Price_2020_Biochemistry__

It is known that the humanin (HN) peptide binds Abeta protecting against its cytotoxic effects while acetylcholinesterase (AChE) binding to Abeta increases its aggregation and cytotoxicity. HN is also known to bind insulin-like growth factor binding protein-3 (IGFBP-3). Here, we examined regulation of Abeta conformations by HN, AChE, and IGFBP-3 both in vitro and in the conditioned media from A549 and H1299 lung cancer cells. Our in vitro results show that IGFBP-3 binds HN and blocks it from binding Abeta in the absence or presence of AChE; HN and AChE can simultaneously bind Abeta but not in the presence of IGFBP-3; HN is unable to reduce aggregation of Abeta in the presence of IGFBP-3; and HN abolishes aggregation of Abeta induced by addition of AChE, in the absence of IGFBP-3. In the media, AChE and HN can simultaneously bind Abeta. While both AChE and HN are detected upon using 6E10 Abeta antibodies, only AChE is detected with the Abeta, 17-24 antibody 4G8, the anti-oligomer A11, and the anti-amyloid fibrils LOC antibodies. No signal was observed for IGFBP-3 with any of the anti-amyloid antibodies used. Exogenously added IGFBP-3 reduced the amount of HN found in a complex using 6E10 antibodies and correlated with a concomitant increase in amyloid oligomers. Immunodepletion of HN from the media of A549 and H1299 cells increased the relative abundance of oligomer versus total Abeta, the A11-positive prefibrillar oligomers, and to a lesser extent, the LOC-positive fibrillar oligomers, and correlated with diminished cell viability and increased apoptosis.