Alcoholism Appears to Saps Muscle Strength

Muscle weakness is a common symptom of both long-time alcoholics and patients with mitochondrial disease. Now researchers have found a common link: mitochondria that are unable to self-repair. The results were recently published online in The Journal of Cell Biology. The link to self-repair provides researchers both a new way to diagnose mitochondrial disease, and a new drug target.

Journal of Cell Biology

Mitochondria repair their broken components by fusing with other mitochondria and exchanging their contents. Damaged parts are segregated for recycling and replaced with properly functioning proteins donated from healthy mitochondria.

While fusion is one major method for mitochondrial quality control in many types of cells, researchers have puzzled over the repair mechanism in skeletal muscle — a type of tissue that relies constantly on mitochondria for power, making repair a frequent necessity. However, mitochondria are squeezed so tightly in between the packed fibers of muscle cells, that most researchers assumed that fusion among mitochondria in this tissue type was impossible.

An inkling that fusion might be important for the normal muscle function came from research on two mitochondrial diseases: Autosomal Dominant Optical Atropy disease, and a type of Charcot-Marie-Tooth disease. A symptom of both disease is muscle weakness and patients with both these diseases carry a mutation in one of the three genes involved in mitochondrial fusion.

To investigate whether mitochondria in the muscle could indeed fuse to regenerate, first author Veronica Eisner, Ph.D., a postdoctoral fellow at Thomas Jefferson University created a system to tag the mitochondria in skeletal muscle of rats with two different colors and then watch if they mingled. First, she created a rat model whose mitochondria expressed the color red at all times. She also genetically engineered the mitochondria in the cells to turn green when zapped with a laser, creating squares of green-shining mitochondria within the red background. To her surprise, the green mitochondria not only mingled with the red, exchanging contents, but were also able to travel to other areas where only red-colored mitochondria had been. The results were exciting in that they showed “for the first time that mitochondrial fusion occurs in muscle cells,” says Dr. Eisner.

The researcher team, led by Dr. Gyorgy Hajnoczky, M.D., Ph.D., Director of Jefferson’s MitoCare Center and professor in the department of Pathology, Anatomy & Cell Biology, then showed that of the mitofusin fusion proteins, Mfn1 was most important in skeletal muscle cells.

Once they had identified Mfn1, they were able to test whether mitochondrial fusion was the culprit in other examples of muscle weakness, such as alcoholism. One long-term symptom of alcoholism is the loss of muscle strength. The researchers showed that the Mfn1 abundance went down as much as 50 percent in rats on a regular alcohol diet-while other fusion proteins were unchanged, and that this decrease was coupled with a massive decrease in mitochondrial fusion. When Mfn1 was restored, so was the mitochondrial fusion. They also linked the decreased Mfn1 and mitochondrial fusion to increased muscle fatigue.

“That alcohol can have a specific effect on this one gene involved in mitochondrial fusion suggests that other environmental factors may also specifically alter mitochondrial fusion and repair,” says Dr. Hajnoczky.

“The work provides more evidence to support the concept that fission and fusion — or mitochondrial dynamics — may be responsible for more than just a subset of mitochondrial diseases we know of,” says Dr. Hajnoczky. “In addition, knowing the proteins involved in the process gives us the possibility of developing a drug.”

- MFP News Services
- 4/22/14

Researchers Discover Influenza May Have a Major Flaw

Flu epidemics cause up to half a million deaths worldwide each year, and emerging strains continually threaten to spread to humans and cause even deadlier pandemics. A study published by Cell Press on April 10 in the journal Immunity reveals that a drug that inhibits a molecule called prostaglandin E2 increases survival rates in mice infected with a lethal dose of the H1N1 flu virus. The findings pave the way for an urgently needed therapy that is highly effective against the flu virus and potentially other viral infections.

“Drugs that specifically target prostaglandin E2 pathways have already been developed and tested in animals, so our results have excellent potential for clinical translation, not only for the treatment of influenza, but also other viral respiratory infections that interact with similar host immune pathways,” says senior study author Maziar Divangahi of McGill University.

McGill University Health Centre

Despite the worldwide use of vaccination and other antiviral interventions, the flu virus remains a persistent threat to human health. To investigate molecular pathways that could be targeted by novel interventions, Divangahi and his team became interested in ibuprofen, which is commonly used to manage flu-like symptoms. By inhibiting a molecule called cyclooxygenase (COX), ibuprofen and other nonsteroidal anti-inflammatory drugs (NSAIDs) lower the production of prostaglandins—immune molecules that contribute to pain and fever. But COX inhibition has produced conflicting effects on immune responses and survival rates in animals infected with the flu virus, highlighting the importance of clarifying the role of prostaglandins in antiviral immunity.

In the new study, Divangahi and his team found that mice genetically engineered to lack prostaglandin E2 showed enhanced immune responses, lower viral levels in the lungs, and better survival rates following infection with a lethal dose of the H1N1 flu virus compared with infected mice that were not genetically modified. Similarly, mice treated with a compound that inhibits prostaglandin E2 showed enhanced antiviral immunity and survival rates following infection with a lethal dose of the flu virus compared with untreated mice.

“We believe that previous studies produced conflicting results because COX inhibition affects all prostaglandins, not just prostaglandin E2,” Divangahi says. “Our findings suggest that different prostaglandins have different roles in antiviral immunity and that specific inhibition of prostaglandin E2 will be much more effective than NSAIDs at protecting against influenza infection.”

- MFP News Services
- 4/21/14

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