Up to half of people with Alzheimer's disease experience severe, clinically disabling sleep disruption — often cited by caregivers as one of the most exhausting parts of the disease. The prevailing assumption has been that amyloid plaques themselves, or the neurons they damage, are the direct cause. A new study from the University of Kentucky, published in Alzheimer's & Dementia, points to a different culprit: microglia, the brain's resident immune cells, reacting to those plaques.
Depleting Immune Cells, Not Plaques
Led by first author Nicholas J. Constantino and senior author Shannon L. Macauley, the research team worked with APP/PS1 mice, a standard model that develops amyloid plaques similar to those seen in human Alzheimer's disease. The mice also develop the sleep disruption characteristic of the disease, primarily a loss of deep, non-rapid eye movement (NREM) sleep.
The researchers treated the mice for two weeks with PLX3397 (pexidartinib), a drug that inhibits CSF1R, a receptor microglia depend on to survive. The treatment depleted the brain's microglial population by 87%. The mice's sleep was then measured and compared with untreated APP/PS1 mice.
The result: mice with microglia depleted gained more than two hours of NREM sleep per night — despite the fact that their amyloid plaque burden was unchanged. The plaques were still there. The immune cells reacting to them were not, and the sleep loss reversed anyway.
What the Finding Overturns
The result separates two things that are usually treated as a single problem: the presence of amyloid plaques, and the downstream inflammatory cascade that microglia mount in response to them. If plaques themselves directly disrupted the sleep-regulating circuitry, removing microglia without clearing plaques should have done little. Instead, sleep normalized almost as if the plaques weren't there.
That points to microglial-driven neuroinflammation, not plaque burden itself, as the more direct mechanical cause of Alzheimer's-associated sleep loss. It also helps explain a pattern that has puzzled researchers: therapies that successfully clear amyloid plaques in patients don't reliably improve sleep, which is difficult to square with a plaques-cause-sleep-loss model but fits naturally if microglia are the actual driver.
Why This Could Matter for Treatment
Most Alzheimer's drug development in the past two decades has centered on clearing amyloid plaques, an approach that has shown only modest clinical benefit and no consistent effect on sleep. This study suggests a separate, more targetable pathway: the neuroinflammatory response itself. If microglial activity — rather than plaque burden — is what's driving sleep disruption, then anti-inflammatory or microglia-modulating approaches could offer a way to address one of Alzheimer's more debilitating symptoms without needing to solve plaque clearance first.
The caveat is significant: this is a mouse study using a drug that broadly depletes microglia, a blunt approach that would carry real risks in humans, since microglia also perform essential immune surveillance functions in the brain. Translating the finding into a viable human therapy would likely require a more selective way to dial down harmful inflammatory microglial activity without eliminating the cells' protective functions.
What This Means for Patients
For the roughly one-quarter to one-half of Alzheimer's patients experiencing significant sleep disruption, and the caregivers managing it, this research doesn't yet translate into a new treatment. But it reframes what the target should be. Sleep disruption in Alzheimer's has often been treated as an unavoidable symptom of the disease's progression, managed with sedatives or behavioral strategies rather than addressed at its biological root. This study suggests the root cause may be more specific — and more addressable — than previously thought: not the plaques themselves, but the brain's inflammatory response to them. That reframing could eventually open a path to therapies aimed specifically at restoring sleep in Alzheimer's patients, independent of progress on amyloid-targeted treatments.
