Molecular pathogenesis of human amyloidosis: Lessons from β₂‐microglobulin‐related amyloidosis

Abstract

Amyloidosis refers to a group of diseases with amyloid fibrils deposited in various organs and is classified into more than 30 diseases in humans based on the kind of amyloid protein.In order to elucidate the molecular pathogenesis of human amyloidosis, we studied the molecular mechanism of amyloid fibril formation in vitro. We first developed a novel fluorometric method to determine amyloid fibrils in vitro based on the unique characteristics of thioflavin T. We next proposed a nucleation-dependent polymerization model to explain the general mechanism of amyloid fibril formation in vitro. Based on this model, we characterized the biological molecular interactions that promote or inhibit amyloid fibril formation in vitro and developed models of pathological molecular environment for inducing human β 2 -microglobulin-related amyloidosis in long-term hemodialysis patients. We also proposed a novel and attractive cytotoxic mechanism of β 2 -microglobulin amyloid fibrils, that is, the disruption of endosomal/lysosomal membranes by endocytosed amyloid fibrils. These findings may be useful to elucidate the molecular pathogenesis of other kinds of human amyloidosis.

Fluorescent dyes in the context of DNA‐binding: The case of Thioflavin T

“…In that case, the photoexcited state cannot relax into the twisted one and a fluorescence light‐up is observed. Due to this characteristic, ThT has become a “gold standard” for visualizing and quantifying the presence of amyloid fibrils and it has been successfully used as a G‐quadruplex specific fluorescent sensor . Recent studies have also investigated the affinity of ThT binding to single and double stranded DNA …”

An unusual case of Aβ2M amyloid deposition in bladder cancer in a non‐dialysis patient

“…A nucleation‐dependent polymerization model could explain the general mechanisms of amyloid fibril formation in vitro . This model consists of nucleation and extension phases …”

Force spectroscopy reveals the presence of structurally modified dimers in transthyretin amyloid annular oligomers

“…However, certain mutations in the TTR sequence can greatly enhance the process of aggregation even though no particular amyloidogenic hotspot can be assigned . In spite of this, in vitro aggregation of WT TTR and of most of its amyloidogenic variants is often induced by mild acidification, which has been proposed to mimic the lysosomal environment associated with the conversion of proteins and peptides into their amyloidogenic form . The resulting aggregates typically bind the amyloid markers Thioflavin‐T and Congo red, display a high content of β‐sheets, but lack the morphology of fibrils extracted from patient samples …”

“…While the mechanisms of amyloid toxicity remain unclear for the most part, interference with the cell membrane appears to be required . Amyloid fibrils have been increasingly recognized as a condensed state of misfolded proteins, which is less harmful than the amyloid oligomers associated with them .…”

“…1,8 In spite of this, in vitro aggregation of WT TTR and of most of its amyloidogenic variants is often induced by mild acidification, 9 which has been proposed to mimic the lysosomal environment associated with the conversion of proteins and peptides into their amyloidogenic form. [9][10][11] The resulting aggregates typically bind the amyloid markers Thioflavin-T and Congo red, 12,13 display a high content of β-sheets, 14 but lack the morphology of fibrils extracted from patient samples. 12,15 While partial unfolding of the TTR monomer and disassembly of the tetramer is a prerequisite for fibrillation, 16,17 there is strong debate over the details of the rest of the aggregation pathway.…”