PROJECT SUMMARY/ABSTRACT Knee osteoarthritis (OA) is a leading source of disabling pain, affecting nearly 20% of US adults over 45, which will only increase as our population ages. Although remarkable research and clinical efforts are being poured into discovering vital disease-modifying treatments (i.e., reversing joint damage, joint replacement), therapeutics targeting pain caused by knee OA are lacking. Given the high burden of pain in this disorder (e.g., sleeplessness, immobility, depression), and the fact that current treatments are invasive, lack long-term efficacy, carry high risk of severe side effects, and are inconsistent as analgesics (e.g., knee replacement, nerve ablation, and opioids)—adequate pain therapeutics are urgently needed. Peripheral nerves or dorsal root ganglion (DRG) are generally the first neurons to transmit pain, thus targeting DRG can prevent aberrant pain from initiating a nervous system cascade resulting in chronic, maladaptive changes to neural circuits. Furthermore, DRG are located outside of the blood brain barrier, providing an easily accessible therapeutic target. However, it is important to precisely target DRG populations transmitting knee OA pain, to preserve beneficial populations like those responsible for knee proprioception and stabilization. Relatedly, recent clinical gains have been made by precisely targeting specific functional alterations in DRG during pain states caused by small fiber neuropathy and postoperative pain. Additionally, the basic science pain research field has suffered from a lack of translation from commonly used models to clinical pathologies, but exciting advances are being made by applying basic science approaches in relevant mediums like human tissues. Here I propose that identifying the DRG populations driving knee OA-induced changes in nociceptive neural circuits in addition to identifying the OA-induced alterations within these DRG populations, will provide avenues for potential therapeutics. In the mentored K99 phase, my mentor Julie Kauer, PhD, and my advisors Stuart Goodman, MD, PhD, Gregory Corder, PhD, Elizabeth Serafin, MS, and Lu Chen, PhD, will support my career development and training. Building upon my current work demonstrating that the TRPV1- expressing DRG population drives inflammatory injury-mediated spinal potentiation, 1) I will determine if knee OA initiates spinal potentiation via TRPV1-expressing DRG neurons innervating the knee. Additionally, 2) I will profile DRG neurons active in knee OA pain using the TRAP (Transient Recombination in Active Populations) technique in combination with behavioral assays, transcriptomic analysis, and electrophysiology. Finally, in the independent phase 3) I will use a co-culture system with human-derived DRG neurons and knee tissue recovered from arthroplasties to investigate the genetic, population-level activity, and functional changes within DRG neurons in an osteoarthritic joint environment. This will generate leads to build upon in my future research program and generate fundable projects for a multiyear investigation of knee OA pain.

PROJECT NARRATIVE Knee osteoarthritis is a primary cause of disability and chronic pain, with less than optimal first-line treatments that are often invasive and inaccessible to patients—leading to an overreliance on analgesics like opioids, which are dangerous, addictive, and ineffective with long-term use. The high burden of knee osteoarthritis- induced pain warrants the need to develop novel analgesic strategies. This proposal combines cutting-edge basic science techniques with clinically relevant models of knee osteoarthritis, to confront the problem of knee osteoarthritis pain head-on and generate leads for future research into novel analgesics.