| | |  | | NEWSLETTER ::: NO. 19 ::: NOV 2019 | | GROWING KIDNEYS IN THE LAB | | Kidneys are not only fascinating organs, they are essential to our survival. Unfortunately, severely damaged kidneys have no capacity to regenerate. Recent achievements are fueling hope that lab-grown tissue could soon replace diseased organs. |  | | The term ‘regenerative medicine’ is trending. Thanks to the latest technological advances, it is now possible to grow patient-specific cells into various miniature organs (organoids) in the lab. Recently, a miniature heart 3D printed from human cells was revealed to the public, and several clinical trials to treat eye disease, spinal cord injury, or Parkinson’s disease with tissue generated from patient-derived pluripotent stem cells are underway in Japan. These stunning reports raise expectations that kidneys could also soon be grown in the lab. So, what is the current state of regenerative medicine in nephrology?
More than 10 years ago, Shinya Yamanaka discovered that inserting only four genes into skin-derived cells (fibroblasts) could turn these into induced pluripotent stem cells (iPSCs). This breakthrough held the promise that iPSCs could be the building blocks of new organs of any type. The main difficulty since has been to guide iPSCs to differentiate into a desired tissue type. Persistent efforts by a number of groups around the world have recently led to the identification of conditions that guide pluripotent stem cells through a series of transformations resulting in small tissue aggregates that resemble miniature kidneys in the culture dish. | | FROM STEM CELL TO MINIATURE KIDNEY | Interestingly, iPSCs need about four weeks to become kidney organoids and undergo various steps that recapitulate embryonic development along the way. Therefore, it is not surprising that the conditions, growth factors, and chemical stimulants currently used to induce renal tissue in vitro are heavily based on intimate knowledge of embryonic renal development.
While the advances are stunning, kidney organoids are far from perfect. The time that kidney organoids can be kept in culture is not yet sufficient to induce full maturation into differentiated tissue of an adult kidney. Currently, they mostly resemble foetal, still developing kidneys. Kidney organoids are generally small (a few millimetres in diameter at best) and will require connection to a vascular system delivering oxygen and nutrients to these organoids if they are to grow bigger and more complex. | | GENERATING KIDNEY CELLS | No doubt further technological advances are likely to vastly improve organoids. However, alternative strategies to generate kidney cells in culture have recently emerged. For example, it is possible to transform fibroblasts directly into a target tissue without the prior need to generate pluripotent cells. Our research group recently found four transcription factors that convert fibroblasts into cells that have functional properties of renal tubules. Our approach is termed direct reprogramming and results in the generation of induced renal tubular epithelial cells (iRECs) (see text box below). Instead of recreating the entire kidney, direct reprogramming focuses on a particular renal cell type. The aim is not to produce a transplantable kidney, but rather to guide the transformation of cells into a particular tissue of interest.
Both iPSC-based organoids and direct reprogramming offer enormous opportunities already today. Kidney organoids and reprogrammed cells offer the advantage of modeling kidney diseases using human tissue. In contrast to animal studies, in vitro models are scalable, and could easily be used to screen new chemical compounds or existing drug libraries. In general, they will diversify the portfolio of models that mimic kidney disease, making it easier to understand pathogenetic mechanisms and to find therapeutic targets. In addition, in vitro generated tissue could also help to speed up drug development more generally. Currently, many promising drugs fail to reach the clinic because of severe renal side effects.
In some areas this is already a reality. For example, a promising treatment for the debilitating brain disorder caused by the zika virus was found using brain-derived organoids. In the long term, optimized protocols will allow these technologies to individualize disease modeling and make treatments more precise. Individual disease-causing mutations, and even the overall genetic background of a patient, can dramatically influence disease progression or severity. Creating kidney tissue from patients’ own cells will therefore make it possible to explore which treatment will benefit which patient best. | | DIRECTLY REPROGRAMMED INDUCED RENAL TUBULE EPITHELIAL CELLS (IRECS) |  | | iRECs can self-organize into tubular networks. Green: green fluorescent protein located to the cell membranes. Blue: nuclear stain.
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Direct reprogramming can change one cell type into a different one. In most cases, a small set of transcription factors can induce conversion of cell identities. Our research group recently found four factors (EMX2, HNF1B, HNF4A, and PAX8) that are able to turn fibroblasts directly into cells that closely resemble renal tubules. iRECs express typical epithelial markers and tubular specific proteins. The overall transcriptomic profile is similar to that of primary tubule cells, but some differences and a residual fibroblast signature remain. When seeded in 3D matrigel, iRECs form hollow, polarized spheroids, and even lengthy tubular structures in decellularized kidney scaffolds. iRECs have typical features of proximal tubule cells; for example, they can take up small proteins by endocytosis and have microvilli on their apical surface. However, among the reprogrammed cells are also some that display markers of other tubular segments. An ERC-Starting Grant (DiRECT) aims to develop this technology further. The technology platform within the NCCR will allow other research groups direct access to reprogrammed cells and the method of reprogramming. | | | Soeren Lienkamp is an assistant professor at the Institute of Anatomy of the University of Zurich. He joined the NCCR Kidney.CH as a platform leader in 2019. |
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| | | | Kidney - Control of Homeostasis | | is a Swiss research initiative, headquartered at University of Zurich, which brings together leading specialists in experimental and clinical nephrology and physiology from the universities of Bern, Fribourg, Geneva, Lausanne, and Zurich, and corresponding university hospitals. |
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