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Sean Silverman, Wenxin Ma, Wai T Wong; Temporal Changes in Complement Gene Expression During Photoreceptor Degeneration in a Mouse Model of Retinitis Pigmentosa. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4536.
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© ARVO (1962-2015); The Authors (2016-present)
Photoreceptor (PR) degeneration in retinitis pigmentosa (RP) has been associated with immunological activation and microglial responses. However, contributing immune mechanisms are incompletely understood. We investigated the presence and pattern of complement expression and activation in a mouse model of RP.
Retinas from mice harboring the Pde6brd10 mutation and C57Bl6 WT controls were analyzed on postnatal days (P) 16, 21, 24, 27, and 30. mRNA expression of complement genes was analyzed with rtPCR, and complement expression and localization was performed using immunohistochemistry.
Comparisons between rd10 retinas prior to (P16) and during rod degeneration (P21-30) revealed significant upregulation of mRNA expression of genes in the complement system. Classical pathway components including C1qa (3.02±1.07 fold increase (X)), C1qb (4.93±1.15X), C4b (15.51±1.25X), and C1inh (6.19±1.37X) displayed significant increases at P21(p<0.01 for all comparisons) that were maintained or increased up to P30. Among complement genes in the alternative cascade, C3 (12.63±1.57X) and Cfb (23.92±0.29X) showed significant upregulation at P21 (p<0.01), and tended to decrease thereafter. Expression of complement receptors which are typically enriched in microglia C3aR (6.25±0.62X), C5aR (3.93±0.88X), and CR3 (3.72±0.57X) were also increased, peaking at P24 (p<0.01). In contrast, expression levels of these complement genes in age-matched WT retinas were largely stable. Immunofluorescence analyses demonstrated low levels of immunopositivity for complement proteins in WT controls and in the P16 rd10 retina. However, increased C1QA and C4 immunopositivity was observed beginning at P21, colocalizing to activated microglia in the ONL. Punctate C3b immunopositivity also emerged in the OPL and ONL at P21. CFH immunopositivity was strongly increased at P27 in the ONL, despite minor changes in mRNA levels.
Expression of multiple complement molecules was significantly increased in the rd10 retina, temporally coincident with the onset of PR degeneration. Immunocolocalization of C1QA and C4 expression to activated microglia suggests microglial involvement in complement-mediated mechanisms. Future investigations into the involvement of complement in microglia-PR interactions and degeneration are warranted.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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