Picture a small fire igniting in a corner of your kitchen. With the right fire extinguisher, you could swiftly control it. However, when the sprinkler system activates, it floods your entire home, transforming a manageable issue into extensive damage. Similarly, researchers suggest that a comparable phenomenon may unfold in the brains of Alzheimer’s patients.
Amyloid plaques—sticky protein aggregates accumulating in the brain—act like that fire. Microglia, the brain’s immune cells, respond like sprinklers. Although their intent is to protect, their reactions can exacerbate the problem.
Recently, a team at the University of Kentucky has pinpointed this detrimental process for the first time and developed methods to halt it.
Brain Immune Cells and Sleep Deprivation in Alzheimer’s Disease
Published in Alzheimer’s Disease and Dementia, research led by Dr. Shannon L. McCauley, Associate Professor of Physiology at the UK Medical School, alongside lead author Dr. Nicholas J. Constantino, highlights microglia as key culprits in sleep deprivation in animal models of Alzheimer’s.
When researchers administered a drug that temporarily eradicated most microglia, the animals enjoyed over two additional hours of sleep each night. McCauley described these results as a potential “paradigm shift” in the treatment of Alzheimer’s disease.
Previously, sleep deprivation related to Alzheimer’s was believed to be triggered mainly by neuronal damage or the presence of amyloid plaques. The new findings indicate a deeper immunological response, akin to a “whole-house response.”
“Our study reveals that it’s not just the plaques or malfunctioning neurons causing sleep deprivation; it’s actually microglia,” said McCauley. “When microglia react to plaques, they initiate a complex inflammatory response, keeping the brain overly stimulated, like a party that never ends.”
Tracking Sleep and Brain Activity
To differentiate changes tied to Alzheimer’s from those associated with normal aging, researchers examined two mouse groups: one genetically predisposed to develop amyloid plaques and the other consisting of “wild-type” mice.
Animals were studied at 6 months, when plaques began forming, and again at 18 months, during a stage indicative of advanced disease.
Researchers utilized advanced technologies to monitor sleep and brain activity meticulously. Mice were fitted with head-mounted devices to record electroencephalography (EEG) and electromyography (EMG), capturing electrical patterns and muscle activity while determining sleep stages.
Additionally, to visualize the microglial activity described by McCauley, researchers employed light-sheet microscopy, rendering brain tissue transparent to create detailed 3D imagery of both amyloid plaques and immune cells throughout the brain.
Temporary Microglia Removal
To confirm microglia’s role in sleep disruption, scientists tested the drug pexidartinib (PLX3397), initially developed for cancer treatment but effective in blocking microglial survival signals.
After 14 days on the drug, approximately 87% of microglia were temporarily eliminated, allowing researchers to assess improvements in sleep quality.
The team employed a mathematical technique to classify brain electrical activity into periodic (normal brain waves) and aperiodic (background noise), akin to checking whether a car’s engine runs at high speed even while idling.
Impact of Early Plaque Formation on Sleep
McCauley expressed surprise at the findings. While plaque buildup and sleep disturbances decreased, they did not worsen in tandem.
“Initially, we expected that as plaques increased, sleep issues would amplify,” Constantino explained. “However, sleep disturbances and cortical brain activity at six months showed minimal change after 18 months, despite plaque levels more than doubling.”
This “ceiling effect” suggests that early microglial activity triggered by initial plaque formation may establish sleep issues, with additional plaques not substantially worsening sleep disruption.
Alzheimer’s and Restorative Sleep
The study distinguished normal aging effects from Alzheimer’s-specific impacts. Regular aging primarily reduces REM sleep, vital for dreams and memory consolidation, whereas amyloid pathology specifically affects NREM sleep, the critical restorative sleep phase.
“Restorative sleep is essential for bodily repair, learning, memory, and clearing toxins,” McCauley noted. “Loss of NREM sleep disrupts the brain’s cleansing cycles, creating a harmful feedback loop that exacerbates damage.”
This suggests that sleep deprivation could further impair the brain’s waste removal processes, compounding the problem.
Restoration of Over Two Hours of Sleep
The most astonishing findings emerged when microglia were depleted. Mice with Alzheimer’s exhibited over two additional hours of sleep nightly after most immune cells were removed, enhancing restorative NREM sleep and dream sleep, crucial for memory retention.
Notably, this improvement occurred despite unchanged amyloid plaque levels, indicating that the inflammatory response to plaques might be a reversible cause of sleep deprivation, treatable independent of plaque itself.
This raises significant questions for future research: could restoring essential sleep in individuals aid in breaking the Alzheimer’s cycle?
A Collaborative Research Environment
This breakthrough originated from a collaborative atmosphere in McCauley’s lab at the Sanders-Brown Center on Aging. McCauley praised her team’s initiative, curiosity, and commitment to discovery.
She promotes a culture of “calculated risk-taking,” quoting Wayne Gretzky: “You miss 100% of the shots you don’t take.”
Constantino emphasized the confidence gained from working in this supportive environment, highlighting its role in tackling complex problems across various disciplines.
“Dr. McCauley instilled in me the importance of embracing uncertainty and failures as part of the research journey,” he said, noting how unexpected results often lead to the most intriguing discoveries.
When challenges arise, McCauley encourages her team to persist and to delve deeper: “Track your data and continue questioning what’s truly happening.”
This approach has led researchers to explore microglia as a therapeutic target, breaking away from the field’s traditional focus on neurons.
Portable EEG for Early Detection
The broader objective of this research is to devise affordable, non-invasive tools for individuals with Alzheimer’s. Current findings open various pathways for future inquiry.
Researchers have identified brain electrical activity patterns that differentiate Alzheimer’s-related changes from normal aging aspects. They believe EEG technology could evolve into a “readily accessible, affordable, long-term biomarker for Alzheimer’s disease.”
“Portable EEG systems could monitor Alzheimer’s risk factors in home settings, allowing for screenings without the need for expensive or invasive procedures,” McCauley remarked.
This technology could facilitate local clinics across Kentucky in screening at-risk patients before they travel to specialized facilities for comprehensive evaluations.
Calming Microglia Without Total Elimination
McCauley’s lab is currently exploring methods to reduce microglial overactivity without completely removing these cells. They are examining established medications, such as the diabetes drug metformin and the anti-epileptic Stiripentol, to see if they can modulate microglial energy processing and mitigate overstimulation.
By minimizing the hyperactive state of these immune cells, the research team aims to restore healthy sleep and improve quality of life long before significant memory loss occurs.
“Targeting this process could enhance daily life, attention, cognition, and reduce confusion,” McCauley stated.
Identifying both the root cause and effective tools is critical for finding viable solutions. Progress is evident on both fronts in McCauley’s lab.
Research reported in this publication was supported by the National Institute on Aging of the National Institutes of Health under award numbers R01AG068330, R01AG093847, and P30AG072946, and by the National Institute of General Medicine of the National Institutes of Health under award numbers P30GM127211 and P20GM148326. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
This research was supported by a $287,236 award from the Alzheimer’s Disease Treatment Fund.
This research was supported by a $250,000 award from the CART Fund (Coin for Alzheimer’s Disease Research Trust).
Source: www.sciencedaily.com