Organoid-on-a-chip model of human ARPKD reveals mechanosensing pathomechanisms for drug discovery

Genetically modified organoids for tissue engineering and regenerative medicine

To date, genetically modified organoids are emerging as a promising 3D modeling tool aimed at solving genetically relevant clinical and biomedical problems for regenerative medicine and tissue engineering. As an optimal vehicle for gene delivery, genetically modified organoids can enhance or reduce the expression of target genes through virus and non-virus-based gene transfection methods to achieve tissue regeneration. Animal experiments and preclinical studies have demonstrated the beneficial role of genetically modified organoids in various aspects of organ regeneration, including thymus, lacrimal glands, brain, lung, kidney, photoreceptors, etc. Furthermore, the technology offers a potential treatment option for various diseases, such as Fabry disease, non-alcoholic steatohepatitis, and Lynch syndrome. Nevertheless, the uncertain safety of genetic modification, the risk of organoid application, and bionics of current genetically modified organoids are still challenging. This review summarizes the researches on genetically modified organoids in recent years, and describes the transfection methods and functions of genetically modified organoids, then introduced their applications at length. Also, the limitations and future development directions of genetically modified organoids are included.

Progress in the Application of Organoids-On-A-Chip in Diseases

With the rapid development of the field of life sciences, traditional 2D cell culture and animal models have long been unable to meet the urgent needs of modern biomedical research and new drug development. Establishing a new generation of experimental models and research models is of great significance for deeply understanding human health and disease processes, and developing effective treatment measures. As is well known, long research and development cycles, high risks, and high costs are the "three mountains" facing the development of new drugs today. Organoids and organ-on-chips technology can highly simulate and reproduce the human physiological environment and complex reactions in vitro, greatly improving the accuracy of drug clinical efficacy prediction, reducing drug development costs, and avoiding the defects of drug testing animal models. Therefore, organ-on-chips have enormous potential in medical diagnosis and treatment.

3D Bioprinting for Engineered Tissue Constructs and Patient-Specific Models: Current Progress and Prospects in Clinical Applications

Advancements in bioprinting technology are driving the creation of complex, functional tissue constructs for use in tissue engineering and regenerative medicine. Various methods, including extrusion, jetting, and light-based bioprinting, have their unique advantages and drawbacks. Over the years, researchers and industry leaders have made significant progress in enhancing bioprinting techniques and materials, resulting in the production of increasingly sophisticated tissue constructs. Despite this progress, challenges still need to be addressed in achieving clinically relevant, human-scale tissue constructs, presenting a hurdle to widespread clinical translation. However, with ongoing interdisciplinary research and collaboration, the field is rapidly evolving and holds promise for personalized medical interventions. Continued development and refinement of bioprinting technologies have the potential to address complex medical needs, enabling the development of functional, transplantable tissues and organs, as well as advanced in vitro tissue models.

Ciliopathy organoid models: a comprehensive review

Cilia are membrane-bound organelles found on the surface of most mammalian cell types and play numerous roles in human physiology and development, including osmo- and mechanosensation, as well as signal transduction. Ciliopathies are a large group of, usually rare, genetic disorders resulting from abnormal ciliary structure or ciliary dysfunction that have a high collective prevalence. Autosomal dominant or recessive polycystic kidney disease (ADPKD/ARPKD), Bardet-Biedl-Syndrome, and primary ciliary dyskinesia (PCD) are the most frequent etiologies. Rodent and zebrafish models have improved the understanding of ciliopathy pathophysiology. Yet, the limitations of these genetically modified animal strains include the inability to fully replicate the phenotypic heterogeneity found in humans, including variable multiorgan involvement. Organoids, self-assembled three-dimensional cell-based models derived from human induced pluripotent stem cells (iPSCs) or primary tissues, can recapitulate certain aspects of the development, architecture, and function of the target organ "in the dish." The potential of organoids to model patient-specific genotype-phenotype correlations has increased their popularity in ciliopathy research and led to the first preclinical organoid-based ciliopathy drug screens. This review comprehensively summarizes and evaluates current ciliopathy organoid models, focusing on kidney, airway, liver, and retinal organoids, as well as the specific methodologies used for their cultivation and for interrogating ciliary dysfunction.

Epigenetics of Hypertensive Nephropathy

Hypertensive nephropathy (HN) is a leading cause of chronic kidney disease (CKD) and end-stage renal disease (ESRD), contributing to significant morbidity, mortality, and rising healthcare costs. In this review article, we explore the role of epigenetic mechanisms in HN progression and their potential therapeutic implications. We begin by examining key epigenetic modifications-DNA methylation, histone modifications, and non-coding RNAs-observed in kidney disease. Next, we discuss the underlying pathophysiology of HN and highlight current in vitro and in vivo models used to study the condition. Finally, we compare various types of HN-induced renal injury and their associated epigenetic mechanisms with those observed in other kidney injury models, drawing inferences on potential epigenetic therapies for HN. The information gathered in this work indicate that epigenetic mechanisms can drive the progression of HN by regulating key molecular signaling pathways involved in renal damage and fibrosis. The limitations of Renin-Angiotensin-Aldosterone System (RAAS) inhibitors underscore the need for alternative treatments targeting epigenetic pathways. This review emphasizes the importance of further research into the epigenetic regulation of HN to develop more effective therapies and preventive strategies. Identifying novel epigenetic markers could provide new therapeutic opportunities for managing CKD and reducing the burden of ESRD.

Flavonoids attenuate inflammation of HGF and HBMSC while modulating the osteogenic differentiation based on microfluidic chip

BACKGROUND

When inflammation occurs in periodontal tissues, a dynamic cellular crosstalk interacts between gingival fibroblasts and bone marrow mesenchymal stem cells (BMSCs), which plays a crucial role in the biological behaviour and differentiation of the cells. Recently, flavonoids are increasingly recognized for their therapeutic potential in modulating inflammation and osteogenic differentiation. Owing to their varied molecular structures and mechanisms, there are more needs that flavonoid compounds should be identified by extensive screening. However, current drug research mostly relies on static, single-type cell cultures. In this study, an innovative bionic microfluidic chip system tailored for both soft and hard tissues was developed to screen for flavonoids suitable for treating periodontitis.

METHODS

This study developed a microfluidic system that bionically simulates the soft and hard structures of periodontal tissues. Live/dead staining, reactive oxygen species (ROS) staining, and RT-qPCR analysis were employed. These techniques evaluated the effects of flavonoid compounds on the levels of inflammatory factors and ROS contents in HGF and HBMSC under LPS stimulation. Additionally, the impact of these compounds on osteogenic induction in HBMSC and the exploration of the underlying mechanisms were assessed.

RESULTS

The microfluidic chip used in this study features dual chambers separated by a porous membrane, allowing cellular signal communication via bioactive factors secreted by cells in both layers under perfusion. The inflammatory response within the chip under LPS stimulation was lower compared to individual static cultures of HGF and HBMSC. The selected flavonoids-myricetin, catechin, and quercetin-significantly reduced cellular inflammation, decreased ROS levels, and enhanced osteogenic differentiation of BMSCs. Additionally, fisetin, silybin, and icariside II also demonstrated favorable outcomes in reducing inflammation, lowering ROS levels, and promoting osteogenic differentiation through the Wnt/β-catenin pathway.

CONCLUSIONS

The bionic microfluidic chip system provides enhanced capabilities for drug screening and evaluation, delivering a more precise assessment of drug efficacy and safety compared to traditional in vitro methods. This study demonstrates the efficacy of flavonoids in influencing osteogenic processes in BMSCs primarily through the Wnt/β-catenin pathway. These results uncover the potential of flavonoids as therapeutic medicine for treating periodontitis, meriting further research and development.

Scalable production of uniform and mature organoids in a 3D geometrically-engineered permeable membrane

The application of organoids has been limited by the lack of methods for producing uniformly mature organoids at scale. This study introduces an organoid culture platform, called UniMat, which addresses the challenges of uniformity and maturity simultaneously. UniMat is designed to not only ensure consistent organoid growth but also facilitate an unrestricted supply of soluble factors by a 3D geometrically-engineered, permeable membrane-based platform. Using UniMat, we demonstrate the scalable generation of kidney organoids with enhanced uniformity in both structure and function compared to conventional methods. Notably, kidney organoids within UniMat show improved maturation, showing increased expression of nephron transcripts, more in vivo-like cell-type balance, enhanced vascularization, and better long-term stability. Moreover, UniMat's design offers a more standardized organoid model for disease modeling and drug testing, as demonstrated by polycystic-kidney disease and acute kidney injury modeling. In essence, UniMat presents a valuable platform for organoid technology, with potential applications in organ development, disease modeling, and drug screening.

Dynamic Kidney Organoid Microphysiological Analysis Platform

Kidney organoids, replicating human development, pathology, and drug responses, are a promising model for advancing bioscience and pharmaceutical innovation. However, reproducibility, accuracy, and quantification challenges hinder their broader utility for advanced biological and pharmaceutical applications. Herein, we present a dynamic kidney organoid microphysiological analysis platform (MAP), designed to enhance organoid modeling and assays within physiologically relevant environments, thereby expanding their utility in advancing kidney physiology and pathology research. First, precise control of the dynamic microenvironment in MAP enhances the ability to fine-tune nephrogenic intricacies, facilitating high-throughput and reproducible human kidney organoid development. Also, MAP's miniaturization of kidney organoids significantly advances pharmaceutical research by allowing for detailed analysis of entire nephron segments, which is crucial for assessing the nephrotoxicity and safety of drugs. Furthermore, the MAP's application in disease modeling faithfully recapitulates pathological development and functions as a valuable testbed for therapeutic exploration in polycystic kidney diseases. We envision the kidney organoid MAP enhancing pharmaceutical research, standardizing processes, and improving analytics, thereby elevating the quality and utility of organoids in biology, pharmacology, precision medicine, and education.

Molecular characterization of PANoptosis-related genes in chronic kidney disease

Chronic kidney disease (CKD) is characterized by fibrosis and inflammation in renal tissues. Several types of cell death have been implicated in CKD onset and progression. Unlike traditional forms of cell death, PANoptosis is characterized by the crosstalk among programmed cell death pathways. However, the interaction between PANoptosis and CKD remains unclear. Here, we used bioinformatics methods to identify differentially expressed genes and differentially expressed PANoptosis-related genes (DE-PRGs) using data from the GSE37171 dataset. Following this, we further performed gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, and gene set enrichment analysis using the data. We adopted a combined approach to select hub genes, using the STRING database and CytoHubba plug-in, and we used the GSE66494 as a validation dataset. In addition, we constructed ceRNA, transcription factor (TF)-gene, and drug-gene networks using Cytoscape. Lastly, we conducted immunohistochemical analysis and western blotting to validate the hub genes. We identified 57 PANoptosis-associated genes as DE-PRGs. We screened nine hub genes from the 57 DE-PRGs. We identified two hub genes (FOS and PTGS2) using the GSE66494 database, Nephroseq, immunohistochemistry, and western blotting. A common miRNA (Hsa-miR-101-3p) and three TFs (CREB1, E2F1, and RELA) may play a crucial role in the onset and progression of PANoptosis-related CKD. In our analysis of the drug-gene network, we identified eight drugs targeting FOS and 52 drugs targeting PTGS2.

Organoids-On-a-Chip for Personalized Precision Medicine

The development of personalized precision medicine has become a pivotal focus in modern healthcare. Organoids-on-a-Chip (OoCs), a groundbreaking fusion of organoid culture and microfluidic chip technology, has emerged as a promising approach to advancing patient-specific treatment strategies. In this review, the diverse applications of OoCs are explored, particularly their pivotal role in personalized precision medicine, and their potential as a cutting-edge technology is highlighted. By utilizing patient-derived organoids, OoCs offer a pathway to optimize treatments, create precise disease models, investigate disease mechanisms, conduct drug screenings, and individualize therapeutic strategies. The emphasis is on the significance of this technological fusion in revolutionizing healthcare and improving patient outcomes. Furthermore, the transformative potential of personalized precision medicine, future prospects, and ongoing advancements in the field, with a focus on genomic medicine, multi-omics integration, and ethical frameworks are discussed. The convergence of these innovations can empower patients, redefine treatment approaches, and shape the future of healthcare.

Xenotransplantation - a shortcut to construct tissue complexity in organoids

Our knowledge of human biology is mainly originated from studies using animal models. However, interspecies differences between human and model organisms may lead to imprecise extrapolation of results obtained from model organisms. Organoids are three-dimensional cell clusters derived from pluripotent or adult stem cells that self-organize into organ-like structures reminiscent of the cognate organ. The establishment of human organoids makes it possible to study organ or tissue pathophysiology that is specific to human beings. However, most organoids do not have organ-specific vasculature, neurons, and immune cells, hence limiting their utility in emulating complex pathophysiological phenotypes. Among the various approaches to address these limitations, xenotransplantation represents a promising 'shortcut'. We will discuss recent advance in constructing tissue complexity in organoids, with a special focus on xenotransplantation.

Regulation of Enterocyte Brush Border Membrane Primary Na-Absorptive Transporters in Human Intestinal Organoid-Derived Monolayers

In the small intestine, sodium (Na) absorption occurs primarily via two apical transporters, Na-hydrogen exchanger 3 (NHE3) and Na-glucose cotransporter 1 (SGLT1). The two primary Na-absorptive pathways were previously shown to compensatorily regulate each other in rabbit and rat intestinal epithelial cells. However, whether NHE3 and SGLT1 regulate one another in normal human enterocytes is unknown, mainly due to a lack of appropriate experimental models. To investigate this, we generated 2D enterocyte monolayers from human jejunal 3D organoids and used small interfering RNAs (siRNAs) to knock down NHE3 or SGLT1. Molecular and uptake studies were performed to determine the effects on NHE3 and SGLT1 expression and activity. Knockdown of NHE3 by siRNA in enterocyte monolayers was verified by qPCR and Western blot analysis and resulted in reduced NHE3 activity. However, in NHE3 siRNA-transfected cells, SGLT1 activity was significantly increased. siRNA knockdown of SGLT1 was confirmed by qPCR and Western blot analysis and resulted in reduced SGLT1 activity. However, in SGLT1 siRNA-transfected cells, NHE3 activity was significantly increased. These results demonstrate for the first time the functionality of siRNA in patient-derived organoid monolayers. Furthermore, they show that the two primary Na absorptive pathways in human enterocytes reciprocally regulate one another.

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.

Establishment of advanced tumor organoids with emerging innovative technologies

Tumor organoids have emerged as a crucial preclinical model for multiple cancer research. Their high establishment rates, stability, and ability to replicate key biological features of original tumor cells in vivo render them invaluable for exploring tumor molecular mechanisms, discovering potential anti-tumor drugs, and predicting clinical drug efficacy. Here, we review the establishment of tumor organoid models and provide an extensive overview of organoid culturing strategies. We also emphasize the significance of integrating cellular components of the tumor microenvironment and physicochemical factors in the organoid culturing system, highlighting the importance of artificial intelligence technology in advancing organoid construction. Moreover, we summarize recent advancements in utilizing organoid systems for novel anti-cancer drug screening and discuss promising trends for enhancing advanced organoids in next-generation disease modeling.

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.

Advances in Microfluidic Technologies in Organoid Research

Organoids have emerged as major technological breakthroughs and novel organ models that have revolutionized biomedical research by recapitulating the key structural and functional complexities of their in vivo counterparts. The combination of organoid systems and microfluidic technologies has opened new frontiers in organoid engineering and offers great opportunities to address the current challenges of existing organoid systems and broaden their biomedical applications. In this review, the key features of the existing organoids, including their origins, development, design principles, and limitations, are described. Then the recent progress in integrating organoids into microfluidic systems is highlighted, involving microarrays for high-throughput organoid manipulation, microreactors for organoid hydrogel scaffold fabrication, and microfluidic chips for functional organoid culture. The opportunities in the nascent combination of organoids and microfluidics that lie ahead to accelerate research in organ development, disease studies, drug screening, and regenerative medicine are also discussed. Finally, the challenges and future perspectives in the development of advanced microfluidic platforms and modified technologies for building organoids with higher fidelity and standardization are envisioned.

Genetic landscape and clinical outcomes of autosomal recessive polycystic kidney disease in Kuwait

Background

Autosomal recessive polycystic kidney disease (ARPKD), a rare genetic disorder characterized by kidney cysts, shows complex clinical and genetic heterogeneity. This study aimed to explore the genetic landscape of ARPKD in Kuwait and examine the intricate relationship between its genes and clinical presentation to enhance our understanding and contribute towards more efficient management strategies for ARPKD.

Methods

This study recruited 60 individuals with suspected ARPKD from 44 different families in Kuwait. The participants were of different ethnicities and aged 0-70 years. Additionally, 33 were male, 15 were female, and 12 had indeterminant sex due to congenital anomalies. Comprehensive clinical data were collected. Mutations were identified by next-generation whole exome sequencing and confirmed using Sanger sequencing.

Results

Of the 60 suspected ARPKD cases, 20 (33.3 %) died within hours of birth or by the end of the first month of life and one (1.7 %) within 12 months of birth. The remaining 39 (65.0 %) cases were alive, at the time of the study, and exhibited diverse clinical features related to ARPKD, including systematic hypertension (5.0 %), pulmonary hypoplasia (11.7 %), dysmorphic features (40.0 %), cardiac problems (8.3 %), cystic liver (5.0 %), Potter syndrome (13.3 %), developmental delay (8.3 %), and enlarged cystic kidneys (100 %). Twelve mutations, including novel truncating mutations, were identified in 31/60 cases (51.7 %) from 17/44 families (38.6 %). Additionally, 8/12 (66.7 %) mutations were in the PKHD1 gene, with the remaining four in different genes: NPHP3, VPS13P, CC2D2A, and ZNF423.

Conclusions

This study highlights the spectrum of clinical features and genetic mutations of patients with ARPKD in Kuwait. It highlights the necessity for personalized approaches to improve ARPKD diagnosis and treatment, offering crucial insights into managing ARPKD.

A perfusable, vascularized kidney organoid-on-chip model

The ability to controllably perfuse kidney organoids would better recapitulate the native tissue microenvironment for applications ranging from drug testing to therapeutic use. Here, we report a perfusable, vascularized kidney organoid on chip model composed of two individually addressable channels embedded in an extracellular matrix (ECM). The channels are respectively seeded with kidney organoids and human umbilical vein endothelial cells that form a confluent endothelium (macrovessel). During perfusion, endogenous endothelial cells present within the kidney organoids migrate through the ECM towards the macrovessel, where they form lumen-on-lumen anastomoses that are supported by stromal-like cells. Once micro-macrovessel integration is achieved, we introduced fluorescently labeled dextran of varying molecular weight and red blood cells into the macrovessel, which are transported through the microvascular network to the glomerular epithelia within the kidney organoids. Our approach for achieving controlled organoid perfusion opens new avenues for generating other perfused human tissues.

Decoupling shear stress and pressure effects in the biomechanics of autosomal dominant polycystic kidney disease using a perfused kidney-on-chip

Kidney tubular cells are submitted to two distinct mechanical forces generated by the urine flow: shear stress and hydrostatic pressure. In addition, the mechanical properties of the surrounding extracellular matrix modulate tubule deformation under constraints. These mechanical factors likely play a role in the pathophysiology of kidney diseases as exemplified by autosomal dominant polycystic kidney disease, in which pressure, flow and matrix stiffness have been proposed to modulate the cystic dilation of tubules with PKD1 mutations. The lack of in vitro systems recapitulating the mechanical environment of kidney tubules impedes our ability to dissect the role of these mechanical factors. Here we describe a perfused kidney-on-chip with tunable extracellular matrix mechanical properties and hydrodynamic constraints, that allows a decoupling of shear stress and flow. We used this system to dissect how these mechanical cues affect Pkd1 -/- tubule dilation. Our results show two distinct mechanisms leading to tubular dilation. For PCT cells (proximal tubule), overproliferation mechanically leads to tubular dilation, regardless of the mechanical context. For mIMCD-3 cells (collecting duct), tube dilation is associated with a squamous cell morphology but not with overproliferation and is highly sensitive to extracellular matrix properties and hydrodynamic constraints. Surprisingly, flow alone suppressed Pkd1 -/- mIMCD-3 tubule dilation observed in static conditions, while the addition of luminal pressure restored it. Our in vitro model emulating nephron geometrical and mechanical organization sheds light on the roles of mechanical constraints in ADPKD and demonstrates the importance of controlling intraluminal pressure in kidney tubule models.

Role of biophysics and mechanobiology in podocyte physiology

Podocytes form the backbone of the glomerular filtration barrier and are exposed to various mechanical forces throughout the lifetime of an individual. The highly dynamic biomechanical environment of the glomerular capillaries greatly influences the cell biology of podocytes and their pathophysiology. Throughout the past two decades, a holistic picture of podocyte cell biology has emerged, highlighting mechanobiological signalling pathways, cytoskeletal dynamics and cellular adhesion as key determinants of biomechanical resilience in podocytes. This biomechanical resilience is essential for the physiological function of podocytes, including the formation and maintenance of the glomerular filtration barrier. Podocytes integrate diverse biomechanical stimuli from their environment and adapt their biophysical properties accordingly. However, perturbations in biomechanical cues or the underlying podocyte mechanobiology can lead to glomerular dysfunction with severe clinical consequences, including proteinuria and glomerulosclerosis. As our mechanistic understanding of podocyte mechanobiology and its role in the pathogenesis of glomerular disease increases, new targets for podocyte-specific therapeutics will emerge. Treating glomerular diseases by targeting podocyte mechanobiology might improve therapeutic precision and efficacy, with potential to reduce the burden of chronic kidney disease on individuals and health-care systems alike.

Investigational agents for autosomal dominant polycystic kidney disease: preclinical and early phase study insights

INTRODUCTION

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is the most common inherited kidney condition caused by a single-gene mutation. It leads patients to kidney failure in more than 50% of cases by the age of 60, and, given the dominant inheritance, this disease is present in the family history in more than 90% of cases.

AREAS COVERED

This review aims to analyze the set of preclinical and early-phase studies to provide a general view of the current progress on ADPKD therapeutic options. Articles from PubMed and the current status of the trials listed in clinicaltrials.gov were examined for the review.

EXPERT OPINION

Many potential therapeutic targets are currently under study for the treatment of ADPKD. A few drugs have reached the clinical phase, while many are currently still in the preclinical phase. Organoids could be a novel approach to the study of drugs in this phase. Other than pharmacological options, very important developing approaches are represented by gene therapy and the use of MiRNA inhibitors.

Advancing preclinical drug evaluation through automated 3D imaging for high-throughput screening with kidney organoids

High-throughput drug screening is crucial for advancing healthcare through drug discovery. However, a significant limitation arises from availablein vitromodels using conventional 2D cell culture, which lack the proper phenotypes and architectures observed in three-dimensional (3D) tissues. Recent advancements in stem cell biology have facilitated the generation of organoids-3D tissue constructs that mimic human organsin vitro. Kidney organoids, derived from human pluripotent stem cells, represent a significant breakthrough in disease representation. They encompass major kidney cell types organized within distinct nephron segments, surrounded by stroma and endothelial cells. This tissue allows for the assessment of structural alterations such as nephron loss, a characteristic of chronic kidney disease. Despite these advantages, the complexity of 3D structures has hindered the use of organoids for large-scale drug screening, and the drug screening pipelines utilizing these complexin vitromodels remain to be established for high-throughput screening. In this study, we address the technical limitations of kidney organoids through fully automated 3D imaging, aided by a machine-learning approach for automatic profiling of nephron segment-specific epithelial morphometry. Kidney organoids were exposed to the nephrotoxic agent cisplatin to model severe acute kidney injury. An U.S. Food and Drug Administration (FDA)-approved drug library was tested for therapeutic and nephrotoxicity screening. The fully automated pipeline of 3D image acquisition and analysis identified nephrotoxic or therapeutic drugs during cisplatin chemotherapy. The nephrotoxic potential of these drugs aligned with previousin vivoand human reports. Additionally, Imatinib, a tyrosine kinase inhibitor used in hematological malignancies, was identified as a potential preventive therapy for cisplatin-induced kidney injury. Our proof-of-concept report demonstrates that the automated screening process, using 3D morphometric assays with kidney organoids, enables high-throughput screening for nephrotoxicity and therapeutic assessment in 3D tissue constructs.

Advancements in therapeutic development: kidney organoids and organs on a chip

The use of animal models in therapeutic development has long been the standard practice. However, ethical concerns and the inherent species differences have prompted a reevaluation of the experimental approach in human disease studies. The urgent need for alternative model systems that better mimic human pathophysiology has led to the emergence of organoids, innovative in vitro models, to simulate human organs in vitro. These organoids have gained widespread acceptance in disease models and drug development research. In this mini review, we explore the recent strides made in kidney organoid differentiation and highlight the synergistic potential of incorporating organ-on-chip systems. The emergent use of microfluidic devices reveals the importance of fluid flow in the maturation of kidney organoids and helps decipher pathomechanisms in kidney diseases. Recent research has uncovered their potential applications across a wide spectrum of kidney research areas, including hemodynamic forces at stake in kidney health and disease, immune cell infiltration, or drug delivery and toxicity. This convergence of cutting-edge technologies not only holds promise for expediting therapeutic development but also reflects an acknowledgment of the need to embrace innovative and more human-centric research models.

Advances and potential of regenerative medicine in pediatric nephrology

The endogenous capacity of the kidney to repair is limited, and generation of new nephrons after injury for adequate function recovery remains a need. Discovery of factors that promote the endogenous regenerative capacity of the injured kidney or generation of transplantable kidney tissue represent promising therapeutic strategies. While several encouraging results are obtained after administration of stem or progenitor cells, stem cell secretome, or extracellular vesicles in experimental kidney injury models, very little data exist in the clinical setting to make conclusions about their efficacy. In this review, we provide an overview of the cutting-edge knowledge on kidney regeneration, including pre-clinical methodologies used to elucidate regenerative pathways and describe the perspectives of regenerative medicine for kidney patients.

Organoids and organoids-on-a-chip as the new testing strategies for environmental toxicology-applications & advantages

An increasing number of harmful environmental factors are causing serious impacts on human health, and there is an urgent need to accurately identify the toxic effects and mechanisms of these harmful environmental factors. However, traditional toxicity test methods (e.g., animal models and cell lines) often fail to provide accurate results. Fortunately, organoids differentiated from stem cells can more accurately, sensitively and specifically reflect the effects of harmful environmental factors on the human body. They are also suitable for specific studies and are frequently used in environmental toxicology nowadays. As a combination of organoids and organ-on-a-chip technology, organoids-on-a-chip has great potential in environmental toxicology. It is more controllable to the physicochemical microenvironment and is not easy to be contaminated. It has higher homogeneity in the size and shape of organoids. In addition, it can achieve vascularization and exchange the nutrients and metabolic wastes in time. Multi-organoids-chip can also simulate the interactions of different organs. These advantages can facilitate better function and maturity of organoids, which can also make up for the shortcomings of common organoids to a certain extent. This review firstly discussed the limitations of traditional toxicology testing platforms, leading to the introduction of new platforms: organoids and organoids-on-a-chip. Next, the applications of different organoids and organoids-on-a-chip in environmental toxicology were summarized and prospected. Since the advantages of the new platforms have not been sufficiently considered in previous literature, we particularly emphasized them. Finally, this review also summarized the opportunities and challenges faced by organoids and organoids-on-a-chip, with the expectation that readers will gain a deeper understanding of their value in the field of environmental toxicology.

Engineering physiological environments to advance kidney organoid models from human pluripotent stem cells

During embryogenesis, the mammalian kidney arises because of reciprocal interactions between the ureteric bud (UB) and the metanephric mesenchyme (MM), driving UB branching and nephron induction. These morphogenetic processes involve a series of cellular rearrangements that are tightly controlled by gene regulatory networks and signaling cascades. Here, we discuss how kidney developmental studies have informed the definition of procedures to obtain kidney organoids from human pluripotent stem cells (hPSCs). Moreover, bioengineering techniques have emerged as potential solutions to externally impose controlled microenvironments for organoid generation from hPSCs. Next, we summarize some of these advances with major focus On recent works merging hPSC-derived kidney organoids (hPSC-kidney organoids) with organ-on-chip to develop robust models for drug discovery and disease modeling applications. We foresee that, in the near future, coupling of different organoid models through bioengineering approaches will help advancing to recreate organ-to-organ crosstalk to increase our understanding on kidney disease progression in the human context and search for new therapeutics.

Open-Source System for Real-Time Functional Assessment of In Vitro Filtration Barriers

The integrity of the barrier between blood and the selective filtrate of solutes is important for homeostasis and its disruption contributes to many diseases. Microphysiological systems that incorporate synthetic or natural membranes with human cells can mimic biological filtration barriers, such as the glomerular filtration barrier in the kidney, and they can readily be used to study cellular filtration processes as well as drug effects and interactions. We present an affordable, open-source platform for the real-time monitoring of functional filtration status in engineered microphysiological systems. Using readily available components, our assay can linearly detect real-time concentrations of two target molecules, FITC-labeled inulin and Texas Red-labeled human-serum albumin, within clinically relevant ranges, and it can be easily modified for different target molecules of varying sizes and tags. We demonstrate the platform's ability to determine the concentration of our target molecules automatically and consistently. We show through an acellular context that the platform enables real-time tracking of size-dependent diffusion with minimal fluid volume loss and without manual extraction of media, making it suitable for continuous operational monitoring of filtration status in microphysiological system applications. The platform's affordability and integrability with microphysiological systems make it ideal for many precision medicine applications, including evaluation of drug nephrotoxicity and other forms of drug discovery.

Microfluidics: a concise review of the history, principles, design, applications, and future outlook

Microfluidic technologies have garnered significant attention due to their ability to rapidly process samples and precisely manipulate fluids in assays, making them an attractive alternative to conventional experimental methods. With the potential for revolutionary capabilities in the future, this concise review provides readers with insights into the fascinating world of microfluidics. It begins by introducing the subject's historical background, allowing readers to familiarize themselves with the basics. The review then delves into the fundamental principles, discussing the underlying phenomena at play. Additionally, it highlights the different aspects of microfluidic device design, classification, and fabrication. Furthermore, the paper explores various applications, the global market, recent advancements, and challenges in the field. Finally, the review presents a positive outlook on trends and draws lessons to support the future flourishing of microfluidic technologies.

Kidney organoid models reveal cilium-autophagy metabolic axis as a therapeutic target for PKD both in vitro and in vivo

Human pluripotent stem cell-derived kidney organoids offer unprecedented opportunities for studying polycystic kidney disease (PKD), which still has no effective cure. Here, we developed both in vitro and in vivo organoid models of PKD that manifested tubular injury and aberrant upregulation of renin-angiotensin aldosterone system. Single-cell analysis revealed that a myriad of metabolic changes occurred during cystogenesis, including defective autophagy. Experimental activation of autophagy via ATG5 overexpression or primary cilia ablation significantly inhibited cystogenesis in PKD kidney organoids. Employing the organoid xenograft model of PKD, which spontaneously developed tubular cysts, we demonstrate that minoxidil, a potent autophagy activator and an FDA-approved drug, effectively attenuated cyst formation in vivo. This in vivo organoid model of PKD will enhance our capability to discover novel disease mechanisms and validate candidate drugs for clinical translation.

Advancements and application prospects of three-dimensional models for primary liver cancer: a comprehensive review

Primary liver cancer (PLC) is one of the most commonly diagnosed cancers worldwide and a leading cause of cancer-related deaths. However, traditional liver cancer models fail to replicate tumor heterogeneity and the tumor microenvironment, limiting the study and personalized treatment of liver cancer. To overcome these limitations, scientists have introduced three-dimensional (3D) culture models as an emerging research tool. These 3D models, utilizing biofabrication technologies such as 3D bioprinting and microfluidics, enable more accurate simulation of the in vivo tumor microenvironment, replicating cell morphology, tissue stiffness, and cell-cell interactions. Compared to traditional two-dimensional (2D) models, 3D culture models better mimic tumor heterogeneity, revealing differential sensitivity of tumor cell subpopulations to targeted therapies or immunotherapies. Additionally, these models can be used to assess the efficacy of potential treatments, providing guidance for personalized therapy. 3D liver cancer models hold significant value in tumor biology, understanding the mechanisms of disease progression, and drug screening. Researchers can gain deeper insights into the impact of the tumor microenvironment on tumor cells and their interactions with the surrounding milieu. Furthermore, these models allow for the evaluation of treatment responses, offering more accurate guidance for clinical interventions. In summary, 3D models provide a realistic and reliable tool for advancing PLC research. By simulating tumor heterogeneity and the microenvironment, these models contribute to a better understanding of the disease mechanisms and offer new strategies for personalized treatment. Therefore, 3D models hold promising prospects for future PLC research.

Organoid assessment technologies

Despite enormous advances in the generation of organoids, robust and stable protocols of organoids are still a major challenge to researchers. Research for assessing structures of organoids and the evaluations of their functions on in vitro or in vivo is often limited by precision strategies. A growing interest in assessing organoids has arisen, aimed at standardizing the process of obtaining organoids to accurately resemble human-derived tissue. The complex microenvironment of organoids, intricate cellular crosstalk, organ-specific architectures and further complicate functions urgently quest for high-through schemes. By utilizing multi-omics analysis and single-cell analysis, cell-cell interaction mechanisms can be deciphered, and their structures can be investigated in a detailed view by histological analysis. In this review, we will conclude the novel approaches to study the molecular mechanism and cell heterogeneity of organoids and discuss the histological and morphological similarity of organoids in comparison to the human body. Future perspectives on functional analysis will be developed and the organoids will become mature models.

Navigating the kidney organoid: insights into assessment and enhancement of nephron function

Kidney organoids are three-dimensional structures generated from pluripotent stem cells (PSCs) that are capable of recapitulating the major structures of mammalian kidneys. As this technology is expected to be a promising tool for studying renal biology, drug discovery, and regenerative medicine, the functional capacity of kidney organoids has emerged as a critical question in the field. Kidney organoids produced using several protocols harbor key structures of native kidneys. Here, we review the current state, recent advances, and future challenges in the functional characterization of kidney organoids, strategies to accelerate and enhance kidney organoid functions, and access to PSC resources to advance organoid research. The strategies to construct physiologically relevant kidney organoids include the use of organ-on-a-chip technologies that integrate fluid circulation and improve organoid maturation. These approaches result in increased expression of the major tubular transporters and elements of mechanosensory signaling pathways suggestive of improved functionality. Nevertheless, continuous efforts remain crucial to create kidney tissue that more faithfully replicates physiological conditions for future applications in kidney regeneration medicine and their ethical use in patient care.NEW & NOTEWORTHY Kidney organoids are three-dimensional structures derived from stem cells, mimicking the major components of mammalian kidneys. Although they show great promise, their functional capacity has become a critical question. This review explores the advancements and challenges in evaluating and enhancing kidney organoid function, including the use of organ-on-chip technologies, multiomics data, and in vivo transplantation. Integrating these approaches to further enhance their physiological relevance will continue to advance disease modeling and regenerative medicine applications.

Application of colloidal photonic crystals in study of organoids

As alternative disease models, other than 2D cell lines and patient-derived xenografts, organoids have preferable in vivo physiological relevance. However, both endogenous and exogenous limitations impede the development and clinical translation of these organoids. Fortunately, colloidal photonic crystals (PCs), which benefit from favorable biocompatibility, brilliant optical manipulation, and facile chemical decoration, have been applied to the engineering of organoids and have achieved the desirable recapitulation of the ECM niche, well-defined geometrical onsets for initial culture, in situ multiphysiological parameter monitoring, single-cell biomechanical sensing, and high-throughput drug screening with versatile functional readouts. Herein, we review the latest progress in engineering organoids fabricated from colloidal PCs and provide inputs for future research.

Elucidating the Proximal Tubule HNF4A Gene Regulatory Network in Human Kidney Organoids

SIGNIFICANCE STATEMENT

HNF4 genes promote proximal tubule differentiation in mice, but their function in human nephrogenesis is not fully defined. This study uses human pluripotent stem cell (PSC)-derived kidney organoids as a model to investigate HNF4A and HNF4G functions. The loss of HNF4A , but not HNF4G , impaired reabsorption-related molecule expression and microvilli formation in human proximal tubules. Cleavage under targets and release using nuclease (CUT&RUN) sequencing and CRISPR-mediated transcriptional activation (CRISPRa) further confirm that HNF4A directly regulates its target genes. Human kidney organoids provide a good model for studying transcriptional regulation in human kidney development.

BACKGROUND

The proximal tubule plays a major role in electrolyte homeostasis. Previous studies have shown that HNF4A regulates reabsorption-related genes and promotes proximal tubule differentiation during murine kidney development. However, the functions and gene regulatory mechanisms of HNF4 family genes in human nephrogenesis have not yet been investigated.

METHODS

We generated HNF4A -knock out (KO), HNF4G -KO, and HNF4A/4G -double KO human pluripotent stem cell lines, differentiated each into kidney organoids, and used immunofluorescence analysis, electron microscopy, and RNA-seq to analyze them. We probed HNF4A-binding sites genome-wide by cleavage under targets and release using nuclease sequencing in both human adult kidneys and kidney organoid-derived proximal tubular cells. Clustered Regularly Interspaced Short Palindromic Repeats-mediated transcriptional activation validated HNF4A and HNF4G function in proximal tubules during kidney organoid differentiation.

RESULTS

Organoids lacking HNF4A , but not HNF4G , showed reduced expression of transport-related, endocytosis-related, and brush border-related genes, as well as disorganized brush border structure in the apical lumen of the organoid proximal tubule. Cleavage under targets and release using nuclease revealed that HNF4A primarily bound promoters and enhancers of genes that were downregulated in HNF4A -KO, suggesting direct regulation. Induced expression of HNF4A or HNF4G by CRISPR-mediated transcriptional activation drove increased expression of selected target genes during kidney organoid differentiation.

CONCLUSIONS

This study reveals regulatory mechanisms of HNF4A and HNF4G during human proximal tubule differentiation. The experimental strategy can be applied more broadly to investigate transcriptional regulation in human kidney development.

Integration of Patient-Derived Organoids and Organ-on-Chip Systems: Investigating Colorectal Cancer Invasion within the Mechanical and GABAergic Tumor Microenvironment

Three-dimensional (3D) in vitro models are essential in cancer research, but they often neglect physical forces. In our study, we combined patient-derived tumor organoids with a microfluidic organ-on-chip system to investigate colorectal cancer (CRC) invasion in the tumor microenvironment (TME). This allowed us to create patient-specific tumor models and assess the impact of physical forces on cancer biology. Our findings showed that the organoid-on-chip models more closely resembled patient tumors at the transcriptional level, surpassing organoids alone. Using 'omics' methods and live-cell imaging, we observed heightened responsiveness of KRAS mutant tumors to TME mechanical forces. These tumors also utilized the γ-aminobutyric acid (GABA) neurotransmitter as an energy source, increasing their invasiveness. This bioengineered model holds promise for advancing our understanding of cancer progression and improving CRC treatments.

Kidney Bioengineering for Transplantation

The kidney is an important organ for maintenance of homeostasis in the human body. As renal failure progresses, renal replacement therapy becomes necessary. However, there is a chronic shortage of kidney donors, creating a major problem for transplantation. To solve this problem, many strategies for the generation of transplantable kidneys are under investigation. Since the first reports describing that nephron progenitors could be induced from human induced pluripotent stem cells, kidney organoids have been attracting attention as tools for studying human kidney development and diseases. Because the kidney is formed through the interactions of multiple renal progenitors, current studies are investigating ways to combine these progenitors derived from human induced pluripotent stem cells for the generation of transplantable kidney organoids. Other bioengineering strategies, such as decellularization and recellularization of scaffolds, 3-dimensional bioprinting, interspecies blastocyst complementation and progenitor replacement, and xenotransplantation, also have the potential to generate whole kidneys, although each of these strategies has its own challenges. Combinations of these approaches will lead to the generation of bioengineered kidneys that are transplantable into humans.

Micro-Engineered Organoid-on-a-Chip Based on Mesenchymal Stromal Cells to Predict Immunotherapy Responses of HCC Patients

Hepatocellular carcinoma (HCC) is one of the most lethal cancers worldwide. Patient-derived organoid (PDO) has great potential in precision oncology, but low success rate, time-consuming culture, and lack of tumor microenvironment (TME) limit its application. Mesenchymal stromal cells (MSC) accumulate in primary site to support tumor growth and recruit immune cells to form TME. Here, MSC and peripheral blood mononuclear cells (PBMC) coculture is used to construct HCC organoid-on-a-chip mimicking original TME and provide a high-throughput drug-screening platform to predict outcomes of anti-HCC immunotherapies. HCC-PDOs and PBMC are co-cultured with MSC and Cancer-associated fibroblasts (CAF). MSC increases success rate of biopsy-derived PDO culture, accelerates PDO growth, and promotes monocyte survival and differentiation into tumor-associated macrophages. A multi-layer microfluidic chip is designed to achieve high-throughput co-culture for drug screening. Compared to conventional PDOs, MSC-PDO-PBMC and CAF-PDO-PBMC models show comparable responses to chemotherapeutic or targeted anti-tumor drugs but more precise prediction potential in assessing patients' responses to anti-PD-L1 drugs. Moreover, this microfluidic platform shortens PDO growth time and improves dimensional uniformity of organoids. In conclusion, the study successfully constructs microengineered organoid-on-a-chip to mimic TME for high-throughput drug screening, providing novel platform to predict immunotherapy response of HCC patients.

Cancer-on-chip: a 3D model for the study of the tumor microenvironment

The approval of anticancer therapeutic strategies is still slowed down by the lack of models able to faithfully reproduce in vivo cancer physiology. On one hand, the conventional in vitro models fail to recapitulate the organ and tissue structures, the fluid flows, and the mechanical stimuli characterizing the human body compartments. On the other hand, in vivo animal models cannot reproduce the typical human tumor microenvironment, essential to study cancer behavior and progression. This study reviews the cancer-on-chips as one of the most promising tools to model and investigate the tumor microenvironment and metastasis. We also described how cancer-on-chip devices have been developed and implemented to study the most common primary cancers and their metastatic sites. Pros and cons of this technology are then discussed highlighting the future challenges to close the gap between the pre-clinical and clinical studies and accelerate the approval of new anticancer therapies in humans.

An integrated organoid omics map extends modeling potential of kidney disease

Kidney organoids are a promising model to study kidney disease, but their use is constrained by limited knowledge of their functional protein expression profile. Here, we define the organoid proteome and transcriptome trajectories over culture duration and upon exposure to TNFα, a cytokine stressor. Older organoids increase deposition of extracellular matrix but decrease expression of glomerular proteins. Single cell transcriptome integration reveals that most proteome changes localize to podocytes, tubular and stromal cells. TNFα treatment of organoids results in 322 differentially expressed proteins, including cytokines and complement components. Transcript expression of these 322 proteins is significantly higher in individuals with poorer clinical outcomes in proteinuric kidney disease. Key TNFα-associated protein (C3 and VCAM1) expression is increased in both human tubular and organoid kidney cell populations, highlighting the potential for organoids to advance biomarker development. By integrating kidney organoid omic layers, incorporating a disease-relevant cytokine stressor and comparing with human data, we provide crucial evidence for the functional relevance of the kidney organoid model to human kidney disease.

Advances and challenges toward developing kidney organoids for clinical applications

Kidney organoids have enabled modeling of human development and disease. While methods of generating the nephron lineage are well established, new protocols to induce another lineage, the ureteric bud/collecting duct, have been reported in the past 5 years. Many reports have described modeling of various hereditary kidney diseases, with polycystic kidney disease serving as the archetypal disease, by using patient-derived or genome-edited kidney organoids. The generation of more organotypic kidneys is also becoming feasible. In this review, I also discuss the significant challenges for more sophisticated disease modeling and for realizing the ambitious goal of generating transplantable synthetic kidneys.

Experimental Models of Polycystic Kidney Disease: Applications and Therapeutic Testing

Polycystic kidney diseases (PKDs) are genetic disorders characterized by the formation and expansion of numerous fluid-filled renal cysts, damaging normal parenchyma and often leading to kidney failure. Although PKDs comprise a broad range of different diseases, with substantial genetic and phenotypic heterogeneity, an association with primary cilia represents a common theme. Great strides have been made in the identification of causative genes, furthering our understanding of the genetic complexity and disease mechanisms, but only one therapy so far has shown success in clinical trials and advanced to US Food and Drug Administration approval. A key step in understanding disease pathogenesis and testing potential therapeutics is developing orthologous experimental models that accurately recapitulate the human phenotype. This has been particularly important for PKDs because cellular models have been of limited value; however, the advent of organoid usage has expanded capabilities in this area but does not negate the need for whole-organism models where renal function can be assessed. Animal model generation is further complicated in the most common disease type, autosomal dominant PKD, by homozygous lethality and a very limited cystic phenotype in heterozygotes while for autosomal recessive PKD, mouse models have a delayed and modest kidney disease, in contrast to humans. However, for autosomal dominant PKD, the use of conditional/inducible and dosage models have resulted in some of the best disease models in nephrology. These have been used to help understand pathogenesis, to facilitate genetic interaction studies, and to perform preclinical testing. Whereas for autosomal recessive PKD, using alternative species and digenic models has partially overcome these deficiencies. Here, we review the experimental models that are currently available and most valuable for therapeutic testing in PKD, their applications, success in preclinical trials, advantages and limitations, and where further improvements are needed.

Advancing organoid design through co-emergence, assembly, and bioengineering

Human adult stem cells and patient-derived induced pluripotent stem cells represent promising tools to understand human biology, development, and disease. Under a permissive environment, stem cell derivatives can self-organize and reconstruct their native milieu, resulting in the creation of organ-like entities known as organoids. Although organoids represent a breakthrough in the stem cell field, there are still considerable shortcomings preventing their widespread use, namely their variability, limited function, and reductionist size. In the past few years, sophisticated methodologies have been proposed to allow the design of organoids with improved biological fidelity and physiological relevance. Here, we summarize these emerging technologies and provide insights into how they can be utilized to fulfill the potential of stem cells.

Repurposing small molecules for Nephronophthisis and related renal ciliopathies

Nephronophthisis is an autosomal recessive tubulo-interstitial nephropathy, belonging to the ciliopathy disorders, characterized by fibrosis and/or cysts. It is the most common genetic cause of renal failure in children and young adults. Clinically and genetically heterogeneous, it is caused by variants in ciliary genes resulting in either an isolated kidney disease or syndromic forms in association with other manifestations of ciliopathy disorders. No curative treatment is currently available. Over the past two decades, advances in understanding disease mechanisms have identified several dysregulated signaling pathways, some shared with other cystic kidney diseases. Notably, molecules previously developed to target these pathways have shown promising beneficial effects in orthologous mouse models. In addition to these knowledge-based repurposing approaches, unbiased "in cellulo" phenotypic screens of "repurposing" libraries identified small molecules able to rescue the ciliogenesis defects observed in nephronophthisis conditions. Those compounds appeared to act on relevant pathways and, when tested, showed beneficial nephronophthisis-associated kidney and/or extra-renal defects in mice. In this review, we have summarized those studies which highlight the drug repurposing strategies in the context of a rare disorders such as nephronophthisis-related ciliopathies, with broad genetic heterogeneity and systemic manifestations but with shared disease mechanisms.

Human pluripotent-stem-cell-derived organoids for drug discovery and evaluation

Human pluripotent stem cells (hPSCs) and three-dimensional organoids have ushered in a new era for disease modeling and drug discovery. Over the past decade, significant progress has been in deriving functional organoids from hPSCs, which have been applied to recapitulate disease phenotypes. In addition, these advancements have extended the application of hPSCs and organoids for drug screening and clinical-trial safety evaluations. This review provides an overview of the achievements and challenges in using hPSC-derived organoids to conduct relevant high-throughput, high-contentscreens and drug evaluation. These studies have greatly enhanced our knowledge and toolbox for precision medicine.

Strategies for Improving Vascularization in Kidney Organoids: A Review of Current Trends

Kidney organoids possess the potential to revolutionize the treatment of renal diseases. However, their growth and maturation are impeded by insufficient growth of blood vessels. Through a PubMed search, we have identified 34 studies that attempted to address this challenge. Researchers are exploring various approaches including animal transplantation, organ-on-chips, and extracellular matrices (ECMs). The most prevalent method to promote the maturation and vascularization of organoids involves transplanting them into animals for in vivo culture, creating an optimal environment for organoid growth and the development of a chimeric vessel network between the host and organoids. Organ-on-chip technology permits the in vitro culture of organoids, enabling researchers to manipulate the microenvironment and investigate the key factors that influence organoid development. Lastly, ECMs have been discovered to aid the formation of blood vessels during organoid differentiation. ECMs from animal tissue have been particularly successful, although the underlying mechanisms require further research. Future research building upon these recent studies may enable the generation of functional kidney tissues for replacement therapies.

ATP/ADP biosensor organoids for drug nephrotoxicity assessment

Drug nephrotoxicity is a common healthcare problem in hospitalized patients and a major limitation during drug development. Multi-segmented kidney organoids derived from human pluripotent stem cells may complement traditional cell culture and animal experiments for nephrotoxicity assessment. Here we evaluate the capability of kidney organoids to investigate drug toxicity in vitro. Kidney organoids express renal drug transporters, OAT1, OAT3, and OCT2, while a human proximal tubular cell line shows the absence of OAT1 and OAT3. Tenofovir and aristolochic acid (AA) induce proximal tubular injury in organoids which is ameliorated by an OAT inhibitor, probenecid, without damage to podocytes. Similarly, cisplatin causes proximal tubular damage that can be relieved by an OCT inhibitor, cimetidine, collectively suggesting the presence of functional OATs and OCTs in organoid proximal tubules. Puromycin aminonucleoside (PAN) induced segment-specific injury in glomerular podocytes in kidney organoids in the absence of tubular injury. Reporter organoids were generated with an ATP/ADP biosensor, which may be applicable to high-throughput screening in the future. In conclusion, the kidney organoid is a useful tool for toxicity assessment in the multicellular context and may contribute to nephrotoxicity assessment during drug development.

Can Kidney Organoid Xenografts Accelerate Therapeutic Development for Genetic Kidney Disorders?

A number of genetic kidney diseases can now be replicated experimentally, using kidney organoids generated from human pluripotent stem cells. This methodology holds great potential for drug discovery. Under in vitro conditions, however, kidney organoids remain developmentally immature, develop scarce vasculature, and may contain undesired off-target cell types. Those critical deficiencies limit their potential as disease-modeling tools. Orthotopic transplantation under the kidney capsule improves the anatomic maturity and vascularization of kidney organoids, while reducing off-target cell content. The improvements can translate into more accurate representations of disease phenotypes and mechanisms in vivo . Recent studies using kidney organoid xenografts highlighted the unique potential of this novel methodology for elucidating molecular mechanisms driving monogenic kidney disorders and for the development ofnovel pharmacotherapies.

Modeling human liver organ development and diseases with pluripotent stem cell-derived organoids

The discoveries of human pluripotent stem cells (PSCs) including embryonic stem cells and induced pluripotent stem cells (iPSCs) has led to dramatic advances in our understanding of basic human developmental and cell biology and has also been applied to research aimed at drug discovery and development of disease treatments. Research using human PSCs has been largely dominated by studies using two-dimensional cultures. In the past decade, however, ex vivo tissue "organoids," which have a complex and functional three-dimensional structure similar to human organs, have been created from PSCs and are now being used in various fields. Organoids created from PSCs are composed of multiple cell types and are valuable models with which it is better to reproduce the complex structures of living organs and study organogenesis through niche reproduction and pathological modeling through cell-cell interactions. Organoids derived from iPSCs, which inherit the genetic background of the donor, are helpful for disease modeling, elucidation of pathophysiology, and drug screening. Moreover, it is anticipated that iPSC-derived organoids will contribute significantly to regenerative medicine by providing treatment alternatives to organ transplantation with which the risk of immune rejection is low. This review summarizes how PSC-derived organoids are used in developmental biology, disease modeling, drug discovery, and regenerative medicine. Highlighted is the liver, an organ that play crucial roles in metabolic regulation and is composed of diverse cell types.

Glucose absorption drives cystogenesis in a human organoid-on-chip model of polycystic kidney disease

In polycystic kidney disease (PKD), fluid-filled cysts arise from tubules in kidneys and other organs. Human kidney organoids can reconstitute PKD cystogenesis in a genetically specific way, but the mechanisms underlying cystogenesis remain elusive. Here we show that subjecting organoids to fluid shear stress in a PKD-on-a-chip microphysiological system promotes cyst expansion via an absorptive rather than a secretory pathway. A diffusive static condition partially substitutes for fluid flow, implicating volume and solute concentration as key mediators of this effect. Surprisingly, cyst-lining epithelia in organoids polarize outwards towards the media, arguing against a secretory mechanism. Rather, cyst formation is driven by glucose transport into lumens of outwards-facing epithelia, which can be blocked pharmacologically. In PKD mice, glucose is imported through cysts into the renal interstitium, which detaches from tubules to license expansion. Thus, absorption can mediate PKD cyst growth in human organoids, with implications for disease mechanism and potential for therapy development.

Role of extracellular matrix components and structure in new renal models in vitro

The extracellular matrix (ECM), a complex set of fibrillar proteins and proteoglycans, supports the renal parenchyma and provides biomechanical and biochemical cues critical for spatial-temporal patterning of cell development and acquisition of specialized functions. As in vitro models progress towards biomimicry, more attention is paid to reproducing ECM-mediated stimuli. ECM's role in in vitro models of renal function and disease used to investigate kidney injury and regeneration is discussed. Availability, affordability, and lot-to-lot consistency are the main factors determining the selection of materials to recreate ECM in vitro. While simpler components can be synthesized in vitro, others must be isolated from animal or human tissues, either as single isolated components or as complex mixtures, such as Matrigel or decellularized formulations. Synthetic polymeric materials with dynamic and instructive capacities are also being explored for cell mechanical support to overcome the issues with natural products. ECM components can be used as simple 2D coatings or complex 3D scaffolds combining natural and synthetic materials. The goal is to recreate the biochemical signals provided by glycosaminoglycans and other signaling molecules, together with the stiffness, elasticity, segmentation, and dimensionality of the original kidney tissue, to support the specialized functions of glomerular, tubular, and vascular compartments. ECM mimicking also plays a central role in recent developments aiming to reproduce renal tissue in vitro or even in therapeutical strategies to regenerate renal function. Bioprinting of renal tubules, recellularization of kidney ECM scaffolds, and development of kidney organoids are examples. Future solutions will probably combine these technologies.