Recent studies demonstrate that peripheral
amylin treatment reduces pathology in mouse models of
Alzheimer's disease (AD). However, soluble and aggregated
amylin are distinct species; while
amylin is a physiological
neuropeptide,
amylin aggregation is a pathological factor for diabetes. We thus hypothesized that because of their similarity in secondary structures,
amylin antagonizes
amyloid-β
peptide (Aβ)-induced AD pathology in neurons with a dose-dependent pattern. To test the hypothesis, we conducted both in vitro and in vivo experiments with different doses of
amylin and with its analog,
pramlintide. Here we report that a high concentration of either Aβ or
amylin alone induced tau phosphorylation (pTau) in primary neurons. Interestingly, with a low concentration,
amylin had direct effects to reverse the Aβ-induced pTau, as well as damaged neuronal synapses and neurite disorganization. However, when the concentration was high (10.24 μM),
amylin lost the effects against the Aβ-induced cellular AD pathology and, together with Aβ, worsened
tauopathy in neurons. In the 5XFAD AD mouse model, daily peripheral
amylin treatment with a low dose (200 μg/kg) more effectively reduced
amyloid burden, and increased synapse, but with a high dose (800 μg/kg), it more effectively reduced
tauopathy. Correspondingly,
amylin treatment improved learning and memory in these mice. It demonstrates that
amylin has a dose-dependent U-shape effect against AD pathogenesis. Within a physiological range,
amylin is a neuroprotective
hormone against AD in neurons; but when both Aβ and
amylin concentrations are elevated, imbalance of Aβ and
amylin may contribute to brain AD pathogenesis.