Critical Roles for Fibroblast Growth Factor Receptors in Bladder Development

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 DESCRIPTION (provided by applicant): Developmental bladder defects can lead to numerous health problems throughout life including pediatric kidney failure, urinary tract infections, stone, and urinary retention; however, genetic determinants of bladder diseases are largely unknown. The application's broad long-term objectives are to elucidate the molecular control of bladder development to develop effective therapies for structural bladder disease. Presently, most of the molecular control of bladder development is unknown. Fibroblast growth factor receptor 2 (Fgfr2) is expressed in developing bladder mesenchyme (future muscle and lamina propria); however, global deletion of Fgfr2 in mice leads to early embryonic lethality prior to the onset of urinary tract development, making the roles of the receptor in bladder development unclear. To circumvent the early lethality of the global knockouts, a Tbx18cre line was used to conditionally delete Fgfr2 in the bladder mesenchyme (Fgfr2BM-/-). Preliminary data show that while Fgfr2BM-/- embryonic bladders total bladder volumes are unchanged, the mutants have a relative reduction in the volume of the outer condensing mesenchyme (future muscle) and a decrease in muscle marker expression vs. controls. Conversely, Fgfr2BM-/- bladders have a relative increase in volume of the inner mesenchyme (future lamina propria) and higher expression of early collagen markers with infiltration into the muscle. Early postnatal mutant bladders have histological abnormalities and functional defects including decreases in contractility, poor compliance, and high pressures; aged Fgfr2BM-/- mice develop severe bladder distention with fibrosis and myogenic failure (resembling atonic bladders) and also develop kidney injury. Mechanistically, Fgfr2BM-/- embryonic bladders appear to have increased sonic hedgehog (Shh) activity (and other pathways downstream of hedgehog such as Wnt and Bmp4), which likely mispatterns the mesenchyme. Fgfr2 suppression of hedgehog appears to by regulation of Hh co-receptors Cdon and Boc. Finally preliminary bladder culture experiments suggest a rescue of mutant bladder muscle defects with low doses of a hedgehog inhibitor. The overarching hypothesis is that loss of Fgfr signaling in bladder mesenchyme leads to early developmental patterning defects that have significant postnatal consequences. To test the hypothesis, the following aims are proposed: Aim1: Characterize the progressive histological, functional, and signaling defects in Fgfr2BM-/- bladders. Structural and molecular bladder mispatterning will be interrogated in Fgfr2BM-/- embryos and newborn mice. Structural and functional consequences of developmental bladder mispatterning will be determined in postnatal mice. Signaling defects downstream of Fgfr2 will also be characterized in mutant bladders. Aim 2: Determine the molecular mechanisms driving the patterning defects in the Fgfr mutants. Perturbations in hedgehog signaling (and other potential pathways downstream of hedgehog such as Bmp4 and Wnt) will be interrogated in embryonic Fgfr2BM-/- bladders. Chemical and genetic approaches will be used ex vivo and in vivo to attempt rescue of bladder defects in Fgfr2BM-/- mice.