Posts tagged stem cells
Articles and news from the latest research reports.
(Image caption: These are mature nerve cells generated from human cells using enhanced transcription factors. Credit: Fahad Ali)
Functional nerve cells from skin cells
A new method of generating mature nerve cells from skin cells could greatly enhance understanding of neurodegenerative diseases, and could accelerate the development of new drugs and stem cell-based regenerative medicine.
The nerve cells generated by this new method show the same functional characteristics as the mature cells found in the body, making them much better models for the study of age-related diseases such as Parkinson’s and Alzheimer’s, and for the testing of new drugs.
Eventually, the technique could also be used to generate mature nerve cells for transplantation into patients with a range of neurodegenerative diseases.
By studying how nerves form in developing tadpoles, researchers from the University of Cambridge were able to identify ways to speed up the cellular processes by which human nerve cells mature. The findings are reported in the May 27th edition of the journal Development.
Stem cells are our master cells, which can develop into almost any cell type within the body. Within a stem cell, there are mechanisms that tell it when to divide, and when to stop dividing and transform into another cell type, a process known as cell differentiation. Several years ago, researchers determined that a group of proteins known as transcription factors, which are found in many tissues throughout the body, regulate both mechanisms.
More recently, it was found that by adding these proteins to skin cells, they can be reprogrammed to form other cell types, including nerve cells. These cells are known as induced neurons, or iN cells. However, this method generates a low number of cells, and those that are produced are not fully functional, which is a requirement in order to be useful models of disease: for example, cortical neurons for stroke, or motor neurons for motor neuron disease.
In addition, for age-related diseases such as Parkinson’s and Alzheimer’s, both of which affect millions worldwide, mature nerve cells which show the same characteristics as those found in the body are crucial in order to enhance understanding of the disease and ultimately determine the best way to treat it.
"When you reprogramme cells, you’re essentially converting them from one form to another but often the cells you end up with look like they come from embryos rather than looking and acting like more mature adult cells," said Dr Anna Philpott of the Department of Oncology, who led the research. "In order to increase our understanding of diseases like Alzheimer’s, we need to be able to work with cells that look and behave like those you would see in older individuals who have developed the disease, so producing more ‘adult’ cells after reprogramming is really important."
By manipulating the signals which transcription factors send to the cells, Dr Philpott and her collaborators were able to promote cell differentiation and maturation, even in the presence of conflicting signals that were directing the cell to continue dividing.
When cells are dividing, transcription factors are modified by the addition of phosphate molecules, a process known as phosphorylation, but this can limit how well cells can convert to mature nerves. However, by engineering proteins which cannot be modified by phosphate and adding them to human cells, the researchers found they could produce nerve cells that were significantly more mature, and therefore more useful as models for disease such as Alzheimer’s.
Additionally, very similar protein control mechanisms are at work to mature important cells in other tissues such as pancreatic islets, the cell type that fails to function effectively in type 2 diabetes. As well as making more mature nerves, Dr Philpott’s lab is now using similar methods to improve the function of insulin-producing pancreas cells for future therapeutic applications.
"We’ve found that not only do you have to think about how you start the process of cell differentiation in stem cells, but you also have to think about what you need to do to make differentiation complete - we can learn a lot from how cells in developing embryos manage this," said Dr Philpott.
Newborns a hope for spinal injuries
It all started at a symposium five years ago. Catherine Gorrie, an expert in spinal cord injury, was listening to a presentation about the differences between the developing brains of children and the mature ones of adults when she had an “aah-haa” moment.
“I began to wonder if there is something in the spines of children that could be manipulated for repair,” says Dr Gorrie, a neuroscientist at the University of Technology, Sydney (UTS). It made sense. Dr Gorrie already knew that the more adaptable, or “plastic”, spinal cords of infants responded more efficiently to injury than did those of adults.
If she could tease out the factors that encouraged generic cells, so-called stem cells, in the spines of newborns to become new nerve cells, neurones, Dr Gorrie reasoned that it should be possible to mimic the process and help repair spinal cord injuries in people of all ages. That would be incredibly important because, to date, there is no cure for spinal cord injury and no proven drug treatment.
Herpes-loaded stem cells used to kill brain tumors
Harvard Stem Cell Institute (HSCI) scientists at Massachusetts General Hospital have a potential solution for how to more effectively kill tumor cells using cancer-killing viruses. The investigators report that trapping virus-loaded stem cells in a gel and applying them to tumors significantly improved survival in mice with glioblastoma multiforme, the most common brain tumor in human adults and also the most difficult to treat.
The work, led by Khalid Shah, MS, PhD, an HSCI Principal Faculty member, is published in the Journal of the National Cancer Institute. Shah heads the Molecular Neurotherapy and Imaging Laboratory at Massachusetts General Hospital.
Cancer-killing or oncolytic viruses have been used in numerous phase 1 and 2 clinical trials for brain tumors but with limited success. In preclinical studies, oncolytic herpes simplex viruses seemed especially promising, as they naturally infect dividing brain cells. However, the therapy hasn’t translated as well for human patients. The problem previous researchers couldn’t overcome was how to keep the herpes viruses at the tumor site long enough to work.
Shah and his team turned to mesenchymal stem cells (MSCs)—a type of stem cell that gives rise to bone marrow tissue—which have been very attractive drug delivery vehicles because they trigger a minimal immune response and can be utilized to carry oncolytic viruses. Shah and his team loaded the herpes virus into human MSCs and injected the cells into glioblastoma tumors developed in mice. Using multiple imaging markers, it was possible to watch the virus as it passed from the stem cells to the first layer of brain tumor cells and subsequently into all of the tumor cells.
“So, how do you translate this into the clinic?” asked Shah, who also is an Associate Professor at Harvard Medical School.
“We know that 70-75 percent of glioblastoma patients undergo surgery for tumor debulking, and we have previously shown that MSCs encapsulated in biocompatible gels can be used as therapeutic agents in a mouse model that mimics this debulking,” he continued. “So, we loaded MSCs with oncolytic herpes virus and encapsulated these cells in biocompatible gels and applied the gels directly onto the adjacent tissue after debulking. We then compared the efficacy of virus-loaded, encapsulated MSCs versus direct injection of the virus into the cavity of the debulked tumors.”
Using imaging proteins to watch in real time how the virus combated the cancer, Shah’s team noticed that the gel kept the stem cells alive longer, which allowed the virus to replicate and kill any residual cancer cells that were not cut out during the debulking surgery. This translated into a higher survival rate for mice that received the gel-encapsulated stem cells.
“They survived because the virus doesn’t get washed out by the cerebrospinal fluid that fills the cavity,” Shah said. “Previous studies that have injected the virus directly into the resection cavity did not follow the fate of the virus in the cavity. However, our imaging and side-by-side comparison studies showed that the naked virus rarely infects the residual tumor cells. This could give us insight into why the results from clinical trials with oncolytic viruses alone were modest.”
The study also addressed another weakness of cancer-killing viruses, which is that not all brain tumors are susceptible to the therapy. The researchers’ solution was to engineer oncolytic herpes viruses to express an additional tumor-killing agent, called TRAIL. Again, using mouse models of glioblastoma—this time created from brain tumor cells that were resistant to the herpes virus—the therapy led to increased animal survival.
“Our approach can overcome problems associated with current clinical procedures,” Shah said. “The work will have direct implications for designing clinical trials using oncolytic viruses, not only for brain tumors, but for other solid tumors.”
Further preclinical work will be needed to use the herpes-loaded stem cells for breast, lung and skin cancer tumors that metastasize to the brain. Shah predicts the approach will enter clinical trials within the next two to three years.
Stem Cell Therapy Shows Promise for MS in Mouse Model
Mice crippled by an autoimmune disease similar to multiple sclerosis (MS) regained the ability to walk and run after a team of researchers led by scientists at The Scripps Research Institute (TSRI), University of Utah and University of California (UC), Irvine implanted human stem cells into their injured spinal cords.
Remarkably, the mice recovered even after their bodies rejected the human stem cells. “When we implanted the human cells into mice that were paralyzed, they got up and started walking a couple of weeks later, and they completely recovered over the next several months,” said study co-leader Jeanne Loring, a professor of developmental neurobiology at TSRI.
Thomas Lane, an immunologist at the University of Utah who co-led the study with Loring, said he had never seen anything like it. “We’ve been studying mouse stem cells for a long time, but we never saw the clinical improvement that occurred with the human cells that Dr. Loring’s lab provided,” said Lane, who began the study at UC Irvine.
The mice’s dramatic recovery, which is reported online ahead of print by the journal Stem Cell Reports, could lead to new ways to treat multiple sclerosis in humans.
"This is a great step forward in the development of new therapies for stopping disease progression and promoting repair for MS patients,” said co-author Craig Walsh, a UC Irvine immunologist.
Stem Cell Therapy for MS
MS is an autoimmune disease of the brain and spinal cord that affects more than a half-million people in North America and Europe, and more than two million worldwide. In MS, immune cells known as T cells invade the upper spinal cord and brain, causing inflammation and ultimately the loss of an insulating coating on nerve fibers called myelin. Affected nerve fibers lose their ability to transmit electrical signals efficiently, and this can eventually lead to symptoms such as limb weakness, numbness and tingling, fatigue, vision problems, slurred speech, memory difficulties and depression.
Current therapies, such as interferon beta, aim to suppress the immune attack that strips the myelin from nerve fibers. But they are only partially effective and often have significant adverse side effects. Loring’s group at TSRI has been searching for another way to treat MS using human pluripotent stem cells, which are cells that have the potential to transform into any of the cell types in the body.
Loring’s group has been focused on turning human stem cells into neural precursor cells, which are an intermediate cell type that can eventually develop into neurons and other kinds of cells in the nervous system. In collaboration with Lane’s group, Loring’s team has been testing the effects of implanting human neural precursor cells into the spinal cords of mice that have been infected with a virus that induces symptoms of MS.
A Domino Effect
The transformation that took place in the largely immobilized mice after the human neural precursor cells were injected into the animals’ damaged spinal cords was dramatic. “Tom called me up and said, ‘You’re not going to believe this,’” Loring said. “He sent me a video, and it showed the mice running around the cages. I said, ‘Are you sure these are the same mice?’”
Even more remarkable, the animals continued walking even after the human cells were rejected, which occurred about a week after implantation. This suggests that the human stem cells were secreting a protein or proteins that had a long-lasting effect on preventing or impeding the progression of MS in the mice, said Ron Coleman, a TSRI graduate student in Loring’s lab who was first author of the paper with Lu Chen of UC Irvine. “Once the human stem cells kick that first domino, the cells can be removed and the process will go on because they’ve initiated a cascade of events,” said Coleman.
The scientists showed in the new study that the implanted human stem cells triggered the creation of white blood cells known as regulatory T cells, which are responsible for shutting down the autoimmune response at the end of an inflammation. In addition, the implanted cells released proteins that signaled cells to re-myelinate the nerve cells that had been stripped of their protective sheaths.
A Happy Accident
The particular line of human neural precursor cells used to heal the mice was the result of a lucky break. Coleman was using a common technique for coaxing human stem cells into neural precursor cells, but decided partway through the process to deviate from the standard protocol. In particular, he transferred the developing cells to another Petri dish.
“I wanted the cells to all have similar properties, and they looked really different when I didn’t transfer them,” said Coleman, who was motivated to study MS after his mother died from the disease. This step, called “passaging,” proved key. “It turns out that passaging alters the types of proteins that the cells express,” he said.
Loring called the creation of the successful neural precursor cell line a “happy accident.” “If we had used common techniques to create the cells, they wouldn’t have worked,” she said. “We’ve shown that now. There are a dozen different ways to make neural precursor cells, and only this one has worked so far. We now know that it is incredibly important to make the cells the same way every time.”
Hot On the Trail
The team is now working to discover the particular proteins that its unique line of human precursor cells release. One promising candidate is a class of proteins known as transforming growth factor beta, or TGF-B, which other studies have shown is involved the creation of regulatory T cells. Experiments by the scientists showed that the human neural precursor cells released TGF-B proteins while they were inside the spinal cords of the impaired mice. However, it’s also likely that other, as yet unidentified, protein factors may also be involved in the mice’s healing.
If the team can pinpoint which proteins released by the neural precursor cells are responsible for the animals’ recovery, it may be possible to devise MS treatments that don’t involve the use of human stem cells. “Once we identify the factors that are responsible for healing, we could make a drug out of them,” said Lane. Another possibility, Loring said, might be to infuse the spinal cords of humans affected by MS with the protein factors that promote healing.
A better understanding of what makes these human neural precursor cells effective in mice will be key to developing either of these therapies for humans. “We’re on the trail now of what these cells do and how they work,” Loring said.
(Source: scripps.edu)
(Image caption: These images show the movement of patient-derived neural progenitor cells from a sphere of neurons in a migration assay. How far and quickly the neurons move indicates whether they may behave atypically in the brain. Credit: Courtesy of the Salk Institute for Biological Studies)
New stem cell research points to early indicators of schizophrenia
Using new stem cell technology, scientists at the Salk Institute have shown that neurons generated from the skin cells of people with schizophrenia behave strangely in early developmental stages, providing a hint as to ways to detect and potentially treat the disease early.
The findings of the study, published online in April’s Molecular Psychiatry, support the theory that the neurological dysfunction that eventually causes schizophrenia may begin in the brains of babies still in the womb.
"This study aims to investigate the earliest detectable changes in the brain that lead to schizophrenia," says Fred H. Gage, Salk professor of genetics. "We were surprised at how early in the developmental process that defects in neural function could be detected."
Currently, over 1.1 percent of the world’s population has schizophrenia, with an estimated three million cases in the United States alone. The economic cost is high: in 2002, Americans spent nearly $63 billion on treatment and managing disability. The emotional cost is higher still: 10 percent of those with schizophrenia are driven to commit suicide by the burden of coping with the disease.
Although schizophrenia is a devastating disease, scientists still know very little about its underlying causes, and it is still unknown which cells in the brain are affected and how. Previously, scientists had only been able to study schizophrenia by examining the brains of patients after death, but age, stress, medication or drug abuse had often altered or damaged the brains of these patients, making it difficult to pinpoint the disease’s origins.
The Salk scientists were able to avoid this hurdle by using stem cell technologies. They took skin cells from patients, coaxed the cells to revert back to an earlier stem cell form and then prompted them to grow into very early-stage neurons (dubbed neural progenitor cells or NPCs). These NPCs are similar to the cells in the brain of a developing fetus.
The researchers generated NPCs from the skin cells of four patients with schizophrenia and six people without the disease. They tested the cells in two types of assays: in one test, they looked at how far the cells moved and interacted with particular surfaces; in the other test, they looked at stress in the cells by imaging mitochondria, which are tiny organelles that generate energy for the cells.
On both tests, the Salk team found that NPCs from people with schizophrenia differed in significant ways from those taken from unaffected people.
In particular, cells predisposed to schizophrenia showed unusual activity in two major classes of proteins: those involved in adhesion and connectivity, and those involved in oxidative stress. Neural cells from patients with schizophrenia tended to have aberrant migration (which may result in the poor connectivity seen later in the brain) and increased levels of oxidative stress (which can lead to cell death).
These findings are consistent with a prevailing theory that events occurring during pregnancy can contribute to schizophrenia, even though the disease doesn’t manifest until early adulthood. Past studies suggest that mothers who experience infection, malnutrition or extreme stress during pregnancy are at a higher risk of having children with schizophrenia. The reason for this is unknown, but both genetic and environmental factors likely play a role.
"The study hints that there may be opportunities to create diagnostic tests for schizophrenia at an early stage," says Gage, who holds the Vi and John Adler Chair for Research on Age-Related Neurodegenerative Disease.
Kristen Brennand, the first author of the paper and assistant professor at Icahn School of Medicine at Mount Sinai, said the researchers were surprised that the skin-derived neurons remained in such an early stage of development. “We realized they weren’t mature neurons but only as old as neurons in the first trimester,” Brennand says. “So we weren’t studying schizophrenia but the things that go wrong a long time before patients actually get sick.”
Interestingly, the study also found that antipsychotic medication such as clozapine and loxapine did not improve migration in NPCs (in particular, loxapine actually worsened migration in these cells).
"That was an experiment that gave the opposite results from what we were expecting," says Brennand. "Though in hindsight, using drugs that treat symptoms might not be helpful in trying to prevent the disease."
The next steps to this work will be to increase the sample size to a broader range of patients and to look at hundreds or thousands of patient samples, says Brennand.
Mouse study offers new clues to cognitive decline
New research suggests that certain types of brain cells may be “picky eaters,” seeming to prefer one specific energy source over others. The finding has implications for understanding the cognitive decline seen in aging and degenerative diseases such as Alzheimer’s and multiple sclerosis.
(Image caption: Neural stem cells differentiate into three different cell types: neurons (purple), oligodendrocytes (red), which produce axon insulation, and astrocytes (green), which also support neurons. Cell nuclei are shown in blue. Credit: Liana Roberts Stein)
Studying mice, investigators from Washington University School of Medicine in St. Louis showed that a specific energy source called NAD is important in cells responsible for maintaining the overall structure of the brain and for performing complex cognitive functions. NAD (nicotinamide adenine dinucleotide) is a molecule that harvests energy from nutrients in food and converts it into a form cells can use.
The work appears in two journal articles — in the May 8 issue of The EMBO Journal, a publication of the European Molecular Biology Organization, and in a recent issue of The Journal of Neuroscience.
“We are interested in understanding how cells make NAD and what implications that has for cellular function, especially in the context of aging and longevity,” said Shin-ichiro Imai, MD, PhD, professor of developmental biology and of medicine and senior author of both papers. “We know, for example, NAD levels decrease with age in tissues such as muscle and fat. We wanted to find out if the same is true in the brain.”
The investigators looked at two types of brain cells: adult neural stem cells, responsible for maintaining supplies of neurons and their supporting cells, and forebrain neurons, vital for performing complex cognitive tasks.
In The EMBO Journal, they reported that NAD levels decreased with age in the mouse hippocampus, a vital region of the brain for cognition. The researchers then used genetic techniques to find out what would happen when NAD manufacturing is turned off in the adult neural stem cells of the mouse brain.
“Neural stem cells are very metabolically expensive, so you might expect them to be particularly vulnerable to loss of an energy source,” said first author Liana Roberts Stein, PhD, postdoctoral researcher in Imai’s lab. “There are other energy sources for brain cells, such as glucose, but no one had ever looked at where NAD is coming from in these cells.”
According to the researchers, there are four pathways of NAD synthesis, and the scientists focused on just one. They wanted to find out whether this particular pathway — a longtime focus of Imai’s lab — is important for these cells or if the other routes could compensate.
The pathway begins with the B vitamin nicotinamide. Cells take dietary nicotinamide and, with a helper protein called Nampt, manufacture a molecule called NMN, which then is processed further to make NAD. When Stein eliminated Nampt from neural stem cells, several significant changes took place.
Levels of NAD dropped, and the neural stem cells stopped dividing; they stopped renewing themselves; and they stopped being able to create important cells that insulate axons, the “wires” that carry electrical signals throughout the brain. With less insulation, these signals slow down, impairing brain function.
Imai and Stein pointed out possible therapeutic implications of this finding, especially in light of what is known about cognitive decline in aging and certain diseases.
“Scientists have shown that with age there actually isn’t a large decrease in the total neuron population,” Stein said. “But there is quite a substantial decrease in white matter, which is primarily composed of cells that function in axon insulation. This pathway also could be relevant in conditions involving loss of cells that make this insulation, like multiple sclerosis.”
Imai and Stein also found they could prevent the loss of the neural stem cells missing Nampt by giving the mice NMN, the next molecule in the chain of events leading to NAD.
“We gave the mice NMN in their drinking water for 12 months,” Stein said. “And at the higher dose, we saw a rescue of the neural stem cell pool in aged mice.”
Imai called this finding exciting because it supports the possibility of a future NMN supplement.
“We think that NMN could convey a similar effect in people,” Imai said. “A future clinical trial for NMN will tell us if it has any efficacy in humans.”
In addition to maintaining stem cell populations and keeping the brain supplied with all its cell types, the investigators showed that NAD also is vital for the process of cognition itself.
Reporting in The Journal of Neuroscience, they showed that neurons of the mouse forebrain depend heavily on NAD in normal cognitive function. Instead of deleting Nampt in stem cells, this time Stein deleted it only in neurons of the forebrain. All other cells were normal, including those that make axon insulation.
Without Nampt and its eventual product, NAD, in forebrain neurons, the behavior of the mice changed dramatically, according to the investigators.
“The mice were really hyperactive, with a twofold increase in activity levels,” Stein said. “They also showed a loss of anxiety-like behaviors. These mice didn’t seem to sense or fear potentially threatening situations and showed fairly drastic memory defects.”
Stein pointed out that these neurons are in a region of the brain known to be particularly vulnerable to neurodegenerative conditions from Alzheimer’s disease to stroke.
“It’s possible that these neurons’ dependence on Nampt is responsible for their extreme susceptibility to these conditions,” she said. “It would be interesting to model some of these diseases in mice and see if supplementing NMN provides any benefit to their behavior or memory.”
“We haven’t done that study yet,” Imai added. “But this is the direction the entire field is going.”
(Source: news.wustl.edu)
Stem cells from teeth can make brain-like cells
University of Adelaide researchers have discovered that stem cells taken from teeth can grow to resemble brain cells, suggesting they could one day be used in the brain as a therapy for stroke.
In the University’s Centre for Stem Cell Research, laboratory studies have shown that stem cells from teeth can develop and form complex networks of brain-like cells. Although these cells haven’t developed into fully fledged neurons, researchers believe it’s just a matter of time and the right conditions for it to happen.
"Stem cells from teeth have great potential to grow into new brain or nerve cells, and this could potentially assist with treatments of brain disorders, such as stroke," says Dr Kylie Ellis, Commercial Development Manager with the University’s commercial arm, Adelaide Research & Innovation (ARI).
Dr Ellis conducted this research as part of her Physiology PhD studies at the University, before making the step into commercialisation. The results of her work have been published in the journal Stem Cell Research & Therapy.
"The reality is, treatment options available to the thousands of stroke patients every year are limited," Dr Ellis says. "The primary drug treatment available must be administered within hours of a stroke and many people don’t have access within that timeframe, because they often can’t seek help for some time after the attack.
"Ultimately, we want to be able to use a patient’s own stem cells for tailor-made brain therapy that doesn’t have the host rejection issues commonly associated with cell-based therapies. Another advantage is that dental pulp stem cell therapy may provide a treatment option available months or even years after the stroke has occurred," she says.
Dr Ellis and her colleagues, Professors Simon Koblar, David O’Carroll and Stan Gronthos, have been working on a laboratory-based model for actual treatment in humans. As part of this research Dr Ellis found that stem cells derived from teeth developed into cells that closely resembled neurons.
"We can do this by providing an environment for the cells that is as close to a normal brain environment as possible, so that instead of becoming cells for teeth they become brain cells," Dr Ellis says.
"What we developed wasn’t identical to normal neurons, but the new cells shared very similar properties to neurons. They also formed complex networks and communicated through simple electrical activity, like you might see between cells in the developing brain."
This work with dental pulp stem cells opens up the potential for modelling many more common brain disorders in the laboratory, which could help in developing new treatments and techniques for patients.
In a cloning first, scientists create stem cells from adults
Scientists have moved a step closer to the goal of creating stem cells perfectly matched to a patient’s DNA in order to treat diseases, they announced on Thursday, creating patient-specific cell lines out of the skin cells of two adult men.
The advance, described online in the journal Cell Stem Cell, is the first time researchers have achieved “therapeutic cloning” of adults. Technically called somatic-cell nuclear transfer, therapeutic cloning means producing embryonic cells genetically identical to a donor, usually for the purpose of using those cells to treat disease.
Study finds modified stem cells offer potential pathway to treat Alzheimer’s disease
UC Irvine neurobiologists have found that genetically modified neural stem cells show positive results when transplanted into the brains of mice with the symptoms and pathology of Alzheimer’s disease. The pre-clinical trial is published in the journal Stem Cells Research and Therapy, and the approach has been shown to work in two different mouse models.
Alzheimer’s disease, one of the most common forms of dementia, is associated with accumulation of the protein amyloid-beta in the brain in the form of plaques. While the search continues for a viable treatment, scientists are now looking into non-pharmaceutical ways to slow onset of this disease.
One option being considered is increasing the production of the enzyme neprilysin, which breaks down amyloid-beta, and shows lower activity in the brains of people with Alzheimer’s disease. Researchers from UC Irvine investigated the potential of decreasing amyloid-beta by delivering neprilysin to mice brains.
“Studies suggest that neprilysin decreases with age and may therefore influence the risk of Alzheimer’s disease,” said Mathew Blurton-Jones, an assistant professor of neurobiology & behavior. “If amyloid accumulation is the driving cause of Alzheimer’s disease, then therapies that either decrease amyloid-beta production or increase its degradation could be beneficial, especially if they are started early enough.”
The brain is protected by a system called the blood-brain-barrier that restricts access of cells, proteins, and drugs to the brain. While the blood-brain-barrier is important for brain health, it also makes it challenging to deliver therapeutic proteins or drugs to the brain. To overcome this, the researchers hypothesized that stem cells could act as an effective delivery vehicle. To test this hypothesis the brains of two different mouse models (3xTg-AD and Thy1-APP) were injected with genetically modified neural stem cells that over-expressed neprilysin.
These genetically modified stem cells were found to produce 25-times more neprilysin than control neural stem cells, but were otherwise equivalent to the control cells. The genetically modified and control stem cells were then transplanted into the hippocampus or subiculum of the mice brains – two areas of the brain that are greatly affected by Alzheimer’s disease. The mice transplanted with genetically modified stem cells were found to have a significant reduction in amyloid-beta plaques within their brains compared to the controls. The effect remained even one month after stem cell transplantation. This new approach could provide a significant advantage over unmodified neural stem cells because neprilysin-expressing cells could not only promote the growth of brain connections but could also target and reduce amyloid-beta pathology.
Before this can be investigated in humans, more work needs to be done to see if this affects the accumulation of soluble forms of amyloid-beta. Further investigation is also needed to determine whether this new approach improves cognition more than the transplantation of un-modified neural stem cells.
“Every mouse model of Alzheimer’s disease is different and develops varying amounts, distribution, and types of amyloid-beta pathology,” Blurton-Jones said. “By studying the same question in two independent transgenic models, we can increase our confidence that these results are meaningful and applicable to Alzheimer’s disease. But there is clearly a great deal more research needed to determine whether this kind of approach could eventually be translated to the clinic.”
Researchers search for earliest roots of psychiatric disorders
Newborns whose mothers were exposed during pregnancy to any one of a variety of environmental stressors — such as trauma, illness, and alcohol or drug abuse — become susceptible to various psychiatric disorders that frequently arise later in life. However, it has been unclear how these stressors affect the cells of the developing brain prenatally and give rise to conditions such as schizophrenia, post-traumatic stress disorder, and some forms of autism and bipolar disorders.
Now, Yale University researchers have identified a single molecular mechanism in the developing brain that sheds light on how cells may go awry when exposed to a variety of different environmental insults. The findings, to be published in the May 7 issue of the journal Neuron, suggest that different types of stressors prenatally activate a single molecular trigger in brain cells that may make exposed individuals susceptible to late-onset neuropsychiatric disorders.
The researchers found that mouse embryos exposed to alcohol, methyl-mercury, or maternal seizures all activate in the developing brain cells a single gene — HSF1 or heat shock factor — which protects and enables some of the brain cells to survive prenatal insult. Mice lacking the HSF1 gene showed structural brain abnormalities and were prone to seizures after birth, even after exposure to very low levels of the toxins.
In addition, researchers created stem cells — which are capable of becoming many different tissue types, including neurons — from biopsies of individuals diagnosed with schizophrenia. Genes from these “schizophrenic” stem cells responded more dramatically when exposed to environmental insults than stem cells obtained from non-schizophrenic individuals. The findings provide support to the thesis that stress induces vulnerable cells to malfunction.
“It appears that different types of environmental stressors can trigger the same condition if they occur at the same period of prenatal development,” said Yale’s Pasko Rakic, senior author of the study. “Conversely, the same environmental stressor may cause different pathologies, if it occurs at different times during pregnancy.”
Since HSF1 activation can potentially serve as a permanent marker of the stressed/damaged cell, it opens the possibility of identifying these cells in adults in order to explore the pathogenesis of postnatal disorders and how to protect vulnerable cells.