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Abstract: SA-OR48

Identification of Molecular Mechanisms Regulating Mammalian Nephrogenesis Duration and Nephron Endowment

Session Information

Category: Development, Stem Cells, and Regenerative Medicine

  • 500 Development, Stem Cells, and Regenerative Medicine

Authors

  • Jarmas, Alison E., Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, United States
  • Chaturvedi, Praneet, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, United States
  • Kopan, Raphael, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, United States
Background

Nephron endowment generated during development confers lifelong renal filtration function, and is established via nephron progenitor cell (NPC) interactions with the adjacent stroma and ureteric bud (UB). Two salient, incompletely understood features of nephrogenesis are (1) the coordinated cessation of nephrogenesis in independent niches and (2) a striking 10-fold variation in nephron number between kidneys from different individuals. Preterm births are associated with premature cessation of nephrogenesis and are consequently susceptible to early-onset chronic kidney disease (CKD) and end-stage renal disease (ESRD). We leverage multiple mouse models exhibiting consistent differences in nephron number to identify mechanisms promoting prolonged nephrogenesis and/or increased nephron endowment.

Methods

NPCs from mice with elevated nephron numbers and delayed cessation (Six2TGC; Tsc1, herein Tsc1+/-) were evaluated via single-cell transcriptomics, translatome profiling (bulk RNA-Seq of Rpl10a-associated transcripts), metabolic indicators (in vitro glycolysis assays and in vivo hypoxia studies), and immunofluorescence. Candidate genes emerging from the RNA analyses were validated with in vivo genetic models for nephron number and cessation timing phenotypes.

Results

Translatome analysis revealed age and genotype-dependent patterns in signaling pathway components that were not observed in the single cell transcriptome, including differential translation of Wnt antagonists over agonists (such as Rspondin-3) in Tsc1+/– NPCs. Moreover, compared to postnatal day 0 niches, Wnt agonists are less robustly translated in younger (embryonic day 14) niches, resulting in high Fgf20 levels and low R-spondin levels promoting a self-renewal environment. Further, the selective differential translation observed in the Tsc1+/- model was not associated with globally elevated mTORC1 activity or changes in cellular metabolic activities.

Conclusion

We propose a model in which the tipping point for nephron progenitor exit from the niche is controlled by the gradual increase in stability of Wnt/Fzd complexes in individual cells, enhancing the response to UB-derived Wnt9b inputs and driving differentiation. Consistent with this, loss of one Rspo3 allele in nephron progenitors delayed cessation and increased nephron numbers in vivo.

Funding

  • NIDDK Support