Tumor necrosis factor and its p55 and p75 receptors are not required for axonal lesion‐induced microgliosis in mouse fascia dentata

Abstract

Tumor necrosis factor (TNF) is a potent pro-inflammatory and neuromodulatory cytokine. In the CNS it is produced primarily by microglia and considered to regulate microglial activation. On the basis of previous observations of increased microglial TNF mRNA synthesis in areas of anterograde axonal and terminal degeneration in mice, we studied the effect of TNF and its p55 and p75 receptors on axonal lesion-induced microglial activation in fascia dentata following transection of the perforant path (PP) projection. Unexpectedly, cell counting showed that the axonal lesion-induced microglial response in TNF and TNF-p55p75 receptor knock out mice and C57BL/6 mice was similar 5 days after the lesion. In addition, the microglial expression of the lysosomal-associated antigen CD68, and the clearance of MBP(+) myelin debris appeared similar in TNF and TNF-p55p75 receptor knock out mice compared to C57BL/6 mice. Quantitative PCR and in situ hybridization showed the expression of TNF mRNA to be maximally upregulated 6 h after the lesion, and confirmed that TNF mRNA was still upregulated 5 days after lesion when microglial numbers, CD11b mRNA level, and cellular TNF-p55 and -p75 receptor mRNA level reached maximum. However, in spite of the induction of TNF mRNA, TNF protein level remained at base-line in fascia dentata using immunohistochemistry and ELISA. In conclusion, the results showed a lower than expected lesion-induced increase in TNF protein, and that neither TNF nor its receptors were required for the axonal lesion-induced microglial morphological transformation and proliferation or for the initial clearance of degenerated myelin in the PP-deafferented fascia dentata.

Microglia Protect Neurons against Ischemia by Synthesis of Tumor Necrosis Factor

“…This was partly attributable to our finding of comparable neocortical volumes and CD11b mRNA levels and partly because we, despite reports about a stimulatory role of TNF on microglial proliferation in vitro (Théry and Mallat, 1993), failed to observe significant differences in microglial numbers in both unmanipulated hippocampus and perforant pathway-deafferented dentate gyrus in TNF-KO, TNFp55Rp75R-KO, TNF-p55R-KO, and WT mice (Babcock et al, 2006;Fenger et al, 2006). Although undetectable in the volumetric data in this study, and in conventional microglial stainings, we cannot exclude that the cellular composition and fine structure of neocortex may differ between TNF-KO and WT mice, or that there are regional adjustments of microglia as a result of different homeostatic requirements by cortical and hippocampal neurons.…”

Stimulation of Adult Oligodendrogenesis by Myelin-Specific T Cells

“…43 In the CNS, TNF is expressed primarily by microglia or infiltrating macrophages in response to injury, 96 and is induced by inflammatory cytokines such as IFN-␥ 97 or by cell-cell contact with activated myelin-reactive T cells. 98,99 Using the PP lesion model, our group has previously demonstrated a transient increase in TNF mRNA expression levels at 2 days post lesion, 34 which was increased by the presence of IFN-␥. 100 This was confirmed in the present study, in which a marked increase in TNF mRNA expression was observed in T PLP mice at 2 days post lesion and persisted at 7 days post lesion.…”

“…Sections were rinsed and incubated using monoclonal rat anti-BrdU antibody (AB6326; dilution 1:100; Abcam Ltd., Cambridge, England), which was detected using biotinylated goat anti-rat Ig antibody (RPN 1005; dilution 1:200; Amersham Pharmacia Biotech, Inc.), and alkaline phosphatase-conjugated streptavidin (P396; Dako A/S), and incubated in an alkaline phosphatase developer as previously described. 34 …”

“…Primers and probes for tumor necrosis factor (TNF)-␣ and IFN-␥ and the -chain of the CD3 complex were used as previously described. 34,37 For IL-4, we used forward primer 5=-AAACATGGGAAAACTCCA-3= and reverse primer 5=-CAGCTTATCGATGAATCCA-3=); for IL-10, forward primer 5=-AGGACTTTAAGGGTTACT-3= and reverse primer 5=-AAT-GCTCCTTGATTTCTG-3=; for IL-17, forward primer 5=-GCTTCATCTGTGTCTCTG-3= and reverse primer 5=-GAACGGTTGAGGTAGTCT-3=). For NG2, we used forward primer 5=-TCCCGGAGAGAGGTGGAAGAG-3= and reverse primer 5=-GGTCCATCTCTGAGGCATTAGC, and probe 5=-AAGGCGTCTGTCTGTGTCTCACTTC-CATCA-3=.…”

Original article Toll-like receptors as an innate immunity bridge to neuroinflammation in medulloblastoma

“…Results of the present study show that such pathogens may be also produced by dead medulloblastoma cells. The role of TLRs in pathology of the CNS was a subject of numerous studies, which documented the implication of TLR 2 signalling in glia responses associated with repair by the clearance of myelin debris [6,9,10].…”