Normal functioning of the lower urinary tract requires integrated activities of the nervous and the urinary system. This depends on proper developmental and anatomic relationships between the ureters, bladder and autonomic and sensory nerves. Maldevelopment of these structures can cause congenital anomalies of kidneys or lower urinary tract (CAKUT) including primary or secondary vesicoureteral reflux, megaureter, ureterocele and obstruction, and bladder dysfunction. These diseases represent a significant decrease in quality of life for patients, pose a large burden on the health care system, and are a major cause of chronic kidney disease in children. Large gaps exist in our understanding of mechanisms of how the lower urinary tract structures attain their final anatomical and morphological relationships within the urinary tract and with structures outside the urinary tract due to complex anatomy of this region and dearth of tools that can serve as biological reagents and models that recapitulate the human conditions. In our previous work we have elucidated novel roles of Gdnf-Ret signaling pathway in the development of the kidneys and patterning of the Wolffian duct and have developed a plethora of mouse reagents to manipulate this signaling system to glean insights into the biology of urinary tract. The glial cell line-derived neurotrophi 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. RET activation leads to phosphorylation of key docking tyrosines that bind intracellular adaptors and activate specific signal transduction pathways such as PLC? and PI3K and MAPK that are involved in cell survival, proliferation, migration and differentiation. GFL-RET signaling is implicated in many human diseases including peripheral neuropathy, Alzheimer's, Parkinson's, Hirschsprung's disease, stroke, and urinary tract malformations in humans and are targetable for therapy in a number of disorders. Our preliminary data suggest that RET signaling is important in pelvic ganglia formation and bladder innervation, there is potential for cross interactions between ureter maturation and pelvic ganglia and cloaca, and made a novel observation of cell death in the cloaca before CND degeneration that may be the mechanism of fusion of WD and cloaca. We hypothesize that Gdnf-Ret signaling plays a crucial role in interactions between the lower urinary tract and the pelvic autonomic nervous system and provides a model system to understand the interrelationships in sculpting a successful lower urinary tract and its innervation Three Aims are proposed.
In Aim 1 we will identify GFL-Ret specific pathways that are important in pelvic ganglia development, axonal growth and bladder autonomic innervation in Ret null and individual tyrosine mutant mice during ontogeny.
In Aim 2 we will examine the mutual impact of WD and the pelvic ganglia development by using Cre-deletor strains for each of these regions and determine if Gdnf from cloaca is the guidance cue for WD and pelvic ganglia.
In Aim 3 we will delineate the mechanism of WD and cloaca fusion prior to UB budding and CND degeneration by taking advantage of RetTyr mutants with contrasting defects in WD growth and analyze cloacal -WD autonomous and dependent events in their fusion.
Molecular and developmental perturbations that disrupt proper anatomical and molecular relationships between the ureter, cloaca and the pelvic ganglia can result in urinary tract anomalies and aberrant function such as urinary tract obstruction, vesicoureteral reflux, and incontinence, neurogenic and overactive bladder. The proposed research investigates the interactions between these components in sculpting the lower urinary tract by using GDNF-RET signaling system as a model in mice, and explores novel areas that test urinary tract intrinsic and extrinsic factors in maintaining homeostasis. RET pathway mutations are associated with renal and lower urinary tract anomalies and congenital nervous system defects. It is also a target for therapy in neurodegenerative disorders. Our preliminary studies suggest novel roles of this pathway in the lower urinary tract and bladder innervation. The proposal will elucidate these interactions that can potentially lead to mechanism-based therapies for urinary tract disorders.
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