Protection against ß-amyloid neurotoxicity by a non-toxic endogenous N-terminal ß-amyloid fragment and its active hexapeptide core sequence.

ABSTRACT

High levels (µM) of beta amyloid (Aß) oligomers are known to trigger neurotoxic effects, leading to synaptic impairment, behavioral deficits, and apoptotic cell death. The hydrophobic C-terminal domain of Aß, together with sequences critical for oligomer formation, is essential for this neurotoxicity. However, Aß at low levels (pM-nM) has been shown to function as a positive neuromodulator and this activity resides in the hydrophilic N-terminal domain of Aß. An N-terminal Aß fragment (1-15/16), found in cerebrospinal fluid, was also shown to be a highly active neuromodulator and to reverse Aß-induced impairments of long-term potentiation. Here, we show the impact of this N-terminal Aß fragment and a shorter hexapeptide core sequence in the Aß fragment (Aßcore 10-15) to protect or reverse Aß-induced neuronal toxicity, fear memory deficits and apoptotic death. The neuroprotective effects of the N-terminal Aß fragment and Aßcore on Aß-induced changes in mitochondrial function, oxidative stress, and apoptotic neuronal death were demonstrated via mitochondrial membrane potential, live reactive oxygen species, DNA fragmentation and cell survival assays using a model neuroblastoma cell line (differentiated NG108-15) and mouse hippocampal neuron cultures. The protective action of the N-terminal Aß fragment and Aßcore against spatial memory processing deficits in amyloid precursor protein/PSEN1 (5XFAD) mice was demonstrated in contextual fear conditioning. Stabilized derivatives of the N-terminal Aßcore were also shown to be fully protective against Aß-triggered oxidative stress. Together, these findings indicate an endogenous neuroprotective role for the N-terminal Aß fragment, while active stabilized N-terminal Aßcore derivatives offer the potential for therapeutic application.