Apolipoprotein E forms stable complexes with recombinant Alzheimer's disease beta-amyloid precursor protein

Area of Science:

• Neuroscience
• Biochemistry
• Molecular Biology

Background:

• Apolipoprotein E (apoE) is genetically linked to Alzheimer's disease (AD) incidence.
• ApoE forms stable complexes with beta-amyloid peptide (Abeta) in vitro.
• Abeta is the primary component of senile plaques in AD.

Purpose of the Study:

• To investigate the binding interaction between apoE and full-length Abeta precursor protein (APP).
• To characterize the nature and potential pathological relevance of apoE-APP complexes.

Main Methods:

• Utilized maltose-binding-protein-APP fusion protein and human very-low-density lipoprotein (VLDL).
• Performed saturation-binding experiments to determine binding stoichiometry and affinity.
• Investigated complex stability under various conditions (SDS, reducing agents).
• Analyzed complex formation using different apoE sources (CSF, delipidated VLDL, recombinant) and isoforms (apoE3, apoE4).

Main Results:

• Detected a specific interaction between apoE and APP, inhibited by Abeta or anti-apoE antibody.
• Characterized a single binding equilibrium with 1:1 stoichiometry and a dissociation constant of 15 nM.
• Confirmed formation of SDS-stable apoE-APP complexes, independent of reducing conditions but dissociable by SDS under reducing conditions.
• Observed high-molecular-mass aggregate formation, with Abeta amino acids 14-23 implicated in binding.
• Found no differences in interaction with apoE3 versus apoE4 isoforms.

Conclusions:

• Apolipoprotein E forms stable complexes with the Abeta moiety of APP, mirroring interactions with isolated Abeta.
• These apoE-APP complexes exhibit characteristics similar to apoE-Abeta complexes.
• The findings suggest a potential pathological role for apoE-APP interactions in vivo, particularly in Alzheimer's disease.