The human brain, as it turns out, is far more malleable than we once thought. Even adult brains. But they are subject to age-related diseases and disorders, such as dementia and diminished cognitive function.
There is hope that medical science may be able to replace brain cells and restore memory in aging patients thanks to new discoveries in neural stem cell techniques. Researchers at the Texas A&M Health Science Center College of Medicine recently published new findings in the journal Stem Cells Translational Medicine that suggests a new technique for preparing donor neural stem cells and grafting them into an aged brain can regenerate tissue that has succumbed to structural, chemical, and functional changes, as well as a host of neurocognitive changes that can be attributed to aging.
The study, titled “Grafted Subventricular Zone Neural Stem Cells Display Robust Engraftment and Similar Differentiation Properties and Form New Neurogenic Niches in the Young and Aged Hippocampus,” was led by Ashok K. Shetty, Ph.D., a professor in the Department of Molecular and Cellular Medicine. associate director of the Institute for Regenerative Medicine, and research career scientist at the Central Texas Veterans Health Care System.
Shetty and his team at Texas A&M focus on the aged hippocampus, which plays an important role in making new memories and connecting them to emotions. They took healthy donor neural stem cells and implanted them into the hippocampus of an animal model, essentially enabling them to regenerate tissue.
The hippocampus in the aging brain
“We chose the hippocampus because it’s so important in learning, memory and mood function,” Shetty said. “We’re interested in understanding aging in the brain, especially in the hippocampus, which seems particularly vulnerable to age-related changes.”
The volume of this part of the brain seems to decrease during the aging process, and this decrease may be related to age-related decline in neurogenesis (production of new neurons) and the memory deficits some people experience as they grow older.
The aged hippocampus also exhibits signs of age-related degenerative changes in the brain, such chronic low-grade inflammation and increased reactive oxygen species.
Bharathi Hattiangady, assistant professor at the Texas A&M College of Medicine and co-first author of the study said his team was excited to discover that the aged hippocampus can accept grafted neural stem cells as well as the young hippocampus does, a discovery that has significant implications for treating age-related neurodegenerative disorders.
“It’s interesting that even neural stem cell niches can be formed in the aged hippocampus,” Hattiangady says.
Shetty’s previous research focused on the benefits of resveratrol (an antioxidant that is famously found in red wine and the skin of red grapes, as well as in peanuts and some berries) to the hippocampus. Although the results indicated important benefits for preventing memory loss in aging brains, his newest work demonstrates a way to affect the function of the hippocampus more directly.
Neural stem cell grafting
In this new study, the team found that the neural stem cells engrafted well onto the hippocampus in the young animal models (which was expected) as well as the older ones that would be, in human terms, about 70 years old. Not only did these implanted cells survive, they divided several times to make new cells.
“They had at least three divisions after transplantation,” Shetty said. “So the total yield of graft-derived neurons and glia (a type of brain cell that supports neurons) were much higher than the number of implanted cells, and we found that in both the young and aged hippocampus, without much difference between the two.”
In both old and young brains, a small percentage of the grafted cells retained their stemness feature—an essential characteristic of a stem cell that distinguishes it from ordinary cells—and continuously produced new neurons. This is called creating a new ‘niche’ of neural stem cells, and these niches seemed to be functioning well. They were still producing new neurons at least three months after implantation, and these neurons are capable of migrating to different parts of the brain.
Past efforts to rejuvenate brains using fetal neurons in this way weren’t nearly as successful. Immature cells, such as neural stem cells, seem to do a better job because they can tolerate the hypoxia (lack of oxygen) and trauma of the brain grafting procedure better than post-mitotic or relatively mature neurons. When researchers tried in the past to implant these partially differentiated cells into the aged hippocampus, they didn’t do nearly as well. The research team used a new technique of preparing the donor neural stem cells, which Shetty says is why this result has never been seen before.
The researchers used donor cells from the sub-ventricular zone of the brain, an area called the “brain marrow,” because it is analogous to bone marrow in that it holds a number of neural stem cells that persist throughout life. These neural stem cells continuously produce new neurons that migrate to the olfactory system. They also respond to injury signals in conditions such as stroke and traumatic brain injury and replace some of the lost cerebral cortical neurons.
Induced pluripotent cells from skin
Even a small stem cell sample is good enough to expand in culture, so the procedure isn’t terribly invasive. However, in the future, a single skin cell might suffice, as similar neural stem cells can be obtained in large numbers from skin. In fact, it is well known in medical science that a number of cells in the body—including skin cells—can be modified in such a way to create induced pluripotent stem cells.
With these cells, scientists can do any number of things, such as making neural stem cells that will make both more of themselves, and make new neurons. It’s not necessary to get the cells from the brain, just take a skin biopsy and push them into neural stem cells, according to Shetty.
Although the way the grafted cells thrived is promising, there is still a good deal of work to be done to determine if the extra grey matter actually improves cognition.
“Next, we want to test what impact, if any, the implanted cells have on behavior and determine if implanting neural stem cells can actually reverse age-related learning and memory deficits,” Shetty said. “That’s an area that we’d like to study in the future.
“I’m always interested in ways to rejuvenate the aged brain to promote successful aging, which we see when elderly persons exhibit normal cognitive function and the ability to make memories.”
Researchers at the University of Toronto have developed a tracer ink—a “stem cell tattoo”—that provides the ability to monitor stem cells in unprecedented detail after they’re injected.
The research findings, titled “Bifunctional Magnetic Silica Nanoparticles for Highly Efficient Human Stem Cell Labeling,” was published in June in the Journal of Magnetic Resonance Imaging. Already emerging as an ideal probe for noninvasive cell tracking, the technology has the potential to revolutionize stem cell research by arming scientists with the ability to visually follow the pathways and effectiveness of stem cell therapies in the body, in real time.
“Tattoo” tracer can help further development of stem cell therapies
University of Toronto biomedical engineering professor Hai-Ling Margaret Cheng, a biomedical engineer who specializes in medical imaging, says the new technology allows researchers to actually see and track stem cells after they’re injected. Cheng hopes the technique will help expedite the development and use of stem cell therapies.
Working with colleague Xiao-an Zhang, an assistant professor of chemistry at the University of Toronto, Scarborough, Cheng developed a singular chemical compound known as a contrast agent that acts as a tracer. Composed of manganese, an element that naturally occurs in the body, this tracer compound, called MnAMP, bathes stem cells in a green solution, rendering them traceable inside the body under MRI.
Stem cell tracer ink allows long term cell tracking
The contrast agent “ink” first enters a stem cell by penetrating its membrane. Once inside, it stimulates a chemical reaction that prevents it from seeping out of the cell the same way it entered. Previous versions of contrast agents easily escaped cells. By establishing a way to contain the ink within the cell’s walls, the research team achieved the ability to track the cells long term once they are inside the body.
According to Cheng, some basic contrast agents are already available for use in humans, but none are capable of tracking cells over a long period of time. Contrast agents work by illuminating the deepest and darkest corners of a person’s internal architecture so they appear clearly under X-rays, computed tomography (CT) scans and MRIs. An example of a currently used contrasting agent would be the barium sulfate solution given to patients to help diagnose certain disorders of the esophagus, stomach, or intestines.
The thick substance coats the esophagus and other areas of the body with an illuminating compound, making them visible in an x-ray or CT scan. But the barium solution is eliminated from the body within 2 – 3 days or less. Before the stem cell tattoo tracer ink was developed, surgery was the only option for scientists to get a literal glance of a cells’ destiny after it was injected into the body. Now, researchers can track the results in real time, without resorting to any invasive procedures.
“Before, we could not visually track the cells once they were introduced into the body,” Cheng says. “Now we have the ability to view cells in a non-invasive manner using MRI, and monitor them for potentially a very long time.”
Cell tracer technology still in developmental stage
Currently the tracer ink technology is still in the early development phase and requires more animal testing. Cheng is hopeful it can proceed to human clinical trials in about 10 years. While Cheng has already proven that tattooing an animal’s embryonic stem cell doesn’t affect its ability to transform into a functional heart cell, rat, or even a pig (which better represents a human’s size), larger models are up for evaluation next.
In those test cases, researchers will cut off and reduce blood flow in the animals to mimic the effects of damage caused by a human heart attack. Cardiac stem cells pre-tagged with Cheng’s ink tracer technology will then be injected into the damaged tissue. Using MRI to monitor the luminous inked stem cells in action, researchers can non-invasively follow where in the body they’re traveling and more easily determine if the new cells are responsible for restoring normal heart rhythm.
Before it can be tested in humans, the chemical tracer will also have to pass rigorous toxicology tests to ensure its safety.
Researchers from Harvard University and the University of Nottingham have developed a new filling that stimulates stem cells in dental pulp to regenerate and even regrow teeth damaged by disease and decay. According to Newsweek Magazine, the discovery earned a prize from the Royal Society of Chemistry after judges described it as a “new paradigm for dental treatments.”
The treatment is believed to potentially eliminate the need for root canals.
Filling materials stimulate stem cells to encourage dentin growth
The filling works by stimulating the body’s natural store of stem cells to encourage the growth of dentin—the bony material that makes up the majority of the tooth—allowing patients to effectively regrow teeth that are damaged through dental disease. The filling’s synthetic biomaterials are used similarly to dental fillings, placed in direct contact with pulp tissue in the damaged tooth. This stimulates the tissue’s native stem cell population to repair and regenerate pulp tissue and the surrounding dentin.
The discovery is a significant step forward from current methods to treat cavities, which involve drilling out decay and putting in a filling made of gold; porcelain; silver amalgam (which consists of mercury mixed with silver, tin, zinc, and copper); or tooth-colored plastic or composite resin. When these fillings fail to halt the tooth’s decay, a root canal is needed to remove the pulp of the tooth, damaging it even further.
Alternative to traditional fillings in teeth
Researchers hope to develop the technique with industry partners in order to make it available for dental patients as an alternative to traditional fillings. Marie Curie research fellow Adam Celiz says that existing dental fillings are toxic to cells and are therefore incompatible with pulp tissue inside the tooth.
“In cases of dental pulp disease and injury, a root canal is typically performed to remove the infected tissues,” Celiz says.
The promise of using therapeutic biomaterials to bring stem cell medicine to restorative dentistry could significantly impact millions of dental patients each year. In fact, the approach is so promising it won second prize in the materials category of the Royal Society of Chemistry’s Emerging Technology Competition for 2016.
Competition entries were judged on the degree of innovation of the technology, its potential impact, and the quality of the science behind it. Increasing innovation in the chemical sciences is a key element of the Royal Society of Chemistry’s industry strategy.
Effective and practical approach to regenerating teeth
The stem cell stimulating filling promises to change the future of dentistry, according to David Mooney, Pinkas Family Professor of Bioengineering at the John Paulson School of Engineering and Applied Sciences at Harvard and the Wyss Institute for Biologically Inspired Engineering.
“’These materials may provide an effective and practical approach to allow a patient to regenerate components of their own teeth,’ Pinkas says.
Stem cells can induce regenerative, self-healing qualities in any tissue found in the body and can, as a result, provide unlimited potential for medical applications. Current studies are underway worldwide to learn how stem cells may be used to prevent or cure diseases and injuries such as Parkinson’s disease, type 1 diabetes, heart disease, spinal cord injury, muscular dystrophy, Alzheimer’s disease, strokes, burns, osteoarthritis, vision and hearing loss, and more. Stem cells may also be used to replace or repair tissue damaged by disease or injury.
Stem cell research has never been more advanced, and as a result many different types of treatments are currently offered on the market. Unfortunate
ly, some providers are practicing quackery in stem cell therapies, and an abundance of well-intentioned scientific and medical personnel are prematurely publicizing their work. These providers and publishers have cast an unfair shadow of mistrust on this very important branch of medical research and potential treatments.
On the other hand, the contributions of professional medical and stem cell societies and other organizations require self-regulation through accreditation and certification, development of standards, and creation of a platform for collaboration among stakeholders.
Professional Guidelines for responsible Stem Cell Research
International Society for Stem Cell Research (ISSCR) is the largest professional organization of stem cell scientists. In 2007, ISSCR impaneled a broad international taskforce to develop a set of professional guidelines for responsible translational stem cell research. Their principles include high standards of preclinical evidence, peer review, scrupulous review of clinical protocol by an Institutional Review Board (IRB), rigorous informed consent, and publication of results whether positive or negative.
The general scientific consensus is that most stem cell therapies are not ready for marketing or commercialization. But the industries that are providing these treatments are increasingly sophisticated and organized, and are challenging established regulatory frameworks.
The International Society for Cellular Therapy (ISCT) has an interest in the promotion of stem cell research and development, but it also is interested in a broader range of cell-based interventions such as immune cell interventions, reproductive medicine, and gene therapy. The ISCT taskforce has working groups on definitions, scientific evidence and biological rationale, laboratory cell processing, clinical practice, regulation, commercial implications, communications, and policy.
Develop terminology, define levels of scientific evidence in new guidelines for stem cell research
The key goals are to develop an appropriate terminology, define the levels of scientific evidence needed to justify routine use or commercialization of a stem cell therapy, address questions of “experimental” and “innovative” use, and understand the global regulatory landscape in order to identify gaps and contradictions.
The ISSCR published revised guidelines for research and clinical translation involving stem cells on May 12, 2016. These new guidelines update and combine guidelines on stem cell research and clinical translation previously issued in 2006 and 2008 Jonathan Kimmelman, Associate Professor of Biomedical Ethics at McGill University, chaired the ISSCR Guidelines Update Task Force. The task force was made up of 25 experts in basic research, clinical research, and bioethics, and received feedback from 85 external individuals and organizations.
2016 guidelines: covering new ground in stem cell research
The 2016 guidelines cover new ground in areas such as gene editing and induced pluripotent stem cells. They introduce a new focus on the communication of results. The task force recognizes that results and potential applications can be exaggerated, leading to distorted understandings of research outcomes in the scientific community, popular press, and among potential patients. The “14-day rule” limiting experimentation on human embryos or embryo-like structures is upheld in these guidelines, although one task-force member has suggested that this may soon be open to revision.
In May, 2016 ISSCR released the following list of all of the new topics addressed in the revised guidelines as part of the announcement of its report:
- Define an Embryo Research Oversight (EMRO) process to encompass both human embryonic stem cell research and human embryo research that may not explicitly pertain to stem cells or generating new stem cell lines;
- Exclude the generation of induced pluripotent stem cells (iPS cells) from specific stem cell research oversight, and instead call on the existing human subjects review processes to oversee donor cell recruitment (iPS cells behave like embryonic stem cells but are derived by reprogramming more differentiated tissue cells);
- Support laboratory-based research that entails gene editing of the nuclear genomes of human sperm, egg, or embryos, when performed under rigorous review, but hold that any attempt to apply this clinically would be premature and should be prohibited at this time;
- Define principles for evaluating both basic and clinically applied research on mitochondrial replacement therapy, in concordance with recent deliberations in the U.K., U.S., and elsewhere;
- Determine that where there is no undue financial inducement to participate, it may be acceptable to compensate women who donate eggs for research;
- Recognize that the development of increasingly complex in vitro models of early stages of human development should undergo specialized review;
- Highlight opportunities to strengthen preclinical studies in stem cell research, including reproducibility and stringent standards for experimental design;
- Call for robust standards for preclinical and clinical research evidence as clinical trials progress and rigorous evaluation for safety and efficacy before marketing approval;
- Address the valuable contributions made by patients or patient groups to support clinical research and a framework to ensure this is achieved without compromising the integrity of the research;
- Highlight the responsibility of all groups communicating stem cell science and medicine—scientists, clinicians, industry, science communicators, and media—to present accurate, balanced reports of progress and setbacks.
The good news is that stem cell research is evolving into a highly respected and in-demand branch of healing that many consider to be the future of medicine. Since pluripotent stem cells have the ability to differentiate into any type of cell, they are used in the development of medical treatments for a wide range of conditions including physical trauma, degenerative conditions, and genetic diseases (in combination with gene therapy). Further treatments using stem cells are being developed due to stem cells’ ability to repair extensive tissue damage.
Great levels of success and potential have been achieved from research using adult stem cells. In early 2009, the FDA approved the first human clinical trials using embryonic stem cells. Embryonic stem cells are pluripotent, which means they can become any cell type of the body, with the exception of placental cells. More and more is being discovered about the plasticity of adult stem cells, increasing the potential number of cell types an adult stem cell can become.
Chronic lung diseases are the third leading causes of death in the U.S. Chronic lung diseases include a collection of illnesses that cause airflow blockage and breathing-related issues, including primarily chronic obstructive pulmonary disease (COPD), bronchitis, emphysema and asthma. Lung disease involves changes in cells within the lungs, and while research on lung stem cell therapies may not only shed light on their causes, it may provide the groundwork for future treatments.
Stem cells in the lung
Human lungs are hard working organs. In an average lifetime, human lungs take 20-40 million breaths and experience a daily airflow of between 1,850 and 2,640 gallons. Human lungs are made up of two distinct regions:
- The conducting airway tubes, including the trachea, bronchi, and bronchioles.
- The gas exchange regions, or alveolar spaces.
Medical researchers have discovered that these regions each contain unique types of stem cells and progenitor cells. In normal lungs, an abundance of progenitor cells is present in each region, which divide to replace old or damaged lung cells to keep the lungs healthy. The progenitor cells include tracheal basal cells, bronchiolar secretory cells (known as club cells), and alveolar type 2 cells. Progenitor cell division is believed to be sufficient to renew the lung’s structure throughout normal adult life.
Stem cells are far less abundant than progenitors, but are found in both embryonic and adult lungs. Some stem cells assist in initial lung development, while others help repair and regenerate the lung throughout one’s lifetime. Problematic stem cells may actually contribute to lung diseases. In mouse lungs, certain rare stem cells have been located in the conducting airway tubes after to severe injury—for example, flu infection. These rare cells can divide and produce new cells that contribute to both the airway and gas exchange regions. These cells have also been grown in vitro and used as a proof-of-concept treatment in injured mouse lungs.
Adult mesenchymal stem cells (hMSCs)
Adult human mesenchymal stem cells (hMSCs) are the focus of a number of clinical applications. The advantage of hMSCs is that they are immuno-modulatory— capable of modifying or regulating one or more immune functions—and versatile due to the anti-inflammatory and regenerative bioactive molecules they secrete.
hMSCs have the potential to orchestrate reparative processes in diseased or injured tissues. Much of the diversity and uniqueness of hMSCs is defined by their response to the environment of injured tissue. hMSCs are sensitive to their site-specific microenvironment, and scientists anticipate that these cells will deliver the bioactive agents in a site-specific manner quite different from the way pharmaceutical drugs work in the treatment of lung diseases.
hMSCs are non-hematopoietic, multi-potent progenitor cells with the capacity to generate bone marrow stromal cells as well as adipocytes, chondrocytes, and osteocytes in suitable tissue and other organ sites.
Studying lung stem cells sheds light on the causes of lung disease
A better understanding of lung stem cell and progenitor cell biology can improve our knowledge of how the healthy lung works. This in turn will shed light on the causes of lung diseases such as chronic obstructive pulmonary disease (COPD). Such research could lead to the development of new treatments for lung disease. In fact, lung stem cells may be used in future therapies to repair or regenerate the lungs of patients with severe lung damage or disease.
Lung stem cells have most frequently been identified and characterized in mice. Studies on mice have allowed researchers to identify the differences between embryonic and adult lung stem cells, discover the role of stem cells in lung repair, and investigate how changes to lung stem cells may lead to lung disease. A current focus of research includes testing if the same stem and progenitor cell populations can be identified in human lungs.
Identifying progenitor and stem cells before and after lung injury
Researchers are also working to determine the role of stem cells in various human lung diseases, including lung cancer and COPD. They have begun examining potential clinical applications of stem cell therapies with several ‘first-in-human’ studies to investigate whether lung stem cells might enhance organ replacement or regeneration in patients.
The future of stem cells in treating lung disease
As researchers continue to improve their understanding of the exact identity and function of human lung stem cells, the potential for clinical applications will be divulged. Researchers will identify methods to control lung stem cells, which can then be tested as treatments for lung diseases. Further research will also investigate the uses of lung stem cells for personalized medicine.