title: Exogenous MD-2 confers lipopolysaccharide responsiveness to human corneal epithelial cells with intracellular expression of TLR4 and CD14.
abstract: In the present study, we aimed to investigate the responsiveness of human corneal epithelial cells (HCECs) to lipopolysaccharide (LPS) in vitro and to elucidate the underlying molecular mechanism(s) controlling the LPS responsiveness. The expression and subcellular localization of toll-like receptor 4 (TLR4) and CD14 and the expression of myeloid differentiation (MD)-2 were studied in SDHCEC1 cells, one HCEC cell line. Upon exposure to different concentrations of LPS, cell responses were evaluated by examining nuclear factor-kappaB (NF-κB) activation and the production of interleukin (IL)-8. The influence of soluble MD-2 on LPS responsiveness were assessed in SDHCEC1 cells pretreated with MD-2-containing conditioned medium before LPS challenge. SDHCEC1 cells expressed both TLR4 and CD14 intracellularly and had no detectable expression of MD-2 transcripts. Unresponsiveness to LPS at doses of up to 1,000 ng/ml was observed in SDHCEC1 cells, which was evidenced by no evident NF-κB activation and IL-8 production. The addition of MD-2 conditioned medium significantly induced NF-κB activation and enhanced the production of IL-8 as compared with the treatment with the control medium (p < 0.05). Meanwhile, the total mRNA amounts of TLR4 and CD14 and the surface expression of the two proteins were significantly (p < 0.05) increased by the pretreatment with MD-2 conditioned medium. LPS hyporesponsiveness of HCECs is largely due to deficient LPS receptor complex formation caused by lack of MD-2 expression. Exogenous MD-2 is capable of restoring the LPS responsiveness, at least partially, through promoting the surface expression of TLR4 and CD14.
authors.affiliation: Department of Ophthalmology, Changhai Hospital, Second Military Medical University, 174 Changhai Road, Shanghai, 200433, China.
authors.forename: Li-Li
authors.initials: LL
authors.lastname: Lang
authors.forename: Lin
authors.initials: L
authors.lastname: Wang
authors.forename: Lin
authors.initials: L
authors.lastname: Liu
mesh_terms: D002460:Cell Line; D017077:Culture Media, Conditioned; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D019573:Epithelium, Corneal / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D006801:Humans; D016209:Interleukin-8 / Q000096:biosynthesis; D018950:Lipopolysaccharide Receptors / Q000235:genetics / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology; D051218:Lymphocyte Antigen 96 / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D016328:NF-kappa B / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
chemical_list: C508606:CXCL8 protein, human; D017077:Culture Media, Conditioned; D016209:Interleukin-8; C495377:LY96 protein, human; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D051218:Lymphocyte Antigen 96; D016328:NF-kappa B; D012333:RNA, Messenger; D011994:Recombinant Proteins; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4