The extracellular chaperone clusterin influences amyloid formation and toxicity by interacting with prefibrillar structures

Abstract

Clusterin is an extracellular chaperone present in all disease-associated extracellular amyloid deposits, but its roles in amyloid formation and protein deposition in vivo are poorly understood. The current study initially aimed to characterize the effects of clusterin on amyloid formation in vitro by a panel of eight protein substrates. Two of the substrates (Alzheimer's beta peptide and a PI3-SH3 domain) were then used in further experiments to examine the effects of clusterin on amyloid cytotoxicity and to probe the mechanism of clusterin action. We show that clusterin exerts potent effects on amyloid formation, the nature and extent of which vary greatly with the clusterin:substrate ratio, and provide evidence that these effects are exerted via interactions with prefibrillar species that share common structural features. Proamyloidogenic effects of clusterin appear to be restricted to conditions in which the substrate protein is present at a very large molar excess; under these same conditions, clusterin coincorporates with substrate protein into insoluble aggregates. However, when clusterin is present at much higher but still substoichiometric levels (e.g., a molar ratio of clusterin:substrate=1:10), it potently inhibits amyloid formation and provides substantial cytoprotection. These findings suggest that clusterin is an important element in the control of extracellular protein misfolding.

Ultrasensitive Measurement of Ca2+ Influx into Lipid Vesicles Induced by Protein Aggregates

“…We observed that both species reduced very significantly the degree of Ca 2+ influx while incubation with an anti ‐GFP antibody, as a control that does not bind to the Aβ peptide, had no detectable effect. These results are consistent with previous reports that clusterin30, 31 and Nb3 bind to oligomers of the Aβ peptide, resulting in the reduction of Ca 2+ influx into neuronal cells 7, 11. We then carried out a series of dilution experiments to find the concentration required to reduce the Ca 2+ influx by half; we obtained values of 0.1±0.02 n m and 18±3.4 n m for clusterin and Nb3, respectively (Figure 3 b,c).…”

Mutations linked to interstitial lung disease can abrogate anti-amyloid function of prosurfactant protein C

“…Chaperones have little apparent substrate specificity and are as a rule promiscuous, recognising common features of unfolded proteins like exposed hydrophobic patches. The extracellular protein clusterin, also known as apolipoprotein J, can prevent amyloid formation by binding to prefibrillar species, and it may thus confer protection to extracellular amyloid formation [39,40]. SP-C, by design, has a high tendency to misfold and aggregate into amyloid fibrils, mediated by its polyVal domain [41].…”

Inflammation in Alzheimer’s Disease and Molecular Genetics: Recent Update

“…In addition, recent studies have revealed that the concentration of CLU in the CSF and plasma of AD patients is significantly elevated (Sihlbom et al 2008;Thambisetty et al 2010). Interestingly, as a chaperone protein, CLU has been proven to interact with Ab peptides and this interaction plays an important role in Ab aggregation, toxicity and clearance (Baig et al 2012;DeMattos et al 2002;Narayan et al 2012;Yerbury et al 2007). Also, several studies have suggested that CLU is a potential modulator of inflammation in AD pathogenesis.…”