Molecular Physiology and Neurogenomics of GFL-RET Signaling in Urothelial Homeostasis and Sensorimotor Dysfunction

Washington University, Saint Louis MO

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Abstract

Proper functioning of the bladder requires its integrated interactions with the sensory and autonomic nervous systems (ANS), disruption of which can lead to a number of debilitating bladder diseases including overactive bladder (OAB) and interstitial cystitis/bladder pain syndrome (IC/BPS). We will define some of the molecular and genetic mechanisms that regulate interdependency of the urothelium and the sensory and autonomic nervous systems in normal and diseases states by using glial cell line-derived neurotrophic factor (GDNF) family ligands (GFLs) ?RET signaling as a paradigm. The activated receptor tyrosine kinase RET autophosphorylates key docking sites, Y1015 and Y1062, that we have shown to have distinct roles; each differentially activates PI3K, MAPK and PLC? signal transduction pathways and cell survival, migration, renewal and axonal growth. The GFL-RET signaling system has known roles as therapeutic targets in somatic pain and neurodegenerative diseases, in modulating the function of a number of TRP and voltage gated ion channels, including purinergic receptors and neuropeptides important in pain, but the mechanisms are not clear, and very little is known regarding the bladder. RET is expressed in the majority of dorsal root ganglia (DRG) sensory and pelvic ganglia neurons in mature animals. In the bladder unmyelinated C-fibers (about half are Ret-positive) transduce sensory signals in injury. Using the expertise of Drs. Gereau and Lai in bladder physiology, of Dr. Mysorekar in bladder injury models (Core B), and a unique allelic series of Gdnf and Ret mutants, we have made novel observations that Gdnf-Ret signaling in Ret+ sensory afferent and autonomic efferent neurons has a role in bladder innervation, pain and voiding. We hypothesize that GFL-RET signaling has undiscovered roles in regulating bladder sensorimotor function, urothelial integrity in normal and injury states. The proposed Aims fill a critical gap in the field by providing fundamental insights into GFL-RET mediated regulation of urothelium and bladder innervation using preclinical mouse models (Aims 1, 2, Core B), identification of novel Ret+ sensory neuron genes associated with bladder injury (Aim 3, Core B) and translating this knowledge by identifying deleterious variations in genes associated with nociception and inflammation in patients with BPS and OAB (Aim 3; Core C). Thus, these studies on one of the major neurotrophic factor signaling pathways in bladder and its innervation with a focus on models and diseases reminiscent of lower urinary tract disorders fit well with the overall theme of the Center. The novel disease models and biological approaches to address interdependence of urothelium and the nervous system in Aims 1 and 2 and the genomic data, discovery and validation (Aim 3) will serve as an avenue for trainees through the education and enrichment program, and other investigators through the opportunity pool for an enriching environment and resource to leverage. The insights gained will pave the way for therapy or prevention of OAB and IC/BPS and diseases associated with bladder neuropathy.