Loss of Fibroblast Growth Factor Receptor 2 (FGFR2) Leads to Defective Bladder Urothelial Regeneration after Cyclophosphamide Injury.

Cyclophosphamide may cause hemorrhagic cystitis and eventually bladder urothelial cancer. Genetic determinants for poor outcomes are unknown. We assessed actions of fibroblast growth factor receptor (FGFR) 2 in urothelium after cyclophosphamide exposure. Conditional urothelial deletion of Fgfr2 (Fgfr2KO) did not affect injury severity or proliferation of keratin 14+ (KRT14+) basal progenitors or other urothelial cells 1 day after cyclophosphamide exposure. Three days after cyclophosphamide exposure, Fgfr2KO urothelium had defective regeneration, fewer cells, larger basal cell bodies and nuclei, paradoxical increases in proliferation markers, and excessive replication stress versus controls. Fgfr2KO mice had evidence of pathologic basal cell endoreplication associated with absent phosphorylated ERK staining and decreased p53 expression versus controls. Mice with conditional deletion of Fgfr2 in urothelium enriched for KRT14+ cells reproduced Fgfr2KO abnormalities after cyclophosphamide exposure. Fgfr2KO urothelium had defects up to 6 months after injury versus controls, including larger basal cells and nuclei, more persistent basal and ectopic lumenal KRT14+ cells, and signs of metaplasia (attenuated E-cadherin staining). Mice missing one allele of Fgfr2 also had (less severe) regeneration defects and basal cell endoreplication 3 days after cyclophosphamide exposure versus controls. Thus, reduced FGFR2/ERK signaling apparently leads to abnormal urothelial repair after cyclophosphamide exposure from pathologic basal cell endoreplication. Patients with genetic variants in FGFR2 or its ligands may have increased risks of hemorrhagic cystitis or urothelial cancer from persistent and ectopic KRT14+ cells.