Stromal netrin-1 coordinates renal arteriogenesis and mural cell differentiation

The kidney vasculature has a complex architecture that is essential for renal function. The molecular mechanisms that direct development of kidney blood vessels are poorly characterized. We identified a regionally-restricted, stroma-derived signaling molecule, netrin-1 (Ntn1), as a regulator of renal vascular patterning. Stromal progenitor (SP)-specific ablation of netrin-1 (Ntn1^SPKO) resulted in smaller kidneys with fewer glomeruli, as well as profound defects of the renal artery and transient blood flow disruption. Notably, Ntn1 ablation resulted in loss of arterial vascular smooth muscle cell (vSMC) coverage and in ectopic SMC deposition at the kidney surface. This was accompanied by dramatic reduction of arterial tree branching that perdured postnatally. Transcriptomic analysis of Ntn1^SPKO kidneys revealed dysregulation of vSMC differentiation, including downregulation of Klf4 which we find expressed in a subset of SPs. Stromal Klf4 deletion similarly resulted in decreased smooth muscle coverage and arterial branching, however without the disruption of renal artery patterning and perfusion seen in Ntn1^SPKO. These data suggest a stromal Ntn1-Klf4 axis that regulates stromal differentiation, and reinforce stromal-derived smooth muscle as a key regulator of renal blood vessel formation.