Acute myocardial infarction (AMI) is the leading cause of death among aged Americans, with increased mortality in postmenopausal women compared to age-matched men. Ischemia- reperfusion (I/R) injury and associated cell death increases with age;however, the predominant cell death type associated with AMI in aged females has yet to be elucidated. In this regard, mitochondria have been targeted as mediators of apoptosis, autophagy and necrosis. An emerging concept also includes a key role for programmed necrosis (PN) in the regulation of cell death via the mitochondrial permeability transition pore's (PTP) sensitivity to calcium overload, excess reactive oxygen species (ROS), and ATP depletion. As such, cell fate relies heavily on ATP production via mitochondrial respiration (MR) and ROS production. Activation of receptor interacting protein kinases (RIP1 and RIP3) and formation of a necrosome in concert with Fas-associated death domain protein (FADD) and TNF receptor-associated death domain (TRADD) are also key features of PN. However it is still debated whether MR increases or decreases with age in females. Further, it is unknown whether age- associated increases in PN contribute to increased AMI in older females. Here, we propose the novel hypothesis that PN, resulting in reduced MR and altered signaling downstream of RIP1 and RIP3 (including increased ROS production and PTP opening), is a key regulator of cell death in the aged female rat heart following I/R injury. Using adult and aged female Fisher 344 rats, a coronary artery ligation (CAL) model of I/R will be used to address the question. First, an evaluation of all types of cell death will include infarct assessment using TTC TUNEL staining, DNA laddering, and western blotting for protein markers of cell death signaling pathways. Second, the involvement of the mitochondria will be determined through assessment of respiration rate, calcium retention capacity (CRC), and fluorescent detection of superoxide, peroxynitrite, and hydrogen peroxide. The molecular basis of PN will be further analyzed using co- immunoprecipitation and co-localization methods. The findings from this study will be invaluable in establishing the phenotype of cell death characteristic of I/R injury in the aged female heart and may supply clear evidence of the mitochondria as a therapeutic target for AMI.
Heart disease remains the leading cause of death in older women. Menopausal loss of estrogen and increased cardiovascular disease risk may be linked to an increased mitochondrial calcium sensitivity leading to increased incidence of cell death following ischemia/reperfusion injury. By studying the loss of estrogen, mitochondrial function, and markers of programmed necrosis, apoptosis, and autophagy within a true model of aging and menopause, new therapies for the treatment and prevention of heart disease in post-menopausal women may be realized.
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