title: Toll-like receptor 4 signaling is involved in IgA-stimulated mesangial cell activation.
abstract: OBJECTIVE
  Deposition of polymeric IgA1 in the kidney mesangium is the hallmark of IgA nephropathy, but the molecular mechanisms of IgA-mediated mesangial responses and inflammatory injuries remain poorly understood. We hypothesize that Toll-like receptor 4 (TLR4) is involved in IgA-induced mesangial cell activation.
  
  
  METHODS
  Mouse mesangial cells were stimulated with lipopolysaccharide (LPS) (1 μg/mL), IgA (20 μg/mL), or both, and TLR4 expression was measured by real time RT-PCR and Western blot. Intracellular responses to LPS or IgA were assessed by Western blot for ERK1/2, JNK, p38 MAP kinases (MAPKs), Iκ-Bα degradation and fibronectin secretion. MCP-1 secretion was assessed by ELISA. Small interfering RNA (siRNA) of TLR4 was used to confirm that the effects were caused by TLR4 activity.
  
  
  RESULTS
  LPS- or IgA-treatment upregulated the levels of TLR4 mRNA and protein in cultured MMC at 24 h. LPS and IgA induced rapid phosphorylation of MAPKs, but degradation of Iκ-Bα was observed only in LPS-treated MMC. LPS, but not IgA, induced increased secretion of MCP-1 and fibronectin at 24 h or 48 h. Combined LPS and IgA treatment did not cause additional increases in TLR4 mRNA and protein levels or Iκ-Bα degradation, and MCP-1 and fibronectin secretions were less than with LPS alone. LPS- or IgA-induced TLR4 protein levels and MAPK activation were inhibited by transfection with TLR4 siRNA.
  
  
  CONCLUSIONS
  These results indicate that the activation of MAPKs and MCP-1 secretion are mediated by TLR4, at least in part, in IgA-treated mesangial cells. TLR4 is involved in mesangial cell injury by induction of pro-inflammatory cytokines in IgA nephropathy.
authors.affiliation: Department of Pathology, Yonsei University College of Medicine, 250 Seongsan-ro, Seodaemun-gu, Seoul 120-752, Korea.
authors.forename: Beom Jin
authors.initials: BJ
authors.lastname: Lim
authors.forename: Dahye
authors.initials: D
authors.lastname: Lee
authors.forename: Soon Won
authors.initials: SW
authors.lastname: Hong
authors.forename: Hyeon Joo
authors.initials: HJ
authors.lastname: Jeong
mesh_terms: D000818:Animals; D018932:Chemokine CCL2 / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005353:Fibronectins / Q000378:metabolism; D005922:Glomerulonephritis, IGA / Q000378:metabolism*; D020672:I-kappa B Proteins / Q000378:metabolism; D050527:Mesangial Cells / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D000072000:NF-KappaB Inhibitor alpha; D010766:Phosphorylation; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction; D051197:Toll-Like Receptor 4 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: C491768:Ccl2 protein, mouse; D018932:Chemokine CCL2; D005353:Fibronectins; D020672:I-kappa B Proteins; C000606205:Nfkbia protein, mouse; D012333:RNA, Messenger; D051197:Toll-Like Receptor 4; D000072000:NF-KappaB Inhibitor alpha; D048049:Extracellular Signal-Regulated MAP Kinases