptors that the RPE supports.
Isolated porcine melanosomes were introduced by phagocytosis into cultures of the human cell line ARPE-19. For some experiments the melanosomes were coated with the green light absorbing photosensitizer Rose Bengal (RB) or were photobleached with visible light to increase melanin's photoreactivity. Cultures were subjected to sub-lethal photic stress using blue (400-410nm) or green (540-570nm) light. The effects of stress in the subcellular domain of each granule were determined by quantifying granule movement by live cell imaging; images were captured at 5 sec intervals over minutes to hours before and after irradiation.
Granule movement slows for at least several hours in RPE cells exposed to sub-lethal photic stress. The highly localized effect of RB plus green light slows all organelles. However, irradiation with blue light does not affect all granules equivalently, even within the same cells, suggesting that endogenous RPE chromophores, antioxidants and even the cytoskeletal scaffold itself are not uniformly distributed. Photobleaching of granules makes them more sensitive to blue light-induced slowing of motility.
Sub-lethal photic stress to the RPE may impair the cell’s ability to move and position organelles, especially when their contents are photoreactive. This is relevant for RPE melanosomes in situ which may become more photoreactive with aging due to time dependent photo-oxidation of melanin or fusion with lipofuscin. Further, stress-induced impairments of organelle motility could produce inefficient translocation of phagosomes and mis-localization of melanosomes and other organelles in the aging RPE
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