Posts tagged PINK1
Articles and news from the latest research reports.
Applying Proteomics to Parkinson’s
Scientists studying two genes that are mutated in an early-onset form of Parkinson’s disease have deciphered how normal versions of these genes collaborate to help rid cells of damaged mitochondria. Mitochondria are the cell’s primary energy source, and maintaining their health is critical for cellular function. Mitochondrial dysfunction may underlie multiple neurodegenerative diseases, including Parkinson’s.
(Image caption: PARKIN (green) is localized on damaged mitochondria. Image: Harper Lab)
In their analysis published in Molecular Cell, Harvard Medical School researchers used powerful quantitative mass spectrometry and live-cell imaging approaches to elucidate a multistep mechanism by which the two proteins mutated in Parkinson’s disease—PINK1 and PARKIN—mark mitochondria as damaged by attaching chains of a small protein called ubiquitin. This work paves the way for a deeper understanding of what molecular steps are defective when these proteins are mutated in patients with Parkinson’s disease.
“The PINK1-PARKIN pathway has been studied for many years, yet its mechanisms weren’t clearly defined,” said Wade Harper, Bert and Natalie Vallee Professor of Molecular Pathology in the Department of Cell Biology at HMS and senior author of the paper. “Combining imaging and advanced mass spectrometry approaches has allowed us for the first time to determine with molecular precision the biochemical output of the PINK1-PARKIN pathway in living cells.”
One hypothesis about the origin of Parkinson’s disease suggests that neurons place high energy demands on their mitochondria. When mitochondria become damaged and their energy production falls, they must be cleared away; if not, cell death results when the damaged mitochondria create harmful chemicals called reactive oxygen species.
People who have certain early-onset mutations in PINK1 or PARKIN genes may live normal lives until they enter their 30s when movement disorders begin to appear, reflecting the loss of neurons that make the neurotransmitter dopamine. These neurons seem to be the cells that are the most sensitive to an inability to remove damaged mitochondria.
Only in the last few years have scientists understood that the enzymes PARKIN and PINK1 work together to remove damaged mitochondria. The PINK1 kinase, an enzyme that transfers phosphate to other proteins, is activated specifically on damaged mitochondria where it then functions to promote accumulation of PARKIN on the mitochondrial surface. Once there, PARKIN—a ubiquitin ligase— marks numerous proteins on the surface of the mitochondria with chains of ubiquitin, which in turn target the damaged mitochondria for removal from the cell.
In their new work, Harper’s team identifies a multistep “feed-forward” mechanism that involves intertwined ubiquitylation and phosphorylation in a sequence of reactions that successively build on one another. To the authors’ knowledge, this is the first report of a feed-forward mechanism of this type.
The team, led by postdoctoral fellow Alban Ordureau, found that PINK1 actually has two functions in a multistep pathway. First, PINK1 phosphorylates PARKIN, greatly stimulating its ability to attach ubiquitin to mitochondrial substrates. Second, PINK1 phosphorylates ubiquitin chains that PARKIN has just built. Unexpectedly, these phosphorylated ubiquitin chains then bind tightly to activated PARKIN, thereby facilitating its retention on the mitochondrial surface and furthering ubiquitin chain assembly through a feed-forward mechanism. Eventually these chains become so dense that the damaged mitochondria are marked for degradation.
“Our finding that PARKIN binds phosphorylated-ubiquitin chains as its mechanism of retention on damaged mitochondria was completely unexpected,” Harper said. “Ubiquitin has been studied for almost 40 years, but only recently has regulation of ubiquitin by phosphorylation emerged as a major focus for the field.”
Methods employed in this study have their origins in prior work of Steven Gygi, HMS professor of cell biology and a co-author of the paper, who developed ways to quantify ubiquitin chains more than a decade ago. Harper says there is “enormous potential in the application of these approaches to understand how defects in the ubiquitin system lead to disease.”
The team also included Brenda Schulman, a Howard Hughes Medical Institute investigator, the co-director of the Cancer Genetics, Biochemistry and Cell Biology Program at St. Jude Children’s Research Hospital and a leading expert on ubiquitin biochemistry.
“This is a very intricate pathway,” Ordureau said. “We were surprised by our findings at every step.”
(Source: hms.harvard.edu)
Researchers identify new gene involved in Parkinson’s disease
A team of UCLA researchers has identified a new gene involved in Parkinson’s disease, a finding that may one day provide a target for a new drug to prevent and potentially even cure the debilitating neurological disorder.
Parkinson’s disease is the second most common neurodegenerative disorder after Alzheimer’s disease, and there is no cure for the progressive and devastating illness. About 60,000 Americans are diagnosed with Parkinson’s disease each year. It is estimated that as many as 1 million Americans live with Parkinson’s disease, which is more than the number of people diagnosed with multiple sclerosis, muscular dystrophy and Lou Gehrig’s disease combined.
In Parkinson’s disease, multiple neurons in the brain gradually break down or die. This leads to the movement impairments, such as tremor, rigidity, slowness in movement and difficulty walking, as well as depression, anxiety, sleeping difficulties and dementia, said Dr. Ming Guo, the study team leader, associate professor of neurology and pharmacology and a practicing neurologist at UCLA.
A handful of genes have been identified in inherited cases of Parkinson’s disease. Guo’s team was one of two groups worldwide that first reported in 2006 in the journal Nature that two of these genes, PTEN-induced putative kinase 1 (PINK1) and PARKIN, act together to maintain the health of mitochondria – the power house of the cell that is important in maintaining brain health. Mutations in these genes lead to early-onset Parkinson’s disease.
Guo’s team has further shown that when PINK1 and PARKIN are operating correctly, they help maintain the regular shape of healthy mitochondria and promote elimination of damaged mitochondria. Accumulation of unhealthy or damaged mitochondria in neurons and muscles ultimately results in Parkinson’s disease.
In this study, the team found that the new gene, called MUL1 (also known as MULAN and MAPL), plays an important role in mediating the pathology of the PINK1 and PARKIN. The study, performed in fruit flies and mice, showed that providing an extra amount of MUL1 ameliorates the mitochondrial damage due to mutated PINK/PARKIN, while inhibiting MUL1 in mutant PINK1/PARKIN exacerbates the damage to the mitochondria. In addition, Guo and her collaborators found that removing MUL1 from mouse neurons of the PARKIN disease model results in unhealthy mitochondria and degeneration of the neurons.
The five-year study appears June 4, 2014, in eLife, a new, open access scientific journal for groundbreaking biomedical and life research sponsored by the Howard Hughes Medical Institute (United States), the Wellcome Trust (United Kingdom) and Max Plank Institutes (Germany).
"We are very excited about this finding," Guo said. "There are several implications to this work, including that MUL1 appears to be a very promising drug target and that it may constitute a new pathway regulating the quality of mitochondria."
Guo characterized the work as “a major advancement in Parkinson’s disease research.”
"We show that MUL1 dosage is key and optimizing its function is crucial for brain health and to ward off Parkinson’s disease," she said. "Our work proves that mitochondrial health is of central importance to keep us from suffering from neurodegeneration. Further, finding a drug that can enhance MUL1 function would be of great benefit to patients with Parkinson’s disease."
Going forward, Guo and her team will test these results in more complex organisms, hoping to uncover additional functions and mechanisms of MUL1. Additionally, the team will perform small molecule screens to help identify potential compounds that specifically target MUL1. Further, they will examine if mutations in MUL1 exist in some patients with inherited forms of Parkinson’s.
(Source: eurekalert.org)
(Image caption: Various functions of PINK1 within a representative dopaminergic neuron)
New discoveries place lack of energy at the basis of Parkinson’s Disease
Neuroscientists Vanessa Moraïs and Bart De Strooper from VIB and KU Leuven have demonstrated how a defect in the gene Pink1 results in Parkinson’s disease. By mapping this process at a molecular level, they have provided the ultimate proof that a deficient energy production process in cells can result in Parkinson’s disease. These insights are so revolutionary that they have been published in the leading journal Science.
Vanessa Moraïs (VIB/KU Leuven):
“Having Parkinson’s disease means that you can no longer tell your own body what to do. The hope of finding a solution to this has stimulated me for many years to unravel what goes wrong in the cells of Parkinson’s patients. This research is an important step forwards.”
Bart De Strooper (VIB/KU Leuven):
“Parkinson’s disease is one of the research focuses in our department. It gives great satisfaction that we have unraveled a molecular process responsible for the faulty energy production process in cells of Parkinson’s patients. This confirms our belief that repairing the energy production in cells is a possible therapeutic strategy.”
Faulty energy production forms the basis of Parkinson’s disease
Mitochondria are cell components that produce the energy required by a cell to function. The action of these mitochondria – and therefore the energy production in cells – is disrupted in Parkinson’s disease. The exact mechanism was unknown. In recent years, scientists have described various gene defects (mutations) in Parkinson’s patients that result in decreased activity of the mitochondria, including a mutation in the Pink1 gene.
Molecular mechanism provides ultimate proof
Vanessa Moraïs studied the link between Pink1, mitochondria and Parkinson’s disease in fruit-flies and mice with a defective Pink1 gene. These model organisms exhibited symptoms of Parkinson’s disease as a result of this defect. She was able to demonstrate that the defect in Pink1 resulted in the so-called ‘Complex I’ – a protein complex with a crucial role in the energy production of mitochondria – not being phosphorylated adequately, resulting in decreased energy production. When Moraïs and her colleagues ensured correct phosphorylation of Complex I, the Parkinson’s symptoms decreased or disappeared in mice and in patient-derived stem cell lines. The scientists thereby demonstrated that the lack of phosphorylation causes Parkinson’s disease in patients with a defect Pin1 gene.
Further research in Parkinson’s patients with defective Pink1 gene
This study reveals that repairing the phosphorylation of Complex I could be a treatment strategy for Parkinson’s disease. The VIB scientists have already used cells from Parkinson’s patients with a defective Pink1 gene to demonstrate that repairing the phosphorylation results in increased energy production. However, will this cause the symptoms of Parkinson’s disease to decrease or disappear? Only tests on patients can answer this question. According to the scientists, the best strategy would be to start with the sub-group of patients with a defective Pink1 gene. But before starting clinical trials, a lot of aspects still have to be tested.
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.
Quality control of mitochondria as a defense against disease
Scientists from the Montreal Neurological Institute and Hospital in Canada have discovered that two genes linked to hereditary Parkinson’s disease are involved in the early-stage quality control of mitochondria. The protective mechanism, which is reported in The EMBO Journal, removes damaged proteins that arise from oxidative stress from mitochondria.
“PINK1 and parkin, are implicated in selectively targeting dysfunctional components of mitochondria to the lysosome under conditions of excessive oxidative damage within the organelle,” said Edward Fon, Professor at the McGill Parkinson Program at the Montreal Neurological Institute and Hospital. “Our study reveals a quality control mechanism where vesicles bud off from mitochondria and proceed to the lysosome for degradation. This method is distinct from the degradation pathway for damaged whole mitochondria which has been known for some time. It is also an early response, proceeding on a timescale of hours instead of days.”
The deterioration of mechanisms designed to maintain the integrity and function of mitochondria throughout the lifetime of a cell has been suggested to underlie the progression of several neurodegenerative diseases, including Parkinson’s disease. When mitochondria, the “power plants” of the cell that provide energy, malfunction they can contribute to Parkinson’s disease. If they are to survive and function mitochondria need to degrade oxidized and damaged proteins.
In the study, immunofluorescence and confocal microscopy were used to observe how the vesicles “pinch off” from mitochondria with their damaged cargo. “Our conclusion is that the loss of this PINK1 and parkin-dependent trafficking system impairs the ability of mitochondria to selectively degrade oxidized and damaged proteins and leads, over time, to the mitochondrial dysfunction noted in hereditary Parkinson’s disease,” said Heidi McBride, Professor in the Neuromuscular Group in the Department of Neurology and Neurosurgery at the Montreal Neurological Institute and Hospital.
Both salvage pathways are operational in the cell. If the vesicular pathway, the first line of defense, is overwhelmed and the damage is irreversible then the entire organelle is targeted for degradation.
(Source: embo.org)