Effects of [beta]-amyloid, transferrin and aluminum on cultured hippocampal neurons
The involvement of aluminum and beta-amyloid protein in diseases such as Alzheimer's disease (AD) and Down's syndrome (DS) have yet to be determined. The research presented in this dissertation examined roles for these compounds using tissue culture models. Hippocampal neurons were exposed to transferrin loaded with aluminum (TF-AL) and analyzed for changes in viability and neurite outgrowth. TF-AL was highly neurotoxic to Day 0 neurons, but did not significantly affect the survival of Day 4 neurons exposed for 72 h. These neurons instead had reduced MAP-2 and tau immunoreactive processes. The findings of this study support the theory that transferrin delivers aluminum to neurons influencing neuritic behavior and survival. Effects of amyloid on cultured neurons were also characterized. Because amyloid in the mature AD plaque is aggregated and relatively immobile, I attempted to simulate effects of an established AD plaque by exposing hippocampal neurons to aged [beta]25-35 coated onto the culture surface. I report that neurons have an affinity for [beta]25-35 and that [beta]25-35 supports the attachment, growth, and survival of cultured hippocampal neurons. When hippocampal neurons were serum deprived, however, significant [beta]25-35 neurotoxicity was observed compared to serum-deprived control cultures. Using the same culture system, I further examined [beta]25-35 toxicity using culture medium supplemented with modified N2 (MN2) or each of its components (i.e. progesterone, insulin, rat apotransferrin, putrescine and sodium selenite). When serum was replaced with MN2, [beta]25-35 supported the attachment, growth and survival of cultured hippocampal neurons. When neurons were exposed to each component of MN2 individually, only rat apotransferrin and sodium selenite significantly protected against [beta]25-35 toxicity. In view of the antioxidant properties of these compounds, vitamin E was also tested. Vitamin E supplemented medium significantly protected against [beta]25-35 neurotoxicity. This survival was comparable to neuronal survival in medium containing MN2. These findings are supportive of the theory that deficiencies in AD and DS contribute to neurodegeneration and that free radical formation may be involved.