Posts tagged parkinson's disease

A mix of serendipity and dogged laboratory work allowed a diverse team of University of Pittsburgh scientists to report in the Oct. 1 issue of Nature Cell Biology that they had solved the mystery of a basic biological function essential to cellular health.

By discovering a mechanism by which mitochondria – tiny structures inside cells often described as “power plants” – signal that they are damaged and need to be eliminated, the Pitt team has opened the door to potential research into cures for disorders such as Parkinson’s disease that are believed to be caused by dysfunctional mitochondria in neurons.

"It’s a survival process. Cells activate to get rid of bad mitochondria and consolidate good mitochondria. If this process succeeds, then the good ones can proliferate and the cells thrive," said Valerian Kagan, Ph.D., D.Sc., a senior author on the paper and professor and vice chair of the Pitt Graduate School of Public Health’s Department of Environmental and Occupational Health. "It’s a beautiful, efficient mechanism that we will seek to target and model in developing new drugs and treatments."

Dr. Kagan, who, as a recipient of a Fulbright Scholar grant, currently is serving as visiting research chair in science and the environment at McMaster University in Ontario, Canada, likened the process to cooking a Thanksgiving turkey.

"You put the turkey in the oven and the outside becomes golden, but you can’t just look at it to know it’s ready. So you put a thermometer in, and when it pops up, you know you can eat it," he said. "Mitochondria give out a similar ‘eat me’ signal to cells when they are done functioning properly."

Cardiolipins, named because they were first found in heart tissue, are a component on the inner membrane of mitochondria. When a mitochondrion is damaged, the cardiolipins move from its inner membrane to its outer membrane, where they encourage the cell to destroy the entire mitochondrion.

However, that is only part of the process, says Charleen T. Chu, M.D., Ph.D., professor and the A. Julio Martinez Chair in Neuropathology in the Pitt School of Medicine’s Department of Pathology, another senior author of the study. “It’s not just the turkey timer going off; it’s a question of who’s holding the hot mitt to bring it to the dining room?” That turns out to be a protein called LC3. One part of LC3 binds to cardiolipin, and LC3 causes a specialized structure to form around the mitochondrion to carry it to the digestive centers of the cell.

The research arose nearly a decade ago when Dr. Kagan had a conversation with Dr. Chu at a research conference. Dr. Chu, who studies autophagy, or “self-eating,” in Parkinson’s disease, was seeking a change on the mitochondrial surface that could signal to LC3 to bring in the damaged organelle for recycling. It turned out they were working on different sides of the same puzzle.

Together with Hülya Bayır, M.D., research director of pediatric critical care medicine, Children’s Hospital of Pittsburgh of UPMC and professor, Pitt’s Department of Critical Care Medicine, and a team of nearly two dozen scientists, the three senior authors worked out how the pieces of the mitochondria signaling problem fit together.

Now that they’ve worked out the basic mechanism, Dr. Chu indicates that many more research directions will likely follow.

"There are so many follow-up questions," she said. "What is the process that triggers the cardiolipin to move outside the mitochondria? How does this pathway fit in with other pathways that affect onset of diseases like Parkinson’s? Interestingly, two familial Parkinson’s disease genes also are linked to mitochondrial removal."

Dr. Bayir explained that while this process may happen in all cells with mitochondria, it is particularly important that it functions correctly in neuronal cells because these cells do not divide and regenerate as readily as cells in other parts of the body.

"I think these findings have huge implications for brain injury patients," she said. "The mitochondrial ‘eat me’ signaling process could be a therapeutic target in the sense that you need a certain level of clearance of damaged mitochondria. But, on the other hand, you don’t want the clearing process to go on unchecked. You must have a level of balance, which is something we could seek to achieve with medications or therapy if the body is not able to find that balance itself."

(Source: upmc.com)

Scientists at the Centre for Addiction and Mental Health (CAMH) and University Health Network (UHN) have found a new link between early-onset Parkinson’s disease and a piece of DNA missing from chromosome 22. The findings help shed new light on the molecular changes that lead to Parkinson’s disease.

The study appears online today in JAMA Neurology.

Among people aged 35 to 64 who were missing DNA from a specific part of chromosome 22, the research team found a marked increase in the number of cases of Parkinson’s disease, compared to expected rates of Parkinson’s disease in the general population from the same age group.

The deletion, which occurs when a person is born with about 50 genes missing on one chromosome 22, is associated with 22q11.2 deletion syndrome. People with this condition may have heart or other birth defects, learning or speech difficulties, and some develop schizophrenia. It occurs in an estimated 1 in 2,000 to 4,000 births, but is believed to be under-diagnosed.

“22q11.2 deletion syndrome has been fairly well studied in childhood and adolescence, but less is known about its effects as people age,” said Dr. Anne Bassett, Director of CAMH’s Clinical Genetics Research Program and Director of the Dalglish Family Hearts and Minds Clinic at UHN, the world’s first clinic dedicated to adults with 22q11.2 deletion syndrome. A few cases of patients with the syndrome who had Parkinson’s disease symptoms had been previously reported, which suggested that the two conditions might be linked.

Parkinson’s disease is one of the most common neurodegenerative disorders worldwide, typically affecting people over the age of 65. Earlier onset of Parkinson’s disease, before age 50, is rare and has been associated with several other genetic changes that are not on chromosome 22.

The researchers studied 159 adults with 22q11.2 deletion syndrome to discover how many had been clinically diagnosed with Parkinson’s disease. For three individuals with the deletion and Parkinson’s disease who were deceased, brain tissue was also examined.

“Through a post-mortem examination, we were able to show that all three patients had a loss of neurons that was typical of that seen in Parkinson’s disease. The examination also helped to show that the symptoms of Parkinson’s disease were not related to side effects of the medications commonly used to treat schizophrenia,” added Dr.Rasmus Kiehl, neuropathologist in UHN’s Laboratory Medicine Program, who co-authored the report with CAMH graduate student Nancy Butcher. The team also found that Parkinson’s disease in 22q11.2 deletion syndrome is associated with abnormal accumulations of protein called Lewy bodies in the brain in some, but not all cases, just as in another genetic form of Parkinson’s disease.

The findings highlight the complexity of clinical care when both Parkinson’s disease and 22q11.2 deletion syndrome are present. “Our results may inform best practices in the clinic in these cases,” said Dr. Bassett, Senior Scientist in CAMH’s Campbell Family Mental Health Research Institute.

Because patients with 22q11.2DS who have schizophrenia are often prescribed anti-psychotic medications, they may experience side-effects such as tremors and muscle stiffness, similar to symptoms of Parkinson’s disease.

As a result, the researchers found that anti-psychotic use delayed the diagnosis of Parkinson’s disease – and the opportunity for treatment – by up to 10 years.

For people with early-onset Parkinson’s disease, who also have other features that could indicate 22q11.2 deletion syndrome, clinical genetic testing for the deletion on chromosome 22 should be considered, the researchers suggest.

“Our discovery that the 22q11.2 deletion syndrome is associated with Parkinson’s disease is very exciting,” said Dr. Anthony Lang, Director of the Movement Disorders Program at the Krembil Neuroscience Centre of Toronto Western Hospital. “The varying pathology that we found is reminiscent of certain other genetic causes of Parkinson’s disease, and opens new directions to search for novel genes that could cause its more common form. Studies of patients with 22q11.2 deletion syndrome before they ever develop clinical features of Parkinson’s disease may not only provide important information on the effectiveness of screening methods for early detection of the disease, but also allow for future ‘neuroprotective treatments’ to be introduced at the ultimate time when they can have a chance to make an important impact on preventing the disease or slowing its course.” 

“Most people with 22q11.2 deletion syndrome will not develop Parkinson’s disease,” emphasizes Dr. Bassett. “But it does occur at a rate higher than in the general population. We will now be on the look-out for this so we can provide the best care for patients.”

(Source: camh.ca)

Today’s primary tool for diagnosing Parkinson’s disease is the diagnostic ability of the physician, who can generally identify the clinical symptoms only when the disease is at a relatively advanced stage. A new joint study by researchers at the University of Haifa and Rambam Hospital that compared the handwriting of 40 sick and healthy subjects suggests an innovative and noninvasive method of diagnosing Parkinson’s at a fairly early stage.

“Identifying the changes in handwriting could lead to an early diagnosis of the illness and neurological intervention at a critical moment,” explains Prof. Sara Rosenblum, of the University of Haifa’s Department of Occupational Therapy, who initiated the study.

The methods for diagnosing Parkinson’s today are a physician evaluation or a test called SPECT, which uses radioactive material to image the brain. The latter, however, is no more effective in diagnosing the illness than an expert doctor and it exposes the patient to unnecessary radiation.

Studies from recent years show that there are unique and distinctive differences between the handwriting of patients with Parkinson’s disease and that of healthy people. However, most studies that to date have focused on handwriting focused on motor skills (such as the drawing of spirals) and not on writing that involves cognitive abilities, such as signing a check, copying addresses, etc.

According to Prof. Rosenblum, Parkinson’s patients report feeling a change in their cognitive abilities before detecting a change in their motor abilities and therefore a test of cognitive impairment like the one performed in this study could attest to the presence of the disease and offer a way to diagnose it earlier.

This research was conducted in cooperation with Dr. Ilana Schlesinger, head of the Center for Movement Disorders and Parkinson’s Disease at Haifa’s Rambam Medical Center and occupational therapists working in the hospital. In the study, the researchers asked the subjects to write their names and gave them addresses to copy, two everyday tasks that require cognitive abilities. Participants were 40 adults with at least 12 years of schooling, half healthy and half known to be in the early stages of Parkinson’s disease (before obvious motor signs are visible).

The writing was done on a regular piece of paper that was placed on electronic tablet, using a special pen with pressure-sensitive sensors operated by the pen when it hit the writing surface. A computerized analysis of the results compared a number of parameters: writing form (length, width and height of the letters), time required, and the pressure exerted on the surface while performing the assignment.

Analysis of the results showed significant differences between the patients and the healthy group, and all subjects, except one, had their status correctly diagnosed (97.5% accuracy). The Parkinson’s disease patients wrote smaller letters (“micrograph”), exerted less pressure on the writing surface, and took more time to complete the task. According to Prof. Rosenblum a particularly noticeable difference was the length of time the pen was in the air between the writing of each letter and each word.

“This finding is particularly important because while the patient holds the pen in the air, his mind is planning his next action in the writing process, and the need for more time reflects the subject’s reduced cognitive ability. Changes in handwriting can occur years before a clinical diagnosis and therefore can be an early signal of the approaching disease,” Prof. Rosenblum said.

According to Dr. Schlesinger, validating these findings in a broader study would allow this method to be used for a preliminary diagnosis of the disease in a safe and non-invasive fashion. “This study is a breakthrough toward an objective diagnosis of the disease,” said Dr. Schlesinger, adding, “Publication of the study in the journal of the European Neurological Society aroused great interest at the International Congress of Parkinson’s Disease and Movement held last week in Sydney, Australia.”

The researchers note that this diagnostic method has the added benefit of reducing the load on the health system, because the test can be performed by a professional other than a doctor. After the results are in, patients can be referred to a doctor for further treatment and testing if necessary. The researchers are currently using the method in a new experiment, in which they use handwriting analysis to evaluate the degree of Parkinson’s patients’ improved functioning after they have brain pacemakers implanted.

(Source: newswise.com)

UCSF Researchers Seek Way to Boost Parkin to Fight Both Diseases

A protein at the center of Parkinson’s disease research now also has been found to play a key role in causing the destruction of bacteria that cause tuberculosis, according to scientists led by UC San Francisco microbiologist and tuberculosis expert Jeffery Cox, PhD.

The protein, named Parkin, already is the focus of intense investigation in Parkinson’s disease, in which its malfunction is associated with a loss of nerve cells. Cox and colleagues now report that Parkin also acts on tuberculosis, triggering destruction of the bacteria by immune cells known as macrophages. Results appear online today (September 4, 2013) in the journal Nature.

The finding suggests that disease-fighting strategies already under investigation in pre-clinical studies for Parkinson’s disease might also prove useful in fighting tuberculosis, according to Cox. Cox is investigating ways to ramp up Parkin activity in mice infected with tuberculosis using a strategy similar to one being explored by his UCSF colleague Kevan Shokat, PhD, as a way to ward off neurodegeneration in Parkinson’s disease.

Globally, tuberculosis kills 1.4 million people each year, spreading from person to person through the air. Parkinson’s disease, the most common neurodegenerative movement disorder, also affects millions of mostly elderly people worldwide.

Cox homed in on the enzyme Parkin as a common element in Parkinson’s and tuberculosis through his investigations of how macrophages engulf and destroy bacteria. In a sense the macrophage — which translates from Greek as “big eater” — gobbles down foreign bacteria, through a process scientists call xenophagy.

Mycobacterium tuberculosis, along with a few other types of bacteria, including Salmonella and leprosy-causing Mycobacterium leprae, are different from other kinds of bacteria in that, like viruses, they need to get inside cells to mount a successful infection.

The battle between macrophage and mycobacterium can be especially intense. M. tuberculosis invades the macrophage, but then becomes engulfed in a sac within the macrophage that is pinched off from the cell’s outer membrane. The bacteria often escape this intracellular jail by secreting a protein that degrades the sac, only to be targeted yet again by molecular chains made from a protein called ubiquitin. Previously, Cox discovered molecules that escort these chained mycobacteria to more secure confinement within compartments inside cells called lysosomes, where the bacteria are destroyed.

The cells of non-bacterial organisms ranging in complexity from baker’s yeast to humans also use a similar mechanism — called autophagy — to dispose of their own unneeded molecules or worn out cellular components. Among the most abundant and crucial of these components are the cell’s mitochondria, metabolic powerhouses that convert food molecules into a source of energy that the cell can readily use to carry out its everyday housekeeping chores, as well as its more specialized functions.

Like other cellular components, mitochondria can wear out and malfunction, and often require replacement. The process through which mitochondria are disposed of, called mitophagy, depends on Parkin.

Cox became curious about the enzyme when he learned that specific, naturally occurring variations in the Parkin gene, called polymorphisms, are associated with increased susceptibility to tuberculosis infection.

“Because of the commonalities between mitophagy and the xenophagy of intracellular mycobacteria, as well as the links between Parkin gene polymorphisms and increased susceptibility to bacterial infection in humans, we speculated that Parkin may also be recruited to M. tuberculosis and target it for xenophagy,” Cox said.

In both mouse and human macrophages infected with M. tuberculosis in the lab, Parkin played a key role in fighting the bacteria, Cox and colleagues found. In addition, genetically engineered mice lacking Parkin died when infected with M. tuberculosis, while mice with normal Parkin survived infection.

The involvement of Parkin in targeting both damaged mitochondria and infectious mycobacteria arose long ago in evolution, Cox argues. As part of the Nature study, the research team found that Parkin-deficient mice and flies – creatures quite distant from humans in evolutionary time – also are more sensitive than normal mice and flies to intracellular bacterial infections.

Looking back more than 1 billion years, Cox noted that mitochondria evolved from bacteria that were taken up by cells in a symbiotic relationship.

In the same way that the immune system recognizes infectious bacteria as foreign, Cox said, “The evolutionary origin of mitochondria from bacteria suggests that perhaps mitochondrial dysfunction triggers the recognition of a mitochondrian as non-self.”

Having now demonstrated the importance of Parkin in fighting mycobacterial infection, Cox has begun working with Shokat to find a way to boost Parkin activity against cell-invading bacteria. “We are exploring the possibility that small-molecule drugs could be developed to activate Parkin to better fight tuberculosis infection,” Cox said.

(Source: newswise.com)

EPFL scientists exonerated a process thought to play a role in causing Parkinson’s disease; rather than triggering toxic aggregates in neurons, it turns out that it actually slows down the disease, pharmas have now new tracks to explore

Clues left at the scene of the crime don’t always point to the guilty party, as EPFL researchers investigating Parkinson’s disease have discovered. It is generally accepted that the disease is aggravated when a specific protein is transformed by an enzyme. The EPFL neuroscientists were able to show that, on the contrary, this transformation tends to protect against the progression of the disease. This surprising conclusion could radically change therapeutic approaches that are currently being developed by pharmaceutical companies. The research is to appear in an article in the Proceedings of the National Academy of Sciences (PNAS).

Parkinson’s disease is characterized by the accumulation of a protein known as alpha-synuclein in the brain. If too much of it is produced or if it’s not eliminated properly, it then aggregates into small clumps inside the neurons, eventually killing them. Several years ago scientists discovered that these aggregated proteins in the brain had undergone a transformation known as “phosphorylation” — a process in which an enzyme adds an extra chemical element to a protein, thus modifying its properties.

The investigators’ conclusion that the enzyme’s activity could be responsible for the disease seems eminently reasonable. If phosphorylation and protein aggregation go hand in hand, then it makes sense that one should cause the other. This is the assumption that researchers and pharmaceutical companies made as they tried to reduce the phosphorylation by deactivating an enzyme involved in the process. But they have been following a false lead, as the EPFL team was able to show.

The scientists even discovered that the phosphorylation of the protein has positive effects. On the one hand, it considerably reduces the toxic aggregation of the protein, and on the other, it helps the cell eliminate the protein. “The two phenomena are undoubtedly related, and together could play a role in the reduction of alpha-synuclein toxicity, but we don’t yet understand the impact of both processes at each stage of the disease,” explains neurobiologist Abid Oueslati, first author on the study.

Going back to the beginning

To reach this conclusion, the biologists had to explore the initial disease conditions. They injected into rat neurons what were thought to be the elements needed to trigger the disease: an overexpression of alpha-synuclein and the enzyme that phosphorylates it (PLK2).

To their surprise, the group of animals subjected to both of the parameters — overproduction of the protein and phosphorylation — lost nearly 70% fewer neurons than another group in which only the protein was overexpressed. Consequently, they had fewer lesions, and less Parkinson symptoms.

"We owe this discovery to unique tools that we developed, in collaboration with the Aebischer group, in order to study the effect of this transformation at the molecular level. ," explains Hilal Lashuel, who directed the study. Our study revealed the limitations of the most commonly used approach, which uses genetic mutations to mimic this process.

Lashuel thinks it is highly probable that the phosphorylation of the proteins takes place after they are aggregated, that is to say once the disease is already established. Or it could be a defense mechanism of the neurons, an attempt to try and slow down the progression of the disease from the beginning.

The scientists’ research opens doors for the development of future drug therapies. “The lesson we learned from this research is that everything you find at the scene of a crime is not necessarily involved in the crime. By remaining fixated on that assumption, we may lose sight of the bigger picture.”

(Source: eurekalert.org)

The active ingredient in an over-the-counter skin cream might do more than prevent wrinkles. Scientists have discovered that the drug, called kinetin, also slows or stops the effects of Parkinson’s disease on brain cells.

Scientists identified the link through biochemical and cellular studies, but the research team is now testing the drug in animal models of Parkinson’s. The research is published in the August 15, 2013 issue of the journal Cell.

“Kinetin is a great molecule to pursue because it’s already sold in drugstores as a topical anti-wrinkle cream,” says HHMI investigator Kevan Shokat of the University of California, San Francisco. “So it’s a drug we know has been in people and is safe.”

Parkinson’s disease is a degenerative disease that causes the death of neurons in the brain. Initially, the disease affects one’s movement and causes tremors, difficulty walking, and slurred speech. Later stages of the disease can cause dementia and broader health problems. In 2004, researchers studying an Italian family with a high prevalence of early-onset Parkinson’s disease discovered mutations in a protein called PINK1 associated with the inherited form of the disease.

Since then, studies have shown that PINK1 normally wedges into the membrane of damaged mitochondria inside cells that causes another protein, Parkin, to be recruited to the mitochondria, which are organelles responsible for energy generation. Neurons require high levels of energy production, therefore when mitochondrial damage occurs, it can lead to neuronal death. However, when Parkin is present on damaged mitochondria, studding the mitochondrial surface, the cell is able to survive the damage. In people who inherit mutations in PINK1, however, Parkin is never recruited to the organelles, leading to more frequent neuronal death than usual.

Shokat and his colleagues wanted to develop a way to turn on or crank up PINK1 activity, therefore preventing an excess of cell death, in those with inherited Parkinson’s disease. But turning on activity of a mutant enzyme is typically more difficult than blocking activity of an overactive version.

“When we started this project, we really thought that there would be no conceivable way to make something that directly turns on the enzyme,” says Shokat. “For any enzyme we know that causes a disease, we have ways to make inhibitors but no real ways to turn up activity.”

His team expected it would have to find a less direct way to mimic the activity of PINK1 and recruit Parkin. In the hopes of more fully understanding how PINK1 works, they began investigating how PINK1 binds to ATP, the energy molecule that normally turns it on. In one test, instead of adding ATP to the enzymes, they added different ATP analogues, versions of ATP with altered chemical groups that slightly change its shape. Scientists typically must engineer new versions of proteins to be able to accept these analogs, since they don’t fit into the typical ATP binding site. But to Shokat’s surprise, one of the analogs—kinetin triphosphate, or KTP—turned on the activity of not only normal PINK1, but also the mutated version, which doesn’t bind ATP.

“This drug does something that chemically we just never thought was possible,” says Shokat. “But it goes to show that if you find the right key for the right lock, you’ll be able to open the door.”

To test whether the binding of KTP to PINK1 led to the same consequences as the usual ATP binding, Shokat’s group measured the activity of PINK1 directly, as well as the downstream consequences of this activity, including the amount of Parkin recruited to the mitochondrial surface, and the levels of cell death. Adding the precursor of KTP, kinetin, to cells—both those with PINK1 mutations and those with normal physiology—amplified the activity of PINK1, increased the level of Parkin on damaged mitochondria, and decreased levels of neuron death, they found.

“What we have here is a case where the molecular target has been shown to be important to Parkinson’s in human genetic studies,” says Shokat. “And now we have a drug that specifically acts on this target and reverses the cellular causes of the disease.”

The similar results in cells with and without PINK1 mutations suggest that kinetin, which is a precursor to KTP, could be used to treat not only Parkinson’s patients with a known PINK1 mutation, but to slow progression of the disease in those without a family history by decreasing cell death.

Shokat is now performing experiments on the effects of kinetin in mice with various forms of Parkinson’s disease. However, the usefulness of animal models in Parkinson’s research has been debated, and therefore the positive results from the cellular data, he says, is as good an indicator as results in animals that this drug has potential to treat Parkinson’s in humans. Initial human studies will likely focus on the small population of patients with PINK1 mutations, and if successful in that group the drug could later be tested in a wider array of Parkinson’s patients.

(Source: hhmi.org)