| Amyloid-beta (Abeta) peptides are naturally circulating peptides that have been found in low levels in the cerebrospinal fluid and plasma of healthy, non-demented individuals. AP peptides are also found composing the amyloid plaques in brains of Alzheimer's disease (AD) and Down's syndrome (DS) patients. A variety of heterogeneous peptides are released through proteolytic processing of the Amyloid Precursor Protein (APP). AR peptides are considered the causative agents that initiate the development of AD. The Amyloid Cascade Hypothesis suggests that the aggregation of Abeta peptides in the brain induces the formation of toxic structures which then causes the neurodegeneration and ultimately neuronal loss in the diseased brain. One of the major AR peptides found in plaques is the full-length Abeta1-42, which has been extensively studied. Another more recently discovered AP species found in plaques is the amino (N) terminally truncated, pyroglutamylated peptide, Abetap3-42. Although this peptide is abundantly found in AD and DS brain, only a few studies have been published regarding its properties. The research goal of this thesis was to study the aggregation properties and toxicity of Abetap3-42, specifically as compared to Abeta1-42.; To monitor aggregation kinetics, we used spectrofluorimetry, biochemical analysis, and electron microscopy (EM). Cellular toxicity was measured by analyzing morphology and viability. Our data show that Abetap3-42 aggregates slower than full-length Abeta1-42. In mixtures with Abeta1-42 it inhibits early phases of Abeta1-42 aggregation. These conclusions are corroborated by morphological analyses using EM. Toxicity studies using hippocampal neurons and PC12 cells demonstrate that both AP peptides are toxic at high concentrations and that this toxicity depends on their structural form. Furthermore, it appears that such toxicity may be mediated by peptide binding to different parts of the cell.; The results presented here are partially consistent with the notion that the extent of aggregation and toxicity are correlated. Thus we observed lower propensity of Abetap3-42 to aggregate, yet equally detrimental effects on PC12 cells as seen with Abeta1-42. Overall, this study contributes to further understanding the role of Abetap3-42 in AD pathology and provides insight into rationale therapeutic strategies aimed at reducing the Abeta burden in the AD brain. |
