Calcium Dysregulation and Membrane Disruption as a Ubiquitous Neurotoxic Mechanism of Soluble Amyloid Oligomers*♦

Abstract

Increasing evidence suggests that amyloid peptides associated with a variety of degenerative diseases induce neurotoxicity in their intermediate oligomeric state, rather than as monomers or fibrils. To test this hypothesis and investigate the possible involvement of Ca 2؉ signaling disruptions in amyloid-induced cytotoxicity, we made homogeneous preparations of diseaserelated amyloids (A␤, prion, islet amyloid polypeptide, polyglutamine, and lysozyme) in various aggregation states and tested their actions on fluo-3-loaded SH-SY5Y cells. Application of oligomeric forms of all amyloids tested (0.6 -6 g ml ؊1 ) rapidly (ϳ5 s) elevated intracellular Ca 2؉ , whereas equivalent amounts of monomers and fibrils did not. Ca 2؉ signals evoked by A␤42 oligomers persisted after depletion of intracellular Ca 2؉ stores, and small signals remained in Ca 2؉ -free medium, indicating contributions from both extracellular and intracellular Ca 2؉ sources. The increased membrane permeability to Ca 2؉ cannot be attributed to activation of endogenous Ca 2؉ channels, because responses were unaffected by the potent Ca 2؉ -channel blocker cobalt (20 m). Instead, observations that A␤42 and other oligomers caused rapid cellular leakage of anionic fluorescent dyes point to a generalized increase in membrane permeability. The resulting unregulated flux of ions and molecules may provide a common mechanism for oligomer-mediated toxicity in many amyloidogenic diseases, with dysregulation of Ca 2؉ ions playing a crucial role because of their strong trans-membrane concentration gradient and involvement in cell dysfunction and death.Alzheimer disease (AD) 1 is characterized by the appearance in the brain of plaques, containing extracellular deposits of amyloid ␤-peptide (A␤) that result from altered proteolytic processing of amyloid precursor protein, together with intracellular neurofibrillary tangles containing misfolded tau (1).Brain regions with plaques and tangles exhibit reduced numbers of synapses, and neurites associated with plaques and tangles are often damaged, suggesting a pivotal role for A␤ in the neuropathology of AD (2-5). Moreover, numerous other neurodegenerative disorders (including Huntington, Parkinson, and prion diseases) are also associated with the formation and accumulation of amyloid fibrils in specific brain areas (6, 7). These commonalities suggest a general mechanism of action for the more than 100 human amyloid-related diseases, whereby normally soluble peptides and proteins undergo aberrant folding (8).Aggregation of A␤ proceeds through several conformational states, including dimers, spherical oligomers composed of 10 -24 monomers, and strings of oligomers (protofibrils), before finally assuming an insoluble fibrillar conformation (9). The initial formulation of the "amyloid hypothesis" of AD specifically implicated fibrillar amyloid deposits (10). However, more recent evidence suggests that soluble oligomers may be the principal neurotoxic agent (11-15). Soluble A␤ oligomers are found in the cerebrospinal fluid of ...

Using model membranes for the study of amyloid beta:lipid interactions and neurotoxicity

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Beta-amyloid disrupted synaptic vesicle endocytosis in cultured hippocampal neurons

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