MSCs: what’s in a name?

Whether they are "stem" or "stromal", from adult tissues or from umbilical cord blood, MSCs are being used for a lot of clinical trials. Read more

Mopping up immune troublemakers after transplant

Memory CD8+ T cells play an important role in kidney transplant rejection, and they resist drugs that would otherwise improve Read more

Tracking a frameshift through the ribosome

Ribosomal frameshifting, visualized through X-ray Read more

induced pluripotent stem cells

Stem cells driven into selective suicide

The term “stem cell” is increasingly stretchy. Orthopedic specialists have been using it when referring to bone marrow concentrate or platelet rich plasma, which are marketed as treatments for joint pain. At Lab Land, we have an interest in pluripotent stem cells, which can differentiate into many types of tissues.

For many applications, the stem cells are actually impurities that need to be removed, because pluripotent stem cells are capable of becoming teratomas, a type of tumor. For quality control, researchers want to figure out how to ensure that the stem-cell-derived cardiac muscle or neural progenitor or pancreas cells (or whatever) are as pure as possible.

Cardiologist and stem cell expert Chunhui Xu has been continuing a line of investigation on this topic. In a recent paper in ACS Chemical Biology, her team showed that “suicide-inducing molecules” can eliminate undifferentiated stem cells from a mixture of cells. This stem-cell-derived mixture was mostly cardiac muscle cells or their progenitors, which Xu’s team wants to use for therapeutic purposes.

Other labs have used metabolic selection – depriving cells of glucose and giving them only lactate –as a selective method for eliminating stem cells from cardiac muscle cultures. This paper shows that the “selective suicide” method works for early-stage differentiation cultures, containing cardiac progenitors, while the metabolic method works only for late-stage cultures contains beating cardiomyocytes.

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For nanomedicine, cell sex matters

The biological differences between male and female cells may influence their uptake of nanoparticles, which have been much discussed as specific delivery vehicles for medicines.

Vahid Serpooshan, PhD

New Emory/Georgia Tech BME faculty member Vahid Serpooshan has a recent paper published in ACS Nano making this point. He and his colleagues from Brigham and Women’s Hospital and Stanford/McGill/UC Berkeley tested amniotic stem cells, derived from placental tissue. They found that female amniotic cells had significantly higher uptake of nanoparticles (quantum dots) than male cells. The effect of cell sex on nanoparticle uptake was reversed in fibroblasts. The researchers also found out that female versus male amniotic stem cells exhibited different responses to reprogramming into induced pluripotent stem cells (iPSCs).

Female human amniotic stem cells with nanoparticles .Green: quantum dots/ nanoparticles; red: cell staining; blue: nuclei.

“We believe this is a substantial discovery and a game changer in the field of nanomedicine, in taking safer and more effective and accurate steps towards successful clinical applications,” says Serpooshan, who is part of the Department of Pediatrics and the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory.

Serpooshan’s interests lie in the realm of pediatric cardiology. His K99 grant indicates that he is planning to develop techniques for recruiting and activating cardiomyoblasts, via “a bioengineered cardiac patch delivery of small molecules.” Here at Emory, he joins labs with overlapping interests such as those of Mike Davis, Hee Cheol Cho and Nawazish Naqvi. Welcome!

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Long-lasting blood vessel repair in animals via stem cells

Stem cell researchers at Emory University School of Medicine have made an advance toward having a long-lasting “repair caulk” for blood vessels. The research could form the basis of a treatment for peripheral artery disease, derived from a patient’s own cells. Their results were recently published in the journal Circulation.

A team led by Young-sup Yoon, MD, PhD developed a new method for generating endothelial cells, which make up the lining of blood vessels, from human induced pluripotent stem cells.. When endothelial cells are surrounded by a supportive gel and implanted into mice with damaged blood vessels, they become part of the animals’ blood vessels, surviving for more than 10 months.

“We tried several different gels before finding the best one,” Yoon says. “This is the part that is my dream come true: the endothelial cells are really contributing to endogenous vessels. When I’ve shown these results to people in the field, they say ‘Wow.'”

Previous attempts to achieve the same effect elsewhere had implanted cells lasting only a few days to weeks, although those studies mostly used adult stem cells, such as mesenchymal stem cells or endothelial progenitor cells, he says.

“When cells are implanted on their own, many of them die quickly, and the main therapeutic benefits are from growth factors they secrete,” he adds. “When these endothelial cells are delivered in a gel, they are protected. It takes several weeks for most of them to migrate to vessels and incorporate into them.” Read more

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Direct reprogramming into endothelial cells

Direct reprogramming has become a trend in the regenerative medicine field. It means taking readily available cells, such as skin cells or blood cells, and converting them into cells that researchers want for therapeutic purposes, skipping the stem cell stage.

In a way, this approach follows in Nobel Prize winner Shinya Yamanaka’s footsteps, but it also tunnels under the mountain he climbed. Direct reprogramming has been achieved for target cell types such as neurons and insulin-producing beta cells.

Young-sup Yoon, MD, PhD

In Circulation Research, Emory stem cell biologist Young-sup Yoon, MD, PhD and colleagues recently reported converting human skin fibroblast cells into endothelial cells, which line and maintain the health of blood vessels.

Once reprogrammed, a patient’s own cells could potentially be used to treat conditions such as peripheral artery disease, or to form vascular grafts. Exactly how reprogrammed cells should be deployed clinically still needs to be worked out.

In cardiovascular disease, many clinical trials have been performed using bone marrow cells that were not reprogrammed. Emory readers may be familiar with studies conducted by Arshed Quyyumi, MD and colleagues, in which treatment was delivered after patients’ heart attacks. In those studies, sorted progenitor cells, some of which could become endothelial cells, were introduced into the heart. To provide the observed effects, the introduced cells were more likely supplying supportive growth factors.

In contrast, Yoon’s team is able to produce cells that already have endothelial character hammered into them. The authors have applied for a patent. The co-first authors were instructor Sang-Ho Lee, PhD and Changwon Park, PhD, assistant professor of pediatrics. Read more

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Cardiac ‘disease in a dish’ models advance arrhythmia research

New research illustrates how “disease in a dish” stem cell technology can advance cardiology.

Scientists led by Chunhui Xu, PhD derived cardiac muscle cells from a teenaged boy with an inherited heart arrhythmia, and used them to study how his cells respond to drugs. They did this not through a cardiac biopsy, but by converting some of the boy’s skin cells into induced pluripotent stem cells, and then into cardiac muscle cells.

Xu, director of the Cardiomyocyte Stem Cell Lab in Emory’s Department of Pediatrics, says this approach has been helpful in the study of other inherited arrhythmias and cardiomyopathies (example: 2011 Nature paper on long QT syndrome). In addition, Xu says, human-derived cardiac muscle cells could be used for toxicology testing for new drugs, since the molecules that regulate human cardiac muscle cells functions are distinct from those in animal models.

The findings were published on September 7 in Disease Models & Mechanisms.

The boy who provided the cells has CPVT (catecholaminergic polymorphic ventricular tachycardia), as do some of his relatives. CPVT, which occurs in about 1 in 10,000 people, is a major cause of sudden cardiac death in people younger than 40.

CPVT_arrhythmia smaller

In the patient whose cells are described in the paper, the drug flecainide could suppress arrhythmias that would otherwise appear during exercise. Electrocardiography from Preininger et al, Disease Models & Mechanisms (2016) via Creative Commons.

Arrhythmias in CPVT are almost exclusively brought on by activities that generate high levels of epinephrine, also known as adrenaline: heavy exertion, sports or emotional stress. Thus, affected individuals need to take medication regularly and usually should avoid competitive sports. The boy in the study also had an implanted cardiac defibrillator.

CPVT is generally treatable with beta-blockers, but about 25 percent of patients – including the boy in the study — are inadequately protected from arrhythmias by beta-blockers. Taking the drug flecainide, also used to treat atrial fibrillation, provides him an additional level of control.

Xu and her colleagues could duplicate those effects with his cardiac muscle cells in culture, by observing the ability of the drugs to suppress aberrant “calcium sparks.”

“We were able to recapitulate in a petri dish what we had seen in the patient,” says co-author Peter Fischbach, MD, chief academic officer at Children’s Healthcare of Atlanta’s Sibley Heart Center and associate professor of pediatrics at Emory University School of Medicine. “The hope is that in the future, we will be able to do that in reverse order.” Read more

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Strain differences in Zika infection genes

Scientists have revealed molecular differences between how the African and Asian strains of Zika virus infect neural progenitor cells. The results could provide insights into the Zika virus’ recent emergence as a global health emergency, and also point to inhibitors of the p53 pathway as potential leads for drugs that could protect brain cells from cell death.

The findings, from the Emory/Johns Hopkins/Florida State team that showed this spring that neural progenitor cells are particularly vulnerable to Zika infection (related paper), were published this week in Nucleic Acid Research. The manuscript was also posted on BioRxiv before publication.

Zika infection genes

Overlap in gene expression changes when neural progenitor cells are infected by African or Asian strains of Zika virus. Diagram from Nucleic Acids Research via Creative Commons.

Zika virus was first discovered in Uganda in the 1940s, and two distinct lineages of Zika diverged sometime in the second half of the 20th century: African and Asian. The strains currently circulating in the Western Hemisphere, which have been linked to microcephaly in infants and Guillain-Barre syndrome in adults, are more closely related to the Asian lineage.

The research team catalogued and compared genes turned on and off by Asian and African strains of Zika virus, as well as dengue virus, in human neural progenitor cells. The authors describe dengue as inducing more robust changes in gene expression than either strain of Zika. Although they show that dengue can infect neural progenitor cells like Zika can, dengue infection does not stunt the cells’ growth or lead to cell death.

“This shows that the differences between Zika and dengue are not at the level of being able to infect neural progenitors, but more about the harm Zika causes when it does infect those cells,” says senior author Peng Jin, PhD, professor of human genetics at Emory University School of Medicine. Read more

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Stay out, stray stem cells

Despite the hubbub about pluripotent stem cells’ potential applications, when it comes time to introduce products into patients, the stem cells are actually impurities that need to be removed.

That’s because this type of stem cell is capable of becoming teratomas – tumors — when transplanted. For quality control, researchers want to figure out how to ensure that the stem-cell-derived cardiac muscle or neural progenitor or pancreas cells (or whatever) are as pure as possible. Put simply, they want the end product, not the source cells.

Stem cell expert Chunhui Xu (also featured in our post last week about microgravity) has teamed up with biomedical engineers Ximei Qian and Shuming Nie to develop an extremely sensitive technique for detecting stray stem cells.PowerPoint Presentation

The technique, described in Biomaterials, uses gold nanoparticles and Raman scattering, a technology previously developed by Qian and Nie for cancer cell detection (2007 Nature Biotech paper, 2011 Cancer Research paper on circulating tumor cells). In this case, the gold nanoparticles are conjugated with antibodies against SSEA-5 or TRA-1-60, proteins that are found on the surfaces of stem cells. Read more

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Microgravity means more cardiac muscle cells

Cardiac muscle cells derived from stem cells could eventually be used to treat heart diseases in children or adults, reshaping hearts with congenital defects or repairing damaged tissue.

srep30956-f2

Cardiomyocytes produced with the help of simulated microgravity. Red represents the cardiac muscle marker troponin, and green is cadherin, which helps cells stick to each other. Blue = cell nuclei. From Jha et al SciRep (2016).

Using the right growth factors and conditions, it is possible to direct pluripotent stem cells into becoming cardiac muscle cells, which form spheres that beat spontaneously. Researchers led by Chunhui Xu, PhD, director of the Cardiomyocyte Stem Cell Laboratory in Emory’s Department of Pediatrics, are figuring out how to grow lots of these muscle cells and keep them healthy and adaptable.

As part of this effort, Xu and her team discovered that growing stem cells under “simulated microgravity” for a few days stimulates the production of cardiac muscle cells, several times more effectively than regular conditions. The results were published on Friday, Aug. 5 in Scientific Reports. The first author of the paper is postdoctoral fellow Rajneesh Jha, PhD. Read more

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Addendum on CRISPR

An excellent example of the use of CRISPR gene editing technology came up at the Emory-Children’s Pediatric Research Center’s Innovation Conference this week.

Marcela Preininger, who is working with cardiomyocyte stem cell specialist Chunhui Xu, described her work (poster abstract 108) on cells derived from a 12 year old patient with an inherited cardiac arrhythmia syndrome: catecholaminergic polymorphic ventricular tachycardia or CPVT. Her team has obtained skin fibroblasts from the patient, and converted those cells into induced pluripotent stem cells, which can then be differentiated into cardiac muscle cells or cardiomyocytes.

Working with TJ Cradick, director of the Protein Engineering Facility at Georgia Tech, Preininger is testing out CRISPR gene editing as a means of correcting the defect in this patient’s cells, outside the body. Cradick says that while easy and efficient, RNA-directed CRISPR can be lower in specificity compared to the protein-directed TALEN technology.

From Preininger’s abstract:

Once the mutation has been corrected at the stem cell level, we will investigate whether the repaired (mutation-free) iPS cells can be differentiated into functional cardiomyocytes with normal Ca2+ handling properties, while closely monitoring the cells for mutagenic events. Pharmacological restoration of the normal myocardial phenotype will also be optimized and explored in our model.

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Souped-up method for iPS cell reprogramming

Peng Jin and collaborators led by Da-Hua Chen from the Institute of Zoology, Chinese Academy of Sciences have a new paper in Stem Cell Reports. They describe a souped-up method for producing iPS cells (induced pluripotent stem cells).

Production of iPS cells in the laboratory is becoming more widespread. Many investigators, including those at Emory, are using the technology to establish “disease in a dish” models and derive iPS cells from patient donations, turning them into tools for personalized medicine research.

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