Funktionelle Charakterisierung von Age-Related Maculopathy Susceptibility 2 - ARMS2

Age-related macular degeneration (AMD) is a heritable, progressive neurodegenerative disease and the leading cause of blindness in developed countries. AMD is characterized by the formation of drusen between the retinal pigment epithelium and Bruch's membrane. The progressive accumulation of drusen leads to the degeneration of photoreceptors and of pigmented epithelial cells. Beside age, genetic mutations represent the major risk factors for the development of AMD. Genome-wide linkage studies identified polymorphisms predominantly in complement genes such as CFH (Complement Factor H), CFB (Complement Factor B), C2, C3 and CFI (Complement Factor I )to be associated with AMD, indicating the major impact of innate immunity in disease development. Strongly associated with AMD is a polymorphism in a gene on chromosome 10q26, that was named ARMS2 (Age-Related Susceptibility Maculopathy 2) and which encodes a small protein with so far unclear functions. The ARMS2 risk variant includes the rs10490924 polymorphism, which leads to an alanine – serine exchange at amino acid position 69 (A69S). This polymorphism is in strong linkage disequilibrium with an InDel-mutation in the 3 'UTR, which contributes to ARMS2 mRNA instability. Both mutations are associated with an increased risk of AMD development in Caucasian and Japanese populations. An additional rs2736911 polymorphism, which results in a premature stop codon at protein position 38 (R38Stop) was described to be associated as a risk factor in the Chinese population.The present work describes for the first time the function of the ARMS2 protein. Recombinant ARMS2 binds to late apoptotic and necrotic cell surfaces, but not to native, living cells. Attached to surfaces, ARMS2 activates complement and increases C3b opsonization by the alternative pathway. Thereby surface attached ARMS2 recruits the complement activator properdin, which stabilizes C3 convertases and enhances C3b opsonization on the cell surface. Furthermore, ARMS2 expression is identified in human monocytes, as well as in microglia cells, the latter representing phagocytes in the retina. Thus low ARMS2 levels as caused by the ARMS2 risk haplotype likely reduce phagocytosis and clearance of dying cells in the retina. The ongoing accumulation of drusen and cell debris subsequently induces complement activation accompanied by a chronic inflammation. The results improve the understanding of AMD pathology and may help to develop a new complement-based therapy

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

Background Age-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. Methods Recombinant 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. Results Here, 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). Conclusions ARMS2 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

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

Acknowledgements: The authors thank all German AMD patients for their participation. We also thank Maria Pötsch (Leibniz Institute for Natural Product Reseach and Infection Biology, Jena) for MS analyses. Funding: This research was supported by the German Council “Deutsche Forschungs-Gemeinschaft” SK46, Zi432, LA1206, the “Pro Retina” foundation and the Thuringian Ministry of Science and Education, Germany. HN is a member of the DFG-funded excellence cluster ImmunoSensation (EXC 1023). YL is a doctoral researcher at the International Leibniz Research School (ILRS), part of the Jena school of Microbial Communication (JSMC). Availability of data and materials: Materials are available at [email protected] reviewedPublisher PD

The 10q26 Risk Haplotype of Age-Related Macular Degeneration Aggravates Subretinal Inflammation by Impairing Monocyte Elimination

International audienceA minor haplotype of the 10q26 locus conveys the strongest genetic risk for age-related macular degeneration (AMD). Here, we examined the mechanisms underlying this susceptibility. We found that monocytes from homozygous carriers of the 10q26 AMD-risk haplotype expressed high amounts of the serine peptidase HTRA1, and HTRA1 located to mononuclear phagocytes (MPs) in eyes of non-carriers with AMD. HTRA1 induced the persistence of monocytes in the subretinal space and exacerbated pathogenic inflammation by hydrolyzing thrombospondin 1 (TSP1), which separated the two CD47-binding sites within TSP1 that are necessary for efficient CD47 activation. This HTRA1-induced inhibition of CD47 signaling induced the expression of pro-inflammatory osteopontin (OPN). OPN expression increased in early monocyte-derived macrophages in 10q26 risk carriers. In models of subretinal inflammation and AMD, OPN deletion or pharmacological inhibition reversed HTRA1-induced pathogenic MP persistence. Our findings argue for the therapeutic potential of CD47 agonists and OPN inhibitors for the treatment of AMD

Additional file 1: Figure S1. of Age-related macular degeneration associated polymorphism rs10490924 in ARMS2 results in deficiency of a complement activator

Expression vector with ARMS2 coding sequence. (PDF 268 kb