In Vivo Detection of Oxidized Proteins: A Practical Approach to Tissue-Derived Mitochondria

Mitochondria are the major producers of free radical oxygen species (ROS) as well as the major target of oxidative damage. Defects in the mitochondrial respiratory chain complexes can increase ROS production and reduce ROS removal, leading to oxidative modification of proteins, lipids, and DNA. AAA proteases of the inner mitochondrial membrane, paraplegin and AFG3L2, participate in the biogenesis and maintenance of respiratory chain complexes. These proteins form hetero-oligomeric paraplegin/AFG3L2 and homo-oligomeric AFG3L2 complexes named m -AAA proteases. Inactivation of m -AAA proteases causes respiratory defects and altered mitochondrial morphology both in yeast and in mammals. In fact, mouse models defective for Afg3l2 display a very severe neurological syndrome and die within two weeks after birth. They display widespread morphological alterations of mitochondria in the central and peripheral nervous system and deficiencies in respiratory chain complex I and in complex III, which are major producers of ROS in physiological and especially in pathological conditions. Therefore, an efficient and reliable methodology to monitor the effect of increased ROS production is useful for accurately phenotyping cellular and animal models mutants in m -AAA. By measuring carbonyl formation as marker of protein oxidation, we have shown that respiratory defects cause oxidative damage in Afg3l2 mutants, indicating that oxidative stress is crucial in the pathogenesis of m- AAA deficiency.