Congenital or acquired nephron deficit results in hypertension and chronic kidney disease, both clinically significant diseases without a cure. Nephron abundance varies amongst individuals and populations, with demonstrated influence of genetics and maternal nutritional status on nephron number in humans. Availability of nephron progenitor cells (NPC) during development is a critical driver of nephron endowment at birth. Self- renewal of NPC ensures a supply of cells for nephrogenesis until the cessation of nephrogenesis at post-natal day 4 in mice and 35 weeks gestation time in humans. Fundamental questions that remain unanswered are what causes self-renewal arrest, and how can this process be manipulated? The nephron progenitor niche in which the NPCs reside provides extrinsic cues such as nutrients and morphogens that drive cell intrinsic signaling and metabolic pathways to promote NPC availability for subsequent nephrogenesis. The tumor suppressor and transcription factor p53 is a key regulator of cellular and tissue homeostasis. Cell competition studies in Drosophila implicate p53 as a sensor and modulator of adaptive metabolic changes to maintain cell viability. Our studies show that conditional p53 deletion in the nephron progenitor cells induces progressive depletion of the self-renewing progenitors, and subsequently nephron deficit and adult-onset hypertension. Selective loss of the Cited1+ self-renewing progenitors, but not of the non-renewing progenitor cells, suggest the NPC prematurely transition to the non-self-renewing pool. Our functional studies indicate reduced energy metabolism by decreased oxidative phosphorylation (Oxphos), ATP and ROS levels in Six2p53-/- cells, corroborating our RNA-Seq data that top down-regulated genes belong to energy metabolism pathways. Both ATP production by Oxphos and biomass synthesis by glycolysis are critical drivers of stem cell self-renewal. We therefore hypothesized that p53 is required for the metabolic homeostasis of nephron progenitors and thus enables their self-renewal in response to niche cues. To test our hypothesis we propose the following experiments:
Specific Aim 1 will compare the metabolic profile of p53+/+ and p53-/- NPC, and determine the ability of Cited1+ NPC to respond via an adaptive metabolic response to altered glucose and O2 levels and assess their ability to self-renew (maintain and expand the Cited1 population) under these conditions.
Specific Aim 2 will examine the cross-talk between metabolic and signaling pathways that promote self-renewal.
Specific Aim 3 will test the hypothesis that p53 maintains metabolic homeostasis by regulating transcription of energy metabolism genes in the NPC. How the metabolic status of the NPC switches the cellular program from self-renewal to differentiation can have potentially huge implications on how the maternal environment influences progenitor stemness. Elucidating these molecular details will be vital to develop advanced therapies for using stem cells in applications such as regenerative medicine.
Low nephron endowment results in hypertension and chronic kidney disease, both clinically significant diseases without a cure. Availability of nephron progenitor cells (NPC) during kidney development is a major determinant of nephron number at birth. Critical questions that remain unanswered are what regulates NPC self-renewal, and how can this process be manipulated? The proposed work explores mechanisms of NPC renewal by energy metabolism.
| Saifudeen, Zubaida (2017) Tissue-Specific Functions of p53 During Kidney Development. Results Probl Cell Differ 60:111-136 |
| Liu, Jiao; Edgington-Giordano, Francesca; Dugas, Courtney et al. (2017) Regulation of Nephron Progenitor Cell Self-Renewal by Intermediary Metabolism. J Am Soc Nephrol 28:3323-3335 |
| El-Dahr, Samir S; Li, Yuwen; Liu, Jiao et al. (2017) p63+ ureteric bud tip cells are progenitors of intercalated cells. JCI Insight 2: |
