Chronic pain affects more than 50 million Americans per year, resulting in extraordinary personal and societal costs. Adding to the dilemma, deaths involving prescription opiate analgesics have almost quadrupled in the last ten years. The clinical challenge of pain management is underscored by evidence that chronic pain is mechanistically distinct from acute pain, therefore a thorough understanding of the molecular and cellular mechanisms underlying the transition to chronic pain is fundamental to improving and expanding treatment options. Hyperalgesic priming is a compelling model of the transition to chronic pain in which an initial injury resolves, but leaves the animal in a primed state in which a second insult induces a greatly prolonged pain response. While previous studies have explored the development of sustained mechanical hypersensitivity, we have adapted this model to examine sustained hypersensitivity mediated by nociceptors expressing the heat-gated ion channel TRPV1, which can drive pain in a range of inflammatory and neuropathic conditions. Experiments proposed here will test the contribution to heat hyperalgesic priming of adenylyl cyclase isoform AC2, which has not been previously characterized in sensory neurons, and which is insensitive to inhibition by Gi/o-coupled receptors such as opioid receptors. Preliminary analysis indicates that AC2 is highly expressed in TRPV1-expressing neurons and required for the manifestation of heat hyperalgesic priming.
Specific Aim 1 will examine the impact of AC2 gene deletion and pharmacological inhibition on behavioral nociceptive thresholds at baseline, in acute hyperalgesia and in the setting of hyperalgesic priming.
Specific Aim 2 will determine whether AC2 and the downstream effector Epac are functionally coupled through AKAP family member scaffolding proteins by co-immunoprecipitation-mass spectrometry, and will determine the impact of deleting identified AKAP genes on Epac signaling and nociceptor function in vitro using a CRISPR/Cas9-based approach.
Specific Aim 3 will determine the consequences for Epac function of AC2 and AKAP gene deletion through Epac-dependent PKC phospho- substrate profiling and behavioral assessment of heat hyperalgesia. This proposal will use innovative approaches to explore novel mechanisms contributing to the development of persistent hyperalgesia.
Intractable pain is a major clinical challenge that poses a heavy societal burden and is driving a national controversy over the use of potentially dangerous opioid analgesics. This project tests the contribution of non- canonical adenylyl cyclase signaling in the persistent thermal sensitization of peripheral nociceptive sensory neurons using a novel ?heat hyperalgesic priming? model of the transition from acute to chronic pain. Experiments proposed here will test the contribution of a novel mechanism for this transition, dynamic scaffolding of adenylyl cyclase isoform AC2 and its downstream effector Epac, elucidate downstream consequences of adenylyl cyclase/Epac scaffolding and expand our understanding of G protein-coupled receptor signal integration through adenylyl cyclase isoforms in chronic pain.
