Parkinson’s Patients May Want to Limit Protein Intake

BALTIMORE, MD – Scientists may have discovered how the most common genetic cause of Parkinson’s disease destroys brain cells and devastates many patients worldwide. The study was partially funded by the National Institutes of Health’s National Institute of Neurological Disorders and Stroke; the results may help scientists develop new therapies.

National Institutes of Health - National Institute of Neurological Disorders and Stroke

“This may be a major discovery for Parkinson’s disease patients,” said Ted Dawson, M.D., Ph.D., director of the Johns Hopkins University Morris K. Udall Center of Excellence for Parkinson’s Disease, Baltimore, MD. Dr. Dawson and his wife Valina Dawson, Ph.D., director of the Johns Hopkins University Stem Cell and Neurodegeneration Programs at the Institute for Cell Engineering, led the study published in Cell.

John Hopkins University

The investigators found that mutations in a gene called leucine-rich repeat kinase 2 (LRRK2; pronounced “lark two” or “lurk two”) may increase the rate at which LRRK2 tags ribosomal proteins, which are key components of protein-making machinery inside cells. This could cause the machinery to manufacture too many proteins, leading to cell death.

“For nearly a decade, scientists have been trying to figure out how mutations in LRRK2 cause Parkinson’s disease,” said Margaret Sutherland, Ph.D., a program director at National Institute of Neurological Disorders and Stroke. “This study represents a clear link between LRRK2 and a pathogenic mechanism linked to Parkinson’s disease.”

Affecting more than half a million people in the United States, Parkinson’s disease is a degenerative disorder that attacks nerve cells in many parts of the nervous system, most notably in a brain region called the substantia nigra, which releases dopamine, a chemical messenger important for movement. Initially, Parkinson’s disease causes uncontrolled movements; including trembling of the hands, arms, or legs. As the disease gradually worsens, patients lose ability to walk, talk or complete simple tasks.

For the majority of cases of Parkinson’s disease, a cause remains unknown. Mutations in the LRRK2 gene are a leading genetic cause. They have been implicated in as many as 10 percent of inherited forms of the disease and in about 4 percent of patients who have no family history. One study showed that the most common LRRK2 mutation, called G2019S, may be the cause of 30-40 percent of all Parkinson’s cases in people of North African Arabic descent.

LRRK2 is a kinase enzyme, a type of protein found in cells that tags molecules with chemicals called phosphate groups. The process of phosphorylation helps regulate basic nerve cell function and health. Previous studies suggest that disease-causing mutations, like the G2019S mutation, increase the rate at which LRRK2 tags molecules. Identifying the molecules that LRRK2 tags provides clues as to how nerve cells may die during Parkinson’s disease.

In this study, the researchers used LRRK2 as bait to fish out the proteins that it normally tags. Multiple experiments performed on human kidney cells suggested that LRRK2 tags ribosomal proteins. These proteins combine with other molecules, called ribonucleic acids, to form ribosomes, which are the cell’s protein-making factories.

Further experiments suggested that disease-causing mutations in LRRK2 increase the rate at which it tags two ribosomal proteins, called s11 and s15. Moreover, brain tissue samples from patients with LRRK2 mutations had greater levels of phosphorylated s15 than seen in controls.

Next, the researchers investigated whether phosphorylation could be linked to cell death, by studying nerve cells derived from rats or from human embryonic stem cells. Genetically engineering the cells to have a LRRK2 mutant gene increased the amount of cell death and phosphorylated s15. In contrast, the researchers prevented cell death when they engineered the cells to also make a mutant s15 protein that could not be tagged by LRRK2.

“These results suggest that s15 ribosome protein may play a critical role in the development of Parkinson’s disease,” said Dr. Dawson.

How might phosphorylation of s15 kill nerve cells? To investigate this, Dr. Dawson and his colleagues performed experiments on fruit flies.

Previous studies on flies showed that genetically engineering dopamine-releasing nerve cells to overproduce the LRRK2 mutant protein induced nerve cell damage and movement disorders. Dr. Dawson’s team found that the brains of these flies had increased levels of phosphorylated s15 and that engineering the flies so that s15 could not be tagged by LRRK2 prevented cell damage and restored normal movement.

Interestingly, the brains of the LRRK2 mutant flies also had abnormally high levels of all proteins, suggesting that increased s15 tagging caused ribosomes to make too much protein. Treating the flies with low doses of anisomycin, a drug that blocks protein production, prevented nerve cell damage and restored the flies’ movement even though levels of s15 phosphorylation remained high.

“Our results support the idea that changes in the way cells make proteins might be a common cause of Parkinson’s disease and possibly other neurodegenerative disorders,” said Dr. Dawson.

Dr. Dawson and his colleagues think that blocking the phosphorylation of s15 ribosomal proteins could lead to future therapies as might other strategies which decrease bulk protein synthesis or increase the cells’ ability to cope with increased protein metabolism. They also think that a means to measure s15 phosphorylation could also act as a biomarker of LRRK2 activity in treatment trials of LRRK2 inhibitors.

- MFP Wire Services
- 4/19/14

Lactate Metabolism Target Slows Growth in Lung Cancer Model

BOSTON, MA – Cancer cells generate energy differently than normal cells, a characteristic that helps them to survive and metastasize. A major goal in the field of cancer metabolism is to find ways to overcome this survival advantage.

Now a research team led by investigators in the Cancer Center at Beth Israel Deaconess Medical Center has found that targeting the enzyme responsible for the final step of glucose metabolism not only halts tumor growth in non-small-cell lung cancer, but actually leads to the regression of established tumors.

Beth Israel Deaconess Medical Center

Importantly, the new findings, which appear in the journal Cell Metabolism, also show that cancer initiating cells –tumor cells that possess stem-cell like characteristics which can give rise to new tumors – are susceptible to LDH-A inhibition.

“We’ve known for almost 100 years that increased lactate production is associated with aggressive tumors,” says the study’s senior author Pankaj Seth, PhD, an investigator in the Division of Interdisciplinary Medicine and Biotechnology at Beth Israel Deaconess Medical Center and Assistant Professor of Medicine at Harvard Medical School. “So our team had a straightforward question: If you were to inhibit the production of lactate, what would happen? And we found that not only did tumors stop growing, they actually regressed. Most exciting, we also showed that inhibition of LDH-A impacts cancer initiating cells, a population of aggressive tumor cells not targeted by most current therapies.”

Altered energy metabolism is a defining biochemical characteristic of cancer cells, and was first observed nearly a century ago by German scientist Otto Warburg in what has now become known as the “Warburg Effect.” While normal cells usually produce most of their energy needs from burning fuels using oxygen, cancer’s energy production is dependent on sugar or glucose, a process known as fermentative glycolysis.

“Cancer cells rely on anaerobic fermentation for the conversion of glucose to lactate,” explains Seth. “This state of fermentative glycolysis is catalyzed by the A form of the LDH enzyme. LDH-A is elevated in cancer cells, and this enables tumor cells to convert the majority of their glucose stores into lactate, regardless of oxygen availability. This shifts the function of glucose metabolites from simple energy production to accelerated cell growth and replication.” For this reason, he explains, LDH-A and the possibility of inhibiting its activity has been identified as a promising target in cancer treatments focused on preventing cancer cells from proliferating.

Non-small cell lung cancer is highly glycolytic, accounts for more than 85 percent of all lung cancers and is the leading cause of cancer deaths. Fermentative glycolysis is promoted in Non-small cell lung cancer through oncogenic mutations in two critical proteins, K-RAS and EGFR. The investigators, therefore, created inducible LDH-A mouse models of non-small cell lung cancer expressing oncogenic K-RAS and EGFR.

“We wanted an established tumor so that we could ascertain how much LDH-A inhibition was needed,” says Seth. By genetically adjusting LDH-A levels and comparing the results with that of a small molecule inhibitor, the team showed that when LDH-A was inhibited, not only did the tumors stop growing, they actually regressed in size from the point they were before LDH-A inhibition.

Next, the investigators obtained a small molecule LDH-A inhibitor drug and observed similar effects in cell culture experiments. These results further demonstrated that blocking fermentative glycolysis impacted cancer initiating cells, the small population of tumor-forming, self-renewing cancer cells associated with aggressive disease and poor prognosis.

To investigate the metabolic consequences of LDH-A inhibition, Seth collaborated with co-corresponding author Teresa Fan, PhD, of the University of Kentucky. They conducted a metabolic analysis in which glucose atoms labeled with the stable isotope of carbon were followed as the glucose was converted through the glycolytic pathway into a variety of products. These experiments were carried out in cultured lung cancer cells in the mouse model and in thin slices of human lung tumor tissue.

“The latter is a modern version of Warburg’s original experiment,” explains Seth. “Together, these experiments showed that LDH-A inhibition affects metabolism, as expected, and underlies the regression of tumors when there is insufficient enzyme to support growth and survival.”

“The field of cancer metabolism has seen a resurgence in recent years,” adds study coauthor Vikas P. Sukhatme, MD, PhD, Beth Israel Deaconess Medical Center Chief Academic Officer and Victor J. Aresty Professor of Medicine at Harvard Medical School. “Findings such as these, conducted in genetically engineered mouse models that are the gold standard by which to judge this data, offer hope that drugs targeting metabolic pathways may one day become part of our armamentarium against this dreadful disease.”

- MFP News Services
- 4/19/14

New Insights On How Bird Flu Virus Spreads May Prevent Pandemics

The H5N1 bird flu virus has infected and killed hundreds of people, despite the fact that, at the moment, the virus can’t spread easily between people. The death toll could become much worse if the virus became airborne. A study published recently by Cell Press in the journal Cell has revealed a minimal set of mutations allowing H5N1 to be transmitted through the air from one ferret to another. The findings will be invaluable for future surveillance programs and may provide early warning signals of the emergence of potential pandemic strains.

“By gaining fundamental knowledge about how the influenza virus adapts to mammals and becomes airborne, we may ultimately be able to identify viruses that pose a public health risk among the large number of influenza viruses that are circulating in animals,” says senior study author Ron Fouchier of Erasmus Medical Center. “If we can do this, we might be able to prevent some pandemics in the future.”

Erasmus Medical Center

The H5N1 virus has caused serious outbreaks in domestic poultry in Asia and the Middle East and has infected people in 15 countries. The virus must be transmissible through air for a pandemic to occur, and Fouchier and his colleagues previously identified several H5N1 mutations linked to airborne transmission through aerosol or respiratory droplets. But, until now, the minimal set of mutations required for airborne transmission was not clear, hindering the ability of scientists to predict and prepare for pandemics.

In the new study, the researchers identified five mutations that are sufficient for airborne transmission of H5N1 between ferrets—one of the best models of influenza transmissibility available today. Two mutations improved the binding of the virus to cells in the upper respiratory tract of mammals; two other mutations enabled the virus to replicate more efficiently; and the remaining mutation increased the stability of the virus.

“This type of analysis provides a more complete picture of the changes that may constitute increased risk of H5N1 transmissibility,” says Peter Palese of the Icahn School of Medicine at Mount Sinai, who coauthored an Essay accompanying the research paper. “Assessment of how adaptations in ferrets affect viral fitness, virulence, and transmission is sorely needed in order to gain a truly holistic perspective of the likelihood that these viruses might cause a pandemic and what characteristics such a pandemic might exhibit.”

- MFP News Service
- 4/18/14