How Stem Cell Therapy Protects Bone In Lupus


Systemic Lupus Erythematosis, otherwise known as lupus, is an autoimmune disease cause your own immune system attacking various cells and tissues in your body. Lupus patients can suffer from fatigue, joint pain and selling and show a marked increased risk or osteoporosis.

Clinical trials have established that infusions of mesenchymal stem cells (MSCs) can significantly improve the condition of lupus patients, but exactly why these cells help these patients is not completely clear. Certainly suppression of inflammation is probably part of the mechanism by which these cells help lupus patients, but how do these cells improve the bone health of lupus patients?

Songtao Shi and his team at the University of Pennsylvania have used an animal model of lupus to investigate this very question. In their hands, transplanted MSCs improve the function of bone marrow stem cells by providing a source of the FAS protein. FAS stimulates bone marrow stem cell function by means of a multi-step, epigenetic mechanism.

This work by Shi and his colleagues has implications for other cell-based treatment strategies for not only lupus, but other diseases as well.

“When we used transplanted stem cells for these diseases, we didn’t know exactly what they were doing, but saw that they were effective,” said Shi. “Now we’ve seen in a model of lupus that bone-forming mesenchymal stem cell function was rescued by a mechanism that was totally unexpected.”

In earlier work, Shi and his group showed that mesenchymal stem cell infusions can be used to treat various autoimmune diseases in particular animals models. While these were certainly highly desirable results, no one could fully understand why these cells worked as well as they did. Shi began to suspect that some sort of epigenetic mechanism was at work since the infused MSCs seemed to permanently recalibrate the gene expression patterns in cells.

In order to test this possibility, Shi and others found that lupus mice had a malfunctioning FAS protein that prevented their bone marrow MSCs from releasing pro-bone molecules that are integral for bone maintenance and deposition.

A deficiency for the FAS protein prevents bone marrow stem cells from releasing a microRNA called miR-29b.  The failure to release miR-29b causes its concentrations to increase inside the cells.  miR-29b can down-regulate an enzyme called DNA methyltransferase 1 (Dnmt1), and the buildup of miR-29b inhibits Dnmt1, which causes decreased methylation of the Notch1 promoter and activation of Notch signaling.  Methylation of the promoters of genes tends to shut down gene expression, and the lack of methylation of the Notch promoter increases Notch gene expression, activating Notch signaling.  Unfortunately, increased Notch signaling impaired the differentiation of bone marrow stem cells into bone-making cells.  Transplantation of MSCs brings FAS protein to the bone marrow stem cells by means of exosomes secreted by the MSCs.  The FAS protein in the MSC-provided exosomes reduce intracellular levels of miR-29b, which leads to higher levels of Dnmt1.  Dnmt1 methylates the Notch1 promoter, thus shutting down the expression of the Notch gene, and restoring bone-specific differentiation.

Shi and others are presently investigating if this FAS-dependent process is also at work in other autoimmune diseases.  If so, then stem cell treatments might convey similar bone-specific benefits.

MSC Transplantation Reduces Bone Loss via Epigenetic Regulation of Notch Signaling in Lupus


Mesenchymal stem cells from bone marrow, fat, and other tissues have been used in many clinical trials, experiments, and treatment regimens. While these cells are not magic bullets, they do have the ability to suppress unwanted inflammation, differentiate into bone, cartilage, tendon, smooth muscle, and fat, and can release a variety of healing molecules that help organs from hearts to kidneys heal themselves.

Mesenchymal stem cell transplantation (MSCT) is the main means by which mesenchymal stem cells are delivered to patients for therapeutic purposes. However, the precise mechanisms that underlie the success of these cells are not fully understood. In a paper by from the University Of Pennsylvania School Of Dental Medicine published in the journal Cell Metabolism, MSCT were able to re-establish the bone marrow function in MRL/lpr mice. The MRL/lpr mouse is a genetic model of a generalized autoimmune disease sharing many features and organ pathology with systemic lupus erythematosus (SLE). Such mice show bone loss and poor bone deposition, a condition known as “osteopenia.” Because mesenchymal stem cells are usually the cells in bone marrow that differentiate into osteoblasts (which make bone) a condition like osteopenia results from defective mesenchymal stem cell function.

In this paper, Shi and his coworkers and collaborators showed that the lack of the Fas protein in the mesenchymal stem cells from MRL/lpr mice prevents them from releasing a regulatory molecule called “miR-29b.” This regulatory molecule, mir-29b, is a small RNA molecule known as a microRNA. MicroRNAs regulate the expression of other genes, and the failure to release miR-29b increases the intracellular levels of miR-29b. This build-up in the levels of miR-29b causes the downregulation of an enzyme called “DNA methyltransferase 1” or Dnmt1. This is not surprising, since this is precisely what microRNAs do – they regulate genes. Dnmt1 attaches methyl groups (CH3 molecules) to the promoter or control regions of genes.

Decrease in the levels of Dnmt1 causes hypomethylation of the Notch1 promoter. When promoters are heavily methylated, genes are poorly expressed. When very methyl groups are attached to the promoters, then the gene has a greater chance of being highly expressed. Robust expression of the Notch1 genes activates Notch signaling. Increased Notch signaling leads to impaired bone production, since differentiation into bone-making cells requires mesenchymal stem cells to down-regulate Notch signaling.

When normal mesenchymal stem cells are transplanted into the bone marrow of MRL/lpr mice, they release small vesicles called exosomes that transfer the Fas protein to recipient MRL/lpr bone marrow mesenchymal stem cells. The presence of the Fas protein reduces intracellular levels of miR-29b, and this increases Dnmt1-mediated methylation of the Notch1 promoter. This decreases the expression of Notch1 and improves MRL/lpr BMMSC function.

fx1

These findings elucidate the means by which MSCT rescues MRL/lpr BMMSC function. Since MRL/lpr mice are a model system for lupus, it suggests that donor mesenchymal stem cell transplantation into lupus patients provides Fas protein to the defective, native mesenchymal stem cells, thereby regulating the miR-29b/Dnmt1/Notch epigenetic cascade that increases differentiation of mesenchymal stem cells into osteoblasts and bone deposition rates.

Stem Cell-Based Exosomes Heal Hearts After a Heart Attack


A new paper in the journal Circulation Research by a research team from the Temple University School of Medicine (TUSM) has examined the use of tiny stem cell-based vesicles to help limit the damage caused by a heart attack. Even those these experiments were performed with laboratory mice, the result are very promising.

A heart attack tends to badly damage it, and since the heart has little innate ability to repair itself, it has to compensate by growing large and flabby, which can lead to congestive heart failure, Congestive heart failure is currently responsible for one in nine deaths in the United States.

The research team of Raj Kishore at the Temple University School of Medicine turned to exosomes to heal the heart. Exosomes are tiny sacks secreted by cells that act as messengers that pass messengers between cells in various parts of the body. While these extracellular vesicles are secreted by nearly all types of cell, exosomes from stem cells might be a useful tool in mitigating damage caused by heart attacks.

Exosomes
Exosomes

“If your goal is to protect the heart, this is a pretty important finding,” Dr. Kishore said. “You can robustly increase the heart’s ability to repair itself without using the stem cells themselves. Our work shows a unique way to regenerate the heart using secreted vesicles from embryonic stem cells.”  Kishore’s group is also beginning to determine those members of this “work crew” within the vesicles may be responsible for the damage repair.

Previous studies have shown that injecting damaged hearts with stem cells increases heart function after a heart attack. However, the injected cells tend to not survive very long when placed in the damaged heart, and most of their benefits are due to molecules that the administered stem cells secrete. Pluripotent stem cells (embryonic stem cells, for example) run the risk of creating a tumor made up of a mass of cells of different tissue types, known as a teratoma. Therefore, Khan’s tram approached the problem from a slightly different angle by injecting only the exosomes made by stem cells. It was known that this would avoid the teratoma problem, and could have positive effects on damaged heart tissue.

Exosome poster

The study examined mice that had suffered heart attacks. These animals were split into two groups; one group received exosomes from mouse embryonic stem cells, and the other group were injected with fibroblast exosomes.

The results were extremely promising. The mice that had received stem cell-derived exosomes exhibited improved heart function, less scar tissue, lower levels of programmed cell death and better capillary development around the damaged area. There was also a higher presence of cardiac progenitor cells – the heart’s own stem cells – in the stem cell exosome-injected mice. Overall, the heartbeat of the mice was stronger than those in the control group, with less unhealthy enlargement of the organ.

Khan and others examined an abundant gene-regulating molecule (microRNA) from the stem cell-derived exosomes, known as miR-294. They introduced this microRNA into cultured cardiac stem cells. This microRNA recapitulated many of the positive effects of the stem cell exosomes that had been observed in the animal study.

Khan and his coworker plan to continue their research by studying the effects of individual microRNAs on damaged heart tissue.

“Our work shows that the best way to regenerate the heart is to augment the self-repair capabilities and increase the heart’s own capacity to heal,” says researcher Dr Mohsin Khan. “This way, we’re avoiding risks associated with teratoma formation and other potential complications of using full stem cells. It’s an exciting development in the field of heart disease.”

Temple University Lab Shows Exosomes from Stem Cells Heal Hearts After a Heart Attack


Temple University stem cell researcher Raj Kishore, who serves as the Director of the Stem Cell Therapy Program at the Center for Translational Medicine at Temple University School of Medicine (TUSM), and his colleagues have used exosomes from stem cells to induce tissue repair in the damaged heart. The results of this fascinating research made the cover of the June 19, 2015 edition of the leading cardiovascular research journal, Circulation Research.

“If your goal is to protect the heart, this is a pretty important finding,” Dr. Kishore said. “You can robustly the heart’s ability to repair itself without using the stem cells themselves. Our work shows a unique way to regenerate the heart using secreted vesicles from embryonic stem cells.” Kishore’s group is in the early stages of characterizing the molecules in these exosomes that are responsible for inducing and potentiating tissue repair.

The heart beats throughout the lifetime of an individual. Despite its apparent constancy, the heart possess little to no ability to repair itself. When heart muscle is damaged in a heart attack, the heart is unable to replace the dead tissue and grow new contracting heart muscle. Instead, after a heart attack, it compensates for lost pumping ability by enlarging, a phenomenon known as ”remodeling.” .Remodeling, however, come with a high price, since the heart grows beyond the ability of the sparse cardiac circulatory system to properly convey blood to the enlarged heart muscle. Consequently, heart contraction weakens, leading to a condition known as congestive heart failure, which contributes to, or causes one in nine deaths in the United States. Heart disease is our nation’s leading killer.

Given the fact that heart disease is the result of the death of heart muscle cells, this condition seems to tailor-made for stem cell therapy. A variety of animal experiments with stem cells from bone marrow, muscle, fat, or embryos have shown that stem cells can regenerate heart muscle. However, the regeneration of the heart is much more complicated than was originally thought. For example, injecting damaged hearts with stem cells turned out to be a rather ineffective strategy because the heart, after a heart attack, is a very hostile place for newly infused cells. Dr. Kishore noted, “People know if they inject hundreds of stem cells into an organ, you’re going to be very lucky to find two of them the next day. They die. It’s as though you’re putting them into the fire and the fire burns them.”

Dr. Kishore has used a very different approach for regenerative medicine. Over 10 years ago, cancer researchers discovered tiny sacks excreted by cells that they called “exosomes.” These exosomes were thought to be involved with waste disposal, but later work showed that they were more mini-messengers, carry telegrams between cells. Exosomes proved to be one way a primary tumor communicated with distant metastases. Researchers later discovered that nearly all cell types excrete exosomes. Dr. Kishore and his team began to study the exosomes of stem cells to determine if these small vesicles could solve the heart-repair problem.

In 2011, Kishore’s team published the first paper to ever examine stem cell exosomes and heart repair. This paper established Kishore and his research team as a pioneer in exosome research and in the use of exosomes in the treatment of heart disease. A year after that paper, there were a total of 52 papers published on exosomes, but today there are 7,519 papers reporting on exosome research. Among those studies, only 13 or 14 have examined exosomes in heart disease. This new paper by Dr. Kishore’s team marks its third contribution to the science of exosomes and heart repair.

In the current study, Kishore and others used a mouse model of heart attack. Also involved in the research are Dr. Kishore’s colleagues from Temple’s Center for Translational Medicine, the Cardiovascular Research Center, and the Department of Pharmacology, as well as researchers from the Feinberg Cardiovascular Research Institute at Northwestern University in Chicago.

In this study, after suffering a heart attack, the mice received exosomes from either embryonic stem cells or exosomes from fibroblasts. Mice that received the fibroblast-derived exosomes served as the control group. The results were unmistakable. Mice that received exosomes from embryonic stem cells showed significantly improved heart function after a heart attack compared to the control group. More heart muscle cells in these mice survived after the heart attack, and their hearts also exhibited less scar tissue. Fewer heart cells committed suicide — a process known as programmed cell death, or apoptosis. Also, hearts from mice treated with embryonic stem cell-derived exosomes showed greater capillary development around the areas of injury. The increased density of blood vessels improved circulation and oxygen supply to the heart muscle. Further, there was a marked increase in endogenous cardiac progenitor cells, which is the hearts own internal stem cell population. These cells survived and created new heart cells. The heartbeat was more powerful in the experimental group compared to the control group, and the kind of unhealthy enlargement that compensates for tissue damage was minimized.

Vishore’s group also tested the effect of one of the most abundant gene-regulating molecules (microRNAs) found in the stem cell exosome; a microRNA called miR-294. When purified miR-294 alone was introduced to cardiac stem cells in the laboratory, it mimicked many of the effects seen when the entire exosome was delivered. “To a large extent, this micro-RNA alone can recapitulate the activity of the exosome,” Dr. Kishore said. “But we can never say it is responsible for all of the response because embryonic stem cell exosomes have many other microRNAs.”

Future research will examine both exosome therapy and the use of specific microRNAs for heart repair in large-animal models of heart attack with a view to eventually testing these components in human patients in clinical trials.

“Our work shows that the best way to regenerate the heart is to augment the self-repair capabilities and increase the heart’s own capacity to heal,” Dr. Kishore said. “This way, we’re avoiding risks associated with teratoma formation and other potential complications of using full stem cells. It’s an exciting development in the field of heart disease.”

A New Way to Mend Broken Hearts


Salk Institute researchers have discovered a way to heal injured hearts by reactivating long dormant molecular machinery found in the heart cells. This significant finding could open the door to new therapies for heart disorders in humans.

These new results were published in the November 6th, 2014 edition of the journal Cell Stem Cell. Although adult mammals don’t normally regenerate damaged tissue, they seem to retain a latent ability to do so. When the Salk team inhibited four different molecules that suppress genetic programs that lead to organ regeneration, they observed a dramatic improvement in heart regeneration and healing in laboratory mice.

These experiments provide proof-of-concept for a new type of clinical treatment in the fight against heart disease, which, according to the US Centers for Disease Control and Prevention, kills about 600,000 people each year in the United States alone.

“Organ regeneration is a fascinating phenomenon that seemingly recapitulates the processes observed during development. However, despite our current understanding of how embryogenesis and development proceeds, the mechanisms preventing regeneration in adult mammals have remained elusive,” says the study’s senior author Juan Carlos Izpisua Belmonte, holder of the Roger Guillemin Chair and primary investigator in the Gene Expression Laboratory and the Salk Institute.

We have within every cell of our bodies, the genes for organ regeneration. For several years, Izpisua Belmonte and his coworkers have attempted to clarify the genes that organism uses during embryonic development and during tissue healing highly regenerative organisms such as the zebrafish.

An injured zebrafish heart showing proliferating cells in the wounded area of the heart (red) and cardiac muscle cells (green).
An injured zebrafish heart showing proliferating cells in the wounded area of the heart (red) and cardiac muscle cells (green).

In 2003, Izpisua Belmonte’s laboratory first identified the signals that precede zebrafish heart regeneration, which they followed-up with a 2010 Nature paper, in which scientists from Izpisua Belmonte’s laboratory described how regeneration occurred in the zebrafish. Rather than stem cells invading injured heart tissue, the cardiac cells themselves reverted to a precursor-like state (a process called ‘dedifferentiation’). Dedifferentiation allowed the cells to proliferate within the damaged tissue.

n a dish, heart muscle cells return to a precursor-like state after pro-regenerative treatment with microRNA inhibitors. Green shows a disorganized cardiomyocyte cytoskeleton indicative of cell dedifferentiation; red shows mitochondrial organization.
In a dish, heart muscle cells return to a precursor-like state after pro-regenerative treatment with microRNA inhibitors. Green shows a disorganized cardiomyocyte cytoskeleton indicative of cell dedifferentiation; red shows mitochondrial organization.

They next determined if mammals retained any of the molecular players responsible for this kind of regenerative reprogramming. However, such an experiment came with some risks, recalls Ignacio Sancho-Martinez, a postdoctoral researcher in Izpisua Belmonte’s lab.

“When you speak about these things, the first thing that comes to peoples’ minds is that you’re crazy,” he says. “It’s a strange-sounding idea, since we associate regeneration with salamanders and fish, but not mammals.”

What are the things that cause a heart to regenerate in these smaller animals? Extensive work on the regenerating hearts of fish and salamanders failed to reveal anything concrete. Therefore, the laboratory changed its tack. “Instead, we thought, ‘If fish know how to do it, there must be something they can teach us about it,’” says the study’s first author Aitor Aguirre, a postdoctoral researcher in Izpisua Belmonte’s group.

The team focused on microRNAs, which control the expression of many genes. They used an extensive genetic screen for microRNAs that changed their expression levels during the healing of the zebrafish heart and that were found in the mammalian genome.

Their studies uncovered four molecules in particular–MiR-99, MiR-100, Let-7a and Let-7c–that fit their criteria. All were heavily repressed during heart injury in zebrafish and they were also present in rats, mice and humans.

However, in studies of mammalian cells in a culture dish and studies of living mice with heart damage, the group saw that the levels of these molecules were high in adults and failed to decline after the heart experienced injury. Therefore, Izpisua Belmonte’s team used adeno-associated viruses that could specifically infect the heart to target each of those four microRNAs and experimentally suppress their expressing levels.

Injecting these inhibitors into the hearts of mice that had suffered a heart attack triggered the regeneration of cardiac cells, and improved numerous physical and functional aspects of the heart, such as the thickness of its walls and its ability to pump blood. The scarring caused by the heart attack was significantly reduced with treatment compared to controls.

The improvements were still obvious three and six months after treatment–a long time in a mouse’s life. “The good thing is that the success was not limited to the short-term, which is quite common in cardiac regenerative biology,” Sancho-Martinez says.

The new study focused only on a handful of 70 some microRNA candidates that turned up in their initial screen. These other molecules might also play a part in heart cell proliferation, healing scars and promoting the formation of new blood vessels–all processes critical for heart repair, Sancho-Martinez says. The data are available so that other research groups can focus on molecules that interest them.

The next step for Izpisua Belmonte’s team is to move into larger animals and see whether “regenerative reprogramming” can work in larger hearts, and for extended periods after treatment, says Sancho-Martinez. And, although the virus packaging disappeared from the animals’ bodies by 2 weeks after treatment, the scientists are working on a new way to deliver the inhibitors to avoid the need for viruses altogether.

A Molecular Switch that Determines Stem Cell Or Neuron


A University of California, San Diego School of Medicine research team has provided new information about a well-known protein that provides the switch for cells to become neurons. This protein is part of a regulatory circuit that can push an immature neural cell to become a functional neuron.

Postdoctoral fellow Chih-Hong Lou and his colleagues worked with principal investigator Miles F. Wilkinson, who is a professor in the Department of Reproductive Medicine, and is also a member of the UC San Diego Institute for Genomic Medicine. These data were published in the February 13 online issue of the journal Cell Reports. These data may also elucidate a still poorly understood process – neuron specification – and might significantly accelerate the development of new therapies for specific neurological disorders, such as autism and schizophrenia.

Wilkinson, Lou and others discovered that the conversion of immature cells to neurons is controlled by a protein called UPF1. UPF1 works in a pathway called the “nonsense-mediated RNA decay” or NMD pathway. The NMD pathway provides a quality control mechanism that eliminates faulty messenger RNA (mRNA) molecules.

mRNA molecules are synthesized from DNA in the nucleus of cells and are exported to the cytoplasm where they are translated by ribosomes into protein. All proteins are encoded by stretches of DNA known as genes and the synthesis of an RNA copy of this stretch of DNA is called transcription. After the transcription of a messenger RNA molecule, is goes to the cytoplasm and is used as the template for the synthesis of a specific protein. Occasionally, mistakes are made in the transcription of mRNAs, and such aberrant mRNAs will either be translated into junk protein, or are so damaged that they cannot be recognized by ribosomes. Such junk mRNAs will gum up the protein synthesis machinery, but cells have the NMD pathway that degrades junk mRNAs to prevent the collapse of the protein synthesis machinery.

UPF1 mechanism

A second function for the NMD pathway is to degrade a specific group of normal mRNAs to prevent the production of particular proteins. This NMD function is physiologically important, but until now it had not been clear why it is important.

Wilkinson and others have discovered that UPF1, in combination with a particular class of microRNAs, acts as a molecular switch to determine when immature (non-functional) neural cells take the plunge and differentiate into non-dividing (functional) neurons. In particular, UPF1 directs the degradation of a specific mRNA that encodes for a protein in the TGF-beta signaling pathway, which promotes neural differentiation. The destruction of this mRNA prevents the proper functioning of the TGF-beta signaling pathway and neural differentiation fails to occur. Therefore, Wilkinson, Lou and co-workers identified, for the first time, a molecular pathway in which NMD drives a normal biological response.

NMD also promotes the decay of mRNAs that encode proliferation inhibitors, which Wilkinson said might explain why NMD stimulates the proliferative state characteristic of stem cells. There are many potential clinical ramifications for these findings,” Wilkinson said. “One is that by promoting the stem-like state, NMD may be useful for reprogramming differentiated cells into stem cells more efficiently.

Wilkinson continued: “Another implication follows from the finding that NMD is vital to the normal development of the brain in diverse species, including humans. Humans with deficiencies in NMD have intellectual disability and often also have schizophrenia and autism. Therapies to enhance NMD in affected individuals could be useful in restoring the correct balance of stem cells and differentiated neurons and thereby help restore normal brain function.”

Co-authors on this paper include Ada Shao, Eleen Y. Shum, Josh L. Espinoza and Rachid Karam, from the UCSD Department of Reproductive Medicine; and Lulu Huang, from Isis Pharmaceuticals.

Funding for this research came, in part, from National Institutes of Health (grant GM-58595) and the California Institute for Regenerative Medicine.

Teaching Old Neural Stem Cells New Tricks


In our brains, cells called neurons produce nerve impulses and are responsible for thinking, learning memory, reasoning, and so on. Neurons do not exist in isolation, but in combination with cells called glial cells that support the neurons, nourish them, and protects them from stress damage. Neurons and glial cells are replenished by brain-specific neural stem cell populations in the brain.

Unfortunately, the neural stem cell population in our brains tends to produce far fewer neurons as they age. This deficit of new neurons can play a role in the onset of neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease. Also, our own “senior moments” when we forget where we placed our iPod or car keys comes from a loss of neurons as we age.

Fortunately, some recent research might change this trend. A team from Japan’s Keio University, and the Riken national research institute, has reported the discovery of a small RNA molecule (micro-RNA) that controls neuron production in young mice. When this micro-RNA was manipulated in older mice, their neural stem cells started to make neurons again. The Japanese team also has reasons to believe that the same mechanism is at work in human brains as well. This research was reported in the journal Proceedings of the National Academies of Science. The mechanism is believed to exist in humans as well.

Senior Author Hideyuki Okano said, “We observed the neurogenic-to-gliogenic switching in developing NSCs.” Translation: Okano and his team examined embryonic mouse brains and their neural stem cell (NSC) populations. They found what many other groups have previously observed: that the developing embryonic brain NSCs create neurons first, then switch over to making glial cells later. Okano’s team also discovered the microRNA-17/106-p38 axis that is responsible for this initial neuron-to-glial cell switch during embryonic development.

When they manipulated this embryonic microRNA-17/106-p38 pathway in older, post-natal NSCs in culture, these older post-natal NSCs switched from making glial cells to producing neurons.

In culture, NSCs are difficult to control, since getting large supplies of neurons from cell cultures that various research groups call NSCs is very difficult.

Nevertheless, “there is general agreement that neurogenesis (make neurons) largely precedes gliogenesis (making glial cells) during CNS development in vertebrates,” Okano explained. And adult NSCs, according to Okano, clearly can produce neurons in the body, “whereas they exhibit strong gliogenic characteristics under culture conditions in vitro (that is, in the laboratory).”

Adult NSCs in two regions of the brain—the subventricular zone and hippocampus—also “make neurons, even though transplant studies have shown us that the adult CNS is a gliogenic environment.”

Subventricular Zone

So it seems clear that old NSCs can make neurons, at least under certain conditions. However, it is very difficult to determine the age at which NSCs begin making substantially more glial cells than neurons. According to Okano, “It is difficult to clearly explain the association between total glial cell number and changes in NSC abilities. Moreover, there is less evidence about gliogenic ability of aged NSCs because most of studies about NSCs have mainly focused on the neurogenic ability. “

Still, Okano says: “There are some reports about decline of neurogenesis ability of NSCs with age. These reports indicate that reduction in paracrine Wnt3 factors, and increase of (chemokine) CCL11 concentration in blood, impaired adult neurogenesis in the hippocampus, for example.”

Could the group’s microRNA approach improve memory in humans? Okano believes so, but says more work needs to be done.

“We observed the neurogenic effect by overexpression of miR-17 in primary cultured neurospheres” – spheres of a variety of cells, including NSCs—“derived from the SVZ at postnatal day 30. Similar phenomenon by overexpression of miR-106b-25 cluster has been reported by another group.”

Okano also warns that his approach has only been attempted in cultured cells. He cautioned, “There is no evidence using knock-out mice. Therefore, the functions of them in adult neurogenesis and learning/memory functions are still unclear.”

Next, Okano’s group will develop “a useful method for precise manipulation of cytogenesis from NSCs. “

However, he says, “we think that further understanding of basic molecular mechanisms underlying the neural development is also an important issue.” He will study the ways in which his microRNA system interacts with other glia-producing genes. He wants to fully understand the mechanisms underlying “the end of neurogenic competence and acquisition of gliogenic competence.”

Finally, the group will “examine the significance of miR-17/p38 pathway in various somatic stem cells other than NSCs,” he says.