Three-Dimensional Renal Organoids from Whole Kidney Cells: Generation, Optimization, and Potential Application in Nephrotoxicology In Vitro

Single-Cell Advances in Investigating and Understanding Chronic Kidney Disease and Diabetic Kidney Disease

Chronic kidney disease (CKD) and its subset diabetic kidney disease are progressive conditions that affect >850 million people worldwide. Diabetes, hypertension, and glomerulonephritis are the most common causes of CKD, which is associated with significant patient morbidity and an increased risk of cardiovascular events, such as heart failure, ultimately leading to premature death. Despite newly approved drugs, increasing evidence shows that patients respond to treatment differently given the complexity of disease heterogeneity and complicated pathophysiology. This review article presents an integrative approach to understanding and addressing CKD through the lens of precision medicine and therapeutics. Advancements in single-cell omics technologies and artificial intelligence can be leveraged to explore the intricate cellular mechanisms underlying CKD and diabetic kidney disease pathogenesis. Dissecting the cellular heterogeneity and identifying rare cell populations using single-cell approaches will facilitate uncovering novel therapeutic targets and biomarkers for personalized treatment strategies. Finally, we discuss the potential of artificial intelligence-driven analyses in predicting disease progression and treatment response, thereby paving the way for tailored interventions.

Origins and Molecular Mechanisms Underlying Renal Vascular Development

Kidneys play a crucial role in maintaining homeostasis within the body, and this function is intricately linked to the vascular structures within them. For vascular cells in the kidney to mature and function effectively, a well-coordinated spatial alignment between the nephrons and complex network of blood vessels is essential. This arrangement ensures efficient blood filtration and regulation of the electrolyte balance, blood pressure, and fluid levels. Additionally, the kidneys are vital in regulating the acid-base balance and producing hormones involved in erythropoiesis and blood pressure control. This article focuses on the vascular development of the kidneys, summarizing the current understanding of the origin and formation of the renal vasculature, and the key molecules involved. A comprehensive review of existing studies has been conducted to elucidate the cellular and molecular mechanisms governing renal vascular development. Specific molecules play a critical role in the development of renal vasculature, contributing to the spatial alignment between nephrons and blood vessels. By elucidating the cellular and molecular mechanisms involved in renal vascular development, this study aims to advance renal regenerative medicine and offer potential avenues for therapeutic interventions in kidney disease.

Organoids: development and applications in disease models, drug discovery, precision medicine, and regenerative medicine

Organoids are miniature, highly accurate representations of organs that capture the structure and unique functions of specific organs. Although the field of organoids has experienced exponential growth, driven by advances in artificial intelligence, gene editing, and bioinstrumentation, a comprehensive and accurate overview of organoid applications remains necessary. This review offers a detailed exploration of the historical origins and characteristics of various organoid types, their applications-including disease modeling, drug toxicity and efficacy assessments, precision medicine, and regenerative medicine-as well as the current challenges and future directions of organoid research. Organoids have proven instrumental in elucidating genetic cell fate in hereditary diseases, infectious diseases, metabolic disorders, and malignancies, as well as in the study of processes such as embryonic development, molecular mechanisms, and host-microbe interactions. Furthermore, the integration of organoid technology with artificial intelligence and microfluidics has significantly advanced large-scale, rapid, and cost-effective drug toxicity and efficacy assessments, thereby propelling progress in precision medicine. Finally, with the advent of high-performance materials, three-dimensional printing technology, and gene editing, organoids are also gaining prominence in the field of regenerative medicine. Our insights and predictions aim to provide valuable guidance to current researchers and to support the continued advancement of this rapidly developing field.

Progress and breakthroughs in human kidney organoid research

The three-dimensional (3D) kidney organoid is a breakthrough model for recapitulating renal morphology and function in vitro, which is grown from stem cells and resembles mammalian kidney organogenesis. Currently, protocols for cultivating this model from induced pluripotent stem cells (iPSCs) and patient-derived adult stem cells (ASCs) have been widely reported. In recent years, scientists have focused on combining cutting-edge bioengineering and bioinformatics technologies to improve the developmental accuracy of kidney organoids and achieve high-throughput experimentation. As a remarkable tool for mechanistic research of the renal system, kidney organoid has both potential and challenges. In this review, we have described the evolution of kidney organoid establishment methods and highlighted the latest progress leading to a more sophisticated kidney transformation research model. Finally, we have summarized the main applications of renal organoids in exploring kidney disease.

Applications of 3D organoids in toxicological studies: a comprehensive analysis based on bibliometrics and advances in toxicological mechanisms

A mechanism exploration is an important part of toxicological studies. However, traditional cell and animal models can no longer meet the current needs for in-depth studies of toxicological mechanisms. The three-dimensional (3D) organoid derived from human embryonic stem cells (hESC) or induced pluripotent stem cells (hiPSC) is an ideal experimental model for the study of toxicological effects and mechanisms, which further recapitulates the human tissue microenvironment and provides a reliable method for studying complex cell-cell interactions. This article provides a comprehensive overview of the state of the 3D organoid technology in toxicological studies, including a bibliometric analysis of the existing literature and an exploration of the latest advances in toxicological mechanisms. The use of 3D organoids in toxicology research is growing rapidly, with applications in disease modeling, organ-on-chips, and drug toxicity screening being emphasized, but academic communications among countries/regions, institutions, and research scholars need to be further strengthened. Attempts to study the toxicological mechanisms of exogenous chemicals such as heavy metals, nanoparticles, drugs and organic pollutants are also increasing. It can be expected that 3D organoids can be better applied to the safety evaluation of exogenous chemicals by establishing a standardized methodology.

Revealing the clinical potential of high-resolution organoids

The symbiotic interplay of organoid technology and advanced imaging strategies yields innovative breakthroughs in research and clinical applications. Organoids, intricate three-dimensional cell cultures derived from pluripotent or adult stem/progenitor cells, have emerged as potent tools for in vitro modeling, reflecting in vivo organs and advancing our grasp of tissue physiology and disease. Concurrently, advanced imaging technologies such as confocal, light-sheet, and two-photon microscopy ignite fresh explorations, uncovering rich organoid information. Combined with advanced imaging technologies and the power of artificial intelligence, organoids provide new insights that bridge experimental models and real-world clinical scenarios. This review explores exemplary research that embodies this technological synergy and how organoids reshape personalized medicine and therapeutics.

ECM-derived biomaterials for regulating tissue multicellularity and maturation

Recent breakthroughs in developing human-relevant organotypic models led to the building of highly resemblant tissue constructs that hold immense potential for transplantation, drug screening, and disease modeling. Despite the progress in fine-tuning stem cell multilineage differentiation in highly controlled spatiotemporal conditions and hosting microenvironments, 3D models still experience naive and incomplete morphogenesis. In particular, existing systems and induction protocols fail to maintain stem cell long-term potency, induce high tissue-level multicellularity, or drive the maturity of stem cell-derived 3D models to levels seen in their in vivo counterparts. In this review, we highlight the use of extracellular matrix (ECM)-derived biomaterials in providing stem cell niche-mimicking microenvironment capable of preserving stem cell long-term potency and inducing spatial and region-specific differentiation. We also examine the maturation of different 3D models, including organoids, encapsulated in ECM biomaterials and provide looking-forward perspectives on employing ECM biomaterials in building more innovative, transplantable, and functional organs.

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.

Porcine Kidney Organoids Derived from Naïve-like Embryonic Stem Cells

The scarcity of donor kidneys greatly impacts the survival of patients with end-stage renal failure. Pigs are increasingly becoming potential organ donors but are limited by immunological rejection. Based on the human kidney organoid already established with the CHIR99021 and FGF9 induction strategy, we generated porcine kidney organoids from porcine naïve-like ESCs (nESCs). The derived porcine organoids had a tubule-like constructure and matrix components. The porcine organoids expressed renal markers including AQP1 (proximal tubule), WT1 and PODO (podocyte), and CD31 (vascular endothelial cells). These results imply that the organoids had developed the majority of the renal cell types and structures, including glomeruli and proximal tubules. The porcine organoids were also identified to have a dextran absorptive function. Importantly, porcine organoids have a certain abundance of vascular endothelial cells, which are the basis for investigating immune rejection. The derived porcine organoids might serve as materials for immunosuppressor screening for xenotransplantation.

Renal Organoids from Whole Kidney Cells

Organoid technology, as a three-dimensional (3D) culture method, provides a feasible tool to self-organize multiple types of organ-specific cells, construct inherent anatomic structures, and display functional biological activities. For the purpose of renal regeneration, renal organoids are considered as predictive options to form functional kidney substitutions in vitro. Here, we describe an accessible and convenient way to generate renal organoids without differentiation procedures using whole kidney cells.

Strategic use of organoids and organs-on-chip as biomimetic tools

Organoid development and organ-on-a-chip are technologies based on differentiating stem cells, forming 3D multicellular structures resembling organs and tissues in vivo. Hence, both can be strategically used for disease modeling, drug screening, and host-pathogen studies. In this context, this review highlights the significant advancements in the area, providing technical approaches to organoids and organ-on-a-chip that best imitate in vivo physiology.

Advantages and Potential Benefits of Using Organoids in Nanotoxicology

Organoids are microtissues that recapitulate the complex structural organization and functions of tissues and organs. Nanoparticles have several specific properties that must be considered when replacing animal models with in vitro studies, such as the formation of a protein corona, accumulation, ability to overcome tissue barriers, and different severities of toxic effects in different cell types. An increase in the number of articles on toxicology research using organoid models is related to an increase in publications on organoids in general but is not related to toxicology-based publications. We demonstrate how the quantitative assessment of toxic changes in the structure of organoids and the state of their cell collections provide more valuable results for toxicological research and provide examples of research methods. The impact of the tested materials on organoids and their differences are also discussed. In conclusion, we highlight the main challenges, the solution of which will allow researchers to approach the replacement of in vivo research with in vitro research: biobanking and standardization of the structural characterization of organoids, and the development of effective screening imaging techniques for 3D organoid cell organization.

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.

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.

Human Stem Cell and Organoid Models to Advance Acute Kidney Injury Diagnostics and Therapeutics

Acute kidney injury (AKI) is an increasingly common problem afflicting all ages, occurring in over 20% of non-critically ill hospitalized patients and >30% of children and >50% of adults in critical care units. AKI is associated with serious short-term and long-term consequences, and current therapeutic options are unsatisfactory. Large gaps remain in our understanding of human AKI pathobiology, which have hindered the discovery of novel diagnostics and therapeutics. Although animal models of AKI have been extensively studied, these differ significantly from human AKI in terms of molecular and cellular responses. In addition, animal models suffer from interspecies differences, high costs and ethical considerations. Static two-dimensional cell culture models of AKI also have limited utility since they have focused almost exclusively on hypoxic or cytotoxic injury to proximal tubules alone. An optimal AKI model would encompass several of the diverse specific cell types in the kidney that could be targets of injury. Second, it would resemble the human physiological milieu as closely as possible. Third, it would yield sensitive and measurable readouts that are directly applicable to the human condition. In this regard, the past two decades have seen a dramatic shift towards newer personalized human-based models to study human AKI. In this review, we provide recent developments using human stem cells, organoids, and in silico approaches to advance personalized AKI diagnostics and therapeutics.

Enhanced Microvasculature Formation and Patterning in iPSC–Derived Kidney Organoids Cultured in Physiological Hypoxia

Stem cell–derived kidney organoids have been shown to self-organize from induced pluripotent stem cells into most important renal structures. However, the structures remain immature in culture and contain endothelial networks with low connectivity and limited organoid invasion. Furthermore, the nephrons lose their phenotype after approximately 25 days. To become applicable for future transplantation, further maturation in vitro is essential. Since kidneys in vivo develop in hypoxia, we studied the modulation of oxygen availability in culture. We hypothesized that introducing long-term culture at physiological hypoxia, rather than the normally applied non-physiological, hyperoxic 21% O₂, could initiate angiogenesis, lead to enhanced growth factor expression and improve the endothelial patterning. We therefore cultured the kidney organoids at 7% O₂ instead of 21% O₂ for up to 25 days and evaluated nephrogenesis, growth factor expression such as VEGF-A and vascularization. Whole mount imaging revealed a homogenous morphology of the endothelial network with enhanced sprouting and interconnectivity when the kidney organoids were cultured in hypoxia. Three-dimensional vessel quantification confirmed that the hypoxic culture led to an increased average vessel length, likely due to the observed upregulation of VEGFA-189 and VEGFA-121, and downregulation of the antiangiogenic protein VEGF-A165b measured in hypoxia. This research indicates the importance of optimization of oxygen availability in organoid systems and the potential of hypoxic culture conditions in improving the vascularization of organoids.

Promotion of Cyst Formation from a Renal Stem Cell Line Using Organ-Specific Extracellular Matrix Gel Format Culture System

Researchers have long awaited the technology to develop an in vitro kidney model. Here, we establish a rapid fabricating technique for kidney-like tissues (cysts) using a combination of an organ-derived extracellular matrix (ECM) gel format culture system and a renal stem cell line (CHK-Q cells). CHK-Q cells, which are spontaneously immortalized from the renal stem cells of the Chinese hamster, formed renal cyst-like structures in a type-I collagen gel sandwich culture on day 1 of culture. The cysts fused together and expanded while maintaining three-dimensional structures. The expression of genes related to kidney development and maturation was increased compared with that in a traditional monolayer. Under the kidney-derived ECM (K-ECM) gel format culture system, cyst formation and maturation were induced rapidly. Gene expressions involved in cell polarities, especially for important material transporters (typical markers Slc5a1 and Kcnj1), were restored. K-ECM composition was an important trigger for CHK-Q cells to promote kidney-like tissue formation and maturation. We have established a renal cyst model which rapidly expressed mature kidney features via the combination of K-ECM gel format culture system and CHK-Q cells.

Tissue Culture Models of AKI: From Tubule Cells to Human Kidney Organoids

AKI affects approximately 13.3 million people around the world each year, causing CKD and/or mortality. The mammalian kidney cannot generate new nephrons after postnatal renal damage and regenerative therapies for AKI are not available. Human kidney tissue culture systems can complement animal models of AKI and/or address some of their limitations. Donor-derived somatic cells, such as renal tubule epithelial cells or cell lines (RPTEC/hTERT, ciPTEC, HK-2, Nki-2, and CIHP-1), have been used for decades to permit drug toxicity screening and studies into potential AKI mechanisms. However, tubule cell lines do not fully recapitulate tubular epithelial cell properties in situ when grown under classic tissue culture conditions. Improving tissue culture models of AKI would increase our understanding of the mechanisms, leading to new therapeutics. Human pluripotent stem cells (hPSCs) can be differentiated into kidney organoids and various renal cell types. Injury to human kidney organoids results in renal cell-type crosstalk and upregulation of kidney injury biomarkers that are difficult to induce in primary tubule cell cultures. However, current protocols produce kidney organoids that are not mature and contain off-target cell types. Promising bioengineering techniques, such as bioprinting and "kidney-on-a-chip" methods, as applied to kidney nephrotoxicity modeling advantages and limitations are discussed. This review explores the mechanisms and detection of AKI in tissue culture, with an emphasis on bioengineered approaches such as human kidney organoid models.

The Nephrotoxin Puromycin Aminonucleoside Induces Injury in Kidney Organoids Differentiated from Induced Pluripotent Stem Cells

Kidney diseases, including acute kidney injury (AKI) and chronic kidney disease (CKD), which can progress to end stage renal disease (ESRD), are a worldwide health burden. Organ transplantation or kidney dialysis are the only effective available therapeutic tools. Therefore, in vitro models of kidney diseases and the development of prospective therapeutic options are urgently needed. Within the kidney, the glomeruli are involved in blood filtration and waste excretion and are easily affected by changing cellular conditions. Puromycin aminonucleoside (PAN) is a nephrotoxin, which can be employed to induce acute glomerular damage and to model glomerular disease. For this reason, we generated kidney organoids from three iPSC lines and treated these with PAN in order to induce kidney injury. Morphological observations revealed the disruption of glomerular and tubular structures within the kidney organoids upon PAN treatment, which were confirmed by transcriptome analyses. Subsequent analyses revealed an upregulation of immune response as well as inflammatory and cell-death-related processes. We conclude that the treatment of iPSC-derived kidney organoids with PAN induces kidney injury mediated by an intertwined network of inflammation, cytoskeletal re-arrangement, DNA damage, apoptosis and cell death. Furthermore, urine-stem-cell-derived kidney organoids can be used to model kidney-associated diseases and drug discovery.

Kidney organoids: current knowledge and future directions

The kidney is a highly complex organ in the human body. Although creating an in vitro model of the human kidney is challenging, tremendous advances have been made in recent years. Kidney organoids are in vitro kidney models that are generated from stem cells in three-dimensional (3D) cultures. They exhibit remarkable degree of similarities with the native tissue in terms of cell type, morphology, and function. The establishment of 3D kidney organoids facilitates a mechanistic study of cell communications, and these organoids can be used for drug screening, disease modeling, and regenerative medicine applications. This review discusses the cellular complexity during in vitro kidney generation. We intend to highlight recent progress in kidney organoids and the applications of these relatively new technologies.

Drug-Induced Nephrotoxicity Assessment in 3D Cellular Models

The kidneys are often involved in adverse effects and toxicity caused by exposure to foreign compounds, chemicals, and drugs. Early predictions of these influences are essential to facilitate new, safe drugs to enter the market. However, in current drug treatments, drug-induced nephrotoxicity accounts for 1/4 of reported serious adverse reactions, and 1/3 of them are attributable to antibiotics. Drug-induced nephrotoxicity is driven by multiple mechanisms, including altered glomerular hemodynamics, renal tubular cytotoxicity, inflammation, crystal nephropathy, and thrombotic microangiopathy. Although the functional proteins expressed by renal tubules that mediate drug sensitivity are well known, current in vitro 2D cell models do not faithfully replicate the morphology and intact renal tubule function, and therefore, they do not replicate in vivo nephrotoxicity. The kidney is delicate and complex, consisting of a filter unit and a tubular part, which together contain more than 20 different cell types. The tubular epithelium is highly polarized, and maintaining cellular polarity is essential for the optimal function and response to environmental signals. Cell polarity depends on the communication between cells, including paracrine and autocrine signals, as well as biomechanical and chemotaxis processes. These processes affect kidney cell proliferation, migration, and differentiation. For drug disposal research, the microenvironment is essential for predicting toxic reactions. This article reviews the mechanism of drug-induced kidney injury, the types of nephrotoxicity models (in vivo and in vitro models), and the research progress related to drug-induced nephrotoxicity in three-dimensional (3D) cellular culture models.

Recent Advances in Kidney Bioengineering

Kidney disease is an epidemic that affects more than 600 million people worldwide. The socioeconomic impacts of the disease disproportionately affect Hispanic and non-Hispanic Black Americans, making the disease an issue of social inequality. The urgency of this situation has only become worse during the COVID-19 pandemic, as those who are hospitalized for COVID-19 have an increased risk of kidney failure. For researchers, the kidney is a complex organ that is difficult to accurately model and understand. Traditional cell culture models are not adequate for studying the functional intricacies of the kidney, but recent experiments have offered improvements for understanding these systems. Recent progress includes organoid modeling, 3D bioprinting, decellularization, and microfluidics. Here, we offer a review of the most recent advances in kidney bioengineering.

Organoid Technology: A Reliable Developmental Biology Tool for Organ-Specific Nanotoxicity Evaluation

Engineered nanomaterials are bestowed with certain inherent physicochemical properties unlike their parent materials, rendering them suitable for the multifaceted needs of state-of-the-art biomedical, and pharmaceutical applications. The log-phase development of nano-science along with improved "bench to beside" conversion carries an enhanced probability of human exposure with numerous nanoparticles. Thus, toxicity assessment of these novel nanoscale materials holds a key to ensuring the safety aspects or else the global biome will certainly face a debacle. The toxicity may span from health hazards due to direct exposure to indirect means through food chain contamination or environmental pollution, even causing genotoxicity. Multiple ways of nanotoxicity evaluation include several in vitro and in vivo methods, with in vitro methods occupying the bulk of the "experimental space." The underlying reason may be multiple, but ethical constraints in in vivo animal experiments are a significant one. Two-dimensional (2D) monoculture is undoubtedly the most exploited in vitro method providing advantages in terms of cost-effectiveness, high throughput, and reproducibility. However, it often fails to mimic a tissue or organ which possesses a defined three-dimensional structure (3D) along with intercellular communication machinery. Instead, microtissues such as spheroids or organoids having a precise 3D architecture and proximate in vivo tissue-like behavior can provide a more realistic evaluation than 2D monocultures. Recent developments in microfluidics and bioreactor-based organoid synthesis have eased the difficulties to prosper nano-toxicological analysis in organoid models surpassing the obstacle of ethical issues. The present review will enlighten applications of organoids in nanotoxicological evaluation, their advantages, and prospects toward securing commonplace nano-interventions.

Renal Ciliopathies: Sorting Out Therapeutic Approaches for Nephronophthisis

Nephronophthisis (NPH) is an autosomal recessive ciliopathy and a major cause of end-stage renal disease in children. The main forms, juvenile and adult NPH, are characterized by tubulointerstitial fibrosis whereas the infantile form is more severe and characterized by cysts. NPH is caused by mutations in over 20 different genes, most of which encode components of the primary cilium, an organelle in which important cellular signaling pathways converge. Ciliary signal transduction plays a critical role in kidney development and tissue homeostasis, and disruption of ciliary signaling has been associated with cyst formation, epithelial cell dedifferentiation and kidney function decline. Drugs have been identified that target specific signaling pathways (for example cAMP/PKA, Hedgehog, and mTOR pathways) and rescue NPH phenotypes in in vitro and/or in vivo models. Despite identification of numerous candidate drugs in rodent models, there has been a lack of clinical trials and there is currently no therapy that halts disease progression in NPH patients. This review covers the most important findings of therapeutic approaches in NPH model systems to date, including hypothesis-driven therapies and untargeted drug screens, approached from the pathophysiology of NPH. Importantly, most animal models used in these studies represent the cystic infantile form of NPH, which is less prevalent than the juvenile form. It appears therefore important to develop new models relevant for juvenile/adult NPH. Alternative non-orthologous animal models and developments in patient-based in vitro model systems are discussed, as well as future directions in personalized therapy for NPH.

Bioengineered Kidney Models: Methods and Functional Assessments

Investigations into bioengineering kidneys have been extensively conducted owing to their potential for preclinical assays and regenerative medicine. Various approaches and methods have been developed to improve the structure and function of bioengineered kidneys. Assessments of functional properties confirm the adequacy of bioengineered kidneys for multipurpose translational applications. This review is to summarize the studies performed in kidney bioengineering in the past decade. We identified 84 original articles from PubMed and Mendeley with keywords of kidney organoid or kidney tissue engineering. Those were categorized into 5 groups based on their approach: de-/recellularization of kidney, reaggregation of kidney cells, kidney organoids, kidney in scaffolds, and kidney-on-a-chip. These models were physiologically assessed by filtration, tubular reabsorption/secretion, hormone production, and nephrotoxicity. We found that bioengineered kidney models have been developed from simple cell cultures to multicellular systems to recapitulate kidney function and diseases. Meanwhile, only about 50% of these studies conducted functional assessments on their kidney models. Factors including cell composition and organization are likely to alter the applicability of physiological assessments in bioengineered kidneys. Combined with recent technologies, physiological assessments importantly contribute to the improvement of the bioengineered kidney model toward repairing and refunctioning the damaged kidney.

Phenotypic screening with target identification and validation in the discovery and development of E3 ligase modulators

The use of phenotypic screening was central to the discovery and development of novel thalidomide analogs, the IMiDs (immunomodulatory drugs) agents. With the discovery that these agents bind the E3 ligase, CRL4^CRBN, and alter its substrate specificity, there has been a great deal of endeavor to discover other small molecules that can modulate alternative E3 ligases. Furthermore, the chemical properties necessary for drug discovery and the rules by which neo-substrates are selected for degradation are being defined in the context of phenotypic alterations in specific cellular systems. This review gives a detailed summary of these recent advances and the methodologies being exploited to understand the mechanism of action of emerging protein degradation therapies.

Formation and optimization of three-dimensional organoids generated from urine-derived stem cells for renal function in vitro

Background

Organoids play an important role in basic research, drug screening, and regenerative medicine. Here, we aimed to develop a novel kind of three-dimensional (3D) organoids generated from urine-derived stem cells (USCs) and to explore whether kidney-specific extracellular matrix (kECM) could enable such organoids for renal function in vitro.

Methods

USCs were isolated from human urine samples and cultured with kECM extraction to generate 3D organoids in vitro. Eight densities from 1000 to 8000 cells per organoids were prepared, and both ATP assay and Live/Dead staining were used to determine the optimal USC density in forming organoids and kECM additive concentration. The morphology and histology of as-made organoids were evaluated by hematoxylin and eosin (H.E.) staining, immunofluorescence staining and whole mount staining. Additionally, RT-qPCR was implemented to detect renal-related gene expression. Drug toxicity test was conducted to evaluate the potential application for drug screening. The renal organoids generated from whole adult kidney cells were used as a positive control in multiple assessments.

Results

The optimized cell density to generate ideal USC-derived organoids (USC-organoids) was 5000 cells/well, which was set as applying density in the following experiments. Besides, the optimal concentration of kECM was revealed to be 10%. On this condition, Live/Dead staining showed that USC-organoids were well self-organized without significant cell death. Moreover, H.E. staining showed that compact and viable organoids were generated without obvious necrosis inside organoids, which were very close to renal organoids morphologically. Furthermore, specific proximal tubule marker Aquaporin-1 (AQP1), kidney endocrine product erythropoietin (EPO), kidney glomerular markers Podocin and Synaptopodin were detected positively in USC-organoids with kECM. Nephrotoxicity testing showed that aspirin, penicillin G, and cisplatin could exert drug-induced toxicity on USC-organoids with kECM.

Conclusions

USC-organoids could be developed from USCs via an optimal procedure. Combining culture with kECM, USC-organoid properties including morphology, histology, and specific gene expression were identified to be similar with real renal organoids. Additionally, USC-organoids posed kECM in vitro showed the potential to be a drug screening tool which might take the place of renal organoids to some extent in the future.

Organoids: An invaluable tool in pharmacology

Advances in stem cell cultures and human-induced pluripotent stem cells have inculcated interests in a rapidly evolving concept – ”organoids.” These are three-dimensional (3D) structures mimicking some of the phenomena of the real organs at anatomical, multicellular, and functional levels in vitro. Organoids have been proven to be better than two-dimensional cell culture in replicating the functionality, architectural, and geometrical features of tissues in vivo. Recent advancements have led to the generation of models for organ development and disease, finding applications in the drug discovery, screening of novel compounds, and personalized medicine. Since organoids follow the same natural pathway as the normal tissue or pathology, they can be used to study the expression of various genotypes and phenotypic variations across different species. In the light of these advancements, organoids are now being merged with bioengineering to come up with even better and reliable models to predict the disease progression and effectiveness of precision medicines, few of its important applications. This article discusses the various aspects of this emerging concept along with its uses, both in the present times and near future, with a special focus on pharmacological applications.