Submitted on April 1, 2008
Revised on January 21, 2009
Accepted on January 21, 2009
Dying cells activate mesangial cells via Tlr2/Myd88 rather than Tlr3/Trif in immune complex glomerulonephritis
Julia Lichtnekert, Volker Vielhauer, Daniel Zecher, Onkar P Kulkarni, Sebastian Clauss, Stephan Segerer, Veit Hornung, Tanya N. Mayadas1, Bruce Beutler2, Shizuo Akira3, and Hans-Joachim Anders4*
1 Brigham and Women's Hospital
2 Scripps Research Institute
3 Osaka University
4 University of Munich
* To whom correspondence should be addressed. E-mail: hjanders{at}med.uni-muenchen.de.
Viral RNA or bacterial products can activate glomerular mesangial cells via a subset of Toll-like receptors (TLR). Because Tlr2-deficient mice were recently found to have attenuated nephrotoxic serum nephritis (NSN) we hypothesized that endogenous TLR agonists can activate glomerular mesangial cells. Primary mesangial cells from C57BL/6 mice expressed Tlr1-6 and Tlr11 mRNA at considerable levels and produced Il-6 when being exposed to the respective Tlr ligands. Exposure to necrotic cells activated cultured primary mesangial cells to produce Il-6 in a Tlr2/Myd88-dependent manner. Apoptotic cells activated cultured mesangial cells only when being enriched to high numbers. Apoptotic cell-induced Il-6 release was MyD88-dependent and only purified apoptotic cell RNA-induced Trif signaling in mesangial cells. Does Trif signaling contribute to disease activity in glomerulonephritis? To answer this question we induced autologous NSN by injection of NS raised in rabbits in Trif-mutant and wild-type mice. Lack of Trif did not alter the functional and histomorphological abnormalities of NSN including the evolution of anti-rabbit IgG and anti-rabbit-specific nephritogenic T cells. We therefore conclude that apoptotic cell RNA is a poor activator of Trif signaling in mesangial cells and that necrotic cell releases rather activate mesangial cells via the Tlr2/Myd88 signaling pathway.
