Abstract
Alzheimer’s disease (AD) is rapidly becoming one of the most significant challenges facing modern medicine. Currently there is no cure for this neurodegenerative disease. Memory defects arise from gross atrophy of specific brain regions and intensive research efforts have focused on the central role of a toxic build up of the amyloid-β (Aβ) protein. The amyloid-β precursor protein (APP) may play a key role in the pathogenesis of AD as it is proteolytically processed to produce Aβ. APP can also be processed via a mutually exclusive non-amyloidogenic pathway, to produce secreted amyloid precursor protein-α (sAPPα). sAPPα is neurotrophic and neuroprotective, and can restore memory mechanisms, contrasting the negative effects of Aβ. The balance between the concentration of Aβ and sAPPα may be important, with an increase in Aβ and a decrease in sAPPα potentially contributing to the pathology of AD. sAPPα stimulates the activity of a number of signalling pathways, however downstream genetic targets of these cascades have not yet been fully established. Recently, small peptide motifs within sAPPα have been shown to be capable of mimicking sAPPα’s functions, and may provide novel therapeutic agents for the treatment of AD. It is unknown what role the smallest reported bioactive motif, RER, plays within the full-length protein. Furthermore, it is unclear if RER is capable of mimicking the neuroprotective and gene expression inducing functions of sAPPα, critical for its success as a therapeutic peptide.
This project has applied biochemical and molecular biological techniques to characterize the neuroprotective effects of sAPPα, and to determine the ability of sAPPα to stimulate gene expression. The role of the RER motif in full-length sAPPα, and as a dissociated tripeptide, has been evaluated. A variant sAPPα protein, sAPPαAER (designed and produced in the research group) was purified, and assayed along with a chemically synthesized RER peptide for both neuroprotection and the ability to induce gene expression. sAPPα’s effects on the transcriptome of organotypic rat hippocampal slices was assessed using microarray analysis.
These results have shown that sAPPα is indeed neuroprotective and capable of rapidly inducing the expression of several genes as early as 15-30min. The sAPPαAER variant was as effective as the native sAPPα in producing these effects, indicating other active domains may be present within the sAPPα protein. Nevertheless, the isolated RER tripeptide is capable of mimicking the neuroprotective and gene expression inducing effects of full-length sAPPα. Through microarray analysis of organotypic hippocampal slices, this study has uncovered several new putative targets for sAPPα signalling. sAPPα rapidly activated the expression of immediate early genes, several miRNA precursor genes, and genes with neurotrophic functions. Over a longer period of treatment sAPPα modulated a different set of genes related to immune responses, cellular proliferation, inflammation, transcription and survival.