Abstract
Kidney function is directly linked to the number of nephrons which are generated until 32–36 weeks gestation in humans. Failure to make nephrons during development leads to congenital renal malformations, whilst nephron loss in adulthood occurs in progressive renal disease. Therefore, an understanding of the molecular processes which underlie human nephron development may help design new treatments for renal disease. Mesenchyme to epithelial transition (MET) is critical for forming nephrons, and molecular pathways which control rodent MET have been identified. However, we do not know whether they are relevant in human kidney development. In this study, we isolated mesenchymal cell lines derived from human first trimester kidneys in monolayer culture and investigated their differentiation potential. We found that the mesenchymal cells could convert into osteogenic, but not adipogenic or endothelial lineages. Furthermore, addition of lithium chloride led to MET which was accompanied by increases in epithelial (CDH1) and tubular (ENPEP) markers and downregulation of renal progenitor (SIX2, EYA1, CD133) and mesenchymal markers (HGF, CD24). Prior to phenotypic changes, lithium chloride altered Wnt signalling with elevations in AXIN2, GSK3β phosphorylation and β-catenin. Collectively, these studies provide the first evidence that lithium-induced Wnt activation causes MET in human kidneys. Therapies targeting Wnts may be critical in the quest to regenerate nephrons for human renal diseases.
Highlights
Healthy mature human kidneys contain around 1 million nephrons[1, 2], yet they originate from only a few hundred cells during development
Foetal renal mesenchymal cells have the capacity to differentiate into renal epithelia, stroma and endothelia in vivo, but it is uncertain whether they may be able to generate other lineages
Effect of lithium chloride on foetal kidney mesenchymal cell gene expression we examined changes in gene expression using three replicates in each of the three independent mesenchymal cell lines following stimulation with 20 mM lithium chloride for seven days by qRT-PCR (Fig. 3a). mRNA levels of the renal progenitor markers sine oculis homeobox homologue 2 (SIX2)[20] (9.7 ± 0.1-fold, p < 0.001), eyes absent homologue 1 (EYA1)[20] (4.8 ± 0.7-fold, p < 0.01) and prominin-1 (CD133)[21] (3.1 ± 1.0-fold, p < 0.05) were significantly decreased in cells exposed to lithium chloride compared with untreated cells
Summary
Healthy mature human kidneys contain around 1 million nephrons[1, 2], yet they originate from only a few hundred cells during development. A critical early step in nephron formation is Studies in rodents have identified that a critical signalling pathway that can induce MET is the activation of Official journal of the Cell Death Differentiation Association. Transgenic mice with a complete loss of Wnt[413] or lack of β-catenin activity in renal mesenchymal progenitor cells are unable to form mature renal epithelial structures[14]. We do not yet know whether the activation of canonical Wnt signalling is relevant in human foetal kidney development. Addition of lithium led to human MET in vitro accompanied by activation of Wnt signalling pathways.
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