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Erica Fletcher, Samuel Mills, Ursula Greferath, Robyn Guymer, Malcolm Plunkett, Andrew Jobling; Microglial response to nanosecond laser application to the retinal pigment epithelium. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5591.
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© ARVO (1962-2015); The Authors (2016-present)
Microglia, the resident immune cells of the retina, respond to injury with characteristic morphological and pro-inflammatory effects. However, under physiological or low levels of retinal stress, their response is different, having neuroprotective effects. The aim of this work was to characterise microglial changes in response to subtle, non- lethal retinal injury induced by a novel nanosecond laser.
C57Bl6J mice and Cx3cr1GFP/+ were treated with a 2RT (retinal rejuvenation therapy) nanosecond laser (Ellex Pty Ltd ; Q-switched YAG laser 532nm) at varying energies from 0.065mJ to 0.3mJ. Retinae and RPE were assessed 1 hour to 14 days later for structural integrity (Nissl stain; phalloidin labelling), cell death (TUNEL labelling), and gliosis (GFAP immunolabelling). Microglial number and morphology was quantified using Metamorph software, and PCR microarrays were used to characterise the changes in expression of cytokine and chemokines.
Laser treatment at 0.065mJ and higher doses produced localized loss of the RPE that healed over 7-14 days. In contrast to higher doses, laser treatment at 0.065mJ produced no overt structural changes in the retina, no TUNEL labelling of the ONL, or GFAP labelling of Müller cells. Despite this, retinal microglial response was rapid (1 hour), with photoreceptor-microglial interaction observed and extension of microglial processes into the sub-retinal space. Microglia showed no evidence of activation, with cell number, soma size and process morphology remaining unchanged. The sub-lethal injury resulted in up-regulation of genes involved in chemotaxis (Ccl2, Ccl7) and an increase in the neuroprotective cytokine, leukemia inhibitory factor (Lif). Increasing the severity of the retinal injury (0.13mJ) reduced the expression of possible neuroprotective agents (Ctf1, Il9), and increased inflammatory cytokines (IL6, Cxcl10).
Microglia respond rapidly to the nanosecond laser in the absence of photoreceptor cell death or Müller cell gliosis. The neuronal interaction and increased expression of neurotrophic agents suggests that microglia may aid in cell survival after mild retinal insult.
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