Do caloric restriction and aging affect mitochondrial protein oxidation in heart and brain tissue?

Despite advances in understanding, the process of aging remains an irreversible, complex biological phenomenon, with numerous enigmatic aspects and disputed theories/factors. The prominent mitochondrial free radical theory of ageing (MRFA) postulates an increase of (oxidatively) damaged biomolecules in mitochondria as driver for cellular ageing. Our objective is to gain insight into oxidative protein changes in mitochondria during the aging process, which are influenced by caloric restriction (CR), a crucial factor for organs such as the heart and brain.

Crude mitochondrial fractions were isolated from the heart and brain tissues of same rats (Rattus norvegicus), ages 6.5 months (young) and 27 months (old), fed ad libitum or on a CR diet (CR: intake about 60 % of ad libitum fed animals). We have utilized an untargeted proteome approach, which enabled us to comprehensively compare the amount of identified oxidized peptides with non-oxidized peptides under DDA mode.

For cerebrum, the total changes in oxidative posttranslational modifications (oxPTMs) were found to be relatively minor. The age of the subjects did not significantly affect the levels of heart transmembrane/mitochondrial oxPTMs, but there was a decline in cerebrum transmembrane oxPTMs with age, which was further reduced by CR. The changes in heart transmembrane/mitochondrial oxPTMs were significant, with a general trend of reduced amount of oxPTM due to CR.

It is of great importance to study individual oxPTM modifications to identify aging mediators. Here, monooxidation, methionine oxidation, and carbonylation were the most frequently observed oxPTMs. Long-term and short-term CR significantly decreased monooxidation and carbonylation in heart. For cerebrum, there was no uniform trend – for instance monooxidation decreased for short-term CR, but increased under long-term CR in comparison to AL.

In conclusion, these results revealed that the alterations of oxPTMs are affected by age, diet, and tissue. Concerning the MRFA theory for aging and effect of CR, the differing outcomes for cerebrum and heart suggest that other factors, such as mitochondrial proteome composition or structure, affect ROS production and/or accumulation of oxPTMS.