title: Iron-induced Local Complement Component 3 (C3) Up-regulation via Non-canonical Transforming Growth Factor (TGF)-β Signaling in the Retinal Pigment Epithelium.
abstract: Dysregulation of iron homeostasis may be a pathogenic factor in age-related macular degeneration (AMD). Meanwhile, the formation of complement-containing deposits under the retinal pigment epithelial (RPE) cell layer is a pathognomonic feature of AMD. In this study, we investigated the molecular mechanisms by which complement component 3 (C3), a central protein in the complement cascade, is up-regulated by iron in RPE cells. Modulation of TGF-β signaling, involving ERK1/2, SMAD3, and CCAAT/enhancer-binding protein-δ, is responsible for iron-induced C3 expression. The differential effects of spatially distinct SMAD3 phosphorylation sites at the linker region and at the C terminus determined the up-regulation of C3. Pharmacologic inhibition of either ERK1/2 or SMAD3 phosphorylation decreased iron-induced C3 expression levels. Knockdown of SMAD3 blocked the iron-induced up-regulation and nuclear accumulation of CCAAT/enhancer-binding protein-δ, a transcription factor that has been shown previously to bind the basic leucine zipper 1 domain in the C3 promoter. We show herein that mutation of this domain reduced iron-induced C3 promoter activity. In vivo studies support our in vitro finding of iron-induced C3 up-regulation. Mice with a mosaic pattern of RPE-specific iron overload demonstrated co-localization of iron-induced ferritin and C3d deposits. Humans with aceruloplasminemia causing RPE iron overload had increased RPE C3d deposition. The molecular events in the iron-C3 pathway represent therapeutic targets for AMD or other diseases exacerbated by iron-induced local complement dysregulation.
authors: From the F. M. Kirby Center for Molecular Ophthalmology, Scheie Eye Institute.
authors: Yafeng
authors: Y
authors: Li
authors: From the F. M. Kirby Center for Molecular Ophthalmology, Scheie Eye Institute.
authors: Delu
authors: D
authors: Song
authors: From the F. M. Kirby Center for Molecular Ophthalmology, Scheie Eye Institute.
authors: Ying
authors: Y
authors: Song
authors: From the F. M. Kirby Center for Molecular Ophthalmology, Scheie Eye Institute.
authors: Liangliang
authors: L
authors: Zhao
authors: From the F. M. Kirby Center for Molecular Ophthalmology, Scheie Eye Institute.
authors: Natalie
authors: N
authors: Wolkow
authors: Penn Molecular Profiling Facility, and.
authors: John W
authors: JW
authors: Tobias
authors: Department of Pharmacology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania 19104.
authors: Wenchao
authors: W
authors: Song
authors: From the F. M. Kirby Center for Molecular Ophthalmology, Scheie Eye Institute, jdunaief@mail.med.upenn.edu.
authors: Joshua L
authors: JL
authors: Dunaief
mesh_terms: D000818:Animals; D051743:CCAAT-Enhancer-Binding Protein-delta / Q000378:metabolism; D002460:Cell Line; D003176:Complement C3 / Q000378:metabolism*; D005786:Gene Expression Regulation; D055785:Gene Knockdown Techniques; D006801:Humans; D007501:Iron / Q000737:chemistry; D019190:Iron Overload; D008024:Ligands; D008268:Macular Degeneration / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008875:Middle Aged; D055213:Retinal Pigment Epithelium / Q000378:metabolism*; D015398:Signal Transduction; D051900:Smad3 Protein / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: D003176:Complement C3; D008024:Ligands; C497790:SMAD3 protein, human; D051900:Smad3 Protein; C497791:Smad3 protein, mouse; C508960:TGFB1 protein, human; C508961:Tgfb1 protein, mouse; D053773:Transforming Growth Factor beta1; D051743:CCAAT-Enhancer-Binding Protein-delta; D007501:Iron
keywords: AMD; C3; CCAAT/Enhancer-binding Protein (C/EBP); Extracellular Signal-regulated Kinase (ERK); Iron; RPE; SMAD3; Signaling; Transforming Growth Factor β (TGF-β)