Novel heterozygous mutation in alpha-2-macroglobulin (A2M) suppressing the binding of amyloid-beta (A beta)

Introduction: Many studies have suggested that the alpha-2-macroglobulin (A2M) gene may be involved in the pathogenesis of Alzheimer's disease (AD). A2M encoded by the A2M gene can specifically bind to the beta-amyloid peptide and prevent fiber formation. Methods: The patient in this study had progressive memory loss at the age of 60 years and underwent a series of neuropsychological tests, cranial magnetic resonance imaging (MRI), cerebrospinal fluid (CSF) biomarker analysis, and whole-exome sequencing (WES) to evaluate possible mutations. We used in silico tools and three-dimensional (3D) protein structure prediction to analyze the pathogenicity of the mutation and used a co-immunoprecipitation experiment to study the effect of mutations on amyloid-beta (A beta) binding. Results: Based on neuropsychological tests, cranial MRI, and CSF biomarker analysis, the patient was diagnosed with AD. WES showed that there was a missense mutation in A2M (c.1229A > C, p.N410T). Bioinformatics analysis showed that this mutation was pathogenic. Moreover, 3D protein structure analysis showed that the A2M Asn410 residue was an N-glycosylation site, which was necessary for A2M activation to bind to A beta. Missense mutations led to the loss of glycosylation at this site, which suppressed the binding of A beta. The functional experiment also confirmed the prediction: the interaction between A2M and A beta from the patient's plasma was weakened. Conclusions: Our results demonstrate that this novel A2M p.N410T mutation may have a pathogenic role in AD, by altering the binding interactions between A2M and A beta.