Researchers See Promise in Transplanted Fetal Stem Cells for Parkinson’s

Researchers at Harvard-affiliated McLean Hospital have found that fetal dopamine cells transplanted into the brains of patients with Parkinson’s disease were able to remain healthy and functional for up to 14 years, a finding that could lead to new and better therapies for the illness.

The discovery, reported in the June 5, 2014 issue of the journal Cell Reports, could pave the way for researchers to begin transplanting dopamine neurons taken from stem cells grown in laboratories, a way to get treatments to many more patients in an easier fashion.

"We have shown in this paper that the transplanted cells connect and live well and do all the required functions of nerve cells for a very long time," said Ole Isacson, MD (DR MED SCI), director of the Neuroregeneration Research Institute at McLean and a professor of neurology and neuroscience at Harvard Medical School.

The researchers looked at the brains of five patients who got fetal cell transplants over a period of 14 years and found that their dopamine transporters (DAT), proteins that pump the neurotransmitter dopamine, and mitochondria, the power plants of cells, were still healthy at the time the patients died, in each case of causes other than Parkinson’s.

The fact that these cells had remained healthy indicated that the transplants had been successful and that the transplanted cells had not been corrupted as some researchers had suggested they likely had been in other studies, said Dr. Isacson, lead author of the paper.

"These findings are critically important for the rational development of stem cell-based dopamine neuronal replacement therapies for Parkinson’s," the paper concluded.

So far, about 25 patients worldwide have been treated with this particular method of transplanting fetal dopamine cells over a period of two decades and most saw their symptoms improve markedly, he said.

Fetal cell transplants can reduce both Parkinson’s symptoms for many years and can reduce the need for dopamine replacement drugs, even though they can take months or years to start working, the paper said.

However, Dr. Isacson said proof had been lacking that the transplanted cells were able to remain healthy — until this study. This is important for research in the transplant field to move ahead, he said.

All of the patients were in the late stages of Parkinson’s disease at the time of their transplants. Parkinson’s is a disease characterized by tremors, rigidity, slowness of movement and poor balance. It is a chronic, progressive disease that results when dopamine-producing nerve cells in a part of the brain die or are impaired.

Dr. Isacson said there was a need to understand how transplanted neurons could survive despite ongoing disease process in the patients’ brains. He said there has been controversy among scientists, some of whom believe that the transplanted cells could be corrupted by toxic proteins associated with the disease process, even at the same time patients seemed to be doing better.

"Everything we saw looked very healthy," he said, referring to the dopamine transporters and mitochondria cells.

He said the method used to transplant the cells into these patients’ brains was different than another method used on about 60 other patients worldwide. In some of those other trials, scientists said the cells might have been damaged as a result of the disease process.

It may have been that the method used on the patients in this study, which injected tiny bits of liquefied dopamine nerve cells into the brain via a thin needle, was superior to the method used in other studies, which transplanted larger chunks of nerve cells using a larger needle, he said. The transplants on the patients in this study were done in Canada.

In this study, the researchers led by Dr. Isacson compared the patients’ own dopamine producing cells with the transplanted ones. “We found very different patterns,” he said.

The difference was seen in the DAT and mitochondria, which were unhealthy around the patients’ own dopamine neurons and healthy around the transplanted ones. “The transplanted cells don’t have the disease,” he said.

"This is very important in the quest for new therapies," he added.

It is very difficult to obtain dopamine nerve cells from fetal tissue, he said. It would be far easier to grow the cells in a laboratory from stem cells, he noted. There have been no stem cell transplants as of yet for Parkinson’s patients.

The control of dendritic branching by mitochondria

A fundamental difference between neurons in real brains and those in artificial neural networks is the way the neurons in each are connected. In artificial nets, the synapses between neurons often have adjustable strengths, but the structure and scale of the input dendritic field generally counts for little. For real neurons, where a “connection” between cells is not just a synapse but rather a whole net unto itself, structure and scale are everything. The architect of this dendritic structure is neither a DNA code nor a spontaneous developmental physics that condenses order from a protein-lipid chaos. This structure is in fact the byproduct of competitive, yet cooperative mitochondria that administer that code to themselves and to their host to control its interaction with other similarly controlled hosts.

Reseachers from Osaku University have found that if mitochondria are depleted from developing dendrites in pyramidal cells, there is increased branching in the proximal region of the dendrites. In their paper last week in the Journal of Neuroscience, they also show that these dendrites grow longer. Since mitochondria distribute not just energy but also metabolites, proteins, and mRNAs throughout the cell, these results may be somewhat surprising. However depending on what manipulations have been done to alter the mitochondria, many things might be expected to happen to dendrites and the cell in general.

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Study confirms mitochondrial deficits in children with autism

Children with autism experience deficits in a type of immune cell that protects the body from infection. Called granulocytes, the cells exhibit one-third the capacity to fight infection and protect the body from invasion compared with the same cells in children who are developing normally.

The cells, which circulate in the bloodstream, are less able to deliver crucial infection-fighting oxidative responses to combat invading pathogens because of dysfunction in their tiny energy-generating organelles, the mitochondria.

The study is published online in the journal Pediatrics.

“Granulocytes fight cellular invaders like bacteria and viruses by producing highly reactive oxidants, toxic chemicals that kill microorganisms. Our findings show that in children with severe autism the level of that response was both lower and slower,”  said Eleonora Napoli, lead study author and project scientist in the Department of Molecular Biosciences in the UC Davis School of Veterinary Medicine. “The granulocytes generated less highly reactive oxidants and took longer to produce them.”

The researchers also found that the mitochondria in the granulocytes of children with autism consumed far less oxygen than those of the typically developing children — another sign of decreased mitochondrial function.

Mitochondria are the main intracellular source of oxygen free radicals, which are very reactive and can harm cellular structures and DNA. Cells can repair typical levels of oxidative damage. However, in the children with autism the cells produced more free radicals and were less able to repair the damage, and as a result experienced more oxidative stress. The free radical levels in the blood cells of children with autism were 1 ½ times greater than those without the disorder.

The study was conducted using blood samples of children enrolled in the Childhood Risk of Autism and the Environment (CHARGE) Study and included 10 children with severe autism age 2 to 5 and 10 age-, race- and sex-matched children who were developing typically.

In an earlier study the research team found decreased mitochondrial fortitude in another type of immune cell, the lymphocytes. Together, the findings suggest that deficiencies in the cells’ ability to fuel brain neurons might lead to some of the cognitive impairments associated with autism. Higher levels of free radicals also might contribute to autism severity.

“The response found among granulocytes mirrors earlier results obtained with lymphocytes from children with severe autism, underscoring the cross-talk between energy metabolism and response to oxidative damage,” said Cecilia Giulivi, professor in the Department of Molecular Biosciences in the UC Davis School of Veterinary Medicine and the study’s senior author.

“It also suggests that the immune response seems to be modulated by a nuclear factor named NRF2,” that controls antioxidant response to environmental factors and may hold clues to the gene-environment interaction in autism, Giulivi said.

(Image credit)

Fast contractions and depolarizations in mitochondria revealed with multiparametric imaging

When something bad happens to otherwise healthy neurons it’s easy to blame the usual suspects—the mitochondria. In some cases the nucleus might be the one at fault, as in a de novo mutation in a critical gene or in some other runaway error process in the instruction pipeline. Other times there could be leakage into the brain of toxins, bacteria, or even overzealous patriot cells of the host. But by and large, it’s the mitochondria who bear responsibility for nearly everything the brain does and so it is they who must accept it when it fails. To better understand how these organelles function, researchers have turned to special imaging methods that let them observe multiple aspects of their behavior all at once.

In one of the most revealing studies of its kind to date, researchers in Germany were able to observe the tiny contractions that mitochondria undergo during their complex shifts through different redox states and levels of depolarization. Publishing in a recent issue of Nature Medicine they relate these effects to pH and calcium concentration in the both the mitochondria and surrounding axon, and also to the larger spiking activity of the neuron.

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Neuroimaging: Live from inside the cell

A novel imaging technique provides insights into the role of redox signaling and reactive oxygen species in living neurons, in real time. Scientists of the Technische Universität München (TUM) and the Ludwig-Maximilians-Universität München (LMU) have developed a new optical microscopy technique to unravel the role of “oxidative stress” in healthy as well as injured nervous systems. The work is reported in the latest issue of Nature Medicine.

Reactive oxygen species are important intracellular signaling molecules, but their mode of action is complex: In low concentrations they regulate key aspects of cellular function and behavior, while at high concentrations they can cause “oxidative stress”, which damages organelles, membranes and DNA. To analyze how redox signaling unfolds in single cells and organelles in real-time, an innovative optical microscopy technique has been developed jointly by the teams of LMU Professor Martin Kerschensteiner and TUM Professor Thomas Misgeld, both investigators of the Munich Cluster for Systems Neurology (SyNergy).

“Our new optical approach allows us to visualize the redox state of important cellular organelles, mitochondria, in real time in living tissue” Kerschensteiner says. Mitochondria are the cell’s power plants, which convert nutrients into usable energy. In earlier studies, Kerschensteiner and Misgeld had obtained evidence that oxidative damage of mitochondria might contribute to the destruction of axons in inflammatory diseases such as multiple sclerosis.

The new method allows them to record the oxidation states of individual mitochondria with high spatial and temporal resolution. Kerschensteiner explains the motivation behind the development of the technique: “Redox signals have important physiological functions, but can also cause damage, for example when present in high concentrations around immune cells.”

First surprises
Kerschensteiner and Misgeld used redox-sensitive variants of the Green Fluorescent Protein (GFP) as visualization tools. “By combining these with other biosensors and vital dyes, we were able to establish an approach that permits us to simultaneously monitor redox signals together with mitochondrial calcium currents, as well as changes in the electrical potential and the proton (pH) gradient across the mitochondrial membrane,” says Thomas Misgeld.

The researchers have applied the technique to two experimental models, and have arrived at some unexpected insights. On the one hand, they have been able, for the first time, to study redox signal induction in response to neural damage – in this case, spinal cord injury – in the mammalian nervous system. The observations revealed that severance of an axon results in a wave of oxidation of the mitochondria, which begins at the site of damage and is propagated along the fiber. Furthermore, an influx of calcium at the site of axonal resection was shown to be essential for the ensuing functional damage to mitochondria.

Perhaps the most surprising outcome of the new study was that the study’s first author, graduate student Michael Breckwoldt, was able to image, also for the first time, spontaneous contractions of mitochondria that are accompanied by a rapid shift in the redox state of the organelle. As Misgeld explains, “This appears to be a fail-safe system that is activated in response to stress and temporarily attenuates mitochondrial activity. Under pathological conditions, the contractions are more prolonged and may become irreversible, and this can ultimately result in irreparable damage to the nerve process.”

Researchers examine metabolism in defective cells

UAlberta researchers are taking a closer look at how two metabolic pathways interact to increase the lifespan of cells with mitochondrial defects. Magnus Friis (PhD ’10) is the lead author of the study, which was published online on April 10 and will be published in the April 24 issue of Cell Reports.

Mitochondria produce energy for cells through oxidative metabolism, but the process produces toxic byproducts that can accumulate and cause defects in the cell’s mitochondria. These defects, in turn, affect the cell’s ability to generate energy and can potentially lead to cell death and are associated with aging and various neurological diseases.

Friis, a postdoctoral fellow in Mike Schultz’s biochemistry lab, examined how dietary changes at the cell level can affect cell health. He exposed normal and defective yeast cells to two different energy sources: glucose, the preferred sugar of cells, and raffinose, a natural sugar found in vegetables and whole grains.

“[The dietary intervention] is a general shift in what we’re feeding the cells to get them to do something different with their whole nutrient metabolism,” Friis noted. “There are signaling pathways that allow a cell to sense its environment and co-ordinate events to allow the cell to adapt to what’s going on. In this case, [cells are responding to] which nutrients are available.”

Friis and Schultz examined two nutrient signaling pathways called the AMPK pathway and the retrograde response. AMPK responds to energy deficits in the cell by down-regulating energy consuming processes, which are often associated with cell growth, and up-regulating energy producing processes. The retrograde response pathway is specific to the yeast used in the study and supplies key amino acids to the cell by changing the metabolic process of the mitochondria.  

When activated individually, neither the AMPK pathway nor the retrograde response provided substantial benefits to cells with damaged mitochondria. When activated simultaneously, clear benefits became evident.

“We looked at the effect activating both pathways had on maintenance of cellular viability in what’s called a chronological aging experiment,” Friis said. “Even when they had defective mitochondria, the cells with the retrograde response and AMPK simultaneously activated during growth were able to live as long as cells with normal mitochondrial function.”

Working in collaboration with John Paul Glaves, a postdoctoral fellow in Bryan Sykes’ lab, and Tao Huan, a PhD student in Liang Li’s lab, Friis measured the molecules produced during the metabolic process. They found that the defective cells had higher levels of branched chain amino acids and trahelose, a carbohydrate found in yeast that can serve an energy source, similar to glycogen in human cells.

“By activating AMPK, we’ve removed certain blocks in metabolism. With the retrograde response, we’ve changed the amino acid metabolism in a way that allowed the cells to accumulate storage carbohydrates, which stabilize their function,” Friis said.

Activated AMPK and retrograde response pathways allow the cell to accumulate a storage carbohydrate, which can be metabolize normally despite mitochondrial defects that affect the cell’s metabolism. The additional energy stabilizes cell function and prevents premature cell death often caused by defects in mitochondria.

“No matter how many people are working on the problem in humans, mitochondrial disorders are too complicated to figure out the nuts and bolts without the work that Magnus is doing,” Schultz said. “This research opens the concept, a new concept on how to deal with these metabolic problems.”

Scientists find potential target for treating mitochondrial disorders

Mitochondria, long known as “cellular power plants” for their generation of the key energy source adenosine triphosphate (ATP), are essential for proper cellular functions. Mitochondrial defects are often observed in a variety of diseases, including cancer, Alzheimer’s disease, and Parkinson’s disease, and are the hallmarks of a number of genetic mitochondrial disorders whose manifestations range from muscle weakness to organ failure. Despite a fairly strong understanding of the pathology of such genetic mitochondrial disorders, efforts to treat them have been largely ineffective.

But now, graduate student Walter Chen and postdoctoral researcher Kivanc Birsoy, both part of Whitehead Institute Member David Sabatini’s lab, have unraveled how to rescue cells suffering from mitochondrial dysfunction, a finding that may lead to new therapies for this condition.

To find genetic mutations that would rescue the cells, Chen and Birsoy mimicked mitochondrial dysfunction in a haploid genetic system developed by former Whitehead Fellow Thijn Brummelkamp. After suppressing mitochondrial function using the drug antimycin, Chen and Birsoy saw that cells with mutations inactivating the gene ATPIF1 were protected against loss of mitochondrial function.

The protein ATPIF1 is part of a backup system to save starving cells. When cells are deprived of oxygen and sugars, a mitochondrial complex that usually produces ATP, called ATP synthase, switches to consuming it, a state that can be harmful to an already starving cell. ATPIF1 interacts with ATP synthase to shut it down and prevent it from consuming the mitochondrion’s dwindling ATP supply but, in the process, also worsens the mitochondrion’s membrane potential.

“In these diseases of mitochondrial dysfunction, in a sense, it’s a false starvation situation for the cell—there are plenty of nutrients, but because there’s a block in the mitochondria’s normal function, the mitochondria behave as if there’s not enough oxygen,” says Chen, who with Birsoy, authored a paper in the journal Cell Reports describing this work. “So in these situations, activation of ATPIF1 is not good, because there are still many nutrients around to provide ATP. Instead, blocking ATPIF1 is therapeutic because it allows for maintenance of the membrane potential.”

Liver cells are frequently affected in patients with severe mitochondrial disease, so Chen and Birsoy tested the effects of mitochondrial dysfunction in the liver cells of control mice and mice with ATPIF1 genetically knocked out. Again, the liver cells with suppressed ATPIF1 function dealt better with mitochondrial dysfunction than liver cells with normal ATPIF1 activity.

“It’s very simple—if you get rid of ATPIF1, you survive in the presence of mitochondrial dysfunction,” says Birsoy. “From what we see so far, there are no major side effects from blocking ATPIF1 in mice.”

For Chen and Birsoy, the next step in this line of research is to test the effects of ATPIF1 suppression in mouse models of mitochondrial dysfunction. Then they will try to identify therapeutics that effectively block ATPIF1 function.