Mouse Study Shows Drug Improves Brain's Garbage Disposal System

A drug called rolipram appears to boost activity in the brain’s “garbage disposal” system, which has been shown to decrease toxic proteins associated with Alzheimer’s disease and other neurodegenerative disorders and improve cognition in mice.

“We have shown for the first time that it’s possible to use a drug to activate this disposal system in neurons and effectively slow down disease,” said study leader Karen E. Duff, Ph.D., professor of pathology and cell biology at Columbia University Medical Center. “This has the potential to open up new avenues of treatment for Alzheimer’s and many other neurodegenerative diseases.”

Rolipram was first developed in the early 1990s as a potential antidepressant, but effective dosage brought with it significant gastrointestinal side effects such as nausea, so it is not a good fit for use in humans. But similar drugs that do not induce nausea could go into clinical trials very quickly, according to the researchers.

To remain healthy, brain cells must continually clear out old, worn, or damaged proteins, a task performed by a small molecular cylinder called the proteasome. The proteasome acts as a kind of garbage disposal, grinding up the old proteins so they can be recycled into new ones. In neurodegenerative diseases, proteins tagged for destruction accumulate in the brain’s neurons, suggesting that the cell’s proteasomes are impaired.

In the mouse study, the researchers first discovered that tau — a toxic protein that accumulates in Alzheimer’s and other brain degenerative diseases — sticks to the proteasome and slows down the protein disposal process.

Administering rolipram activated the proteasome and restored protein disposal to normal levels, according to the study’s findings. The drug also improved the memory of diseased mice to levels seen in healthy mice.

Rolipram has been tested before in mice and was shown to improve memory, but the mechanism for how this occurred was unclear. The new research shows that by inhibiting of the PDE-4 enzyme, rolipram produces a physical change in the proteasome that increases its activity, the researchers explained.

“We still don’t know exactly where the activation is happening, but what’s new is that we can modify the proteasome to increase its activity. There could be many other ways to do this,” said the study’s first author, Natura Myeku, Ph.D., an associate research scientist in pathology and cell biology at Columbia University Medical Center.

Drugs that target proteasomes in this way should work for any disease caused by the accumulation of abnormal proteins, including Alzheimer’s, Huntington’s, Parkinson’s, and frontotemperoral dementia, the researchers added.

“Treatments that speed up these cell disposal mechanisms should, in theory, only degrade abnormal proteins. We don’t need to know what the toxic form of the protein is,” Duff said. “In Alzheimer’s disease, there are at least four different types: amyloid, tau, alpha-synuclein, and TDP43. A well-functioning proteasome can clear out everything at once.”

The study was published in Nature Medicine.

Source: Columbia University Medical Center