Vascular Amyloid in an Alzheimer's Mouse Model
Kimbrough, Ian F.
MetadataShow full item record
Alzheimer disease accounts for ~80% of dementia cases worldwide. Traditionally, one of the pathological hallmarks of this disease is Amyloid beta (A ) plaques. A is a 36-43 amino acid peptide formed from improperly cleaved amyloid precursor protein (APP). When APP is cleaved incorrectly in the brain, it forms sticky monomers. These monomers can usually be cleared from the brain and do not pose any hazards to normal brain functioning. However, in cases of disease these monomers can clump together to form A oligomers, or plaques. In addition to plaques, incorrectly cleaved A can also aggregate on vessels in the brain. Previous research has shown that these amyloid aggregates can displace astrocytic endfeet from blood vessels. This can cause the blood brain barrier to leak and prevent proper regulation of the diameter of vessels in the brain. This regulatory ability of the vessels in the brain is called functional hyperemia, and it enables precise control of where nutrient- lled blood is directed. When vascular amyloid surrounds the vessel and displaces astrocytic endfeet, it has been shown to cause a loss of this ability. This inhibits the brain’s ability to direct nutrients to areas of need and could be a major contributor to the cognitive decline seen in patients with Alzheimer Disease. In addition, any leakage of the blood brain barrier is very unhealthy for the surrounding tissue, as the blood brain barrier exists for the purpose of keeping toxins separate from the brain parenchyma. We do not currently understand how exactly these vascular amyloid plaques cause blood brain barrier failure. However, we have found that areas of the vasculature laden with vascular amyloid do demonstrate a downregulation in expression of the tight junction proteins ZO1 and Claudin 5. These tight junction proteins are responsible for holding the endothelial cells of the vasculature together to seal the blood brain barrier. To demonstrate that this decreased expression of tight junction proteins was not just a failure of the antibodies to penetrate through the vascular amyloid, the tissue was also stained for vinculin, a component of the cytoskeleton found directly beside these tight junctions. There was no di erence in vinculin labeling between areas with and without an amyloid burden, indicating that the amyloid is not preventing antibody penetration and that there is a true loss of tight junction protein expression. Addionally, we studied whether these damaging vascular amyloid plaques display a preference for certain kinds of vessels in the brain, based either on vessel size or vessel type. We showed that vascular amyloid does have a preference for arterioles and venules over capillaries, arteries, and veins. However, we were unable to distinguish with certainty whether amyloid displayed a preference for either arterioles or venules due to shortcomings in our DIC imaging.