title: Oxidative stress sensitizes retinal pigmented epithelial (RPE) cells to complement-mediated injury in a natural antibody-, lectin pathway-, and phospholipid epitope-dependent manner.
abstract: Uncontrolled activation of the alternative complement pathway (AP) is thought to be associated with age-related macular degeneration. Previously, we have shown that in retinal pigmented epithelial (RPE) monolayers, oxidative stress reduced complement inhibition on the cell surface, resulting in sublytic complement activation and loss of transepithelial resistance (TER), but the potential ligand and pathway involved are unknown. ARPE-19 cells were grown as monolayers on transwell plates, and sublytic complement activation was induced with H2O2 and normal human serum. TER deteriorated rapidly in H2O2-exposed monolayers upon adding normal human serum. Although the effect required AP activation, AP was not sufficient, because elimination of MASP, but not C1q, prevented TER reduction. Reconstitution experiments to unravel essential components of the lectin pathway (LP) showed that both ficolin and mannan-binding lectin can activate the LP through natural IgM antibodies (IgM-C2) that recognize phospholipid cell surface modifications on oxidatively stressed RPE cells. The same epitopes were found on human primary embryonic RPE monolayers. Likewise, mouse laser-induced choroidal neovascularization, an injury that involves LP activation, could be increased in antibody-deficient rag1(-/-) mice using the phospholipid-specific IgM-C2. In summary, using a combination of depletion and reconstitution strategies, we have shown that the LP is required to initiate the complement cascade following natural antibody recognition of neoepitopes, which is then further amplified by the AP. LP activation is triggered by IgM bound to phospholipids. Taken together, we have defined novel mechanisms of complement activation in oxidatively stressed RPE, linking molecular events involved in age-related macular degeneration, including the presence of natural antibodies and neoepitopes.
authors.affiliation: Department of Ophthalmology, Medical University of South Carolina, Charleston, South Carolina 29425, USA.
authors.forename: Kusumam
authors.initials: K
authors.lastname: Joseph
authors.forename: Liudmila
authors.initials: L
authors.lastname: Kulik
authors.forename: Beth
authors.initials: B
authors.lastname: Coughlin
authors.forename: Kannan
authors.initials: K
authors.lastname: Kunchithapautham
authors.forename: Mausumi
authors.initials: M
authors.lastname: Bandyopadhyay
authors.forename: Steffen
authors.initials: S
authors.lastname: Thiel
authors.forename: Nicole M
authors.initials: NM
authors.lastname: Thielens
authors.forename: V Michael
authors.initials: VM
authors.lastname: Holers
authors.forename: Bärbel
authors.initials: B
authors.lastname: Rohrer
mesh_terms: D000818:Animals; D002460:Cell Line; D015922:Complement C1q / Q000235:genetics / Q000378:metabolism*; D003170:Complement Pathway, Alternative; D037582:Complement Pathway, Mannose-Binding Lectin; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007075:Immunoglobulin M / Q000097:blood*; D051379:Mice; D018345:Mice, Knockout; D016877:Oxidants / Q000494:pharmacology; D018384:Oxidative Stress; D010743:Phospholipids / Q000097:blood*; D055213:Retinal Pigment Epithelium / Q000378:metabolism* / Q000473:pathology
chemical_list: D018398:Homeodomain Proteins; D007075:Immunoglobulin M; D016877:Oxidants; D010743:Phospholipids; C064658:RAG-1 protein; D015922:Complement C1q; D006861:Hydrogen Peroxide
keywords: Age-related Macular Degeneration; Antibodies; Choroidal Neovascularization; Complement System; Epithelium; Lectin Complement Pathway; Lipid Peroxidation; Natural Antibodies; Oxidative Stress; Retinal Pigment Epithelium