ABSTRACT
High levels of the adipocytokine leptin are associated with reduced risk of Alzheimer's disease. Leptin treatment also reduces ß-amyloid (Aß) levels in in vivo and in vitro models of Alzheimer's disease. Aß and leptin interact with the Akt/mammalian target of rapamycin complex 1 (mTORC1) signaling pathway. Akt/mTORC1 activation reduces tau phosphorylation through the inhibition of the downstream enzyme GSK-3ß. mTORC1 also regulates translation of many proteins including leptin. While Aß has been shown to inactivate Akt, inhibit mTORC1, and facilitate the phosphorylation of tau, leptin activates both Akt and mTORC1 and reduces tau phosphorylation. However, the extent to which Aß may modulate leptin expression and increase tau phosphorylation involving Akt/mTORC1 has not been determined. In this study, we show that incubation of organotypic slices from rabbit hippocampus with Aß down-regulates leptin expression, inhibits Akt, activates GSK-3ß, increases tau phosphorylation, and inactivates mTORC1. Leptin treatment reverses Aß effects by alleviating Akt inhibition, preventing GSK-3ß activation, reducing tau phosphorylation, and activating mTORC1. On the other hand, Rapamycin, an allosteric inhibitor of mTORC1, down-regulates leptin expression, increases tau phosphorylation, and does not affect Akt and GSK-3ß. Our results demonstrate for the first time that Aß regulates leptin expression and tau phosphorylation through mTORC1.
