Funded Projects

Immune checkpoint proteins regulate the immune system to prevent it from indiscriminately attacking cells. Some cancers activate these immune checkpoints to avoid attack, and drugs that target certain immune checkpoints are approved for cancer treatment. The same pathway may also be involved in pain because immune checkpoint proteins, such as programmed death 1 (PD-1) and the molecule that binds to it (programmed death ligand 1 [PD-L1]), also are found in sensory neurons, microglia, and macrophages. This project will investigate PD-1/PD-L1 in different cell populations to determine their contribution to pain and to the effects of opioids such as morphine. This knowledge may help identify new drugs for pain management that modify immune checkpoint activity.

As many as 64% of patients with Temporomandibular Joint Disorders (TMJDs) report symptoms consistent with Irritable Bowel Syndrome (IBS). However the underlying connection between these comorbid conditions is unclear and treatment options are poor. As such, pain management for these Chronic Overlapping Pain Conditions (COPCs) is a challenge for physicians and patients. This project will determine whether the convergence of pain from different peripheral tissues and perceived stress occurs in the brain and elicits a change in central neural processing of painful stimuli. This project will identify and validate specific lipids, enzymes and metabolic pathways that change expression in the brain during the transition from acute to chronic overlapping pain that can be therapeutically targeted to treat COPCs. Multi-disciplinary approaches will be used to combine brain imaging, visualization of spatial distribution of molecules, genetics, pharmacological and behavioral research techniques.

Identification of new targets and mechanisms underlying chronic neuropathic pain is essential for the discovery of novel treatments and preventative tactics for better neuropathic pain management. A recent exploration of next-generation RNA sequencing identified a large, native, full-length long noncoding RNA (lncRNA) in mouse and human dorsal root ganglion (DRG). It was named as nerve injury-specific lncRNA (NIS-lncRNA), since its expression was found increased in injured DRGs, in response to peripheral nerve injury, but not in response to inflammation. Preliminary findings revealed that blocking the nerve injury-induced increases in DRG NIS-lncRNA levels ameliorated neuropathic pain. This project will validate NIS-lncRNA as a therapeutic target in animal models of neuropathic pain and in cell-based functional assays utilizing human DRG neurons. Completion of this proposal will advance neuropathic pain management and might provide a novel, non-opioid pain therapeutic target.

Spinal cord injury (SCI) impairs sensory transmission leading to chronic, debilitating neuropathic pain. While our understanding of the molecular basis underlying the development of chronic pain has improved, the available therapeutics provide limited relief. In the lab, we have shown the timing of exercise is critical to meaningful sensory recovery. Early administration of a sustained locomotor exercise program in spinal cord–injured rats prevents the development of neuropathic pain, while delaying similar locomotor training until pain was established was ineffective at ameliorating it. The time elapsed since the injury occurred also indicates the degree of inflammation in the dorsal horn. We have previously shown that chronic SCI and the development of neuropathic pain correspond with robust increases in microglial activation and the levels of pro-inflammatory cytokines. This proposal seeks to lengthen the therapeutic window where rehabilitative exercise can successfully suppress neuropathic pain by pharmacologically reducing inflammation in dorsal root ganglia.

Spinal cord injury (SCI) impairs sensory transmission and leads to chronic, debilitating neuropathic pain. While our understanding of the development of chronic pain has improved, the available therapeutics provide limited relief. We will examine the peripheral immune and inflammatory response. Secondary inflammation in response to SCI is a series of temporally ordered events: an acute, transient upregulation of chemokines, followed by the recruitment of monocytes/macrophages and generation of an inflammatory environment at the lesion site in the spinal cord, but also surrounding primary nociceptors in the dorsal root ganglia (DRG). These events precede neuropathic pain development. Previous work indicates that after SCI, macrophage presence in the DRG correlates with neuropathic pain. We propose to study: 1) whether the phenotype of macrophages that infiltrate the DRG is different than those that persist chronically after SCI and 2) how manipulation of macrophage phenotype affects nociceptor activity and pain development.

An important component of neuropathic pain is spontaneous or ongoing pain, such as burning pain or intermittent paroxysms of sharp and shooting pain, which may result from abnormal spontaneous activity in sensory nerves. However, due to technical limitations, spontaneous activity in sensory neurons in vivo has not been well studied. Using in vivo imaging in genetically-modified mice, preliminary findings identified spontaneously-firing clusters of neurons formed within the dorsal root ganglia (DRG) after traumatic nerve injury that exhibits increased spontaneous pain behaviors. Furthermore, preliminary evidence has been collected that cluster firing may be related to abnormal sympathetic sprouting in the sensory ganglia. This project will test the hypothesis that cluster firing is triggered by abnormal sympathetic inputs to sensory neurons, and that it underpins spontaneous paroxysmal pain in neuropathic pain models. Findings from this project will identify potential novel therapeutic targets for the treatment of neuropathic pain.

Effective treatments are elusive for the majority of patients with neuropathic pain. Reactive oxygen and nitrogen species (ROS/RNS) are involved in neuropathic pain, because they drive mitochondrial dysfunction, cytokine production, and neuronal hyperexcitability; therefore, stimulation of endogenous antioxidants is predicted to simultaneously resolve multiple neuropathic pain mechanisms. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor that is a potential therapeutic target because it regulates the expression of a large number of endogenous antioxidant-related genes and can be activated with a single drug. This project will test the hypothesis that Nrf2 activation increases multiple endogenous antioxidants, therefore reversing neuropathic pain behaviors and counteracting neuropathic pain mechanisms that are driven by ROS/RNS and could provide an effective pain therapy, with minimal abuse/addictive potential.

There is an urgent unmet need for more efficacious analgesics that act via a non-opioid pathway. Mitogen Activated Protein Kinase-interacting kinase 2 (MNK2) is an enzyme that has been implicated in pain signaling, and there is compelling evidence that inhibiting MNK2 has significant pain-reducing effects with few side-effects. Since MNK2 selective inhibitors have not yet been identified, selective inhibition of MNK2 with a small molecule has not been possible. The development of such compounds will enable studies that will illuminate key differences between MNK2 and MNK1. More importantly, from a therapeutic standpoint, highly selective MNK2 inhibitors may prove to have enhanced efficacy and a more favorable side-effect profile than molecules that inhibit both MNK2 and MNK1. This project will support the design and synthesis of at least one MNK2 inhibitor, with >100-fold selectivity over MNK1, that may be developed into a lead compound for treating neuropathic pain.

Many chronic pain conditions are dependent upon activity of the sympathetic nervous system. Sympathetic blockade is used clinically in chronic pain conditions, but the clinical and preclinical evidence for this practice is incomplete. We propose that certain pathological pain conditions require intact sympathetic innervation of the sensory nervous system at the level of the dorsal root ganglion (DRG) and that release of sympathetic transmitters enhances local inflammation and leads to pain. Our preliminary data show large, rapid, and long-lasting reduction of pain behaviors and inflammatory responses following a"microsympathectomy" (mSYMPX) in both neuropathic and inflammatory pain models. Our aims are to: 1) characterize the effects of mSYMPX on pain and on local inflammation in the DRG; 2) explore the molecular mechanisms for sympathetic regulation of inflammatory responses in the DRG; and 3) assess the functional role of sympathetic transmitters in the sympathetically mediated inflammatory responses in the DRG.

Neuropathic pain conditions are difficult to treat, and novel non-narcotic analgesics are desperately needed. The G protein-coupled receptor 160 (GPR160) has emerged as a novel target for analgesic development, as GPR160 in the spinal cord may play a role in the transition from acute to chronic pain. Cocaine- and Amphetamine-Regulated transcript peptide (CARTp) was identified as a ligand for GPR160. Blocking endogenous CARTp signaling in the spinal cord attenuates neuropathic pain, whereas intrathecal injection of CARTp evokes painful hypersensitivity in rodents through GPR160-dependent extracellular signal-regulated kinase (ERK) and cyclic AMP response element-binding pathways (CREB). This project will isolate and biochemically characterize GPR160 and establish methods for biochemical characterization of GPR160 interaction with CARTp activator. Researchers will miniaturize and optimize biochemical assay and scale up protein production for future high throughput biochemical screening to identify potent inhibitors of GPR160 activation. These studies are critical for defining the molecular mechanism of CARTp/GPR160 interactions and initiating large-scale screens for new inhibitors to develop novel therapeutics.

Neuropathic pain is a debilitating affliction present in 26% of diabetic patients, with substantial impact on the quality of life. Despite this significant impact and prevalence, current therapies for painful diabetic neuropathy (PDN) are only partially effective, and the molecular mechanisms underlying neuropathic pain in diabetes are not well understood. Our long-term goal is to elucidate the molecular mechanisms responsible for PDN in order to provide targets for the development of therapeutic agents. Our objective is to identify the molecular cascade linking CXCR4/SDF-1 chemokine signaling to DRG nociceptor hyper-excitability, neuropathic pain, and small fiber degeneration. Our aims will determine: 1) the ion-channel current profile of the nociceptor hyper-excitable state produced by CXCR4/SDF-1 signaling in PDN; 2) the gene expression profile of the nociceptor hyper-excitable state produced by CXCR4/SDF-1 signaling in PDN; and 3) the specific features of nociceptor mitochondrial dysfunction produced by CXCR4/SDF-1 signaling in PDN.

Using neural tissues from pain patients, this project will investigate mechanisms of neuronal and/or immune dysfunction driving chronic pain. The researchers will use spatial transcriptomics on human dorsal root ganglion (DRG) and spinal cord tissues to examine the cellular expression profile for these targets using the 10X Genomics Visium technology. The use of tissues from control surgical patients and organ donors as well as surgical patients with neuropathic pain will enable validation of expression of these targets in human tissue as well as indication of their potential involvement in neuropathic pain. This collaborative effort will use DRGs removed from pain-phenotyped patients during neurological surgery, as well as lumbar DRGs and spinal cord from organ donors. This study will map the spatial transcriptomes at approximately single cell resolution in the human DRG and spinal cord.

A substantial proportion of Americans seeking emergency care after traumatic stress exposure (TSE) are at a high risk of chronic pain and opioid use/misuse. Physiologic systems involved in the stress response could possibly play a critical role in the development of chronic pain after TSE. FK506-binding protein 51 (FKBP51) is an intracellular protein known to affect glucocorticoid negative feedback inhibition and component of stress response, provides an important non-opioid therapeutic target for such chronic pain. This project will test the hypothesis that functional inhibition of FKBP51 prevents or reduces enduring stress-induced hyperalgesia in a timing, dose, and duration-dependent manner in animal models of single prolonged stress alone and in combination with surgery. This project will also test if FKBP51 inhibition enhances recovery following TSE via reduction in pro-inflammatory responses in peripheral and central tissues. It will also test whether FKBP51 inhibition effects cardiotoxicity or addiction. Completion of these studies will increase understanding of FKBP51 as a novel therapeutic target for the prevention of chronic pain and opioid use/misuse resulting from TSE.