Mitochondria in aging and Alzheimer's disease

Two significant risk factors are inextricably linked with Alzheimer's disease: advancing age, and accumulation of the amyloid-beta peptide. Over the age of 65 the risk of developing Alzheimer's disease increases almost exponentially with age, and the amyloid-beta rich neuritic plaques of the Alzheimer's disease brain are a histopathological hallmark of the disease. Since its identification as a major constituent of neuritic plaques amyloid-beta has attracted intense research focus as the primary causative agent in the development of Alzheimer's disease. As a result, numerous reports now exist to propose potential neurotoxic mechanisms mediated by amyloid-beta. Despite these research efforts, there is still a scarcity of information on the biologic link between aging and amyloid-beta in Alzheimer's disease, and although increasing evidence indicates that intracellular amyloid-beta is acutely toxic, there is also a paucity of information on the mechanisms of neurotoxicity mediated by intracellular amyloid-beta. Functional decline of mitochondria with aging is well established, and growing evidence attributes this decline to loss of mitochondrial DNA integrity in postmitotic cells including neurons. Oxidative stress due to mitochondrial failure may drive increased amyloidogenic processing of the amyloid-beta precursor protein, contributing to a loss of amyloid-beta precursor protein functionality and increased amyloid-beta production. Importantly, recent data show that amyloid-beta accumulates within mitochondria of the Alzheimer's disease brain. We speculate that age-related somatic mutation of mitochondrial DNA may be an important factor underlying sporadic Alzheimer's disease.

Lack of glutathione peroxidase-1 exacerbates Abeta-mediated neurotoxicity in cortical neurons

The aetiologies of Alzheimer's disease (AD) are complex and multifactorial. Current therapies are largely ineffective, as the pathophysiological pathways are poorly understood. Observations in AD autopsies, as well as in vivo and in vitro observations in transgenic mice, have implicated oxidative stress as pathogenic in AD. This study used the Glutathione Peroxidase-1 knockout mouse (Gpx1--/--) model to investigate the role of antioxidant disparity in neuropathologies. Cultured neurons from control and Gpx1--/-- embryos were treated with AD-related peptides and the degree of cell loss compared. Results show that antioxidant disparity makes Gpx1--/-- cells more susceptible to Abeta toxicity. Surrogate replacement of Gpx1 with the reactive oxygen species scavenger N-acetyl cysteine and the Gpx1 mimetic ebselen, reverses the Gpx1--/-- increased susceptibility to Abeta toxicity. Such results support a role for oxidative stress in AD-related neuronal loss. This study is the first to report such findings using the Gpx1--/-- model, and supports a role for oxidative stress as one of the contributing factors, in development of AD-like pathologies.