Derivation of induced pluripotent stem cell lines from New Zealand donors

A genetically inducible endothelial niche enables vascularization of human kidney organoids with multilineage maturation and emergence of renin expressing cells

Vascularization plays a critical role in organ maturation and cell-type development. Drug discovery, organ mimicry, and ultimately transplantation hinge on achieving robust vascularization of in vitro engineered organs. Here, focusing on human kidney organoids, we overcame this hurdle by combining a human induced pluripotent stem cell (iPSC) line containing an inducible ETS translocation variant 2 (ETV2) (a transcription factor playing a role in endothelial cell development) that directs endothelial differentiation in vitro, with a non-transgenic iPSC line in suspension organoid culture. The resulting human kidney organoids show extensive endothelialization with a cellular identity most closely related to human kidney endothelia. Endothelialized kidney organoids also show increased maturation of nephron structures, an associated fenestrated endothelium with de novo formation of glomerular and venous subtypes, and the emergence of drug-responsive renin expressing cells. The creation of an engineered vascular niche capable of improving kidney organoid maturation and cell type complexity is a significant step forward in the path to clinical translation. Thus, incorporation of an engineered endothelial niche into a previously published kidney organoid protocol allowed the orthogonal differentiation of endothelial and parenchymal cell types, demonstrating the potential for applicability to other basic and translational organoid studies.

Genetically engineering endothelial niche in human kidney organoids enables multilineage maturation, vascularization and de novo cell types

Vascularization plays a critical role in organ maturation and cell type development. Drug discovery, organ mimicry, and ultimately transplantation in a clinical setting thereby hinges on achieving robust vascularization of in vitro engineered organs. Here, focusing on human kidney organoids, we overcome this hurdle by combining an inducible ETS translocation variant 2 (ETV2) human induced pluripotent stem cell (iPSC) line, which directs endothelial fate, with a non-transgenic iPSC line in suspension organoid culture. The resulting human kidney organoids show extensive vascularization by endothelial cells with an identity most closely related to endogenous kidney endothelia. Vascularized organoids also show increased maturation of nephron structures including more mature podocytes with improved marker expression, foot process interdigitation, an associated fenestrated endothelium, and the presence of renin+ cells. The creation of an engineered vascular niche capable of improving kidney organoid maturation and cell type complexity is a significant step forward in the path to clinical translation. Furthermore, this approach is orthogonal to native tissue differentiation paths, hence readily adaptable to other organoid systems and thus has the potential for a broad impact on basic and translational organoid studies.

Synthesis, Antibacterial Activity, and Nephrotoxicity of Polymyxin B Analogues Modified at Leu-7, d-Phe-6, and the N-Terminus Enabled by S-Lipidation

With the post-antibiotic era rapidly approaching, many have turned their attention to developing new treatments, often by structural modification of existing antibiotics. Polymyxins, a family of lipopeptide antibiotics that are used as a last line of defense in the clinic, have recently developed resistance and exhibit significant nephrotoxicity issues. Using thiol-ene chemistry, the facile preparation of six unique S-lipidated building blocks was demonstrated and used to generate lipopeptide mimetics upon incorporation into solid-phase peptide synthesis (SPPS). We then designed and synthesized 38 polymyxin analogues, incorporating these unique building blocks at the N-terminus, or to replace hydrophobic residues at positions 6 and 7 of the native lipopeptides. Several polymyxin analogues bearing one or more S-linked lipids were found to be equipotent to polymyxin, showed minimal kidney nephrotoxicity, and demonstrated activity against several World Health Organisation (WHO) priority pathogens. The S-lipidation strategy has demonstrated potential as a novel approach to prepare innovative new lipopeptide antibiotics.

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.

Modeling oxidative injury response in human kidney organoids

Background

Hemolysis occurs in many injury settings and can trigger disease processes. In the kidney, extracellular hemoglobin can induce damage via several mechanisms. These include oxidative stress, mitochondrial dysfunction, and inflammation, which promote fibrosis and chronic kidney disease. Understanding the pathophysiology of these injury pathways offers opportunities to develop new therapeutic strategies.

Methods

To model hemolysis-induced kidney injury, human kidney organoids were treated with hemin, an iron-containing porphyrin, that generates reactive oxygen species. In addition, we developed an induced pluripotent stem cell line expressing the biosensor, CytochromeC-GFP (CytoC-GFP), which provides a real-time readout of mitochondrial morphology, health, and early apoptotic events.

Results

We found that hemin-treated kidney organoids show oxidative damage, increased expression of injury markers, impaired functionality of organic anion and cation transport and undergo fibrosis. Injury could be detected in live CytoC-GFP organoids by cytoplasmic localization of fluorescence. Finally, we show that 4-(phenylthio)butanoic acid, an HDAC inhibitor with anti-fibrotic effects in vivo, reduces hemin-induced human kidney organoid fibrosis.

Conclusion

This work establishes a hemin-induced model of kidney organoid injury. This platform provides a new tool to study the injury and repair response pathways in human kidney tissue and will assist in the development of new therapeutics.

Protocol for Large-Scale Production of Kidney Organoids from Human Pluripotent Stem Cells

Kidney organoids represent a physiologically advanced model for studying the mechanisms of kidney development and disease. Here, we describe a simple two-step protocol for the differentiation of human pluripotent stem cells into kidney organoids. Our approach involves suspension culture that allows for rapid and cost-effective bulk production of organoids, which is well suited for large-scale assays such as drug screening. The organoids correspond to fetal human kidney tissue and may be of limited use for modeling adult kidney function. For complete details on the use and execution of this protocol, please refer to Przepiorski et al. (2018).