Alzheimer's disease is a progressive, degenerative brain disorder that initially manifests itself as memory loss and confusion and gradually leads to a seriously impaired ability to carry out daily activities. According to the National Institute of Neurological Disorders and Stroke, Alzheimer's is the principal cause of dementia in people over the age of 65. The symptoms of Alzheimer's disease arise because nerve cells in the brain become damaged and eventually die. Certain proteins in the brain are linked to the death of nerve cells seen in Alzheimer's disease.
Amyloid Precursor Protein
Amyloid precursor protein occurs mainly in the synapses of nerve cells. Synapses are the junctions between nerve cells across which a nerve signal passes from one cell to another. Scientists believe that amyloid precursor protein may serve to govern both the formation of synapses and a nerve cell phenomenon called neural plasticity, the ability of nerve cells to adapt to new conditions. The role of amyloid precursor protein in the generation of the plaques characteristic of Alzheimer's disease has received intense scrutiny.
Beta-Amyloid Proteins
When amyloid precursor protein undergoes normal enzymatic degradation in the brain, the fragments produced are called beta-amyloid proteins. In Alzheimer's disease, these proteins accumulate to form amyloid plaques that reside between nerve cells. The National Institute on Aging summarizes an article published online in "Science" on December 9, 2010, in which researchers state that beta-amyloid proteins accumulate because they are not cleared efficiently in the diseased brain. The resulting amyloid plaques generate a series of physiological events that leads to nerve cell death and the decline of brain function.
Normal Tau Protein
In a nerve cell, axons are projections that carry nerve signals away from the body of the cell. Normal tau protein occurs in the axons of brain nerve cells where it functions to secure the structure of microtubules, cylindrical passageways that are the support scaffold of the nerve cell and conduct nutrients and other materials from one part of the cell to another. Normal tau protein is vital to the proper functioning of the nerve cell.
Abnormal Tau Protein
In Alzheimer's disease, the tau protein structure changes from its normal, soluble form to an abnormal insoluble form that leads to the generation of twisted strands called neurofibrillary tangles. These tangles can't support the microtubules, and therefore they collapse and the nerve cell eventually dies. The formation of neurofibrillary tangles may be one of the causes of Alzheimer's disease.
References
- National Institute of Neurological Disorders and Stroke: NINDS Alzheimer's Disease Information Page
- American Health Assistance Foundation: Alzheimer's Disease Research: Plaques and Tangles
- EDinformatics.com: Alzheimer's Update 2009: Amyloid Precursor Protein
- National Institute on Aging: Alzheimer's Disease Education and Referral Center: Impaired Clearance, Not Overproduction of Toxic Proteins, May Underlie Alzheimer's Disease
- University of California at San Francisco Memory and Aging Center: Unfolding the Role of Tau: The Pathological Hallmark of Tauopathies Still Holds Mysteries
