The researchers showed that rolipram activates the brain’s garbage disposal system, eliminating excess tau proteins (glowing red dots).Columbia University Medical Center
Several neurological disorders, such as Alzheimer’s disease, are characterized by proteins that accumulate in the brain. One protein, called tau, clumps into twisted threads known as tangles. These are a hallmark of Alzheimer’s disease and several other neurodegenerative disorders known as tauopathies.
Our cells have a waste disposal system that works like a combination garbage disposal and recycler. The system, called a proteasome, is a hollow, cylindrical structure that breaks down defective proteins into smaller pieces. The pieces can then be recycled into new proteins needed by the cell.
A research team led by Dr. Karen E. Duff at Columbia University set out to assess whether abnormal tau buildup might be due to defects in proteasome function. The study was supported by NIH’s National Institute of Neurological Disorders and Stroke (NINDS) and National Institute of General Medical Sciences (NIGMS). Results appeared in the January 2016 issue of Nature Medicine.
The researchers used a genetically engineered mouse model of tauopathy. The mice accumulate tau and develop cognitive deficits. The team found that tau accumulation was associated with decreased proteasome activity. Using a cell culture model, they determined that tau aggregates impair proteasome function.
Proteasome function is activated by a pathway involving protein kinase A and cyclic AMP (cAMP). The scientists hypothesized that activating this pathway might increase proteasome function.
When the genetically engineered mice were given a drug that increases cAMP levels (rolipram), they showed increased proteasome function, reduced aggregated tau levels, and improved cognitive performance. The drug was effective in the early stages of degeneration, but not in the later stages of tauopathy. It had no effect on normal healthy mice.
“These results show, for the first time, that you can activate the proteasome in the brain using a drug and effectively slow down the disease, or prevent it from taking a hold,” Duff says. “The proteasome system we are studying also degrades proteins associated with a number of other neurodegenerative diseases such as Parkinson’s, Huntington’s, frontotemporal degeneration, and amyotrophic lateral sclerosis. We may be able to apply these findings to other disorders that accumulate proteins.”
The researchers plan to search libraries of FDA-approved drugs or new molecules for compounds that work more efficiently than rolipram or activate proteasomes by different pathways.