Bim Is Elevated in Alzheimer's Disease Neurons and Is Required for β-Amyloid-Induced Neuronal Apoptosis.

The molecules that mediate neuron death in Alzheimer's disease (AD) are largely unknown. We report that β-amyloid (Aβ), a death-promoting peptide implicated in the pathophysiology of AD, induces the proapoptotic protein Bcl-2 interacting mediator of cell death (Bim) in cultured hippocampal and cortical neurons. We further find that Bim is an essential mediator of Aβ-induced neurotoxicity. Our examination of postmortem AD human brains additionally reveals upregulation of Bim in vulnerable entorhinal cortical neurons, but not in cerebellum, a region usually unaffected by AD. Accumulating evidence links inappropriate induction/activation of cell cycle-related proteins to AD, but their roles in the disease have been unclear. We find that the cell cycle molecule cyclin-dependent kinase 4 (cdk4) and its downstream effector B-myb, are required for Aβ-dependent Bim induction and death in cultured neurons. Moreover, neurons that overexpress Bim in AD brains also show elevated levels of the cell cycle-related proteins cdk4 and phospho-Rb. Our observations indicate that Bim is a proapoptotic effector of Aβ and of dysregulated cell cycle proteins in AD and identify both Bim and cell cycle elements as potential therapeutic targets. [ABSTRACT FROM AUTHOR]