Clusterin in Alzheimer’s Disease: An Amyloidogenic Inhibitor of Amyloid Formation

Background: Clusterin is a heterodimeric glycoprotein (α- and β-chain), which has been described as an extracellular molecular chaperone. In humans, clusterin is an amyloid associated protein, co-localizing with fibrillar deposits in Alzheimer’s disease. To clarify its implication in the disease, we provide evidence that clusterin has intrinsic amyloidogenic properties, which are intertwined with its inhibitory effect on amyloid-β fibril formation.Methods: Aggregation-prone regions of human clusterin were predicted by AMYLPRED. Synthetic peptide-analogues of each region underwent in vitro aggregation assays, namely, examination with transmission electron microscopy, X-Ray diffraction from oriented fibers, ATR FT-IR spectroscopy, and Congo Red birefringence assays. The same peptide-analogues were co-incubated with amyloid-β and their potential as inhibitors was tested with thioflavin T fluorescence emission measurements and transmission electron microscopy. Molecular dynamics simulations were performed to gain insight into the interaction between amyloid-β and the peptide-analogues.Results: Clusterin peptide-analogues form amyloid-like fibrils, as revealed by transmission electron microscopy. They can form fibers that give cross-β X-ray diffraction patterns and ATR FT-IR spectroscopy confirms the dominance of β-strand secondary structure. They also exhibit apple-green birefringence, when stained with Congo Red and examined between crossed polars of a polarizing light microscope. Furthermore, when amyloid-β is co-incubated with clusterin’s peptide analogues, it shows decreased thioflavin T fluorescence emission over time, while the formation of amyloid-β amyloid fibrils is diminished, as confirmed by transmission electron microscopy. The inhibitory effect of clusterin-peptide analogues on amyloid-β fibril formation was ascertained though molecular dynamics simulations. Conclusions: Clusterin has multiple aggregation-prone regions in its α-chain and these regions have a functional role in the inhibition of amyloid-β fibril formation.