Renal progenitors: Roles in kidney disease and regeneration

Kidney disease is a devastating condition that affects millions of people worldwide, and its prevalence predicted to significantly increase. The kidney is complex organ encompassing many diverse cell type organized in a elaborate tissue architecture, makin regeneration a challenging feat. In recent years, there ha been a surge in the field of stem cell research to develo regenerative therapies for various organ systems. Here we review some recent progressions in characterizing th role of renal progenitors in development, regeneration and kidney disease in mammals. We also discuss how the zebrafish provides a unique experimental anima model that can provide a greater molecular and genet understanding of renal progenitors, which may contribut to the development of potential regenerative therapies fo human renal afflictions.

Acetylsalicylic acid interferes with embryonic kidney growth and development by a prostaglandin-independent mechanism

AIM To evaluate the effects of the non-selective, non-steroidal anti-infammatory drug （NSAID） acetylsalicylic acid （ASA）, on ex vivo embryonic kidney growth and development.METHODS Pairs of fetal mouse kidneys at embryonic day 12.5 were cultured ex vivo in increasing concentrations of ASA （0.04-0.4 mg/mL） for up to 7 d. One organ from each pair was grown in control media and was used as the internal control for the experimental contralateral organ. In some experiments, organs were treated with ASA for 48 h and then transferred either to control media alone or control media containing 10 μmol/L prostaglandin E2 （PGE2） for a further 5 d. Fetal kidneys were additionally obtained from prostaglandin synthase 2 homozygous null or heterozygous （PTGS2-/- and PTGS2-/＋） embryos and grown in culture. Kidney cross-sectional area was used to determine treatment effects on kidney growth. Whole-mount labelling to fluorescently detect laminin enabled crude determination of epithelial branching using confocal microscopy.RESULTSIncreasing ASA concentration （0.1, 0.2 and 0.4 mg/mL） significantly inhibited metanephric growth （P 〈 0.05）. After 7 d of culture, exposure to 0.2 mg/mL and 0.4 mg/mL reduced organ size to 53% and 23% of control organ size respectively （ P 〈 0.01）. Addition of 10 μmol/L PGE2 to culture media after exposure to 0.2 mg/mL ASA for 48 h resulted in a return of growth area to control levels. Application of control media alone after cessation of ASA exposure showed no benefit on kidney growth. Despite the apparent recovery of growth area with 10 μmol/L PGE2, no obvious renal tubular structures were formed. The number of epithelial tips generated after 48 h exposure to ASA was reduced by 40% （0.2 mg/mL; P 〈 0.05） and 47% （0.4 mg/mL; P 〈 0.01）. Finally, growth of PTGS2-/- and PTGS2＋/- kidneys in organ culture showed no differences, indicating that PTGS2 derived PGE2 may at best have a minor role.CONCLUSIONASA reduces early renal growth and development but the role of prostaglandins in this may be minor.

Regulation of kidney development by the Mdm2/Mdm4-p53 axis

While p53 activity is required for tumour suppression, unconstrained p53 activity on the other hand is detrimental to the organism, resulting in inappropriate cellular death or proliferation defects. Unimpeded p53 activity is lethal in the developing embryo, under- lining the need for maintaining a tight control on p53 activity during this period. The critical role of the negative regulators of p53, Mdm2 and Mdm4, in vertebrate development came to light by fatal disruption of embryogenesis that was observed with Mdm2 and Mdm4 gene deletions in mice. Embryonic lethality was rescued only by superimposing p53 removal. Here we summarize the contri- bution of the Mdm2/Mdm4-p53 axis that occurs at multiple steps of kidney development. Conditional, cell type-specific deletions reveal distinct functions of these proteins in renal morphogenesis. The severe impact on the renal phenotype from targeted gene deletions underscores the critical role played by the Mdm2/Mdm4-p53 nexus on nephrogenesis, and emphasizes the need to monitor patients with aberrations in this pathway for kidney function defects and associated cardiovascular dysfunction.