Identification of human nephron progenitors capable of generation of kidney structures and functional repair of chronic renal disease

Novel biomarkers related to oxidative stress and immunity in chronic kidney disease

Introduction

The incidence of chronic kidney disease (CKD) has been increasing in recent years, gradually becoming a global health crisis. Due to limited treatment options, novel molecular pathways are urgently required to advance the treatment and diagnosis of CKD.

Materials and methods

The characteristics of differentially expressed genes (DEGs) in CKD patients were analyzed using Gene Expression Omnibus (GEO) database, and genes related to oxidative stress were retrieved from the Genecard database. Subsequently, a comprehensive approach was applied, including immune infiltration analysis, weighted gene co-expression network analysis (WGCNA) and protein-protein interaction (PPI) network analysis, to identify hub genes among differentially expressed immune-related oxidative stress genes (DEIOSGs). Validation of hub genes was performed using an external data set, and diagnostic potential capability was evaluated through receiver operating curve (ROC) analysis. In animal experiments, the expression of hub genes in CKD was confirmed by inducing a CKD model through a 5/6 nephrectomy procedure. Finally, the relationship between these hub genes and clinical characteristics were assessed using the Nephroseq v5 database.

Results

29 DEIOSGs were identified by comprehensive bioinformatics analysis. PPI analysis screened the hub genes NCF2, S100A9, and SELL. ROC analysis demonstrated excellent diagnostic efficacy. Further validation from other databases and animal experiments confirmed a substantial upregulation in the expression of hub genes in CKD. Additionally, clinical correlation analysis established a clear link between hub gene expression and renal function deterioration.

Conclusions

Our study confirms NCF2, S100A9, and SELL as diagnostic biomarkers associated with immune response and oxidative stress in CKD, suggesting their potential as novel targets for CKD diagnosis and treatment.

Great potential of renal progenitor cells in kidney: From the development to clinic

The mammalian renal organ represents a pinnacle of complexity, housing functional filtering units known as nephrons. During embryogenesis, the depletion of niches containing renal progenitor cells (RPCs) and the subsequent incapacity of adult kidneys to generate new nephrons have prompted the formulation of protocols aimed at isolating residual RPCs from mature kidneys and inducing their generation from diverse cell sources, notably pluripotent stem cells. Recent strides in the realm of regenerative medicine and the repair of tissues using stem cells have unveiled critical signaling pathways essential for the maintenance and generation of human RPCs in vitro. These findings have ushered in a new era for exploring novel strategies for renal protection. The present investigation delves into potential transcription factors and signaling cascades implicated in the realm of renal progenitor cells, focusing on their protection and differentiation. The discourse herein elucidates contemporary research endeavors dedicated to the acquisition of progenitor cells, offering crucial insights into the developmental mechanisms of these cells within the renal milieu and paving the way for the formulation of innovative treatment modalities.

Association between the prognostic nutritional index (PNI) and all-cause mortality in patients with chronic kidney disease

BACKGROUND

Nutrition and immunity play an important role in many chronic diseases. The prognostic nutritional index (PNI) has been proposed as a comprehensive indicator of an individual's immune and nutritional status. However, there is a lack of evidence regarding the association between the PNI and mortality in patients with chronic kidney disease (CKD).

METHODS

We used National Health and Nutrition Examination Survey (NHANES) data from 2001-2014 for participants with CKD. Mortality data were obtained from the National Death Index and matched to NHANES participants. Cox proportional hazards models were used to estimate hazard ratios for all-cause mortality.Results: The patients were 72.5 ± 9.8 years old, and 47.57% were male. The median follow-up was 58 months, and the mortality rate in patients with CKD was 30.27%. A higher PNI protected against all-cause mortality in patients with CKD, with an adjusted hazard ratio (aHR) of 0.98 (95% confidence interval (CI): 0.97-0.99). After grouping according to PNI quartiles, statistically significant between-group differences were observed in survival probabilities. The aHR for the lowest PNI quartile compared to the highest PNI quartile was 1.64 (95% CI: 1.26-2.14). Sensitivity analysis further supported this association. Restricted cubic spline analysis revealed an L-shaped association between the PNI and all-cause mortality in patients with CKD, with a critical value of 50.5.

CONCLUSIONS

The PNI is a protective factor in patients with CKD, with an L-shaped decrease in all-cause mortality with an increasing PNI.

OCT4 induces long-lived dedifferentiated kidney progenitors poised to redifferentiate in 3D kidney spheroids

Upscaling of kidney epithelial cells is crucial for renal regenerative medicine. Nonetheless, the adult kidney lacks a distinct stem cell hierarchy, limiting the ability to long-term propagate clonal populations of primary cells that retain renal identity. Toward this goal, we tested the paradigm of shifting the balance between differentiation and stemness in the kidney by introducing a single pluripotency factor, OCT4. Here we show that ectopic expression of OCT4 in human adult kidney epithelial cells (hKEpC) induces the cells to dedifferentiate, stably proliferate, and clonally emerge over many generations. Control hKEpC dedifferentiate, assume fibroblastic morphology, and completely lose clonogenic capacity. Analysis of gene expression and histone methylation patterns revealed that OCT4 represses the HNF1B gene module, which is critical for kidney epithelial differentiation, and concomitantly activates stemness-related pathways. OCT4-hKEpC can be long-term expanded in the dedifferentiated state that is primed for renal differentiation. Thus, when expanded OCT4-hKEpC are grown as kidney spheroids (OCT4-kSPH), they reactivate the HNF1B gene signature, redifferentiate, and efficiently generate renal structures in vivo. Hence, changes occurring in the cellular state of hKEpC following OCT4 induction, long-term propagation, and 3D aggregation afford rapid scale-up technology of primary renal tissue-forming cells.

Identifying effective diagnostic biomarkers and immune infiltration features in chronic kidney disease by bioinformatics and validation

Background: Chronic kidney disease (CKD), characterized by sustained inflammation and immune dysfunction, is highly prevalent and can eventually progress to end-stage kidney disease. However, there is still a lack of effective and reliable diagnostic markers and therapeutic targets for CKD. Methods: First, we merged data from GEO microarrays (GSE104948 and GSE116626) to identify differentially expressed genes (DEGs) in CKD and healthy patient samples. Then, we conducted GO, KEGG, HPO, and WGCNA analyses to explore potential functions of DEGs and select clinically significant modules. Moreover, STRING was used to analyse protein-protein interactions. CytoHubba and MCODE algorithms in the cytoscape plug-in were performed to screen hub genes in the network. We then determined the diagnostic significance of the obtained hub genes by ROC and two validation datasets. Meanwhile, the expression level of the biomarkers was verified by IHC. Furthermore, we examined immunological cells' relationships with hub genes. Finally, GSEA was conducted to determine the biological functions that biomarkers are significantly enriched. STITCH and AutoDock Vina were used to predict and validate drug-gene interactions. Results: A total of 657 DEGs were screened and functional analysis emphasizes their important role in inflammatory responses and immunomodulation in CKD. Through WGCNA, the interaction network, ROC curves, and validation set, four hub genes (IL10RA, CD45, CTSS, and C1QA) were identified. Furthermore, IHC of CKD patients confirmed the results above. Immune infiltration analysis indicated that CKD had a significant increase in monocytes, M0 macrophages, and M1 macrophages but a decrease in regulatory T cells, activated dendritic cells, and so on. Moreover, four hub genes were statistically correlated with them. Further analysis exhibited that IL10RA, which obtained the highest expression level in hub genes, was involved in abnormalities in various immune cells and regulated a large number of immune system responses and inflammation-related pathways. In addition, the drug-gene interaction network contained four potential therapeutic drugs targeting IL10RA, and molecular docking might make this relationship viable. Conclusion: IL10RA and its related hub molecules might play a key role in the development of CKD and could be potential biomarkers in CKD.

In vitro methods to ensure absence of residual undifferentiated human induced pluripotent stem cells intermingled in induced nephron progenitor cells

Cell therapies using human induced pluripotent stem cell (hiPSC)-derived nephron progenitor cells (NPCs) are expected to ameliorate acute kidney injury (AKI). However, using hiPSC-derived NPCs clinically is a challenge because hiPSCs themselves are tumorigenic. LIN28A, ESRG, CNMD and SFRP2 transcripts have been used as a marker of residual hiPSCs for a variety of cell types undergoing clinical trials. In this study, by reanalyzing public databases, we found a baseline expression of LIN28A, ESRG, CNMD and SFRP2 in hiPSC-derived NPCs and several other cell types, suggesting LIN28A, ESRG, CNMD and SFRP2 are not always reliable markers for iPSC detection. As an alternative, we discovered a lncRNA marker gene, MIR302CHG, among many known and unknown iPSC markers, as highly differentially expressed between hiPSCs and NPCs, by RNA sequencing and quantitative RT-PCR (qRT-PCR) analyses. Using MIR302CHG as an hiPSC marker, we constructed two assay methods, a combination of magnetic bead-based enrichment and qRT-PCR and digital droplet PCR alone, to detect a small number of residual hiPSCs in NPC populations. The use of these in vitro assays could contribute to patient safety in treatments using hiPSC-derived cells.

Potential Strategies for Kidney Regeneration With Stem Cells: An Overview

Kidney diseases are a major health problem worldwide. Despite advances in drug therapies, they are only capable of slowing the progression of kidney diseases. Accordingly, potential kidney regeneration strategies with stem cells have begun to be explored. There are two different directions for regenerative strategies, de novo whole kidney fabrication with stem cells, and stem cell therapy. De novo whole kidney strategies include: 1) decellularized scaffold technology, 2) 3D bioprinting based on engineering technology, 3) kidney organoid fabrication, 4) blastocyst complementation with chimeric technology, and 5) the organogenic niche method. Meanwhile, stem cell therapy strategies include 1) injection of stem cells, including mesenchymal stem cells, nephron progenitor cells, adult kidney stem cells and multi-lineage differentiating stress enduring cells, and 2) injection of protective factors secreted from these stem cells, including growth factors, chemokines, and extracellular vesicles containing microRNAs, mRNAs and proteins. Over the past few decades, there have been remarkable step-by-step developments in these strategies. Here, we review the current advances in the potential strategies for kidney regeneration using stem cells, along with their challenges for possible clinical use in the future.

Urine-Derived Kidney Progenitor Cells in Cystinosis

Nephropathic cystinosis is an inherited lysosomal storage disorder caused by pathogenic variants in the cystinosin (CTNS) gene and is characterized by the excessive shedding of proximal tubular epithelial cells (PTECs) and podocytes into urine, development of the renal Fanconi syndrome and end-stage kidney disease (ESKD). We hypothesized that in compensation for epithelial cell losses, cystinosis kidneys undertake a regenerative effort, and searched for the presence of kidney progenitor cells (KPCs) in the urine of cystinosis patients. Urine was cultured in a specific progenitor medium to isolate undifferentiated cells. Of these, clones were characterized by qPCR, subjected to a differentiation protocol to PTECs and podocytes and assessed by qPCR, Western blot, immunostainings and functional assays. Cystinosis patients voided high numbers of undifferentiated cells in urine, of which various clonal cell lines showed a high capacity for self-renewal and expressed kidney progenitor markers, which therefore were assigned as cystinosis urine-derived KPCs (Cys-uKPCs). Cys-uKPC clones showed the capacity to differentiate between functional PTECs and/or podocytes. Gene addition with wild-type CTNS using lentiviral vector technology resulted in significant reductions in cystine levels. We conclude that KPCs present in the urine of cystinosis patients can be isolated, differentiated and complemented with CTNS in vitro, serving as a novel tool for disease modeling.

Therapeutic role of uterine-derived stem cells in acute kidney injury

BACKGROUND

Acute kidney injury (AKI) causes abrupt deterioration in kidney function that disrupts metabolic, electrolyte and fluid homeostasis. Although the prevalence of AKI is steadily increasing, no definitive treatment options are available, leading to severe morbidity and mortality. We evaluated the role of uterine-derived multipotent stem cells in kidney regeneration after ischemic AKI.

METHODS

Female C57BL/6J mice were hysterectomized and subsequently subject to AKI by either unilateral or bilateral renal ischemia-reperfusion injury. Uterine-derived cells (UDCs), containing a population of uterine stem cells, were isolated from the uteri of female transgenic DsRed mice and injected intravenously to AKI mice. Engraftment of DsRed cells was analyzed by flow cytometry while serum creatinine levels were determined colorimetrically. Expression of UDC markers and cytokine markers were analyzed by immunohistochemical and qRT-PCR methods, respectively. The Kaplan-Meier method was used to analyze survival time while unpaired t test with Welch's correction used for data analysis between two groups.

RESULTS

Mice with an intact uterus, and hence an endogenous source of UDCs, had a higher survival rate after bilateral ischemic AKI compared to hysterectomized mice. Mice treated with infusion of exogenous UDCs after hysterectomy/AKI had lower serum creatinine levels and higher survival rates compared to controls that did not receive UDCs. Engraftment of labeled UDCs was significantly higher in kidneys of bilateral ischemic AKI mice compared to those that underwent a sham surgery. When unilateral ischemic AKI was induced, higher numbers of UDCs were found in the injured than non-injured kidney. Immunofluorescence staining demonstrated double-positive DsRed/Lotus tetragonolobus agglutinin (LTA) positive cells and DsRed/CD31 positive cells indicating contribution of UDCs in renal tubular and vascular regeneration. Expression of Cxcl12, Bmp2, Bmp4, and Ctnf in renal tissue was significantly higher in the UDCs injection group than the control group.

CONCLUSIONS

UDCs engrafted injured kidneys, contributed to proximal tubule and vascular regeneration, improved kidney function and increased survival in AKI mice. UDC administration is a promising new therapy for AKI. Endogenous uterine stem cells likely also preserve kidney function, suggesting a novel interaction between the uterus and kidney. We suggest that hysterectomy may have a detrimental effect on response to renal injury.

Gene therapy with Pellino-1 improves perfusion and decreases tissue loss in Flk-1 heterozygous mice but fails in MAPKAP Kinase-2 knockout murine hind limb ischemia model

OBJECTIVES

In the United States, over 8.5 million people suffer from peripheral arterial disease (PAD). Previously we reported that Pellino-1(Peli1) gene therapy reduces ischemic damage in the myocardium and skin flaps in Flk-1 [Fetal Liver kinase receptor-1 (Flk-1)/ Vascular endothelial growth factor receptor-2/VEGFR2] heterozygous (Flk-1^+/-) mice. The present study compares the angiogenic response and perfusion efficiency following hind limb ischemia (HLI) in, Flk-1^+/- and, MAPKAPKINASE2 (MK2^-/-) knockout (KO) mice to their control wild type (WT). We also demonstrated the use of Peli1 gene therapy to improve loss of function following HLI.

STUDY DESIGN AND METHODS

Femoral artery ligation (HLI) was performed in both Flk-1^+/-and MK2^-/-mice along with their corresponding WT. Another set of Flk-1^+/- and MK2^-/- were injected with either Adeno-LacZ (Ad.LacZ) or Adeno-Peli1 (Ad.Peli1) after HLI. Hind limb perfusion was assessed by laser doppler imaging at specific time points. A standardized scoring scale is used to quantify the extent of ischemia. Histology analysis performed includes capillary density, fibrosis, pro-angiogenic and anti-apoptotic proteins.

RESULTS

Flk-1^+/- and MK2^-/- had a slower recovery of perfusion efficiency in the ischemic limbs than controls. Both Flk-1^+/-and MK2^-/-KO mice showed decreased capillary density and capillary myocyte ratios with increased fibrosis than their corresponding wild types. Ad.Peli1 injected ischemic Flk-1^+/- limb showed improved perfusion, increased capillary density, and pro-angiogenic molecules with reduced fibrosis compared to Ad.LacZ group. No significant improvement in perfusion was observed in MK2^-/- ischemic limb after Ad. Peli1 injection.

CONCLUSION

Deletion of Flk-1 and MK2 impairs neovascularization and perfusion following HLI. Treatment with Ad. Peli1 results in increased angiogenesis and improved perfusion in Flk-1^+/- mice but fails to rectify perfusion in MK2 KO mice. Overall, Peli1 gene therapy is a promising candidate for the treatment of PAD.

Generation of Induced Nephron Progenitor-like Cells from Human Urine-Derived Cells

Background: Regenerative medicine strategies employing nephron progenitor cells (NPCs) are a viable approach that is worthy of substantial consideration as a promising cell source for kidney diseases. However, the generation of induced nephron progenitor-like cells (iNPCs) from human somatic cells remains a major challenge. Here, we describe a novel method for generating NPCs from human urine-derived cells (UCs) that can undergo long-term expansion in a serum-free condition. Results: Here, we generated iNPCs from human urine-derived cells by forced expression of the transcription factors OCT4, SOX2, KLF4, c-MYC, and SLUG, followed by exposure to a cocktail of defined small molecules. These iNPCs resembled human embryonic stem cell-derived NPCs in terms of their morphology, biological characteristics, differentiation potential, and global gene expression and underwent a long-term expansion in serum-free conditions. Conclusion: This study demonstrates that human iNPCs can be readily generated and expanded, which will facilitate their broad applicability in a rapid, efficient, and patient-specific manner, particularly holding the potential as a transplantable cell source for patients with kidney disease.

Human Kidney Spheroids and Monolayers Provide Insights into SARS-CoV-2 Renal Interactions

BACKGROUND

Although coronavirus disease 2019 (COVID-19) causes significan t morbidity, mainly from pulmonary involvement, extrapulmonary symptoms are also major componen ts of the disease. Kidney disease, usually presenting as AKI, is particularly severe among patients with COVID-19. It is unknown, however, whether such injury results from direct kidney infection with COVID-19's causative virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), or from indirect mechanisms.

METHODS

Using ex vivo cell models, we sought to analyze SARS-CoV-2 interactions with kidney tubular cells and assess direct tubular injury. These models comprised primary human kidney epithelial cells (derived from nephrectomies) and grown as either proliferating monolayers or quiescent three-dimensional kidney spheroids.

RESULTS

We demonstrated that viral entry molecules and high baseline levels of type 1 IFN-related molecules were present in monolayers and kidney spheroids. Although both models support viral infection and replication, they did not exhibit a cytopathic effect and cell death, outcomes that were strongly present in SARS-CoV-2-infected controls (African green monkey kidney clone E6 [Vero E6] cultures). A comparison of monolayer and spheroid cultures demonstrated higher infectivity and replication of SARS-CoV-2 in actively proliferating monolayers, although the spheroid cultures exhibited high er levels of ACE2. Monolayers exhibited elevation of some tubular injury molecules-including molecules related to fibrosis (COL1A1 and STAT6) and dedifferentiation (SNAI2)-and a loss of cell identity, evident by reduction in megalin (LRP2). The three-dimensional spheroids were less prone to such injury.

CONCLUSIONS

SARS-CoV-2 can infect kidney cells without a cytopathic effect. AKI-induced cellular proliferation may potentially intensify infectivity and tubular damage by SARS-CoV-2, suggesting that early intervention in AKI is warranted to help minimize kidney infection.

Heat shock protein A12B gene therapy improves perfusion, promotes neovascularization, and decreases fibrosis in a murine model of hind limb ischemia

BACKGROUND

Heat shock protein A12B expressed in endothelial cells is important and required for angiogenesis to form functional vessels in ischemic tissue. We have previously shown the cardioprotective effects of heat shock protein A12B overexpression in a rat model of diabetic myocardial infarction. In this study, we aim to explore the role of heat shock protein A12B in a surgically-induced murine hind-limb ischemia model.

MATERIALS AND METHODS

Adult 8- to 12-week-old C57BL/6J mice were divided into 2 groups: treated with Adeno.LacZ (control group) and with Adeno.HSPA12B (experimental group) and, with both groups subjected to right femoral artery ligation. Immediately after surgery, mice in both groups received either Adeno.HSPA12B or Adeno.LacZ (1 × 10⁹ plaque forming units) in both the semimembranosus and gastrocnemius muscles of the right limb. The left limb served as the internal control. Both groups underwent serial laser Doppler imaging preoperatively, and again postoperatively until 28 days. Immunohistochemical analysis was performed 3 and 28 days post-surgery.

RESULTS

Mice in the Adeno.HSPA12B gene therapy group showed improved motor function and a significantly higher blood perfusion ratio on postoperative days 21 and 28, along with better motor function. Immunohistochemical analysis showed increased expression of vascular endothelial growth factor, thioredoxin-1, heme oxygenase, and hypoxia-inducible factor 1α, along with a decreased expression of A-kinase-anchoring protein 12 and thioredoxin-interacting protein levels. The Adeno.HSPA12B-treated group also showed increased capillary and arteriolar density and an increased capillary-myocyte ratio, along with reduced fibrosis compared to the Adeno.LacZ group.

CONCLUSION

Our study demonstrates that targeted Adeno.HSPA12B gene delivery into ischemic muscle enhances perfusion and angiogenic protein expression. This molecule shows promise for the management of peripheral vascular disease as a potential target for clinical trials and subsequent drug therapy.

Mixing Cells for Vascularized Kidney Regeneration

The worldwide rise in prevalence of chronic kidney disease (CKD) demands innovative bio-medical solutions for millions of kidney patients. Kidney regenerative medicine aims to replenish tissue which is lost due to a common pathological pathway of fibrosis/inflammation and rejuvenate remaining tissue to maintain sufficient kidney function. To this end, cellular therapy strategies devised so far utilize kidney tissue-forming cells (KTFCs) from various cell sources, fetal, adult, and pluripotent stem-cells (PSCs). However, to increase engraftment and potency of the transplanted cells in a harsh hypoxic diseased environment, it is of importance to co-transplant KTFCs with vessel forming cells (VFCs). VFCs, consisting of endothelial cells (ECs) and mesenchymal stem-cells (MSCs), synergize to generate stable blood vessels, facilitating the vascularization of self-organizing KTFCs into renovascular units. In this paper, we review the different sources of KTFCs and VFCs which can be mixed, and report recent advances made in the field of kidney regeneration with emphasis on generation of vascularized kidney tissue by cell transplantation.

A Modular Differentiation System Maps Multiple Human Kidney Lineages from Pluripotent Stem Cells

Recent studies using human pluripotent stem cells (hPSCs) have developed protocols to induce kidney-lineage cells and reconstruct kidney organoids. However, the separate generation of metanephric nephron progenitors (NPs), mesonephric NPs, and ureteric bud (UB) cells, which constitute embryonic kidneys, in in vitro differentiation culture systems has not been fully investigated. Here, we create a culture system in which these mesoderm-like cell types and paraxial and lateral plate mesoderm-like cells are separately generated from hPSCs. We recapitulate nephrogenic niches from separately induced metanephric NP-like and UB-like cells, which are subsequently differentiated into glomeruli, renal tubules, and collecting ducts in vitro and further vascularized in vivo. Our selective differentiation protocols should contribute to understanding the mechanisms underlying human kidney development and disease and also supply cell sources for regenerative therapies.

Regenerative treatments for kidney diseases: The closest and fastest strategies to solving related medical and economic problems

Recent advances in developmental biology and stem cell biology have led to the increased availability of extrarenal stem cells, including mesenchymal/stromal stem cells (MSCs), renal stem or progenitor cells isolated from embryonic and adult kidneys, and kidney lineage cells or tissues generated from human pluripotent stem cells (hPSCs), such as human embryonic stem cells and human-induced pluripotent stem cells. Regenerative medicine strategies for kidney diseases are largely categorized into the transplantation of reconstructed kidney organs and cell therapies. Reconstruction is being attempted by hPSC-derived kidney lineage cells with various strategies, such as self-organization, interspecies blastocyst complementation, utilization of a xenogeneic organ niche, decellularization and repopulation, and 3D bioprinting. However, cell therapies using extrarenal stem cells, such as MSCs, and renal stem or progenitor cells derived from embryonic and adult kidneys or differentiated from hPSCs have been investigated in animal models of both acute kidney injury and chronic kidney disease. Indeed, multiple clinical trials using MSCs, bone marrow stem cells, and kidney-derived cells have already been carried out. This review summarizes the current status and future perspective of kidney regenerative medicine strategies and discusses the closest and fastest strategies to solving the medical and economic problems associated with kidney diseases.

Ex Vivo Expanded 3D Human Kidney Spheres Engraft Long Term and Repair Chronic Renal Injury in Mice

End-stage renal disease is a worldwide epidemic requiring renal replacement therapy. Harvesting tissue from failing kidneys and autotransplantation of tissue progenitors could theoretically delay the need for dialysis. Here we use healthy and end-stage human adult kidneys to robustly expand proliferative kidney epithelial cells and establish 3D kidney epithelial cultures termed "nephrospheres." Formation of nephrospheres reestablishes renal identity and function in primary cultures. Transplantation into NOD/SCID mice shows that nephrospheres restore self-organogenetic properties lost in monolayer cultures, allowing long-term engraftment as tubular structures, potentially adding nephron segments and demonstrating self-organization as critical to survival. Furthermore, long-term tubular engraftment of nephrospheres is functionally beneficial in murine models of chronic kidney disease. Remarkably, nephrospheres inhibit pro-fibrotic collagen production in cultured fibroblasts via paracrine modulation, while transplanted nephrospheres induce transcriptional signatures of proliferation and release from quiescence, suggesting re-activation of endogenous repair. These data support the use of human nephrospheres for renal cell therapy.

Role of Pericytes in the Development of the Renin/Angiotensin System: Induction of Functional Renin in Cultures of Pericytes

Renal pericytes have a critical importance for angiogenesis and vascular remodeling, medullary blood flow regulation, and development of fibrosis. An emerging role for kidney pericytes is their ability to induce renin expression and synthesis. Here, we present methods for purification of human renal pericytes, their primary culture, and differentiation into renin-producing cells. Possible applications of these protocols include investigations into (1) renin cell recruitment mechanisms, (2) modulation of renin expression/secretion by small molecules, and (3) renin expression/secretion in nonrenal pericytes. A potential therapeutic application of this work is the identification of new players regulating the renin-angiotensin system.

Human kidney clonal proliferation disclose lineage-restricted precursor characteristics

In-vivo single cell clonal analysis in the adult mouse kidney has previously shown lineage-restricted clonal proliferation within varying nephron segments as a mechanism responsible for cell replacement and local regeneration. To analyze ex-vivo clonal growth, we now preformed limiting dilution to generate genuine clonal cultures from one single human renal epithelial cell, which can give rise to up to 3.4 * 10⁶ cells, and analyzed their characteristics using transcriptomics. A comparison between clonal cultures revealed restriction to either proximal or distal kidney sub-lineages with distinct cellular and molecular characteristics; rapidly amplifying de-differentiated clones and a stably proliferating cuboidal epithelial-appearing clones, respectively. Furthermore, each showed distinct molecular features including cell-cycle, epithelial-mesenchymal transition, oxidative phosphorylation, BMP signaling pathway and cell surface markers. In addition, analysis of clonal versus bulk cultures show early clones to be more quiescent, with elevated expression of renal developmental genes and overall reduction in renal identity markers, but with an overlapping expression of nephron segment identifiers and multiple identity. Thus, ex-vivo clonal growth mimics the in-vivo situation displaying lineage-restricted precursor characteristics of mature renal cells. These data suggest that for reconstruction of varying renal lineages with human adult kidney based organoid technology and kidney regeneration ex-vivo, use of multiple heterogeneous precursors is warranted.

Therapeutic potential of human induced pluripotent stem cells and renal progenitor cells in experimental chronic kidney disease

BACKGROUND

Chronic kidney disease (CKD) is a global public health problem. Cell therapy using pluripotent stem cells represents an attractive therapeutic approach for the treatment of CKD.

METHODS

We transplanted mitomycin C (MMC)-treated human induced pluripotent stem cells (hiPSCs) and renal progenitor cells (RPCs) into a CKD rat model system. The RPC and hiPSC cells were characterized by immunofluorescence and qRT-PCR. Untreated 5/6 nephrectomized rats were compared to CKD animals receiving the same amount of MMC-treated hiPSCs or RPCs. Renal function, histology, and immunohistochemistry were evaluated 45 days post-surgery.

RESULTS

We successfully generated hiPSCs from peripheral blood and differentiated them into RPCs expressing renal progenitor genes (PAX2, WT1, SIX2, and SALL1) and podocyte-related genes (SYNPO, NPHS1). RPCs also exhibited reduced OCT4 expression, confirming the loss of pluripotency. After cell transplantation into CKD rats, the body weight change was significantly increased in both hiPSC and RPC groups, in comparison with the control group. Creatinine clearance (CCr) was preserved only in the hiPSC group. Similarly, the number of macrophages in the kidneys of the hiPSC group reached a statistically significant reduction, when compared to control rats. Both treatments reduced positive staining for the marker α-smooth muscle actin. Histological features showed decreased tubulointerstitial damage (interstitial fibrosis and tubular atrophy) as well as a reduction in glomerulosclerosis in both iPSC and RPC groups.

CONCLUSIONS

In conclusion, we describe that both MMC-treated hiPSCs and RPCs exert beneficial effects in attenuating CKD progression. Both cell types were equally efficient to reduce histological damage and weight loss caused by CKD. hiPSCs seem to be more efficient than RPCs, possibly due to a paracrine effect triggered by hiPSCs. These results demonstrate that the use of MMC-treated hiPSCs and RPCs improves clinical and histological CKD parameters, avoided tumor formation, and therefore may be a promising cell therapy strategy for CKD.

Successful Introduction of Human Renovascular Units into the Mammalian Kidney

BACKGROUND

Cell-based therapies aimed at replenishing renal parenchyma have been proposed as an approach for treating CKD. However, pathogenic mechanisms involved in CKD such as renal hypoxia result in loss of kidney function and limit engraftment and therapeutic effects of renal epithelial progenitors. Jointly administering vessel-forming cells (human mesenchymal stromal cells [MSCs] and endothelial colony-forming cells [ECFCs]) may potentially result in in vivo formation of vascular networks.

METHODS

We administered renal tubule-forming cells derived from human adult and fetal kidneys (previously shown to exert a functional effect in CKD mice) into mice, alongside MSCs and ECFCs. We then assessed whether this would result in generation of "renovascular units" comprising both vessels and tubules with potential interaction.

RESULTS

Directly injecting vessel-forming cells and renal tubule-forming cells into the subcutaneous and subrenal capsular space resulted in self-organization of donor-derived vascular networks that connected to host vasculature, alongside renal tubules comprising tubular epithelia of different nephron segments. Vessels derived from MSCs and ECFCs augmented in vivo tubulogenesis by the renal tubule-forming cells. In vitro coculture experiments showed that MSCs and ECFCs induced self-renewal and genes associated with mesenchymal-epithelial transition in renal tubule-forming cells, indicating paracrine effects. Notably, after renal injury, renal tubule-forming cells and vessel-forming cells infused into the renal artery did not penetrate the renal vascular network to generate vessels; only administering them into the kidney parenchyma resulted in similar generation of human renovascular units in vivo.

CONCLUSIONS

Combined cell therapy of vessel-forming cells and renal tubule-forming cells aimed at alleviating renal hypoxia and enhancing tubulogenesis holds promise as the basis for new renal regenerative therapies.

The FGF, TGFβ and WNT axis Modulate Self-renewal of Human SIX2+ Urine Derived Renal Progenitor Cells

Human urine is a non-invasive source of renal stem cells with regeneration potential. Urine-derived renal progenitor cells were isolated from 10 individuals of both genders and distinct ages. These renal progenitors express pluripotency-associated proteins- TRA-1-60, TRA-1-81, SSEA4, C-KIT and CD133, as well as the renal stem cell markers -SIX2, CITED1, WT1, CD24 and CD106. The transcriptomes of all SIX2⁺ renal progenitors clustered together, and distinct from the human kidney biopsy-derived epithelial proximal cells (hREPCs). Stimulation of the urine-derived renal progenitor cells (UdRPCs) with the GSK3β-inhibitor (CHIR99021) induced differentiation. Transcriptome and KEGG pathway analysis revealed upregulation of WNT-associated genes- AXIN2, JUN and NKD1. Protein interaction network identified JUN- a downstream target of the WNT pathway in association with STAT3, ATF2 and MAPK1 as a putative negative regulator of self-renewal. Furthermore, like pluripotent stem cells, self-renewal is maintained by FGF2-driven TGFβ-SMAD2/3 pathway. The urine-derived renal progenitor cells and the data presented should lay the foundation for studying nephrogenesis in human.

Molecular characterization of nephron progenitors and their early epithelial derivative structures in the nephrogenic zone of the canine fetal kidney

Nephron progenitors (NPs) and nephrogenesis have been extensively studied in mice and humans and have provided insights into the mechanisms of renal development, disease and possibility of NP-based therapies. However, molecular features of NPs and their derivatives in the canine fetal kidney (CFK) remain unknown. This study was focused to characterize the expression of potential markers of canine NPs and their derivatives by immuno-fluorescence and western blot analysis. Transcription factors (TFs) SIX1 and SIX2, well-characterized human NP markers, were expressed in NPs surrounding the ureteric bud in the CFK. Canine NPs also expressed ITGA8 and NCAM1, surface markers previously used to isolate NPs from the mouse and human fetal kidneys. TF, PAX2 was detected in the ureteric bud, NPs and their derivative structures such as renal vesicle and S-shaped body. This study highlights the similarities in dog, mouse and human renal development and characterizes markers to identify canine NPs and their derivatives. These results will facilitate the isolation of canine NPs and their functional characterization to develop NP-based therapies for canine renal diseases.

Activin Is Superior to BMP7 for Efficient Maintenance of Human iPSC-Derived Nephron Progenitors

Kidney formation is regulated by the balance between maintenance and differentiation of nephron progenitor cells (NPCs). Now that directed differentiation of NPCs from human induced pluripotent stem cells (iPSCs) can be achieved, maintenance and propagation of NPCs in vitro should be beneficial for regenerative medicine. Although WNT and FGF signals were previously shown to be essential for NPC propagation, the requirement for BMP/TGFβ signaling remains controversial. Here we reveal that activin has superior effects to BMP7 on maintenance efficiency of human iPSC-derived NPCs. Activin expanded ITGA8⁺/PDGFRA^-/SIX2-GFP⁺ NPCs by 5-fold per week at 80%-90% efficiency, and the propagated cells possessed robust capacity for nephron formation both in vitro and in vivo. The expanded cells also maintained their nephron-forming potential after freezing. Furthermore, the protocol was applicable to multiple non-GFP-tagged iPSC lines. Thus, our activin-based protocol will be applicable to a variety of research fields including disease modeling and drug screening.

Fibrosis in tissue engineering and regenerative medicine: treat or trigger?

Fibrosis is a life-threatening pathological condition resulting from a dysfunctional tissue repair process. There is no efficient treatment and organ transplantation is in many cases the only therapeutic option. Here we review tissue engineering and regenerative medicine (TERM) approaches to address fibrosis in the cardiovascular system, the kidney, the lung and the liver. These strategies have great potential to achieve repair or replacement of diseased organs by cell- and material-based therapies. However, paradoxically, they might also trigger fibrosis. Cases of TERM interventions with adverse outcome are also included in this review. Furthermore, we emphasize the fact that, although organ engineering is still in its infancy, the advances in the field are leading to biomedically relevant in vitro models with tremendous potential for disease recapitulation and development of therapies. These human tissue models might have increased predictive power for human drug responses thereby reducing the need for animal testing.

Direct reprogramming to human nephron progenitor-like cells using inducible piggyBac transposon expression of SNAI2-EYA1-SIX1

All nephrons in the mammalian kidney arise from a transient nephron progenitor population that is lost close to the time of birth. The generation of new nephron progenitors and their maintenance in culture are central to the success of kidney regenerative strategies. Using a lentiviral screening approach, we previously generated a human induced nephron progenitor-like state in vitro using a pool of six transcription factors. Here, we sought to develop a more efficient approach for direct reprogramming of human cells that could be applied in vivo. PiggyBac transposons are a non-viral integrating gene delivery system that is suitable for in vivo use and allows for simultaneous delivery of multiple genes. Using an inducible piggyBac transposon system, we optimized a protocol for the direct reprogramming of HK2 cells to induced nephron progenitor-like cells with expression of only 3 transcription factors (SNAI2, EYA1, and SIX1). Culture in conditions supportive of the nephron progenitor state further increased the expression of nephron progenitor genes. The refined protocol was then applied to primary human renal epithelial cells, which integrated into developing nephron structures in vitro and in vivo. Such inducible reprogramming to nephron progenitor-like cells could facilitate direct cellular reprogramming for kidney regeneration.

Parallel generation of easily selectable multiple nephronal cell types from human pluripotent stem cells

Human pluripotent stem cells (hPSCs) provide a source for the generation of defined kidney cells and renal organoids applicable in regenerative medicine, disease modeling, and drug screening. These applications require the provision of hPSC-derived renal cells by reproducible, scalable, and efficient methods. We established a chemically defined protocol by application of Activin A, BMP4, and Retinoic acid followed by GDNF, which steered hPSCs to the renal lineage and resulted in populations of SIX2+/CITED1+ metanephric mesenchyme- (MM) and of HOXB7+/GRHL2+ ureteric bud (UB)-like cells already by 6 days. Transcriptome analysis corroborated that the PSC-derived cell types at day 8 resemble their renal vesicle and ureteric epithelial counterpart in vivo, forming tubular and glomerular renal cells 6 days later. We demonstrate that starting from hPSCs, our in vitro protocol generates a pool of nephrogenic progenitors at the renal vesicle stage, which can be further directed into specialized nephronal cell types including mesangial-, proximal tubular-, distal tubular, collecting duct epithelial cells, and podocyte precursors after 14 days. This simple and rapid method to produce renal cells from a common precursor pool in 2D culture provides the basis for scaled-up production of tailored renal cell types, which are applicable for drug testing or cell-based regenerative therapies.

Concise Reviews: Stem Cells and Kidney Regeneration: An Update

Significant progress has been made to advance stem cell products as potential therapies for kidney diseases: various kinds of stem cells can restore renal function in preclinical models of acute and chronic kidney injury. Nonetheless this literature contains contradictory results, and for this reason, we focus this review on reasons for apparent discrepancies in the literature, because they contribute to difficulty in translating renal regenerative therapies. Differences in methodologies used to derive and culture stem cells, even those from the same source, in addition to the lack of standardized renal disease animal models (both acute and chronic), are important considerations underlying contradictory results in the literature. We propose that harmonized rigorous protocols for characterization, handling, and delivery of stem cells in vivo could significantly advance the field, and present details of some suggested approaches to foster translation in the field of renal regeneration. Our goal is to encourage coordination of methodologies (standardization) and long‐lasting collaborations to improve protocols and models to lead to reproducible, interpretable, high‐quality preclinical data. This approach will certainly increase our chance to 1 day offer stem cell therapeutic options for patients with all‐too‐common renal diseases. Stem Cells Translational Medicine2019;8:82–92

Recapitulating kidney development: Progress and challenges

Decades of research into the molecular and cellular regulation of kidney morphogenesis in rodent models, particularly the mouse, has provided both an atlas of the mammalian kidney and a roadmap for recreating kidney cell types with potential applications for the treatment of kidney disease. With advances in both our capacity to maintain nephron progenitors in culture, reprogram to kidney cell types and direct the differentiation of human pluripotent stem cells to kidney endpoints, renal regeneration via cellular therapy or tissue engineering may be possible. Human kidney models also have potential for disease modelling and drug screening. Such applications will rely upon the accuracy of the model at the cellular level and the capacity for stem-cell derived kidney tissue to recapitulate both normal and diseased kidney tissue. In this review, we will discuss the available cell sources, how well they model the human kidney and how far we are from application either as models or for tissue engineering.

Regenerative medicine in kidney disease: where we stand and where to go

The kidney is a complex organ with more than 20 types of specialized cells that play an important role in maintaining the body's homeostasis. The epithelial tubular cell is formed during embryonic development and has little proliferative capacity under physiological conditions, but after acute injury the kidney does have regenerative capacity. However, after repetitive or severe lesions, it may undergo a maladaptation process that predisposes it to chronic kidney injury. Regenerative medicine includes various repair and regeneration techniques, and these have gained increasing attention in the scientific literature. In the future, not only will these techniques contribute to the repair and regeneration of the human kidney, but probably also to the construction of an entire organ. New mechanisms studied for kidney regeneration and repair include circulating stem cells as mesenchymal stromal/stem cells and their paracrine mechanisms of action; renal progenitor stem cells; the leading role of tubular epithelial cells in the tubular repair process; the study of zebrafish larvae to understand the process of nephron development, kidney scaffold and its repopulation; and, finally, the development of organoids. This review elucidates where we are in terms of current scientific knowledge regarding these mechanisms and the promises of future scientific perspectives.

Regenerating the kidney using human pluripotent stem cells and renal progenitors

INTRODUCTION

Chronic kidney disease is a major health-care problem worldwide and its cost is becoming no longer affordable. Indeed, restoring damaged renal structures or building a new kidney represents an ambitious and ideal alternative to renal replacement therapy. Streams of research have explored the possible application of pluripotent stem cells (SCs) (embryonic SCs and induced pluripotent SCs) in different strategies aimed at regenerate functioning nephrons and at understanding the mechanisms of kidney regeneration.

AREAS COVERED

In this review, we will focus on the main potential applications of human pluripotent SCs to kidney regeneration, including those leading to rebuilding new kidneys or part of them (organoids, scaffolds, biological microdevices) as well as those aimed at understanding the pathophysiological mechanisms of renal disease and regenerative processes (modeling of kidney disease, genome editing). Moreover, we will discuss the role of endogenous renal progenitors cells in order to understand and promote kidney regeneration, as an attractive alternative to pluripotent SCs.

EXPERT OPINION

Opportunities and pitfalls of all these strategies will be underlined, finally leading to the conclusion that a deeper knowledge of the biology of pluripotent SCs is mandatory, in order to allow us to hypothesize their clinical application.

High-Throughput Screening Enhances Kidney Organoid Differentiation from Human Pluripotent Stem Cells and Enables Automated Multidimensional Phenotyping

Organoids derived from human pluripotent stem cells are a potentially powerful tool for high-throughput screening (HTS), but the complexity of organoid cultures poses a significant challenge for miniaturization and automation. Here, we present a fully automated, HTS-compatible platform for enhanced differentiation and phenotyping of human kidney organoids. The entire 21-day protocol, from plating to differentiation to analysis, can be performed automatically by liquid-handling robots, or alternatively by manual pipetting. High-content imaging analysis reveals both dose-dependent and threshold effects during organoid differentiation. Immunofluorescence and single-cell RNA sequencing identify previously undetected parietal, interstitial, and partially differentiated compartments within organoids and define conditions that greatly expand the vascular endothelium. Chemical modulation of toxicity and disease phenotypes can be quantified for safety and efficacy prediction. Screening in gene-edited organoids in this system reveals an unexpected role for myosin in polycystic kidney disease. Organoids in HTS formats thus establish an attractive platform for multidimensional phenotypic screening.

Development of new method to enrich human iPSC-derived renal progenitors using cell surface markers

Cell therapy using renal progenitors differentiated from human embryonic stem cells (hESCs) or induced pluripotent stem cells (hiPSCs) has the potential to significantly reduce the number of patients receiving dialysis therapy. However, the differentiation cultures may contain undifferentiated or undesired cell types that cause unwanted side effects, such as neoplastic formation, when transplanted into a body. Moreover, the hESCs/iPSCs are often genetically modified in order to isolate the derived renal progenitors, hampering clinical applications. To establish an isolation method for renal progenitors induced from hESCs/iPSCs without genetic modifications, we screened antibodies against cell surface markers. We identified the combination of four markers, CD9⁻CD140a⁺CD140b⁺CD271⁺, which could enrich OSR1⁺SIX2⁺ renal progenitors. Furthermore, these isolated cells ameliorated renal injury in an acute kidney injury (AKI) mouse model when used for cell therapy. These cells could contribute to the development of hiPSC-based cell therapy and disease modeling against kidney diseases.

Renal Subcapsular Transplantation of PSC-Derived Kidney Organoids Induces Neo-vasculogenesis and Significant Glomerular and Tubular Maturation In Vivo

Human pluripotent stem cell (hPSC)-derived kidney organoids may facilitate disease modeling and the generation of tissue for renal replacement. Long-term application, however, will require transferability between hPSC lines and significant improvements in organ maturation. A key question is whether time or a patent vasculature is required for ongoing morphogenesis. Here, we show that hPSC-derived kidney organoids, derived in fully defined medium conditions and in the absence of any exogenous vascular endothelial growth factor, develop host-derived vascularization. In vivo imaging of organoids under the kidney capsule confirms functional glomerular perfusion as well as connection to pre-existing vascular networks in the organoids. Wide-field electron microscopy demonstrates that transplantation results in formation of a glomerular basement membrane, fenestrated endothelial cells, and podocyte foot processes. Furthermore, compared with non-transplanted organoids, polarization and segmental specialization of tubular epithelium are observed. These data demonstrate that functional vascularization is required for progressive morphogenesis of human kidney organoids.

Renal lineage cells as a source for renal regeneration

The mammalian kidney is a highly complex organ, composed of various cell types within a unique structural framework. Nonetheless, in recent years, giant leaps in our understanding of nephrogenesis and the origin of new cells in the adult kidney have resulted in novel routes to regenerate damaged nephrons. While several strategies can be envisioned to achieve this aim, one common theme is the reliance on renal lineage cells, as extrarenal cells, such as bone marrow-derived cells, have been shown to be devoid of renal differentiation capacity. Herein, we will present the main motivation for the pursuit for cell-based therapies, which is the ever growing problem of chronic kidney disease (CKD), and discuss different strategies toward replenishing the damaged renal parenchyma. These include transplantation of fetal kidney grafts or fetal kidney stem cells, directed differentiation of pluripotent stem cells into kidney epithelia, establishment of renal progenitors from the adult kidney, and genetic reprogramming of mature kidney cells into a progenitor state. Taken together with novel techniques recapitulating the three-dimensional developmental environment, these advances are expected to take the field into a new era, bringing us closer than ever to the day when kidney stem cell-based therapy becomes a viable therapeutic option.

A Children's Oncology Group and TARGET initiative exploring the genetic landscape of Wilms tumor

We performed genome-wide sequencing and analyzed mRNA and miRNA expression, DNA copy number, and DNA methylation in 117 Wilms tumors, followed by targeted sequencing of 651 Wilms tumors. In addition to genes previously implicated in Wilms tumors (WT1, CTNNB1, AMER1, DROSHA, DGCR8, XPO5, DICER1, SIX1, SIX2, MLLT1, MYCN, and TP53), we identified mutations in genes not previously recognized as recurrently involved in Wilms tumors, the most frequent being BCOR, BCORL1, NONO, MAX, COL6A3, ASXL1, MAP3K4, and ARID1A. DNA copy number changes resulted in recurrent 1q gain, MYCN amplification, LIN28B gain, and MIRLET7A loss. Unexpected germline variants involved PALB2 and CHEK2. Integrated analyses support two major classes of genetic changes that preserve the progenitor state and/or interrupt normal development.

Peroxisome proliferator-activated receptor gamma (PPARγ) is central to the initiation and propagation of human angiomyolipoma, suggesting its potential as a therapeutic target

Angiomyolipoma (AML), the most common benign renal tumor, can result in severe morbidity from hemorrhage and renal failure. While mTORC1 activation is involved in its growth, mTORC1 inhibitors fail to eradicate AML, highlighting the need for new therapies. Moreover, the identity of the AML cell of origin is obscure. AML research, however, is hampered by the lack of in vivo models. Here, we establish a human AML‐xenograft (Xn) model in mice, recapitulating AML at the histological and molecular levels. Microarray analysis demonstrated tumor growth in vivo to involve robust PPARG‐pathway activation. Similarly, immunostaining revealed strong PPARG expression in human AML specimens. Accordingly, we demonstrate that while PPARG agonism accelerates AML growth, PPARG antagonism is inhibitory, strongly suppressing AML proliferation and tumor‐initiating capacity, via a TGFB‐mediated inhibition of PDGFB and CTGF. Finally, we show striking similarity between AML cell lines and mesenchymal stem cells (MSCs) in terms of antigen and gene expression and differentiation potential. Altogether, we establish the first in vivo human AML model, which provides evidence that AML may originate in a PPARG‐activated renal MSC lineage that is skewed toward adipocytes and smooth muscle and away from osteoblasts, and uncover PPARG as a regulator of AML growth, which could serve as an attractive therapeutic target.

Concise Review: Kidney Generation with Human Pluripotent Stem Cells

Chronic kidney disease (CKD) is a worldwide health care problem, resulting in increased cardiovascular mortality and often leading to end-stage kidney disease, where patients require kidney replacement therapies such as hemodialysis or kidney transplantation. Loss of functional nephrons contributes to the progression of CKD, which can be attenuated but not reversed due to inability to generate new nephrons in human adult kidneys. Human pluripotent stem cells (hPSCs), by virtue of their unlimited self-renewal and ability to differentiate into cells of all three embryonic germ layers, are attractive sources for kidney regenerative therapies. Recent advances in stem cell biology have identified key signals necessary to maintain stemness of human nephron progenitor cells (NPCs) in vitro, and led to establishment of protocols to generate NPCs and nephron epithelial cells from human fetal kidneys and hPSCs. Effective production of large amounts of human NPCs and kidney organoids will facilitate elucidation of developmental and pathobiological pathways, kidney disease modeling and drug screening as well as kidney regenerative therapies. We summarize the recent studies to induce NPCs and kidney cells from hPSCs, studies of NPC expansion from mouse and human embryonic kidneys, and discuss possible approaches in vivo to regenerate kidneys with cell therapies and the development of bioengineered kidneys. Stem Cells 2017;35:2209-2217.

How to grow a kidney: patient-specific kidney organoids come of age

The notion of regrowing a patient's kidney in a dish has fascinated researchers for decades and has spurred visions of revolutionary clinical applications. Recently, this option has come closer to reality. Key technologies have been developed to generate patient-specific pluripotent stem cells and to edit their genome. Several laboratories have devised protocols to differentiate patient-specific pluripotent stem cells into kidney cells or into in vitro organoids that resemble the kidney with respect to cell types, tissue architecture and disease pathology. This was possible because of rapidly expanding knowledge regarding the cellular and molecular basis of embryonic kidney development. Generating kidney cells or organoids from patient-specific stem cells may prove to be clinically useful in several ways. First, patient-specific kidney cells or organoids could be used to predict an individual's response to stressors, toxins or medications and thereby develop personalized treatment decisions. Second, patient-specific stem cells harbour the individual's genetic defects. This may potentially enable genetic rescue attempts to establish the significance of a genetic defect in a stem cell-derived organoid or it may allow testing of patient-specific targeted therapies for kidney disease in vitro. From a tissue engineering perspective, patient-specific kidney organoids might provide a key advance towards engineering immunocompatible transplantable kidneys. This review article summarizes recent developments in the field and discusses its current limitations and future perspectives.

Evidence of In Vitro Preservation of Human Nephrogenesis at the Single-Cell Level

During nephrogenesis, stem/progenitor cells differentiate and give rise to early nephron structures that segment to proximal and distal nephron cell types. Previously, we prospectively isolated progenitors from human fetal kidney (hFK) utilizing a combination of surface markers. However, upon culture nephron progenitors differentiated and could not be robustly maintained in vitro. Here, by culturing hFK in a modified medium used for in vitro growth of mouse nephron progenitors, and by dissection of NCAM⁺/CD133⁻ progenitor cells according to EpCAM expression (NCAM⁺/CD133⁻/EpCAM⁻, NCAM⁺/CD133⁻/EpCAM^dim, NCAM⁺/CD133⁻/EpCAM^bright), we show at single-cell resolution a preservation of uninduced and induced cap mesenchyme as well as a transitioning mesenchymal-epithelial state. Concomitantly, differentiating and differentiated epithelial lineages are also maintained. In vitro expansion of discrete stages of early human nephrogenesis in nephron stem cell cultures may be used for drug screening on a full repertoire of developing kidney cells and for prospective isolation of mesenchymal or epithelial renal lineages for regenerative medicine.

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mNPEM enables in vitro preservation of human renal embryonic CM and epithelia

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EpCAM allows further dissection of expanded NCAM⁺CD133⁻ early nephric population

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Single-cell analysis unveils a continuous lineage hierarchy in nephrogenesis and WT

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Splice isoform switching confirms a unified MET hierarchy in nephrogenesis and WT

Human Kidney-Derived Cells Ameliorate Acute Kidney Injury Without Engrafting into Renal Tissue

Previous studies have suggested that CD133⁺ cells isolated from human kidney biopsies have the potential to ameliorate injury following intravenous (IV) administration in rodent models of kidney disease by integrating into damaged renal tissue and generating specialized renal cells. However, whether renal engraftment of CD133⁺ cells is a prerequisite for ameliorating injury has not yet been unequivocally resolved. Here, we have established a cisplatin‐induced nephropathy model in immunodeficient rats to assess the efficacy of CD133⁺ human kidney cells in restoring renal health, and to determine the fate of these cells after systemic administration. Specifically, following IV administration, we evaluated the impact of the CD133⁺ cells on renal function by undertaking longitudinal measurements of the glomerular filtration rate using a novel transcutaneous device. Using histological assays, we assessed whether the human kidney cells could promote renal regeneration, and if this was related to their ability to integrate into the damaged kidneys. Our results show that both CD133⁺ and CD133⁻ cells improve renal function and promote renal regeneration to a similar degree. However, this was not associated with engraftment of the cells into the kidneys. Instead, after IV administration, both cell types were exclusively located in the lungs, and had disappeared by 24 hours. Our data therefore indicate that renal repair is not mediated by CD133⁺ cells homing to the kidneys and generating specialized renal cells. Instead, renal repair is likely to be mediated by paracrine or endocrine factors. Stem Cells Translational Medicine2017;6:1373–1384

Role of CD56 in Normal Kidney Development and Wilms Tumorigenesis

The cell-surface glycoprotein CD56 has three major isoforms that play important roles in cell adhesion and signaling, which may promote cell proliferation, differentiation, survival, or migration. It is an important molecule in normal kidney development and acts as a key marker in Wilms tumor stem and progenitor cells. Here, we review the structural and genetic features of the CD56 glycoprotein, and summarize its roles in the normal versus diseased metanephric blastema. We discuss areas of CD56-related research that may complement or improve existing Wilms tumor treatment strategies, including the antibody-drug conjugate lorvotuzumab mertansine that binds to CD56.

Growth Factor Regulation in the Nephrogenic Zone of the Developing Kidney

New nephrons are induced by the interaction between mesenchymal progenitor cells and collecting duct tips, both of which are located at the outer edge of the kidney. This leading edge of active nephron induction is known as the nephrogenic zone. Cell populations found within this zone include collecting duct tips, cap mesenchyme cells, pretubular aggregates, nephrogenic zone interstitium, hemoendothelial progenitor cells, and macrophages. The close association of these dynamic progenitor cell compartments enables the intricate and synchronized patterning of the epithelial and the vascular components of the nephron. Understanding signaling interactions between the distinct progenitor cells of the nephrogenic zone are essential to determining the basis for new nephron formation, an important goal in regenerative medicine. A variety of technologies have been applied to define essential signaling pathways, including organ culture, mouse genetics, and primary cell culture. This chapter provides an overview of essential signaling pathways and discusses how these may be integrated.

Direct Isolation and Characterization of Human Nephron Progenitors

Mature nephrons originate from a small population of uninduced nephrogenic progenitor cells (NPs) within the cap mesenchyme. These cells are characterized by the coexpression of SIX2 and CITED1. Many studies on mouse models as well as on human pluripotent stem cells have advanced our knowledge of NPs, but very little is known about this population in humans, since it is exhausted before birth and strategies for its direct isolation are still limited. Here we report an efficient protocol for direct isolation of human NPs without genetic manipulation or stepwise induction procedures. With the use of RNA‐labeling probes, we isolated SIX2⁺CITED1⁺ cells from human fetal kidney for the first time. We confirmed their nephrogenic state by gene profiling and evaluated their nephrogenic capabilities in giving rise to mature renal cells. We also evaluated the ability to culture these cells without complete loss of SIX2 and CITED1 expression over time. In addition to defining the gene profile of human NPs, this in vitro system facilitates studies of human renal development and provides a novel tool for renal regeneration and bioengineering purposes. Stem Cells Translational Medicine2017;6:419–433

Imaging technologies for monitoring the safety, efficacy and mechanisms of action of cell-based regenerative medicine therapies in models of kidney disease

The incidence of end stage kidney disease is rising annually and it is now a global public health problem. Current treatment options are dialysis or renal transplantation, which apart from their significant drawbacks in terms of increased morbidity and mortality, are placing an increasing economic burden on society. Cell-based Regenerative Medicine Therapies (RMTs) have shown great promise in rodent models of kidney disease, but clinical translation is hampered due to the lack of adequate safety and efficacy data. Furthermore, the mechanisms whereby the cell-based RMTs ameliorate injury are ill-defined. For instance, it is not always clear if the cells directly replace damaged renal tissue, or whether paracrine effects are more important. Knowledge of the mechanisms responsible for the beneficial effects of cell therapies is crucial because it could lead to the development of safer and more effective RMTs in the future. To address these questions, novel in vivo imaging strategies are needed to monitor the biodistribution of cell-based RMTs and evaluate their beneficial effects on host tissues and organs, as well as any potential adverse effects. In this review we will discuss how state-of-the-art imaging modalities, including bioluminescence, magnetic resonance, nuclear imaging, ultrasound and an emerging imaging technology called multispectral optoacoustic tomography, can be used in combination with various imaging probes to track the fate and biodistribution of cell-based RMTs in rodent models of kidney disease, and evaluate their effect on renal function.

Hedgehog Gli signalling in kidney fibrosis

Kidney fibrosis is the common final pathway of virtually all progressive injury to the kidney and a promising therapeutic target in chronic kidney disease (CKD). The Hedgehog pathway has been reported to be critical in kidney development, and recent evidence suggests a role in kidney injury and fibrosis. This review provides an overview of recent data suggesting an important role of Gli transcriptional activators in kidney injury and repair. We have reported that the hedgehog transcriptional activator Gli1 specifically marks perivascular mesenchymal stem cells, which are an important source of kidney myofibroblasts. Genetic ablation of these cells ameliorated kidney and heart fibrosis and stabilized organ function after injury. Recent data suggest that Gli2 is an important driver of myofibroblast cell cycle progression and a promising therapeutic target in kidney fibrosis progression and CKD. However, the non-canonical mechanism of Gli activation in kidney fibrosis remains an open question, and further studies are needed to elucidate the role of Hedgehog Gli and Gli1⁺ perivascular cells in human kidney fibrosis.