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Mikiko Nagashima, Peter F. Hitchcock; Exploring the mechanisms that govern microglia dynamics during photoreceptor death and regenerative neurogenesis in zebrafish. Invest. Ophthalmol. Vis. Sci. 2020;61(7):2498.
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© ARVO (1962-2015); The Authors (2016-present)
In the zebrafish retina, Müller glia serve as intrinsic stem cells that possess the ability to regenerate retinal neurons. Acute inflammation is necessary and sufficient for the neurogenic response of intrinsic stem cells. Microglia are endogenous immune cells of the macrophage lineage within the central nervous system that secrete cytokines and chemokines, which govern inflammation. Midkine-a is a small, heparin-binding cytokines/growth factors that is strongly induced following various tissue damage. In this study, we characterized microglia dynamics following photoreceptor death in zebrafish and examined the role of Midkine-a in governing those events.
Zebrafish lines, AB-wildtype, csf1raj4e1, and mdkami5001 were used. Photoreceptors were selectively ablated by exposing fish to intense light. To label microglia, anti-4C4 antibody and transgenic reporter, Tg(mpeg:EGFP) were used. TUNEL assay was performed to label dying cells. Immunocytochemistry was used to label proliferating cells and Lysosomal-Associated Membrane Protein-1.
Following photoreceptor cell death, microglia undergo rapid and dynamic morphological changes followed by accumulation in the damaged subretinal space and outer nuclear layer. Microglia deficiency in the mutant, csf1raj4e1, results in a reduced number of Müller glia-derived progenitors. By 2 days post lesion microglia are co-labeled with TUNEL-positive dying photoreceptors and Lysosomal-Associated Membrane Protein-1. In wildtype animals, most apoptotic cells are cleared by 3 days post lesion. Although microglia activate and migrate in the mdkami5001, dying photoreceptors are not phagocytosed.
In response to photoreceptor death, microglia activate and migrate to phagocytose dying cells. Depleting microglia diminishes proliferation of the intrinsic stem cells and progenitors. Midkine-a may play a role in orchestrating inflammatory events by mediating microglial phagocytosis.
This is a 2020 ARVO Annual Meeting abstract.
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