The balancing effect between MAPK and NFkB pathways for the transcriptional regulation of Toll-like receptors

Toll-like receptors (TLR) are a family of pattern recognition receptors crucial for pathogen pattern recognition. Upon activation, TLRs induce innate immune responses such as cytokine production. However irregular TLR activities can provide fatal, hence fine tuning of the TLR induced responses are necessary. The TLR mediated immune responses are controlled by the positive/negative regulation of TLR signalling pathways, relocation of TLR proteins and modulation of TLR transcription. Systematic analyses of the agonist-induced transcriptional changes of TLRs were shown for the first time in my thesis. In my experiments, I have shown that each agonist induced a unique pattern of TLR transcription. Following PAM stimulation, mRNA levels of the cognate TLR1/2 increased whereas mRNA levels of the cross-regulating TLR4, 7/8/9 reduced in both cell lines and splenic macrophages from different mice strains. Through investigation of the signalling pathways responsible for mediating such TLR transcriptional changes, I then discovered the balancing effect between NFκB and MAPK signalling pathways. PAM induced TLR transcriptional changes were controlled by the additive and/or antagonistic interference between MAPK signalling cascades, ERK, JNK, P38 and NFκB signalling pathways. This was the first time that signalling synergy between MAPK and NFκB pathways were shown. Furthermore, PAM induced transcription of TLR1 and TLR8 may be partially regulated by the indirect feedback mediated by protein production. Importantly, the maintenance of the basal TLR mRNA expression also required activation of both MAPK and NFκB signalling pathways. In addition, signalling control for TLR transcription induced by different agonists (PAM vs. LPS) or in different species (chicken vs. mice) was compared. LPS induced transcriptional changes of the cross-regulating TLR1/2 and 3 but not the cognate TLR4 in RAW cells. The LPS induced TLR transcriptional changes required activation of a combination of MAPK and NFκB signalling pathways which shared both similarities and differences to the PAM induced signalling activation. In chicken, PAM induced more potent signalling activation, regulating the TLR transcriptional changes at a lower concentration than in mice. Overall, this thesis demonstrates that the transcriptional regulation of TLRs is complex, mediated by the coordination between MAPK and NFκB signalling pathways. These studies have significant implications in providing detailed insight of TLR transcriptional regulation which plays an important role in the regulation of TLR mediated innate immune responses. Please watch the following videos that I made for: A short introduction about TLR regulation - https://youtu.be/LTDdEZ3S97o A short explanation about TLR signalling - https://youtu.be/51IY5XhdJR8