Repairing Bladders with Bone Marrow Stem Cells and Bladder Acellular Matrix


The bladder is subject to several different types of conditions that can compromise its function. Cancer of the bladder can necessitate its removal. A congenital condition called exstrophy causes the bladder to protrude through a hole in the abdominal wall also requires surgical repair of the bladder. Finally, trauma to the bladder as in the case of trampoline athletes or people who have had surgical damage to the bladder, may also repair bladder repair.

In order to repair the bladder, extra tissue must be added to it. Finding tissue to act as bladder has not been easy. In the past, surgeons have used grafts from skin, bladder submucosa, omentum, dura, peritoneum, colon, small intestine, and synthetic polymers have been used to augment the bladder. All of these compounds have their pluses and minuses for reconstructing a bladder, but all of them do not appropriately recapitulate the mechanical, structural, and functional properties of the bladder.

Currently a surgical procedure called enterocystoplasty is the most effective surgical solution for augmentation of the bladder. This procedure uses a small piece of the large intestine to increase the size of the bladder, and while it certainly improves continence, it has several complications associated, which include, metabolic disturbances, urinary stones (urolithiasis), increased mucus production, infections and increased risk of cancer of the bladder. Is there a better way?

A collaborative research project between Daniel L. Coutu from ETH Zürich, in Basel, Switzerland, Wally Mahfouz, Oleg Loutochin, and Jacques Corcos from McGill University, in Montreal, Canada, Wally Mahfouz from Alexandria University in Alexandria, Egypt, and Jacques Galipeau from Emory University in Atlanta, Georgia examined the use of bladder a cellular matrices or BAMs in combination with bone marrow-derived mesenchymal stromal cells to repair bladders in laboratory animals.

BAMs consist of bladders from animals that have been completely stripped of their cells with detergents and enzymes. Once all the cells and cell remnants have been removed, these BAMs can be molded into the form of a bladder, after which cells are reapplied. BAMs contain all the chemical nooks and crannies for cells to find, attach to, then and differentiate. Also, the bladder is a relatively simple tissue in that it has an inner epithelium (urothelium) that sits on a basement membrane, a smooth muscle layer surrounding the urothelium, and an outer serosa layer that is an extension of the peritoneum that it covered by an adventitia of connective tissue. A bladder matrix devoid of cells has all the right structures for cells to occupy, bit it needs to be repopulated with cells.

Corcos and his collaborators purchased pig bladders from slaughter houses and subjected them to detergents and enzymes until no cells were left on them. Then they used mesenchymal stromal cells from the bone marrow of rats to reseed the bladders with new cells. These structures were then used to repair the bladders to laboratory rats whose bladders had been partially removed. All the animals were then tested for retention of urine, muscle tone, pressure tolerance, and other indicators of bladder function.

The results of these tests demonstrated that the engineered bladders not only worked, but worked quite well. Some animals only received the BAM without cells, and these animals had bladders that worked better than nothing, but not terribly well. However, the animals that received BAM + mesenchymal stem cells had bladders that, for all intents and purposes, showed normal function by 6 months after the procedure.

Another significant finding of this study is that none of the animals that received BAMs had to be given any anti-rejection drugs. The immune systems of these animals did not reject the animal-based matrices.

Finally, post-mortem examinations of these animal bladders established that smooth muscle regeneration and nerve and blood vessels regeneration was also robust in these animals.

Before this procedure can work in humans, it will need to work in larger animal systems. Rat urinary systems are similar to humans, but not the same. The large advance in this study is the observation that internal bladder tissues such as smooth muscle, nerves and blood vessels can be regenerated with mesenchymal stem cells. These stem cells probably secrete a variety of molecules that promote the growth of blood vessels and nerves into the bladder.

In the words of these authors: “we demonstrated the in vivo superiority of MSCs-seeded BAMs compared with unseeded BAMs in bladder tissue engineering. Our approach is fully translatable to large animals and humans, where autologous MSCs could be seeded on allogeneic, cadaveric or xenogenic BAMs. The method presented here is a viable alternative to current treatment modalities and should prevent most complications associated with them. This study demonstrates the superiority of MSCs-seeded BAM compared to BAM alone in bladder augmentation and provides a strong basis to test our novel approach in large animal models and eventually in humans.”

Amen.

Transplanted Mesenchymal Stem Cells Prevent Bladder Scarring After Spinal Cord Injury


A collaborative research effort between laboratories from Canada and South Korea have shown that a cultured mesenchymal stem cell line called B10 can differentiate into smooth muscle cells and improve bladder function after a spinal cord injury.

Spinal cord injury can affect the lower portion of the urinary tract. Overactive bladder, urinary retention, and increased bladder thickness and fibrosis (bladder scarring) can result from spinal cord injuries. Human mesenchymal stem cells (MSCs) can differentiate under certain conditions into smooth muscle. For this reason, MSCs have therapeutic potential for patients who have suffered from spinal cord injuries.

Seung U. Kim and his colleagues from Gachon University Gil Hospital in Inchon, South Korea have made an immortalized human mesenchymal stem cell line by transfecting primary cell cultures of fetal human bone marrow mesenchymal stem cells with a retroviral vector that contains the v-myc oncogene. This particular cells line, which they called HM3.B10 (or B10 for short), grows well in culture and can also differentiates into several different cell types.

In this present study, which was published in the journal Cell Transplantation, Kim and his colleagues and collaborators injected B10 hMSCs directly into the bladder wall of mice that had suffered a spinal cord injury but were not treated showed no such improvement.

“Human MSCs can secrete growth factors,” said study co-author Seung U. Kim of the Division of Neurology at the University of British Columbia Hospital, Vancouver, Canada. “In a previous study, we showed that B 10 cells secrete various growth factors including hepatocyte growth factor (HGF) and that HGF inhibits collagen deposits in bladder outlet obstructions in rats more than hMSCs alone. In this study, the SCI control group that did not receive B10 cells showed degenerated spinal neurons and did not recover. The B10-injected group appeared to have regenerated bladder smooth muscle cells.”

Four weeks after the initial spinal cord injury, the mice in the B10-treated group received injections of B10 cells transplanted directly into the bladder wall. Kim and his team used magnetic resonance imaging (MRI) to track the transplanted B10 cells. The injected B10 cells had been previously labeled with fluorescent magnetic particles, which made them visible in an MRI.

“HGF plays an essential role in tissue regeneration and angiogenesis and acts as a potent antifibrotic agent,” explained Kim.

These experiments also indicated that local stem cell injections rather than systemic, intravenous infusion was the preferred method of administration, since systemic injection caused the hMSCs get stuck largely in the blood vessels of the lungs instead of the bladder.

The ability of the mice to void their bladders was assessed four weeks after the B10 transplantations. MRI analyses clearly showed strong signals in the bladder as a result of the labeled cells that had been previously transplanted. Post-mortem analyses of the bladders of the transplanted group showed even more pronounced differences, since the B10-injected animals had improved smooth muscle cells and reduced scarring.

These results suggest that MSC-based cell transplantation may be a novel therapeutic strategy for bladder dysfunction in patients with SCI.

“This study provides potential evidence that an human [sic] stable immortalized MSC line could be useful in the treatment of spinal cord injury-related problems such as bladder dysfunction.” said Dr. David Eve, associate editor of Cell Transplantation and Instructor at the Center of Excellence for Aging & Brain Repair at the University of South Florida. “Further studies to elucidate the mechanisms of action and the long-term effects of the cells, as well as confirm the optimal route of administration, will help to illuminate what the true benefit of these cells could be.”

Human Umbilical Cord Mesenchymal Stem Cells Form Prostate Gland Tissues


Repairing the prostate gland is an important goal in regenerative medicine. However, finding the right cell for the job has proven to be a slow and tedious search.

To that end, Wei-Qiang Gao and his colleagues from Shanghai Jiao Tong University in Shanghai, China, used mesenchymal stem cells from human umbilical cord (hUC-MSCs) to test the ability of these cells to differentiate into prostate-specific cells. They combined hUC-MSCs with rat urogenital sinus stromal cells (rUGSSs) and then transplanted these cells into the renal capsule of BLB/c nude mice for two months. Cells tend to grow very well under the kidney capsule because this particular microenvironment has a very rich blood supply. Also the rUGSSs provide soluble, secreted factors that induce the hUC-MSCs to differentiate into prostate-specific cells.

After removing the implanted tissue, analyses of the implanted cells showed that the hUC-MSCs differentiated into prostate epithelial-like cells. This was confirmed by the presence of prostate specific antigen on the surfaces of these hUC-MSCs. Prostate specific antigen is only found on prostate cells, which is the reason why this protein is such a good indicator of prostate cancer. Also, the hUC-MSCs formed prostatic glandular structures that had the same cellular architecture as a normal prostate (see figure F below). Additionally, the human origin of the hUC-MSCs was further confirmed by the detection of a protein called human nuclear antigen, which is specific to human cells.

Human UC-MSCs combined with rUGSSs can generate prostate glands. Mice were sacrificed 2 months after co-transplantation surgery, and the kidneys from the cell implanted nude mice were collected. (A) Graft initiated with hUC-MSCs alone and (B) rUGSSs alone were used as negative control, respectively. (C) Graft derived with hUC-MSCs and rUGSSs. (D–F) Histological analyses of the sections of the graft stained for haematoxylin and eosin (H&E). (D) Note that while hUC-MSCs alone and (E) rUGSSs single cell type transplantation fail to regenerate prostate glandular structures. (F) co-transplantation of hUC-MSCs and rUGSSs gives rise to prostate glandular structures. Scale bar 50 mm.
Human UC-MSCs combined with rUGSSs can generate prostate glands. Mice were sacrificed 2 months after co-transplantation surgery, and the kidneys from the cell implanted nude mice were collected. (A) Graft initiated with hUC-MSCs alone and (B) rUGSSs alone were used as negative control, respectively. (C) Graft derived with hUC-MSCs and rUGSSs. (D–F) Histological analyses of the sections of the graft stained for haematoxylin and eosin (H&E). (D) Note that while hUC-MSCs alone and (E) rUGSSs single cell type transplantation fail to regenerate prostate glandular structures. (F) co-transplantation of hUC-MSCs and rUGSSs gives rise to prostate glandular structures. Scale bar 50 mm.

This interesting paper shows that hUC-MSCs can differentiate into epithelial-like cells that are normally derived from embryonic endodermal tissue. This implies that MSCs from umbilical cord can be used to repair not only prostate glands, but also other endodermally-derived tissues.

Amniotic Fluid Stem Cells Aid Kidney Transplantation Success in a Pig Model


When a kidney patient receives a new kidney, the donated kidney undergoes a brief loss of blood supply followed by a restoration of the blood supply. This phenomenon is called ischemia/reperfusion (IR), and IR tends to cause cell death, followed by rather extensive scarring. Tissue scarring is called tissue fibrosis and a scarred kidney can lead to so-called transplant dysfunction, which means that the transplanted kidney does not work terrible well, and this can cause transplant failure.

Previous studies in laboratory rodents have shown that mesenchymal stem cells from amniotic fluid (afMSCs) are beneficial in protecting against transplant-induced fibrosis (Perin L, et al. PLoS One 2010;5:e9357; Hauser PV, et al. Am J Pathol 2010;177:2011-2021).

Now a research group at INSERM, France led by Thierry Hauet has developed a pig-based model of kidney autotransplantation that is comparable to the human situation with regards to the structure of the kidney and the damage that results from renal ischemia (for papers, see Jayle C, et al. Am J Physiol Renal Physiol 2007; 292: F1082-1093; and Rossard L, et al. Curr Mol Med 2012; 12: 502-505). On the strength of these previous experiments, Hauet’s group has published a new paper in Stem Cells Translational Medicine in which they report that porcine afMSCs can protect against IR-related kidney injuries in pigs.

Hauet and others showed that porcine afMSCs could be easily collected at birth and cultured. These cells showed the ability to differentiate into fat, and bone cells, made many of the same cell surface markers as other types of mesenchymal stem cells (e.g., CD90, CD73, CD44, and CD29), but showed a diminished ability to differentiate into blood vessel cells. When afMSCs are added to extirpated kidneys during the reperfusion (reoxygenation) process in an “in vitro” (fancy way of saying “in a culture dish”) model of organ-preservation, these stem cells significantly increased the survival of blood vessel (endothelial) cells. Endothelial cells are one of the main targets of ischemic injury, and the added cells bucked up these endothelial cells and rescued them from programmed cell death. In addition to these successes, Hauet and others showed that adding intact porcine afMSCs was not necessary, since addition of the culture medium used to grow the afMSCs (conditioned medium or CM) also rescued kidney endothelial cell death. The afMSC-treated kidneys survived because they had significantly larger numbers of blood vessels, and this seems to be the main factor that causes the extirpated kidney to survive intact.

While these experiments were successful, Hauet and others know that unless they were able to show that these cells improved kidney transplant outcomes in a living animal, their research would not be deemed clinically relevant. Therefore, Hauet and others injected afMSCs into the renal artery of pigs that had received a kidney transplant six days after the transplant. IR injuries following kidney transplants led to increased serum creatinine levels, but those pigs that had been infused with afMSCs showed reduced creatinine levels and lower protein levels in their urine (proteinuria). In fact, seven days after the stem cell infusion, the urine creatinine and protein levels had returned to pre-transplant levels. Three months after the transplant, the pigs were put down, and then the kidneys were subjected to tissue analyses. Microscopic examination of tissue slices from these kidneys showed that afMSC injection preserved the structural integrity of microscopic details of the kidneys and reduced the signs of inflammation. Control animals that were not treated with afMSCs showed disruption of the microscopic structures of the kidneys and extensive inflammation and scarring. Also, because the kidney controls blood chemistry, a comparison of the blood chemistries of these two groups of animals showed that the blood chemistries of the afMSC-treated animals were normal as opposed to the control animals.

Amniotic Fluid Stem Cells Aid Kidney Transplantation in Porcine Model

Molecular analyses also showed a whole host of pro-blood vessel molecules in the kidneys of the afMSC-treated pigs. VEGFA (pro-angiogenic growth factor), and Ang1 (capillary structure strengthening and maintenance of vessel stability), proteins were increased in the kidneys of afMSC animals compared to control animals. Thus the infused stem cells increased the expression of pro-blood vessel molecules, which led to the formation of larger quantities of blood vessels, reduced cell death and decreased inflammation.

These findings demonstrate the beneficial effects of infused afMSCs on kidney transplant. Since afMSCs are easy to isolate and grow in culture, secrete proangiogenic and growth factors, and can differentiate into many cell lineages, including renal cells (see Perin L, et al. Cell Prolif 2007; 40: 936-948; De Coppi P, et al. Nat Biotechnol 2007; 25: 100-106; and In ‘t Anker PS, et al. Stem Cells 2004;22:1338-1345). This makes these cells a viable candidate for clinical application. This study also highlights pigs as a preclinical model as a powerful tool in the assessment of stem cell-based therapies in organ transplantation.

Stem Cells from Abdominal Fat Helps Fight Kidney Disease


Researchers from Chicago, Illinois have shown that a fatty fold of tissue within the abdomen contains a rich source of stem cells that can help heal diseased kidneys.

Scientists from the laboratory of Ashok K. Singh at Hospital of Cook County used a rat model of chronic kidney disease to examined the efficacy of these cells.

In past experiments, transplanted stem cells have failed to live very long in the body of the recipient. To solve this problem, Singh and his co-workers connected the a fatty fold of tissue located close to the kidney called the “omentum” to the kidney. The omentum is a wonderfully rich source of stem cells and by connecting the kidney to the omentum, Singh and his colleagues subjected the diseased kidney to a constant supply of stem cells.

Omentum

After 12 weeks of being connected to the kidney, the kidney showed significant signs of improvement.

The progression of chronic kidney disease was slowed due to this continuous migration of stem cells from the omentum to the diseased kidney. The influx of these stem cells seemed to direct healing of the kidney.

This experiment is significant in that it suggests that resident stem cells that facilitate healing of the kidney, but only when they are in contact with the tissue over a long period of time. Also, it implies that a supposedly useless organ that lies close to the kidney can be fused with the kidney to heal it with a patient’s own stem cells. This therapeutic strategy seems to be ideal for kidney patients.

UC Davis Stem Cell Scientists Make Bladder Cells from Pluripotent Stem Cells


Patients who suffer from malformation of the spinal cord or have suffered a severe spinal cord injury sometimes have bladder malfunction as well. Replacing a poorly functioning bladder is a goal of regenerative medicine, but it is not an easy goal. The bladder is lined with a special cell population called “urothelium.” Urothelium is found throughout the urinary tract and it is highly elastic. Persuading stem cells to form a proper urothelium has proved difficult.

Urothelium
From http://ocw.tufts.edu/data/4/221158/221174_xlarge.jpg

Now scientists from the University of California, Davis (my alma mater), have succeeded in devising a protocol for differentiating human pluripotent stem cells into urothelium. The laboratory of Eric Kurzock, chief of the division of pediatric urologic surgery at UC Davis Children’s Hospital, published this work in the journal Stem Cells Translational Medicine. This work is quite exciting, since it provides a way to potentially replace bladder tissue for patients whose bladders are too small or do not function properly.

Kurzock explained: “Our goal is to use human stem cells to regenerate tissue in the lab that can be transplanted into patients to augment or replace their malfunctioning bladders,”

In order to make bladder cells in the laboratory, Kurzrock and his coworkers used two different types of human pluripotent stem cells. First, they used two types of induced pluripotent stem cells (iPS cells). The first came from laboratory cultures of human skin cells that were genetically engineered and cultured to form iPS cultures. The second iPS line was derived from umbilical cord blood cells that had been genetically reprogrammed into an embryonic stem cell-like state.

Even though further work is needed to establish that bladder tissues made from such stem cells are safe or effective for human patients, Kurzrock thinks that iPS cell–derived bladder grafts made from a from a patient’s own skin or umbilical cord blood cells represent the ideal tissue source for regenerative bladder treatments. This type of tissue would be optimal, he said, because it lowers the risk of immunological rejection that typifies most transplants.

One of the truly milestone developments in this research is the protocol Kurzrock and his colleagues developed to direct pluripotent stem cells to differentiate into bladder cells. This protocol was efficient and, most importantly, allowed the stem cells to proliferate in culture over a long period of time. This is crucial in order to have enough material for therapeutic purposes.

“What’s exciting about this discovery is that it also opens up an array of opportunities using pluripotent cells,” said Jan Nolta, professor and director of the UC Davis Stem Cell program and a co-author on the new study. “When we can reliably direct and differentiate pluripotent stem cells, we have more options to develop new and effective regenerative medicine therapies. The protocols we used to create bladder tissue also provide insight into other types of tissue regeneration.”

To hone their urothelium-differentiation protocol, Kurzrock and his colleagues used human embryonic stem cells obtained from the National Institutes of Health’s human stem cell repository. These cells were successfully differentiated into bladder cells. Afterwards, the Kurzrock group used the same protocol to coax iPS cells made from skin and umbilical cord blood into urothelium. Not only did these cells look like urothelium, but they also expressed the protein “uroplakin,” which is unique to the bladder and helps make it impermeable to toxins in urine.

In order to bring this protocol to the clinic, the cells must proliferate, differentiate and express bladder-specific proteins without depending on any animal or human products. They must do all these things independent of signals from other human cells, said Kurzrock. Therefore, for future research, Kurzrock and his colleagues plan to modify their laboratory cultures so that they will not require any animal and human products, which will allow use of the cells in patients.

Kurzrock’s primary goal as a physician is with children who suffer from spina bifida and other pediatric congenital disorders. Currently, when he surgically reconstructs a child’s defective bladder, he must use a segment of their own intestine. Because the function of intestine, which absorbs food, is almost the opposite of bladder, bladder reconstruction with intestinal tissue may lead to serious complications, including urinary stone formation, electrolyte abnormalities and cancer. According to Kurzrock, developing a stem cell alternative not only will be less invasive, but should prove to be more effective, too, he said.

Another patient group who might benefit from this research is bladder cancer patients. More than 70,000 Americans each year are diagnosed with bladder cancer, according to the National Cancer Institute. “Our study may provide important data for basic research in determining the deviations from normal biological processes that trigger malignancies in developing bladder cells,” said Nolta. More than 90 percent of patients who need replacement bladder tissue are adults with bladder cancer. Kurzrock said “cells from these patients’ bladders cannot be used to generate tissue grafts because the implanted tissue could carry a high risk of becoming cancerous. On the other hand, using bladder cells derived from patients’ skin may alleviate that risk. Our next experiments will seek to prove that these cells are safer.”

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.