High-Throughput Functional Analysis of CFTR and Other Apically Localized Proteins in iPSC-Derived Human Intestinal Organoids

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.

Genome-engineering technologies for modeling and treatment of cystic fibrosis

Cystic fibrosis (CF) is an autosomal recessive disease caused by defects in the CF transmembrane conductance regulator (CFTR) protein. Due to the genetic nature of the disease, interventions in the genome can target any underlying alterations and potentially provide permanent disease resolution. The current development of gene-editing tools, such as designer nuclease technology capable of genome correction, holds great promise for both CF and other genetic diseases. In recent years, Cas9-based technologies have enabled the generation of genetically defined human stem cell and disease models based on induced pluripotent stem cells (iPSC). In this article, we outline the potential and possibilities of using CRISPR/Cas9-based gene-editing technology in CF modeling.

PSC-derived intestinal organoids with apical-out orientation as a tool to study nutrient uptake, drug absorption and metabolism

Intestinal organoids recapitulate many features of the in vivo gastrointestinal tract and have revolutionized in vitro studies of intestinal function and disease. However, the restricted accessibility of the apical surface of the organoids facing the central lumen (apical-in) limits studies related to nutrient uptake and drug absorption and metabolism. Here, we demonstrate that pluripotent stem cell (PSC)-derived intestinal organoids with reversed epithelial polarity (apical-out) can successfully recapitulate tissue-specific functions. In particular, these apical-out organoids show strong epithelial barrier formation with all the major junctional complexes, nutrient transport and active lipid metabolism. Furthermore, the organoids express drug-metabolizing enzymes and relevant apical and basolateral transporters. The scalable and robust generation of functional, apical-out intestinal organoids lays the foundation for a completely new range of organoid-based high-throughput/high-content in vitro applications in the fields of nutrition, metabolism and drug discovery.

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.

Advances in Preclinical In Vitro Models for the Translation of Precision Medicine for Cystic Fibrosis

The development of preclinical in vitro models has provided significant progress to the studies of cystic fibrosis (CF), a frequently fatal monogenic disease caused by mutations in the gene encoding the CF transmembrane conductance regulator (CFTR) protein. Numerous cell lines were generated over the last 30 years and they have been instrumental not only in enhancing the understanding of CF pathological mechanisms but also in developing therapies targeting the underlying defects in CFTR mutations with further validation in patient-derived samples. Furthermore, recent advances toward precision medicine in CF have been made possible by optimizing protocols and establishing novel assays using human bronchial, nasal and rectal tissues, and by progressing from two-dimensional monocultures to more complex three-dimensional culture platforms. These models also enable to potentially predict clinical efficacy and responsiveness to CFTR modulator therapies at an individual level. In parallel, advanced systems, such as induced pluripotent stem cells and organ-on-a-chip, continue to be developed in order to more closely recapitulate human physiology for disease modeling and drug testing. In this review, we have highlighted novel and optimized cell models that are being used in CF research to develop novel CFTR-directed therapies (or alternative therapeutic interventions) and to expand the usage of existing modulator drugs to common and rare CF-causing mutations.

Anion Transport Across Human Gallbladder Organoids and Monolayers

Fluid and anion secretion are important functions of the biliary tract. It has been established that cAMP regulates Na⁺ absorption through NHE3. However, mechanisms of gallbladder anion transport are less defined. We created organoids and organoid-derived monolayers from human gallbladder tissue to measure organoid swelling and transepithelial electrophysiology. In our in vitro models, forskolin-stimulation caused organoid swelling and increased transepithelial anion transport. Full organoid swelling required Cl⁻while changes in short-circuit current were HCO₃⁻-dependent. Organoids and monolayers from an individual homozygous for the cystic fibrosis-causing ΔF508 CFTR mutation had no apical expression of CFTR and minimal changes in transepithelial current and conductance with forskolin treatment. However, organoid swelling remained intact. Dilution potential studies revealed that forskolin treatment increased the paracellular permeability to anions relative to cations. These data suggest a novel paracellular contribution to forskolin-stimulated fluid transport across the gallbladder epithelium.