Troy/TNFRSF19 marks epithelial progenitor cells during mouse kidney development that continue to contribute to turnover in adult kidney.

During kidney development, progressively committed progenitor cells give rise to the distinct segments of the nephron, the functional unit of the kidney. Similar segment-committed progenitor cells are thought to be involved in the homeostasis of adult kidney. However, markers for most segment-committed progenitor cells remain to be identified. Here, we evaluate Troy/TNFRSF19 as a segment-committed nephron progenitor cell marker. Troy is expressed in the ureteric bud during embryonic development. During postnatal nephrogenesis, Troy+ cells are present in the cortex and papilla and display an immature tubular phenotype. Tracing of Troy+ cells during nephrogenesis demonstrates that Troy+ cells clonally give rise to tubular structures that persist for up to 2 y after induction. Troy+ cells have a 40-fold higher capacity than Troy- cells to form organoids, which is considered a stem cell property in vitro. In the adult kidney, Troy+ cells are present in the papilla and these cells continue to contribute to collecting duct formation during homeostasis. The number of Troy-derived cells increases after folic acid-induced injury. Our data show that Troy marks a renal stem/progenitor cell population in the developing kidney that in adult kidney contributes to homeostasis, predominantly of the collecting duct, and regeneration.

A Perspective on a Urine-Derived Kidney Tubuloid Biobank from Patients with Hereditary Tubulopathies.

Inherited kidney tubulopathies comprise a group of rare diseases with a significant societal impact, as lifelong treatment is often required and no therapies are available to prevent progression of renal damage. Diagnosis of inherited tubulopathies has improved with the advances of next generation sequencing. However, difficulties remain, such as a lack of genotype-phenotype correlation and unknown pathogenicity of newly identified variants. In addition, treatment remains mainly symptomatic. Both diagnosis and treatment can be improved by addition of in vitro functional studies to clinical care. Urine-derived kidney organoids ("tubuloids") are a promising platform for these studies. International collections of patient-derived tubuloids in a living biobank offer additional advantages for drug development and pathophysiological studies. In this review, we discuss how diagnosis and treatment of tubulopathies can be improved by in vitro studies using a tubuloid biobank. We also address practical challenges in the development of such biobank. Impact statement This review provides readers insight into aspects related to diagnosis and treatment of hereditary kidney tubulopathies that can be improved. In addition, it explains why in vitro functional analyses using a kidney organoid model (tubuloids) may be useful as a method to improve these aspects. Finally, the additional advantages and practical hurdles of collecting tubuloid lines in a biobank are discussed.

Culture and analysis of kidney tubuloids and perfused tubuloid cells-on-a-chip.

Advanced in vitro kidney models are of great importance to the study of renal physiology and disease. Kidney tubuloids can be established from primary cells derived from adult kidney tissue or urine. Tubuloids are three-dimensional multicellular structures that recapitulate tubular function and have been used to study infectious, malignant, metabolic, and genetic diseases. For tubuloids to more closely represent the in vivo kidney, they can be integrated into an organ-on-a-chip system that has a more physiological tubular architecture and allows flow and interaction with vasculature or epithelial and mesenchymal cells from other organs. Here, we describe a detailed protocol for establishing tubuloid cultures from tissue and urine (1-3 weeks), as well as for generating and characterizing tubuloid cell-derived three-dimensional tubular structures in a perfused microfluidic multi-chip platform (7 d). The combination of the two systems yields a powerful in vitro tool that better recapitulates the complexity of the kidney tubule with donor-specific properties.

Human Organoids: Tools for Understanding Biology and Treating Diseases.

Organoids are in vitro-cultured three-dimensional structures that recapitulate key aspects of in vivo organs. They can be established from pluripotent stem cells and from adult stem cells, the latter being the subject of this review. Organoids derived from adult stem cells exploit the tissue regeneration process that is driven by these cells, and they can be established directly from the healthy or diseased epithelium of many organs. Organoids are amenable to any experimental approach that has been developed for cell lines. Applications in experimental biology involve the modeling of tissue physiology and disease, including malignant, hereditary, and infectious diseases. Biobanks of patient-derived tumor organoids are used in drug development research, and they hold promise for developing personalized and regenerative medicine. In this review, we discuss the applications of adult stem cell-derived organoids in the laboratory and the clinic.

An organoid biobank for childhood kidney cancers that captures disease and tissue heterogeneity.

Kidney tumours are among the most common solid tumours in children, comprising distinct subtypes differing in many aspects, including cell-of-origin, genetics, and pathology. Pre-clinical cell models capturing the disease heterogeneity are currently lacking. Here, we describe the first paediatric cancer organoid biobank. It contains tumour and matching normal kidney organoids from over 50 children with different subtypes of kidney cancer, including Wilms tumours, malignant rhabdoid tumours, renal cell carcinomas, and congenital mesoblastic nephromas. Paediatric kidney tumour organoids retain key properties of native tumours, useful for revealing patient-specific drug sensitivities. Using single cell RNA-sequencing and high resolution 3D imaging, we further demonstrate that organoid cultures derived from Wilms tumours consist of multiple different cell types, including epithelial, stromal and blastemal-like cells. Our organoid biobank captures the heterogeneity of paediatric kidney tumours, providing a representative collection of well-characterised models for basic cancer research, drug-screening and personalised medicine.

Tubuloids derived from human adult kidney and urine for personalized disease modeling.

Adult stem cell-derived organoids are three-dimensional epithelial structures that recapitulate fundamental aspects of their organ of origin. We describe conditions for the long-term growth of primary kidney tubular epithelial organoids, or 'tubuloids'. The cultures are established from human and mouse kidney tissue and can be expanded for at least 20 passages (>6 months) while retaining a normal number of chromosomes. In addition, cultures can be established from human urine. Human tubuloids represent proximal as well as distal nephron segments, as evidenced by gene expression, immunofluorescence and tubular functional analyses. We apply tubuloids to model infectious, malignant and hereditary kidney diseases in a personalized fashion. BK virus infection of tubuloids recapitulates in vivo phenomena. Tubuloids are established from Wilms tumors. Kidney tubuloids derived from the urine of a subject with cystic fibrosis allow ex vivo assessment of treatment efficacy. Finally, tubuloids cultured on microfluidic organ-on-a-chip plates adopt a tubular conformation and display active (trans-)epithelial transport function.

Epigenetic Regulation of Matrix Metalloproteinase-1 and -3 Expression in Mycobacterium tuberculosis Infection.

In pulmonary tuberculosis (TB), the inflammatory immune response against Mycobacterium tuberculosis (Mtb) is associated with tissue destruction and cavitation, which drives disease transmission, chronic lung disease, and mortality. Matrix metalloproteinase (MMP)-1 is a host enzyme critical for the development of cavitation. MMP expression has been shown to be epigenetically regulated in other inflammatory diseases, but the importance of such mechanisms in Mtb-associated induction of MMP-1 is unknown. We investigated the role of changes in histone acetylation in Mtb-induced MMP expression using inhibitors of histone deacetylases (HDACs) and histone acetyltransferases (HAT), HDAC siRNA, promoter-reporter constructs, and chromatin immunoprecipitation assays. Mtb infection decreased Class I HDAC gene expression by over 50% in primary human monocyte-derived macrophages but not in normal human bronchial epithelial cells (NHBEs). Non-selective inhibition of HDAC activity decreased MMP-1/-3 expression by Mtb-stimulated macrophages and NHBEs, while class I HDAC inhibition increased MMP-1 secretion by Mtb-stimulated NHBEs. MMP-3 expression, but not MMP-1, was downregulated by siRNA silencing of HDAC1. Inhibition of HAT activity also significantly decreased MMP-1/-3 secretion by Mtb-infected macrophages. The MMP-1 promoter region between -2,001 and -2,942 base pairs from the transcriptional start site was key in control of Mtb-driven MMP-1 gene expression. Histone H3 and H4 acetylation and RNA Pol II binding in the MMP-1 promoter region were increased in stimulated NHBEs. In summary, epigenetic modification of histone acetylation via HDAC and HAT activity has a key regulatory role in Mtb-dependent gene expression and secretion of MMP-1 and -3, enzymes which drive human immunopathology. Manipulation of epigenetic regulatory mechanisms may have potential as a host-directed therapy to improve outcomes in the era of rising TB drug resistance.

Pluripotent stem cell-derived kidney organoids: An in vivo-like in vitro technology.

Organoids are self-organizing, multicellular structures that contain multiple cell types, represent organ structure and function, and can be used to model organ development, maintenance and repair ex vivo. Organoids, derived from embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs) or adult stem cells, are cultured in extracellular matrix (ECM). Organoid cultures have been developed for multiple organs and for the kidney, pluripotent stem cell (PSCs) derived organoid technology has rapidly developed in the last three years. Here, we review available PSC differentiation protocols, focusing on the pluripotent stem cells to initiate the organoid culture, as well as on growth factors and ECM used to regulate differentiation and expansion. In addition, we will discuss the read out strategies to evaluate organoid phenotype and function. Finally, we will indicate how the choice of both culture parameters and read out strategy should be tailored to specific applications of the organoid culture.

Development and application of human adult stem or progenitor cell organoids.

Adult stem or progenitor cell organoids are 3D adult-organ-derived epithelial structures that contain self-renewing and organ-specific stem or progenitor cells as well as differentiated cells. This organoid culture system was first established in murine intestine and subsequently developed for several other organs and translated to humans. Organoid cultures have proved valuable for basic research and for the study of healthy tissue homeostasis and the biology of disease. In addition, data from proof-of-principle experiments support promising clinical applications of adult stem or progenitor cell organoids. Although renal organoids have many potential applications, an adult stem or progenitor cell organoid culture system has not yet been developed for the kidney. The development of such a system is likely to be challenging because of the intricate renal architecture. Differentiated 3D cultures and stem or progenitor cell 3D sphere cultures are, however, available for the kidney. These cultures indicate the feasibility of renal organoid culture and provide a solid basis for its development. In this Review, we discuss the state-of-the-art of human adult stem or progenitor cell organoid culture and the potential of renal organoids as tools in basic and clinical research.