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Maanasa Indaram, Wenxin Ma, Lian Zhao, Robert N Fariss, Ignacio R Rodriguez, Wai T Wong; Interaction of 7-ketocholesterol (7KCh) with retinal microglia (RMG): a potential contribution to age-related macular degeneration (AMD) pathogenesis. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1334.
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Age-related accumulation of outer retinal oxidized lipids, including 7KCh, have been implicated in AMD pathogenesis. As RMG also accumulate in the outer retina with aging and AMD, we examined the interaction between 7KCh and RMG to understand their combined contribution to AMD-related pathological processes.
7KCh was localized in the young and aged mouse retina by immunohistochemistry. RMG cultured from the retina and exposed to varying concentrations of 7KCh were evaluated using morphological, cellular motility, and molecular (q-PCR, ELISA) assays. Conditioned media from RMG were tested on 661W photoreceptors and primary endothelial cells in survival and angiogenesis assays respectively. Subretinal transplantation of 7KCh and 7KCh-exposed RMG were performed in young adult mice to assess chemotactic and angiogenic in vivo effects of 7KCh.
While immunopositivity for 7KCh in the subretinal space was low in young (2-month old) mice, it increased in aged (24-month old) mice and was concentrated in RMG, indicating age-related 7KCh accumulation in the outer retina and uptake by RMG. RMG demonstrated dose-dependent chemotaxis towards 7KCh in Transwell-migration assays in vitro as well as in subretinal implantations of 7KCh in vivo. 7KCh exposure exerted marked effects on RMG physiology, including the induction of cell death at concentrations >16μM. At subtoxic concentrations, 7KCh exposure induced RMG activation as evidenced by morphology change and increased expression of activation (CD68 , F4/80) and M1 polarization (TNFα, IL6, IL1β) markers. RMG expression of neuroprotective factors (BDNF, NGF, CNTF) were significantly reduced by 7KCh exposure, decreasing RMG-mediated neuroprotection to oxidatively-stressed 661W photoreceptor cells. RMG expression of angiogenic factors (VEGF, PDGFβ, and ICAM) were elevated by 7KCh exposure, increasing RMG-associated angiogenesis in vitro as well as in in vivo CNV assays with subretinal implantation of 7KCh-exposed RMG.
Age-related accumulation of 7KCh in the outer retina may exert pathological effects via its recruitment and transformation of RMG in the subretinal space. RMG, following transformation by 7KCh, can contribute to a more pro-inflammatory and pro-angiogenic immune environment in the outer retina, and predispose towards atrophic and neovascular events in AMD progression.
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