Gregory O. Dussor - US grants

The proposed studies will test the hypothesis that neuronal nicotinic receptor agonists produce antinociception at peripheral sites of action. The specific aims of these studies will be to assess the antinociceptive effects of neuronal nicotinic receptor activation in the complete Freund's adjuvant (CFA) and chronic constriction injury (CCI) models of experimental pain. In addition, molecular biological techniques will be utilized to determine the expression and distribution of neuronal nicotinic receptors along peripheral sensory neuronal processes originating in the trigeminal ganglion. The effects on neuronal nicotinic receptor expression under conditions of inflammatory and neuropathic experimental pain and the extent to which these alterations are dependent upon nerve growth factor will also be assessed. Thus, the present studies will examine the role that peripheral neuronal nicotinic receptors play in the antinociceptive effects seen due to nicotinic agonists. The development of analgesic drugs with distinct mechanisms than those of opioids or non-steroidal anti inflammatory drugs (NSAIDS) is important due to the undesirable side effects of these drugs and their ineffectiveness in certain types of neuropathic pain. Establishing a peripheral site of action for nicotinic analgesic drugs holds out the advantage of eliminating any potential central nervous system side effects of centrally acting nicotinic analgesics.

DESCRIPTION (provided by applicant): Migraine headache was once thought to be predominately of vascular origin but it is now increasingly appreciated that its genesis and progression also involves maladaptive changes in the nervous system. Migraine represents the most common neurological disorder affecting up to 33% of women and 13% of men at some point in their lives. Despite its widespread prevalence, the pathophysiology that leads to migraine headache is still poorly understood and pharmacological treatment is only effective in about 50% of migraine sufferers. Developing new treatments with greater efficacy than those currently available is limited, in part, by a lack of new therapeutic targets. Thus, the identification of new targets that contribute to the pathophysiology of migraine headache is of critical importance for more effective migraine therapies. Prior preclinical work has found that trigeminal pain-sensing neurons (nociceptors) innervating the cranial meninges (i.e. the dura mater) are sensitive to substances released from mast cells. Mast cells can be activated following stress and increased estrogen levels, both of which are associated with migraines in humans. However, the cellular mechanisms by which mast-cell induced signaling is initiated are unknown. The hypothesis of this proposal is that decreased extracellular pH within the dura following mast-cell degranulation leads to activation of dural afferents via the opening of acid-sensing ion channels (ASICs). Recent studies in the laboratory have found that identified dural afferents respond to small drops in pH with currents generated by ASICs. Following exposure to mast cell mediators, these small pH drops lead to firing of action potentials. Preliminary studies also show that direct application of decreased pH solutions to the dura mater of awake animals elicit behaviors thought to be relevant to migraine pain. The proposed studies will explore ASIC-mediated dural afferent excitability and migraine-related pain behaviors in response to drops in pH by addressing the following questions. Are ASIC currents and pH-induced excitability of dural afferents increased by mast cell mediators and do these factors lead to enhanced afferent activity following small drops in pH? Does activation of ASIC channels on neuronal endings within the dura produce signs of afferent signaling and which ASIC proteins are expressed on dural afferent endings? Do mast-cell mediators increase the migraine-related behavior induced by activation of ASICs within the dura? The goal of this proposal is to determine the role of ASICs on sensory endings within the dura and how these channels might contribute to afferent signaling and migraine headache. If ASICs are found to play an important role in migraine pathophysiology, this finding would identify new targets for the pharmacological treatment of migraine and could lead to new therapies with increased efficacy over those currently available. Developing drugs targeting ASICs may ultimately provide relief to the large numbers of migraine patients that are not being adequately treated by currently available therapies.

DESCRIPTION (provided by applicant): Post-surgical pain represents an important clinical problem that is a major cause of chronic pain and a burden on healthcare systems. Treatments that target molecular events that underlie post-surgical acute and chronic pain may offer better management of post-surgical pain and reduce the proportion of patients (as high as 50%) that develop chronic pain after surgey. The focus of this research effort is to further develop two potential mechanisms for the pharmacological manipulation of pain: adenosine monophosphate activated kinase (AMPK) activators and peptides that disrupt voltage-gated sodium channel type 1.7 (Nav1.7) / extracellular signal regulated kinase (ERK) interactions. AMPK is an energy sensing kinase that endogenously regulates cellular pathways involved in growth and proliferation and emerging evidence suggests that activation of AMPK decreases the excitability of neurons. We have demonstrated that diverse AMPK activators prevent and reverse post-surgical pain via inhibition of mammalian target of rapamycin (mTOR) and ERK signaling pathways. Moreover, AMPK activators inhibit excitability and evoked hyperexcitability of sensory neurons. Nav1.7 is expressed primarily in the peripheral nervous system and plays an important role in setting the excitability of the neuron. Human genetic studies have demonstrated a crucial role for Nav1.7 in pain processing and recent evidence suggests that Nav1.7 also plays an important role in acquired pain disorders yet mechanisms through which Nav1.7 is regulated are only now coming into focus. Our preliminary data strongly suggest that AMPK activators are linked to interference with ERK mediated phosphorylation of Nav1.7. This process decreases the excitability of sensory neurons and reduces hyperexcitability induced by algogens linked to post-surgical pain. The goal of this proposal is to test the hypothesis that AMPK activators represent a new therapeutic avenue for the treatment of post-surgical pain through aims examining: 1) the pharmacology of AMPK activators in behavioral models of post-surgical pain, 2) mechanisms of AMPK regulation of mTOR and ERK in sensory neurons and 3) AMPK-mediated regulation of ERK interactions with Nav1.7. We anticipate developing a rationale for two novel therapeutic avenues for the treatment of pain under this proposal: 1) AMPK activators and 2) peptides that disrupt ERK/Nav1.7 interactions. Hence, the present application will utilize a multidisciplinary approach to tackle the problem of post-surgical pain with the goal of advancing novel therapies toward the clinic.

Migraine is the most common neurological disorder, the 3rd most common disease on earth, and the 8th most disabling. Currently available treatments fail to effectively manage migraine in most patients. Development of new therapeutics has been slow due in large part to a poor understanding of the underlying pathology of migraine. Endogenous proteases, released in the meninges by resident mast cells, have been proposed as a potential driver of migraine pain via an action on protease activated receptor type 2 (PAR2). Unfortunately the evidence for this mechanism relies on imprecise pharmacological tools and lacks genetic validation. The central hypothesis of this multi-PI research program is that PAR2 expression in nociceptors that project to the meninges plays a key role in the pathogenesis of migraine pain by linking meningeal protease release to sensitization of the trigeminal nociceptive system. The primary objectives of this proposal are to develop next generation PAR2 antagonists, to use these tools to validate PAR2 as a migraine pain target and to use mouse genetics to identify the specific role of PAR2 expression in meningeal projecting nociceptors to migraine pain. Our first aim will be to use our established PAR2 development pipeline to design new PAR2 antagonists with improved drug-like properties to probe PAR2 function in the context of a mouse model of migraine pain. Our second aim will use pharmacological tools in a novel mouse migraine model to further understand the potential role of PAR2 in migraine and signaling pathways engaged by PAR2 to evoke pain from the dura. Our final aim will use mouse genetics to study the cell type-specific role of PAR2 in migraine pain. Our work will result in: 1) the discovery and development of novel high potency antagonists for PAR2; 2) the development of an innovative new target for migraine pain; and 3) provide the first genetic verification of the cell type-specific action of PAR2 in the pain pathway. Taken together, successful studies will provide a preclinical rationale for the further development and testing of PAR2 ligands for the treatment of migraine and other forms of pain.

Women consistently report higher headache-related disabilities, higher relapse rate, more frequent, longer lasting, and more severe headaches than men. Hence, there is an urgent need to customize migraine management schemes based on sex-specific pain mechanisms. Accordingly, our long-term goal is to define sex-specific mechanisms of migraine, and utilize this knowledge to provide more effective sex- based personalized migraine management schemes. It is well accepted that the pathogenesis of headache syndromes, especially migraine, are sex-dependent due to important contributions of gonadal hormones (GnH). First, some reports show that migraine attacks in female and males are accompanied by a rise in plasma levels of prolactin (PRL). Second, we and others demonstrated that PRL responsiveness in pain pathways is sex-dependent and strictly controlled by estrogen. There is a critical gap in knowledge pertaining to whether and how the PRL system sex- dependently regulates migraine. The objective of this proposal is to identify mechanisms linking the PRL system to stress- and sex-dependent regulation of certain types of migraine. Our preliminary data demonstrate that PRL applied to cranial dura induces long-lasting facial allodynia in females, but not males. PRL also sensitizes mustard oil-evoked CGRP release from female, but not male dura. Finally, to further link the PRL system to migraine, we showed that a PRL receptor (Prlr) antagonist blocks CGRP- induced migraine behavior in females. Thus, our central hypothesis is that PRL acting through the Prlr on dural-innervating sensory neurons mediates female-specific mechanisms contributing to migraine. The rationale for the proposed study is that it 1) greatly expands our knowledge of sex differences in migraine mechanisms; and 2) provides translational potential by offering therapeutic targets for sex-based migraine management. Our hypothesis is tested by interconnected yet independent aims. Aim 1 examines sex-specific expression and regulation of PRL and Prlr in the trigemino-vascular system. Aim 2 determines how PRL and Prlr sex-specifically modulate the activity of dural afferents and migraine- like behavior in stress-induced migraine models. Aim 3 assesses a link between CGRP-induced migraine behavioral responses and the dural PRL system. The proposed study is innovative since it defines conceptually novel sex-specific regulatory mechanisms for certain migraine models based on PRL signaling. The proposed research is significant as it advances our understanding of sex differences in migraine mechanisms ? an understudied area where increasing basic science knowledge has the potential to lead to better sex-based personalized therapeutics.

The World Health Organization ranks migraine as the 3rd most prevalent disease worldwide and 8th most disabling (4th most in women) making it the most common neurological disorder. One of the primary reasons for the disabling nature of migraine is the poor efficacy of currently available therapeutics. Less than 50% of patients achieve complete relief with acute agents such as triptans and only half of patients achieve 50% relief with preventative agents. Development of new therapeutics has been slow due to a lack of understanding of the underlying pathophysiology of migraine. Our long-term goal is to identify new therapeutic targets for this common and debilitating disorder. One of the most consistent triggers for migraine is administration of a nitric oxide (NO) donor. Approximately 75% of human migraine patients will develop an attack within 6 hours of NO donor administration. Mechanisms by which NO donors trigger migraine are unknown. The objective of this proposal is to test whether the reaction product of NO and superoxide, peroxynitrite (PN), contributes to migraine pathophysiology. Studies over the last decade have shown that PN is an important activator/sensitizer of sensory neurons in preclinical pain models of neuropathic, inflammatory, and cancer pain and agents that eliminate PN have demonstrated efficacy in preclinical pain models. However, no studies have examined whether PN contributes to migraine despite the observation that the only pain state triggered by administration of a PN-producing stimulus is migraine (NO donors do not directly cause other types of pain). Thus, we propose to test the hypothesis that the effects of NO on migraine are due to PN formation. The rationale for the proposed study is that it 1) greatly expands our knowledge of mechanisms underlying one of the most common migraine triggers; and 2) provides translational potential by offering new therapeutic targets for migraine. We will test this hypothesis with 2 Aims using preclinical rodent models: Aim 1 will test the efficacy of PN scavengers and decomposition catalysts against NO donor-induced migraine behavior and NO donor-induced activity in trigeminal (dural) neurons. Aim 2 will test the efficacy of PN scavengers and decomposition catalysts against NO donor-induced mast cell degranulation, CGRP release, and protein tyrosine nitration in the dura. This innovative study will for the first time investigate the role of PN in migraine and will use novel behavioral models that mimic conditions relevant to migraine. The significance of the proposal is that it advances our understanding of migraine mechanisms and has the potential to lead to better therapeutics.