Exploring the Multifaceted Role of WT1 in Kidney Development and Disease

With the recent shift in the disease spectrum, kidney diseases such as acute kidney injury and chronic kidney disease have increasingly become a focus of attention. In addition to environmental factors, nephrologists and scholars have emphasized the molecular mechanisms and embryonic origins of kidney disease [1]. For instance, genetic mutations or abnormal molecular expression during embryonic development or early life can lead to Congenital Anomalies of the Kidney and Urinary Tract (CAKUT) [2], which, in turn, can cause diseases such as renal agenesis, renal dysplasia, duplicated kidneys, and hydronephrosis. Wilms’ tumor protein 1 (WT1) is an important molecule in kidney development, a protein with zinc finger structures, and has at least 36 isoforms [3]. WT1 is involved in the formation and development of renal units and affects tissues such as the adrenal glands and gonads, which share a common origin with kidneys. Mutations in the WT1 gene can lead to abnormal expression of the WT1 protein, resulting in CAKUT and even the development of Wilms’. Changes in WT1 expression are also observed in some common kidney diseases or even in tissues that normally do not express WT1, where abnormal expression of WT1 can occur during tumor development. Given the important role of WT1 in kidney development and disease, we conducted a systematic review of the molecular structure and function of WT1, its role in kidney development, and its impact on kidney disease.

Wilms’ tumor 1 gene (WT1) was first discovered by German scientist Max Wilms in 1990 in cases of nephroblastoma [4]. Nephroblastoma, a malignant kidney tumor in children, has an incidence rate of approximately 0.1‰ [5]. The encoded WT1 protein has zinc finger structures and a molecular weight of 52–54 kD. Its zinc finger structures can bind to DNA or RNA, playing the role of transcription factors [6]. The various isoforms of this protein contain approximately 126–522 amino acids (aa), with an N-terminal domain rich in proline/glutamine for DNA binding and four zinc finger structures at the C-terminal [7]. There are numerous isoforms [3], such as WT1 A, WT1 B, WT1 D, WT1 E, and WT1 F, which are the main isoforms. They play important roles in the development of the urogenital system, occurrence and development of tumors, and cell proliferation [8].

The gene encoding it is WT1, located on the short arm of chromosome 11 in region 1 band 3 (11p13), with a length of approximately 50 kb, containing 10 exons, and is rich in GC homologous sequences [9]. This gene is also known as AWT1, GUD, NPHS4, WAGR, WIT-2, WT1, or WT33. In mammals, WT1 produces at least 36 protein isoforms during transcription and translation because of site differences, whereas non-mammals produce only two protein isoforms, which differ by three amino acids, one containing the KTS domain (lysine, threonine, and serine) and the other does not. The functional differences between these isoforms are not yet fully understood, but some clues suggest that there are functional differences between them [10]. For example, Frasier syndrome [11] caused by a WT1 mutation can cause pseudohermaphroditism and focal segmental glomerulosclerosis (FSGS), and a dominant WT1 mutation can cause an allele to express only the isoform without the KTS domain (−KTS), leading to a decrease in the +KTS−KTS ratio and causing the disease.

Studies have shown that WT1 is specifically expressed in multiple organ tissues. There is significant expression of WT1 in the endometrium, kidney, ovary, spleen, and testis, and in the appendix, bladder, heart, placenta, and prostate. Therefore, WT1 is involved in the embryonic development of most important organs, such as in the embryonic development of the heart, kidney, spleen, and retina, WT1 also participates in the expression of certain other genes and the regulation of signaling pathways [12, 13]. WT1 is barely expressed in other tissues, which reflects the tissue specificity of WT1 expression. In postnatal individuals, WT1 is predominantly specifically expressed in podocytes within the kidney, with minor expression also observed in the parietal epithelial cells of the glomerular capsule. Although it was previously thought that the WT1 gene is a tumor suppressor gene [14], an increasing number of studies have found that in normal tissues such as the breast, epithelium, mesenchyme, hematopoietic system, and nerves that do not express WT1, when they undergo cancerous changes, the WT1 gene may show abnormal expression or upregulation, suggesting that the WT1 gene may actually be an oncogene [15, 16]. Mutations in WT1 can cause abnormalities in the urinary and reproductive systems, such as Denys-Drash syndrome, which is a set of clinical syndromes caused by WT1 mutations, including nephropathy, pseudohermaphroditism, and nephroblastoma [17].

In the kidney, WT1 is predominantly expressed by podocytes. The human WT1 gene sequence contains 10 exons with a gene length of approximately 50 kb, which can transcribe an mRNA of approximately 3 kb in length. Because of different transcription start sites and splicing parts, the transcribed mRNA also has some differences. For example, transcription can start from different sites such as −69CTG, +127ATG, AW1, and int 5, whereas two exons that can be spliced are exons 5 and 9, where exon 5 is transcribed and translated into a sequence containing 17 amino acids, and exon 9 encodes a sequence containing 3 amino acids (lysine-threonine-serine, KTS, which is located between the 3rd and 4th zinc finger structures) [18]. Thus, mRNA is translated into proteins to form more isoforms, including the main isoforms such as WT1 A, WT1 E, WT1 F, WT1 G, WT1 H, WT1 I, WT1 J, WT1 K, WT1 L, WT1 M, WT1 N, WT1 O, WT1 B, and WT1 D, whereas WT1 C has no biological function. Depending on whether these isoforms contain KTS, they can be divided into two types: lacking the KTS sequence (−KTS) and containing the KTS sequence (+KTS) (as shown in Fig. 1). When and where the isoform is expressed is tissue-specific and regulated by development. For example, the −KTS isoform can often bind to DNA and function as a transcriptional regulator, whereas the +KTS isoform often has a higher affinity for RNA [7]. In experiments with cloned mouse LβT2 cells, Bagchi found that the two isoforms of WT1 (−KTS and +KTS) have different effects on LHβ and Egr1. Reducing the expression of WT1 (−KTS) can reduce the activation of GnRH on LHβ and Egr1, but simultaneously reducing WT1 (−KTS) and (+KTS) can increase endogenous LHβ transcription, but prevent the activation of GnRH on LHβ [19].

Posttranscriptional editing also occurred at the mRNA level. In mammals, direct nucleotide modification occurs, most commonly through deamination (cytidine nucleotide conversion to uridine or adenosine conversion to inosine). However, in the mRNA of WT1, a different editing mechanism is involved in the mRNA of play. At the 839th nucleotide, uridine is converted to cytidine, leading to a change in the encoded amino acid from leucine to proline. This results in reduced inhibitory regulation of growth-promoting genes [18].

After editing at the transcriptional and posttranscriptional levels, the WT1 protein was ultimately translated into different sizes (126aa to 522aa). Although this process can produce more than 36 isoforms, a common feature of these isoforms is that they all contain four zinc finger structures at the C-terminus. This structure determines the ability of the WT1 protein to bind to DNA and RNA and its role as a transcription factor. The identified crystal structure of WT1 protein showed that it binds to the major groove of DNA through its four zinc finger structures to activate or repress target gene transcription [20].

After the WT1 protein is encoded, most of it is transported from the cytoplasm to the nucleus, where it binds to its target gene sequence (5′-GCGGGGGCG-3′), thereby promoting or inhibiting the expression of related genes. Reported target genes include insulin-like growth factors (IGFs) and their receptors (IGF1R), platelet-derived growth factor A (PDGFA), epidermal growth factor (EGF), transforming growth factor beta (TGF-β), macrophage colony-stimulating factor, multidrug resistance gene 1 (MDR1), Bcl-2, c-MYC, human telomerase reverse transcriptase, and cyclin E [9]. In addition, the WT1 protein is involved in the transcriptional regulation of genes related to vascular endothelium and its own transcriptional regulation [21].

WT1 is a multifunctional protein capable of both activating and repressing its downstream target genes. As a transcription factor, WT1 can bind to the DNA with a zinc finger structure of Cys2-His2 at the C-terminus, which specifically identifies the corresponding DNA sequence. The consensus binding target sequence for WT1 is GCGGGGGCG, a motif commonly found in the promoter regions of numerous growth regulatory genes [22]. WT1’s transcriptional regulatory function includes both activation and repression mechanisms. The N-terminus domain enriched in glutamate and proline residues is crucial for transcriptional regulation. The regulatory outcome of WT1 – whether activation or repression – is contingent upon several factors, including the type of tissue, the specific WT1 isoform involved, and its interactions with other genetic elements [21, 23‒26]. This nuanced regulatory capacity underscores the complexity of WT1’s function in cellular processes.

WT1 exhibits the following crucial biological functions as illustrated in Figure 2. WT1 plays a fundamental role in embryonic development, particularly in kidney organogenesis [27]. In early kidney development, WT1 is recognized as an essential molecule for normal kidney development [28]. The process is initiated when the ureteric bud invades the metanephric mesenchyme, triggering both ureteric bud branching and mesenchymal-to-epithelial transition (MET) of the metanephric mesenchyme, processes in which WT1 is indispensable [29]. It has been found that missense mutations in WT1 can lead to downregulation of podocyte-specific markers such as nephrin, synaptopodin, and CD2AP. In adult kidneys, WT1 remains highly expressed in glomerular podocytes and is presented in lower amounts in the visceral epithelial cells of Bowman’s capsule, highlighting its critical role in maintaining renal function throughout the life cycle. Beyond the kidney, current studies indicate that WT1 is also involved in the development of gonads, heart, blood vessels, and the nervous system [30, 31].

WT1 is also recognized for its involvement in cell cycle regulation. It modulates the expression levels of mitotic checkpoint complex by directly interacting with MAD2, thereby plays an important regulatory role in spindle assembly checkpoints and maintaining genome stability during cell division [32].

Furthermore, the role of WT1 in tumorigenesis is complex and context-dependent [33‒36]. On one hand, it functions as a tumor suppressor gene [37, 38], initially identified for its role in the development of Wilms’ tumors, where it inhibits cell growth by interfering with pathways such as cell proliferation signals. On the other hand, WT1 can also act as an oncogene [28, 39], enhancing the antiapoptotic ability of tumor cells and promoting cell proliferation by regulating the proto-oncogene KRAS [29]. Notably, WT1 is highly expressed in leukemia cells, especially in acute myeloid leukemia [40]. As research progresses, it is anticipated that additional functions of WT1 will continue to be uncovered, further expanding our understanding of its multifaceted roles in cellular processes.

During the development and maintenance of normal kidney function, a series of molecules and signaling pathways are involved and interwoven to form a network of molecular and signaling pathways in podocytes. The important signaling pathways were as follows:

The WNT/β-catenin signaling pathway is important for kidney development and maintenance of normal function. WNT is a secreted glycoprotein rich in cysteine residues, which can be synthesized and secreted by many tissue cells, and is the initial step in activating the Wnt/β-catenin signaling pathway. Jing et al. [41] found that downregulating podocyte WT1 expression using WT1 siRNA can activate the Wnt/β-catenin signaling pathway by recruiting LRP6 to the clathrin-mediated endocytic pathway, thereby inducing podocyte apoptosis.

The NOTCH signaling pathway plays an important role in kidney development. However, in mature mammals and humans, NOTCH signaling molecules are not expressed. Activation of NOTCH signaling in adults often indicates the occurrence of chronic kidney disease. Asfahani deleted the WT1 gene in adult mice using the CRE-LoxP recombinase system and found that the NOTCH system in podocytes was activated with an increase in Notch1 and its transcriptional targets, including Nrarp [42], suggesting that downregulation of WT1 may activate the NOTCH signaling pathway.

The RA signaling pathway, also known as the retinoic acid signaling pathway, consists of retinoic acid receptors (RARs) and retinoic acid X receptors. Each family can be divided into three subtypes, α, β, and γ, based on their different gene encodings. The expression of RAR-α and RAR-β can be detected during embryonic development of the kidney and is closely related to kidney development, renal interstitial fibrosis, and kidney tissue cell damage. Guadix et al. [43] observed in epicardial cells that WT1 affects RA signaling in the embryonic epicardium by transcriptionally activating Raldh2.

The GDNF/RET signaling pathway plays a crucial role in early kidney development. GDNF is a glycoprotein secreted by the metanephric mesenchyme during early kidney development. Its receptor, tyrosine kinase (RET), is present on ureteric bud cells and regulates cell proliferation, movement, and adhesion during the early development of the kidney. Menshykau et al. [44] studied the role of the GDNF/RET signaling pathway in the branching morphogenesis of the ureteric bud during the early development of the kidney through the Turing mechanism principle, suggesting that the GDNF signal can guide the outward growth of the ureteric bud and stimulate the expression of RET receptors. In the metanephric matrix, WT1 regulates the expression of PAX2, which results in the activation of the GDNF/RET signaling pathway [45].

The JAK/STAT signaling pathway, mediated by cytokines, is widely involved in cell proliferation, differentiation, apoptosis, and immune regulation, which is an important signaling pathway. This pathway mainly consists of tyrosine kinase-related receptors, tyrosine kinases (JAK), and the transcription factor STAT. Cytokines can activate the JAK/STAT signaling pathway, and the activated JAK/STAT pathway can produce cytokines. It is important for the inflammatory response in the kidney. Li et al. [46], in a study using an exogenous WT1-transfected U937 cell line (a monocyte cell line with silenced WT1), found that the isoform of WT1 (+17aa/−KTS) may promote the production of cytokines, thereby activating the JAK/STAT signaling pathway, promoting the proliferation of the U937 cell line, and reducing apoptosis induced by etoposide.

There are many other signaling pathways in the kidney, such as the AMPK/SIRT1 signaling pathway [46], Hippo signaling pathway, CCL2/CCR2 signaling pathway, and mTORC2/Akt signaling pathway, all of which play indispensable roles in the development and maintenance of kidney function.

In the early stages of kidney development, WT1 is involved in cell differentiation, proliferation, mesenchymal-epithelial transition (MET), and apoptosis [47, 48]. WT1 can not only bind to DNA to regulate downstream molecules at the transcriptional level but also exert control at the posttranscriptional level, such as through mRNA splicing and interactions with other proteins.

As is well known, WT1 has played an important role in the early embryonic development of the kidney. With the invasion of the ureteric bud into the metanephric mesenchyme, WT1 is induced, initially expressed in cells around the tip of the ureteric bud, then forming “comma-shaped bodies,” and ultimately only expressed in the podocytes of the glomerulus and a small amount in the visceral epithelial cells of Bowman’s capsule in the kidney. Even in adults, WT1 continues to play an indispensable role in maintaining homeostasis and normal function of organs, such as the kidney, and in the occurrence of tumors.

The kidney is vital for balancing water, electrolytes, and acid-base levels, excreting waste, secreting erythropoietin, and facilitating vitamin D activation. Understanding the embryonic development of the kidney, which originates from the intermediate mesoderm, is essential for comprehending its function and potential developmental disorders. Human kidney development progresses through three successive stages: pronephros, mesonephros, and metanephros. The first two stages mimic evolutionary processes, while the metanephros becomes the functional kidney post-birth. Metanephros development begins in the fifth week of embryogenesis, arising from the ureteric bud and metanephric mesenchyme. The ureteric bud branches from the mesonephric duct, invading the metanephric mesenchyme, where metanephric blastema cells form through mutual induction.

Cell proliferation and apoptosis are prevalent throughout kidney development, while WT1 is extensively involved in these processes [47, 48]. Molecules participating in kidney development are divided into transcription factors, growth factors, and adhesion molecules. Transcription factors are represented by the homeobox (HOX), sine oculis homeobox 2 (Six2), and the paired box (PAX), etc. Growth factors with positive effects include ANGPT1, BMP7, EGF, FGFs, GDNF, GDF11, HGF, IGFI, IGFII, LIF, PDGFA, PDGFB, TGF-α, and vascular epithelial growth factor, whereas those with negative growth effects include TGF-β and TNF-α.

WT1, as a very important factor in the process of kidney embryonic development, has been involved since the early stages of embryonic development [49, 50]. Initially, WT1 is expressed by nephron progenitor cells in the mesenchyme in a small but detectable amount, and its expression is significantly increased before mesenchymal cells aggregate and undergo MET. Since then, WT1 has maintained high expression during kidney development, and as development progresses, it is limited to the proximal part of the S-shaped body and is ultimately expressed in the podocytes of the kidney.

Looking at the entire process of kidney development, WT1 mainly reflects three major aspects. First, it participates in early development of the kidney and plays an important role in the MET of the metanephric mesenchyme. Through research on fetal kidney development, Liu and Da [51] found that the chromatin openness states of WT1 in nephron progenitor cells, peritubular aggregate, renal vesicle/comma-shaped body, S-shaped body podocyte precursor cells, and podocyte clusters align closely with gene expression levels [52]. Kreidberg et al. [53] observed in mice that the knockout of WT1 can lead to lethal changes in the underdevelopment of the kidneys and testes and found that at 11 weeks of pregnancy, metanephric blastema cells undergo apoptosis. Essafi et al. [54] found that WT1 regulates the kidney MET process via Wnt4. However, in other tissues or tumors, this situation may be the opposite [51]. The process of WT1 regulating MET is tissue- and cell-specific, because in the development of the heart, WT1 regulates the opposite process, epithelial-to-mesenchymal transition [54, 55]. Second, it participates in the later stages of kidney development after MET. Hu et al. found that after treating pregnant mice with tamoxifen, at 11.5 days of embryonic development, Wt1 was completely inactivated, and kidney development was stalled at the “comma-shaped body” stage and did not continue to develop, indicating that Wt1 is necessary for kidney development after MET [56]. Ozdemir and Hohenstein [57] also found similar results, and the removal of Wt1 expression can lead to the underdevelopment of the renal unit. Third, as an important transcription factor, it can regulate the transcription of many other genes related to cell proliferation and even regulate the expression of proteins at the posttranscriptional level. WT1 binds to DNA through the 5′-GCGGGGGCG-3′ sequence and affects the activity of the promoter, thereby affecting the transcription of other genes, including IGFs and their receptors (IGF1R), PDGFA, EGF, TGF-β, M-CSF, multidrug resistance gene 1 (MDR1), Bcl-2, c-MYC, human telomerase reverse transcriptase, and cyclin E. WT1 can regulate its own expression by binding to its own gene, which is rich in GC sequences.

WT1 is pivotal in the development of podocytes, the specialized cells that form filtration barrier in the kidney’s glomeruli. As a transcription factor, WT1 orchestrates the expression of a series of downstream genes, including BMPER/PAX2/MAGI2, MYH9, and NPHS1 [52]. These targets form an intricate regulatory network that controls podocyte differentiation and maintenance. BMPER/PAX2/MAGI2 regulates the WNT signaling pathway in podocytes. The WNT signaling pathway plays a crucial role in various biological processes, including cell proliferation, differentiation, and migration. During kidney development, precise regulation of the WNT signaling pathway is essential for the differentiation and maturation of podocytes. For instance, BMPER (bone morphogenetic protein and activin membrane-bound inhibitor) can modulate BMP (bone morphogenetic protein) signaling, thereby affecting the WNT signaling pathway. PAX2, also known as paired box 2, functions as a transcription factor involved in the early stages of kidney development, including the formation of renal tubules. MAGI2, membrane-associated guanylate kinase inverted 2, is thought to modulate the activity of WNT signaling pathway-related proteins by interacting with various other proteins, thereby affecting the structure and function of podocytes. MYH9 encodes the heavy chain of myosin, a protein involved in actin filament organization, which is important in maintaining the structural integrity of podocytes. NPHS1, which encoding nephrin, is undeniably crucial in preserving the normal morphology of the slit diaphragm, a key component of the glomerular filtration barrier. These genes, regulated by WT1, are fundamental to the proper development and function of podocytes, highlighting the central role of WT1 in renal biology.

However, the upstream molecules that regulate WT1 during kidney development are poorly understood [58, 59]. Dehbi et al. [60] found through transfection and other means in human embryonic kidney cell experiments that members of the NF-κB/Rel family are important for activating the expression of WT1 and are at the upstream level of regulating WT1 activation. Tabei et al. [61] found that the miR-143/145 cluster induced by TGF-β1 can inhibit the expression of Wilms tumor 1 in human podocytes. Arellano-Rodríguez et al. [62] intervened in mice with lipopolysaccharide and found that after treatment for 24–36 h, the expression of WT1 in podocytes was downregulated, accompanied by downregulation of nephrin mRNA and upregulation of TNF-α and IL-1β mRNA. Although it was not possible to directly prove the upstream molecules of WT1, it provided clues for identifying the upstream molecules of WT1. Bollig confirmed through zebrafish research that in pronephros tissue, a highly conserved retinoic acid response element regulates the expression of wt1A [63]. In addition, there are studies on the upstream molecules of WT1 in other tissues and cells [64]. For example, Tuna and Itamochi [65] confirmed that in breast cancer MCF-7 cell lines, treating cells with IGFI can increase the expression of WT1 by 77% and found that IGFI regulates WT1 through Akt [65] and regulates the expression of WT1 by upregulating and downregulating HER2 gene expression in the above cell lines [66]. Bansal and others, in the study of myeloid leukemia cells, found that adding Hsp90 inhibitors 17-AAG or STA-9090 can downregulate the expression of WT1, thereby inhibiting the proliferation of leukemia cells [67]. A study of the endometrium of the removed uterus found that progesterone can induce decidualization by regulating the isoforms of WT1 in endometrial stromal cells [68]. However, whether there is a similar correlation in kidney podocytes needs to be confirmed.

Although WT1 can be widely expressed in multiple organs and tissues during the embryonic development stage, after birth, WT1 is only expressed in kidney podocytes, mesothelium, Sertoli cells of the testis, and granulosa cells of the ovary [69] and is also expressed in 1% of bone marrow cells. In adults, WT1 continues to be expressed in kidney podocytes, indicating that WT1 plays an important role in podocytes. Chau et al. [70] found that after knocking out the Wt1 gene in young or adult mice, glomerulosclerosis can occur after just a few days. However, there is still a lack of research on the role of WT1 in kidney development under physiological conditions after birth.

As a marker of podocytes, the importance of WT1 is not only recognized in the embryonic development of the kidney and the maturation process of podocytes but is also increasingly valued in kidney diseases, especially podocyte-related diseases (Table 1). For example, in hereditary kidney diseases, mutations in WT1 at different stages can cause different types of syndromes. In glomerular diseases, an increasing number of scholars have realized that in pathological states, the expression of WT1 in podocytes can be significantly reduced. Guo et al. [71] found that in a transgenic mouse model with a WT1 knockout, a decrease in WT1 expression can lead to crescentic glomerulonephritis or mesangial sclerosis. A study from the Netherlands showed that in patients with ANCA-associated glomerulonephritis, the number of positive cells expressing WT1 was significantly lower than that in the control group, which is considered to be due to the loss or at least a decrease in the function of WT1 during ANCA-associated vasculitis [72]. Therefore, on the one hand, mutations in the WT1 gene can lead to podocyte diseases, and on the other hand, when podocytes undergo pathological changes, a decrease in the expression of WT1 can also be observed.

WT1 plays an important role in hereditary kidney disease. It has been recognized that the loss of WT1 expression at different stages of kidney development can lead to different clinical syndromes in children. If the loss of WT1 occurs very early in the embryo, it can lead to developmental disorders of multiple organ systems, resulting in a lethal outcome in the embryo. Subsequently, deficiencies in WT1 expression at various stages can lead to the following syndromes.

This is the earliest recognized syndrome associated with WT1, mainly due to the loss of WT1 and Pax6 at 11p13 [73], leading to clinical manifestations such as Wilms’ tumor, aniridia, genitourinary malformations, and mental retardation [74]. In these patients, the incidence of Wilms’ tumor can be close to 50% [80], and 40–60% of patients progress to end-stage renal disease before the age of 20 [81].

This syndrome is mainly characterized by Wilms’ tumor, rapidly progressive glomerulonephritis, and genitourinary abnormalities, especially male pseudohermaphroditism [17]. Kidney lesions are characterized by diffuse mesangial sclerosis. Although mature glomerular mesangial cells do not express WT1, this outcome may be due to developmental and paracrine effects [75]. Mutations are mainly located in the region, WT1 encoding the zinc finger structure. Studies have shown that podocyte abnormalities in Denys-Drash syndrome occur at an earlier stage of development, when podocytes have not yet undergone significant differentiation. Podocytes in this state can continuously express VEGF-A (the activated form of VEGF165), which under normal circumstances is secreted during the “S-shaped body” stage, thereby stimulating the proliferation, migration, and differentiation of glomerular capillaries [82].

The main clinical manifestations of this syndrome include pseudohermaphroditism, gonadoblastoma, and glomerular diseases, such as FSGS. The incidence of Wilms’ tumor is significantly lower than that in Denys-Drash syndrome, and it is caused by a point mutation at the splice donor site at intron 9 of the WT1 gene [11]. Additionally, several studies have documented cases where missense mutations within exon 9 result in FSGS presentation [77, 78].

Clinical manifestations include male pseudohermaphroditism, abnormal development of female internal genitalia, complex congenital heart defects, and diaphragmatic hernia [76]. Mutations are mainly located in the region encoding the zinc finger structure that binds to DNA, including the corresponding mutations in Drash syndrome. This phenomenon indicates that mutations and phenotypes do not correspond one-to-one; there are always exceptions, which may be related to the interaction with other genes and environmental factors.

With the improvement of living standards and the widespread use of antibiotics, nephrotic syndrome has replaced acute glomerulonephritis as one of the main types of primary glomerular diseases in children. Among primary nephrotic syndromes, some are ineffective in hormone treatment, that is, steroid-resistant nephrotic syndrome, accounting for approximately 20–40% of primary nephrotic syndromes, of which about 29.5% of cases are caused by single-gene mutations [83]. Increasing evidence has shown that WT1 mutations can lead to primary nephrotic syndrome. Chernin analyzed 52 cases of nephrotic syndrome patients with WT1 mutations (from 51 families) and found that these patients had a total of 24 mutations in WT1. Patients with KTS region mutations in WT1 had a later onset and slower progression to end-stage renal disease phase 5 than patients with missense mutations [84]. Professor Guan et al. [85] team determined the expression of nephrin, podocin, α-actin, and WT1 in podocytes of renal biopsy samples from 19 children with nephrotic syndrome by immunofluorescence and compared with the control group. Although there was no statistical significance, it was observed that the average expression level of WT1 was significantly lower than that of the control group.

WT1 is expressed throughout life in mature podocytes, indicating that WT1 is important for maintaining the normal function of podocytes. However, there are currently very few studies on the changes in WT1 expression in acute glomerulonephritis, and some studies have suggested a connection between the two. Guo et al. [71], through experiments of knocking out and inducing artificial chromosome transfection in mouse models, found that a decrease in WT1 expression can lead to crescentic glomerulonephritis and mesangial sclerosis, and whether it ultimately leads to the former or the latter is dose-dependent on the expression level.

There are currently few studies on the role of WT1 in IgA nephropathy, but there are some interesting findings. For example, Tasar et al. [86] reported the renal biopsy WT1 immunohistochemistry of 128 patients with IgA nephropathy (16–76 years old), and the results showed that 11.2% of the patients had WT1 staining in the cytoplasm of podocytes. Through clinical follow-up, it was found that these patients are often accompanied by mesangial area/peripheral C4d positivity that often progresses to ESRD [86]. There are also case reports pointing out that a missense mutation in WT1 (c.1397C>T; p.Ser466Phe) causes IgA nephropathy in a family [79].

Very few studies have been conducted on the relationship between Henoch-Schonlein purpura nephropathy and WT1, but Japanese scholars such as Ohsaki et al. [87] conducted a study on urine sediment cell analysis and found that various kidney diseases (IgA nephropathy, Henoch-Schonlein purpura nephropathy, membranous glomerulonephritis, diabetic nephropathy, and minimal change in primary nephrotic syndrome) can lead to the shedding of podocytes, thereby finding WT1-positive cells in the urine.

Systemic lupus erythematosus is an important cause of secondary glomerulonephritis in children, and Bollain-Y-Goytia et al. [88] found that, compared with the normal control group, patients with stage III or IV systemic lupus erythematosus had reduced expression of WT1 in glomeruli, and more podocytes were lost from the urine. Perez-Hernandez et al. [89] analyzed the urine of 32 patients with systemic lupus erythematosus for podocalyxin, synaptopodin, podocin, nephrin, and WT1 protein and mRNA and found that with disease progression, the above podocyte differentiation and maturation markers were more severely lost from the urine, suggesting that the above protein analysis can be used as an assessment marker for the progression of lupus nephritis.

Hepatitis B virus-associated nephropathy is another important cause of secondary glomerulonephritis in children, with clinical manifestations of hematuria and/or proteinuria; the pathological type is often membranous nephropathy. Zhang et al. [90] analyzed the podocytes of 19 patients with hepatitis B virus-associated nephropathy and found that the number of WT1-positive podocytes in these patients was significantly lower than that in the control group.

WT1 is an important transcription factor from embryonic development to individual growth, with up to more than 36 isoforms that play different roles in the body. For example, the −KTS isoform mainly binds to DNA and regulates the expression of downstream genes, whereas the +KTS isoform is mainly involved in posttranscriptional regulation of RNA. However, the specific roles and mechanisms of many isoforms of WT1 need to be elucidated. The physiological functions of WT1 mainly include development-related processes, tumor occurrence and development, and maintenance of the normal physiological functions of organs that continuously express WT1, such as the kidneys.

In terms of embryonic development, WT1 not only plays an important role in the kidney but also in other organ tissues. This has been confirmed in animal models in which WT1 is knocked out during the embryonic period, leading to lethal changes. These studies suggest that WT1 may participate in the development of multiple organ systems during embryonic development and that its participation is essential. Therefore, some scholars have pointed out the possibility of “stemness” of WT1 in some organs.

Although WT1 is continuously expressed in kidney podocytes, mesothelium, Sertoli cells of the testis, granulosa cells of the ovary, and 1% of bone marrow cells, it has almost no regenerative capacity as a well-differentiated specialized cell (with characteristic primary and secondary foot processes) in kidney podocytes. When damaged by a disease, podocytes are often left with outcomes such as vacuolar degeneration and shedding, and their repair ability is very limited. Why is it that in some tumor cells, such as leukemia cells, the expression of WT1 can be reactivated, while kidney podocytes that continuously express WT1 are so “fragile?” The mechanism by which WT1 maintains normal function of kidney podocytes after birth requires further research.

As an important cellular transcription factor, WT1 determines its ability to interact with other molecules. Currently, it is known that many molecules are affected by WT1, such as nephrin, podocin, and synaptopodin, which are very important for maintaining podocyte stability, and genes closely related to kidney embryonic development are also regulated by WT1, such as Pax2, Sox11, Wnt4, Gas1, and Pbx2. Recently, due to the importance of WT1 in oncology and being considered to some extent as a tumor cell-specific antigen, scholars are paying increasing attention to the upstream molecules of WT1, hoping to control the occurrence and development of tumors by controlling WT1, thus inventing a WT1 vaccine [91, 92]. Research on the upstream molecules of WT1 has been reported in tissues, such as breast cancer and the heart. However, it is a pity that as a very key molecule for maintaining the normal function of podocytes in the kidney, there is very little research on its upstream molecules in the kidney. If protein molecules that affect the expression of WT1 can be found in the kidney tissue, it will provide new therapeutic targets for many podocyte diseases in clinical practice. Current research on WT1 also suggests that different isoforms of WT1 may play different important roles in tissues, and these important roles still need to be further elucidated.

The authors declare that they have no conflicts of interest.

This study was supported by the National Natural Science Foundation of the China Joint Fund for Regional Innovation and Development (No. U21A20333), Sichuan Science and Technology Program (No. 2023NSFSC0530, No. 2023ZYD0118), and Research Grant of Chengdu Science and Technology Bureau (No. 2022-GH03-00013-HZ, No. 2023-YF06-00024-HZ).

J.L. and Y.L. wrote the manuscript. Y.L. corrected the article. X.Z. and H.L. assisted in writing and corrected the article.