A fruit fly lives at the bottom of a test tube, and its cells operate like a city with millions of power plants. In each plant, that is, in each mitochondrion, cleanup crews work to break down damaged proteins. With age, the crews get tired, trash piles up, and the city starts to malfunction.
Scientists decided to hire extra cleanup workers, but not ordinary ones: a special complex called ClpXP. It consists of two parts: a barrel called ClpP, where proteins are cut into pieces, and a motor called ClpX, which unfolds the protein and pushes it inside. Both parts are needed for the complex to work, so the researchers simultaneously switched on the clpX and clpP genes in the flies.
At first, the cleanup crew was switched on at full power, and this hit the power plant: the activity of respiratory chain complex II dropped sharply. So the power was reduced to a gentle level, and the harm disappeared while the benefit remained. Female fruit flies began to live 9% longer than their genetically identical sisters with the genes switched off. There was no effect in males.
Importantly, the cleanup crew did not trigger an alarm signal. Normally, protein damage in mitochondria activates the stress response UPRmt, but here it was absent. This means that the lifespan extension is not linked to hormesis, that is, to beneficial stress, but works through another, still unknown mechanism.
Flies with extra cleanup workers climbed the wall of the test tube better, both when young and in middle age. This suggests that protein cleanup supports not only lifespan but also its quality. For now, this is fundamental knowledge, but it points to mitochondrial proteases as a possible target for future geroprotectors.
The ClpXP complex consists of 14 ClpP subunits forming a barrel and 6 ClpX subunits working as an ATP-dependent unfolding machine. In fruit flies and humans, there are about 25 resident proteases in mitochondria, but ClpXP is considered one of the main quality controllers.
In Greg Egan's novel Permutation City, characters manipulate cellular processes to achieve immortality; the idea of targeted protease activation for lifespan extension echoes such an engineering approach to aging.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.