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Parkinson’s Disease Damaged Neurons Learn to Heal Themselves with Help of Modified White Blood Cells

Scientists at the UNC Eshelman School of Pharmacy are creating white blood cells that teach brain cells to heal the damage caused by degenerative neurological disorders like Parkinson’s disease.

The research is in PLOS ONE. (full open access)

Research: “GDNF-Transfected Macrophages Produce Potent Neuroprotective Effects in Parkinson’s Disease Mouse Model” by Yuling Zhao, Matthew J. Haney, Richa Gupta, John P. Bohnsack, Zhijian He, Alexander V. Kabanov, and Elena V. Batrakova in PLOS ONE doi:10.1371/journal.pone.0106867

Image: These are white blood cells reengineered by scientists at UNC-Chapel Hill deliver exosomes (red) loaded proteins that stimulate the growth of damaged nerve fibers (green and yellow). Researchers at the UNC Eshelman School of Pharmacy this technique can be developing into a potential treatment for Parkinson’s disease. Credit: Elena Batrakova/UNC Eshelman School Of Pharmacy.

Parkinson gene: Nerve growth factor halts mitochondrial degeneration

Neurodegenerative diseases like Parkinson’s disease involve the death of thousands of neurons in the brain. Nerve growth factors produced by the body, such as GDNF, promote the survival of the neurons; however, clinical tests with GDNF have not yielded in any clear improvements. Scientists from the Max Planck Institute of Neurobiology in Martinsried and their colleagues have now succeeded in demonstrating that GDNF and its receptor Ret also promote the survival of mitochondria, the power plants of the cell. By activating the Ret receptor, the scientists were able to prevent in flies and human cell cultures the degeneration of mitochondria, which is caused by a gene defect related to Parkinson’s disease. This important new link could lead to the development of more refined GDNF therapies in the future.

In his “Essay on the Shaking Palsy” of 1817, James Parkinson provided the first description of a disease that today affects almost 280,000 people in Germany. The most conspicuous symptom of Parkinson’s disease is a slow tremor, which is usually accompanied by an increasing lack of mobility and movement in the entire body. These symptoms are visible manifestations of a dramatic change that takes place in the brain: the death of large numbers of neurons in the Substantia nigra of the midbrain.

Despite almost 200 years of research into Parkinson’s, its causes have not yet been fully explained. It appears to be certain that, in addition to environmental factors, genetic mutations also play a role in the emergence of the disease. A series of genes is now associated with Parkinson’s disease. One of these is PINK1, whose mutation causes mitochondrial dysfunction. Mitochondria are a cell’s power plants and without them, a cell cannot function properly or regenerate. Scientists from the Max Planck Institute of Neurobiology and their colleagues from Munich and Martinsried have now discovered a hitherto unknown link that counteracts mitochondrial dysfunction in the case of a PINK1 mutation.

The PINK1 gene emerged at a very early stage in evolutionary history and exists in a similar form for example in humans, mice and flies. In the fruit fly Drosophila, a mitochondrial defect triggered by a PINK1 mutation manifests in the fraying of the muscles. Less visible, the flies’ neurons also die. The scientists studied the molecular processes involved in these changes and discovered that the activation of the Ret receptor counteracts the muscle degeneration. “This is a really interesting finding which links the mitochondrial degeneration in Parkinson’s disease with nerve growth factors,” reports Rüdiger Klein, the head of the research study. Ret is not an unknown factor for the Martinsried-based neurobiologists: “We already succeeded in demonstrating a few years ago in mice that neurons without the Ret receptor die prematurely and in greater numbers with increasing age,” says Klein.

The Ret receptor is the cells’ docking site for the growth factor GDNF, which is produced by the body. Various studies carried out in previous years showed that the binding of GDNF to its Ret receptor can prevent the early death of neurons in the Substantia nigra. However, clinical studies on the influence of GDNF on the progression of Parkinson’s in patients did not lead to any clear improvement in their condition.

The new findings from basic research suggest that the mitochondrial metabolism is boosted or re-established through Ret/GNDF. “Based on this finding, existing therapies could be refined or tailored to specific patient groups,” hopes Pontus Klein, who conducted the study within the framework of his doctoral thesis. This hope does not appear to be completely unfounded: The scientists have already discovered a Ret/GDNF effect in human cells with a PINK1 defect similar to that observed in the fruit fly. It may therefore be possible to search for metabolic defects in the mitochondria of Parkinson’s patients in future. A specially tailored GDNF therapy could then provide a new therapeutic approach for patients who test positively.

Engineered stem cell advance points toward treatment for ALS

Transplantation of human stem cells in an experiment conducted at the University of Wisconsin-Madison improved survival and muscle function in rats used to model ALS, a nerve disease that destroys nerve control of muscles, causing death by respiratory failure.

ALS (amyotrophic lateral sclerosis) is sometimes called “Lou Gehrig’s disease.“ According to the ALS Association, the condition strikes about 5,600 Americans each year. Only about half of patients are alive three years after diagnosis. 

In work recently completed at the UW School of Veterinary Medicine, Masatoshi Suzuki, an assistant professor of comparative biosciences, and his colleagues used adult stem cells from human bone marrow and genetically engineered the cells to produce compounds called growth factors that can support damaged nerve cells.

The researchers then implanted the cells directly into the muscles of rats that were genetically modified to have symptoms and nerve damage resembling ALS.

In people, the motor neurons that trigger contraction of leg muscles are up to three feet long. These nerve cells are often the first to suffer damage in ALS, but it’s unclear where the deterioration begins. Many scientists have focused on the closer end of the neuron, at the spinal cord, but Suzuki observes that the distant end, where the nerve touches and activates the muscle, is often damaged early in the disease.

The connection between the neuron and the muscle, called the neuro-muscular junction, is where Suzuki focuses his attention. “This is one of our primary differences,” Suzuki says. “We know that the neuro-muscular junction is a site of early deterioration, and we suspected that it might be the villain in causing the nerve cell to die. It might not be an innocent victim of damage that starts elsewhere.”

Previously, Suzuki found that injecting glial cell line-derived neurotropic factor (GDNF) at the junction helped the neurons survive. The new study, published in the journal Molecular Therapy on May 28, expands the research to show a similar effect from a second compound, called vascular endothelial growth factor.

In the study, Suzuki found that using stem cells to deliver vascular endothelial growth factor alone improved survival and delayed the onset of disease and the decline in muscle function. That result mirrored his earlier study with GDNF.

But the real advance, Suzuki says, was finding an even better result from using stem cells that create both of these two growth factors. “In terms of disease-free time, overall survival, and sustaining muscle function, we found that delivering the combination was more powerful than either growth factor alone. The results would provide a new hope for people with this terrible disease.”

The new research was supported by the ALS Association, the National Institutes of Health, the University of Wisconsin Foundation, and other groups. 

The injected stem cells survived for at least nine weeks, but did not become neurons. Instead, their contribution was to secrete one or both growth factors. 

Originally, much of the enthusiasm for stem cells focused on the hope of replacing damaged cells, but Suzuki’s approach is different. “These motor nerve cells have extremely long connections, and replacing these cells is still challenging. But we aim to keep the neurons alive and healthy using the same growth factors that the body creates, and that’s what we have shown here.”

For the test, Suzuki used ALS model rats with a mutation that is found in a small percentage of ALS patients who have a genetic form of the disease. “This model has been accepted as the best test bed for ALS experiments,” says Suzuki. 

By using adult mesenchymal stem cells, the technique avoided the danger of tumor that can arise with the transplant of embryonic stem cells and related “do-anything” cells.  Importantly, mesenchymal stem cells have been already used in clinical trials for various human diseases.

In the future, Suzuki hopes to apply his approach by using clinical grade stem cells. "Because this is a fatal and untreatable disease, we hope this could enter a clinical trial relatively soon.”

New information on Parkinson’s: GDNF not needed by the midbrain dopamine system

A key factor in the motor symptoms associated with Parkinson’s disease is the gradual destruction of dopamine neurons. The glial cell-derived neurotrophic factor, or GDNF, has been proven to protect dopamine neurons in test tube conditions and in test animal models for Parkinson’s disease. GDNF and its close relative, neurturin, have also been used in experimental treatments of patients with severe Parkinson’s disease. The results have been promising, but vary widely in terms of efficacy. At the moment, two companies are conducting tests to determine the clinical effects of GDNF on Parkinson’s sufferers.

According to an article published in Nature Neuroscience in 2008, removing GDNF from adult mice through gene technology causes significant damage to the midbrain dopamine system as well as triggers motor disorders. The article concluded that GDNF is vital to the maintenance and function of dopamine neurons.

At the same time, Academy of Finland Research Fellow Jaan-Olle Andressoo, from Professor Mart Saarma’s research group at the Institute of Biotechnology, had developed a mouse model that was equivalent to the model used in the other study, with minor technical differences. In Andressoo’s model, GDNF was removed from the central nervous system towards the end of the fetal period through gene deletion, and the mice remained healthy until high age. They studied the brains of the GDNF knockout mice together with the research group of University Lecturer Petteri Piepponen, based in the Faculty of Pharmacy.

“We decided to confirm the previous result using the mouse model Andressoo developed, and noticed that the complete absence of GDNF did not cause significant changes to the amount or function of dopamine neurons. Since the result surprised us, we wanted to verify it using two alternative methods, one of which was identical to the method in the previously published article,” explains Dr Jaan-Olle Andressoo.

In addition, some of the experiments were conducted in parallel at Professor Anders Björklund’s laboratory at Lund University. The Lund tests similarly indicated no changes to the dopamine systems or the behaviour of the mice. This clearly established that GDNF is not a necessary component of the dopamine system.

The manuscript including the new research results was approved for publication in the same series as the previous study. However, the study was subjected to even closer scrutiny than is associated with the normal publication procedure.

“The editors considered the manuscript to be a correction, so in addition to the normal peer review, they sent it to the researchers who published the previous results for comments. Ultimately, our results were deemed indisputable,” Dr Petteri Piepponen says.

Lou Gehrig's Disease Study: Renewing Brain's Aging Support Cells May Help Neurons Survive

Lou Gehrig’s disease, also known as amyotrophic lateral sclerosis, or ALS, attacks muscle-controlling nerve cells – motor neurons – in the brain, brainstem and spinal cord, leading to progressive weakness and eventual paralysis of muscles throughout the body. Patients typically survive only three to five years after diagnosis.

Now, with publication of a study by investigators at the Cedars-Sinai Board of Governors Regenerative Medicine Institute, ALS researchers know the effects of the attack are worsened, at least in part, by the aging and failure of support cells called astrocytes, which normally provide nutrients, housekeeping, structure and other forms of assistance for neurons.

Earlier studies suggested the possible involvement of these support cells in ALS development and progression, but the new research is believed to be the first to directly measure the effects of aging on the ability of astrocytes to sustain motor neurons. Results are published online in Neurobiology of Aging.

The Cedars-Sinai researchers first tried to repeat previous studies showing that astrocytes from laboratory animals with an ALS mutation failed to support normal motor neurons. They were surprised to find that very young ALS astrocytes were supportive, but ALS astrocytes from older animals were not. More surprisingly, it wasn’t just diseased astrocytes that were affected by age. The scientists discovered – and reported for the first time – that even normal aging of astrocytes reduces their ability to support motor neurons.

“Aging astrocytes lose their ability to support motor neurons in general, and they clearly fail to help those attacked by ALS,” said Clive Svendsen, PhD, professor and director of the Board of Governors Regenerative Medicine Institute, the article’s senior author.

He said old astrocytes and ALS-affected astrocytes have lower death rates in the petri dish than younger ones – they seem to hang around longer and accumulate. But while older astrocytes and those with the ALS mutation live longer, they appear to have significant damage to their DNA. Instead of being cleared away for replacement by new, healthy cells, the old, defective cells become useless clutter, producing chemicals that cause harmful inflammation. The process is accelerated in ALS astrocytes.

“Our findings have implications for scientists studying neurodegenerative diseases like ALS and Alzheimer’s and the aging process in general. In younger animals modeling ALS and in older ‘normal’ animals, the accumulations of defective astrocytes in the nervous system look similar,” said Melanie Das, PhD, a student in the Cedars-Sinai Graduate Program in Biomedical Science and Translational Medicine, the article’s first author.

After establishing the effects of aging on astrocytes, the researchers took another step – evaluating the potential therapeutic effects of a specially engineered protein.

“We found that by culturing aging astrocytes and those harboring the ALS mutation with a neuron-protective protein called GDNF, we could increase motor neuron survival. We already knew that GDNF was protective directly on motor neurons, but we believe this is the first time that the delivery of GDNF has been shown to have a direct beneficial effect on astrocytes, perhaps resetting their aging clock, which ultimately benefits neurons,” Svendsen said.

Svendsen and scientists in his laboratory have studied GDNF extensively, devising experimental methods to restore beneficial levels in the brain and spinal cord – where the disease originates – and in muscles, at the point where nerve fibers connect with muscle fibers to stimulate muscle action. Several large GDNF-related research projects taking shape at Cedars-Sinai are funded by the California Institute for Regenerative Medicine.

“Our major CIRM-funded programs, aimed at engineering young stem cell-derived astrocytes to secrete GDNF, then transplanting those cells back into patients, take on even greater importance, given this aging phenomenon,” said Svendsen, the Kerry and Simone Vickar Family Foundation Distinguished Chair in Regenerative Medicine.