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

Abstract

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.

Keywords: development; function; kidney; organoid; physiology.

Graphical abstract

Figure 1.

Kidney organoid structures and cellular components. A: three-dimensional (3-D) images of kidney organoids on day 49 of differentiation. B and C: immunostaining displaying organoid glomeruli (B) and tubules (C). D: an electron microscope image showing brush border-like structures (#) and mitochondria (*) in organoid tubules. E: immunofluorescence microscopy displaying segments of proximal, loops of Henle, and distal tubules. F: single-nuclear RNA sequencing of healthy human kidneys from the Human Biomolecular Atlas Program (HuBMAP) and Kidney Precision Medicine Project (KPMP) revealing the expression of cadherin-1 (CDH1) in proliferating proximal tubules, loops of Henle, and distal nephrons. G: immunostaining showing organoid vasculature and stromal cells. The images of A were kindly provided by Ken Hiratsuka, B–E were from Morizane et al. (14), and G were from Gupta et al. (22).

Figure 2.

Functions identified in the kidney organoids in each nephron segment. An illustration summarizing studies of kidney organoid function in each nephron segment is shown. BK_Ca, large-conductance Ca²⁺-activated K⁺ channel; EB, ethidium bromide; ENaC, epithelial Na⁺ channel; FPE, fluid-phase endocytosis; OCT2, organic cation transporter 2; RBE, receptor-based endocytosis; Rho123, rhodamine 123; ROMK, renal outer medullary K⁺ channel; 6CF, 6-carboxyfluorescein.

Figure 3.

Flow-induced vascularization and mechanosensing biological processes. A: an illustration of the kidney organoid-on-chip model. B: immunostaining displaying vascularized kidney organoids under flow. C and D: differentially expressed genes in kidney organoids cultured under flow and their GO terms implicated in mechanosensing signals. The images of A and B were taken from Homan et al. (74) and C and D were from Hiratsuka et al. (75). GPCR, G protein-coupled receptor; ROS, reactive oxygen species; TGF, transforming growth factor.

Figure 4.

Key metrics for successful differentiation of kidney organoids. At days 7–9 of differentiation, the nephron progenitor cells (NPC) express SIX2, as shown by the immunostaining in two-dimensional (2-D) cultures. Matured three-dimensional (3-D) organoids must comprise podocyte clusters, proximal tubular epithelial cells, and distal tubular epithelial cells, as evidenced by podocalyxin (PODXL), Lotus tetragonolobus lectin (LTL), and cadherin 1 (CDH1) staining, respectively. They also bear CD31-positive endothelial cells and MEIS-positive interstitial stromal cells. Cellular polarity must be verified, with apical staining of PODXL within the podocyte clusters, conversely to nephrin (NPHS1) and synaptopodin (SYNPO) basal staining, and luminal staining of MDR1 in the proximal tubular epithelial cells.