The dysregulated autophagy signaling is partially responsible for defective podocyte development in wt1a mutant zebrafish

Abstract

Podocytes are essential elements of the glomerular filtration barrier and relevant to many kidney diseases. But the molecular mechanism in podocyte development is still unclear. Wilms tumor protein (WT1) is an essential factor for urogenital system development. Zebrafish have two wt1 genes, naming wt1a and wt1b. Here, we examined the roles of both wt1 genes in zebrafish embryonic development employing the CRISPR/Cas9 technology. The homozygous wt1a mutants displayed developmental malformations including pericardial edema, yolk sac edema and failure of glomerulus development. Loss of wt1a function disrupted podocyte differentiation and inhibited expression of podocin and nephrin. In contrast, the homozygous wt1b mutants were phenotypically normal and had no severe phenotypes of nephrogenesis defects that were observed in wt1b morpholino knockdown embryos. Therefore, wt1a plays an essential role in kidney development, whereas wt1b might not be essential for kidney development. Interestingly, from previous studies we knew that autophagy is involved in podocyte differentiation. By detecting the protein level of P62 and LC3A/B, we found the autophagy signal was greatly reduced in wt1a mutants. To better understand the relationship between autophagy signal and wt1a function in podocyte development, rapamycin was added to activate autophagy in wt1a-mutated embryos. As a result, podocyte injury was ameliorated in wt1a homozygous mutants by rapamycin treatment. In conclusion, our findings not only confirmed the essential function of wt1a during kidney development, but also provided a possible way for treatment of diseases involving podocyte injury.