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

Human iPSC-derived nephron progenitor cells treat acute kidney injury and chronic kidney disease in mouse models

The number of patients requiring dialysis therapy continues to increase worldwide because of the lack of effective treatments for chronic kidney disease (CKD). Furthermore, no curative treatments for acute kidney injury (AKI) have been established. The therapeutic effects of human induced pluripotent stem cell-derived nephron progenitor cells (hiPSC-NPCs) on AKI have been reported in mice but not clinically confirmed. There are also no reports examining the therapeutic potential of hiPSC-NPCs on CKD. Although large numbers of uniform hiPSC-NPCs are required for cell therapies for AKI and CKD, effective expansion cultures remain to be developed. Here, we established a culture medium for cells that enabled more than 100-fold proliferation of hiPSC-NPCs from multiple hiPSC lines in two passages. We demonstrated that hiPSC-NPCs expanded by our medium named CFY or by their conditioned medium alone attenuated kidney injury and improved survival in cisplatin-induced AKI mice. We also observed that hiPSC-NPCs prevented kidney functional decline, interstitial fibrosis, and senescence in aristolochic acid-induced CKD mice. In addition, we found c-MET to be a specific cell surface marker for hiPSC-NPCs and confirmed that purified c-MET+ hiPSC-NPCs had therapeutic effects on AKI and CKD mice. Furthermore, we found that hiPSC-NPCs exerted their therapeutic effects in AKI and CKD mice by secreting vascular endothelial growth factor A. Expanded hiPSC-NPCs may be useful cell therapies for AKI and CKD and may open avenues for treating kidney diseases.

Generation of human-pig chimeric renal organoids using iPSC technology

Porcine organs and human induced pluripotent stem cell (iPSC)-derived organoids as alternative organs for human transplantation have garnered attention, but both face technical challenges. Interspecies chimeric organ production using human iPSCs shows promise in overcoming these challenges. Our group successfully generated chimeric renal organoids using human iPSC-derived nephron progenitor cells (NPCs) and fetal mouse kidneys. However, the current technology is limited to rodents. Therefore, this study focused on producing human-pig chimeric renal organoids, as pigs are the most promising species for xenotransplantation. Modification of existing culture systems enables continuous renal development in both species, resulting in the successful creation of human-pig chimeric renal organoids. Moreover, this method can be applied to generate humanized xenogeneic kidneys for future clinical applications. This study provides evidence that optimizing culture conditions enables the early-stage kidney development beyond species barriers, thus laying the foundation for accelerating research on humanized xenogeneic kidney fabrication for clinical purposes.

Long-term expandable mouse and human-induced nephron progenitor cells enable kidney organoid maturation and modeling of plasticity and disease

Nephron progenitor cells (NPCs) self-renew and differentiate into nephrons, the functional units of the kidney. Here, manipulation of p38 and YAP activity allowed for long-term clonal expansion of primary mouse and human NPCs and induced NPCs (iNPCs) from human pluripotent stem cells (hPSCs). Molecular analyses demonstrated that cultured iNPCs closely resemble primary human NPCs. iNPCs generated nephron organoids with minimal off-target cell types and enhanced maturation of podocytes relative to published human kidney organoid protocols. Surprisingly, the NPC culture medium uncovered plasticity in human podocyte programs, enabling podocyte reprogramming to an NPC-like state. Scalability and ease of genome editing facilitated genome-wide CRISPR screening in NPC culture, uncovering genes associated with kidney development and disease. Further, NPC-directed modeling of autosomal-dominant polycystic kidney disease (ADPKD) identified a small-molecule inhibitor of cystogenesis. These findings highlight a broad application for the reported iNPC platform in the study of kidney development, disease, plasticity, and regeneration.

Hedgehog signaling is required for the maintenance of mesenchymal nephron progenitors

Mesenchymal nephron progenitors (mNPs) give rise to all nephron tubules in the mammalian kidney. Since premature depletion of these cells leads to low nephron numbers, high blood pressure, and various renal diseases, it is critical that we understand how mNPs are maintained. While Fgf, Bmp, and Wnt signaling pathways are known to be required for the maintenance of these cells, it is unclear if any other signaling pathways also play roles. In this report, we explored the role of Hedgehog signaling in mNPs. We found that loss of either Shh in the collecting duct or Smo from the nephron lineage resulted in premature depletion of mNPs. Transcriptional profiling of mNPs with different Smo dosages suggested that Hedgehog signaling inhibited Notch signaling and upregulated the expression of Fox transcription factors such as Foxc1 and Foxp4. Consistent with these observations, we found that ectopic expression of Jag1 caused the premature depletion of mNPs as seen in the Smo mutant kidney. We also found that Foxc1 was capable of binding to mitotic condensed chromatin, a feature of a mitotic bookmarking factor. Our study demonstrates a previously unappreciated role of Hedgehog signaling in preventing premature depletion of mNPs by repressing Notch signaling and likely by activating the expression of Fox factors.

SMAD2/3 signaling regulates initiation of mouse Wolffian ducts and proximal differentiation in Müllerian ducts

Male and female reproductive tracts develop from anterior intermediate mesoderm with similar differentiation processes. The anterior intermediate mesoderm develops into the mesonephros, and the Wolffian duct initiates by epithelialization in the mesonephros. The Müllerian duct invaginates from the coelomic epithelium of the cranial mesonephros for ductal formation and is then regionalized into proximal to caudal female reproductive tracts. In this study, we focused on the epithelialization of the Wolffian duct, initiation of the Müllerian duct, and the regionalization step of the Müllerian ducts as a continuous process. By using intermediate mesodermal cells from mouse pluripotent stem cells, we identified that inhibition of SMAD2/3 signaling might be involved in the differentiation into mesenchymal cells, after which mesonephric cells might be then epithelialized during differentiation of the Wolffian duct. Aggregation of coelomic epithelial cells might be related to initiation of the Müllerian duct. Transcriptomic analysis predicted that consensus sequences of SMAD3/4 were enriched among highly expressed genes in the proximal Müllerian duct. SMAD2/3 signaling to regulate differentiation of the Wolffian duct was continuously activated in the proximal Müllerian duct and was involved in proximal and oviductal regionalization. Therefore, SMAD2/3 signaling may be finely tuned to regulate differentiation from initiation to regionalization steps.

Recombinant Laminin-511 Fragment (iMatrix-511) Coating Supports Maintenance of Human Nucleus Pulposus Progenitor Cells In Vitro

The angiopoietin-1 receptor (Tie2) marks specific nucleus pulposus (NP) progenitor cells, shows a rapid decline during aging and intervertebral disc degeneration, and has thus sparked interest in its utilization as a regenerative agent against disc degeneration. However, the challenge of maintaining and expanding these progenitor cells in vitro has been a significant hurdle. In this study, we investigated the potential of laminin-511 to sustain Tie2+ NP progenitor cells in vitro. We isolated cells from human NP tissue (n = 5) and cultured them for 6 days on either standard (Non-coat) or iMatrix-511 (laminin-511 product)-coated (Lami-coat) dishes. We assessed these cells for their proliferative capacity, activation of Erk1/2 and Akt pathways, as well as the expression of cell surface markers such as Tie2, GD2, and CD24. To gauge their regenerative potential, we examined their extracellular matrix (ECM) production capacity (intracellular type II collagen (Col2) and proteoglycans (PG)) and their ability to form spherical colonies within methylcellulose hydrogels. Lami-coat significantly enhanced cell proliferation rates and increased Tie2 expression, resulting in a 7.9-fold increase in Tie2-expressing cell yields. Moreover, the overall proportion of cells positive for Tie2 also increased 2.7-fold. Notably, the Col2 positivity rate was significantly higher on laminin-coated plates (Non-coat: 10.24% (±1.7%) versus Lami-coat: 26.2% (±7.5%), p = 0.010), and the ability to form spherical colonies also showed a significant improvement (Non-coat: 40.7 (±8.8)/1000 cells versus Lami-coat: 70.53 (±18.0)/1000 cells, p = 0.016). These findings demonstrate that Lami-coat enhances the potential of NP cells, as indicated by improved colony formation and proliferative characteristics. This highlights the potential of laminin-coating in maintaining the NP progenitor cell phenotype in culture, thereby supporting their translation into prospective clinical cell-transplantation products.

Human iPSCs as Model Systems for BMP-Related Rare Diseases

Disturbances in bone morphogenetic protein (BMP) signalling contribute to onset and development of a number of rare genetic diseases, including Fibrodysplasia ossificans progressiva (FOP), Pulmonary arterial hypertension (PAH), and Hereditary haemorrhagic telangiectasia (HHT). After decades of animal research to build a solid foundation in understanding the underlying molecular mechanisms, the progressive implementation of iPSC-based patient-derived models will improve drug development by addressing drug efficacy, specificity, and toxicity in a complex humanized environment. We will review the current state of literature on iPSC-derived model systems in this field, with special emphasis on the access to patient source material and the complications that may come with it. Given the essential role of BMPs during embryonic development and stem cell differentiation, gain- or loss-of-function mutations in the BMP signalling pathway may compromise iPSC generation, maintenance, and differentiation procedures. This review highlights the need for careful optimization of the protocols used. Finally, we will discuss recent developments towards complex in vitro culture models aiming to resemble specific tissue microenvironments with multi-faceted cellular inputs, such as cell mechanics and ECM together with organoids, organ-on-chip, and microfluidic technologies.

Modeling kidney development, disease, and plasticity with clonal expandable nephron progenitor cells and nephron organoids

Nephron progenitor cells (NPCs) self-renew and differentiate into nephrons, the functional units of the kidney. Here we report manipulation of p38 and YAP activity creates a synthetic niche that allows the long-term clonal expansion of primary mouse and human NPCs, and induced NPCs (iNPCs) from human pluripotent stem cells. Cultured iNPCs resemble closely primary human NPCs, generating nephron organoids with abundant distal convoluted tubule cells, which are not observed in published kidney organoids. The synthetic niche reprograms differentiated nephron cells into NPC state, recapitulating the plasticity of developing nephron in vivo. Scalability and ease of genome-editing in the cultured NPCs allow for genome-wide CRISPR screening, identifying novel genes associated with kidney development and disease. A rapid, efficient, and scalable organoid model for polycystic kidney disease was derived directly from genome-edited NPCs, and validated in drug screen. These technological platforms have broad applications to kidney development, disease, plasticity, and regeneration.

Production of kidney organoids arranged around single ureteric bud trees, and containing endogenous blood vessels, solely from embryonic stem cells

There is intense worldwide effort in generating kidney organoids from pluripotent stem cells, for research, for disease modelling and, perhaps, for making transplantable organs. Organoids generated from pluripotent stem cells (PSC) possess accurate micro-anatomy, but they lack higher-organization. This is a problem, especially for transplantation, as such organoids will not be able to perform their physiological functions. In this study, we develop a method for generating murine kidney organoids with improved higher-order structure, through stages using chimaeras of ex-fetu and PSC-derived cells to a system that works entirely from embryonic stem cells. These organoids have nephrons organised around a single ureteric bud tree and also make vessels, with the endothelial network approaching podocytes.

Single-cell multiomics reveals the complexity of TGFβ signalling to chromatin in iPSC-derived kidney organoids

TGFβ1 plays a regulatory role in the determination of renal cell fate and the progression of renal fibrosis. Here we show an association between SMAD3 and the histone methyltransferase, EZH2, during cell differentiation; ChIP-seq revealed that SMAD3 and EZH2 co-occupy the genome in iPSCs and in iPSC-derived nephron progenitors. Through integration of single cell gene expression and epigenome profiling, we identified de novo ACTA2^+ve/POSTN^+ve myofibroblasts in kidney organoids treated with TGFβ1, characterised by increased SMAD3-dependent cis chromatin accessibility and gene expression associated with fibroblast activation. We have identified fibrosis-associated regulons characterised by enrichment of SMAD3, AP1, the ETS family of transcription factors, and NUAK1, CREB3L1, and RARG, corresponding to enriched motifs at accessible loci identified by scATACseq. Treatment with the EZH2 specific inhibitor GSK343, blocked SMAD3-dependent cis co-accessibility and inhibited myofibroblast activation. This mechanism, through which TGFβ signals directly to chromatin, represents a critical determinant of fibrotic, differentiated states.

Enhanced metanephric specification to functional proximal tubule enables toxicity screening and infectious disease modelling in kidney organoids

While pluripotent stem cell-derived kidney organoids are now being used to model renal disease, the proximal nephron remains immature with limited evidence for key functional solute channels. This may reflect early mispatterning of the nephrogenic mesenchyme and/or insufficient maturation. Here we show that enhanced specification to metanephric nephron progenitors results in elongated and radially aligned proximalised nephrons with distinct S1 - S3 proximal tubule cell types. Such PT-enhanced organoids possess improved albumin and organic cation uptake, appropriate KIM-1 upregulation in response to cisplatin, and improved expression of SARS-CoV-2 entry factors resulting in increased viral replication. The striking proximo-distal orientation of nephrons resulted from localized WNT antagonism originating from the organoid stromal core. PT-enhanced organoids represent an improved model to study inherited and acquired proximal tubular disease as well as drug and viral responses.

Regrow or Repair: An Update on Potential Regenerative Therapies for the Kidney

Fifteen years ago, this journal published a review outlining future options for regenerating the kidney. At that time, stem cell populations were being identified in multiple tissues, the concept of stem cell recruitment to a site of injury was of great interest, and the possibility of postnatal renal stem cells was growing in momentum. Since that time, we have seen the advent of human induced pluripotent stem cells, substantial advances in our capacity to both sequence and edit the genome, global and spatial transcriptional analysis down to the single-cell level, and a pandemic that has challenged our delivery of health care to all. This article will look back over this period of time to see how our view of kidney development, disease, repair, and regeneration has changed and envision a future for kidney regeneration and repair over the next 15 years.

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.

Kidney organoids: Research in developmental biology and emerging applications

Kidney organoids generated from human pluripotent stem cells (hPSCs) have drastically changed the field of stem cell research on human kidneys within a few years. They are self-organizing multicellular structures that contain nephron components such as glomeruli and renal tubules in most cases, but hPSC-derived ureteric buds, the progenitors of collecting ducts and ureters, can also form three-dimensional organoids. Today's challenges facing human kidney organoids are further maturation and anatomical integrity in order to achieve a complete model of the developing kidneys and ultimately a complete adult organ. Since chronic kidney disease (CKD) and impaired kidney function are an increasing burden on public health worldwide, there is an urgent need to develop effective treatments for various renal conditions. In this regard, hPSC-derived kidney organoids may impact medicine by providing new translational approaches. The unique ability of kidney organoids derived from disease-specific hPSCs to reproduce human diseases caused by genetic alterations may help provide the next generation of kidney disease models. Recent advances in the field of kidney organoid research have been generally accompanied by progress in developmental biology and other technological breakthroughs. In this review, we consider the current trends in kidney organoid technology, especially focusing on the relationship to the study of human kidney development, and discuss the remaining hurdles and prospects in regenerating human kidney structures beyond organoids.

Impaired NEPHRIN localization in kidney organoids derived from nephrotic patient iPS cells

Mutations in the NPHS1 gene, which encodes NEPHRIN, cause congenital nephrotic syndrome, resulting from impaired slit diaphragm (SD) formation in glomerular podocytes. We previously reported NEPHRIN and SD abnormalities in the podocytes of kidney organoids generated from patient-derived induced pluripotent stem cells (iPSCs) with an NPHS1 missense mutation (E725D). However, the mechanisms underlying the disease may vary depending on the mutations involved, and thus generation of iPSCs from multiple patients is warranted. Here we established iPSCs from two additional patients with different NPHS1 mutations and examined the podocyte abnormalities in kidney organoids derived from these cells. One patient had truncating mutations, and NEPHRIN was undetectable in the resulting organoids. The other patient had a missense mutation (R460Q), and the mutant NEPHRIN in the organoids failed to accumulate on the podocyte surface to form SD precursors. However, the same mutant protein behaved normally when overexpressed in heterologous cells, suggesting that NEPHRIN localization is cell context-dependent. The localization of another SD-associated protein, PODOCIN, was impaired in both types of mutant organoids in a cell domain-specific manner. Thus, the new iPSC lines and resultant kidney organoids will be useful resources for dissecting the disease mechanisms, as well as for drug development for therapies.

Cellular and Molecular Mechanisms of Kidney Development: From the Embryo to the Kidney Organoid

Development of the metanephric kidney is strongly dependent on complex signaling pathways and cell-cell communication between at least four major progenitor cell populations (ureteric bud, nephron, stromal, and endothelial progenitors) in the nephrogenic zone. In recent years, the improvement of human-PSC-derived kidney organoids has opened new avenues of research on kidney development, physiology, and diseases. Moreover, the kidney organoids provide a three-dimensional (3D) in vitro model for the study of cell-cell and cell-matrix interactions in the developing kidney. In vitro re-creation of a higher-order and vascularized kidney with all of its complexity is a challenging issue; however, some progress has been made in the past decade. This review focuses on major signaling pathways and transcription factors that have been identified which coordinate cell fate determination required for kidney development. We discuss how an extensive knowledge of these complex biological mechanisms translated into the dish, thus allowed the establishment of 3D human-PSC-derived kidney organoids.

Small molecule TCS21311 can replace BMP7 and facilitate cell proliferation in in vitro expansion culture of nephron progenitor cells

Several groups have developed in vitro expansion cultures for mouse metanephric nephron progenitor cells (NPCs) using cocktails of small molecules and growth factors including BMP7. However, the detailed mechanisms by which BMP7 acts in the NPC expansion remain to be elucidated. Here, by performing chemical screening for BMP substitutes, we identified a small molecule, TCS21311, that can replace BMP7 and revealed a novel inhibitory role of BMP7 in JAK3-STAT3 signaling in NPC expansion culture. Further, we found that TCS21311 facilitates the proliferation of mouse embryonic NPCs and human induced pluripotent stem cell-derived NPCs when added to the expansion culture. These results will contribute to understanding the mechanisms of action of BMP7 in NPC proliferation in vitro and in vivo and to the stable supply of NPCs for regenerative therapy, disease modeling and drug discovery for kidney diseases.

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.