Despite the prevalence of pain originating from the teeth (dental, or odontogenic, pain) and its impact on patients’ lives, the cellular and molecular mechanisms of odontogenic pain are still not completely understood. The teeth are unique structures, innervated by sensory neurons that originate in the trigeminal ganglia. Factors that increase the sensitivity of these neurons, such as inflammatory cytokines, may contribute to odontogenic pain associated with dental pulp inflammation. To address this, a calcium imaging-based mouse trigeminal ganglion (TG) neuron sensitisation assay was established as part of this project. Short-term exposure to tumour necrosis factor alpha (TNFα), but not to interleukin 1 beta (IL-1β), was found to sensitise the transient receptor potential (TRP) ion channels TRPA1 and TRPV1 on TG neurons. This assay provides the opportunity to test other molecules relevant to odontogenic pain for their ability to sensitise TG neurons. Previous research suggests that initiation of dentine hypersensitivity, a type of odontogenic pain evoked by thermal, osmotic, chemical, evaporative, or mechanical stimuli to the exposed dentine, might involve both neurons and odontoblasts, the specialised mineralising cells in the teeth. In this project, mouse odontoblast-like (OB) cells were used as a cellular model to study the sensory function of odontoblasts in vitro. OB cells were demonstrated to express functional TRPV4 ion channels, known to be involved in thermal, osmotic, and mechanosensation. TRPV4 activation was also found to stimulate ATP release from OB cells, highlighting a potential means for odontoblast communication with dental afferent fibres. 3 In addition, this study was the first to demonstrate the odontoblast ability to detect biologically relevant acids. Both an acid-induced increase in OB cell intracellular calcium concentrations and subsequent ATP release were detected. These processes were found to be independent of TRPV4 activity. Finally, to address the ability of odontoblasts to transmit sensory information to adjacent neurons, a co-culture approach was used to directly study intercellular communication between mouse OB cells and TG neurons. Pharmacological activation of TRPV4 was chosen as an odontoblast-selective stimulus, based on the functional expression of TRPV4 ion channels in OB cells, but not in mouse TG neurons. Blocking purinergic signalling disrupted the interaction between stimulated OB cells and TG neurons, demonstrating the importance of ATP as a primary mediator. Taken together, the findings described in this thesis support the ability of odontoblasts to detect physiologically-relevant stimuli and respond with a release of ATP to modulate the activity of adjacent sensory neurons. Thus, this interaction may play an important role in the initiation of odontogenic pain in vivo.
|Date of Award
|1 Apr 2019
|Andrew Grant (Supervisor) & Stephen McMahon (Supervisor)