The Tetrapeptide HAEE Promotes Amyloid-Beta Clearance from the Brain

Alzheimer's disease is characterized by the accumulation of neurotoxic forms of amyloid-beta (Aβ) in the brain, leading to synaptic dysfunction, neuroinflammation, and neuronal death. The tetrapeptide HAEE crosses the blood-brain barrier (BBB), inhibits the formation of toxic Aβ oligomers, and reduces amyloid burden in vivo. However, the mechanisms of HAEE's anti-amyloidogenic effect remained incompletely understood. In this study, we investigated the mechanism of HAEE-dependent Aβ clearance both in vitro and in vivo. Using ELISA, we assessed the HAEE effect on the levels of Aβ, IL-6, and TNFα in mouse brain tissue following intracerebroventricular administration. The mechanism of the anti-Aβ effect of HAEE was studied using primary brain cell cultures and a BBB transwell model through ELISA, flow cytometry, and microscopy. We showed that HAEE reduced Aβ level by 35% and IL-6 level by 40% in mouse brain tissue. HAEE enhanced Aβ clearance via LRP1- and PgP-dependent Aβ transport through the BBB and doubled the rate of Aβ degradation by microglia. In addition to inhibition of Aβ aggregation, HAEE dissolved already formed Aβ oligomers. The HAEE-induced decrease in IL-6 levels in the mouse brain was associated with reduced pro-inflammatory activation of microglia. Thus, HAEE's effect against Aβ-related neuropathologies is realized through a decrease in the level of toxic Aβ oligomer and inhibition of neuroinflammation.