The role of carbohydrate component of recombinant α7 nicotinic acetylcholine receptor extracellular domain in its immunogenicity and functional effects of resulting antibodies

Abstract

Nicotinic acetylcholine receptors of α7 subtype (α7 nAChRs) attenuate the inflammatory cytokines production by macrophages and are involved in pathogenesis of Alzheimer disease by directly influencing the processing of amyloid-beta (Aβ) precursor protein in the brain. Previously we found that regular injections of bacterial lipopolysaccharide (LPS) decreased the level of α7 nAChRs and stimulated accumulation of Aβ peptide (1–42) in the brain of mice resulting in memory impairment. Similar effects were observed in mice immunized with recombinant extracellular domain (1–208) of α7 nAChR subunit. However, the mechanism of inflammation-like effect of α7-specific antibodies remained unclear. The aim of the present study was to reveal the impact of carbohydrate component of recombinant α7(1–208) produced in yeast in the functional effect of resulting antibodies. For this purpose, C57Bl/6 mice were immunized with either initial α7(1–208) or with that pre-treated with endoglycosidase. Control groups of mice obtained injections of either LPS or complete Freund’s adjuvant. Mice were tested for memory performance, their blood sera were examined for the presence and fine specificity of α7(1–208)-specific antibodies and the brain preparations were studied for the levels of α7 nAChR, Aβ(1–42) and interleukin-6. It was found that the original α7(1–208) was more immunogenic than the deglycosylated one, and their epitopes were recognized with different efficiency. In contrast to LPS and original α7(1–208), deglycosylated α7(1–208) did not stimulate interleukin-6 elevation in the brain, i.e. had no pro-inflammatory effect. Nevertheless, immunizations with either the original or deglycosylated α7(1–208) resulted in similar decrease of α7 nAChRs, accumulation of Aβ(1–42) in the brain and significant episodic memory decline, comparable to those exerted by LPS injections. We conclude that the decrease of α7 nAChR density, caused by α7(1–208)-specific antibody, is critical for Aβ(1–42) accumulation and episodic memory impairment, while pro-inflammatory capacity of α7(1–208)-specific antibody plays a secondary role for the development of Alzheimer-like symptoms.