Ureteric Epithelium Research Articles

Isthmin-1: A critical regulator of branching morphogenesis and metanephric mesenchyme condensation during early kidney development.

Isthmin-1 (Ism1) was first described to be syn-expressed with Fgf8 inXenopus. However, its biological role has not been elucidated until recent years. Despite of accumulated evidence that Ism1 participates in angiogenesis, tumor invasion, macrophage apoptosis, and glucose metabolism, the cognate receptors for Ism1 remain largely unknown. Ism1 deficiency in mice results in renal agenesis (RA) with a transient loss of Gdnf transcription and impaired mesenchyme condensation at E11.5. Ism1 binds to and activates Integrin α8β1 to positively regulate Gdnf/Ret signaling, thus promoting mesenchyme condensation and ureteric epithelium branching morphogenesis. Here, we propose the hypothesis underlying the mechanism by which Ism1 regulates branching morphogenesis during early kidney development.

Extramammary Paget's disease with ureteral metastasis: A case report

AbstractExtramammary Paget's disease (EMPD) is a skin cancer that can metastasize to distant lymph nodes and organs. However, there are no reports showing histological evidence of metastasis to the ureter. Here we report a case of EMPD that metastasized to the ureter in an 80‐year‐old man. The primary EMPD was resected and the right inguinal lymph node metastasis was dissected. Radiation therapy was administered around the right inguinal lymph nodes postoperatively. Four years later, a thickening of the wall of the right ureter was found, and a total right nephroureterectomy was performed due to suspicion of primary ureteral cancer. Histological examination showed nests of atypical cells in the renal adventitia and the surrounding lymphatic vessels, muscular layer and mucosal layer, but not in the ureteral epithelium. Immunohistochemical staining of tumour cells was positive for carcinoembryonic antigen, cytokeratin 7 and gross cystic disease fluid protein‐15 and was negative for cytokeratin 20. These results are consistent with a primary skin lesion. Although EMPD is not a frequent source of ureteral metastasis, EMPD can metastasize to the ureter. This case implies the feasibility of an accurate preoperative diagnosis through immunostaining, offering the potential to circumvent nephroureterectomy and instead facilitate appropriate management using a ureteral stent.

Regeneration of the ureter using a scaffold-free live-cell structure created with the bio-three-dimensional printing technique.

Ureteral strictures, which can be caused by ureteral injury, radiation therapy, ureterolithiasis, urinary tract infections, and ureteral endometriosis, typically require ureteral reconstruction. Although tissue engineering, autologous alternative tissue transplantation, and surgical techniques applying various flaps have been carried out for ureteral regeneration, all with some success, each method has its advantages and disadvantages. As an alternative, we created the first artificial ureter structures using only live cells and grafted them into healthy rat ureters. Spheroids were created using normal human dermal fibroblasts and human umbilical vein endothelial cells and subsequently laminated using a bio-three-dimensional printer. After molding the laminated spheroids into tubular structures, the artificial ureters were transplanted into live rats. After 2-12 weeks, the animals were sacrificed and their gross and pathological features were examined. In the artificial ureteral lumen of rats with Grade 0-1 hydronephrosis, regeneration of the ureteral epithelium was observed, the thickness of which increased over the course of the experiment. Regeneration of the muscular layer was also observed, extending from the normal ureteral side toward the artificial ureter structure over time. However, complete regeneration was not observed at the end of 12 weeks. Although ureteral peristalsis was noted in all cases, it was weaker than expected. Therefore, we achieved short-segment ureteral regeneration using a cell-only structure. This finding suggests that by applying alternative strategies to this method, such as changing the cell type and composition, regeneration over the entire length of the ureter may be possible in the future. STATEMENT OF SIGNIFICANCE: Until now, ureteral regeneration techniques have been dominated by the use of high-molecular-weight compounds and autologous tissues, and there have been no reports of regeneration using structures made entirely of cells. This is the first report of ureteral regeneration using a tubular structure made from stacked spheroids. Although this study only attained short-segment ureteral regeneration, regeneration of the ureter over a much longer proportion of its length can be achieved in the future by applying other strategies, such as changing the cell type. This study provides a foundation to achieve the future goal of complete regeneration.

Rap1 regulates lumen continuity via Afadin in renal epithelia

The continuity of a lumen within an epithelial tubule is critical for its function. We previously found that the F-actin binding protein Afadin is required for timely lumen formation and continuity in renal tubules formed from the nephrogenic mesenchyme in mice. Afadin is a known effector and interactor of the small GTPase Rap1, and in the current study, we examine the role of Rap1 in nephron tubulogenesis. Here, we demonstrate that Rap1 is required for nascent lumen formation and continuity in cultured 3D epithelial spheroids and in vivo in murine renal epithelial tubules derived from the nephrogenic mesenchyme, where its absence ultimately leads to severe morphogenetic defects in the tubules. By contrast, Rap1 is not required for lumen continuity or morphogenesis in renal tubules derived from the ureteric epithelium, which differ in that they form by extension from a pre-existing tubule. We further demonstrate that Rap1 is required for correct localization of Afadin to adherens junctions both in vitro and in vivo. Together, these results suggest a model in which Rap1 localizes Afadin to junctional complexes, which in turn regulates nascent lumen formation and positioning to ensure continuous tubulogenesis.

β-Catenin in the kidney stroma modulates pathways and genes to regulate kidney development.

Kidney development is regulated by cellular interactions between the ureteric epithelium, mesenchyme, and stroma. Previous studies demonstrate essential roles for stromal β-catenin in kidney development. However, how stromal β-catenin regulates kidney development is not known. We hypothesize that stromal β-catenin modulates pathways and genes that facilitate communications with neighboring cell populations to regulate kidney development. We isolated purified stromal cells with wild type, deficient, and overexpressed β-catenin by fluorescence-activated cell sorting and conducted RNA Sequencing. A Gene Ontology network analysis demonstrated that stromal β-catenin modulates key kidney developmental processes, including branching morphogenesis, nephrogenesis and vascular formation. Specific stromal β-catenin candidate target genes that may mediate these effects included secreted, cell-surface and transcriptional factors that regulate branching morphogenesis and nephrogenesis (Wnts, Bmp, Fgfr, Tcf/Lef) and secreted vascular guidance cues (Angpt1, VEGF, Sema3a). We validated established β-catenin targets including Lef1 and novel candidate β-catenin targets including Sema3e which have unknown roles in kidney development. These studies advance our understanding of gene and biological pathway dysregulation in the context of stromal β-catenin misexpression during kidney development. Our findings suggest that during normal kidney development, stromal β-catenin may regulate secreted and cell-surface proteins to communicate with adjacent cell populations.

Temporally and spatially regulated collagen XVIII isoforms are involved in ureteric tree development via the TSP1-like domain

Collagen XVIII (ColXVIII) is a component of the extracellular matrix implicated in embryogenesis and control of tissue homoeostasis. We now provide evidence that ColXVIII has a specific role in renal branching morphogenesis as observed in analyses of total and isoform-specific knockout embryos and mice. The expression of the short and the two longer isoforms differ temporally and spatially during renal development. The lack of ColXVIII or its specific isoforms lead to congenital defects in the 3D patterning of the ureteric tree where the short isoform plays a prominent role. Moreover, the ex vivo data suggests that ColXVIII is involved in the kidney epithelial tree patterning via its N-terminal domains, and especially the Thrombospondin-1-like domain common to all isoforms. This morphogenetic function likely involves integrins expressed in the ureteric epithelium. Altogether, the results point to an important role for ColXVIII in the matrix-integrin-mediated functions regulating renal development.

Unraveling a challenging diagnosis: Role of a TNF inhibitor

<h3>Background</h3> The generation of reporter lines for cell identity, lineage, and physiologic state has provided a powerful tool in advancing the dissection of mouse kidney morphogenesis at a molecular level. Although use of this approach is not an option for studying human development <i>in vivo</i>, its application in human induced pluripotent stem cells (iPSCs) is now feasible. <h3>Methods</h3> We used CRISPR/Cas9 gene editing to generate ten fluorescence reporter iPSC lines designed to identify nephron progenitors, podocytes, proximal and distal nephron, and ureteric epithelium. Directed differentiation to kidney organoids was performed according to published protocols. Using immunofluorescence and live confocal microscopy, flow cytometry, and cell sorting techniques, we investigated organoid patterning and reporter expression characteristics. <h3>Results</h3> Each iPSC reporter line formed well patterned kidney organoids. All reporter lines showed congruence of endogenous gene and protein expression, enabling isolation and characterization of kidney cell types of interest. We also demonstrated successful application of reporter lines for time-lapse imaging and mouse transplantation experiments. <h3>Conclusions</h3> We generated, validated, and applied a suite of fluorescence iPSC reporter lines for the study of morphogenesis within human kidney organoids. This fluorescent iPSC reporter toolbox enables the visualization and isolation of key populations in forming kidney organoids, facilitating a range of applications, including cellular isolation, time-lapse imaging, protocol optimization, and lineage-tracing approaches. These tools offer promise for enhancing our understanding of this model system and its correspondence with human kidney morphogenesis.

Establishment of Mini-pig Model of Ureteral Stricture by Electrocoagulation Under Ureteroscopy

To establish a mini-pig model of ureteral stricture by using electrocoagulation under ureteroscopy. Twelve female mini-pigs were included. Their ureters on one side and contralateral side were randomly divided into electrocoagulation and control groups, respectively. In the electrocoagulation group, the middle ureter was circumferentially electrocoagulated by using a self-made electrocoagulation device with the ureteroscope under direct vision, while the control group underwent ureteroscopy only without electrocoagulation. At 30 and 90 days after electrocoagulation, the glomerular filtration rate (GFR), formation of ureteral stricture, and histomorphological changes of ureteral tissues of each group were detected. At 90 days after surgery, ureteroscopy and retrograde urography revealed ureteral stricture formation in the middle ureter in the electrocoagulation group. GFR was gradually decreased over time with prolonged washout half-time in the electrocoagulation group. A compensatory increase in GFR was observed in the control group. Hematoxylin and eosin staining and Masson's Trichrome staining revealed fibroblast infiltration and fibrous tissue hyperplasia in the superficial muscular layers, and the muscular layers were arranged disorderly in the electrocoagulation group. Immunohistochemical staining showed accumulation and disorganization of ureteric epithelium in the narrow segment. In the control group, the epithelium was arranged neatly with normal structure. A mini-pig model of ureteral stricture was successfully established using electrocoagulation under ureteroscopy. This method has the advantages of being simple to implement, having high accuracy and high success rate, which can provide an ideal animal model for studying ureteral stricture.

Comparative whole-genome transcriptome analysis in renal cell populations reveals high tissue specificity of MAPK/ERK targets in embryonic kidney

BackgroundMAPK/ERK signaling is a well-known mediator of extracellular stimuli controlling intracellular responses to growth factors and mechanical cues. The critical requirement of MAPK/ERK signaling for embryonic stem cell maintenance is demonstrated, but specific functions in progenitor regulation during embryonic development, and in particular kidney development remain largely unexplored. We previously demonstrated MAPK/ERK signaling as a key regulator of kidney growth through branching morphogenesis and normal nephrogenesis where it also regulates progenitor expansion. Here, we performed RNA sequencing-based whole-genome expression analysis to identify transcriptional MAPK/ERK targets in two distinct renal populations: the ureteric bud epithelium and the nephron progenitors.ResultsOur analysis revealed a large number (5053) of differentially expressed genes (DEGs) in nephron progenitors and significantly less (1004) in ureteric bud epithelium, reflecting likely heterogenicity of cell types. The data analysis identified high tissue-specificity, as only a fraction (362) of MAPK/ERK targets are shared between the two tissues. Tissue-specific MAPK/ERK targets participate in the regulation of mitochondrial energy metabolism in nephron progenitors, which fail to maintain normal mitochondria numbers in the MAPK/ERK-deficient tissue. In the ureteric bud epithelium, a dramatic decline in progenitor-specific gene expression was detected with a simultaneous increase in differentiation-associated genes, which was not observed in nephron progenitors. Our experiments in the genetic model of MAPK/ERK deficiency provide evidence that MAPK/ERK signaling in the ureteric bud maintains epithelial cells in an undifferentiated state. Interestingly, the transcriptional targets shared between the two tissues studied are over-represented by histone genes, suggesting that MAPK/ERK signaling regulates cell cycle progression and stem cell maintenance through chromosome condensation and nucleosome assembly.ConclusionsUsing tissue-specific MAPK/ERK inactivation and RNA sequencing in combination with experimentation in embryonic kidneys, we demonstrate here that MAPK/ERK signaling maintains ureteric bud tip cells, suggesting a regulatory role in collecting duct progenitors. We additionally deliver new mechanistic information on how MAPK/ERK signaling regulates progenitor maintenance through its effects on chromatin accessibility and energy metabolism.

DevKidCC allows for robust classification and direct comparisons of kidney organoid datasets

BackgroundWhile single-cell transcriptional profiling has greatly increased our capacity to interrogate biology, accurate cell classification within and between datasets is a key challenge. This is particularly so in pluripotent stem cell-derived organoids which represent a model of a developmental system. Here, clustering algorithms and selected marker genes can fail to accurately classify cellular identity while variation in analyses makes it difficult to meaningfully compare datasets. Kidney organoids provide a valuable resource to understand kidney development and disease. However, direct comparison of relative cellular composition between protocols has proved challenging. Hence, an unbiased approach for classifying cell identity is required.MethodsThe R package, scPred, was trained on multiple single cell RNA-seq datasets of human fetal kidney. A hierarchical model classified cellular subtypes into nephron, stroma and ureteric epithelial elements. This model, provided in the R package DevKidCC (github.com/KidneyRegeneration/DevKidCC), was then used to predict relative cell identity within published kidney organoid datasets generated using distinct cell lines and differentiation protocols, interrogating the impact of such variations. The package contains custom functions for the display of differential gene expression within cellular subtypes.ResultsDevKidCC was used to directly compare between distinct kidney organoid protocols, identifying differences in relative proportions of cell types at all hierarchical levels of the model and highlighting variations in stromal and unassigned cell types, nephron progenitor prevalence and relative maturation of individual epithelial segments. Of note, DevKidCC was able to distinguish distal nephron from ureteric epithelium, cell types with overlapping profiles that have previously confounded analyses. When applied to a variation in protocol via the addition of retinoic acid, DevKidCC identified a consequential depletion of nephron progenitors.ConclusionsThe application of DevKidCC to kidney organoids reproducibly classifies component cellular identity within distinct single-cell datasets. The application of the tool is summarised in an interactive Shiny application, as are examples of the utility of in-built functions for data presentation. This tool will enable the consistent and rapid comparison of kidney organoid protocols, driving improvements in patterning to kidney endpoints and validating new approaches.

A Novel Method for Urinary Tract Reconstruction in Transplanted Embryonic Kidneys Using the Hybrid Stent: A Pig Study.

A Novel Method for Urinary Tract Reconstruction in Transplanted Embryonic Kidneys Using the Hybrid Stent: A Pig Study.

FGFR2 signaling enhances the SHH-BMP4 signaling axis in early ureter development.

The patterned array of basal, intermediate and superficial cells in the urothelium of the mature ureter arises from uncommitted epithelial progenitors of the distal ureteric bud. Urothelial development requires signaling input from surrounding mesenchymal cells, which, in turn, depend on cues from the epithelial primordium to form a layered fibro-muscular wall. Here, we have identified FGFR2 as a crucial component in this reciprocal signaling crosstalk in the murine ureter. Loss of Fgfr2 in the ureteric epithelium led to reduced proliferation, stratification, intermediate and basal cell differentiation in this tissue, and affected cell survival and smooth muscle cell differentiation in the surrounding mesenchyme. Loss of Fgfr2 impacted negatively on epithelial expression of Shh and its mesenchymal effector gene Bmp4. Activation of SHH or BMP4 signaling largely rescued the cellular defects of mutant ureters in explant cultures. Conversely, inhibition of SHH or BMP signaling in wild-type ureters recapitulated the mutant phenotype in a dose-dependent manner. Our study suggests that FGF signals from the mesenchyme enhance, via epithelial FGFR2, the SHH-BMP4 signaling axis to drive urothelial and mesenchymal development in the early ureter.

ARTIFICIAL INTELLIGENCE, VIRTUAL REALITY AND ROBOTICS IN COLORECTAL SURGERY USING MASTER-CLASS TECHNOLOGICAL INNOVATIONS

ARTIFICIAL INTELLIGENCE, VIRTUAL REALITY AND ROBOTICS IN COLORECTAL SURGERY USING MASTER-CLASS TECHNOLOGICAL INNOVATIONS

Harnessing developmental plasticity to pattern kidney organoids.

Methods for deriving the ureteric epithelium (UE) invitro could improve understanding of kidney development and patterning. In this issue of Cell Stem Cell, Howden etal. (2021) identified transcriptionally distinct cell populations in human induced pluripotent stem cell (iPSC)-derived distal nephron (DN) epithelia that were inducible to UE phenotype within kidney organoids.

Plasticity of distal nephron epithelia from human kidney organoids enables the induction of ureteric tip and stalk.

During development, distinct progenitors contribute to the nephrons versus the ureteric epithelium of the kidney. Indeed, previous human pluripotent stem-cell-derived models of kidney tissue either contain nephrons or pattern specifically to the ureteric epithelium. By re-analyzing the transcriptional distinction between distal nephron and ureteric epithelium in human fetal kidney, we show here that, while existing nephron-containing kidney organoids contain distal nephron epithelium and no ureteric epithelium, this distal nephron segment alone displays significant invitro plasticity and can adopt a ureteric epithelial tip identity when isolated and cultured in defined conditions. "Induced" ureteric epithelium cultures can be cryopreserved, serially passaged without loss of identity, and transitioned toward a collecting duct fate. Cultures harboring loss-of-function mutations in PKHD1 also recapitulate the cystic phenotype associated with autosomal recessive polycystic kidney disease.

Branching morphogenesis as a driver of renal development.

Branching morphogenesis is an integral developmental mechanism central to the formation of a range of organs including the kidney, lung, pancreas and mammary gland. The ramified networks of epithelial tubules it establishes are critical for the processes of secretion, excretion and exchange mediated by these tissues. In the kidney, branching serves to establish the collecting duct system that transports urine from the nephrons into the renal pelvis, ureter and finally the bladder. Generally speaking, the formation of these networks in different organs begins with the specification and differentiation of simple bud-like organ anlage, which then undergo a process of elaboration, typically by bifurcation. This process is often governed by the interaction of progenitor cells at the tips of the epithelia with neighboring mesenchymal cell populations which direct the branching process and which often themselves differentiate to form part of the adult organ. In the kidney, the tips of ureteric bud elaborate through a dynamic cell signaling relationship with overlying nephron progenitor cell populations. These cells sequentially commit to differentiation and the resulting nephrons reintegrate with the ureteric epithelium as development progresses. This review will describe recent advances in understanding the how the elaboration of the ureteric bud is patterned and consider the extent to which this process is shared with other organs.

Monitoring and maintaining the differentiation status of human ipsc derived kidney organoids

Background & Aim Human induced pluripotent stem cell (iPSC) derived kidney organoids resemble first trimester fetal kidney and offer a great model for studying kidney development and disease. During early renal development, the inductive interaction between two intermediate mesoderm (IM)-derived progenitor cell populations, the ureteric bud and the kidney mesenchyme, promotes nephron and collecting duct formation. Protocols are developed to in vitro differentiate human iPSC into ureteric epithelium and metanephric mesenchyme simultaneously, and then aggregate them to generate a complex multicellular kidney organoids. However, this is a complex procedure with unpredictable outcomes. Furthermore, after 25 days of culture, kidney organoids start to degenerate and form fibrotic and cartilage tissue. We investigated how kidney organoid differentiation can be monitored and how the survival of kidney organoids can be prolonged. Methods, Results & Conclusion We treated five human iPSC with CHIR99021 and followed by FGF9 to induce IM for 7 days. These IM like cells were formed into cell pellets and transferred to air-liquid interface for a further 18 up to 32 days. Successfully differentiated organoids demonstrate glomerular and tubular structures in H&E section, while failed differentiation results in amorphous fibrotic tissue. The same iPSC line had variable results among batch to batch. Along the differentiation process, LDH activity was measured to monitor organoid metabolism, which reached a peak on days 7∼9. LDH peaks higher than 50 milliunits/ml indicated excessive necrosis and resulted in abnormal organoid formation. We observed that iPSC with elevated OCT4 expression showed induced capacity to differentiate into kidney organoids. Furthermore high TGFβ expression at day 7 was associated with fibrosis in the kidney organoids. As shortage of oxygen supply to kidney organoids due to lack of functional vasculature limits their long term stability, we split the organoids on day 8 and day 21 and placed the organoids on a shaker on day 21 to allow for better oxygen supply. Using this method, it was possible to preserve the kidney organoids for 2 additional weeks with maintenance of glomerular and tubular structures. Taken together, these data will help us to monitor the differentiation and prolong the culture time of kidney organoids.

Mutational analysis of genes with ureteric progenitor cell-specific expression in branching morphogenesis of the mouse kidney.

Ureteric progenitor cells (UPCs) within the branch tips of the arborizing ureteric epithelium of the kidney's developing collecting system establish the shape and cellular organization of the collecting network, and drive the nephrogenic program through their interactions with nephron progenitor cells. In a previous study, expression screening identified a cohort of genes showing UPC-enriched expression including D17H6S56E-5, Hs3st3a1, Hs3st3b1, and Tmem59l. Each of these is also enriched in branch tips of assembling airways of the developing lungs. Here, we used Crispr-CAS9 directed gene editing to mutate each of these targets to address their potential role(s) in UPC programs. Single (D17H6S56E-5 and Tmem59l) and double (Hs3st3a1 and Hs3st3b1) mutants were viable, fertile, and displayed varying frequencies of ureter duplications and no overt lung phenotype. Ureter duplications arise spontaneously through multiple outgrowths of the ureteric bud at the onset of kidney development. Tmem59l mutants and Hs3st3a1/Hs3st3b1 compound mutants showed a weakly penetrant, but statistically significant increase in duplicated ureters compared to C57BL6/J and SW wild-type mouse strains. Tmem59l and Hs3st3a1/Hs3st3b1 activities contribute to the regulatory programs restricting ureteric outgrowth in the developing mouse kidney. However, the low penetrance of the observed phenotype precludes a detailed analysis of their specific actions.

A Toolbox to Characterize Human Induced Pluripotent Stem Cell-Derived Kidney Cell Types and Organoids.

The generation of reporter lines for cell identity, lineage, and physiologic state has provided a powerful tool in advancing the dissection of mouse kidney morphogenesis at a molecular level. Although use of this approach is not an option for studying human development in vivo, its application in human induced pluripotent stem cells (iPSCs) is now feasible. We used CRISPR/Cas9 gene editing to generate ten fluorescence reporter iPSC lines designed to identify nephron progenitors, podocytes, proximal and distal nephron, and ureteric epithelium. Directed differentiation to kidney organoids was performed according to published protocols. Using immunofluorescence and live confocal microscopy, flow cytometry, and cell sorting techniques, we investigated organoid patterning and reporter expression characteristics. Each iPSC reporter line formed well patterned kidney organoids. All reporter lines showed congruence of endogenous gene and protein expression, enabling isolation and characterization of kidney cell types of interest. We also demonstrated successful application of reporter lines for time-lapse imaging and mouse transplantation experiments. We generated, validated, and applied a suite of fluorescence iPSC reporter lines for the study of morphogenesis within human kidney organoids. This fluorescent iPSC reporter toolbox enables the visualization and isolation of key populations in forming kidney organoids, facilitating a range of applications, including cellular isolation, time-lapse imaging, protocol optimization, and lineage-tracing approaches. These tools offer promise for enhancing our understanding of this model system and its correspondence with human kidney morphogenesis.

Single cell analysis of the developing mouse kidney provides deeper insight into marker gene expression and ligand-receptor crosstalk.

Recent advances in the generation of kidney organoids and the culture of primary nephron progenitors from mouse and human have been based on knowledge of the molecular basis of kidney development in mice. Although gene expression during kidney development has been intensely investigated, single cell profiling provides new opportunities to further subsect component cell types and the signalling networks at play. Here, we describe the generation and analysis of 6732 single cell transcriptomes from the fetal mouse kidney [embryonic day (E)18.5] and 7853 sorted nephron progenitor cells (E14.5). These datasets provide improved resolution of cell types and specific markers, including subdivision of the renal stroma and heterogeneity within the nephron progenitor population. Ligand-receptor interaction and pathway analysis reveals novel crosstalk between cellular compartments and associates new pathways with differentiation of nephron and ureteric epithelium cell types. We identify transcriptional congruence between the distal nephron and ureteric epithelium, showing that most markers previously used to identify ureteric epithelium are not specific. Together, this work improves our understanding of metanephric kidney development and provides a template to guide the regeneration of renal tissue.