Advances and challenges toward developing kidney organoids for clinical applications

Kidney organoids: a 3-dimensional tool to unmask permeability factors in primary and recurrent FSGS

Primary focal segmental glomerulosclerosis is a glomerular disorder associated with a high risk of recurrence after transplantation. Compelling evidence supports the existence of circulating permeability factors whose identity remains elusive. In the current issue of Kidney International, Gupta et al. propose that kidney organoid can respond to these factors in patients with focal segmental glomerulosclerosis and may serve as a potential platform for predicting disease recurrence. Future studies are required to identify the critical factors driving focal segmental glomerulosclerosis recurrence and to develop a standardized organoid platform for predicting clinical outcome.

From organoids to organoids-on-a-chip: Current applications and challenges in biomedical research

ABSTRACT

The high failure rates in clinical drug development based on animal models highlight the urgent need for more representative human models in biomedical research. In response to this demand, organoids and organ chips were integrated for greater physiological relevance and dynamic, controlled experimental conditions. This innovative platform-the organoids-on-a-chip technology-shows great promise in disease modeling, drug discovery, and personalized medicine, attracting interest from researchers, clinicians, regulatory authorities, and industry stakeholders. This review traces the evolution from organoids to organoids-on-a-chip, driven by the necessity for advanced biological models. We summarize the applications of organoids-on-a-chip in simulating physiological and pathological phenotypes and therapeutic evaluation of this technology. This section highlights how integrating technologies from organ chips, such as microfluidic systems, mechanical stimulation, and sensor integration, optimizes organoid cell types, spatial structure, and physiological functions, thereby expanding their biomedical applications. We conclude by addressing the current challenges in the development of organoids-on-a-chip and offering insights into the prospects. The advancement of organoids-on-a-chip is poised to enhance fidelity, standardization, and scalability. Furthermore, the integration of cutting-edge technologies and interdisciplinary collaborations will be crucial for the progression of organoids-on-a-chip technology.

Generation of kidney organoids derived from human expanded potential stem cells

The establishment of human expanded potential stem cell (hEPSC) presents a unique cellular platform for translational research in kidney organoids. We generated SIX2 reporter and doxycycline (DOX)-inducible YAP overexpression in hEPSC lines using CRISPR-Cas9. Chemical compounds and DOX were added to the culture medium to induce Hippo-YAP signaling, respectively. The hEPSC line containing the SIX2-mCherry reporter gene accurately reflected SIX2 expression in vitro, enabling the real-time tracking of kidney organoid development. A comparative analysis revealed that inhibiting the Hippo-YAP signaling pathway before nephron progenitor cell (NPC) generation effectively increased the number of NPCs, resulting in a more nephron-like structure. However, prolonged inhibition hindered the further maturation of the kidney organoids, leading to differentiation stagnation. Therefore, activating YAP before NPC generation facilitates their maturation, offering effective induction strategies improving kidney organoid differentiation efficiency.

Application progress of bio-manufacturing technology in kidney organoids

Kidney transplantation remains a pivotal treatment modality for kidney disease, yet its progress is significantly hindered by the scarcity of donor kidneys and ethical dilemmas surrounding their procurement. As organoid technology evolves and matures, the creation of bionic human kidney organoids offers profound potential for advancing kidney disease research, drug nephrotoxicity screening, and regenerative medicine. Nevertheless, current kidney organoid models grapple with limitations such as constrained cellular differentiation, underdeveloped functional structures, and a crucial absence of vascularization. This deficiency in vascularization, in particular, stunts organoid development, restricts their size, diminishes filtration capabilities, and may trigger immune inflammatory reactions through the resulting ischemic microenvironment. Hence, the achievement of vascularization within kidney organoids and the successful establishment of functional microvascular networks constitutes a paramount goal for their future progression. In this review, we provide an overview of recent advancements in biotechnology domains, encompassing organ-on-a-chip technology, biomimetic matrices, and bioprinting, with the aim of catalyzing technological breakthroughs that can enhance the vascularization of kidney organoids and broaden their applicability. These technologies hold the key to unlocking the full potential of kidney organoids as a transformative therapeutic option for kidney disease.

Advances and Challenges in Modeling Autosomal Dominant Polycystic Kidney Disease: A Focus on Kidney Organoids

Autosomal dominant polycystic kidney disease (ADPKD) is a prevalent hereditary disorder characterized by distinct phenotypic variability that has posed challenges for advancing in-depth research. Recent advancements in kidney organoid construction technologies have enabled researchers to simulate kidney development and create simplified in vitro experimental environments, allowing for more direct observation of how genetic mutations drive pathological phenotypes and disrupt physiological functions. Emerging technologies, such as microfluidic bioreactor culture systems and single-cell transcriptomics, have further supported the development of complex ADPKD organoids, offering robust models for exploring disease mechanisms and facilitating drug discovery. Nevertheless, significant challenges remain in constructing more accurate ADPKD disease models. This review will summarize recent advances in ADPKD organoid construction, focusing on the limitations of the current techniques and the critical issues that need to be addressed for future breakthroughs. New and Noteworthy: This review presents recent advancements in ADPKD organoid construction, particularly iPSC-derived models, offering new insights into disease mechanisms and drug discovery. It focuses on challenges such as limited vascularization and maturity, proposing potential solutions through emerging technologies. The ongoing optimization of ADPKD organoid models is expected to enhance understanding of the disease and drive breakthroughs in disease mechanisms and targeted therapy development.

Integrating 3D Bioprinting and Organoids to Better Recapitulate the Complexity of Cellular Microenvironments for Tissue Engineering

Organoids, with their capacity to mimic the structures and functions of human organs, have gained significant attention for simulating human pathophysiology and have been extensively investigated in the recent past. Additionally, 3D bioprinting, as an emerging bio-additive manufacturing technology, offers the potential for constructing heterogeneous cellular microenvironments, thereby promoting advancements in organoid research. In this review, the latest developments in 3D bioprinting technologies aimed at enhancing organoid engineering are introduced. The commonly used bioprinting methods and materials for organoids, with a particular emphasis on the potential advantages of combining 3D bioprinting with organoids are summarized. These advantages include achieving high cell concentrations to form large cellular aggregates, precise deposition of building blocks to create organoids with complex structures and functions, and automation and high throughput to ensure reproducibility and standardization in organoid culture. Furthermore, this review provides an overview of relevant studies from recent years and discusses the current limitations and prospects for future development.

Progress of Induced Pluripotent Stem Cell-Derived Renal Organoids in Clinical Application

Background

Kidney disease has become a growing public health problem worldwide, and there is an urgent need to develop reliable models for investigating novel and effective treatment strategies. In recent years, kidney organoids, as novel models different from traditional two-dimensional cells and model animals, have attracted more and more attention. Current advances have allowed the generation of kidney organoids from the directed differentiation of induced pluripotent stem cells (iPSCs), which possess similar characteristics to embryonic stem cells, but bypass ethical constraints and have a wide range of sources.

Summary

Herein, the methods of generating renal organoids from iPSCs, the applications of iPSC-derived renal organoids in disease modeling, drug effectiveness detection, and regenerative medicine as well as the challenges were reviewed.

Key Messages

iPSC-derived renal organoids can be used to model kidney diseases and are great models for studying kidney injury and toxicity. Many efforts are needed to finally apply organoids into clinical application.

Epithelial tubule interconnection driven by HGF-Met signaling in the kidney

The formation of functional epithelial tubules is critical for the development and maintenance of many organ systems. While the mechanisms of tubule formation by epithelial cells are well studied, the process of tubule anastomosis-where tubules connect to form a continuous network-remains poorly understood. In this study, we utilized single-cell RNA sequencing to analyze embryonic mouse kidney tubules undergoing anastomosis. Our analysis identified hepatocyte growth factor (HGF) as a key potential mediator of this process. To investigate this further, we developed an assay using epithelial spheroids with fluorescently tagged apical surfaces, allowing us to visualize and quantify tubule-tubule connections. Our results demonstrate that HGF promotes tubule anastomosis, and it does so through the MAPK signaling pathway and MMPs, independently of cell proliferation. Remarkably, treatment with HGF and collagenase was sufficient to induce tubule anastomosis in embryonic mouse kidneys. These findings provide a foundational understanding of how to enhance the formation of functional tubular networks. This has significant clinical implications for the use of in vitro-grown kidney tissues in transplant medicine, potentially improving the success and integration of transplanted tissues.

Mouse embryonic kidney transplantation identifies maturation defects in the medulla

Kidney organoids are connected to the host circulation and mature after transplantation. However, they are still immature compared to the adult kidneys, and their precise maturation stages remain unclear. By transplanting the mouse embryonic kidney as a model system for organoid transplantation, we report here the maturation defects of the graft, especially in the medulla. Single cell profiling of the developing kidneys in vivo identified gene sets associated with the maturation of the collecting duct epithelium and medullary stroma. These data revealed an upregulation of genes associated with channel/transporter functions and immune defense, as well as a downregulation of neuronal genes. Using these marker genes, we found that the maturation of the collecting duct and medullary stroma in the grafts barely corresponds to the perinatal stage, which was confirmed histologically by using representative genes. Thus, the gene sets obtained serve as maturation coordinates for the renal medulla and will be helpful in analyzing its maturation defects after transplantation. They will also provide a useful basis for further maturation of transplanted kidney organoids.

Advances in Diagnosis and Treatment of Inherited Kidney Diseases in Children

Background

Inherited kidney diseases (IKDs) in children pose unique diagnostic and therapeutic challenges. IKD significantly impact patient quality of life, morbidity, mortality, and cost to the healthcare system. With over 150 genetic abnormalities, they account for approximately 30% of cases requiring renal replacement therapy. There is an urgent need to advance both diagnosis and treatment strategies. In this review, we present recent advances in diagnosis and treatment for facilitating personalized treatment approaches.

Summary

The diagnostic landscape for IKDs have evolved significantly, emphasizing precise genetic identification and classification of these disorders. Recent advancements include the refinement of genetic testing techniques, such as whole exome sequencing, which has improved the accuracy of diagnosing specific diseases and facilitated early intervention strategies. Additionally, this review categorizes IKDs based on genetic abnormalities and clinical manifestations, enhancing understanding and management approaches. Finally, it summarizes the corresponding treatment, and lists the application of emerging therapeutic options such as gene therapy and organoids, which show promise in transforming treatment outcomes.

Key Messages

This review summarizes the common types of IKDs in children, including their diagnosis and treatment advances, and provides an update on the status of gene therapy development for these disorders.

Cadherin adhesion complexes direct cell aggregation in the epithelial transition of Wnt-induced nephron progenitor cells

In the developing mammalian kidney, nephron formation is initiated by a subset of nephron progenitor cells (NPCs). Wnt input activates a β-catenin (Ctnnb1)-driven, transcriptional nephrogenic program and the mesenchymal to epithelial transition (MET) of NPCs. Using an in vitro mouse NPC culture model, we observed that activation of the Wnt pathway results in the aggregation of induced NPCs, which is an initiating step in the MET program. Genetic removal showed aggregation was dependent on β-catenin. Modulating extracellular Ca2+ levels showed cell-cell contacts were Ca2+ dependent, suggesting a role for cadherin (Cdh)-directed cell adhesion. Molecular analysis identified Cdh2, Cdh4 and Cdh11 in NPCs, and the β-catenin directed upregulation of Cdh3 and Cdh4 accompanying the MET of induced NPCs. Mutational analysis of β-catenin supported a role for a Lef/Tcf-β-catenin-mediated transcriptional response in the cell aggregation process. Genetic removal of all four cadherins, and independent removal of α-catenin or of β-catenin-α-catenin interactions, abolished aggregation, but not the inductive response to Wnt pathway activation. These findings, and data in an accompanying article highlight the role of β-catenin in linking transcriptional programs to the morphogenesis of NPCs in mammalian nephrogenesis.

Unveiling the functional roles of patient-derived tumour organoids in assessing the tumour microenvironment and immunotherapy

Recent studies have established the pivotal roles of patient-derived tumour organoids (PDTOs), innovative three-dimensional (3D) culture systems, in various biological and medical applications. PDTOs, as promising tools, have been established and extensively used for drug screening, prediction of immune response and assessment of immunotherapeutic effectiveness in various cancer types, including glioma, ovarian cancer and so on. The overarching goal is to facilitate the translation of new therapeutic modalities to guide personalised immunotherapy. Notably, there has been a recent surge of interest in the co-culture of PDTOs with immune cells to investigate the dynamic interactions between tumour cells and immune microenvironment. A comprehensive and in-depth investigation is necessary to enhance our understanding of PDTOs as promising testing platforms for cancer immunotherapy. This review mainly focuses on the latest updates on the applications and challenges of PDTO-based methods in anti-cancer immune responses. We strive to provide a comprehensive understanding of the potential and prospects of PDTO-based technologies as next-generation strategies for advancing immunotherapy approaches.

Kidney organoids: steps towards better organization and function

Kidney organoids - 3D representations of kidneys made either from pluripotent or tissue stem cells - have been available for well over a decade. Their application could confer notable benefits over longstanding in vivo approaches with the potential for clinically aligned human cells and reduced ethical burdens. They been used, at a proof-of-concept level, in development in disease modeling (including with patient-derived stem cells), and in screening drugs for efficacy/toxicity. They differ from real kidneys: they represent only foetal-stage tissue, in their simplest forms they lack organ-scale anatomical organization, they lack a properly arranged vascular system, and include non-renal cells. Cell specificity may be improved by better techniques for differentiation and/or sorting. Sequential assembly techniques that mimic the sequence of natural development, and localized sources of differentiation-inducing signals, improve organ-scale anatomy. Organotypic vascularization remains a challenge: capillaries are easy, but the large vessels that should serve them are absent from organoids and, even in cultured real kidneys, these large vessels do not survive without blood flow. Transplantation of organoids into hosts results in their being vascularized (though probably not organotypically) and in some renal function. It will be important to transplant more advanced organoids, with a urine exit, in the near future to assess function more stringently. Transplantation of human foetal kidneys, followed by nephrectomy of host kidneys, keeps rats alive for many weeks, raising hope that, if organoids can be produced even to the limited size and complexity of foetal kidneys, they may one day be useful in renal replacement.

Generating kidney organoids based on developmental nephrology

Over the past decade, the induction protocols for the two types of kidney organoids (nephron organoids and ureteric bud organoids) from pluripotent stem cells (PSCs) have been established based on the knowledge gained in developmental nephrology. Kidney organoids are now used for disease modeling and drug screening, but they also have potential as tools for clinical transplantation therapy. One of the options to achieve this goal would be to assemble multiple renal progenitor cells (nephron progenitor, ureteric bud, stromal progenitor) to reproduce the organotypic kidney structure from PSCs. At least from mouse PSCs, all the three progenitors have been induced and assembled into such "higher order" kidney organoids. We will provide an overview of the developmental nephrology required for the induction of renal progenitors and discuss recent advances and remaining challenges of kidney organoids for clinical transplantation therapy.

Highly parallel production of designer organoids by mosaic patterning of progenitors

Organoids derived from human stem cells are a promising approach for disease modeling, regenerative medicine, and fundamental research. However, organoid variability and limited control over morphological outcomes remain as challenges. One open question is the extent to which engineering control over culture conditions can guide organoids to specific compositions. Here, we extend a DNA "velcro" cell patterning approach, precisely controlling the number and ratio of human induced pluripotent stem cell-derived progenitors contributing to nephron progenitor (NP) organoids and mosaic NP/ureteric bud (UB) tip cell organoids within arrays of microwells. We demonstrate long-term control over organoid size and morphology, decoupled from geometric constraints. We then show emergent trends in organoid tissue proportions that depend on initial progenitor cell composition. These include higher nephron and stromal cell representation in mosaic NP/UB organoids vs. NP-only organoids and a "goldilocks" initial cell ratio in mosaic organoids that optimizes the formation of proximal tubule structures.

Advancements in Research on Genetic Kidney Diseases Using Human-Induced Pluripotent Stem Cell-Derived Kidney Organoids

Genetic or hereditary kidney disease stands as a pivotal cause of chronic kidney disease (CKD). The proliferation and widespread utilization of DNA testing in clinical settings have notably eased the diagnosis of genetic kidney diseases, which were once elusive but are now increasingly identified in cases previously deemed CKD of unknown etiology. However, despite these diagnostic strides, research into disease pathogenesis and novel drug development faces significant hurdles, chiefly due to the dearth of appropriate animal models and the challenges posed by limited patient cohorts in clinical studies. Conversely, the advent and utilization of human-induced pluripotent stem cells (hiPSCs) offer a promising avenue for genetic kidney disease research. Particularly, the development of hiPSC-derived kidney organoid systems presents a novel platform for investigating various forms of genetic kidney diseases. Moreover, the integration of the CRISPR/Cas9 technique into this system holds immense potential for efficient research on genetic kidney diseases. This review aims to explore the applications of in vitro kidney organoids generated from hiPSCs in the study of diverse genetic kidney diseases. Additionally, it will delve into the limitations of this research platform and outline future perspectives for advancing research in this crucial area.

Induced pluripotent stem cells derived renal tubular cells from a patient with pseudohypoparathyroidism and its response to parathyroid hormone stimulation

INTRODUCTION

Creating induced pluripotent stem cells (iPSCs) from somatic cells of patients with genetic diseases offers a pathway to generate disease-specific iPSCs carrying genetic markers. Differentiating these iPSCs into renal tubular cells can aid in understanding the pathophysiology of rare inherited renal tubular diseases through cellular experiments.

MATERIALS AND METHODS

Two Japanese patients with Pseudohypoparathyroidism (PHP), a 49-year-old woman and a 71-year-old man, were studied. iPSC-derived tubular cells were established from their peripheral blood mononuclear cells (PBMCs). We examined changes in intracellular and extracellular cyclic adenosine monophosphate (cAMP) levels in these cells in response to parathyroid hormone (PTH) stimulation.

RESULTS

Renal tubular cells, differentiated from iPSCs of a healthy control (648A1), showed a PTH-dependent increase in both intracellular and extracellular cAMP levels. However, the renal tubular cells derived from the PHP patients' iPSCs showed inconsistent changes in cAMP levels upon PTH exposure.

CONCLUSION

We successfully created disease-specific iPSCs from PHP patients' PBMCs, differentiated them into tubular cells, and replicated the distinctive response of the disease to PTH in vitro. This approach could enhance our understanding of the pathophysiology of inherited renal tubular diseases and contribute to developing effective treatments.

Cadherin Adhesion Complexes Direct Cell Aggregation in the Epithelial Transition of Wnt-Induced Nephron Progenitor Cells

In the developing mammalian kidney, nephron formation is initiated by a subset of nephron progenitor cells (NPCs). Wnt input activates a β-catenin ( Ctnnb1 )-driven, transcriptional nephrogenic program. In conjunction, induced mesenchymal NPCs transition through a pre-tubular aggregate to an epithelial renal vesicle, the precursor for each nephron. How this critical mesenchymal-to-epithelial transition (MET) is regulated is unclear. In an in vitro mouse NPC culture model, activation of the Wnt pathway results in the aggregation of induced NPCs into closely-packed, cell clusters. Genetic removal of β-catenin resulted in a failure of both Wnt pathway-directed transcriptional activation and the formation of aggregated cell clusters. Modulating extracellular Ca 2+ levels showed cell-cell contacts were Ca 2+ -dependent, suggesting a role for cadherin (Cdh)-directed cell adhesion. Molecular analysis identified Cdh2 , Cdh4 and Cdh11 in uninduced NPCs and the up-regulation of Cdh3 and Cdh4 accompanying the Wnt pathway-induced MET. Genetic removal of all four cadherins, and independent removal of α-catenin, which couples Cdh-β-catenin membrane complexes to the actin cytoskeleton, abolished cell aggregation in response to Wnt pathway activation. However, the β-catenin driven inductive transcriptional program was unaltered. Together with the accompanying paper (Bugacov et al ., submitted), these data demonstrate that distinct cellular activities of β-catenin - transcriptional regulation and cell adhesion - combine in the mammalian kidney programs generating differentiated epithelial nephron precursors from mesenchymal nephron progenitors.

Summary statement

Our study highlights the role of Wnt-β-catenin pathway regulation of cadherin-mediated cell adhesion in the mesenchymal to epithelial transition of induced nephron progenitor cells.