The Transformation of Ordinary Skin Cells into Functional Brain Cells

A paper in Nature Biotechnology from research groups at Case Western Reserve School of Medicine describes a technique that directly converts skin cells to the specific type of brain cells that suffer destruction in patients with multiple sclerosis, cerebral palsy, and other so-called myelin disorders. This particular breakthrough now enables “on demand” production of those cells that wrap or “myelinate” the axons of neurons.

Myelin is a sheath that wraps the extension of neurons called the axons. Neurons are the conductive cells that initiate and propagate nerve impulses. Neurons contain cell extensions known as axons that connect with other neurons. The nerve impulse runs from the base of the cell body of the neurons, down the axon, to the neuron to which it is connected. An insulating myelin sheath that surrounds the axon increases the speed at which nerve impulses move down the axon. When this myelin sheath is damaged, nerve impulse conduction goes awry as does nerve function. For example, patients with multiple sclerosis (MS), cerebral palsy (CP), and rare genetic disorders called leukodystrophies, myelinating cells are destroyed are not replaced.


The new technique discussed in this Nature Biotechnology paper, directly converts skin cells called fibroblasts, which are rather abundant in the skin and most organs, into oligodendrocytes, the type of cell that constructs the myelin sheath in the central nervous system.


“Its ‘cellular alchemy,'” explains Paul Tesar, PhD, assistant professor of genetics and genome sciences at Case Western Reserve School of Medicine and senior author of the study. “We are taking a readily accessible and abundant cell and completely switching its identity to become a highly valuable cell for therapy.”

Tesar and his group used a technique called “cellular reprogramming,” to manipulate the levels of three naturally occurring proteins to induce the fibroblasts to differentiate into the cellular precursors to oligodendrocytes (called oligodendrocyte progenitor cells, or OPCs).


Led by Case Western Reserve researchers and co-first authors Fadi Najm and Angela Lager, Tesar’s research team rapidly generated billions of these induced OPCs (called iOPCs). They demonstrated that iOPCs could regenerate new myelin coatings around nerves after being transplanted to mice—a result that offers hope the technique might be used to treat human myelin disorders.

Demyelinating diseases damage the oligodendrocytes and cause loss of the insulating myelin coating. A cure for these diseases requires replacement of the myelin coating by replacement oligodendrocytes.

Until now, OPCs and oligodendrocytes could only be obtained from fetal tissue or pluripotent stem cells. These techniques have been valuable, but have distinct limitations.

“The myelin repair field has been hampered by an inability to rapidly generate safe and effective sources of functional oligodendrocytes,” explains co-author and myelin expert Robert Miller, PhD, professor of neurosciences at the Case Western Reserve School of Medicine and the university’s vice president for research. “The new technique may overcome all of these issues by providing a rapid and streamlined way to directly generate functional myelin producing cells.”

Even though this initial study used mouse cells, the next critical next step is to demonstrate feasibility and safety of human cells in a laboratory setting. If successful, the technique could have widespread therapeutic application to human myelin disorders.

“The progression of stem cell biology is providing opportunities for clinical translation that a decade ago would not have been possible,” says Stanton Gerson, MD, professor of Medicine-Hematology/Oncology at the School of Medicine and director of the National Center for Regenerative Medicine and the UH Case Medical Center Seidman Cancer Center. “It is a real breakthrough.”

Getting Neurons Made From Stem Cells to Show Activity After Transplantation

Stem cells can differentiate into neurons, but can they integrate into the wider neural network and contribute to the function of the central nervous system? The evidence for this is scant. Even though transplanted stem cells can increase the function of the nervous system or decrease or halt the deterioration of the nervous system, there is little direct evidence that neurons made from stem cells can connect and signal to other neurons.

Until now.

The laboratory of clinical neurologist Stuart Lipton at the Sanford-Burnham Medical Research Institute has used embryonic stem cells for this experiment. They differentiated these stem cells into neurons and implanted them into the brains of laboratory rodents. However, transplanting them, they also genetically engineered these neurons so that they would express genes from bacteria that encode fast-acting light-activated ion channels. These ion channels would cause the neurons to activate a nerve impulse if a light was shined on them. This provided a way to artificially activate these neurons to determine if they were connected to other neurons and integrated into the central nervous system and it neural network.

This technique is called “optogenetics,” and it is a relatively new field of molecular biology. By using genes from particular species of bacteria that encode light-activated ion channels, cells that normally do not respond to light can be engineered to respond to particular frequencies of light. The use of optogenetics in stem cells is also novel, but this increasingly powerful technology is capturing the imaginations of more and more scientists every day.

To continue with our story, what happened to the implanted stem cell-derived neurons when they were illuminated? They made nerve impulses, but ion changes were detected in neurons that were located far from the implanted neurons. The only reasonable explanation for these observations is that the implanted neurons are forming proper neural connections with other neurons and any nerve impulses established in the implanted neurons stimulate nerve impulses in connected neurons that then activate neurons in all the neural pathways connected to them.

Lipton said of his work, “We showed for the first time that embryonic stem cells that we’ve programmed to become neurons can integrate into existing brain circuits and fire patterns of electrical activity that are critical for consciousness and neural network activity.”

Even more interestingly, Lipton and his team implanted neurons into a portion of the brain known as the “hippocampus.” This structure helps to consolidate information from short-term memory to long-term memory. It also helps with spatial navigation. Since the rate at which neurons generate or “fire” nerve impulses varies from one region of the brain to another, Lipton wanted to know if his stem cell-derived neurons would fire at the same rate as those native neurons in the hippocampus of the laboratory rodent. The answer was a clear yes. The implanted neurons fired at roughly the same rate as the surrounding, endogenous hippocampal neurons. This suggests that the implanted neurons adapt and ultimately become physiologically like those neurons around them.


Lipton sees great potential for clinical treatments in this work: “Based on these results, we might be able to restore brain activity – and thus restore motor and cognitive function – by transplanting easily manipulated neuronal cells derived from embryonic stem cells.”

Lipton’s optimism is infectious to one extent, but I think we must temper it by realizing that Lipton shined lights on his neurons, and that this is something that we cannot do to the brains of human beings. However, if neurons that respond to other neurons can be made and implanted into the brains of Alzheimer’s disease patients, for example, then this could definitely restore cognitive ability in patients with neurodegenerative diseases.

Neural Stem Cells Produce Myelin in Human Clinical Trial

Neurons are the cells in the brain that conduct nerve impulses. Nerve impulse conduction is the result of ion movements across the membrane of neurons, and these ion movements are mediated by ion channels embedded in the cell membranes of the neurons. Neurons consist of a main cell body that houses the nucleus, and two sets of extensions: axons that conduct nerve impulses away from the cell body and dendrites that conduct the nerve impulse toward the cell body. The axons of some neurons are coated with a layer of insulation that increases the speed at which neural impulses are conducted. This insulating layer is called the “myelin sheath,” and damage to the myelin sheath can decrease conductivity through these neurons and decrease nervous system function.

Spinal cord injury damages the myelin sheath that insulated spinal nerves. Also diseases such as multiple sclerosis can damage the myelin sheath of nerves and cause neural degeneration. Drug treatments can only delay the inevitable, but replacing the lost myelin sheaths is one of the holy grail goals of regenerative medicine.

We might be closer to such a goal than previously thought. A Phase 1 clinical trial at the University of California, San Francisco that was sponsored by Stem Cells Inc. has shown that a neural stem cell line can be safely transplanted into the brain of patients who suffer from demyelination diseases. Furthermore, these patients were devoid of side effects from the transplant one year after the procedure. However even more exciting is that these transplanted cells seem to have successfully engrafted into the brains of these patients and have produced new myelin sheaths.

This investigation was designed to determine the safety and preliminary efficacy of implanted neural stem cells and the results are extremely encouraging, according to the principal investigator for this trial, David H. Rowitch, MD, PhD, who is also professor of pediatrics and neurological surgery at UCSF, and chief of neonatology at UCSF Benioff Children’s Hospital and a Howard Hughes Medical Institute Investigator.

The co-principal investigator for this trial, Nalin Gupta, MD, PhD, associate professor of neurological surgery and pediatrics and chief of pediatric neurological surgery at UCSF Benioff Children’s Hospital, said: “For the first time, we have evidence that transplanted neural stem cells are able to produce new myelin in patients with a severe myelination disease.” Gupta continued: “We also saw modest gains in neurological function, and while these can’t necessarily be attributed to the intervention because this was an uncontrolled trial with a small number of patients, the findings represent an important first step that strongly supports further testing of this approach as a means to treat the fundamental pathology in the brain of these patients.”

In this trial, human neural stem cells that had been developed by Stem Cells, Inc., a Newark, California biotechnology company, were directly injected into the brains of four children who had been diagnosed with an early-onset, fatal form of a condition known as Pelizaeus-Merzbacher disease (PMD). PMD is a genetic disease that typically occurs in males and affects brain-specific stem cells known as oligodendrocytes that construct the myelin sheath that insulate the neurons of the central nervous system. Defective oligodendrocytes prevent deposition of a functional myelin sheath and without a myelin sheath the white matter neural tracts are unable to correctly propagate nerve signals. This results in neurological dysfunction and neurodegeneration. Patients with early-onset PMD can neither walk nor talk and also have trouble breathing and undergo progressive neurological deterioration leading to death between ages 10 and 15.

All the PMD children who participated in this clinical trial were given standard neurological examinations and developmental assessments before and after the transplant procedures, which were conducted from 2010-2011. All patients also underwent magnetic resonance imaging (MRI) in order to assess myelin formation.

After the neural stem cells had been transplanted, Rowitch and his collaborators found evidence that the stem cells had successfully engrafted into the brains of the children. There was also indication that they were receiving blood and nutrients from the surrounding tissue and integrating into the brain. Rowitch likens stem cells engraftment to a “plant taking root.” This is a very significant finding because the engrafted cells were not the patients’ own stem cells. The implanted cells were not rejected by the patients.

The MRIs provided another very exciting piece of evidence, albeit and indirect piece of evidence, that the transplanted stem cells had become oligodendrocytes and were producing myelin. According to Rowitch: “There is no non-invasive way to test this definitively, but our MRI findings suggest myelination in the regions that have been transplanted.”

These neural stem cells have the capacity to differentiate into a wide variety of neural cell types. The differentiation of the neural stem cells appears to be greatly influenced by the environment into which the cells find themselves. The sites chosen for the Phase I study were determined by pre-clinical experiments done with animals. Investigators, at Oregon Health & Science University’s Papé Family Pediatric Research Institute published their animal work in the same issue of Science Translational Medicine. Stem Cells Inc’s neural stem cells were injected into mice and differentiated into oligodendrocytes and formed myelin. “The animal study is consistent with the MRI findings from the clinical trial and further supports the possibility of donor-derived myelination in human patients,” said Rowitch.

Dr. Arnold Kriegstein, who is the director of the Eli and Edythe Broad Center of Regeneration Medicine and Stem Cell Research at UCSF said: “This is a landmark study for the field. Without such studies in human patients, we won’t really know how transplanted cells behave –whether they disperse or migrate, whether they engraft or degenerate and die, whether immune-suppressing regimens really work or not. It’s only through these investigations that we will be able to refine the necessary procedures and technologies and make progress toward cell-based therapies for this disease and related disorders.”

Human Neurons Derived from Adult Brain Cells

A research group from Mainz, Germany have discovered a protocol that can reprogram a particular type of brain cell from human brains into new neurons.

Within the brain, neurons are the cells responsible for nerve impulses. Learning and memory, personality, volition and responses to stimuli are functions of neurons. When large numbers of neurons die, the patient suffers and their memory leaves them, their personality changes, or worse. Neurodegenerative diseases such as Alzheimer’s disease or Parkinson’s disease cause the death of large numbers of neurons and it is the death of neurons that is responsible for the symptoms of disease like these.

Benedikt Berninger, a faculty member of the Institute of Physiological Chemistry, at the Johannes Gutenberg University Mainz, Germany, and the senior author of this research said, “This works aims at converting cells that are present throughout the brain but themselves are not nerve cells into neurons. The ultimate goal we have in mind is that this may one day enable us to induce such conversion within the brain itself and provide a novel strategy for repairing the injured or diseased brain.”

The cells used by Berninger’s laboratory are known as “pericytes.” Pericytes are found in close association with blood vessels and are important in maintaining the blood-brain-barrier. Pericytes have also been shown to play a role in wound healing in other parts of the body.

Berninger chose pericytes for his research because he wanted to “target these cells and entice them to make nerve cells,” so that he and his research team could “take advantage of this injury response.”

When the converted neurons were subjected to further tests, they produced the normal types of electrical-chemical signals usually found in neurons, and also extended their connections to other neurons. This provided evidence that the converted cells could integrate into neural networks.

In their paper (Karow, et al., Cell Stem Cell 2012 11(4): 471), Berninger’s team write, “While much needs to be learnt (sic) about adapting a direct neuronal reprogramming strategy to meaningful repair in vivo, our data provide strong evidence for the notion that neuronal reprogramming of cells of pericytic origin within the damaged brain may become a viable approach to replace degenerated neurons.”