Research An intrinsic surveillance system allows mitochondria to respond to stress before cellular damage occurs

Mitochondria are constantly exposed to reactive oxygen species (ROS), but how they detect and respond to early oxidative stress has remained unclear. In this study, researchers from the Vögtle lab together with collaboration partners at the University of Freiburg uncovered an intrinsic mitochondrial surveillance mechanism that activates the mitochondrial unfolded protein response (UPR^mt) before damage spreads to the rest of the cell.

Using a novel chemogenetic approach to generate low levels of ROS directly within the mitochondrial matrix, the team showed that mild oxidative stress is sufficient to trigger a protective response without inducing detectable cytosolic damage signals. They identified the mitochondrial presequence proteases MPP and Oct1 as highly sensitive redox targets that become inactivated through oxidative modification. This impairs protein maturation and leads to the formation of proteotoxic aggregates within the mitochondrial matrix. The matrix disaggregase Hsp78 detects these aggregates, that initiate a protective transcriptional program to maintain mitochondrial function. The findings reveal that mitochondria can autonomously monitor their own protein homeostasis and respond to stress at a very early stage. By redefining how the UPR^mt is initiated, this work provides new insights into mitochondrial quality control and may help explain how cells cope with the gradual oxidative stress associated with aging and mitochondrial disease.