Alzheimer’s disease is usually known for causing memory loss, confusion, and difficulty thinking clearly. However, scientists now know that the disease often begins many years, or even decades, before these well-known symptoms appear.
Some people first notice changes such as poor sleep, anxiety, depression, or trouble paying attention long before memory problems develop. These early changes suggest that Alzheimer’s quietly damages certain parts of the brain long before doctors can diagnose it.
A new study from researchers at the University of California, San Francisco (UCSF) has uncovered an important clue that may explain why some brain cells are damaged earlier than others.
The research, published in the journal Alzheimer’s & Dementia, suggests that the way certain brain cells handle cholesterol could make them much more vulnerable to Alzheimer’s disease.
Cholesterol is often thought of as something that affects heart health, but it is also essential for the brain. Brain cells need cholesterol to build cell membranes, send signals to one another, and maintain healthy connections.
The brain actually produces most of its own cholesterol because very little enters from the bloodstream. Keeping cholesterol at the right level is therefore very important for healthy brain function.
The UCSF team wanted to understand why some brain regions are damaged very early in Alzheimer’s disease while others remain relatively healthy.
To answer this question, they studied brain tissue donated by people after death. The samples came from the Neurodegenerative Disease Brain Bank at UCSF and the Biobank for Aging Studies at the University of São Paulo.
The scientists compared two nearby brain regions from the same individuals. One was the Locus Coeruleus, or LC, which helps control sleep, attention, mood, stress responses, and inflammation. This region is one of the first parts of the brain affected by Alzheimer’s disease.
The other was the Substantia Nigra, or SN, which produces dopamine and is much less affected during the early stages of Alzheimer’s, even though it is important in Parkinson’s disease.
Because these two regions are similar in many ways, the researchers believed that comparing them might reveal why one is more vulnerable.
The team examined which genes were active inside the neurons using a technique called RNA analysis. They discovered a major difference in the way the two groups of neurons handled cholesterol.
The researchers found that neurons in the Locus Coeruleus appeared to have an unusually high demand for cholesterol. They produced more cholesterol themselves and also absorbed much more from their surroundings than neurons in the Substantia Nigra.
This increased appetite for cholesterol may have an unexpected downside. The LC neurons contained much larger amounts of a protein called the low-density lipoprotein receptor, or LDLR.
This receptor normally helps cells absorb cholesterol. However, it may also allow harmful amyloid-beta oligomers to enter brain cells. These small protein clumps are believed to play an important role in Alzheimer’s disease because they damage neurons and interfere with normal brain function.
In comparison, neurons in the Substantia Nigra produced higher levels of another molecule that helps break down LDLR. With fewer cholesterol receptors available, these neurons may be less likely to take up harmful amyloid-beta proteins, giving them greater protection.
The researchers confirmed these findings by examining the brain tissue under a microscope. They clearly saw higher levels of LDLR in neurons from the Locus Coeruleus, supporting the idea that differences in cholesterol handling may help explain why this brain region is damaged so early.
The study also found differences in other biological processes, including the way neurons handled metals and responded to stress. Even so, cholesterol regulation appeared to be one of the strongest differences between the two regions.
These findings could help explain why sleep problems, anxiety, and depression sometimes appear years before memory loss. Because the Locus Coeruleus helps regulate these functions, early damage to this area may produce these symptoms long before Alzheimer’s spreads to memory centres of the brain.
Although the results are promising, the study does not mean cholesterol itself causes Alzheimer’s disease. More research is needed to understand exactly how these brain processes work and whether new treatments can safely target them.
Scientists hope that future medicines might reduce the entry of harmful proteins into vulnerable neurons or improve the way brain cells regulate cholesterol. If successful, such treatments could protect brain cells earlier in the disease and possibly delay the development of memory loss.
The study adds another important piece to the Alzheimer’s puzzle and offers hope that one day doctors may be able to identify and treat the disease much earlier, before irreversible brain damage occurs.
If you care about brain health, please read studies about inflammation that may actually slow down cognitive decline in older people, and low vitamin D may speed up cognitive decline.
For more health information, please see recent studies about common exercises that could protect against cognitive decline, and results showing that this MIND diet may protect your cognitive function, prevent dementia.
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