Type III Nrg1 Back Signaling Enhances Functional TRPV1 along Sensory Axons Contributing to Basal and Inflammatory Thermal Pain Sensation Sarah E. Canetta1,3,5, Edlira Luca2,3,5, Elyse Pertot4, Lorna W. Role1,3,5, David A. Talmage3,5,6* 1 Department of Neurobiology and Behavior, Columbia University, New York, New York, United States of America, 2 Integrated Department, Columbia University, New York, New York, United States of America, 3 Department of Neurobiology and Behavior, State University of New York at Stony Brook, Stony Brook, New York, United States of America, 4 Department of Biological Science, State University of New York at Stony Brook, Stony Brook, New York, United States of America, 5 Center for Nervous System Disorders, State University of New York at Stony Brook, Stony Brook, New York, United States of America, 6 Department of Pharmacological Science, State University of New York at Stony Brook, Stony Brook, New York, United States of America Abstract Type III Nrg1, a member of the Nrg1 family of signaling proteins, is expressed in sensory neurons, where it can signal in a bi- directional manner via interactions with the ErbB family of receptor tyrosine kinases (ErbB RTKs) [1]. Type III Nrg1 signaling as a receptor (Type III Nrg1 back signaling) can acutely activate phosphatidylinositol-3-kinase (PtdIns3K) signaling, as well as regulate levels of a7* nicotinic acetylcholine receptors, along sensory axons [2]. Transient receptor potential vanilloid 1 (TRPV1) is a cation-permeable ion channel found in primary sensory neurons that is necessary for the detection of thermal pain and for the development of thermal hypersensitivity to pain under inflammatory conditions [3]. Cell surface expression of TRPV1 can be enhanced by activation of PtdIns3K [4,5,6], making it a potential target for regulation by Type III Nrg1. We now show that Type III Nrg1 signaling in sensory neurons affects functional axonal TRPV1 in a PtdIns3K-dependent manner. Furthermore, mice heterozygous for Type III Nrg1 have specific deficits in their ability to respond to noxious thermal stimuli and to develop capsaicin-induced thermal hypersensitivity to pain. Cumulatively, these results implicate Type III Nrg1 as a novel regulator of TRPV1 and a molecular mediator of nociceptive function. Citation: Canetta SE, Luca E, Pertot E, Role LW, Talmage DA (2011) Type III Nrg1 Back Signaling Enhances Functional TRPV1 along Sensory Axons Contributing to Basal and Inflammatory Thermal Pain Sensation. PLoS ONE 6(9): e25108. doi:10.1371/journal.pone.0025108 Editor: Lin Mei, Medical College of Georgia, United States of America Received June 7, 2011; Accepted August 24, 2011; Published September 20, 2011 Copyright: 2011 Canetta et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by grants from: The National Alliance for Research on Schizophrenia and Depression/Baer Foundation, The National Institutes of Health Grants: TL1RR025158, T32 GM08224 and NS29071. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: david.talmage@stonybrook.edu Introduction Type III Nrg1, a member of the Nrg1 family of signaling proteins, is expressed in sensory neurons where it has been shown to be important for receptor localization as well as nociceptive sensory neuron survival [2,7]. The Nrg1 gene has also been identified as a candidate schizophrenia susceptibility gene [8,9,10], and levels of the Type III isoform were reported to be decreased in post-mortem tissue of some schizophrenics [11]. Schizophrenia patients are impaired in their ability to perceive painful stimuli, particularly under inflammatory conditions [12,13,14,15,16,- 17,18]. We therefore investigated whether reducing levels of Type III Nrg1 alters response to nociceptive stimuli under normal and inflammatory conditions. Transient receptor potential vanilloid 1 (TRPV1) is a cation- permeable ion channel found in primary sensory neurons that contributes to the detection of thermal pain and is necessary for the development of thermal hyperalgesia under inflammatory conditions [3,19]. Membrane surface expression of TRPV1 can be enhanced by activation of phosphatidylinositol-3-kinase (PtdIns3K) [4,5,6] and increased levels of functional surface TRPV1 along sensory neuron axons contribute to behavioral sensitization to pain [20]. Type III Nrg1 can signal in a bi-directional manner after interactions with the ErbB family of receptor tyrosine kinases (ErbB RTKs). Type III Nrg1 can serve as a ligand to activate ErbB RTKs and initiate signaling in ErbB-expressing cells [21]. Additionally, Type III Nrg1 can signal as a receptor when stimulated by interaction with ErbB RTKs or depolarization [1,22]; Type III Nrg1 signaling as a receptor (Type III Nrg1 back signaling) can have both transcriptional and non-transcriptional effects [1,2,22,23]. In particular, Type III Nrg1 back signaling can acutely activate PtdIns3K along sensory neuron axons [2] making TRPV1 a potential molecular link between Type III Nrg1, schizophrenia and alterations in pain sensation. We now show that mice heterozygous for Type III Nrg1 [7] have specific deficits in their ability to respond to noxious thermal stimuli, and in their ability to develop capsaicin-induced thermal hypersensitivity to pain. These particular behavioral deficits are reminiscent of mice that lack the receptor TRPV1 [3,19]. A reduction in levels of Type III Nrg1 is associated with a reduction in functional TRPV1 along sensory neuron axons. Furthermore, acute stimulation of Type III Nrg1 back signaling in WT sensory neuron axons leads to an increase in functional TRPV1 in a phosphatidylinositol-3-kinase (PtdIns3K)-dependent manner. In addition to shedding insight into the function of Type III Nrg1 in PLoS ONE | www.plosone.org 1 September 2011 | Volume 6 | Issue 9 | e25108