ID1 and kidney injury: Based on the accumulating evidence for the role of Id proteins in angiogenesis and mesenchymal cell fate determination including endothelial-mesenchymal transition and endothelial paracrine signaling, we hypothesized that changes in microvascular Id expression levels following kidney injury may regulate both vessel repair and contribute to the development of interstitial fibrosis as a result of changes in mesenchymal cell phenotype.