Nusse Laboratory at Sanford Identifies Elusive Mouse Liver Stem Cell


Stanford University life science researchers have managed to successfully identify a stem cell population that has eluded many laboratories for some time. Essentially, the Stanford team has discovered a previously unknown population of liver cells in mice that function as liver stem cells. Such a find could aid drug testing and increase our present understanding of liver biology and disease.

Researchers in the laboratory of Roel Nusse at the Stanford University School of Medicine have identified a cell type in the liver of laboratory mice that can both self-renew and make new liver cells. This discovery by Nusse and others settles a long-standing conundrum of how the liver maintains itself when liver cells grow old and die.

“There’s always been a question as to how the liver replaces dying hepatocytes,” said professor of developmental biology Roel Nusse, PhD. “Most other tissues have a dedicated population of cells that can divide to make a copy of themselves, which we call self-renewal, and can also give rise to the more-specialized cells that make up that tissue. But there never was any evidence for a stem cell in the liver.”

It was assumed for some time that mature hepatocytes (liver cells) would themselves divide to replace a dying neighbor. However, hepatocytes have an abnormal amount of DNA, which would make cell division extremely difficult.

Nusse and his team published this research in the Aug. 5 edition of the journal Nature. The first author of this paper, Bruce Wang, MD, an assistant professor of gastroenterology and hepatology at the University of California-San Francisco, led the research while serving as a visiting scholar in Nusse’s lab.

The liver is a large, multi-lobed organ that filters toxins from the blood, synthesizes blood proteins, and makes digestive enzymes and bile. It is involved in many important metabolic processes. The liver contains a central vein that carries blood through it. The stem cells identified by Wang and Nusse are found adjacent to this vein.

Classically, hepatocytes were largely thought to be all alike. Most mature hepatocytes are “polyploid,” which means that they have more than the normal two copies of each chromosome. With all this extra DNA, it makes it difficult or even impossible, for these cells to divide normally, but this extra DNA might confer other benefits.

“If it’s not necessary for a cell to maintain the capacity to divide, it can do whatever it wants with its genome,” said Nusse. “Red blood cells, for instance, have no DNA. Muscle cells have many copies of each chromosome.” Having extra copies of chromosomes might allow these cells to make large amounts of particular proteins quickly, for example.

However, the cell population identified by Wang and Nusse in the livers of laboratory mice is diploid, and have only two copies of each chromosome. These cells can divide to make carbon copies of themselves, or to make cells that begin their lives as diploid but then acquire additional copies of their chromosomes as they move away from the central vein into the main body of the liver.

“People in the field have always thought of hepatocytes as a single cell type,” said Wang. “And yet the cell we identified is clearly different from others in the liver. Maybe we should accept that there may be several subtypes of hepatocytes, potentially with different functions.”

To identify liver-specific stem cells, Wang and Nusse identified cells that express the protein Axin2. They found these axin2-expressing cells surrounding the central vein. Axin2 is produced by cells in response to the presence of members of the Wnt signaling protein family, and decades of research by Nusse and other laboratories have shown that the Wnt proteins play a critical role in embryonic development, and in the growth and maintenance of stem cells throughout the body.

Interestingly, Wang and Nusse, and others showed that the endothelial cells that line the interior surface of the central vein in the liver produce Wnt2 and Wnt9b. These secreted Wnt proteins confer stem cell properties on the neighboring hepatocytes that surround the central vein.

Finally, Nusse’s team discovered that a portion of the descendants of the Axin2-expressing cells move outward from the central vein over time, become polyploid and begin to express other, hepatocyte-specific genes. About one year after being born, these descendant cells had effectively replaced about 30 percent of the entire mouse liver, and made up about 40 percent of all hepatocytes in the liver.

These newly identified liver stem cells also express genes associated with very early embryonic development, which may give a clue as to when and where they arise.

“Perhaps these stem cells in the adult liver actually arise very early in development,” said Nusse, “when the embryo sets aside a certain population of cells to maintain the organ during adult life.”

Although the current research was conducted in mice, it is possible that there are more than just one kind of hepatocyte in humans as well, and this realization could transform the study of liver biology. For example, hepatocytes have proven notoriously difficult to grow in laboratory culture for study or for use in drug testing.

“The most common reason that promising new drugs for any type of condition fail is that they are found to be toxic to liver,” said Wang. “Researchers have been trying for decades to find a way to maintain hepatocytes in the laboratory on which to test the effects of potential medications before trying them in humans. Perhaps we haven’t been culturing the right subtype. These stem cells might be more likely to fare well in culture.”

There’s also an opportunity to better understand human disease.

“Does liver cancer arise from a specific subtype of cells?” said Wang. “This model also gives us a way to understand how chromosome number is controlled. Does the presence of the Wnt proteins keep the stem cells in a diploid state? These are fundamental biological questions we can now begin to address.”

Treating Colon Cancer By Activating Damaged Genes


What if doctors could turn cancer cells into healthy cells? It would change everything about how we treat cancer. Researchers may have discovered a way to do that in colorectal cancer.

What if we could turn the clock back on cancer cells and return them to their healthy status?   A new study in animals might have accomplished exactly that.

A research team from the Memorial Sloan Kettering Cancer Center has reactivated a defective gene in mice with colorectal cancer.  This gene, adenomatous polyposis coli, or Apc, is commonly defective in colorectal cancer cells.  Approximately 90 percent of colorectal tumors have a loss-of-function mutation of this gene.

At the onset of this research project, The Sloan Kettering group suppressed the expression of the Apc gene in mice.  The Apc gene encodes a protein that regulates an important cell signaling pathway known as the Wnt signal pathway.  Suppression of Apc activates the Wnt signaling pathway, which helps cancer cells grow and survive.

Afterwards, they reactivated the Apc gene, which returned Wnt signaling to its normal levels and the cancerous tumors stopped growing, and normal intestinal function was restored in four days. By two weeks after Apc was reactivated, the tumors were gone and there were no lingering signs of no signs of cancer relapse during the six-month follow-up.

The same approach turned out to be effective in mice with colorectal cancer tumors that result from activating mutations in the Kras gene and loss-of-function mutations in the p53 gene.  In humans, about half of colorectal tumors have these mutations

This study was published in the prestigious international journal, Cell, by Scott Lowe and his colleagues.  “Treatment regimens for advanced colorectal cancer involve combination chemotherapies that are toxic and largely ineffective, yet have remained the backbone of therapy over the last decade,” said Lowe.

Apc reactivation might very well be the way to improved treatment for colorectal cancer.  It is doubtful it will be helpful in other types of cancer, but in the future, it might become so.  “The concept of identifying tumor-specific driving mutations is a major focus of many laboratories around the world,” said Lukas Dow, Ph.D., of Weill Cornell Medical College, who is the first author of this study.

“If we can define which types of mutations and changes are the critical events driving tumor growth, we will be better equipped to identify the most appropriate treatments for individual cancers,” said Dow.

Colorectal cancer begins in the colon or rectum, and it remains the second-most prevalent cause of cancer death in developed countries.

According to the Surveillance, Epidemiology, and End Results Program, in 2012, there were 1,168,929 people living with colon and rectal cancer in the United States.

Estimates postulate that there will be 132,700 new cases of colorectal cancer in the United States in 2015, and about 49,700 people will lose their lives to this disease. Worldwide, colorectal cancer is the cause of approximately 700,000 deaths each year.

Internist and gastroenterologist Dr. Frank Malkin expressed optimism regarding genetic research into colorectal cancer.  He said in an interview with the medical news service, Healthline: “They’ve identified a suppressor gene that can turn a tumor on and off. It can suppress the cancer and destroy it rapidly. That’s very promising.”

Cancers are normally treated with a combination of surgery, chemotherapy, and radiation.  These rather harsh treatments can take a lasting toll.  Easier and more effective treatments could change the lives of cancer patients.

Michelle Gordon, D.O., FACOS, FACS, finds it encouraging. “If this treatment is to be believed, all current modalities will be obsolete.”

However, Malkin and Gordon both cautioned that it is simply too early to bring this strategy to the clinic to treat human patients.

“There are so many unknowns when taking a mouse model to humans,” Gordon told Healthline. “This may be the foundational step that will lead to curing most colorectal cancers. This study can provide hope to future generations of colorectal cancer [patients], but I believe a cure is decades away.”

Researchers know Apc mutations initiate colorectal cancer, but they are unsure if Apc mutations are involved in promoting tumor growth after the cancer has developed.

The next step in this work will examine the ability of Apc reactivation to affect tumors that have spread or metastasized to distant locations in the body.  Lowe and his colleagues are also hard at work to determine precisely how Apc works.  That will help scientists develop safe treatments that change cancer cells into normal cells. Such a drug could make colorectal cancer treatment easier, faster, and safer.

How this research will impact other types of cancer remains unclear.  “Cure rates for colorectal cancers are better than they used to be, especially when treated in the early stages,” said Malkin.  Nevertheless, it is still far better to stop tumors before they start.

According to Malkin, the number of colon cancer cases has dropped dramatically since routine colonoscopy screening began. A colonoscopy allows doctors to find and remove polyps before they turn cancerous.  Malkin also looks forward to genetic research that will identify those at greater risk for colorectal cancers.

“Right now, we’re using colonoscopy to screen people over 50, most who don’t have the genetic predisposition and will never get colorectal cancer,” he said. “We don’t yet have the genetic studies that would help us identify high-risk patients so we don’t have to screen everyone.”

I must admit that I remain skeptical as to whether or not this will work.  The reasons for my skepticism lie in the fact that tumor cells in the colon are the result of a series of mutations in cells that cause the cells to overgrow and eventually become invasive.  Colorectal carcinoma cells have mutations in several genes and not just Apc.  Apc reactivation worked in these mice because this was the only gene affected in these animals.  In a cancerous human colon, the cancer cells have a variety of mutations.  Kurt Vogelstein’s work at Johns Hopkins has shown this in great detail.  If Lowe could demonstrate the efficacy of his treatment in mice with humanized immune systems that have been infected with human colorectal carcinoma cells, then I will believe that this technique could work in human patients.  For now, I remain skeptical.

A More Efficient Way to Make Induced Pluripotent Stam cells


Mark Stadtfeld and his colleagues at the NYU Longone Medical Center has devised a new method for making induced pluripotent stem cells that greatly increases efficiency at which these cells are made.

Induced pluripotent stem cells or iPSCs are made from mature, adult cells by mean of a combination of genetic engineering and cell culture techniques. In short, the expression of four genes is forced in adult cells; Oct4, Sox2, Klf4, and c-Myc or OSKM. The proteins encoded by these four genes cooperatively work to drive a fraction of the cells into an immature state that resembles that of embryonic stem cells. These cells are them grown in cell culture systems that select for those cells that can grow continuously and form colonies of cells derived from progenitor cells. These cell colonies are them repeated isolated a re-cultured until an iPSC line has been established.

Unfortunately, this process is rather inefficient and tedious, since less than one percent or so of the reprogrammed cells actually undergo successful reprogramming. Additionally, it can take several weeks to properly establish an iPSC line. Thus, stem cell scientists have been looking at several different ways to boost the efficiency of this process.

Stadtfeld and his coworkers tried to add compounds to the cultured cells to determine if the culture conditions could actually augment the efficiency of the reprogramming process. “We especially wanted to know if these compounds could be combined to obtain stem cells at high-efficiency,” said Stadtfeld.

The compounds to which Stadtfeld was referring were two cell signaling proteins called Wnt and TFG-beta. Both of these compounds regulate a host of cell growth processes. Stadtfeld wanted to try regulating both of these pathways at the same time, in addition to providing cells with ascorbic acid, which is also known as vitamin C. Even vitamin C is more popularly known as an antioxidant, vitamin C also can remodel chromatin (that tight structure into which cells package their DNA).

When mouse skin fibroblasts were treated with OSKM and a compound that activates Wnt signaling, the efficiency of iPSC derivation increased slightly. The same thing was observed if fibroblasts were treated with OSKM and a compound that inhibits TGF-beta signaling or vitamin C. However, when all three of these compounds were combined, OSKM-engineered fibroblasts were reprogrammed at an efficiency of close to 80 percent. When different cell types were used as the starting cell, such as blood progenitor cells, the efficiency jumped to close to 100 percent; a result that was also observed if liver progenitor cells were used as the starting cell.

Stadtfeld is confident that these dramatic increases in iPSC derivation should improve future studies with iPSCs, since his protocol should make iPSC derivation more predictable. “It’s just a lot easier this way to study the mechanisms that govern reprogramming, as well as detect any undesired features that might develop in iPSCs,” he said.

Vitamin C and the two compounds used to manipulate the Wnt and TGF-β pathways have been widely used in research and have few unknown or hazardous effects. However, OKSM has in some cases caused undesired features in iPSCs, such as increased mutation rates. Stadtfeld believes that by making iPSC induction more rapid and efficient, his new technique might also make the resulting stem cells safer. “Conceivably it reduces the risk of abnormalities by smoothening out the reprogramming process,” Dr. Stadtfeld says. “That’s one of the issues we’re following up.”

Micro-Grooved Surfaces Influence Stem Cell Differentiation


Martin Knight and his colleagues from the Queen Mary’s School of Engineering and Materials Science and the Institute of Bioengineering in London, UK have shown that growing adult stem cells on micro-grooved surfaces disrupts a particular biochemical pathway that specified the length of a cellular structure called the “primary cilium.” Disruption of the primary cilium ultimately controls the subsequent behavior of these stem cells.

Primary cilia are about one thousand times narrower than a human hair. They are found in most cells and even though they were thought to be irrelevant at one time, this is clearly not the case.

Primary Cilium

The primary cilium acts as a sensory structure that responds to mechanical and chemical stimuli in the environment, and then communicates that external signal to the interior of the cell.  Most of the basic research on this structure was done using a single-celled alga called Chlamydomonas.

Martin Knight and his team, however, are certain that primary cilia in adult stem cells play a definite role in controlling cell differentiation.  Knight said, “Our research shows that they [primary cilia] play a key role in stem cell differentiation.  We found it’s possible to control stem cell specialization by manipulating primary cilia elongation, and that this occurs when stem cells are grown on these special grooved surfaces.”

When mesenchymal stromal cells were grown on grooved surfaces, the tension inside the cells was altered, and this remodeled the cytoskeleton of the cells.  Cytoskeleton refers to a rigid group of protein inside of cells that act as “rebar.” for the cell.  If you have ever worked with concrete, you will know that structural use of concrete requires the use of reinforcing metal bars to prevent the concrete from crumbling under the force of its own weight.  In the same way, cytoskeletal proteins reinforce the cell, give it shape, help it move, and help it resist shear forces.  Remodeling of the cytoskeleton can greatly change the behavior of the cell.

The primary cilium is important for stem cell differentiation.  Growing mesenchymal stromal cells on micro-grooved surfaces disrupts the primary cilium and prevents stem cell differentiation.  This simple culture technique can help maintain stem cells in an undifferentiated state until they have expanded enough for therapeutic purposes.

Once again we that there are ways to milk adult stem cells for all they are worth.  Destroying embryos is simply not necessary to save the lives of patients.

A Molecular Switch that Causes Stem Cell Aging


A study from the Cincinnati Children’s Hospital Medical Center, in collaboration with the University of Ulm in Germany has discovered a molecular switch that causes the aging of blood stem cells. This same work suggests a therapeutic strategy to delay stem cell aging.

Hematopoietic stem cells (HSCs) reside in the bone marrow and make all the red and white blood cells that populate the bloodstream. Proper HSC function is absolutely vital to the ongoing production of different types of blood cells that allow the immune system to fight infections and organs to receive adequate quantities of oxygen.

Hartmut Geiger from the Cincinnati Children’s Hospital Medical Center and the University of Ulm was the senior researcher on this project. Dr. Geiger said, “Although there is a large amount of data showing that blood stem cell function declines during aging, the molecular processes that cause this remain largely unknown. This prevents rational approaches to attenuate stem cell aging. This study puts us significantly closer to that goal through novel findings that show a distinct switch in a molecular pathway is very critical to the aging process.”

The pathway to which Dr. Geiger referred is the Wnt signaling pathway, which plays a foundational role in animal development, cell-cell communication, tissue generation, and is also involved in the pathology of various diseases.

Crystal structure of XWnt8
Crystal structure of XWnt8

Analysis of mouse models and cultured HSCs showed that under normal conditions, Wnt signaling in HSCs occurred through the so-called “canonical” Wnt signaling pathway. The canonical Wnt signaling pathway utilizes the typical components of Wnt signaling that were first identified in the fruit fly and then isolated and characterized in vertebrates (shown below).

Canonical Wnt signaling

However, Wnt proteins can also signaling through other, distinct signal transduction pathways, and these types of pathways are collectively known as “noncanonical” Wnt signaling pathway. In aging HSCs, a switch from canonical Wnt signaling to noncanonical Wnt signaling marked the onset of HSC aging.  See below for one example of non-canonical Wnt signaling.

Non-canonical Wnt signaling

To test this observation, Geiger’s group overexpressed Wnt5 in HSCs (a Wnt protein known to induced signaling through noncanonical Wnt signaling pathways), and immediately, the HSCs began to show the signs of aging.

One of the targets of Wnt5 signaling is a protein called Cdc42, which influences the cytoskeleton of cells.  Therefore, Geiger and his crew asked if Cdc42 was activated in those HSCs that overexpressed Wnt5.  The answer to this question was a clear “yes.”  Then they treated cultured HSCs with a molecule that inhibited Cdc42 activity.  This treatment reversed the aging process in HSCs.

To test their hypothesis in a living animal, Geiger and others removed a copy of the Wnt5 gene from HSCs in laboratory mice.  Mice that lacked functional Wnt5 protein in HSCs, showed rejuvenation of the aged HSCs.  Mice that lacked both copies of the Wnt5 gene showed a delayed aging process in their HSCs.

Even though this study has definitely made an important contribution to understanding HSC aging, more work is needed before a therapeutic strategy is in place.

Stem Cell Transplant Repairs the Damage that Results from Inflammatory Bowel Disease


A source of stem cells from the digestive tract can repair a type of inflammatory bowel disease when transplanted into mice has been identified by British and Danish scientists.

This work resulted from a collaboration between stem cell scientists at the Wellcome Trust-Medical Research Council/Cambridge Stem Cell Institute at Cambridge University, and the Biotech Research and Innovation Centre (BRIC) at the University of Copenhagen, Denmark. This research paves the way for patient-specific regenerative therapies for inflammatory bowel diseases such as ulcerative colitis.

All tissues in out body probably contain a stem cell population of some sort, and these tissue-specific stem cells are responsible for the lifelong maintenance of these tissues, and, ultimately, organs. Organ-specific stem cells tend to be restricted in their differentiation abilities to the cell types within that organ. Therefore, stem cells from the digestive tract will tend to differentiate into cell types typically found in the digestive tract, and skin-based stem cells will usually form cell types found in the skin.

When this research team examined developing intestinal tissue in mouse fetuses, they discovered a stem cell population that differed from the adult stem cells that have already been described in the gastrointestinal tract. These new-identified cells actively divided and could be grown in the laboratory over a long period of time without terminally differentiating into adult cell types. When exposed to the right conditions, however, these cells could differentiate into mature intestinal tissue.

Fordham_CellStemCell_GraphicalAbstract

Could these cells be used to repair a damaged bowel? To address this question, this team transplanted these cells into mice that suffered from a type of inflammatory bowel disease, and within three hours the stem cells has attached to the damaged areas of the mouse intestine. integrated into the intestine, and contributed to the repair of the damaged tissue.

“We found that the cells formed a living plaster (British English for a bandage) over the damaged gut,” said Jim Jensen, a Wellcome Trust researcher and Lundbeck Foundation fellow, who led the study. “They seemed to response to the environment they had been placed in and matured accordingly to repair the damage. One of the risks of stem cell transplants like this is that the cells will continue to expand and form a tumor, but we didn’t see any evidence of that with this immature stem cell population from the gut.”

Because these cells were derived from fetal intestines, Jensen and his team sought to establish a new source of intestinal progenitor cells.  Therefore, Jensen and others isolated cells with similar characteristics from both mice and humans, and  made similar cells similar cells by reprogramming adult human cells in to induced pluripotent stem cells (iPSCs) and growing them in the appropriate conditions.  Because these cells grew into small spheres that consisted of intestinal tissue, they called these cells Fetal Enterospheres (FEnS).

Established cultures of FEnS expressed lower levels of Lgr5 than mature progenitors and grew in the presence of the Wnt antagonist Dkk1 (Dickkopf).  New cultures can be induced to form mature intestinal organoids by exposure to the signaling molecule Wnt3a. Following transplantation in a model for colon injury, FEnS contributed to regeneration of the epithelial lining of the colon by forming epithelial crypt-like structures that expressed region-specific differentiation markers.

“We’ve identified a source of gut stem cells that can be easily expanded in the laboratory, which could have huge implications for treating human inflammatory bowel diseases. The next step will be to see whether the human cells behave in the same way in the mouse transplant system and then we can consider investigating their use in patients,” Jensen said.

Isolation of Pancreatic Stem Cells


There has been a robust debate as to whether or not the pancreas has a stem cell population. Several studies suggested that the pancreatic duct cells could differentiate into hormone-secreting pancreatic cells. Unfortunately, when the cells of the pancreatic duct are marked, they clearly never contribute to regeneration of the pancreas. According to an article that appeared in the journal Developmental Cell by Oren Ziv, Benjamin Glaser, and Yuval Dor entitled “The Plastic Pancreas,” tying off the pancreatic duct kills off the acinar cells, but it leads to a large increase in the number of hormone-secreting beta cells. Something seems to be contributing cells to the adult pancreas. However when lineage studies tried to confirm that the pancreatic duct cells formed the new cells, it failed to find any connection between the new cells in the pancreas and the duct.

Pancreas

Recent experiments from Chris Wright’s lab suggest that the acinar cells are a population of progenitor cells that divide and differentiate into different kinds of pancreatic cell types after injury to the pancreas. A similar result was observed in work by Desai and others. If that’s not odd enough for you, another set of experiments from Pedro Herrera research group has shown once all the insulin-secreting beta cells are killed off, the adjacent glucagon-secreting cells transdifferentiate into insulin-secreting beta cells. Therefore, something interesting is afoot in the pancreas.

All these experiments were done with rodents. Whether or not they are transferable to human remains uncertain. Nevertheless, a fascinating paper in EMBO Journal from Hans Clevers lab at the Hubrecht Institute, Utrecht, Netherlands haws succeeded in culturing pancreatic precursor cells.

Here’s how they did it. Clevers and his crew took the pancreatic duct of mice and partially tied it off. In order to stem cells from the digestive tract to grow, they must upregulate a signaling pathway called the “Wnt” pathway. The Wnt pathway is quiet in the pancreas, but one the pancreas is injured, the Wnt pathway swings into gear and the cells begin to divide.

When Clevers and company dropped pancreatic duct tissue into culture, Wnt signaling activity soared and the cells grew into a mini-organ (organoid) that resembled and tiny pancreas in a culture dish. In fact, a single cell taken from the pancreatic duct could be cultured into an organoid.

Establishment of the pancreas organoids from adult pancreatic ducts. (A) Scheme representing the isolation method of the pancreatic ducts and the establishment of the pancreatic organoid culture. The pancreatic ducts were isolated from adult mouse pancreas after digestion, handpicked manually and embedded in matrigel. Twenty-four hours after, the pancreatic ducts closed and generated cystic structures. After several days in culture, the cystic structures started folding and budding. (B) Representative serial DIC images of a pancreatic organoid culture growing at the indicated time points. Magnifications: × 10 (days 0, 2, 4, 6, and 8) and × 4 (day 10 onwards). (C) Growth curves of pancreas cultures originated from isolated pancreatic ducts cultured as described in Materials and methods. Note that the cultures followed an exponential growth curve within each time window analysed. Graphs illustrate the number of cells counted per well at each passage from passages P1–P3 (left), P5–P7 (middle) and P10–P12 (right). The doubling time (hours) is indicated in each graph. Data represent mean±s.e.m., n=2. (D) Representative DIC images of XGAL staining in WT (left), Axin2-LacZ (middle) and Lgr5-LacZ (right) derived pancreas organoids.
Establishment of the pancreas organoids from adult pancreatic ducts. (A) Scheme representing the isolation method of the pancreatic ducts and the establishment of the pancreatic organoid culture. The pancreatic ducts were isolated from adult mouse pancreas after digestion, handpicked manually and embedded in matrigel. Twenty-four hours after, the pancreatic ducts closed and generated cystic structures. After several days in culture, the cystic structures started folding and budding.  (B) Representative serial DIC images of a pancreatic organoid culture growing at the indicated time points. Magnifications: × 10 (days 0, 2, 4, 6, and 8) and × 4 (day 10 onwards). (C) Growth curves of pancreas cultures originated from isolated pancreatic ducts cultured as described in Materials and methods. Note that the cultures followed an exponential growth curve within each time window analysed. Graphs illustrate the number of cells counted per well at each passage from passages P1–P3 (left), P5–P7 (middle) and P10–P12 (right). The doubling time (hours) is indicated in each graph. Data represent mean±s.e.m., n=2. (D) Representative DIC images of XGAL staining in WT (left), Axin2-LacZ (middle) and Lgr5-LacZ (right) derived pancreas organoids.

This experiment shows that there are techniques for growing unlimited quantities of pancreatic cells.  The therapeutic possibilities of this technology is tremendous.  In Clever’s own words, “We have found a way to activate the Wnt pathway to produce an unlimited expansion of pancreatic stem cells isolated from mice.  By changing the growth conditions we can select two different fates for the stem cells and generate large numbers of either hormone-producing beta cells or pancreatic duct cells.”

Can this work with human pancreatic duct cells?  That is the $64,000 question.   Clevers and his groups will almost certainly try to answer this questions next.  If Clevers and his crew can get this to work, then the possibilities are vast indeed.