Stem cell stories that caught our eye: two studies of the heart and cool stem cell art

Here are some stem cell stories that caught our eye this past week. Some are groundbreaking science, others are of personal interest to us, and still others are just fun.

Image from Scope Blog.

Image from Scope Blog.

Understanding Heart Defects. Healthy heart tissue is made up of smooth, solid muscle, which is essential for normal heart function. Patients with a heart defect called left ventricular non-compaction (LVNC), lack normal heart tissue in their left ventricle – the largest, strongest blood-pumping chamber – and instead have spongy-looking tissue.

LVNC occurs during early heart development where pieces of heart muscle fail to condense (compact) and instead form an airy, sponge-like network that can leave patients at risk for heart failure and other complications.

A team at Stanford is interested in learning how LVNC occurs in humans, and they’re using human stem cells for the answer. Led by CIRM grantee Joe Wu, the scientists generated induced pluripotent stem cells (iPSCs) from four patients with LVNC. iPSCs are cells that can be turned into any other cell in the body, so Wu turned these cells into iPSC-derived heart muscle in a dish.

Wu’s team was particularly interested in determining why some LVNC patients have symptoms of disease while others seem perfectly normal. After studying the heart muscle cells derived from the four LVNC patients, they identified a genetic mutation in a gene called TBX20. This gene produces a type of protein called a cardiac transcription factor, which controls the expression of other heart related genes.

Upon further exploration, the scientists found that the genetic mutation in TBX20 prevented LVNC heart muscle cells from dividing at their normal rate. If they blocked the signal of mutant TBX20, the heart cells went back to their normal activity and created healthy looking heart tissue.

This study was published in Nature Cell Biology and covered by the Stanford Medicine Scope blog. In an interview with Scope, Joe Wu highlighted the big picture of their work:

Joseph Wu Stanford

Joseph Wu Stanford

“This study shows the feasibility of modeling such developmental defects using human tissue-specific cells, rather than relying on animal cells or animal models. It opens up an exciting new avenue for research into congenital heart disease that could help literally the youngest — in utero — patients.”

Stem Cell Heart Patch. Scientists from the University of Wisconsin, Madison are creating stem cell-based heart patches that they hope one day could be used to treat heart disease.

In a collaboration with Duke and the University of Alabama at Birmingham, they’re developing 3D stem cell-derived patches that contain the three main cell types found in the heart: cardiomyocytes (heart muscle cells), fibroblasts (support cells), and endothelial cells (cells that line the insides of blood vessels). These patches would be transplanted into heart disease patients to replace damaged heart tissue and improve heart function.

As with all research that has the potential for reaching human patients, the scientists must first determine whether the heart patches are safe in animal models. They plan to transplant the heart patches into a pig model – chosen because pigs have similar sized hearts compared to humans.

In a UW-Madison News release, the director of the UW-Madison Stem Cell and Regenerative Medicine Center Timothy Kamp, hinted at the potential for this technology to reach the clinic.

“The excitement here is we’re moving closer to patient applications. We’re at a stage when we need to see how these cells do in a large animal heart attack model. We’ll be making patches of heart muscle that can be applied to these injured areas.”

Kamp and his team still have a lot of work to do to perfect their heart patch technology, but they are thinking ahead. Two issues that they are trying to address are how to prevent a patient’s immune system from rejecting the heart patch transplant, and how to make sure the heart patches beat in sync with the heart they are transplanted into.

Check out the heart patches in action in this video:

(Video courtesy of Xiaojun Lian)

Cool Stem Cell Art! When I was a scientist, I worked with stem cells all the time. I grew them in cell culture dishes, coaxed them to differentiate into brain cells, and used a technique called immunostaining to take really beautiful, colorful pictures of my final cell products. I took probably thousands of pictures over my PhD and postdoc, but sadly, only a handful of these photos ever made it into journal publications. The rest collected dust either on my hard drive or in my lab notebook.

It’s really too bad that at the time I didn’t know about this awesome stem cell art contest called Cells I See run by the Centre for Commercialization of Regenerative Medicine (CCRM) in Ontario Canada and sponsored by the Stem Cell Network.

The contest “is about the beauty of stem cells and biomaterials, seen directly through the microscope or through the interpretive lens of the artist.” Scientists can submit their most prized stem cell images or art, and the winner receives a cash prize and major science-art street cred.

The submission deadline for this year’s contest was earlier this month, and you can check out the contenders on CCRM’s Facebook page. Even better, you can vote for your favorite image or art by liking the photo. The last date to vote is October 15th and the scientist whose image has the most likes will be the People’s Choice winner. CCRM will also crown a Grand Prize winner at the Till & McCulloch Stem Cell Meeting in October.

I’ll leave you with a few of my favorite photos, but please don’t let this bias your vote =)!

"Icy Astrocytes" by Samantha Yammine

“Icy Astrocytes” by Samantha Yammine (Vote here!)

"Reaching for organoids" by Amy Wong

“Reaching for organoids” by Amy Wong (Vote here!)

"Iris" by Sabiha Hacibekiroglu

“Iris” by Sabiha Hacibekiroglu (Vote here!)

CIRM Grantees Reflect on Ten Years of iPS Cells

For the fourth entry for our “Ten Years of Induced Pluripotent Stem (iPS) Cells” series, which we’ve been posting all month, I reached out to three of our CIRM grantees to get their perspectives on the impact of iPSC technology on their research and the regenerative medicine field as a whole:

granteesStep back in time for us to August 2006 when the landmark Takahashi/Yamanaka Cell paper was published which described the successful reprogramming of adult skin cells into an embryonic stem cell-like state, a.k.a. induced pluripotent stem (iPS) cells. What do you remember about your initial reactions to the study?

Sheng Ding, MD, PhD
Senior Investigator, Gladstone Institute of Cardiovascular Disease
Shinya had talked about the (incomplete) iPS cell work well before his 2006 publication in several occasions, so seeing the paper was not a total surprise.

Alysson Muotri, PhD
Associate Professor, UCSD Dept. of Pediatrics/Cellular & Molecular Medicine
At that time, I was a postdoc. I was in a meeting when Shinya first presented his findings. I think he did not give the identity of the 4 factors at that time. I was very excited but remember hearing rumors in the corridors saying the data was too good to be true. Soon after, the publication come out and it was a lot of fun reading it.

Joseph Wu, MD, PhD
Director, Stanford Cardiovascular Institute
I remember walking to the parking lot after work. One of my colleagues called me on my cell phone and he asked if I had seen “the Cell paper” published earlier that day. I said I haven’t and I would look it up when I get back home. I read it that night and found it quite interesting because the concept was simple but yet powerful.

How soon after the publication did you start using the iPSC technique in your own research? At that time, what research questions were you able to start exploring that weren’t possible in the “pre-iPS” era?

I think many of us in the (pluripotent stem cell) field quickly jumped on this seminal discovery and started working on the iPSC technology itself as, at the time, there were many aspects of the discovery that would need to be better understood and further improved for its applications.

Immediately after the first mouse Cell paper, but I started with human cells. There were some concerns if the 4 factors will also work in humans. Nonetheless, I start using the mouse cDNA factors in human cells and it worked! I was amazed to witness the transformation and see the iPSC colonies in my dish – I showed the results to everyone in the lab.

Soon after, the papers showing that the procedure worked in human cells were published but I already knew that. Thus, I started to apply this to model disease, my main focus. In 2010, we published the modeling of the first neurodevelopmental disease using the iPSC technology. It is still a landmark publication, and I am very happy to be among the pioneers who believed in the Yamanaka technology.

We started working on iPS cells about a couple of months after the initial publication. To our surprise, it was incredibly easy to reproduce, and we were able to get successful clones after a few initial attempts, in part because we had already been working on human embryonic stem (ES) cells for several years.

I think the biggest advantage of iPS cells is that we can know the medical record of the donor. So we can study the correlation between the donor’s underlying genetic makeup and their resulting cellular and whole-body characteristics using iPS cells as a platform for integrating these analyses. Examining these correlations is simply not possible with ES cells since no adult donor exists.

Dr. Ding, what do you think made you and your research team especially skilled at pioneering the use of small molecules to replace the “Yamanaka” reprogramming factors?

We had been working on identifying and using small molecules to modulate stem cell fate (including cell proliferation, differentiation, and reprogramming) before iPS cell technology was reported. So when the iPS cell work was reported, it was obvious to us that we could apply our expertise in small molecule discovery to better understand and improve iPS cell reprogramming and replace the genetic factors by pharmacological approaches.

Now, come back to the present and reflect on how the paper has impacted your research over the past 10 years. Describe some of the key findings your lab has made over the past 10 years through iPSC studies

We’ve worked on three aspects that are related to iPS cell research: one is to identify small molecule drugs that can functionally replace the genetic reprogramming factors, and enhance reprogramming efficiency and iPS cell quality (to mitigate risks associated with genetic manipulation, to make the iPS cell generation process more robust and efficient, and reduce the cost etc).

Second is to better understand the reprogramming mechanisms, that would allow us to improve reprogramming and better utilize cellular reprogramming technology. For example, we had uncovered and characterized several fundamental mechanisms underlying the reprogramming process.

The third is to “repurpose/re-direct” the iPS cell reprogramming into directly generating tissue/organ-specific precursor cells without generating iPS cell (itself, which is tumorigenic and needs to be differentiated for most of its applications). This so-called “Cell-Activation and Signaling-Directed/CASD” reprogramming approach allowed us to directly generate cells in the brain, heart, pancreas, liver, and blood vessels.

My lab has focused on the use of iPS cells to model autism spectrum disorder, a condition that is very heterogeneous both clinically and genetically. Previous models for autism, such as animals and postmortem tissues, were limited because we could not have access to live neurons to test experimentally several hypotheses. Thus, the attractiveness of the iPS cell model, by capturing the genome of patients in pluripotent stem cells and then guide them to become neural networks.

While the modeling in a dish was a great potential, there were some clear limitations too: the variability in the system was too high for example. My lab has worked hard to develop a chemically-defined culture media (iDEAL) to grow iPS cells and reduce the variability in the system. Moreover, we have developed robust protocols to analyze the morphology and electrophysiological properties of cortical neurons derived from iPS cells. We have used these methods to learn more about how genes impact neuronal networks and to screen drugs for several diseases.

We also used these methods to create cerebral organoids or “mini-brains” in a dish and have applied this technology to test the impact of several genetic and environmental factors. For example, we recently showed that the Zika virus could target neural progenitor cells in these organoids, leading to defects in the human developing cortex. Without this technology, we would be limited to mouse models that do not recapitulate the microcephaly of the babies born in Brazil.

Our lab has taken advantage of the iPS cell platform to better understand cardiovascular diseases and to advance the precision medicine initiative. For example, we have used iPS cells to elucidate the molecular mechanisms of diseases related to an enlarged heart, cardiac arrhythmias, viral- and chemotherapy-induced heart disease, the genetics of coronary artery disease, among other diseases. We have also used iPS cells for testing the safety and efficacy of various cardiovascular drugs (i.e., “clinical trial in a dish”).

How are your findings important in terms of accelerating stem cell treatments to patients with unmet medical needs?

Better understanding the reprogramming process and developing small molecule drugs for enhancing reprogramming would allow more effective generation of safe stem cells with reduced cost for treating diseases or doing research.

We work with two concepts. First, we screen drugs that could repair the disorder at a cellular level in a dish, hoping these drugs will be useful for a large fraction of autistic individuals. This approach can also be used to stratify the autistic population, finding subgroups that are more responsive to a particular drug. This strategy should help future clinical trials.

In parallel, we also work with the idea of personalized medicine by using patient-derived cells to create “disease in a dish” models in the lab. We then examine the genomic information of these cells to help us find drugs that are more specific to that individual. This approach should allow us to better design the treatment, testing ideal drugs and dosage, before prescribing it to the patient.

The iPS cell technology provides us with an unprecedented glimpse into cardiovascular developmental biology. With this knowledge, we should be able to better understand how cardiac and vascular cells regenerate in the heart during different phases of human life and also during times of stress such as in the case of a heart attack. However, to be able to translate this knowledge into clinical care for patients will take a significant amount of time. This is because we still need to tackle the issues of immunogenicity, tumorigenicity, and safety for products that are derived from ES and iPS cells. Equally importantly, we need to understand how transplanted cells integrate into the patient because based on our experience so far, most of the injected cells die upon transplant into the heart. Finally, the economics of this type of personalized regenerative medicine is a daunting challenge.

Finally, it’s foolhardy to predict the future but, just for fun, imagine that I revisit you in August 2026. What key iPSC-related accomplishments do you think your lab will achieve by then?

We are hoping to have cell-based therapy and small molecule drugs developed based on iPS cell-related research for treating human diseases. Particularly, we are also hoping our cellular reprogramming research would lead us to identify and develop small molecule drugs that control tissue/organ regeneration in vivo [in an animal].

We hope to have improved several steps on the neural differentiation, dramatically reducing costs and increasing efficiency.

We would like to use the iPS cell platform to discover several new drugs (or repurpose existing drugs) for our cardiovascular patients; to replace the current industry standard of drug toxicity testing using the hERG assay (which I believe is outdated); to predict what medications patients should be taking (i.e., precision cardiovascular medicine); and to elucidate risk index of genetic variants (in combination with genome editing approach).

Chemo-Induced Heart Failure: Using Stem Cells to Identify Those at Risk

The good news is you’re cancer free, the bad news is you need a heart transplant.

It almost sounds like the punchline to a joke, but it’s no laugher matter because the scenario is real for some cancer patients.  Chemotherapy is a life saver for many but certain doses can be so toxic that it’s often hard to tell which symptoms are due to the cancer and which are due to the drug. Doxorubicin, used to treat around 50% of people diagnosed with breast cancer, is particularly awful. It’s been estimated that about 8% of those treated with doxorubicin experience side effects to the heart with symptoms ranging from arrhythmias to congestive heart failure severe enough to require heart transplantation.


doxorubicin, a chemotherapy drug that carries a risk of serious heart damage

Avoiding the fire after jumping out of the frying pan
To avoid this predicament, doctors need a way to screen for an increased risk of heart damage due to doxorubicin before a patient even sets foot in a chemotherapy clinic. A CIRM-funded Stanford research team has made a big step toward that goal. Reporting yesterday in Nature Medicine, the scientists describe a non-invasive laboratory method that could help pinpoint which breast cancer patients are most likely to experience so-called doxorubicin-induced cardiotoxicity, or DIC.

Eight woman with breast cancer who had received doxorubicin treatment were recruited for the study. Four suffered from DIC while the other four did not. Skin samples were obtained from each person as well as four healthy volunteers. In the lab, the skin fibroblasts were reprogrammed into embryonic-like induced pluripotent stem cells (iPS) and then specialized into beating heart muscle cells or cardiomyocytes.

Chemo-induced heart damage in a dish
To find out if these patient-derived heart cells in the lab reflect what happened inside the patients’ hearts, the team compared the effects of doxorubicin on the different groups of cells. Looking at cell survival and the rhythmic beating of the heart cells, differences emerged. Lead author Paul Burridge summarized the results in a university press release:

“We found that cells from the patients who had experienced doxorubicin toxicity responded more negatively to the presence of the drug. They beat more irregularly in response to increased levels of doxorubicin, and we saw a significant increase in cell death after 72 hours of exposure to the drug when we compared those cells to cells from healthy controls or patients who didn’t have heart damage.”

Screen Shot 2016-04-19 at 9.27.23 AM

iPS-derived heart muscle cells from patients without (DOX, first row) and with (DOXTOX, bottom row) doxorubicin toxicity were treated with increasing amounts of the doxorubicin. The regular green stripe patterns indicate normal, intact muscle structures. By 0.1 µM of drug (second column), the DOXTOX structures become disarrayed while the DOX cells remain intact. Image: Burridge et al. Nat Med. 2016 Apr 18.

So how exactly does doxorubicin wreak havoc on the heart and why are some patients more sensitive to the drug?

Feeling the burn of reactive oxygen species (ROS)
The answers, in part, lie inside cellular structures called mitochondria where calories, stored in the form of sugar and fat, are “burned” to generate the body’s energy needs.  A harmful byproduct of this energy metabolism is reactive oxygen species (ROS), a chemically reactive form of oxygen that damages the mitochondria and other cell components. This damage is especially bad for heart cells which are 35% mitochondria by volume due to their intense energy needs as they busily beat for a lifetime.

Now, earlier research studies had pointed to ROS production in mitochondria as a key deliverer of doxorubicin’s destructive effects on the hearts of chemotherapy patients. So the Stanford team investigated the drug’s effects on ROS production and on mitochondria function in context of their patient derived heart cells. In response to doxorubicin, the scientists found that the cells from patients with doxorubicin induced heart damage generated more ROS compared to the cells from patients who had no heart damage. Along with the higher ROS production, mitochondria function was more compromised in the doxorubicin-sensitive heart cells.

And even in the absence of treatment, there was a lower baseline function and quantity of mitochondria in the doxorubicin-sensitive cells. These results suggest some underlying genetic differences in the heart muscle cells of patients with DIC. The team plans to perform DNA comparisons to pinpoint the genes involved and ultimately help patients survive cancer without the fear of swapping it for another life threatening illness.

iPS cells: opening new paths for helping cancers patients
Compared to tools he had previously relied on, Joseph Wu, the team leader and director of the Stanford’s Cardiovascular Institute, is very excited about his lab’s future research possibilities:

“In the past, we’ve tried to model this doxorubicin toxicity in mice by exposing them to the drug and then removing the heart for study. Now we can continue our studies in human cells with iPS-derived heart muscle cells from real patients. One day we may even be able to predict who is likely to get into trouble.”

Stem Cells become Tool to Screen for Drugs; Fight Dangerous Heart Infections.

A Stanford study adds a powerful example to our growing list of diseases that have yielded their secrets to iPS-type stem cells grown in a dish. These “disease-in-a-dish” models have become one of the most rapidly growing areas of stem cell science. But this time they did not start with skin from a patient with a genetic disease and see how that genetic defect manifests in cells in a dish. Instead they started with normal tissue and looked at how the resulting cells reacted to viral infection.

They were looking at a nasty heart infection called viral myocarditis, which can begin to cause damage to heart muscle within hours and often leads to death. Existing antiviral drugs have only a modest impact on reducing these infections. So even though there is an urgent need to find better drugs, animal models have not proven very useful and there is no ready supply of human heart tissue for lab study.

To create a ready supply of human heart tissue Joseph Wu’s CIRM-funded team at Stanford started with skin samples from three healthy donors, reprogrammed them into iPS cells and then matured those into heart muscle tissue. Then they took one of the main culprits of this infection, coxsackievirus, and labeled it with a fluorescent marker so they could track its activity in the heart cells.

They were able to verify that the virus infected the cells in a dish just as they do in normal heart tissue. And when they tried treating the cells with four existing antiviral drugs they saw the same modest decrease in the rate of infected cells seen in patients. For one of the drugs that had been shown to cause some heart toxicity, they also saw some damage to the cells in the dish.

They propose that their model can now be used to screen thousands of compounds for potentially more effective and safer drugs. They published their results in Circulation Research July 15.

What a Difference Differentiation can Make: a Little Change can Reduce the Risk of Rejection

No one likes to be rejected. It hurts. But while rejection is something most of us experience at least a couple of times in our life, researchers at Stanford have found a way to reduce the risk of rejection, at least when it comes to one form of stem cells. Reporting in the latest issue of Nature Communications they have found that turning iPS or induced pluripotent stem cells into other, more specialized kinds of cells, can reduce the risk the immune system will attack them.

Our immune systems are things of beauty. They hunt out invaders like viruses and when they spot something that shouldn’t be there, they attack it. It’s a critical part of our body’s way of fighting off disease and staying healthy.

However, the immune system is not perfect. Researchers have known for some time that when you take skin from an individual and turn it into an iPS cell – one that is capable of turning into any other cell in the body – and then transplant that cell back into the same individual their immune system often attacks it. So far, the only individuals this has been done with are mice, but we assume the same would happen in people.

So Joseph Wu and his CIRM-funded Stanford team decided to see what would happen if they took those same iPS cells and, before transplanting them back into the individual they came from, turned them into a more specialized form of cell. The results were encouraging: the immune system didn’t wage an attack.

Dr. Joseph Wu, Stanford University School of Medicine

Dr. Joseph Wu, Stanford University School of Medicine

Researchers were not sure why the body would attack something that was created from its own tissue, but speculated that turning ordinary skin cells into iPS cells created a kind of cell that the immune system hadn’t seen before, or at least hadn’t seen since it since it was an embryo.

In the Stanford news release, Wu said this finding could be really important in helping avoid rejection in organ or other tissue transplants:

“Induced pluripotent stem cells have tremendous potential as a source for personalized cellular therapeutics for organ repair. This study shows that undifferentiated iPS cells are rejected by the immune system upon transplantation in the same recipient, but that fully differentiating these cells allows for acceptance and tolerance by the immune system without the need for immunosuppression.” 

The team first transplanted some iPS cells into genetically identical recipient mice. The transplants were rejected and within 42 days there were no signs that any cells had survived.

Then they took the same kind of iPS cell and differentiated, or ‘re-programmed,’ them so that they turned into endothelial cells, the kind found in the inner lining of blood vessels. Then they transplanted those cells into the mice. At the same time they took some of the mice’s own endothelial cells out, and transplanted them back into genetically identical mice to see how they would compare. Both sets of cells, the iPS-turned-into endothelial and the endothelial cells, survived for at least 63 days after transplantation.

When the researchers repeated the experiment and examined the areas where the cells had been transplanted, they found much greater signs of immune system activity in the mice that were given iPS cells compared to the mice who got iPS cells that had been turned into endothelial cells, and the mice that just got endothelial cells.

For Wu, the bottom line was simple:

“This study certainly makes us optimistic that differentiation — into any nonpluripotent cell type — will render iPS cells less recognizable to the immune system. We have more confidence that we can move toward clinical use of these cells in humans with less concern than we’ve previously had.” 

 We work closely with Joseph Wu and his team on a number of other different projects, most focusing on heart disease.

kevin mccormack