Mechanisms of Endosomal Signaling of Itch

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Project Summary Itch is a complex physiological process that incorporates detection of irritants by sensory neurons in the skin which activate spinal interneurons and ultimately, cortical projection neurons to generate a response. G protein-coupled receptors (GPCRs) play an integral role at each level of itch sensation and transmission. Although conventionally considered cell surface receptors that are desensitized and internalized following ligand binding, new evidence has established the ability of GPCRs to signal from endosomes. However, little is known about the mechanisms that regulate endosomal signaling of GPCRs and nothing is known about the role of endosomal GPCRs signaling in itch or whether endosomal GPCRs are a viable therapeutic target for itch. This proposal hypothesizes that: 1. Gastrin releasing peptide receptor (GRPR) and neurokinin 1 receptor (NK1R), two key receptors in itch transmission in the spinal cord, can recruit and assemble multi- protein complexes from the endosomal compartment that facilitate endosomal signaling and mediate prolonged hyperexcitability of spinal interneurons. That the ability of GRPR and NK1R to signaling from endosomes leads to itch transmission in the spinal cord and endocytic inhibitors that block GRPR and NK1R endosomal signaling can inhibit scratching behavior in mice. 2. Targeting endosomal signaling of GRPR and NK1R using nanoparticles is a more effective strategy in inhibiting itch than targeting cell surface receptors. Endosomal signaling of GRPR and NK1R will be characterized in model cell lines, spinal interneurons that mediate itch transmission, and in intact animals. Pharmaceutical and genetic approaches will be used to inhibit endosomal trafficking of GRPR and NK1R. Aim 1 will characterize the importance of endosomal trafficking and signaling of GRPR and NK1R in spinal interneurons for the transmission of itch. The role of endosomal signaling in itch will be addressed by electrophysiology, and by itch behavioral assays in intact animals. Aim 2 will characterize the ability of GRPR to traffic to endosomes and assemble the multi-protein complexes that result in subcellular specific signaling events. These signaling complexes will be studied using advanced biophysical and imaging approaches with high spatiotemporal resolution. Aim 3 will use advanced chemical biology, nanoengineering and nanoparticle encapsulation to deliver GRPR and NK1R antagonists to endosomes, probing the importance of endosomal signaling of GRPR and NK1R in itch transmission and to determine whether endosomal GPCRs are a viable therapeutic target.