Kidney Tubular Cells Formed from Stem Cells


A collaborative effort between several research teams has successfully directed stem cells to differentiate into kidney tubular cells. This is a significant advance that could hasten the day when stem cell-based treatments are used to treat kidney failure.

Chronic kidney disease is a major global public health problem. Unfortunately, once patients progress to kidney failure, their treatment options are limited to dialysis and kidney transplantation. Regenerative medicine, whose goal is to rebuild or repair tissues and organs, might offer a promising alternative.

A team of researchers from the Harvard Stem Cell Institute (Cambridge, Mass.), Brigham and Women’s Hospital (Boston) and Keio University School of Medicine (Tokyo) that included Albert Lam, M.D., Benjamin Freedman, Ph.D. and Ryuji Morizane, M.D., Ph.D., has been diligently developing strategies for the past five years to develop strategies to direct human pluripotent stem cells (human embryonic stem cells or hESCs and human induced pluripotent stem cells or iPSCs) to differentiate into kidney cells for the purposes of kidney regeneration.

“Our goal was to develop a simple, efficient and reproducible method of differentiating human pluripotent stem cells into cells of the intermediate mesoderm, the earliest tissue in the developing embryo that is fated to give rise to the kidneys,” said Dr. Lam. Lam also noted that these intermediate mesoderm cells would be the “starting blocks” for deriving more specific kidney cells.

Lam and his collaborators discovered a blend of chemicals which, when added to stem cells in a precise sequence, caused the stem cells to turn off their stem cell-specific genes and activate those genes found in kidney cells. Furthermore, the activation of the kidney-specific genes occurred in the same order that they turn on during embryonic kidney development.

At E10.5, the metanephric mesenchyme (red) comprises a unique subpopulation of the nephrogenic cord (yellow). Expression of the Glial-derived neurotrophic factor (Gdnf) is resticted to the metanephric mesenchyme by the actions of transcriptional activators, secreted factors, and inhibitors. GDNF binds the Ret receptor and promotes the formation of the ureteric bud, an outgrowth from the nephric duct (blue). Ret initially depends upon the Gata3 transcription factor for its expression in the nephric duct. Spry1 acts as an intracellular inhibitor of the Ret signal transduction pathway. BMP4 inhibits GDNF signaling and is in turn inhibited by the Grem1 binding protein. At 11.5, the ureteric bud has branched, forming a T-shaped structure. Each ureteric bud tip is surrounded by a cap of condensed metanephric mesenchyme. Reciprocal signaling between the cap mesenchyme and ureteric bud, as well as signals coming from stromal cells (red), maintain expression of Ret in the bud tips and Gdnf in the cap mesenchyme. Nephrons are derived from cap mesenchyme cells that form pretubular aggregates and then renal vesicles on either side of each ureteric bud tip. Wnt9b and Wnt4 induce nephron formation and are necessary for maintaining ureteric bud branching. The Six2 transcription factor prevents ectopic nephron formation. BMP7 promotes survival of the cap mesenchyme. Not all genes implicated in metanephros formation are shown for clarity (see text for further details). Green arrows indicate the ligand-receptor interaction between GDNF and Ret. Black arrows indicate the epistasis between genes but in most cases it is not known if the interactions are direct. T-shaped symbols indicate inhibitory interactions.
At E10.5, the metanephric mesenchyme (red) comprises a unique subpopulation of the nephrogenic cord (yellow). Expression of the Glial-derived neurotrophic factor (Gdnf) is resticted to the metanephric mesenchyme by the actions of transcriptional activators, secreted factors, and inhibitors. GDNF binds the Ret receptor and promotes the formation of the ureteric bud, an outgrowth from the nephric duct (blue). Ret initially depends upon the Gata3 transcription factor for its expression in the nephric duct. Spry1 acts as an intracellular inhibitor of the Ret signal transduction pathway. BMP4 inhibits GDNF signaling and is in turn inhibited by the Grem1 binding protein. At 11.5, the ureteric bud has branched, forming a T-shaped structure. Each ureteric bud tip is surrounded by a cap of condensed metanephric mesenchyme. Reciprocal signaling between the cap mesenchyme and ureteric bud, as well as signals coming from stromal cells (red), maintain expression of Ret in the bud tips and Gdnf in the cap mesenchyme. Nephrons are derived from cap mesenchyme cells that form pretubular aggregates and then renal vesicles on either side of each ureteric bud tip. Wnt9b and Wnt4 induce nephron formation and are necessary for maintaining ureteric bud branching. The Six2 transcription factor prevents ectopic nephron formation. BMP7 promotes survival of the cap mesenchyme. Not all genes implicated in metanephros formation are shown for clarity (see text for further details). Green arrows indicate the ligand-receptor interaction between GDNF and Ret. Black arrows indicate the epistasis between genes but in most cases it is not known if the interactions are direct. T-shaped symbols indicate inhibitory interactions.

The investigators were able to differentiate both hESCs and human iPSCs into cells that expressed the PAX2 and LHX1 genes, which are two key elements of the intermediate mesoderm; the developmental tissue from which the kidney develops. The iPSCs were derived by reprogramming fibroblasts obtained from adult skin biopsies into pluripotent cells. The differentiated cells expressed multiple genes found in intermediate mesoderm and spontaneously produced tubular structures that expressed those genes found in mature kidney tubules.

The researchers could then differentiate the intermediate mesoderm cells into kidney precursor cells that expressed the SIX2, SALL1 and WT1 genes. These three genes designate an embryonic tissue called the “metanephric cap mesenchyme.” Metanephric cap mesenchyme is a critical tissue for kidney differentiation. During kidney development, the metanephric cap mesenchyme contains a population of progenitor cells that give rise to nearly all of the epithelial cells of the kidney (epithelial cells or cells in a sheet, generate the lion’s share of the tubules of the kidney).

Metanephric cap mesenchyme is is red
Metanephric cap mesenchyme is is red

The cells also continued to behave like kidney cells when transplanted into adult or embryonic mouse kidneys. This gives further hope that these investigators might one day be able to create kidney tissues that could function in a patient and would be fully compatible with the patient’s immune system.

The findings are published online in Journal of the American Society of Nephrology.

Artificial Skin Created Using Umbilical Cord Stem Cells


Major burn patients usually must wait weeks for artificial skin to be grown in the laboratory to replace their damaged skin, buy a Spanish laboratory has developed new protocols and techniques that accelerate the growth of artificial skin from umbilical cord stem cells. Such laboratory-grown skin can be frozen and stored in tissue banks and used when needed.

Growing skin in the laboratory requires the acquisition of keratinocytes, those cells that compose the skin and the mucosal covering inside our mouths.  Keratinocytes can be cultured in the laboratory, but they have a long cell cycle, which means that they take a really long time to divide.  Consequently, cell cultures of keratinocytes tend to take a very long time to grow.

Keratinocytes in culture
Keratinocytes in culture

As they grow, the keratinocytes respond to connective tissue underneath them to receive the cues that tell them how to connect with each other and form either skin or oral mucosa.  In patients with severe burns, however, the underlying connective tissue is also often damaged.  Therefore, finding a way to not only accelerate the growth of cultured keratinocytes, but also to provide the underlying structure that directs the cells to form a proper epithelium is essential.

Remember that severe burn patients are living on borrowed time.  Without a proper skin covering, water loss is severe and dehydration is a genuine threat.  Also, infection is another looming threat.  Therefore, the treatment of a burn patient is a race against time.

Because umbilical cord stem cells grow quickly and effectively in culture, they might be able to differentiate into keratinocytes and form the structures associated with oral mucosa and skin.

University of Granada researchers used a new type of epithelial covering to grow their artificial skin in addition to a biomaterial made of fibrin (the stiff, cable-like protein that forms clots) and agarose to provide the underlying connective tissue. In case you might need a refresher, an epithelium refers to a layer of cells that have distinct connects with each other and form a discrete layer. Epithelia can form single or multiple layers and can be composed of long, skinny cells, short, flat cells, or boxy cells.  An epithelium is a membrane-like tissue composed of one or more layers of cells separated by very little intervening substances.  Epithelia cover most internal and external surfaces of the body and its organs.

Previous work from this same research group showed that stem cells from Wharton’s jelly (connective tissue within the umbilical cord), could be converted into epithelial cells. This current study confirms and extends this previous work and applies it to growing skin, and oral mucosa.

“Creating this new type of skin suing stem cells, which can be stored in tissue banks, mains that it can be used instantly when injuries are caused, and which would bring the application of artificial skin forward many weeks,” said Antonio Campos, professor of histology and one of the authors of this study.

By growing the Wharton’s jelly stem cells on their engineered matrix in a three-dimensional culture system, Campos and his colleagues saw that the stem cells stratified (formed layers), and expressed a bunch of genes that are peculiar to skin and other types of epithelia that cover surfaces (e.g., cytokeratins 1, 4, 8, and 13; plakoglobin, filaggrin, and involucrin).  When examined with an electron microscope, the cells had truly formed the kinds of tight connections and junctions that are so common to skin epithelia.

Electron microscopy analysis of controls and three-dimensional bioactive models of H-hOM and H-hS. SEM images (top) corresponding to N-hOM and N-hS controls showed a tight superficial layer of flat polygonal cells with desquamation signs in which cells were covering the entire surface, whereas samples kept in vitro for 2 weeks showed immature differentiation patterns, and samples implanted in vivo for 40 days tended to resemble the structure of the native control tissues, with flattened cells and evident signs of desquamation. Scale bars = 50 μm. TEM samples (bottom) were analyzed after 40 days of in vivo implantation and demonstrated that in vivo-implanted tissues were mature and well-differentiated, with numerous intercellular junctions, abundant cell organelles, and a collagen-rich stroma. Scale bars = 1 μm. Abbreviations: H-hOM, heterotypical human oral mucosa; H-hS, heterotypical human skin; N-hOM, native human oral mucosa; N-hS, native human skin; SEM, scanning electron microscopy; TEM, transmission electron microscopy.
Electron microscopy analysis of controls and three-dimensional bioactive models of H-hOM and H-hS. SEM images (top) corresponding to N-hOM and N-hS controls showed a tight superficial layer of flat polygonal cells with desquamation signs in which cells were covering the entire surface, whereas samples kept in vitro for 2 weeks showed immature differentiation patterns, and samples implanted in vivo for 40 days tended to resemble the structure of the native control tissues, with flattened cells and evident signs of desquamation. Scale bars = 50 μm. TEM samples (bottom) were analyzed after 40 days of in vivo implantation and demonstrated that in vivo-implanted tissues were mature and well-differentiated, with numerous intercellular junctions, abundant cell organelles, and a collagen-rich stroma. Scale bars = 1 μm. Abbreviations: H-hOM, heterotypical human oral mucosa; H-hS, heterotypical human skin; N-hOM, native human oral mucosa; N-hS, native human skin; SEM, scanning electron microscopy; TEM, transmission electron microscopy.

The authors conclude the article with this statement: “All these findings support the idea that HWJSCs could be useful for the development of human skin and oral mucosa tissues for clinical use in patients with large skin and oral mucosa injuries.”  Think of it folks – new skin for burn patients, quickly, safely and ethically.

Now back to reality – this is exciting, but it is a a pre-clinical study.  Larger animals studies must show the efficacy and safety of this protocol before human trials can be considered, but you must admit that it looks exciting; and without killing any embryos.

See I. Garzón, et al., Stem Cells Trans MedAugust 2013 vol. 2 no. 8625-632.