Amyloid β peptide toxicity in differentiated PC12 cells: Calpain‐calpastatin, caspase, and membrane damage

Amyloid β peptide (Aβ) is implicated in the pathogenesis of Alzheimer's disease (AD). The peptide is toxic to neurons, possibly by causing initial synaptic dysfunction and neuronal membrane dystrophy, promoted by increased cellular Ca2+. Calpain (Ca2+-dependent protease) and caspase have also been implicated in AD. There is little information on communication between the two proteases or on the involvement of calpastatin (the specific calpain inhibitor) in Aβ toxicity. We studied the effects of Aβ25–35 (sAβ) on calpain, calpastatin, and caspase in neuronal-like differentiated PC12 cells. sAβ-treated cells exhibited primarily cell membrane damage (varicosities along neurites, enhanced membrane permeability to propidium iodide, without apparent nuclear changes of apoptosis, and little poly (ADP-ribose) polymerase [PARP] degradation). The sAβ-induced membrane damage is in contrast with staurosporine-induced damage (nuclear apoptotic changes, PARP degradation, without membrane propidium iodide permeability). sAβ led to activation of caspase-8 and calpain, promotion of calpastatin degradation (by caspase-8 and by calpain), and enhanced degradation of fodrin (mainly by calpain). The results support the idea that Aβ causes primarily neuronal membrane dysfunction, and point to cross-talk between calpain and caspase (protease activation and degradation of calpastatin) in Aβ toxicity. Increased expression of calpastatin and/or decrease in calpain and caspase-8 may serve as means for ameliorating early symptoms of AD. © 2008 Wiley-Liss, Inc.