Neuronal Calcium Signaling, Mitochondrial Dysfunction, and Alzheimer's Disease

Abstract

Alzheimer's disease (AD) is the most common neurodegenerative disorder among the aged worldwide. AD is characterized by extensive synaptic and neuronal loss that leads to impaired memory and cognitive decline. The cause of AD is not completely understood and no effective therapy has been developed. The accumulation of toxic amyloid-β₄₂ (Aβ₄₂) peptide oligomers and aggregates in AD brain has been proposed to be primarily responsible for the pathology of the disease, an idea dubbed the 'amyloid hypothesis' of AD etiology. In addition to the increase in Aβ₄₂ levels, disturbances in neuronal calcium (Ca²⁺) signaling and alterations in expression levels of Ca²⁺ signaling proteins have been observed in animal models of familial AD and in studies of postmortem brain samples from sporadic AD patients. Based on these data, the 'Ca²⁺ hypothesis of AD' has been proposed. In particular, familial AD has been linked with enhanced Ca²⁺ release from the endoplasmic reticulum and elevated cytosolic Ca²⁺ levels. The augmented cytosolic Ca²⁺ levels can trigger signaling cascades that affect synaptic stability and function and can be detrimental to neuronal health, such as activation of calcineurin and calpains. Here we review the latest results supporting the 'Ca²⁺ hypothesis' of AD pathogenesis. We further argue that over time, supranormal cytosolic Ca²⁺ signaling can impair mitochondrial function in AD neurons. We conclude that inhibitors and stablizers of neuronal Ca²⁺ signaling and mitochondrial function may have therapeutic potential for AD treatment. We also discuss latest and planned AD therapeutic trials of agents targeting Ca²⁺ channels and mitochondria.