Crim1KST264/KST264 Mice Implicate Crim1 in the Regulation of Vascular Endothelial Growth Factor-A Activity during Glomerular Vascular Development

Abstract

Crim1, a transmembrane cysteine-rich repeat-containing protein that is related to chordin, plays a role in the tethering of growth factors at the cell surface. Crim1 is expressed in the developing kidney; in parietal cells, podocytes, and mesangial cells of the glomerulus; and in pericytes that surround the arterial vasculature. A gene-trap mouse line with an insertion in the Crim1 gene (Crim1 KST264/KST264 ) displayed perinatal lethality with defects in multiple organ systems. This study further analyzed the defects that are present within the kidneys of these mice. Crim1 KST264/KST264 mice displayed abnormal glomerular development, illustrated by enlarged capillary loops, podocyte effacement, and mesangiolysis. When outbred, homozygotes that reached birth displayed podocyte and glomerular endothelial cell defects and marked albuminuria. The podocytic co-expression of Crim1 with vascular endothelial growth factor-A (VEGF-A) suggested a role for Crim1 in the regulation of VEGF-A action. Crim1 and VEGF-A were shown to interact directly, providing evidence that cysteine-rich repeat-containing proteins can bind to non-TGF-␤ superfamily ligands. Crim1 KST264/KST264 mice display a mislocalization of VEGF-A within the developing glomerulus, as assessed by immunogold electron microscopy and increased activation of VEGF receptor 2 (Flk1) in the glomerular endothelial cells, suggesting that Crim1 regulates the delivery of VEGF-A by the podocytes to the endothelial cells. This is the first in vivo demonstration of regulation of VEGF-A delivery and supports the hypothesis that Crim1 functions to regulate the release of growth factors from the cell of synthesis.

The extracellular regulation of bone morphogenetic protein signaling

“…It is not clear, however, whether this reflects the normal function of CRIM1. The phenotypes of CRIM1 knockdowns in mice and zebrafish have been difficult to interpret, and might indicate the involvement of CRIM1 in other pathways (Kinna et al, 2006;Pennisi et al, 2007;Wilkinson et al, 2007). Loss of an apparent CRIM1 homolog (CRM-1) from C. elegans actually reduces BMP signaling (Fung et al, 2007).…”

High nephron endowment protects against salt-induced hypertension

“…Baseline conscious renal function was determined in WT (n ϭ 23) and Tgfb2 ϩ/Ϫ (n ϭ 22) mice from 24-h urine samples (22,26). Urine samples were stored at Ϫ20°C for subsequent analysis.…”

Renal organogenesis

“…They also show enriched expression of Crim1, a transmembrane regulator of growth factors that we have previously described within the kidney. 44,45 We have previously localized the expression of…”

“…45 We see a disruption to VEGF signaling from the podocyes, such that you get a disruption to glomerular vascular development and glomerulur cysts. 44 You also get digital anomalies, lens defects as well as other defects. 45 We have really focused on what that gene is doing in terms of development and haven't challenged the mice to ask how they respond to repair.…”