Are Pax proteins potential therapeutic targets in kidney disease and cancer?

The Role of the PAX Genes in Renal Cell Carcinoma

Renal cell carcinoma (RCC) is a significant oncological challenge due to its heterogeneous nature and limited treatment options. The PAX developmental gene family encodes nine highly conserved transcription factors that play crucial roles in embryonic development and organogenesis, which have been implicated in the occurrence and development of RCC. This review explores the molecular landscape of RCC, with a specific focus on the role of the PAX gene family in RCC tumorigenesis and disease progression. Of the various RCC subtypes, clear cell renal cell carcinoma (ccRCC) is the most prevalent, characterized by the loss of the von Hippel-Lindau (VHL) tumor suppressor gene. Here, we review the published literature on the expression patterns and functional implications of PAX genes, particularly PAX2 and PAX8, in the three most common RCC subtypes, including ccRCC, papillary RCC (PRCC), and chromophobe RCC (ChRCC). Further, we review the interactions and potential biological mechanisms involving PAX genes and VHL loss in driving the pathogenesis of RCC, including the key signaling pathways mediated by VHL in ccRCC and associated mechanisms implicating PAX. Lastly, concurrent with our update regarding PAX gene research in RCC, we review and comment on the targeting of PAX towards the development of novel RCC therapies.

Identification and function of the Pax gene Bmgsb in the silk gland of Bombyx mori

Paired box (Pax) genes are highly conserved throughout evolution, and the Pax protein is an important transcription factor of embryonic development. The Pax gene Bmgsb is expressed in the silk glands of silkworm, but its biological functions remain unclear. This study aimed to investigate the expression pattern of Bmgsb in the silk gland and explore its functions using RNA interference (RNAi). Here, we identified eight Pax genes in Bombyx mori. Phylogenetic analysis showed that the B. mori Pax genes were highly homologous to the Pax genes in other insects and highly evolutionarily conserved. The tissue expression profile showed that Bmgsb was expressed in the anterior silk gland and anterior part of the middle silk gland (AMSG). RNAi of Bmgsb resulted in defective development of the AMSG, and the larvae were mostly unable to cocoon in the wandering stage. RNA-seq analysis showed that the fibroin genes fib-l, fib-h and p25, cellular heat shock response-related genes and phenol oxidase genes were considerably upregulated upon Bmgsb knockdown. Furthermore, quantitative reverse transcription-PCR results showed that the fibroin genes and ubiquitin proteolytic enzyme-related genes were significantly upregulated in the AMSG after Bmgsb knockdown. This study provides a foundation for future research on the biological functions of B. mori Pax genes. In addition, it demonstrates the important roles of Bmgsb in the transcriptional regulation of fibroin genes and silk gland development.

Pax protein depletion in proximal tubules triggers conserved mechanisms of resistance to acute ischemic kidney injury preventing transition to chronic kidney disease

Acute kidney injury (AKI) is a common condition that lacks effective treatments. In part, this shortcoming is due to an incomplete understanding of the genetic mechanisms that control pathogenesis and recovery. Identifying the molecular and genetic regulators unique to nephron segments that dictate vulnerability to injury and regenerative potential could lead to new therapeutic targets to treat ischemic kidney injury. Pax2 and Pax8 are homologous transcription factors with overlapping functions that are critical for kidney development and are re-activated in AKI. Here, we examined the role of Pax2 and Pax8 in recovery from ischemic AKI and found them upregulated after severe AKI and correlated with chronic injury. Surprisingly, proximal-tubule-selective deletion of Pax2 and Pax8 resulted in a less severe chronic injury phenotype. This effect was mediated by protection against the acute insult, similar to pre-conditioning. Prior to injury, Pax2 and Pax8 mutant mice develop a unique subpopulation of proximal tubule cells in the S3 segment that displayed features usually seen only in acute or chronic injury. The expression signature of these cells was strongly enriched with genes associated with other mechanisms of protection against ischemic AKI including caloric restriction, hypoxic pre-conditioning, and female sex. Thus, our results identified a novel role for Pax2 and Pax8 in mature proximal tubules that regulates critical genes and pathways involved in both the injury response and protection from ischemic AKI.

Immune landscape of the kidney allograft in response to rejection

Preventing kidney graft dysfunction and rejection is a critical step in addressing the nationwide organ shortage and improving patient outcomes. While kidney transplants (KT) are performed more frequently, the overall number of patients on the waitlist consistently exceeds organ availability. Despite improved short-term outcomes in KT, comparable progress in long-term allograft survival has not been achieved. Major cause of graft loss at 5 years post-KT is chronic allograft dysfunction (CAD) characterized by interstitial fibrosis and tubular atrophy (IFTA). Accordingly, proactive prevention of CAD requires a comprehensive understanding of the immune mechanisms associated with either further dysfunction or impaired repair. Allograft rejection is primed by innate immune cells and carried out by adaptive immune cells. The rejection process is primarily facilitated by antibody-mediated rejection (ABMR) and T cell-mediated rejection (TCMR). It is essential to better elucidate the actions of individual immune cell subclasses (e.g. B memory, Tregs, Macrophage type 1 and 2) throughout the rejection process, rather than limiting our understanding to broad classes of immune cells. Embracing multi-omic approaches may be the solution in acknowledging these intricacies and decoding these enigmatic pathways. A transition alongside advancing technology will better allow organ biology to find its place in this era of precision and personalized medicine.

GLI1+ perivascular, renal, progenitor cells: The likely source of spontaneous neoplasia that created the AGMK1-9T7 cell line

The AGMK1-9T7 cell line has been used to study neoplasia in tissue culture. By passage in cell culture, these cells evolved to become tumorigenic and metastatic in immunodeficient mice at passage 40. Of the 20 x 106 kidney cells originally plated, less than 2% formed the colonies that evolved to create this cell line. These cells could be the progeny of some type of kidney progenitor cells. To characterize these cells, we documented their renal lineage by their expression of PAX-2 and MIOX, detected by indirect immunofluorescence. These cells assessed by flow-cytometry expressed high levels of CD44, CD73, CD105, Sca-1, and GLI1 across all passages tested; these markers have been reported to be expressed by renal progenitor cells. The expression of GLI1 was confirmed by immunofluorescence and western blot analysis. Cells from passages 13 to 23 possessed the ability to differentiate into adipocytes, osteoblasts, and chondrocytes; after passage 23, their ability to form these cell types was lost. These data indicate that the cells that formed the AGMK1-9T7 cell line were GLI1+ perivascular, kidney, progenitor cells.

Pax Protein Depletion in Proximal Tubules Triggers Conserved Mechanisms of Resistance to Acute Ischemic Kidney Injury and Prevents Transition to Chronic Kidney Disease

Acute kidney injury (AKI) is a common condition that lacks effective treatments. In part this shortcoming is due to an incomplete understanding of the genetic mechanisms that control pathogenesis and recovery. Pax2 and Pax8 are homologous transcription factors with overlapping functions that are critical for kidney development and are re-activated in AKI. In this report, we examined the role of Pax2 and Pax8 in recovery from ischemic AKI. We found that Pax2 and Pax8 are upregulated after severe AKI and correlate with chronic injury. Surprisingly, we then discovered that proximal-tubule-selective deletion of Pax2 and Pax8 resulted in a less severe chronic injury phenotype. This effect was mediated by protection against the acute insult, similar to preconditioning. Prior to injury, Pax2 and Pax8 mutant mice develop a unique subpopulation of S3 proximal tubule cells that display features usually seen only in acute or chronic injury. The expression signature of these cells was strongly enriched with genes associated with other mechanisms of protection against ischemic AKI including caloric restriction, hypoxic preconditioning, and female sex. Taken together, our results identify a novel role for Pax2 and Pax8 in mature proximal tubules that regulates critical genes and pathways involved in both injury response and protection from ischemic AKI.

TRANSLATIONAL STATEMENT

Identifying the molecular and genetic regulators unique to the nephron that dictate vulnerability to injury and regenerative potential could lead to new therapeutic targets to treat ischemic kidney injury. Pax2 and Pax8 are two homologous nephron-specific transcription factors that are critical for kidney development and physiology. Here we report that proximal-tubule-selective depletion of Pax2 and Pax8 protects against both acute and chronic injury and induces an expression profile in the S3 proximal tubule with common features shared among diverse conditions that protect against ischemia. These findings highlight a new role for Pax proteins as potential therapeutic targets to treat AKI.

PAX2 Gene Mutation in Pediatric Renal Disorders-A Narrative Review

The PAX2 gene is a transcription factor that is essential for the development of the urinary system among other transcription factors. The role of PAX2 is highlighted from the seventh week of gestation, when it is involved in development processes and the emergence of nephrons and collecting tubes. Being an important factor in renal development, mutations of this gene can produce severe alterations in the development of the urinary tract, namely congenital anomalies of the kidneys and urinary tract. The first reported cases described with the PAX2 mutation included both renal anomalies and the involvement of other organs, such as the eyes, producing renal coloboma syndrome. Over the years, numerous cases have been reported, including those with only renal and urinary tract anomalies. The aim of this review is to present a summary of pediatric patients described to have mutations in the PAX2 gene to contribute to a better understanding of the genetic mechanism causing anomalies of the kidneys and urinary tract. In this review, we have included only pediatric cases with renal and urinary tract disorders, without the involvement of other organs. From what we know so far from the literature, this is the first review gathering pediatric patients presenting the PAX2 mutation who have been diagnosed exclusively with renal and urinary tract disorders.

Identification of renal cyst cells of type I Nephronophthisis by single-nucleus RNA sequencing

Background: Nephronophthisis (NPH) is the most common genetic cause of end-stage renal disease (ESRD) in childhood, and NPHP1 is the major pathogenic gene. Cyst formation at the corticomedullary junction is a pathological feature of NPH, but the mechanism underlying cystogenesis is not well understood. The isolation and identification of cystic cell subpopulation could help to identify their origins and provide vital clues to the mechanisms underlying cystogenesis in NPH. Methods: Single-nucleus RNA sequencing (snRNA-seq) was performed to produce an atlas of NPHP1 renal cells. Kidney samples were collected from WT (Nphp1 +/+) mice and NPHP1 (Nphp1 del2-20/del2-20) model mice. Results: A comprehensive atlas of the renal cellular landscape in NPHP1 was generated, consisting of 14 basic renal cell types as well as a subpopulation of DCT cells that was overrepresented in NPHP1 kidneys compared to WT kidneys. GO analysis revealed significant downregulation of genes associated with tubular development and kidney morphogenesis in this subpopulation. Furthermore, the reconstruction of differentiation trajectories of individual cells within this subpopulation confirmed that a specific group of cells in NPHP1 mice become arrested at an early stage of differentiation and proliferate to form cysts. We demonstrate that Niban1 is a specific molecular marker of cystic cells in both mice and human NPHP1. Conclusion: In summary, we report a novel subpopulation of DCT cells, marked by Niban1, that are classified as cystic cells in the NPHP1 mice kidney. These results offer fresh insights into the cellular and molecular basis of cystogenesis in NPH.

Growth associated protein 43 deficiency promotes podocyte injury by activating the calmodulin/calcineurin pathway under hyperglycemia

Podocyte injury is a crucial factor in the pathogenesis of diabetic kidney disease (DKD), and finding potential therapeutic interventions that can mitigate podocyte injury holds significant clinical relevance. This study was to elucidate the role of growth associated protein-43(Gap43) in podocyte injury of high glucose (HG). We confirmed the expression of Gap43 in human glomerulus and found that Gap43 expression was downregulated in podocytes of patients with DKD and HG-treated podocytes in vitro. Gap43 knockdown in podocytes promoted podocyte apoptosis, increased migration ability and decreased nephrin expression, while overexpression of Gap43 markedly suppressed HG-induced injury. Moreover, the increased expression and activity of calcineurin (CaN) were also abrogated by overexpression Gap43 in HG. Pretreatment with a typical CaN inhibitor FK506 in Gap43 knockdown podocytes restored the injury. Mechanistically, co-immunoprecipitation experiments suggested that Gap43 could bind to calmodulin (CaM). Pull-down assay further demonstrated that Gap43 and CaM directly interacts with each other via amino acids 30-52 of Gap43 and amino acids 133-197 of CaM. In addition, we also identified Pax5 as potential transcription inhibitor factor mediating Gap43 expression. In conclusion, the study indicated that the Gap43/CaM-CaN pathway may be exploited as a promising therapeutic target for protecting against podocyte injury in high glucose.

Omics profiling identifies the regulatory functions of the MAPK/ERK pathway in nephron progenitor metabolism

Nephron endowment is defined by fetal kidney growth and crucially dictates renal health in adults. Defects in the molecular regulation of nephron progenitors contribute to only a fraction of reduced nephron mass cases, suggesting alternative causative mechanisms. The importance of MAPK/ERK activation in nephron progenitor maintenance has been previously demonstrated, and here, we characterized the metabolic consequences of MAPK/ERK deficiency. Liquid chromatography/mass spectrometry-based metabolomics profiling identified 42 reduced metabolites, of which 26 were supported by in vivo transcriptional changes in MAPK/ERK-deficient nephron progenitors. Among these, mitochondria, ribosome and amino acid metabolism, together with diminished pyruvate and proline metabolism, were the most affected pathways. In vitro cultures of mouse kidneys demonstrated a dosage-specific function for pyruvate in controlling the shape of the ureteric bud tip, a regulatory niche for nephron progenitors. In vivo disruption of proline metabolism caused premature nephron progenitor exhaustion through their accelerated differentiation in pyrroline-5-carboxylate reductases 1 (Pycr1) and 2 (Pycr2) double-knockout kidneys. Pycr1/Pycr2-deficient progenitors showed normal cell survival, indicating no changes in cellular stress. Our results suggest that MAPK/ERK-dependent metabolism functionally participates in nephron progenitor maintenance by monitoring pyruvate and proline biogenesis in developing kidneys.

Clinicopathological Relevance of PAX8 Expression Patterns in Acute Kidney Injury and Chronic Kidney Diseases

Transcription factor PAX8, expressed during embryonic kidney development, has been previously detected in various kidney tumors. In order to investigate expression of PAX8 transcription factor in acute kidney injury (AKI) and chronic kidney diseases (CKD), immunohistochemical analysis was performed. Presence, location and extent of PAX8 expression were analyzed among 31 human kidney samples of AKI (25 autopsy cases, 5 kidney biopsies with unknown etiology and 1 AKI with confirmed myoglobin cast nephropathy), as well as in animals with induced postischemic AKI. Additionally, expression pattern was analyzed in 20 kidney biopsy samples of CKD. Our study demonstrates that various kidney diseases with chronic disease course that results in the formation of tubular atrophy and interstitial fibrosis, lead to PAX8 expression in the nuclei of proximal tubules. Furthermore, patients with PAX8 detected within the damaged proximal tubuli would be carefully monitored, since deterioration in kidney function was observed during follow-up. We also showed that myoglobin provoked acute kidney injury followed with large extent of renal damage, was associated with strong nuclear expression of PAX8 in proximal tubular cells. These results were supported and followed by data obtained in experimental model of induced postischemic acute kidney injury. Considering these findings, we can assume that PAX8 protein might be involved in regeneration process and recovery after acute kidney injury. Thus, accordingly, all investigation concerning PAX8 immunolabeling should be performed on biopsy samples of the living individuals.

Cyclin-dependent kinase 4-related tubular epithelial cell proliferation is regulated by Paired box gene 2 in kidney ischemia-reperfusion injury

Paired box 2 (Pax2) is a transcription factor essential for kidney development and is reactivated in proximal tubular epithelial cells (PTECs) during recovery from kidney injury. However, the role of Pax2 in this process is still unknown. Here the role of Pax2 reactivation during injury was examined in the proliferation of PTECs using an ischemia-reperfusion injury (IRI) mouse model. Kidney proximal tubule-specific Pax2 conditional knockout mice were generated by mating kidney androgen-regulated protein-Cre and Pax2 flox mice. The degree of cell proliferation and fibrosis was assessed and a Pax2 inhibitor (EG1) was used to evaluate the role of Pax2 in the hypoxic condition of cultured PTECs (O₂ 5%, 24 hours). The number of Pax2-positive cells and Pax2 mRNA increased after IRI. Sirius red staining indicated that the area of interstitial fibrosis was significantly larger in knockout mice 14 days after IRI. The number of Ki-67-positive cells (an index of proliferation) was significantly lower in knockout than in wild-type mice after IRI, whereas the number of TUNEL-positive cells (an index of apoptotic cells) was significantly higher in knockout mice four days after IRI. Expression analyses of cell cycle-related genes showed that cyclin-dependent kinase 4 (CDK4) was significantly less expressed in the Pax2 knockout mice. In vitro data showed that the increase in CDK4 mRNA and protein expression induced by hypoxia was attenuated by EG1. Thus, Pax2 reactivation may be involved in PTEC proliferation by activating CDK4, thereby limiting kidney fibrosis.

Detection of De Novo PAX2 Variants and Phenotypes in Chinese Population: A Single-Center Study

Background:PAX2 is a nuclear transcription factor gene that is highly conserved among species. Variants within PAX2 could result in optic nerve colobomas and kidney hypoplasia. However, little clinical and genetic information is currently available about PAX2 variants in Chinese children.

Objective: This study aims to further understand the clinical manifestations and genetic characteristics of PAX2 variants in Chinese population.

Methods: In this single-center retrospective study, we analyzed the clinical data of 10 children identified as carriers of PAX2 variants by gene sequencing. All the variants found in this study were analyzed using in silico prediction and American College of Medical Genetics and Genomics (ACMG) standards and guidelines.

Results: The mean age for developing the first symptom in 10 unrelated children was 7.2 years old. Proteinuria and bilateral kidney dysplasia were found in every patient. Two children underwent kidney histological examination; one child showed high-intensity C1q deposition in the kidney, and the other child showed focal segmental glomerular sclerosis (FSGS). Three children had PAX2-related ocular abnormalities, including nystagmus, retinal exudation, amblyopia, microphthalmia, microcornea, and total blindness. In addition, one patient had the comorbidity of oculocutaneous albinism (OCA). Eight different PAX2 variants were found in ten patients, three of which were reported for the first time.

Conclusion: We reported some patients with unique manifestations and comorbidities, and we reported three variants that have not been previously identified. The PAX2 gene is prone to spontaneous variants, and the outcome of patients is unfavorable. Because of the lack of specific therapy, genetic testing should be recommended for individuals with obvious evidence of kidney dysplasia and eye abnormalities, and kidney protective treatment should be initiated early.

Identification of Pax protein inhibitors that suppress target gene expression and cancer cell proliferation

The Pax family of developmental control genes are frequently deregulated in human disease. In the kidney, Pax2 is expressed in developing nephrons but not in adult proximal and distal tubules, whereas polycystic kidney epithelia or renal cell carcinoma continues to express high levels. Pax2 reduction in mice or cell culture can slow proliferation of cystic epithelial cells or renal cancer cells. Thus, inhibition of Pax activity may be a viable, cell-type-specific therapy. We designed an unbiased, cell-based, high-throughput screen that identified triazolo pyrimidine derivatives that attenuate Pax transactivation ability. We show that BG-1 inhibits Pax2-positive cancer cell growth and target gene expression but has little effect on Pax2-negative cells. Chromatin immunoprecipitation suggests that these inhibitors prevent Pax protein interactions with the histone H3K4 methylation complex at Pax target genes in renal cells. Thus, these compounds may provide structural scaffolds for kidney-specific inhibitors with therapeutic potential.

The spatially resolved transcriptional profile of acute T cell-mediated rejection in a kidney allograft

Analysis of the transcriptional profile of graft biopsies represents a promising strategy to study T cell-mediated-rejection (TCMR), also known as acute cellular rejection. However, bulk RNA sequencing of graft biopsies may not capture the focal nature of acute rejection. Herein, we used the whole exome GeoMX Digital Space Profiling platform to study five tubular and three glomerular regions of interest in the kidney graft biopsy from a patient with a chronic-active TCMR episode and in analogous areas from two different normal kidney control biopsies. All kidney sections were from paraffin blocks. Overall, inflammatory genes were significantly upregulated in the tubular areas of the TCMR biopsy and showed an enrichment for gene-ontology terms associated with T-cell activation, differentiation, and proliferation. Enrichment analysis of the 100 genes with the highest coefficient of variation across the TCMR tubular regions of interest revealed that these highly variable genes are involved in kidney development and injury and interestingly do not associate with the 2019 Banff classification pathology scores within the individual regions of interest. Spatial transcriptomics allowed us to unravel a previously unappreciated variability across different areas of the TCMR biopsy related to the graft response to the alloimmune attack, rather than to the immune cells. Thus, our approach has the potential to decipher clinically relevant, new pathogenic mechanisms, and therapeutic targets in acute cellular rejection and other kidney diseases with a focal nature.

Pax5 mediates the transcriptional activation of the CD81 gene

CD81 is an integral membrane protein of the tetraspanin family and forms complexes with a variety of other cell surface membrane proteins. CD81 is involved in cell migration and B cell activation. However, the mechanism of the transcriptional regulation of the CD81 gene remains unclear. Here, we revealed that CD81 transcriptional activation was required for binding of the transcription factor Pax5 at the Pax5-binding sequence (-54)GCGGGAC(-48) located upstream of the transcriptional start site (TSS) of the CD81 gene. The reporter assay showed that the DNA sequence between - 130 and - 39 bp upstream of the TSS of the CD81 gene had promoter activity for CD81 transcription. The DNA sequence between - 130 and - 39 bp upstream of TSS of CD81 harbors two potential Pax5-binding sequences (-87)GCGTGAG(-81) and (-54)GCGGGAC(-48). Reporter, electrophoresis mobility shift, and chromatin immunoprecipitation (ChIP) assays disclosed that Pax5 bound to the (-54)GCGGGAC(-48) in the promoter region of the CD81 gene in order to activate CD81 transcription. Pax5 overexpression increased the expression level of CD81 protein, while the Pax5-knockdown by shRNA decreased CD81 expression. Moreover, we found that the expression level of CD81 was positively correlated with Pax5 expression in human tumor cell lines. Because CD81 was reported to be involved in cell migration, we evaluated the effects of Pax5 overexpression by wound healing and transwell assays. The data showed that overexpression of either Pax5 or CD81 promoted the epithelial cell migration. Thus, our findings provide insights into the transcriptional mechanism of the CD81 gene through transcription factor Pax5.

Chemical Synthesis of the PAX Protein Inhibitor EG1 and Its Ability to Slow the Growth of Human Colorectal Carcinoma Cells

Colorectal cancer is primarily a disease of the developed world. The incidence rate has continued to increase over time, reflecting both demographic and lifestyle changes, which have resulted in genomic and epigenomic modifications. Many of the epigenetic modifications occur in genes known to be closely associated with embryonic development and cellular growth. In particular, the paired box (PAX) transcription factors are crucial for correct tissue development during embryogenesis due to their role in regulating genes involved in proliferation and cellular maintenance. In a number of cancers, including colorectal cancer, the PAX transcription factors are aberrantly expressed, driving proliferation and thus increased tumour growth. Here we have synthesized and used a small molecule PAX inhibitor, EG1, to inhibit PAX transcription factors in HCT116 colorectal cell cultures which resulted in reduced proliferation after three days of treatment. These results highlight PAX transcription factors as playing an important role in the proliferation of HCT116 colorectal cancer cells, suggesting there may be a potential therapeutic role for inhibition of PAX in limiting cancer cell growth.

Study of cellular heterogeneity and differential dynamics of autophagy in human embryonic kidney development by single-cell RNA sequencing

Background

Autophagy is believed to participate in embryonic development, but whether the expression of autophagy-associated genes undergoes changes during the development of human embryonic kidneys remains unknown.

Methods

In this work, we identified 36,151 human renal cells from embryonic kidneys of 9–18 gestational weeks in 16 major clusters by single-cell RNA sequencing (scRNA-seq), and detected 1350 autophagy-related genes in all fetal renal cells. The abundance of each cell cluster in Wilms tumor samples from scRNA-seq and GDC TARGET WT datasets was detected by CIBERSORTx. R package Monocle 3 was used to determine differentiation trajectories. Cyclone tool of R package scran was applied to calculate the cell cycle scores. R package SCENIC was used to investigate the transcriptional regulons. The FindMarkers tool from Seurat was used to calculate DEGs. GSVA was used to perform gene set enrichment analyses. CellphoneDB was utilized to analyze intercellular communication.

Results

It was found that cells in the 13th gestational week showed the lowest transcriptional level in each cluster in all stages. Nephron progenitors could be divided into four subgroups with diverse levels of autophagy corresponding to different SIX2 expressions. SSBpod (podocyte precursors) could differentiate into four types of podocytes (Pod), and autophagy-related regulation was involved in this process. Pseudotime analysis showed that interstitial progenitor cells (IPCs) potentially possessed two primitive directions of differentiation to interstitial cells with different expressions of autophagy. It was found that NPCs, pretubular aggregates and interstitial cell clusters had high abundance in Wilms tumor as compared with para-tumor samples with active intercellular communication.

Conclusions

All these findings suggest that autophagy may be involved in the development and cellular heterogeneity of early human fetal kidneys. In addition, part of Wilms tumor cancer cells possess the characteristics of some fetal renal cell clusters.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02154-w.

Pax2 and Pax8 Proteins Regulate Urea Transporters and Aquaporins to Control Urine Concentration in the Adult Kidney

BACKGROUND

As the glomerular filtrate passes through the nephron and into the renal medulla, electrolytes, water, and urea are reabsorbed through the concerted actions of solute carrier channels and aquaporins at various positions along the nephron and in the outer and inner medulla. Proliferating stem cells expressing the nuclear transcription factor Pax2 give rise to renal epithelial cells. Pax2 expression ends once the epithelial cells differentiate into mature proximal and distal tubules, whereas expression of the related Pax8 protein continues. The collecting tubules and renal medulla are derived from Pax2-positive ureteric bud epithelia that continue to express Pax2 and Pax8 in adult kidneys. Despite the crucial role of Pax2 in renal development, functions for Pax2 or Pax8 in adult renal epithelia have not been established.

METHODS

To examine the roles of Pax2 and Pax8 in the adult mouse kidney, we deleted either Pax2, Pax8, or both genes in adult mice and examined the resulting phenotypes and changes in gene expression patterns. We also explored the mechanism of Pax8-mediated activation of potential target genes in inner medullary collecting duct cells.

RESULTS

Mice with induced deletions of both Pax2 and Pax8 exhibit severe polyuria that can be attributed to significant changes in the expression of solute carriers, such as the urea transporters encoded by Slc14a2, as well as aquaporins within the inner and outer medulla. Furthermore, Pax8 expression is induced by high-salt levels in collecting duct cells and activates the Slc14a2 gene by recruiting a histone methyltransferase complex to the promoter.

CONCLUSIONS

These data reveal novel functions for Pax proteins in adult renal epithelia that are essential for retaining water and concentrating urine.

Graft immaturity and safety concerns in transplanted human kidney organoids

For chronic kidney disease, regeneration of lost nephrons with human kidney organoids derived from induced pluripotent stem (iPS) cells is proposed to be an attractive potential therapeutic option. It remains unclear, however, whether organoids transplanted into kidneys in vivo would be safe or functional. Here, we purified kidney organoids and transplanted them beneath the kidney capsules of immunodeficient mice to test their safety and maturity. Kidney organoid grafts survived for months after transplantation and became vascularized from host mouse endothelial cells. Nephron-like structures in grafts appeared more mature than kidney organoids in vitro, but remained immature compared with the neighboring mouse kidney tissue. Ultrastructural analysis revealed filtration barrier-like structures, capillary lumens, and tubules with brush border in the transplanted kidney organoids, which were more mature than those of the kidney organoids in vitro but not as organized as adult mammalian kidneys. Immaturity was a common feature of three separate differentiation protocols by immunofluorescence analysis and single cell RNA sequencing. Stroma of transplanted kidney organoid grafts were filled with vimentin-positive mesenchymal cells, and chondrogenesis, cystogenesis, and stromal expansion were observed in the long term. Transcription profiles showed that long-term maintenance after kidney organoid transplantation induced transcriptomic reprogramming with prominent suppression of cell-cycle-related genes and upregulation of extracellular matrix organization. Our data suggest that kidney organoids derived from iPS cells may be transplantable but strategies to improve nephron differentiation and purity are required before they can be applied in humans as a therapeutic option.