Embryonal hyperplasia of Bowman's capsular epithelium in patients with WT1 mutations

WT1 exon 10 missense variant in a pediatric patient with focal segmental glomerulosclerosis with embryonal hyperplasia

A 6-year-old boy was diagnosed with chromosomal abnormalities (48,XYY, + 21[11]/46,XY[19]) at 4 months of age after a physical examination revealed an undescended testis and a dwarf penis. He also had mild renal dysfunction and severe proteinuria, and kidney biopsy at 2 years of age revealed focal segmental glomerulosclerosis. Genetic analysis to investigate suspected WT1 gene abnormalities revealed a novel variant in NM_024426.6:exon10:c.1506 T > A (p.(Asp502Glu)). His kidney function deteriorated rapidly, leading to the induction of peritoneal dialysis at 5 years of age. Although this variant had not been previously reported, bilateral nephrectomy was performed to prevent any progression of the tumor. Histopathology showed all the glomeruli observed within the observation area to be completely sclerotic, while also showing evidence of embryonal hyperplasia. This case was not a hot spot for Denys-Drash syndrome, but it had a similar phenotype and pathology that could have been derived from a WT1 gene abnormality.

miR-193a as a potential mediator of WT-1/synaptopodin in the renoprotective effect of losartan on diabetic kidney

Diabetic nephropathy (DN) is the most common complication of diabetic patients, and has become a global healthcare problem. In this study, we used diabetic mice to evaluate the effect of Losartan on diabetic nephropathy, in which the experimental animals were divided into three groups: non-diabetic mice (db/m group), untreated-diabetic mice (db/db group), and Losartan-treated diabetic mice (db/db-losartan). Next, immunohistochemistry and immunofluorescence were used to detect WT-1 and synaptopodin expression, respectively. Protein levels of WT-1, synaptopodin, claudin1, and Pax-2 were assessed by Western blotting and real-time PCR. The miR-193a mRNA levels were quantitated by real-time PCR. The results showed that albuminuria was increased in diabetic mice compared with control animals and was significantly ameliorated by treatment with Losartan. In addition, Losartan significantly upregulated the immunopositive cell numbers of WT-1, the expression of WT-1 and synaptopodin in renal tissue. By contrast, expression of claudin1 and Pax-2 in renal tissue were decreased in db/db-losartan group. Besides, expression of miR-193a was decreased significantly in db/db-losartan group compared to the untreated diabetic group. Thus, Losartan has renoprotective effects on the control of tissue damage possibly by inhibiting the expression of miR-193a, thereby promoting the repair of podocyte injury in mice with diabetic nephropathy.

PAX2 is dispensable for in vitro nephron formation from human induced pluripotent stem cells

The kidney is formed by reciprocal interactions between the nephron progenitor and the ureteric bud, the former of which gives rise to the epithelia of nephrons consisting of glomeruli and renal tubules. The transcription factor PAX2 is essential for this mesenchymal-to-epithelial transition of nephron progenitors, as well as ureteric bud lineage development, in mice. PAX2 mutations in humans cause renal coloboma syndrome. We previously reported the induction of nephron progenitors and three-dimensional nephron structures from human induced pluripotent stem (iPS) cells. Here we generate iPS cells lacking PAX2, and address the role of PAX2 in our in vitro induction protocol. While PAX2-null human nephron progenitors were properly formed, they unexpectedly became epithelialised to form glomeruli and renal tubules. However, the mutant glomerular parietal epithelial cells failed to transit to the squamous morphology, retaining the shape and markers of columnar epithelia. Therefore, PAX2 is dispensable for mesenchymal-to-epithelial transition of nephron progenitors, but is required for morphological development of glomerular parietal epithelial cells, during nephron formation from human iPS cells in vitro.

The effects of angiotensin-II receptor blockers on podocyte damage and glomerular apoptosis in a rat model of experimental streptozotocin-induced diabetic nephropathy

The aim of the study was to determine in a rat model of streptozotocin-induced diabetic nephropathy the expression of: WT-1 (for podocyte loss in the glomerulus), TGF-beta 1 (for tissue damage), caspase-3 and bax (for glomerular apoptosis) and the possible protective effects of an angiotensin II type 1 receptor blocker. Three groups of male Wistar albino rats were used. The first group consisted of non-diabetic control rats. The second group was the untreated diabetic rats. The third group consisted of diabetic rats treated with Irbesartan, which is an angiotensin II receptor antagonist, widely used in treatment for hypertension. Immunohistochemical stainings for TGF-beta 1, bax, caspase-3 and WT-1 were performed. The microalbuminuria levels of the Irbesartan-treated diabetic group were lower than those of the untreated diabetic group (P<0.01). The immunostaining of TGF-beta 1, bax and caspase-3 was decreased in glomeruli of the Irbesartan-treated diabetic group compared to the untreated diabetic group. WT-1 immunopositive podocyte numbers were found to be significantly lower in the untreated diabetic group than in the other groups (P<0.01). In the Irbesartan-treated diabetic group, the WT-1 immunopositive cell numbers were higher compared to the untreated diabetic group (P<0.01). We conclude that the decrease in the number of podocytes is an early marker of diabetic nephropathy, AT1 receptor blocker has renoprotective effects on the regulation of renal hemodynamics and on the control of tissue damage by preventing podocyte loss, which leads to decrease of bax and caspase-3 expressions of apoptosis related proteins, and may prevent glomerular cell apoptosis via angiotensin II.

Myogenesis in Wilms' tumors is associated with mutations of the WT1 gene and activation of Bcl-2 and the Wnt signaling pathway

Wilms tumors with WT1 mutations [ WT1(-)] have a stromal-predominant histology with varying extents of rhabdomyogenesis. These tumors also frequently have mutations in the beta-catenin gene ( CTNNB1). We have investigated the molecular events that may explain the origins of rhabdomyogenesis in WT1(-) tumors. Of 35 Wilms tumors, we identified 12 with WT1 mutations, of which 9 carried CTNNB1 mutations. We compared WT1 wild-type tumors [ WT1(+)] with WT1(-) tumors for histological features, localization of beta-catenin, Bcl-2 expression, and apoptosis using an in-situ end-labeling technique. WT1(+) tumors showed triphasic and blastemal- and epithelial predominant-histology. Expression of WT1, beta-catenin, and Bcl-2 recapitulated those of normal kidney epithelial development. Localization of beta-catenin was observed in the cytoplasm and cytoplasmic membrane of early glomerular epithelial structures. Bcl-2 is also expressed in condensing blastema and early glomerular epithelial structures which had little apoptosis. WT1(-) tumors, regardless of whether CTNNB1 mutations were detected or not, showed a stromal-rich phenotype with abundant expression of beta-catenin in the nucleus of the rhabdomyoblasts. Bcl-2 was expressed in rhabdomyoblasts, but not in blastemal cells undergoing apoptosis, suggesting that WT1 regulates Bcl-2 positively in the epithelial pathway, but negatively in the myogenic pathway. These data indicate that mutations in WT1 might alter the Wnt signaling pathway and Bcl-2 related-apoptosis. In WT1(-) tumors, the nuclear accumulation of beta-catenin and Bcl-2 expression are associated with rhabdomyogenesis, and dysregulation of Bcl-2 may be a mechanism by which the histogenesis (loss of blastemal component, muscle differentiation) may be explained.