Considering the Electron Transport Chain in Aging
The electron transport chain is the core piece of biological machinery inside mitochondria, the cell's power plants. It occupies a central place in the various free radical theories of aging as well. A good number of longevity-related mutations in laboratory animals appear to alter electron transport chain function as their primary mode of operation, and a good case is made for a large portion of degenerative aging to rest atop damage to the mitochondrial genes that encode proteins essential to proper electron transport chain function.
Most biogerontologists agree that oxygen (and nitrogen) free radicals play a major role in the process of aging. The evidence strongly suggests that the electron transport chain, located in the inner mitochondrial membrane, is the major source of reactive oxygen species in animal cells.It has been reported that there exists an inverse correlation between the rate of superoxide/hydrogen peroxide production by mitochondria and the maximum longevity of mammalian species. However, no correlation or most frequently an inverse correlation exists between the amount of antioxidant enzymes and maximum longevity. Although overexpression of the antioxidant enzymes SOD1 and CAT (as well as SOD1 alone) have been successful at extending maximum lifespan in Drosophila, this has not been the case in mice. Several labs have overexpressed SOD1 and failed to see a positive effect on longevity. [Although overexpression of CAT has been shown to extend life in mice by some groups].
An explanation for this failure is that there is some level of superoxide damage that is not preventable by SOD, such as that initiated by the hydroperoxyl radical inside the lipid bilayer, and that accumulation of this damage is responsible for aging. I therefore suggest an alternative approach to testing the free radical theory of aging in mammals. Instead of trying to increase the amount of antioxidant enzymes, I suggest using molecular biology/transgenics to decrease the rate of superoxide production, which in the context of the free radical theory of aging would be expected to increase longevity.
Personally I think the better approach to testing theory here is to implement mitochondrial repair or replacement, both of which are very feasible, and see what effect that has on older animals. It will both extend life and produce some degree of rejuvenation if the mitochondrial free radical theory of aging is correct.
I agree with your emphasis on rejuvenation, but this is a case where I think basic research would also be warrantable. Unlike the other categories of ageing damage, there is a major open question as to the extent of contribution of the mitochondrial mechanism. Addressing this question would tell us something useful for designing therapies.
I wonder if it's feasible to introduce human mitochondria into mouse embryos, replacing the mouse mitochondrial lineage with the human, or if the phylogenetic distance is too great.