|Acute podocyte vascular endothelial growth factor (VEGF-A) knockdown disrupts alphaVbeta3 integrin signaling in the glomerulus. |
Veron, D; Villegas, G; Aggarwal, PK; Bertuccio, C; Jimenez, J; Velazquez, H; Reidy, K; Abrahamson, DR; Moeckel, G; Kashgarian, M; Tufro, A
Podocyte or endothelial cell VEGF-A knockout causes thrombotic microangiopathy in adult mice. To study the mechanism involved in acute and local injury caused by low podocyte VEGF-A we developed an inducible, podocyte-specific VEGF-A knockdown mouse, and we generated an immortalized podocyte cell line (VEGF(KD)) that downregulates VEGF-A upon doxycycline exposure. Tet-O-siVEGF:podocin-rtTA mice express VEGF shRNA in podocytes in a doxycycline-regulated manner, decreasing VEGF-A mRNA and VEGF-A protein levels in isolated glomeruli to ~20% of non-induced controls and urine VEGF-A to ~30% of control values a week after doxycycline induction. Induced tet-O-siVEGF:podocin-rtTA mice developed acute renal failure and proteinuria, associated with mesangiolysis and microaneurisms. Glomerular ultrastructure revealed endothelial cell swelling, GBM lamination and podocyte effacement. VEGF knockdown decreased podocyte fibronectin and glomerular endothelial alpha(V)beta(3) integrin in vivo. VEGF receptor-2 (VEGFR2) interacts with beta(3) integrin and neuropilin-1 in the kidney in vivo and in VEGF(KD) podocytes. Podocyte VEGF knockdown disrupts alpha(V)beta(3) integrin activation in glomeruli, detected by WOW1-Fab. VEGF silencing in cultured VEGF(KD) podocytes downregulates fibronectin and disrupts alpha(V)beta(3) integrin activation cell-autonomously. Collectively, these studies indicate that podocyte VEGF-A regulates alpha(V)beta(3) integrin signaling in the glomerulus, and that podocyte VEGF knockdown disrupts alpha(V)beta(3) integrin activity via decreased VEGFR2 signaling, thereby damaging the three layers of the glomerular filtration barrier, causing proteinuria and acute renal failure.
|Semaphorin3a regulates endothelial cell number and podocyte differentiation during glomerular development. |
Reidy, KJ; Villegas, G; Teichman, J; Veron, D; Shen, W; Jimenez, J; Thomas, D; Tufro, A
Development (Cambridge, England)
Semaphorin3a (Sema3a), a chemorepellant guidance protein, plays crucial roles in neural, cardiac and peripheral vascular patterning. Sema3a is expressed in the developing nephron, mature podocytes and collecting tubules. Sema3a acts as a negative regulator of ureteric bud branching, but its function in glomerular development has not been examined. Here we tested the hypothesis that Sema3a regulates glomerular vascular development using loss- and gain-of-function mouse models. Sema3a deletion resulted in defects in renal vascular patterning, excess endothelial cells within glomerular capillaries, effaced podocytes with extremely wide foot processes and albuminuria. Podocyte Sema3a overexpression during organogenesis resulted in glomerular hypoplasia, characterized by glomerular endothelial cell apoptosis, delayed and abnormal podocyte foot process development, a complete absence of slit diaphragms and congenital proteinuria. Nephrin, WT1 and VEGFR2 were downregulated in Sema3a-overexpressing kidneys. We conclude that Sema3a is an essential negative regulator of endothelial cell survival in developing glomeruli and plays a crucial role in podocyte differentiation in vivo. Hence, a tight regulation of Sema3a dosage is required for the establishment of a normal glomerular filtration barrier.