Stem cell-derived kidney organoids: engineering the vasculature.

Kidney organoids can be generated from human pluripotent stem cells (PSCs) using protocols that resemble the embryonic development of the kidney. The renal structures thus generated offer great potential for disease modeling, drug screening, and possibly future therapeutic application. At the same time, use of these PSC-derived organoids is hampered by lack of maturation and off-target differentiation. Here, we review the main protocols for the generation of kidney organoids from human-induced PSCs, discussing their advantages and limitations. In particular, we will focus on the vascularization of the kidney organoids, which appears to be one of the critical factors to achieve maturation and functionality of the organoids.

Efficient Vascularization of Kidney Organoids through Intracelomic Transplantation in Chicken Embryos.

Kidney organoids derived from human induced pluripotent stem cells contain nephron-like structures that resemble those in the adult kidney to a certain degree. Unfortunately, their clinical applicability is hampered by the lack of a functional vasculature and consequently limited maturation in vitro. The transplantation of kidney organoids in the celomic cavity of chicken embryos induces vascularization by perfused blood vessels, including the formation of glomerular capillaries, and enhances their maturation. This technique is very efficient, allowing for the transplantation and analysis of large numbers of organoids. This paper describes a detailed protocol for the intracelomic transplantation of kidney organoids in chicken embryos, followed by the injection of fluorescently labeled lectin to stain the perfused vasculature, and the collection of transplanted organoids for imaging analysis. This method can be used to induce and study organoid vascularization and maturation to find clues for enhancing these processes in vitro and improve disease modeling.

Spatial dynamic metabolomics identifies metabolic cell fate trajectories in human kidney differentiation.

Accumulating evidence demonstrates important roles for metabolism in cell fate determination. However, it is a challenge to assess metabolism at a spatial resolution that acknowledges both heterogeneity and cellular dynamics in its tissue microenvironment. Using a multi-omics platform to study cell-type-specific dynamics in metabolism in complex tissues, we describe the metabolic trajectories during nephrogenesis in the developing human kidney. Exploiting in situ analysis of isotopic labeling, a shift from glycolysis toward fatty acid ß-oxidation was observed during the differentiation from the renal vesicle toward the S-shaped body and the proximal tubules. In addition, we show that hiPSC-derived kidney organoids are characterized by a metabolic immature phenotype that fails to use mitochondrial long-chain fatty acids for energy metabolism. Furthermore, supplementation of butyrate enhances tubular epithelial differentiation and maturation in cultured kidney organoids. Our findings highlight the relevance of understanding metabolic trajectories to efficiently guide stem cell differentiation.

Vasculogenesis in kidney organoids upon transplantation.

Human induced pluripotent stem cell-derived kidney organoids have potential for disease modeling and to be developed into clinically transplantable auxiliary tissue. However, they lack a functional vasculature, and the sparse endogenous endothelial cells (ECs) are lost upon prolonged culture in vitro, limiting maturation and applicability. Here, we use intracoelomic transplantation in chicken embryos followed by single-cell RNA sequencing and advanced imaging platforms to induce and study vasculogenesis in kidney organoids. We show expansion of human organoid-derived ECs that reorganize into perfused capillaries and form a chimeric vascular network with host-derived blood vessels. Ligand-receptor analysis infers extensive potential interactions of human ECs with perivascular cells upon transplantation, enabling vessel wall stabilization. Perfused glomeruli display maturation and morphogenesis to capillary loop stage. Our findings demonstrate the beneficial effect of vascularization on not only epithelial cell types, but also the mesenchymal compartment, inducing the expansion of ´on target´ perivascular stromal cells, which in turn are required for further maturation and stabilization of the neo-vasculature. The here described vasculogenic capacity of kidney organoids will have to be deployed to achieve meaningful glomerular maturation and kidney morphogenesis in vitro.

Renal Subcapsular Transplantation of PSC-Derived Kidney Organoids Induces Neo-vasculogenesis and Significant Glomerular and Tubular Maturation In Vivo.

Human pluripotent stem cell (hPSC)-derived kidney organoids may facilitate disease modeling and the generation of tissue for renal replacement. Long-term application, however, will require transferability between hPSC lines and significant improvements in organ maturation. A key question is whether time or a patent vasculature is required for ongoing morphogenesis. Here, we show that hPSC-derived kidney organoids, derived in fully defined medium conditions and in the absence of any exogenous vascular endothelial growth factor, develop host-derived vascularization. In vivo imaging of organoids under the kidney capsule confirms functional glomerular perfusion as well as connection to pre-existing vascular networks in the organoids. Wide-field electron microscopy demonstrates that transplantation results in formation of a glomerular basement membrane, fenestrated endothelial cells, and podocyte foot processes. Furthermore, compared with non-transplanted organoids, polarization and segmental specialization of tubular epithelium are observed. These data demonstrate that functional vascularization is required for progressive morphogenesis of human kidney organoids.

Use and predictors of oral complementary and alternative medicine by patients with inflammatory bowel disease: a population-based, case-control study.

BACKGROUND: The use of complementary and alternative medicine (CAM) in the general population and in patients with chronic diseases has increased markedly in recent decades. We aimed to determine the prevalence, type, and predictors of oral CAM use among patients with inflammatory bowel disease (IBD) compared with the general population in a large, population-based, case-control study. METHODS: Overall, 1370 patients with IBD and 598 control subjects in Canterbury, New Zealand, were recruited. Environmental and phenotypic data were obtained through a questionnaire and case note review. Predictors of oral CAM use were identified using binary logistic regression. RESULTS: In the previous year, 44.1% of patients with IBD and 42.3% of control subjects used oral CAM (odds ratio [OR], 1.078; 95% confidence interval [CI], 0.885-1.312). The types of oral CAM used most frequently were vitamins (Crohn's disease [CD], 25.2%; ulcerative colitis, 23.7%; control subjects, 24.9%), followed by herbs (CD 15.1%, ulcerative colitis 15.2%, control subjects 12.8%), and dietary supplements (CD, 8.5%; ulcerative colitis 12.6%, control subjects 12.1%). Female gender (OR, 1.61; 95% CI, 1.25-2.08), younger age (P = 0.005), higher education (P = 0.002), higher income (P = 0.04), being a vegetarian (OR, 3.58; 95% CI, 1.97-6.48) and a middle social class at birth (P = 0.024) were independent predictors of oral CAM use in patients with IBD. Disease phenotype was not associated with oral CAM use. In control subjects, female gender (OR, 2.67; 95% CI, 1.85-3.86), higher education (P = 0.003) and a diagnosis of asthma (P = 0.017) predicted oral CAM use. CONCLUSIONS: Oral CAM use is common in, and does not differ between, patients with IBD and the general population in Canterbury, New Zealand. Socio-demographic factors, and not disease phenotype, predict oral CAM use in patients with IBD.