Experimental Drug Has Potential Against Alzheimer’s Disease

The drug reversed Alzheimer’s in mice through removing garbage from their brain cells. The research seems like a notable milestone against Alzheimer’s disease.

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Researchers at Albert Einstein College of Medicine have designed an experimental drug that reversed key symptoms of Alzheimer’s disease in mice. The drug works by reinvigorating a cellular cleaning mechanism that gets rid of unwanted proteins by digesting and recycling them. The study was published online today in the journal Cell.

“Discoveries in mice don’t always translate to humans, especially in Alzheimer’s disease,” said co-study leader Ana Maria Cuervo, M.D., Ph.D., the Robert and Renée Belfer Chair for the Study of Neurodegenerative Diseases, professor of developmental and molecular biology, and co-director of the Institute for Aging Research at Einstein. “But we were encouraged to find in our study that the drop-off in cellular cleaning that contributes to Alzheimer’s in mice also occurs in people with the disease, suggesting that our drug may also work in humans.” In the 1990s, Dr. Cuervo discovered the existence of this cell-cleaning process, known as chaperone-mediated autophagy (CMA) and has published 200 papers on its role in health and disease.

CMA becomes less efficient as people age, increasing the risk that unwanted proteins will accumulate into insoluble clumps that damage cells. In fact, Alzheimer’s and all other neurodegenerative diseases are characterized by the presence of toxic protein aggregates in patients’ brains. The Cell paper reveals a dynamic interplay between CMA and Alzheimer’s disease, with loss of CMA in neurons contributing to Alzheimer’s and vice versa. The findings suggest that drugs for revving up CMA may offer hope for treating neurodegenerative diseases.

Establishing CMA’s Link to Alzheimer’s

Dr. Cuervo’s team first looked at whether impaired CMA contributes to Alzheimer’s. To do so, they genetically engineered a mouse to have excitatory brain neurons that lacked CMA. The absence of CMA in one type of brain cell was enough to cause short-term memory loss, impaired walking, and other problems often found in rodent models of Alzheimer’s disease. In addition, the absence of CMA profoundly disrupted proteostasis — the cells’ ability to regulate the proteins they contain. Normally soluble proteins had shifted to being insoluble and at risk for clumping into toxic aggregates.

Dr. Cuervo suspected the converse was also true: that early Alzheimer’s impairs CMA. So she and her colleagues studied a mouse model of early Alzheimer’s in which brain neurons were made to produce defective copies of the protein tau. Evidence indicates that abnormal copies of tau clump together to form neurofibrillary tangles that contribute to Alzheimer’s. The research team focused on CMA activity within neurons of the hippocampus — the brain region crucial for memory and learning. They found that CMA activity in those neurons was significantly reduced compared to control animals.

What about early Alzheimer’s in people — does it block CMA too? To find out, the researchers looked at single-cell RNA-sequencing data from neurons obtained postmortem from the brains of Alzheimer’s patients and from a comparison group of healthy individuals. The sequencing data revealed CMA’s activity level in patients’ brain tissue. Sure enough, CMA activity was somewhat inhibited in people who had been in the early stages of Alzheimer’s, followed by much greater CMA inhibition in the brains of people with advanced Alzheimer’s.

“By the time people reach the age of 70 or 80, CMA activity has usually decreased by about 30% compared to when they were younger,” said Dr. Cuervo. “Most peoples’ brains can compensate for this decline. But if you add neurodegenerative disease to the mix, the effect on the normal protein makeup of brain neurons can be devastating. Our study shows that CMA deficiency interacts synergistically with Alzheimer’s pathology to greatly accelerate disease progression.”

A New Drug Cleans Neurons and Reverses Symptoms

In an encouraging finding, Dr. Cuervo and her team developed a novel drug that shows potential for treating Alzheimer’s. “We know that CMA is capable of digesting defective tau and other proteins,” said Dr. Cuervo. “But the sheer amount of defective protein in Alzheimer’s and other neurodegenerative diseases overwhelms CMA and essentially cripples it. Our drug revitalizes CMA efficiency by boosting levels of a key CMA component.”

In CMA, proteins called chaperones bind to damaged or defective proteins in cells of the body. The chaperones ferry their cargo to the cells’ lysosomes — membrane-bound organelles filled with enzymes, which digest and recycle waste material. To successfully get their cargo into lysosomes, however, chaperones must first “dock” the material onto a protein receptor called LAMP2A that sprouts from the membranes of lysosomes. The more LAMP2A receptors on lysosomes, the greater the level of CMA activity possible. The new drug, called CA, works by increasing the number of those LAMP2A receptors.

“You produce the same amount of LAMP2A receptors throughout life,” said Dr. Cuervo. “But those receptors deteriorate more quickly as you age, so older people tend to have less of them available for delivering unwanted proteins into lysosomes. CA restores LAMP2A to youthful levels, enabling CMA to get rid of tau and other defective proteins so they can’t form those toxic protein clumps.” (Also this month, Dr. Cuervo’s team reported in Nature Communications that, for the first time, they had isolated lysosomes from the brains of Alzheimer’s disease patients and observed that reduction in the number of LAMP2 receptors causes loss of CMA in humans, just as it does in animal models of Alzheimer’s.)

The researchers tested CA in two different mouse models of Alzheimer’s disease. In both disease mouse models, oral doses of CA administered over 4 to 6 months led to improvements in memory, depression, and anxiety that made the treated animals resemble or closely resemble healthy, control mice. Walking ability significantly improved in the animal model in which it was a problem. And in brain neurons of both animal models, the drug significantly reduced levels of tau protein and protein clumps compared with untreated animals.

“Importantly, animals in both models were already showing symptoms of disease, and their neurons were clogged with toxic proteins before the drugs were administered,” said Dr. Cuervo. “This means that the drug may help preserve neuron function even in the later stages of disease. We were also very excited that the drug significantly reduced gliosis — the inflammation and scarring of cells surrounding brain neurons. Gliosis is associated with toxic proteins and is known to play a major role in perpetuating and worsening neurodegenerative diseases.”

Treatment with CA did not appear to harm other organs even when given daily for extended periods of time. The drug was designed by Evripidis Gavathiotis, Ph.D.,, professor of biochemistry and of medicine and a co-leader of the study.

Drs. Cuervo and Gavathiotis have teamed up with Life Biosciences of Boston, Mass., to found Selphagy Therapeutics, which is currently developing CA and related compounds for treating Alzheimer’s and other neurodegenerative diseases.

The study is titled, “Chaperone-mediated autophagy prevents collapse of the neuronal metastable proteome.” The study’s other co-leader and first author is Mathieu Bourdenx, Ph.D., a postdoctoral fellow in Dr. Cuervo’s lab and also a junior researcher at the Institute of Neurodegenerative Diseases, University of Bordeaux, France. Additional Einstein authors include: Adrián Martín-Segura, Aurora Scrivo, Susmita Kaushik, Ph.D., Inmaculada Tasset, Ph.D., Antonio Diaz and Yves R. Juste.

Experimental Drug Quickly Reduces Age-Related Mental Decline

The compound, known as ISRIB, holds potential for reversing numerous cognitive problems in humans. Mice are used in scientific studies due to having genes that are approximately 85 percent similar to the genes of humans.

Just a few doses of an experimental drug 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 December 1, 2020 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.

“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.”

Could Rebooting Cellular Protein Production Hold the Key to Aging and Other Diseases?

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).

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, Walter and colleagues have found.

In particular, recent animal studies by Walter and Rosi, made possible by early philanthropic support from The Rogers Family Foundation, 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.”

ISRIB Improves Cognition, Boosts Neuron and Immune Cell Function

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, much better than animals of the same age who didn’t receive the drug.

The researchers then tested how long this cognitive rejuvenation lasted and whether it could generalize to other cognitive skills. Several weeks after the initial ISRIB treatment, they trained the same mice to find their way out of a maze whose exit changed daily — a test of mental flexibility for aged mice who, like humans, tend to get increasingly stuck in their ways. The mice who had received brief ISRIB treatment three weeks before still performed at youthful levels, while untreated mice continued to struggle.

To understand how ISRIB might be improving brain function, the researchers studied the activity and anatomy of cells in the hippocampus, a brain region with a key role in learning and memory, just one day after giving animals a single dose of ISRIB. They found that common signatures of neuronal aging disappeared literally overnight: neurons’ electrical activity became more sprightly and responsive to stimulation, and cells showed more robust connectivity with cells around them while also showing an ability to form stable connections with one another usually only seen in younger mice.

The researchers are continuing to study exactly how the ISR disrupts cognition in aging and other conditions and to understand how long ISRIB’s cognitive benefits may last. Among other puzzles raised by the new findings is the discovery that ISRIB also alters the function of the immune system’s T cells, which also are prone to age-related dysfunction. The findings suggest another path by which the drug could be improving cognition in aged animals, and could have implications for diseases from Alzheimer’s to diabetes that have been linked to heightened inflammation caused by an aging immune system.

“This was very exciting to me because we know that aging has a profound and persistent effect on T cells and that these changes can affect brain function in the hippocampus,” said Rosi. “At the moment, this is just an interesting observation, but it gives us a very exciting set of biological puzzles to solve.

ISRIB May Have Wide-Ranging Implications for Neurological Disease

It turns out that chronic ISR activation and resulting blockage of cellular protein production may play a role in a surprisingly wide array of neurological conditions. Below is a partial list of these conditions, based on a recent review by Walter and colleague Mauro Costa-Mattioli of Baylor College of Medicine, which could potentially be treated with an ISR-resetting agent like ISRIB:

  • Frontotemporal Dementia
  • Alzheimer’s Disease
  • Amyotrophic Lateral Sclerosis (ALS)
  • Age-related Cognitive Decline
  • Multiple Sclerosis
  • Traumatic Brain Injury
  • Parkinson’s Disease
  • Down Syndrome
  • Vanishing White Matter Disorder
  • Prion Disease

ISRIB has been licensed by Calico, a South San Francisco, Calif. company exploring the biology of aging, and the idea of targeting the ISR to treat disease has been picked up by other pharmaceutical companies, Walter says.

One might think that interfering with the ISR, a critical cellular safety mechanism, would be sure to have serious side effects, but so far in all their studies, the researchers have observed none. This is likely due to two factors, Walter says. First, it takes just a few doses of ISRIB to reset unhealthy, chronic ISR activation back to a healthier state, after which it can still respond normally to problems in individual cells. Second, ISRIB has virtually no effect when applied to cells actively employing the ISR in its most powerful form — against an aggressive viral infection, for example.

Naturally, both of these factors make the molecule much less likely to have negative side effects — and more attractive as a potential therapeutic. According to Walter: “It almost seems too good to be true, but with ISRIB we seem to have hit a sweet spot for manipulating the ISR with an ideal therapeutic window.