Investigating a positive biological role for the A Beta peptide

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Abstract Despite a century of research and countless clinical trials, Alzheimer's Disease (AD) etiology is still poorly understood and treatment options are incredibly limited. The histopathology of the disorder, has generally focused on the accumulation of neurotoxic plaques in the brain which are composed of the Aβ peptide, a cleavage product of the Amyloid Precursor Protein (APP). This peptide has received much attention in the AD field due to its role in Familial Alzheimer's Disease (FAD), a genetic form of the disease with rapid but similar disease progression. Importantly, FAD is caused by the autosomal dominant inheritance of mutations, in APP and the presenilin genes. This is significant because presenilin is the catalytic component of the γ-secretase complex that cleaves APP, releasing Aβ. Since anti-amyloidogenic and anti-γ-secretase agents have been largely ineffective in treating AD, and often even seem to worsen the condition in AD patients, alternative mechanisms need to be considered. One such mechanism is altered insulin signaling. There are significant links between AD and Type II diabetes (T2D), and signs of altered insulin resistance have been identified in the brains of AD patients. This is important as insulin signaling also plays a role in memory formation. We believe that these two distinct areas of AD research may actually be closely linked. We believe that it is irrefutable that Aβ plays a pivotal role in AD pathogenesis, however we also believe that this role has not been fully illustrated. It has been suggested in select publications that Aβ competes with insulin for binding to both the insulin receptor and the insulin degrading enzyme. We believe that this activity is responsible for regulating insulin signaling in the brain. When Aβ levels are altered, insulin signaling may proceed unregulated resulting in brain insulin resistance with age, as occurs in the periphery of T2D patients. Our hypothesis is that Aβ plays a positive biological role in insulin signaling regulation, and that this regulation is altered in AD. To test this hypothesis, we will generate animal models that expresses both Aβ and insulin at physiologically accurate levels. In Aim 1, we propose to use the newly developed CRISPR technology to generate a physiologically relevant fly model of FAD. In Aim 2, we will use in vitro techniques to test the concept that Aβ and insulin work in tandem to modulate insulin signaling levels. Finally, in Aim 3, we will use the new FAD fly model to determine if Aβ is required in the brain to regulate insulin signaling, and if this balance is altered in AD. Upon conclusion of the experiments proposed, we will have determined if Aβ plays a positive biological role in the regulation of insulin signaling, and if alterations in this regulatory role may contribute to AD pathogenesis. Further, we will have developed a new, physiologically accurate fly model of AD which will be an invaluable tool in both our future studies and in the work of other groups investigating the cause of this devastating disorder.