3D organoid-derived human glomeruli for personalised podocyte disease modelling and drug screening. Nat Commun. 2018;9:5167. [PMID: 30514835 PMCID: PMC6279764 DOI: 10.1038/s41467-018-07594-z]

Enriching iPSC research diversity: Harnessing human biobank collections for improved ethnic representation

Biobanks of human biosamples and cell lines are indispensable for biomedical research on human health and disease and for drug development projects. Many human cell line biobanks worldwide hold collections of lymphoblastoid cell lines (LCLs), representing thousands of affected and control donors from diverse ethnic/ancestry groups. In recent years, induced human pluripotent stem cells (iPSCs) and differentiated human cells derived from these iPSCs have become indispensable for applied biomedical research. Establishing iPSCs remains a laborious and costly step towards generating differentiated human cells. To address this research need, several non-profit and commercial biobanks have established iPSC collections for distribution to researchers, thereby serving as a resource for generating differentiated human cells. The most common starting materials for generation of iPSCs are a skin biopsy for harvesting fibroblasts, or a blood sample for collection of peripheral blood mononuclear cells. However untapped resources include the large established collections of biobanked human LCLs which can be reprogrammed to iPSCs using a variety of published protocols including the use of non-integrating episomal vectors. Many biobanks curate LCLs from diverse ethnic/ancestry populations, an aspect largely absent in most established iPSC biobanks which tend to primarily reflect populations from developed countries. Here, we call upon researchers across the breadth of iPSC research to tap the unique resource of existing and diverse human LCL collections for establishing biobanked iPSC panels that better represent the varied human ethnic (and hence genomic) diversity, thereby benefiting precision medicine and drug development research on a global scale.

Kidney Disease Modeling with Organoids and Organs-on-Chips

Kidney disease is a global health crisis affecting more than 850 million people worldwide. In the United States, annual Medicare expenditures for kidney disease and organ failure exceed $81 billion. Efforts to develop targeted therapeutics are limited by a poor understanding of the molecular mechanisms underlying human kidney disease onset and progression. Additionally, 90% of drug candidates fail in human clinical trials, often due to toxicity and efficacy not accurately predicted in animal models. The advent of ex vivo kidney models, such as those engineered from induced pluripotent stem (iPS) cells and organ-on-a-chip (organ-chip) systems, has garnered considerable interest owing to their ability to more accurately model tissue development and patient-specific responses and drug toxicity. This review describes recent advances in developing kidney organoids and organ-chips by harnessing iPS cell biology to model human-specific kidney functions and disease states. We also discuss challenges that must be overcome to realize the potential of organoids and organ-chips as dynamic and functional conduits of the human kidney. Achieving these technological advances could revolutionize personalized medicine applications and therapeutic discovery for kidney disease.

A genetically inducible endothelial niche enables vascularization of human kidney organoids with multilineage maturation and emergence of renin expressing cells

Vascularization plays a critical role in organ maturation and cell-type development. Drug discovery, organ mimicry, and ultimately transplantation hinge on achieving robust vascularization of in vitro engineered organs. Here, focusing on human kidney organoids, we overcame this hurdle by combining a human induced pluripotent stem cell (iPSC) line containing an inducible ETS translocation variant 2 (ETV2) (a transcription factor playing a role in endothelial cell development) that directs endothelial differentiation in vitro, with a non-transgenic iPSC line in suspension organoid culture. The resulting human kidney organoids show extensive endothelialization with a cellular identity most closely related to human kidney endothelia. Endothelialized kidney organoids also show increased maturation of nephron structures, an associated fenestrated endothelium with de novo formation of glomerular and venous subtypes, and the emergence of drug-responsive renin expressing cells. The creation of an engineered vascular niche capable of improving kidney organoid maturation and cell type complexity is a significant step forward in the path to clinical translation. Thus, incorporation of an engineered endothelial niche into a previously published kidney organoid protocol allowed the orthogonal differentiation of endothelial and parenchymal cell types, demonstrating the potential for applicability to other basic and translational organoid studies.

Missense Mutant Gain-of-Function Causes Inverted Formin 2 (INF2)-Related Focal Segmental Glomerulosclerosis (FSGS)

Inverted formin-2 (INF2) gene mutations are among the most common causes of genetic focal segmental glomerulosclerosis (FSGS) with or without Charcot-Marie-Tooth (CMT) disease. Recent studies suggest that INF2, through its effects on actin and microtubule arrangement, can regulate processes including vesicle trafficking, cell adhesion, mitochondrial calcium uptake, mitochondrial fission, and T-cell polarization. Despite roles for INF2 in multiple cellular processes, neither the human pathogenic R218Q INF2 point mutation nor the INF2 knock-out allele is sufficient to cause disease in mice. This discrepancy challenges our efforts to explain the disease mechanism, as the link between INF2-related processes, podocyte structure, disease inheritance pattern, and their clinical presentation remains enigmatic. Here, we compared the kidney responses to puromycin aminonucleoside (PAN) induced injury between R218Q INF2 point mutant knock-in and INF2 knock-out mouse models and show that R218Q INF2 mice are susceptible to developing proteinuria and FSGS. This contrasts with INF2 knock-out mice, which show only a minimal kidney phenotype. Co-localization and co-immunoprecipitation analysis of wild-type and mutant INF2 coupled with measurements of cellular actin content revealed that the R218Q INF2 point mutation confers a gain-of-function effect by altering the actin cytoskeleton, facilitated in part by alterations in INF2 localization. Differential analysis of RNA expression in PAN-stressed heterozygous R218Q INF2 point-mutant and heterozygous INF2 knock-out mouse glomeruli showed that the adhesion and mitochondria-related pathways were significantly enriched in the disease condition. Mouse podocytes with R218Q INF2, and an INF2-mutant human patient's kidney organoid-derived podocytes with an S186P INF2 mutation, recapitulate the defective adhesion and mitochondria phenotypes. These results link INF2-regulated cellular processes to the onset and progression of glomerular disease. Thus, our data demonstrate that gain-of-function mechanisms drive INF2-related FSGS and explain the autosomal dominant inheritance pattern of this disease.

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.

Evaluation of the impact of iPSC differentiation protocols on transcriptomic signatures

Human induced pluripotent stem cells (iPSC) have the potential to produce desired target cell types in vitro and allow for the high-throughput screening of drugs/chemicals at population level thereby minimising the cost of drug discovery and drug withdrawals after clinical trials. There is a substantial need for the characterisation of the iPSC derived models to better understand and utilise them for toxicological relevant applications. In our study, iPSC (SBAD2 or SBAD3 lines obtained from StemBANCC project) were differentiated towards toxicologically relevant cell types: alveolar macrophages, brain capillary endothelial cells, brain cells, endothelial cells, hepatocytes, lung airway epithelium, monocytes, podocytes and renal proximal tubular cells. A targeted transcriptomic approach was employed to understand the effects of differentiation protocols on these cell types. Pearson correlation and principal component analysis (PCA) separated most of the intended target cell types and undifferentiated iPSC models as distinct groups with a high correlation among replicates from the same model. Based on PCA, the intended target cell types could also be separated into the three germ layer groups (ectoderm, endoderm and mesoderm). Differential expression analysis (DESeq2) presented the upregulated genes in each intended target cell types that allowed the evaluation of the differentiation to certain degree and the selection of key differentiation markers. In conclusion, these data confirm the versatile use of iPSC differentiated cell types as standardizable and relevant model systems for in vitro toxicology.

Proteomics applications in next generation induced pluripotent stem cell models

INTRODUCTION

Induced pluripotent stem (iPS) cell technology has transformed biomedical research. New opportunities now exist to create new organoids, microtissues, and body-on-a-chip systems for basic biology investigations and clinical translations.

AREAS COVERED

We discuss the utility of proteomics for attaining an unbiased view into protein expression changes during iPS cell differentiation, cell maturation, and tissue generation. The ability to discover cell-type specific protein markers during the differentiation and maturation of iPS-derived cells has led to new strategies to improve cell production yield and fidelity. In parallel, proteomic characterization of iPS-derived organoids is helping to realize the goal of bridging in vitro and in vivo systems.

EXPERT OPINIONS

We discuss some current challenges of proteomics in iPS cell research and future directions, including the integration of proteomic and transcriptomic data for systems-level analysis.

Integration of pan-omics technologies and three-dimensional in vitro tumor models: an approach toward drug discovery and precision medicine

Despite advancements in treatment protocols, cancer is one of the leading cause of deaths worldwide. Therefore, there is a need to identify newer and personalized therapeutic targets along with screening technologies to combat cancer. With the advent of pan-omics technologies, such as genomics, transcriptomics, proteomics, metabolomics, and lipidomics, the scientific community has witnessed an improved molecular and metabolomic understanding of various diseases, including cancer. In addition, three-dimensional (3-D) disease models have been efficiently utilized for understanding disease pathophysiology and as screening tools in drug discovery. An integrated approach utilizing pan-omics technologies and 3-D in vitro tumor models has led to improved understanding of the intricate network encompassing various signalling pathways and molecular cross-talk in solid tumors. In the present review, we underscore the current trends in omics technologies and highlight their role in understanding genotypic-phenotypic co-relation in cancer with respect to 3-D in vitro tumor models. We further discuss the challenges associated with omics technologies and provide our outlook on the future applications of these technologies in drug discovery and precision medicine for improved management of cancer.

Human pluripotent stem cell-derived kidney organoids: Current progress and challenges

Human pluripotent stem cell (hPSC)-derived kidney organoids share similarities with the fetal kidney. However, the current hPSC-derived kidney organoids have some limitations, including the inability to perform nephrogenesis and lack of a corticomedullary definition, uniform vascular system, and coordinated exit pathway for urinary filtrate. Therefore, further studies are required to produce hPSC-derived kidney organoids that accurately mimic human kidneys to facilitate research on kidney development, regeneration, disease modeling, and drug screening. In this review, we discussed recent advances in the generation of hPSC-derived kidney organoids, how these organoids contribute to the understanding of human kidney development and research in disease modeling. Additionally, the limitations, future research focus, and applications of hPSC-derived kidney organoids were highlighted.

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.

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.

PODO/TERT256 - A promising human immortalized podocyte cell line and its potential use for in vitro research at different oxygen levels

Podocytes are of key interest for the prediction of nephrotoxicity as they are especially sensitive to toxic insults due to their central role in the glomerular filtration apparatus. However, currently, prediction of nephrotoxicity in humans remains insufficiently reliable, thus highlighting the need for advanced in vitro model systems using human cells with improved prediction capacity. Recent approaches for refining in vitro model systems focus on closely replicating physiological conditions as observed under the in vivo situation typical of the respective nephron section of interest. PODO/TERT256, a human immortalized podocyte cell line, were employed in a semi-static transwell system to evaluate its potential use as a human podocyte in vitro system for modelling potential human glomerular toxicity. Furthermore, the impact of routinely employed excessive oxygen tension (21 % - AtmOx), when compared to the physiological oxygen tensions (10 % - PhysOx) observed in vivo, was analyzed. Generally, cultured PODO/TERT256 formed a stable, contact-inhibited monolayer with typical podocyte morphology (large cell body, apical microvilli, finger-like cytoplasmic projections (reminiscent of foot processes), and interdigitating cell-cell junctions) and developed a size-selective filtration barrier. PhysOx, however, induced a more pronounced in vivo like phenotype, comprised of significantly larger cell bodies, significantly enhanced filtration barrier size-selectivity, and a remarkable re-localization of nephrin to the cell membrane, thus suggesting an improved in vitro replication of in vivo characteristics. Preliminary toxicity characterization with the known glomerulotoxin doxorubicin (DOX) suggested an increasing change in filtration permeability, already at the lowest DOX concentrations tested (0.01 μM) under PhysOx, whereas obvious changes under AtmOx were observed as of 0.16 μM and higher with a near all or nothing effect. The latter findings suggested that PODO/TERT256 could serve as an in vitro human podocyte model for studying glomerulotoxicity, whereby culturing at PhyOx tension appeared critical for an improved in vivo-like phenotype and functionality. Moreover, PODO/TERT256 could be incorporated into advanced human glomerulus systems in vitro, recapitulating microfluidic conditions and multiple cell types (endothelial and mesenchymal cells) that can even better predict human glomerular toxicity.

Precision nephrotoxicity testing using 3D in vitro models

Nephrotoxicity is a significant concern during the development of new drugs or when assessing the safety of chemicals in consumer products. Traditional methods for testing nephrotoxicity involve animal models or 2D in vitro cell cultures, the latter of which lack the complexity and functionality of the human kidney. 3D in vitro models are created by culturing human primary kidney cells derived from urine in a 3D microenvironment that mimics the fluid shear stresses of the kidney. Thus, 3D in vitro models provide more accurate and reliable predictions of human nephrotoxicity compared to existing 2D models. In this review, we focus on precision nephrotoxicity testing using 3D in vitro models with human autologous urine-derived kidney cells as a promising approach for evaluating drug safety.

Using biophysical cues and biomaterials to improve genetic models

With the advent of induced pluripotent stem cells and modern differentiation protocols, many advances in our understanding of disease have been made possible by in vitro disease modeling; in some cases, their use may have supplanted animal models. Yet in vitro models often rely on rigid cell culture substrates that could limit our ability to completely reproduce human disease in a dish. Nascent work, however, suggests that the combination of biomaterials and/or advanced microphysiological systems-which better recapitulate tissue properties-with stem cells expressing disease mimicking genetics, could substantially improve current disease modeling efforts where genetics alone is insufficient. This review will highlight such recent advances as well as review current challenges that the fields must overcome to create more personalized therapeutics in the future.

Cellulose nanofibril matrix drives the dynamic formation of spheroids

Multicellular spheroids, which mimic the natural organ counterparts, allow the prospect of drug screening and regenerative medicine. However, their application is hampered by low processing efficiency or limited scale. This study introduces an efficient method to drive rapid multicellular spheroid formation by a cellulose nanofibril matrix. This matrix enables the facilitated growth of spheroids (within 48 h) through multiple cell assembly into size-controllable aggregates with well-organized physiological microstructure. The efficiency, dimension, and conformation of the as-formed spheroids depend on the concentration of extracellular nanofibrils, the number of assembled cells, and the heterogeneity of cell types. The above strategy allows the robust formation mechanism of compacted tumoroids and hepatocyte spheroids.

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.

Production of Highly Uniform Midbrain Organoids from Human Pluripotent Stem Cells

Brain organoids have been considered as an advanced platform for in vitro disease modeling and drug screening, but numerous roadblocks exist, such as lack of large-scale production technology and lengthy protocols with multiple manipulation steps, impeding the industrial translation of brain organoid technology. Here, we describe the high-speed and large-scale production of midbrain organoids using a high-throughput screening-compatible platform within 30 days. Micro midbrain organoids (µMOs) exhibit a highly uniform morphology and gene expression pattern with minimal variability. Notably, µMOs show dramatically accelerated maturation, resulting in the generation of functional µMOs within only 30 days of differentiation. Furthermore, individual µMOs display highly consistent responsiveness to neurotoxin, suggesting their usefulness as an in vitro high-throughput drug toxicity screening platform. Collectively, our data indicate that µMO technology could represent an advanced and robust platform for in vitro disease modeling and drug screening for human neuronal diseases.

iPSC-derived type IV collagen α5-expressing kidney organoids model Alport syndrome

Alport syndrome (AS) is a hereditary glomerulonephritis caused by COL4A3, COL4A4 or COL4A5 gene mutations and characterized by abnormalities of glomerular basement membranes (GBMs). Due to a lack of curative treatments, the condition proceeds to end-stage renal disease even in adolescents. Hampering drug discovery is the absence of effective in vitro methods for testing the restoration of normal GBMs. Here, we aimed to develop kidney organoid models from AS patient iPSCs for this purpose. We established iPSC-derived collagen α5(IV)-expressing kidney organoids and confirmed that kidney organoids from COL4A5 mutation-corrected iPSCs restore collagen α5(IV) protein expression. Importantly, our model recapitulates the differences in collagen composition between iPSC-derived kidney organoids from mild and severe AS cases. Furthermore, we demonstrate that a chemical chaperone, 4-phenyl butyric acid, has the potential to correct GBM abnormalities in kidney organoids showing mild AS phenotypes. This iPSC-derived kidney organoid model will contribute to drug discovery for AS.

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.

The role of organoids in cancer research

Organoids are established through in vitro 3D culture, and they can mimic the structure and physiological functions of organs or tissues in vivo. Organoids have attracted much attention in recent years. They can provide a reliable technology platform for cancer research and treatment and are a valuable preclinical model for academic research and personalized medicine. A number of studies have confirmed that organoids have great application prospects in new drug development, drug screening, tumour mechanism research, and precision medicine. In this review, we mainly focus on recent advances in the application of organoids in cancer research. We also discussed the opportunities and challenges facing organoids, hoping to indicate directions for the development of organoids in the future.

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.

Transformative Materials to Create 3D Functional Human Tissue Models In Vitro in a Reproducible Manner

Recreating human tissues and organs in the petri dish to establish models as tools in biomedical sciences has gained momentum. These models can provide insight into mechanisms of human physiology, disease onset, and progression, and improve drug target validation, as well as the development of new medical therapeutics. Transformative materials play an important role in this evolution, as they can be programmed to direct cell behavior and fate by controlling the activity of bioactive molecules and material properties. Using nature as an inspiration, scientists are creating materials that incorporate specific biological processes observed during human organogenesis and tissue regeneration. This article presents the reader with state-of-the-art developments in the field of in vitro tissue engineering and the challenges related to the design, production, and translation of these transformative materials. Advances regarding (stem) cell sources, expansion, and differentiation, and how novel responsive materials, automated and large-scale fabrication processes, culture conditions, in situ monitoring systems, and computer simulations are required to create functional human tissue models that are relevant and efficient for drug discovery, are described. This paper illustrates how these different technologies need to converge to generate in vitro life-like human tissue models that provide a platform to answer health-based scientific questions.

Integrated analysis of copy number variation-associated lncRNAs identifies candidates contributing to the etiologies of congenital kidney anomalies

Congenital anomalies of the kidney and urinary tract (CAKUT) are disorders resulting from defects in the development of the kidneys and their outflow tract. Copy number variations (CNVs) have been identified as important genetic variations leading to CAKUT, whereas most CAKUT-associated CNVs cannot be attributed to a specific pathogenic gene. Here we construct coexpression networks involving long noncoding RNAs (lncRNAs) within these CNVs (CNV-lncRNAs) using human kidney developmental transcriptomic data. The results show that CNV-lncRNAs encompassed in recurrent CAKUT associated CNVs have highly correlated expression with CAKUT genes in the developing kidneys. The regulatory effects of two hub CNV-lncRNAs (HSALNG0134318 in 22q11.2 and HSALNG0115943 in 17q12) in the module most significantly enriched in known CAKUT genes (CAKUT_sig1, P = 1.150 × 10^-6) are validated experimentally. Our results indicate that the reduction of CNV-lncRNAs can downregulate CAKUT genes as predicted by our computational analyses. Furthermore, knockdown of HSALNG0134318 would downregulate HSALNG0115943 and affect kidney development related pathways. The results also indicate that the CAKUT_sig1 module has function significance involving multi-organ development. Overall, our findings suggest that CNV-lncRNAs play roles in regulating CAKUT genes, and the etiologies of CAKUT-associated CNVs should take account of effects on the noncoding genome.

Perturbations in podocyte transcriptome and biological pathways induced by FSGS associated circulating factors

Background

Focal segmental glomerulosclerosis (FSGS) is frequently associated with heavy proteinuria and progressive renal failure requiring dialysis or kidney transplantation. However, primary FSGS also has a ~40% risk of recurrence of disease in the transplanted kidney (rFSGS). Multiple circulating factors have been identified to contribute to the pathogenesis of primary and rFSGS including soluble urokinase-type plasminogen activator receptor (suPAR) and patient-derived CD40 autoantibody (CD40autoAb). However, the downstream effector pathways specific to individual factors require further study. The tumor necrosis factor, TNF pathway activation by one or more circulating factors present in the sera of patients with FSGS has been supported by multiple studies.

Methods

A human in vitro model was used to study podocyte injury measured as the loss of actin stress fibers. Anti-CD40 autoantibody was isolated from FSGS patients (recurrent and non-recurrent) and control patients with ESRD due to non-FSGS related causes. Two novel human antibodies-anti-uPAR (2G10) and anti-CD40 antibody (Bristol Meyer Squibb, 986090) were tested for their ability to rescue podocyte injury. Podocytes treated with patient derived antibody were transcriptionally profiled using whole human genome microarray.

Results

Here we show that podocyte injury caused by sera from FSGS patients is mediated by CD40 and suPAR and can be blocked by human anti-uPAR and anti-CD40 antibodies. Transcriptomic studies to compare the molecules and pathways activated in response to CD40 autoantibody from rFSGS patients (rFSGS/CD40autoAb) and suPAR, identified unique inflammatory pathways associated with FSGS injury.

Conclusions

We identified several novel and previously described genes associated with FSGS progression. Targeted blockade of suPAR and CD40 pathways with novel human antibodies showed inhibition of podocyte injury in FSGS.

Partner, Neighbor, Housekeeper and Dimension: 3D versus 2D Glomerular Co-Cultures Reveal Drawbacks of Currently Used Cell Culture Models

Signaling-pathway analyses and the investigation of gene responses to different stimuli are usually performed in 2D monocultures. However, within the glomerulus, cells grow in 3D and are involved in direct and paracrine interactions with different glomerular cell types. Thus, the results from 2D monoculture experiments must be taken with caution. We cultured glomerular endothelial cells, podocytes and mesangial cells in 2D/3D monocultures and 2D/3D co-cultures and analyzed cell survival, self-assembly, gene expression, cell-cell interaction, and gene pathways using live/dead assay, time-lapse analysis, bulk-RNA sequencing, qPCR, and immunofluorescence staining. Without any need for scaffolds, 3D glomerular co-cultures self-organized into spheroids. Podocyte- and glomerular endothelial cell-specific markers and the extracellular matrix were increased in 3D co-cultures compared to 2D co-cultures. Housekeeping genes must be chosen wisely, as many genes used for the normalization of gene expression were themselves affected in 3D culture conditions. The transport of podocyte-derived VEGFA to glomerular endothelial cells confirmed intercellular crosstalk in the 3D co-culture models. The enhanced expression of genes important for glomerular function in 3D, compared to 2D, questions the reliability of currently used 2D monocultures. Hence, glomerular 3D co-cultures might be more suitable in the study of intercellular communication, disease modelling and drug screening ex vivo.

Kidney Organoid Derived from Human Pluripotent and Adult Stem Cells for Disease Modeling

Kidney disease affects a significant portion of the global population, yet effective therapies are lacking despite advancements in identifying genetic causes. This limitation can be attributed to the absence of adequate in vitro models that accurately mimic human kidney disease, hindering targeted therapeutic development. However, the emergence of human induced pluripotent stem cells (PSCs) and the development of organoids using them have opened up a way to model kidney development and disease in humans, as well as validate the effects of new drugs. To fully leverage their capabilities in these fields, it is crucial for kidney organoids to closely resemble the structure and functionality of adult human kidneys. In this review, we aim to discuss the potential of using human PSCs or adult kidney stem cell-derived kidney organoids to model genetic kidney disease and renal cancer.

Genetically engineering endothelial niche in human kidney organoids enables multilineage maturation, vascularization and de novo cell types

Vascularization plays a critical role in organ maturation and cell type development. Drug discovery, organ mimicry, and ultimately transplantation in a clinical setting thereby hinges on achieving robust vascularization of in vitro engineered organs. Here, focusing on human kidney organoids, we overcome this hurdle by combining an inducible ETS translocation variant 2 (ETV2) human induced pluripotent stem cell (iPSC) line, which directs endothelial fate, with a non-transgenic iPSC line in suspension organoid culture. The resulting human kidney organoids show extensive vascularization by endothelial cells with an identity most closely related to endogenous kidney endothelia. Vascularized organoids also show increased maturation of nephron structures including more mature podocytes with improved marker expression, foot process interdigitation, an associated fenestrated endothelium, and the presence of renin+ cells. The creation of an engineered vascular niche capable of improving kidney organoid maturation and cell type complexity is a significant step forward in the path to clinical translation. Furthermore, this approach is orthogonal to native tissue differentiation paths, hence readily adaptable to other organoid systems and thus has the potential for a broad impact on basic and translational organoid studies.

Merits and challenges of iPSC-derived organoids for clinical applications

Induced pluripotent stem cells (iPSCs) have entered an unprecedented state of development since they were first generated. They have played a critical role in disease modeling, drug discovery, and cell replacement therapy, and have contributed to the evolution of disciplines such as cell biology, pathophysiology of diseases, and regenerative medicine. Organoids, the stem cell-derived 3D culture systems that mimic the structure and function of organs in vitro, have been widely used in developmental research, disease modeling, and drug screening. Recent advances in combining iPSCs with 3D organoids are facilitating further applications of iPSCs in disease research. Organoids derived from embryonic stem cells, iPSCs, and multi-tissue stem/progenitor cells can replicate the processes of developmental differentiation, homeostatic self-renewal, and regeneration due to tissue damage, offering the potential to unravel the regulatory mechanisms of development and regeneration, and elucidate the pathophysiological processes involved in disease mechanisms. Herein, we have summarized the latest research on the production scheme of organ-specific iPSC-derived organoids, the contribution of these organoids in the treatment of various organ-related diseases, in particular their contribution to COVID-19 treatment, and have discussed the unresolved challenges and shortcomings of these models.

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.

A proof-of-concept assay for quantitative and optical assessment of drug-induced toxicity in renal organoids

Kidneys are complex organs, and reproducing their function and physiology in a laboratory setting remains difficult. During drug development, potential compounds may exhibit unexpected nephrotoxic effects, which imposes a significant financial burden on pharmaceutical companies. As a result, there is an ongoing need for more accurate model systems. The use of renal organoids to simulate responses to nephrotoxic insults has the potential to bridge the gap between preclinical drug efficacy studies in cell cultures and animal models, and the stages of clinical trials in humans. Here we established an accessible fluorescent whole-mount approach for nuclear and membrane staining to first provide an overview of the organoid histology. Furthermore, we investigated the potential of renal organoids to model responses to drug toxicity. For this purpose, organoids were treated with the chemotherapeutic agent doxorubicin for 48 h. When cell viability was assessed biochemically, the organoids demonstrated a significant, dose-dependent decline in response to the treatment. Confocal microscopy revealed visible tubular disintegration and a loss of cellular boundaries at high drug concentrations. This observation was further reinforced by a dose-dependent decrease of the nuclear area in the analyzed images. In contrast to other approaches, in this study, we provide a straightforward experimental framework for drug toxicity assessment in renal organoids that may be used in early research stages to assist screen for potential adverse effects of compounds.

Advancing drug discovery for glomerulopathies using stem-cell-derived kidney models

Chronic kidney disease (CKD) is an epidemic that affects millions worldwide. The glomerulus, a specialized unit of the nephron, is highly susceptible to injury. Human induced pluripotent stem cells (iPSCs) have emerged as an attractive resource for modeling kidney disease and therapeutic discovery.

3D Bioprinting for Next-Generation Personalized Medicine

In the past decade, immense progress has been made in advancing personalized medicine to effectively address patient-specific disease complexities in order to develop individualized treatment strategies. In particular, the emergence of 3D bioprinting for in vitro models of tissue and organ engineering presents novel opportunities to improve personalized medicine. However, the existing bioprinted constructs are not yet able to fulfill the ultimate goal: an anatomically realistic organ with mature biological functions. Current bioprinting approaches have technical challenges in terms of precise cell deposition, effective differentiation, proper vascularization, and innervation. This review introduces the principles and realizations of bioprinting with a strong focus on the predominant techniques, including extrusion printing and digital light processing (DLP). We further discussed the applications of bioprinted constructs, including the engraftment of stem cells as personalized implants for regenerative medicine and in vitro high-throughput drug development models for drug discovery. While no one-size-fits-all approach to bioprinting has emerged, the rapid progress and promising results of preliminary studies have demonstrated that bioprinting could serve as an empowering technology to resolve critical challenges in personalized medicine.

Recent methods of droplet microfluidics and their applications in spheroids and organoids

Droplet microfluidic techniques have long been known as a high-throughput approach for cell manipulation. The capacity to compartmentalize cells into picolitre droplets in microfluidic devices has opened up a range of new ways to extract information from cells. Spheroids and organoids are crucial in vitro three-dimensional cell culture models that physiologically mimic natural tissues and organs. With the aid of developments in cell biology and materials science, droplet microfluidics has been applied to construct spheroids and organoids in numerous formats. In this article, we divide droplet microfluidic approaches for managing spheroids and organoids into three categories based on the droplet module format: liquid droplet, microparticle, and microcapsule. We discuss current advances in the use of droplet microfluidics for the generation of tumour spheroids, stem cell spheroids, and organoids, as well as the downstream applications of these methods in high-throughput screening and tissue engineering.

The "3Ds" of Growing Kidney Organoids: Advances in Nephron Development, Disease Modeling, and Drug Screening

A kidney organoid is a three-dimensional (3D) cellular aggregate grown from stem cells in vitro that undergoes self-organization, recapitulating aspects of normal renal development to produce nephron structures that resemble the native kidney organ. These miniature kidney-like structures can also be derived from primary patient cells and thus provide simplified context to observe how mutations in kidney-disease-associated genes affect organogenesis and physiological function. In the past several years, advances in kidney organoid technologies have achieved the formation of renal organoids with enhanced numbers of specialized cell types, less heterogeneity, and more architectural complexity. Microfluidic bioreactor culture devices, single-cell transcriptomics, and bioinformatic analyses have accelerated the development of more sophisticated renal organoids and tailored them to become increasingly amenable to high-throughput experimentation. However, many significant challenges remain in realizing the use of kidney organoids for renal replacement therapies. This review presents an overview of the renal organoid field and selected highlights of recent cutting-edge kidney organoid research with a focus on embryonic development, modeling renal disease, and personalized drug screening.

Tubuloid culture enables long-term expansion of functional human kidney tubule epithelium from iPSC-derived organoids

Kidney organoids generated from induced pluripotent stem cells (iPSC) have proven valuable for studies of kidney development, disease, and therapeutic screening. However, specific applications have been hampered by limited expansion capacity, immaturity, off-target cells, and inability to access the apical side. Here, we apply recently developed tubuloid protocols to purify and propagate kidney epithelium from d7+18 (post nephrogenesis) iPSC-derived organoids. The resulting 'iPSC organoid-derived (iPSCod)' tubuloids can be exponentially expanded for at least 2.5 mo, while retaining expression of important tubular transporters and segment-specific markers. This approach allows for selective propagation of the mature tubular epithelium, as immature cells, stroma, and undesirable off-target cells rapidly disappeared. iPSCod tubuloids provide easy apical access, which enabled functional evaluation and demonstration of essential secretion and electrolyte reabsorption processes. In conclusion, iPSCod tubuloids provide a different, complementary human kidney model that unlocks opportunities for functional characterization, disease modeling, and regenerative nephrology.

Kidney Organoids Generated Using an Allelic Series of NPHS2 Point Variants Reveal Distinct Intracellular Podocin Mistrafficking

BACKGROUND

NPHS2 variants are the most common cause of steroid-resistant nephrotic syndrome in children >1 month old. Missense NPHS2 variants were reported to cause mistrafficking of the encoded protein, PODOCIN, but this conclusion was on the basis of overexpression in some nonpodocyte cell lines.

METHODS

We generated a series of human induced pluripotent stem cell (iPSC) lines bearing pathogenic missense variants of NPHS2 , encoding the protein changes p.G92C, p.P118L, p.R138Q, p.R168H, and p.R291W, and control lines. iPSC lines were also generated from a patient with steroid-resistant nephrotic syndrome (p.R168H homozygote) and a healthy heterozygous parent. All lines were differentiated into kidney organoids. Immunofluorescence assessed PODOCIN expression and subcellular localization. Podocytes were transcriptionally profiled and PODOCIN-NEPHRIN interaction interrogated.

RESULTS

All variant lines revealed reduced levels of PODOCIN protein in the absence of reduced transcription. Although wild-type PODOCIN localized to the membrane, distinct variant proteins displayed unique patterns of subcellular protein trafficking, some unreported. P118L and R138Q were preferentially retained in the endoplasmic reticulum (ER); R168H and R291W accumulated in the Golgi. Podocyte profiling demonstrated minimal disease-associated transcriptional change. All variants displayed podocyte-specific apoptosis, which was not linked to ER stress. NEPHRIN-PODOCIN colocalization elucidated the variant-specific effect on NEPHRIN association and hence NEPHRIN trafficking.

CONCLUSIONS

Specific variants of endogenous NPHS2 result in distinct subcellular PODOCIN localization within organoid podocytes. Understanding the effect of each variant on protein levels and localization and the effect on NEPHRIN provides additional insight into the pathobiology of NPHS2 variants.

PODCAST

This article contains a podcast at https://dts.podtrac.com/redirect.mp3/www.asn-online.org/media/podcast/JASN/2023_01_05_JASN2022060707.mp3.

Large-Scale Production of Kidney Organoids from Human Pluripotent Stem Cells

Kidney organoids differentiated from human pluripotent stem cells (hPSC) have advanced the study of kidney diseases by providing an in vitro system that outperforms traditional monolayer cell culture and complements animal models. This chapter describes a simple two-stage protocol that generates kidney organoids in suspension culture in less than 2 weeks. In the first stage, hPSC colonies are differentiated into nephrogenic mesoderm. In the second stage of the protocol, renal cell lineages develop and self-organize into kidney organoids that contain fetal-like nephrons with proximal and distal tubule segmentation. A single assay generates up to 1000 organoids, thereby providing a rapid and cost-efficient method for the bulk production of human kidney tissue. Applications include the study of fetal kidney development, genetic disease modelling, nephrotoxicity screening, and drug development.

Generating Human Glomeruli from Pluripotent Stem Cells for Disease Modelling and Drug Screening

The functional unit of human kidney is the nephron. This structure is composed of a glomerulus, connected to a tubule that drains into a collecting duct. The cells which make up the glomerulus are critically important to the appropriate function of this specialised structure. Damage to glomerular cells, particularly the podocytes, is the primary cause of numerous kidney diseases. However, access to and the subsequent culture of human glomerular cells is limited. As such, the ability to generate human glomerular cell types from induced pluripotent stem cells (iPSCs) at scale has garnered great interest. Here, we describe a method to isolate, culture and study 3D human glomeruli from induced pluripotent stem cell (iPSC)-derived kidney organoids in vitro. These 3D glomeruli retain appropriate transcriptional profiles and can be generated from any individual. As isolated glomeruli, they have applicability for disease modelling and drug discovery.

Kidney organoids: a pioneering model for kidney diseases

The kidney is a vital organ that regulates the bodily fluid and electrolyte homeostasis via tailored urinary excretion. Kidney injuries that cause severe or progressive chronic kidney disease have driven the growing population of patients with end-stage kidney disease, leading to substantial patient morbidity and mortality. This irreversible kidney damage has also created a huge socioeconomical burden on the healthcare system, highlighting the need for novel translational research models for progressive kidney diseases. Conventional research methods such as in vitro 2D cell culture or animal models do not fully recapitulate complex human kidney diseases. By contrast, directed differentiation of human induced pluripotent stem cells enables in vitro generation of patient-specific 3D kidney organoids, which can be used to model acute or chronic forms of hereditary, developmental, and metabolic kidney diseases. Furthermore, when combined with biofabrication techniques, organoids can be used as building blocks to construct vascularized kidney tissues mimicking their in vivo counterpart. By applying gene editing technology, organoid building blocks may be modified to minimize the process of immune rejection in kidney transplant recipients. In the foreseeable future, the universal kidney organoids derived from HLA-edited/deleted induced pluripotent stem cell (iPSC) lines may enable the supply of bioengineered organotypic kidney structures that are immune-compatible for the majority of the world population. Here, we summarize recent advances in kidney organoid research coupled with novel technologies such as organoids-on-chip and biofabrication of 3D kidney tissues providing convenient platforms for high-throughput drug screening, disease modelling, and therapeutic applications.

Selecting the right therapeutic target for kidney disease

Kidney disease is a complex disease with several different etiologies and underlying associated pathophysiology. This is reflected by the lack of effective treatment therapies in chronic kidney disease (CKD) that stop disease progression. However, novel strategies, recent scientific breakthroughs, and technological advances have revealed new possibilities for finding novel disease drivers in CKD. This review describes some of the latest advances in the field and brings them together in a more holistic framework as applied to identification and validation of disease drivers in CKD. It uses high-resolution ‘patient-centric’ omics data sets, advanced in silico tools (systems biology, connectivity mapping, and machine learning) and ‘state-of-the-art‘ experimental systems (complex 3D systems in vitro, CRISPR gene editing, and various model biological systems in vivo). Application of such a framework is expected to increase the likelihood of successful identification of novel drug candidates based on strong human target validation and a better scientific understanding of underlying mechanisms.

What can we learn from kidney organoids?

The ability to generate 3-dimensional models of the developing human kidney via the directed differentiation of pluripotent stem cells-termed kidney organoids-has been hailed as a major advance in experimental nephrology. Although these provide an opportunity to interrogate human development, model-specific kidney diseases facilitate drug screening and even deliver bioengineered tissue; most of these prophetic end points remain to be realized. Indeed, at present we are still finding out what we can learn and what we cannot learn from this approach. In this review, we will summarize the approaches available to generate models of the human kidney from stem cells, the existing successful applications of kidney organoids, their limitations, and remaining challenges.

Unraveling the mystery of efficacy in Chinese medicine formula: New approaches and technologies for research on pharmacodynamic substances

Traditional Chinese medicine (TCM) is the key to unlock treasures of Chinese civilization. TCM and its compound play a beneficial role in medical activities to cure diseases, especially in major public health events such as novel coronavirus epidemics across the globe. The chemical composition in Chinese medicine formula is complex and diverse, but their effective substances resemble "mystery boxes". Revealing their active ingredients and their mechanisms of action has become focal point and difficulty of research for herbalists. Although the existing research methods are numerous and constantly updated iteratively, there is remain a lack of prospective reviews. Hence, this paper provides a comprehensive account of existing new approaches and technologies based on previous studies with an in vitro to in vivo perspective. In addition, the bottlenecks of studies on Chinese medicine formula effective substances are also revealed. Especially, we look ahead to new perspectives, technologies and applications for its future development. This work reviews based on new perspectives to open horizons for the future research. Consequently, herbal compounding pharmaceutical substances study should carry on the essence of TCM while pursuing innovations in the field.

Translating Organoids into Artificial Kidneys

Purpose of Review

Kidney disease affects more than 13% of the world population, and current treatment options are limited to dialysis and organ transplantation. The generation of kidney organoids from human-induced pluripotent stem (hiPS) cells could be harnessed to engineer artificial organs and help overcome the challenges associated with the limited supply of transplantable kidneys. The purpose of this article is to review the progress in kidney organoid generation and transplantation and highlight some existing challenges in the field. We also examined possible improvements that could help realize the potential of organoids as artificial organs or alternatives for kidney transplantation therapy.

Recent Findings

Organoids are useful for understanding the mechanisms of kidney development, and they provide robust platforms for drug screening, disease modeling, and generation of tissues for organ replacement therapies. Efforts to design organoids rely on the ability of cells to self-assemble and pattern themselves into recognizable tissues. While existing protocols for generating organoids result in multicellular structures reminiscent of the developing kidney, many do not yet fully recapitulate the complex cellular composition, structure, and functions of the intact kidney. Recent advances toward achieving these goals include identifying cell culture conditions that produce organoids with improved vasculature and cell maturation and functional states. Still, additional improvements are needed to enhance tissue patterning, specialization, and function, and avoid tumorigenicity after transplantation.

Summary

This report focuses on kidney organoid studies, advancements and limitations, and future directions for improvements towards transplantation.

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

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

Functional characterization of ion channels expressed in kidney organoids derived from human induced pluripotent stem cells

Kidney organoids derived from human or rodent pluripotent stem cells have glomerular structures and differentiated/polarized nephron segments. Although there is an increasing understanding of the patterns of expression of transcripts and proteins within kidney organoids, there is a paucity of data regarding functional protein expression, in particular on transporters that mediate the vectorial transport of solutes. Using cells derived from kidney organoids, we examined the functional expression of key ion channels that are expressed in distal nephron segments: the large-conductance Ca2+-activated K+ (BKCa) channel, the renal outer medullary K+ (ROMK, Kir1.1) channel, and the epithelial Na+ channel (ENaC). RNA-sequencing analyses showed that genes encoding the pore-forming subunits of these transporters, and for BKCa channels, key accessory subunits, are expressed in kidney organoids. Expression and localization of selected ion channels was confirmed by immunofluorescence microscopy and immunoblot analysis. Electrophysiological analysis showed that BKCa and ROMK channels are expressed in different cell populations. These two cell populations also expressed other unidentified Ba2+-sensitive K+ channels. BKCa expression was confirmed at a single channel level, based on its high conductance and voltage dependence of activation. We also found a population of cells expressing amiloride-sensitive ENaC currents. In summary, our results show that human kidney organoids functionally produce key distal nephron K+ and Na+ channels.NEW & NOTEWORTHY Our results show that human kidney organoids express key K+ and Na+ channels that are expressed on the apical membranes of cells in the aldosterone-sensitive distal nephron, including the large-conductance Ca2+-activated K+ channel, renal outer medullary K+ channel, and epithelial Na+ channel.

3D proximal tubule-on-chip model derived from kidney organoids with improved drug uptake

Three-dimensional, organ-on-chip models that recapitulate kidney tissue are needed for drug screening and disease modeling. Here, we report a method for creating a perfusable 3D proximal tubule model composed of epithelial cells isolated from kidney organoids matured under static conditions. These organoid-derived proximal tubule epithelial cells (OPTECs) are seeded in cylindrical channels fully embedded within an extracellular matrix, where they form a confluent monolayer. A second perfusable channel is placed adjacent to each proximal tubule within these reusable multiplexed chips to mimic basolateral drug transport and uptake. Our 3D OPTEC-on-chip model exhibits significant upregulation of organic cation (OCT2) and organic anion (OAT1/3) transporters, which leads to improved drug uptake, compared to control chips based on immortalized proximal tubule epithelial cells. Hence, OPTEC tubules exhibit a higher normalized lactate dehydrogenase (LDH) release, when exposed to known nephrotoxins, cisplatin and aristolochic acid, which are diminished upon adding OCT2 and OAT1/3 transport inhibitors. Our integrated multifluidic platform paves the way for personalized kidney-on-chip models for drug screening and disease modeling.

Disease Modeling with Kidney Organoids

Kidney diseases often lack optimal treatments, causing millions of deaths each year. Thus, developing appropriate model systems to study human kidney disease is of utmost importance. Some of the most promising human kidney models are organoids or small organ-resembling tissue collectives, derived from human-induced pluripotent stem cells (hiPSCs). However, they are more akin to a first-trimester fetal kidney than an adult kidney. Therefore, new strategies are needed to advance their maturity. They have great potential for disease modeling and eventually auxiliary therapy if they can reach the maturity of an adult kidney. In this review, we will discuss the current state of kidney organoids in terms of their similarity to the human kidney and use as a disease modeling system thus far. We will then discuss potential pathways to advance the maturity of kidney organoids to match an adult kidney for more accurate human disease modeling.

Integrating basic science with translational research: the 13th International Podocyte Conference 2021

The 13th International Podocyte Conference was held in Manchester, UK, and online from July 28 to 30, 2021. Originally planned for 2020, this biannual meeting was postponed by a year because of the coronavirus disease 2019 (COVID-19) pandemic and proceeded as an innovative hybrid meeting. In addition to in-person attendance, online registration was offered, and this attracted 490 conference registrations in total. As a Podocyte Conference first, a day for early-career researchers was introduced. This premeeting included talks from graduate students and postdoctoral researchers. It gave early career researchers the opportunity to ask a panel, comprising academic leaders and journal editors, about career pathways and the future for podocyte research. The main meeting over 3 days included a keynote talk and 4 focused sessions each day incorporating invited talks, followed by selected abstract presentations, and an open panel discussion. The conference concluded with a Patient Day, which brought together patients, clinicians, researchers, and industry representatives. The Patient Day was an interactive and diverse day. As well as updates on improving diagnosis and potential new therapies, the Patient Day included a PodoArt competition, exercise and cooking classes with practical nutrition advice, and inspirational stories from patients and family members. This review summarizes the exciting science presented during the 13th International Podocyte Conference and demonstrates the resilience of researchers during a global pandemic.

Transplanted organoids empower human preclinical assessment of drug candidate for the clinic

Pharmacodynamic (PD) studies are an essential component of preclinical drug discovery. Current approaches for PD studies, including the analysis of novel kidney disease targeting therapeutic agents, are limited to animal models with unclear translatability to the human condition. To address this challenge, we developed a novel approach for PD studies using transplanted, perfused human kidney organoids. We performed pharmacokinetic (PK) studies with GFB-887, an investigational new drug now in phase 2 trials. Orally dosed GFB-887 to athymic rats that had undergone organoid transplantation resulted in measurable drug exposure in transplanted organoids. We established the efficacy of orally dosed GFB-887 in PD studies, where quantitative analysis showed significant protection of kidney filter cells in human organoids and endogenous rat host kidneys. This widely applicable approach demonstrates feasibility of using transplanted human organoids in preclinical PD studies with an investigational new drug, empowering organoids to revolutionize drug discovery.