p53-Mediated Regulation of Wnt/β-catenin Signaling in Nascent Nephron Formation

Wnt/β-catenin gradient is required for the progression of nephrogenesis. Current model dictates Wnt/β-catenin activity emanating from the UB (yellow arrow) is required to induce nephrogenesis, but must be down-regulated for MET to occur (left panel). In p53-/- metanephroi, sustained β-catenin levels result in developmental arrest (right panel). Cm, cap mesenchyme which are Nephron Progenitor Cells; u, ureteric epithelia; p, pretubular aggregate; r, renal vesicle.

Wnt/β-catenin gradient is required for the progression of nephrogenesis. Current model dictates Wnt/β-catenin activity emanating from the UB (yellow arrow) is required to induce nephrogenesis, but must be down-regulated for MET to occur (left panel). In p53-/- metanephroi, sustained β-catenin levels result in developmental arrest (right panel). Cm, cap mesenchyme which are Nephron Progenitor Cells; u, ureteric epithelia; p, pretubular aggregate; r, renal vesicle.

Reduced nephron number from birth is strongly associated to development of adult-onset diseases such as hypertension, chronic renal failure and type 2 diabetes, thus significantly influencing long-term renal health. Nephron endowment is influenced by self-renewal of the multipotent nephron progenitor cell (NPC) population and its ability to differentiate to nascent nephrons. p53 is best known for its role as a tumor suppressor by regulating cell cycle, differentiation and apoptosis pathways and more recently for its role in restricting self-renewal of neural and hematopoietic stem cells. Differentiation of NPC to nascent nephrons requires tight regulation of β-catenin activity. Sustained β-catenin levels in NPC result in nephrogenesis arrest and failure of induced mesenchyme to epithelial transition (MET), indicating a requirement for attenuated β-catenin signaling for MET to occur. Transcription factor p53 is a well-known regulator of β-catenin levels and activity. Indeed, p53-/- metanephroi demonstrate elevated total β-catenin levels and marked reduction in nascent nephrons and decreased number of glomeruli. Moreover, p53-/- kidneys exhibit large caps of mesenchyme at UB tips associated with delayed mesenchyme to epithelium transition and subsequent nephron deficit. Our preliminary findings place p53 upstream to the Wnt signaling pathway, a key regulator of progenitor cell renewal and nephrogenesis. Genome-wide microarray coupled with ChIP-Seq show Wnt pathway members as primary targets for p53 regulation in the developing kidney. Therefore, we hypothesize that p53 restricts Wnt/β-catenin signaling in the NPC during MET. Accordingly, we will determine whether conditional inactivation of p53 in nephron progenitor cells causes sustained β-catenin activity in nascent nephrons. Next, by mosaic deletion of p53 from the NPC we will deteremine whether arrest in nephrogenesis is beta-catenin dependent. Finally, we will investigate whether decrease in β-catenin dosage by conditional removal of one β-catenin allele from the NPC of p53-depleted NPC metanephroi rescues the nephrogenesis arrest.