Stromal netrin-1 coordinates renal arteriogenesis and mural cell differentiation

The kidney vasculature has a uniquely complex architecture that is essential to proper renal function. Little is known about the molecular mechanisms that direct where and when blood vessels form during kidney development. We identified a regionally-restricted, stroma-derived signaling molecule, netrin-1 (Ntn1), as a putative regulator of vascular patterning. We generated a stromal progenitor-specific knockout of netrin-1 ( Ntn1 SPKO ) that resulted in smaller postnatal kidneys with altered epithelial development and profound defects in arterial and capillary architecture. We also found significant loss of arterial vascular smooth muscle cell (vSMC) coverage and ectopic smooth muscle cell deposition at the kidney cortex. Transcriptomic analysis of Ntn1 SPKO kidneys revealed downregulation of Klf4, which we find expressed in stromal progenitors. Deletion of Klf4 in the stroma largely phenocopies loss of Ntn1, and expression of Klf4 in Ntn1 SPKO kidneys rescues ectopic vSMC deposition. Vascular defects observed in Ntn1 SPKO are transient, as both arterial and smooth muscle coverage defects resolve late in development, however ectopic peripheral smooth muscle perdures perinatally. These data suggest a stromal-intrinsic Ntn1-Klf4 axis acting as an essential mediator of stromal crosstalk and vascular progenitor differentiation.