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Sergio Caballero, David L Kent, Maria B Grant; Cell Recruitment and Molecular Changes to the Retina following Sub-threshold Micropulse Retinal Phototherapy. Invest. Ophthalmol. Vis. Sci. 2016;57(12):4422.
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© ARVO (1962-2015); The Authors (2016-present)
Sub threshold retinal phototherapy (SRP) has been shown to be clinically efficacious for the treatment of retinal disease including diabetic macular edema without visible signs of retinal damage. SRP delivers short impulse light energy absorbed by the retinal pigment epithelium (RPE) only, sparing the neurosensory retina and achieving photo stimulation rather than photocoagulation. We investigated the use of SRP stimulation of the RPE and choroid to recruit hematopoietic stem cells (HSC) to the RPE.
GFP chimeric mice were generated by bone marrow ablation through irradiation of female C57Bl/6J and reconstituting with bone marrow cells from C57BL/6-Tg(ACTB-EGFP) donor males. 4 months later, mice were subjected to SRP of the retina in one eye using an infrared laser (Iridex OcuLight SLx MicroPulse 810nm) coupled to a slit lamp. Variable duty cycles of 5, 10, 15 and 20% (n=5 animals each duty cycle) for 0.1sec at 250mW and a spot size set to 50µm were used to establish optimal conditions. 20-30 applications were administered to each eye circumferentially placed between 50-100 µm from the optic disc. Another cohort of 5 animals did not receive laser application and was used as negative control. mRNA expression for hsp70 and 90, crystalline, HIF-1α, VEGF, CXCL-12, and CXCR-4 in both the neurosensory retina and the posterior cup was determined. Retinas were processed for immunohistochemistry for GFP.
No visible laser burn or scar was noted. GFP+ cells migrated to the RPE layer in a duty cycle-dependent fashion. hsp70 mRNA peaked at 2h post-laser in the neural retina and at 4h in the posterior cup. mRNA for hsp90A dramatically peaked in both the neural retina and the posterior cup at 2h. mRNA for CXCL12 and its receptor CXCR4 in the posterior cup occurred 2h post laser injury, and increased further by 4h. HIF-α mRNA was reduced at 2h, but increased at 4h; however, only in the posterior cup. VEGF mRNA increased at 4-6h post laser.
Bone marrow-derived cells are recruited to the retina including the RPE layer following sub threshold laser. The sub-threshold laser likely stimulates the extracellular environment of the RPE-photoreceptor layers resulting in release of hsp70, hsp90 and crystalline induction, which is then followed by cytokine release (CXCL12 and VEGF) that sustain the tissue signals to recruit bone marrow cells to the retina.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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