The overall aim of this research is to use non-viral liposomal delivery systems as direct gene transfer vectors to study the efficacy of nerve growth factor in the therapy of Alzheimer's disease (AD) pathogenesis. Neurotrophic factors (viz., nerve growth factor [NGF]) exogenous delivery to the aged brain may prevent neuronal degeneration. NGF's large molecular weight preludes easy permeation across the blood brain barrier. Consequently, in order to obtain therapeutic effects, the peptide must be directly administered to the brain by using non-viral gene delivery methods for expressing NGF, brain tissue should secrete NGF in a biological active form permitting chronic, well tolerated and regionally specific NGF production. In AD, this approach could be utilized to retard cholinergic neuronal degeneration. Specifically, non-viral gene delivery vectors will be developed to optimize gene expression in brain tissue after direct injection. Three variables will be investigated in the optimization of this delivery system. Initially, the addition of an endosomal membrane rupturing agent which will increase the amount of nucleic acid reaching the cell's cytoplasm will be tested. The second objective will focus on the inclusion of nuclear peptide localization sequences to facilitate the transfer of vector to the nucleus. A third component involves the synthesis of cationic lipids which will form smaller, enzymatic-resistive DNA-complexes leading to enhanced distribution and cellular uptake within the brain. After optimization of the liposomal delivery vehicle in vitro, it will be used to test several hypotheses on the influence of NGF-gene transfer into the brain. The influence of gene transfer on the cholinergic system, NGF- receptor up regulation, and memory-related behaviors will be explored using two model systems: axotomy of septal cholinergic neurons and the aging rat. These studies are expected to demonstrate that NGF-gene delivery can protect cholinergic neurons and improve behavior in hypofunctional animals, and that the newly developed gene-transfer vehicles are superior to present techniques based on reconstituted virosomes.
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