Abnormal sensory activity plays a major role in bladder diseases such as interstitial cystitis/painful bladder syndrome (IC/PBS), sensory neuropathy in uremia, and age related bladder dysfunction in neurodegenerative diseases such as Parkinson's. Identifying molecular and genetic mechanisms regulating urinary tract sensation in normal and disease states is essential for rational design of therapies for bladder sensory disorders and risk stratification. The glial cell line-derived neurotrophic factor (GDNF) family of ligands (GFLs) are neurotrophic factors that bind to one of the coreceptors GFR? (1-4) and activate the receptor tyrosine kinase RET. GFL-RET signaling promotes sensory neuron survival and axonal growth and prevents axonal degeneration. We demonstrated that RET activation leads to phosphorylation of key docking tyrosines that bind intracellular adaptors and activate specific signal transduction pathways such as PLC? and PI3K/MAPK to regulate proliferation, survival and migration of autonomic and eneteric neurons, and collecting system progenitors. We discovered distinct tissue-specific roles of Ret-docking tyrosines in the urinary tract and autonomic ganglia and that Ret is important in somatic pain sensation. Our preliminary data show high RET expression in human sensory ganglia (DRG) and in urothelial, submucosal and myenteric nerves in the bladder suggesting an unexplored role for GFL-RET signaling in bladder function. We observed that Ret-null mice have severely reduced bladder innervation. Using our unique Ret mutant mice we found that Ret+ sensory neurons innervate the bladder and that Gdnf haploinsufficiency reduces pain in an acute cystitis model. These results collectively support an important role for GFL-RET signaling in bladder function and health. We hypothesize that GFL-RET signaling has a critical role in regulating bladder sensation in nave and injured states, and that RET mutations found in humans affect the health of sensory neurons.
Three specific aims are proposed.
In Aim 1 we will identify physiologically relevant RET-activated signaling pathways that regulate bladder sensation in normal and injured states using a battery of unique RET-mutant mice.
In Aim 2 we will determine the regulation of select ion channels (TRPV1, TRPA1 and voltage-gated sodium and potassium channels) by specific RET- activated pathways in bladder afferent DRG neurons using calcium imaging and electrophysiology analysis.
In Aim 3 we will decipher the roles of RET mutations found in humans in primary sensory neuron survival, axonal growth and degeneration. These results will provide insights into how GFL-RET signaling can be targeted for therapy in sensory dysfunction in bladder diseases. GFLs are currently in clinical trials for neurodegenerative disease and chronic pain. This will allow accelerated clinical translation of the proposed studies.
The biological basis of normal and noxious sensory responses from the pelvic viscera are not clearly understood. Delineating molecular mechanisms and the role of the sensory nervous system in diseases affecting the bladder such as urinary tract malformations, painful bladder/interstitial cystitis, incontinence, acute and chronic cystitis due to UTI is important because of the adverse consequences of these diseases. Recent studies from preclinical models and in humans suggest that the neurotrophic factor GFL-RET signaling pathway may be important in bladder innervation, and in the survival and function of postnatal sensory neurons. The proposed research leverages the expertise of an interdisciplinary team of investigators and utilizes innovative genetically engineered mice to study specific mechanisms dependent on GFL-RET signaling in survival of sensory neurons and pain function, and the role of RET mutations found in patients with urinary tract malformations in sensory neurons. We expect these studies will lead to rationally designed therapies that modulate GFL-RET signaling in bladder sensory disorders and preclinical screening of impact of RET mutations in sensory neurons.