The underlying hypothesis is that an age-related accumulation of oxidative damage to mitochondria causes increasing mitochondrial dysfunction resulting in impaired Ca 2+ regulation, greater production of reactive oxygen species (Aim 1), and greater release of death-related proteins in response to insult (Aim 2). Calpains, Ca2+-activated cysteine proteases, are impacted by both Ca 2+ dysregulation and oxidative stress. Preliminary results suggest that m-calpain is associated with mitochondria, where its substrates may include many cell-death related proteins (Aim 3). Mitochondrial calpain would be ideally situated for regulation by mitochondrial Ca 2+ release and redox mechanisms, similar to the recently described mitochondrial nitric oxide synthase. The age-related alterations in mitochondrial function and cell death proteins are hypothesized to be exacerbated in vulnerable brain regions in AIzheimer's disease (AD), as compared to resistant brain regions and mitochondrial function in elderly individuals with less severe cognitive decline and neuropathology (Aim 4). However, increased oxidative stress in aging and AD may limit the activity of calpain and other cysteine proteases, possibly protecting against the consequences of Ca 2+ dysregulation but also limiting the proteolysis of substrate proteins (Aim 4). To examine the basic premise, that an age-related accumulation of oxidative damage to mitochondria results in their dysfunction, iwe will examine the efficacy of long-term anti-oxidant (lipoic acid) and NMDA receptor antagonism (memantine) intervention in attenuating the age-related alterations in mitochondrial function (Aim 5). The above studies of mitochondrial function will be performed on synaptic and non-synaptic mitochondrial fractions isolated from the cortex and cerebellum of rats of ages 1-24 months, and from human brain autopsy tissues obtained from individuals with various levels of cognitive function and AD-related europathology. The maximum postmortem interval is 5h. While many aspects of mitochondrial dysfunction have been examined in aging and AD, few studies have examined isolated mitochondria and even fewer have evaluated synaptic vs. non-synaptic mitochondria. Together, the studies outlined in this project will provide a comprehensive evaluation of mitochondrial function and dysfunction in aging and AD, and the relationship of mitochondrial dysfunction to the age-related Ca2+ deregulation and oxidative stress.
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