High-mobility group box 1, an endogenous ligand of toll-like receptors 2 and 4, induces astroglial inflammation via nuclear factor kappa B pathway

Background: Neuroinflammation has a definitive role in neurodegenerative diseases, such as Parkinson’s and Alzheimer’s disease. In addition to its pathoge- nic ligands, toll-like receptors (TLRs) can be activated by damaged endogenous molecules that induce inflammatory signalling pathways such as high-mobility group box 1 protein (HMGB1).  Materials and methods: Using an ex-vivo rat optic nerve (RON) model, we sought to determine the effects of lipopolysaccharides (LPS; TLR4 agonist), zymosan (TLR2 agonist) or HMGB1 — with or without TLR2/4 antagonists, on the expression of glial fibrillary acidic protein (GFAP) and nuclear factor kappa B (NF-ҡβ) for signalling pathway and astrocyte reactivity, using double immunohistochemistry; as well as on the modulation of the neurotoxicity. HMGB1-treated RON had significantly higher expression and co-localisation of GFAP and NF-ҡβ as compared to the un- treated control, which was a similar result to those treated with LPS and zymosan.  Results: Moreover, the HMGB1-induced inflammation was blocked by TLR2/4 antagonists (p = 0.05). However, the HMGB1-induced cell death was unblocked by TLR antagonists. Overall, HMGB1 endogenously mediates the signalling me- chanisms of neuroinflammation through TLR2/4.  Conclusions: Whereas, the neuronal death mechanism resulting from HMGB1 could be caused by a different signalling pathway. Gaining an understanding of these mechanisms may help researchers discover new therapeutic targets for neurodegenerative diseases.

Mapping tenascin-C interaction with toll-like receptor 4 reveals a new subset of endogenous inflammatory triggers

Pattern recognition underpins innate immunity; the accurate identification of danger, including infection, injury, or tumor, is key to an appropriately targeted immune response. Pathogen detection is increasingly well defined mechanistically, but the discrimination of endogenous inflammatory triggers remains unclear. Tenascin-C, a matrix protein induced upon tissue damage and expressed by tumors, activates toll-like receptor 4 (TLR4)-mediated sterile inflammation. Here we map three sites within tenascin-C that directly and cooperatively interact with TLR4. We also identify a conserved inflammatory epitope in related proteins from diverse families, and demonstrate that its presence targets molecules for TLR detection, while its absence enables escape of innate immune surveillance. These data reveal a unique molecular code that defines endogenous proteins as inflammatory stimuli by marking them for recognition by TLRs