Expression of proteins involved in mitochondrial fusion, fission and energy production is altered by age, sex and Alzheimer’s disease

Abstract

AbstractBackgroundAge is the biggest risk factor for Alzheimer’s disease (AD) but being female also increases risk with ∼63% of AD patients being female. This sex difference could partly be explained by menopause‐related oestrogen deficiencies during ageing. Oestrogen is neuroprotective and it is highly probable this deficiency after the menopause affects neuronal survival and contributes to the onset of AD. Oestrogen receptors are found in mitochondria and evidence suggests that the neuroprotective effect of oestrogen involves supporting mitochondrial function. The clear link between mitochondrial dysfunction and the pathophysiology of AD suggests a decrease in the beneficial effects of oestrogen on mitochondrial function after the menopause would have serious consequences. We hypothesise that alterations in oestrogen, due to ageing and the menopause, affect mitochondrial function and contribute to the increased susceptibility of women to AD.MethodLevels of mitochondrial proteins, dynamin‐related protein‐1 (DRP‐1), mitofusin‐1/2 (Mfn1/2), mitochondrial dynamin‐like GTPase (OPA1) and the electron transport chain (ETC) complexes 1‐5, were measured using immunoblotting in frontal cortical brain samples from young (20‐36), middle‐aged (40‐53) and old (64‐99) men and women with no history of dementia and in AD patients (Braak stage 5/6, 69‐92 age).ResultIn female AD brains a significant decrease was observed in Mnf1 and DRP‐1 compared to age‐matched females and in OPA1 in male AD compared to old male brains. Mnf2 and ETC complex 3 (cytochrome reductase) were significantly increased in female AD compared to male AD brains. DRP‐1 was significantly decreased in old males compared to middle‐aged males, while ETC complex 2 (succinate dehydrogenase) was significantly increased in old females compared to young females.ConclusionWe demonstrate for the first time age, sex and disease differences in the expression of proteins involved in various aspects of mitochondrial function including fusion, fission and energy production. These changes could underlie previous findings showing a range of mitochondrial abnormalities in AD brains and support the ‘mitochondrial cascade hypothesis’ that mitochondrial dysfunction is the primary event causing β‐amyloid deposition, synaptic degeneration, and NFT formation (Swerdlow et al., J. Alz. Dis. 2010 20:Suppl 2, 265‐79.). Our findings could partly explain female vulnerability to AD development.