Calcium in Alzheimer's disease pathogenesis: Too much, too little or in the wrong place?

Our understanding of the molecular genetics and biochemical pathology of Alzheimer's disease has progressed tremendously in the past decade. The metabolism of amyloid β-peptide is being unraveled, and specific anti-amyloid therapies are now in clinical trials worldwide. The precise biophysical structure of the amyloid β-peptide that causes neuronal dysfunction remains under investigation, as does the interaction between amyloid peptides and tau hyperphosphorylation, but these two molecules likely play key roles in neuronal dysfunction in Alzheimer's disease. Despite these advances, the cell biology of neuronal dysfunction and cell death in the Alzheimer's disease brain remains poorly understood. This brief review will explore the role of calcium (Ca²⁺) in neuronal death occurring during Alzheimer's disease. The evidence for glutamate receptor-mediated Ca²⁺ overload, or excitotoxicity, and other derangements of Ca²⁺ homeostasis in cell culture and animal models of Alzheimer's disease is reviewed. Finally, we raise the possibility that some of the neuronal death observed in Alzheimer's disease might be associated with a reduction in rather than an increase in cytosolic Ca²⁺ levels, an idea with potentially important therapeutic implications.