TNFα-induced p38 MAPK activation regulates TRPA1 and TRPV4 activity in human odontoblast-like cells

Objectives: Odontoblasts express multiple mechano-sensitive ion channels, including members of the transient receptor potential (TRP) channel family. TRPA1 and TRPV4 are candidate mechano-sensitive TRP channels that play pivotal roles in inflammatory pain and mechanical hyperalgesia, however the effects of inflammation on the activity of these channels is not known. The objective of the current work was to determine whether TNFα directly sensitises TRPA1 and TRPV4 in odontoblasts.
Methods: Dental pulp cells were derived by explant culture and differentiated towards an odontoblast phenotype in the presence of β-glycerophosphate. The odontoblast phenotype of the cells was confimmed by the expression of dentin sialophosphoprotein (DSP). Cells were treated with tumour necrosis factor alpha (TNFα) and the TRPA1 and TRPV4 gene and protein expression was determined by q-RT-PCR and immunohistochemistry. Functional studies of channel activity employed calcium imaging. Western blotting was used to study the signalling pathway involved in TNFα modultaion of TRP channels.
Results: Short treatment of odontoblast-like cells with TNFα significantly enhanced TRPA1 and TRPV4 responses to their specific chemical agonists and to membrane stretch. This enhanced channel activity was accompanied by expression of phospho-p38MAPK. Furthermore, treatment of cells with the p38 inhibitor SB202190, significantly reduced TNFα effects, suggesting signalling via the p38MAPK pathway. When cells were treated with TNFα for 24hrs there was an up regulation inTRPA1 expression but down regulation of TRPV4. The induced TRPA1 expression was significantly reduced by treatment with SB202190.
Conclusions: Our findings demonstrated that TNFα is capable of enhancing TRPA1 and TRPV4 responses via the p38MAPK pathway and inhibitors of p38MAPK might therefore constitute a novel drug target for pain and inflammation mediated by non-neuronal TRP expressing cells.