Testing the link between isoaspartate and Alzheimer’s disease etiology

Abstract

Isoaspartate (isoAsp) is a damaging amino acid residue formed in proteins as a result of spontaneous deamidation. IsoAsp disrupts the secondary and higher order structures of proteins, damaging their functions and making them prone to aggregation. An association has been suggested between isoAsp and Alzheimer's Disease (AD). Here we strengthened the link between isoAsp and AD by novel approaches to isoAsp analysis in blood human serum albumin (HSA), the most abundant blood protein, a major carrier of amyloid beta (Aβ) peptide and phosphorylated tau (pTau) protein in blood and a key participant in their clearance pathway. We discovered a reduced amount of anti-isoAsp antibodies (P < .0001), an elevated isoAsp level in HSA (P < .001), more HSA aggregates (P < .0001) and increased levels of free Aβ (P < .01) in AD blood compared to healthy controls. We also found that deamidation significantly reduces HSA capacity to bind with Aβ and pTau (P < .05). These findings support the presence in AD of a bottleneck in clearance of Aβ and pTau leading to their increased concentrations in brain and facilitating their aggregations there.

Deamidation-related blood biomarkers show promise for early diagnostics of neurodegeneration

“…The IgG antibodies were puri ed from plasma using the Melon Gel IgG Puri cation Kit (Thermo Fisher Scienti c, San Diego, CA, USA). To determine in each sample the amount of IgG against aged HSA (aHSA, ≈ 60% isoAsp), the puri ed IgG antibodies were used as the primary antibody in the indirect ELISA [17], while the secondary antibody was Goat anti-Human IgG (H + L) Secondary Antibody conjugated with HRP (Thermo Fisher Scienti c, San Diego, CA, USA). To eliminate the effect of sample location on the plate, the data were normalized by the average reading in each row and column.…”

“…Our recent ndings have strengthened the link between isoAsp and AD pathology [17]. Using a novel enzyme-linked immunosorbent assay (ELISA) [18], we discovered that the accumulation of isoAsp in human serum albumin (HSA) leads to a diminished HSA capacity to carry Aß and pTau, and thus to clear these damaging molecules in the blood circulatory system, which has been recognized as a major contributor to their accumulation in brain [19].…”

“…Using a novel enzyme-linked immunosorbent assay (ELISA) [18], we discovered that the accumulation of isoAsp in human serum albumin (HSA) leads to a diminished HSA capacity to carry Aß and pTau, and thus to clear these damaging molecules in the blood circulatory system, which has been recognized as a major contributor to their accumulation in brain [19]. By studying an Amsterdam cohort, we have found that isoAsp levels in HSA strongly correlate with AD [17]. Furthermore, native immunoglobulins (IgGs) speci c to deamidated HSA that could protect the human organism from the damaging effect of deamidation have been found signi cantly reduced in AD [17].…”

“…By studying an Amsterdam cohort, we have found that isoAsp levels in HSA strongly correlate with AD [17]. Furthermore, native immunoglobulins (IgGs) speci c to deamidated HSA that could protect the human organism from the damaging effect of deamidation have been found signi cantly reduced in AD [17]. However, questions remained related to the performance of these biomarkers in non-Caucasian patients, speci city to AD of these biomarkers, and their ability to detect early disease stages.…”

First Experimental Evidence for Reversibility of Ammonia Loss from Asparagine

“…IsoAsp differs from Asp by the rearrangement to the backbone of a CH 2 side chain group, which distorts the secondary protein structure and can hamper protein function [ 3 ]. Moreover, deamidated proteins, such as human serum albumin (HSA), tend to lose their native conformation and start to aggregate [ 4 , 5 ], eventually contributing to the onset of neurodegenerative diseases [ 6 , 7 , 8 ].…”