Evaluation of mechanistic role of artemin/GFRα3 signaling in osteoarthritis pain

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PROJECT SUMMARY Arthritis affects almost 60M adult Americans and is increasing in incidence, with osteoarthritis (OA) being the most common form of arthritis. OA occurs due to degeneration of tissues comprising joints, and is associated with pain. OA pain is a major contributor to the burden of chronic pain in society. About 80% of persons with OA suffer movement limitations, and 25% cannot perform major activities of daily living. Current treatment options are limited to steroid injections, nonsteroidal anti-inflammatory drugs (NSAIDS), opioids and non- pharmacological approaches (exercise, weight loss). Unfortunately, each of these therapeutic approaches are problematic. Exercise, which helps weight management, is difficult for patients due to ongoing pain. NSAIDS can cause gastrointestinal irritation and bleeding and increase risk of heart attack or stroke, and opioids are associated with addiction and abuse (and can actually worsen chronic pain). Clearly, there is a critical need to identify new therapeutic targets and/or treatments for individuals suffering from OA pain. Here, we propose that a heretofore unrecognized neural pathway is a critical component of OA pain. This pathway involves ARTN, its receptor GFRα3, and ‘pain’ channels on nerves (transient receptor potential [TRP] channels). Activation of this pathway initiates and maintains OA pain. The central hypothesis (based on preliminary data in multiple species [mouse, dog, cat, human]) is that ARTN, released from synovium of the OA joint in response to injury, results in de novo increase in its receptor, GFRα3, in local and distant sensory nerves, producing local and widespread pain and hypersensitivity via Proto-oncogene tyrosine-protein kinase receptor (RET)-mediated upregulation of multiple downstream TRP receptors. In this proposal, we will use multiple OA models and clinically relevant outcome measures, and leverage our unique access to dogs with naturally occurring OA, to achieve the following aims: Aim 1: To test the hypothesis that ARTN expression is increased in OA and is responsible for pain. Aim 2: To test the hypothesis that ARTN/GFRα3 signaling is responsible for behaviorally manifested OA pain both in early and late stage disease. Aim 3: To test the hypothesis that RET-dependent ARTN/GFRα3 signaling results in changes in multiple TRP channel expression and activation. Aim 4: To test/validate involvement of the above-described key molecules in a naturally occurring large animal model of OA (dog). Overall, this will be the first work investigating the role and mechanisms of ARTN/GFRα3/TRP channel in OA pain and sensitivity. Based on solid, clinically relevant preliminary data, and leveraging PI expertise from two different and complementary disciplines, successful completion of this proposed work has the potential to identify clinically relevant neural mechanisms leading to the development of novel, effective therapeutics for the treatment of OA-pain in humans.