Category Archives: Stem Cells

July 17, 2013 Hematopoietic stem cells -- bone marrow-derived adult stem cells that give rise to the wide variety of specialized blood cells -- come in two flavors: the reserve force sits quietly waiting to be called upon while the active arm continually proliferates spawning billions of blood cells every day. In their latest study, researchers at the Stowers Institute for Medical Research reveal a new mechanism that is critical in maintaining the delicate balance between the two.

Publishing in the July 17 advance online issue of Nature, the team led by Stowers Investigator Linheng Li, Ph.D., reports that genomic imprinting, a process that specifically shuts down one of the two gene copies found in each mammalian cell, prevents the reservists from being called up prematurely.

"Active HSCs (hematopoietic stem cells) form the daily supply line that continually replenishes worn-out blood and immune cells while the reserve pool serves as a backup system that replaces damaged active HSCs and steps in during times of increased need," explains Li. "In order to maintain a long-term strategic reserve of hematopoietic stem cells that lasts a lifetime it is very important to ensure that the back-up crew isn't mobilized all at once. Genomic imprinting provides an additional layer of regulation that does just that."

Sexual reproduction yields progeny with two copies, or alleles, for each gene, one from the mother and one from the father. Most genes are expressed from both copies but in mammals and marsupials a small subset of genes receives a mark, or "imprint" during the development of egg or sperm cells. These genomic imprints not only differentiate between genes of maternal and paternal origin and but specifically shut down one copy of those genes in the offspring.

Genomic imprinting is an important mechanism for regulating fetal growth and development and, not surprisingly, faulty imprinting has been linked to human disease. But whether imprinting also plays a role in adult stem cells had remained elusive.

Earlier mouse studies by Li and his collaborators had indicated that the expression of several imprinted genes changes as hematopoietic stem cells embark on their journey from quiescent reserve cells to multi-lineage progenitor cells, which form the many highly specialized cell types that circulate within the blood stream.

For the current study, the Stowers researchers focused on a differentially imprinted control region, which drives the reciprocal expression of H19 from the maternal allele and Igf2 (Insulin growth factor 2) from the paternal allele.

The study's first author Aparna Venkatraman, Ph.D., formerly a postdoc in the Li Lab and now an independent investigator at the Centre for Stem Cell Research at the Christian Medical College in Vellore, India, developed a mouse model that allowed her to specifically excise the imprinting control region from the maternal allele. As a result, the H19 gene, which restricts growth, was no longer active while the Igf2 gene, which promotes cell division, was now expressed from both the paternal and the maternal allele.

To gauge the effect off the loss of imprinting control on the maintenance of the quiescent hematopoietic stem cell pool, Venkatraman analyzed the numbers of quiescent, active and differentiated hematopoietic stem cells in mouse bone marrow.

"A large number of quiescent hematopoietic stem cells was activated simultaneously when the epigenetic control provided by genomic imprinting was removed," explains Venkatraman. "It created a wave of activated stem cells that moved through the different maturation stages."

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Genomic imprinting maintains a reserve pool of blood-forming stem cells in mouse bone marrow

Cocktail of molecules turns adult mouse cells into embryonic-like ones

By Meghan Rosen

Web edition: July 18, 2013

Whipping up a batch of stem cells just got easier.

A new recipe for transforming adult cells into embryonic-like ones calls for a chemical cocktail to erase signs of age. By adding just seven small molecules, scientists can turn back time for mature mouse cells, converting them into pluripotent stem cells. These cells hover at the brink of developing into virtually any type of tissue.

Researchers have previously created pluripotent stem cells using cloning, or by dosing a dish of adult cells with master genes that flip grown-up cells back to a youthful state. But cloning cells and tinkering with genes can be expensive and technically tricky.

So biologist Pingping Hou of Peking University in Beijing and colleagues scoured a collection of about 10,000 chemicals and found a combination that mimicked the cell-programming effects of master genes. Adding the combo to adult mouse cells turned them into pluripotent stem cells, which the researchers could then make into brain, lung or muscle tissue, Hou and colleagues report July 18 in Science.

If the chemical method works in human cells, it could one day make stem cells for medical use, the researchers suggest.

Suggested Reading

M. Rosen. Cloning produces human embryonic stem cells. Science News. Vol. 183, June 15, 2013, p. 5. Available online: [Go to]

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News in Brief: Stem cells made with just seven chemicals

July 18, 2013 Gingivae represent a unique soft tissue that serves as a biological barrier to cover the oral cavity side of the maxilla and mandible. Recently, the gingivae were identified as containing mesenchymal stem cells (GMSCs). However, it is unknown whether the GMSCs are derived from cranial neural crest cells (CNCC) or the mesoderm.

Today, the International and American Associations for Dental Research (IADR/AADR) published a paper titled "Gingivae Contain Neural-crest- and Mesoderm-derived Mesenchymal Stem Cells." The paper, written by lead author Songtao Shi, Center for Craniofacial Molecular Biology, Ostrow School of Dentistry, University of Southern California, Los Angeles, USA, is published in the OnlineFirst portion of the IADR/AADR Journal of Dental Research.

In this study, Shi and his team of researchers demonstrated that around 90 percent of GMSCs are derived from CNCC and 10 percent from the mesoderm. In comparison with mesoderm MSCs (M-GMSCs), CNCC-derived GMSCs (N-GMSCs) show an elevated capacity to differentiate into neural cells and chondrocytes as well as to modulate immune cells. When transplanted into mice with dextran sulfate sodium-induced colitis, N-GMSCs showed superior effects in ameliorating inflammatory-related disease phenotype in comparison with the M-GMSC treatment group.

Further research is required to understand the interaction between the neural crest cell derived and mesoderm derived gingivae mesenchymal stem cells (N-GMSCs and M-GMSCs) in terms of their functional roles in gingival immune defense and wound healing.

"The tooth and surrounding tissues are a rich source of stem cells, and this JDR manuscript demonstrates that gingivae contain highly proliferative stem cells from two different embryonic origins and that these cells exhibit distinct behaviors," said JDR Associate Editor Jacques Nr. "These results suggest that gingivae, an easily accessible tissue, are an attractive source for stem cells that can be used in tissue regeneration."

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Dental research: Gingival stem cells can be used in tissue regeneration

Newswise LA JOLLA, CA---- Stem cells are key to the promise of regenerative medicine: the repair or replacement of injured tissues with custom grown substitutes. Essential to this process are induced pluripotent stem cells (iPSCs), which can be created from a patient's own tissues, thus eliminating the risk of immune rejection. However, Shinya Yamanaka's formula for iPSCs, for which he was awarded last year's Nobel Prize, uses a strict recipe that allows for limited variations in human cells, restricting their full potential for clinical application.

Now, in this week's issue of Cell Stem Cell, the Salk Institute's Juan Carlos Izpisua Belmonte and his colleagues show that the recipe for iPSCs is far more versatile than originally thought. For the first time, they have replaced a gene once thought impossible to substitute, creating the potential for more flexible recipes that should speed the adoption of stem cells therapies.

Stem cells come in two types: embryonic stem cells (ESCs), which are immature cells that have never differentiated into specific cell types, and induced pluripotent stem cells, which are mature cells that have been reprogrammed back into an undifferentiated state. After the initial discovery in 2006 by Yamanaka that introducing four different genes into a mature cell could suffice for reprogramming the cell to pluripotency, most researchers adopted his recipe.

Izpisua Belmonte and his colleagues took a fresh approach and discovered that pluripotency (the stem cell's ability to differentiate into nearly any kind of adult cell) can also be accomplished by balancing the genes required for differentiation. These genes code for "lineage transcription factors," proteins that start a stem cell down the path to differentiate first into a particular cell lineage, or type, such as a blood cell versus a skin cell, and then finally into a specific cell, such as a white blood cell.

"Prior to this series of experiments, most researchers in the field started from the premise that they were trying to impose an 'embryonic-like' state on mature cells," says Izpisua Belmonte, who holds the Institute's Roger Guillemin Chair. "Accordingly, major efforts had focused on the identification of factors that are typical of naturally occurring embryonic stem cells, which would allow or further enhance reprogramming."

Despite these efforts, there seemed to be no way to determine through genetic identity alone that cells were pluripotent. Instead, pluripotency was routinely evaluated by functional assays. In other words, if it acts like a stem cell, it must be a stem cell.

That condition led the team to their key insight. "Pluripotency does not seem to represent a discrete cellular entity but rather a functional state elicited by a balance between opposite differentiation forces," says Izpisua Belmonte.

Once they understood this, they realized the four extra genes weren't necessary for pluripotency. Instead, it could be achieved by altering the balance of "lineage specifiers," genes that were already in the cell that specified what type of adult tissue a cell might become.

"One of the implications of our findings is that stem cell identity is actually not fixed but rather an equilibrium that can be achieved by multiple different combinations of factors that are not necessarily typical of ESCs," says Ignacio Sancho-Martinez, one of the first authors of the paper and a postdoctoral researcher in Izpisua Belmonte's laboratory.

The group was able to show that more than seven additional genes can facilitate reprogramming to iPSCs. Most importantly, for the first time in human cells, they were able to replace a gene from the original recipe called Oct4, which had been replaced in mouse cells, but was still thought indispensable for the reprogramming of human cells. Their ability to replace it, as well as SOX2, another gene once thought essential that had never been replaced in combination with Oct4, demonstrated that stem cell development must be viewed in an entirely new way.

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Salk Scientists Discover More Versatile Approach to Creating Stem Cells

Turning human cells into stem cells without changing their genes could lead to therapies that do not carry a risk of generating mutations.

Andrew Brookes/Corbis

Scientists have demonstrated a new way to reprogram adult tissue to become cells as versatile as embryonic stem cells without the addition of extra genes that could increase the risk of dangerous mutations or cancer.

Researchers have been striving to achieve this since 2006, when the creation of so-called induced pluripotent (iPS) cells was first reported. Previously, they had managed to reduce the number of genes needed using small-molecule chemical compounds, but those attempts always required at least one gene, Oct42, 3.

Now, writing in Science, researchers report success in creating iPS cells using chemical compounds only what they call CiPS cells1.

Hongkui Deng, a stem-cell biologist at Peking University in Beijing, and his team screened 10,000 small molecules to find chemical substitutes for the gene. Whereas other groups looked for compounds that would directly stand in for Oct4, Deng's team took an indirect approach: searching for small-molecule compounds that could reprogram the cells in the presence of all the usual genes except Oct4.

Then came the most difficult part. When the group teamed the Oct4 replacements with replacements for the other three genes, the adult cells did not become pluripotent, or able to turn into any cell type, says Deng.

The researchers tinkered with the combinations of chemicals for more than a year, until they finally found one that produced some cells that were in an early stage of reprogramming. But the cells still lacked the hallmark genes indicating pluripotency. By adding DZNep, a compound known to catalyse late reprogramming stages, they finally got fully reprogrammed cells, but in only very small numbers. One further chemical increased efficiency by 40 times. Finally, using a cocktail of seven compounds, the group was able to get 0.2% of cells to convert results comparable to those from standard iPS production techniques.

The team proved that the cells were pluripotent by introducing them into developing mouse embryos. In the resulting animals, the CiPS cells had contributed to all major cell types, including liver, heart, brain, skin and muscle.

People have always wondered whether all factors can be replaced by small molecules. The paper shows they can, says Rudolf Jaenisch, a cell biologist at the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts, who was among the first researchers to produce iPS cells. Studies of CiPS cells could give insight into the mechanisms of reprogramming, says Jaenisch.

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Stem cells reprogrammed using chemicals alone

MONDAY, July 15 (HealthDay News) -- Scientists who used adult stem cells to create functional and long-lasting blood vessels in mice say this research could lead to new treatments for cardiovascular disease.

The Massachusetts General Hospital team used so-called induced pluripotent stem cells (iPSCs) -- which are reprogrammed adult cells with many of the characteristics of embryonic stem cells -- from both healthy adults and people with type 1 diabetes to generate blood vessels on the outer surface of the brain or under the skin of mice.

The study was published online July 15 in the journal PNAS Early Edition.

"The discovery of ways to bring mature cells back to a 'stem-like' state that can differentiate into many different types of tissue has brought enormous potential to the field of cell-based regenerative medicine, but the challenge of deriving functional cells from these iPSCs still remains," study co-senior author Rakesh Jain, director of the Steele Laboratory for Tumor Biology at Mass General, said in a hospital news release.

"Our team has developed an efficient method to generate vascular precursor cells from human iPSCs and used them to create networks of engineered blood vessels in living mice," Jain said.

Being able to regenerate or repair blood vessels could be a major advance in the treatment of cardiovascular disease -- the leading cause of death in the United States -- as well as other conditions caused by blood vessel damage, such as the vascular complications of diabetes.

Commenting in the news release, study co-lead author Dr. Rekha Samuel said: "The potential applications of iPSC-generated blood vessels are broad -- from repairing damaged vessels supplying the heart or brain to preventing the need to amputate limbs because of the vascular complication of diabetes." Samuel, formerly with the Steele Laboratory, is now at the Christian Medical College, in Vellore, India.

While the findings of the new study are promising, scientists note that research involving animals often fails to produce similar results in humans.

-- Robert Preidt

Copyright 2013 HealthDay. All rights reserved.

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Scientists Create Blood Vessels in Mice Using Human Stem Cells

July 16, 2013 Magnets could be a tool for directing stem cells' healing powers to treat conditions such as heart disease or vascular disease.

By feeding stem cells tiny particles made of magnetized iron oxide, scientists at Emory and Georgia Tech can then use magnets to attract the cells to a particular location in the body after intravenous injection.

The results are published online in the journal Small and will appear in an upcoming issue.

The paper was a result of collaboration between the laboratories of W. Robert Taylor, MD, PhD, and Gang Bao, PhD. Taylor is professor of medicine and biomedical engineering and director of the Division of Cardiology at Emory University School of Medicine. Bao is professor in the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University. Co-first authors of the paper are postdoctoral fellows Natalia Landazuri, PhD, and Sheng Tong, PhD. Landazuri is now at the Karolinska Institute in Sweden.

The type of cells used in the study, mesenchymal stem cells, are not embryonic stem cells. Mesenchymal stem cells can be readily obtained from adult tissues such as bone marrow or fat. They are capable of becoming bone, fat and cartilage cells, but not other types of cell such as muscle or brain. They secrete a variety of nourishing and anti-inflammatory factors, which could make them valuable tools for treating conditions such as cardiovascular disease or autoimmune disorders.

Magnetized iron oxide nanoparticles are already FDA-approved for diagnostic purposes with MRI (magnetic resonance imaging). Other scientists have tried to load stem cells with similar particles, but found that the coating on the particles was toxic or changed the cells' properties. The nanoparticles used in this study have a polyethylene glycol coating that protects the cell from damage. Another unique feature is that the Emory/Tech team used a magnetic field to push the particles into the cells, rather than chemical agents used previously.

"We were able to load the cells with a lot of these nanoparticles and we showed clearly that the cells were not harmed," Taylor says. "The coating is unique and thus there was no change in viability and perhaps even more importantly, we didn't see any change in the characteristics of the stem cells, such as their capacity to differentiate. This was essentially a proof of principle experiment. Ultimately, we would target these to a particular limb, an abnormal blood vessel or even the heart."

The particles are coated with the nontoxic polymer polyethylene glycol, and have an iron oxide core that is about 15 nanometers across. For comparison, a DNA molecule is 2 nanometers wide and a single influenza virus is at least 100 nanometers wide.

The particles appear to become stuck in cells' lysosomes, which are parts of the cell that break down waste. The particles stay put for at least a week and leakage cannot be detected. The scientists measured the iron content in the cells once they were loaded up and determined that each cell absorbed roughly 1.5 million particles.

Once cells were loaded with iron oxide particles, the Emory/Tech team tested the ability of magnets to nudge the cells both in cell culture and in living animals. In mice, a bar-shaped rare earth magnet could attract injected stem cells to the tail (see photo). The magnet was applied to the part of the tail close to the body while the cells were being injected. Normally most of the mesenchymal stem cells would become deposited in the lungs or the liver.

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Steering stem cells with magnets

Washington, July 16 : Researchers at Massachusetts General Hospital (MGH) have used vascular precursor cells derived from human induced pluripotent stem cells (iPSCs) to generate, in mice, functional blood vessels that lasted as long as nine months.

In their report, the investigators describe using iPSCs - reprogrammed adult cells that have many of the characteristics of embryonic stem cells - from both healthy adults and from individuals with type 1 diabetes to generate blood vessels on the outer surface of the brain or under the skin of mice.

"The discovery of ways to bring mature cells back to a 'stem-like' state that can differentiate into many different types of tissue has brought enormous potential to the field of cell-based regenerative medicine, but the challenge of deriving functional cells from these iPSCs still remains," Rakesh Jain, PhD, director of the Steele Laboratory for Tumor Biology at MGH and co-senior author of the study, said.

"Our team has developed an efficient method to generate vascular precursor cells from human iPSCs and used them to create networks of engineered blood vessels in living mice," he said.

The ability to regenerate or repair blood vessels could make a crucial difference in the treatment of cardiovascular disease -- which continues to be the number one cause of death in the US -- and other conditions caused by blood vessel damage, such as the vascular complications of diabetes.

In addition, providing a vascular supply to newly-generated tissue remains one of the greatest barriers facing efforts to build solid organs through tissue engineering.

Several previous studies have generated from iPSCs the types of cells required to build blood vessels -- endothelial cells that line vessels and connective tissue cells that provide structural support -- but those cells could not form long-lasting vessels once introduced into animal models.

"The biggest challenge we faced during the early phase of this project was establishing a reliable protocol to generate endothelial cell lines that produced great quantities of precursor cells that could generate strong, durable blood vessels," co-senior author Dai Fukumura, MD, PhD, also of the Steele Lab, said.

The MGH team adapted a method originally used to derive endothelial cells from human embryonic stem cells (hESCs).

But while that method used a single protein marker to identify vascular progenitors, the researchers sorted out iPSC-derived cells that expressed not only that protein but also two other protein markers of vascular potential.

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Long lasting blood vessels created in mice using human stem cells