Alzheimer's disease is a progressive, incurable and ultimately fatal form of dementia. The symptoms of Alzheimer's disease occur because of the loss of neurons. However, the exact form of cell disease that Alzheimer's causes is not yet known. Researchers have, on the other hand, developed several theories to explain how Alzheimer's causes cell death in the brain.
Amyloid
One of the key features of Alzheimer's disease is the presence of deposits of aggregated protein, which are also called amyloid fibrils. These fibrils are primarily made up of a protein known as A-beta, which can form the starting core for these clumps of protein. Large amyloid aggregates, known as amyloid plaques, can be seen in brain tissue samples of Alzheimer's disease patients' brains. Scientists also believe that there is a possibility that smaller intermediates of these proteins clumps, called oligomers, could also play a role in the development of Alzheimer's disease.
Amyloid and Protein Misfolding
One theory about how Alzheimer's disease develops is the ability of these amyloid fibrils to disrupt the internal workings of neurons. All cells, including neurons, have the ability to process damaged or misfolded proteins to prevent them from damaging the cell. The misfolded A-beta proteins could, on the other hand, overload these systems, allowing damaged proteins to build up. This build-up could ultimately be toxic to the neurons.
Amyloid and Apoptosis
Another way in which A-beta and cell disease are linked is through a process known as apoptosis. Apoptosis is a mechanism by which severely damaged cells self-destruct, which limits the damage done to surrounding cells. Aggregates of A-beta can activate the cell's apoptotic system, causing neurons to die.
Amyloid and Oxidative Damage
A-beta aggregates can also cause the generation of molecules called reactive oxygen species. These unstable forms of oxygen can damage a cell's DNA, proteins and even the cell membrane itself. If the protein aggregates found in Alzheimer's disease caused enough damage to neurons, the affected neurons would die.
Amyloid and Vascular Problems
Amyloid fibrils can also accumulate in the blood vessels that provide blood to neurons in the brain. One theory in Alzheimer's disease pathology is that the amyloid plaques could restrict blood flow to neurons. In this sense, the amyloid would essentially cause a series of small strokes, which would kill off neurons and lead to impaired brain function.
