Molecular indices of oxidative stress and mitochondrial dysfunction occur early and often progress with severity of Alzheimer's disease

Abstract

Glucose uptake and energy metabolism in the brain are regulated by insulin and insulin-like growth factors (IGF). Recent studies demonstrated progressive deficiencies in brain insulin and IGF production and responsiveness, and linked these abnormalities to acetylcholine deficiency in Alzheimer's disease (AD). We extended this line of research by attempting to correlate the deficits in insulin/IGF signaling and energy production with mitochondrial dysfunction, oxidative injury, and compensatory cyto-protective responses in brains with different Braak Stage severities of AD. Real time quantitative RT-PCR analysis of frontal lobe tissue demonstrated significantly reduced expression of mitochondria-encoded Complex IV and V genes, with relative preservation of genes encoding Complexes I, II and III. In addition, AD was associated with significantly increased expression of the p53 pro-apoptosis gene, all 3 isoforms of nitric oxide synthase (NOS 1–3), and NADPH-oxidase (NOX) 1 and NOX 3, beginning early in the course of disease. Activation of cyto-protective mechanisms in AD brains was limited since the expression levels of uncoupling protein (UCP) 2, 4, and 5, and peroxisome-proliferator activated receptor (PPAR) α and δ genes were significantly reduced, whereas PPAR-γ expression was selectively increased. The results demonstrate that AD is associated with early and striking increases in the molecular indices of oxidative stress, including up-regulation of NOS and NOX genes, which could impair the function of Complexes IV and V within the electron transport chain. The simultaneous reductions in cyto-protective mechanisms (UCP and PPAR), could allow oxidative injury to go unchecked and persist or increase over time. Adopting strategies to reduce the effects of NOS and NOX activities, and improve the actions of UCPs and PPARs may help in the treatment of AD.