Chronic therapy-refractory trigeminal pain is a major medical problem, with temporo-mandibular-joint (TMJ) pain the most prevalent form of head-face pain. One of the obstacles to development of rationally targeted therapies lies in the shortcomings of available animal models for TMJD. Another roadblock is the lack of clear understanding of molecular, cellular and neural-circuit mechanisms that underlie TMJ pain and dysfunction. We have recently adapted bite-force measurements as read-out of TMJ inflammatory pain in mice, and applied this novel methodology to Trpv4-/- mice. The "osmo-mechano"-TRP, TRPV4, expressed in TMJ-innervating trigeminal ganglion (TG) neurons, is critical for bite-force reduction after TMJ-inflammation. Also, the expression of other pain-relate TRP channels ("pain TRPs"), and activation of extracellular signal-regulated protein kinase (ERK) in the TG after TMJ inflammation are regulated by TRPV4. Based on these mechanistic findings, our first aim is to investigate whether TRPV4 regulates other pain-related TRP channels through ERK in TG neurons. For this aim, we propose (1) to ascertain whether TRPV4- dependent "pain TRP" expression in the TG in TMJ-inflammation is neuronal, and co-localizes with TRPV4 expression;(2) to test the role of TRPV4 in regulating "pain-TRPs" in TG neurons by using Trpv4 sensory neuron-specific knockout mice;(3) to better define the role of ERK in regulating "pain TRPs" in TG neurons by using mice expressing neuron-specific dominant negative mitogen activated protein kinase-kinase (dnMEK). Considering the chronicity of TMJD pain in clinical patients, in addition, we propose to develop a longer-lasting TMJ inflammation by injecting chemical irritant loaded onto carbon nanoparticles, so that a slow-release" formulation results. By development of a longer-lasting arthritogenic irritant, our mouse model will more accurately reflect patients'cardinal complaints of chronic pain. We will verify th critical role of Trpv4 in a more chronic model. This research plan will elucidate the distinct roleof "pain-TRP" channels in TMJ pain. Amongst those, TRPV4 could possibly function as a significant regulator of pro-nociceptive signaling in TG sensory neurons that innervate the TMJ. Moreover, research as proposed will advance our understanding of the mechanisms of the persistent nature of TMJ pain and lead to more rational and effective treatments. The research agenda is embedded in a training plan that takes full advantage of rich and diverse institutional resources available at Duke University and UNC-Chapel Hill, so that the applicant will be positioned well to develop an independent career in TMJ pain research.
Temporomandibular joint disorder (TMJD) constitutes a highly significant healthcare problem in the US because of its prevalence, relative therapy-refractoriness and chronic course, yet it is ineffectively treated because of a lack of fundamental understanding, which in turn is rooted in the shortcomings of available animal models for TMJD. This project will use a mouse model to investigate molecular and cellular mechanisms in trigeminal ganglion sensory neurons that are critical for pathological TMJ pain and develop a more long-term TMJD model, which is more representative of pain chronicity. This application, through its research plan with focus on the TRPV4 ion channel, previously shown to be critical for inflammatory TMJ pain by the applicant, will advance our understanding of the mechanisms of persistent TMJ pain and lead to more rational and effective treatments, while at the same time providing a training opportunity for the applicant to become a fully independent investigator in TMJ research.