Clinical Aspects of WT1 and the Kidney

The recruitment mechanisms and potential therapeutic targets of podocytes from parietal epithelial cells

Podocytes are differentiated postmitotic cells which cannot be replaced after podocyte injury. The mechanism of podocyte repopulation after injury has aroused wide concern. Parietal epithelial cells (PECs) are heterogeneous and only a specific subpopulation of PECs has the capacity to replace podocytes. Major progress has been achieved in recent years regarding the role and function of a subset of PECs which could transdifferentiate toward podocytes. Additionally, several factors, such as Notch, Wnt/ß-catenin, Wilms’ tumor-1, miR-193a and growth arrest-specific protein 1, have been shown to be involved in these processes. Finally, PECs serve as a potential therapeutic target in the conditions of podocyte loss. In this review, we discuss the latest observations and concepts about the recruitment of podocytes from PECs in glomerular diseases as well as newly identified mechanisms and the most recent treatments for this process.

Suspicion of Frasier's Syndrome in the Nephrology Unit of the State University Hospital of Haiti: Case Study and Review of Literature

Objective

Frasier syndrome is a rare genetic nephropathy characterized by the presence of progressive glomerulopathy with proteinuria associated with male pseudo hermaphroditism. This case study described a picture of a young boy where the clinical suspicion context reminded the Frasier syndrome. To our knowledge, this case is the first described in Haiti.

Case Study

This is a 19-year-old young phenotypically male, born with a genital anomaly, was seen on referral at the nephrology/dialysis unit of the internal medicine department of the State University Hospital of Haiti for evaluation and follow-up. Insidious progression of symptoms had occurred over 3 years. Over three months of outpatient follow-up, he had four sets of renal labs drawn, and all showed impaired renal function. At the ultrasound, a bilateral cryptorchidism is described in the inguinal, and presence of functional ovaries with follicles of variable size scattered in the parenchyma. So, in the light of these anamnestic, clinical and paraclinical findings, we concluded to the diagnosis of end-stage renal failure by progressive glomerulopathy in a context of Frasier's syndrome.

Conclusion

With any clinical picture consisting of genital anomalies at birth, renal symptomatology during childhood and the diagnosis of renal failure during adolescence, rare genetic nephropathies, such as Frasier syndrome must be considered.

Case Report: Rare Case of Synchronous Neck Metastasis From Metachronous Bilateral Renal Cell Carcinoma

Renal cell carcinoma (RCC) is a malignant tumor that can metastasize easily. Hence, many patients have already developed metastasis when they are diagnosed. It is also one of the most common tumors that metastasize to the head and neck through extranodal disease. Herein, we reported a case of a 53-year-old man with cervical metastasis from bilateral RCC. Interestingly, whole exome sequencing (WES) and clonal evolution analysis revealed that bilateral renal tumor lesions and neck metastases (squamous cell carcinoma) share the same subclones and a large number of gene variants, while the pathological morphology is different (left nephrotic foci, a mixed pattern of mucinous tubular and spindle cell carcinoma (MTSCC) with papillary adenoma; right renal foci, papillary renal cell carcinoma (PRCC)). This was first reported in RCCs to the best of our knowledge. This case suggests that genotype analysis can be a powerful supplementary examination for clinical histopathological diagnosis. Gene detection has great significance for the accurate diagnosis and treatment of RCC metastasis or multiple lesions.

A novel WT1 gene mutation in a chinese girl with denys-drash syndrome

OBJECTIVE

Denys-Drash syndrome (DDS) is defined by the triad of Wilms tumor, nephrotic syndrome, and/or ambiguous genitalia. Genetic testing may help identify new gene mutation sites and play an important role in clinical decision-making.

METHODS

We present a patient with an XY karyotype and female appearance, nephropathy, and Wilms tumor in the right kidney. Genomic DNA was extracted from peripheral blood cells according to standard protocols. "Next-generation" sequencing (NGS) was performed to identify novel variants. The variant was analyzed with Mutation Taster, and its function was explored by a cell growth inhibition assay.

RESULTS

We found the first case of Denys-Drash syndrome with the uncommon missense mutation (c.1420C>T, p.His474 Tyr) in the WT1 gene. In silico analysis, the variant was predicted "disease-causing" by Mutation Taster. The mutated variant showed a weaker effect in inhibiting tumor cells than wild-type WT1.

CONCLUSIONS

The uncommon missense mutation (c.1420C>T, p.His474 Tyr) in the WT1 gene may be a crucial marker in DDS.

Podocyte apoptosis in diabetic nephropathy by BASP1 activation of the p53 pathway via WT1

AIMS

Diabetic nephropathy (DN) is a leading cause of end-stage renal disease. BASP1 (brain acid-soluble protein) is up-regulated in podocyte-specific protein phosphatase 2A knockout mice (Pod-PP2A-KO) that develop kidney dysfunction. Here, we explore the role of BASP1 for podocytes in DN.

METHODS

BASP1 was assessed in kidneys from DN patients and DN mouse models, podocyte specific BASP1 knockout mice (Pod-BASP1-KO mice) were generated and studied in vivo. Furthermore, podocyte injury and apoptosis were measured after BASP1 knockdown and overexpression in a mouse podocyte cell line (MPC5). Potential signalling pathways involved in podocyte apoptosis were detected.

RESULTS

BASP1 expression was up-regulated in DN patients compared to normal controls. BASP1 specific deletion in podocytes protected against podocyte injury by reducing the loss of expression of slit diaphragm molecules and foot process effacement in the DN model. BASP1 promoted actin cytoskeleton rearrangements and apoptosis in the MPC5 podocyte line. Molecules involved in the p53 pathway were down-regulated in BASP1 knockdown podocytes treated with high glucose compared to controls. BASP1 promoted podocyte apoptosis and P53 pathway activation through co-repression with Wilms' tumour 1 transcription factor (WT1).

CONCLUSION

BASP1 activates the p53 pathway through modulation of WT1 to induce podocyte apoptosis in diabetic nephropathy.

New Insights into Potocki-Shaffer Syndrome: Report of Two Novel Cases and Literature Review

Potocki-Shaffer syndrome (PSS) is a rare non-recurrent contiguous gene deletion syndrome involving chromosome 11p11.2. Current literature implies a minimal region with haploinsufficiency of three genes, ALX4 (parietal foramina), EXT2 (multiple exostoses), and PHF21A (craniofacial anomalies, and intellectual disability). The rest of the PSS phenotype is still not associated with a specific gene. We report a systematic review of the literature and included two novel cases. Because deletions are highly variable in size, we defined three groups of patients considering the PSS-genes involved. We found 23 full PSS cases (ALX4, EXT2, and PHF21A), 14 cases with EXT2-ALX4, and three with PHF21A only. Among the latter, we describe a novel male child showing developmental delay, café-au-lait spots, liner postnatal overgrowth and West-like epileptic encephalopathy. We suggest PSS cases may have epileptic spasms early in life, and PHF21A is likely to be the causative gene. Given their subtle presentation these may be overlooked and if left untreated could lead to a severe type or deterioration in the developmental plateau. If our hypothesis is correct, a timely therapy may ameliorate PSS phenotype and improve patients’ outcomes. Our analysis also shows PHF21A is a candidate for the overgrowth phenotype.

Protective effect of umbilical cord mesenchymal stem cells combined with resveratrol against renal podocyte damage in NOD mice

BACKGROUND

The role of chronic inflammation initiated by persistent hyperglycemia in podocyte injury has attracted increasing attention. The advanced glycation end products (RAGE) receptor- nuclear factor-kappa B (NF-кB) signaling pathway is involved in the occurrence of inflammation. We speculate that treatment with human umbilical cord mesenchymal stem cells (hUCMSCs) combined with resveratrol can block this signaling pathway and protect podocyte function.

METHODS

Non obesity diabetes(NOD) mice were randomly divided into 5 groups: NOD-T1DM, Res, hUCMSCs, hUCMSCs + Res and insulin (INS)groups. Mice without diabetes were classified as NOD control group(NOD group). Blood glucose(BG), blood urea nitrogen(BUN), serum creatinine(SCr), 24-h urine albumin excretion rate (UAER) were measured. The expression of nephrin, WT1 and RAGE, MCP-1 in renal tissues were detected by Western blot, expression of NF-кB protein(P65) was determined by immunohistochemistry.

RESULTS

The combined treatment of hUCMSCs and Resveratrol can reduce BG, BUN, SCr, 24-h UAER, and the expression of the inflammatory factors MCP-1, RAGE and NF-кB; increase the number of podocytes and the expression of the podocyte-related proteins nephrin and WT1 in type 1 diabetes mellitus, and improve renal pathological structure.

CONCLUSIONS

Combining of hUCMSCs and resveratrol can better protect renal podocyte function, and the effects on the reduction of blood glucose and renal injury are better than those obtained by insulin treatment. This indicated that the combination of Res and hUCMSCs may be a novel therapeutic method for the treatment of DN.

Role for first zinc finger of WT1 in DNA sequence specificity: Denys-Drash syndrome-associated WT1 mutant in ZF1 enhances affinity for a subset of WT1 binding sites

Wilms tumor protein (WT1) is a Cys2-His2 zinc-finger transcription factor vital for embryonic development of the genitourinary system. The protein contains a C-terminal DNA binding domain with four tandem zinc-fingers (ZF1-4). An alternative splicing of Wt1 can add three additional amino acids-lysine (K), threonine (T) and serine (S)-between ZF3 and ZF4. In the -KTS isoform, ZF2-4 determine the sequence-specificity of DNA binding, whereas the function of ZF1 remains elusive. Three X-ray structures are described here for wild-type -KTS isoform ZF1-4 in complex with its cognate DNA sequence. We observed four unique ZF1 conformations. First, like ZF2-4, ZF1 can be positioned continuously in the DNA major groove forming a 'near-cognate' complex. Second, while ZF2-4 make base-specific interactions with one DNA molecule, ZF1 can interact with a second DNA molecule (or, presumably, two regions of the same DNA molecule). Third, ZF1 can intercalate at the joint of two tail-to-head DNA molecules. If such intercalation occurs on a continuous DNA molecule, it would kink the DNA at the ZF1 binding site. Fourth, two ZF1 units can dimerize. Furthermore, we examined a Denys-Drash syndrome-associated ZF1 mutation (methionine at position 342 is replaced by arginine). This mutation enhances WT1 affinity for a guanine base. X-ray crystallography of the mutant in complex with its preferred sequence revealed the interactions responsible for this affinity change. These results provide insight into the mechanisms of action of WT1, and clarify the fact that ZF1 plays a role in determining sequence specificity of this critical transcription factor.

Mutation spectrum of genes associated with steroid-resistant nephrotic syndrome in Chinese children

Approximately 20% of children with idiopathic nephrotic syndrome do not respond to steroid therapy. More than 30 genes have been identified as disease-causing genes for the steroid-resistant nephrotic syndrome (SRNS). Few reports were from the Chinese population. The coding regions of genes commonly associated with SRNS were analyzed to characterize the gene mutation spectrum in children with SRNS in central China. The first phase study involved 38 children with five genes (NPHS1, NPHS2, PLCE1, WT1, and TRPC6) by Sanger sequencing. The second phase study involved 33 children with 17 genes by next generation DNA sequencing (NGS. 22 new patients, and 11 patients from first phase study but without positive findings). Overall deleterious or putatively deleterious gene variants were identified in 19 patients (31.7%), including four NPHS1 variants among five patients and three PLCE1 variants among four other patients. Variants in COL4A3, COL4A4, or COL4A5 were found in six patients. Eight novel variants were identified, including two in NPHS1, two in PLCE1, one in NPHS2, LAMB2, COL4A3, and COL4A4, respectively. 55.6% of the children with variants failed to respond to immunosuppressive agent therapy, while the resistance rate in children without variants was 44.4%. Our results show that screening for deleterious variants in some common genes in children clinically suspected with SRNS might be helpful for disease diagnosis as well as prediction of treatment efficacy and prognosis.

Denys-Drash syndrome associated WT1 glutamine 369 mutants have altered sequence-preferences and altered responses to epigenetic modifications

Mutations in human zinc-finger transcription factor WT1 result in abnormal development of the kidneys and genitalia and an array of pediatric problems including nephropathy, blastoma, gonadal dysgenesis and genital discordance. Several overlapping phenotypes are associated with WT1 mutations, including Wilms tumors, Denys-Drash syndrome (DDS), Frasier syndrome (FS) and WAGR syndrome (Wilms tumor, aniridia, genitourinary malformations, and mental retardation). These conditions vary in severity from individual to individual; they can be fatal in early childhood, or relatively benign into adulthood. DDS mutations cluster predominantly in zinc fingers (ZF) 2 and 3 at the C-terminus of WT1, which together with ZF4 determine the sequence-specificity of DNA binding. We examined three DDS associated mutations in ZF2 of human WT1 where the normal glutamine at position 369 is replaced by arginine (Q369R), lysine (Q369K) or histidine (Q369H). These mutations alter the sequence-specificity of ZF2, we find, changing its affinity for certain bases and certain epigenetic forms of cytosine. X-ray crystallography of the DNA binding domains of normal WT1, Q369R and Q369H in complex with preferred sequences revealed the molecular interactions responsible for these affinity changes. DDS is inherited in an autosomal dominant fashion, implying a gain of function by mutant WT1 proteins. This gain, we speculate, might derive from the ability of the mutant proteins to sequester WT1 into unproductive oligomers, or to erroneously bind to variant target sequences.