Tissue acidosis is known to accompany tissue injury, ischemia, and other pathophysiological events, and is thought to contribute to the perception of pain in these contexts. Acid sensing ion channels (ASICs) are expressed in a subset of primary afferent nerve fibers which mediate pain signals (nociceptors) and these channels are candidates as transducers of acidosis-triggered pain responses. A recent study from the Julius Lab identified a component of Texas coral snake (Micrurus tener tener) venom, MitTx, as a potent activator of ASIC1. They also found that MitTx targets ASIC1 to cause pain in mice, underlining the importance of ASIC1 in pain and promoting the notion that non-proton ligands may exist for ASICs. Here I propose to characterize the MitTx-ASIC interaction to learn about the mechanisms by which this non-proton ligand activates these channels using biophysical and biochemical approaches. In parallel, I will pursue multiple strategies for producing and purifying recombinant MitTx in order to produce biochemical quantities of this toxin and in order to allow for genetic modification of the toxin as a tool for detailed pharmacological analysis. I will also take up a search for endogenous activators/potentiators of ASICs which may mimic the effect of MitTx to persistently activate ASICs in some pathophysiological states. These putative factors may act in concert with protons to shape the severity and duration of ASIC-mediated pain responses. This proposal will introduce me to many new techniques and research areas, expanding my expertise into protein biochemistry and physiology to complement my background in electrophysiology and ion channel biophysics. This fellowship in the Julius lab will provide me with the training and experience necessary to embark on a career as an independent scientist, focused on elucidating molecular mechanisms underlying important physiological and pathophysiological processes.

Public Health Relevance

The long-term goal of this project is to characterize the properties of MitTx-induced activation of acid sensing ion channels and to probe a putative endogenous factor that similarly activates these channels. MitTx studies in our lab have elucidated the importance of the ASIC1 subtypes in pain, and these studies will further elucidate the mechanism of non-proton activation of this and other ASICs. This project will thus provide valuable insight into molecular determinants of pain transduction from both endogenous and exogenous factors and characterize putative targets for therapeutics aimed at preventing or attenuating pain due to chronic pain syndromes and other painful pathologic states.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Postdoctoral Individual National Research Service Award (F32)
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Special Emphasis Panel (ZRG1-F02B-M (20))
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Chen, Daofen
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University of California San Francisco
Schools of Medicine
San Francisco
United States
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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