Interaction of amyloid beta with humanin and acetylcholinesterase is modulated by ATP

Humanin (HN) is known to bind amyloid beta (A beta)-inducing cytoprotective effects, while binding of acetylcholinesterase (AChE) to A beta increases its aggregation and cytotoxicity. Previously, we showed that binding of HN to A beta blocks aggregation induced by AChE and that HN decreases but does not abolish A beta-AChE interactions in A549 cell media. Here, we set out to shed light on factors that modulate the interactions of A beta with HN and AChE. We found that binding of either HN or AChE to A beta is not affected by heparan sulfate, while ATP, thought to reduce misfolding of A beta, weakened interactions between AChE and A beta but strengthened those between A beta and HN. Using media from either A549 or H1299 lung cancer cells, we observed that more HN was bound to A beta upon addition of ATP, while levels of AChE in a complex with A beta were decreased by ATP addition to A549 cell media. Exogenous addition of ATP to either A549 or H1299 cell media increased interactions of endogenous HN with A beta to a comparable extent despite differences in AChE expression in the two cell lines, and this was correlated with decreased binding of exogenously added HN to A beta. Treatment with exogenous ATP had no effect on cell viability under all conditions examined. Exogenously added ATP did not affect viability of cells treated with AChE-immunodepleted media, and there was no apparent protection against the cytotoxicity resulting from immunodepletion of HN. Moreover, exogenously added ATP had no effect on the relative abundance of oligomer versus total A beta in either cell line.