Just a few doses of an experimental drug that reboots protein production in cells can reverse age-related declines in memory and mental flexibility in mice, according to a new study by UC San Francisco scientists.
The drug, called ISRIB, has already been shown in laboratory studies to restore memory function months after traumatic brain injury (TBI), reverse cognitive impairments in Down Syndrome, prevent noise-related hearing loss, fight certain types of prostate cancer, and even enhance cognition in healthy animals.
In the new study, published Dec. 1 in the open-access journal eLife, researchers showed rapid restoration of youthful cognitive abilities in aged mice, accompanied by a rejuvenation of brain and immune cells that could help explain improvements in brain function—and with no side effects observed.
“ISRIB’s extremely rapid effects show for the first time that a significant component of age-related cognitive losses may be caused by a kind of reversible physiological “blockage” rather than more permanent degradation,” said Susanna Rosi, PhD, Lewis and Ruth Cozen Chair II and professor in the departments of Neurological Surgery and of Physical Therapy and Rehabilitation Science.
“The data suggest that the aged brain has not permanently lost essential cognitive capacities, as was commonly assumed, but rather that these cognitive resources are still there but have been somehow blocked, trapped by a vicious cycle of cellular stress,” added Peter Walter, PhD, a professor in the UCSF Department of Biochemistry and Biophysics and a Howard Hughes Medical Institute investigator. “Our work with ISRIB demonstrates a way to break that cycle and restore cognitive abilities that had become walled off over time.”
Rebooting cellular protein production holds key to aging
Walter has won numerous scientific awards, including the Breakthrough, Lasker and Shaw prizes, for his decades-long studies of cellular stress responses. ISRIB, discovered in 2013 in Walter’s lab, works by rebooting cells’ protein production machinery after it gets throttled by one of these stress responses – a cellular quality control mechanism called the integrated stress response (ISR; ISRIB stands for ISR InhiBitor).
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The ISR normally detects problems with protein production in a cell—a potential sign of viral infection or cancer-promoting gene mutations—and responds by putting the brakes on cell’s protein-synthesis machinery. This safety mechanism is critical for weeding out misbehaving cells, but if stuck in the ‘on’ position in a tissue like the brain, it can lead to serious problems, as cells lose the ability to perform their normal activities, according to Walter and colleagues.
In particular, their recent animal studies have implicated chronic ISR activation in the persistent cognitive and behavioral deficits seen in patients after TBI, by showing that, in mice, brief ISRIB treatment can reboot the ISR and restore normal brain function almost overnight.
The cognitive deficits in TBI patients are often likened to premature aging, which led Rosi and Walter to wonder if the ISR could also underlie purely age-related cognitive decline. Aging is well known to compromise cellular protein production across the body, as life’s many insults pile up and stressors like chronic inflammation wear away at cells, potentially leading to widespread activation of the ISR.
“We’ve seen how ISRIB restores cognition in animals with traumatic brain injury, which in many ways is like a sped-up version of age-related cognitive decline,” said Rosi, who is director of neurocognitive research in the UCSF Brain and Spinal Injury Center and a member of the UCSF Weill Institute for Neurosciences. “It may seem like a crazy idea, but asking whether the drug could reverse symptoms of aging itself was just a logical next step.”
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Signature effects of aging disappeared literally overnight
In the new study, researchers led by Rosi lab postdoc Karen Krukowski, PhD, trained aged animals to escape from a watery maze by finding a hidden platform, a task that is typically hard for older animals to learn. But animals who received small daily doses of ISRIB during the three-day training process were able to accomplish the task as well as youthful mice—and much better than animals of the same age who didn’t receive the drug.
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