Abstract
Although the molecular mechanisms underlying the pathology of amyloidoses are not well understood, the interaction between amyloid proteins and cell membranes is thought to play a role in several amyloid diseases. Amyloid fibrils of β2-microglobulin (β2m), associated with dialysis-related amyloidosis (DRA), have been shown to cause disruption of anionic lipid bilayers in vitro. However, the effect of lipid composition and the chemical environment in which β2m-lipid interactions occur have not been investigated previously. Here we examine membrane damage resulting from the interaction of β2m monomers and fibrils with lipid bilayers. Using dye release, tryptophan fluorescence quenching and fluorescence confocal microscopy assays we investigate the effect of anionic lipid composition and pH on the susceptibility of liposomes to fibril-induced membrane damage. We show that β2m fibril-induced membrane disruption is modulated by anionic lipid composition and is enhanced by acidic pH. Most strikingly, the greatest degree of membrane disruption is observed for liposomes containing bis(monoacylglycero)phosphate (BMP) at acidic pH, conditions likely to reflect those encountered in the endocytic pathway. The results suggest that the interaction between β2m fibrils and membranes of endosomal origin may play a role in the molecular mechanism of β2m amyloid-associated osteoarticular tissue destruction in DRA.
Highlights
The aggregation of proteins into amyloid fibrils is associated with many debilitating disorders, including type II diabetes mellitus, Alzheimer’s, Parkinson’s, Creutzfeldt-Jakob disease and dialysis-related amyloidosis (DRA) [1]
We demonstrate that b2m fibril-induced membrane damage is modulated by lipid composition and pH, with membrane damage being enhanced by the presence of anionic lipids at acidic pH
Fragmented b2m fibrils were subsequently formed by vigorous agitation to decrease the weight average length to 0.3060.01 mm (1 S.E., sample size = 763 fibrils) (Fig. 1B(ii))
Summary
The aggregation of proteins into amyloid fibrils is associated with many debilitating disorders, including type II diabetes mellitus, Alzheimer’s, Parkinson’s, Creutzfeldt-Jakob disease and dialysis-related amyloidosis (DRA) [1]. Xue et al [14] have demonstrated that interaction of liposomes with b2m fibrils results in membrane damage that is detectable by dye release experiments. This b2m fibril-induced membrane damage is paralleled by a decrease in apparent cell viability, as measured by the reduction of 3-(4,5dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) [14]. We examine membrane damage resulting from the interaction of b2m monomers, fragmented and unfragmented fibrils with lipid bilayers using dye release, tryptophan fluorescence quenching and confocal microscopy assays. Observations presented here suggest that disruption of endosome function, as a result of b2m fibril-lipid interactions, may play a role in b2m amyloid pathology
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