Functional Human Podocytes Generated in Organoids from Amniotic Fluid Stem Cells

Abstract

Generating kidney organoids using human stem cells could offer promising prospects for research and therapeutic purposes. However, no cell-based strategy has generated nephrons displaying an intact threedimensional epithelial filtering barrier. Here, we generated organoids using murine embryonic kidney cells, and documented that these tissues recapitulated the complex three-dimensional filtering structure of glomerular slits in vivo and accomplished selective glomerular filtration and tubular reabsorption. Exploiting this technology, we mixed human amniotic fluid stem cells with mouse embryonic kidney cells to establish three-dimensional chimeric organoids that engrafted in vivo and grew to form vascularized glomeruli and tubular structures. Human cells contributed to the formation of glomerular structures, differentiated into podocytes with slit diaphragms, and internalized exogenously infused BSA, thus attaining in vivo degrees of specialization and function unprecedented for donor stem cells. In conclusion, human amniotic fluid stem cell chimeric organoids may offer new paths for studying renal development and human podocyte disease, and for facilitating drug discovery and translational research.

Amniotic Fluid Stem Cells within Chimeric Kidney Rudiments Differentiate to Functional Podocytes after Transplantation into Mature Rat Kidneys

“…Finally, to show functionality, dual immunogold staining for a human-specific antigen and BSA was performed to show that hAFSC-derived podocytes were able to endocytose albumin. An interesting finding of the study by Xinaris et al 12 is that the hAFSCs had a marked propensity to form podocytes and rarely formed proximal tubule cells. The reasons for this are not entirely clear, but Xinaris et al 12 obtained the same result using two different hAFSC lines, indicating that the tendency of the hAFSCs to form podocytes was not a peculiarity of any one particular hAFSC line.…”

“…In this issue of the Journal of the American Society of Nephrology, Xinaris et al 12 have extended these studies to (1) explore whether reaggregated mouse rudiments can perform ultrafiltration, (2) assess the nephrogenic potential of human amniotic fluid stem cells (hAFSCs) within chimeric rudiments comprised of reaggregated mouse metanephroi, and (3) determine whether the hAFSCs within the chimeras can generate mature, functional podocytes after transplantation into mature rat kidneys. Using electron microscopy, Xinaris et al 12 first show that, after transplantation into the kidneys of uninephrectomized athymic adult rats, reaggregated mouse kidney rudiments could generate vascularized glomeruli, some of which contained mature podocytes with well developed foot processes and slit diaphragms.…”

“…Using electron microscopy, Xinaris et al 12 first show that, after transplantation into the kidneys of uninephrectomized athymic adult rats, reaggregated mouse kidney rudiments could generate vascularized glomeruli, some of which contained mature podocytes with well developed foot processes and slit diaphragms. The functionality of the glomeruli was then investigated using fluorescently labeled dextrans of low (10 and 70 kD) and high (155 kD) molecular masses.…”

“…Some of the nephrons that formed within the chimeric rudiments were found to be capable of performing ultrafiltration, which was evidenced by their ability to filter the low-molecular mass dextrans but exclude the high-molecular mass dextran. Xinaris et al 12 then evaluated the nephrogenic potential of the hAFSCs. In contrast to a previous study, 8 Xinaris et al 12 showed that hAFSCs within chimeric rudiments cultured in vitro had a limited capacity to integrate into developing renal structures, but if genetically modified with an adenovirus vector encoding GDNF, they could become incorporated into the condensed metanephric mesenchyme.…”

“…An important aspect of the study by Xinaris et al 12 is that it shows how transplanted chimeric rudiments could potentially be used to model diseases affecting human podocytes. For instance, the use of hAFSCs with mutations in genes that affect podocyte differentiation, growth, survival, and/or function would allow detailed studies of the processes of disease initiation and progression and the evaluation of possible therapies.…”