Larry H Bernstein, MD, FCAP, Curator
http://pharmaceuticalintelligence/7/8/2014/Proteins and cellular adaptation to stress
There are two recent articles that are, if not interesting, possibly important in the direction of cellular regulation, adaptation, and decline. One deals with apoptosis, or cell death, which is synchronized with recovery of membrane and protein breakdown for reuse in synthesis and maintenance. The other is a new perspective to Alzhemier’s Disease, for which there is no effective pharmacotherapy. In both cases, the stresses of the cell are critical to the responce to the environment. This is not just about the classical transcriptomics story. This is a perfect followup to the just posted research on the regulatory role of a small RNA that is related to, but distinct from silencing RNA, and also the revelations about lncRNA.
Protein Helps Cells Adapt—or Die
Scientists show how cell stress both prevents and promotes cell suicide in a study that’s equally divisive.
By Ruth Williams | July 3, 2014
A cellular stress pathway called the unfolded-protein-response (UPR) both activates and degrades death receptor 5 protein (DR5), which can promote or prevent cell suicide, according to a paper published in Science today (July 3). The theory is that initial stress blocks cell suicide, or apoptosis, to give the cell a chance to adapt, but that if the stress persists, it eventually triggers apoptosis.
“This work has made the most beautiful simplification of all this big complex mess. Basically, they identified and pinpointed the specific protein involved in the switching decision and explain how the decision is made,” said Alexei Korennykh, a professor of molecular biology at Princeton University, who was not involved in the work.
But Randal Kaufman of the Sanford-Burnham Medical Research Institute in La Jolla, California, was not impressed. He questioned the physiological relevance of the experiments supporting the authors’ main conclusions about this key cellular process.
Protein folding in a cell takes place largely in the endoplasmic reticulum (ER), but if the process goes awry, unfolded proteins accumulate, stressing the ER. This triggers the UPR, which shuts down translation, degrades unfolded proteins, and increases production of protein-folding machinery. If ER stress is not resolved, however, the UPR can also induce apoptosis.
Two main factors control the UPR—IRE1a and PERK. IRE1a promotes cell survival by activating the transcription factor XBP1, which drives expression of cell-survival genes. PERK, on the other hand, activates a transcription factor called CHOP, which in turn drives expression of the proapoptotic factor DR5.
Peter Walter of the University of California, San Francisco, and his colleagues have now confirmed that CHOP activates DR5, showing that it is a cell-autonomous process. But they have also found that IRE1a suppresses DR5, directly degrading its mRNA through a process called regulated IRE1a-dependent degradation (RIDD). Inhibition of IRE1a in a human cancer cell line undergoing ER stress both prevented DR5 mRNA decay and increased apoptosis.
However, in an e-mail to The Scientist, Kaufman expressed concern that “the significance of RIDD has not been demonstrated in a physiologically-relevant context.”
Walter insisted that the evidence for RIDD’s existence is “crystal clear.” His only concession was that “the effects aren’t 100 percent,” he said, because “RIDD degrades mRNA by a few-fold,” making it difficult to measure.
This RIDD debate aside, the researchers have also sparked a rumpus with their finding that IRE1a expression switches off just 24 hours after ER stress initiation, leaving PERK to drive the cell toward apoptosis. “We and others have evidence that suggests another model,” said Scott Oakes, a professor of pathology at the University of California, San Francisco, “which is that both PERK and IRE1a under high stress will send out death signals.”
Whether IRE1a promotes or inhibits apoptosis under extreme stress “is controversial,” said Ira Tabas, a professor at Columbia University in New York City. But it’s essential that scientists figure it out. Cell death from ER stress is a pathological process in many major diseases, Tabas said, and there are IRE1a inhibitors in pharmaceutical development. “It is very important because under high stress you have two different views here,” said Oakes. “One is that you want to keep IRE1a on, the other is that you want to shut it off.”
Because ER stress is central to many diseases, “a lot of people are passionate about it,” said Tabas, explaining the polemic views. “Who’s right? . . . I think it depends on the context in which the experiments are done—one pathway may be important in some settings, and another pathway may be important in different settings,” he suggested. What might help to resolve the issues, he said, will be “in vivo causation studies using actual disease models.”
Researchers will continue to debate. So, said Walter, “we’ll have to see what holds-up five years from now.”
M. Lu et al., “Opposing unfolded-protein-response signals converge on death receptor 5 to control apoptosis,” Science, 345:98-101, 2014.
Tags stress response, protein folding, disease/medicine, cell & molecular biology and apoptosis
Protein May Hold the Key to Who Gets Alzheimer’s
By PAM BELLUCK MARCH 19, 2014
It is one of the big scientific mysteries of Alzheimer’s disease: Why do some people whose brains accumulate the plaques and tangles so strongly associated with Alzheimer’s not develop the disease?
Now, a series of studies by Harvard scientists suggests a possible answer, one that could lead to new treatments if confirmed by other research.
The memory and thinking problems of Alzheimer’s disease and other dementias, which affect an estimated seven million Americans, may be related to a failure in the brain’s stress response system, the new research suggests. If this system is working well, it can protect the brain from abnormal Alzheimer’s proteins; if it gets derailed, critical areas of the brain start degenerating.
“This is an extremely important study,” said Li-Huei Tsai, director of the Picower Institute for Learning and Memory at the Massachusetts Institute of Technology, who was not involved in the research but wrote a commentary accompanying the study. “This is the first study that is really starting to provide a plausible pathway to explain why some people are more vulnerable to Alzheimer’s than other people.”
An image of tau tangles in the brain, often a hallmark of Alzheimer’s disease.
The research, published on Wednesday in the journal Nature, focuses on a protein previously thought to act mostly in the brains of developing fetuses. The scientists found that the protein also appears to protect neurons in healthy older people from aging-related stresses. But in people with Alzheimer’s and other dementias, the protein is sharply depleted in key brain regions.
Experts said if other scientists could replicate and expand upon the findings, the role of the protein, called REST, could spur development of new drugs for dementia, which has so far been virtually impossible to treat. But they cautioned that much more needed to be determined, including whether the decline of REST was a cause, or an effect, of brain deterioration, and whether it was specific enough to neurological diseases that it could lead to effective therapies.
“You’re going to see a lot of papers now following up on it,” said Dr. Eric M. Reiman, executive director of the Banner Alzheimer’s Institute in Phoenix, who was not involved in the study. “While it’s a preliminary finding, it raises an avenue that hasn’t been considered before. And if this provides a handle on which to understand normal brain aging, that will be great, too.”
REST, a regulator that switches off certain genes, is primarily known to keep fetal neurons in an immature state until they develop to perform brain functions, said Dr. Bruce A. Yankner, a professor of genetics at Harvard Medical School and the lead author of the new study. By the time babies are born, REST becomes inactive, he said, except in some areas outside the brain like the colon, where it seems to suppress cancer.
While investigating how different genes in the brain change as people age, Dr. Yankner’s team was startled to find that REST was the most active gene regulator in older brains. The researchers have found that this protein, normally active in fetuses, may also protect the neurons in older people. It is not yet possible to measure the levels of this protein that is a gene regulator called REST, in living people.
“Why should a fetal gene be coming on in an aging brain?” he wondered. He hypothesized that it was because in aging, as in birth, brains encounter great stress, threatening neurons that cannot regenerate if harmed.
His team discovered that REST appears to switch off genes that promote cell death, protecting neurons from normal aging processes like energy decrease, inflammation and oxidative stress.
Analyzing brains from brain banks and dementia studies, the researchers found that brains of young adults ages 20 to 35 contained little REST, while healthy adults between the ages of 73 and 106 had plenty. REST levels grew the older people got, so long as they did not develop dementia, suggesting that REST is related to longevity.
But in people with Alzheimer’s, mild cognitive impairment, frontotemporal dementia and Lewy body dementia, the brain areas affected by these diseases contained much less REST than healthy brains.
This was true only in people who actually had memory and thinking problems. People who remained cognitively healthy, but whose brains had the same accumulation of amyloid plaques and tau tangles as people with Alzheimer’s, had three times more REST than those suffering Alzheimer’s symptoms. About a third of people who have such plaques will not develop Alzheimer’s symptoms, studies show.
REST levels dropped as symptoms worsened, so people with mild cognitive impairment had more REST than Alzheimer’s patients. And only key brain regions were affected. In Alzheimer’s, REST steeply declined in the prefrontal cortex and hippocampus, areas critical to learning, memory and planning. Other areas of the brain not involved in Alzheimer’s showed no REST drop-off.
It is not yet possible to analyze REST levels in the brains of living people, and several Alzheimer’s experts said that fact limited what the new research could prove.
John Hardy, an Alzheimer’s researcher at University College London, cautioned in an email that information from post-mortem brains could not prove that a decline in REST caused dementia because death might produce unrelated damage to brain cells.
To investigate further, the team conducted what both Dr. Tsai and Dr. Reiman called a “tour de force” of research, examining REST in mice, roundworms and cells in the lab.
“We wanted to make sure the story was right,” Dr. Yankner said. “It was difficult to believe at first, to be honest with you.”
Especially persuasive was that mice genetically engineered to lack REST lost neurons as they aged in brain areas afflicted in Alzheimer’s.
Dr. Yankner said REST appeared to work by traveling to a neuron’s nucleus when the brain was stressed. In dementia, though, REST somehow gets diverted, traveling with toxic dementia-related proteins to another part of the neuron where it is eventually destroyed.
Experts said the research, while intriguing, left many unanswered questions. Bradley Wise of the National Institute on Aging’s neuroscience division, which helped finance the studies, said REST’s role needed further clarification. “I don’t think you can really say if it’s a cause of Alzheimer’s or a consequence of Alzheimer’s” yet, he said.
Dr. Samuel E. Gandy, an Alzheimer’s researcher at Mount Sinai Medical Center, wondered if REST figured only in neurodegenerative diseases or in other diseases, too, which could make it difficult to use REST to develop specific treatments or diagnostic tests for dementia.
“My ambivalence is, is this really a way that advances our understanding of the disease or does this just tell us this is even more complicated than we thought?” he said.
Dr. Yankner’s team is looking at REST in other neurological diseases, like Parkinson’s. He also has thoughts about a potential treatment, lithium, which he said appears to stimulate REST function, and is considered relatively safe.
But he and other experts said it was too early. “I would hesitate to start rushing into lithium treatment” unless rigorous studies showed that it could forestall dementia, said Dr. John C. Morris, an Alzheimer’s researcher at Washington University in St. Louis.
Still, Dr. Morris said, the REST research the team conducted so far is “very well done, and certainly helps support this idea that we’ve all tried to understand about why Alzheimer’s is age-associated and why, while amyloid is necessary for the development of Alzheimer’s disease, it certainly is not sufficient.”
He added, “There have to be some other processes and triggers that result in Alzheimer’s.”
Correction: March 19, 2014
Because of an editing error, an earlier version of this article misstated the gender of Dr. Li-Huei Tsai. Dr. Tsai is a woman.
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