cKit+ cells Do Make Heart Muscle After All

In the heart lies a population of cells that contains a protein called cKit, and are, therefore, called cKit+ cells. cKit+ cells have been the subject of a good deal of attention by researchers, but unfortunately, these have become the focus of a good deal of controversy.

When cKit+ cells were first discovered, there was a good deal of excitement about them, since they seemed to be able to make heart muscle cells and replace damaged heart muscle cells in the heart of living creatures (Beltrami AP, et al., Cell. 2003 Sep 19;114(6):763-76). In 2012, the results of a Phase I clinical trial with cKit+ cells (SCIPIO) were published (Chugh AR et al., Circulation 2012 Sep 11;126(11 Suppl 1):S54-64). This trial seemed to show that patients who received their own cKit+ cells had significant increases in heart function after a heart attack. Follow-up work in pigs even appeared to confirm that infused cKit+ cells could differentiate into heart muscle and integrate into the walls of the heart (Bolli R et al., Circulation 2013 Jul 9;128(2):122-31). So the cells were able to regenerate heart muscle in mice, pigs, and humans. It is not an understatement to say that cKit+ cells were once thought to be the key to cardiac regeneration.

The first trouble in paradise came from mouse experiments. While cKit+ cells could indeed improve the function of damaged hearts, the evidence for engraftment of the cells into the walls of the heart was wanting. Scientists in the laboratory of Jeff Molkentin Cincinnati Children’s Hospital Medical Center reported in a high-profile paper in the journal Nature that cKit+ cells can readily produce cardiac blood vessel cells, they rarely make heart muscle cells (cardiomyocytes). Because Molkentin and his team had carefully marked and traced the cells that they implanted into mice, the result was pretty devastating to the status of cKit+ cells. Molkentin’s results, however, conflicted with data from the laboratory of Bernardo Nadal-Ginard from King’s College London, who showed that heart regeneration in laboratory rodents depends on cKit+ cells and depleting cKit+ populations from the heart abolishes the ability of the heart to repair itself (Ellison GM, et al., Cell. 2013 Aug 15;154(4). Technical differences between the two papers, however, made comparisons between them difficult.

The next issues came with the SCIPIO publication itself. Two of the figures appeared to have some mistakes in them. Piero Anversa from Brigham and Women’s Hospital’s, the senior author of the SCIPIO study, admitted that there might be problems with the figures but insisted that the clinical data of the trial were sound. Other concerns about SCIPIO were expressed as well in print.  Add to that the fact that Anversa had to retract one of his earlier papers, and the whole edifice of SCIPIO and cKit+ cells seemed to totter.  These issues knocked cKit+ cells off their pedestal. At the very least, they put a hold on the SCIPIO trial until other questions had been resolved.

A new study by Joshua Hare and his group from the University of Miami Miller School of Medicine has stirred up the controversy pot once again. Hare and his team have published a paper in the journal PNAS in which they showed that cKit+ cells can readily form heart muscle cells in culture. However, apparently the cKit+ cells are finicky and only form heart muscle conditions if the conditions are just right. These results from Hare’s group might (and oh what a big might) explain why other groups have not been able to replicate the results of either Anversa or Nadal-Ginard. In Hare’s own words, “It’s not that the [cKit+] cells don’t have the capacity [to form heart muscle], but they’re entering the heart at a time that’s nonpermissive for them to become cardiac myocytes.”

In a nutshell, Hare and his team used mouse induced pluripotent stem cells (iPSCs) and differentiated them into heart muscle cells. They found that if you inhibited bone morphogenetic protein (BMP) signaling in these cells, an integral signaling event in the development of the heart; the iPSCs would express cKit and differentiate into heart muscle cells. The Hare group also used fate-mapping techniques to trace the developmental origin of cKit+ cells in the heart and they discovered that cKit+ cells are derived from the neural crest cells that delaminate from the closing neural tube during the formation of the central nervous system and migrate throughout the body to form a whole host of cell types and contribute to many different tissues.

Unlike Molkentin’s group, Hare and his crew did not observe an increased tendency for cKit+ cells to form heart blood vessel (endothelium) cells. Hare was somewhat unsure why this might be the case, but suggested that the different ways that the two teams labeled their cells for fate mapping purposes might be at least part of the issue.

Despite his success at showing that cKit+ cells can become heart muscle cells, Hare does not think that his work necessarily explains the results of the SCIPIO clinical trial, but he does think that his work might suggest how the regenerative capacities of cKit+ cells might be augmented.

Bernardo Nadal-Ginard found Hare’s work “convincing,” but added that “the paper claims the quandary and the dispute is over. But, unfortunately, it is not.” I think we can say “Amen” to that, since more work almost certainly needs to be done. Nadal-Ginard also brought up a very good point when he added that no one really knows the frequency with which cKit+ cells differentiate into heart muscle cells or other cells types or even the rate with which they replace dead or dying cells. Hare’s paper did not focus on quantitating such events, and since it did not examine the ability of cKit+ cells to repopulate a living heart, these are still questions that must be addressed.

Cornell University’s Michael Kotlikoff also made an excellent point by noting that Hare’s team did not show that cKit+ cells have the same ability to regenerate a living heart in laboratory animals as they do in culture. In an article in The Scientist by Kerry Grens, Kotlikoff said, “They never show the myogenic potential of those cells and don’t show them giving rise to cardiomyogensis” in vivo. Kotlikoff continued: “The expression of [cKit], per se, is not sufficient to identify cells as precursors and the further presumption that signaling processes observed in in vitro differentiation experiments limit such cells from undergoing myogenesis in the adult heart, the stage at which clinical regenerative efforts are focused, is not supported by data,” he added.

Hare almost certainly is either planning or is presently carrying out such experiments with laboratory mice. Presently, however, Hare has founded a company called Vestion, whose goal is to establish off-the-shelf regenerative heart therapies. According the Kerry Grens, Hare is also a part of two planned clinical trials that will administer cKit+ cells to patients with heart failure.

Piero Anversa, who remains a big fan of cKit+ cells despite their knocks, spoke approvingly of Hare’s paper and added, “To say human trials should be stopped because the experiment didn’t work in the mouse is a bit aggressive. The answer is going to be in the trial. If the trial goes well we win, if the trial doesn’t go well, we lose.”

Umbilical Cord Blood Contains c-kit+ Cells that Can Differentiate into Heart-like Cells

Bone contains a wide variety of stem cells whose potential are only beginning to be tapped. One cell population possesses a cell surface protein called c-kit, and these c-kit+ progenitor cells seem to support myocardial regeneration. Do c-kit+ cells from umbilical cord blood have the same capacity?

Luciana Teofili from the Catholic University of the Sacred Heart in Rome, Italy and her colleagues purified c-kit+ cells from umbilical cord blood by means of magnetic beads that were coated with c-kit-binding antibodies. Teofili and others induced heart muscle differentiation in these cells with several different protocols. Then the expression of cardiac markers (GATA4, GATA6, β-myosin heavy chain, α-sarcomeric actin and cardiac Troponin T) was investigated, and whole-cell current and voltage-clamp recordings were performed.

The c-kit+ cells from umbilical cord blood showed a rather immature gene profile, and by themselves, they did not differentiate into heart muscle-like cells in culture. In contrast, if whole mononuclear cells from umbilical cord blood were subjected to the same treatment, several if the employed protocols produced large, adherent cells that expressed several heart muscle-specific genes and exhibited an excitability much like that of heart muscle cells.

Formation of these heart muscle-like cells was prevented if the c-kit+ cells were removed from the other cells. Tracking studies showed that the c-kit+ cells were the ones that differentiated into heart muscle-like cells, but they only did so when they were together with c-kit– cells.

Thus umbilical cord blood contains progenitors endowed with the ability to differentiate into heart muscle-like cells. The cells with this potential reside in the c-kit+ fraction but they require the presence of abundant accessory cells to differentiate properly.

These preliminary observations suggest that it is a good idea to consider the storage of the umbilical cord blood of patients with prenatal diagnosis of congenital heart diseases. Such conditions might be potentially amenable to myocardial regenerative therapies with umbilical blood-based stem cells.

This paper was published in the journal Cytotherapy, but it must be said that the evidence that these cells differentiated into heart muscle cells was not completely convincing.

Stem Cell Factor Delivery into Heart Muscle After Heart Attack May Enhance Cardiac Repair and Reverse Injury

Stem Cell Factor or SCF is a small peptide that circulates throughout the bloodstream and eventually finds its way to the bone marrow where it summons bone marrow-based stem cells to the sight of injury for tissue repair purposes. Unfortunately, it takes injured tissues time to express SCF at high enough levels to recruit bone marrow stem cells to come and accelerate tissue healing. This is particularly the case in the heart after a heart attack. For this reason, scientists are trying to find new and better ways to increase SCF production in the damaged heart.

To that end, cardiologists at the Icahn School of Medicine at Mount Sinai have discovered that delivering SCF directly to damaged heart muscle after a heart attack seems to augment heart muscle repair and regenerate injured tissue.

“Our discoveries offer insight into the power of stem cells to regenerate damaged muscle after a heart attack,” said lead study author Kenneth Fish, Director of the Cardiology Laboratory for Translational Research, Cardiovascular Research Center, Mount Sinai Heart, Icahn School of Medicine at Mount Sinai.

In this study, Fish and his colleagues used gene transfer to administer SCF to the heart shortly after inducing heart attacks in a pig model system in order to test its regenerative repair response. Fish and his coworkers developed a novel SCF gene transfer delivery system that stimulated the recruitment and expansion of adult cardiac stem cells directly to injury sites that reversed heart attack damage. In addition, the gene therapy improved cardiac function, decreased the death of heart muscle cells, increased regeneration of heart tissue blood vessels, and reduced the formation of heart tissue scarring.

“It is clear that the expression of the stem cell factor gene results in the generation of specific signals to neighboring cells in the damaged heart resulting in improved outcomes at the molecular, cellular, and organ level,” says Roger J. Haijar, senior study author and Director of the Cardiovascular Research Center at Mount Sinai. “Thus, while still in the early stages of investigation, there is evidence that recruiting this small group of stem cells to the heart could be the basis of novel therapies for halting the clinical deterioration in patients with advanced heart failure.”

The cell surface receptor for SCF is the c-Kit protein, and cells that possess the c-Kit protein are called c-Kit+ cells. c-Kit+ cells not only respond to SCF, but serve as resident cardiac stem cells that naturally increase in numbers after a heart attack and through cell proliferation are directly involved in cardiac repair.

To date, there is a great need for new interventional strategies for cardiomyopathy to prevent the progression of this disease to heart failure. Heart disease is the number one cause of death in the United States, with cardiomyopathy or an enlarged heart from heart attack or poor blood supply due to clogged arteries being the most common cause of the condition. Cardiomyopathy also causes a loss of heart muscle cells and changes in heart shape, which lead to the heart’s decreased pumping efficiency.

“Our study shows our SCF gene transfer strategy can mobilize a promising adult stem cell type to the damaged region of the heart to improve cardiac pumping function and reduce myocardial infarction sizes resulting in improved cardiac performance and potentially increase long-term survival and improve quality of life in patients at risk of progressing to heart failure,” says Dr. Fish.

“This study adds to the emerging evidence that a small population of adult stem cells can be recruited to the damaged areas of the heart and improve clinical outcomes,” says Dr. Hajjar.

Heart Cells Expressing Stem Cell Factor Show Less Cell Death After a Heart Attack

Stem Cell Factor is a cell surface protein that is expressed by several different cells, including tissue fibroblasts, heart cells, cells in the bone marrow, and blood vessel cells. Stem Cell Factor (SCF) plays important roles in the migration, proliferation, and adhesion of any cell that expresses the receptor for SCF, a molecule called c-kit. Cells that express c-kit include cardiac stem cells, endothelial progenitor cells, and hematopoietic stem cells. When c-kit binds to SCF, the SCF-containing cell activate their Akt /PI3K pathway, and this pathway prevents cells from dying and drives them to divide, differentiate, more, adhere, and even secrete new molecules.


Fu-Li Xang in the laboratory of Qingping Feng at the University of Western Ontario has done several experiments with SCF in the heart. His goal is to determine if heart cells that have SCF fare better after a heart attack than hearts that do not have quite so much SCF.

To that end, Feng and his team showed that SCF does help heal the heart after a heart attack in 2009 (Xiang et al, Circulation 120: 1065-74). The next step was to determine if SCF could attenuate cell death in the heart that results from a heart attack.



The strategy behind this experiments involved making genetically engineered mice that expressed lots of SCF in their heart muscle. The particular mouse strain that Feng and his crew made had the SCF gene activated by a heart muscle-specific promoter, but the expression of SCF could be shut off by giving the mice the drug doxycycline. These SCF transgenic mice and normal mice were given heart attacks and then some were treated with a doxycycline while others were given a drug called LY294002, which inhibits the Akt pathway. These animals were then analyzed three hours after the induced heart attack and the amount of cell death, the size of the infact, the number of stem cells that moved into the heart were all measured.


The upshot of all this work is this: SCF decreased the amount of cell death by about 40%. Also the size of the infarct was also smaller. These benefits were abrogated by the co-administration of either doxycycline or LY294002. When a search for molecules that are indicative of cell death were examined, the results were completely unsurprising: the markers of cells death like fragmented DNA or caspase-3 were decreased in the SCF mice and this attenuation was abrogated by co-administration with doxycycline or LY294002.

Other experiments examined the activation of the Akt/PI3K pathway in the SCF-expressing animals, and it was quite clear that the SCF-expressing animals showed a robustly active Akt/PI3K pathway compared to the non-SCF-expressing mice.

A different experiment examined the presence of c-kit-expressing cells in the hearts of these mice. Remember that c-kit expressing cells are stem cells that have been recruited to the heart by the SCF. Once again, it was exceedingly clear that the SCF-expressing mice had hearts with a large excess of c-kit-expressing cells and this recruitment of stem cells was abrogated by neutralizing c-kit with an antibody against it. The incoming stem cells also tend to secrete a host of interesting molecules that help heal the heart, and one of these molecules, HGF (hepatic growth factor), which also goes up in concentration in the hearts of the SCF-expressing mice, is blocked by a drug called crizotinib. If SCF-expressing mice were pre-treated with crizotinib, the infarct size tended to be just as large as the non-SCF-expressing cells.

Feng and his group also examined the resident stem cells in the heart, the cardiac stem cells population, which, by the way, also express c-kit. These cells also were induced to express HGF and IGF (insulin-like growth factor) as a result of SCF, and if the c-kit receptor was blocked with an antibody, then this effect was abrogated.

There is a lot of data in this paper, but the news is almost all good. Basically SCF will recruit stem cells to the heart after a heart attack and this recruitment happens quickly (within 3 hours) and does the heart a world of good. Translating this work into human patients will not be easy, but SCF is available. If it could be localized to the heart by some means soon after a heart attack, there is good reason to believe, based on these pre-clinical results that it would do the patient quite a bit of good. The next piece is figuring our how to go about doing just that.

Heart Muscle in Young Children May Be Capable of Regeneration

The heart of young children might possess untapped potential for regeneration, according to new research. For decades, scientists believed that after a child’s first few days of life, cardiac muscle cells did not divide. Heart growth was thought to occur by means of enlargement of muscle cells.

This view, however, has been seriously challenged in the last few years. New findings in mice that have recently been published in the journal Cell seriously question this dogma. These results have serious implications for the treatment of congenital heart disorders in humans.

Researchers at Emory University School of Medicine have discovered that in 15-day old mice, cardiac muscle cells undergo a precisely timed spurt of cell division that lasts about a day. The total number of cardiac muscle cells in the heart increases by about 40% during this time when the child’s body is growing rapidly. To give you some perspective, a 15-day-old mouse is roughly comparable to a child in kindergarten, and puberty occurs at day 30-35 in mice.

This burst of cell division is driven by a surge of thyroid hormone. This suggests that thyroid hormone might be able to aid in the treatment of children with congenital heart defects. Small trials have even tested thyroid hormone in children with congenital heart defects.

These findings also have broader hints for researchers who are developing regenerative heart therapies. Activating the regenerative potential of the muscle cells themselves is a strategy that is an alternative to focusing on the heart’s stem cells, according to senior author Ahsan Husain, PhD, professor of medicine (cardiology) at Emory University School of Medicine.

“It’s not as dramatic as in fish or amphibians, but we can show that in young mice, the entire heart is capable of regeneration, not just the stem cells,” he says.

This Emory group collaborated with Robert Graham, MD, executive director of the Victor Change Cardiac Research Institute in Australia.

One test conducted by these groups was to determine how well 15-day old mice can recover from the blockage of a coronary artery. Consistent with previous research, newborn (day 2) mice showed a high level of repair after such an injury, but at day 21, endogenous heart repair was quite poor. The 15-day old mice recovered better than the day 21 mice, indicating that some repair is still possible at day 15.

This discovery was an almost accidental finding while Naqvi and Husain were investigating the role of the c-kit gene. The c-kit gene is an important marker for stem cells in cardiac muscle growth. Adult mice that lack a functional c-kit gene in the heart have more cardiac muscle cells. When do these differences appear?

“We started counting the cardiomyocyte cell numbers from birth until puberty,” Naqvi says. “It was a fascinating thing, to see the numbers increasing so sharply on one day.” According to Naqvi, c-kit-deficient and wild-type mice both have a spurt of proliferation early in life but the differences in cardiac muscle cells between the c-kit+ and c-kit- mice appear later.

“Probably, previous investigators did not see this burst of growth because they were not looking for it,” Husain says. “It occurs during a very limited time period.” Even if in humans, the proliferation of cardiac muscle cells does not take place in such a tight time period as it does in mice, the finding is still relevant for human medicine, he says. “Cardiomyocyte proliferation is happening long after the immediate postnatal period,” Husain says. “And cells that were once thought incapable of dividing are the ones doing it.”

Naqvi and Husain plan to continue to investigate the relationships between thyroid hormone, nutrition during early life, and cardiac muscle growth.

Reference: N. Naqvi et al. A Proliferative Burst during Preadolescence Establishes the Final Cardiomyocyte Number. Cell 157, 795-807, 2014.

Doubts About Cardiac Stem Cells

Within the heart resides a cell population called “c-kit cells,” which have the ability to proliferate when the heart is damaged. Several experiments and clinical trials from several labs have provided some evidence that these cells are the resident stem cell population in the heart that can repair the heart after an episode of cardiac injury.

Unfortunately, a few new studies, and in particular, one that was recently published in the journal Nature, seem to cast doubt on these results. Jeff Molkentin of Cincinnati Children’s Hospital Medical Center and his co-workers have used rather precise cell lineage tracing studies in mice to follow c-kit cells and their behavior after a heart attack. His results strongly suggest that c-kit cells rarely produce heart muscle cells, but they do readily differentiate into cardiac endothelium, which lines blood vessels.

“The conclusion I am led to from this is that the c-kit cell is not a cardiac stem cell, at least in term of its normal, in vivo role,” said Charles Murry, a heart regeneration researcher at the University of Washington who was not involved in this study.

Molkentin’s study is what some stem cells researchers are calling the nail in the coffin for c-kit cells. In fact the Molkentin paper is simply the latest in a series of papers that were unable to reproduce the results of others when it comes to c-kit cells. Worse still, one of the leading laboratories in the c-kit work, Piero Anversa at Harvard Medical School, has had to retract on of this papers and there is also some concern about his publication regarding the SCIPIO trial. Eduardo Marbán, an author of the new study and a cardiologist at the Cedars-Sinai Heart Institute in Los Angeles, said, “There’s been a tidal wave in the last few weeks of rising skepticism,” Nevertheless, the present dispute is not yet settled, and many scientists still regard the regenerative powers of c-kit cells as a firmly established fact.

In his laboratory, Piero Anversa and his colleagues and collaborators have shown that c-kit cells—cardiac progenitor cells expressing the cell surface protein c-kit—can produce new heart muscle cells (cardiomyocytes). Anversa and others also helped usher these cells, which are also known as CPCs or cardiac progenitor cells, into clinical trials to test whether they might help repair damaged cardiac tissue. This culminated in the SCIPIO trial, which showed that patients treated with their own CPCs showed long-lasting and remarkable improves in heart function.

Follow-up work by other research teams, however, has not been able to confirm these studies, and their work has raised doubts about the potential of c-kit cells to actually build new heart muscle. In his contribution to the c-kit controversy, Molkentin and his colleagues genetically engineered mouse strains in which any c-kit-expressing cells and their progeny would glow green. To do this, they inserted a green fluorescent protein gene next to the c-Kit locus. Therefore any c-kit-expressing cells in the heart would not only glow green, but whatever cell type they differentiated into would also glow green. After inducing heart attacks in these mice, Molkentin and others discovered that only 0.027 percent of the heart muscle cells in the mouse heart originated from c-kit cells. “C-kit cells in the heart don’t like to make myocytes,” Molkentin told The Scientist. “We’re not saying anything that’s different” from groups that have not had success with c-kit cells in the past,” Molkentin continued, “we’re just saying we did it in a way that’s unequivocal.”

Molkentin’s study did not address why there’s a discrepancy between his results and those of Anversa and another leader in the c-kit field, Bernardo Nadal-Ginard, an honorary professor at King’s College London. Last year in a paper published in the journal Cell, Nadal-Ginard and his colleagues showed that heart regeneration in rodents relies on c-kit positive cells and that depleting these cells abolishes the regenerative capacity of the heart.

In an email to a popular science news publication known as The Scientist, Nadal-Ginard suggested that technical issues with Molkentin’s mouse model could have affected his results, causing too few c-kit cells to be labeled. Additionally, “the work presented by Molkentin used none of our experimental approaches; therefore, it is not possible to compare the results,” Nadal-Ginard said in an e-mail.

Anversa said his lab is working with the same mouse model Molkentin used, “but our data are too preliminary to make any specific comment. Time will tell.”

Molkentin’s paper seems point to further problems with Aversa’s work with c-kit cells.  Last month, one of the papers Anvera and his group had published in the journal Circulation had to be retracted because the data used the write that paper were “sufficiently compromised.”  Then a few days later, the paper describing the results of the SCIPIO study that appeared the journal The Lancet expressed concern about supplemental data that was included with the published results.  These data came from the human clinical trial that treated heart patients with their own c-kit cells.  Harvard Medical School and Brigham and Women’s Hospital are investigating what went wrong with this study and the publication itself.

Regardless of Anversa’s present tribulations, Marbán is advancing another type of heart-specific stem cell, called cardiosphere-derived cells or CDCs.  Marbán and his colleagues have already used CDCs in a human clinical trial known as the CADUCEUS trial.  In this trial, heart attack patients treated with CDCs saw their heart scars shrink.  Marbán said he had been a true believer in c-kit cells, until the data started mounting against them. “The totality of the evidence now says the c-kit cell is no longer a cardiomyocyte progenitor,” he said.

Now even if c-kit cells do not make new heart muscle, it is possible that they heal the heart through other means.  The patients in the SCIPIO trial saw real, genuine improvements in their heart function and these results cannot be so cavalierly dismissed.  In fact, Murry said that just because the mechanistic basis for the human study remains in doubt, promising clinical results should not be dismissed. “Those results can be considered independent,” he said.  Molkentin also added that it’s possible that c-kit cells work in unknown ways to repair heart tissue.  Since clinical treatments involves high levels of c-kit cells that have been immersed in culture conditions, “Perhaps these cells act a little different,” Molkentin said.

Nadal-Ginard also noted that discrepancies do exist between his data and those of others, and that these discrepancies should not be papered over, but should be robustly debated and addressed.  He said he’d be willing to work with Molkentin to get to the bottom of it. “The concept under dispute is too important for the field of regenerative medicine—and regenerative cardiology, in particular—to turn into a philosophical/dogmatic argument instead of settling it in a proper scientific manner.”  Here here.

Cardiac Stem Cells Offer New Hope for Treatment of Heart Failure

Scientists from the United Kingdom have, for the first time, highlighted the natural regenerative abilities of a group of stem cells that live in our hearts. This particular study shows that these cells are responsible for repairing and regenerating muscle tissue that has been damaged by a heart attack. Such damage to the heart can lead to heart failure.

There is a robust debate as to the regenerative capacity of cardiac stem cells (CSCs) in the hearts a adult human beings. While many scientists are convinced that CSCs in the hearts of newborns have good regenerative ability, many remain unconvinced that adult CSCs can do similar things (see Zaruba, M.M., et al., Circulation 121, 1992–2000 and Jesty, S.A., et al., Proc. Natl. Acad. Sci. USA 109, 13380–13385). Nevertheless, an earlier paper showed that when introduced into heart muscle after a heart attack, CSCs will regenerate the lost heart muscle and blood vessels lost in the infarct (see Beltrami, A.P., et al., Cell 114, 763–776). Resolving this disagreement requires a different type of experiment.

In this paper, Bernardo Nadal-Ginard and colleagues from the and his collaborators at the Stem Cell and Regenerative Biology Unit at the Liverpool John Moores University in Liverpool and his collaborators from Italy used a different way to affect the heart. When heart attacks are experimentally induced in the heart of rodents, the infarcts are large and they kill off large numbers of CSCs. Therefore, Nadal-Ginard and others induced severe diffuse damage of the heart muscle that also spared the CSCs. They gave the mice a large dose of a drug called isoproterenol, which acts as a “sympathomimetic.” This is confusing science talk that simply means that the drug speeds the heart rate to the point where the heart muscle exhausts itself and then starts to die off. This treatment, however, spares the CSCs (see Ellison, G.M., et al., J. Biol. Chem. 282, 11397–11409).

When the heart muscle was damaged, the CSCs differentiated into heart muscle cells and other heart-specific cells and repaired the damage in the heart. Also, the repairing cells were in the heart and were not the result of bone marrow stem cells that migrated to the bone marrow, thus putting to rest a controversy that has lasted for some years that CSCs are the result of bone marrow stem cells that migrate to the heart.

Elimination of CSCs prevents heart repair after heart damage. If, however, these heart-based stem cells are replaced after damage, the heart repairs itself and the heart recovers its function, anatomical integrity, and cellular structure.

In other experiments, removal of cardiac stem cells (CSCs) and re-injection after a heart attack shows that the CSCs can home in and repair the damaged heart.

c-kit CSCs repair heart

Since Nadal-Ginard showed that CSCs have a capacity to home to the damaged heart, less invasive treatments might be possible and that these treatments might even prevent heart failure after a heart attack in the future.

In a healthy heart, the quantity of CSCs is sufficient to repair heart muscle tissue. However, once the heart is damaged many of the CSCs are also damaged and cannot multiply or produce new muscle tissue. In these cases it could be possible to replace damaged CSCs with new ones that have been grown in the laboratory and administered intravenously.,

These new approaches involved maintaining or increasing the activity of CSCs in order to renew heart muscle and replace old, damaged cells. This new strategy will only require intravenous administration of CSCs and not require open heart procedures that require such a long time to recover.

These findings are very promising. The nest step is a clinical trial, which is due to start early 2014 and is aimed at assessing the safety and effectiveness of CSCs for preventing and treating heart failure in humans.

A New Blood Vessel-Generating Stem Cell Discovered With Therapeutic Potential

The laboratory of Petri Salven at the University of Helsinki, Helsinki, Finland, has discovered a new type of stem cell that play a decisive role in the growth of new blood vessels. These stem cells are found in the walls of blood vessels and if protocols are developed to isolated these stem cells, they might very well provide news ways to treat cardiovascular diseases, cancer and many other diseases.

The growth of new blood vessels is known angiogenesis. Angiogenesis is required for the repair of damaged tissues or organs. A downside of angiogenesis is that tumors often secrete angiogenic factors that induce the circulatory system to remodel itself so that new blood vessels grow into the tumor and feed it so that it can grow faster. Thus angiogenesis research tries to promote the growth of new blood vessels when they are needed and inhibit angiogenesis when it is unwanted.

Several drugs that inhibit angiogenesis have been introduced as adjuvant cancer treatments. For example, the drug bevacizumab (Avastin) is a monoclonal antibody that specifically recognizes and binds to an angiogenic factor known as vascular endothelial growth factor or VEGF. When VEGF receptors on the surface of normal endothelial cells. When VEGF binds to receptors on the surfaces of endothelial cells, a signal is sent within those cells that initiate the growth and survival of new blood vessels. Bevacizumab binds tightly to VEGF, which prevents it from binding and activating the VEGF receptor.

Other angiogenesis inhibitors include sorafenib (Nexavar) and sunitinib (Sutent), which are small molecular inhibitors of the receptors that bind the angiogenic factors and the downstream targets of those receptors. Unfortunately, the present crop of angiogenesis inhibitors are not all that effective under certain conditions and they are also extremely expensive and have some very undesirable side effects.

Professor Salven has studied angiogenesis for some time, and his research has focused on the endothelial cells that compose blood vessels. Where do these cells come from and how can we make more or less of them as needed?

A long-standing assumption by scientists in the angiogenesis field was that new endothelial cells came from stem cells found in the bond marrow. This assumption makes sense since there are several stem cell populations in bone marrow that express blood vessel markers and can form blood vessels in culture. However, in 2008, Salven’s group published a paper that demonstrated that new endothelial cells could not come from bone marrow stem cells (see Purhonen S, et al., (2008). Proc Natl Acad Sci U S A. 105(18): 6620-5). Therefore, the mystery remained – from where do new endothelial cells come?

Salven has recently solved this conundrum in his recent paper that appeared in PLoS Biology. According to Salven, “We succeeded in isolating endothelial cells with a high rate of division in the blood vessels of mice. We found that these same cells in human blood vessels and blood vessels growing in malignant tumors in humans. These cells are known as vascular endothelial stem cells, abbreviated VESC. In a cell culture, one such cell is able to produce tends of millions of new blood vessels wall cells.”

Slaven continued: “Our study found that these important stem cells can be found as single cells among the ordinary endothelial cells in blood vessel walls. When the process of angiogenesis is launched, these cells begin to produce new blood vessel wall cells.”

Salven’s colleagues have tested the effects of these new endothelial cells in mice. A particular mouse strain that carries a mutation in the c-kit gene was examined in these experiments. The c-kit gene encodes a cell surface protein called CD117, which is a vital element in the cells that form blood vessels. IN these c-kit mutant mice, new growth of new blood vessels was very poor and the growth of malignant tumors was also quite poor. However, if new stem cells from animals that did not possess a mutation in the c-kit gene were implanted into these mutant mice, blood vessels quickly formed.

As previously mentioned, the cell surface protein CD117 does seem to mark VESCs, but other cells other than VESCs have CD117 on their surfaces. Therefore, isolating all CD177-expression cells only enriches preparations for VESCs; it does not isolate VESCs. Presently, Salven and his group are searching for better surface molecules that can be used to more effectively isolated VESCs from surrounding tissue. If this isolation succeeds, then it will be possible to isolated and propagate VESCs from patients with cardiovascular diseases and expand them in culture for therapeutic purposes.

Another potentially fertile field of research is to find a way to inhibit the activity of VESCs to prevent tumors from remodeling the circulatory system. By cutting of their blood supply, tumors will not only grow slower, but also not spread nearly as quickly.

See: Fang S, Wei J, Pentinmikko N, Leinonen H, Salven P (2012) Generation of Functional Blood Vessels from a Single c-kit+ Adult Vascular Endothelial Stem Cell. PLoS Biol 10(10): e1001407. doi:10.1371/journal.pbio.1001407