Retinal degeneration and subretinal Iba1⁺ accumulation in complement factor H-deficient mice are associated with increased gene expression of phagocytic markers

Abstract

Purpose : Over-activation of the alternative pathway is strongly associated with age-related macular degeneration. We previously reported that subretinal Iba1⁺ cell accumulation and retinal degeneration was observed in complement factor H knock-out mice on a factor P background (Cfh^-/-Cfp^+/+; Liao S-M, 2017 ARVO Abstract). In order to confirm and further investigate the photoreceptor (PR) thinning observed in a subset of these animals, both homozygous (Cfh^-/-) and heterozygous mice (Cfh^+/-) were evaluated for ocular abnormalities.

Methods : Male and female Cfh^-/- (n=26), Cfh^+/- (n=20) and WT littermate (n=18) mice were aged from 4 weeks to 11 months. Animals were assessed by fundus photography and optical coherence tomography (OCT). Ocular flat mounts and tissue sections were examined for Iba1⁺ cells, and gene expression was assessed by Taqman. The two-tailed t-test was used for statistical analyses.

Results : Cfh^-/- mice (19%) exhibited retinal flecks by fundus imaging as early as 5 weeks of age, with incidence and severity progressing over time (77% by 7 months), and OCT revealed PR thinning in 50% of these animals. Histological evaluation of 4 week old Cfh^-/- mice identified numerous Iba1⁺ subretinal cells and PR loss (↓32%, p<0.001). This correlated with increased expression of phagocytic markers Trem2 (p<0.001), Aif1 (p<0.001), Tmem119 (p<0.01), Csf1r (p<0.001), and mitochondrial stress gene Hspd1 (p<0.001). A reduction in rod-specific Gnat1 expression (p<0.01), but no change in cone-specific Gnat2 mRNA was evident in young Cfh^-/- mice. The partial complement activation in Cfh^+/- mice resulted in delayed onset of retinal flecks with a modest increase in expression of Trem2 (p<0.001), Aif1 (p<0.001), Csf1r (p<0.001) and Hspd1 (p<0.01). No eye abnormalities were observed in WT littermates.

Conclusions : Young Cfh^-/- mice displayed retinal flecks, accumulation of subretinal Iba1⁺ cells, and a subset also exhibited retinal degeneration. The PR loss affected rods prior to cones, and correlated with elevated gene expression of phagocytic and mitochondrial stress markers. Cfh^+/- mice displayed a delayed onset of retinal flecks and a more moderate elevation in phagocytic and mitochondrial stress gene expression. Further investigation is required to determine if the subretinal Iba1⁺ cells are a consequence of or contribute to PR loss in Cfh^-/- mice.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.