Natural plant products have served as tremendously valuable tools for deciphering cellular and molecular mechanisms contributing to somatosensation, nociception, and pain. Notable examples include the use of natural analgesics, such as morphine (from the opium poppy) and salicylate (from willow bark) to discover opioid receptors and cyclooxgenases, respectively. Other important examples include the use of natural irritants, such as capsaicin (from chili peppers) and menthol (from mint leaves) to identify ion channels that detect heat and cold, respectively. Indeed, each of these proteins represents a validated or potential target for pharmacological management of acute or chronic pain. Plants are not unique in their capacity to produce chemical agents that target sensory neurons or other excitable cells. Indeed, venoms from animals (ranging from arachnids to mammals) represent a vast pharmacopoeia that has great potential to yield novel agents with which to identify or characterize receptors, ion channels, or other signaling molecules that contribute to sensory transduction. Indeed, in the previous funding period we identified two such toxins - one from spider and another from snake - that serve as novel, potent, and highly selective agonists for TRPV1 and ASIC1 channels, respectively. In each case, these toxins enabled elucidation of the activated, fully open state of the channel at atomic resolution, providing unprecedented insights into structural mechanisms underlying channel gating and modulation. This proposal builds on our success and expertise in toxin discovery and characterization, with the goal of expanding the repertoire of pharmacological agents with which to study known or novel somatosensory receptors.
The first aim i s focused on characterizing two spider toxins that we identified in a sensory neuron- based screening assay, and which target a specific voltage-gated sodium channel (Nav) subtype expressed by these cells. We propose to identify the Nav channel domain(s) that specifies toxin sensitivity and accounts for its subtype selectivity. Furthermore, we shall test toxin selectivity in vivo using mouse genetics, and identify the subpopulation of sensory neurons that mediate the excitatory and algogenic actions of these toxins in cellular and behavioral paradigms.
The second aim i s focused on characterizing two novel toxins - one from centipede and the other from snake - that we also identified by functional screening, and which activate primary afferent sensory neurons to elicit nocifensive responses in mice. We propose to identify the molecular targets of these toxins and determine the signaling mechanisms through which they activate sensory neurons of the pain pathway. These studies will uncover novel sensory transduction molecules and/or provide powerful new tools for determining how known transducers work to modulate nociceptor excitability. Information gleaned from this work will provide important pharmacologic leads and insights pertinent to the development of analgesic agents.

Public Health Relevance

Cell surface receptors and ion channels play essential roles in cellular communication throughout the body, including all aspects of nervous system function. In this proposal, we describe strategies for discovering and exploiting natural toxins with the goal of developing new tools with which to study the structure and function of receptors and ion channels that contribute to pain sensation. Results from this work will provide a more in- depth understanding of how these receptors and channels respond to noxious (pain-producing) stimuli under normal and/or pathological conditions, all of which is relevant to elucidating processes that contribute to acute and chronic pain. Results from these studies will provide important new information for the rational design of novel therapeutic drugs that target receptors and channels whose activities contribute to a variety of persistent pain syndromes.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Method to Extend Research in Time (MERIT) Award (R37)
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Somatosensory and Chemosensory Systems Study Section (SCS)
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Oshinsky, Michael L
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University of California San Francisco
Schools of Medicine
San Francisco
United States
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Osteen, Jeremiah D; Sampson, Kevin; Iyer, Vivek et al. (2017) Pharmacology of the Nav1.1 domain IV voltage sensor reveals coupling between inactivation gating processes. Proc Natl Acad Sci U S A 114:6836-6841
Zhang, Chuchu; Medzihradszky, Katalin F; Sánchez, Elda E et al. (2017) Lys49 myotoxin from the Brazilian lancehead pit viper elicits pain through regulated ATP release. Proc Natl Acad Sci U S A 114:E2524-E2532
Gao, Yuan; Cao, Erhu; Julius, David et al. (2016) TRPV1 structures in nanodiscs reveal mechanisms of ligand and lipid action. Nature 534:347-51
Osteen, Jeremiah D; Herzig, Volker; Gilchrist, John et al. (2016) Selective spider toxins reveal a role for the Nav1.1 channel in mechanical pain. Nature 534:494-9
Cao, Erhu; Cordero-Morales, Julio F; Liu, Beiying et al. (2013) TRPV1 channels are intrinsically heat sensitive and negatively regulated by phosphoinositide lipids. Neuron 77:667-79