SEOUL, November 05 (AJP) - A protein best known for switching genes on and off can latch onto the sticky protein behind Alzheimer's disease and steer it into less harmful clumps, a South Korean research team led by KAIST said Thursday.
In mice bred to develop Alzheimer's-like brain damage, an engineered version of the protein cut amyloid beta deposits in the cortex and hippocampus by about 53 percent compared with untreated animals. It also calmed signs of inflammation in the brain and improved one measure of memory.
Amyloid beta is a small protein that clumps abnormally in the brains of Alzheimer's patients and piles up as plaque. Along the way it forms toxic aggregates that can damage nerve cells. Most strategies aim to stop the clumping or clear away what has built up. This team instead changed the path the protein takes as it clumps.
The work was led by Lim Mi-hee, a professor in KAIST's Department of Chemistry, with teams from Jeonbuk National University, the Korea Research Institute of Bioscience and Biotechnology, the Korea Basic Science Institute and the Institute for Basic Science.
Their tool was a zinc finger protein. Zinc fingers are small protein folds held in shape by a zinc ion, and cells use them mainly to grip DNA or RNA and control which genes are active. Artificial versions are already used in biotechnology to target specific genes.
The researchers reasoned that the same folded surface could grip other proteins as well. They focused on ZF2-4, a run of three linked zinc fingers from PARIS, a protein associated with neurodegenerative conditions.
Computer simulations and laboratory tests showed ZF2-4 binding directly to the parts of amyloid beta that drive fiber formation. The binding appeared in solution, on cell surfaces and in brain tissue from Alzheimer's model mice.
Once bound, amyloid beta stopped growing into the long, tangled fibers linked to toxicity. It formed shapeless clumps instead, which interacted less with cell membranes and did less damage to cells. When the team added ZF2-4 to fibers that had already formed, the long, branching strands broke into short, thin fragments, and their toxicity dropped.
Getting a protein into the brain is hard. The blood-brain barrier, a tight lining of cells along the brain's blood vessels, keeps most substances out, including many drugs. The team attached a small molecule that helps carry cargo across the barrier, creating a version called ZF2-4-P9.
In laboratory barrier tests, ZF2-4-P9 crossed more readily than the original protein. After it was injected into the abdomen of mice, it was detected in their brain tissue.
The researchers then treated APP/PS1 mice, a strain engineered to build up amyloid plaque. Deposits in the cortex and in the hippocampus, a region central to memory and learning, fell by about 53 percent compared with the control group.
Treated mice also showed less overactivation of microglia, the brain's resident immune cells. Microglia protect the brain, but when overactive they can feed inflammation. Their activation fell by about 29 percent in the cortex and about 50 percent in the hippocampus.
In behavior tests, treated mice were better at telling a familiar object from a new one, a measure known as recognition memory. Other memory and learning tests showed no statistically significant improvement.
The team also tested each of the three zinc fingers on its own. Two of them, ZF2 and ZF4, did most of the work. A hairpin-shaped fold in each, along with the amino acid sequence that forms it, determined how strongly the protein redirected amyloid beta.
That finding gives scientists a basis for designing zinc fingers aimed at specific disease proteins. The researchers said they hope to extend the approach to other proteins that clump in neurodegenerative disease, including alpha-synuclein, which is linked to Parkinson's disease, and tau.
"Using this principle could help design new protein-based therapeutics that target specific disease proteins in the future," Lim said.
All of the results come from mice. The team said treatment effects and long-term safety would need further testing before the approach could be tried in people. In materials released with the study, the researchers listed remaining hurdles. These include the protein's stability in the body, how efficiently it reaches the brain and how long it stays there, and the risk of binding to the wrong proteins or provoking an immune response.
The study was published online Sept. 30 in Advanced Science. Its co-first authors were Park Seong-min, a former KAIST postdoctoral researcher now at the Korea Basic Science Institute (KBSI), Hwang Yun-ha, a doctoral student at Jeonbuk National University, and Kwak Ji-min, a student in KAIST's integrated master's and doctoral program.
[Reference Information]
Journal/Source: Advanced Science
Title: Zinc Fingers as Programmable Metalloprotein Scaffolds for Altering Pathogenic Biomolecular Phase Transitions
Link/DOI: 10.1002/advs.77886
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