title: Bacterial endotoxin activates retinal pigment epithelial cells and induces their degeneration through IL-6 and IL-8 autocrine signaling.
abstract: Inflammation is a major contributing factor to many blinding disorders including uveitis, diabetic retinopathy, and age-related macular degeneration. Here we examined the response of the retinal pigment epithelium (RPE) to physiological levels of lipopolysaccharide (LPS) to understand the role of this epithelium in inflammatory retinal conditions. Expression of a group of inflammatory mediators was identified by gene array analysis and confirmed by PCR and immunocytochemistry in primary human RPE cultures and ARPE19. The effects of LPS on the expression of these cytokines and RPE survival were examined by PCR, Luminex bead, and MTT assays. RPE cells express many cytokine receptors including IL-1R, -4R, -6R, -8RA, IFNAR1, IFNGR1/2 and secrete a range of pro- and anti-inflammatory cytokines including IL-4, -6, -8, -10, -17, IFN-gamma, MCP-1, and VEGF. LPS increases IL-13RA1 and IFNAR1, and decreases IL-7R receptor expression. It also increases RPE secretion of IL-4, -6, -8, -10, IFN-gamma and MCP-1, and is toxic to RPE cells at LC(50)=17.7 microg/ml. LPS toxicity is mediated by IL-6 and IL-8 through an autocrine feedback loop. Silencing IL-6R and IL-8RA gene expression by siRNA blocks death by their respective ligands or LPS. These findings imply that RPE cells are acutely sensitive to inflammatory stress and that over secretion of IL-6 and IL-8 by this epithelium during inflammatory stimulus may be an underlying factor in the progression of some retinal pathologies.
authors.affiliation: Department of Neural and Behavioral Sciences, Pennsylvania State University College of Medicine, Hershey, PA, USA.
authors.forename: Kar Wah
authors.initials: KW
authors.lastname: Leung
authors.forename: Colin J
authors.initials: CJ
authors.lastname: Barnstable
authors.forename: Joyce
authors.initials: J
authors.lastname: Tombran-Tink
mesh_terms: D019898:Autocrine Communication / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D001426:Bacterial Proteins / Q000494:pharmacology; D002478:Cells, Cultured; D018450:Disease Progression; D004305:Dose-Response Relationship, Drug; D004731:Endotoxins / Q000494:pharmacology*; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D020869:Gene Expression Profiling; D006801:Humans; D007249:Inflammation / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism / Q000502:physiology*; D016209:Interleukin-8 / Q000378:metabolism / Q000502:physiology*; D008875:Middle Aged; D020411:Oligonucleotide Array Sequence Analysis; D018121:Receptors, Cytokine / Q000235:genetics / Q000378:metabolism; D012162:Retinal Degeneration / Q000139:chemically induced* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D055213:Retinal Pigment Epithelium / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D014018:Tissue Distribution
chemical_list: D001426:Bacterial Proteins; C508606:CXCL8 protein, human; D004731:Endotoxins; C508600:IL6 protein, human; D015850:Interleukin-6; D016209:Interleukin-8; D018121:Receptors, Cytokine