Secreted amyloid precursor protein alpha as a therapeutic for insulin signaling dysfunction in the nervous system

Abstract

Background: The amyloid precursor protein (APP) cleavage product secreted amyloid precursor protein alpha (sAPPα) is a neurotrophic factor demonstrated to be protective to neurons. Despite evidence that sAPPα activates the insulin signaling ,the effects of sAPPα on diabetes-induced pathology are unknown.

Hypothesis: We hypothesized that sAPPα could inhibit neuronal dysfunction in an animal model of diabetes. This hypothesis was tested in 3 aims.

AIM 1: To determine if sAPPα could inhibit the development of Alzheimer’s-like pathology in diabetic brain tissue.

AIM 2: To examine if sAPPα could slow the development of diabetes-induced peripheral neuropathy.

AIM 3: In our final aim, we examined the effects of sAPPα overexpressing neural stem cells (sAPPα-NSCs) engrafted into the hippocampi on Morris water maze (MWM) performance of healthy mice.

Results: Analysis of brain tissue from diabetic sAPPα mice revealed that sAPPα blocked the development of Alzheimer’s-like pathology in the form of aberrant tau phosphorylation. Additionally, sAPPα decreased diabetes-induced activation of the unfolded protein response (UPR), a sign that diabetic sAPPα mice maintained better overall brain health compared to diabetic controls.

We found that sAPPα slowed the development of diabetes-induced thermal hypoalgesia, an indicator of sensory neuropathy, in our model. Cell culture experiments demonstrated that the neurotrophic effects of sAPPα in the PNS are associated with up-regulation of the neuroprotective transcription factor NFκB and increased expression of the mitochondrial antioxidant MnSOD.

In the final set of experiments, we found that hippocampal injections of sAPPα-NSCs altered Morris water maze (MWM) performance of healthy SAMR1 mice. Although future studies are required to determine the effects of sAPPα-NSCs on cognition, these preliminary results nevertheless warrant future studies investigating the therapeutic potential of sAPPα-NSCs.

Conclusion: In total, the results presented in this thesis demonstrate that sAPPα can inhibit pathology in the diabetic nervous system. Therefore, the data generated from these studies has provided a foundation for the development of sAPPα based therapeutics, potentially in the form of sAPPα-NSCs, as a treatment option for diabetes and AD.