Functional maturation of kidney organoid tubules: PIEZO1-mediated Ca2+ signaling

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

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

Postnatal renal tubule development: roles of tubular flow and flux

PURPOSE OF REVIEW

Postnatal renal tubule development is critical to adult kidney function. Several postnatal changes regulate the differentiation and proliferation of renal tubular cells. Here, we review the literature and our efforts on thick ascending limb (TAL) development in Bartter syndrome (BS).

RECENT FINDINGS

Glomerular filtrate quickly increases after birth, imposing fluid shear stress and circumferential stretch on immature renal tubules. Recent studies showed that kidney organoids under flow (superfusion) have better development of tubular structures and the expression of cilia and solute transporters. These effects are likely mediated by mechanosensors, such as cilia and the piezo1 channel. Improved renal oxygenation and sodium pump-dependent active transport can stimulate mitochondrial respiration and biogenesis. The functional coupling between transport and mitochondria ensures ATP supply for energy-demanding reactions in tubular cells, including cell cycle progression and proliferation. We recently discovered that postnatal renal medulla maturation and TAL elongation are impaired in Clc-k2-deficient BS mice. Primary cultured Clc-k2-deficient TAL cells have G1-S transition and proliferation delay. These developmental defects could be part of the early pathogenesis of BS and worsen the phenotype.

SUMMARY

Understanding how tubular flow and transepithelial ion fluxes regulate renal tubule development may improve the treatment of congenital renal tubulopathies.

Unleashing the power of biomaterials to enhance organoid differentiation and function

Biomaterials are revolutionizing organoid development by offering tunable platforms that provide instructive cues, which enhance cell fate transitions, tissue-level functions and reproducibility. These advances are crucial for harnessing the translational potential of organoids.

Mechanosensing by Piezo1 and its implications in the kidney

Piezo1 is an essential mechanosensitive transduction ion channel in mammals. Its unique structure makes it capable of converting mechanical cues into electrical and biological signals, modulating biological and (patho)physiological processes in a wide variety of cells. There is increasing evidence demonstrating that the piezo1 channel plays a vital role in renal physiology and disease conditions. This review summarizes the current evidence on the structure and properties of Piezo1, gating modulation, and pharmacological characteristics, with special focus on the distribution and (patho)physiological significance of Piezo1 in the kidney, which may provide insights into potential treatment targets for renal diseases involving this ion channel.

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

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

Organoid assessment technologies

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

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

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