Primary renal hypoplasia in humans and mice with PAX2 mutations: evidence of increased apoptosis in fetal kidneys of Pax21Neu +/- mutant mice

Abstract

PAX2 mutations cause renal-coloboma syndrome (RCS), a rare multi-system developmental abnormality involving optic nerve colobomas and renal abnormalities. End-stage renal failure is common in RCS, but the mechanism by which PAX2 mutations lead to renal failure is unknown. PAX2 is a member of a family of developmental genes containing a highly conserved 'paired box' DNA-binding domain, and encodes a transcription factor expressed primarily during fetal development in the central nervous system, eye, ear and urogenital tract. Presently, the role of PAX2 during kidney development is poorly understood. To gain insight into the cause of renal abnormalities in patients with PAX2 mutations, kidney anomalies were analyzed in patients with RCS, including a large Brazilian kindred in whom a new PAX2 mutation was identified. In a total of 29 patients, renal hypoplasia was the most common congenital renal abnormality. To determine the direct effects of PAX2 mutations on kidney development fetal kidneys of mice carrying a Pax2 (1Neu)mutation were examined. At E15, heterozygous mutant kidneys were approximately 60% of the size of wild-type littermates, and the number of nephrons was strikingly reduced. Heterozygous 1Neu mice showed increased apoptotic cell death during fetal kidney development, but the increased apoptosis was not associated with random stochastic inactivation of Pax2 expression in mutant kidneys; Pax2 was shown to be biallelically expressed during kidney development. These findings support the notion that heterozygous mutations of PAX2 are associated with increased apoptosis and reduced branching of the ureteric bud, due to reduced PAX2 dosage during a critical window in kidney development.

Rescue of Defective Branching Nephrogenesis in Renal-Coloboma Syndrome by the Caspase Inhibitor, Z-VAD-fmk

“…In previous studies, we have shown that PAX2 haploinsufficiency causes renal hypoplasia associated with reduced nephron number (oligonephronia), detectable in the early stages (E15) of kidney development in the mouse (9). Here, we confirm that heterozygous Pax2 1Neu fetal (E17.5) mice have a selective increase in apoptosis of UB cells; we also directly demonstrate a significant deficit in arborization of the PAX2 mutant UB.…”

“…However, the highest levels of PAX2 expression during renal development are seen in the arborizing UB, and we have recently shown that it appears to suppress programmed cell death pathways in that lineage (8,9). PAX2 strongly suppresses apoptosis in cultured renal cells (8), and we noted a striking increase in apoptotic (TUNEL-positive) UB cells of E15 fetal kidneys of mice heterozygous for the PAX2 1Neu mutation (9). We have hypothesized (10) that the principal factor causing oligomeganephronia in RCS is loss of PAX2 anti-apoptotic function in the branching UB.…”

“…It may determine cell fate during nephric duct formation (6), activate GDNF in metanephric mesenchyme (7), and activate cell adhesion molecules and cytoskeletal elements during conversion of metanephric mesenchyme into epithelial cells of the emerging nephron (8). However, the highest levels of PAX2 expression during renal development are seen in the arborizing UB, and we have recently shown that it appears to suppress programmed cell death pathways in that lineage (8,9). PAX2 strongly suppresses apoptosis in cultured renal cells (8), and we noted a striking increase in apoptotic (TUNEL-positive) UB cells of E15 fetal kidneys of mice heterozygous for the PAX2 1Neu mutation (9).…”

Calcineurin A–Binding Protein, a Novel Modulator of the Calcineurin-Nuclear Factor of Activated T-Cell Signaling Pathway, Is Overexpressed in Wilms' Tumors and Promotes Cell Migration

“…Inhibition of PAX2 in renal cell lines reduces proliferation as well as resistance to cisplatin treatment (26,28). Analyses of the Pax2 +/− kidney phenotype also support a role for Pax2 in cell survival (30)(31)(32)(33). Expression of PAX2 correlates with increased migration of Kaposi sarcoma cells and endothelial cells isolated from renal tumors (29,34).…”

Genetics of vesicoureteral reflux

“…66 similarly, reduced PaX2 signaling caused by a heterozygous Pax2 mutation has been shown to result in shortened intravesical ureters, caudally shifted ureteric buds, reduced bud branching, small hypoplastic kidneys with reduced nephron number and particularly vur. 51,67 the transcription factor Lim1 (also known as homeobox protein Lhx1) is a homeobox gene expressed in the organizer region of mouse embryos. Conditional knockout of Lim1 in the ureteric bud and mesonephric duct has been shown to delay bud formation, slow mesonephric duct migration to the bladder, and cause the kidneys to be small and malformed, with dilated refluxing ureters.…”