Contribution of the vasculature to the Alzheimer's disease process

One of the pathological hallmarks of Alzheimer's disease (AD) brain is extracellular β-amyloid (Aβ) plaques containing 39-42 amino acid Aβ peptides. The deposition of Aβ around blood vessels, known as Cerebral amyloid angiopathy (CAA), is also a common feature in AD brain. Vascular density and cerebral blood flow are reduced in AD brains, and vascular risk factors such as hypertension and diabetes are also risk factors for AD. We have shown previously that Aβ peptides can potently inhibit angiogenesis both in-vitro and in-vivo, but the mechanism of action for this effect is not known. Therefore, my first hypothesis was that particular amino acid sequence(s) within the Aβ peptide are required for inhibition of angiogenesis. From this aim, I found a peptide sequence which was critical for anti-angiogenic activity (HHQKLVFF). This sequence contains a heparan sulfate proteoglycan growth factor binding domain implying that Aβ can interfere with growth factor signaling. Leading on from this, my second hypothesis was that Aβ can inhibit angiogenesis by binding to growth factor receptors. I found that Aβ can bind to Vascular Endothelial Growth Factor Receptor-2 (VEGFR-2), and showed that this is one mechanism by which Aβ can inhibit angiogenesis. Since the vasculature is disrupted in AD brains, I investigated whether a strategy to increase brain vascularization would be beneficial against AD pathology. Therefore, my third hypothesis was that voluntary exercise (which is known to increase brain vascularization in rodents) can ameliorate Aβ pathology, increase brain vascularization, and improve behavioral deficits in a transgenic mouse model of AD. I found that exercise has no effect on Aβ pathology, brain vascularization or behavioral deficits. Therefore, in the transgenic mouse model that I used, exercise is an ineffective therapeutic strategy against AD pathology and symptoms.