Complement is regulated in the RPE by both systemically derived and locally produced CFH.

Abstract

Purpose : AMD is a multifactorial disease with a contribution from genetic abnormalities in Complement factor H (CFH). CFH regulates C3, and is highly abundant in plasma, but can also be produced in the eye. Its origin, whether from the plasma or the RPE, under stress is unknown. This information is essential for designing effective therapy targeting complement regulation in the RPE. The purpose of this study was to determine the major source of CFH in the RPE, and how this source regulates complement C3.

Methods : MX1-cre-CFH^fl/fl mice were injected intra-hepatically (IH), intravitreally (Ivt), or both IH and Ivt with ribonucleic acid (plpC) to reduce CFH in the liver, the eye, or both, respectively. Mice were then Ivt injected with 4HNE to activate complement. Total RNA and protein were extracted for RT-qPCR and Western analysis, respectively.

Results : Mice with Ivt injected PlpC had a 93% reduction in mRNA, but only a 33% reduction in CFH protein in the RPE compared to BSS injected animals (p≤ 0.05 and p≤0.03) while CFH mRNA and protein from the liver was unchanged. Mice with IH injected plpC had no change in CFH mRNA or protein in the RPE despite an 81% and 66% reduction in CFH mRNA and protein in the liver compared to BSS injected mice (p≤0.02 and p≤ 0.03 respectively). Mice that received Ivt and IH plpC injections had >90% reduction in CFH mRNA and protein in the RPE and liver (all p≤0.04), compared to BSS injected mice, while CFH was not reduced in BSS-injected mice. When stimulated with 4HNE, non-knockdown mice had increased CFH and C3d protein in the RPE compared to PBS injected mice (p≤0.04). In contrast, mice stimulated with 4HNE after Ivt OR IH plpC injection had no change in CFH or C3d protein in the RPE relative to PBS injected CFH knockdown controls. Mice stimulated with 4HNE after Ivt and IH plpC had unchanged C3d in the RPE compared to BSS injected double knockdown controls; however these mice were also depleted of C3 and CFB in the RPE, suggestive of hypocomplementemia.

Conclusions : Complement C3 regulation in the RPE relies on CFH derived from both systemic and ocular sources. Neither source alone can sufficiently regulate C3. Further studies are required to address how this may affect the overall complement activation.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.