Diverse Effects of Various Toll-Like Receptor 2 Ligands on Neuronal Activity and Cell Death

The role of Toll-like receptor 2 (TLR2) in the central nervous system (CNS) is critical in several conditions including neurological disorders such as pain, and neurodegenerative disorders such as Parkinson's disease. Therefore, understanding TLR2 function in the CNS is of considerable importance. In this study, we investigated neuronal responses to individual TLR2 ligands. The expression levels of cytokines increased in the culture in the presence of TLR2 ligands. Additionally, increased lactate dehydrogenase (LDH) was noted during lipoteichoic acid (LTA) stimulation. During LTA stimulation, a decrease in the peak amplitude of Ca^{2 +} oscillations was observed. MnTBAP, which is a reactive oxygen species (ROS) blocker, inhibited the LTA-induced cell death but had no effect on the peak amplitude of the Ca^{2 +} spike. Conversely, Pam3CSK4 (P3C) stimulation increased the number of Ca^{2 +} peaks, which was inhibited by a tumor necrosis factor alpha (TNFα) signaling inhibitor. Our study revealed that several TLR2 ligands, each with different specificities, elicited diverse responses in primary cortical cells. In conclusion, TLR1-TLR2 and TLR2-TLR6 signaling reduces the peak amplitude and induces cell death, and TLR1-TLR2 signaling enhances Ca^{2 +} dynamics via a TNFα pathway.