Aβ25-35-induced autophagy and apoptosis are prevented by the CRMP2-derived peptide ST2-104 (R9-CBD3) via a CaMKKβ/AMPK/mTOR signaling hub

We previously reported that the peptide ST2-104 (CBD3, for Ca2+ channel-binding domain 3), derived from the collapsin response mediator protein 2 (CRMP2)-a cytosolic phosphoprotein, protects neuroblastoma cells against β-amyloid (Aβ) peptide-mediated toxicity through engagement of a phosphorylated CRMP2/NMDAR pathway. Abnormal aggregation of Aβ peptides (e.g., Aβ25-35) leads to programmed cell death (apoptosis) as well autophagy-both of which contribute to Alzheimer's disease (AD) progression. Here, we asked if ST2-104 affects apoptosis and autophagy in SH-SY5Y neuroblastoma challenged with the toxic Aβ25-35 peptide and subsequently mapped the downstream signaling pathways involved. ST2-104 protected SH-SY5Y cells from death following Aβ25-35 peptide challenge by reducing apoptosis and autophagy as well as limiting excessive calcium entry. Cytotoxicity of SHY-SY5Y cells challenged with Aβ25-35 peptide was blunted by ST2-104. The autophagy activator Rapamycin blunted the anti-apoptotic activity of ST2-104. ST2-104 reversed Aβ25-35-induced apoptosis via inhibiting Ca2+/CaM-dependent protein kinase kinase β (CaMKKβ)-mediated autophagy, which was partly enhanced by STO-609 (an inhibitor of CaMKKβ). ST2-104 attenuated neuronal apoptosis by inhibiting autophagy through a CaMKKβ/AMPK/mTOR signaling hub. These findings identify a mechanism whereby, in the face of Aβ25-35, the concerted actions of ST2-104 leads to a reduction in intracellular calcium overload and inhibition of the CaMKKβ/AMPK/mTOR pathway resulting in attenuation of autophagy and cellular apoptosis. These findings define a mechanistic framework for how ST2-104 transduces "outside" (calcium channels) to "inside" signaling (CaMKKβ/AMPK/mTOR) to confer neuroprotection in AD.