Factor-H-related protein 1 (FHR1), a promotor of para-inflammation in age-related macular degeneration

Age-related macular degeneration (AMD), a multifactorial type of retinal degeneration represents the most common cause for blindness in elderly. Polymorphisms in complement factor-H increase, while absence of factor-H-related protein-1 (FHR1) decreases the AMD risk, currently explained by their opposing relationship. Here we identify a FHR1-driven pathway fostering chronic cellular inflammation. FHR1 accumulates below the retinal pigment epithelium (RPE) in AMD donor tissue and similarly the murine homolog, muFHR1 is abundant in three AMD-relevant mouse models. These mouse models express the muFHR1 receptor EGF-like module-containing mucin-like hormone receptor 1 (Emr1) on the RPE and on invading mononuclear phagocytes (MP), where both cells form clusters via muFHR1/Emr1. FHR1 ignited EMR2-dependent Ca²⁺-signals and gene expression in both human RPE cell line and in vivo where muFHR1 affects Emr1⁺ cells (RPE and MP) gene expression shown by RNAseq analysis. As muFHR1 deletion in mice revealed significantly reduced MP invasion and neoangiogenesis in laser-induced choroidal neovascularization, we hypothesize that FHR1 accumulates, stabilizes and activates MP in the stage of RPE degeneration.