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Jeff S Mumm, David T White, Sumitra Sengupta; Microglial regulation of stem cell responsiveness and cell replacement kinetics during retinal regeneration. Invest. Ophthalmol. Vis. Sci. 2016;57(12):2231.
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© ARVO (1962-2015); The Authors (2016-present)
Discrete immune cell types have recently been implicated in promoting neuronal regeneration following traumatic brain injury in regenerative species. However, whether the immune system similarly regulates regeneration following selective neuronal cell apoptosis, as per neurodegenerative disorders, is unknown. We hypothesized that microglia stimulate responsiveness of retinal stem cells to selective retinal cell death, thereby controlling cell regeneration kinetics, and have investigated this theory using an inducible zebrafish model of retinitis pigmentosa.
Transgenic zebrafish lines expressing complementary fluorescent reporters in different immune/retinal cell types, and enabling selective rod cell ablation, facilitated multi-color intravital time-lapse imaging of immune cell behaviors following induction of rod cell death (or puncture wound controls). Resulting 4D imaging data was quantified using automated cell tracking software. Immunohistochemistry was applied to confirm observed chemotactic immune cell responses and to further evaluate immune cell activation via established hallmarks (e.g., proliferation and phagocytosis). Simultaneous co-ablation of microglia and rod photoreceptors, and immunomodulators, were used to test the role of microglia during rod cell loss and regeneration.
Neutrophils, peripheral macrophages, and microglia all responded to puncture wound controls. Conversely, only peripheral macrophages and microglia responded to rod cell death. However, whereas microglia acted directly within the retina - translocating to the rod cell layer, proliferating, and phagocytosing dying rod cells - peripheral macrophages did not enter they eye. Co-ablation of microglia and rod cells and subsequent quantification of the kinetics of: (1) rod cell clearance, (2) stem/progenitor cell proliferation, and (3) rod cell regeneration, revealed that the rate of stem/progenitor proliferation and rod cell replacement was dependent on the presence of microglia.
The data support our hypothesis, implicating microglia as the primary responder to selective retinal cell apoptosis and consistent with data suggesting microglia are active during early phases of retinal degenerative disease. Moreover, we define roles for microglia in regulating retinal stem/progenitor cell proliferation and rod cell regeneration kinetics in a zebrafish model of retinitis pigmentosa.
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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