Binding of ApoE Isoforms to Aβ Peptides and Effects on Their Fibrillization

Alzheimer's disease (AD) is the most widespread neurodegenerative disease, strongly linked to amyloid depositions in the brain consisting of amyloid β (Aβ) peptides. The likelihood of developing late-onset Alzheimer's disease (LOAD) is influenced by the specific isoforms of apolipoprotein E (ApoE), with ApoE4 being the strongest known genetic risk factor for LOAD. Strong evidence suggests that ApoE impacts AD by modulating Aβ aggregation and clearance, although the precise molecular mechanisms remain incompletely understood. Microscale thermophoresis (MST) is a powerful technique for characterizing molecular interactions in solution, which has been used to determine various binding constants, although not the binding of ApoE to Aβ peptides. MST results show that ApoE isoforms bind Aβ1-40 and Aβ1-42 with low micromolar affinity. For Aβ1-42, ApoE3 shows the strongest binding (K _d = 0.72 μM) and ApoE4 shows the weakest binding (K _d = 2.80 μM). For Aβ1-40, ApoE4 shows the strongest binding (K _d = 1.59 μM) and ApoE2 shows the weakest binding (K _d = 5.29 μM). The MST results show that ApoE interacts with Aβ peptides at supraphysiological peptide concentrations. However, ApoE inhibited the fibrillization of Aβ1-42 peptide at substoichiometric concentrations, which might be related to blocking Aβ fibril elongation in vivo. The estimated IC₅₀ values indicate that ApoE4 has a slightly stronger, and ApoE2 a slightly weaker, inhibitory effect on Aβ1-42 fibrillization.