Neuronal hyperactivity and the gradual loss of neuron function are key features of Alzheimer’s disease. Now researchers led by Li-Huei Tsai, director of MIT’s Picower Institute for Learning and Memory, have identified the cells most susceptible to this damage, suggesting a good target for treatment. Even more exciting, Tsai and her colleagues have found a way to reverse neurodegeneration and other symptoms by interfering with an enzyme that is typically overactive in the brains of Alzheimer’s patients.
In one study, the researchers used single-cell RNA sequencing to distinguish two populations of neurons in the mammillary bodies, a pair of structures in the hypothalamus that play a role in memory and are affected early in the disease. Previous work by Tsai’s lab found that they had the highest density of amyloid beta plaques, abnormal clumps of protein that are thought to cause many Alzheimer’s symptoms.
The researchers found that neurons in the lateral mammillary body showed much more hyperactivity and degeneration than those in the larger medial mamillary body. They also found that this damage led to memory impairments in mice and that they could reverse those impairments with a drug used to treat epilepsy.
In the other study, the researchers treated mice with a peptide that blocks a hyperactive version of an enzyme called CDK5, which plays an important role in development of the central nervous system. They found dramatic reductions in neurodegeneration and DNA damage in the brain, and the mice got better at tasks such as learning to navigate a water maze.
CDK5 is activated by a smaller protein known as P35, allowing it to add a phosphate molecule to its targets. However, in Alzheimer’s and other neurodegenerative diseases, P35 breaks down into a smaller protein called P25, which allows CDK5 to phosphorylate other molecules—including the Tau protein, leading to the Tau tangles that are another characteristic of Alzheimer’s.
Pharmaceutical companies have tried to target P25 with small-molecule drugs, but these drugs also interfere with other essential enzymes. The MIT team instead used a peptide—a string of amino acids, in this case a sequence matching that of a CDK5 segment that is critical to binding P25.
In tests on neurons in a lab dish, the researchers found that treatment with the peptide moderately reduced CDK5 activity. But in a mouse model that has hyperactive CDK5, they saw myriad beneficial effects, including reductions in DNA damage, neural inflammation, and neuron loss.
The treatment also produced dramatic improvements in a different mouse model of Alzheimer’s, which has a mutant form of the Tau protein. Tsai hypothesizes that the peptide might confer resilience to cognitive impairment in the brains of people with Tau tangles.
“We found that the effect of this peptide is just remarkable,” she says. “We saw wonderful effects in terms of reducing neurodegeneration and neuroinflammatory responses, and even rescuing behavior deficits.”
The researchers hope the peptide could eventually be used as a treatment not only for Alzheimer’s but for frontotemporal dementia, HIV-induced dementia, diabetes-linked cognitive impairment, and other conditions.
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