Yonsei Med J.  2011 Jul;52(4):610-615. 10.3349/ymj.2011.52.4.610.

Toll-Like Receptor 4 Signaling is Involved in IgA-Stimulated Mesangial Cell Activation

• Lim BJ
• Lee D
• Hong SW
• Jeong HJ

• KMID: 1727993
• DOI: http://doi.org/10.3349/ymj.2011.52.4.610

Abstract

PURPOSE
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.
MATERIALS AND METHODS
Mouse mesangial cells were stimulated with lipopolysaccharide (LPS) (1 microg/mL), IgA (20 microg/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), Ikappa-Balpha 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 Ikappa-Balpha 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 Ikappa-Balpha 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.
CONCLUSION
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.

Keyword

IgA nephropathy; mesangial cell; cytokine; toll-like receptor

MeSH Terms

Animals
Chemokine CCL2/secretion
Enzyme-Linked Immunosorbent Assay
Extracellular Signal-Regulated MAP Kinases/metabolism
Fibronectins/secretion
Glomerulonephritis, IGA/*metabolism
I-kappa B Proteins/metabolism
Mesangial Cells/*metabolism/secretion
Mice
Mice, Transgenic
Phosphorylation
RNA Interference
RNA, Messenger/metabolism
*Signal Transduction
Toll-Like Receptor 4/antagonists & inhibitors/genetics/*metabolism