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Cardiovascular Medicine, Genetics, Research, Science, Stanford News, Stem Cells

Stem cell study explains how mutation common in Asians affects heart health

Stem cell study explains how mutation common in Asians affects heart health

10011881004_d5ab6d7cd9_zMany Asians carry a mutation that causes their faces to flush when they drink alcohol. The affected gene is called ALDH2, and it also plays a role in cardiovascular health. Carriers are more susceptible to coronary artery disease and tend to recover more poorly than non-carriers from the damage caused by a heart attack. Now Stanford cardiologist Joseph Wu, MD, PhD, and postdoctoral scholar Antje Ebert, PhD, have learned why.

The researchers used a type of stem cell called an induced pluripotent stem cell, or iPS cell, to conduct the study. The stem cells are made from easily obtained tissue like skin, and they can be coaxed in the laboratory to become other types of tissue, like heart muscle cells. It’s one of the first times iPS cells have been used to examine ethnic-specific differences among populations. The research was published yesterday in Science Translational Medicine.

From our release:

The study showed that the ALDH2 mutation affects heart health by controlling the survival decisions cells make during times of stress. It is the first time ALDH2, which is involved in many common metabolic processes in cells of all types, has been shown to play a role in cell survival. In particular, ALDH2 activity, or the lack of it, influences whether a cell enters a state of programmed cell death called apoptosis in response to stressful growing conditions. [...]

The use of heart muscle cells derived from iPS cells has opened important doors for scientists because tissue samples can be easily obtained and maintained in the laboratory for study. Until recently, researchers had to confine their studies to genetically engineered mice or to human heart cells obtained through a heart biopsy, an invasive procedure that yields cells which are difficult to keep alive long term in the laboratory.

You’ve likely read about Wu’s previous work with heart muscle cells derived from iPS cells. Now he’s shown iPS cells are also a good way to compare the effect of genetic differences among populations, and he has big plans. More details about his plans from our release:

Wu is working to start a biobank at the Stanford Cardiovascular Institute of iPS cells from about 1,000 people of many different ethnic backgrounds and health histories. “This is one of my main priorities,” he said. “For example, in California, we boast one of the most diverse populations on Earth. We’d like to include male and female patients of major representative ethnicities, age ranges and cardiovascular histories. This will allow us to conduct ‘clinical trials in a dish’ on these cells, a very powerful new approach, to learn which therapies work best for each group. This would help physicians to understand for the first time disease process at a population level through observing these cells as surrogates.”

Previously: Induced pluripotent stem cell mysteries explored by Stanford researchers, A new era for stem cells in cardiac medicine? A simple, effective way to generate patient-specific heart muscle cells and “Clinical trial in a dish” may make common medicines safer, say Stanford scientists

Photo by Nicholas Raymond

Neuroscience, Research, Stanford News, Stem Cells

Cellular padding could help stem cells repair injuries

Cellular padding could help stem cells repair injuries

The idea of using stem cells to heal injuries seems so obvious. If you have a spinal cord injury, why not inject some new cells that can replace the ones that are lost?

Unfortunately, the very act of injecting those cells is rife with trouble. The scraping as they move through the needle damages the cells and can even kill them. Then, once in the site of the injury, the cells can easily ooze away into other tissue, or die from the onslaught of chemicals in the injury.

Material scientists Sarah Heilshorn, PhD, is trying to help these cells with a type of gel that can protect and support them, allowing them to live long enough to possibly repair the injury. A grant from Stanford Bio-X, the pioneering interdisciplinary life sciences institute, is now helping Heilshorn and her colleagues, neurosurgeon Giles Plant, PhD, and chemical engineer Andrew Spakowitz, PhD, get the project off the ground.

In a story I wrote about the work, Heilshorn equates the gel to ketchup:

It’s pretty thick, but when you bang on the bottle the sauce flows smoothly through the neck, then firms back up on the plate – a process she calls self-healing. “We want our polymers to self-heal better than ketchup,” she said. “It flows a bit across the plate.”

Her goal is to develop a polymer that supports the cells when they are loaded in a syringe, but then flows freely through the needle, padding and protecting the cells, then firming up quickly when it reaches the site of injury. “We don’t want the cells to flow away,” she says.

These Seed grants from Bio-X have been credited as part of what has made the institute so successful in bringing together people from diverse disciplines to solve biomedical problems. “The seed grants are the special Bio-X glue that brings teams of faculty from all over the university to tackle complex problems in human health using new approaches,” said Carla Shatz, PhD, who directs Bio-X.

We’ll be writing about a few of the most exciting projects being funded with the recently announced 2014 Bio-X Seed grants over the next few weeks.

Previously: They said “Yes”: The attitude that defines Stanford Bio-X

Research, Science, Stanford News, Stem Cells

Induced pluripotent stem cell mysteries explored by Stanford researchers

Induced pluripotent stem cell mysteries explored by Stanford researchers

Induced pluripotent stem cells, also called iPS cells, made from easily accessible skin or other adult cells, are ideal for disease modeling, drug discovery and, possibly, cell therapy. That’s because they can be generated in large numbers and grown indefinitely in the laboratory. They also reflect the genetic background of the person from whom they were generated. However, some fundamental questions still remain before they’re ready for the full glare of the clinical limelight. Does it matter what type of starting cells scientists use to create the pluripotent stem cells? And what’s the best control to use when studying the effect of a particular, patient-specific mutation?

Now Stanford cardiologist Joseph Wu, MD, PhD, and his colleagues have addressed and answered these questions. Their work was published yesterday in two back-to-back papers in the Journal of the American College of Cardiology. (Each paper is also accompanied by an editorial.) As Wu explained in an e-mail to me:

If your goal is to generate healthy iPS cell derivatives for regenerative therapy, it’s important to know whether the starting material makes a difference. For example, if I’m treating Alzheimer’s disease, is there a benefit to using iPS cell-derived brain cells made from brain cells? Likewise, if I’m treating a skin disorder, is there a benefit to using iPS cell-derived skin cells made from skin cells? As cardiologists, we are asked this quite often and each time, I had to say “I don’t know.” So we decided to do a study comparing the differentiation and functional ability of iPS cell-derived cardiomyocytes generated from two different sources: skin and heart. We also wanted to devise more efficient ways for researchers to quickly and easily create their own “designer” iPS cell lines to study particular mutations.

To answer the first question, the researchers created iPS cells from two types of starter cells: human fetal skin cells and cardiac progenitor cells. Not surprisingly, only the cardiac progenitor cells expressed genes known to be expressed in heart tissue. Wu and his colleagues then exposed the newly created pluripotent stem cells to growing conditions that favor the development of heart muscle cells called cardiomyocytes. They found that, although iPS cells derived from cardiac progenitor cells were more efficient at becoming cardiomyocytes, both types of starting material produced heart muscle cells that functioned similarly after a period of growth in the laboratory. As Wu explained:

These two populations of cells are essentially no different from one another over time. It appears that they lost the memory of their starting material (this memory is stored in the form of chemical tags on the cells’ DNA in a phenomena known as epigenetic marking). This suggests that I could take my own skin cells, make iPS cells and then create specialized brain, heart, liver or kidney cells for cell therapy. This is much easier than biopsying each tissue, and could be a good way to create universal iPS cell lines for research or cell therapy.

In the second paper, Wu and his colleagues devised a way to introduce specific mutations into iPS cells before transforming them into particular tissues. The approach relies on the use of what’s known as “dominant negative” mutations that exert their disruptive effect even when the unmutated gene is still present. This is important because it’s much easier and quicker than previous similar efforts, which required a complicated, time-consuming procedure to snip out and then replace individual genes. The technique also allows researchers to generate two cell lines that are identical except for the mutation under study. That way researchers can be confident that differences between the cell lines are due only to that mutation, which is particularly important when the lines are used to test the effect of therapeutic drugs. Again, from Wu:

Investigators can make their own designer iPS cell lines to study particular mutations with genetically identical controls to use in their experiments. We won’t have to make new iPS cells from each patient, which is laborious and time consuming. Instead we can create standardized lines to study many different mutations alone and in combination. This has the potential to revolutionize the field of disease modeling and drug discovery.

The two papers describe ongoing research in the Wu lab designed to optimize iPS cells for a variety of applications. The group, including graduate student Arun Sharma, recently published research using human iPS cell-derived cardiomyocytes to investigate the effect of various antiviral drugs againse coxsackievirus, a leading cause of an infection of the middle layer of the heart wall in children and the elderly. The research is the first time that iPS cell-derived heart muscle has been used to investigate the mechanisms behind an acquired viral disease.

Previously: A new era for stem cells in cardiac medicine? A simple, effective way to generate patient-specific heart muscle cells, “Clinical trail in a dish” may make common medicines safer, say Stanford scientists and Lab-made heart cells mimic common cardiac disease in Stanford study

Cancer, Research, Science, Stanford News, Stem Cells

Radiation therapy may attract circulating cancer cells, according to new Stanford study

Radiation therapy may attract circulating cancer cells, according to new Stanford study

Localized radiation therapy for breast cancer kills cancer cells at the tumor site. But, in a cruel irony, Stanford radiation oncologist Edward Graves, PhD, and research associate Marta Vilalta, PhD, have found that the dying cells in the breast may send out a signal that recruits other cancer cells back to the site of the initial tumor. Their work was published today in Cell Reports. As Graves explained in an e-mail to me:

Cancer spreads by shedding tumor cells into the circulation, where they can travel to distant organs and form secondary lesions.  We’ve demonstrated with this study that cancer radiation therapy may actually attract these circulating tumor cells, or CTCs, back to the primary tumor, which may lead to the regrowth of the tumor after radiation therapy.

The researchers studied mouse and human breast cancer cells growing in a laboratory dish, as well as human breast cancer cells implanted into mice. They found that irradiated cells secreted a molecule called granulocyte macrophage colony stimulating factor, or GM-CSF. Blocking the expression of GM-CSF by the cells inhibited (but didn’t completely block) their ability to recruit other cells to the cancer site. The finding is particularly interesting, since physicians sometimes give cancer patients injections of GM-CSF to enhance the growth of infection-fighting white blood cells that can be damaged during chemotherapy. As Graves explained, “This work has important implications for clinical radiotherapy, and for the use of GM-CSF in treating neutropenia in cancer patients during therapy.”

The researchers say, however, that cancer patients shouldn’t eschew radiation therapy. Rather, the finding may help clinicians devise better ways to fight the disease – perhaps by blocking GM-CSF signaling. Graves concluded:

It should be emphasized that radiation therapy remains one of the most effective treatments for cancer. Our findings will help us to further optimize patient outcomes following this already potent therapy.

Previously: Using 3-D technology to screen for breast cancer, Blood will tell: In Stanford study, tiny bits of circulating tumor DNA betray hidden cancers and Common drug class targets breast cancer stem cells, may benefit more patients, says study

Research, Science, Stanford News, Stem Cells

A new era for stem cells in cardiac medicine? A simple, effective way to generate patient-specific heart muscle cells

A new era for stem cells in cardiac medicine? A simple, effective way to generate patient-specific heart muscle cells

Ford assembly lineIn the early 1900s, Henry Ford was lauded for his use of the assembly line, which allowed the rapid, reliable and uniform production of over 15 million Model T automobiles. By codifying each step of production and using identical, interchangeable parts, he brought car ownership within reach of the average American and changed the face of our country.

Now Stanford cardiologist Joseph Wu, MD, PhD, and instructor Paul Burridge, PhD, have done something similar with stem cells. They’ve devised a way to create large numbers of heart muscle cells called cardiomyocytes from stem cells without using human or animal-derived products, which can vary in composition and concentration among batches. Their technique was published Sunday in Nature Methods. Wu, who is the director of the Stanford Cardiovascular Institute explained to me in an e-mail:

This technique solves an important hurdle for the use of iPS-derived heart cells. In order to fully realize the potential of these cells in drug screening and cell therapy, it’s necessary to be able to reliably generate large numbers at low cost. Due to their chemically defined nature, this system is highly reproducible, massively scalable and substantially reduces costs to allow the production of billions of cardiomyocytes matching a specific patient’s heart phenotype.

Chemically defined cell culture means that scientists know exactly what (and how much) is in the liquid in which the cells are grown. In contrast, many common cell culture methods involve the use of nutrient-rich broth derived from animal or human sources. These liquids are teaming with proteins, some known and some unknown, that can promote stem cell growth. They get the job done, but their components can vary among batches and the outcome isn’t always reproducible.

In the new method, Wu and his colleagues collected cells from the skin or blood of an individual. They used a virus called the Sendai virus encoding four reprogramming genes to create induced pluripotent stem cells. These cells were then grown in a liquid in which everything needed for growth was precisely defined. As Wu explained, “This approach gives us an opportunity to fully understand the molecular and macromolecular requirements for cardiac differentiation and eliminates any animal-derived components that were previously used.”

The researchers found they were able to produce about 100 cardiomyocytes for every one stem cell by following a systematic series of steps and using a growing medium that contained just three well-defined components. They showed the technique worked on 11 different batches of induced pluripotent stem cells. The cardiomyocytes were more than 95 percent pure, making it easier to get large numbers of cells to study disease processes or to test the effects of compounds during drug development. According to Wu:

We can use this approach to assess the effect of a particular medication on a specific patient’s heart cells, to discover new drugs, to better understand the process of heart development and to generate cardiomyocytes for use in regenerative medicine approaches, such as for injection into the heart to aid recovery after a heart attack. The system also serves as a platform to study cardiomyocyte subtype specification and maturation.

Of course, stem cells are nothing like automobiles, and regular people aren’t lining up clamoring for a fresh vial of heart muscle cells. But it’s possible that the ability to reliably generate large numbers of cardiomyocytes for study and therapy could be as transformative to cardiac medicine as the Model T was to our grandparents and great grandparents.

Previously: Oh grow up! “Specialized” stem cells tolerated by the immune system, say Stanford researchers, Stem cell medicine for hearts? Yes, please, says one amazing family and “Clinical trial in a dish” may make common medicines safer, say Stanford scientists
Photo by Kyle Harris

Evolution, Genetics, Research, Science, Stanford News, Stem Cells

It’s a blond thing: Stanford researchers suss out molecular basis of hair color

It's a blond thing: Stanford researchers suss out molecular basis of hair color

blond hair, brighter

It’s all over the news today: Blonds aren’t stupid.

Well, that’s what most of the media would have you believe is the take-home message of the latest research by developmental biologist David Kingsley, PhD. And although I’m happy to see such great coverage, I’m hoping that readers realize that Kingley’s study on human hair color, which was published yesterday in Nature Genetics (subscription required), describes something much more subtle, and less superficial. From our release:

The study describes for the first time the molecular basis for one of our most noticeable traits. It also outlines how tiny DNA changes can reverberate through our genome in ways that may affect evolution, migration and even human history.

Kingsley, who is known for his study of a tiny fish called the threespine stickleback, is interested in learning how organism adapt to new environments by developing new traits. He’s found that this type of adaptation is most-often accomplished by changes in DNA regulatory regions that affect when, where and how a gene is expressed, rather than through (possibly disruptive) changes in the genes themselves.

In this case, he and his colleagues turned his attention to the blond hair common to many northern European and Icelanders. A previous study had shown that a single nucleotide change on human chromosome 12 was a major driver in hair color. As explained in the release:

The researchers found that the blond hair commonly seen in Northern Europeans is caused by a single change in the DNA that regulates the expression of a gene that encodes a protein called KITLG, also known as stem cell factor. This change affects how much KITLG is expressed in the hair follicles without changing how it’s expressed in the rest of the body. Introducing the change into normally brown-haired laboratory mice yields an animal with a decidedly lighter coat — not quite Norma Jeane to Marilyn Monroe, but significant nonetheless.

The involvement of KITLG, with its critical role in stem cell biology, is certainly interesting. But there’s also a more global lesson about the specificity of gene expression their effect on phenotype:

The study shows that even small, tissue-specific changes in the expression of genes can have noticeable morphological effects. It also emphasizes how difficult it can be to clearly connect specific DNA changes with particular clinical or phenotypic outcomes. In this case, the change is subtle: A single nucleotide called an adenine is replaced by another called a guanine on human chromosome 12. The change occurs over 350,000 nucleotides away from the KITLG gene and only alters the amount of gene expression about 20 percent — a relatively tiny blip on a biological scale more often assessed in terms of gene expression being 100 percent “on” or “off.”

“What we’re seeing is that this regulatory region exercises exquisite control over where, and how much, KITLG expression occurs,” said Kingsley. “In this case, it controls hair color. In another situation — perhaps under the influence of a different regulatory region — it probably controls stem cell division. Dialing up and down the expression of an essential growth factor in this manner could be a common mechanism that underlies many different traits.”

And now, the hook that excited most of the news media:

[Kingsley] added: “It’s clear that this hair color change is occurring through a regulatory mechanism that operates only in the hair. This isn’t something that also affects other traits, like intelligence or personality. The change that causes blond hair is, literally, only skin deep.”

Previously: Something fishy: Threespine stickleback genome published by Stanford researchers, Hey guys, sometimes less really is more , Tickled by stickle(backs) and Blond hair evolved more than once, and why it matters
Photo by Traci Lawson

Research, Science, Stanford News, Stem Cells

“Alert” stem cells speed damage response, say Stanford researchers

"Alert" stem cells speed damage response, say Stanford researchers

191855419_350c4827a2_zStanford neurologist and longevity researcher Thomas Rando, MD, PhD and his colleagues have found that adult stem cells (those that hang around in mature tissues to facilitate tissue repair) have a surprising ability to notice, and respond, to damage in distant parts of the body. The researchers termed the response an  “alert” state; the cells are no longer resting deeply, but are also not yet committed to possibly unnecessary action. (As I was writing our release, I kept envisioning the stem cells like dogs frozen in a point, waiting for further movement or instructions.)

Their study was published last week in Nature. As I explained:

The researchers were studying the response of mouse muscle stem cells, or satellite cells, to muscle injury. Conventional wisdom holds that adult stem cells are by nature quiescent — a term that indicates a profound resting state characterized by small size and no cell division. It’s a kind of cellular deep freeze. In contrast, most other cells cycle through rounds of DNA replication and cell division in discrete, well-defined phases. A quiescent stem cell can “wake up” and enter the cell cycle in response to local signals of damage or other regeneration needs.

Rando and his colleagues were studying this activation process in laboratory mice by watching how muscle stem cells in one leg respond to a nearby muscle injury in the same leg. (Mice were anesthetized prior to a local injection of muscle-damaging toxin; they were given pain relief and antibiotics during the recovery period.) The researchers had planned to observe the quiescent muscle stem cells in the uninjured leg as a control for their experiment. However, they instead saw something unexpected.

“The muscle stem cells in the uninjured leg had definitely changed,” said Rando, who is director of the Rehabilitation Research & Development Center of Excellence at the Veterans Affairs Palo Alto Health Care System. “They were very clearly biochemically different from completely dormant, quiescent cells, and from fully activated stem cells. We termed this state an ‘alert’ state of quiescence.”

These alert stem cells were able to respond to subsequent, nearby damage much more quickly and efficiently than completely quiescent cells, the researchers found. They also learned that the stem cells’ response encompasses several tissue types in addition to the one in which the injury occurred. More from the release:

Surprisingly, the muscle stem cells also became alert in response to bone or minor skin injuries — injuries in which the cells are not known to play any regenerative role.

Conversely, other non-muscle adult stem cells, including hematopoietic stem cells in the bone marrow and mesenchymal stem cells in the muscle, became alert in response to muscle damage.

“It is clear that this alert state is a systemic response,” said Rando.

Continue Reading »

Cardiovascular Medicine, Immunology, Research, Science, Stanford News, Stem Cells

Oh, grow up! “Specialized” stem cells tolerated by immune system, say Stanford researchers

Oh, grow up! "Specialized" stem cells tolerated by immune system, say Stanford researchers

3075268200_419b9e73b7_zMany of us know by now that stem cells are remarkably fluid in the types of cells they can become. But this fluidity, or pluripotency, comes with a price. Several studies have shown that the body’s immune system will attack and reject even genetically identical transplanted stem cells, making it difficult to envision their usefulness for long-term therapies.

Now Stanford cardiologist Joseph Wu, MD, PhD, and his colleagues have shown that coaxing the stem cells to become more-specialized (a process known as differentiation) before transplantation allows the body to recognize and tolerate the cells. Their research was published today in Nature Communications (subscription required).

From our release:

In a world teeming with microbial threats, the immune system is a necessary watchdog. Immune cells patrol the body looking not just for foreign invaders, but also for diseased or cancerous cells to eradicate. The researchers speculate that the act of reprogramming adult cells to pluripotency may induce the expression of cell-surface molecules the immune system has not seen since the animal (or person) was an early embryo. These molecules, or antigens, could look foreign to the immune system of a mature organism.

Previous studies have suggested that differentiation of iPS cells could reduce their tendency to inflame the immune system after transplantation, but this study is the first to closely examine, at the molecular and cellular level, why that might be the case.

Postdoctoral scholars Patricia Almeida, PhD, and Nigel Kooreman, MD, and assistant professor of medicine Everett Meyer, MD, PhD, share lead authorship of the study. They found that laboratory mice accepted grafts of endothelial cells made from stem cells much more readily than they did the stem cells themselves. As Wu, who also directs the Stanford Cardiovascular Institute said in our release:

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.

Previously: New technique prevents immune-system rejection of embryonic stem cells and Overcoming immune response to stem cells essential for therapies, say Stanford researchers
Photo by Umberto Salvagnin

Stanford News, Stem Cells, Surgery, Videos

Stanford reconstructive surgeon Jill Helms reminds us that “beauty isn’t defined by our faces alone”

Stanford reconstructive surgeon Jill Helms reminds us that "beauty isn't defined by our faces alone"

Jill Helms, PhD, a professor of plastic and reconstructive surgery at Stanford, leads a team of scientists that are working on methods to activate a patient’s own stem cells at the site of an injury to speed up tissue healing. In this TEDxStanford video, Helms discusses how surgical scars can sometimes impede growth of a patient’s body, such as the repair of a child’s cleft palate, and the potential of using stem cells to enhance the body’s natural healing process.

As previously mentioned here, Helms delivered a talk on the topic of beauty reconsidered, and she reminds us at the end of the video that “beauty isn’t defined by our faces alone.” She says, “Beauty is compassion, kindness and warmth, and that’s internal beauty. That’s the most important beauty.”

Previously: A spotlight on TEDxStanford’s “awe-inspiring” and “deeply moving” talks and Stanford study shows protein bath may rev up sluggish bone-forming cells

Research, Stanford News, Stem Cells

Studying the inner ear and advancing research in developmental biology

Studying the inner ear and advancing research in developmental biology

hellerResearcher Stefan Heller, PhD, came to Stanford in 2005 from Harvard. His laboratory focuses on inner ear development and works on approaches to regenerate sensory hair cells, scarce sensory receptor cells that are essential for our senses of hearing and balance.

As I explained in an article about his arrival, Heller’s goal was to come here and collaborate with others to devise “a variety of possible cures for deafness from drug therapy treatment – which could be as simple as an application of ear drops-to stem cell transplantation into the inner ear to remedy hearing loss.” Since then, his lab has continued to add to the body of research on the inner ear’s early development and to pave the way towards regenerative therapies for hearing loss. The researchers’ most recent milestone (subscription required) – during which they designed the most detailed 3-D model to date of the otocyst, the embryonic structure in vertebrates that develops into the inner ear in the adult – was published online this month in the journal Cell.

In a video on the journal website, Heller and the lead author of the study, Robert Durruthy-Durruthy, a PhD candidate, describe the mathematical method used that allows the 3-D reconstruction of the developing inner ear. Russ Altman, PhD and Assaf Gottlieb, PhD, from Stanford bioengineering were collaborators of the study.

Heller recently described to me how microfluidics technology developed in the lab of Stanford bioengineering professor Stephen Quake, PhD, was essential to analyze single cells in order to develop the blue prints for their 3-D model. The approach is new in biology, Heller said. Much like dismantling the engine of a car into its smallest parts, taking apart a simple organ into single cells results in the challenge of putting the pieces back together.  “Our new method provides a good strategy for such reconstructions,” Heller said.

Heller also explained how this advancement will help as he continues researching early ear development and working on growing inner ear sensory hair cells, the linchpin for hearing. (Hair cells exist in limited numbers in human ears and once they are gone, hearing loss occurs.) He said:

This [paper] gives us deep insight into how this organ forms in early development. It identifies the different cell types and defines them in much more detail than previously known. It provides details about the inner ear progenitor cells that we are trying to generate from stem cells. Having this blue print will help us to generate sensory hair cells more efficiently and hopefully to regenerate hair cells at some time in the future.

The technology, Heller said, can also benefit others: “It can be used to reconstruct all kinds of things, other simple organs, perhaps even simple multicellular organisms, or structures like tumors.”

Previously: Regenerating sensory hair cells to restore hearing to noise-damaged ears, Stanford chair of otolaryngology discusses future regenerative therapies for hearing loss, Stefan Heller discusses stem cell research on Science Friday and Growing new inner ear cells a step toward a cure for deafness
Photo by Steve Fisch

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