A team at the University of Kentucky has identified a counterintuitive culprit in Alzheimer's disease: the brain's own immune system may be causing more harm than the hallmark plaques themselves.
Researchers discovered that specialized immune cells called microglia, which normally protect the brain, trigger a cascade of inflammation when they respond to amyloid plaques. This overreaction appears to be the primary driver of sleep loss in Alzheimer's patients, not the plaques or damaged neurons as previously thought.
In a study published in Alzheimer's and Dementia, scientists led by Shannon L. Macauley used a drug to temporarily eliminate most microglia in mice with Alzheimer's pathology. The animals regained more than two hours of sleep per day, despite having no reduction in amyloid plaques. The finding suggests sleep disruption in Alzheimer's may be reversible, opening a new avenue for treatment.
"Basically, the microglia are partying all night and keeping the brain awake," Macauley said, describing how the immune cells activate an elaborate inflammatory cascade in response to plaques.
Tracking the Brain's Electrical Signature
The researchers studied two groups of mice: one genetically prone to developing amyloid plaques and a control group that aged normally. Both were examined at six months, when plaques first emerge, and again at 18 months, representing advanced disease.
Using small head-mounted devices, the team recorded electroencephalography and electromyography to map precisely when animals were awake, in deep restorative sleep, or dreaming. They also employed light sheet microscopy, which renders brain tissue transparent and uses a laser to create detailed three-dimensional images of plaques and immune cells throughout the brain.
Researchers administered a drug called Pexidartinib, originally developed for cancer research, which blocks the signaling pathway microglia depend on for survival. After 14 days, approximately 87 percent of the brain's immune cells were temporarily removed.
The results challenged expectations. Despite amyloid plaques more than doubling between six and 18 months, the amount of lost sleep remained essentially flat. This ceiling effect suggests that the initial immune response triggered by early plaques is sufficient to establish the sleep problem. Additional plaques do not proportionally worsen sleep disruption.
Importantly, Alzheimer's pathology selectively reduced non-rapid eye movement sleep, the deeply restorative stage critical for physical repair, learning, and clearing toxins from the brain. In contrast, normal aging primarily affected REM sleep, associated with dreaming. This distinction suggests Alzheimer's targets the brain's primary cleaning cycle.
"When Alzheimer's patients lose this stage, they lose their brain's primary cleaning cycle, creating a feed-forward loop that may drive further damage," Macauley explained. Poor sleep reduces the brain's ability to clear waste, potentially contributing to more plaques and more sleep disruption.
The study identified patterns of electrical brain activity that distinguish Alzheimer's changes from normal aging. Researchers now believe portable EEG systems could eventually serve as an affordable, noninvasive biomarker for the disease, allowing screening in home environments or local clinics before requiring expensive specialized testing.
Macauley's laboratory is now investigating safer alternatives to completely eliminating microglia. The team is studying existing medications, including the diabetes drug Metformin and the antiseizure drug Stiripentol, to determine whether they can reduce microglial overactivity while keeping the cells intact. The goal is to restore healthy sleep and improve quality of life years before memory loss develops.
Author Jessica Williams: "If this pans out, it rewrites the playbook on Alzheimer's treatment from chasing plaques to calming the immune fire that burns the house down."
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