Age-related macular degeneration associated polymorphism rs10490924 in ARMS2 results in deficiency of a complement activator

Abstract

BackgroundAge-related macular degeneration (AMD) is the leading cause of blindness in developed countries. The polymorphism rs10490924 in the ARMS2 gene is highly associated with AMD and linked to an indel mutation (del443ins54), the latter inducing mRNA instability. At present, the function of the ARMS2 protein, the exact cellular sources in the retina and the biological consequences of the rs10490924 polymorphism are unclear.MethodsRecombinant ARMS2 was expressed in Pichia pastoris, and protein functions were studied regarding cell surface binding and complement activation in human serum using fluoresence-activated cell sorting (FACS) as well as laser scanning microscopy (LSM). Biolayer interferometry defined protein interactions. Furthermore, endogenous ARMS2 gene expression was studied in human blood derived monocytes and in human induced pluripotent stem cell-derived microglia (iPSdM) by PCR and LSM. The ARMS2 protein was localized in human genotyped retinal sections and in purified monocytes derived from AMD patients without the ARMS2 risk variant by LSM. ARMS2 expression in monocytes under oxidative stress was determined by Western blot analysis.ResultsHere, we demonstrate for the first time that ARMS2 functions as surface complement regulator. Recombinant ARMS2 binds to human apoptotic and necrotic cells and initiates complement activation by recruiting the complement activator properdin. ARMS2-properdin complexes augment C3b surface opsonization for phagocytosis. We also demonstrate for the first time expression of ARMS2 in human monocytes especially under oxidative stress and in microglia cells of the human retina. The ARMS2 protein is absent in monocytes and also in microglia cells, derived from patients homozygous for the ARMS2 AMD risk variant (rs10490924).ConclusionsARMS2 is likely involved in complement-mediated clearance of cellular debris. As AMD patients present with accumulated proteins and lipids on Bruch’s membrane, ARMS2 protein deficiency due to the genetic risk variant might be involved in drusen formation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12974-016-0776-3) contains supplementary material, which is available to authorized users.

On phagocytes and macular degeneration

“…The authors show that ARMS2 binds to cell debris, where it promotes C3b generation and opsonization for phagocytosis by MPs. 10q26 risk-allele carriers would therefore lack necessary opsonization, promoting debris accumulation and AMD (Micklisch et al, 2017).…”

“…pathogenic subretinal inflammation (Calippe et al, 2017;Levy et al, 2015a;Levy et al, 2015b;Liao et al, 2013;Micklisch et al, 2017). Importantly, the affected genes are all expressed in MPs and the consequences of the disease-associated variants directly affect MP function.…”

Association between Drusen Burden Determined by OCT and Genetic Risk in Early and Intermediate Age-Related Macular Degeneration

“…One study found that ARMS2 was expressed in human monocytes and microglia cells and facilitated removal of cellular debris by local complement activation; the A69S variant resulted in ARMS2 deficiency, possibly impairing the removal of cellular debris at Bruch's membrane, leading to the development of drusen. 52 On the other hand, another study reported that ARMS2 mRNA and protein are expressed at extremely low levels in eye tissues, and presented support for HTRA1 as the risk factor for AMD. 53 We found that the OCT algorithm yielded drusen measurements that were highly associated with the manual CARMS grading.…”

Polysialinsäure zur Immunmodulation im Tiermodell der feuchten altersabhängigen Makuladegeneration (AMD)

“…Dieser Wirkung liegt eine direkte Hemmung des alternativen Komplementwegs zugrunde [29]. Eine Fehlregulation des alternativen Komplementwegs wiederum kann als Mitursache für die gestörte Mikroglia-/Makrophagenhomöostase in der Netzhaut von AMD-Patienten betrachtet werden [34]. Der in der vorliegenden Studie beobachtete antiangiogene, leckagereduzierende Effekt durch Polysialinsäure könnte einerseits durch die Verminderung des CNV-begünstigenden zellulären inflammatorischen Prozesses entstehen und andererseits durch eine Verminderung des komplementvermittelten Schadens am RPE/Aderhautkomplex erklärt werden [35].…”