Mitochondria are the power plants of the cell, generating chemical fuel stores that can be used to power cellular processes. They are important in aging, and this has a lot to do with the generation of reactive oxygen species (ROS) that happens as a side-effect of their operation. Researchers have shown that benefits to health and longevity can be realized in laboratory animals by targeting antioxidants to mitochondria in order to soak up some ROS before they cause harm. Other research focuses on repairing the damage that mitochondria inflict upon themselves this way, so as to stop it from contributing to degenerative aging.
There is general agreement that mitochondria play an important role in the aging process, but the role of mitochondrial oxidative stress remains controversial. Most previous work looking at mitochondrial oxidative stress has focused on damage to DNA, proteins, and lipids with age or in response to manipulation of cellular antioxidants. The interaction between oxidative damage and aging has been called into question in recent years by studies demonstrating little effect on aging and lifespan in mice with genetically modified antioxidant systems. A notable exception is the life extension and protection against multiple diseases in mice that express catalase in the mitochondria, which suggests that the cellular location and type of reactive oxygen species is an important factor.
Our laboratory is interested in whether redox inhibition of mitochondrial function contributes to age-related energy deficits in vivo in mouse and human skeletal muscle. [We] tested this hypothesis using a mitochondrial targeted peptide, SS-31, known to reduce mitochondrial H2O2 production.
SS-31 reduced the high mitochondrial H2O2 production from aged permeabilized muscle fibers [but] had no effect on young fibers. In the aged mice, one hour after in vivo treatment with SS-31 the cellular redox status [was] more reduced. This was accompanied by improved mitochondrial [function] in vivo in the skeletal muscle, while there was no effect on the mitochondrial energetics in young skeletal muscle. In addition to the improvements in muscle energetics, one hour and one week of SS-31 treatment resulted in improved muscle performance and increased exercise tolerance, respectively, in the old mice.
This rapid reversal of in vivo energy deficits supports the hypothesis that mitochondrial deficits in aged skeletal muscle are, at least in part, due to reversible redox sensitive inhibition. Thus assessing the role of mitochondrial oxidative stress in aging and disease will require careful attention to changes to the in vivo redox environment and the mechanisms by which these changes can affect cell function.