A biochemical and genetic analysis of the mitochondrial permeability transition pore in aging and disease.

摘要

The central role of mitochondria in energy production via oxidative phosphorylation is well known, but it is less appreciated that mitochondria generate most of cellular reactive oxygen species (ROS) as toxic by-products. ROS are detoxified in part by the mitochondrial manganese superoxide dismutase (Sod2 ), but excess ROS are thought to damage the cell and contribute to aging and disease. Moreover, mitochondria have been shown to play a key role in apoptosis, via activation of the mitochondrial permeability transition pore (mtPTP) and release of apoptotic proteins. This regulation of apoptosis is linked to energy metabolism through the mitochondrial inner membrane protein, the adenine nucleotide translocator (ANT).; To examine the role of mitochondrial ROS in aging and disease, mice partially or completely lacking Sod2 were examined (chapter 2). Mice heterozygous for Sod2 (+/−) exhibited a reduction in mitochondrial function at an early age, a state that was not achieved in wild-type mice until old age. The increase in oxidative stress also hypersensitized the mtPTP of Sod2 (+/−) mice, resulting in increased apoptosis. Thus, chronic mitochondrial oxidative stress sensitizes the mtPTP and this leads to premature cell death.; The mechanism by which oxidative stress sensitizes the mtPTP is unknown. It has been proposed that ROS react with the ANT, which is thought to associate with the voltage dependent anion channel to form the mtPTP. However, this thesis demonstrates that inactivation of both Ant1 and Ant2 in mouse liver does not prevent mtPTP activation, but rather alters its regulation by several effectors. Hence the ANTs are regulatory, not structural, components of the mtPTP (chapter 3).; Systemic inactivation of Ant2 results in embryonic lethality due to cardiac developmental defects (chapter 4), while inactivation of Ant1 results in an adult-onset cardiomyopathy. Since ANT2 is hypothesized to have a greater effect on mtPTP regulation than ANT1, the developmental defects seen in Ant2-deficient mice may be due to improper apoptotic remodeling of the heart.; Thus, the ANTs are regulators of the mtPTP and central to cardiac development. Moreover, regulation of the mtPTP by oxidative stress is vital to modulating apoptosis and senescence.