Lithium induces mesenchymal-epithelial differentiation during human kidney development by activation of the Wnt signalling system.

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.