Abstract: SA-PO539

Hedgehog-TGFβ Signaling in Foxd1+ Stromal Cells Controls Stromal Patterning and Nephron Formation

Session Information

  • Developmental Biology
    November 04, 2017 | Location: Hall H, Morial Convention Center
    Abstract Time: 10:00 AM - 10:00 AM

Category: Developmental Biology and Inherited Kidney Diseases

  • 401 Developmental Biology

Authors

  • Rowan, Christopher, The Hospital for Sick Children, Toronto, Ontario, Canada
  • Rosenblum, Norman D., The Hospital for Sick Children, Toronto, Ontario, Canada
Background

In the embryonic mammalian kidney, signals from Foxd1+ stromal cells are critical in establishing a full complement of nephrons. Yet, the molecular mechanisms that control stromal-nephrogenic cell interactions are largely unknown. Previously, we demonstrated that homozygous deficiency of SMO, a cell surface Hedgehog signaling effector, in the stromal lineage (Smo-nullstroma) results in a 42% decrease in nephron number. Remarkably, low nephron number is preceded by expansion of SIX2+ nephron progenitors and a relative block of mesenchymal to epithlial conversion [ASN 2014]. Here, we identify molecular mechanisms that control nephrogenesis in Smo-nullstroma mice.

Methods

RNA expression was assayed by RNASeq, quantitative (q)PCR, and in situ hybridization. Functional assays were performed in cultured mouse embryonic kidney explants using neutralizing antibodies and vivo-morpholinos (MO). TGFβ receptor II deficiency was generated in a CRE-dependent manner under the control of cell-specific promoters.

Results

RNASeq of wild type and Smo-nullstroma E13.5 kidney tissue demonstrated decreased expression of Tgfb2 in mutant tissue. qPCR showed a 30% decrease in Tgfb2 in Smo-nullstroma mutant kidney tissue and in FACS-isolated mutant Foxd1+ stromal cells. In situ hybridization demonstrated decreased Tgfb2 expression, and immunostaining demonstrated decreased expression of the TGFβ intracellular effector pSMAD2/3 in Smo-nullstroma mutant kidneys. Treatment of wild type embryonic kidney explants with neutralizing antibody or MO specific to TGFβ2 resulted in 65% (P=0.017) and 35% (P=0.003) fewer nephrons, respectively (n=3 per group). CRE-dependent deletion of TGFβ receptor II (Tgfbr2, specific to TGFβ ligands) within Foxd1+ stromal cells (Tgfbr2-nullstroma) caused a 1.3-fold increase in SIX2+ nephron progenitors (P=0.01, n=8/genotype), as observed in Smo-nullstroma mice, and mispatterning of stromal cells in vivo. Tgfbr2 deficiency targeted to either ureteric or SIX2+ nephron progenitor cells, alone, caused neither of these pathologic effects (n=3/genotype). However, Tgfbr2 deficiency in both Foxd1+ and Six2+ cells concurrently caused hypoplasia in addition to defects observed in Tgfbr2-nullstroma mice.

Conclusion

We conclude that HH-TGFβ signaling exerts both cell autonomous and non-cell autonomous effects to control nephron formation and stromal patterning.

Funding

  • Government Support - Non-U.S.