Observed decreases in complex I-dependent OXPHOS capacity are not predicted entirely by decreased complex I content.
However, both assembly knockdown strains have marginally increased complex I content and significantly decreased complex V content (Table 3).
In fact, it is known that many patients of PD have decreased complex I activity [7], [8].
The decreased Complex I activity was not sufficient to cause an overall decrease in Complex I+III activity, and in fact there was a 19% increase (p<0.05) in Complex I+III activity in the fat-1 animals.
As seen in the figure, however, there are both outliers (decreased complex I rates with no decrease in EC50) and an apparent ceiling effect when complex I rates are increased.
To investigate whether the decreased complex activities cause increased ROS production or increased ROS inhibits the complex activities in the dOpa1+/− mutant files, we studied their mitochondrial aconitase activity.
Ischemia/reperfusion (I/R) injury is characterized by decreased complex I respiration [4] and increased formation of reactive oxygen species (ROS) [5], [6], which in turn induce further damage to complex I, lipids, mtDNA, mitochondrial proteins and other cellular targets.
These data indicate that decreased complex activities are the primary underlying mechanism and the secondary increase of ROS reinforces vicious cycle and results in catastrophic mitochondrial dysfunction, including decrease in ATP production.
The mechanism responsible for decreased Complex I-linked ROS production in the fat-1 mice could be due to either direct or indirect actions of n-3 fatty acids on mitochondria.
Likewise, these Lto1 mutations decreased complex formation with Yae1.
Notably, individuals with Leigh syndrome can exhibit decreased complex I activity and abundance.
