Nephron progenitor maintenance is controlled through FGFs and Sprouty1 Interaction

Abstract

The nephron progenitor cells (NPCs) give rise to all segments of functional nephrons and are of great interest due to their potential as a source for novel treatment strategies for kidney disease. Fibroblast growth factor (FGF) signal plays pivotal roles in generating and maintaining NPCs during kidney development. However, molecule(s) regulating FGF signal during nephron development is not known. Sprouty (SPRY) is an antagonist of receptor tyrosine kinases. During kidney development, SPRY1 is expressed in the ureteric buds (UBs) and regulates UB branching by antagonizing Ret-GDNF signal. Here, we provide evidence that SPRY1 expressed in NPCs modulates activity of FGF signal in NPCs and regulates NPC stemness. Haploinsufficiency of Spry1 rescues bilateral renal agenesis and premature NPC differentiation caused by loss of Fgf9 and Fgf20. In addition, haploinsufficiency of Spry1 rescues NPC proliferation and cell death defects induced by loss of Fgf9 and Fgf20. In the absence of SPRY1, FGF9 and FGF20, another FGF ligand, FGF8 promotes nephrogenesis. Deleting both Fgf8 and Fgf20 results in kidney agenesis and defects in NPC proliferation and cell death. Rescue of loss of Fgf9 and Fgf20 induced renal agenesis by Spry1 haploinsufficiency was reversed when one copy of Fgf8 was deleted. These findings indicate the importance of the balance between positive and negative signal during NPC maintenance. Failure of the balance may underlie some human congenital kidney malformation. Significance StatementNephrons are functional units of kidney to filter blood to excrete wastes and regulate osmolarity and ion concentrations. Nephrons are derived from nephron progenitors. Nephron progenitors are depleted during kidney development which makes it unable to regenerate nephrons. Therefore, understanding signaling molecules regulating nephron progenitor generation and maintenance is of great interest for the future kidney regenerative medicine. Here, we show that Sprouty1 regulates nephron progenitor maintenance by inhibiting FGF signal. Deletion of Sprouty1 rescues renal agenesis and nephron progenitor depletion in the Fgf9/20 loss-of-function kidneys. Further decrease of FGF signal by deleting one copy of Fgf8 makes kidneys irresponsive to Sprouty1 resulting in failure of nephron progenitor maintenance. This study thus identifies the reciprocal function of FGF-Sprouty1 signal during nephron progenitor development.