αB-Crystallin inhibits the cell toxicity associated with amyloid fibril formation by κ-casein and the amyloid-β peptide

• DOI: 10.1007/s12192-010-0212-z
• Publication Date: 2010-07-14T02:26:30Z
• Authors: Francis C. Dehle; Heath Ecroyd; Ian F. Musgrave; John A. Carver
• Keywords: Protein Folding; Time Factors; genetic association; beta casein; animal cell; Social and Behavioral Sciences; casein; binding affinity; crystallin; Physical Sciences and Mathematics; enzyme inhibition; 0303 health sciences; associated; fibril; formation; article; amyloid; Life Sciences; Caseins; Amyloid-ß; Hydrogen-Ion Concentration; peptide; 3. Good health; Parkinson disease; kappa casein; cytotoxicity; ?-Casein; Alzheimer disease; Amyloid fibril; Amyloid; Cell Survival; Small heat-shock protein; alphab; Cell Line; 03 medical and health sciences; inhibits; Animals; controlled study; kappa; cell viability; nonhuman; Amyloid beta-Peptides; prion diseas aB-Crystallin; toxicity; alpha-Crystallin B Chain; cell; Peptide Fragments; Rats; Cell toxicity; amyloid beta protein; Keywords: alpha crystallin; beta; CMMB

Amyloid fibril formation is associated with diseases such as Alzheimer's, Parkinson's, and prion diseases. Inhibition of amyloid fibril formation by molecular chaperone proteins, such as the small heat-shock protein αB-crystallin, may play a protective role in preventing the toxicity associated with this form of protein misfolding. Reduced and carboxymethylated κ-casein (RCMκ-CN), a protein derived from milk, readily and reproducibly forms fibrils at physiological temperature and pH. We investigated the toxicity of fibril formation by RCMκ-CN using neuronal model PC12 cells and determined whether the inhibition of fibril formation altered its cell toxicity. To resolve ambiguities in the literature, we also investigated whether fibril formation by amyloid-β1-40 (Aβ(1-40)), the peptide associated with Alzheimer's disease, was inhibited by αB-crystallin and if this affected the toxicity of Aβ. To this end, either RCMκ-CN or Aβ(1-40) was incubated at neutral pH to induce fibril formation before treating PC12 cells and assessing cell viability. Incubated (fibrillar) RCMκ-CN was more toxic to PC12 cells than native RCMκ-CN with the highest level of toxicity being associated with mature fibrils and protofibrils. Furthermore, the toxicity of RCMκ-CN was attenuated when its fibril formation was inhibited, either through the chaperone action of αB-crystallin or when it interacted with its natural binding partners in milk, α(S)- and β-casein. Likewise, incubating Aβ(1-40) with αB-crystallin inhibited both Aβ(1-40) fibril formation and the associated cell toxicity. Importantly, by inhibiting fibril formation, αB-crystallin prevents the cell toxicity associated with protein misfolding.