Worms Offer Clue to Long Life

and Good Health. Who would have thought?

Matt Gill, Ph.D. Photo courtesy of Scripps, by James McEntee

A team of researchers, led by Scripps scientist Matthew Gill, recently identified a new pathway affecting lifespan. Thanks to what they’ve learned from the lowly worm, there may come a time when we humans may enjoy a healthy old age.

Gill, 38, has been working with worms, (Caenorhabditis elegans – nematodes or roundworms) for more than a dozen years and, for three years, studying the molecule, N-Acylethanolamine (NAE) in worms, and how NAEs relate to diet and lifespan.

“Despite the fact that the worm is only a millimeter long, has 959 cells and lives in the soil, actually its biology and physiology are similar to humans,” Gill said. “So, we can learn important lessons from worms that apply to human physiology.”

For example, worms have two-thirds of the genes known to be involved in human diseases, he explained.  “We can look at the worm and try to understand how disease progresses and find therapeutics to address those diseases.”

Two discoveries since the 1980s laid groundwork for possible interventions in the aging process, which, Gill explained, had been considered a difficult prospect since it had so many complex angles.

But then, single gene mutations were discovered in the worm that could double and triple its life span. “Instead of 20 days, it would live 40 days or 60 days,” he said. “This was a major step forward in how we think about aging.”

Then in 1997, came a real breakthrough. “One of those genes was cloned and we found out what the protein was that was being encoded. It turned out to a receptor similar to an insulin receptor that we have in humans.

“This was not just a gene specific to worms, but the same gene affects lifespan across species. Now we have a pathway that seems to be conserved across species that affects lifespan in a profound way.”

Also, researchers had discovered through studying these genes in the worm, fruit fly, yeast and mice, that there are different methods to extend lifespan and one of the most robust ways is through dietary restriction.

For example, if researchers reduced a mouse’s dietary intake, its lifespan was extended and the occurrence of age-related diseases (cancer is a major cause of death in mice) is prevented or delayed.

But, the scientists wanted to know, how do dietary restrictions work and what physiological changes take place that allow the animal to live an extended period of time? Also, many were interested to know whether dietary restrictions extend lifespan in humans.

People are trying to figure that out, too, Gill said. But, in any case, “if we can understand the genes, processes, and pathways involved in making dietary restrictions work in a simple animal, then maybe we can discover key molecules that can act as targets for drug discovery.

“And this leads to the idea put forth by a number of people to discover a calorie restriction mimetic. This would be a drug that would give you the benefits of calorie restriction but without you reducing food intake.

“It’s not about living longer, but delaying the onset of age-related disease.”

So, Gill’s study focuses on the molecules N-acylethanolamnes (NAEs) and endocannabinoids. These signaling molecules act between cells to coordinate a cell’s response to a particular input, and they are involved in response to food. Their levels change when an animal or person has low food or high food, and the molecules can control energy use in animals, “so we thought they would be a good candidate for response in dietary restriction and also, if they were involved in dietary restriction, they may have an impact on lifespan.”

The researchers set out to find these molecules, and they found that the worm has at least 6 NAEs, two of which are similar to endocannobinoids in mammals, and that the levels of these molecules change with food availability.

“When the researchers feed the worms bacteria (its food), the levels of those molecules are high. But when they reduce the levels of food, the NAEs drop down. If they add food back, the levels go back,” he said.

“We saw these molecules are responsive to food.”

“But, if we made an animal that’s deficient in NAEs, we found that the worm was long lived, so there was a correlation between low NAEs and an extended lifespan.”

Then, with one of the worms deficient in NAEs, they added back one of the NAEs, “with exciting results,” he said.

“Just adding one of these molecules back to this worm suddenly shortened its lifespan dramatically. Instead of living 25 or 30 days. Now it was living 15 days.

“Usually with these dietary restrictions, there would be a reduced level of those molecules and that would signal to the animal that food is low, and it needs to change its physiology to use nutrients more efficiently.

“But that one molecule added back in, tricked the worm into thinking it was in an environment where there was plenty of food.”

The worm can manage up to a certain point, but then it reaches a crisis, he said. “ It tries to live its normal lifespan of 25 days, but it crashes and burns. After 15 days, it can’t go any further.

“The implication, in terms of relevance to humans: this is a pretty well known signaling pathway in response to food, but it never had been demonstrated that it had impact an aging.

This study adds another pathway and set of molecules that scientists know are involved in dietary restriction, and, therefore, potentially another target for drug discovery. “If we can manipulate the NAE pathway with a small molecule, then maybe we can find something that will act with one of these dietary restriction mimetics.”

Now, the aim at Scripps is two-fold, he said. “One is to go into more details in the mechanism of how these molecules affect lifespan in a worm, and exactly how they work. Secondly is a discovery angle. NAEs are known to interact with certain receptors in humans but we don’t know the receptors in worms, and if we find these new receptors in the worm, it might lead us to find a new receptor in humans. A new receptor in humans becomes a new target for drug discovery.

“And given the role of these pathways in food sensing, energy balance and aging, there’s a potential in the long term that we can find something that has profound impact on obesity, diabetes, age-related diseases and aging itself.”

Prion Proteins

Corinne Lasmezas, DVM, PhD, and a team of researchers at The Scripps Research Institute’s Department of Infectology, are working to find cures for prion diseases as well as age-related brain disorders. These all are fatal neurodegenerative diseases. Included in this group of neurodegenerative diseases are Alzheimer’s disease, Parkinson’s disease, Huntington’s disease and Fronto-Temporal Dementia.

There are no cures, Lasmezas said. “For Alzheimer’s, there are five FDA-approved drugs, but although they can delay the symptoms, they don’t cure the disease.”

However, the Scripps researchers have identified one blocking neuroprotective compound and four suppressing compounds that hold promise.

In humans, Creutzfeldt-Jakob Disease is a rare prion disease that is inherited, can occur for no known reason or through exposure to contaminated products. Kuru is another prion disease. It was found in young men, women and children in a tribe in Papua New Guinea who ate human brain as part of a funerary rite.

In animals, prion diseases include Mad Cow Disease, scrapie found in sheep and goats, and chronic wasting disease found in deer and elk.

Lasmezas, whose work provided the proof that Mad Cow Disease had been transmitted to humans in 1996, explained that there is a similarity in prion diseases and age-related brain disorders – they have types of proteins that misfold.

“Prion diseases are transmissible, but we didn’t know what the infectious agent causing these diseases was. This was an enigma,” Lasmezas said.

“Usually, we get infectious diseases through bacteria or a virus. Sometimes, diseases are caused by parasites or fungi. But none of these diseases were caused by any of these agents.”

Finally, she explained, scientists found dark plaques in brain matter consisting of fibers made of protein. “The infectious agents turned out to be proteins,” and, hence, they were called prions, (proteinaceous infectious particles). Later, Dr. Charles Weissmann, chair of Scripps Department of Infectology, found that the prion proteins were produced in the cells. But, how, the scientists wanted to know, is it possible that a protein, produced by our cells, can be infectious and harmful?

“Every protein has a shape. When a protein changes its shape, it can’t perform its function and it can become harmful. This is what happens in prion diseases. The protein changes shape (misfolds), induces other proteins to change shape, forms chains and then forms plaque. This process is harmful to the brain.”

When a neuron gets sick, she explained, it retracts its extensions, so it can’t communicate anymore. Its overall metabolism slows down and the neuron accumulates junk, which it tries to contain in little pockets, called vacuoles.

“If at this point, we could intervene, we could revert that fate and go back to having healthy neurons. Otherwise, the neuron loses its extensions; it becomes full of vacuoles and dies. Like prion diseases, in most age-related neurodegenerative diseases, proteins (other than the prion protein) also change shape.”

To understand how these misfolded proteins kill the neurons, Lasmezas’ team engineered a normal protein. “We put them on neurons, and they were fine.  If we cooked the protein for 15 minutes, though, the protein changed its shape and started making a chain (oligomers) and if we put that on neurons, it was very toxic.”

Then, the researchers found a method to produce the toxic protein.

They took healthy neurons and put them in a culture. When a normal form of the protein was added to a culture, nothing happened to the neuron. But when they put the toxic form on the neurons, the neurons lost their extensions, became full of vacuoles and died.

Next, the researchers developed a test to find drugs to prevent neuron death in prion disease and Alzheimer’s disease. “We tested a small collection of compounds and through that test, we found a neuroprotective compound.

“Then we repeated the culture experiment using the toxic prion protein, and the neurons started losing extensions and accumulate vacuoles. But when we added the neuroprotective compound, the neurons started resuming their shape in three hours and in two days they were perfectly happy. They grew back their extensions.

“This showed us that we can find neuroprotective compounds that can block the toxic protein and also revert neurons that were going to die. It was a strong signal of hope that we can find cures for those neurodegenerative diseases.”

To make sure, the researchers adopted a second strategy, based on a finding of Scripps Research scientist Charles Weissmann in 1993, that mice that don’t have the prion protein couldn’t be infected by prion disease. “So the elimination of the prion protein is protective against prion disease,” she explained.

“Recently, a researcher at Yale found that not having prion protein protected against Alzheimer disease. The aggressive form of the Alzheimer’s protein only attacks the neuron with the prion protein. We wanted to verify this finding.

“What we did, we took a cell line that expresses a prion protein at its surface and infected it with the destructive toxic Alzheimer’s protein, and the neurons died.

“Then with neurons without the prion protein, we added the toxic Alzheimer’s protein and nothing happened.”

Lasmezas and Weissmann teamed up to develop a screening test to find drugs that eliminate the prion protein from the neuronal surface to cure prion disease and Alzheimer’s.  “At Scripps, we have a great drug discovery platform led by Peter Hodder. There is a robot that can screen a hundred thousand compounds per day.”

“We did a preliminary screening using a drug collection of 1,280 compounds, followed by a whole battery of tests and ended up finding four compounds that suppress the prion protein.”

The researchers now have one neuroprotective compound and four compounds that suppress prion proteins, and they are actively investigating their therapeutic effect in prion and Alzheimer’s disease models.

Equally important, the researchers also have two high throughput screening tests that can be adapted to screen for other neurodegenerative diseases.

AND AS A SIDE NOTE:

In addition to asking Scripps scientist Corinne Lasmezas about toxic prion proteins, the culprit in Mad Cow Disease, let’s ask her to get to the meat of the matter.

What cuts of beef are ok to eat? Lasmezas, whose work provided the proof that Mad Cow Disease had been transmitted to humans in 1996, said these days, any cut is ok. “It was beef brain that caused the disease (brain used to be in sausages, ground meat and even baby food), but that’s prohibited. Brain is not mixed into foods anymore,” she said.

A type of protein that misfolds like prion protein is also the culprit in Alzheimer’s Disease. So, here’s a second quick question for Lasmezas. Is there anything we can do to guard against getting Alzheimer’s?

A healthy lifestyle reduces the risk, she said. “The brain needs energy and you need to have a healthy cardiovascular system to bring the brain oxygen and nutrients.”

The brain needs exercise, too.

“The more you exercise your brain, you make new networks and increase your cognitive reserve. Exercise does influence how the brain ages.”

In addition, Lasmezas drinks green tea. “It has EGCG in it, which has been found to slightly decrease the production of the Alzheimer’s protein,” she said

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