Bacterial endotoxins increases Cdk5 activity in trigeminal ganglia neurons

Objectives: Cellular and molecular mechanisms involved in tooth pain are far to be understood. Dental pulp is highly innervated by primary afferents of trigeminal ganglia (TG) neurons, which sense innocuous and noxious stimuli and transmit it to CNS. During development of caries disease, Gram+ and Gram- bacteria colonize the dental pulp and release lipopolysaccharides (LPS) and lipoteichoic acid (LTA), respectively. Interestingly, LPS sensitize trigeminal neurons but the role of LTA is not known yet. Our group is studying the role of the protein kinase Cdk5 in dental pain. We found TNF-α treatment increased p35 expression and Cdk5 activity in TG neurons. Therefore, in the present work we evaluated the effect of LPS and LTA over Cdk5 kinase activity in trigeminal neurons.
Methods: By immunofluorescence (IF) we evaluated whether LPS and LTA treatments at different times (1, 3 and 24 h) increased canonical (P-P65, component of NFkB) and non-canonical signaling pathways (P-ERK1/2, Egr1) in primary cultures of mouse trigeminal neurons. In addition, we analyze immunolocalization of Cdk5, p35, TRPV1 (a known Cdk5 substrate) and Cdk5-mediated TRPV1 phosphorylation (P-TRPV1) in this culture treated by LPS or LTA.
Results: We found that LPS and LTA treatment increased immunolocalization and nuclear translocation of Phospho-P65, a component of its canonical pathway. In addition, we found that LPS and LTA significant increased Cdk5 and p35 immunodetection. More importantly, we found that LPS and LTA increased P-TRPV1 in primary cultures of mouse trigeminal neurons.
Conclusions: Altogether, our results demonstrate that bacterial endotoxins, as LPS but also LTA, sensitize trigeminal neurons through Cdk5/p35-mediated TRPV1 phosphorylation, suggesting a possible new molecular mechanism implicated in dental pain.